α-Tocopherol suppresses hepatic steatosis by increasing CPT-1 expression in a mouse model of diet-induced nonalcoholic fatty liver disease.

AIM: Antioxidant therapy for with vitamin E appears to be effective for the treatment of nonalcoholic fatty liver disease　(NAFLD). However, the mechanism of action and optimal therapeutic dosage is unclear. The present study was undertaken to examine whether the effects of α-tocopherol (α-Toc) on NAFLD are dose-dependent in a diet-induced obese model. METHODS: Male mice were fed standard chow, high-fat (HF) diet, HF diet with low-dose, or with high dose of α-Toc supplementation. Histological findings, triglyceride content, and the levels of protein expression related to fatty acid synthesis/oxidation such as carnitine palmitoyltransferase I (CPT-1) of liver were evaluated. In addition, 2-tetradecylglycidic acid (TDGA), a CPT-1 inhibitor, was administered to mice fed HF diet with low-dose of α-Toc. Finally, HepG2 cells in fat-loaded environment were treated with 0-50 µM α-Toc. RESULTS: Treatment of low-dose of α-Toc decreased HF-induced hepatic fat accumulation, but this finding was not observed in treatment of high dose of α-Toc. HF-induced reduction of CPT-1 was attenuated with low-dose of α-Toc but not with high dose of α-Toc. TDGA suppressed the improvement of histological findings in liver induced by low-dose of α-Toc treatment. CPT-1 expression in HepG2 cells increased in response to low-dose of α-Toc, but not in high dose. CONCLUSIONS: Dual action of α-Toc on CPT-1 protein levels was observed. The effect of vitamin E on NAFLD may be not be dose-dependent.

Supplementation of branched-chain amino acids decreases fat accumulation in the liver through intestinal microbiota-mediated production of acetic acid.

Non-alcoholic fatty liver disease (NAFLD) is a significant problem because its prevalence is increasing worldwide. Recent animal studies have identified gut microbiota as a potentially important player in the pathogenesis of NAFLD. Previously, we reported that the administration of branched-chain amino acids (BCAAs) reduces hepatic fat accumulation in experimental animal models. This study aimed to clarify how changes in the intestinal microbial flora following the administration of BCAAs affect a high-fat diet (HF)-induced fat accumulation in the liver. We examined whether the administration of BCAAs alters the development of hepatic fat accumulation as well as intestinal microbial flora. The oral administration of BCAAs (3% kcal) induced a significant increase in Ruminococcus flavefaciens (R. flavefaciens) and portal acetic acid levels, and it reduced hepatic fat accumulation in HF-fed rats. In addition, BCAAs reduced the expression of the lipogenesis-related genes FAS and ACC in the liver. Furthermore, we observed that R. flavefaciens is essential for promoting a BCAA-induced reduction in hepatic fat accumulation. These data suggest that BCAA treatment induces the proliferation of intestinal flora including R. flavefaciens and that portal acetic acid synthesized from intestinal flora improves NAFLD by downregulating the expression of FAS and ACC in the liver.

Isoleucine prevents the accumulation of tissue triglycerides and upregulates the expression of PPARalpha and uncoupling protein in diet-induced obese mice.

In this study, we investigated the effects of the branched-chain amino acid l-isoleucine (Ile) on both obesity and glucose/fat homeostasis in mice that were fed a high-fat (45% energy) diet. The mice were divided into different treatment groups and given a high-fat diet for 6 wk. During the last 4 wk, Ile was dissolved and added to the drinking water to a final concentration of 2.5%. The control mice received vehicle alone. The mice in the Ile group had an almost 6% lower body weight gain and 49% less epididymal white adipose tissue (WAT) mass with the control group (P < 0.05). The hepatic and skeletal muscle triglyceride (TG) concentrations and degree of hyperinsulinemia in the Ile group mice were also lower than the control group by 38, 47, and 39%, respectively (P < 0.05). The WAT leptin concentration was also lower, whereas that of adiponectin was higher, in the Ile group compared with the control group (P < 0.05). The hepatic levels of protein CD36/fatty acid translocase, PPARalpha, and uncoupling protein (UCP) 2 and the levels of UCP3 in skeletal muscle were all greater in the Ile group than in the control mice (P < 0.05). These results demonstrate that the liver and muscle TG concentrations are both lowered by Ile treatment. In addition, the PPARalpha and UCP expression levels in the mouse tissues were greater in the Ile group compared with the controls. Our current data thus suggest that supplementation with Ile might be useful in the treatment of metabolic syndrome.