Lipid peroxides poisoning

[Progecitor]

It has been already clear that lipid peroxidation plays a role in my case, however the way we and doctors consider this process is partly false. Of course many studies touch on this matter, so it would seem unlikely that something so “commonplace” could be the cause of such a particular and rare disease as POIS. What makes POIS different however is not quality, but rather quantity, which is also accompanied by a qualitative transformation making it kind of a next level disease. During sexual activity and especially at ejaculation an excessive amount of ROS is produced. There could be numerous reasons for this and the root may be different between POISers. However the important thing is that excessive ROS establishes a junction point in this process and downstream from this it practically explains everything about the peculiarities of POIS and its symptoms at least from my point of view. The next step after ROS production is lipid peroxidation and this is the crucial step that leads to symptoms. During lipid peroxidation numerous lipid peroxidation products (LPOs) are released and these are emerging as disease biomarkers as they are involved in practically every kind of disease (e.g. diabetes, neurodegenerative diseases, cancer, infections, etc.). LPOs are clearly elevated in POIS as well, even if none have bothered to measure it so far. However elevation is only a mild term for what actually happens in POIS as LPOs are produced in such a brutally excessive manner that they transform from simple biomarkers to actual toxic agents that profoundly poison our bodies giving rise to a sepsis-like state. Probably numerous LPOs are involved in POIS, but I chose 4-Hydroxynonenal (4-HNE or HNE) as a model example as it is one of the most researched one along with malondialdehyde (MDA). From my point of view probably the most important fact is that many LPOs activate TRPV1 and TRPA1, which serve as biological alarms. This practically explains the burning pain I get, which is the most persistent indicator for my POIS. As I feel this burning pain, even if a bit reduced, in the chronic phase of POIS, it must mean that ROS release after ejaculation is exorbitant and thus production of LPOs as well in the following cascade of events.
4-HNE as an inflammatory mediator plays a role in many diseases. 4-HNE is partly responsible for lethal covid-19 and clearly must be involved in postcovid as well. It drives the development of senescence and autoimmunity by forming protein adducts and thus impairing many biological processes. 4-HNE can modulate many factors that have been discussed in relation to POIS. Even just from a theoretical view it is crystal clear that excessive lipid peroxidation can explain the entirety of the POIS phenomenon. The following quotes are meant to serve as partial evidence for this theory. The first few studies are especially noteworthy as they are practically discussing the probable root (ROS) causes of POIS.

Oxidative stress (OS) in pathologies of male reproductive disorders
ROS, the toxic derivates of oxygen metabolism, mediate some important male reproductive functions such as sperm capacitation, hyperactivation, and acrosome reactions. However, excess generation of ROS impairs redox balance in the reproductive tract, leading to cellular and molecular damage.
Germ cells are a significant source of ROS that are critical for the sperm maturation process alongside other signaling functions. Following spermatogenesis, ROS are important in epididymal transport and maturation associated mostly with motility. ROS further mediate postejaculation maturation in the female reproductive tract, in which case redox switches are required for capacitation, acrosome reaction, sperm-zona binding, and oocyte fusion for successful fertilization.
ROS are generated from spermatids and mature spermatozoa directly through a mechanism of ROS-induced ROS generation.
Sources of ROS in the male reproductive tract:
- Leukocytes
Seminal plasma contains a substantial quantity of peroxidase-positive leukocytes (polymorphonuclear leukocytes, chiefly neutrophils, 50%-60%) as well as activated macrophages (20%-30%). If the number of leukocytes in the seminal plasma exceeds 1 x 10^6 WBC/mL of semen, the condition is referred to as leukocytospermia. In a state of inflammation, leukocytes generate 100-times greater ROS than that produced in normal state. This response is triggered as a defense mechanism that also induces nicotinamide adenine dinucleotide phosphate (NADPH) production via the hexose monophosphate (HMP) shunt. Leukocyte-mediated immune response against male urogenital inflammation involves ROS generation as the prime mechanism and is thus responsible for the induction of OS. The concomitant increase in levels of proinflammatory mediators (IL-8, IL-6, and TNFa) together with a decrease in antioxidant capacity during inflammation can trigger respiratory burst, leading to OS.
- Immature spermatozoa
Abnormalities in spermiogenesis often result in excess cytoplasm retention in the mid-piece of matured spermatozoa, referred to as excess residual cytoplasm. Sperm with excess cytoplasm, or teratozoospermic sperm, generate greater amounts of ROS than what is produced by morphologically normal spermatozoa. The key enzyme for ROS production in sperm, NADPH oxidase, differs from those in leukocytes, the former being calcium dependent, while in leukocyte it is protein kinase-C (PKC) dependent.
- Autoimmune/inflammatory conditions
Non-infective or non-bacterial chronic prostatitis is a very common prostate pathology resulting in high seminal OS. This accounts for more than 90% of all prostatitis cases, affecting 10% of all men worldwide. These conditions generally trigger autoimmune responses against self-antigens of a prostate or seminal origin. These exaggerated responses induce proinflammatory mediators and trigger increased seminal leukocytes, thereby generating excessive ROS and leading to OS. A speculated mechanism that evokes this autoimmune response is probably the polymorphism of interleukin 10 (IL-10), which is an antiinflammatory TH-2 cytokine. A decrease in IL-10 may initiate the TH-1 dependent immune responses that activate T-lymphocytes against prostate antigens. Inflammatory cytokines like TNF-a, IFN-g, and IL-1B initiate chemotaxis and leukocytes activation. These leukocytes serve as major sources of seminal OS, leading to severe disruption of sperm membrane integrity and significantly reduces semen quality.
- Cryptorchidism and varicocele
- Hyperthermia and oxygen insufficiency
- Spermatic cord torsions, testicular ischemia
Adequate erection requires nitric oxide (NO) through transcription of nitric oxide synthase (NOS) for vasodilation and penile engorgement with blood. MPO-dependent oxidized low density lipoprotein (LDL) has been shown to reduce endothelial NOS mRNA expression and is correlated with poor International Index of Erectile Function (IIEF) scores, alongside increased inflammatory markers including IL8.
Sperm plasma membrane is rich in PUFAs with unconjugated double bonds within their methylene groups. Unregulated increase in sperm intracellular ROS aids a progressive reaction cascade inducing LPO. As this is a self-propagating autocatalytic reaction, it accounts for 60% of sperm membrane fatty acids damage and, thus, sperm membrane fluidity is compromised. Induction of LPO follows a progressive destructive chain of reactions till it terminates. “Initiation” of oxidative damage is via hydrogen atom isolation from the loosened bond with carbon. This is followed by further free radicals (FRs) and lipid radical production. The FRs interact with oxygen giving rise to peroxyl radicals that further take hydrogen atoms from membrane lipids. This autocatalytic reaction continues in the “propagation” phase of oxidative damage, rapidly damaging cellular components. The existing FRs keep attacking the succeeding lipids by yielding toxic aldehydes through degradation of hydroperoxide. Cytotoxic peroxyl and alkyl radicals are repeatedly produced till formation of a stable end product, malondialdehyde (MDA), that marks the “termination” of the peroxidation chain. Hydrophilic 4-hydroxynonenal is also a crucial LPO product that affects proteomics and genomics of spermatozoa.
LPO can be assessed by MDA, thiobarbituric acid assays (TBARS), or 4-hydroxynonenal (4-HNE).
https://sci-hub.st/https://www.sciencedirect.com/science/article/abs/pii/B9780128159729000020

Seminal leukocyte contamination can contribute to oxidative stress in the ejaculate while, in the germ line, the dysregulation of electron transport in the sperm mitochondria, elevated NADPH oxidase activity, or the excessive stimulation of amino acid oxidase action are all potential contributors to oxidative stress.
They were the first to point out the vulnerability of mammalian spermatozoa to peroxidative damage because of their high cellular content of polyunsaturated fatty acids, and the first to identify the particular vulnerability of plasmalogen to this process.
In addition to H2O2 and O2•-, spermatozoa also generate another free radical, nitric oxide (NO), as well as other powerful oxidants such as peroxynitrite (ONOO-) or hypochlorous acid (HOCl), as well as peroxyl radicals (ROO•), alkoxyl radicals (RO•), and organic hydroperoxides (ROOH), any, and all of which, can be damaging to spermatozoa when generated in excess.
Every single human semen sample is contaminated with leukocytes, comprised largely of peroxidase-positive eosinophils and neutrophils, macrophages, and a lesser number of B- and T- lymphocytes.
Interleukin-8 (IL-8) has been found to correlate with sperm DNA damage and sperm vitality in certain studies, but no other cytokine. Alternatively, other studies found significantly increased levels of IL-2, IL-4, IL-6, IFN-g, and, particularly, TNF-a in human semen in association with leukocytospermia. These, and other seminal cytokine-like molecules such as resistin, are clearly indicative of a proinflammatory state and are intimately associated with the induction of leucocyte infiltration.
So why does leukocytic infiltration occur? Presumably, a variety of pro-inflammatory states generated by such conditions as varicocele, spinal cord injury, cigarette smoking, obesity, and infection, including COVID-19, promote the local expression of cytokines such as IL-8 that, in turn, stimulate an influx of leucocytes into the male reproductive tract. If, as is generally assumed, these cells enter the ejaculate via the secondary sexual glands, then the first time that leucocytes will come into contact with the spermatozoa will be at the moment of ejaculation, when the spermatozoa will be protected by a pool of powerful and diverse antioxidants in the seminal plasma. Alternatively, if the leukocytic infiltration is secondary to orchitis or epididymitis, then the implications for sperm function are significantly greater since the leukocytes will have had more time to overwhelm the local antioxidant protection offered by the male reproductive tract and damage the spermatozoa.
Once the lipid peroxidation process has been initiated, the aldehydes generated as a result of this process will form adducts with proteins, including several that are involved in the orchestration of mitochondrial electron transport. This leads to electron leakage, O2•- generation, and the precipitation of yet more lipoperoxidative damage in a self-perpetuating spiral. Spermatozoa are particularly vulnerable to this process because they are so enriched in the polyunsaturated fatty acids that drive the lipid peroxidation process.
The ability of 4-HNE to adduct these proteins and stimulate mitochondrial ROS generation is also reinforced by the tendency of this aldehyde to form adducts with aldehyde dehydrogenase (ALDH), a key enzyme in the protection of spermatozoa against oxidative stress.
Similarly, the parent estrogen (estradiol-17B) has been found to induce mitochondrial ROS generation in high doses, possibly after being converted to catechol estrogens that are much more redox active than estradiol-17B and constitute powerful inducers of mitochondrial ROS generation by human spermatozoa, as well as other cell types.
Many of the antioxidant polyphenols that are actually known to be beneficial for sperm function induce ROS generation at complex III, from whence the toxic oxygen metabolites are released into the intramembranous space and, ultimately, the cytoplasm, with minimal induction of cellular damage. Damage occurs when ROS are released into the mitochondrial matrix, whereupon they induce lipid peroxidation and the total disruption of sperm function due to the formation of toxic electrophiles, such as 4-HNE, that form adducts with both DNA and a range of functionally important proteins.
Another group of compounds that are involved in the stimulation of mitochondrial ROS generation by human spermatozoa are polyunsaturated fatty acids (PUFA). Exposure of these cells to free, unesterified, unsaturated fatty acids elicits a powerful mitochondrial ROS response in human spermatozoa; the more unsaturated the fatty acid, the more reactive oxygen metabolites are generated. Thus, the major PUFAs in human spermatozoa, arachidonic and docosahexaenoic acids, are capable of inducing significant mitochondrial ROS formation in these cells, promoting peroxidative damage and generating both a loss of sperm motility and an increase in oxidative DNA damage.
Mitochondrial ROS generation is also a distinctive feature of spermatozoa as they enter the intrinsic apoptotic pathway. Spermatozoa are capable of undergoing a truncated form of apoptosis characterized by rapid motility loss, mitochondrial ROS generation, caspase activation in the cytosol, cytoplasmic vacuolization, and oxidative DNA damage. In many ways, death via the intrinsic apoptotic cascade is the default destiny for this cell type as all ejaculated spermatozoa are preordained to become senescent and die except, of course, the cell that successfully achieves fertilization, which are rewarded with a certain measure of immortality.
Another class of enzymes thought to be involved in the production of ROS by human spermatozoa are the NADPH oxidases (NOX). NOX5 is unusual in that it possesses EF-hand motifs that render the enzyme responsive to calcium. This feature explains why reagents that elevate intracellular calcium levels, such as divalent cation ionophores (A23187 and ionomycin) and progesterone, have been found to be capable of triggering ROS generation by human spermatozoa via mechanisms that can be blocked by DPI (diphenylene iodonium), SOD (superoxide dismutase), zinc, and the calcium chelator BAPTA. It is possible that NOX5, and the ROS generation it triggers, are key regulators of sperm function, shutting down tyrosine phosphatase activity, orchestrating cholesterol efflux from the plasma membrane, enhancing cAMP generation, and precipitating the cytoplasmic alkalinization needed to drive calcium influx via Catsper.
Depletion of Antioxidants: It is always difficult to differentiate the cause and effect in such circumstances - did the lack of antioxidant protection induce a state of oxidative stress or did the excessive generation of ROS by spermatozoa, infiltrating leukocytes, or, in cases of obesity, adipocytes lead to the depletion of antioxidant equivalents from the semen?
3. Capacity of Spermatozoa to Repair Oxidative Damage
We have already mentioned the particular importance of aldehyde dehydrogenase. Phospholipase A2 (PLA2) is also critical because this enzyme cleaves oxidized fatty acids from the second position of membrane phospholipids so that they can be neutralized by glutathione.
Another molecule that is known to possess both PLA2 and peroxidase activities is peroxiredoxin 6. Spermatozoa address the formation of oxidatively-damaged DNA with a severely truncated base excision repair pathway which is initiated by OGG1 (8-oxoguanine glycosylase).
https://www.mdpi.com/2076-3921/11/2/306?trk=public_post_main-feed-card-text

Lipid peroxidation (LPO) is an autocatalytic process involving three main steps resulting in formation of end products, namely nonreactive malondialdehyde and 4-hydroxynonenal (4-HNE), which are disastrous for the genome and proteome as they can cause double-stranded DNA breaks.
It is well known that sperm, while in the testes are protected from immune system via the blood-testis barrier. Once they enter epididymis and move along the duct, the sperm are protected by antioxidant enzymes secreted by the epididymal epithelium into the lumen. Once ejaculation occurs, while located in the urethra sperm might come into contact with activated phagocytic leukocytes producing free radicals as a result of an infection. Inflammatory process affecting prostate or seminal vesicles such as prostatitis can trigger peroxidase-positive leucocytes and they can produce exorbitant level of ROS. This condition is described as leukocytospermia and often requires pharmacotherapy. As a result of such inflammation an increase in proinflammatory cytokines, such as interleukin (IL)-8 occurs in tandem with a decrease in the enzymatic antioxidant SOD that leads to production of high levels of ROS. Correlation between impaired sperm function and seminal plasma with elevated levels of ROS, TNF-a, IL-6 and IL-8 was found to result in an increased LPO of sperm membrane.
Another marker is hyperviscosity of seminal plasma associated with increased levels of MDA and impaired antioxidant status. Urobacteria infections that affect prostate and seminal vesicles can also contribute to increased seminal plasma viscosity and an increase in ROS production. The presence of a large number of round cells imply possible oxidative stress caused by leukocytospermia or immature spermatozoa. To distinguish leukocytes from germ cells a peroxidase test is required, CD45 (leukocyte common antigen) immunostaining or measurement of seminal elastase. Visualization of excessive residual cytoplasm in abnormal sperm is indicative for high levels of ROS.
https://www.researchgate.net/profile/Ekaterina-Pavlova-2/publication/372703662_Spermatozoa_under_Oxidative_Stress_Risk_or_Benefit/links/64ff30e825ee6b7564e11e2d/Spermatozoa-under-Oxidative-Stress-Risk-or-Benefit.pdf

With less than 1% of the immune system present in the epididymis, spermatozoa appear to use reactive oxygen species (ROS), including H2O2, as a defense mechanism against pathogens. Second, spermatozoa appear to produce low levels of H2O2 to drive a signal transduction pathway known as capacitation, a process essential for fertilization. In particular, low levels of ROS are beneficial for the cell, however, higher, uncontrolled levels are detrimental.
Given that sperm motility is severally affected in infertile men, it has been speculated that oxidative stress results in lipid peroxidation in the sperm plasma membrane, which then leads to decreased motility.
We have recently demonstrated that excessive ROS generation within spermatozoa leads to the production of the toxic lipid-derived compound 4-hydroxynonenal (4-HNE). During oxidative stress, levels of 4-HNE rise significantly such that it can accumulate in the membrane at concentrations up to 5 mM. Not surprisingly, high 4-HNE levels have been implicated in the onset of many oxidative-related pathologies such as cardiovascular and neurodegenerative diseases. We have recently demonstrated that high doses of 4-HNE (between 200 and 400 uM) induce oxidative stress and inhibit sperm motility within 3 h.
Furthermore, it was recognized that the effect of ROS was downstream from the action of cAMP.
The Epigenetic Effects of 4-HNE
Perhaps one of the most significant findings of this study has been the identification of a 4-HNE adduct on histone-lysine N-methyltransferase. This enzyme plays a key role in the addition of a methyl group to either lysine or arginine on histones.
https://academic.oup.com/biolreprod/article/92/4/108,%201-10/2434086

These findings indicate androgen-deprivation induces OS in the rat ventral prostate (VP) through elevation of ROS anabolism and diminution of antioxidant detoxification. Androgen replacement partially reduces OS in rat VP to precastration levels. Expression of Noxs remained high amid a broad-based recovery of antioxidant defense mechanism(s).
Induction of high levels of ROS subjects the cell to a state of oxidative stress (OS), which may damage cellular DNA, proteins, and lipids and result in cell-cycle arrest, cellular senescence, and cell death.
Enzymes such as glutathione reductase (GR), glucose-6-phosphate dehydrogenase (G6PDH), gamma-glutamyl transpeptidase (GGTP), and glutathione synthetase (GS) play major interactive roles in the replenishment of cellular reducing power. Other antioxidant molecules include thioredoxin (Txn), a protein thiol that directly detoxifies ROS and serves as an electron donor to other antioxidant enzymes, including peroxiredoxin 5 Prdx5.
OS in prostate was demonstrated by immunohistochemical detection of 8-OHdG and 4-HNE protein adducts, both of which are biomarkers for OS.
In castrated animals treated with testosterone for 7 days, the amount of 4-HNE protein adducts was significantly reduced, and they presented a patchy distribution in the glandular epithelium with diffuse and heterogeneous cytoplasmic staining.
However, in the castrates with testosterone replacement, Nox1 exhibited only a trend of reduction in expression as compared with values in castrates but remained onefold elevated over levels in intact controls.
It is currently unknown why ductal epithelia express such a high level of OS constitutively. One possible explanation may be related to previously reported retrograde transport of genotoxic substances or pathogens from the urethra to prostatic ducts, a mechanism implicated in prostatitis of the human gland.
It has been demonstrated that protein kinase C mediates the regulation of gene expression for NAD(P)H oxidases by angiotensin II in vascular smooth muscle cells and by zinc in neuronal cells.
Our results clearly demonstrate that expression of NAD(P)H oxidases in rat VP is dependent on the androgen status of the animal.
Ectopic expression of Nox1 in fibroblasts induces proliferation and transformation, but that expression of Nox4 induces senescence. In human prostate cancer cells, overexpression of Nox1 increases tumorigenicity and anti-sense inhibition of Nox5 suppresses proliferation and triggers apoptosis.
The first group of VP genes includes SOD2, Gpx1, Txn, and Prdx5. These genes are most likely regulated by androgen directly; their expression declines on androgen withdrawal and rebounds to precastration levels on testosterone replacement.
The second set of VP genes, including catalase, GR, GGTP, and GS, are insensitive to androgen withdrawal but are significantly up-regulated on testosterone replacement in castrated animals. Intriguingly, this set of genes, except for catalase, are more distantly related to the removal of ROS but closely associated with replenishment of GSH.
Degeneration and constriction of the vascular system in the prostate were found to be early events after castration, leading to reduced oxygen tension in prostate epithelial cells and activation of hypoxia- and stress-signaling pathways. Similarly, oxygen deprivation alone and combined oxygen and glucose deprivation induce ROS production in microvasculature and neurons, respectively. It is therefore logical to speculate that castration induces a hypoxic environment in the regressing prostate that leads directly or indirectly to elevation of OS in this gland.
https://www.sciencedirect.com/science/article/pii/S0002944010636061

Low levels of reactive oxygen species (ROS) and calcium are necessary for sperm function. NADPH oxidase 5 (NOX5) is a membrane enzyme which produces ROS. This enzyme is dependent on calcium for its activity.
Overall, progesterone is one of the most important stimulators of the human sperm. For instance, progesterone induces calcium entry into the human sperm through the CatSper channel and calcium is the main activator of the NOX5 enzyme.
Indeed, other studies have shown that adding either catalase or SOD will result in the loss of sperm fertilizing ability.
As was mentioned in the introduction, calcium activates the NOX5 enzyme. So it is likely that the CatSper channel affects sperm motility either directly or indirectly. For instance, it can be assumed that calcium stimulates NOX5 activity and ROS generation. Calcium and ROS can stimulate the signaling pathways that are involved in sperm motility. Therefore, we conclude that probably the actions of CatSper and NOX5 are somewhat linked together.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5775990/

Are Sensory TRP Channels Biological Alarms for Lipid Peroxidation?
These ion channels are fundamentally detectors and signal converters for body-damaging environments such as heat and cold temperatures, mechanical attacks, and potentially toxic substances. When messages initiated by TRP activation arrive at the brain, we perceive pain, which results in our preparing defensive responses. Excessive activation of the sensory neuronal TRP channels upon prolonged stimulations sometimes deteriorates the inflammatory state of damaged tissues by promoting neuropeptide release from expresser neurons. These same paradigms may also work for pathologic changes in the internal lipid environment upon exposure to oxidative stress. Surprisingly, accumulating information about the identities of their chemical stimulators and their categorization suggests that those include many of LPO products.
LPO products that activate TRPA1, including 8-iso prostaglandins (PGs) and related cyclopentenone PGs also fall into this category. In addition, environmental pollutants including formaldehyde, acetaldehyde, industrial isothiocyanate, hypochlorite, and acrolein (which is also produced during endogenous LPO processes), have been shown to cause irritation, coughing, and pain by stimulating TRPA1 through the same covalent binding mechanism.
TRPV1 is not only activated by the pungent vanilloids, but also by noxiously high temperatures (>42 °C), hyperosmolalities, acidic pH (protons), a variety of lipidergic irritating chemicals, and polyamines, which indicates that TRPV1 is a polymodal detector sensitive to thermal, mechanical, and chemical insults.
In any case, TRPV1/TRPA1-double positive C-fibers are referred to as polymodal nociceptors because they can sense an extremely extensive number of damaging signals. Such polymodal nociceptors are found not only in somatosensory nerves but also in the visceral nerves.
3. Lipid Peroxidation (LPO) Products Activate TRPA1 and TRPV1
As discussed above, the two major nociceptive TRP ion channels, TRPA1 and TRPV1, act as warning alarms of damaging environments and molecules. TRPA1 and TRPV1 sense these signals, either directly or indirectly, and in turn transduce and relay them to the brain. The resultant pain perception prepares the body for defense. As listed above, the two TRPs are already known to detect a multitude of pathologically generated lipids. Furthermore, several reports have shown that TRPA1 and TRPV1 are also responsive to a certain reactive oxygen species generated during oxidative stress.
These primary compounds are chemically unstable and later decompose to more stable but still reactive secondary LPO compounds (4-hydroxy-2-nonenal (4-HNE), 4-oxo-2-nonenal (4-ONE), etc.). HpETEs can also be metabolized into hydroxy derivatives (hyroxyeicosatetraenoic acids: HETEs) by the glutathione (GSH)-utilizing antioxidant enzyme glutathione peroxidase.
When LPO products containing alpha,beta-unsaturated carbons are present in the cytosol, N-terminal lysine (epsilon-amino group), cysteine (sulfhydryl group), or histidine (imidazolyl group) of TRPA1 nucleophilically attacks those carbons to form covalent bonds (Michael addition).
In the case of some LPO products including 4-HNE, 4-ONE, hexanal, and methylglyoxal, Schiff base formation with the amines of lysine residues of a target protein is known to occur, and this reaction appears to be less reversible than Michael addition.
Acrolein is an environmental pollutant created by combustion of organic matters and is also generated endogenously in metal-catalyzed oxidation of PUFAs such as linoleic acid, arachidonic acid, eicosapentaenoic acid, and docosahexaenoic acid. Acrolein is among the most reactive LPO products (~100 times more reactive than 4-HNE in terms of electrophilicity).
Lipid hydroperoxides generated from PUFAs may undergo complex non-enzymatic LPO processes, which are in general constituted by alkoxyl radical formation, further oxygenation, and fragmentation. Consequently, 2-alkenals with diverse carbon lengths are formed, among which the best examples in TRP channel studies have been 4-HNE, 4-ONE, and 4-hydroxy-2-hexenal (4-HHE). 4-HNE and 4-ONE are generated from omega-6 PUFAs including arachidonic acid and linoleic acid while 4-HHE is formed from omega-3 PUFAs such as docoshexaenoic acid, eicosapentaenoic acid, and linolenic acid. Compared to lipid hydroperoxides, these fragmented end products are more chemically stable and diffusible through cell membranes and thus can travel to locations outside of those where they were originally produced. GSH conjugation (which is also a Michael addition) seems to be the major step for 2-alkenal scavenging, and this reaction can be both spontaneous and catalyzed by glutathione-S-transferases. However, because this reaction is reversible, alkenals occasionally travel as far as a GSH-bound form, dissociate again, and then covalently bind to local proteins, which may contribute to spreading of oxidative disease regions. Physiological 4-HNE levels are variable (0.3–100 uM, the plasma level is generally lower than tissue levels). Under disease states during oxidative insults, two to more than 100-fold increases have been detected (5 uM–5 mM). 4-ONE was once reported to achieve a comparable level with that of 4-HNE in vitro. Modest TRPV1 activation by 4-ONE was also observed in the hundred-micromolar range. At such concentrations, which can be reached under pathological conditions, TRPV1 might also take part in raising the alarm to elevated levels of 4-HNE.
Certain alkanals such as pentanal and hexanal have been shown to be increased during LDL peroxidation. Only pentanal was tested at millimolar ranges, and it was found to induce intracellular Ca2+ increases in nociceptive populations of rodent trigeminal neurons.
Lysophosphatidylcholine (LPC) may be enzymatically released from oxidized phospholipids in oxLDLs. In vivo animal injection of LPC leads to cold hypersensitivity, and thus LPC is among nociceptive endogenous molecules that exert their effect via TRPM8 activation.
Malondialdehyde might be interesting since it is present in larger amounts (about 80-fold) than HNEs in the body, but is a relatively weak electrophile and seldom targets cysteine, different from other reactive secondary products.
Lipofuscin is a granular pigment progressively formed in various tissues during aging. The accumulation of lipofuscin is closely associated with diseases related to aging such as macular degeneration and Alzheimer disease. It is a collection of multi-type LPO products including malondialdehyde and other lipids described above, as well as their protein adducts, and exposure to extreme oxidative stress may exacerbate lipofuscin accumulation.
HNEs are among the LPO products known to modify phosphatidyl ethanolamine.
TRPA1 and TRPV1 are central sensory alarms for acute pain to avoid potentially harmful damage. In a chronic disease stage, however, those are often turned into important aggravating factors amplifying neurogenic inflammation. For LPO processes as well, it should be cautiously considered whether tuning on those two alert signals simply indicates a DEFCON-type warning or contributes to a deteriorating state of war that has already begun. Indeed, TRPA1-mediated neuronal excitation by 4-HNE, isoprostanes, acrolein, and crotonaldehyde causes the release of neuropeptides such as CGRP or substance P, which are key amplifiers of neurogenic inflammation signaling in the periphery and potentiators for nociceptive synaptic strength in the central synapse. Cortical spreading depression, which is considered to be a mechanism for migraine aura, appears to be associated with increased levels of reactive oxygen species and LPO products, and their interactions with TRPA1 and the resulting CGRP release may exacerbate migraine pathology. If TRPA1/TRPV1 are important players for pathological pain development during oxidative stress, it might be conceivable that LPO levels in the serum or urine, can be utilized as indices for quantitatively determining how pain shifts towards chronic and pathological states. Similar concepts are becoming more and more recognized in other diseases including colon cancer and atherosclerosis.
https://www.mdpi.com/1422-0067/15/9/16430

[Progecitor]

Part 2

4-Hydroxynonenal is a uremic toxin. 4-Hydroxynonenal (HNE), one of the major end products of lipid peroxidation, has been shown to be involved in signal transduction and available evidence suggests that it can affect cell cycle events in a concentration-dependent manner. Increased levels of uremic toxins can stimulate the production of reactive oxygen species. This seems to be mediated by the direct binding or inhibition by uremic toxins of the enzyme NADPH oxidase (especially NOX4 which is abundant in the kidneys and heart).
Shortness of breath from fluid buildup in the space between the lungs and the chest wall (pleural effusion) can also be present.
http://www.t3db.ca/toxins/T3D4180

The toxic effects of ROS lead to lipid peroxidation (LPO) and production of 4-hydroxynonenal and malondialdehyde (MDA). The results of LPO induce oxidative damage in the tissues. The antioxidant defense system of the cells that protect against oxidative stress, including superoxide dismutase (SOD), catalase (CAT), and glutathione (GSH), eliminates the excessive ROS.
https://www.jrpsjournal.com/article.asp?issn=2322-1232;year=2019;volume=8;issue=2;spage=217;epage=223;aulast=Khodaei

HNE is an amphiphilic molecule; in fact, it is water soluble and also exhibits strong lipophilic properties. Consequently, HNE tends to concentrate in biomembranes, where phospholipids, like phosphatidylethanolamine, and proteins, such as transporters, ion channels, and receptors, quickly react with HNE. In addition, since it is a highly electrophilic molecule, it easily reacts with low molecular weight compounds, such as glutathione, and at higher concentrations with DNA. An increasing amount of literature indicates that HNE, depending on the concentrations, can potently activate stress response mechanisms, such as mitogen-activated protein kinases (MAPKs), detoxification mechanisms, and inflammatory responses, contributing to cell survival against cytotoxic stress. Furthermore, HNE may modulate redox-sensitive transcription factors such as nuclear factor-kappa B (NFkB), activator protein-1 (AP1), and nuclear factor (erythroid-derived 2)-like 2 (Nrf2). Moreover, its proven interaction with a variety of enzymes and kinases variously involved in cell signaling strongly support its important role in pathophysiology as a cell signaling messenger.
Liver tissue generally has the highest capacity to metabolize HNE, while in other cells, the metabolism of HNE is not so fast, but still very efficient. Usually, HNE, even at very high lipid peroxidation rates, cannot accumulate in an unlimited manner.
HNE protein adducts are easily detectable in peripheral blood, where they primarily involve albumin, transferrin, and immunoglobulins, and also proteins related to blood coagulation, lipid transport, blood pressure regulation, and protease inhibition.
HNE can modify mitochondrial proteins such as cytochrome c, impairing mitochondrial metabolism.
HNE can activate a variety of signal transduction pathways including the Erk pathway, p38MAPK, c-Jun N-terminal kinases (JNK) pathway, and epidermal growth factor receptor (EGFR) pathway. In addition, it can upregulate the extrinsic and intrinsic apoptotic pathways. Moreover, it can regulate the activity of critical transcription factors involved in OS responses such as Nrf2 and peroxisome-proliferator activated receptors (PPARs).
https://www.researchgate.net/profile/Roxane-Prieux/publication/333096253_Involvement_of_4-hydroxy-2-nonenal_in_pollution-induced_skin_damage/links/5e1238fe92851c8364b26db7/Involvement-of-4-hydroxy-2-nonenal-in-pollution-induced-skin-damage.pdf

4-hydroxy 2-nonenal (HNE), a highly toxic and most abundant stable end product of lipid peroxidation, has been implicated in the tissue damage, dysfunction, injury associated with aging and other pathological states such as cancer, Alzheimer, diabetes, cardiovascular and inflammatory complications. HNE is one of the most reactive and under some conditions represents 95 % of the generated aldehydes. The biological occurrence of this molecule appears within the range of 0.1–1 uM. Steady-state concentration of HNE can easily reach 5 uM to 5 mM or more within membranes during various pathological conditions.
The HNE could be reduced to DHN by aldose reductase (AR) or oxidized to HNA by ALDH1. Also, HNE could conjugate with proteins, and more readily with glutathione (GSH) catalyzed by the glutathione S-transferases (GSTs) such as hGSTA4-4 and hGST5.8 to form GS-HNE. The GS-HNE could be reduced by AR to GS-DHN. Both GS-HNE and GS-DHN are actively transported out by multidrug resistance associated protein (MRP) and Ral-binding protein (RLIP76). Recent studies indicate that RLIP76 is responsible for significant (70%) transport of the GS-conjugates of HNE in cultured cells.
At concentrations > 100 uM, HNE and related aldehydes cause lethal toxicity, and at these concentrations, inhibition of glycolytic enzymes, mitochondrial respiration, DNA and protein synthesis also occurs. Low concentrations of HNE have been shown to disturb cellular calcium homeostasis. These aldehydes act as 'toxic second messengers'.
Poli et al have demonstrated that inhibitors of PKC can significantly prevent HNE-induced AP-1 nuclear binding.
HNE also increases the expression and synthesis of the main fibrogenic cytokine, the transforming growth factor beta1 (TGF B1), by macrophages. Besides up-regulation of the inflammatory and TGF B1, HNE has recently been reported to induce the expression and synthesis of monocyte chemotactic protein-1 (MCP1), which plays a major role in atherosclerosis.
The involvement of lipid peroxidation product HNE has been demonstrated in important neurodegenerative diseases such as Alzheimer's disease (AD), Parkinson's desease (PD), multiple sclerosis and other diseases such as cancer, diabetes, inflammatory complications, atherosclerosis, osteoporosis, cataract and age-related macular degeneration.
Increased formation of HNE and protein-HNE has been shown in many inflammatory diseases, such as endotoxemia, ischaemia-reperfusion injury, atherosclerosis, and rheumatoid arthritis.  Further, a recent study by Spite et al indicates that GS-HNE is a more potent inducer of inflammation than nonconjugated HNE. Infact, GS-HNE has been shown to directly activate human neutrophils to generate superoxide anions, which in turn may facilitate HNE generation in a feedback cycle.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3964795/

The oxidative products can build up extensively as they are a result of self-propagating peroxidation chain reactions. The elevation of ROS can be considered a generic response to disease processes.
OS has also been considered as a potential causative agent in tumour genesis, with enhanced oxidative activity in tumour tissues, and elevated aldehyde concentrations in the exhaled breath of patients with cancer probably generated through OS resulting from lipid peroxidation of cell membranes particularly the peroxidation of polyunsaturated fatty acids (PUFAs), such as arachidonic, linoleic acid and linolenic acid (which are cell membrane components) and to a lesser extent monounsaturated fatty acids (MUFAs) e.g. oleic.
PUFAs are very susceptible to oxidation and can form hydroperoxides upon contact with oxygen in air, even without the need for enzymatic mediation.
Apart from pentane and ethane, many markers of oxidative stress have been proposed, e.g. lipid hydroperoxides, 4-hydroxynonenal (4-HNE), 4-hydroxyhexenal, malondialdehyde (MDA) and isoprostane.
4-HNE in particular has been extensively reported in association with OS and lipid oxidative breakdown, especially from n-6 PUFAs, mainly arachidonic and linoleic acids. Since then 4-HNE has been reported in breath condensate, including 4-hydroxy-2-octenal, 4-hydroxy-2-decenal and 4-hydroxy-2-undecenal.
A very large number of esters were found in the human body, 213 were reported in the review of volatiles from the healthy body, so more discussion of the routes to their origins would be interesting. Work has been reported on the ease in which faeces can be used to synthesise esters from carboxylic acids. Therefore acids and alcohols from oxidation of unsaturated fatty acids and in particular under OS conditions could react with themselves or with other gut acids/alcohols to synthesise a wide range of esters.
During heavy oxidative stress, e.g., in patients with severe rheumatologic diseases such as rheumatoid arthritis, systemic sclerosis, lupus erythematosus, chronic lymphedema, or chronic renal failure, serum 4-HNE is increased to concentrations up to 3- to 10-fold higher than physiologic concentrations. 4-HNE (and MDA) have been nominated as major final products of lipid peroxidation.
https://sci-hub.st/https://iopscience.iop.org/article/10.1088/1752-7163/ab7f9d/meta

4-Hydroxynonenal is generated in the oxidation of lipids containing polyunsaturated omega-6 fatty acids, such as arachidonic and linoleic acids, and of their 15-lipoxygenase metabolites, namely 15-hydroperoxyeicosatetraenoic and 13-hydroperoxyoctadecadienoic acids. Although they are the most studied ones, in the same process other oxygenated alpha,beta-unsaturated aldehydes (OaBUAs) are generated also, which can also come from omega-3 fatty acids, such as 4-oxo-trans-2-nonenal, 4-hydroxy-trans-2-hexenal, 4-hydroperoxy-trans-2-nonenal and 4,5-epoxy-trans-2-decenal.
PUFA are very labile and easily oxidizable, thus the maximum beneficial effects of PUFA supplements may not be obtained if they contain significant amounts of toxic OaBUAs, which as commented on above, are being considered as possible causal agents of numerous diseases.
https://en.wikipedia.org/wiki/4-Hydroxynonenal

When activated, neutrophil NADPH oxidases consume large quantities of oxygen to rapidly generate ROS, a process that is referred to as the oxidative burst. These ROS are required for the efficient removal of phagocytized cellular debris and pathogens. In chronic inflammatory diseases, neutrophils are exposed to increased levels of oxidants and pro-inflammatory cytokines that can further prime oxidative burst responses and generate lipid oxidation products such as 4-hydroxynonenal (4-HNE).
Taken together, these data suggest that 4-HNE-induces a pleiotropic mechanism to inhibit neutrophil function. These mechanisms may contribute to the immune dysregulation associated with chronic pathological conditions where 4-HNE is generated.
Phagocytosis is an innate mechanism for the clearance of pathogens and apoptotic and senescent cells by the immune system.
Clinically, inefficient phagocytosis can increase the incidence of bacterial and fungal infections, skin abscess, inflammatory bowel disease, oral ulcers and organ damage.
Non-enzymatic lipid peroxidation induced by oxidants such as superoxide, hydrogen peroxide, hypochlorous acid and peroxynitrite generates reactive lipid species such as 4-hydroxynonenal (4-HNE) from polyunsaturated fatty acids (PUFA) of membrane lipid bilayers.
Experimental models of inflammatory diseases demonstrate that 4-HNE is produced by activated neutrophils which can serve as a potent chemoattractant for further leukocyte recruitment to the inflammatory foci.
Acute and chronic inflammatory responses such as those associated with inflammatory disease are suggested to induce generation of 4-HNE in tissue and vascular compartments. Rapid recruitment of neutrophils to the site of injury and increased oxidative stress support this hypothesis. Accumulation of 4-HNE and 4-HNE–modified proteins has been detected in aging and in various diseases such as cancer, atherosclerosis, neurodegenerative disorders, metabolic syndrome, diabetes and autoimmune diseases. Recent studies have suggested that 4-HNE can range from 0.05 to 0.15 uM in healthy human blood and serum. Under pathological conditions, the tissue and plasma membrane concentration of 4-HNE increases significantly and can reach >100 uM in locations close to the core of the lipid peroxidation sites.
Although neutrophils are designed to survive the reactivity of the inflammatory foci, prolonged inflammation combined with inadequate antioxidant defenses can make these cells susceptible to oxidative modifications by reactive lipids.
Exposure of 4-HNE to isolated cells can modify key glycolytic enzymes such as glyceraldehyde-3-phosphate dehydrogenase and glucose-6-phosphate dehydrogenase. In order to meet the rapidly changing cellular energy and metabolite demands of activation, phagocytic cells increase the metabolic rate through glycolysis and/or switch the metabolic phenotype from oxidative to glycolytic.
Oxidative burst plays critical roles in the cellular function of neutrophils. Clinical conditions such as chronic granulomatous disease have chronic inflammation and inefficient clearance of cellular debris due to defective NADPH oxidase activity. When neutrophils undergo an oxidative burst, large quantities of ROS are generated within a short duration and at a high concentration close to the cellular compartment. In addition, activated neutrophils undergo rapid apoptosis and NETosis, releasing DNA, myeloperoxidase and proteases creating a highly reactive and oxidative environment capable of inducing lipid peroxidation and generating reactive lipid species such as 4-HNE.
In this study we demonstrate that the non-enzymatic lipid peroxidation product, 4-HNE can inhibit phagocytosis, oxidative burst and cellular metabolism, the key functions that regulate the immune response of human neutrophils and monocytes.
Previous studies have shown that 4-HNE has the potential to act as chemotactic agent to attract neutrophils to the site of inflammation. It is likely that neutrophils at sites of inflammation or tissue injury get exposed to very high concentrations of reactive aldehydes and other intermediates of oxidative stress that exceed the concentrations used in this study. 4-HNE treatment inhibits the initial rate, peak and total amount of respiratory burst suggesting inhibition of multiple pathways associated with oxidative burst.
Since this reactive lipid intermediate is produced at sites of inflammation the partial suppression of this essential mechanism of innate immunity may promote a chronic inflammatory response and the failure to kill pathogens.
https://www.sciencedirect.com/science/article/pii/S2213231716300490

The macrocyclic pyrrolizidine alkaloid senecionine is metabolized in the rat liver by the mixed function oxidase system to 4-hydroxyhexenal, and that the hepatoxicity of these alkaloids is likely mediated by this aldehyde.
Enzymes with functional SH-groups inactivated by 4-hydroxyalkenals can be reactivated, for example, by excess GSH or cysteine.
Although it seems rather unlikely that HNE or other aldehydes can reach overall concentrations in the range of 100 uM in cells or organs, it is conceivable that such levels may be built up locally near or within peroxidizing membranes for a short time because of their high lipophilicity. It has been calculated, for example, that the concentration of HNE in the lipid bilayer of isolated peroxidizing microsomes is about 4.5 mM, and it has been proposed that HNE might attack critical target proteins within the lipid bilayer.
High concentrations of 4-hydroxyaikenals in the millimolar range are acutely toxic for mammalian cells and lead to cell death within 1 h or less. Preceding or accompanying cell death are a multitude of effects such as rapid depletion of glutathione, decrease in protein thiols, onset of lipid peroxidation, disturbance of calcium homeostasis, inhibition of DNA, RNA, and protein synthesis, inhibition of respiration and glycolysis, lactate release, and morphological changes.
A disarrangement of the cytoskeletal proteins could also explain the reports that cultured hepatocytes show, after exposure to HNE (100 uM) an altered morphology with a spherical shape and an intense granular structure.
It was shown that HNE inhibits the key reaction, that is, pyridine nucleotide hydrolysis. The consequence would be an overload of mitochondria with Ca2+ and an inhibition of Ca2+-dependent mitochondrial enzymes. The cytotoxicity of HNE could therefore in part be due to a disturbance of mitochondrial functions.
In experiments with HeLa cells it has been demonstrated that HNE treatment (150 uM, 1 h) causes the binding of a specific protein, probably the HSF, to the DNA-HSE sequence regulating the expression of the hsp 70. Exactly the same effects were observed after exposure of cells to heat.
Recently it was shown that MDA can also be formed enzymatically from spermine. A polyamine oxidase converts spermine into 3-amino-propanal which is then oxidized by an aminoxidase to MDA. Formation of MDA by this enzymatic process was observed in homogenates of transformed kidney cells supplemented with spermine. Spermidine cannot be converted enzymatically to MDA.
Thus all lipids containing omega-6 PUFAS (18:2, 20:4) will give rise to 4-hydroxynonenal and hexanal, whereas omega-3 PUFAS will form 4-hydroxyhexenal and propanal. Similarly malonaldehyde will be formed from lipids containing PUFAS with 3 or more methylene interrupted double bonds (mainly 20:4 and 22:6).
Even very low HNE can produce some remarkable effects: Stimulation of phospholipase C and adenylate cyclase, recruitment of neutrophils, reduction of c-myc expression, induction of genotoxic effects.
https://scholar.google.com/scholar?hl=en&as_sdt=0%2C5&q=Chemistry+and+biochemistry+of+4-hydroxynonenal%2C+malonaldehyde+and+related+aldehydes&btnG=

Malondialdehyde as a Potential Oxidative Stress Marker for Allergy-Oriented Diseases: An Update
We considered studies involving both paediatric and adult patients affected by rhinitis, asthma, urticaria and atopic dermatitis.
Exogenous factors, such as UV exposure, chronic stress, intense exercise, infections, allergens and pollutants, also contribute to ROS production.
In this process, called lipid peroxidation, both the lipid hydroperoxides and the lipid peroxyl radicals can undergo cyclization and cleavage processes, resulting in the formation of secondary products.
Oral treatment with antihistamines influences the levels of these oxidative stress markers, leading to a statistically significant decrease in the erythrocyte values.
Based on the considered cohorts of non-allergic and mixed asthmatic patients, there is a clear consensus among all authors: the MDA levels assessed in the blood samples were found to be elevated in the affected patients. Furthermore, these levels were associated with increased asthma severity and poorer disease control.
https://www.mdpi.com/1420-3049/28/16/5979

4-Hydroxynonenal contributes to NGF withdrawal-induced neuronal apoptosis
We show that HNE-adduct immunoreactivity is dramatically increased after NGF-withdrawal in an NADPH oxidase-dependent manner. Moreover, HNE-adducts appear to contribute to NGF-deprivation-induced apoptotic signal transduction because microinjected HNE-adduct antiserum protects sympathetic neurons from NGF withdrawal. In conclusion, this report suggests the direct contribution of endogenously generated HNE in the stimulation of apoptotic signal transduction in neurons.
https://onlinelibrary.wiley.com/doi/abs/10.1046/j.1471-4159.2003.01749.x

Physiological concentration of 4-HNE ranges from 0.1 to 3 uM, whereas high concentrations of 4-HNE (10 uM to 5 mM) have been reported following toxic insults.
Recently, it has been shown by us and others that cytotoxic concentrations of 4-HNE in PC12 cells alter the sensitivity of dopamine (DA)-D2, cholinergic-muscarinic, benzodiazepine and serotonin (5-HT)2A receptors.
The early increase in total cellular Ca2+ via NMDA receptors and other pathways triggered due to the profound energy failure has also been reported in various neurodegenerative disorders. 4-HNE induced neurodegeneration by elevating cytosolic Ca2+ levels are largely suggested due to activation of 2Na+/Ca2+ transporter-mediated efflux from mitochondria in experimental models of neuronal disorder. Mitochondrial calcium accumulation and oxidative stress have shown to trigger the opening of a high-conductance pore in the inner mitochondrial membrane and leads to collapse the electrochemical potential for H+, thereby arresting ATP production and triggering production of reactive oxygen species.
https://scholar.google.com/scholar?hl=en&as_sdt=0%2C5&q=NGF+induced+differentiated+PC12+cells+as+in+vitro+tool+to+study+4-hydroxynonenal+induced+cellular+damage&btnG=

Modulation of D1-like dopamine receptor function by aldehydic products of lipid peroxidation
The 4-HNE and nonenal were most effective in modulating both the specific D1-like receptor binding and function as measured by adenylate cyclase activation.
In rat striata, 4-HNE causes inactivation of the dopaminergic transporter through binding to the protein, resulting in reduced uptake of dopamine. 4-HNE also impairs the functions of other transporters such as the glucose transporter and glutamate transporter, causing disruption of cellular calcium homeostasis. Although 4-HNE has previously been shown to disrupt coupling and function of muscarinic cholinergic receptors and metabotropic glutamate receptors, the effect of lipid peroxidation on dopaminergic receptors and their signaling pathways remains an enigma.
https://www.sciencedirect.com/science/article/abs/pii/S0006899302042798

The fact that aldose reductase (AR), aldehyde reductases, and aldehyde dehydrogenases can essentially compete for various aldehydes, makes it challenging to determine specific physiological role for AR.
It is possible that activation of aldehyde dehydrogenase 2 (ALDH2) reduces 4-HNE accumulation and protects hearts from I/R injury. Could the accumulation of 4-HNE observed in the diabetic hearts (especially during I/R) be due to lack of ALDH2?
https://www.frontiersin.org/journals/endocrinology/articles/10.3389/fendo.2021.636267/full

Oxidative stress is widely known to be a major contributor in the pathogenesis of dry eye disease (DED). 4-Hydroxynonenal (4-HNE), a well-known byproduct frequently measured as an indicator of oxidative stress-induced lipid peroxidation, has been shown to be elevated in both human and murine corneal DED samples.
A significant increase in activation of NF-kB and production of pro-inflammatory cytokines IL-6 and IL-8 was observed after treatment with 4-HNE. Exposure to N-acetylcysteine (NAC), an antioxidant and ROS scavenger, antagonized the oxidative effects of 4-HNE on human corneal epithelial cells.
https://link.springer.com/article/10.1007/s00417-020-04647-2

4-Hydroxynonenal (4-HNE) can increase the synthesis of interleukin-8 (IL-8) in bronchial epithelium cells (16HBE). 4-HNE increased the expression of Interleukin-8 in bronchial epithelium cells, via increasing the transcription activities of AP-1 by ERK1 cell signal transduction pathways. Ginkgolide B inhibited synthesis of IL-8 by blocking ERK1-AP1 transduction pathways.
https://europepmc.org/article/med/18953964

Septic encephalopathy (SE) is a frequent complication in severe sepsis. The data show progressive oxidative damage to the hippocampus, identified by increased 4-hydroxynonenal expression, associated with an increase in Nox2 gene expression in the first days after sepsis. Pharmacological inhibition of Nox2 with apocynin completely inhibits hippocampal oxidative damage in septic animals as well as the development of long-term cognitive impairment in the survivors.
https://link.springer.com/article/10.1186/cc12996

4-HNE is considered one of the major mediators of oxidative stress in cells and tissues, that collectively lead to cell senescence by affecting the expression of various senescence-related signaling pathways (such as NF-kB, Nrf2, Akt/PKB, and mTOR).
The compound 4-HNE and the 4-HNE-protein complex are often detected in patients diagnosed with neurodegenerative diseases. Studies have shown that patients with AD, PD, HD, or ALS have increased levels of 4-HNE-protein adducts in their body fluid. The 4-HNE-protein adducts can induce autoimmunity, and may be associated with the development of neurodegenerative diseases.
Additionally, some studies have shown that in addition to the direct relationship between 4-HNE/a-syn and dopaminergic transmission changes, 4-HNE can directly affect dopamine transmission by acting on dopamine receptors and promotes the pathogenesis of PD.
Toxic aldehydes such as 4-HNE, produced via LPO due to the accumulation of ROS, play an important role in the development of aging-related diseases.
This review also found that the toxic effect of 4-HNE on lipoprotein is related to the formation of atherosclerosis, and its response to collagen may be the cause of cardiovascular tissue sclerosis. 4-HNE can activate various molecules, such as NF-kB and NOX4, to induce RPE apoptosis, lysosomal imbalance, and lipofuscin production, resulting in photoreceptor cell destruction and consequently, age-related visual impairment such as AMD.
https://www.hindawi.com/journals/jir/2022/2233906/

Cilostazol Attenuates 4-hydroxynonenal-enhanced CD36 Expression on Murine Macrophages via Inhibition of NADPH Oxidase-derived Reactive Oxygen Species Production
HNE-enhanced expression of CD36 was reduced by these inhibitors, which indicated a role for NADPH oxidase and 5-LO on CD36 expression.
https://synapse.koreamed.org/articles/1025660

4-Hydroxynonenal enhances CD36 expression on murine macrophages via p38 MAPK-mediated activation of 5-lipoxygenase
Increased levels of 4-hydroxynonenal (HNE) and 5-lipoxygenase (5-LO) coexist in atherosclerotic lesions but their relationship in atherogenesis is unclear. HNE (10 uM) enhanced CD36 expression in association with an increased uptake of oxLDL. Collectively, these data suggest that p38 MAPK-mediated activation of 5-LO by HNE might enhance CD36 expression, consequently leading to the formation of macrophage foam cells.
https://www.sciencedirect.com/science/article/abs/pii/S0891584908007557

Protein adducts of malondialdehyde and 4-hydroxynonenal contribute to trichloroethene-mediated autoimmunity via activating Th17 cells
TCE exposure has also been implicated in the development of various autoimmune diseases (ADs), such as systemic lupus erythematosus (SLE), systemic sclerosis and fasciitis, both from occupational and environmental exposures.
https://www.sciencedirect.com/science/article/abs/pii/S0300483X11005063

Niacin restriction upregulates NADPH oxidase and reactive oxygen species (ROS) in human keratinocytes
NAD+ is a substrate for many enzymes, including poly(ADP-ribose) polymerases and sirtuins, which are involved in fundamental cellular processes including DNA repair, stress responses, signaling, transcription, apoptosis, metabolism, differentiation, chromatin structure, and life span.
These alterations result, at least in part, from increased expression and activity of NADPH oxidase, whose downstream effects can be reversed by nicotinamide or NADPH oxidase inhibitors. Our data support the hypothesis that glutamine is a likely alternative energy source during niacin deficiency and we suggest a model for NADPH generation important in ROS production.
https://www.sciencedirect.com/science/article/abs/pii/S0891584907006818

4-HNE is known to alter permeability of the blood-brain barrier during oxidative stress, thus penetrating into the brain from the blood vessels. Under such circumstances, it could trigger the vicious circle of lipid peroxidation within the brain, which may be important for the pathology of the neurodegenerative diseases, trauma, and shock as well as for inflammatory processes and even brain tumors.
It should be mentioned here that accumulation of 4-HNE in blood vessels progresses by aging, reaching its plateau between the age of 60 to 65 years. Accumulation of 4-HNE in arteries, notably in the aorta, is also known to be influenced by fat-rich food and (oxidative) stress. Furthermore, in obese, diabetic patients, the blood-originating 4-HNE accumulates in adipose tissues and alters growth and metabolism of the (pro)adipocytes, which might cause inflammation relevant for metabolic syndrome and systemic vascular stress that is not only chronic but also acute. In favor of this assumption are recent findings revealing vascular stress as a possible cause of abundant blood-originating 4-HNE accumulation in the lungs of patients with SARS-CoV-2 infection associated with the lethal outcome of COVID-19.
Our results revealed significantly elevated levels of 4-HNE in patients with Post-Traumatic Stress Disorder.
https://www.mdpi.com/2218-273X/11/9/1365

Post-mortem Findings of Inflammatory Cells and the Association of 4-Hydroxynonenal with Systemic Vascular and Oxidative Stress in Lethal COVID-19
The results revealed abundant 4-HNE in the vital organs, but the primary origin of 4-HNE was sepsis-like vascular stress, not an oxidative burst of the inflammatory cells. The most affected organs were the lungs with diffuse alveolar damage and the brain with edema and reactive astrocytes, whereas despite acute tubular necrosis, 4-HNE was not abundant in the kidneys, which had prominent SOD2.
Myeloperoxidase (MPO), a mediator of inflammation and oxidative stress, was found to be several-fold upregulated in the lungs and whole blood of COVID-19 patients.
4-HNE is a well-known modulator of cellular functions and was found to induce NLRP3, resulting in inflammasome activation, while it is also acknowledged as a reliable biomarker of ferroptosis, occurring also in lethal COVID-19. Through the activation of the extracellular signal-regulated kinases (ERK) pathway, 4-HNE upregulates HO-1, while its effect on SOD2 depends on the duration of exposure.
Our preliminary findings revealed the association of 4-HNE with lethal outcomes in COVID-19 patients, reflecting altered redox homeostasis and sepsis-like systemic vascular and oxidative stress mediated by the 4-HNE protein adducts, not being associated with the cytokine storm or even inflammation itself.
The results of this study summarize the most important common autopsy findings of patients who died after aggressive COVID-19 and confirm our preliminary findings on 4-HNE as an important factor of SAR-CoV-2 infection causing sepsis-like systemic vascular and oxidative stress. Namely, 4-HNE protein adducts were found in all the vital organs and were associated especially with inflammation, edema, and tissue destruction. This was most prominent in the lungs and brain, while in the other vital organs analyzed, 4-HNE was less pronounced.
Therefore, the lipid peroxidation trigger and 4-HNE mediated systemic vascular and oxidative stress could be associated with an uncontrolled (auto)immune stress response, which may lead to ARDS and MOF, as observed in our patients.
https://www.mdpi.com/2073-4409/11/3/444

Both in vivo and in vitro experiments showed that HNE can be catabolically disposed via omega- and omega-1-oxidation in rat liver and kidney, with little activity in brain and heart. Dietary experiments showed that omega- and omega-1-hydroxylation of HNA in rat liver were dramatically up-regulated by a ketogenic diet, which lowered HNE basal level. HET0016 inhibition and mRNA expression level suggested that the cytochrome P450 4A are main enzymes responsible for the NADPH-dependent omega- and omega-1-hydroxylation of HNA/HNE.
https://www.jbc.org/article/S0021-9258(20)33315-9/fulltext

[Progecitor]

There is a theory on the antioxidant effects of sleeping that fits my personal experiences really well. As we have an elevated base level of lipid peroxidation we show signs of sleep deprivation even when rested. This is one of the most evident links to ME/CFS and other similar conditions. The constant presence of depression and fatigue is a clear indication of the ongoing oxidative stress. When I am tired previously effective supplements have a way reduced benefit on POIS. In my case conventional sleep deprivation leads to a kind of super POIS state, which is a superposition of the condition and indicates a very robust oxidative stress. I also wake up feeling better when I dreamt, but I hardly ever dream or remember the fact if I did, which indicates a lack of paradoxical sleep, especially in the acute POIS phase.

Current experimental evidence suggests that sleep deprivation promotes oxidative stress. Wakefulness involves high neuronal metabolism to maintain neuronal electrical potentials, which requires a great amount of oxygen, resulting in a significant production of oxidants. Thus, sleep represents a state with an increased antioxidant activity which promotes a brain protection against free radicals via a diminution in oxidant production. The ROS and other oxidative stress markers could be accumulated in the brain tissue during wakefulness, and after reaching out a threshold, they could behave as sleep promoters.
In the present report we addressed evidence that supports the hypothesis that sleep is a dynamic-resting state with antioxidative properties. In order to accomplish the aim of the present paper we also contemplated in our revision evidence that suggests that oxidative stress may be the inductor of sleep and thus confirmed its antioxidant properties.
Paradoxical sleep (PS, also called rapid eye movement (REM) sleep) is associated with high neuronal metabolic activity and loss of muscular tone, whereas slow-wave sleep (SWS) is characterized by low neuronal metabolic activity. The original hypothesis about the antioxidant properties of sleep referred that SWS would accomplishes for the most antioxidative part of sleep. This assumption would be confirmed once SWS is associated with low neuronal metabolic activity and therefore with less oxygen consumption. The experimental data extracted from PSD points out to a different perspective: paradoxical sleep plays a significant role as antioxidative element and whenever prevented, oxidative stress increases.
https://onlinelibrary.wiley.com/doi/full/10.1155/2015/234952

[Progecitor]

Regarding our cognitive problems it has been already clear that we have at least a mild cognitive impairment (MCI) by definition. However after reading this article it is also clear that we are extremely susceptible to developing Alzheimer’s disease as well, as at least in POIS mode we show all the warning signs of it very evidently.

The 4 red flags are the following:

1. Poor memory
Amen said the first warning sign is that your memory is worse than it was 10 years ago.
While occasional forgetfulness is a normal part of aging, people with dementia struggle to recall recent events, conversations or major details.
The hippocampus — a brain region responsible for forming new memories — is one of the first areas affected by Alzheimer’s.

2. Poor judgment and impulsivity
Damage to your frontal lobes, key areas for decision-making and reasoning, can lead to difficulties in understanding risks, tackling everyday problems and managing finances.
It’s “sort of like your [brain] is going offline,” Amen explained.

3. Short attention span
People with Alzheimer’s can have trouble concentrating or paying attention long enough to complete tasks that were once simple.
Amen said this occurs when “distractibility — not like ADHD that you’ve had your whole life — seems to be accelerating.”

4. Low mood
Research has found that up to half of Alzheimer’s patients suffer depressive symptoms, which is much more than the general population.
Patients frequently experience emotional changes like irritability or severe mood swings and often have less control over their feelings because the disease is affecting brain areas responsible for emotion regulation.
They may become confused or anxious about change, or about situations that take them outside of their comfort zone.
https://nypost.com/2024/12/12/health/4-warning-signs-that-may-indicate-early-alzheimers-disease/

While the parallelism should be pretty evident for all of us, I can add some of my own thoughts on this:

1. The word recall problems or the loss of short term and contextual memory are clear sings of poor memory. I can’t even recall a simple telephone number half a minute after hearing it.
2. The professor put it very aptly when he said that it is like our brain goes offline, this is precisely how I feel in acute POIS, even my inner monologue dies or it is very basic.
3. At least my attention span may be close to normal when at rest, though in bad POIS I have this psychogenic nausea, which deters me even from otherwise pleasant activities. Also at times when I do a lot of physical work, there comes a time when I begin to feel my thoughts drifting away incessantly and it feels like I am losing my grasp on reality.
4. I have some level of brain fog and blurry vision all the time. Anhedonia is my middle name practically. Joy is a very distant feeling in my life, however the opposite is also true. Even though one of my close relative had died recently, I only knew that I was sad, but I simply could not feel it and hence I couldn’t even cry.

So what we can do about this? Well, probably not much. However doing nothing, as I had done for two decades, is really just the worst idea. When I take great amounts of antioxidants I sometimes feel some cursory anti-depressive effect. This is very indicative of the underlying issue being excessive lipid peroxidation, which is also supported by theoretical research. Exorbitant ROS production is a dynamic process while in POIS and that is the reason why the alleviation is only temporary and not complete. Unfortunately regular laboratory blood tests are incapable to reveal this, which gives a false sense of healthiness, ultimately converted to gaslighting in a common setting. Of course POIS, ME/CFS, long covid, etc all have this in common. They are only variations of the same process. I only wish doctors could understand and diagnose this evident process before trying to guess at the root of these diseases as it would make everything so much easier. 4-HNE and other LPOs are clear culprits and therefore while refining the diagnostic method researchers should focus on them with utmost effort.