Yadav Sanjay, Dhawan Alok, Seth Prahlad K, Singh Ram L, Parmar Devendra
Industrial Toxicology Research Centre, P.O. Box 80, M.G. Marg, Lucknow, 226001, India.
Mol Cell Biochem. 2006 Jul;287(1-2):91-9. doi: 10.1007/s11010-005-9080-8. Epub 2006 May 4.
Studies initiated to investigate the presence of cytochrome P4503A (CYP3A) isoenzymes in brain revealed constitutive mRNA and protein expression of CYP3A1 in rat brain. Western blotting studies showed that pretreatment with CYP3A inducer such as pregnenolone-16alpha -carbonitrile (PCN) significantly increased the cross reactivity comigrating with hepatic CYP3A1 and CYP3A2 in rat brain microsomes. RT-PCR studies have also shown increase in mRNA expression of CYP3A1 following pretreatment of rats with PCN. The ability of rat brain microsomes to catalyze the demethylation of erythromycin, known to be mediated by CYP3A isoenzymes in liver and significant increase in the activity of erythromycin demethylase (EMD) following pretreatment with dexamethasone or PCN have indicated that CYP3A isoenzymes expressed in brain are functionally active. Kinetic studies revealed that increase in the enzyme activity following pretreatment with PCN resulted in increase in the apparent affinity (Km) and Vmax of the reaction. Similarities in the inhibition of the constitutive and inducible brain and liver EMD activity following in vitro addition of ketoconazole, a inhibitor specific for CYP3A catalysed reactions and anti-CYP3A have further indicated that like in liver, CYP3A isoenzymes catalyse the activity of EMD in rat brain. Data also revealed regional differences in the activity of EMD in the brain. Relatively higher constitutive as well as inducible mRNA expression of CYP3A1 in hypothalamus and hippocampus, the brain regions responsive to steroid hormones have suggested that CYP3A isoenzymes may not only be involved in the process of detoxication mechanism but also in the metabolism of endogenous substrates in brain.
旨在研究细胞色素P4503A（CYP3A）同工酶在大脑中存在情况的研究表明，大鼠大脑中存在CYP3A1的组成型mRNA和蛋白质表达。蛋白质印迹研究显示，用CYP3A诱导剂如孕烯醇酮-16α-腈（PCN）预处理可显著增加大鼠脑微粒体中与肝脏CYP3A1和CYP3A2共迁移的交叉反应性。逆转录聚合酶链反应（RT-PCR）研究也表明，用PCN预处理大鼠后，CYP3A1的mRNA表达增加。大鼠脑微粒体催化红霉素去甲基化的能力（已知在肝脏中由CYP3A同工酶介导）以及用地塞米松或PCN预处理后红霉素脱甲基酶（EMD）活性的显著增加表明，大脑中表达的CYP3A同工酶具有功能活性。动力学研究表明，用PCN预处理后酶活性的增加导致反应的表观亲和力（Km）和最大反应速度（Vmax）增加。体外添加酮康唑（一种对CYP3A催化反应具有特异性的抑制剂和抗CYP3A）后，对组成型和诱导型脑和肝脏EMD活性的抑制作用相似，这进一步表明，与肝脏一样，CYP3A同工酶催化大鼠脑中EMD的活性。数据还显示了脑中EMD活性的区域差异。下丘脑和海马体中CYP3A1相对较高的组成型以及诱导型mRNA表达，这两个脑区对类固醇激素有反应，表明CYP3A同工酶可能不仅参与解毒机制，还参与大脑中内源性底物的代谢。
