Department of Pharmacology and Toxicology, Queen's University, Kingston, ON, Canada K7L 3N6.
J Pharmacol Exp Ther. 2010 Sep 1;334(3):981-7. doi: 10.1124/jpet.110.168492. Epub 2010 May 25.
Heme oxygenases (HOs) catalyze the degradation of heme to biliverdin, carbon monoxide (CO), and free iron. The two major isoforms, HO-1 (inducible) and HO-2 (constitutive), are involved in a variety of physiological functions, including inflammation, apoptosis, neuromodulation, and vascular regulation. Major tools used in exploring these actions have been metalloporphyrin analogs of heme that inhibit the HOs. However, these tools are limited by their lack of selectivity; they affect other heme-dependent enzymes, such as cytochromes P450 (P450s), soluble guanylyl cyclase (sGC), and nitric-oxide synthase (NOS). Our laboratory has successfully synthesized a number of nonporphyrin azole-based HO inhibitors (QC-xx) that had little or no effect on sGC and NOS activity. However, their effects on various P450 isoforms have yet to be fully elucidated. To determine the effects of the QC-xx inhibitors on P450 enzyme activity, microsomal preparations of two rat P450 isoforms (2E1 and 3A1/3A2) and two human P450 supersome isoforms (3A4 and 2D6) were incubated with varying concentrations of HO inhibitor, and the activity was determined by spectrophotometric or fluorometric analysis. Results indicated that some QC compounds demonstrated little to no inhibition of the P450s, whereas others did inhibit these P450 isoforms. Four structural regions of QC-xx were analyzed, leading to the identification of structures that confer a decreased effect on both rat and human P450 isoforms studied while maintaining an inhibitory effect on the HOs.
血红素加氧酶（HOs）催化血红素降解为胆红素、一氧化碳（CO）和游离铁。两种主要同工酶，HO-1（诱导型）和 HO-2（组成型），参与多种生理功能，包括炎症、细胞凋亡、神经调节和血管调节。用于探索这些作用的主要工具是血红素的金属卟啉类似物，它可以抑制 HOs。然而，这些工具的局限性在于它们缺乏选择性；它们会影响其他依赖血红素的酶，如细胞色素 P450（P450s）、可溶性鸟苷酸环化酶（sGC）和一氧化氮合酶（NOS）。我们的实验室已经成功合成了一些非卟啉唑基 HO 抑制剂（QC-xx），它们对 sGC 和 NOS 活性几乎没有影响。然而，它们对各种 P450 同工酶的影响尚未完全阐明。为了确定 QC-xx 抑制剂对 P450 酶活性的影响，用两种大鼠 P450 同工酶（2E1 和 3A1/3A2）和两种人 P450 超合体同工酶（3A4 和 2D6）的微粒体制剂孵育不同浓度的 HO 抑制剂，并通过分光光度法或荧光分析法测定活性。结果表明，一些 QC 化合物对 P450 的抑制作用很小或没有，而其他化合物则抑制这些 P450 同工酶。分析了 QC-xx 的四个结构区域，确定了结构，这些结构在保持对 HOs 的抑制作用的同时，降低了对所研究的大鼠和人 P450 同工酶的影响。
