Beneficial effects versus toxicity of medium-chain triacylglycerols in rats with NASH.

BACKGROUND/AIMS: Replacing long-chain triacylglycerols (LCT) with medium-chain triacylglycerols (MCT) reduces alcohol-induced liver injury. Because of the similarity of the pathogenesis of alcohol-induced liver damage and non-alcoholic steatohepatitis (NASH), our aim was to assess whether MCT is also beneficial in NASH. METHODS: We used a rat NASH model in which corn oil (35% of total calories) was isocalorically replaced with MCT. RESULTS: Partial replacement of LCT did not ameliorate hepatic fat accumulation, 4-hydroxynonenal, collagen type I and its mRNA but it increased TNF-alpha and its mRNA (p<0.001). However, in rats given the high-fat diet restricted to 2/3 of the amount they were consuming, these adverse effects decreased, with and without MCT including less liver steatosis and lower triacylglycerols, but without beneficial effects of MCT. When 70% of the fat calories were replaced with MCT with no LCT remaining in the diet, no steatosis developed and hepatic TNF-alpha was low. When all MCT were given with carbohydrates (instead of LCT) hepatic TNF-alpha also decreased (p<0.001). CONCLUSIONS: MCT are not hepatotoxic, provided the diet contains no significant amount of LCT. Total replacement of dietary LCT with MCT fed ad libitum is beneficial whereas partial replacement becomes hepatotoxic, unless the dietary intake is restricted.

Role of medium-chain triglycerides in the alcohol-mediated cytochrome P450 2E1 induction of mitochondria.

BACKGROUND: Chronic alcohol consumption is known to induce cytochrome P450 2E1 (CYP2E1) leading to lipid peroxidation, mitochondrial dysfunction and hepatotoxicity. We showed that replacement of dietary long-chain triglycerides (LCT) by medium-chain triglycerides (MCT) could be protective. We now wondered whether the induction of mitochondrial CYP2E1 plays a role and whether liver injury could be avoided through mitochondrial intervention. METHODS: Rats were fed 4 different isocaloric liquid diets. The control group received our standard dextrin-maltose diet with intake limited to the average consumption of the 3 alcohol groups fed ad libitum the alcohol containing Lieber-DeCarli liquid diet. The fat was either 32% of calories as LCT (alcohol), or 16% as LCT + 16% as MCT (alcohol-MCT 16%), or 32% as MCT only (alcohol-MCT 32%). RESULTS: After 21 days, compared to the controls, the alcohol and both alcohol-MCT groups had a significant increase in mitochondrial CYP2E1 (p < 0.05 for both). As shown before, the same was found for the microsomal CYP2E1. When MCT replaced all the fat, like in the alcohol-MCT 32% group, CYP2E1 was significantly reduced by 40% in mitochondria (p < 0.05) and 30% in microsomes (p < 0.01). In mitochondria, 4-hydroxynonenal (4-HNE), a parameter of oxidative stress, paralleled CYP2E1. Compared to controls, alcohol and alcohol-MCT 16% significantly raised mitochondrial 4-HNE (p < 0.001), whereas the alcohol-MCT 32% diet brought it down to control levels (p < 0.001). Mitochondrial reduced glutathione (GSH) was also significantly lowered by alcohol consumption (p < 0.05), and it increased to almost normal levels with alcohol-MCT 32% (p = 0.006). These changes in the mitochondria reflected the reduction observed in total liver in which alcohol-MCT 32% decreased the alcohol-induced steatosis with a diminution of triglycerides (p < 0.001) and of the pro-inflammatory cytokine tumor necrosis factor-alpha (p < 0.001). CONCLUSION: Mitochondria participate in the induction of CYP2E1 by alcohol and contribute to lipid peroxidation and GSH depletion. Thus, lipid composition of the diet is an important determinant for the beneficial effect of MCT, with a diet containing a mixture of LCT/MCT being ineffective.

The Combination of S-adenosylmethionine and Dilinoleoylphosphatidylcholine Attenuates Non-alcoholic Steatohepatitis Produced in Rats by a High-Fat Diet.

In the pathogenesis of non-alcoholic steatohepatitis (NASH), oxidative stress resulting from free radicals generated by cytochrome P4502E1 (CYP2E1) plays a major role suggesting the importance of antioxidants. The objective of this study was to assess in a high-fat diet (HF) rat model the effects of the combination of s-adenosylmethionine (SAMe) plus dilinoleoylphosphatidylcholine (DLPC) in the treatment of NASH. To test the hypothesis that these two antioxidants are beneficial in NASH, male Sprague-Dawley rats were fed five different diets for six weeks: control, HF diet and HF plus SAMe and DLPC or their combination. As expected, the HF diet significantly increased hepatic triacylglycerols and CYP2E1 levels. However, only the combination diet opposed this effect, consistent with different actions of the two antioxidants. Next, 24 additional rats divided in two groups were fed the HF or the HF+SAMe+DLPC diets for 3 weeks. Dietary intake was similar, but liver triacylglycerols dropped from 76.1+/-6.8 to 49.4+/-3.5 mg/g (p=0.002) and hepatic CYP2E1 mRNA decreased after treatment (p=0.01) with a trend for less CYP2E1 protein. This was accompanied by a 41% reduction of hepatic 4-hydroxynonenal (4-HNE) (p=0.008), reflecting control of oxidative stress. Furthermore, the hepatic inflammatory cytokine tumor necrosis factor-alpha (TNF-alpha) mRNA and TNF-alpha protein decreased (p=0.05 and p=0.01 respectively) with attenuation of alpha1(I) procollagen mRNA and type I collagen levels (p=0.01 and p=0.02, respectively). We concluded that the combination SAMe+DLPC might be beneficial in NASH by reducing oxidative stress and associated liver injury.

Acarbose attenuates experimental non-alcoholic steatohepatitis.

The alpha-glucosidase inhibitor acarbose is beneficial in the prevention of type 2 diabetes. To determine whether it attenuates the commonly associated non-alcoholic steatohepatitis (NASH), we used an experimental NASH model. Rats were fed ad libitum a nutritionally adequate high fat diet (71% of calories as fat) with or without acarbose (200 mg/1000 calories) for 3 weeks. All rats given the high fat diet only developed typical NASH whereas acarbose attenuated several of the characteristic hepatic alterations of NASH: there was less steatosis and inflammation, with a significant reduction in the mRNA of the hepatic inflammatory cytokine TNF-alpha and of its protein. There was also a decrease in the CYP2E1 mRNA and in collagen, with similar trends for CYP2E1 protein and procollagen mRNA. Because acarbose attenuates many of the hepatic alterations associated with experimental NASH, it is now indicated to determine whether it exerts similar beneficial effects in patients afflicted by this disease.

Model of nonalcoholic steatohepatitis.

BACKGROUND: Obesity and diabetes are frequently associated with nonalcoholic steatohepatitis (NASH), but studies have been hampered by the absence of a suitable experimental model. OBJECTIVE: Our objective was to create a rat model of NASH. DESIGN: Sprague-Dawley rats were fed a high-fat, liquid diet (71% of energy from fat, 11% from carbohydrates, 18% from protein) or the standard Lieber-DeCarli diet (35% of energy from fat, 47% from carbohydrates, 18% from protein). The diets were given ad libitum or as two-thirds of the amount consumed ad libitum. RESULTS: Rats fed the high-fat diet ad libitum for 3 wk developed panlobular steatosis, whereas those fed the standard diet had few fat droplets. Accordingly, total lipid concentrations with the high-fat and standard diets were 129.9 +/- 9.1 ( +/- SEM) and 66.7 +/- 4.6 mg/g liver, respectively (P < 0.001). The high-fat diet caused abnormal mitochondria and mononuclear inflammation, which were accompanied by increased hepatic tumor necrosis factor alpha (TNF-alpha; P < 0.001), TNF-alpha messenger RNA (mRNA) (P < 0.001), collagen type 1, and alpha1(I) procollagen mRNA (P < 0.001). In addition, these rats had increased cytochrome P4502E1 (CYP2E1) mRNA (P < 0.001), which was accompanied by CYP2E1 induction (P < 0.001) and oxidative stress with increased 4-hydroxynonenal (P < 0.001). Plasma insulin was elevated, which reflected insulin resistance, a NASH pathogenic factor. Rats fed a restricted high-fat diet developed only mild steatosis with attenuated biochemical changes, whereas those given a restricted standard diet had normal livers. CONCLUSION: This rat model reproduces the key features of human NASH and provides a realistic experimental model for elucidating its treatment.