Taniguchi M, Yasutake A, Takedomi K
Division of Food and Nutrition, Nakamura Gakuen University, Fukuoka, Japan.
Br J Nutr. 2000 Aug;84(2):211-7.
Effects of dietary protein and S-containing amino acids on oxidative damage were investigated in rat liver. After feeding rats for 3 weeks from weaning, lower GSH levels and higher metallothionein (MT) levels were found in the liver of rats fed on a 10% soyabean-protein-isolate (SPI)-based diet than those fed on a 10% casein-based diet. After injection of N-nitrosodimethylamine (NDMA) at 20 mg/kg body weight, increases in lipid peroxide, determined as thiobarbituric-acid reactive substances (TBARS), and gamma-glutamyltransferase (GGT) activity in the liver were observed in the 10% SPI diet group. By supplementing the 10% SPI diet with 0.3% cystine or methionine, GSH levels were increased, while MT levels were decreased, and elevation in TBARS levels after NDMA injection was diminished. On the other hand, increase in GGT activity could be prevented only by methionine supplement. On a 20% SPI or casein diet, TBARS concentration and GGT activity were not altered after NDMA injection with concomitant increase in GSH levels and decrease in MT levels. These results indicate that sufficient amounts of methionine and cystine in a diet are important to protect the liver from oxidative damage after NDMA administration, and GSH plays a primary role in the cellular protective function when compared with MT.
在大鼠肝脏中研究了膳食蛋白质和含硫氨基酸对氧化损伤的影响。从断奶开始喂养大鼠3周后，发现以10%大豆分离蛋白（SPI）为基础的饮食喂养的大鼠肝脏中谷胱甘肽（GSH）水平较低，金属硫蛋白（MT）水平较高，而以10%酪蛋白为基础的饮食喂养的大鼠则相反。以20mg/kg体重注射N-亚硝基二甲胺（NDMA）后，10%SPI饮食组大鼠肝脏中脂质过氧化物（以硫代巴比妥酸反应性物质（TBARS）测定）增加，γ-谷氨酰转移酶（GGT）活性升高。在10%SPI饮食中补充0.3%的胱氨酸或蛋氨酸后，GSH水平升高，而MT水平降低，NDMA注射后TBARS水平的升高减弱。另一方面，只有补充蛋氨酸才能防止GGT活性增加。在20%SPI或酪蛋白饮食中，注射NDMA后TBARS浓度和GGT活性没有改变，同时GSH水平升高，MT水平降低。这些结果表明，饮食中足够量的蛋氨酸和胱氨酸对于保护肝脏免受NDMA给药后的氧化损伤很重要，并且与MT相比，GSH在细胞保护功能中起主要作用。
