AdipoRon, the first orally active adiponectin receptor activator, attenuates postischemic myocardial apoptosis through both AMPK-mediated and AMPK-independent signalings

Abstract

Adiponectin (APN) is a cardioprotective molecule. Its reduction in diabetes exacerbates myocardial ischemia/reperfusion (MI/R) injury. Although APN administration in animals attenuates MI/R injury, multiple factors limit its clinical application. The current study investigated whether AdipoRon, the first orally active molecule that binds APN receptors, may protect the heart against MI/R injury, and if so, to delineate the involved mechanisms. Wild-type (WT), APN knockout (APN-KO), and cardiomyocyte specific-AMPK dominant negative (AMPK-DN) mice were treated with vehicle or AdipoRon (50 mg/kg, 10 min prior to MI) and subjected to MI/R (30 min/3-24 h). Compared with vehicle, oral administration of AdipoRon to WT mice significantly improved cardiac function and attenuated postischemic cardiomyocyte apoptosis, determined by DNA ladder formation, TUNEL staining, and caspase-3 activation (all P < 0.01). MI/R-induced apoptotic cell death was significantly enhanced in mice deficient in either APN (APN-KO) or AMPK (AMPK-DN). In APN-KO mice, AdipoRon attenuated MI/R injury to the same degree as observed in WT mice. In AMPK-DN mice, AdipoRon's antiapoptotic action was partially inhibited but not lost. Finally, AdipoRon significantly attenuated postischemic oxidative stress, as evidenced by reduced NADPH oxidase expression and superoxide production. Collectively, these results demonstrate for the first time that AdipoRon, an orally active APN receptor activator, effectively attenuated postischemic cardiac injury, supporting APN receptor agonists as a promising novel therapeutic approach treating cardiovascular complications caused by obesity-related disorders such as type 2 diabetes.

Keywords: adipokines; apoptosis; diabetes; reperfusion injury.

Fig. 1.

Oral AdipoRon administration significantly improved ±dP/dt_max in wild-type (WT), adiponectin knockout (APN^−/−), and cardiomyocyte-specific AMPKα2 mutant transgenic mice (AMPK-DN); n = 14–16 animals/group. *P < 0.05, **P < 0.01 vs. MI/R + vehicle. P values between myocardiac ischemia/reperfusion (MI/R) vs. Sham are all < 0.01 (not labeled, the same for all figures).

Fig. 2.

Oral AdipoRon administration significantly enhanced left ventricular (LV) ejection fraction (EF%) determined by echocardiography in WT, APN^−/−, and AMPK-DN mice. Note attenuated response to AdipoRon treatment in AMPK-DN mice vs. WT mice. However, a significant portion of cardioprotection is retained in AMPK-DN mice; n = 14–16 animals/group. *P < 0.05, **P < 0.01 vs. MI/R + vehicle.

Fig. 3.

Oral AdipoRon administration significantly attenuated postischemic cardiac apoptosis determined by DNA ladder formation (A) and caspase-3 activation (B) in WT and APN^−/− mice. AdipoRon also significantly inhibited DNA ladder formation and reduced caspase-3 activity in AMPK-DN mice, albeit to a lesser extent than seen in WT mice; n = 6–8 animals/group. *P < 0.05, **P < 0.01 vs. MI/R + vehicle.

Fig. 4.

Oral AdipoRon administration significantly attenuated postischemic cardiac apoptosis determined by TUNEL staining in WT and APN^−/− mice. AdipoRon also significantly inhibited TUNEL staining in AMPK-DN mice, albeit to a lesser extent than seen in WT mice; n = 6–8 animals/group. *P < 0.05, **P < 0.01 vs. MI/R + vehicle.

Fig. 5.

A: AdipoRon activated AMPK signaling (determined by ACC phosphorylation) in WT but not in AMPK-DN animals. AdipoRon significantly inhibited ischemia/reperfusion-induced superoxide production, determined by DHE staining (B), lucigenin-enhanced luminescence assay (C), and gp91^phox overexpression (D) in AMPK-DN mice; n = 6–8 animals/group for DHE staining and Western analysis; n = 9–11 animals/group for lucigenin-enhanced luminescence assay. *P < 0.05, **P < 0.01 vs. MI/R + vehicle.