| Background and ObjectiveInfectious brain edema is one of the major pathologic changes of cerebral and systematic diseases, including vascular edema and cytotoxic edema, and has high fatality rate and disability rate. The molecular mechanism of how water is cumulated and removed is so littled understood that the therapy of brain edema is limited. Recent research showed thatβ1 integrin is high expressed in astrocytes, and plays important role in nourishing neural cells and maintaining the integrity of BBB; while expression and activity of matrix metalloproteinase-2 (MMP-2 ) is enhanced after cerebral ischemia, and is associated with enhanced permeability of microcerebral blood vessel, disruption of BBB integrity, invasion of inflamed cells and brain edema. The infectious brain edema was established by applying lipopolysaccharide (LPS) carotid injection in our experiment. On the basis of brain edema, the change of brain water content, Evens blue (EB),β1 integrin,β1 integrin mRNA and MMP-2 are monitored. The regularity of brain edema proceed is discussed, and the relationship of brain edema andβ1 integrin and MMP-2 is researched. The experiment will help us understand pathogenesis of brain edema induced by LPS, and provide new measures of therapy for brain edema.Methods50 healthy 1 month-old SD rats whose weight was from 70g to 100g, male or female, were randomly divided into two groups: normal saline group (NS group, n=10), 0.1ml normal saline was injected by carotid for each rat; LPS group (LPS group, n=40), each rat was applied 100μg LPS. LPS group was divided into four groups: 6h, 12h, 24h and 48h. And each group had 10 rats. 5 rats of each group weren't injected EB to carry out immunohistochemistry. Rats were decapitated at different time points, and brain tissue samples were prepared. The water content of brain tissue is determined by measuring both wet weight and dry weight. The EB content of brain tissue is determined by the methods of formamide. Immunohistochemistry was used to investigate theβ1 integrin and MMP-2 expression, and the methods of RT-PCR were used to detect the expression forβ1 integrin mRNA in the brain tissue at different time courses of both LPS and the control groups. The data is analyzed with statistical software of SPSS12.0, allmeasurement data express in: mean±standard deviation(x±s ) the comparison among multiple exponent adopts one-ways ANOVA, Pearson correlation analysis is to carried out between the different variances, p<0.05 means the difference is significant.Results(1) Histopathological change: In LPS group, it could be found that the space among vessels became broaden, inflammatory cells infiltrated. Gliocyte became tumefied. Neurocyte became vacuolar degeneration and nuclear necrosis. (2)Brain water content: In LPS group, brain water content increased after LPS was injected 6h, and elevated maximally at 12h. Compared with NS group, brain water content was higher in LPS group at each time point, except for 48h. The difference was significant (p<0.01). (3) Brain EB content: Compared with the control group, brain water content increased after LPS was injected 6h, and elevated maximally at 12h. Brain EB content was higher in LPS group compared with NS group, at each time point expect 48h, The difference was significant (p<0.01), except for 48h (p<0.05). (4) The change ofβ1 integrin expression: Theβ1 integrin expression in brain tissue is obviously decreased after 6h injected LPS, and as the time of brain damage prolonged the expression level ofβ1 integrin decreased, reaches the bottom 48h after injection, Compared with NS group, the difference was significant (p<0.01). (5) The change ofβ1 integrin mRNA expression: Theβ1 integrin expression in brain tissue is obviously down regulation after 6h injected LPS, reaches the bottom 48h after injection.Compared with NS group, the difference was significant (p<0.01). (6) The change of MMP-2 expression: The MMP-2 expression in brain tissue is obviously increased after 6h injected LPS, reaches the peak 24h after injection, reduces gradually afterwards. Compared with NS group, the difference was significant (p<0.01). (7) Relative as the time prololged correlation analysis among brain water content, EB content, the expression ofβ1 integrin the expression ofβ1 integrin mRNA: Brain water content and EB content appear positive correlation (r=0.755, p<0.01) .The level of MMP-2 and brain water content appear positive correlation (r=0.712, p<0.01) .The level of MMP-2 and EB content appear positive correlation (r=0.891, p<0.01) .The level ofβ1 integrin and MMP-2 protein appear negative correlation (r=-0.586,p<0.01) . The level ofβ1 integrin and mRNA appear positive correlation (r=0.813,p<0.01) .Conclusions(1) By injecting LPS into infant rats'carotid, the animal model of infectious brain edema could be stable established, companied with increasing brain water content and destroyed blood brain barrier. Histopathological changes were vascular and cytotoxic brain edema. (2)After injecting LPS into rats' carotid, the expression ofβ1 integrin and mRNA were down regulated,β1 integrin is closely related with the developing of the edema. (3)After injecting LPS into rats' carotid, the expression of MMP-2 was up regulated. MMP-2 is closely related with the developing of the edema. (4) Correlative analysis of brain tissue water content, EB content, MMP-2 content, expression capacity ofβ1 integrin and expression capacity ofβ1 integrin mRNA in LPS group showed that brain tissue water content and EB content are positively correlated, suggesting that brain edema is concerned with disruption of BBB; MMP-2 content andβ1 integrin are negatively correlated, suggesting that reduction ofβ1 integrin and increase of MMP-2 may have effect on maintaining of AC normal shape, which is associated with enhanced permeability of BBB;The expression of MMP-2 is negatively correlated with water content and the expression level ofβ1 integrin decrease with the time of brain edema prolonged suggesting that those two participated in the development of brainedema.
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