BS55 Inhibition of RHO KINASE2 is associated with vasorelaxation but not reduction in myocardial contractility

Introduction

The benefits of non-selective ROCK1/2 inhibitors in cardioprotection are well-known, especially in the treatment of hypertension and vasospastic angina. Fasudil, (a commonly used ROCK1/2 inhibitor) reduces infarct size and no re-flow following ischaemia/reperfusion, however it induces hypotension, which is undesirable during acute myocardial infarction (MI). ROCK inhibitors are novel agents, as they induce vasodilation by acting directly on vascular smooth muscle cells (VSMC), and myosin light chain phosphatase (MLCP), to prevent phosphorylation of myosin light chain kinase (MLC2). This is beneficial during lethal reperfusion injury when an increase in coronary vascular tone may contribute towards microvascular damage and obstruction (MVO). The ideal ROCKi for coronary circulation protection, would be a potent vasodilator, but would not compromise blood pressure or myocardial contractility.

Aims

We investigated i) The vasodilatory properties of Chroman 1 (Ch1) (a selective ROCK 2 inhibitor), relative to Fasudil, to ascertain whether this agent could demonstrate effective vasorelaxation and ii) Performed a dose response experiment using a rat model in-vivo, to test the effects of Ch1 on myocardial contractility and left ventricular ejection fraction (LVEF%), mean arterial pressure (MAP) and heart rate.

Methods

Thoracic aorta of male SD rats was dissected and 3mm segments were suspended into a tissue bath. These vascular rings were pre-constricted with 1µM PE and treated with [10-12]-[10-5]mM Ch1, or [10-9]-[10-5]mM Fasudil, or DMSO control. Separately, male SD rats were anaesthetised with isoflurane, intubated and ventilated. LVEF% was measured in-vivo using echocardiography in a closed chest rat model, following the addition of Ch1 (30-300µg/kg) administered i.p, at 15-minute intervals. Blood pressure and heart rate were recorded at baseline and throughout.

Results

Ch1 is a potent vasodilator of aortic rings compared to Fasudil, (EC50 Ch1 9.6x10-8 vs EC50 Fasudil 9.0 x10-6) , and to DMSO control, (n=6) (figure 1). In-vivo, echocardiography demonstrated no significant difference in baseline LVEF% between groups, (Ch1 81.4% vs vehicle 82.6%, p>0.05, n=5) nor after cumulative addition of Ch1 (Ch1 76.6% vs vehicle 81.0 %, p=0.97, n=5). At doses of 300µg/kg, mean arterial pressure (MAP) was reduced in the Ch1 treatment group, (76 vs 92mmHg, p=0.02, n=5) however, average MAP did not fall below 70mmHg and normalised by the end of the period. There were no significant differences in mean HR (BPM) between groups.

Conclusion

ROCK2 inhibition is associated with significant VSMC relaxation, but not a reduction in LVEF% or myocardial contractility. This suggests that the contractile effects of ROCK2 are vascular specific. Ch1 may be a suitable drug for further studies of I/R and MVO.

Conflict of Interest

n/a