Effect of genipin on the biliary excretion of cholephilic compounds in rats

Genipin, a metabolite of geniposide, is reported to stimulate the insertion of multidrug resistance protein 2 (Mrp2) in the bile canalicular membrane, and to cause choleresis by increasing the biliary excretion of glutathione, which has been considered to be a substrate of Mrp2. In the present study, the effect of colchicine on the choleretic effect of genipin was investigated. The effect of genipin on the biliary excretion of the substrates of bile salt export pump and Mrp2 was also studied.

After bile duct cannulation into rats, genipin was administered at the rate of 0.2 mumol/min/100 g, and the effect of colchicine pretreatment (0.2 mg/100 g) was examined. Metabolites of genipin in the bile were examined by a thin layer chromatography. Taurocholate (TC), sulfobromophthalein (BSP), and pravastatin were infused at the rate of 1.0, 0.2 and 0.3 mumol/min/100 g, respectively, and the effect of genipin co-administration was examined.

Genipin increased bile flow and the biliary glutathione excretion, and those increases were not inhibited by colchicine. The biliary excretion of genipin glucuronide was less than 10% of the genipin excreted into bile. The biliary excretion of TC, BSP, and pravastatin was unchanged by genipin co-administration.

It was indicated that colchicine-sensitive vesicular transport has no role on the genipin-induced insertion of Mrp2 to the canalicular membrane. Choleresis of genipin is considered to be mainly due to the increased biliary glutathione excretion by genipin, not by the biliary excretion of glucuronide. TC had no effect on the biliary glutathione excretion.