Networks of gut bacteria relate to cardiovascular disease in a multi-ethnic population: the HELIUS study

Abstract

Aims: Gut microbiota have been linked to blood lipid levels and cardiovascular diseases (CVDs). The composition and abundance of gut microbiota trophic networks differ between ethnicities. We aim to evaluate the relationship between gut microbiotal trophic networks and CVD phenotypes.

Methods and results: We included cross-sectional data from 3860 individuals without CVD history from 6 ethnicities living in the Amsterdam region participating in the prospective Healthy Life in Urban Setting (HELIUS) study. Genetic variants were genotyped, faecal gut microbiota were profiled, and blood and anthropometric parameters were measured. A machine learning approach was used to assess the relationship between CVD risk (Framingham score) and gut microbiota stratified by ethnicity. Potential causal relationships between gut microbiota composition and CVD were inferred by performing two-sample Mendelian randomization with hard CVD events from the Pan-UK Biobank and microbiome genome-wide association studies summary data from a subset of the HELIUS cohort (n = 4117). Microbial taxa identified to be associated with CVD by machine learning and Mendelian randomization were often ethnic-specific, but some concordance across ethnicities was found. The microbes Akkermansia muciniphila and Ruminococcaceae UCG-002 were protective against ischaemic heart disease in African-Surinamese and Moroccans, respectively. We identified a strong inverse association between blood lipids, CVD risk, and the combined abundance of the correlated microbes Christensenellaceae-Methanobrevibacter-Ruminococcaceae (CMR). The CMR cluster was also identified in two independent cohorts and the association with triglycerides was replicated.

Conclusion: Certain gut microbes can have a potentially causal relationship with CVD events, with possible ethnic-specific effects. We identified a trophic network centred around Christensenellaceae, Methanobrevibacter, and various Ruminococcaceae, frequently lacking in South-Asian Surinamese, to be protective against CVD risk and associated with low triglyceride levels.

Keywords: Atherosclerosis; Cardiovascular diseases; HELIUS study; Mendelian randomization; Microbiome; Trophic networks.

Graphical Abstract

Figure 1

Study design. To study the relation between microbes and CVD risk, we predicted the Framingham score with faecal microbiome data using a machine learning approach. To study causal relations between gut microbes and CVD events, we performed a two-step MR approach. For this, summary statistics from a GWAS in the multi-ethnic HELIUS cohort with microbes and in the multi-ethnic Pan-UKBB cohort were used. Bacteria correlated to bacteria deemed to be causally related with CVD events based on Mendelian randomization were compared with results from the machine learning approach. As a third method, an unbiased hierarchical clustering approach was used to identify co-occurring bacterial trophic networks. GWAS, genome-wide association study. Images from Flaticon.com.

Figure 2

Results for the African-Surinamese subgroup. (A) The 30 most important features to predict Framingham score based on the faecal gut microbiota composition. *The bacteria were present in the SumTn of A. muciniphila, indicating that this bacterium is part of the trophic network that has a protective effect against ischaemic heart disease (n = 998). (B) Scatter plot of instruments with sensitivity analyses. (C) Forestplot with the effect of all SNPs used for the Mendelian randomization for A. muciniphila. IVW, inverse variance weighted.

Figure 3

Results for the Moroccan subgroup. (A) The 30 most important features to predict Framingham score based on the faecal gut microbiota composition (n = 489). *The bacterium was present in the SumTn of Ruminoccocaceae UCG-002, which was protective against ischaemic heart disease, indicating that this bacterium may be part of the trophic network that has a protective effect against ischaemic heart disease. (B) Scatter plot of instruments with sensitivity analyses. (C) Forestplot with the effect of all SNPs used for the Mendelian randomization for Ruminoccocaceae UCG-002. IVW, inverse variance weighted.

Figure 4

Heatmap of 16S faecal microbiome data of combined ethnicities. Six clusters were identified with this heatmap. The Prevotella enterotype-associated cluster, bacteria related to metformin, the CMR cluster core and a larger bacterial cluster, the Bacteroides cluster and a small intestinal bacterial cluster. Bacteria related to the heatmap based on n = 4117 individuals of different ethnicities. Hierarchical cluster based on Euclidean distances from a Spearman correlation.

Figure 5

High plasma triglyceride level prevalence and average CMR abundance between ethnicities. South-Asian Surinamese had the lowest abundance of CMR but the highest prevalence of elevated triglyceride levels, followed by the Turkish, Dutch, and Moroccan subgroups. Eurasians and Sub-Saharan groups have different CMR-dependent triglyceride associations. Asterisks and P-value indicate results from Mann–Whitney U testing comparing CMR abundance between individuals with normal fasting triglyceride levels or increased triglyceride levels (≥1.7 mmol/L or use of lipid-lowering drugs). Higher CMR abundance is seen in individuals with lower prevalence of elevated triglyceride levels. R² indicates the result of a linear regression between average CMR abundance from Eurasian subgroups (e.g. SA, T, D, and M). SA, South-Asian Surinamese; T, Turkish; D, Dutch; M, Moroccan; AS, African-Surinamese; G, Ghanaian.