Neuroprotective Role Of A Novel N-acetyl Serotonin Derivative After Subarachnoid Hemorrhage In A Rat Model

Background and purpose:Subarachnoid hemorrhage (SAH) accounts for only5%of all stroke incidents. However, due to its high rate of death and complications, the management of SAH remains to be one of the toughest challenges faced by neurosurgeons.Early brain injury (EBI) refers to the secondary cerebral injury caused by a series of pathophysiologic changes in brain following the acute stage of SAH (0-3days). An increasing number of researches have showed that the severity of EBI is closely related to the prognosis of SAH. Apoptosis, especially neuronal apoptosis, as the critical point in EBI, has been the main focus in the last few years in SAH studies. Injured neurons after SAH may be associated with delayed neurological deterioration and poor long-term outcome.Tropomyosin-Related Kinase B (TrkB) is a high affinity receptor of several endogenous neurotrophins. TrkB signal pathways are highly associated with the pathophysiologic mechanisms of various central nervous system disorders. It has been proved that TrkB activation can ameliorate EBI and improve outcomes in ischemic stroke models. However, few studies have revealed the role of TrkB in SAH models.N-acetyl serotonin (NAS) was once considered only as the precursor of melatonin from serotonin. N-[2-(5-hydroxy-1H-indol-3-yl) ethyl]-2-oxopiperidine-3-carboxamide (HIOC), an NAS’s derivative, selectively activates TrkB more potency than NAS. However, we are not aware of a study on the effects of HIOC in stroke models. This study is to investigate the potential role of HIOC on ameliorating early brain injury and improving outcome after experimental SAH by activating TrkB related signaling pathway.Material and methods:One hundred and fifty-six adult male Sprague-Dawley rats were used. SAH model was induced by endovascular perforation. TrkB small interfering RNA (siRNA) or scramble siRNA was injected intracerebroventricularly (icv.)24hours before SAH was induced. HIOC was administrated intracerebroventricularly3hours after SAH and compared with brain-derived neurotrophic factor (BDNF) treatment group. SAH grade and neurologic scores were evaluated for the outcome study. For the mechanism study, the protein level of TrkB, phosphorylated TrkB (p-TrkB), phosphorylated extracellular signal regulated kinase (p-ERK), B-cell lymphoma2(Bcl-2) and cleaved caspase3(CC3) in perforation side of the brain hemisphere were detected by Western blots; the co-localization of TrkB and neuron was observed by double immunofluorescence staining; and neuronal injury was determined by terminal deoxynucleotidyl transferase-mediated uridine5’-triphosphate-biotin nick end-labeling (TUNEL) staining.Results:1. Knocking down of TrkB expression in brain by icv. injection of TrkB siRNA24hours before SAH decreased the expression of p-TrkB and Bcl-2and aggravated neurologic deficits24hours after SAH.2. Intracerebroventricularly injection of HIOC after SAH can ameliorate neurologic deterioration. The high dosage of HIOC (30ug) treatment group had better neurologic outcome scores than that of the low dosage group (6ug).3. Intracerebroventricularly injection of HIOC after SAH activated TrkB/ERK pathway, decreased neuronal cell death, and improved neurobehavioral outcome. These effects were abolished by TrkB siRNA, while not affected by scramble siRNA. 4. TrkB can be activated in both HIOC and BDNF treatment groups after SAH. There is no significant difference on the anti-apoptosis effects between two groups, while HIOC was more potent than BDNF in reduction of apoptosis24hours post-SAH.Conclusion:We conclude that administration of HIOC activated TrkB/ERK signaling cascade and attenuated early brain injury after SAH. HIOC may be a promising agent for further treatment for SAH and other stroke events.