Proatherogene Genexpression in peripheren mononukleären Zellen bei obstruktiver Schlafapnoe: Effekt von Adipositas und Continuous Positive Airway Pressure - Therapie
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Philipps-Universität Marburg
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Abstract
Background, aims and method:
The highly prevalent obstructive sleep apnea syndrome (OSAS) that leads to chronic intermittent hypoxia (CIH) independently disposes for arteriosclerosis and related cardiovascular endpoints by inducing inflammation, endothelial dysfunction, and insulin resistance. Only few preliminary studies haveshown a pro-atherogenic gene expression in circulating peripheral blood mononuclear cells (PBMCs) with OSAS. However, the individual contribution of OSAS and obesity, i.e. mostly overlapping conditions, are presently unknown. Furthermore, the bidirectional interaction between metabolic syndrome and OSAS is a major difficulty in previous studies. Therefore the effect of OSAS on gene expression in PBMC without confounding factors (e.g. obesity) is currently not well understood. The aim of this study was to identify, if the gene expression of pro-atherogenic and hypoxia-inducible cytokines and enzymes like IL-6, IL-1 beta�, COX-2, TNF-alpha, VEGFA, SOCS-3, SOD-2, GDF-15, GSS and GSR in peripheral blood mononuclear cells of patients with moderate to severe OSAS (Apnea-hypopnea index, AHI>15 N/h) can be attributed to OSAS, obesity or the interaction of both. Therefore, patients were stratified for BMI< 30kg=m2 (n=5) and BMI> 30kg=m2 (n=10) and compared to ageand BMI-matched healthy control subjects (BMI<30 kg=m2: n=7, BMI>30kg=m2: n=6). In addition, the effect of 3-5 months home-based CPAP therapy was analysed in smaller subgroups (n=7, because of deficient compliance) in a longitudinal-sectional study design. In order to understand the reaction to oxidative stress caused by OSAS and the analysed gene expression of GSS and GSR, the intracellular concentrations of glutathione were measured in pooled groups with higher number of cases (controls: BMI<30 kg=m2: n=12, BMI>30 kg=m2: n=13; OSAS-patients: BMI<30 kg=m2: n=8, BMI>30 kg=m2: n=20). Moreover, the three precursor amino acids (glycine, glutamate, cystein) of glutathione were analysed in PBMC and plasma in these groups.
Results:
In the study population for the PCR-analysis, significant higher gene expressions were found for IL-1�beta, IL-6, COX-2 and SOCS-3 between OSAS-patients and controls. In stratification no significance could be shown between non-obese patients and controls, whereas the obese strata have multiple significant differences (IL-1�beta,IL-6, COS-2, VEGFa, ABCG-1, SOCS-3, CD-36, GSS and GSR). As the ’analysis of
variances’ (ANOVA) shows, IL-1beta�, VEGF-A, COX-2 and SOCS-3 are influenced by OSAS, whereas obesity only has impact on GSR. Furthermore the ANOVA shows an interaction of obesity and OSAS in the expression of IL-1beta� and VEGF-A. The duration of the application of the cPAP-therapy was 5.1+-0.7 h/total sleep time for all patients (n=7). Except for IL-6 and GDF-15, all gene expressions show a significant reduction after 3-5 months of home-based cPAP therapy. Suprisingly the intracellular concentration of reduced glutathion was twice as high in obese controls, non-obese and obese patients as in non-obese controls. The results of the glutathione measurement are furthermore reflected in the ratio of reduced glutathione to glutathione disulfide (GSH:GSSG). In contrast to our expectation, the ratio of OSAS patients is 8-9:1 and matches their physiological status, whereas control subjects show rates of 5-6.5:1. Analysing the amino acids, ANOVA shows a significant influence of OSAS, obesity and their interaction on extracellular glutamate levels. Furthermore, the extracellular cystine concentration is significant influenced by obesity.
Discussion and conclusions:
Because of the limited number of cases the findings of this study are only indicative and can be the basis of a hypothesis. However as a main result of this study we show that OSAS independently causes an up- regulation of the relevant pro-atherogenic and pro- inflammatory gene expression in PBMC with or without interaction of obesity and increasis cardiovscular risk. This is important as numerous studies on obesity and low level inflammation have not controlled for OSAS by exclusion or grading. It is important to highlight that we, unlike other studies, critically chose a reference (house-keeping) gene, that was relatively stable under both tested conditions, of which hypoxia (as inherent in OSAS-conditions) may putatively have the most profound and general effect on most cells. Among the gene products tested, we found that the most commonly published ones in the field of OSAS and PBMCs (i.e. �beta-actin and TBP) were hypoxia-sensitive to a considerable degree. The most stable and reliable reference gene we found was beta�- Glucuronidase (GUSB),
which is only used and published in a few studies dealing with PBMCs. The applicationduration of 3 to 5 months of home-based cPAP therapy lowers most of the elevated gene expressions (except IL-6 and GDF-15), in some cases even below control levels. This might be due to the AHI of control subjects (6.01+-1,31 N/h) that is slightly higher than that of patients in therapy. This leads us to the conclusion that already mild
OSAS (AHI>5 N/h, but <15 N/h) might imply a change in gene expression levels of pro-atherogenic cytokines and might increase the risk for cardiovascular events. The physological status of GSH:GSSG and high concentration of reduced GSH might be due to the hypoxia-inducible via NRF2 activated Xc- system. But even with all these results, it is difficult to fully understand and gauge the effects of oxidative stress caused
by OSAS. An in-depth analysis of this effect, as well as further studies of other antioxidative protective systems are needed. All in all larger future studies should take into account the potentially significant interaction
of BMI and OSAS. A stratification for BMI and AHI as well as controlled cPAP therapy seems to help understand the separate influences of obesity and OSAS on proatherogenic factors. We propose that studies on obesity and low inflammation should control carefully for OSAS as it might be a strong and often ignored confounder.
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Dates
Created: 2020Issued: 2020-12-07Updated: 2020-12-07
Faculty
Medizin
Publisher
Philipps-Universität Marburg
Language
ger
Data types
DoctoralThesis
Keywords
proinflammatorycpapproatherogenproatherogenicAdipositasproinflammatorischsleep apneaCPAPOSASobesity
DDC-Numbers
610
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Boneberg, Raphael: Proatherogene Genexpression in peripheren mononukleären Zellen bei obstruktiver Schlafapnoe: Effekt von Adipositas und Continuous Positive Airway Pressure - Therapie. : Philipps-Universität Marburg 2020-12-07. DOI: https://doi.org/10.17192/z2020.0427.
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This item has been published with the following license: In Copyright