Takahashi K, Matsumoto T, Ogata N, Mizunoe Y, Tanaka M, Kumazawa J
Department of Urology, Faculty of Medicine, Kyushu University, Fukuoka, Japan.
J Urol. 1993 Feb;149(2):386-9. doi: 10.1016/s0022-5347(17)36100-1.
Hyperosmolarity in the renal medulla inhibits host defenses against bacterial pyelonephritis. Urea and NaCl contribute most to high osmolarity in the renal medulla. We therefore examined the inhibitory mechanism of urea on superoxide generation by human polymorphonuclear leukocytes. Superoxide production was inhibited by high concentration of urea. This inhibition was found to be direct and immediate. In addition, direct inactivation of NADPH oxidase, the key enzyme complex of superoxide generation, was shown by an NADPH oxidase activity assay using cell lysates of polymorphonuclear leukocytes stimulated by phorbol myristate acetate. The inhibitory effect of urea on NADPH oxidase was reversed by washing urea out of the assay system of cell lysates. Kinetic analysis of the inhibition of NADPH oxidase activity by urea showed decreased Vmax and Km, suggesting uncompetitive inhibition. These findings suggested that urea inactivated polymorphonuclear leukocyte superoxide production through a direct and uncompetitive inhibition of NADPH oxidase.
肾髓质的高渗状态会抑制机体对细菌性肾盂肾炎的防御。尿素和氯化钠对肾髓质的高渗状态起主要作用。因此，我们研究了尿素对人多形核白细胞产生超氧化物的抑制机制。高浓度尿素可抑制超氧化物的产生。这种抑制作用是直接且即时的。此外，通过使用佛波酯刺激的多形核白细胞裂解物进行NADPH氧化酶活性测定，发现超氧化物产生的关键酶复合物NADPH氧化酶被直接灭活。通过从细胞裂解物测定系统中洗去尿素，可逆转尿素对NADPH氧化酶的抑制作用。尿素对NADPH氧化酶抑制作用的动力学分析显示Vmax和Km降低，提示为非竞争性抑制。这些发现表明，尿素通过直接和非竞争性抑制NADPH氧化酶来使多形核白细胞超氧化物产生失活。
