Cytochrome c: a non-invasive biomarker of drug-induced liver injury.

Limitations of existing biomarkers to detect liver injury in experimental animals highlight the need for additional tools to predict human toxicity. The utility of cytochrome c (cyt c) as a biomarker in serum and urine was evaluated in two rodent liver injury models. Adult Sprague-Dawley rats treated with acetaminophen or D-galactosamine (GalN) showed dose- and time-dependent histomorphological changes and TUNEL staining in liver consistent with hepatocellular necrosis, apoptosis and inflammation up to 72 h. Matching changes in serum alanine transaminase (ALT), aspartate transaminase (AST) and cyt c peaked at 24 h for either drug at the highest dose, cyt c falling rapidly at 48 hours with ALT and AST remained high. Intracellular transit of cyt c from mitochondria to the cytoplasm in damaged hepatocytes, and then to peripheral circulation, was observed by immunohistochemistry. Correlation coefficients between cyt c and serum diagnostic tests indicate the liver to be the primary source of cyt c. Urinary analysis for cyt c revealed time-dependent increase at 6 h, peaking at 24 h in GalN-treated rats in contrast with irregular patterns of urinary ALT and AST activity. Histological changes detected at 6 h preceded altered ALT, AST and cyt c at 12 and 18 h, respectively, in GalN-treated rats. These studies demonstrate cyt c to be a useful indicator of hepatic injury in rodents and support its utility as a non-invasive predictor of drug-induced hepatotoxicity, when utilized as a potential urinary biomarker.