Effect of increasing age on tissue dolichol levels in ad libitum fed and food-restricted rats
Dolichols are long hydrophobic molecules broadly distributed in all tissues and cellular membranes of eukariotic cells. Dolichol affects membrane structure and fluidity, membrane-associated protein activities, and membrane sensitivity to oxidative stress. Reports have shown that dolichols exhibit a remarkable (6- to 30-fold) age-related increase in the tissues of adult and mature rats and of old flies, mice, and humans. In our longitudinal study, the age-related accumulation of dolichol was monitored in the liver tissue of male Sprague Dawley rats fed ad libitum up to age of 27 months. In addition 24-month-old rats subjected to different regimens of anti-aging diet restriction (40% calorie restriction or every-other-day feeding ad libitum) were tested. A parallel study of the accumulation of carbonyl in liver protein (a proposed biomarker of aging) was made. In addition, the age-related decline of liver autophagy/proteolysis was studied in isolated liver cells, in view of the essential role of this function in liver membrane maintenance. Results show that an age-dependent accumulation of dolichol can be observed in the liver of the rats fed ad libitum but not in the liver of 24-month-old food-restricted rats, that accumulation of dolichol precedes the accumulation of altered liver proteins, and that dolichol accumulation is accompanied by a decline in liver autophagy. It is concluded that dolichol accumulation satisfies the proposed primary and secondary applicable criteria and the desirable features required to be qualified as a biomarker of aging.