Identification of early proteomic markers for hepatic steatosis

The identification of biomarkers for disease state, drug efficacy, and toxicity is becoming increasingly important for drug discovery and development. We have used two-dimensional differential in-gel electrophoresis and mass spectrometry to identify proteomic markers associated with hepatocellular steatosis in rats after dosing with a compound (CDA) in preclinical development. Rats were dosed daily for up to 5 days with CDA for measurement of blood biochemical parameters, histological, and proteomic analysis. Alterations in plasma glucose and liver transaminases were detected from dosing day 3 onward, and livers showed trace levels of hepatocellular vacuolation from 6 h which increased in extent and severity over the 5 day time course. The number of significantly altered protein spots increased over the 5 day time course, and Ingenuity Pathway Analysis showed that the predominant functions altered by CDA treatment were cell death and cellular assembly and organization. This included alterations in secreted proteins, endoplasmic reticulum and mitochondrial chaperones, antioxidant proteins, and enzymes involved in fatty acid biosynthesis. Comparative in vitro dosing studies showed similar alterations to the proteome, neutral lipid accumulation, and mitochondrial dehydrogenase activity in response to CDA treatment of cultured rat hepatocytes. The finding that several proteins showed significant changes in abundance before the onset of overt toxicity in vivo suggested that these could serve as predictive biomarkers of compounds with a propensity to induce liver steatosis. These markers underwent further direct analysis in the in vitro hepatocyte toxicity model to determine their utility in the development of high throughput assays for drug-induced steatosis.