Evaluation of the Antidepressant Activity, Hepatotoxicity and Blood Brain Barrier Permeability of Methyl Genipin

Geniposide (GE) is the main bioactive component of Gardeniae Fructus. The hepatotoxicity of geniposide limited clinical application. In order to get a new geniposide derivative that has less hepatotoxicity and still possesses the antidepressant activity, a new C-1 hydroxyl methylation derivative named methyl genipin (MG) was synthesized from geniposide. In the present study, we demonstrated that MG did not increase the liver index, alanine aminotransferase (ALT) and aspirate aminotransferase (AST). Histopathological examination suggested that no toxic damages were observed in rats treated orally with MG (0.72 mmol/kg). More importantly, a 7-day treatment with MG at 0.13, 0.26, and 0.52 mmol/kg/day could reduce the duration of immobility. It showed that the antidepressant-like effects of MG were similar to GE in the tail suspension test and the forced swim test. Furthermore, we found MG could be detected in the brain homogenate of mice treated orally with MG 0.52 mmol/kg/day for 1 day by HPLC. The area under the curve (AUC) of MG in the brain homogenate was enhanced to 21.7 times that of GE. The brain amount and distribution speed of MG were improved significantly after oral administration. This study demonstrated that MG possessed the antidepressant effects and could cross the blood-brain barrier, but had less hepatotoxicity.