Cross-sectional analysis of gut microbiome and clinical risk factors in maintenance hemodialysis patients (COSMIC)

The bacteria within our gut appear to have an effect on nearly every aspect of our health. Little is known about how hemodialysis treatment and kidney failure influence the bacterial composition in our gut and in turn how this influences our health. Emerging evidence suggests that perhaps some of these bacteria are a major source of molecules that may build up and cause harm to the health of hemodialysis patients. This study helped us understand more about the relationship between gut bacteria and clinical risk factors in hemodialysis patients. In addition, it will shape future interventional studies to improve health in this population.

Methods: In this cross-sectional study, ten MHD patients (7M, 50 ± 4years, 80% African American) were assessed on a non-dialysis day. Assessment included: bone and body composition by DEXA; arterial function by applanation tonometry; and dietary intake through dietary recalls over the 48h prior to the fecal sample collection. Participants were asked to collect a complete fecal sample; DNA was extracted and the V4 hypervariable region of the bacterial 16S rRNA gene was sequenced using Illumina MiSeq. Sequence data was analyzed using QIIME 1.9.1. Descriptive statistics were reported while Spearman correlations were used to compare GM operational taxonomic units (representative of ≥1% of total bacterial population) and clinical risk factors.

Conclusions: Similar to other metabolic diseases, the GM showed a high Firmicutes-to-Bacteroidetes ratio at the phyla level. However, at the genus level there was high variability across individuals with some bacteria associated with positive health outcomes. Akkermansia, a gram-negative bacteria that preferentially colonizes the mucus layer and is associated with improved metabolic health, was expressed in low concentrations and was not present in some individuals, similar to Prevotella, which previously has been associated with higher dietary fiber intake. This association, however, was not found because it was present in only one individual. In addition, dietary fiber intake was less than 50% of the recommendation (6.26±2.48g/1000kcal). Finally, Faecalibacterium, which contains the machinery for the production of butyrate, was strongly associated with lower arterial stiffness, which is an independent risk factor for cardiovascular mortality in this population.  Further studies should aim to explore the relationship between the GM and cardiovascular health in MHD patients.