低蛋白配伍α-酮酸饮食对慢性肾衰竭大鼠体内氧化应激水平的影响

Effects of low protein diet supplement with α-keto acid on oxidative stress in rats with chronic renal failure

目的研究低蛋白配伍α-酮酸饮食对慢性肾衰竭大鼠体内氧化应激水平的影响。方法 40只雄性SD大鼠随机分为对照组(行剥离肾包膜假手术,n=10)和模型组(行两步法肾大部切除术,n=30)。模型组1周后根据不同喂养方式分为以下亚组:正常蛋白组(NPD组,n=10,以含18%酪蛋白的饲料喂养)、低蛋白组(LPD组,n=10,以含6%酪蛋白的饲料喂养)、低蛋白+α-酮酸组(LK组,n=10,以含5%酪蛋白+1%α-酮酸的饲料喂养)。对照组以含18%酪蛋白的饲料喂养。观察各组大鼠体质量及血、尿生化指标的改变,生化指标包括血肌酐(Scr)、尿素氮(BUN)、白蛋白(Alb)、总蛋白(TP)和24 h尿蛋白排泄量。分光光度法测定血清和肾皮质匀浆中丙二醛(MDA)、超氧化物歧化酶(SOD)和谷胱甘肽过氧化物酶(GSH-Px)水平。放射免疫法测定肾皮质匀浆中肾素和血管紧张素Ⅱ(AngⅡ)活性;ELISA法测定血浆中AngⅡ的活性。结果饲养12周后,各模型组大鼠的体质量、Alb和TP水平与对照组比较,差异均无统计学意义(均P>0.05)。饲养4、8、12周时,各模型组大鼠的24 h尿蛋白排泄量均显著高于对照组(均P<0.05);其中LPD组和LK组均显著低于NPD组(均P<0.05),LK组较LPD组进一步降低(P<0.05)。LK组大鼠肾皮质匀浆中肾素活性和AngⅡ活性均较NPD组显著降低(均P<0.05)。与对照组比较,各模型组大鼠血清和肾皮质匀浆中MDA水平均显著升高(均P<0.05),SOD和GSH-Px水平均显著降低(均P<0.05);其中LPD组和LK组MDA水平较NPD组显著降低(均P<0.05),SOD和GSH-Px水平显著升高(均P<0.05)。相关性分析结果显示:肾皮质匀浆中MDA水平与AngⅡ的活性呈正相关(r=0.892,P<0.001),而SOD和GSH-Px水平均与AngⅡ的活性呈负相关(r值分别为-0.978和-0.965,均P<0.001)。结论低蛋白配伍α-酮酸饮食在维持营养状态稳定的前提下具有肾脏保护作用,可改善慢性肾衰竭大鼠体内增强的氧化应激及减少蛋白尿排泄;该作用可能与营养治疗本身有关,也可能与抑制肾脏局部肾素—血管紧张素系统的活性有关。

Objective To investigate the effects of low protein diet supplement with a- keto acid on oxidative stress in rats with chronic renal failure. Methods Forty male SD rats were randomly divided into control group （ nephrocapsectomy, n = 10） and model group （two-step subtotal nephrectomy, n = 30）. Rats in model group were subdivided into normal protein diet group （NPD group, n = 10, 18% casein protein）, low protein diet group （LPD group, n = 10, 6% casein protein） and c^-keto acid supplemented low protein group （LK group, n = 10, 5% casein protein ＋ 1% ct-keto acid） according to different ways of feeding one week later. Rats in control group were fed with 18% casein protein. The blood and urine parameters including serum creatinine （Scr）, blood urea nitrogen （ BUN）, albumin （Alb）, total protein （TP） and 24 h urinary protein excretion were detected 12 weeks later. Spectrophotography was used to measure levels of malonaldehyde （MDA）, superoxide dismutase （SOD） and glutathione peroxidase （GSH-Px） in serum and homogenate. The activity of renin and angiotensin 1I （Ang 1I ） in homogenate was determined by radioimmunoassay, and the activity of Ang 1I in plasma was detected by ELISA. Results There was no significant difference in the body weight, Alb and TP between each model subgroup and control group after 12 weeks of feeding （P 〉 0.05）. After 4. 8 and 12 weeks of feeding. 24 h Droteinuriaexcretion in each model subgroup were significantly higher than those in control group （P 〈 0.05）, 24 h proteinuria excretion in LPD group and LK group were significantly lower than those in NPD group （P 〈 0.05）, and 24 h proteinuria excretion in LK group were significantly lower than those in LPD group （P 〈 0.05）. The activity of renin and Ang I1 in homogenate in LK group was significantly lower than that in NPD group （P 〈 0.05）. Compared with control group, the levels of MDA both in serum and homogenate in model subgroups were significantly higher （P 〈 0.05）, the levels of SOD and GSH-Px both in serum and homogenate in model subgroups were significantly lower （P 〈 0.05）, the levels of MDA in LPD group and LK group were significantly lower than that in NPD group（P 〈0.05）, and the levels of SOD and GSH-Px in LPD group and LK group were significantly higher than those in NPD group （P 〈 0.05）. Correlation analysis revealed that the level of MDA in kidney homogenate was positively related to the activity of Ang l] （r = 0. 892, P 〈 0. 001）, and the levels of SOD and GSH-Px in kidney homogenate were negatively related to the activity of Ang 1I （ r = - 0. 978, P 〈 0. 001 ; r = - 0. 965, P 〈 0. 001）. Conclusion Renoprotective effects of reduced oxidative stress and proteinuria are exhibited by low protein diet supplement with a-keto acid therapy in rats with chronic renal failure without malnutrition. The favorable effects may be directly related to the nutrition therapy itself, or may be indirectly related to the suppression of intrarenal renin-angiotensin system activity.