Protein deficiency potentiates lipid peroxidation in growing rats exposed to hyperoxia

Abstract

Growing male Wistar rats (70–80 g body weight) were fed ad libitum casein or soybean protein isolate (SPI) based diets containing 5 or 20% protein for 3 weeks. Half of animals were exposed to 95% oxygen, 12 hours/day during the last five days of the experimental diet period. Lipid peroxidation as measured by thiobarbituric acid reactive substances (TBARS) was increased in the plasma and liver, but not in the lung of animals exposed to hyperoxia. However, hyperoxia increased antioxidant enzyme activities as well as glutathione (GSH) concentration in the lung, suggesting that the increased defense mechanism against oxy-radicals accounted for lower TBARS concentrations in the lung. For plasma and liver, hyperoxia increased GSH concentrations but not superoxide dismutase (SOD) and glutathione peroxidase (GPx) activities. Besides hyperoxia, low protein diet, either casein or SPI, significantly affected TBARS formation of the lung and liver. Although SOD and GPx activities were higher in the liver and lung of low protein groups, TBARS were not decreased in these organs. Since GSH concentrations were decreased in the lung and liver of animals fed low protein diet, being more significant in the liver than lung, it was suggested that GSH played a crucial role in eliminating oxy-radicals produced during low protein diet. These results indicate that hyperoxia as well as protein deficiency potentiates the in vivo lipid peroxidation.