Selective ROCK2 inhibition reduces microvascular obstruction but does not reduce myocardial infarction after ischaemia and reperfusion

Myocardial ischaemia/reperfusion (I/R) injury causes infarction, microvascular obstruction (MVO), and haemorrhage. MVO, often driven by vasospasm, lacks effective therapy. The non-selective ROCK inhibitor fasudil, used for cerebral vasospasm, limits infarct size after myocardial I/R, but the roles of individual ROCK isoforms in limiting infarction and MVO remain unclear. To determine the contribution of ROCK2 to myocardial and microvascular obstruction and to assess the vasodilatory potential of ROCK2 inhibition. ROCK1/2 expression was analysed in rat hearts by RNAscope. Vascular myography assessed arterial responses to ROCK inhibitors. Rats underwent 30 min coronary occlusion and 180 min reperfusion, with ROCK2 inhibitor KD025 (100 mg/kg i.p.) or vehicle administered before reperfusion. Infarct size (%AAR) and MVO (%AAR) were quantified by TTC and Thioflavin S staining, respectively. Infarct size was also compared in WT and ROCK2 + / − mice. ROCK2 mRNA was more highly expressed than ROCK1 in both myocardium and coronary vasculature. The dual ROCK1/2 inhibitor, fasudil (10 mg/kg), reduced infarct size (34.5 ± 5.7 vs 55.8 ± 4.7%, P = 0.02, n = 6), whereas the ROCK2-selective KD025 (100 mg/kg) had no effect (43.7 ± 5.5 vs 48.3 ± 4.9%, P = 0.87, n = 8) and also showed no vasodilation ex vivo. ROCK2 + / − mice were similar to WT. However, KD025 reduced MVO% in rats (21.8 ± 2.5 vs 32.2 ± 1.8%, P = 0.04, n = 8), as did 3 mg/kg fasudil (19.2 ± 4.1 vs 32.2 ± 1.8%, P = 0.01, n = 6). Dual ROCK1/2 inhibition protects myocardium from I/R injury, whereas selective ROCK2 inhibition or deficiency does not, implicating ROCK1 in infarct limitation. In contrast, ROCK2 inhibition reduced MVO, identifying ROCK2 as a potential microvascular target. • ROCK2 is more highly expressed than ROCK1 in the heart and coronary vasculature. • Fasudil, a dual ROCK1/2 inhibitor, reduces infarct size in rats subject to ischaemia/reperfusion. • The ROCK2-selective KD025 reduces microvascular obstruction, but does not reduce infarct size. • Infarct size in ROCK2 heterozygous mice is similar to WT.