Prabhakar S S
Division of Nephrology, Department of Internal Medicine, Texas Tech University Health Sciences Center, Lubbock, Texas 79430, USA.
Am J Physiol Renal Physiol. 2001 Jul;281(1):F179-88. doi: 10.1152/ajprenal.2001.281.1.F179.
Alterations of intrarenal nitric oxide (NO) synthesis play an important role in the pathogenesis and progression of diabetic nephropathy. We tested the hypothesis that hyperglycemia modulates intrarenal NO synthesis, which might mediate the mesangial cell proliferation and matrix production. Murine mesangial cells were grown in media containing varying glucose concentrations, and cytokine-induced NO synthesis was assayed by chemiluminescence using an NO analyzer. High media glucose (25 mM) inhibited NO synthesis in a time-dependent fashion. This inhibition was posttranslational as revealed by analysis of inducible nitric oxide synthase (iNOS) gene and protein expression. L-Arginine supplementation partially reversed the inhibition whereas addition of tetrahydrobiopterin (BH4), a cofactor for NOS, restored the inducibility of NO synthesis. The in vitro [3H]citrulline assay for iNOS activity indicated that high glucose decreased BH4 availability whereas examination of the BH4 synthetic pathway suggested decreased BH4 stability rather than synthesis, a defect that was corrected by ascorbic acid. We conclude that hyperglycemia inhibits NO synthesis in mesangial cells by a posttranslational defect that might involve the stability and hence availability of BH4.
肾内一氧化氮（NO）合成的改变在糖尿病肾病的发病机制和进展中起重要作用。我们检验了高血糖调节肾内NO合成这一假说，该合成可能介导系膜细胞增殖和基质产生。将小鼠系膜细胞培养在含有不同葡萄糖浓度的培养基中，使用NO分析仪通过化学发光法检测细胞因子诱导的NO合成。高浓度培养基葡萄糖（25 mM）以时间依赖性方式抑制NO合成。如通过诱导型一氧化氮合酶（iNOS）基因和蛋白表达分析所揭示，这种抑制是翻译后水平的。补充L-精氨酸可部分逆转这种抑制，而添加一氧化氮合酶的辅因子四氢生物蝶呤（BH4）可恢复NO合成的诱导性。用于检测iNOS活性的体外[3H]瓜氨酸试验表明高糖降低了BH4的可用性，而对BH4合成途径的检测提示BH4稳定性降低而非合成减少，抗坏血酸可纠正这一缺陷。我们得出结论，高血糖通过一种可能涉及BH4稳定性及可用性的翻译后缺陷抑制系膜细胞中的NO合成。
