Intestinal microbiota metabolism of l-carnitine, a nutrient in red meat, promotes atherosclerosis

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Abstract

Intestinal microbiota metabolism of choline and phosphatidylcholine produces trimethylamine (TMA), which is further metabolized to a proatherogenic species, trimethylamine-N-oxide (TMAO). We demonstrate here that metabolism by intestinal microbiota of dietary l-carnitine, a trimethylamine abundant in red meat, also produces TMAO and accelerates atherosclerosis in mice. Omnivorous human subjects produced more TMAO than did vegans or vegetarians following ingestion of l-carnitine through a microbiota-dependent mechanism. The presence of specific bacterial taxa in human feces was associated with both plasma TMAO concentration and dietary status. Plasma l-carnitine levels in subjects undergoing cardiac evaluation (n = 2,595) predicted increased risks for both prevalent cardiovascular disease (CVD) and incident major adverse cardiac events (myocardial infarction, stroke or death), but only among subjects with concurrently high TMAO levels. Chronic dietary l-carnitine supplementation in mice altered cecal microbial composition, markedly enhanced synthesis of TMA and TMAO, and increased atherosclerosis, but this did not occur if intestinal microbiota was concurrently suppressed. In mice with an intact intestinal microbiota, dietary supplementation with TMAO or either carnitine or choline reduced in vivo reverse cholesterol transport. Intestinal microbiota may thus contribute to the well-established link between high levels of red meat consumption and CVD risk.

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Figure 1: TMAO production from l-carnitine is a microbiota-dependent process in humans.
Figure 2: The formation of TMAO from ingested l-carnitine is negligible in vegans, and fecal microbiota composition associates with plasma TMAO concentrations.
Figure 3: The metabolism of carnitine to TMAO is an inducible trait and associates with microbiota composition.
Figure 4: Relationship between plasma carnitine concentration and CVD risks.
Figure 5: Dietary l-carnitine accelerates atherosclerosis and inhibits reverse cholesterol transport in a microbiota dependent fashion.
Figure 6: Effect of TMAO on cholesterol and sterol metabolism.

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Acknowledgements

We thank L. Kerchenski and C. Stevenson for assistance in performing the clinical studies; A. Pratt, S. Neale, M. Pepoy and B. Sullivan for technical assistance with human specimen processing and routine clinical diagnostic testing; E. Klipfell, F. McNally and M. Berk for technical assistance; and the subjects who consented to participate in these studies. Mass spectrometry instrumentation used was housed within the Cleveland Clinic Mass Spectrometry Facility with partial support through a Center of Innovation by AB SCIEX. Germ-free mice were obtained from the University of North Carolina Gnotobiotic Facility, which is supported by P30-DK034987-25-28 and P40-RR018603-06-08. This research was supported by US National Institutes of Health grants R01 HL103866 (S.L.H.), P20 HL113452 (S.L.H. and W.H.W.T.), PO1 HL30568 (A.J.L.), PO1 H28481 (A.J.L.), R00 HL096166 (J.M.B.), UH3-DK083981 (J.D.L.), 1RC1DK086472 (R.M.K.) and the Leducq Foundation (S.L.H.). The clinical study GeneBank was supported in part by P01 HL076491, P01 HL098055, R01 HL103931 and the Cleveland Clinic Foundation General Clinical Research Center of the Cleveland Clinic/Case Western Reserve University Clinical and Translational Science Award (1UL1RR024989). S.L.H. is also partially supported by a gift from the Leonard Krieger Fund. Z.W. was partially supported by a Scientist Development Grant from the American Heart Association. E.O. was supported by a MOBILITAS Postdoctoral Research Grant (MJD252). R.A.K. was supported in part by US National Institutes of Health grant T32 GM007250.

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R.A.K. participated in laboratory, mouse and human studies, assisted in statistical analyses, helped design the experiments and drafted the manuscript. Z.W. performed the initial metabolomics study and assisted with mouse and mass spectrometry analyses. B.S.L. synthesized d3- and d9-carnitine for studies, assisted with mass spectrometry analyses and helped draft the manuscript. E.B.B. and X.F. assisted in performance of mass spectrometry analyses of the large human clinical cohort study. Y.W. and L.L. performed the statistical analyses and critically reviewed the manuscript. J.D.S. helped with aortic root atherosclerosis analyses and critical review of the manuscript. J.A.D. assisted in experimental design. J.A.B. and B.T.S. assisted in laboratory and mouse experiments. E.O. and A.J.L. performed and helped interpret mouse cecal microbiota analyses. J.C., F.D.B., H.L., G.D.W., J.D.L. and R.M.K. assisted in human subject microbiota analyses and helped interpret human microbiota data. M.W. and J.M.B. assisted with measurement of bile acid pool size and helped with critical review of the manuscript. W.H.W.T. helped with human studies and critical review of the manuscript. S.L.H. conceived of the idea, helped design the experiments, provided the funding for the study and helped draft and critically revise the manuscript.

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Correspondence to Stanley L Hazen.

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Competing interests

Z.W. and B.S.L. are named as co-inventors on pending patents held by the Cleveland Clinic relating to cardiovascular diagnostics and have the right to receive royalty payments for inventions or discoveries related to cardiovascular diagnostics from Liposciences. W.H.W.T. received research grant support from Abbott Laboratories and served as a consultant for Medtronic and St. Jude Medical. S.L.H. and J.D.S. are named as co-inventors on pending and issued patents held by the Cleveland Clinic relating to cardiovascular diagnostics and therapeutics patents. S.L.H. has been paid as a consultant or speaker by the following companies: Cleveland Heart Lab., Esperion, Liposciences, Merck & Co. and Pfizer. He has received research funds from Abbott, Cleveland Heart Lab., Esperion and Liposciences and has the right to receive royalty payments for inventions or discoveries related to cardiovascular diagnostics from Abbott Laboratories, Cleveland Heart Lab., Frantz Biomarkers, Liposciences and Siemens.

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Koeth, R., Wang, Z., Levison, B. et al. Intestinal microbiota metabolism of l-carnitine, a nutrient in red meat, promotes atherosclerosis. Nat Med 19, 576–585 (2013). https://doi.org/10.1038/nm.3145

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