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BackgroundThere are currently no serum biomarkers capable of distinguishing elevations in serum alanine aminotransferase (ALT) that portend serious liver injury potential from benign elevations such as those occurring during cholestyramine treatment. The aim of the research was to test the hypothesis that newly proposed biomarkers of hepatotoxicity would not significantly rise in serum during elevations in serum ALT associated with cholestyramine treatment, which has never been associated with clinically relevant liver injury.MethodsIn a double-blind placebo-controlled trial, cholestyramine (8g) was administered for 11 days to healthy adult volunteers. Serum from subjects with elevations in alanine aminotransferase (ALT) exceeding three-fold the upper limit of normal (ULN) were utilized for biomarker quantification.ResultsIn 11 of 67 subjects, cholestyramine treatment resulted in ALT elevation by >3x ULN (mean 6.9 fold; range 3–28 fold). In these 11 subjects, there was a 22.4-fold mean increase in serum levels of miR-122 relative to baseline, supporting a liver origin of the serum ALT. Significant elevations were noted in mean levels of necrosis biomarkers sorbitol dehydrogenase (8.1 fold), cytokeratin 18 (2.1 fold) and HMGB1 (1.7 fold). Caspase-cleaved cytokeratin 18, a biomarker of apoptosis was also significantly elevated (1.7 fold). A rise in glutamate dehydrogenase (7.3 fold) may support mitochondrial dysfunction.ConclusionAll toxicity biomarkers measured in this study were elevated along with ALT, confirming the liver origin and reflecting both hepatocyte necrosis and apoptosis. Since cholestyramine treatment has no clinical liver safety concerns, we conclude that interpretation of the biomarkers studied may not be straightforward in the context of assessing liver safety of new drugs.

Thiazolidinedione PPARγ agonists (troglitazone and rosiglitazone) were previously shown to promote colon tumor formation in C57BL/6J-APC min /+ mice, a model for human familial adenomatous polyposis. This study was conducted to determine if another thiazolidinedione PPARγ agonist, pioglitazone, and a PPARγ agonist structurally unrelated to the thiazolidinedione family, NID525, (a tetrazole-substituted phenoxymethylquinolone), would also promote colon tumors in this mouse model. Mice were treated in-feed with the thiazolidinediones troglitazone (150 mg/kg/day), rosiglitazone (20 mg/kg/day), or pioglitazone (150 mg/kg/day), or with NID525 (150 mg/kg/day) for 8 weeks. An increased incidence in colon tumors compared to controls was observed for all of the thiazolidinedione-treated groups as well as the NID525-treated group. These results indicate that the tumor-promoting effect of PPARγ agonists in the colon of C57BL/6J-APC min /+ mice is likely related to the pharmacological activity of this group of drugs and not the thiazolidinedione structure.