Diesterified Nitrone Rescues Nitroso-Redox Levels and Increases Myocyte Contraction Via Increased SR Ca2+ Handling

Nitric oxide (NO) and superoxide (O₂⁻) are important cardiac signaling molecules that regulate myocyte contraction. For appropriate regulation, NO and O₂^.− must exist at defined levels. Unfortunately, the NO and O₂^.− levels are altered in many cardiomyopathies (heart failure, ischemia, hypertrophy, etc.) leading to contractile dysfunction and adverse remodeling. Hence, rescuing the nitroso-redox levels is a potential therapeutic strategy. Nitrone spin traps have been shown to scavenge O₂^.− while releasing NO as a reaction byproduct; and we synthesized a novel, cell permeable nitrone, 2–2–3,4-dihydro-2H-pyrrole 1-oxide (EMEPO). We hypothesized that EMEPO would improve contractile function in myocytes with altered nitroso-redox levels. Ventricular myocytes were isolated from wildtype (C57Bl/6) and NOS1 knockout (NOS1^−/−) mice, a known model of NO/O₂^.− imbalance, and incubated with EMEPO. EMEPO significantly reduced O₂^.− (lucigenin-enhanced chemiluminescence) and elevated NO (DAF-FM diacetate) levels in NOS1^−/− myocytes. Furthermore, EMEPO increased NOS1^−/− myocyte basal contraction (Ca²⁺ transients, Fluo-4AM; shortening, video-edge detection), the force-frequency response and the contractile response to β-adrenergic stimulation. EMEPO had no effect in wildtype myocytes. EMEPO also increased ryanodine receptor activity (sarcoplasmic reticulum Ca²⁺ leak/load relationship) and phospholamban Serine16 phosphorylation (Western blot). We also repeated our functional experiments in a canine post-myocardial infarction model and observed similar results to those seen in NOS1^−/− myocytes. In conclusion, EMEPO improved contractile function in myocytes experiencing an imbalance of their nitroso-redox levels. The concurrent restoration of NO and O₂^.− levels may have therapeutic potential in the treatment of various cardiomyopathies.