Efecto neuroprotector del sildenafilo frente a la isquemia química inducida por la toxina mitocondrial malonato

Phosphodiesterase 5 inhibitors (PDE5i) have recently been reported to exert beneficial effects against ischemia-reperfusion injury in several organs but their neuroprotective effects in brain stroke models are scarce. The present study was undertaken to assess the effects of sildenafil against cell death caused by intrastriatal injection of malonate, an inhibitor of succinate dehydrogenase; which produces both energy depletion and lesions similar to those seen in cerebral ischemia. Our data demonstrate that sildenafil (1.5 mg/kg p.o.), given 30 min before malonate (1.5 ìmol/2 ìl), significantly decreased the lesion volume caused by this toxin. This protective effect cannot be attributed to any effect on reactive oxygen species production. By contrast, our results suggest that inhibition of malonate-induced activation of calpain/p25/cdk5 and ASK-1/MKK3/6/p38 pathways play a key role in the neuroprotective effects of this PDE5i. Sildenafil also increased the expression of two antiapoptotic proteins, namely Bcl-2 and Bcl-xL, as well as the phosphorylation of the prosurvival factor MEF2; effects that might, as well, contribute to prevent the cell death caused by malonate. The neuroprotective effect of sildenafil was not only preventive but also therapeutic. Thus, sildenafil protected hippocampal slices subjected to oxygen and glucose deprivation (OGD) when administered during reoxygenation and also reduced tissue damage caused by malonate if administered up to 3 hours after the injection of the mitochondrial toxin

Sildenafil protects against 3-nitropropionic acid neurotoxicity through the modulation of calpain, CREB and BDNF

In this study we tested whether phosphodiesterase 5 (PDE5) inhibitors, sildenafil and vardenafil, would afford protection against 3-nitropropionic acid (3NP), which produces striatal lesions that closely mimic some of the neuropathological features of Huntington's Disease (HD). The neurotoxin was given over 5 days by constant systemic infusion using osmotic minipumps. Animals treated with PDE5 inhibitors (sildenafil or vardenafil) showed improved neurologic scores, reduced the loss of striatal DARPP-32 protein levels and lesion volumes, and decreased calpain activation produced by 3NP. This protective effect was independent of changes in 3NP-induced succinate dehydrogenase inhibition. Furthermore, striatal p-CREB levels along with the expression of BDNF were significantly increased in sildenafil-treated rats. In summary, PDE5 inhibitors protected against 3NP-induced striatal degeneration by reducing calpain activation and by promoting survival pathways. These data encourage further evaluation of PDE5 inhibitors in transgenic mouse models of HD

Targeting p35/Cdk5 Signalling via CIP-Peptide Promotes Angiogenesis in Hypoxia

Cyclin-dependent kinase-5 (Cdk5) is over-expressed in both neurons and microvessels in hypoxic regions of stroke tissue and has a significant pathological role following hyper-phosphorylation leading to calpain-induced cell death. Here, we have identified a critical role of Cdk5 in cytoskeleton/focal dynamics, wherein its activator, p35, redistributes along actin microfilaments of spreading cells co-localising with p[subscript (Tyr15)]Cdk5, talin/integrin beta-1 at the lamellipodia in polarising cells. Cdk5 inhibition (roscovitine) resulted in actin-cytoskeleton disorganisation, prevention of protein co-localization and inhibition of movement. Cells expressing Cdk5 (D144N) kinase mutant, were unable to spread, migrate and form tube-like structures or sprouts, while Cdk5 wild-type over-expression showed enhanced motility and angiogenesis in vitro, which was maintained during hypoxia. Gene microarray studies demonstrated myocyte enhancer factor (MEF2C) as a substrate for Cdk5-mediated angiogenesis in vitro. MEF2C showed nuclear co-immunoprecipitation with Cdk5 and almost complete inhibition of differentiation and sprout formation following siRNA knock-down. In hypoxia, insertion of Cdk5/p25-inhibitory peptide (CIP) vector preserved and enhanced in vitro angiogenesis. These results demonstrate the existence of critical and complementary signalling pathways through Cdk5 and p35, and through which coordination is a required factor for successful angiogenesis in sustained hypoxic condition