Lalovic Bojan, Phillips Brian, Risler Linda L, Howald William, Shen Danny D
Department of Pharmacy, University of Washington, Box 357630, Seattle, WA 98105, USA.
Drug Metab Dispos. 2004 Apr;32(4):447-54. doi: 10.1124/dmd.32.4.447.
Oxycodone undergoes N-demethylation to noroxycodone and O-demethylation to oxymorphone. The cytochrome P450 (P450) isoforms capable of mediating the oxidation of oxycodone to oxymorphone and noroxycodone were identified using a panel of recombinant human P450s. CYP3A4 and CYP3A5 displayed the highest activity for oxycodone N-demethylation; intrinsic clearance for CYP3A5 was slightly higher than that for CYP3A4. CYP2D6 had the highest activity for O-demethylation. Multienzyme, Michaelis-Menten kinetics were observed for both oxidative reactions in microsomes prepared from five human livers. Inhibition with ketoconazole showed that CYP3A is the high affinity enzyme for oxycodone N-demethylation; ketoconazole inhibited >90% of noroxycodone formation at low substrate concentrations. CYP3A-mediated noroxycodone formation exhibited a mean K(m) of 600 +/- 119 microM and a V(max) that ranged from 716 to 14523 pmol/mg/min. Contribution from the low affinity enzyme(s) did not exceed 8% of total intrinsic clearance for N-demethylation. Quinidine inhibition showed that CYP2D6 is the high affinity enzyme for O-demethylation with a mean K(m) of 130 +/- 33 microM and a V(max) that ranged from 89 to 356 pmol/mg/min. Activity of the low affinity enzyme(s) accounted for 10 to 26% of total intrinsic clearance for O-demethylation. On average, the total intrinsic clearance for noroxycodone formation was 8 times greater than that for oxymorphone formation across the five liver microsomal preparations (10.5 microl/min/mg versus 1.5 microl/min/mg). Experiments with human intestinal mucosal microsomes indicated lower N-demethylation activity (20-50%) compared with liver microsomes and negligible O-demethylation activity, which predict a minimal contribution of intestinal mucosa in the first-pass oxidative metabolism of oxycodone.
羟考酮会发生N - 去甲基化生成去甲羟考酮以及O - 去甲基化生成羟吗啡酮。使用一组重组人细胞色素P450（P450）亚型来鉴定能够介导羟考酮氧化为羟吗啡酮和去甲羟考酮的P450亚型。CYP3A4和CYP3A5对羟考酮N - 去甲基化表现出最高活性；CYP3A5的内在清除率略高于CYP3A4。CYP2D6对O - 去甲基化具有最高活性。在来自五个人肝脏制备的微粒体中，两种氧化反应均观察到多酶米氏动力学。酮康唑抑制实验表明，CYP3A是羟考酮N - 去甲基化的高亲和力酶；在低底物浓度下，酮康唑抑制>90%的去甲羟考酮生成。CYP3A介导的去甲羟考酮生成的平均米氏常数（K(m)）为600±119微摩尔，最大反应速度（V(max)）范围为716至14523皮摩尔/毫克/分钟。低亲和力酶对N - 去甲基化总内在清除率的贡献不超过8%。奎尼丁抑制实验表明，CYP2D6是O - 去甲基化的高亲和力酶，平均K(m)为130±33微摩尔，V(max)范围为89至356皮摩尔/毫克/分钟。低亲和力酶的活性占O - 去甲基化总内在清除率的10%至26%。在五种肝脏微粒体制剂中，去甲羟考酮生成的总内在清除率平均比羟吗啡酮生成的总内在清除率大8倍（10.5微升/分钟/毫克对1.5微升/分钟/毫克）。用人肠黏膜微粒体进行的实验表明，与肝脏微粒体相比，N - 去甲基化活性较低（20 - 50%），且O - 去甲基化活性可忽略不计，这预示着肠黏膜在羟考酮首过氧化代谢中的贡献最小。
