Impact of Heme and Heme Degradation Products on Vascular Diameter in Mouse Visual Cortex

Abstract

BackgroundDelayed cerebral vasospasm is the most common cause of mortality and severe neurological impairment in patients who survive subarachnoid hemorrhage. Despite improvements in the field of diagnostic imaging, options for prevention and medical treatment—primarily with the calcium channel antagonist nimodipine or hemodynamic manipulations—are insufficient. Previous studies have suggested that heme and bilirubin oxidation end products, originating from degraded hemoglobin around ruptured blood vessels, are involved in the development of vasospasm by inhibiting large conductance BKCa potassium channels in vascular smooth muscle cells. In this study, we identify individual heme degradation products regulating arteriolar diameter in dependence of BKCa channel activity.Methods and ResultsUsing differential interference contrast video microscopy in acute brain slices, we determined diameter changes of intracerebral arterioles in mouse visual cortex. In preconstricted vessels, the specific BKCa channel blockers paxilline and iberiotoxin as well as iron‐containing hemin caused vasoconstriction. In addition, the bilirubin oxidation end product Z‐BOX A showed a stronger vasoconstrictive potency than its regio‐isomer Z‐BOX B. Importantly, Z‐BOX A had the same vasoconstrictive effect, independent of its origin from oxidative degradation or chemical synthesis. Finally, in slices of Slo1‐deficient knockout mice, paxilline and Z‐BOX A remained ineffective in changing arteriole diameter.ConclusionsWe identified individual components of the oxidative bilirubin degradation that led to vasoconstriction of cerebral arterioles. The vasoconstrictive effect of Z‐BOX A and Z‐BOX B was mediated by BKCa channel activity that might represent a signaling pathway in the occurrence of delayed cerebral vasospasm in subarachnoid hemorrhage patients.

Mitochondrial uncoupler carbonyl cyanide m‐chlorophenylhydrazone induces vasorelaxation without involving KATP channel activation in smooth muscle cells of arteries

“…Moreover, we further used the BKCa channel blocker paxilline and found that, regardless of whether it was used before or after CCCP treatment, it had no significant effect on CCCP-induced vasorelaxation in endothelium-denuded rat mensenteric arteries (data not shown). Paxilline at 1 μM has been shown to inhibit vasodilatation in arterioles (Joerk et al, 2014), but we observed no effect on CCCP-induced vasorelaxation even with 5 μM, indicating that the BKCa channel is not involved in the CCCP-induced vasorelaxation.…”

Brain iron overload following intracranial haemorrhage

“…Such vasoconstriction is counteracted by nitric oxide (NO) that inhibits ET-1 release, resulting in vasodilation 156. Iron-containing haem has been shown to cause vasoconstriction 157. Indeed, reductions in free-iron levels ameliorate SAH-induced vasosconstriction 158.…”

Simultaneous determination of the bilirubin oxidation end products Z-BOX A and Z-BOX B in human serum using liquid chromatography coupled to tandem mass spectrometry

“…Bilirubin oxidation end products (BOXes) increasingly attract attention because they are suspected to play an important role in delayed cerebral vasospasm after subarachnoid hemorrhage [1][2][3]. In the course of blood clotting and hemolysis large amounts of hemoglobin are liberated.…”