Diosbulbin B: An important component responsible for hepatotoxicity and protein covalent binding induced by Dioscorea bulbifera L.

BACKGROUND: Dioscorea bulbifera L. (DBL) is an herbal medicine used for the treatment of thyroid diseases and tumors in China. However, the hepatotoxicity of DBL limits its wide safe use. Diosbulbin B (DSB) is the most abundant diterpene lactone occurring in DBL. Numbers of studies showed that this furanoterpenoid plays an important role in DBL-induced liver injury and that DSB is metabolized to a cis-enedial intermediate which reacts with protein to form protein covalent binding and induces hepatotoxicity. PURPOSE: The present study aimed to define the association of DSB content in DBL with the severity of DBL hepatotoxicity to ensure the safe use of the herbal medicine in clinical practice and to determine the role of DSB in DBL-induced liver injury. METHODS: Chemical chromatographic fingerprints of DBL were established by UPLC-MS/MS. Their hepatotoxicity potencies were evaluated in vitro and in vivo. Metabolic activation of DSB was evaluated by liver microsomal incubation. Protein modification was assessed by mass spectrometry and immunostaining. RESULTS: The contents of DSB in DBL herbs collected from 11 locations in China varied dramatically with as much as 47-fold difference. The hepatotoxicity potencies of DBL herbs were found to be proportional to the contents of DSB. Intensified protein adduction derived from the reactive metabolite of DSB was observed in mice administered DBL with high contents of DSB. CONCLUSION: The findings not only demonstrated that contents of DSB can be quite different depending on harvest location and special attention needs to pay for quality control of DBL but also suggest DSB is a key contributor for DBL-induced hepatotoxicity.

2-Naphthalenemethanol participates in metabolic activation of 2-methylnaphthalene.

2-Methylnaphthalene (2-MN) is an environmental pollutant. Studies have shown that 2-MN is teratogenic, carcinogenic, and cytotoxic. However, the mechanisms of 2-MN induced toxicities remain unclear.This study aimed to characterise reactive metabolites of 2-MN, to define the metabolic pathway, and to determine the enzymes participating in the metabolic activation.A hydroxylation metabolite of 2-MN, 2-naphthalenemethanol (2-NM), was observed in 2-MN-containing mouse liver microsomes.A glutathione (GSH) conjugate was detected in mouse S9 incubations fortified with 2-MN and GSH. A GSH conjugate and an NAC conjugate were found in mouse liver and urine, respectively, in animals given 2-MN. Hepatic protein covalent binding derived from 2-NM was observed in animals administered 2-MN.Cytochrome P450 enzymes and sulfotransferases participated in the metabolic activation of 2-MN.

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.

Metabolic activation of 3-aminodibenzofuran mediated by P450 enzymes and sulfotransferases.

3-Aminodibenzofuran (3-ADBF) is a potent bladder carcinogen. This study aimed to identify reactive metabolites and the metabolic pathways of 3-ADBF. The in vitro and in vivo studies demonstrated that 3-ADBF was oxidized to the corresponding hydroxylamine by cytochrome P450 enzymes, followed by sulfation of the hydroxyl group mediated by sulfotransferases. The resulting sulfate conjugate was chemically reactive to GSH and cysteine residues of hepatic protein to form the corresponding GSH conjugate and protein adduction. Exposure of 3-ADBF to primary hepatocytes caused protein covalent binding and decreased cell viability. The resultant protein adduction was found to correlate the observed cytotoxicity of 3-ADBF.

Toxicokinetic and bioavailability studies on retrorsine in mice, and ketoconazole-induced alteration in toxicokinetic properties.

Retrorsine (RTS) is a toxic retronecine-type pyrrolizidine alkaloid, which is widely distributed. The purpose of this study was to develop a high-performance liquid chromatography-tandem mass spectrometric (LC-MS/MS) method for serum RTS determination in mice. Serum samples were deproteinated by acetonitrile, separated on a C18 -PFP column and delivered at 0.8 ml/min with an eluting system composed of water containing 0.1% (v/v) formic acid and acetonitrile containing 0.1% (v/v) formic acid as mobile phases. RTS and the internal standard S-hexylglutathione (H-GSH) were quantitatively monitored with precursor-to-product transitions of m/z 352.1 → 120.1 and m/z 392.2 → 246.3, respectively. The method showed excellent linearity over the concentration range 0.05-50 µg/ml, with correlation coefficient r2 = 0.9992. The extraction recovery was >86.34%, and the matrix effect was not significant. Inter- and intra-day precisions (RSD) were <4.99%. The validated LC-MS/MS method was successfully applied to study the toxicokinetic profiles of serum RTS in mice after intravenous, oral administration and co-treated with ketoconazole, which showed that RTS displayed a long half-life (~11.05 h) and good bioavailability (81.80%). Co-administration of ketoconazole (KTZ) increased the peak serum concentration and area under the concentration-time curve and decreased the clearance and mean residence time. Summing up, a new standardized method was established for quantitative determination of RTS in sera.