AIMS: Thiazolidinediones (glitazones) are frequently prescribed antidiabetic drugs commonly used in combination drug regimens. To evaluate the risk of drug-drug interactions, we therefore aimed to systematically investigate the inhibitory and inductive effects of all glitazones on 2 of the most relevant drug transporters, P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP), in vitro. METHODS: The inhibition of P-gp and BCRP was assessed by fluorometric assays quantifying the increase in the intracellular concentration of fluorescent P-gp or BCRP substrates caused by their combination with the glitazones. The induction of mRNA expression was quantified by real-time RT-PCR after the treatment of HuH-7 cells with the respective compounds for 4 days. RESULTS: Rosiglitazone and troglitazone significantly inhibited P-gp and BCRP function and induced mRNA expression of BCRP but not of P-gp. Pioglitazone, which exhibited very low solubility, could only be tested up to 0.5 micromol/l and did not provoke an effect in any of the assays. CONCLUSIONS: After comparison of the in vitro data and published clinical studies, it seems unlikely that the inhibition of BCRP and P-gp by rosiglitazone plays a role in the clinical situation. In contrast, BCRP induction by rosiglitazone might be of relevance in vivo, but has to be verified in dedicated clinical studies.
