Age-related changes in monocyte and platelet cyclooxygenase expression in healthy male humans and rats.

Cyclooxygenase (COX) catalyses the formation of prostanoids that are crucial in maintaining hemostasis and important in inflammation. Animal studies reveal that COX-1 and COX-2 expression increase in some cell types during aging. This study determined age-related changes in COX expression in platelets and monocytes. Platelets and mononuclear cells were isolated from healthy male human volunteers from 18 to 28 and from 55 to 65 years of age, as well as male rats 8 and 54 weeks old for comparison. Western blot analysis was performed using selective antibodies against COX-1 and COX-2, followed by densitometrical analysis. In humans, an age-related increase in COX-2 expression in mononuclear cells was observed, with a 70% increase in the older age group. In rat studies, a 50% increase of COX-2 protein occurred in mononuclear cells of 54-week-old rats, compared with 8-week-old rats. For COX-1, an age-related increase of 50% occurred in rat platelets, but no difference occurred in the platelets' COX-1 levels between young and elderly human age groups. The increased COX-2 in monocytes of older humans, which is mirrored in rats, may have downstream implications in atherosclerosis and cardiovascular risk as mononuclear prostanoids are implicated in atherosclerotic plaque stability.