MRI Characterization And Machanism Of Brian Injury In The Acute Phase Of Experimental Subarachnoid Hemorrhage

Research BackgroundSubarachnoid hemorrhage(SAH)is a devastating disease resulting in high mortality,especially within the first few days after aneurysm rupture1,2.Approximately 12% of patients die before receiving medical attention,33% within 48 h and 50% within 30 days of aSAH.Of the survivors 50% suffer from permanent disability with an estimated lifetime cost a heavy burden to the family and society3.However,the mechanism of brain injury during the acute period remains poorly under-stood,and therapeutic options are limited4,5.MRI is a non-invasive method for collecting structural,physiological,and functional imaging data with high spatial resolution6.It has been widely used for detecting brain injuries such as cerebral edema,acute hydrocephalus7-9,white matter injury10-12,and ischemic lesions13,14 caused by various central nervous system diseases.However,due to longer acquisition time and difficulty in performing of MRI compared to CT scans and the high risk of rebleeding in SAH patients,MRI is rarely performed clinically for the patients in the acute setting after SAH.In the current study,MRI was performed to examine SAH-induced acute hydrocephalus and white and gray matter injury in a rat model.SAH occurs more frequently and with a higher incidence of hydrocephalus in women than in men15-18.Our previous study indicated that the incidence of acute hydrocephalus after experimental SAH was also significantly greater in female rats(75%)than in males(47%)7.This study examines the effect of gender on MRI findings and neurologic outcomes after SAH in rats.Additionally,iron plays an important role in brain injury after experimental intracerebral hemorrhage(ICH)19-21,intraventricular hemorrhage(IVH)22,23,and SAH24.Our previous studies indicated that iron levels in CSF increase almost 14-fold after ICH on the third day and remain high for at least 1 month after experimental ICH.Increases of brain iron levels cause brain edema,oxidative stress,brain atrophy,and neurological deficits following ICH19,25,26.After SAH,the brain is exposed to high concentrations of hemoglobin as erythrocytes lyse27.Hemoglobin and heme are then captured by macrophages in the form of hemoglobin-haptoglobin and heme-hemopexin complexes via the hemoglobin scavenger receptor CD163 and hemopexin scavenger receptor CD91,respectively28,29.Heme oxygenase-1(HO-1)is a key inducible enzyme for heme degradation and iron release.The released iron can be stored in ferritin19,24,30.An iron chelator,deferoxamine,effectively reduced iron and HO-1 levels and ameliorated acute neuronal injury after SAH24.In this study,all experimental SAH rats were graded into 0–4 groups based on blood accumulation in the subarachnoid space.The relationship between MRI grading system after SAH and brain injury severity was determined.SAH patients may be complicated with enlargement of ventricles and acute hydrocephalus,leading to increased intracranial pressure(ICP),reduced cerebral perfusion pressure18,and secondary early brain injury(EBI)31.The mechanism of acute hydrocephalus post SAH remains unknown,cerebrospinal fluid(CSF)circulation obstruction,SAH severity,intraventricular hemorrhage secondary to SAH,ventricular wall injury,CSF dynamic changes,and CSF absorption deficit may participate in its development32.Intraventricular fibrinolysis aimed at lysing intraventricular blood neither reduced permanent shunt dependency nor influenced functional outcome34.Our previous animal studies revealed that not only lysed red blood cell and iron,but thrombin could induce hydrocephalus35,36.We hypothesized that after SAH,the metabolic products of erythrocytes play a role in the development of hydrocephalus and early brain injury.In this study we injected the bloody CSF of human SAH patients into the lateral ventricle of nude rice to investigated the effect of bloody CSF on the ventricle and periventricular brian tissue in the acute phase of SAH.Chapter ? MRI characterization in the acute phase of experimental subarachnoid hemorrhageObjectA number of mechanisms have been proposed for the early brain injury after subarachnoid hemorrhage(SAH)which is found clinically and in experimental models.In this study,we investigated the radiographic characteristics and influence of gender on early brain injury after experimental SAH.MethodsSAH was induced by endovascular perforation in male and female rats.Magnetic resonance imaging was performed in a 7.0-T Varian MR scanner at 24 hours after SAH.The occurrence and size of T2 lesions,ventricular dilation and white matter injury(WMI)was determined on T2 weighted images(T2WI).The effects of SAH on heme oxygenase-1 and fibrin/fibrinogen were examined by Western blotting and immunohistochemistry.SAH severity was assessed using a MRI grading system and neurological function was evaluated according to a modified Garcia's scoring system.ResultsT2-hyperintensity areas and enlarged ventricles were observed in T2 WI coronal sections 24 hours after SAH.The overall incidence of T2-lesions,WMI and hydrocephalus was 54,20 and 63%,respectively.Female rats had a higher incidence of T2-hyperintensity lesions and hydrocephalus,as well as larger T2 lesion volumes and higher average ventricular volume.SAH rats graded at 3-4(our previously validated MRI grading scale)had larger T2 lesion volumes,more hydrocephalus and worse neurological function compared with those graded at 0-2.ConclusionT2-lesion,WMI and hydrocephalus were the most prevalent MRI characteristics 24 hours after experimental SAH.The T2-lesion area matched with fibrinogen/fibrin positive staining in the acute phase of SAH.SAH induced more severe brain injury in females compared to males in the acute phase of SAH.Chapter ? The mechanism of early brain injury induced by intraventricular injection of bloody CSF from SAH patients into nude mice ventricles ObjectTo investigate the mechanism of early brain injury induced by intraventricular injection of human bloody CSF on ventricles and periventricular brain tissue in rude mice. MethodsIntraventricular injection of CSF model was induced in 40 male nude mice by using of stereotaxic apparatus.32 of which were injected with bloody CSF from human SAH patients at different time points after aneurysm rupture.8 mice were injected with normal CSF from human patients as control group.All animals were sacrificed at 24 h after the injection and the specimens were used for immunohistochemistry and electron microscopy.The effects of bloody CSF injection on the heme oxygenase-1 and phosphorylated p44/42 were determined by immunofluorescence and immunohistochemistry.ResultsThe expression of HO-1 in the periventricular area was significantly higher in the bloody CSF injection group than that of the control group 24 hours after the injection.The bloody CSF obtained within 48 hours after the rupture of the aneurysm caused the significantly elevated expression of HO-1 than that obtained at 7 days or 14 days after the ictus.Double labeling immunofluorescence revealed that most HO-1 positive cells were also Iba-1 positive cells.Immunohistochemical staining showed that intraventricular injection of bloody CSF induced the increased expression of phosphorylated p44/42 in the periventricular brain tissue,and double labeling immunofluorescence showed that most phosphorylated p44/42 positive cells were NeuN positive cells rather than Iba-1 positive cell.Electron microscopy showed that the cilia of ependymal cells suffered more injury in the nude mice injected with bloody CSF than that of the control group.The cilia polarity has changed in different directions,and the surrounding white matter was seriously damaged.ConclusionsVentricular injection of human SAH CSF may cause periventricular injury in nude mice.The activation of p-p44/42 inflammatory pathway plays a role in the injury after SAH CSF injection.