Effect of Dietary Advanced Glycation End Products on Mouse Liver

The exact pathophysiology of non-alcoholic steatohepatitis (NASH) is not known. Previous studies suggest that dietary advanced glycation end products (AGEs) can cause oxidative stress in liver. We aim to study the effects of dietary AGEs on liver health and their possible role in the pathogenesis of NASH. METHODS: Two groups of mice were fed the same diet except the AGE content varied. One group was fed a high AGE diet and the second group was fed a regular AGE diet. Liver histology, alanine aminotransferase, aspartate aminotransferase, fasting glucose, fasting insulin, insulin resistance and glucose tolerance were assessed. RESULTS: Histology revealed that neutrophil infiltration occurred in the livers of the high AGE group at week 26; steatosis did not accompany liver inflammation. At week 39 livers from both groups exhibited macro- or micro-steatosis, yet no inflammation was detected. Higher insulin levels were detected in the regular AGE group at week 26 (P = 0.034), compared to the high AGE group. At week 39, the regular AGE group showed higher levels of alanine aminotransferase (P<0.01) and aspartate aminotransferase (P = 0.02) than those of the high AGE group. CONCLUSIONS: We demonstrate that a high AGE diet can cause liver inflammation in the absence of steatosis. Our results show that dietary AGEs could play a role in initiating liver inflammation contributing to the disease progression of NASH. Our observation that the inflammation caused by high AGE alone did not persist suggests interesting future directions to investigate how AGEs contribute to pro-oxidative and anti-oxidative pathways in the liver

Comparison of Fatty-acid Alpha-oxidation By Rat Hepatocytes and By Liver-microsomes Fortified With Nadph, Fe3+ and Phosphate

Rat liver microsomes, when fortified with NADPH, Fe3+ and phosphate, can catalyze the oxidative decarboxylation (alpha-oxidation) of 3-methyl-substituted fatty acids (phytanic and 3-methylheptadecanoic acids) at rates that equal 60-70% of those observed in isolated hepatocytes (Huang, S., Van Veldhoven, P.P., Vanhoutte, F., Parmentier, G., Eyssen, H.J., and Mannaerts, G.P., 1992, Arch. Biochem. Biophys. 296, 214-223). In the present study we set out to identify and compare the products and possible intermediates of alpha-oxidation formed in rat hepatocytes and by rat liver microsomes. In the presence of NADPH, Fe3+ and phosphate, microsomes decarboxylated not only 3-methyl fatty acids but also 2-methyl fatty acids and even straight chain fatty acids. The decarboxylation products of 3-methylheptadecanoic and palmitic acids were purified by highperformance liquid chromatography and identified by gas chromatography/mass spectrometry as 2-methylhexadecanoic and pentadecanoic acids, respectively. Inclusion in the incubation mixtures of glutathione plus glutathione peroxidase inhibited decarboxylation by more than 90%, suggesting that a 2-hydroperoxy fatty acid is formed as a possible intermediate. However, we have not yet been able to unequivocally identify this intermediate. Instead, several possible rearrangement metabolites were identified. In isolated rat hepatocytes incubated with 3-methylheptadecanoic acid, the formation of the decarboxylation product, 2-methylhexadecanoic acid, was demonstrated, but no accumulation of putative intermediates or rearrangement products was observed. Our data do not allow us to draw conclusions on whether the reconstituted microsomal system is representative of the cellular alpha-oxidation system. However, the results we obtained with [3-H-3]-labelled fatty acids indicate that during a-oxidation in intact cells the hydrogen at carbon-3, which carries the methyl branch, is not attacked

Oxidative catabolism of alpha-tocopherol in rat liver microsomes

The goal of this study was to clarify the mechanism responsible for the catabolism of a-tocopherol. The vitamin, bound to albumin, was incubated with rat liver microsomes and appeared to be broken down. Optimal production of the metabolite was obtained when 1 mg of microsomal protein was incubated with 36 muM of alpha -tocopherol in the presence of 1.5 mM of NADPH. Chromatographic and mass spectrometric analyses of the metabolite led to the conclusion that it consists of an omega -acid with an opened chroman ring, although we could not perform nuclear magnetic resonance analysis to confirm this. Our data show that ol-tocopherol is omega -oxidized to a carboxylic acid and that this process can occur in rat liver microsomes in the presence of NADPH and O-2. The oxidation to the quinone structure appears to be a subsequent event that may be artifactual and/or catalyzed by a microsomal enzyme(s)