Refining Antioxidant (ROS & RNS) Therapy in Autism - Selenium and Molybdenum

Today’s post is about further refining antioxidant therapy.

As we saw in a recent post, oxidative and nitrosative stress is a very common feature of autism and is treatable with OTC products.

The cheapest antioxidant, N-acetylcysteine (NAC), looks to be the best one, but there are numerous others with exotic names and equally exotic prices.

Today we just look at selenium and molybdenum.  Selenium was on my to-do list for a long time because it affects some key enzymes call GP_X (glutathione peroxodases).

Molybdenum was enthusiastically recommended in a recent comment and this blog has previously touched on Molybdenum Cofactor Sulfurase (MOCOS).

Rather surprisingly, there is a commercial product that contains NAC, Selenium and Molybdenum. 

Selenium and GP_X (glutathione peroxodases)

There are eight different glutathione peroxodases, but GPx1, GPx2, GPx3, and GPx4 are all made from selenium.

GP_X speeds up the antioxidant reactions that involve glutathione (GSH).

In autism we know that both GSH and GP_X are lacking.

We know how to make more GSH, just take some NAC.  But what about the catalyst GP_X? 

There may be an equally easy way to increase that. 

Selenium and Thyroid  Enzymes

Selenium is also part of the three deiodinase enzymes D1, D2 and D3.

The active thyroid hormone is called T3, but most of what is circulating in your body is the inactive pro-hormone form called T4.

Deiodinase 1 (D1)  both activates T₄ to produce T₃ and inactivates T₄. Besides its increased function in producing extrathyroid T₃, its function is less well understood than D2 or D3.

Deiodinase 2 (D2), located in the ER membrane, converts T₄ into T₃ and is a major source of the cytoplasmic T₃ pool.  It looks like some people with autism may lack D2 in their brain.

Deiodinase 3 (D3) prevents T₄ activation and inactivates T₃. It looks like some people with autism have too much D3 in their brain.

D2 and D3 are important in homeostatic regulation in maintaining T₃ levels at the plasma and cellular levels.

·        In hyperthyroidism D2 is down regulated and D3 is upregulated to clear extra T₃

·        in hypothyroidism D2 is upregulated and D3 is downregulated to increase cytoplasmic T₃ levels

Serum T3 levels remain fairly constant in healthy individuals, but D2 and D3 can regulate tissue specific intracellular levels of T3 to maintain homeostasis since T3 and T4 levels may vary by organ.  

It appears that some people with autism may have central hyperthyroidism, meaning in their brain.

Regular readers may recall this post:-

Central Hypothyroidism or Low Brain D2 Levels in Autism

The major source of the biologically active hormone T3 in the brain is the local intra-brain conversion of T4 to T3, while a small fraction comes from circulating T3. 

As evidence derived from in vitro studies suggests, in response to oxidative stress D3 increases while D2 decreases (Lamirand et al., 2008; Freitas et al., 2010).  As we know in the autistic brain we have a lot of oxidative stress.

Furthermore, in ASD, the lower intra-brain T3 levels occur in the

Absence of a systemic T3 deficiency (Davis et al., 2008), most likely due to the increased activity of D3.

So in some autistic brains we have too much D3 which is inactivating T3 and preventing T4 being converted to T3.

Reduced D2 is reducing the conversion of T4 to T3. 

We would therefore want to increase D2 in some autism.

This can be achieved by:-

·        Reducing oxidative stress, which we are already sold on. 

·        We can also potentially upregulate the gene that produces D2 using some food-based genetic therapy. Kaempferol (KPF) appears to work and may explain why broccoli sprout powder makes some people go hyper and some others cannot sleep  

The Small Polyphenolic Molecule Kaempferol Increases Cellular Energy Expenditure and Thyroid Hormone Activation

The cAMP-responsive gene for type 2 iodothyronine deiodinase (D2), an intracellular enzyme that activates thyroid hormone (T3) for the nucleus, is approximately threefold upregulated by KPF

·        Perhaps low levels of selenium differentially affect the synthesis of D1, D2 and D3?

  

Where does selenium come from? 

We know from Chauham/James that selenium levels are reduced in autism, but we also know that selenium levels vary widely by geography.  

You get selenium from your diet and the level of selenium in the soil varies widely.  It is widely held that most healthy people should have plenty selenium in their diet. 

In the following paper there is an analysis of Selenium status in Europe and the Middle East.

Since we have plenty of Polish readers I have included the chart with the Polish data (on the left).  It shows that Polish people may be a little deficient in selenium.

You can see the level of selenium in Poland is below that needed to optimise plasma GPx activity.

So if you already have reduced GPx activity, because of autism, and you really need to make the most of your limited glutathione (GSH) because you have oxidative/nitrosative stress, then a little extra selenium could be just what the doctor should have ordered.

  

A Review of Dietary Selenium Intake and Selenium Status in Europe and the Middle East

Se is an essential non-metal trace element [3] that is required for selenocysteine synthesis and is essential for the production of selenoproteins [4]. Selenoproteins are primarily either structural or enzymatic [2], acting as catalysts for the activation of thyroid hormone and as antioxidants, such as glutathione peroxidases (GPxs) [5]. GPx activity is commonly used as a marker for Se sufficiency in the body [6], where serum or plasma Se concentrations are believed to achieve maximum GPx expression at 90–100 μg/L (90.01 μg/L as proposed by Duffield and colleagues [7] and 98.7 μg/L according to Alfthan et al. [8]). However, plasma selenoprotein P (SEPP1) concentration is a more suitable marker than plasma GPx activity [9]. Prospective studies provide some evidence that adequate Se status may reduce the risk of some cancers, while elevated risk of type 2 diabetes and some cancers occurs when the Se concentration exceeds 120 μg/L [10]. Higher Se status has been linked to enhanced immune competence with better outcomes for cancer, viral infections, including HIV progression to AIDS, male infertility, pregnancy, cardiovascular disease, mood disorders [2] and, possibly, bone health [11–14].

  

Selenium and NAC for Rats with TBI

Perhaps not surprisingly, selenium and NAC have been found beneficial for Rats unfortunate enough to have sufferred a traumatic brain injury (TBI).

 N-Acetylcysteine and Selenium Modulate Oxidative Stress, Antioxidant Vitamin and Cytokine Values in Traumatic Brain Injury-Induced Rats

It has been suggested that oxidative stress plays an important role in the pathophysiology of traumatic brain injury (TBI). N-acetylcysteine (NAC) and selenium (Se) display neuroprotective activities mediated at least in part by their antioxidant and anti-inflammatory properties although there is no report on oxidative stress, antioxidant vitamin, interleukin-1 beta (IL)-1β and IL-4 levels in brain and blood of TBI-induced rats. We investigated effects of NAC and Se administration on physical injury-induced brain toxicity in rats. Thirty-six male Sprague–Dawley rats were equally divided into four groups. First and second groups were used as control and TBI groups, respectively. NAC and Se were administrated to rats constituting third and forth groups at 1, 24, 48 and 72 h after TBI induction, respectively. At the end of 72 h, plasma, erythrocytes and brain cortex samples were taken. TBI resulted in significant increase in brain cortex, erythrocytes and plasma lipid peroxidation, total oxidant status (TOS) in brain cortex, and plasma IL-1β values although brain cortex vitamin A, β-carotene, vitamin C, vitamin E, reduced glutathione (GSH) and total antioxidant status (TAS) values, and plasma vitamin E concentrations, plasma IL-4 level and brain cortex and erythrocyte glutathione peroxidase (GSH-Px) activities decreased by TBI. The lipid peroxidation and IL-1β values were decreased by NAC and Se treatments. Plasma IL-4, brain cortex GSH, TAS, vitamin C and vitamin E values were increased by NAC and Se treatments although the brain cortex vitamin A and erythrocyte GSH-Px values were increased through NAC only. In conclusion, NAC and Se caused protective effects on the TBI-induced oxidative brain injury and interleukin production by inhibiting free radical production, regulation of cytokine-dependent processes and supporting antioxidant redox system.

  

Dietary selenium stabilizes glutathione peroxidasemRNA in rat liver

  

And now to Molybdenum 

Molybdenum (Mo) is a trace dietary element necessary for human survival.

Low soil concentration of molybdenum in a geographical band from northern China to Iran results in a general dietary molybdenum deficiency, and is associated with increased rates of esophageal cancer.  Compared to the United States, which has a greater supply of molybdenum in the soil, people living in those areas have about 16 times greater risk for esophageal cancer.
So you would not want to have molybdenum deficiency.

Four Molybdenum-dependent enzymes are known, all of them include molybdenum cofactor (Moco) in their active site: sulfite oxidase, xanthine oxidoreductase, aldehyde oxidase, and mitochondrial amidoxime reductase.

Moco cannot be taken up as a nutrient, and thus it requires to made in your body from molybdenum.

If your body cannot make enough Moco you may develop what is called molybdenum cofactor deficiency, which would ultimately kill you. It is ultra rare.

Symptoms include early seizures, low blood levels of uric acid, and high levels of sulphite, xanthine, and uric acid in urine.


When caused by a mutation in the MOCS1 gene it is called the type A variant.

Molybdenum cofactor deficiency may indeed be extremely rare, but MOCS1 is a known autism gene.  Perhaps there exists partial molybdenum cofactor deficiency, which is not rare at all?

Source:-  Identification of candidate intergenic risk loci in autism spectrum disorder

MOCOS (Molybdenum cofactor sulfurase)


Molybdenum cofactor sulfurase is an enzyme that in humans is encoded by the MOCOS gene.

MOCOS sulfurates the molybdenum cofactor of xanthine dehydrogenase (XDH) and aldehyde oxidase (AOX1), which is required for their enzymatic activities.

MOCOS is downregulated in autism and is suggested to induce increased oxidative-stress sensitivity, which would not be good.

So it looks like we need a clever way to upregulate MOCOS.

You need adequate molybdenum cofactor (Moco), for which you do need adequate molybdenum.

You need the genes MOCS1 and MOCOS to be correctly expressed.

SIRT1 activation, which is a future therapy for Alzheimer’s, is suggested to increase MOCOS, as may NRF2.

Sirtuin-activating compounds (STAC) are chemical compounds having an effect on sirtuins, a group of enzymes that use NAD+ to remove acetyl groups from proteins. They are molecules able to prevent aging related diseases like Alzheimer's, diabetes, and obesity.  There is quite a long list that includes ranges from polyphenols such as resveratrol, the flavonols fisetin, and quercetin also butein, piceatannol, isoliquiritigenin,

Fisetin is found in strawberries, cucumbers and supplements.  In normal animals, fisetin can improve memory; it also can have an effect on animals prone to Alzheimer's.

Modulation of p25 and inflammatory pathways by fisetin maintains cognitive function in Alzheimer's disease transgenic mice

Here is the excellent French paper on MOCOS:-

Olfactory stem cells reveal MOCOS as a new player in autism spectrum disorders

With an onset under the age of 3 years, autism spectrum disorders (ASDs) are now understood as diseases arising from pre- and/or early postnatal brain developmental anomalies and/or early brain insults. To unveil the molecular mechanisms taking place during the misshaping of the developing brain, we chose to study cells that are representative of the very early stages of ontogenesis, namely stem cells. Here we report on MOlybdenum COfactor Sulfurase (MOCOS), an enzyme involved in purine metabolism, as a newly identified player in ASD. We found in adult nasal olfactory stem cells of 11 adults with ASD that MOCOS is downregulated in most of them when compared with 11 age- and gender-matched control adults without any neuropsychiatric disorders. Genetic approaches using in vivo and in vitro engineered models converge to indicate that altered expression of MOCOS results in neurotransmission and synaptic defects. Furthermore, we found that MOCOS misexpression induces increased oxidative-stress sensitivity. Our results demonstrate that altered MOCOS expression is likely to have an impact on neurodevelopment and neurotransmission, and may explain comorbid conditions, including gastrointestinal disorders. We anticipate our discovery to be a fresh starting point for the study on the roles of MOCOS in brain development and its functional implications in ASD clinical symptoms. Moreover, our study suggests the possible development of new diagnostic tests based on MOCOS expression, and paves the way for drug screening targeting MOCOS and/or the purine metabolism to ultimately develop novel treatments in ASD.  

Lately, a diminished seric expression of glutathione, glutathione peroxidase, methionine and cysteine has been highlighted in a meta-analysis from 29 studies on ASD subjects.⁴⁵ Along this line, purines and purine-associated enzymes are recognized markers of oxidative stress. ROS are generated during the production of uric acid, catalyzed by xanthine oxidase and XDH.⁴⁶ Conversely, uric acid is nowadays recognized as a protective factor acting as a ROS scavenger.^{47, 48} Interestingly, allopurinol, a xanthine oxidase inhibitor, was found efficient in reducing symptoms, especially epileptic seizures, in ASD patients displaying high levels of uric acid.⁴⁹ However, in our cohort, only 3 out of 10 patients exhibited an abnormal uric acid secretion. It can therefore be postulated that still unknown other MOCOS-associated mechanisms may have a role in the unbalanced stress response observed in ASD OSCs.

Identifying and manipulating downstream effectors of MOCOS will be the next critical step to better understand its mechanisms of action. In parallel, we plan to ascertain some of its upstream regulators. For example, bioinformatic analyses revealed that the promoter region of MOCOS includes conserved binding sites for transcription factors such as GATA3 and NRF2. In addition, other putative interactors, such as the NAD-dependent deacetylase sirtuin-1 (SIRT1), may have a regulatory role on MOCOS expression. Interestingly, these three genes have been associated with ASD, fragile X syndrome, epilepsy and/or oxidative stress.^{54, 55, 56, 57} In conclusion, our study opens an unexplored new avenue for the study of MOCOS in ASD, and could set bases for the development of new diagnostic tools as well as the search of new therapeutics.

Conclusion

It looks like a little extra selenium may be in order to increase those GPx enzymes that are need to speed up aspects of the antioxidant activity of GSH.

When it comes to molybdenum, things get much more complex. You certainly do not want to be deficient in molybdenum and you do not want Molybdenum cofactor deficiency; you also do not want molybdenum cofactor Sulfurase (MOCOS) mis-expression.

It is fair to say that quite likely there is a problem related to molybdenum that affects oxidative stress in autism; but it is not yet clear what to do about it.  I rather doubt the solution is as simple as just a little extra molybdenum, but it is easy to try.

On the plus side, we see that if you have autism, epilepsy and high uric acid you are likely to benefit from allopurinol, which also seems to help in COPD.

There is nothing new about allopurinol possibly be effective in some autism, as from this 25 year old book, Diagnosis and Treatment of Autism.

Again we see that activating NRF2 looks a good idea, that applies to both autism and COPD.

One thing to note is that NRF2 activators are good for cancer prevention, but if you have a cancer you want NRF2 inhibitors.

NRF2 activators include sulforaphane (SFN), R-alphalipoic acid (ALA), resveratrol and curcumin.  SFN is by far the most potent.  Resveratrol and curcumin have a problem with bioavailability.

Nitrosative Stress, Nitric Oxide and Peroxynitrite

In this example of Brain Injury, developing oligodendrocytes are injured and killed by substances released from activated microglia, including nitric oxide and superoxide, which form peroxynitrite. Peroxynitrite has been found to kill these cells through the activation of the 12-lipoxygenase pathway for metabolizing arachidonic acid. Mitochondria may be involved in this pathway as a source of reactive oxygen species.

Much has been written in this blog about oxidative stress, which has now been extremely well researched in autism and more generally. Let’s recap oxidative stress.

The most knowledgeable researcher in this area is Abha Chauhan.  Based on her research and that of others we now know a great deal.  Recall that the body’s key antioxidant is called glutathione (GSH) and when it neutralizes a free radical GSH is converted to its oxidized form, glutathione disulfide (GSSG).  A good measure of oxidative stress is the ratio of  GSH/GSSG.

·        Autism is associated with deficits in glutathione antioxidant defence in selective regions of the brain.

·        In the cerebellum and temporal cortex from subjects with autism, GSH levels are significantly decreased by 34.2 and 44.6 %, with a concomitant increase in the levels of GSSG

·        There is also a significant decrease in the levels of total GSH (tGSH) by 32.9 % in the cerebellum, and by 43.1 % in the temporal cortex of subjects with autism.

·        In contrast, there was no significant change in GSH, GSSG and tGSH levels in the frontal, parietal and occipital cortices in autism

·        The redox ratio of GSH to GSSG was also significantly decreased by 52.8 % in the cerebellum and by 60.8 % in the temporal cortex of subjects with autism, suggesting glutathione redox imbalance in the brain of individuals with autism.

·        Disturbances in brain glutathione homeostasis may contribute to oxidative stress, immune dysfunction and apoptosis, particularly in the cerebellum and temporal lobe, and may lead to neurodevelopmental abnormalities in autism.

·        The activity of glutathione cysteine ligase (GCL), an enzyme for glutathione synthesis is impaired in autism.

·        The protein expression of its modulatory subunit GCLM was decreased in autism.

·        The activities of glutathione peroxidase (GPx) and glutathione S-transferase were decreased in autism.

For those interested, GPx is a family of enzymes that catalyze the reaction that converts GSH to GCCG.  So in order to soak up those free radicals you need both GSH and GPx.

Glutathione cysteine ligase (GCL) is a key enzyme needed to make the antioxidant GSH.  Dysregulation of GCL enzymatic function and activity is known to be involved in many human diseases, such as diabetes, Parkinson's disease, Alzheimer’s disease, COPD, HIV/AIDS, cancer and autism.  Without sufficient GCL your body cannot make enough glutathione (GSH).

I did have some conversation with Abha Chauhan a few years ago when I found that NAC (N-acetyl cysteine), a known precursor to GSH, really does have a positive behavioral impact in autism.  She is clearly very nice, but not the type to make the leap to translating her science into therapy.

As I have shown there are many other treatable aspects of oxidative stress.

The chart below is my annotated version of the original by Professor Helmut Sies, the German “Redox Pioneer”.  He has published 500 scientific papers.

Nitrosative Stress

Finally to nitrogen.

Nitrogen is the most common pure element in the earth, making up 78.1% of the entire volume of the atmosphere.  Although nitrogen is non-toxic, when released into an enclosed space it can displace oxygen, and therefore presents an asphyxiation hazard. 

Nitrogen is an anesthetic agent. Nitrous oxide (N₂O) is commonly known as laughing gas.  It is used in medicine for its unaesthetic and analgesic effects

It is also used as an oxidizer in rocket propellants, and in motor racing to increase the power output of engines, like Mad Max.

In humans we are dealing with Nitric Oxide (NO) and when things go wrong with peroxynitrite and then other Reactive nitrogen species (RNS).  In simple terms Reactive nitrogen species (RNS), like Reactive oxygen species (ROS) are bad news.

Nitric Oxide (NO) itself does lots of good things in your body.  Too much may not be good, but a little more can actually do you good.  NO is a potent vasodilator.

For over 130 years, nitroglycerin has been used to treat heart conditions, such as angina and chronic heart failure.  Nitroglycerin produces nitric oxide (NO). In hospital most patients will receive nitroglycerin during and after a heart attack, people at risk of a heart attack often carry nitroglycerin with them.

If you want to lower your blood pressure or an athlete wanting to legally improve exercise endurance you can increase Nitric Oxide (NO) via diet.  One easy way is to drink beetroot juice, as is common in endurance cycling.  In people with peroxynitrite-derived radicals this may be unwise, because they may have too much NO.

Peroxynitrite

The starting point for the production of those unhelpful Reactive Nitrogen Species (RNS) is this chemical reaction

NO (nitric oxide) + O₂^·− (superoxide) → ONOO⁻ (peroxynitrite)

NO production is affected by the enzyme nitric oxide synthase 2 (NOS2).

Superoxide production is catalyzed by NADPH oxidase.

Superoxide also produces Reactive Oxygen Species (ROS).

NADPH oxidase is implicated in many diseases including schizophrenia and autism.

NADPH oxidase 4 (Nox4) activity decreases mitochondrial function (chain complex I).

Activated microglia (as found in autism) produce both nitric oxide and superoxide and are therefore a source of peroxynitrite.

This has started to get rather complicated. So those interested in NADPH should refer to the literature.

Peroxynitrite can directly react with various biological targets and components of the cell including lipids, thiols, amino acid residues, DNA bases, and low-molecular weight antioxidants.

Additionally peroxynitrite can react with other molecules to form additional types of RNS including nitrogen dioxide (·NO₂) and dinitrogen trioxide (N₂O₃) as well as other types of chemically reactive free radicals.

Nitric Oxide and Peroxynitrite in Health and Disease

I have referred on this blog to Abha Chauhan’s mammoth book on oxidative stress in autism on several occasions.  A work of similar quality but this time on Nitric Oxide and Peroxynitrite, is the paper below, by Hungarian Pal Pacher, who works at the US National Institute of Health’s Section on Oxidative Stress Tissue Injury.  He looks like a citation generating machine.

You could spend a long time reading this paper, but in summary peroxynitrite and its derived products have a negative effect on a very wide range of conditions including all the common neurological conditions, inflammatory diseases and again diabetes.  The answer would be peroxynitrite scavengers.

Nitric Oxide and Peroxynitrite in Health and Disease

The discovery that mammalian cells have the ability to synthesize the free radical nitric oxide (NO) has stimulated an extraordinary impetus for scientific research in all the fields of biology and medicine. Since its early description as an endothelial-derived relaxing factor, NO has emerged as a fundamental signaling device regulating virtually every critical cellular function, as well as a potent mediator of cellular damage in a wide range of conditions. Recent evidence indicates that most of the cytotoxicity attributed to NO is rather due to peroxynitrite, produced from the diffusion-controlled reaction between NO and another free radical, the superoxide anion. Peroxynitrite interacts with lipids, DNA, and proteins via direct oxidative reactions or via indirect, radical-mediated mechanisms. These reactions trigger cellular responses ranging from subtle modulations of cell signaling to overwhelming oxidative injury, committing cells to necrosis or apoptosis. In vivo, peroxynitrite generation represents a crucial pathogenic mechanism in conditions such as stroke, myocardial infarction, chronic heart failure, diabetes, circulatory shock, chronic inflammatory diseases, cancer, and neurodegenerative disorders. Hence, novel pharmacological strategies aimed at removing peroxynitrite might represent powerful therapeutic tools in the future. Evidence supporting these novel roles of NO and peroxynitrite is presented in detail in this review.


Some excerpts:-

·        The different events set in motion by the initial generation of peroxynitrite indicate that potent peroxynitrite decomposition catalysts and PARP inhibitors might represent useful therapeutic agents for debilitating chronic inflammatory diseases

·        In summary, available evidence indicates that NO plays dichotomous roles (promotion vs. suppression) in tumor initiation and progression. The activation of angiogenesis and the induction of DNA mutations represent key aspects of the procarcinogenic effects of NO. Peroxynitrite is emerging as a major NO-derived species responsible for DNA damage, mainly through guanine modifications and the inhibition of DNA repair enzymes. In chronic inflammatory states, the identification of 8-nitroguanine in tissues indicates that nitrative DNA damage consecutive to overproduction of NO and peroxynitrite may represent an essential link between inflammation and carcinogenesis.

·        In summary, the different studies listed above indicate that small amounts of NO produced by eNOS in the vasculature during the early phase of brain ischemia are essential to limit the extent of cerebral damage, whereas higher concentrations of NO, generated initially by nNOS and later by iNOS, exert essentially neurotoxic effects in the ischemic brain. Evidence that such toxicity depends, in large part, on the rapid reaction of NO with locally produced superoxide to generate peroxynitrite will be now exposed

  

·        NO is produced by all brain cells including neurons, endothelial cells, and glial cells (astrocytes, oligodendrocytes, and microglia) by Ca²⁺/calmodulin-dependent NOS isoforms. Physiologically NOS in neurons (nNOS, type I NOS) and endothelial cells (eNOS, type III NOS) produce nanomolar amounts of NO for short periods in response to transient increases in intracellular Ca²⁺, which is essential for the control of cerebral blood flow and neurotransmission and is involved in synaptic plasticity, modulation of neuroendocrine functions, memory formation, and behavioral activity (491, 890, 1229). The brain produces more NO for signal transduction than the rest of the body combined, and its synthesis is induced by excitatory stimuli. Consequently, NO plays an important role in amplifying toxicity in the CNS. Indeed, under various pathological conditions associated with inflammation (e.g., neurodegenerative disorders and cerebral ischemia), large amounts of NO are produced in the brain as a result of the induced expression of iNOS (type II NOS) in glial cells, phagocytes, and vascular cells, which can exert various deleterious roles (39, 491, 890). Thus NO may be a double-edged sword, exerting protective effects by modulating numerous physiological processes and complex immunological functions in the CNS on one hand and on the other hand mediating tissue damage (446, 491, 890). The detailed discussion of the role of NO in the pathophysiology of various neurodegenerative disorders including Parkinson’s disease, Alzheimer’s disease, Huntington’s disease, multiple sclerosis (MS), and amyotrophic lateral sclerosis (ALS), just mentioning a few, is the subject of numerous excellent recent overviews (77, 145, 194, 219, 491, 890, 1003, 1205, 1433) and beyond the scope of this paper. Here we cover only the role of peroxynitrite and protein nitration, which are likely responsible for most deleterious effects of NO in neurodegenerative disorders.

·        Peroxynitrite formation has been implicated in Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, MS, ALS, and traumatic brain injury (reviewed in Refs. 194, 608, 1119, 1284). Nitrotyrosine immunoreactivity has been found in early stages of all of these diseases in human autopsy samples as well as in experimental animal models. Increased nitrite, nitrate, and free nitrotyrosine has been found to be present in the cerebral spinal fluid (CSF) and proposed to be useful marker of neurodegeneration (168; reviewed in Refs. 608, 1119, 1284). Once formed in the diseased brain, peroxynitrite may exert its toxic effects through multiple mechanisms, including lipid peroxidation, mitochondrial damage, protein nitration and oxidation, depletion of antioxidant reserves (especially glutathione), activation or inhibition of various signaling pathways, and DNA damage followed by the activation of the nuclear enzyme PARP (608, 1119, 1284).

·        Uric acid has proven to be a useful inhibitor of tyrosine nitration (although it is not a direct peroxynitrite scavenger) (1271) and has been shown to protect the blood-brain barrier and largely prevent the entry of inflammatory cells into the CNS (566, 567). Additionaly, it also prevented CNS injury after inflammatory cells have already migrated into the CNS (1141). Urate has also proven beneficial in reducing the morbidity associated with viral infections (710, 1141). Interestingly, in humans there is an inverse correlation between affliction with gout and MS (710, 1195). Numerous studies have reported lower levels of uric acid in MS patients favoring the view that reduced uric acid in MS is secondary to its “peroxynitrite scavenging” activity during inflammatory disease, rather than a primary deficiency (reviewed in Ref. 694). These studies have also suggested that serum uric acid levels could be used as biomarkers for monitoring disease activity in MS

  

·        Recent evidence suggests that mitochondrial complex I inhibition may be the central cause of sporadic PD and that derangements in complex I lead to α-synuclein aggregation, which contributes to the demise of dopamine neurons (293). Accumulation and aggregation of α-synuclein may further facilitate the death of dopamine neurons through impairments in protein handling and detoxification (293). As already mentioned above, both mitochondrial complex I and synuclein can be targets for peroxynitrite-induced protein nitration

·        The significance of this intricate interplay may have important ramifications not only for ALS but also for PD and AD (6, 58, 1102). Reactive astrocytes are common hallmark of neurodegeneration, and these results suggest that peroxynitrite may play an important role in promoting this phenotype as well as causing the degeneration of neurons. In ALS, the transformation of astrocytes into a reactive phenotype may explain why ALS is progressive, causing the relentless death of neighboring motor neurons. Interfering in such a cascade to stop the progressive death of motor neurons would not necessarily cure ALS but may keep it from being a death sentence.

·        There is accumulating evidence suggesting that increased oxidative stress and excessive production of NO might contribute to the development of HD by damaging neighboring neurons (reviewed in Refs. 63, 163). Accordingly, increased iNOS expression was observed in neuronal, glial, and vascular cells from brains of HD patients and mouse models of disease (206, 491). Similarly, numerous studies have demonstrated increased 3-NT formation in brain tissues (neurons, glia, and/or vasculature) of mice transgenic for the HD mutation, rats injected into the striatum with quinolinic acid (rat model of HD), and HD patients (300–302, 427, 1022, 1023, 1096, 1117). Importantly, both NOS inhibitors and peroxynitrite scavengers decreased neuronal damage, improved disease progression, and also decreased brain 3-NT content in experimental models (301, 1022, 1117). These results suggest that peroxynitrite might be an important mediator of oxidative damage associated with HD.

·        The pathogenetic role of peroxynitrite in TBI is supported by evidence demonstrating increased brain 3-NT levels following TBI in experimental mouse and rat models (92–94, 423, 507, 508, 898, 1171, 1360), and by the beneficial effects of NOS inhibitor and peroxynitrite scavengers in reducing neuronal injury and improving neurological recovery following injury (423, 508, 898).Collectively, multiple lines of evidence discussed above provide strong support for the important role of peroxynitrite formation and/or protein nitration in neurodegenerative disorders and suggest that the neutralization of this reactive species may offer significant therapeutic benefits in patients suffering from these devastating diseases.

·        Collectively, the evidence reviewed above support the view that peroxyntrite-induced damage plays an important role in numerous interconnected aspects of the pathogenesis of diabetes and diabetic complications. Neutralization of RNS or inhibition of downstream effector pathways including PARP activation may represent a promising strategy for the prevention or reversal of diabetic complications.

·        In conclusion, multiple lines of evidence discussed above and listed in Table 4 suggest that peroxynitrite plays an important role in various forms of cardiovascular dysfunction and injury; pharmacological neutralization of this reactive oxidant or targeting the downstream effector pathways may represent a promising strategy to treat various cardiovascular disorders.

·        In summary, circulatory shock is a leading cause of death in intensive care units. Considerable improvement in our understanding of the molecular and cellular mechanisms of shock over the past 20 years makes it now a reasonable expectation that novel, efficient mechanism-based therapies will emerge in the near future. Considerable evidence now exists that overproduction of NO and superoxide, triggering the generation of large amounts of peroxynitrite, is a central aspect of shock pathophysiology. In addition to direct cytotoxic effects such as the peroxidation of lipids, proteins, and DNA, peroxynitrite also occupies a critical position in a positive feedback loop of inflammatory injury, by (directly or indirectly, via PARP activation) activating proinflammatory signaling and by triggering the recruitment of phagocytes within injured tissues, leading to further NO, superoxide, and peroxynitrite production, which will progressively amplify the initial inflammatory reactions (see sect. VID, Fig. 14). These various observations support the view that future strategies reducing peroxynitrite or its precursors might have a considerable therapeutic impact in clinical circulatory shock.

Peroxynitrite Scavengers

We have already covered two substances in this blog that are potential Peroxynitrite Scavengers:-

Calcium Folinate

This is Roger’s magic pill to treat his Cerebral Folate Deficiency, but it may have application far beyond this, likely rare, condition, for those that tolerate it.

Tetrahydrofolic acid, or tetrahydrofolate, is a folic acid derivative. It has the potential to quench those peroxynitrite-derived radicals.

Tetrahydrofolate and 5-methyltetrahydrofolate are folates with high antioxidant activity. Identification of the antioxidant pharmacophore

The presumed protective effect of folic acid on the pathogenesis of cardiovascular, hematological and neurological diseases and cancer has been associated with the antioxidant activity of folic acid. Peroxynitrite (PON) scavenging activity and inhibition of lipid peroxidation (LPO) of the physiological forms of folate and of structurally related compounds were tested. It was found that the fully reduced forms of folate, i.e. tetrahydrofolate (THF) and 5-methyltetrahydrofolate (5-MTHF), had the most prominent antioxidant activity. It appeared that their protection against LPO is less pronounced than their PON scavenging activity. The antioxidant activity of these forms of folic acid resides in the pterin core, the antioxidant pharmacophore is 4-hydroxy-2,5,6-triaminopyrimidine. It is suggested that an electron donating effect of the 5-amino group is of major importance for the antioxidant activity of 4-hydroxy-2,5,6-triaminopyrimidine. A similar electron donating effect is probably important for the antioxidant activity of THF and 5-MTHF.

Uric Acid

Uric acid has proven to be a useful inhibitor of tyrosine nitration.  It was thought to be a scavenger of peroxynitrite, but our clever Pal from Hungary tells that “it is not a direct peroxynitrite scavenger ….Numerous studies have reported lower levels of uric acid in MS patients favoring the view that reduced uric acid in MS is secondary to its “peroxynitrite scavenging” activity during inflammatory disease, rather than a primary deficiency”.

An old paper:-

Uric acid, a natural scavenger of peroxynitrite, in experimental allergic encephalomyelitis and multiple sclerosis

Uric acid, the naturally occurring product of purine metabolism, is a strong peroxynitrite scavenger, as demonstrated by the capacity to bind peroxynitrite but not nitric oxide (NO) produced by lipopolysaccharide-stimulated cells of a mouse monocyte line. In this study, we used uric acid to treat experimental allergic encephalomyelitis (EAE) in the PLSJL strain of mice, which develop a chronic form of the disease with remissions and exacerbations. Uric acid administration was found to have strong therapeutic effects in a dose-dependent fashion. A regimen of four daily doses of 500 mg/kg uric acid was required to promote long-term survival regardless of whether treatment was initiated before or after the clinical symptoms of EAE had appeared. The requirement for multiple doses is likely to be caused by the rapid clearance of uric acid in mice which, unlike humans, metabolize uric acid a step further to allantoin. Uric acid treatment also was found to diminish clinical signs of a disease resembling EAE in interferon-γ receptor knockout mice. A possible association between multiple sclerosis (MS), the disease on which EAE is modeled, and uric acid is supported by the finding that patients with MS have significantly lower levels of serum uric acid than controls. In addition, statistical evaluation of more than 20 million patient records for the incidence of MS and gout (hyperuricemic) revealed that the two diseases are almost mutually exclusive, raising the possibility that hyperuricemia may protect against MS.

Here we have a paper with the link to Tetrahydrobiopterin (BH₄,), also known as sapropterin, covered in an old post:-

Endothelial Dysfunction - Oxidative Stress, Inflammation and BH4

Interactions of peroxynitrite with uric acid in the presence of ascorbate and thiols: Implications for uncoupling endothelial nitric oxide synthase

It has been suggested that uric acid acts as a peroxynitrite scavenger although it may also stimulate lipid peroxidation. To gain insight into how uric acid may act as an antioxidant, we used electron spin resonance to study the reaction of uric acid and plasma antioxidants with ONOO-. Peroxynitrite reacted with typical plasma concentrations of urate 16-fold faster than with ascorbate and 3-fold faster than cysteine. Xanthine but not other purine-analogs also reacted with peroxynitrite. The reaction between ONOO- and urate produced a carbon-centered free radical, which was inhibited by either ascorbate or cysteine. Moreover, scavenging of ONOO- by urate was significantly increased in the presence of ascorbate and cysteine. An important effect of ONOO- is oxidation of tetrahydrobiopterin, leading to uncoupling of nitric oxide synthase. The protection of eNOS function by urate, ascorbate and thiols in ONOO(-)-treated bovine aortic endothelial cells (BAECs) was, therefore, investigated by measuring superoxide and NO using the spin probe 1-hydroxy-3-methoxycarbonyl-2,2,5,5-tetramethyl-pyrrolidine (CMH) and the NO-spin trap Fe[DETC]2. Peroxynitrite increased superoxide and decreased NO production by eNOS indicating eNOS uncoupling. Urate partially prevented this effect of ONOO- while treatment of BAECs with the combination of either urate with ascorbate or urate with cysteine completely prevented eNOS uncoupling caused by ONOO-. We conclude that the reducing and acidic properties of urate are important in effective scavenging of peroxynitrite and that cysteine and ascorbate markedly augment urate's antioxidant effect by reducing urate-derived radicals.

Xanthine oxidase (XO, sometimes 'XAO') is a form of xanthine oxidoreductase, a type of enzyme that generates reactive oxygen species.^[2] These enzymes catalyze the oxidation of hypoxanthine to xanthine and can further catalyze the oxidation of xanthine to uric acid. These enzymes play an important role in the catabolism of purines in some species, including humans.

Because xanthine oxidase is a metabolic pathway for uric acid formation, the xanthine oxidase inhibitor allopurinol is used in the treatment of gout.

Inhibition of xanthine oxidase has been proposed as a mechanism for improving cardiovascular health.  A study found that patients with chronic obstructive pulmonary disease (COPD) had a decrease in oxidative stress, including glutathione oxidation and lipid peroxidation, when xanthine oxidase was inhibited using allopurinol.

Reactive nitrogen species, such as peroxynitrite that xanthine oxidase can form, have been found to react with DNA, proteins, and cells, causing cellular damage or even toxicity. Reactive nitrogen signaling, coupled with reactive oxygen species, have been found to be a central part of myocardial and vascular function, explaining why xanthine oxidase is being researched for links to cardiovascular health.

We also should recall that abnormalities are common in autism.

The Hyperuricosuric Subtype of Autism, Uridine and Antipurinergic Therapy

So perhaps allopurinol for those with too much uric acid?  Perhaps this is a good marker for peroxynitrites ?

Conclusion

As is often the case there some contradiction in the science.  Is NO good for you or not?  Are both high and low uric acid actually indicating the same biological problem.

It looks like the research into very expensive BH4 therapy might be better directed into peroxynitrite scavengers.

I think we have found the reason why so many people with autism respond to Leucovorin (calcium folinate) and, unlike in our friend Roger, it may not be because of cerebral folate deficiency.

It looks like many other chronic conditions from diabetes to COPD to schizophrenia might also benefit from  calcium folinate.

Before I forget, in the Helmut Sies oxidative stress graphic I did highlight selenium.  The GPx enzymes contain selenium and if there is selenium deficiency the body's key antioxidant mechanism will be compromised. According to Abha Chauhan's book,  "Likewise, levels of exogenous antioxidants were also found to be reduced in autism, including vitamin C, vitamin E, and vitamin A in plasma, and zinc and selenium in erythrocytes (James et al., 2004)".  This might suggest adding a little extra selenium.

I think Allopurinol is worth a look for some autism.  Allopurinol does indeed reduce reactive nitrogen species in COPD (severe asthma), as suggested above.

Xanthine oxidase inhibition reduces reactive nitrogen species production in COPD airways

“These results suggest that oral administration of the xanthine oxidase inhibitor allopurinol reduces airway reactive nitrogen species production in chronic obstructive pulmonary disease subjects. This intervention may be useful in the future management of chronic "