Sphingomyelinase and ceramide analogs induce vasoconstriction and leukocyte–endothelial interactions in cerebral venules in the intact rat brain: Insight into mechanisms and possible relation to brain injury and stroke

Abstract

This study was designed to test the hypothesis that the sphingomyelin-ceramide signaling pathway may be important in proinflammatory-like responses in the intact brain. Effects of neutral sphingomyelinase (N-SMase), ceramide analogs, phosphorylcholine and ceramide metabolites were studied on rat brain cerebral (cortical) venule lumen sizes, leukocyte rolling, velocity and endothelial cell wall adhesion, microvessel permeability, microvessel rupture and focal hemorrhages using in vivo high resolution TV microscopy. Perivascular and close intra-arterial administration of N-SMase, C2-, C8-, and C16-ceramide, but not either phosphorylcholine, C6-ceramide, nervonic (C24:1) ceramide, lignoceric (C24:0) ceramide, C8-ceramide-1-phosphate, glucosylceramide or 1-0-acylceramide, resulted in potent, concentration-dependent constriction (and spasm) of cortical venules, followed by increased leukocyte rolling, decreased leukocyte velocities, increased leukocyte–endothelial wall adhesion, increased venular wall permeability, postcapillary venule rupture and, often, micro-hemorrhaging at high concentrations; angiotensin II, serotonin and PGF2α didn’t demonstrate these characteristics. Pretreatment with either one of three different antioxidants, including inhibitors of NF-κB activation, or two different Ca2+ channel blockers either prevented or attenuated the adverse venular effects of N-SMase and the ceramides. Likewise, pretreatment with either a PKCα–β antagonist or a MAP kinase antagonist also attenuated the adverse venular effects. These results suggest that N-SMase and several ceramides can result in potent venular cerebrovasospasm, leukocyte–endothelial chemoattraction, and microvessel wall permeability changes in the intact rat brain. These proinflammatory-like actions suggest that N-SMase and ceramides could produce brain-vascular damage by reperfusion injury triggering lipid peroxidation, release of reactive oxygen species and activation of diverse signaling pathways: PKCα–β isozymes, MAP kinase and NF-κB.