Galbusera Chiara, Orth Peter, Fedida David, Spector Thomas
Cardiome Pharma Corp., 6190 Agronomy Rd., Vancouver, BC, Canada V6T 1Z3.
Biochem Pharmacol. 2006 Jun 14;71(12):1747-52. doi: 10.1016/j.bcp.2006.02.008. Epub 2006 Feb 23.
Oxypurinol, an inhibitor of xanthine oxidase (XO), is being studied to block XO-catalyzed superoxide radical formation and thereby treat and protect failing heart tissue. Allopurinol, a prodrug that is converted to oxypurinol by xanthine oxidase, is also being studied for similar purposes. Because allopurinol, itself, may be generating superoxide radicals, we currently studied the reaction of allopurinol with xanthine oxidase and confirmed that allopurinol does produce superoxide radicals during its conversion to oxypurinol. At pH 6.8 and 25 degrees C in the presence of 0.02 U/ml of XO, 10 and 20 microM allopurinol both produced 10 microM oxypurinol and 2.8 microM superoxide radical (determined by cytochrome C reduction). The 10 microM allopurinol was completely converted to oxypurinol, while the 20 microM allopurinol required a second addition of xanthine oxidase to complete the conversion. Fourteen percent of the reducing equivalents donated from allopurinol or xanthine reacted with oxygen to form superoxide radicals. Superoxide dismutase prevented the reduction of cytochrome C by these substrates. At higher xanthine oxidase concentrations, or at lower temperatures, more of the 20 microM allopurinol was converted to oxypurinol during the initial reaction. At lower xanthine oxidase concentrations, or higher temperatures, less conversion occurred. At pH 7.8, the amount of superoxide radicals produced from allopurinol and xanthine was nearly doubled. These results indicate that allopurinol is a conventional substrate that generates superoxide radicals during its oxidation by xanthine oxidase. Oxypurinol did not produce superoxide radicals.
氧嘌呤醇是一种黄嘌呤氧化酶（XO）抑制剂，目前正在进行研究，以阻断XO催化的超氧自由基形成，从而治疗和保护衰竭的心脏组织。别嘌呤醇是一种通过黄嘌呤氧化酶转化为氧嘌呤醇的前体药物，也正在进行类似目的的研究。由于别嘌呤醇本身可能会产生超氧自由基，我们目前研究了别嘌呤醇与黄嘌呤氧化酶的反应，并证实别嘌呤醇在转化为氧嘌呤醇的过程中确实会产生超氧自由基。在pH 6.8、25℃、存在0.02 U/ml XO的条件下，10 μM和20 μM的别嘌呤醇均产生了10 μM的氧嘌呤醇和2.8 μM的超氧自由基（通过细胞色素C还原测定）。10 μM的别嘌呤醇完全转化为氧嘌呤醇，而20 μM的别嘌呤醇需要再次添加黄嘌呤氧化酶才能完成转化。别嘌呤醇或黄嘌呤提供的还原当量中有14%与氧气反应形成超氧自由基。超氧化物歧化酶可阻止这些底物对细胞色素C的还原。在较高的黄嘌呤氧化酶浓度下，或在较低的温度下，初始反应过程中20 μM别嘌呤醇更多地转化为氧嘌呤醇。在较低的黄嘌呤氧化酶浓度下，或较高的温度下，转化较少。在pH 7.8时，别嘌呤醇和黄嘌呤产生的超氧自由基数量几乎翻倍。这些结果表明，别嘌呤醇是一种在被黄嘌呤氧化酶氧化过程中产生超氧自由基的常规底物。氧嘌呤醇不会产生超氧自由基。
