Microbiota and pulmonary hypertension: a systematic review on human studies

Background Pulmonary hypertension (PH) is accompanied by unfavorable outcomes and the search for new targets such as metabolites for its treatment is ongoing, therefore, this systematic review gathered evidence of the possible relationship between microbiota and PH. Methods This study was performed based on the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA). Population characteristics, PH etiology, treatment, and, severity, and the source of samples were extracted for each study. Also, microbiome composition and increased or decreased bacteria in metabolites were gathered. The quality assessment was performed based on the Joanna Briggs Institute (JBI) checklist. Results Eight case-controls were included which all were focused on etiologies other than the left heart diseases. The range of mean values for mPAP of PH patients was 38 to 78 mmHg. Oronasopharynx and bronchoalveolar lavage fluid were the sources of samples in two and one studies respectively. The abundance of different bacteria such as Firmicutes, Hemophilus, Prevotella, and, Bacteroides was altered among PH patients compared to controls. In one study TMAO level was significantly increased among patients with higher REVEAL scores. In five studies random forest modeling was employed to differentiate PH patients from controls and the range of accuracy reported by three studies was 80.3–93.8%. Conclusion There is limited evidence regarding the role of microbiome alterations in PH. Both gut and respiratory dysbiosis might play a role in PH pathogenesis and be related to its severity. Clinical trials are needed to investigate the efficacy of probiotics in the treatment of PH.