Susheel Gundewar

Acute Metformin Therapy Confers Cardioprotection Against Myocardial Infarction Via AMPK-eNOS Mediated Signaling

OBJECTIVE—Clinical studies have reported that metformin reduces cardiovascular end points of type 2 diabetic subjects by actions that cannot solely be attributed to glucose-lowering effects. The therapeutic effects of metformin have been reported to be mediated by its activation of AMP-activated protein kinase (AMPK), a metabolite sensing protein kinase whose activation following myocardial ischemia has been suggested to be an endogenous protective signaling mechanism. We investigated the potential cardioprotective effects of a single, low-dose metformin treatment (i.e., 286-fold less than the maximum antihyperglycemic dose) in a murine model of myocardial ischemia-reperfusion (I/R) injury. RESEARCH DESIGN AND METHODS—Nondiabetic and diabetic (db/db) mice were subjected to transient myocardial ischemia for a period of 30 min followed by reperfusion. Metformin (125 μg/kg) or vehicle (saline) was administered either before ischemia or at the time of reperfusion. RESULTS—Administration of metformin before ischemia or at reperfusion decreased myocardial injury in both nondiabetic and diabetic mice. Importantly, metformin did not alter blood glucose levels. During early reperfusion, treatment with metformin augmented I/R-induced AMPK activation and significantly increased endothelial nitric oxide (eNOS) phosphorylation at residue serine 1177. CONCLUSIONS—These findings provide important information that myocardial AMPK activation by metformin following I/R sets into motion events, including eNOS activation, which ultimately lead to cardioprotection.

Dietary nitrite restores NO homeostasis and is cardioprotective in endothelial nitric oxide synthase-deficient mice

Endothelial production of nitric oxide (NO) is critical for vascular homeostasis. Nitrite and nitrate are formed endogenously by the stepwise oxidation of NO and have, for years, been regarded as inactive degradation products. As a result, both anions are routinely used as surrogate markers of NO production, with nitrite as a more sensitive marker. However, both nitrite and nitrate are derived from dietary sources. We sought to determine how exogenous nitrite affects steady-state concentrations of NO metabolites thought to originate from nitric oxide synthase (NOS)-derived NO as well as blood pressure and myocardial ischemia-reperfusion (I/R) injury. Mice deficient in endothelial nitric oxide synthase (eNOS-/-) demonstrated decreased blood and tissue nitrite, nitrate, and nitroso proteins, which were further reduced by low-nitrite (NOx) diet for 1 week. Nitrite supplementation (50 mg/L) in the drinking water for 1 week restored NO homeostasis in eNOS-/- mice and protected against I/R injury. Nitrite failed to alter heart rate or mean arterial blood pressure at the protective dose. These data demonstrate the significant influence of dietary nitrite intake on the maintenance of steady-state NO levels. Dietary nitrite and nitrate may serve as essential nutrients for optimal cardiovascular health and may provide a novel prevention/treatment modality for disease associated with NO insufficiency.

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).

Gene therapy for ischemic heart disease.

Current pharmacologic therapy for ischemic heart disease suffers multiple limitations such as compliance issues and side effects of medications. Revascularization procedures often end with need for repeat procedures. Patients remain symptomatic despite maximal medical therapy. Gene therapy offers an attractive alternative to current pharmacologic therapies and may be beneficial in refractory disease. Gene therapy with isoforms of growth factors such as VEGF, FGF and HGF induces angiogenesis, decreases apoptosis and leads to protection in the ischemic heart. Stem cell therapy augmented with gene therapy used for myogenesis has proven to be beneficial in numerous animal models of myocardial ischemia. Gene therapy coding for antioxidants, eNOS, HSP, mitogen-activated protein kinase and numerous other anti apoptotic proteins have demonstrated significant cardioprotection in animal models. Clinical trials have demonstrated safety in humans apart from symptomatic and objective improvements in cardiac function. Current research efforts are aimed at refining various gene transfection techniques and regulation of gene expression in vivo in the heart and circulation to improve clinical outcomes in patients that suffer from ischemic heart disease. In this review article we will attempt to summarize the current state of both preclinical and clinical studies of gene therapy to combat myocardial ischemic disease. This article is part of a Special Section entitled Special Section: Cardiovascular Gene Therapy.

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

OBJECTIVESnThis 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.nnnBACKGROUNDnBeta(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.nnnMETHODSnMice 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.nnnRESULTSnNebivolol (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.nnnCONCLUSIONSnOur 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.

Developmental programming resulting from maternal obesity in mice: effects on myocardial ischaemia-reperfusion injury.

A comprehensive number of epidemiological and animal studies suggest that prenatal and early life events are important determinants for disorders later in life. Among them, prenatal stress (i.e. stress experienced by the pregnant mother with impact on the fetal ontogeny) has clear programming effects on the cardiovascular system. A fetus developing in adverse conditions becomes an adult who is susceptible to disease, which may include hypertension, insulin resistance, altered blood lipid levels and cardiovascular disease. Recent evidence demonstrates that maternal programming can occur in the absence of other adverse environmental factors. Obesity, which is becoming a problem of large proportions in Western countries, is a possible cause of programming. With over 30% of the population of the USA currently obese, many mothers suffer from obesity during their child‐bearing years (in fact, these conditions are often aggravated during pregnancy). One of the targets of programming is the cardiovascular system, and reported consequences include hypertension, endothelial dysfunction and vascular abnormalities. The overall goal of our study was to investigate the susceptibility of the heart to ischaemia–reperfusion in an animal model of maternal obesity. Our data demonstrate that normal (non‐mutant) offspring from obese agouti mouse dams had an increased susceptibility to ischaemia–reperfusion injury. These data may provide insights into the long‐term cardiovascular consequences of programming.

Subclavian Venoplasty May Reduce Implant Times and Implant Failures in the Era of Increasing Device Upgrades

Background: u2002The incidence of subclavian venous occlusions (SCVOs) may be an increasing problem in the era of device upgrades, especially to cardiac resynchronization therapy. Venoplasty (VP) performed by the electrophysiologist as a way of managing SCVOs may be advantageous.

Left ventricular apical ballooning syndrome after pacemaker implantation in a male

Left apical ballooning syndrome, also known as Takotsubo cardiomyopathy (TTC), characterized by transient left ventricular dysfunction is increasingly recognized worldwide. Predominantly affecting females, this condition mimics myocardial infarction and often occurs in the setting of emotional or physical stress. We report the case of a 77-year-old male who was admitted to the hospital for complete heart block and developed TTC after pacemaker implantation. To our knowledge, this is the first report of TTC development after pacemaker implantation in a male.

Severe left ventricular systolic dysfunction increases atrial fibrillation after ablation of atrial flutter

Background: Atrial fibrillation (Afib) that occurs after a successful atrial flutter (AFL) ablation may negate the potential benefits of the ablation. Afib occurs more often when severe left ventricular systolic dysfunction (LVSD) is present. We hypothesized that even after a successful AFL ablation, the incidence of postablation Afib is increased when severe LVSD is present.

5. Atrial Tachycardia, Atrial Flutter & WPW Syndrome

Introduction Severe left ventricular systolic dysfunction (LVSD) is associated with a high incidence of atrial fibrillation (Afib). Afib that occurs after a successful atrial flutter (AFL) ablation may negate the potential benefits of the ablation. We hypothesized that severe LVSD increases the incidence of post-ablation Afib despite a successful AFL ablation.nnMethods 90 consecutive patients with LVSD who underwent ablation for AFL at Montefiore Medical Center from August 2001 to January 2005 were classified according to the severity of LVSD. Group 1 (n = 36) consisted of patients with EF ≤ 35%, and group 2 (n = 54) consisted of patients with EF 36-55%. There were no statistically significant differences in baseline patient characteristics between the 2 groups. ![Graphic][1] nnResults During a mean follow up of 350 days, Afib occurred in 31% (n = 11; 8 with prior history of AFib) in group 1, and 7.4% (n = 4; all with prior history of Afib) in group 2. Cumulative probability of remaining Afib-free in group 1 vs. group 2 was 75% vs. 96% at 365 days, and 69% vs. 91% at 600 days (p = 0.01). A prior history of Afib did not interact with EF when analyzed with a logistic regression analysis. nn![Figure 1][2] nnFigure 1 nKaplan-Meier estimates of the time to atrial fibrillation occurrence post-ablation in patients with EF ≤ 35% (solid line) and EF 36-55% (dotted line).nnnnConclusion After an AFL ablation, severe LVSD increases the incidence of AFib (31% vs. 7.4%, p = 0.004) independent of a prior history of Afib. This finding may have implications for optimal patient selection for AFL ablation, and the use of adjunctive therapies.nn [1]: /embed/graphic-1.gifn [2]: pending:yes