PPARs (peroxisome-proliferator-activated receptors) are ligand-activated transcriptional factor receptors belonging to the so-called nuclear receptor family. The three isoforms of PPAR (alpha, beta/delta and gamma) are involved in regulation of lipid or glucose metabolism. Beyond metabolic effects, PPARalpha and PPARgamma activation also induces anti-inflammatory and antioxidant effects in different organs. These pleiotropic effects explain why PPARalpha or PPARgamma activation has been tested as a neuroprotective agent in cerebral ischaemia. Fibrates and other non-fibrate PPARalpha activators as well as thiazolidinediones and other non-thiazolidinedione PPARgamma agonists have been demonstrated to induce both preventive and acute neuroprotection. This neuroprotective effect involves both cerebral and vascular mechanisms. PPAR activation induces a decrease in neuronal death by prevention of oxidative or inflammatory mechanisms implicated in cerebral injury. PPARalpha activation induces also a vascular protection as demonstrated by prevention of post-ischaemic endothelial dysfunction. These vascular effects result from a decrease in oxidative stress and prevention of adhesion proteins, such as vascular cell adhesion molecule 1 or intercellular cell-adhesion molecule 1. Moreover, PPAR activation might be able to induce neurorepair and endothelium regeneration. Beyond neuroprotection in cerebral ischaemia, PPARs are also pertinent pharmacological targets to induce neuroprotection in chronic neurodegenerative diseases.

BackgroundGranulocyte colony-stimulating factor (G-CSF) is a pharmacologic agent inducing neutrophil mobilization and a new candidate for neuroprotection and neuroregeneration in stroke. Its effects when used in combination with tissue plasminogen activator (tPA) were explored during the acute phase of ischemic stroke.MethodsWe used a middle cerebral artery occlusion (MCAO) model of cerebral ischemia, associated with treatment with tPA, in male spontaneously hypertensive rats (SHR). Granulocyte colony-stimulating factor (G-CSF; 60 μg/kg) was injected just before tPA. Neutrophil response in peripheral blood and in the infarct area was quantified in parallel to the infarct volume. Protease matrix metallopeptidase 9 (MMP-9) release from circulating neutrophils was analyzed by immunochemistry and zymography. Vascular reactivity and hemorrhagic volume in the infarct area was also assessed.ResultsTwenty four hours after ischemia and tPA, G-CSF administration induced a significant increase of neutrophils in peripheral blood (P <0.05). At 72 hours post-ischemia, G-CSF was significantly associated with an increased risk of hemorrhage in the infarct area (2.5 times more likely; P <0.05) and significant cerebral endothelium-dependent dysfunction. Ex vivo, an increased MMP-9 release from neutrophils after tPA administration correlated to the increased hemorrhagic risk (P <0.05). In parallel, G-CSF administration was associated with a decreased neutrophil infiltration in the infarct area (-50%; P <0.05), with a concomitant significant neuroprotective effect (infarct volume: -40%; P <0.05).ConclusionsWe demonstrate that G-CSF potentiates the risk of hemorrhage in experimental stroke when used in combination with tPA by inducing neutrophilia. This effect is concomitant to an increased MMP-9 release from peripheral neutrophils induced by the tPA treatment. These results highlight the potential hemorrhagic risk of associating G-CSF to thrombolysis during the acute phase of stroke.

Background and Purpose-In a model of mechanical focal ischemia, we investigated the involvement of thrombolysis products (TLP) in recombinant tissue plasminogen activator (rtPA)-induced intracerebral complications and the effects on infarct volume and postischemic endothelial function. Methods-Hemorrhage incidence and severity were evaluated by histomorphometric analysis in male spontaneously hypertensive rats (SHR) subjected to 60-minute intraluminal middle cerebral artery (MCA) occlusion and receiving intravenously 5 hours later either saline, rtPA (3, 10, or 30 mg/kg), or rtPA (10 mg/kg) associated with TLP (rtPAϩTLP). In addition, MCA reactivity was assessed in rtPA-or rtPAϩTLP-treated SHR versus control Wistar-Kyoto rats or SHR. Results-No hemorrhage was observed visually in SHR receiving saline. In contrast, rtPA administration induced hemorrhagic complications in infarcted areas in a dose-independent manner. Administration of rtPAϩTLP solution, containing a high concentration of plasmin, did not affect hemorrhage incidence but significantly increased hemorrhage severity (8.8Ϯ2.3 petechiae versus 3.0Ϯ1.0 petechiae in rtPA group; PϽ0.001). This increased severity was associated with a significant increase of both infarct volume (182Ϯ10 versus 144Ϯ15 mm 3 in rtPA group; PϽ0.01) and postischemic impairment of MCA endothelium-dependent relaxation (9Ϯ0.5% versus 13Ϯ1% in rtPA group; PϽ0.05). Key Words: hemorrhage Ⅲ ischemia, focal Ⅲ plasmin Ⅲ thrombolysis Ⅲ tissue plasminogen activator T hrombolytic therapy with recombinant tissue plasminogen activator (rtPA) has demonstrated improvement in clinical outcome in acute ischemic stroke. 1,2 However, the threat of intracerebral hemorrhage (ICH) is an important barrier to widespread administration of thrombolytic agents. While many factors, such as elevated blood pressure, diabetes, age, and rtPA administration time, contribute to the occurrence of ICH, the underlying mechanisms remain elusive. [3][4][5] ICH are preferentially located in the infarct area, suggesting a role of ischemia per se. 6,7 In response to ischemic and inflammatory stimuli, vascular modifications may also be involved in ICH pathophysiology. 8 In particular, endothelium-dependent relaxation, a marker of ischemia-induced impairment of cerebral vasculature, 9,10 is worsened in vitro by the application of rtPA. 11 It remains unknown whether rtPA directly induces ICH or if the interaction between rtPA and thrombus, via the resulting thrombolysis products (TLP), is involved. Existence of rtPA-induced ICH in thromboembolic models has been well established, 7,12-15 whereas it remains more uncertain in mechanical models of ischemia. 6,16 The difference between the 2 models suggests that thrombus may contribute to the occurrence of ICH. To test this hypothesis, we compared the effects of rtPA or rtPA-induced TLP in a model of mechanical middle cerebral artery (MCA) occlusion on ICH incidence and severity. We also studied infarct volume and MCA endothelial function to investigate the mechanism of ICH occur...

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.xdependent 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.