Nitroxyl (HNO): A novel approach for the acute treatment of heart failure

Abstract

Background: The nitroxyl (HNO) donor, Angeli's salt, exerts positive inotropic, lusitropic, and vasodilator effects in vivo that are cAMP independent. Its clinical usefulness is limited by chemical instability and cogeneration of nitrite which itself has vascular effects. Here, we report on effects of a novel, stable, pure HNO donor (CXL-1020) in isolated myoctyes and intact hearts in experimental models and in patients with heart failure (HF).

Methods and results: CXL-1020 converts solely to HNO and inactive CXL-1051 with a t1/2 of 2 minutes. In adult mouse ventricular myocytes, it dose dependently increased sarcomere shortening by 75% to 210% (50-500 μmol/L), with a ≈30% rise in the peak Ca(2+) transient only at higher doses. Neither inhibition of protein kinase A nor soluble guanylate cyclase altered this contractile response. Unlike isoproterenol, CXL-1020 was equally effective in myocytes from normal or failing hearts. In anesthetized dogs with coronary microembolization-induced HF, CXL-1020 reduced left ventricular end-diastolic pressure and myocardial oxygen consumption while increasing ejection fraction from 27% to 40% and maximal ventricular power index by 42% (both P<0.05). In conscious dogs with tachypacing-induced HF, CXL-1020 increased contractility assessed by end-systolic elastance and provided venoarterial dilation. Heart rate was minimally altered. In patients with systolic HF, CXL-1020 reduced both left and right heart filling pressures and systemic vascular resistance, while increasing cardiac and stroke volume index. Heart rate was unchanged, and arterial pressure declined modestly.

Conclusions: These data show the functional efficacy of a novel pure HNO donor to enhance myocardial function and present first-in-man evidence for its potential usefulness in HF.

Clinical trial registration: URL: http://www.clinicaltrials.gov. Unique identifiers: NCT01096043, NCT01092325.

Keywords: cardiomyopathies; heart contractility; humans; muscle cells; nitroxyl; pharmacology; vasodilator drugs.

Figure 1. Pharmacological decomposition of CXL-1020

A) Decomposition of CXL-1020 in aqueous solution into HNO (measured by nitrous oxide) and CXL-1051. Conversion is rapid, and virtually complete by 15 minutes, with stoichiometry confirming pure generation of HNO and CLX-1051 in equal parts. B) Decomposition of CXL-1020 in human whole blood shows similar rapid pharmacokinetics. IS: internal standard, see supplemental methods.

Figure 2. Influence of CXL-1020 on isolated cardiac myocytes from normal and failing heart

A) (Left) Isolated myocyte sarcomere length (SL, upper tracing) and calcium transients (Ca²⁺, lower tracing) after exposure to CLX-1020. There is a marked rise in sarcomere shortening (SS) and a rise in the peak Ca²⁺ transient, as well as acceleration of the time for re-lengthening and calcium decline. B) Box-plots show percent change in SS and peak Ca²⁺ transient relative to baseline with incremental CXL-1020 dose. Only one dose was tested per myocyte; the sample size at each dose is provided in the plots. C) Percent reduction in sarcomere relengthening and calcium decay time. D) Percent change in SS and peak Ca²⁺ transient following CXL-1020 with or without co-inhibition of PKA (Rp-cAMPs) or soluble guanylate cyclase (ODQ). E) Percent change in SS and re-lengthening rate in myocytes isolated from control or failing hearts that are then exposed to either isoproterenol (ISO, 2.5 nM) or CXL-1020 (50 µM). † - p<0.05; * p<0.01; ** p≤0.001 versus respective (pre-CXL1020, or ISO) baseline, by Wilcoxan Sign-rank Test.

Figure 3. Influence of CXL-1020 in anesthetized dogs over 4-hour infusion

A) Left ventricular and systemic hemodynamics at either 3 or 10 µg/kg/min CXL-1020, with 1 hour of washout (n=6). Ei/Ai= ratio of early to late (atrial) mitral inflow. * P<0.05 versus vehicle control by multiple comparisons test (Student-Newman-Keuls) following repeated measures ANOVA.

Figure 4. Influence of CXL-1020 in conscious heart failure dogs

A) Absolute change in hemodynamic parameters in Group 2 (conscious) heart failure dogs as a function of increasing CXL-1020 dose. P-values in each plot are for a repeated measures analysis of co-variance (with drug dose as the continuous variable, n=5). Post-hoc multiple comparisons test for dose response versus baseline: * - p<0.005; † - p<0.001; ‡ - p≤0.01; § - p=0.02. B) Example pressure volume loops at baseline and after CXL-1020 infusion, showing an increase in the slope of the end-systolic pressure volume relationship (solid line is control, dashed after CXL-1020). C) Box-plot for percent change in hemodynamic parameters before and after 100 mg/kg/min CXL-1020 in normal dogs and the same dogs after inducing heart failure. * - p<0.05, † p<0.01 between groups (n=5 per group, Kruskal-Wallis used to test for effect of heart failure on the response).

Figure 5. Hemodynamic effects of CXL-1020 in patients with symptomatic heart failure

Effects of CXL-1020 at 3, 10 or 20 ug/kg/min on heart rate (HR), mean arterial pressure (MAP), right atrial pressure (RAP), pulmonary capillary wedge pressure (PCWP), stroke volume index (SVI), cardiac index (CI) and systemic vascular resistance (SVR) in 12 patients with symptomatic heart failure ( ‘high dose’ titration group described in Methods). Data show the mean percent change ±SEM at each dose minus theresponse observed in the placebo group at the same time point (e.g. i.e. corrected to placebo). * p<0.05 versus baseline, # - p<0.005 versus baseline.