DNA damage and up-regulation of PARP-1 induced by columbin in vitro and in vivo.

Columbin (CLB) is the most abundant (>1.0%) furan-containing diterpenoid lactone in herbal medicine Tinospora sagittate (Oliv.) Gagnep. The furano-terpenoid was found to be hepatotoxic, but the exact mechanisms remain unknown. The present study demonstrated that administration of CLB at 50 mg/kg induced hepatotoxicity, DNA damage and up-regulation of PARP-1 in vivo. Exposure to CLB (10 µM) induced GSH depletion, over-production of ROS, DNA damage, up-regulation of PARP-1 and cell death in cultured mouse primary hepatocytes in vitro. Co-treatment of mouse primary hepatocytes with ketoconazole (10 µM) or glutathione ethyl ester (200 µM) attenuated the GSH depletion, over-production of ROS, DNA damage, up-regulation of PARP-1, and cell death induced by CLB, while co-exposure to L-buthionine sulfoximine (BSO, 1000 µM) intensified such adverse effects resulting from CLB exposure. These results suggest that the metabolic activation of CLB by CYP3A resulted in the depletion of GSH and increase of ROS formation. The resultant over-production of ROS subsequently disrupted the DNA integrity and up-regulated the expression of PARP-1 in response to DNA damage, and ROS-induced DNA damage was involved in the hepatotoxicity of CLB.

Difference in hepatotoxicity of furan-containing components in cortex dictamni correlates the efficiency of their metabolic activation.

BACKGROUND: Cortex Dictamni (CD) has been associated with an increased risk of liver injury, which may be attributable to the metabolic activation of its furan-containing components (FCC). However, the hepatotoxic potencies of these FCCs and the mechanisms behind the differences in their toxicity intensity remain unknown. METHODS: The constituents of CD extract were determined by LC-MS/MS. Potentially toxic FCCs were screened by a previously published method. Hepatotoxicity of potentially toxic FCCs was evaluated in cultured mouse primary hepatocytes and mice. The ability to deplete hepatic glutathione (GSH), along with the formation of the corresponding GSH conjugates, resulting from the metabolic activation was determined ex vivo in mice. Intrinsic clearance rates (CLint,Vmax/Km) were assessed by a microsome-bases assay. RESULTS: A total of 18 FCCs were detected in CD extract. Among them, four FCCs, including rutaevin (RUT), limonin (LIM), obacunone (OBA) and fraxinellone (FRA) were found to be bioactivated in microsomal incubations. Only FRA displayed significant hepatotoxicity in vitro and in vivo. Similarly, FRA caused GSH depletion and GSH conjugation the most in vivo. The order of CLint for the four FCCs was FRA>>OBA>LIM>RUT. CONCLUSION: FRA is the major toxic FCC component of hepatotoxic CD extract. The hepatotoxicity of FCCs is closely related to the efficiency of their metabolic activation.

Metabolic Activation of Militarine In Vitro and In Vivo.

Bletilla striata is consumed as food and herbal medicine. Militarine (MLT) is a major ingredient in B. striata. Previous studies demonstrated that MLT showed teratogenic toxicity to zebrafish embryos. The present study aimed to identify reactive metabolites possibly involved in the cytotoxicity of MLT and determine the metabolic pathways involved. MLT was found to be hydrolyzed to p-hydroxybenzyl alcohol (HBA) by ß-glucosidase and esterases. The resulting HBA further underwent spontaneous dehydration to form quinone methide. HBA was also metabolized to the corresponding sulfate, followed by departure of the sulfate to generate a quinone methide. The resultant quinone methide reacted with hepatic glutathione (GSH) and protein to form the corresponding GSH conjugate and protein adduction. Additionally, inhibition of sulfotransferases (SULTs) attenuated the susceptibility of hepatocytes to the toxicity of MLT. This study provides that the hydrolytic enzymes ß-glucosidase, esterases, and SULTs participate in the metabolic activation of MLT.