Abstract 204: The NO Redox Sibling, Nitroxyl (HNO), Blocks Cardiomyocyte Hypertrophy via Suppression of NADPH Oxidase
NADPH oxidase-derived superoxide (·O2−) is an important trigger of cardiac remodelling and failure. Current treatments slow but do not reverse disease progression. We have shown that NO is an important antihypertrophic mechanism in the heart. The impact of HNO, an alternate redox form of NO, on cardiac hypertrophy or its triggers has however not been sought. We tested the hypothesis that HNO prevents hypertrophy via suppression of NADPH oxidase in neonatal rat cardiomyocytes, and the role of cGMP-dependent signalling in these actions. Angiotensin II (Ang II, 1μM) induced cardiomyocyte hypertrophy after 48h, on both two-dimensional area (to 192 ± 12%) and protein synthesis (to 149 ± 8%, on phenylalanine incorporation, both n = 12, p<0.001 vs paired control). Both NADPH oxidase Nox2 gene expression and NADPH-driven ·O2− generation increased in parallel, by 2.5 ± 0.5-fold (n = 6, p<0.01 vs paired control) and 2.5 ± 0.4-fold (on lucigenin, n=12, p<0.001 vs paired control). The HNO donor, Angeli’s salt (1μM, replenished 4x/day), prevented all of these Ang II effects: cardiomyocyte area, protein synthesis, Nox2 induction and ·O2− levels were reduced to 105 ± 6%, 106 ± 6%, 1.0 ± 0.5-fold and 1.2 ± 0.2-fold (all p<0.05 vs Ang II), respectively. These antihypertrophic and antioxidant actions of the HNO donor were all mimicked by B-type natriuretic peptide (1μM) and 8-Br-cGMP (1mM). Co-incubation with KT5823 (250nM, to selectively inhibit cGMP-dependent protein kinase) significantly attenuated the antihypertrophic and antioxidant effects of Angeli’s salt, to 143 ± 10% and 2.5 ± 0.5-fold (all p<0.05 vs Ang II+HNO), respectively. Similar attenuation was observed with ODQ (1μM, to selectively inhibit soluble guanylate cyclase). KT5823, ODQ, Angeli’s salt or their respective vehicles had no effect alone. Furthermore, Angeli’s salt completely abolished endothelin-1 (60nM)-induction of cardiomyocyte hypertrophy and ·O2− generation. In conclusion, our results provide the first evidence that HNO prevents cardiac hypertrophy, and that cGMP-dependent suppression of cardiomyocyte NADPH oxidase contributes to these antihypertrophic actions. HNO donors thus represent an innovative pharmacotherapy for the treatment of cardiac hypertrophy.