Induction of Rat Hepatic Cytochrome P450 by Ketamine and Its Toxicological Implications

• Main Authors: Wei-Hung Chan, 詹偉弘
• Other Authors: Tzuu-Huei Ueng
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/43694578468463639352

博士 === 國立臺灣大學 === 毒理學研究所 === 94 === Cytochrome P450 (P450; CYP) plays a pivotal role in the biotransformation of a wide variety of xenobiotics. The activity of P450 is susceptible to induction or inhibition by numerous xenochemicals. Altered P450 activity is a common underlying mechanism of drug-drug interactions and can also affect the bioactivation of xenobiotic toxicity. Ketamine is an intravenous anesthetic that can produce potent analgesic effect and hypnosis simultaneously. In addition, ketamine can cause a trance-like state of mind in humans and consequently has become an abused substance. The development of acute ketamine tolerance is suggested to result from P450 induction by the drug. The aim of the thesis is to investigate the inductive effect of ketamine on rat hepatic P450 and explore its toxicological implications. Firstly, intraperitoneal (ip) administration of 40 mg/kg ketamine to male Wistar rats twice daily for four days was found to increase the levels of hepatic microsomal ethoxycoumarin O-deethylation (ECOD), ethoxyresorufin O-dealkylation (EROD), methoxyresorufin O-dealkylation (MROD) and pentoxyresorufin O-dealkylation (PROD). Further experiments revealed a strong dose-responsive relationship between the dose of ketamine and the increase in PROD activity. The levels of hepatic microsomal erythromycin N-demethylation (END), aniline hydroxylation, P450 content, cytochrome b5 and NADPH-P450 reductase were also increased in rats treated with ketamine 80 mg/kg ip twice daily for our days. The increased levels of PROD, ECOD, MROD and END returned to the pre-induction levels four days after the last dose of ketamine administration. On the other hand, the increase in the activities of EROD and aniline hydroxylation remained higher than the control values four days after the last dose of ketamine administration. Protein blot analysis of liver microsomal proteins revealed that 10, 20, 40, 80 mg/kg ketamine induced CYP2B1/2 by 5-, 6-, 10- and 2-fold, respectively. The amount of CYP1A1/2, 2E1 and 3A proteins was increased by 2-fold after treatment of 80 mg/kg ketamine. The polymerase chain reaction analysis showed a 1.7 fold increase in CYP2B mRNA level after ketamine treatment. In regard to ketamine-related drug interactions, the propofol sleeping time was significantly reduced in ketamine-pretreated rats. The reduction could be effectively reversed by a CYP2B inhibitor orphenadrine. The whole-blood propofol concentration after intravenous infusion declined faster in ketamine-pretreated rats. In ex vivo experiments, the ability of hepatic microsomes to metabolize propofol was enhanced in ketamine-pretreated rats. The enhancement in propofol metabolism could be reversed by the addition of orphenadrine. Regarding the bioactivation of toxicants, the liver damage induced by cocaine or carbon tetrachloride (CCl4) was enhanced after ketamine pretreatment. Orphenadrine could effectively reverse the enhancement of cocaine-induced hepatotoxicity by ketamine but not in the case of CCl4. Neither the detection of inflammatory cytokines nor depletion of Kupffer cells by gadolinium chloride could provide a mechanistic explanation for the potentiation of CCl4 toxicity by ketamine. In conclusion, ketamine can induce several P450 proteins; where CYP2B is the most responsive isoform. CYP2B induction is the major mechanism of reduced anesthetic effect of propofol and enhanced propofol metabolism after ketamine treatment in rats. CYP2B induction also plays a principal role in the potentiation of cocaine-induced hepatotoxicity by ketamine.