Transcript and metabolite analysis of the effects of tamoxifen in rat liver reveals inhibition of fatty acid synthesis in the presence of hepatic steatosis

Abstract

Nonalcoholic steatohepatitis (NASH) is a common feature of the metabolic syndrome and toxic reactions to pharmacological drugs. Tamoxifen, (TMX) a widely used anti-breast cancer drug, can induce NASH and changes in plasma cholesterol levels through mechanisms that are unclear. We studied primary actions of TMX using a short-term treatment (5 days) that induces microvesicular hepatic steatosis and marked hypercholesterolemia in male rats. Using a combined approach of gene expression profiling and NMR-based metabolite analysis, we found that TMX-treated livers have increased saturated fatty acid content despite changes in gene expression, indicating decreased de novo lipogenesis and increased fatty acid oxidation. Our results show that TMX predominantly down-regulates FAS expression and activity as indicated by the accumulation of malonyl-CoA, a known inhibitor of mitochondrial beta-oxidation. In the face of a continued supply of exogenous free fatty acids, the blockade of fatty acid oxidation produced by elevated malonyl-CoA is likely to be the major factor leading to steatosis. Use of a combination of metabolomic and transcriptomic analysis has allowed us to identify mechanisms underlying important metabolic side effects of a widely prescribed drug. Given the broader importance of hepatic steatosis, the novel molecular mechanism revealed in this study should be examined in other forms of steatosis and nonalcoholic steatohepatitis.

Tamoxifen-Induced Anorexia Is Associated With Fatty Acid Synthase Inhibition in the Ventromedial Nucleus of the Hypothalamus and Accumulation of Malonyl-CoA

“…Blood biochemistry. Kits for the measurement of cholesterol, glucose, and triglycerides were obtainded from Roche (21,30). Free fatty acids were measured using the NEFA-C colorimetric kit (Wako Chemicals) (21,30).…”

“…Kits for the measurement of cholesterol, glucose, and triglycerides were obtainded from Roche (21,30). Free fatty acids were measured using the NEFA-C colorimetric kit (Wako Chemicals) (21,30). Plasma leptin and insulin levels were measured by ELISA kits (Crystal) (21,30).…”

“…Free fatty acids were measured using the NEFA-C colorimetric kit (Wako Chemicals) (21,30). Plasma leptin and insulin levels were measured by ELISA kits (Crystal) (21,30). Real-time quantitative PCR.…”

“…Using a systems biology approach, we have recently identified a primary action of TMX selectively decreasing the expression and activity of FAS in liver (21). By analogy, we studied whether the anorectic effect of TMX may be mediated through the inhibition of FAS in the hypothalamus.…”

(−)-UB006: A new fatty acid synthase inhibitor and cytotoxic agent without anorexic side effects

“…However, in our experimental conditions, DTT was not added. For the FAS activity assay, a spectrophotometric method was used [42].…”