Imbalance between xanthine oxidase and nitric oxide synthase signaling pathways underlies mechanoenergetic uncoupling in the failing heart.

Inhibition of xanthine oxidase (XO) in failing hearts improves cardiac efficiency by an unknown mechanism. We hypothesized that this energetic effect is due to reduced oxidative stress and critically depends on nitric oxide synthase (NOS) activity, reflecting a balance between generation of nitric oxide (NO) and reactive oxygen species. In dogs with pacing-induced heart failure (HF), ascorbate (1000 mg) mimicked the beneficial energetic effects of allopurinol, increasing both contractility and efficiency, suggesting an antioxidant mechanism. Allopurinol had no additive effect beyond that of ascorbate. Crosstalk between XO and NOS signaling was assessed. NOS inhibition with N(G)-monomethyl-L-arginine (L-NMMA; 20 mg/kg) had no effect on basal contractility or efficiency in HF, but prevented the +26.2+/-3.5% and +66.5+/-17% enhancements of contractility and efficiency, respectively, observed with allopurinol alone. Similarly, improvements in contractility and energetics due to ascorbate were also inhibited by L-NMMA. Because of the observed NOS-XO crosstalk, we predicted that in normal hearts NOS inhibition would uncover a depression of energetics caused by XO activity. In normal conscious dogs, L-NMMA increased myocardial oxygen consumption (MVO2) while lowering left ventricular external work, reducing efficiency by 31.1+/-3.8% (P<0.005). Lowered efficiency was reversed by XO inhibition (allopurinol, 200 mg) or by ascorbate without affecting cardiac load or systemic hemodynamics. Single-cell immunofluorescence detected XO protein in cardiac myocytes that was enhanced in HF, consistent with autocrine signaling. These data show that both NOS and XO signaling systems participate in the regulation of myocardial mechanical efficiency and that upregulation of XO relative to NOS contributes to mechanoenergetic uncoupling in heart failure.

Treatment of saphenous vein graft thrombosis with distal protection, thrombectomy, and adenosine prior to reperfusion: a complete approach to preserving microvascular integrity.

We report the treatment of an acute myocardial infarction presenting late with thrombotic total occlusion of a saphenous vein graft. A novel approach was used to prevent microvascular obstruction and reperfusion injury, with a distal protection system, a thrombectomy device, and administration of intracoronary adenosine prior to restoration of flow, so that initial reperfusion was done with maximal microvascular vasodilatation.

Elevated uric acid levels predict allograft vasculopathy in cardiac transplant recipients.

BACKGROUND: Cardiac allograft vasculopathy (CAV) poses the greatest threat to the long-term survival of cardiac transplant recipients, and these individuals often exhibit elevated levels of uric acid (UA), a stimulator of T cells. We hypothesized that hyperuricemia is associated with CAV in cardiac transplant recipients. METHODS: UA levels were measured in cardiac transplant recipients between January 2003 and January 2005. Surveillance cardiac catheterizations performed 3 months to 1 year after UA measurement were reviewed. The relationship between UA and CAV was adjusted for possible confounders with propensity scores and confirmed with goodness-of-fit tests. RESULTS: The 105 patients included in this study were a median 63.3 months post-transplant and their left heart catheterizations were performed a median 5.6 months after UA measurement. Focal stenosis was evident in 25 angiograms and 31 showed distal pruning of the coronary arteries. Compared with the lowest quartile of UA, the highest quartile had an increased risk of CAV: odds ratio (OR) 6.11 (95% CI 1.47 to 25.5; p = 0.013) for focal stenosis and OR 4.60 (95% CI 1.34 to 15.8; p = 0.015) for distal pruning. After adjustment, this relationship persisted for both focal stenosis (OR 5.53, 95% confidence interval [CI] 1.29 to 23.7; p = 0.021) and distal pruning (OR 4.21, 95% CI 1.15 to 15.4; p = 0.029). CONCLUSIONS: Elevated UA confers an increased risk of CAV. This association may be causal, with pathophysiologic implications for the role of hyperuricemia in allograft failure and, if substantiated, could have clinical implications for the use of xanthine oxidase inhibitors in cardiac transplant recipients.

Chronic allopurinol administration ameliorates maladaptive alterations in Ca2+ cycling proteins and beta-adrenergic hyporesponsiveness in heart failure.

Xanthine oxidase (XO) activity contributes to both abnormal excitation-contraction (EC) coupling and cardiac remodeling in heart failure (HF). beta-Adrenergic hyporesponsiveness and abnormalities in Ca(2+) cycling proteins are mechanistically linked features of the HF phenotype. Accordingly, we hypothesized that XO influences beta-adrenergic responsiveness and expression of genes whose products participate in deranged EC coupling. We measured inotropic (dP/dt(max)), lusitropic (tau), and vascular (elastance; E(a)) responses to beta-adrenergic (beta-AR) stimulation with dobutamine in conscious dogs administered allopurinol (100 mg po daily) or placebo during a 4-wk induction of pacing HF. With HF induction, the decreases in both baseline and dobutamine-stimulated inotropic responses were offset by allopurinol. Additionally, allopurinol converted a vasoconstrictor effect to dobutamine to a vasodilator response and enhanced both lusitropic and preload reducing effects. To assess molecular correlates for this phenotype, we measured myocardial sarcoplasmic reticulum Ca(2+)-ATPase 2a (SERCA), phospholamban (PLB), phosphorylated PLB (P-PLB), and Na(+)/Ca(2+) transporter (NCX) gene expression and protein. Although SERCA mRNA and protein concentrations did not change with HF, both PLB and NCX were upregulated (P < 0.05). Additionally, P-PLB and protein kinase A activity were greatly reduced. Allopurinol ameliorated all of these molecular alterations and preserved the PLB-to-SERCA ratio. Preventing maladaptive alterations of Ca(2+) cycling proteins represents a novel mechanism for XO inhibition-mediated preservation of cardiac function in HF, raising the possibility that anti-oxidant therapies for HF may ameliorate transcriptional changes associated with adverse cardiac remodeling and beta-adrenergic hyporesponsiveness.

Xanthine oxidase inhibition ameliorates cardiovascular dysfunction in dogs with pacing-induced heart failure.

We hypothesized that chronic xanthine oxidase inhibition (XOI) would have favorable effects on both ventricular and vascular performance in evolving heart failure (HF), thereby preserving ventricular-vascular coupling. In HF, XOI reduces oxidative stress and improves both vascular and myocardial function. Dogs were randomized to receive either allopurinol (100 mg/day p.o.) or placebo following surgical instrumentation for chronic measurement of left-ventricular pressure and dimension and during induction of HF by rapid pacing. In the placebo group (n = 8), HF was characterized by increased LV end-diastolic pressure (LVEDP, 10.2 +/- 5.5 and 29.8 +/- 3.9 mmHg, before and after HF, respectively, P < 0.05), end-diastolic dimension (LVEDD, from 29.5 +/- 3.2 to 34.3 +/- 3.2 mm, P < 0.001), and afterload (arterial elastance, Ea, from 17.9 +/- 1.2 to 42.6 +/- 7.9 mmHg/mm, P < 0.05), and reduced contractility (End-systolic ventricular elastance, Ees, from 10.8 +/- 1.3 to 5.6 +/- 2.3 mmHg/mm, P < 0.05). Thus, ventricular-vascular coupling (Ees/Ea ratio) fell 57.6+/-9% (0.61 +/- 0.1 to 0.16 +/- 0.1, P < 0.05). Allopurinol (n = 9) profoundly attenuated both the Ea increase (from 22.3 +/- 3 to 25.6 +/- 4.6 mmHg/mm, P = NS) and the fall in Ees (from 11.8+/-1.1 to 11.7+/-1, P = NS), thereby preserving the Ees/Ea ratio (from 0.58 +/- 0.1 to 0.56 +/- 0.1, P < 0.001 vs. placebo). Allopurinol did not affect the increase in preload (LVEDP and LVEDD). XO cardiac mRNA and protein were similarly upregulated approximately fourfold in both groups. Allopurinol ameliorates increases in afterload and reductions in myocardial contractility during evolving HF, thereby preserving ventricular-vascular coupling. These results demonstrate a unique and potent hemodynamic profile of XOI, thereby providing further rationale for developing XOIs as a novel HF therapy.

Cardiac repair with intramyocardial injection of allogeneic mesenchymal stem cells after myocardial infarction.

Although clinical trials of autologous whole bone marrow for cardiac repair demonstrate promising results, many practical and mechanistic issues regarding this therapy remain highly controversial. Here, we report the results of a randomized study of bone-marrow-derived mesenchymal stem cells, administered to pigs, which offer several new insights regarding cellular cardiomyoplasty. First, cells were safely injected by using a percutaneous-injection catheter 3 d after myocardial infarction. Second, cellular transplantation resulted in long-term engraftment, profound reduction in scar formation, and near-normalization of cardiac function. Third, transplanted cells were pre-prepared from an allogeneic donor and were not rejected, a major practical advance for widespread application of this therapy. Together, these findings demonstrate that the direct injection of cellular grafts into damaged myocardium is safe and effective in the perii-nfarct period. The direct delivery of cells to necrotic myocardium offers a valuable alternative to intracoronary cell injections, and the use of allogeneic mesenchymal stem cells provides a valuable strategy for cardiac regenerative therapy that avoids the need for preparing autologous cells from the recipient.

Positive inotropic and lusitropic effects of HNO/NO- in failing hearts: independence from beta-adrenergic signaling.

Nitroxyl anion (HNONO(-)), the one-electron reduced form of nitric oxide (NO), induces positive cardiac inotropy and selective venodilation in the normal in vivo circulation. Here we tested whether HNO/NO(-) augments systolic and diastolic function of failing hearts, and whether contrary to NO/nitrates such modulation enhances rather than blunts beta-adrenergic stimulation and is accompanied by increased plasma calcitonin gene-related peptide (CGRP). HNO/NO(-) generated by Angelis' salt (AS) was infused (10 microg/kg per min, i.v.) to conscious dogs with cardiac failure induced by chronic tachycardia pacing. AS nearly doubled contractility, enhanced relaxation, and lowered cardiac preload and afterload (all P < 0.001) without altering plasma cGMP. This contrasted to modest systolic depression induced by an NO donor diethylamine(DEA)NO or nitroglycerin (NTG). Cardiotropic changes from AS were similar in failing hearts as in controls despite depressed beta-adrenergic and calcium signaling in the former. Inotropic effects of AS were additive to dobutamine, whereas DEA/NO blunted beta-stimulation and NTG was neutral. Administration of propranolol to nonfailing hearts fully blocked isoproterenol stimulation but had minimal effect on AS inotropy and enhanced lusitropy. Arterial plasma CGRP rose 3-fold with AS but was unaltered by DEA/NO or NTG, supporting a proposed role of this peptide to HNO/NO(-) cardiotropic action. Thus, HNO/NO(-) has positive inotropic and lusitropic action, which unlike NO/nitrates is independent and additive to beta-adrenergic stimulation and stimulates CGRP release. This suggests potential of HNO/NO(-) donors for the treatment of heart failure.