This may be due to the low dose of NAM used in the present experiments (50 μM) compared with the high concentration used to
inhibit SIRT1 activity in culture cells (5 mM).29 One of the factors associated with the development ICG-001 datasheet and progression of steatosis is the oxidative stress originated by toxic lipid peroxidation catalyzed by CYP2E1, the main enzyme involved in the NAM adenine dinucleotide phosphate (reduced form)-dependent reduction of oxygen leading to lipid peroxidation.30 The CYPs constitute a super-family of heme-containing microsomal mono-oxygenases that play a central role in the detoxification of xenobiotics, as well as in the metabolism of endogenous compounds, including fatty acids. CYP2E1 expression selleck chemicals llc and activity is up-regulated in SAM-deficient, MAT1A-KO mouse liver.31 In contrast, CYP2E1, as well as expression of CYP39A1, an oxygenase catalyzing the rate-limiting step of bile acid synthesis,32 are reduced in GNMT-KO mouse liver, but the expression of two alternative fatty acid hydroxylases (CYP4A10 and CYP4A14, the two major CYP4A genes) is markedly induced. It has been demonstrated that CYP4A enzymes are key intermediates
of an adaptive response to perturbation of hepatic lipid metabolism. Thus, in CYP2E1-KO mice, lipid peroxidation induced by the accumulation of hepatic fatty acids in response to a methyl-deficient diet is mediated by the up-regulation of CYP4A10 and CYP4A14 expression.33 SAM is known selleck products to be an inhibitor of CYP2E1 activity,34 and, although the Ki is relatively
high, it is likely that at the elevated concentration of SAM present in GNMT-KO mouse liver, a direct effect of this molecule on CYP2E1 activity may be also responsible for the induction of CYP4A genes. Again, normalization of SAM content in GNMT-KO mice through NAM treatment prevented the abnormal expression of CYP2E1, CYP39A1, CYP4A10 and CYP4A14. Additionally, NAM treatment prevented the abnormal expression of critical genes involved in the generation of oxidative stress (UCP2, PPARγ, IL6, and iNOS) and liver fibrosis (COL1A1, TIMP-1, and α-SMA) and prevented apoptosis (determined both by PARP cleavage and TUNEL immunostaining). These findings agree with the observation that in whole blood stimulated with endotoxin, NAM is an anti-inflammatory agent inhibiting PARP activation, iNOS expression, and the stimulation of proinflammatory cytokines such as IL6 and iNOS.35 Whether NAM also reduced cellular SAM content in this experimental setting is not known.