ORIGINAL RESEARCH Moderate Renal Impairment and Toxic Metabolites Produced by the Intestinal Microbiome: Dietary Implications Michael Pignanelli, BMSc,* Chrysi Bogiatzi, MD,† , ‡ Gregory Gloor, PhD,§ Emma Allen-Vercoe, PhD,{ Gregor Reid, PhD,** , †† Bradley L. Urquhart, PhD,‡‡ Kelsey N. Ruetz, BMSc,‡‡ Thomas J. Velenosi, PhD,‡‡ and J. David Spence, MD† , §§ Objective: Toxic metabolites produced by the intestinal microbiome from animal proteins, carnitine (mainly from red meat), or phos- phatidylcholine (mainly from egg yolk), have important adverse effects on cardiovascular disease. These are renally eliminated and may be termed gut-derived uremic toxins (GDUT). We hypothesized that even moderate renal impairment and intake of nutrient precursors would raise plasma levels of GDUT. Design: A cohort study. Setting: Academic medical center. Subjects: Patients attending stroke prevention clinics at a university medical center were recruited. Main Outcome Measure: Nutrient intake was assessed by the 131-item Harvard Food Frequency Questionnaire; estimated glomer- ular filtration rate (eGFR) was caculated using the Chronic Kidney Disease-Epidemiology (EPI) equations. Plasma levels of trimethyl- amine n-oxide, p-cresyl sulfate, hippuric acid, p-cresyl glucuronide, pheny acetyl glutamine, and phenyl sulfate were measured by ultra-performance liquid chromatography coupled to quadrupole time-of-flight mass spectrometry. Results: Among 316 patients recruited, the mean (standard deviation [SD]) age was 66.74 (10.42) years; 59.7% were men. Mean eGFR was 76.03 6 20.01; 57 (18%) had eGFR,60 mL/min/1.73 m 2 . Plasma levels of all GDUT were significantly higher even with mod- erate reduction of eGFR. Nutrient intake affected plasma levels of some GDUT; the effects differed by eGFR above and below 60 mL/ min/1.73 m 2 . Plasma levels were obtained fasting, so we probably underestimated the effect of nutrient intake. Conclusions: Even moderate impairment of renal function was associated with higher plasma levels of GDUT. This has dietary im- plications for patients at risk of atherosclerosis, particularly in those with impaired renal function (including the elderly): they should limit intake of animal protein, red meat, and egg yolk. It also points the way to novel approaches to vascular prevention, including more inten- sive dialysis, renal transplantation, and modification of the intestinal microbiome with probiotics or fecal transplantation. Ó 2018 by the National Kidney Foundation, Inc. All rights reserved. Introduction T RADITIONAL RISK FACTORS for coronary heart disease explain only about half of the variance in athero- sclerosis burden. 1 Furthermore, genetic variants may account for only 10.6% of coronary heart disease (CHD) heritability. 2 Despite treatment of traditional risk factors, the residual risk of cardiovascular events with usual care remains 40%. 3 Levels of low-density lipoprotein cholesterol (LDL-C) do not predict progression/regression of atherosclerosis 4 ; nearly half of patients in a stroke prevention clinic had progression of carotid plaque burden despite achieving low levels of LDL-C; this was termed ‘‘resistant atherosclerosis’’. The pro- portion of patients with plaque progression despite a low LDL-C was greater among patients in higher quartiles of * Schulich School of Medicine and Dentistry M.D. candidate (CIHR Summer Research Training Program), London, Canada. † Stroke Prevention & Atherosclerosis Research Centre, Robarts Research Insti- tute, Western University, London, Canada. ‡ Department of Neurology, McMaster University, Hamilton, Canada. § Department of Biochemistry, Schulich School of Medicine and Dentistry, Western University, London, Canada. { Department of Molecular and Cell Biology, University of Guelph, Guelph, Canada. ** Department of Urology, Schulich School of Medicine and Dentistry, Western University, London, Canada. †† Department of Microbiology, Schulich School of Medicine and Dentistry, Western University, London, Canada. ‡‡ Department of Physiology & Pharmacology, Schulich School of Medicine and Dentistry Western University, London, Canada. §§ Divisions of Neurology and Clinical Pharmacology, Western University, London, Canada. Support: The study was funded by the Canadian Institutes of Health Research, grant number 133416. The funding source had no role in the design of the study or in the reporting of the results. Financial Disclosure: E.A-V. has patents on panels of beneficial bacteria. No other author has a relevant conflict of interest. Address correspondence to Dr. J. David Spence, MD, Stroke Prevention & Atherosclerosis Research Centre, Robarts Research Institute, Western University, 1400 Western Road, London, ON N6G 2V4, Canada. E-mail: dspence@ robarts.ca Ó 2018 by the National Kidney Foundation, Inc. All rights reserved. 1051-2276/$36.00 https://doi.org/10.1053/j.jrn.2018.05.007 Journal of Renal Nutrition, Vol -, No - (-), 2018: pp 1-10 1