Plasma protein carbonyl concentration is not enhanced by chronic intake ofhigh-protein diets in adult rats

We tested the hypothesis of whether high dietary protein intake is linked t o oxidative stress as measured by the concentration of reactive carbonyl re sidues in plasma proteins. Three groups of male Wistar mts (similar to 230 g, n = 10) were fed either 15% (15C) 30% (30C), or 60% (60C) casein diets o ver a period of 18 weeks. For comparison, a vitamin E deficient diet (60C-E ) based on diet 60C was given to an additional group to provoke oxidative s tress. Concentrations of alpha-tocopherol in plasma and of reactive carbony l residues in total plasma proteins were measured by high performance liqui d chromatography using fluorescence and by diode array detection after 2,4- dinitrophenylhydrazine reaction, respectively. After 1 week the concentrati on of reactive carbonyl residues in plasma proteins was found to be signifi cantly (P < 0.05) higher in the 60C and 60C-E groups (similar to 2.7 nmol/m g protein) compared with the 15C and 30C groups (similar to 1.7 nmol/mg pro tein). After 14 weeks the 15C (3.4 +/- 1.2 nmol/mg protein) and 60C-E group s (3.9 +/- 1.7 nmol/mg protein) showed a significantly increased concentrat ion of reactive carbonyl residues in plasma protein compared with the 30C a nd 60C groups (2.5 +/- 1.0 nmol/mg protein; 2.6 +/- 0.8 nmol/mg protein). A s expected, chronic vitamin E deficiency (60C-E) resulted in significantly decreased alpha-tocopherol concentrations (3.91 +/- 2.42 mu mol/mL. vs. 31. 3 +/- 4.8 mu mol/mL) and a higher concentration of reactive carbonyl residu es in plasma proteins. These results do not support the hypothesis that a c hronic intake of high-protein diets leads to oxidative stress in adult rats . However, in the non-adapted state (1 week) a high protein intake contribu tes to oxidative modifications of protein-bound amino acid residues. (J. Nu tr, Biochem. 10:268-273, 1999) (C) Elsevier Science Inc 1999. All rights re served.