Research on the expression of aquaporin 9 gene and efficacy of mannitol in neonatal rats with hypoxia-ischemic brain edema

Abstract

Objective To study the relationship between aquaporin 9(AQP 9) gene and brain edema in neonatal rats of hypoxic-ischemic brain damage (HIBD)and the therapeutic mechanism of mannitol. Method Healthy and 7-day-old SD rats were randomly assigned into three groups: sham-operated group, HIBD group and mannitol group. Both HIBD and mannitol group were established on HIBD model. The mannitol group was given mannitol intraperitoneally at 0, 24, 48 h of HIBD. 2 ml/kg of 2% Evans blue (EB) were injected intraperitoneally before sacrifice. 0, 6, 12, 24, 48 and 72 h after HIBD, the outcomes were analyzed including the brain water content, the expression of AQP 9 mRNA measured using RT-PCR and immunofluorescence staining methods, and the permeability of blood-brain barrier (BBB) measured with EB. Result In HIBD group, the brain water content was higher comparing with sham-operated group at 0 h after HIBD(P<0.05 ), and gradually increased over time, reaching peak at 48 h (89.3%±1.9%)and then decreased. In mannitol group, brain water content started to decrease from 1 h after mannitol administration to the bottom at 12 h (86.5%±0.6%), then increased to peak at 72 h (87.2%±1.7%), and brain water content were decreased during 0~48 h comparing with HIBD group. HIBD group′s EB were higher than sham-operated group (P<0.05); Mannitol group′s EB were decreased comparing with HIBD group (except 0 h, P<0.05). AQP 9 mRNA expression in the HIBD group was decreased at 0 h, and reached the bottom at 48 h (0.09±0.07). Comparing with sham-operated group, it was higher in the HIBD group at 0, 6, 72 h, and lower (P< 0.05) at 12, 24, 48 h. Higher AQP 9 mRNA expression were detected in mannitol group than HIBD group and sham-operated group at each time point (with the exception of 48 h) (P< 0.05). AQP 9, which was closely related to water metabolism, were widely found in the pia mater and ependyma using immunofluorescence staining. After ischemia and hypoxia insult, an increase-decrease-increase pattern of AQP 9 expression was found. Conclusion AQP 9 is widely existed in various parts of the brain, influencing brain edema through a variety of pathways.AQP 9 also plays a role in alleviating brain edema in mannitol therapy. Key words: Hypoxia-ischemia, brain; Brain edema; Blood-brain barrier; Aquaporin 9; Mannitol