Diets devoid of methionine and choline [methionine choline-defi cient (MCD)] cause hepatic steatosis and infl ammation that mimics nonalcoholic steatohepatitis in human beings ( 1-3 ). MCD feeding reportedly induces hepatic steatosis through a dual process involving enhanced uptake of fatty acids by the liver as well as impaired secretion of hepatic triglyceride (TG) ( 2 ). Stimulation of fatty acid uptake in MCD-fed animals correlates with hepatic upregulation of fatty acid transport proteins. Suppression of hepatic TG secretion is due to the reduced availability of methionine and choline for phospholipid synthesis, which is critical to the formation of TG-rich VLDL particles ( 4, 5 ). Notably, commercial MCD formulas (MP Biomedicals, Harlan Teklad, and Dyets) not only lack methionine and choline but are also enriched in sucrose and fat. These nutrients can themselves stimulate hepatic lipid accumulation ( 6-8 ); thus, they may accentuate the hepatic lipid accumulation caused by methionine and choline deprivation alone.The role of dietary fat as a determinant of liver injury in the MCD model has been the subject of recent investigation. Somewhat unexpectedly, studies have shown that the fat content of the MCD formula can be varied over a wide range (10% to 40% of calories) without any impact on the amount of TG that accumulates in the liver ( 9, 10 ). Even more surprising is that dietary fat does not affect MCDmediated hepatocellular injury based on biochemical or Abstract Methionine-choline-defi cient (MCD) diets cause steatohepatitis in rodents and are used to study the pathophysiology of fatty liver disease in human beings. The most widely used commercial MCD formulas not only lack methionine and choline but also contain excess sucrose and fat. The objective of this study was to determine whether dietary sucrose in the MCD formula plays a role in the pathogenesis of MCD-related liver disease. We prepared two custom MCD formulas, one containing sucrose as the principal carbohydrate and the other substituting sucrose with starch. Mice fed the sucrose-enriched formula developed typical features of MCD-related liver disease, including hepatic steatosis, hepatocellular apoptosis, alanine aminotransferase elevation, lipid peroxidation, and hepatic infl ammation. In contrast, mice fed MCD-starch were signifi cantly protected against liver injury. MCD-sucrose and MCD-starch mice displayed identical diet-related abnormalities in hepatic fatty acid uptake and triglyceride secretion. Hepatic de novo lipogenesis and triglyceride synthesis, however, were 2 times higher in MCD-sucrose mice than MCDstarch mice ( P < 0.01). Hepatic lipid analysis revealed accumulation of excess saturated fatty acids in MCD-sucrose mice that correlated with hepatocellular injury. Overall, the results indicate that dietary sucrose is critical to the pathogenesis of MCD-mediated steatohepatitis. They suggest that saturated fatty acids, which are products of de novo lipogenesis, are mediators of hepatic toxicity in this model of liver disease. ...

Background Methionine-choline-deficient (MCD) diets cause steatohepatitis in rodents and are used to model fatty liver disease in human beings. Recent studies have identified sucrose as a major contributor to MCD-related liver disease through its ability to promote hepatic de novo lipogenesis. Aims To determine whether glucose and fructose, the two constitutents of sucrose, differ in their capacity to provoke steatohepatitis when incorporated individually into MCD formulas. Materials & Methods MCD and control formulas prepared with either glucose or fructose as the sole source of carbohydrate were fed to mice for 21 days. Liver injury was assessed biochemically and histologically together with hepatic gene expression and fatty acid analysis. Results Mice fed MCD formulas developed similar degrees of hepatic steatosis whether they contained glucose or fructose. By contrast, mice fed MCD-fructose developed significantly more hepatocellular injury than mice fed MCD-glucose, judged by histology, apoptosis staining and serum alanine aminotransferase. Liver injury in MCD-fructose mice coincided with an exaggerated rise in the ratio of long-chain saturated to unsaturated fatty acids in the liver. Notably, hepatic inflammation was not enhanced in mice fed MCD-fructose, correlating instead with hepatic lipid peroxidation, which was equivalent in the two MCD groups. Discussion Fructose is more cytotoxic than glucose when used as the source of carbohydrate in MCD formulas. Conclusion The data suggest the enhanced cytotoxicity of fructose in the MCD model is related to its ability to stimulate de novo lipogenesis, which yields harmful long-chain saturated fatty acids.

BackgroundSaturated fatty acids are toxic to liver cells and are believed to play a central role in the pathogenesis of non-alcoholic steatohepatitis. In experimental steatohepatitis induced by feeding mice a methionine-choline-deficient (MCD) diet, the degree of liver damage is related to dietary sugar content, which drives de novo lipogenesis and promotes the hepatic accumulation of saturated fatty acids. The objective of this study was to determine whether dietary palmitate exerts the same toxicity as carbohydrate-derived palmitate in the MCD model of fatty liver disease.MethodsWe fed mice custom MCS and MCD formulas containing 4 different carbohydrate-fat combinations: starch-oleate, starch-palmitate, sucrose-oleate and sucrose-palmitate.  After 3 wk, we compared their metabolic and disease outcomes.ResultsMice fed the custom MCD formulas developed varying degrees of hepatic steatosis and steatohepatitis, in the order starch-oleate < starch-palmitate < sucrose-oleate < sucrose-palmitate. Liver injury correlated positively with the degree of hepatic lipid accumulation. Liver injury also correlated positively with the amount of palmitate in the liver, but the relationship was weak. Importantly, mice fed MCD starch-palmitate accumulated as much hepatic palmitate as mice fed MCD sucrose-oleate, yet their degree of liver injury was much lower. By contrast, mice fed MCD sucrose-palmitate developed severe liver injury, worse than that predicted by an additive influence of the two nutrients.ConclusionIn the MCD model of steatohepatitis, carbohydrate-derived palmitate in the liver is more hepatotoxic than dietary palmitate. Dietary palmitate becomes toxic when combined with dietary sugar in the MCD model, presumably by enhancing hepatic de novo lipogenesis.