Liver DT-diaphorase activity increases with age and dietary restriction in Lobund-Wistar rats

Abstract

Effects of a 30 percent (%) dietary restriction on liver DT-diaphorase activity toward various substrates were studied in male Lobund-Wistar (L-W) rats throughout the life span. DT-diaphorase catalyzes the reduction of quinones to hydroquinones, thus playing a major role in protecting cells against oxidative stress manifested by quinines. Eighty rats were divided into 2 groups and fed ad libitum or a 30% calorie-restricted diet. Eight rats in each group were killed at 6, 12, 18, 24 and 30 months of age. DT-diaphorase activity in liver cytosol was determined. The specific activity (per mg protein) of the enzyme in the ad libitum group toward 1,4-naphthoquinone (NQ) increased with age from 6 to 30 months, while those toward 2,6-dichlorophenol-indophenol (DCPIP), 2-methyl-1,4-naphthoquinone (MNQ) and ubiquinone0 (UQ0) increased with age from 18 to 30 months. The specific activity of the enzyme toward all four substrates in the restricted group did not change between 6 and 18 months, then increased with age from 18 to 30 months. When the enzyme activity was calculated on a per gram body weight basis or a per gram liver basis, the age-associated patterns of the ad libitum and restricted groups were similar to those on per mg protein basis. Dietary restriction increased the activity of DT-diaphorase on per mg protein basis, per gram body weight basis, or per gram liver basis, at almost all age points. The results suggest that dietary restriction contributes to the delaying of the aging process by decreasing oxidative stress exerted by quinones through increased DT-diaphorase activity.