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Mitochondrial abnormalities are suggested to be associated with the development of nonalcoholic fatty liver. Liver mitochondrial content and function have been shown to improve in oral feeding of acetyl-L-carnitine (ALC) to rodents. Carnitine is involved in the transport of acyl-coenzyme A across the mitochondrial membrane to be used in mitochondrial β-oxidation. We hypothesized that oral administration ALC with the antioxidant lipoic acid (ALC + LA) would benefit nonalcoholic fatty liver. To test our hypothesis, we fed Balb/C mice a standard diet (SF) or SF with ALC + LA or high-fat diet (HF) or HF with ALC + LA for 6 months. Acetyl-L-carnitine and LA were dissolved at 0.2:0.1% (wt/vol) in drinking water, and mice were allowed free access to food and water. Along with physical parameters, insulin resistance (blood glucose, insulin, glucose tolerance), liver function (alanine transaminase [ALT], aspartate transaminase [AST]), liver histology (hematoxylin and eosin), oxidative stress (malondialdehyde), and mitochondrial abnormalities (carbamoyl phosphate synthase 1 and electron microscopy) were done. Compared with SF, HF had higher body, liver, liver-to-body weight ratio, white adipose tissue, ALT, AST, liver fat, oxidative stress, and insulin resistance. Coadministration of ALC + LA to HF animals significantly improved the mitochondrial marker carbamoyl phosphate synthase 1 and the size of the mitochondria in liver. Alanine transaminase and AST levels were decreased. In a nonalcoholic fatty liver mice model, ALC + LA combination improved liver mitochondrial content, size, serum ALT, and AST without significant changes in oxidative stress, insulin resistance, and liver fat accumulation., (© 2013.)

Nonalcoholic fatty liver (NAFL) is a common liver disease, associated with insulin resistance. Betaine has been tested as a treatment for NAFL in animal models and in small clinical trials, with mixed results. The present study aims to determine whether betaine treatment would prevent or treat NAFL in mice and to understand how betaine reverses hepatic insulin resistance. Male mice were fed a moderate high-fat diet (mHF) containing 20% of calories from fat for 7 (mHF) or 8 (mHF8) mo without betaine, with betaine (mHFB), or with betaine for the last 6 wk (mHF8B). Control mice were fed standard chow containing 9% of calories from fat for 7 mo (SF) or 8 mo (SF8). HepG2 cells were made insulin resistant and then studied with or without betaine. mHF mice had higher body weight, fasting glucose, insulin, and triglycerides and greater hepatic fat than SF mice. Betaine reduced fasting glucose, insulin, triglycerides, and hepatic fat. In the mHF8B group, betaine treatment significantly improved insulin resistance and hepatic steatosis. Hepatic betaine content significantly decreased in mHF and increased significantly in mHFB. Betaine treatment reversed the inhibition of hepatic insulin signaling in mHF and in insulin-resistant HepG2 cells, including normalization of insulin receptor substrate 1 (IRS1) phosphorylation and of downstream signaling pathways for gluconeogenesis and glycogen synthesis. Betaine treatment prevents and treats fatty liver in a moderate high-dietary-fat model of NAFL in mice. Betaine also reverses hepatic insulin resistance in part by increasing the activation of IRS1, with resultant improvement in downstream signaling pathways.

Objective: Cytochrome P4502E1 (CYP2E1) expression in the liver is increased in nonalcoholic fatty liver disease. The aim of this study was to determine whether CYP2E1 overexpression in the liver interferes with insulin signaling pathways in a mouse model of nonalcoholic fatty liver disease., Methods: Male mice containing the human CYP2E1 transgene under control of the mouse albumin enhancer-promoter (Tg) and control, nontransgenic mice were fed a diet containing 20% calories from fat for 8 months ad libitum., Measurements: Liver injury was measured by histology and alanine aminotransferase. Malondialdehyde and protein carbonyls were measured as markers of oxidative stress. Total and phosphorylated proteins involved in the insulin signaling cascade were measured by western blotting., Results: Tg mice had higher fasting insulin, and greater hepatic fat accumulation and histological liver injury. Malondialdehyde and protein carbonyls were increased in Tg mice liver indicating increased oxidative stress. Tyrosine phosphorylation of insulin receptor substrates 1 and 2, and serine phosphorylation of PKB/Akt, were significantly decreased in Tg mice. Serine phosphorylation of glycogen synthase kinase 3alpha was decreased in Tg mice and liver glycogen content was decreased correspondingly. Serine phosphorylation of the transcription factor Fox01a was decreased, and expression of the enzyme phosphoenolcarboxykinase was increased in Tg mice., Conclusion: Hepatocyte-specific overexpression of CYP2E1 increased hepatic oxidative stress in the liver, fasting insulin, and histological liver damage. CYP2E1 overexpression reduced hepatic insulin signaling and reduced glycogen storage and increased glucose synthesis. Overall, this study suggests an association of hepatic CYP2E1 with increased oxidative stress, increased systemic insulin resistance, decreased insulin signaling in the liver and increased hepatic fat accumulation.

Objective: To determine whether expression of transcription factors and lipogenic enzymes is altered in liver and adipose tissue of mice with obesity, insulin resistance, and nonalcoholic fatty liver disease., Methods: Mice were fed chow containing 9% of calories from standard fat (SF) or 20% of calories from high fat (HF) and killed after 9 months in the fasted or fed state., Measurements: Liver injury was evaluated by histology and serum aminotransferase levels. Transcription factor expression was measured by real-time PCR. Lipogenic enzymes were measured by real-time PCR and Western blots., Results: HF mice weighed more, had insulin resistance, hepatic steatosis, and focal pericellular hepatic fibrosis. Hepatic expression of sterol regulatory element-binding protein-1c, carbohydrate response element-binding protein, liver X receptor-alpha, acetyl-CoA carboxylase (ACC), and fatty acid synthase (FAS) decreased during fasting in SF and HF mice; however, FAS expression and protein content were higher in the liver of fasted HF mice than of fasted SF mice. In adipose tissue, expression of sterol response element-binding protein-1c, carbohydrate response element-binding protein, liver X receptor-alpha, peroxisome proliferator-activated receptor-gamma, ACC, and FAS decreased with fasting in mice fed SF, but not in HF mice. ACC and FAS expression and protein content remained higher during fasting in HF than in SF mice., Conclusion: Feeding a nutritionally complete diet containing a moderate increase in fat produces obesity and steatohepatitis. During fasting, hepatic FAS expression and protein content are increased in HF mice. Transcription factor expression, and lipogenic enzyme expression and protein concentration do not decline during fasting in adipose tissue from HF mice. De-novo lipogenesis may persist in liver and adipose tissue during fasting in obesity/nonalcoholic fatty liver disease.

Hepatic metabolism of ethanol by cytochrome P450 2E1 (CYP2E1) is believed to contribute to alcoholic liver damage. To further evaluate CYP2E1 in alcoholic liver disease, we created a transgenic mouse containing human CYP2E1 complementary DNA (cDNA) under the control of mouse albumin enhancer-promoter. Two experiments were performed. In the first experiment, transgenic and nontransgenic mice were fed normal chow. In the second experiment, transgenic and nontransgenic mice were pair fed a nutritionally complete liquid diet for 16 weeks. The liquid diet contained 30% of calories as ethanol (or dextrose) and 25% of calories as corn oil. Liver damage was assessed by measuring serum alanine aminotransferase (ALT) levels and examining liver histology. Transgenic animals reproduced and were phenotypically normal. Hepatic levels of CYP2E1 messenger RNA (mRNA), protein, and enzyme activity did not differ between chow-fed transgenic and nontransgenic mice. Livers from transgenic mice fed the alcohol diet contained significantly more CYP2E1 protein and enzyme activity than livers from nontransgenic mice fed the same diet. Transgenic mice receiving the alcohol diet had significantly higher serum ALT levels than nontransgenic mice. Histologic examination of the livers showed higher histologic scores in transgenic mice fed ethanol compared with nontransgenic mice fed ethanol. Ballooning hepatocytes were seen in livers from transgenic mice fed ethanol. Apoptosis, as determined by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling (TUNEL) assay, did not differ between groups. In conclusion, we have produced a transgenic mouse that expresses human CYP2E1 in the liver. When fed a nutritionally complete alcohol diet, transgenic mice develop more liver damage than nontransgenic mice.