5-month-old GNMT-KO mice for 6 weeks with nicotinamide (NAM), a substrate of the enzyme NAM N-methyltransferase. NAM administration markedly reduced hepatic SAM content, prevented DNA hypermethylation, and normalized the expression of critical Pifithrin �� genes involved in fatty acid metabolism, oxidative stress, inflammation, cell proliferation, and apoptosis. More importantly, NAM treatment prevented the development of fatty liver and fibrosis in GNMT-KO mice. Because GNMT expression is down-regulated in patients with cirrhosis, and because some subjects with GNMT mutations have spontaneous liver disease, the clinical implications of the present findings

are obvious, at least with respect to these latter individuals. Because NAM has been used for many years to treat a broad spectrum of diseases (including pellagra and diabetes) without significant side effects, it should be considered in subjects with GNMT mutations. Conclusion: The findings of this study indicate that the anomalous accumulation of SAM in GNMT-KO mice can be corrected by NAM treatment leading to the normalization of the expression of many genes involved in fatty acid metabolism, oxidative stress, inflammation, cell proliferation, and apoptosis, as well as reversion of the appearance

of the pathologic phenotype. (HEPATOLOGY 2010) Expression of glycine N-methyltransferase (GNMT) is predominant in hepatocytes, where it selleck chemicals comprises about 1% of the total soluble protein, but is also found in other tissues such as pancreas and prostate.1 GNMT catalyzes the conversion of glycine into sarcosine (methylglycine), which is then oxidized to regenerate glycine (Fig. 1). The function of this futile cycle is to catabolize excess S-adenosylmethionine (SAM) synthesized by the liver after an increase in methionine concentration (for example, after a protein-rich meal) to maintain

a constant SAM/S-adenosylhomocysteine (SAH) ratio and avoid aberrant methylation reactions.1, 2 Accordingly, individuals learn more with GNMT mutations that lead to inactive forms of the enzyme have elevated blood levels of methionine and SAM, but the concentration of total homocysteine (the product of SAH hydrolysis) is normal.3, 4GNMT knockout (KO) mice recapitulate the situation observed in individuals with mutations of the GNMT gene5, 6 and have elevated methionine and SAM both in serum and liver. These findings indicate that the hepatic reduction in total transmethylation flux caused by the absence of GNMT cannot be compensated by other methyltransferases that are abundant in the liver, such as guanidinoacetate N-methyltransferase, phosphatidylethanolamine N-methyltransferase, or nicotinamide N-methyltransferase (NNMT), and that this situation leads to the accumulation of hepatic SAM and increased transport of this molecule to the blood.