Gut Colonization with Methanogenic Archaea Lowers Plasma Trimethylamine N-oxide Concentrations in Apolipoprotein e−/− Mice

Abstract

A mechanistic link between trimethylamine N-oxide (TMAO) and atherogenesis has been reported. TMAO is generated enzymatically in the liver by the oxidation of trimethylamine (TMA), which is produced from dietary choline, carnitine and betaine by gut bacteria. It is known that certain members of methanogenic archaea (MA) could use methylated amines such as trimethylamine as growth substrates in culture. Therefore, we investigated the efficacy of gut colonization with MA on lowering plasma TMAO concentrations. Initially, we screened for the colonization potential and TMAO lowering efficacy of five MA species in C57BL/6 mice fed with high choline/TMA supplemented diet, and found out that all five species could colonize and lover plasma TMAO levels, although with different efficacies. The top performing MA, Methanobrevibacter smithii, Methanosarcina mazei, and Methanomicrococcus blatticola, were transplanted into Apoe−/− mice fed with high choline/TMA supplemented diet. Similar to C57BL/6 mice, following initial provision of the MA, there was progressive attrition of MA within fecal microbial communities post-transplantation during the initial 3 weeks of the study. In general, plasma TMAO concentrations decreased significantly in proportion to the level of MA colonization. In a subsequent experiment, use of antibiotics and repeated transplantation of Apoe−/− mice with M. smithii, led to high engraftment levels during the 9 weeks of the study, resulting in a sustained and significantly lower average plasma TMAO concentrations (18.2 ± 19.6 μM) compared to that in mock-transplanted control mice (120.8 ± 13.0 μM, p < 0.001). Compared to control Apoe−/− mice, M. smithii-colonized mice also had a 44% decrease in aortic plaque area (8,570 μm [95% CI 19587–151821] vs. 15,369 μm [95% CI [70058–237321], p = 0.34), and 52% reduction in the fat content in the atherosclerotic plaques (14,283 μm [95% CI 4,957–23,608] vs. 29,870 μm [95% CI 18,074–41,666], p = 0.10), although these differences did not reach significance. Gut colonization with M. smithii leads to a significant reduction in plasma TMAO levels, with a tendency for attenuation of atherosclerosis burden in Apoe−/− mice. The anti-atherogenic potential of MA should be further tested in adequately powered experiments.

A Cross-Sectional Study of Compositional and Functional Profiles of Gut Microbiota in Sardinian Centenarians

“…M. smithii was reported to correlate with the consumption of milk products and perform specialized functions beneficial to the host (57, 58). Previous studies have shown that M. smithii can decrease the level of trimethylamine (TMA) which has been shown to correlate with clot-related events such as heart attacks and strokes (41, 59–61). Interestingly, coenzyme M- and F420-related gene families were significantly enriched in the centenarian group in our study; these enzymes are critical for decreasing TMA via methanogenesis (62).…”

The Relationship between Choline Bioavailability from Diet, Intestinal Microbiota Composition, and Its Modulation of Human Diseases

“…Another strategy for targeting TMAO is the use of probiotics (i.e., the ingestion of living microbes in adequate amounts that exert beneficial effects on human health) [ 170 ], with studies reporting promising microbiota re-modeling and TMAO-reducing effects in animal models. Eight weeks of dietary supplementation with Lactobacillus paracasei F19 protected rats from oxidative stress-induced liver damage by restoring the intestinal barrier and microbiota diversity [ 171 ], while gut colonization with M. smithii bacterial species was associated with a reduction in the TMAO concentration and attenuation of atherosclerosis in ApoE -/- mice [ 172 ]. Enterobacter aerogenes is another bacterial strain that has been shown to effectively reduce plasma TMAO and cecal TMAO levels by shifting the ratio of commensals and pathobionts in mice on a high-choline diet [ 173 ].…”

MtcB, a member of the MttB superfamily from the human gut acetogen Eubacterium limosum, is a cobalamin-dependent carnitine demethylase

“…Different microbes thus might contribute to or interfere with the net synthesis of TMA (25). Only one group of microbes that might diminish TMA production has been previously identified (26,27); the methanogenic archaea inhabiting the gut, whose genomes encode the pyrrolysyl-protein MttB, the TMA methyltransferase (1,2). Another route that might conceivably limit TMA production would be competition for the quaternary amines that are precursors to TMA.…”