Endothelial dysfunction in cerebral vessels following carotid artery infusion of phorbol ester in rabbits: the role of polymorphonuclear leukocytes

epsilonPKC confers acute tolerance to cerebral ischemic reperfusion injury

In response to mild ischemic stress, the brain elicits endogenous survival mechanisms to protect cells against a subsequent lethal ischemic stress, referred to as ischemic tolerance. The molecular signals that mediate this protection are thought to involve the expression and activation of multiple kinases, including protein kinase C (PKC). Here we demonstrate that epsilonPKC mediates cerebral ischemic tolerance in vivo. Systemic delivery of psiepsilonRACK, an epsilonPKC-selective peptide activator, confers neuroprotection against a subsequent cerebral ischemic event when delivered immediately prior to stroke. In addition, activation of epsilonPKC by psiepsilonRACK treatment decreases vascular tone in vivo, as demonstrated by a reduction in microvascular cerebral blood flow. Here we demonstrate the role of acute and transient epsilonPKC in early cerebral tolerance in vivo and suggest that extra-parenchymal mechanisms, such as vasoconstriction, may contribute to the conferred protection.

DeltaPKC mediates microcerebrovascular dysfunction in acute ischemia and in chronic hypertensive stress in vivo

Maintaining cerebrovascular function is a priority for reducing damage following acute ischemic events such as stroke, and under chronic stress in diseases such as hypertension. Ischemic episodes lead to endothelial cell damage, deleterious inflammatory responses, and altered neuronal and astrocyte regulation of vascular function. These, in turn, can lead to impaired cerebral blood flow and compromised blood-brain barrier function, promoting microvascular collapse, edema, hemorrhagic transformation, and worsened neurological recovery. Multiple studies demonstrate that protein kinase C (PKC), a widely expressed serine/threonine kinase, is involved in mediating arterial tone and microvascular function. However, there is no clear understanding about the role of individual PKC isozymes. We show that intraperitoneal injection of deltaV1-1-TAT(47-57) (0.2 mg/kg in 1 mL), an isozyme-specific peptide inhibitor of deltaPKC, improved microvascular pathology, increased the number of patent microvessels by 92% compared to control-treated animals, and increased cerebral blood flow by 26% following acute focal ischemia induced by middle cerebral artery occlusion in normotensive rats. In addition, acute delivery of deltaV1-1-TAT(47-57) in hypertensive Dahl rats increased cerebral blood flow by 12%, and sustained delivery deltaV1-1-TAT(47-57) (5 uL/h, 1 mM), reduced infarct size by 25% following an acute stroke induced by MCA occlusion for 90 min. Together, these findings demonstrate that deltaPKC is an important therapeutic target for protection of microvascular structure and function under both acute and chronic conditions of cerebrovascular stress.

Pharmacological neutropenia prevents endothelial dysfunction but not smooth muscle functions impairment induced by middle cerebral artery occlusion

1. The polymorphonuclear neutrophils (PMN) activation and mobilization observed in acute cerebral infarction contribute to the brain tissue damage, but PMN could also be involved in postischemic functional injury of ischemied blood vessel. 2. This study was undertaken to investigate whether pharmacological neutropenia could modify the postischemic endothelial dysfunction in comparison to smooth muscle whose impairment is likely more related to reperfusion and oxidative stress. 3. A cerebral ischemia-reperfusion by endoluminal occlusion of right middle cerebral artery (MCA) was performed 4 days after intravenous administration of vinblastine or 12 h after RP-3 anti-rat neutrophils monoclonal antibody (mAb RP-3) injection into the peritoneal cavity, on male Wistar rats with 1-h ischemia then followed by 24-h reperfusion period. Brain infarct volume was measured by histomorphometric analysis and vascular endothelial and smooth muscle reactivity of MCA was analysed using Halpern myograph. 4. Neutropenia induced a neuroprotective effect as demonstrated by a significant decrease of brain infarct size. In parallel to neuroprotection, neutropenia prevented postischemic impairment of endothelium-dependent relaxing response to acetylcholine. In contrast, smooth muscle functional alterations were not prevented by neutropenia. Ischemia-reperfusion-induced myogenic tone impairment remained unchanged in vinblastine and mAb RP-3-treated rats. Postischemic Kir2.x-dependent relaxation impairment was not prevented in neutropenic conditions. The fully relaxation of smooth muscle response to sodium nitroprusside was similar in all groups. 5. Our results evidenced the dissociate prevention of pharmacologically induced neutropenia on postischemic vascular endothelial and smooth muscle impairment. The selective endothelial protection by neutropenia is parallel to a neuroprotective effect suggesting a possible relationship between the two phenomena.

Cerebral ischemia and reperfusion: the pathophysiologic concept as a basis for clinical therapy

The ischemic penumbra has been documented in the laboratory animal as severely hypoperfused, nonfunctional, but still viable brain tissue surrounding the irreversibly damaged ischemic core. Saving the penumbra is the main target of acute stroke therapy, and is the theoretical basis behind the reperfusion concept. In experimental focal ischemia, early reperfusion has been reported to both prevent infarct growth and aggravate edema formation and hemorrhage, depending on the severity and duration of prior ischemia and the efficiency of reperfusion, whereas neuronal damage with or without enlarged infarction also may result from reperfusion (so-called reperfusion injury). Activated neutrophils contribute to vascular reperfusion damage, yet posthypoxic cellular injury occurs in the absence of inflammatory species. Protein synthesis inhibition occurs in neurons during reperfusion after ischemia, underlying the role that these pathways play in prosurvival and proapoptotic processes that may be differentially expressed in vulnerable and resistant regions of the reperfused brain tissue. Ischemia-induced decreases in the mitochondrial capacity for respiratory activity probably contribute to the ongoing impairment of energy metabolism during reperfusion and possibly also the magnitude of changes seen during ischemia. From these experimental data, the concept of single-drug intervention cannot be effective. Further experimental research is needed, especially of the study of biochemical markers of the injury process to establish the role of several drugs.

Polymorphonuclear leukocyte activation induces cerebral hypoperfusion in rats in the absence of previous ischemia-reperfusion damage

We determined if activation of circulating neutrophils could influence local cerebral blood flow (lCBF) and cerebrovascular reactivity without previous ischemic endothelial activation. After intracarotid infusion of phorbol myristate acetate (PMA, twice in 30 min), Laser-Doppler measurements of lCBF in the parietal cortex of anesthetised rats showed a fall of 34% (P<0.05) at 30 min, but not in the vehicle group nor the group predepleted in polymorphonuclear leukocytes (PMNLs). Blood gases or arterial pressure did not change significantly in any group. The PMNL count fell by 78% at 30 min and reactivity to systemic hypercapnia by 58% at 30-60 min post infusion in the PMA group. These results show that activated PMNLs reduce lCBF and vasoreactivity in the absence of previous cerebral ischemia.

Role of endothelium in hyperemia during cortical spreading depression (CSD) in the rat

The purpose of this study was to examine whether endothelium-mediated dilation is responsible for the cortical hyperemia that occurs during cortical spreading depression (CSD) in rats using three different approaches. The first approach taken was the acute pharmacological inhibition of the predominant endothelium-centered dilator systems, using indomethacin, a cyclooxygenase inhibitor, Nomega-nitro-L-arginine methyl ester (L-NAME), a nitric oxide synthase (NOS) inhibitor, and miconazole, a cytochrome P-450 epoxygenase inhibitor. The second approach used was the acute general pharmacological impairment of endothelial function by the intravascular administration of phorbol 12, 13-dibutyrate (PDBu). The third approach taken was the chronic impairment of endothelium-dependent dilator responses by diet in insulin resistant (IR) rats. Cerebral blood flow (CBF) was measured using laser Doppler flowmetry. CSD was elicited by the topical application of potassium chloride. Pharmacological inhibition of endothelium-dependent dilator factors did not affect CSD. For example, with 20 mg/kg L-NAME, CBF peak of the first series of CSDs was 377 +/- 67% of baseline CBF. After drug administration, CBF peaks of the second and the third series of CSDs were 451 +/- 67% and 390 +/- 69% (n=5, P=n.s.), respectively. Control and IR animals and those treated with indomethacin, miconazole and PDBu showed similar results. We also calculated the area under the CBF curve to fully represent the extent of hyperemia during CSD. However, there were no significant differences in the CBF area with any treatment compared to control animals. Thus, our results provide strong evidence that endothelium-mediated mechanisms have minimal effects on the CSD-associated hyperemia.

Heterogeneity affecting outcome from acute stroke therapy: making reperfusion worse

BACKGROUND

Stroke patients are heterogeneous not only with respect to etiology but also in terms of preexisting clinical conditions. Approximately one fifth of patients with acute stroke are hyperglycemic and/or have had a recent infectious or inflammatory condition. Summary of Review-- Experimental research indicates that these factors can alter and accelerate the evolution of stroke and reperfusion injury, although these effects are complex and some may have a favorable impact. Both conditions involve activation of inflammatory and reactive oxygen mechanisms. In addition, hyperglycemia has concomitant deleterious vascular and metabolic effects that worsen infarct size and encourage hemorrhagic transformation in reperfusion models. Clinical data are less extensive but in general support an adverse impact on outcome.

CONCLUSIONS

After examining these data in detail, we concluded that the presence of these clinical conditions could assist in identification of those at increased risk for complications of reperfusion therapy. Furthermore, consideration of these factors may provide a rational basis for combination therapy and improve the clinical relevance of experimental stroke models.

[Vascular wall modifications after disruption of the circulation leading to cerebral ischemia]

This article describes the modifications occurring in cerebral vessels during the first 24 h after an ischaemic event followed by reperfusion. The phases of occlusion, no-reflow, post-ischaemic hyperaemia and delayed hypoperfusion are dealt with in terms of haemodynamic, morphological, functional and biochemical data, available especially from animal studies. The interactions of platelets and leucocytes with the endothelium and the major role of reactive oxygen species in lesioning the microvasculature, including the blood-brain barrier, are emphasized.

Regulation of the cerebral circulation: role of endothelium and potassium channels

Several new concepts have emerged in relation to mechanisms that contribute to regulation of the cerebral circulation. This review focuses on some physiological mechanisms of cerebral vasodilatation and alteration of these mechanisms by disease states. One mechanism involves release of vasoactive factors by the endothelium that affect underlying vascular muscle. These factors include endothelium-derived relaxing factor (nitric oxide), prostacyclin, and endothelium-derived hyperpolarizing factor(s). The normal vasodilator influence of endothelium is impaired by some disease states. Under pathophysiological conditions, endothelium may produce potent contracting factors such as endothelin. Another major mechanism of regulation of cerebral vascular tone relates to potassium channels. Activation of potassium channels appears to mediate relaxation of cerebral vessels to diverse stimuli including receptor-mediated agonists, intracellular second messenger, and hypoxia. Endothelial- and potassium channel-based mechanisms are related because several endothelium-derived factors produce relaxation by activation of potassium channels. The influence of potassium channels may be altered by disease states including chronic hypertension, subarachnoid hemorrhage, and diabetes.