Causal impact of gut microbiota and associated metabolites on pulmonary arterial hypertension: a bidirectional Mendelian randomization study

Abstract

Background: Patients with pulmonary arterial hypertension (PAH) exhibit a distinct gut microbiota profile; however, the causal association between gut microbiota, associated metabolites, and PAH remains elusive. We aimed to investigate this causal association and to explore whether dietary patterns play a role in its regulation.

Methods: Summary statistics of gut microbiota, associated metabolites, diet, and PAH were obtained from genome-wide association studies. The inverse variance weighted method was primarily used to measure the causal effect, with sensitivity analyses using the weighted median, weighted mode, simple mode, MR pleiotropy residual sum and outlier (MR-PRESSO), and MR-Egger methods. A reverse Mendelian randomisation analysis was also performed.

Results: Alistipes (odds ratio [OR] = 2.269, 95% confidence interval [CI] 1.100-4.679, P = 0.027) and Victivallis (OR = 1.558, 95% CI 1.019-2.380, P = 0.040) were associated with an increased risk of PAH, while Coprobacter (OR = 0.585, 95% CI 0.358-0.956, P = 0.032), Erysipelotrichaceae (UCG003) (OR = 0.494, 95% CI 0.245-0.996, P = 0.049), Lachnospiraceae (UCG008) (OR = 0.596, 95% CI 0.367-0.968, P = 0.036), and Ruminococcaceae (UCG005) (OR = 0.472, 95% CI 0.231-0.962, P = 0.039) protected against PAH. No associations were observed between PAH and gut microbiota-derived metabolites (trimethylamine N-oxide [TMAO] and its precursors betaine, carnitine, and choline), short-chain fatty acids (SCFAs), or diet. Although inverse variance-weighted analysis demonstrated that elevated choline levels were correlated with an increased risk of PAH, the results were not consistent with the sensitivity analysis. Therefore, the association was considered insignificant. Reverse Mendelian randomisation analysis demonstrated that PAH had no causal impact on gut microbiota-derived metabolites but could contribute to increased the levels of Butyricicoccus and Holdemania, while decreasing the levels of Clostridium innocuum, Defluviitaleaceae UCG011, Eisenbergiella, and Ruminiclostridium 5.

Conclusions: Gut microbiota were discovered suggestive evidence of the impacts of genetically predicted abundancy of certain microbial genera on PAH. Results of our study point that the production of SCFAs or TMAO does not mediate this association, which remains to be explained mechanistically.

Keywords: Gut microbiota; Mendelian randomisation; Pulmonary arterial hypertension; Short-chain fatty acids; Trimethylamine N-oxide.

Fig. 1

Study overview. Legend: SCFA, short chain fatty acids; TMAO, trimethylamine N-oxide. The figure illustrates the design of the study. In this study, we aim to investigate the causal relationship between gut microbiota, associated metabolites and PAH, and explore whether dietary patterns mediate the above causal relationship using two-sample Mendelian randomization

Fig. 2

Flow Chart of the Study Design. Legend: SNP, single nucleotide polymorphisms

Fig. 3

Scatter plot of MR results of bacteria on pulmonary arterial hypertension. Legend: Each dot represents the size of the SNP exposure impact in standard deviation units with the accompanying standard error. The lines represent the effect size calculated by the mendelian randomization method with the corresponding color. MR, Mendelian randomization; SNP, single nucleotide polymorphisms

Fig. 4

Forest plot of MR results of bacteria on pulmonary arterial hypertension. Legend: Each line represents the effect size of the corresponding SNP with the accompanying standard error. The red lines represent the average effect size of all SNP calculated by the MR egger and inverse variance weighted method respectively. MR, Mendelian randomization; SNP, single nucleotide polymorphisms

Fig. 5

The leave-one-out analysis of MR results of bacteria on pulmonary arterial hypertension. Legend: The leave-one-out analysis removes a single SNP each time and calculates the meta-analysis effect of the remaining SNPs to observe whether the results change after removing each SNP, and if a SNP is removed, the results change greatly, indicating that the presence of the SNP has a great impact on the results. In this study, after removing a single SNP each time, the overall error bars did not change much, indicating that the results were reliable and not affected by heterogeneity. MR, Mendelian randomization; SNP, single nucleotide polymorphisms