The effect of tetrahydrobiopterin (BH4) on diabetic nephropathy

一氧化氮合酶（NOS）需要四氢生物蝶呤（BH4）作为辅酶。最近的研究表明，NOS活性以bh4依赖的方式调节。糖尿病患者血管中一氧化氮（NO）的合成和代谢受到损害。糖尿病大鼠体内BH4的浓度较低，可能与内皮功能障碍有关。如果糖尿病患者的肾脏有这种缺陷，可能会引起肾病。本研究的目的是阐明BH4在糖尿病中的抗肾病作用。我们以链脲佐菌素（STZ）诱导的糖尿病大鼠作为1型糖尿病模型进行研究。spague - dawley大鼠分为Control组、STZ组、STZ+BH4组。每日口服BH4 20mg/kg BW。STZ组9周出现蛋白尿，14周出现糖尿病肾病。而STZ+BH4组在实验中未发育。STZ组eNOS在肾脏的表达降低，STZ+BH4组eNOS的表达恢复。我们开始寻找BH4在肾脏中的水平是否低，如果是，是否与蛋白尿有关。我们选用大鼠Long-Evans Tokushima Fatty （OLETF）大鼠作为2型糖尿病模型，以Long-Evans Tokushima Otsuka （LETO）大鼠作为健康对照。在研究期间，将OLETF大鼠分为每天口服BH4 （10 mg/kg）和不口服BH4的两组。我们获得了62周龄大鼠的血浆、红细胞和肾脏，并测量了BH4、总生物terin和GTP环水解酶I的活性，GTP环水解酶I是新生BH4合成的关键酶。我们测量了13、37和61周龄大鼠的尿蛋白排泄量，作为肾病的标志物，并用免疫荧光法对它们的肾脏进行抗enos抗体染色。糖尿病大鼠血浆和肾脏BH4和生物蝶呤水平低于对照组。糖尿病大鼠红细胞和肾组织GTP环水解酶活性明显低于对照组。糖尿病大鼠的BH4/生物蝶呤比较小，表明从失活的BH2中回收BH4的二氢蝶呤还原酶在糖尿病中活性较低。13周时，糖尿病大鼠尿蛋白高于对照组；这种差异随着年龄的增长而增加。BH4在37周和61周时抑制糖尿病大鼠的蛋白尿，而不影响体重、血糖或血压。除非给予BH4，否则糖尿病肾脏的抗enos抗体荧光比对照肾脏少。在该糖尿病模型中，由于GTP环水解酶和二氢蝶啶还原酶活性较低，BH4的合成较少。BH4和eNOS-NO系统的缺陷可能导致糖尿病肾病的进展。这些结果表明BH4似乎具有抗肾病作用，并可能阻止糖尿病肾病的进展。少

Nitric oxide synthase (NOS) requires tetrahydrobiopterin (BH4) as a coenzyme. Recent works showed that NOS activity is regulated in a BH4-dependent manner. Nitric oxide (NO) synthesis and metabolism are impaired in blood vessels of diabetic subjects. The concentration of BH4 is low in diabetic rats, probably contributing to endothelial dysfunction. If diabetic kidneys had such deficiency, it might cause nephropathy. The object of this research was to clarify anti-nephropathic effects of BH4 in diabetes meritus.We studied in streptozotocin (STZ) induced diabetic rats as a model of type 1 diabetes. Spargue-Dawley rats were divided by three groups, Control, STZ, STZ+BH4. BH4 was administered orally at 20mg/kg BW daily. STZ group had albuminuria at 9-week, and developed diabetic nephropathy until 14-week. But STZ+BH4 group did not develop during experiment. The renal expression of eNOS was decreased in STZ group, and this decrease was restored in STZ+BH4 group.We set out to find if the BH4 … More level in kidneys is low and, if so, whether it is involved in proteinuria. We used Otsuka Long-Evans Tokushima Fatty (OLETF) rats, with a model of type 2 diabetes, and used Long-Evans Tokushima Otsuka (LETO) rats as healthy controls. OLETF rats were put into groups with or without daily oral doses of BH4 (10 mg/kg) during the study. We obtained plasma, red blood cells, and kidneys from 62-week-old rats and measured BH4, total biopterin, and GTP cyclohydrolase I activity, the key enzyme of de novo BH4 synthesis. We measured urinary protein excretion in the rats at 13, 37, or 61 weeks of age as a marker of nephropathy and stained their kidneys with anti-eNOS antibodies with an immunofluorescent method. Plasma and renal levels of BH4 and biopterin were lower in diabetic rats than in controls. GTP cyclohydrolase activity of red blood cells and renal tissue from diabetic rats was less than that of controls. The BH4/biopterin ratio was smaller in the diabetic rats, suggesting that dihydropteridine reductase, which recycles BH4 from inactive BH2, has low activity in diabetes. Urinary protein was greater in diabetic rats at 13 weeks than in controls ; the difference increased with age. BH4 suppressed proteinuria in diabetic rats at 37 and 61 weeks without affecting body weight, plasma glucose, or blood pressure. Diabetic kidneys had less fluorescence from anti-eNOS antibodies than control kidneys, unless BH4 was given. In this model of diabetes, little BH4 was synthesized, apparently because of GTP cyclohydrolase and dihydropteridine reductase activities were low. Deficiencies of BH4 and of the eNOS-NO system may contribute to the progression of diabetic nephropathy. These results suggest that BH4 seems to have anti-nephropathic effects and may preYent progress of diabetic nephropathy. Less