The Impacts Of Obstructive Sleep Apnea On Gut Microbiota And Atrial Substrate In Patients With Hypertension

Section 1:Gut Microbiota in Hypertensive Patients with versus without Obstructive Sleep ApneaBackgrounds:We investigated the alteration of gut microbiota and the associated metabolic risks in hypertensive patients with obstructive sleep apnea(OSA)comorbidity.Methods:Fecal and blood samples were collected from 52 hypertensive patients,who were divided into 3 groups:A(controls,AHI<5,n=15),B(mild OSA,5<AHI<20,n=17),and C(moderate-to-severe OSA,AHI>20,n=20).The composition of the gut microbiota was studied through 16S rRNA sequencing of variable regions 3-4.Results:Analysis of the results revealed that group C had a significant higher concentration of total cholesterol,low-density lipoprotein and IL-1β compared with group A.The Shannon index showed that bacterial biodiversity was lower in OSA patients.At the phylum level,the ratio of Firmicutes to Bacteroidetes(F/B)was significantly higher in group C than in groups A and B.At the genus level,the relative abundance of short-chain fatty acids(SCFA)-producing bacteria(e.g.,Bacteroides and Prevotella)was lower while the number of inflammation-related bacteria(e.g.,Lactobacillus)was increased in patients with OSA.We found that the IL-1β level was negatively correlated with Bacteroidetes.The area under the receiver operating characteristic curve was 0.672 for F/B ratio in determining hypertensive patients with OSA.Conclusion:In patients with hypertension,OSA was associated with worse gut dysbiosis,as evidenced by decreased levels of short-chain fatty acids-producing bacteria and increased number of inflammation-related bacteria.The differences in gut microbiota discriminate hypertensive patients with OSA from those without and may result in an enhanced inflammatory response and increase the risk of cardiovascular diseases.Section 2:Impact of Obstructive Sleep Apnea on Atrial Substrate in Hypertensive PatientsBackgrounds:Although obstructive sleep apnea(OSA)is strongly associated with incidence of atrial fibrillation(AF),a definitive causal link has not been established.Methods:A total of 105 patients were divided into control(n=52),mild to moderate OSA group(m-OSA,n=27)and severe OSA group(s-OSA,n=26).All patient groups underwent echocardiography and blood tests for interleukin-1β(IL-1β),tumor necrosis factor α(TNF-α),collagen type 1(col-1)and collagen type 3(col-3).In order to exclude the influence of clinical confounding factors such as obesity(high body mass index),we conducted an animal experiment study using lean(non-obese)mice:a total of 12 mice,6 were randomly selected as the experimental group(OSA was simulated in the intermittent hypoxia(IH)environment,and the other 6 mice were used as the control group.The size of atrial myocardium,the degree of fibrosis,and the expression of inflammatory factors were compared between the two groups of mice.Results:In clinical patients,severe OSA group had greater body mass index than control group(28.12±3.43 versus 24.40±3.56 kg/m2,p<0.001).Left atrial diameter was significantly higher in s-OSA group than in Control group(38.35±4.89 versus 35.39±5.29mm,p=0.012).In addition,TNFα level was higher in patients with OSA than in controls(p=0.007).Consistently,plasma IL-1β was significantly elevated in s-OSA and m-OSA group compared with the control group.However,we did not observe significant changes in circulating col-1 and col-3 in patients with OSA.In lean mice exposed to IH for three weeks,wheat germ agglutinin staining and Masson’s staining showed that IH enlarged atrial myocardium and promoted atrial fibrosis.mRNA expression levels of TGFβ、col-1,col-3,IL-6 and TNF-α were significantly elevated in the atria after IH exposure.Conclusion:OSA is associated atrial remodeling and inflammation in humans.Also,OSA causes atrial fibrosis and inflammation in mice.OSA might facilitate the formation of AF substrate.Section 3:Alterations of Gut Microbiota/Metabolites in Obstructive Sleep Apnea and Their Relationship to Atrial SubstrateObjective:To explore the correlation between the changes of intestinal flora and its metabolites and clinical indicators related to atrial fibrillation in patients with OSA.Methods:Eligible hypertensive patients were included,feces and plasma samples were collected,and the intestinal flora composition of hypertensive patients with OSA was analyzed by 16s rRNA.Meanwhile,untargeted metabolomics was used to identify the level of relevant small molecule metabolites in patients’ plasma.The changes were correlated with ultrasound LAD,ECG P wave duration,and plasma inflammation and fibrosis biomarkers.Results:Compared with controls,patients with moderate to severe OSA had prolonged P waves.P wave duration was positively correlated with OSA severity indicators.A total of 905 metabolites were identified by untargeted metabolomics in all patient blood samples.In the positive ion mode,the expression of 11 metabolites increased and the expression of 6 metabolites decreased in the moderate to severe OSA group.In the negative ion mode,the expression of 22 metabolites was increased,while the expression of 5 metabolites was down-regulated in the moderate to severe OSA group.Correlation analysis showed that:19 metabolites related to OSA severity;1 differential metabolite related to P wave duration,but no differential metabolite significantly related to LAD was found;9 differential metabolites related to TNFα level;7 differential metabolites correlated with IL-1β levels;8 differential metabolites correlated with col-1 levels;and 12 differential metabolites correlated with col-3 levels.Conclusion:Hypertensive patients with moderate-to-severe OSA not only have changes in gut microbiota,but also changes in their plasma small molecule metabolites,which are partly related to P wave duration,plasma inflammatory factors and fibrosis biomarkers.This study elucidated the OSA-gut microbiota-metabolites-atrial substrate pathway in hypertensive patients,and the effect of interventions on this pathway deserves further study.