The Study On Oxidative Stress Caused By Intermittent Hypoxia Of Sleep Apnea Mode In Rats

Background and objectiveChronic intermittent hypoxia (CIH) is considered to be one of the most important causes of cardiovascular diseases in OSAHS patients. The repeated hypoxia and reoxygenation cycle is similar to hypoxia-reperfusion injury, which initiates oxidative stress. Oxidative stress induced by CIH is an important pathogenic mechanism of cardiovascular diseases. However, the effect of oxidative stress in cardiovascular diseases injury induced by OSAHS remains unclear and the association between hypoxia degree and oxidative stress is incompletely understood. In this study, we established an OSAHS rat model in different degree of intermittent hypoxia and determined the levels of oxidative stress markers in the serum, endothelial system and myocardial homogenates. Our purpose is to approach the possible mechanisms of endothelial dysfunction induced by CIH.Contents1. The creation of the rat model exposed in different degree of intermittent hypoxia.2. The study on serum levels of oxidative stress markers in different degree of CIH.3. The research about oxidative stress in vascular endothelial system of rats exposed in different degree of CIH.4. The research about oxidative stress in myocardial homogenates of rats exposed in different degree of CIH.MethodsIn the first part, we established an animal model that involved exposing rats to different degree of CIH. One hundred and sixty male Wistar rats were divided randomly into the five groups:5%,7.5%,10%of the intermittent hypoxia group (IH1, IH2and IH3),10%continuous hypoxia group(CH) and the sustained normoxia control group(SC). At the second, fourth, sixth, and eighth weeks, eight rats in each group were sacrificed to collect serum, endothelia cells and myocardial tissues.In the second part, we determined the concentration of malondialdehyde(MDA), the total-antioxidant capability(T-AOC), the activity of superoxide dismutase(SOD) and glutathione peroxidase(GSH-PX) in serum.In the third part, real-time PCR were used to detect the expression levels of NADPH oxidase p22phox, Nox2and thioredoxin(TRX) mRNA in aortic endothelial.In the fourth part, we determined the concentration of malondialdehyde(MDA), the total-antioxidant capability(T-AOC) and the activity of superoxide dismutase(SOD) in myocardial homogenates and then detectet the expression levels of NADPH oxidase p22phox, Nox2and thioredoxin(TRX) mRNA in myocardial tissures.ResultsThe first part:Blood gas analysis show us the minimum PO2in IH-1,2,3group were35.6mmHg,40.3mmHg and48.8mmHg separately; CH group maintained at37.4-39.6mmHg while SC group at98-102mmHg. The second part:1. Serum level of MDA was significantly increased in all three CIH groups, while levels of T-AOC, SOD and GSH-PX were significantly decreased. With the severe of the IH degree and the extending of exposure time, MDA in IHs showed a rising trend, while SOD showed a decreasing trend, especially in IH1group.2. Level of MDA in IHl group was significantly higher than those in IH2and IH3groups at the sixth week (P=0.040,0.013)3. The correlations between MDA and SOD (r=-0.410, P=0.000),MDA and T-AOC (r=-0.428, P=0.000), MDA and GSH-PX (r=-0.462, P=0.000) showed significantly negative correlation.The third part:1. At the sixth week, the expression level of NADPH oxidase p22phox of endothelia cells in IH1group was significantly higher than SC group (P=0.003) and IH3group(P=0.023).2. With the extending of exposure time and the severe of the IH degree, the expression of TRX mRNA of endothelial tissues showed a rising trend. The level in IHl were significantly higher than that of SC group during6-8 weeks.The fourth part:1. Levels of MDA, T-AOC and SOD in myocardial homogenates were significantly different among the groups of IH degrees and the groups at different times. With the severe of the IH degree and the extending of exposure time, MDA in IHs and CH showed a rising trend, while T-AOC and SOD showed a decreasing trend, especially in IH1group.2. At the sixth week, the expression level of NADPH oxidase p22phox of cardiocytes in IH1group was significantly higher than SC group (P=0.003) and CH group(P=0.007) and higher than SC group(P=0.012) at the eighth week.3. The expression of TRX mRNA of cardiocytes in IH1group showed a rising trend with the extending of exposure time. The level in IH1were significantly higher than those of SC group during during6-8weeks. Conclusions1. Chronic intermittent hypoxia in OSAHS can induce oxidative stress, which is most obvious in IH1.2. Oxidative stress induced by intermittent hypoxia shows more serious trend with the extending of exposure time.3. Chronic intermittent hypoxia can induce oxidative stress in endothelial and myocardial tissues of rats. NADPH oxidase can be activated by CIH and play a critical role in the pathogenesis of cardiovascular diseases in OSAHS.4. Thioredoxin(TRX) in endothelial and myocardial tissues can be activated by CIH and play an important role in the pathogenesis of cardiovascular diseases.