Multivalent ligand–receptor interactions elicit inverse agonist activity of AT1 receptor blockers against stretch-induced AT1 receptor activation

Abstract

Type 1 angiotensin II (AT 1 ) receptor has a critical role in the development of load-induced cardiac hypertrophy. Recently, we showed that mechanical stretching of cells activates the AT 1 receptor without the involvement of angiotensin II (AngII) and that this AngII-independent activation is inhibited by the inverse agonistic activity of the AT 1 receptor blocker (ARB), candesartan. Although the inverse agonist activity of ARBs has been studied in terms of their action on constitutively active AT 1 receptors, the structure-function relationship of the inverse agonism they exert against stretch-induced AT 1 receptor activation has not been fully elucidated. Assays evaluating c-fos gene expression and phosphorylated extracellular signal-regulated protein kinases (ERKs) have shown that olmesartan has strong inverse agonist activities against the constitutively active AT 1 receptor and the stretch-induced activation of AT 1 receptor, respectively. Ternary drug-receptor interactions, which occur between the hydroxyl group of olmesartan and Tyr 113 and between the carboxyl group of olmesartan and Lys 199 and His 256 , were essential for the potent inverse agonist action olmesartan exerts against stretch-induced ERK activation and the constitutive activity of the AT 1 -N111G mutant receptor. Furthermore, the inverse agonist activity olmesartan exerts against stretch-induced ERK activation requires an additional drug-receptor interaction involving the tetrazole group of olmesartan and Gln 257 of the AT 1 receptor. These results suggest that multivalent interactions between an inverse agonist and the AT 1 receptor are required to stabilize the receptor in an inactive conformation in response to the distinct processes that lead to an AngII-independent activation of the Keywords: angiotensin II; cardiac hypertrophy; G protein-coupled receptor; inverse agonist; mechanical stress INTRODUCTIONThe type 1 angiotensin II (AT 1 ) receptor is a member of the G proteincoupled receptor (GPCR) family and mediates most of the actions that angiotensin II (AngII) exerts on the cardiovascular system. 1 AT 1 receptor blockers (ARBs) are non-peptide compounds that selectively bind to the AT 1 receptor and inhibit AngII-induced receptor activation. At present, several ARBs are clinically available as a highly effective and well-tolerated class of drugs for the management of hypertension. In addition, clinical trials have indicated that ARBs provide cardiovascular protection that extends beyond blood pressure lowering. 2 Treatment with ARBs effectively prevents cardiac hypertrophy and improves cardiovascular outcomes in patients with hypertension. 2,3 Structurally, most ARBs have a common biphenyl-tetrazole ring and unique side chains, which contribute to drug-specific differences in their pharmacokinetic and pharmacodynamic proper-

In Vitro Antagonistic Properties of a New Angiotensin Type 1 Receptor Blocker, Azilsartan, in Receptor Binding and Function Studies

“…Of interest, AZL has a unique moiety, a 5-oxo-1,2,4-oxadiazole, in place of a tetrazole ring (Kohara et al, 1996). Because the tetrazole ring of existing ARBs may interact with the Gln257, Lys199, or Asn295 residues in AT 1 receptors (Miura et al, 2006;Bhuiyan et al, 2009;Qin et al, 2009), the oxadiazolone in AZL may interact with these residues more strongly than with the tetrazole ring.…”

Insights Into the Activation and Inhibition of Angiotensin II Type 1 Receptor in the Mechanically Loaded Heart

“…57 Each ARB differs in efficacy with regard to its unique chemical structure and molecular interactions with the AT1-R. 58 Structure-function analyses of the AT1-R have advanced our understanding of the molecular mechanism underlying receptor activation and inverse agonism. The AT1-R has 7 TM domains (TM1-7) during diastole (preload) and produces eccentric cardiac hypertrophy.…”

“…This receptor allosterism activates intracellular signaling molecules. 57 As for inverse agonism, ARBs bind to the AT1-R and induce its rotation in the opposite direction of mechanical activation. With clockwise allosterism of the AT1-R, intracellular pro-hypertrophic signaling pathways are inhibited.…”

Elevated pressure causes endothelial dysfunction in mouse carotid arteries by increasing local angiotensin signaling

“…Prolonged organ culture of rabbit aortae at high P TM (3 days, 150 mmHg) causes an ANG II-dependent increase in fibronectin expression (3), indicating that pressure can induce local ANG II signaling in the blood vessel wall. Furthermore, ANG II type 1 receptors (AT 1 Rs) can be directly activated by mechanical stretch, independently of ANG II (1,23,28). The goal of the present experiments was to determine whether or not an acute, transient increase in P TM causes endothelial dysfunction in carotid arteries via ANG II-dependent or ANG II-independent activation of AT 1 Rs.…”