ABSTRACT
The metabolic characteristics of ligustrazin (TMPz) in liver microsomes were investigated in the present study. The reaction phenotyping of TMPz metabolism was also identified by in vitro assessment using recombinant human cytochrome P450 enzymes (CYP) and UDP glucuronosyltransferases (UGT). TMPz was incubated at 37 degrees C with human (HLM) and rat liver microsomes (RLM) in the presence of different co-factors. The metabolic stability and enzyme kinetics of TMPz were studied by determining its remaining concentrations with a LC-MS/MS method. TMPz was only metabolically eliminated in the microsomes with NADPH or NADPH+UDPGA. In the HLM and RLM with NADPH+UDPGA, t1/2, K(m) and V(max) of TMPz were 94.24 +/- 4.53 and 105.07 +/- 9.44 min, 22.74 +/- 1.89 and 33.09 +/- 2.74 micromol x L(-1), 253.50 +/- 10.06 and 190.40 +/- 8.35 nmol x min(-1) x mg(-1) (protein), respectively. TMPz showed a slightly higher metabolic rate in HLM than that in RLM. Its primary oxidative metabolites, 2-hydroxymethyl-3, 5, 6-trimethylpyrazine (HTMP), could undergo glucuronide conjugation. The CYP reaction phenotyping of TMPz metabolism was identified using a panel of recombinant CYP isoforms (rCYP) and specific CYP inhibitors in HLM. CYP1A2, 2C9 and 3A4 were found to be the major CYP isoforms involved in TMPz metabolism. Their individual contributions were assessed b) using the method of the total normalized rate to be 19.32%, 27.79% and 52.90%, respectively. It was observed that these CYP isoforms mediated the formation of HTMP in rCYP incubation. The UGT reaction phenotyping of HTMP glucuronidation was also investigated preliminarily by using a panel of 6 UGT isoforms (rUGT). UGT1A1, 1A4 and 1A6 were the predominant isoforms mediated the HTMP glucuronidation. The results above indicate that the metabolism of TMPz involves multiple enzymes mediated phase I and phase II reactions.
ABSTRACT
The paper is to report the study of the effect of Shenfu injection on the enzyme activity of liver CYP450 and its mRNA level of rat liver. Microsome of rat liver was prepared after intravenous administration of Shenfu injection for 7 days. The enzyme activity was quantified by Cocktail method. Meanwhile, the mRNA expression of CYP1A2, CYP2B1/2, CYP2C11 and CYP3A1 in the liver was detected by RT-PCR. Shenfu injection obviously induced the enzyme activities of CYP2B and CYP2C. Meantime Shenfu injection decreased the enzyme activities of CYP1A2 and CYP3A. The mRNA levels of CYP2B and CYP2C were also induced in rats treated with Shenfu injection. But it obviously inhibited the mRNA level of CYP1A2 and CYP3A. Since the enzyme activity and mRNA level were obviously changed after administration, the potential effect of drug-drug interaction should be concerned.
ABSTRACT
<p><b>OBJECTIVE</b>To explore the interaction between herbal medicines and western drugs based on CYP3A4 enzyme metabolism by using testotesrone as a probe in liver microsome metabolism system in vitro.</p><p><b>METHOD</b>The mixed liver microsome enzymatic system consisting of rat liver microsomes by ultra-high-speed centrifuge was established. The substrate testosterone was added into the system and enzyme CYP3A4 metabolic activity was expressed by the output of 6beta-hydroxy-testosterone which was measured by HPLC method. The proper conditions for testotesrone metabolism in liver microsome system included substrate concentration, incubation time, pH and incubation temperature. When the conditions in vitro were determined, three kinds of Chinese herbal medicinal ingredients (Tetrahydropalmatine, neferine, panax notoginseng saponins) were diluted into different concentrations and incubated with testotesrone in the liver microsomes incubation system, respectively. The results were measured through metabolite production with or without the presence of Chinese medicines. We assessed the Chinese herbal medicinal ingredients effect on the metabolism of CYP3A4 enzyme through 6beta-hydroxy metabolite of testosterone production.</p><p><b>RESULT</b>Liver microsomes were incubated in the system, the testosterone metabolited into 6beta-hydroxy testosterone. The metabolism conditions were proper at the concentration of testosterone 200 micromol x L(-1) which was incubated for 3.5 hours at 37 degrees C in pH 7.0, PBS 0.1 mol x L(-1). The inhibition of tetrahydropalmatine and panax notoginseng saponins on testotesrone were weak with IC50 > 100 micromol x L(-1). The neferine had a little inhibition on testotesrone metabolism, IC50 < 100 micromol L(-1).</p><p><b>CONCLUSION</b>Tetrahydropalmatine and panax notoginseng saponins had no obvious effect on testotesrone metabolism. Neferine had a little effect on testotesrone metabolism. It prompted that drug-interaction could not be apparent between two kinds of Chinese medicines and the CYP3A4 enzyme substrate, Neferine could bring about drug-interaction.</p>