Role of Akt signaling pathway in delayed cerebral vasospasm after subarachnoid hemorrhage in rats

The calcimimetic R-568 attenuates subarachnoid hemorrhage-induced vasospasm through PI3K/Akt/eNOS signaling pathway in the rat model

Cerebral vasospasm (CVS) causes mortality and morbidity in patients after subarachnoid hemorrhage (SAH). The mechanism and adequate treatment of CVS are still elusive. R-568 is a calcimimetic agent known to exert a vasodilating effect. However, there is no report on its vasodilator effect against SAH-induced vasospasm. In the present study, we investigated the therapeutic effect of R-568 on the SAH-induced CVS model in rats. Seventy-two adult male Sprague-Dawley rats were divided into 8 groups: sham surgery; SAH only; SAH + Vehicle, SAH + R-568; SAH + R-568 + Wortmannin (the PI3K inhibitor); SAH + Wortmannin; SAH + R-568 + Calhex-231 (a calcilytic agent); SAH + Calhex-231. SAH was induced by blood (0.3 mL) given by intracisternal injection. R-568 (20 µM) was administered intracisternal immediately prior to experimental SAH. Basilar arteries (BAs) were obtained to evaluate PI3K/Akt/eNOS pathway (immunoblotting) and morphological changes 48 h after SAH. Perimeters of BAs were decreased by 24.1% in the SAH group compared to the control group and the wall thickness was increased by 75.3%. With R-568 treatment, those percentages were 9.6% and 29.6%, respectively, indicating that vasospasm was considerably improved when compared with the SAH group (P < 0.001 in both). While p-PI3K/PI3K and p-Akt/Akt ratio and eNOS protein expression were markedly decreased in the SAH rats, treatment with R-568 resulted in a significant increase in these levels. The beneficial effects of R-568 were partially blocked in the presence of Calhex-231 and completely blocked in the presence of Wortmannin. Herein, we found that treatment with R-568 would attenuate SAH-induced CVS through the PI3K/Akt/eNOS pathway and demonstrate therapeutic promise in CVS treatment following SAH.

The effect of pentoxifylline on cerebral vasospasm following experimental subarachnoid hemorrhage

OBJECTS

Cerebral vasospasm is an important event that occurs following subarachnoid hemorage which has significant mortality and morbidity. The goal in this study was to investigate the effect of pentoxifylline on vasospasm in an experimental subarachnoid hemorrhage model.

METHODS

In this study, 20 male New Zeland White rabbits weighing 3000-3500 g were assigned randomly to four groups. Animals in group 1 served as controls. Animals in group two received only intravenous pentoxifylline injection 3 times in 12 h intervals. In group 3, SAH was induced and no injection was given. Animals in group 4 received intravenous pentoxifylline (6 mg/kg) injections 3 times at 12^th, 24^th and 36^th hours after subarachnoid hemorrhage induction. All animals were sacrificed and basilar arteries were removed at 48th hour. Basilar artery vessel diameters, wall thicknesses and luminal section areas were measured with Spot for Windows version 4.1. Statistical analysis was performed using ANOVA and Kruskall-Wallis tests.

RESULTS

Mean basilar artery luminal section areas and luminal diameters in group 4 were significantly higher compared to group 3 (p < 0.05). Basilar artery wall thicknesses and were found to be higher in group 3 than in other groups and this was also statistically significant (p < 0.05).

CONCLUSION

Our study demonstrated that intravenous administration of pentoxifylline significantly decreases vasospasm after subarachnoid hemorrhage.

Therapeutically Targeting Platelet-Derived Growth Factor-Mediated Signaling Underlying the Pathogenesis of Subarachnoid Hemorrhage-Related Vasospasm

INTRODUCTION

Vasospasm accounts for a large fraction of the morbidity and mortality burden in patients sustaining subarachnoid hemorrhage (SAH). Platelet-derived growth factor (PDGF)-β levels rise following SAH and correlate with incidence and severity of vasospasm.

METHODS

The literature was reviewed for studies investigating the role of PDGF in the pathogenesis of SAH-related vasospasm and efficacy of pharmacological interventions targeting the PDGF pathway in ameliorating the same and improving clinical outcomes.

RESULTS

Release of blood under high pressure into the subarachnoid space activates the complement cascade, which results in release of PDGF. Abluminal contact of blood with cerebral vessels increases their contractile response to PDGF-β and thrombin, with the latter upregulating PDGF-β receptors and augmenting effects of PDGF-β. PDGF-β figures prominently in the early and late phases of post-SAH vasospasm. PDGF-β binding to the PDGF receptor-β results in receptor tyrosine kinase domain activation and consequent stimulation of intracellular signaling pathways, including p38 mitogen-activated protein kinase, phosphatidylinositol-3-kinase, Rho-associated protein kinase, and extracellular regulated kinase 1 and 2. Consequent increases in intracellular calcium and increased expression of genes mediating cellular growth and proliferation mediate PDGF-induced augmentation of vascular smooth muscle cell contractility, hypertrophy, and proliferation.

CONCLUSION

Treatments with statins, serine protease inhibitors, and small molecular pathway inhibitors have demonstrated varying degrees of efficacy in prevention of cerebral vasospasm, which is improved with earlier institution.

Recombinant Osteopontin Stabilizes Smooth Muscle Cell Phenotype via Integrin Receptor/Integrin-Linked Kinase/Rac-1 Pathway After Subarachnoid Hemorrhage in Rats

BACKGROUND AND PURPOSE

Recombinant osteopontin (rOPN) has been reported to be neuroprotective in stroke animal models. The purpose of this study is to investigate a potential role and mechanism of nasal administration of rOPN on preserving the vascular smooth muscle phenotype in early brain injury after subarachnoid hemorrhage (SAH).

METHODS

One hundred and ninety-two male adult Sprague-Dawley rats were used. The SAH model was induced by endovascular perforation. Integrin-linked kinase small interfering RNA was intracerebroventricularly injected 48 hours before SAH. The integrin receptor antagonist fibronectin-derived peptide Gly-Arg-Gly-Asp-Ser-Pro (GRGDSP), focal adhesion kinase inhibitor Fib-14, and Rac-1 inhibitor NSC23766 were administered 1 hour before SAH induction. rOPN was administered via the intracerebroventricular and nasal route after SAH. SAH grade, neurological scores, brain water content, brain swelling, hematoxylin and eosin staining, India ink angiography, Western blots, and immunofluorescence were used to study the mechanisms of rOPN on the vascular smooth muscle phenotypic transformation.

RESULTS

The marker proteins of vascular smooth muscle phenotypic transformation α-smooth muscle actin decreased and embryonic smooth muscle myosin heavy chain (SMemb) increased significantly at 24 and 72 hours in the cerebral arteries after SAH. rOPN prevented the changes of α-smooth muscle actin and SMemb and significantly alleviated neurobehavioral dysfunction, increased the cross-sectional area and the lumen diameter of the cerebral arteries, reduced the brain water content and brain swelling, and improved the wall thickness of cerebral arteries. These effects of rOPN were abolished by GRGDSP, integrin-linked kinase small interfering RNA, and NSC23766. Intranasal application of rOPN at 3 hours after SAH also reduced neurological deficits.

CONCLUSIONS

rOPN prevented the vascular smooth muscle phenotypic transformation and improved the neurological outcome, which was possibly mediated by the integrin receptor/integrin-linked kinase/Rac-1 pathway.

Isoflurane post-treatment ameliorates GMH-induced brain injury in neonatal rats

BACKGROUND AND PURPOSE

This study investigated whether isoflurane ameliorates neurological sequelae after germinal matrix hemorrhage (GMH) through activation of the cytoprotective sphingosine kinase/sphingosine-1-phosphate receptor/Akt pathway.

METHODS

GMH was induced in P7 rat pups by intraparenchymal infusion of bacterial collagenase (0.3 U) into the right hemispheric germinal matrix. GMH animals received 2% isoflurane either once 1 hour after surgery or every 12 hours for 3 days. Isoflurane treatment was then combined with sphingosine-1-phosphate receptor-1/2 antagonist VPC23019 or sphingosine kinase 1/2 antagonist N,N-dimethylsphingosine.

RESULTS

Brain protein expression of sphingosine kinase-1 and phosphorylated Akt were significantly increased after isoflurane post-treatment, and cleaved caspase-3 was decreased at 24 hours after surgery, which was reversed by the antagonists. Isoflurane significantly reduced posthemorrhagic ventricular dilation and improved motor, but not cognitive, functions in GMH animals 3 weeks after surgery; no improvements were observed after VPC23019 administration.

CONCLUSIONS

Isoflurane post-treatment improved the neurological sequelae after GMH possibly by activation of the sphingosine kinase/Akt pathway.