Regulation of peroxisome proliferator-activated receptor γ activity by losartan metabolites

Two active metabolites of the angiotensin type 1 (AT(1)) receptor blocker losartan have been described previously, EXP3174 and EXP3179. Whereas EXP3174 is the main antihypertensive AT(1) receptor-blocking metabolite, the role of EXP3179 is widely unknown. Recently, a subgroup of AT(1) receptor blockers has been identified as ligands for the peroxisome proliferator-activated receptor gamma (PPAR-gamma). Here we characterize the PPAR-gamma-activating properties of the 2 active losartan metabolites. PPAR-gamma activity was measured with a chimeric Gal4-DNA-binding domain-hPPAR gamma-ligand-binding domain (LBD) fusion protein on a Gal4-dependent luciferase reporter system. EXP3179 prominently induced the activation of the PPAR-gamma-LBD reaching a maximum at 100 mu mol/L with a 7.1 +/- 1-fold induction (P < 0.05 versus vehicle-treated cells). Maximum PPAR-gamma-LBD activation by EXP3179 reached 51% of the maximum response induced by the full PPAR-gamma agonist pioglitazone, identifying EXP3179 as a partial PPAR-gamma agonist. EXP3174 did not induce PPAR-gamma-LBD activation. EC50 values were calculated for PPAR-gamma-LBD activity (pioglitazone EC50: 0.88 mu mol/L; EXP3179 EC50: 17.1 mu mol/L; losartan EC50: > 50 mu mol/L). Consistent with the activation of PPAR-gamma, EXP3179 potently induced 3T3-L1 adipocyte differentiation, a typical PPAR-gamma-dependent cell function, and markedly stimulated PPAR-gamma target gene expression. EXP3174 failed to regulate differentiation or PPAR-gamma target gene expression. The present study characterizes the active losartan metabolite EXP3179 as a partial PPAR-gamma agonist. PPAR-gamma activation by EXP3179 may help us to understand the beneficial metabolic effects of losartan observed in clinical trials.