Trimethlyamine-N-oxide (TMAO) was recently identified as a promoter of atherosclerosis. Patients with CKD exhibit accelerated development of atherosclerosis; however, no studies have explored the relationship between TMAO and atherosclerosis formation in this group. This study measured serum concentrations and urinary excretion of TMAO in a CKD cohort (n=104), identified the effect of renal transplant on serum TMAO concentration in a subset of these patients (n=6), and explored the cross-sectional relationship between serum TMAO and coronary atherosclerosis burden in a separate CKD cohort (n=220) undergoing coronary angiography. Additional exploratory analyses examined the relationship between baseline serum TMAO and long-term survival after coronary angiography. Serum TMAO concentrations demonstrated a strong inverse association with eGFR (r 2 =0.31, P,0.001). TMAO concentrations were markedly higher in patients receiving dialysis (median [interquartile range], 94.4 mM [54.8-133.0 mM] for dialysis-dependent patients versus 3.3 mM [3.1-6.0 mM] for healthy controls; P,0.001); whereas renal transplantation resulted in substantial reductions in TMAO concentrations (median [min-max] 71.2 mM [29.2-189.7 mM] pretransplant versus 11.4 mM [8.9-20.2 mM] posttransplant; P=0.03). TMAO concentration was an independent predictor for coronary atherosclerosis burden (P=0.02) and predicted long-term mortality independent of traditional cardiac risk factors (hazard ratio, 1.26 per 10 mM increment in TMAO concentration; 95% confidence interval, 1.13 to 1.40; P,0.001). In conclusion, serum TMAO concentrations substantially increase with decrements in kidney function, and this effect is reversed by renal transplantation. Increased TMAO concentrations correlate with coronary atherosclerosis burden and may associate with long-term mortality in patients with CKD undergoing coronary angiography. Patients with CKD have a high prevalence of cardiovascular comorbidities, which primarily contributes to the exceedingly high mortality in this group. 1,2 For example, the 5-year survival for ESRD patients receiving dialysis is approximately 35%, with .50% of the mortality in this group resulting directly from cardiovascular causes. 1 It is well established that CKD patients exhibit a disproportionate burden of atherosclerosis as compared with individuals having normal kidney function. [2][3][4][5] Furthermore, a higher prevalence of traditional risk factors for the development of atherosclerosis, such as hypertension, diabetes and hyperlipidemia, only partially accounts for the accelerated atherosclerosis in CKD patients, leading to the hypothesis that unique risk factors must be present in this population. 6,7

Patients with chronic kidney disease (CKD) demonstrate complex mineral metabolism derangements and a high prevalence of vitamin D deficiency. However, the optimal method of 25-hydroxyvitamin D (25(OH)D) repletion is unknown, and trials analysing the comparative efficacy of cholecalciferol and ergocalciferol in this population are lacking. We conducted a randomised clinical trial of cholecalciferol 1250 μg (50 000 IU) weekly v. ergocalciferol 1250 μg (50 000 IU) weekly for 12 weeks in forty-four non-dialysis-dependent patients with stage 3–5 CKD. The primary outcome was change in total 25(OH)D from baseline to week 12 (immediately after therapy). Secondary analyses included the change in 1,25-dihydroxyvitamin D (1,25(OH)2D), parathyroid hormone (PTH), D2 and D3 sub-fractions of 25(OH)D and 1,25(OH)2D and total 25(OH)D from baseline to week 18 (6 weeks after therapy). Cholecalciferol therapy yielded a greater change in total 25(OH)D (45·0 (SD 16·5) ng/ml) v. ergocalciferol (30·7 (SD 15·3) ng/ml) from baseline to week 12 (P < 0·01); this observation partially resulted from a substantial reduction in the 25(OH)D3 sub-fraction with ergocalciferol. However, following cessation of therapy, no statistical difference was observed for total 25(OH)D change from baseline to week 18 between cholecalciferol and ergocalciferol groups (22·4 (SD 12·7) v. 17·6 (SD 8·9) ng/ml, respectively; P = 0·17). We observed no significant difference between these therapies with regard to changes in serum PTH or 1,25(OH)2D. Therapy with cholecalciferol, compared with ergocalciferol, is more effective at raising serum 25(OH)D in non- dialysis-dependent CKD patients while active therapy is ongoing. However, levels of 25(OH)D declined substantially in both arms following cessation of therapy, suggesting the need for maintenance therapy to sustain levels.

BackgroundRecent evidence suggests the systemic accumulation of by-products of gut microbes contributes to cardiovascular morbidity in patients with CKD. Limiting the generation of toxic bacterial by-products by manipulating the intestinal microbiota may be a novel strategy for reducing cardiovascular disease in CKD. Rifaximin is a minimally absorbed, oral antibiotic that targets intestinal pathogens and is commonly used as chronic therapy for the prevention of encephalopathy in patients with cirrhosis.MethodsWe conducted a randomized, double-blinded, placebo-controlled trial to determine the effect of a 10-day course of oral rifaximin 550 mg BID versus placebo on circulating concentrations of gut-derived cardiovascular toxins and proinflammatory cytokines in patients with stage 3–5 CKD (n=38). The primary clinical outcome was change in serum trimethylamine N-oxide (TMAO) concentrations from baseline to study end. Secondary outcomes included change in serum concentrations of p-cresol sulfate, indoxyl sulfate, kynurenic acid, deoxycholic acid, and inflammatory cytokines (C-reactive protein, IL-6, IL-1β), and change in composition and diversity of fecal microbiota.ResultsA total of 19 patients were randomized to each of the rifaximin and placebo arms, with n=17 and n=14 completing both study visits in these respective groups. We observed no difference in serum TMAO change (post-therapy minus baseline TMAO) between the rifaximin and placebo groups (mean TMAO change −3.9±15.4 for rifaximin versus 0.5±9.5 for placebo, P=0.49). Similarly, we found no significant change in serum concentrations for p-cresol sulfate, indoxyl sulfate, kynurenic acid, deoxycholic acid, and inflammatory cytokines. We did observe differences in colonic bacterial communities, with the rifaximin group exhibiting significant decreases in bacterial richness (Chao1, P=0.02) and diversity (Shannon H, P=0.05), along with altered abundance of several bacterial genera.ConclusionsShort-term rifaximin treatment failed to reduce gut-derived cardiovascular toxins and inflammatory cytokines in patients with CKD.Clinical Trial registry name and registration number Rifaximin Therapy in Chronic Kidney Disease, NCT02342639

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