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, C(2)-, C(8)-, and
C(16)-ceramide, but not either
phosphorylcholine,
C(6)-ceramide, nervonic (C(24):1)
ceramide, lignoceric (C(24):0)
ceramide, C(8)-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
PGF(2alpha) didn't demonstrate these characteristics. Pretreatment with either one of three different
antioxidants, including inhibitors of
NF-kappaB activation, or two different Ca(2+) channel blockers either prevented or attenuated the adverse venular effects of N-SMase and the
ceramides. Likewise, pretreatment with either a PKCalpha-beta 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: PKCalpha-beta
isozymes, MAP
kinase and
NF-kappaB.