Study on potential hepatotoxicity of rhein in Rhei Radix et Rhizoma based on liver metabolism / 中国中药杂志

The bilirubin metabolism mediated by the phase Ⅱ metabolizing enzyme UGT1A1 in the liver was evaluated to study the potential hepatotoxicity risk based on investigation on the inhibitory effect of rhein and its metabolites on the UGT1A1 enzyme in Rhei Radix et Rhizoma. Firstly, in vitro liver microsomes incubation was used to initiate the phase Ⅱ metabolic reaction to investigate the inhibitory effect of rheinon UGT1A1 enzyme. Secondly, the phase Ⅰ and phase Ⅱ metabolic reactions were initiated to investigate the hepatotoxicity risk of rhein metabolites. It was found that the rhein and its phase Ⅱ metabolites had no significant inhibitory effect on UGT1A1 enzyme, but its phase Ⅰ metabolites significantly reduced UGT1A1 enzyme activity. Based on the metabolites analysis, it is speculated that the rhein phase Ⅰ metabolite rheinhydroxylate and its tautomers have certain hepatotoxicity risks, while the toxicity risk induced by the prototype and phase Ⅱ metabolites of rheinglucoside, rheinglucuronic acid and rhein sulfate is small.

Study on hepatotoxicity of physcion based on liver metabolism in vitro / 中国中药杂志

To evaluate the hepatotoxicity risks of physcion on the basis of the bilirubin metabolism mediated by glucuronidation of UDP-glucuronosyltransferases 1A1(UGT1A1 enzyme). The monomers were added into the rat liver microsomes to test the hepatotoxicity by using bilirubin as UGT1A1 enzyme substrate, with apparent inhibition constant K_i as the evaluation index. Liver microsome incubation in vitro was adopted to initiate phase Ⅱ metabolic reaction and investigate the inhibitory effect of physcion. Then the phase Ⅰ and Ⅱ metabolic reactions were initiated to investigate the comprehensive inhibition of metabolites and prototype components. The results showed that when only the phase Ⅱ reaction was initiated, physcion directly acted on the UGT1A1 enzyme in a prototype form, exhibited weak inhibition and the inhibition type was mixed inhibition; When the phase Ⅰ and Ⅱ reactions were initiated simultaneously, the inhibitory effects of physcion on UGT1A1 enzyme became strong and the inhibition type was mixed inhibition, suggesting that physcion had phase Ⅰ and Ⅱ metabolic processes, and the metabolites had strong inhibitory effect on UGT1A1 enzyme. This experiment preliminarily proved that the metabolites of physcion may be the main components to induce hepatotoxicity.

Prediction of potential drug interactions of apigenin based on molecular docking and in vitro inhibition experiments / 中国中药杂志

The purpose of this study was to investigate the effect of apigenin on UGT1 A1 enzyme activity and to predict the potential drug-drug interaction of apigenin in clinical use. First,on the basis of previous experiments,the binding targets and binding strength of apigenin to UGT1 A1 enzyme were predicted by computer molecular docking method. Then the inhibitory effect of apigenin on UGT1 A1 enzyme was evaluated by in vitro human liver microsomal incubation system. Molecular docking results showed that apigenin was docked into the active region of UGT1 A1 enzyme protein F,consistent with the active region of bilirubin docking,with moderate affinity. Apigenin flavone mother nucleus mainly interacted with amino acid residues ILE343 and VAL345 to form hydrophobic binding Pi-Alkyl. At the same time,the hydroxyl group on the mother nucleus and the amino acid residue LYS346 formed an additional hydrogen bond,which increased the binding of the molecule to the protein. These results suggested that the flavonoid mother nucleus structure had a special structure binding to the enzyme protein UGT1 A1,and the introduction of hydroxyl groups into the mother nucleus can increase the binding ability. In vitro inhibition experiments showed that apigenin had a moderate inhibitory effect on UGT1 A1 enzyme in a way of competitive inhibition,which was consistent with the results of molecular docking. The results of two experiments showed that apigenin was the substrate of UGT1 A1 enzyme,which could inhibit the activity of UGT1 A1 enzyme competitively,and there was a risk of drug interaction between apigenin and UGT1 A1 enzyme substrate in clinical use.

Determination of Active Metabolite and Secondary Metabolite of Irinotecan in Rat Liver Microsomes Incu-bation System by LC-MS/MS / 中国药师

Objective:To establish an LC–MS/MS method for the determination of the active metabolite(SN-38) and secondary metabolite(SN-38G) of irinotecan in rat liver microsomes incubation system, and optimize the incubation conditions. Methods:Meth-anol was selected to precipitate protein in the samples, and then the concentrations were analyzed by LC–MS/MS. All the separation was carried out on a ZORBAX Eclipse XDB-C18 column(2. 1 mm × 50 mm, 3. 5 μm) with the mobile phase of acetonitrile – water (containing 0. 1% formic acid) (23 :77) at a flow rate of 0. 3 ml·min-1. The mass spectrometer was operated with multiple reac-tions monitoring ( MRM) using electrospray ionization ( ESI) . The incubation conditions were optimized by single factor design. Re-sults:SN-38 and SN-38G showed a good linearity ( r≥0. 9972) respectively within the range of 2. 3-920 ng·ml-1 and 2. 5-1000 ng ·ml-1. The intra-and inter-day RSD was below 14. 6%(n=6). The average recovery was within the range of 74. 1%-123. 4% with RSD below 13. 5% (n=6). The optimal incubation conditions were as follows:the concentration of liver microsomal protein was 0. 3 mg·ml-1 and the incubation time was 30 min. Conclusion:The method is rapid, sensitive and accurate in the quantification of SN-38 and SN-38G in the incubation system,which provides methodological basis for the activity determination of UGT1A1 enzyme in vitro.

The investigation of kenitics of UGT1A1 enzyme in different system on the basic of Bilirubin metabolites / 中国药学杂志

OBJECTIVE: To detect the kenitics of UGTIAI enzyme in three different systems. METHODS: A UPLC-MS/MS method was developed to measure the bilirubin. RESULTS: Glucuronidation kinetic constants were analyzed by fitting the Michaelis-Menten equation.As shown in our study, the apparent kinetic parameters of total bilirubin glucuronides were; KRLM>KHLM≈KrUGT1A1LM, VRLM≈VHLM>VrUGT1A1, CLHLM>CLrUGT1A1LM≈CLrRLM indicated that rUGT1A1 had the strongest binding affinity to bilirubin but could not convert it to bilirubin glucuronidations immediately.On the contrary RLM had a weaker binding affinity to the bilirubin, but could conver it rapidly. CONCLUSION: Compared the kinetic in the different systems we could find that HLM almost had the same Km as rUGT1A1 which demonstrated the UGTIAI enzyme was the primary enzyme mediating the metabolism of bilirubin.The difference parameter between three systems is attributed to the species differences.Summarily our study supplies experimental basis for the further