Research Of Endothelium Dysfunction In Cells Subjected To Obstructive Sleep Apnea Style Intermittent Hypoxia

Research of endothelium dysfunction in cells subjected to obstructive sleep apnea style intermittent hypoxiaObjectives:Obstructive sleep apnea syndrome (OSAS) is a common sleep-related respiratory disease. Peopte with chronic IH caused by recurrent apneas are prone to heart and cerebrovascular disease such as hypertension, atherosclerosis. OSAS is characterised by repetitive hypoxia and re-oxygenation which caused to endothelium dysfunction. Endothelium dysfunction manifested as the unbalance of vasoactive substances such as endothelin (ET), nitric oxide (NO) and vascular endothelial growth factor (VEGF). Previous studies on OSAS are limited to epidemiological, clinical and animal studies at present, while very little is known about the molecular mechanisms associated with IH and which factors are related to the severvity of endothelium dysfunction in IH. So using a cell culture model we examined the change of ET-1, NO and VEGF in different IH styles. Materials and methods:Human umbilical vein endothelial cells (ECV304) were exposed to different hypoxia/re-oxygenation conditions. The study includes four parts: (1) compare IH with air mimic control and blank control, (2) compare different frequency IH groups, (3) compare different time limit IH groups, (4) compare IH with continuous hypoxia (CH). After exposure, we examine the targets:1. ET system: level of ET-1 (EIA)2. NO system: level of NO (nitrate reductase method), NOS activity (chemical colorimetric analysis) and the expression of eNOS mRNA (RT-PCR)3. VEOF system: level of VEOF (ELISA) and the expression of KDR mRNA (RT-PCR)Results:1. ET-1:(1) IH, air mimic control and blank control: ET-1 in IH was significantly higher than in air mimic control and blank control, while no difference between air mimic control and blank control(F=59.229, P=0.000).(2) Different frequency IH groups: Extending the duration of each re-oxygenation episode from 1min45s to 8min15s, while maintaining the duration of hypoxic episodes at 15s, resulted in a progressive increase in ET-1. There was a tendency for ET-1 to decrease with 8min15s of re-oxygenation (F=109.056, P=0.000)(3) Different time limit IH groups: We found no significant difference between different time limit IH groups (t=1.304, P=0.215).(4) IH and CH groups: ET-1 in IH was significantly higher than in CH, which was equivalent to the hypoxia duration accumulated during IH (t=2.209, P=0.042).2. NO system:(1) IH, air mimic control and blank control: level of NO, NOS activity and the expression of eNOS mRNA in IH was significantly lower than in air mimic control and blank control (P＜0.05), while no difference between air mimic control and blank control.(2)Different frequency IH groups: Extending the duration of each re-oxygenation episode from 1min45s to 8min15s, while maintaining the duration of hypoxic episodes at 15s, resulted in a progressive decrease in level of NO, NOS activity and the expression of eNOS mRNA. There was a tendency for them to increase with 8min15s of re-oxygenation (P＜0.05).(3)Different time limit IH groups: We found no significant difference between different time limit IH groups (P＞0.05).(4) IH and CH groups: level of NO, NOS activity and the expression of eNOS mRNA in IH was significantly lower than in CH, which was equivalent to the hypoxia duration accumulated during IH(P＜0.05).3. VEGF system:(1) IH, air mimic control and blank control: level of VEGF and the expression of KDR mRNA in IH was significantly higher than in air mimic control and blank control(P＜0.05), while no difference between air mimic control and blank control.(2) Different frequency IH groups: Extending the duration of each re-oxygenation episode from 1min45s to 8min15s, while maintaining the duration of hypoxic episodes at 15s, resulted in a progressive increase in VEGF and KDR mRNA. There was a tendency to decrease with 8min15s of re-oxygenation (P＜0.05).(3) Different time limit IH groups: We found no significant difference between different time limit IH groups (P＞0.05).(4) IH and CH groups: level of VEGF and the expression of KDR mRNA in IH was significantly higher than in CH, which was equivalent to the hypoxia duration accumulated during IH (P＜ 0.05).Conclusions:Obstructive sleep apnea style IH results in increase of ET-1, VEGF system and decrease of NO system, and re-oxygenation is crucial to the change.