Clazosentan Affects Temporal Profile of Endothelin-A Expression in Macro- and Microcirculation after Subarachnoid Hemorrhage.

Subarachnoid hemorrhage is a life-threatening cerebrovascular event, and cerebral vasospasm remains a major cause of poor neurological outcomes. Clazosentan, an endothelin-A receptor antagonist, has been recently approved in Japan to reduce post-subarachnoid hemorrhage vasospasm; however, recurrent vasospasm after cessation of therapy has occasionally been reported, which underlying mechanisms remain unclear. Moreover, endothelin-A receptor is also expressed on pericytes; however, the effects of clazosentan on microvascular endothelin-A receptor remain unexplored. In this study, we employed a rat subarachnoid hemorrhage model to investigate the temporal dynamics of vasospasm and endothelin-A receptor expression in both large arteries and microvessels, and to evaluate the effects of clazosentan administration. Sprague-Dawley rats were assigned to naïve controls, subarachnoid hemorrhage with saline, or subarachnoid hemorrhage with continuous clazosentan administration for 7 days via osmotic pumps. Vasospasm was assessed by arterial wall thickness, and endothelin-A receptor expression was quantified using immunohistochemistry and immunofluorescence, including staining with α-SMA, CD31, and PDGF-β. Clazosentan significantly attenuated vasospasm in the middle and anterior cerebral arteries, and recurrent vasospasm was observed 3 days after cessation of clazosentan, coinciding with sustained upregulation of endothelin-A receptor in these vessels. In microvessels, pericyte density transiently decreased, peaking at a nadir on day 3 post-subarachnoid hemorrhage, while endothelin-A receptor expression on pericytes was highest at the same time point, and further elevated by clazosentan treatment. These findings indicate that clazosentan induces endothelin-A receptor upregulation in both macro- and microcirculation, potentially contributing to recurrent vasospasm after treatment, and highlight the critical role of pericytes in post-subarachnoid hemorrhage vascular regulation.