Current biochemical studies of Non-Alcoholic Fatty Liver Disease (NAFLD) and Non-Alcoholic Steatohepatitis (NASH) suggest a new therapeutic approach: Lin Hz, Yang SQ, Chuckaree C, et al., Metformin’s Reverses Fatty Liver Disease in Obese Leptin-Deficient Mice, Nature Medicine 2000;6(8):998–1003

Abstract The authors’ study population was ob/ob mice that have an inherited genetic deficiency of the appetite suppressing hormone leptin. These mice develop hyperinsulinemia, insulin resistance and fatty livers. Compared with their lean littermates and wild-type C57BL-6 mice, ob/ob mice have hepatomegaly. In this study, the authors compared three different groups of adult mice (age 8–10 wk), including male ob/ob C57BL-6 mice, their lean littermates, and wild type C57BL-6 mice of the same age and sex. The primary purpose of this study was to test the efficacy of Metformin for treatment of fatty liver disease in obese, ob/ob mice that develop hyperinsulinemia or insulin resistance and fatty livers. Metformin therapy was found to eliminate fatty liver disease in this model. The potential mechanisms of the action of metformin was the inhibition of hepatic tumor necrosis factor (TNF)-α and inhibition of several TNF-inducible responses, which are likely to promote hepatic steatosis and necrosis. In these experiments, ob/ob mice were divided into three treatment groups. Group 1 consisted of eight mice that were treated with Metformin and permitted to consume a nutritiously replete liquid mouse diet ad libitum. Mice in Group 2 (n = 8) did not receive Metformin, but were pair-fed the same volume of liquid diet that the mice in the Metformin treated group had consumed on the previous day. Obese ob/ob mice in group 3 (n = 4) and lean mice received no metformin as the mice in group 2, but were permitted to consume the liquid diet ad libitum. Liquid diet was given to facilitate accurate daily comparison of food intake among the various treatment groups. All mice were weighed at the beginning of the study and weekly thereafter until killed and then sera, fat and liver tissues were collected. Tissues were either fixed in buffered formalin and processed from the deceased mice for histology or snap frozen in liquid nitrogen and stored until RNA and proteins were isolated. The feeding protocol was repeated with a second group of 18 ob/ob mice. After 4 wk hepatocytes were obtained by in situ liver perfusion with collagenase and assayed for cellular ATP content. In each experiment hepatocytes isolated from 2–3 mice feeding group were suspended in a medium and pooled for subsequent analysis to evaluate cell viability, determine the number of obtained cells, and to assay cellular ATP content. These experiments were repeated using another 2–3 mice feeding group so that analysis of hepatocytes took place from six ob/ob mice in each feeding group. Thus the final ATP results reflected analysis of hepatocytes from six ob/ob mice in each feeding group. Hepatic steatosis was decreased significantly only in the Metformin treated group. The authors found that metformin’s beneficial effect on the fatty liver disease of mice was not due to its ability to constrain hyperphagia, nor due to decreased caloric ingestion, as the daily caloric intakes of the metformin treated mice and the pair-fed control mice were virtually identical. These caloric intakes were consistently about 20% less than that of another obese control group that was permitted to consume diet ad lib. The authors also observed no significant effect of metformin on serum glucose concentration from fed, ob/ob mice. Metformin is known to reduce hyperinsulinemia by about 40% in both of these obese hyperinsulinemic and insulin-resistant rodent strains. In conclusion, they documented that Metformin improves fatty liver disease, and reverses hepatomegaly, steatosis and aminotransferase abnormalities in mice. In addition, the authors suggest that Metformin may inhibit dieting-induced redistribution of lipid from the liver to adipose tissue depots. In summary, this study identifies a potential treatment for fatty liver disease in humans.