The selective Rho Kinase 2 inhibitor Chroman-1, is a potent vasodilator but does not compromise left ventricular function in-vivo

Abstract Background In the field of cardioprotection, focus is turning to limiting microvascular obstruction (MVO) post myocardial infarction. The development of MVO carries a poor prognosis, which is independent of infarct burden [1]. Commonly used vasodilators in the treatment of MVO e.g., Ca2+ blockers, beta-blockers can induce negatively inotropic effects. This is a serious problem as hypotension and shock during acute MI are harmful. Rho kinase (ROCK) inhibitors induce vasodilation by inhibiting the phosphorylation of myosin light chain kinase (MLC2) in vascular smooth muscle (VSMC) [2]. ROCK1/2 inhibitors are known to cause transient negative inotropic effects [3]. However, the potential side-effects of the selective ROCK2i, Chroman-1 (Ch1) are unknown. Purpose We aimed to i) Confirm the expression of ROCK2 mRNA in aorta and coronary vasculature, ii) To investigate the vasodilatory properties of Ch1 iii) To confirm that Ch1 does not acutely impair left ventricular ejection fraction (LVEF%) and blood pressure in-vivo. Methods RNA scope in-situ hybridisation was performed with a fluorescent, multiplex assay for ROCK1/2 & VSMC mRNA in whole hearts, coronary vasculature and aorta from male SD rats. Thoracic aorta was dissected and 3mm segments suspended into a tissue bath. Vascular rings were constricted with 1µM PE and treated with [10-12]-[10-5]mM Ch1. In a separate set of in-vivo experiments, male SD rats 250-300g were anaesthetised with isoflurane, intubated and ventilated. LVEF% was measured in a closed chest model, following the addition of Ch1 (30-300µg/kg) or DMSO vehicle, administered i.p at 15-minute intervals. Mean arterial pressure (MAP, mmHg) and heart rate (BPM) were measured throughout. Results ROCK2 mRNA was localised to myocardium, aorta and coronary circulation VSMC. Figure 1 demonstrates that Ch1 induced dose dependent vasodilation of PE constricted aortic rings vs control (EC50 Ch1 95% CI [5.1e-008, 2.2e-007] n=6). In-vivo, Ch1 at all doses (30-300µg/kg) did not significantly affect LVEF% (p>0.05, n=5) nor average MAP at doses 30-100µg/kg (p>0.05, n=5). At the highest dose, i.e 300µg/kg, Ch1 decreased average MAP (mmHg) compared to control +/-SEM (76+/-7.1 vs 92+/-2.8, p=0.02, n=5), but not below 70mmHg threshold. Ch1 did not significantly affect mean heart rate at any dose (p>0.05, n=5). Conclusion The selective ROCK2 inhibitor Ch1, induces potent arterial vasodilation, without compromising LVEF% or haemodynamics. It is therefore, a