Small interfering RNA (siRNA) targeting vascular endothelial growth factor inhibits vascular leakage in brain of rats exposed to high altitude

Abstract

To observe the change of expression of vascular endothelial growth factor (VEGF) and vascular leakage in the brain of rats exposed to high altitude with siRNA targeting vascular endothelial growth factor and explore the pathological mechanism and preventive approach of high altitude cerebral edema (HACE). Fifty male Wistar rats were divided randomly into normal control group (Ncon), high altitude control group (Hcon), intraventricular normal saline control group (Scon), intraventricular siRNA group (CVI) and intravenous siRNA group (IVI). Rats in Ncon were raised normally. Rats in Hcon, Scon, CVI and IVI pretreated with intravenous injection of normal saline, intraventricular injection of normal saline, intraventricular injection of siRNA and intravenous injection of siRNA respectively were exposed to a low-pressure cabin mimicking a high altitude of 7000 m for 24 h. The ratio of dry and wet brain weight was calculated and the sodium fluorescein leakage calculated to evaluate the cerebral edema and the blood brain barrier permeability. Also the real-time quantitative RT-PCR was employed to detect the expression of VEGF mRNA and the Western blot the expression of VEGF. Compared with rats in NC, high altitude exposure led to a significant increase in the levels of VEGF mRNA (from 21.6 + or - 3.5 K copies/microg to 36.3 + or - 3.9 K copies/microg, P < 0.01) and protein (from 48 + or - 0.09 to 0.77 + or - 0.12, P < 0.01) in rat brain and fluorescence intensity of sodium fluorescein increased significantly (from 548 + or - 48 rfu/mg to 674 + or - 32 rfu/mg, P < 0.01). Intravenous injection of siRNA targeting to VEGF caused no significant change of expression VEGF mRNA and protein and fluorescence intensity of sodium fluorescein in rat brain (P > 0.05, respectively). While compared with rats in HC, intraventricular injection of siRNA targeting to VEGF caused the significant reduction of expression of VEGF mRNA (from 36.3 + or - 3.9 to 19.9 + or - 4.3, P < 0.01) and protein (from 0.77 + or - 0.12 to 0.44 + or - 0.13, P < 0.01) and fluorescence intensity of sodium fluorescein (from 674 + or - 32 rfu/mg to 542 + or - 77 rfu/mg, P < 0.05) in rat brain. There were no significant change in the ratio of dry and wet brain weight among five groups. VEGF may play a key role in the pathologic process of HACE. Intraventricular injection of siRNA targeting to VEGF inhibits the expression of VEGF and prevent the high altitude-induced vascular leakage. These findings might provide a basis for new preventive approaches of cerebral edema.