Ordinary professor Hôpitaux Universitaires de Genève Geneva, Geneve, Switzerland
Background: The only validated neuroprotective treatment in hypoxia-ischemia encephalopathy of the newborn is controlled hypothermia but with limited benefits. Additional putative neuroprotective drug candidates include sildenafil citrate, a phosphodiesterase-type 5 inhibitor. Objective: In this study, we assessed its ability to reduce HI-induced neuroinflammation through its potential effect on the activation of microglial and infiltrating macrophages. Design/Methods: HI was induced in P10 Sprague–Dawley rats by unilateral carotid permanent artery occlusion and hypoxia and treated by either hypothermia alone, sildenafil alone or combined treatment. Lesion size and glial activation were analyzed by immunohistochemistry, qRT-PCR, and proteomic analyses performed at P13. Results: None of the treatments was associated with a significant reduction in lesion size both in the cerebral cortex and hippocampus, 72h after hypoxia-ischemia. However, significant reductions in both Iba1+ (within the ipsilateral hemisphere) and GFAP+ cells (within the ipsilateral hippocampus) were observed in animals exposed to combined treatment, but not in the other treatment groups. In microglia-sorted cells, pro-inflammatory markers, ie. Il1b, Il6, Nos2, and CD86 were significantly downregulated in the combined treatment group only. These changes were restricted to the ipsilateral hemisphere, were not evidenced in sorted astrocytes, and were not sex-dependent. Proteomic analyses in sorted microglia refined the pro-inflammatory effect of hypoxia-ischemia and confirmed a biologically relevant impact of the combined treatment on specific molecular pathways including genes related to neutrophilic functions.
Conclusion(s): Our findings suggest that sildenafil combined with hypothermia produces maximum effect in mitigating microglia/macrophage activation induced by hypoxia-ischemia through complex proteomic regulation. The regulation of neuroinflammation induced by the synergistic effect of sildenafil combined with hypothermia may represent an interesting therapeutic strategy for neonatal neuroprotection.
