Glutathione (GSH) is a major endogenous antioxidant that can neutralize reactive oxygen species (ROS) in a single bound and even react with itself for form glutathione disulfide (GSSG) (only about 10% is in the GSSG form). Depletion of GSH can lead to mitochondrial dysfunction and cell death. The three amino acids that make up glutathione are glycine, cysteine and glutamate. Specifically, glutamate and cysteine make gamma-glutamylcysteine, then glycine is added to the C-terminal, and glutathione is born. All of the amino acids needed to make glutathione can just be taken up from circulating plasma, if there is enough around. You can supplement amino acids, as well as other nutrients, such as vitamin C, to increase GSH production. The rate limiting amino acid in de novo synthesis of GSH in metabolic disease appears to be glycine. Glycine also participates in protein synthesis, in detoxification reactions, and has anti-inflammatory, cytoprotective and immunomodulatory properties. Glycine was best described by Pérez-Torres as “the smallest non-essential, neutral and metabolically inert amino acid, with a carbon atom bound to two hydrogen atoms, and an amino and a carboxyl group.” It sounds like an impressive amino acid. Research has found plasma glycine, serine and glutamate concentrations to be consistently altered in metabolic diseases, as are plasma branch chain amino acids (BCAA), isoleucine, leucine, and valine. Plasma levels of glycine and serine are lower, while glutamate and BCAAs are elevated. Glycine and serine get used up making GSH, and glutamate is increased once GSH exits the cell and is transaminated by GGT, releasing glutamate into circulation. Non‐alcoholic fatty liver disease NAFLD affects about 25% of the population. Its mildest form is hepatic steatosis which is defined as the accumulation of fat in the liver with no evidence of hepatocellular injury. Progression of liver disease goes from hepatic steatosis, NAFLD, to non‐alcoholic steatohepatitis (NASH). Up to 30% of people with NAFLD develop NASH, a serious illness with inflammation and scarring. Last is liver cirrhosis, scaring of the liver, and hepatocellular carcinoma. Some 20% of people with NASH develops cirrhosis. Though these stages are presented as an orderly progression, clinically that is not always the case. Since the liver is a major metabolic organ liver disease is associated with metabolic diseases, such as obesity, insulin resistance, type 2 diabetes (T2DM), and cardiovascular disease. NAFLD is common in those with T2DM even with normal liver enzymes, so it’s often hiding in plane site putting them at a higher risk for progression. Researchers have noted that an impaired redox balance, primarily a deficiency of NAD+ and GSH is linked with NAFLD. Currently the standard recommendation is weight loss with diet, being physically active, and sometimes including vitamin E supplementation. Some research has shown plant-based diets to be inversely associated with NAFLD. Markers that could identify metabolic disturbances and NAFLD early, as well as supportive therapies, could be beneficial, and to that end I reviewed two current articles. In his 2017 article Mardinoglu, M., et. al. noted that patients with high hepatic steatosis have depleted NAD+ (niacin) and glutathione, but noted that direct supplementation with glutathione may not be effective, as it is cannot enter small intestine cells intact. In personal communications he noted that, “To our knowledge, GSH is an active substance and metabolized mostly in the small intestine. In order to be taken up by the liver it has to be degraded to amino acids.” Glycine has been found consistently low in those with hepatic steatosis. Glycine can be synthesized from serine. During the conversion of serine to glycine, an additional carbon unit is provided for one‐carbon metabolism, and subsequently glutathione is produced. Vegetarians have a higher intake of non-essential amino acids including glycine and serine. After glycine, cysteine can become the limiting amino acid in glutathione production. Increasing L-cysteine can be provided more efficiently with N-Acetylcysteine (NAC). Additionally, NAD+ is also needed for increased fat oxidation. Supplementation with serine and an NAD+ precursor, like tryptophan, niacin, or nicotinamide riboside, along with NAC are expected to increase NAD+, glutathione, and fat oxidation in the liver. Leading to lower levels of oxidative stress, resulting in lower hepatic steatosis and its progression. Adding carnitine may help with the full process of fatty acid metabolism. To test the hypothesis Mardinoglu, M., et. al (2017) put mice on a Western diet and supplemented for two weeks (along time for a mouse) with serine, NAC, and nicotinamide riboside (an NAD+ precursors). Following supplementation plasma glycine and serine were increased, along with decreased short-chain triglycerides and hepatic steatosis. Remember the liver uses fatty acids to make triglycerides. Following the animal study, the researchers conducted a human study with hepatic steatosis. The participants got L-serine (200 mg/kg/day grams) for 14 days. And… plasma levels of liver enzymes (ALT, AST, ALP), and triglycerides all decreased, and an MRI showed decrease hepatic steatosis. Simple support helped. Though I might try just serine first, I may also add NAC, and an NAD+ precursor, and consider adding glycine and carnitine. Another key study by Gaggini, M. et. al. (2018) may help to identify who is most at risk. It included subjects with NAFLD, who were or were not obese, and evaluated if, and how, their plasma amino acids were altered, and the relationship with insulin resistance. Compared to healthy controls, those with NAFLD who were not obese had statically elevated levels of glutamate, isoleucine and valine, while those with NAFLD who were obese had significantly elevated levels of glutamate, all BCAA, and significantly lower levels of glycine and serine. Similar findings were noted with levels of inflammation. Glycine had a significant inverse correlation with hepatic insulin resistance, and glutamate had a positive correlation. The authors realized that glutamate, glycine and serine were consistently impacted by metabolic disease and developed the GSG-Index, Glutamate/ (Serine+Glycine). In their study the GSG-Index was found to be elevated in those with NAFLD, more elevated in NAFLD plus obesity, and highly correlated in liver enzymes. Control subjects had a mean GSG Index of .38. The association of the GSG-Index with increased liver enzymes was assumed to be due to increased glutathione transamination by GGT, releasing glutamate. The GSG-Index was also able to discriminate mild to severe liver fibrosis. The GSG-Index did not correlate with obesity alone. Older research has consistently found those with NAFLD had degradation of glycine and serine, with release of glutamate. Glycine and serine are the limiting substrates for the de novo synthesis of GSH
Granted these are small single studies, but taken together these articles identify possible new tools in an overall assessment, and highlight the benefits of using functional nutrition and lifestyle medicine. This is the area where functional medicine really shines, paying attention to the details and supporting in the right spot.
References: Mardinoglu A, Bjornson E, Zhang C, Klevstig M, Söderlund S, Ståhlman M, Adiels M, Hakkarainen A, Lundbom N, Kilicarslan M, Hallström BM, Lundbom J, Vergès B, Barrett PH, Watts GF, Serlie MJ, Nielsen J, Uhlén M, Smith U, Marschall HU, Taskinen MR, Boren J. Mol Syst Biol. 2017 Mar 2;13(3):916. Personal model-assisted identification of NAD+ and glutathione metabolism as intervention target in NAFLD.
Gaggini M, Carli F, Rosso C, Buzzigoli E, Marietti M, Della Latta V, Ciociaro D, Abate ML, Gambino R2, Cassader M, Bugianesi E, Gastaldelli A. Hepatology. 2018 Jan;67(1):145-158. Altered amino acid concentrations in NAFLD: Impact of obesity and insulin resistance.
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