Ong C E, Coulter S, Birkett D J, Bhasker C R, Miners J O
Department of Clinical Pharmacology, Flinders Medical Centre and Flinders University, Adelaide, Australia.
Br J Clin Pharmacol. 2000 Dec;50(6):573-80. doi: 10.1046/j.1365-2125.2000.00316.x.
To investigate inhibition of recombinant CYP2C8 by: (i) prototypic CYP isoform selective inhibitors (ii) imidazole/triazole antifungal agents (known inhibitors of CYP), and (iii) certain CYP3A substrates (given the apparent overlapping substrate specificity of CYP2C8 and CYP3A).
CYP2C8 and NADPH-cytochrome P450 oxidoreductase were coexpressed in Spodoptera frugiperda (Sf21) cells using the baculovirus expression system. CYP isoform selective inhibitors, imidazole/triazole antifungal agents and CYP3A substrates were screened for their inhibitory effects on CYP2C8-catalysed torsemide tolylmethylhydroxylation and, where appropriate, the kinetics of inhibition were characterized. The conversion of torsemide to its tolylmethylhydroxy metabolite was measured using an h.p.l.c. procedure.
At concentrations of the CYP inhibitor 'probes' employed for isoform selectivity, only diethyldithiocarbamate and ketoconazole inhibited CYP2C8 by > 10%. Ketoconazole, at an added concentration of 10 microM, inhibited CYP2C8 by 89%. Another imidazole, clotrimazole, also potently inhibited CYP2C8. Ketoconazole and clotrimazole were both noncompetitive inhibitors of CYP2C8 with apparent Ki values of 2.5 microM. The CYP3A substrates amitriptyline, quinine, terfenadine and triazolam caused near complete inhibition (82-91% of control activity) of CYP2C8 at concentrations five-fold higher than the known CYP3A Km. Kinetic studies with selected CYP3A substrates demonstrated that most inhibited CYP2C8 noncompetitively. Apparent Ki values for midazolam, quinine, terfenadine and triazolam ranged from 5 to 25 microM.
Inhibition of CYP2C8 occurred at concentrations of ketoconazole and diethyldithiocarbamate normally employed for selective inhibition of CYP3A and CYP2E1, respectively. Some CYP3A substrates have the capacity to inhibit CYP2C8 activity and this may have implications for inhibitory drug interactions in vivo.
研究重组CYP2C8的抑制情况，涉及：（i）原型CYP同工酶选择性抑制剂；（ii）咪唑/三唑类抗真菌药物（已知的CYP抑制剂）；以及（iii）某些CYP3A底物（鉴于CYP2C8和CYP3A明显重叠的底物特异性）。
使用杆状病毒表达系统在草地贪夜蛾（Sf21）细胞中共表达CYP2C8和NADPH - 细胞色素P450氧化还原酶。筛选CYP同工酶选择性抑制剂、咪唑/三唑类抗真菌药物和CYP3A底物对CYP2C8催化的托拉塞米甲苯甲基羟基化的抑制作用，并在适当情况下表征抑制动力学。使用高效液相色谱法测量托拉塞米向其甲苯甲基羟基代谢物的转化。
在所使用的用于同工酶选择性的CYP抑制剂“探针”浓度下，仅二乙基二硫代氨基甲酸盐和酮康唑对CYP2C8的抑制率>10%。添加浓度为10μM的酮康唑对CYP2C8的抑制率为89%。另一种咪唑类药物克霉唑也强烈抑制CYP2C8。酮康唑和克霉唑均为CYP2C8的非竞争性抑制剂，表观Ki值为2.5μM。CYP3A底物阿米替林、奎宁、特非那定和三唑仑在浓度比已知CYP3A Km高五倍时，对CYP2C8产生近乎完全的抑制（对照活性的82 - 91%）。对选定的CYP3A底物进行的动力学研究表明，大多数对CYP2C8的抑制为非竞争性。咪达唑仑、奎宁、特非那定和三唑仑的表观Ki值范围为5至25μM。
在通常分别用于选择性抑制CYP3A和CYP2E1的酮康唑和二乙基二硫代氨基甲酸盐浓度下，会发生对CYP2C8的抑制。一些CYP3A底物具有抑制CYP2C8活性的能力，这可能对体内抑制性药物相互作用有影响。
