| Obstructive sleep apnea syndrome (OSAS) is a common disorder with serious cardiovascular consequences. The pathogenesis of cardiovascular complications in OSAS is not fully understood, but is likely to be a multifactorial process involving a diverse range of mechanisms. Intermittent hypoxia is a pathophysiology feature of OSAS, to be similar to ischemia reperfusion damage, which can cause inflammatory reaction and tissue and cell injury. Therefore, inflammatory processes leading to vascular endothelial injury and dysfunction play a pivotal role in the pathogenesis of OSAS-related cardiovascular complication. In addition, cardiomyocyte apoptosis is an important cellular and molecular basis of ventricular remodeling and heart failure, which are the final outcome of cardiovascular diseases. The pathway of apoptotic signaling involves a caspase activation cascade, and caspase-3is the most critical downstream caspase. In order to explore the association between the frequency of IH and inflammation and further clarify the mechanism of IH-induced inflammatory damage and the cellular mechanism of IH-induced cardiac injury, in the present study we established an animal model that involved exposing rats to different frequencies of IH to observe the serum levels of circulating inflammatory markers and the activation profiles of various transcription factors in myocardial tissue and also detect the expression levels of caspase-3. We also observed the effect of antioxidant intervention which may contribute to provide a new direction and experimental basis for the prevention and treatment of OSAS-related cardiovascular complication.Contents:1. The study on pathogenesis of inflammatory injury in different frequencies of IH rats2. The study on the effect of antioxidant Tempo] intervention on inflammatory injury in IH rats.3. The study on the protein level of caspase-3and the effect of antioxidant Tempol intervention on it in IH rats.Methods:The first part:Adult male Wistar rats were divided randomly into groups according to different frequencies of IH (group IH1:10times/h, group IH2:20times/h, group IH3:30times/h, group IH4:40times/h) and sustained normoxia(group SC), then compared with the group standard fed (group NC). After six weeks, ELISA assay was performed to detect the concentration of serum TNF-a, IL-6, IL-8, CRP, ICAM-1, VEGF and IL-10. Western blotting was performed to detect the protein levels of the transcription factors NF-κB P65in myocardial nuclear and HIF-la in myocardial tissue. Real-time PCR was performed to detect the expression levels of c-fos mRNA in myocardial tissue.The second part:The rats exposed to the IH (30times/h) were divided into two groups(group IH3T0intervened by antioxidant Tempol at the beginning of exposure and group IH3T intervened since the fourth week). After six weeks, the levels of inflammatory markers and transcription factors mentioned above were detected and compared with those levels in group IH3and group SC.The third part:The protein levels of caspase-3in myocardial cell detected by immunohistochemical method in group IH3T0were compared with those levels in group IH3and group SC.Results:The first part:1. Compared with group SC and group NC, serum levels of TNF-a, IL-8, IL-6, CRP, ICAM-1and VEGF were significantly increased in all IH groups, while levels of IL-10were significantly decreased (F’=9.679,24.461,19.359,30.278,27.318,22.564and20.594respectively, P=0.000).2. Compared with group SC and group NC, the levels of NF-κB P65, HIF-1α and c-fos mRNA were significantly increased in IH groups (F=35.089,24.934and22.950respectively, P=0.000).3. The levels of TNF-α, IL-8, IL-6, CRP, ICAM-] and NF-κB P65, c-fos mRNA were increased gradually with increasing frequency of IH in IH groups, while the levels of IL-10were gradually decreased(P<0.01, compared between group IH3and group IH1). but there were no significant differences on these markers between group IH3and group IH4.The point of peak or valley occured when frequency was30times/h. The levels of NF-κB P65were positively correlated with the levels of TNF-a, IL-8, IL-6and ICAM-1(r=0.519,0.574,0.608,0.659and0.576respectively, P=0.002,0.001,0.000,0.000and0.003respectively), while were negatively correlated with the levels of IL-10(r=-0.618, P=0.000).4. The levels of VEGF and HIF-1α continued to rise with increasing frequency in IH groups. The levels of HIF-la were positively correlated with the levels of VEGF(r=0.661, P=0.000).The second part:1. Compared with group IH3T0and group IH3T, the levels of inflammatory markers and transcription factors were higher, while the levels of anti-inflammatory cytokine were lower in group IH3.2. Compared with group SC, the levels of inflammatory markers, transcription factors and anti-inflammatory cytokine mentioned above showed significant differences in group IH3T0and group IH3T(P<0.05).The third part:1. Compared with group SC, the caspase-3activity in myocardial cell were significantly increased in group IH3.2. The caspase-3activity in myocardial cell in group IH3T0were lower than those in group IH3.3. The levels of caspase-3were positively correlated with the levels of NF-kB P65in group IH3(r=0.864, P=0.006).Conclusions:1. IH can lead to systemic and cardiovascular inflammatory injury by imbalance of inflammation and anti-inflammatory system.2. Inflammatory injury induced by IH is partially dependent on the frequency of IH. The relationship between inflammatory injury and the frequency of IH isn’t linear suggests the presence of the body’s compensatory mechanisms and adaptive response.3. IH can cause the activation of different transcription factors, including NF-κB, HIF-1α and AP-1. The preferential activation of NF-κB and AP-1-mediated inflammatory pathways induced by the low and moderate frequency of IH can contribute to the initiation and progression of inflammatory process, while the preferential activation of HIF-1α-mediated adaptive pathway induced by the high frequency of IH may be the protective mechanisms.4. IH may induce the activation of apoptotic pathway protein caspase-3by the activation of NF-κB upregulating expression of proapoptotic genes in myocardial cell.5. Antioxidants can reduce IH-induced inflammatory damage and cardiomyocyte apoptosis by adjusting the oxidant/antioxidant balance to regulate the inflammatory/anti-inflammatory system balance. Antioxidants have a protective effect on IH-induced injury. |
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