Effect of dietary monosodium glutamate on HFCS-induced hepatic steatosis: expression profiles in the liver and visceral fat.

It has previously been shown that patients with nonalcoholic fatty liver disease (NAFLD) exhibit alterations in both hepatic and adipose tissue metabolism, and the dietary factors that contribute to the pathogenesis of NAFLD are likely to be multifactorial. Using C57BL/6J mice, we examined whether chronic exposure to low-dose dietary monosodium glutamate (MSG), high-fructose corn syrup (HFCS), or a combination of the two, vs. control would affect metabolism and hepatic and visceral fat gene expression in adult male progeny. A maternal diet containing 20% HFCS and/or dietary MSG (97.2 +/- 6.3 mg/kg body weight (bw), provided in the drinking water) was offered ad libitum from 3 weeks before mating, and continued throughout gestation and weaning until the progeny reached 32 weeks of age. Liver and abdominal fat gene expression was compared with control animals fed isocaloric standard chow under identical conditions. HFCS induced hepatic steatosis and increased the expression of genes involved in carbohydrate and lipid metabolism. Conversely, dietary MSG elevated serum free fatty acids (FFAs), triglycerides (TGs), high-density lipoprotein-cholesterol (HDL-C), and insulin, together with the expression of hepatic genes involved in lipid metabolism and bile synthesis. The HFCS+MSG combination elevated hepatic TGs, serum FFAs, and TG levels. In visceral white adipose tissue, both MSG and HFCS diets increased the expression of transcription factor Srebf2 and decreased expression of Ppargc1a, while downregulating the expression of mitochondrial respiratory chain components. MSG increased the expression of several genes implicated in adipocytes differentiation. We hypothesize that HFCS may promote hepatic steatosis, whereas dietary MSG induces dyslipidemia and markers of insulin resistance.

Diabetes of the liver: the link between nonalcoholic fatty liver disease and HFCS-55.

Nonalcoholic fatty liver disease (NAFLD) is associated with obesity and insulin resistance. It is also a predisposing factor for type 2 diabetes. Dietary factors are believed to contribute to all three diseases. NAFLD is characterized by increased intrahepatic fat and mitochondrial dysfunction, and its etiology may be attributed to excessive fructose intake. Consumption of high fructose corn syrup-55 (HFCS-55) stands at up to 15% of the average total daily energy intake in the United States, and is linked to weight gain and obesity. The aim of this study was to establish whether HFCS-55 could contribute to the pathogenesis of NAFLD, by examining the effects of HFCS-55 on hepatocyte lipogenesis, insulin signaling, and cellular function, in vitro and in vivo. Exposure of hepatocytes to HFCS-55 caused a significant increase in hepatocellular triglyceride (TG) and lipogenic proteins. Basal production of reactive oxygen metabolite (ROM) was increased, together with a decreased capacity to respond to an oxidative challenge. HFCS-55 induced a downregulation of the insulin signaling pathway, as indicated by attenuated (ser473)phosphorylation of AKT1. The c-Jun amino-terminal kinase (JNK), which is intimately linked to insulin resistance, was also activated; and this was accompanied by an increase in endoplasmic reticulum (ER) stress and intracellular free calcium perturbation. Hepatocytes exposed to HFCS-55 exhibited mitochondrial dysfunction and released cytochrome C (CytC) into the cytosol. Hepatic steatosis and mitochondrial disruption was induced in vivo by a diet enriched with 20% HFCS 55; accompanied by hypoadiponectinemia and elevated fasting serum insulin and retinol-binding protein-4 (RBP4) levels. Taken together our findings indicate a potential mechanism by which HFCS-55 may contribute to the pathogenesis of NAFLD.