Study On Blood-Brain Barrier Dysfunction And Its Mechanism Of Rats At The Early Stage Of Severe Scald

Brain edema is the primary cause to death of severe burn injury patients. However, the symptom of brain edema is usually covered by the other severe burn complications, and is ignored by doctors. Previous study has been shown that formation of edema after severe burn injury is associated with brain-blood barrier (BBB) disruption. The more severe of burn injury, the higher rate of brain edema occurred. However, the specific mechanisms underlying BBB disruption and edema formation after severe burn at early stage yet to be elucidated.Object: To explore the mechanisms of BBB disruption and brain edema formation after severe scald or burn and try to provide new approaches to prevent edema formation of brain and to reduce mortality of patients after severe systemic thermal injury.Material and methods:(1) To explore the correlation of ultra structural changes (including BBB, neurons and synapse) and brain edema of rats following severe burn with transmission electron microscope (TEM).(2) To study the BBB breakdown after severe scald: changes in BBB permeability were determined by detection of Evans blue (EB) content in rat brains with the ultraviolet spectrophotometer; the water content of rats' brain was measured. Furthermore, in order to explore the molecular mechanism of BBB disruption in rats' brain after severe scalds, the expression levels of gene and protein of zonula occludens-one (ZO-1) were analyzed by semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) and western-blot analysis, respectively.(3) To investigate whether disruption of BBB integrity in rats' thermal injury model is associated with the expression of gelatinase B (MMP-9) and glial fibrillary acidic protein (GFAP). The expression changes of MMP-9 and GFAP in rats' brains during early post burn stage were detected by immunohistochemistry analysis. (4) To explore the protective effect on rat BBB following severe burn with Nω-nitro-L-arginine methyl ester (L-NAME) and calcium channel blocker nimodipine, and try to provide new approaches for preventing the BBB from disruption and formation of brain edema in the severe scald in clinic.Results: Brain water content and Evan's blue dye were significantly increased after scald. Expression level of MMP-9 and GFAP in severe scald burn rats' brain were higher than that in the sham control rats, however the expression levels of ZO-1 mRNA and protein were lower than that in the sham rats' brain﹙P<0.01﹚. In addition, vacuolated, swollen endothelium, abnormity of capillary basement membranes of BBB, marked vacuolar degeneration of the end feet of astrocytes, decreased number of synapse, synapse vesicle and broaden synaptic cleft were observed with transmission electron microscope. Furthermore, brain water content and Evan's blue dye decreased, while ZO-1 mRNA and protein significantly increased in severe systemic thermal rats after treatment with L-NAME and nimodipine. The changes of ultra-structure of BBB rats' brain with severe scald almost recovered to, while the expression of MMP-9 decreased to the level of normal control after treatment with L-NAME.Conclusions:(1) The ultrastructural changes of BBB and obviously abnormality of synapse were associated with the significantly increase of BBB permeability following severe scald burn injury.(2) The increase in MMP-9 and GFAP expression and decrease in ZO-1 mRNA and protein were associated with the increased BBB permeability following thermal injury, indicates that MMP-9 and GFAP may contribute to brain edema in peripheral thermal injury.(3) The BBB permeability increased after acute severe scald, which was significantly restricted by pretreatment with L-NAME at the early stage, may be linked to restrain the expression of MMP-9 and to prevent the decrease of ZO-1 mRNA in rats after acute severe scald.(4) The decrease of ZO-1 mRNA level in the severe scald rat's brain was prevented by treatment with nimodipine after severe scald at the early stage, which protected the BBB function from severe scald in rats.