CALORIC RESTRICTION ATTENUATES DITYROSINE CROSS-LINKING OF CARDIAC AND SKELETAL-MUSCLE PROTEINS IN AGING MICE

Oxidative damage, particularly to proteins, has been widely postulated to be a major causative factor in the loss of functional capacity dur ing senescence. The nature of the various mechanisms that may contribu te to protein oxidation is only partially understood. In this study, c oncentrations of two markers for oxidative damage, o,o'-dityrosine and o-tyrosine, were determined using stable isotope dilution gas chromat ography-mass spectrometry in four tissues of the mouse, namely heart, skeletal muscle, brain, and liver, during youth (4 months old), adulth ood (14 months old), and old (30 months old) age. A comparison was mad e between mice that had access to unlimited calories with those that w ere restricted to 60% of the caloric intake of the ad libitum regimen. Caloric restriction of this magnitude extends the average and maximum life span of mice by similar to 40%. In vitro studies demonstrated th at o,o'-dityrosine was generated selectively in proteins exposed to ty rosyl radical, o-Tyrosine increased in proteins oxidized with hydroxyl radical, which also resulted in a variable increase in o,o'-dityrosin e. In mice fed ad libitum, levels of o,o'-dityrosine increased with ag e in cardiac and skeletal muscle but not in liver or brain, In contras t, o-tyrosine levels did not rise with age in any of the tissues exami ned. These results suggest that tyrosyl radical-induced protein oxidat ion increases selectively with age in skeletal muscle and heart, Calor ic restriction prevented the increase in o,o'-dityrosine levels in car diac and skeletal muscle but did not influence o-tyrosine levels in an y of the four tissues. This selective increase in o,o'-dityrosine leve ls and its prevention by a life-prolonging caloric restriction regimen raise the possibility that oxidation of muscle proteins by tyrosyl ra dical contributes to the deterioration of cardiac and skeletal muscle function with advancing age. (C) 1997 Academic Press.