A small difference in the molecular structure of angiotensin II receptor blockers induces AT1 receptor-dependent and -independent beneficial effects

Angiotensin II (Ang II) type 1 (AT(1)) receptor blockers (ARBs) induce multiple pharmacological beneficial effects, but not all ARBs have the same effects and the molecular mechanisms underlying their actions are not certain. In this study, irbesartan and losartan were examined because of their different molecular structures (irbesartan has a cyclopentyl group whereas losartan has a chloride group). We analyzed the binding affinity and production of inositol phosphate (IP), monocyte chemoattractant protein-1 (MCP-1) and adiponectin. Compared with losartan, irbesartan showed a significantly higher binding affinity and slower dissociation rate from the AT(1) receptor and a significantly higher degree of inverse agonism and insurmountability toward IP production. These effects of irbesartan were not seen with the AT(1)-Y113A mutant receptor. On the basis of the molecular modeling of the ARBs-AT(1) receptor complex and a mutagenesis study, the phenyl group at Tyr(113) in the AT(1) receptor and the cyclopentyl group of irbesartan may form a hydrophobic interaction that is stronger than the losartan-AT(1) receptor interaction. Interestingly, irbesartan inhibited MCP-1 production more strongly than losartan. This effect was mediated by the inhibition of nuclear factor-kappa B activation that was independent of the AT(1) receptor in the human coronary endothelial cells. In addition, irbesartan, but not losartan, induced significant adiponectin production that was mediated by peroxisome proliferator-activated receptor-gamma activation in 3T3-L1 adipocytes, and this effect was not mediated by the AT(1) receptor. In conclusion, irbesartan induced greater beneficial effects than losartan due to small differences between their molecular structures, and these differential effects were both dependent on and independent of the AT(1) receptor. Hypertension Research (2010) 33, 1044-1052; doi:10.1038/hr.2010.135; published online 29 July 2010