Daniel W A, Syrek M, Haduch A
Department of Pharmacokinetics and Drug Metabolism, Institute of Pharmacology, Polish Academy of Sciences, Kraków.
Pol J Pharmacol. 1999 Sep-Oct;51(5):435-42.
The aim of the present study was to determine optimum conditions for the study of thioridazine metabolism in rat liver microsomes and to investigate the influence of specific cytochrome P-450 inhibitors on 2- and 5-sulfoxidation, and N-demethylation of thioridazine. Basing on the developed method, the thioridazine metabolism in liver microsomes was studied at linear dependence of the product formation on time, and protein and substrate concentrations (incubation time was 15 min, concentration of microsomal protein was 0.5 mg/ml, substrate concentrations were 25, 50 and 75 nmol/ml). Dixon analysis of tioridazine metabolism carried out in the control liver microsomes, in the absence and presence of specific cytochrome P-450 inhibitors, showed that quinine (CYP2D1 inhibitor), metyrapone (CYP2B1/B2 inhibitor) and alpha-naphthoflavone (CYP1A2 inhibitor) affected while erythromycin (CYP3A inhibitor) and sulfaphenazole (CYP2C9 inhibitor) did not affect the neuroleptic biotransformation. Thus, quinine and metyrapone inhibited competitively thioridazine N-demethylation and mono-2-sulfoxidation. As reflected by Ki values, N-demethylation was inhibited to a higher degree (Ki = 16.5 and 43 microM, respectively) than mono-2-sulfoxidation (Ki = 25 and 137 microM, respectively). On the other hand, alpha-naphthoflavone inhibited competitively not only N-demethylation and mono-2-sulfoxidation, but also 5-sulfoxidation of thioridazine. The calculated Ki values showed that the highest potency of alpha-naphthoflavone to inhibit thioridazine metabolism was observed for N-demethylation and it descended in the following order: N-demethylation (Ki = 13.8 microM) > mono-2-sulfoxidation (Ki = 34 microM) > 5-sulfoxidation (Ki = 70.4 microM). In conclusion, it can be assumed that N-demethylation and mono-2-sulfoxidation are catalyzed by the isoenzymes 2D1, 2B and 1A2 while 5-sulfoxidation only by 1A2; isoenzymes belonging to the subfamilies 2C and 3A seem not to be involved in the metabolism of thioridazine. The obtained results are discussed in the view of species and structure differences in the enzymatic catalysis of phenothiazines' metabolism as well as in relation to their pharmacological and clinical significance.
本研究的目的是确定大鼠肝微粒体中硫利达嗪代谢研究的最佳条件，并研究特定细胞色素P - 450抑制剂对硫利达嗪2 - 和5 - 亚砜化以及N - 去甲基化的影响。基于所建立的方法，在产物形成与时间、蛋白质和底物浓度呈线性关系的条件下研究了肝微粒体中硫利达嗪的代谢（孵育时间为15分钟，微粒体蛋白浓度为0.5mg/ml，底物浓度为25、50和75nmol/ml）。在对照肝微粒体中，在不存在和存在特定细胞色素P - 450抑制剂的情况下对硫利达嗪代谢进行的狄克逊分析表明，奎宁（CYP2D1抑制剂）、美替拉酮（CYP2B1/B2抑制剂）和α - 萘黄酮（CYP1A2抑制剂）有影响，而红霉素（CYP3A抑制剂）和磺胺苯吡唑（CYP2C9抑制剂）对该抗精神病药物的生物转化没有影响。因此，奎宁和美替拉酮竞争性抑制硫利达嗪的N - 去甲基化和单 - 2 - 亚砜化。从Ki值可以看出，N - 去甲基化的抑制程度更高（Ki分别为16.
