Association between imbalanced gut microecology and obstructive sleep apnea-associated hypertension: A prospective observational study

To the Editor: Obstructive sleep apnea (OSA) and hypertension are two strongly linked disorders that frequently coexist in clinics.[1] OSA is an important cause of secondary hypertension and leads to hypertension in up to half of patients with OSA.[1] However, the underlying biological mechanism by which OSA increases the risk of developing hypertension remains uncertain. Dysregulation of the gut microbiome is a key mechanism in the pathogenesis of many chronic diseases.[2] Patients with OSA and patients with hypertension both exhibit altered gut microbiomes, characterized primarily by an increase in lipopolysaccharide-producing and mucus-degrading Gram-negative bacteria, along with a reduction in short-chain fatty acid (SCFA)-producing bacteria.[3,4] Notably, the aberrant gut microbiome has been identified as a crucial contributor to the pathophysiology of hypertension secondary to OSA.[5] However, how the gut microbiome regulates the intestinal microecology and immune activation in patients with OSA-induced hypertension (OSAHTN) remains poorly understood. Hence, we conducted an observational study to investigate whether OSA-induced gut microbiota dysbiosis contributes to the pathogenesis of OSAHTN. The Institutional Review Board of the Second Affiliated Hospital of Fujian Medical University (No. 2020-160) approved the study, and all enrolled participants provided written informed consent. OSA severity was assessed via polysomnography according to the 2017 American Academy of Sleep Medicine diagnostic criteria. Blood pressure (BP) was measured according to the 2018 European Society of Cardiology/European Society of Hypertension (ESC/ESH) Guidelines for the Management of Arterial Hypertension. Patient inclusion criteria were (1) aged 20–50 years; (2) body mass index ≥24 kg/m2; (3) waist-to-hip ratio >0.9; (4) normal blood glucose, transaminase, and creatinine concentrations; (5) completed collection of blood and stool; and (6) reliable data analysis. Exclusion criteria were patients (1) who were currently receiving or had received treatments such as hypertension medication, continuous positive airway pressure treatment, oral orthoses, or uvulopalatopharyngoplasty; (2) who had cancers or known respiratory, cardiac, or renal diseases; (3) who had taken antibiotics, probiotics, or had received gastrointestinal surgery due to gastrointestinal trauma within the last month; and (4) who had apparent primary sleep disorders. Statistical analysis was performed using SPSS software (version 26.0, SPSS Inc., Chicago, IL, USA). Normally distributed continuous data are expressed as means ± standard deviation. One-way analysis of variance (ANOVA) was used when the variances across groups were homogeneous. Participants' basic characteristics were compared between groups via the Student–Newman–Keuls (SNK) analysis. The remaining data were compared between groups using the least significant difference test. If the varainces were hetergeneous, Welch's ANOVA was used, and the Games–Howell method was applied for multiple comparisons. For skewed distributed continuous data, Welch's ANOVA was used, and data are expressed as medians (M) and upper and lower quartiles (P25, P75). The Games–Howell method was used for multiple comparisons. P <0.05 was considered statistically significant. Twelve men without OSA and 35 men with severe OSA were enrolled in this study [Supplementary Figure 1, https://links.lww.com/CM9/C157]. Based on OSA severity and BP, participants were divided into the non-OSA (n = 12, BP <130/85 mmHg, apnea-hypopnea index [AHI] <5 events/h), OSA (n = 11, BP <130/85 mmHg, AHI ≥30 events/h), OSA with prehypertension (OSApHTN; n = 13, 130/85 mmHg ≤BP <140/90 mmHg, AHI ≥30 events/h), or OSAHTN (n = 11, BP ≥140/90 mmHg, AHI ≥30 events/h) group. Age distribution, lifestyle, including smoking, alcohol consumption, and sleeping habit, did not significantly differ between the four groups (P >0.05). Supplemental File 1, https://links.lww.com/CM9/C157 describes the methods of stool sample collection, stool DNA extraction and amplification, and data analysis. The intestinal microbiota composition was determined by 16S rRNA gene amplification and pyrosequencing of the stool samples of all participants. Intra- and intergroup microbiota diversity was compared using alpha- and beta-diversity analyses. The alpha-diversity indices (Chao1, Shannon, and Simpson) revealed no statistically significant differences in intestinal microbial diversity among the four groups [Supplementary Figure 2, https://links.lww.com/CM9/C157]. Conversely, principal coordinate analysis of the microbiomes (via unweighted UniFrac analysis) showed distinctive clustering of the microbial communities in each group. The non-OSA, OSA, and OSAHTN groups showed clear separation, representing three distinct sets of microbial compositions, suggesting three distinct gut environments among these groups. The microbial community of the OSApHTN group was between the OSA and OSAHTN groups, which may indicate a transition from the OSA group to the OSAHTN group [Figure 1A]. Beta-diversity analysis revealed that the gut microbiomes of the OSAHTN group differed significantly from those of the non-OSA (P <0.001), OSA (P <0.001), and OSApHTN (P = 0.004) groups [Figure 1B].Figure 1: Data summary of the 16S rRNA sequencing of the gut microbiotas of enrolled participants. (A) Principal coordinates analysis (PCoA) at the genus level, (B) dissimilarity distribution of the beta-diversity, and (C) Firmicutes/Bacteroidetes ratio. Differences in stool microbiotas at the (D) family level, (E) genus level, and (F) species level. (G) Linear discriminant analysis effect size method identified the most differentially abundant taxa among the four groups. F/B ratio: Firmicutes/Bacteroidetes ratio; LDA: Linear discriminant analysis; OSA: Obstructive sleep apnea; OSAHTN: Patients with OSA combined with hypertension; OSApHTN: Patients with OSA combined with prehypertension; PC1: Principal Component 1; PC2: Principal Component 2; 16 S rRNA: 16 S ribosomal RNA. * P <0.05; † P <0.01; ‡ P <0.001.Stool bacterial abundances were also compared among the groups. At the phylum level, the OSAHTN group exhibited a higher Firmicutes/Bacteroidetes ratio than those of the remaining three groups, but the differences were not statistically significant [Figure 1C]. The relative abundance of Ruminococcaceae at the family level was 0.187, 0.123, 0.916 and 0.896 in non-OSA, OSA, OSApHTN, and OSAHTN groups, respectively. The relative abundance of Ruminococcaceae was significantly reduced in the OSApHTN (P = 0.010) and OSAHTN (P = 0.016) groups compared with that of the non-OSA group [Figure 1D]. The relative abundance of Faecalibacterium at the genus level was 0.149, 0.083, 0.058 and 0.066 in non-OSA, OSA, OSApHTN, and OSAHTN groups, respectively. Faecalibacterium showed only a decreasing trend in the OSA group compared with that of the non-OSA group (P = 0.054); however, it was significantly reduced in the OSApHTN (P = 0.006) and OSAHTN (P = 0.017) groups. The relative abundances of Fusobacterium in the non-OSA, OSA, OSApHTN, and OSAHTN groups were 0.007, 0.023, 0.042, and 0.084, respectively, while those of Blautia were 0.045, 0.045, 0.100, and 0.167 in these groups, respectively. Fusobacterium and Blautia were significantly enriched in the OSAHTN group compared with those of the non-OSA (Fusobacterium, P = 0.012; Blautia, P = 0.002) and OSA (Fusobacterium, P = 0.045; Blautia, P = 0.002) groups [Figure 1E]. The relative abundance of Faecalibacterium prausnitzii at the species level in Non-OSA, OSA, OSApHTN, and OSAHTN groups was 0.144, 0.076, 0.053, 0.063, Bacteroides coprocola was 0.036, 0.004, 0.012, 0.0004, and Bacteroides vulgatus was 0.077, 0.130, 0.068, 0.030 respectively. The relative abundance of Faecalibacterium prausnitzii was significantly reduced in the OSA (P = 0.038), OSApHTN (P = 0.004), and OSAHTN (P = 0.017) groups compared with that of the non-OSA group. Compared with the non-OSA group, the relative abundance of Bacteroides coprocola was significantly reduced in the OSAHTN group (P = 0.037). Interestingly, the OSA group had the highest abundance of Bacteroides vulgatus, followed by the non-OSA (P = 0.167), OSApHTN (P = 0.212), and OSAHTN (P = 0.072) groups [Figure 1F]. Linear discriminant analysis was applied to predict the linear discriminant analysis effect size (LEfSe) and showed significant differences in species abundances among these four groups. When the linear discriminant analysis threshold was set to 3, the taxa represented by gut microbial structure and dominant bacteria differed significantly among the four taxa. The results revealed nine distinctive species, of which, Faecalibacterium prausnitzii, Bacteroides coprocola, and Ruminococcus were the most enriched in the non-OSA group; Sutterella species (spp.) and Parabacteroides merdae were the most enriched in the OSA group; Lachnospiraceae UCG 004 was the most abundant in the OSApHTN group; Actinobacteriota spp. and Coprococcus spp. were the most abundant in the OSAHTN group [Figure 1G]. These findings suggest that the abundances of SCFA-producing bacteria, including Ruminococcus, Faecalibacterium, Faecalibacterium prausnitzii, and Bacteroides coprocola were significantly higher in the non-OSA group than in the remaining three groups. Conversely, the OSAHTN group had a higher abundance of inflammation-associated bacteria, such as Blautia and Fusobacterium, than the other groups, but a lower abundance of SCFA-producing bacteria [Figure 1E]. This study had some limitations. First, this was a single-center study. Second, the population of the investigated cohort was relatively small. Third, the mechanism of OSA-associated dysregulation in the gut microbiome that contributes to development of hypertension secondary to OSA requires further study. Nevertheless, our results clearly showed that the gut microbiome was significantly altered among patients with OSA compared with that of participants without OSA. Importantly, our research demonstrated that OSA-induced gut microbiota dysbiosis, characterized by a decreased abundance of SCFA-producing bacteria and an increased abundance of inflammation-associated bacteria, might be associated with an increased risk of developing secondary hypertension in patients with OSA. Funding This research was sponsored by the Research Project of Jinan Microecological Biomedicine Shandong Laboratory (No. JNL202220B) and the Natural Science Foundation of Fujian Province (No. 2021J01267). Conflicts of interest None.