Juan Pablo Aragon

Exercise Protects Against Myocardial Ischemia–Reperfusion Injury via Stimulation of β3-Adrenergic Receptors and Increased Nitric Oxide Signaling: Role of Nitrite and Nitrosothiols

Rationale: Exercise training confers sustainable protection against ischemia–reperfusion injury in animal models and has been associated with improved survival following a heart attack in humans. It is still unclear how exercise protects the heart, but it is apparent that endothelial nitric oxide synthase (eNOS) and nitric oxide (NO) play a role. Objective: To determine the role of &bgr;3-adrenergic receptors (&bgr;3-ARs), eNOS activation, and NO metabolites (nitrite and nitrosothiols) in the sustained cardioprotective effects of exercise. Methods and Results: Here we show that voluntary exercise reduces myocardial injury in mice following a 4-week training period and that these protective effects can be sustained for at least 1 week following the cessation of the training. The sustained cardioprotective effects of exercise are mediated by alterations in the phosphorylation status of eNOS (increase in serine 1177 and decrease in threonine 495), leading to an increase in NO generation and storage of NO metabolites (nitrite and nitrosothiols) in the heart. Further evidence revealed that the alterations in eNOS phosphorylation status and NO generation were mediated by &bgr;3-AR stimulation and that in response to exercise a deficiency of &bgr;3-ARs leads to an exacerbation of myocardial infarction following ischemia–reperfusion injury. Conclusions: Our findings clearly demonstrate that exercise protects the heart against myocardial ischemia–reperfusion injury by stimulation of &bgr;3-ARs and increased cardiac storage of nitric oxide metabolites (ie, nitrite and nitrosothiols).

The Polysulfide, Diallyl trisulfide, Protects the Ischemic Myocardium by Preservation of Endogenous Hydrogen Sulfide and Increasing Nitric Oxide Bioavailability

Diallyl trisulfide (DATS), a polysulfide constituent found in garlic oil, is capable of the release of hydrogen sulfide (H(2)S). H(2)S is a known cardioprotective agent that protects the heart via antioxidant, antiapoptotic, anti-inflammatory, and mitochondrial actions. Here, we investigated DATS as a stable donor of H(2)S during myocardial ischemia-reperfusion (MI/R) injury in vivo. We investigated endogenous H(2)S levels, infarct size, postischemic left ventricular function, mitochondrial respiration and coupling, endothelial nitric oxide (NO) synthase (eNOS) activation, and nuclear E2-related factor (Nrf2) translocation after DATS treatment. Mice were anesthetized and subjected to a surgical model of MI/R injury with and without DATS treatment (200 μg/kg). Both circulating and myocardial H(2)S levels were determined using chemiluminescent gas chromatography. Infarct size was measured after 45 min of ischemia and 24 h of reperfusion. Troponin I release was measured at 2, 4, and 24 h after reperfusion. Cardiac function was measured at baseline and 72 h after reperfusion by echocardiography. Cardiac mitochondria were isolated after MI/R, and mitochondrial respiration was investigated. NO metabolites, eNOS phosphorylation, and Nrf2 translocation were determined 30 min and 2 h after DATS administration. Myocardial H(2)S levels markedly decreased after I/R injury but were rescued by DATS treatment (P < 0.05). DATS administration significantly reduced infarct size per area at risk and per left ventricular area compared with control (P < 0.001) as well as circulating troponin I levels at 4 and 24 h (P < 0.05). Myocardial contractile function was significantly better in DATS-treated hearts compared with vehicle treatment (P < 0.05) 72 h after reperfusion. DATS reduced mitochondrial respiration in a concentration-dependent manner and significantly improved mitochondrial coupling after reperfusion (P < 0.01). DATS activated eNOS (P < 0.05) and increased NO metabolites (P < 0.05). DATS did not appear to significantly induce the Nrf2 pathway. Taken together, these data suggest that DATS is a donor of H(2)S that can be used as a cardioprotective agent to treat MI/R injury.

Beta3-Adrenoreceptor Stimulation Ameliorates Myocardial Ischemia-Reperfusion Injury Via Endothelial Nitric Oxide Synthase and Neuronal Nitric Oxide Synthase Activation

OBJECTIVES This paper examined whether nebivolol protects the heart via nitric oxide (NO) synthase and NO-dependent signaling in an in vivo model of acute myocardial infarction. BACKGROUND Beta(3)-adrenergic receptor (AR) activation promotes endothelial nitric oxide synthase (eNOS) activity and NO bioavailability. We hypothesized that specific beta(3)-AR agonists would attenuate myocardial ischemia-reperfusion (MI/R) injury via eNOS activation and increased NO bioavailability. METHODS Mice were subjected to 45 min of myocardial ischemia in vivo followed by 24 h of reperfusion (R). Nebivolol (500 ng/kg), CL 316243 (1 μg/kg), BRL-37344 (1 μg/kg), or vehicle (VEH) was administered at the time of R. Myocardial area-at-risk (AAR) and infarct size (INF)/AAR was measured at 24 h of R. Cardiac tissue and plasma were collected to evaluate eNOS phosphorylation, neuronal nitric oxide synthase (nNOS), inducible nitric oxide synthase expression, and nitrite and nitrosothiol levels. RESULTS Nebivolol (500 ng/kg) reduced INF/AAR by 37% (p < 0.001 vs. VEH) and serum troponin-I levels from 41 ± 4 ng/ml to 25 ± 4 ng/ml (p < 0.05 vs. VEH). CL 316243 and BRL-37344 reduced INF by 39% and 42%, respectively (p < 0.001 vs. VEH). Nebivolol and CL 316243 increased eNOS phosphorylation at Ser-1177 (p < 0.05 vs. VEH) and increased nitrite and total nitrosylated protein levels. Nebivolol and CL 316243 significantly increased myocardial nNOS expression. Nebivolol failed to reduce INF after MI/R in beta(3)-AR (-/-), eNOS(-/-), and in nNOS(-/-) mice. CONCLUSIONS Our results indicate that beta(3)-AR agonists protect against MI/R injury. Furthermore, the cardioprotective effects of beta(3)-AR agonists are mediated by rapid eNOS and nNOS activation and increased NO bioavailability.