Nga Cao

HNO/cGMP-dependent antihypertrophic actions of isopropylamine-NONOate in neonatal rat cardiomyocytes: potential therapeutic advantages of HNO over NO˙

Nitroxyl (HNO) is a redox congener of NO. We now directly compare the antihypertrophic efficacy of HNO and NO donors in neonatal rat cardiomyocytes and compare their contributing mechanisms of actions in this setting. Isopropylamine-NONOate (IPA-NO) elicited concentration-dependent inhibition of endothelin-1 (ET1)-induced increases in cardiomyocyte size, with similar suppression of hypertrophic genes. Antihypertrophic IPA-NO actions were significantly attenuated by l-cysteine (HNO scavenger), Rp-8-pCTP-cGMPS (cGMP-dependent protein kinase inhibitor), and 1-H-(1,2,4)-oxodiazolo-quinxaline-1-one [ODQ; to target soluble guanylyl cyclase (sGC)] but were unaffected by carboxy-PTIO (NO scavenger) or CGRP8-37 (calcitonin gene-related peptide antagonist). Furthermore, IPA-NO significantly increased cardiomyocyte cGMP 3.5-fold (an l-cysteine-sensitive effect) and stimulated sGC activity threefold, without detectable NO release. IPA-NO also suppressed ET1-induced cardiomyocyte superoxide generation. The pure NO donor diethylamine-NONOate (DEA-NO) reproduced these IPA-NO actions but was sensitive to carboxy-PTIO rather than l-cysteine. Although IPA-NO stimulation of purified sGC was preserved under pyrogallol oxidant stress (in direct contrast to DEA-NO), cardiomyocyte sGC activity after either donor was attenuated by this stress. Excitingly IPA-NO also exhibited acute antihypertrophic actions in response to pressure overload in the intact heart. Together these data strongly suggest that IPA-NO protection against cardiomyocyte hypertrophy is independent of both NO and CGRP but rather utilizes novel HNO activation of cGMP signaling. Thus HNO acutely limits hypertrophy independently of NO, even under conditions of elevated superoxide. Development of longer-acting HNO donors may thus represent an attractive new strategy for the treatment of cardiac hypertrophy, as stand-alone and/or add-on therapy to standard care.

The concomitant coronary vasodilator and positive inotropic actions of the nitroxyl donor Angeli's salt in the intact rat heart: contribution of soluble guanylyl cyclase-dependent and -independent mechanisms

The NO redox sibling nitroxyl (HNO) elicits soluble guanylyl cyclase (sGC)‐dependent vasodilatation. HNO has high reactivity with thiols, which is attributed with HNO‐enhanced left ventricular (LV) function. Here, we tested the hypothesis that the concomitant vasodilatation and inotropic actions induced by a HNO donor, Angelis salt (sodium trioxodinitrate), were sGC‐dependent and sGC‐independent respectively.

Chronic Administration of the Nitroxyl Donor 1-Nitrosocyclo Hexyl Acetate Limits Left Ventricular Diastolic Dysfunction in a Mouse Model of Diabetes Mellitus In Vivo

Background—Nitroxyl (HNO), a redox congener of nitric oxide (NO·), is a novel regulator of cardiovascular function, combining concomitant positive inotropic, lusitropic, and vasodilator properties. Moreover, HNO exhibits myocardial antihypertrophic and superoxide-suppressing actions. Despite these favorable actions, the impact of chronic HNO administration has yet to be reported in the context of cardiomyopathy. Diabetic cardiomyopathy is characterized by early diastolic dysfunction and adverse left ventricular (LV) structural remodeling, with LV superoxide generation playing a major causal role. We tested the hypothesis that the HNO donor 1-nitrosocyclohexylacetate (1-NCA) limits cardiomyocyte hypertrophy and LV diastolic dysfunction in a mouse model of diabetes mellitus in vivo. Methods and Results—Diabetes mellitus was induced in male FVB/N mice using streptozotocin. After 4 weeks, diabetic and nondiabetic mice were allocated to 1-NCA therapy (83 mg/kg per day IP) or vehicle and followed up for a further 4 weeks. Diabetes mellitus–induced LV diastolic dysfunction was evident on echocardiography-derived E and A wave velocities, E:A ratio, deceleration, and isovolumic relaxation times; LV systolic function was preserved. Increased LV cardiomyocyte size, hypertrophic and profibrotic gene expression, and upregulation of LV superoxide were also evident. These characteristics of diabetic cardiomyopathy were largely prevented by 1-NCA treatment. Selectivity of 1-NCA as an HNO donor was demonstrated by sensitivity of acute 1-NCA to L-cysteine but not to hydroxocobalamin in the normal rat heart ex vivo. Conclusions—Our studies provide the first evidence that HNO donors may represent a promising strategy for treatment of diabetic cardiomyopathy and implies therapeutic efficacy in settings of chronic heart failure.

Small-molecule-biased formyl peptide receptor agonist compound 17b protects against myocardial ischaemia-reperfusion injury in mice

Effective treatment for managing myocardial infarction (MI) remains an urgent, unmet clinical need. Formyl peptide receptors (FPR) regulate inflammation, a major contributing mechanism to cardiac injury following MI. Here we demonstrate that FPR1/FPR2-biased agonism may represent a novel therapeutic strategy for the treatment of MI. The small-molecule FPR1/FPR2 agonist, Compound 17b (Cmpd17b), exhibits a distinct signalling fingerprint to the conventional FPR1/FPR2 agonist, Compound-43 (Cmpd43). In Chinese hamster ovary (CHO) cells stably transfected with human FPR1 or FPR2, Compd17b is biased away from potentially detrimental FPR1/2-mediated calcium mobilization, but retains the pro-survival signalling, ERK1/2 and Akt phosphorylation, relative to Compd43. The pathological importance of the biased agonism of Cmpd17b is demonstrable as superior cardioprotection in both in vitro (cardiomyocytes and cardiofibroblasts) and MI injury in mice in vivo. These findings reveal new insights for development of small molecule FPR agonists with an improved cardioprotective profile for treating MI.

The HNO donor Angeli’s salt offers potential haemodynamic advantages over NO or dobutamine in ischaemia–reperfusion injury in the rat heart ex vivo

Available inotropic pharmacotherapy for acute heart failure (HF) remains largely ineffective at ameliorating marked impairments in contractile function. Nitroxyl (HNO), the redox sibling of NO•, has recently attracted interest as a therapeutic approach for acute HF. We now compare the impact of ischaemia-reperfusion (I-R) injury on acute haemodynamic responsiveness of the HNO donor, Angelis salt (AS), to that of NO and dobutamine. Dose-response curves to bolus doses of AS, diethylamine NONOate (DEA/NO, both 0.001-μmol) and dobutamine (0.1-100 nmol) were performed in rat isolated hearts, following I-R or normoxic perfusion. An additional 10μmol dose of Angelis salt was included, to permit roughly equivalent inotropic responses to dobutamine. Changes in cardiac contraction, heart rate and coronary flow (CF) were determined. Although AS and DEA/NO elicited comparable dose-dependent increases in CF in normoxic hearts, only AS vasodilation was preserved after I-R. AS and dobutamine elicited dose-dependent inotropic responses in normoxic hearts and I-R blunted inotropic responses to both. Dobutamine however increased heart rate, which was exacerbated by I-R; this was not evident with AS. Further, AS infusion during reperfusion (1μM), in a separate cohort of rat hearts, improved recovery of cardiac contractility, with lower incidence of I-R-induced ventricular fibrillation. In conclusion, these observations suggest that HNO offers haemodynamic advantages over NO following I-R. Although I-R suppresses inotropy to both agents, residual contractile responses to AS following I-R is likely free of concomitant pro-arrhythmic events. HNO donors may thus offer haemodynamic advantages over existing pharmacotherapy in acute HF.

The nitroxyl donor isopropylamine-NONOate elicits soluble guanylyl cyclase-dependent antihypertrophic actions: comparison of the potential therapeutic advantages of HNO over NO•

Results IPA-NO elicited concentration-dependent inhibition of endothelin-1 (ET1)-induced increases in neonatal rat cardiomyocyte size, with similar suppression of hypertrophic genes. Antihypertrophic IPA-NO actions were significantly attenuated by L-cysteine (HNO scavenger), Rp-8-pCTPcGMPS (cGMP-dependent protein kinase inhibitor), and ODQ (to target soluble guanylyl cyclase, sGC), but were unaffected by carboxy-PTIO (NO• scavenger) or CGRP837 (calcitonin gene-related peptide antagonist). Furthermore, IPA-NO significantly increased cardiomyocyte cGMP 3.5-fold (an L-cysteine-sensitive effect), and stimulated sGC activity 3-fold, without detectable NO• release. IPA-NO also suppressed ET1-induced cardiomyocyte superoxide generation. The pure NO• donor, DEA-NO, reproduced these IPA-NO actions, but were sensitive to carboxy-PTIO rather than L-cysteine. Although IPA-NO stimulation of purified sGC was preserved under pyrogallol oxidant stress (in direct contrast to DEA-NO), cardiomyocyte sGC activity after either donor were attenuated by this stress. Excitingly IPA-NO also exhibited acute antihypertrophic actions in response to acute pressureoverload in the intact heart, at doses that did not affect coronary perfusion pressure or LV function.

Soluble guanylyl cyclase mediates concomitant coronary vasodilator and positive inotropic actions of the HNO donor Angeli's salt in the intact rat heart

Background The NO redox sibling nitroxyl (HNO) elicits soluble guanylyl cyclase (sGC)-dependent vasodilatation. HNO has high reactivity with thiols (unlike NO), which is attributed with HNO-enhanced left ventricular (LV) function. The present study tested the hypothesis that the concomitant vasodilatation and inotropic actions induced by the HNO donor, Angeli’s salt (sodium trioxodinitrate), are sGC-dependent and sGC-independent, respectively. Materials and methods Haemodynamic responses to bolus doses of Angeli’ ss alt (10pmol - 10μmol), alone and in the presence of selective scavengers of HNO (L-cysteine, 4mM) or NO (hydroxocobalamin HXC, 50µM) or selective inhibitors of sGC (1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one ODQ, 10μM), calcitonin gene-related peptide (CGRP) receptors (CGRP8-37 ,0 .1 μM) or voltage-dependent potassium channels (4-aminopyridine 4-AP, 1mM) were determined in isolated adult male rat hearts. Results Angeli’s salt elicited concomitant, potent dose-dependent increases in coronary flow and LV systolic and diastolic function. Both L-cysteine and ODQ caused a rightward shift in the dose-response curve of each of these effects, implicating HNO and sGC in both the vasodilator and inotropic actions of Angeli’s salt. In contrast, neither HXC, CGRP8-37 nor 4-AP affected Angeli’s salt actions. Conclusion These data suggest that each of the vasodilator, inotropic and lusitropic actions of Angeli’s salt are mediated by L-cysteine-sensitive, HNO/sGC-dependent mechanisms. Our findings represent the first evidence that sGC specifically contributes a significant component of the inotropic and lusitropic actions of an HNO donor in the intact heart. Thus, HNO acutely enhances LV contractile function and LV relaxation, whilst concomitantly unloading the heart, potentially favourable properties for the failing heart.