Glutathione: What is it and why should we care?

There has been a lot of talk about the significance of glutathione in autism and how it might be depleted by mercury exposure. I thought I would attempt to review what we do and do not know about glutathione and autism and how it may relate to mercury toxicity.

Let's start with "What is it?"
Glutathione is defined as: a tripeptide consisting of residues of glutamic acid, cysteine, and glycine, is known to act as a coenzyme in a few enzymatic reactions, but its importance may lie in its role as a nonspecific reducing agent within the cell.

and, Glutathione is the most abundant non-protein thiol compound present in living organisms. Glutathione has many functions beyond removal of toxic metals like mercury. It is essential for maintaining cellular redox state, which every human metabolic process depends upon, in every living cell in our bodies.

So Why should we care?
Many of the mercury hypothesis supporters believe glutathione deficiency makes children more susceptible to thimerosal exposure:

http://www.ewg.org/reports/autism/execsumm.php
Newly published research and follow-up testing by former FDA senior research scientist Dr. Jill James, now of the University of Arkansas for Medical Sciences, has uncovered a unique and consistent metabolic imbalance in autistic children when compared to normal healthy children (James 2004a, 2004b). This impairment manifests as a severe deficit in the body's most important antioxidant and metals detoxifier, glutathione. When compared to normal health children, autistic children showed a significant impairment in every one of five measurements of the body's ability to maintain a healthy glutathione defense. These findings are strong evidence that if these children were exposed to a potentially toxic dose of mercury or other compound they would be much less able to mount an effective defense.


That might lead us to believe that the autistic children in the study had very low levels of glutathione and that they have some sort of genetic or metabolic defect made them unable to produce sufficient quantities of glutathione. So did James et al really find very low gluathione or an impairment in gluathione synthesis?

Here's a diagram from the same page:

The table shows two types of glutathione, active and inactive. It would probably be more accurate if the two types were described as reduced and oxidized but it can get confusing to discuss reduced glutathione which is not the same as decreased glutathione.

According to the table, the autistic subjects had 31% less of the reduced form (GSH) and 33% more of the oxidized form (GSSG) as compared to the non-autistic subjects in the study. Technically these aren't two distinct forms but rather two oxidation states of the same molecule with a clear inverse relationship. When levels of one drop and the other increases. Not what we would want to call a "severe deficit" but possibly suggestive of a pro-oxidative environment.

Decreased synthetic capability is one possible explanation but this would probably result in a significant deficit of total glutathione not an imbalance between the two oxidation states. If James found any evidence of impaired glutathione synthesis in this small group of children it wasn't included in any of her published work. It doesn't sound like the children were suffering from a glutathione deficiency as much as an increased oxidative burden greater than the capacity to recycle and glutathione and maintain full oxidative defense capacity.

James et al also reported an improvement in GSH:GSSG ratio following the administration of certain methyl donor supplements, chiefly methyl-B12 injections. Me-B12 is a wonderful methylator but there are two other ways it might temporarily offset oxidative stressors when injected directly into the bloodstream.

1) Methyl-B12 is an effective anti-oxidant and a nitric oxide scavenger. Nitric oxide may be elevated in some children with autism and reactive nitrogen compounds can contribute to oxidative stress and alterations in reduced glutathione levels.

2) Methyl-B12 can suppress activity of certain types of immune cells which are thought to be a major source of reactive oxygen species during periods of increased immune activation.

The investigators didn't report improvements in autistic behaviors, only changes in markers of oxidative defense systems.

So what about the mercury? Isn't glutathione necessary for the excretion of heavy metals?

One of the many functions of glutathione is conjugation and detoxification of metals and other toxins. It is speculated that children with autism are unable to excrete metals because of a glutathione deficiency. There doesn't seem to be a deficiency, as discussed above, but let's suppose children with autism had significantly lower levels of glutathione. Would it render them unable to detoxify thimerosal from vaccines? Probably not.

If the average human carries around approximately 6 milligrams of mercury how much glutathione should we require to deal with environmental mercury levels ? Even if several molecules of glutathione were required for each mercury molecule, we should have millions of times sufficient glutathione to get the job done. Compare that to the reported upper limit of exposure through vaccines which has been estimated at less than 250 micrograms. A person so severely deficient in glutathione they would be unable to detoxify 250 micrograms of mercury probably wouldn't survive long enough to be vaccinated in the first place. Every breath of air would expose them to lethal levels of ozone, pollutants and other oxidants.

There are genetic glutathione deficiency disorders but symptoms, excluding neurological dysfunction, haven't been reported in children with autism.

"Severe glutathione synthetase (GS) deficiency is a rare genetic disorder with neonatal onset. The enzymatic block of the [gamma]-glutamyl cycle leads to a generalized glutathione deficiency. Clinically affected patients present with severe metabolic acidosis, 5-oxoprolinuria, increased rate of hemolysis and defective function of the central nervous system"

What if the glutathione redox imbalance in the small group of children studied by James was an indication of immune activation and oxidative stress? Does that point to mercury as a cause? Mercury is known to contribute to and trigger oxidative stress but very large quantities would be required in order for it to form a complex with glutathione and deplete total glutathione by excretion with mercury. Mercury can trigger immune activation which can indirectly contribute to oxidative stress but so can thousands of other substances.

In an odd coincidence, Jill James came out with another study reporting the glutathione depleting effects of mercury and it was published around the same time as the autism study. The two are often discussed as if they are one and the same.

Thimerosal Neurotoxicity is Associated with Glutathione Depletion: Protection with Glutathione Precursors

Not surprisingly, cultured neuroblastoma cells, which are low in glutathione to start, were more sensitive to high concentrations of thimerosal. What does that have to do with autism? Hard to tell. I guess that's why the authors included this sentence:

Acute high dose exposures to Thimerosal (mmol/L) in cultured cells were used to study mechanistic aspects of Thimerosal toxicity and not intended to mimic exposures of developing brain cells in vivo to Thimerosal in vaccines (nmol/kg).

OK, so now we know that certain glutathione deficient cell lines are sensitive to high concentrations of mercury and are protected by certain glutathione precursor, which, by the way, can probably bind free mercury and reduce effective exposure levels. Again, I'm not sure why that would be relevant to autism. Other scientists have found that thimerosal can induce death in this same cell line through different mechanisms.

The hypothesis goes something like this: Certain individuals produce less glutathione[1] as a result of various gene mutations/polymorphism,[2] the resulting glutathione deficiency [3]doesn't provide enough glutathione to bind and excrete mercury the way it would in others, exposure to thimerosal in vaccines adds to their toxic burden causing certain brain cells to die[4] from a known neurotoxin.

The parts that are missing from this hypothesis are as follows.

[1] No one has demonstrated that children with autism synthesize less glutathione.

[2] No one has found gene mutations or group of polymorphisms that are strongly associated with autism let alone glutathione activity and autism.

[3] Altered glutathione redox capacity is not the same as a deficiency.

[4] No indication of the type of brains cells and why are they more sensitive to mercury than surrounding cells?

It's also important to remember the differences between free circulating extra-cellular glutathione and intra-cellular glutathione and how levels are affected by various conditions and chemicals. One popular chelation agent, alpha-Lipoic acid, can increase levels of reduced glutathione, probably through anti-oxidant mechanisms but, according to this, may "increase the effects of mercury ions on glutathione concentrations" and here we see that administration of Lipoic acid "did not increase, but rather decreased, the biliary excretion of methylmercury, cadmium, zinc, and copper" which may indicate a difference between the toxicokinetics of inorganic mercury and methyl-mercury.

That's an established fact. Different chemical compounds, different forms of mercury, behave differently and are handled differently by biological systems and different organisms. The primary way environmental mercury enters the food chain is through conversion by bacteria and other microorganisms using methylcobalamin to form methylmercury. If methylcobalamin sounds familiar it's because it is the chemical name for Methyl-B12, aka MB12, MeB12, etc. The form of B12 being used to treat autism by many DAN! Practitioners. Methylcobalamin is an essential reagent for the synthesis of the very toxic form of mercury, methylmercury, and the extremely toxic/lethal form dimethylmercury.

So the substance that is supposed to alleviate mercury induced glutathione depletion in autistic children is very effective at forming methylmercury and at least one chelation agent interferes with excretion of methylmercury through glutathione conjugation.

Proponents of MeB12 injection claim very high rates of improvement in autistic behaviors so why would a substance that effectively converts mercury to it's most toxic form help a person if they are truly mercury toxic?

To read more about the tragic death of Karen Wetterhahn after she was exposed to dimethylmercury read the article titled: The Trembling Edge of Science

For a little perspective on blood levels of mercury in cases of genuine mercury poisoning this part stands out:

Wetterhahn’s accident showed that dimethylmercury was far more toxic than anyone thought. "We’re all exposed to mercury just by being alive," Winn says. "A usual mercury concentration would be ten micrograms per liter of blood or less. If the level rises to 50 micrograms per liter you’ve hit the toxic threshold, the beginning of toxicity. You would begin chelation therapy. A concentration of 200 micrograms per liter is toxic, but not necessarily lethal. Karen had 4,000 micrograms per liter. That’s 80 times the toxic threshold." Merely absorbing a drop or two placed her in the lethal range.

So chelation may have mobilized more mercury causing increased blood levels but unfortunately it wasn't effective enough to save Karen's life. In the case of dimethylmercury intoxication, poor methylation wouldn't seem to be a problem.

Back to the proposed genetic susceptibility. One study, involving a small group of subjects and controls, published in a dubious journal, suggested that certain gene variants, polymorphisms, or combinations of polymorphisms, may be a risk factor for autism in a small percentage of children. Note the liberal use of the words would, could, may and possibly here:

The genetic or environmental factors (or both) that would
initiate oxidative stress and abnormal metabolic profiles in the
autistic children are not clear. It is possibly relevant that, in
autistic children, decreased activity of adenosine deaminase and
increased frequency of adenosine deaminase polymorphisms
have been shown to be associated with low adenosine deaminase
activity (14, 45). The observed increase in adenosine could be
due to either an inhibition of adenosine kinase or an increase in
5-nucleotidase

Increased frequency of common polymorphisms in these pathways
may have contributed to the observed metabolic phenotype,
and studies of that subject, as well as studies to quantify
clinical improvement, are currently underway.

OK,It's possible, other disorders may be more or less associated with similar polymorphisms, but the association isn't always clear even after hundreds of studies. It may be possible, but it is far from being an established fact. Here they discuss glutathione S-transferase polymorphisms and potential risk of lung cancer:

Although more than 100 studies have tested the hypotheses that particular GST alleles either predispose to or protect against lung cancer, the results have been inconsistent, with some studies reporting strong associations and others failing to replicate these findings. Individual association studies are notoriously prone to error, and attempts to combine results from several studies have been complicated by the fact that allele frequencies for many of the alleles differ between populations, by differences in smoking habits, and by differences in criteria for the selection of suitable control groups.

If a hundred studies haven't established an association in a well studied disease like lung cancer, why would we view a single autism study as confirmation. Apparently Jill James agrees that the results are inconclusive and haven't been replicated.

A strange thing happened a few years ago. The mercury parents slowly moved away from the position that autism is completely environmental, most often caused by thimerosal, over to the idea that children with autism were genetically susceptible to the effects of thimerosal. Recently JB Handley, founder of Generation Rescue, went so far as to demand that other autism groups stop "wasting precious resources (money and researcher?s time) in areas that will not benefit our children today. "

Now thimerosal is said to be a trigger rather than a cause. If we don't know the genes or polymorphisms responsible for the theoretical susceptibility, we don't know the pathways and mechanisms that may exploit the susceptibility, and we can't develop a rodent model to demonstrate the susceptibility, how do we know there is one? WE DON'T

Lets' recap what we know and don't know about gluitathione and autism.

We know:

• Elevated markers of oxidative stress have been reported by several research groups.
• Decreased levels of antioxidant capacity have been reported by several research groups.
• One small study involving a small group of children may have detected an altered ratio between two oxidation states of glutathione.
• Redox capacity may have improved following the administration of several anti-oxidant and methyl donor vitamin supplements.
• High concentrations of Mercury can deplete glutathione in glutathione deficient neural cell lines in culture.
• Methylcobalamin converts inorganic mercury to the more toxic methylmercury

We don't know:

• We don't know that children with autism are less able to synthesize or recycle glutathione and glutathione precursors.
• We don't know that children with autism are more likely to possess mutations or sets of genetic variations which interfere with the capacity to manufacture glutathione or excrete mercury or other toxins.
• We don't know that mercury depletes glutathione to any significant degree at the levels achievable through vaccination with thimerosal containing vaccines.
• We don't know that methylcobalamin injections do anything to restore damaged synthetic pathways or levels of total glutathione or that it improves autistic behaviors in children.
• We don't know that oxidative stress and altered glutathione redox ratios contribute to autism in any way.
• We don't know that mercury is the only substance on the planet capable of contributing to oxidative stress that may or may not be more common to autistics.
• We don't know that any child was ever made autistic by thimerosal in vaccines

I don't pretend to understand the biology of autism, toxicology of mercury compounds, or the genetics of glutathione synthesis. What I do understand is that all of these things are stated as absolute facts by many of the mercury parents, DAN! Doctors, and autism professionals.

Let's be honest, when it comes to autism, we know less than is said.

Comments, criticisms, and corrections very much appreciated.