Abstract-Telmisartan, in addition to blocking angiotensin (Ang) II type 1 receptor (AT 1 R), activates peroxisome proliferator activated receptor ␥ (PPAR␥) signaling that interferes with nitric oxide (NO) system. Because aging of endothelial cells (ECs) is hallmarked by a reduction in NO synthesis, we hypothesized that telmisartan increases NO formation by regulated asymmetrical dimethylarginine (ADMA)-dimethylarginine dimethylaminohydrolase (DDAH)-system through blocking AT 1 R and activating PPAR␥ signaling. To test this hypothesis, ECs were cultured with telmisartan, eprosartan, Ang II, and GW9662 (PPAR␥ antagonist) until the twelfth passage. During the process of aging, PPAR␥ protein expression decreased significantly, whereas the expression of AT 1 R increased. Telmisartan reversed these effects and dose-dependently decreased reactive oxygen species and 8-iso-prostaglandin (PG) F 2␣ formation. This effect was associated with an upregulated activity and protein expression of DDAH, accompanied by a decrease in ADMA concentration, an increase in NO metabolites, and delayed senescence. Blockade of PPAR␥ signaling by GW9662 or PPAR␥ small-interference RNA prevented the effect of telmisartan on ADMA-DDAH-NO system. Coincubation with Ang II did not affect the effect of telmisartan-delayed senescence, whereas Ang II itself accelerated endothelial aging. Moreover, AT 1 R blocker eprosartan that did not influence PPAR␥ protein expression had no effect on ADMA system and senescence. We have demonstrated that telmisartan mainly by activating PPAR␥ signaling can alter the catabolism and release of ADMA as an important cardiovascular risk factor. We therefore propose that telmisartan translationally and posttranslationally upregulated DDAH expression via activation of PPAR␥ signaling, causing ADMA to diminish and increase NO synthesis sufficient to delay senescence. Key Words: telmisartan Ⅲ angiotensin II type 1 receptor Ⅲ peroxisome proliferator activated receptor ␥ Ⅲ oxidative stress Ⅲ asymmetrical dimethylarginine Ⅲ nitric oxide Ⅲ aging A ging is a well-documented risk factor for cardiovascular diseases. One of the possible physiopathological mechanisms through which increasing age may lead to cardiovascular damage is the promotion of endothelial dysfunction. 1 Aged human endothelial cells (ECs), which produce less NO, more asymmetrical dimethylarginine (ADMA), a novel cardiovascular risk factor, and more reactive oxygen species (ROS), 2-5 could account for endothelial dysfunction and development of cardiovascular diseases. 6 -10 We and other have previously demonstrated that aging of human ECs can be altered by several different factors contributing to delay or accelerate the process of aging. [2][3][4][5]11,12 These results suggest that the process of endothelial aging may be an influenceable process and raise the possibility of therapies for preventing various cardiovascular diseases in the elderly.Telmisartan, a highly lipophilic angiotensin (Ang) II type 1 receptor (AT 1 R) blocker (ARB), is used for the treatme...