Irinotecan induced disturbance of bile acid homeostasis promotes hepatocellular injury and inflammation

Irinotecan (IX) induced steatohepatitis is a complication that gets increasing clinical attention, but the mechanisms are just beginning to be understood.

The aim of this study was to investigate the effect of IX on bile acid (BA) homeostasis and the impact of BA on IX-induced hepatocellular injury and inflammation.

Methods and Results:

First, we analyzed hepatic bile acids (BA) levels in mice treated with intraperitoneal injections of irinotecan (50 mg/kg) or solvent (saline) every three days for two weeks. Levels of secondary BA were significantly increased in hepatic tissues of IX-treated mice in comparison to control mice. Furthermore, a significant induction in the expression of CYP7A1, the central enzyme of BA synthesis, and ATP-binding cassette (ABC) transporters (ABCG5 and ABCG8), the main transporter of BA efflux, was observed in the IX-treated livers. Next, we analyzed the combined effect of IX and the secondary BA acids taurodeoxycholic acid (TDCA) and glycochenodeoxycholic acid (GCDCA) on primary human hepatocytes (PHH) in vitro. First, we established the dose range in which the BA or IX alone did not affect the viability of PHH by microscopic analysis, XTT-assays and quantification of LDH-leakage into supernatants. Subsequently, we assessed the combined effect of two different concentrations of BA (250 and 500µM) and serial concentrations of IX (up to 100µM) for 24h. Combination with both TDCA and GCDCA significantly enhanced IX-toxicity. Furthermore, combined BA and IX stimulation significantly induced expression of pro-inflammatory genes as well as ABCG5, ABCG8 and CYP7A1 compared to IX or BA alone. Also analysis of liver specimens from IX-treated patients revealed significantly higher expression of BA-metabolizing genes and transporters.

Conclusion:

Irinotecan (IX) treatment disturbs BA homeostasis leading to significantly elevated levels of bile acids in hepatic tissues of mice, and analysis of liver specimens from IX-treated patients indicates the clinical relevance of these findings. Our in vitro model indicates that presence of elevated BA levels make hepatocytes more vulnerable for toxic IX effect and potentiates the IX-induced inflammation further contributing to IX-induced hepatocellular injury. Our data suggest that lowering BA-levels may be a potential therapeutic strategy for the prevention and treatment of IX-induced steatohepatitis. Our findings may have particular relevance for the therapeutic-IX application to cancer patients with cholestasis.