A Metabolomics Approach to Identify Metabolites Associated With Mortality in Patients Receiving Maintenance Hemodialysis.

Introduction: Uremic toxins contributing to increased risk of death remain largely unknown. We used untargeted metabolomics to identify plasma metabolites associated with mortality in patients receiving maintenance hemodialysis. Methods: We measured metabolites in serum samples from 522 Longitudinal US/Canada Incident Dialysis (LUCID) study participants. We assessed the association between metabolites and 1-year mortality, adjusting for age, sex, race, cardiovascular disease, diabetes, body mass index, serum albumin, Kt/Vurea, dialysis duration, and country. We modeled these associations using limma, a metabolite-wise linear model with empirical Bayesian inference, and 2 machine learning (ML) models: Least absolute shrinkage and selection operator (LASSO) and random forest (RF). We accounted for multiple testing using a false discovery rate (pFDR) adjustment. We defined significant mortality-metabolite associations as pFDR < 0.1 in the limma model and metabolites of at least medium importance in both ML models. Results: The mean age of the participants was 64 years, the mean dialysis duration was 35 days, and there were 44 deaths (8.4%) during a 1-year follow-up period. Two metabolites were significantly associated with 1-year mortality. Quinolinate levels (a kynurenine pathway metabolite) were 1.72-fold higher in patients who died within year 1 compared with those who did not (pFDR, 0.009), wheras mesaconate levels (an emerging immunometabolite) were 1.57-fold higher (pFDR, 0.002). An additional 42 metabolites had high importance as per LASSO, 46 per RF, and 9 per both ML models but were not significant per limma. Conclusion: Quinolinate and mesaconate were significantly associated with a 1-year risk of death in incident patients receiving maintenance hemodialysis. External validation of our findings is needed.

Association of urine and plasma ADMA with atherosclerotic risk in DKD cardiovascular disease risk in diabetic kidney disease: findings from the Chronic Renal Insufficiency Cohort (CRIC) study.

BACKGROUND: Chronic kidney disease (CKD) is associated with atherosclerotic cardiovascular disease (ASCVD) risk, especially among those with diabetes. Altered metabolism of solutes that accumulate in CKD [asymmetric dimethylarginine (ADMA), symmetric dimethylarginine (SDMA) and trimethylamine N-oxide (TMAO)] may reflect pathways linking CKD with ASCVD. METHODS: This case-cohort study included Chronic Renal Insufficiency Cohort participants with baseline diabetes, estimated glomerular filtration rate <60 mL/min/1.73 m2, and without prior history for each outcome. The primary outcome was incident ASCVD (time to first myocardial infarction, stroke or peripheral artery disease event) and secondary outcome was incident heart failure. The subcohort comprised randomly selected participants meeting entry criteria. Plasma and urine ADMA, SDMA and TMAO concentrations were determined by liquid chromatography-tandem mass spectrometry. Associations of uremic solute plasma concentrations and urinary fractional excretions with outcomes were evaluated by weighted multivariable Cox regression models, adjusted for confounding covariables. RESULTS: Higher plasma ADMA concentrations (per standard deviation) were associated with ASCVD risk [hazard ratio (HR) 1.30, 95% confidence interval (CI) 1.01-1.68]. Lower fractional excretion of ADMA (per standard deviation) was associated with ASCVD risk (HR 1.42, 95% CI 1.07-1.89). The lowest quartile of ADMA fractional excretion was associated with greater ASCVD risk (HR 2.25, 95% CI 1.08-4.69) compared with the highest quartile. Plasma SDMA and TMAO concentration and fractional excretion were not associated with ASCVD. Neither plasma nor fractional excretion of ADMA, SDMA and TMAO were associated with incident heart failure. CONCLUSION: These data suggest that decreased kidney excretion of ADMA leads to increased plasma concentrations and ASCVD risk.

Type 2 diabetes affects arsenic metabolism via transporters in arsenic trioxide treated acute promyelocytic leukemia patients.

Our study aimed to explore whether type 2 diabetes (T2DM) can affect arsenic metabolism in acute promyelocytic leukemia (APL) patients treated with arsenic trioxide. We found that compared with non-diabetic APL patients, the concentrations of arsenic metabolites in APL patients with T2DM increased significantly and positively correlated with blood glucose (P < 0.05). Meanwhile, APL patients with T2DM were more prone to liver injury and QTc interval prolongation due to altered arsenic methylation capacity. Then we cultured HEK293T cells at different glucose concentrations, and the results showed that the cells with high glucose had higher concentrations of arsenic metabolites compared to other cells. Meanwhile, the high glucose significantly increased the mRNA and protein expression levels of the arsenic uptake transporter AQP7 in HEK293T cells. Overall, our study demonstrated that T2DM can lead to elevated concentrations of arsenic metabolites in APL patients by increasing AQP7 expression.

Efficacy, Safety, and Tolerability of Oral Furosemide Among Patients Receiving Hemodialysis: A Pilot Study.

Introduction: Diuretic use may reduce volume-related complications in hemodialysis. We evaluated the efficacy, safety, and tolerability of furosemide in patients with hemodialysis-dependent kidney failure. Methods: We conducted an open label, single-arm, 18-week, dose titration pilot study of oral furosemide (maximum dose 320 mg/day) among patients receiving maintenance hemodialysis who reported at least 1 cup of urine output per day. The primary efficacy outcome was an increase from baseline to a specified threshold of 24-hour urine volume, with the threshold based on baseline urine volume (<200 ml/day vs. ≥200 ml/day). Safety outcomes included hypokalemia and hypomagnesemia, and tolerability was assessed by prespecified patient-reported symptoms. Results: Of the 39 participants, 28 (72%) received the expected furosemide dose, 3 (8%) underwent dose reduction, 5 (12%) discontinued furosemide without dose reduction, and 3 (8%) underwent dose reduction and subsequently discontinued furosemide. The median (quartile 1, quartile 3) baseline 24-hour urine volume was 290 ml (110, 740), and the maximum, average daily study furosemide dose ranged from 69 mg/day to 320 mg/d. The urine output efficacy outcome was met by 12 (33%), 11 (33%), and 7 (22%) participants at weeks 5, 12, and 18, respectively, in the intention-to-treat analysis, and by 12 (39%), 9 (35%), and 7 (28%) participants at weeks 5, 12, and 18, respectively, in the on-treatment analysis. There were no electrolyte, furosemide level, or patient-reported hearing change safety events. Conclusion: Furosemide was generally safe and well tolerated, but only one-third of participants met the efficacy definition at week 5. The clinical importance of the efficacy findings is uncertain.

Association of Uremic Solutes With Cardiovascular Death in Diabetic Kidney Disease.

RATIONALE & OBJECTIVE: Cardiovascular disease (CVD) is a major cause of mortality among people with diabetic kidney disease (DKD). The pathophysiology is inadequately explained by traditional CVD risk factors. The uremic solutes trimethylamine-N-oxide (TMAO) and asymmetric and symmetric dimethylarginine (ADMA, SDMA) have been linked to CVD in kidney failure with replacement therapy (KFRT), but data are limited in populations with diabetes and less severe kidney disease. STUDY DESIGN: Observational cohort. SETTINGS & PARTICIPANTS: Random subcohort of 555 REGARDS (Reasons for Geographic and Racial Differences in Stroke) study participants with diabetes and estimated glomerular filtration rate (eGFR) <60 mL/min/1.73 m2 at study entry. EXPOSURE: ADMA, SDMA, and TMAO assayed by liquid chromatography-mass spectrometry in plasma and urine. OUTCOME: Cardiovascular mortality (primary outcome); all-cause mortality and incident KFRT (secondary outcomes). ANALYTICAL APPROACH: Plasma concentrations and ratios of urine to plasma concentrations of ADMA, SDMA, and TMAO were tested for association with outcomes. Adjusted Cox regression models were fitted and hazard ratios of outcomes calculated per standard deviation and per doubling, and as interquartile comparisons. RESULTS: The mean baseline eGFR was 44 mL/min/1.73 m2. Cardiovascular death, overall mortality, and KFRT occurred in 120, 285, and 89 participants, respectively, during a mean 6.2 years of follow-up. Higher plasma ADMA and SDMA (HRs of 1.20 and 1.28 per 1-SD greater concentration), and lower ratios of urine to plasma concentrations of ADMA, SDMA, and TMAO (HRs per halving of 1.53, 1.69, and 1.38) were associated with cardiovascular mortality. Higher plasma concentrations of ADMA, SDMA, and TMAO (HRs of 1.31, 1.42, and 1.13 per 1-SD greater concentration) and lower urine to plasma ratios of ADMA, SDMA, and TMAO (HRs per halving of 1.34, 1.37, and 1.26) were associated with all-cause mortality. Higher plasma ADMA and SDMA were associated with incident KFRT by categorical comparisons (HRs of 2.75 and 2.96, comparing quartile 4 to quartile 1), but not in continuous analyses. LIMITATIONS: Single cohort, restricted to patients with diabetes and eGFR < 60 mL/min/1.73 m2, potential residual confounding by GFR, no dietary information. CONCLUSIONS: Higher plasma concentrations and lower ratios of urine to plasma concentrations of uremic solutes were independently associated with cardiovascular and all-cause mortality in DKD. Associations of ratios of urine to plasma concentrations with mortality suggest a connection between renal uremic solute clearance and CVD pathogenesis.

Muscle fibrosis and maladaptation occur progressively in CKD and are rescued by dialysis.

BACKGROUNDSkeletal muscle maladaptation accompanies chronic kidney disease (CKD) and negatively affects physical function. Emphasis in CKD has historically been placed on muscle fiber-intrinsic deficits, such as altered protein metabolism and atrophy. However, targeted treatment of fiber-intrinsic dysfunction has produced limited improvement, whereas alterations within the fiber-extrinsic environment have scarcely been examined.METHODSWe investigated alterations to the skeletal muscle interstitial environment with deep cellular phenotyping of biopsies from patients with CKD and age-matched controls and performed transcriptome profiling to define the molecular underpinnings of CKD-associated muscle impairments. We examined changes in muscle maladaptation following initiation of dialysis therapy for kidney failure.RESULTSPatients with CKD exhibited a progressive fibrotic muscle phenotype, which was associated with impaired regenerative capacity and lower vascular density. The severity of these deficits was strongly associated with the degree of kidney dysfunction. Consistent with these profound deficits, CKD was associated with broad alterations to the muscle transcriptome, including altered ECM organization, downregulated angiogenesis, and altered expression of pathways related to stem cell self-renewal. Remarkably, despite the seemingly advanced nature of this fibrotic transformation, dialysis treatment rescued these deficits, restoring a healthier muscle phenotype. Furthermore, after accounting for muscle atrophy, strength and endurance improved after dialysis initiation.CONCLUSIONThese data identify a dialysis-responsive muscle fibrotic phenotype in CKD and suggest the early dialysis window presents a unique opportunity of improved muscle regenerative capacity during which targeted interventions may achieve maximal impact.TRIAL REGISTRATIONNCT01452412FUNDINGNIH, NIH Clinical and Translational Science Awards (CTSA), and Einstein-Mount Sinai Diabetes Research Center.

Effect of renal impairment on arsenic accumulation, methylation capacity, and safety in acute promyelocytic leukemia (APL) patients treated with arsenic trioxide.

Background: Arsenic trioxide (ATO) was successfully applied to treat acute promyelocytic leukemia (APL).Methods: Inorganic arsenic (iAs), monomethylarsonic acid (MMAV) and dimethyarsinic acid (DMAV) in plasma of 143 APL patients with different renal function were determined. Arsenic methylation capacity was evaluated by iAs%, MMAV%, DMAV%, primary methylation index (PMI, MMAV/iAs), and secondary methylated index (SMI, DMAV/MMAV). Arsenic accumulation with administration frequency were explored. Moreover, safety assessments were performed.Results: Compared with normal renal function, MMAV and DMAV concentrations increased 1.5-4 fold in moderate and severe renal impairment groups, iAs increased 1.3-1.7 fold. APL patients with renal impairment showed lower iAs%, but higher DMAV% and PMI in plasma than those with normal renal function (P < 0.05). MMAV, DMAV, and tAs apparently accumulated with administration frequency in moderate and severe renal dysfunction groups. The incidence of QTc interval prolongation and liver injury increased with the increasing severity of renal impairment.Conclusion: Renal dysfunction may increase exposure to arsenic and arsenic accumulation and affect methylation capacity, then the clinical safety in APL patients treated with ATO. Arsenic-level monitoring and dosing regimen adjustment should be considered in APL patients with moderate and severe renal dysfunction.

Why Is the GFR So High?: Implications for the Treatment of Kidney Failure.

The high GFR in vertebrates obligates large energy expenditure. Homer Smith's teleologic argument that this high GFR was needed to excrete water as vertebrates evolved in dilute seas is outdated. The GFR is proportional to the metabolic rate among vertebrate species and higher in warm-blooded mammals and birds than in cold-blooded fish, amphibians, and reptiles. The kidney clearance of some solutes is raised above the GFR by tubular secretion, and we presume secretion evolved to eliminate particularly toxic compounds. In this regard, high GFRs may provide a fluid stream into which toxic solutes can be readily secreted. Alternatively, the high GFR may be required to clear solutes that are too large or too varied to be secreted, especially bioactive small proteins and peptides. These considerations have potentially important implications for the understanding and treatment of kidney failure.

Intradialytic acid-base changes and organic anion production during high versus low bicarbonate hemodialysis.

The use of high dialysate bicarbonate for hemodialysis in end-stage renal disease is associated with increased mortality, but potential physiological mediators are poorly understood. Alkalinization due to high dialysate bicarbonate may stimulate organic acid generation, which could lead to poor outcomes. Using measurements of ß-hydroxybutyrate (BHB) and lactate, we quantified organic anion (OA) balance in two single-arm studies comparing high and low bicarbonate prescriptions. In study 1 (n = 10), patients became alkalemic using 37 meq/L dialysate bicarbonate; in contrast, with the use of 27 meq/L dialysate, net bicarbonate loss occurred and blood bicarbonate decreased. Total OA losses were not higher with 37 meq/L dialysate bicarbonate (50.9 vs. 49.1 meq using 27 meq/L, P = 0.66); serum BHB increased in both treatments similarly (P = 0.27); and blood lactate was only slightly higher with the use of 37 meq/L dialysate (P = 0.048), differing by 0.2 meq/L at the end of hemodialysis. In study 2 (n = 7), patients achieved steady state on two bicarbonate prescriptions: they were significantly more acidemic when dialyzed against a 30 meq/L bicarbonate dialysate compared with 35 meq/L and, as in study 1, became alkalemic when dialyzed against the higher bicarbonate dialysate. OA losses were similar to those in study 1 and again did not differ between treatments (38.9 vs. 43.5 meq, P = 0.42). Finally, free fatty acid levels increased throughout hemodialysis and correlated with the change in serum BHB (r = 0.81, P < 0.001), implicating upregulation of lipolysis as the mechanism for increased ketone production. In conclusion, lowering dialysate bicarbonate does not meaningfully reduce organic acid generation during hemodialysis or modify organic anion losses into dialysate.

Serum bicarbonate and cardiovascular events in hypertensive adults: results from the Systolic Blood Pressure Intervention Trial.

BACKGROUND: Low serum bicarbonate level is associated with increased mortality, but its role as a predictor of cardiovascular disease (CVD) is unclear. This study evaluates the association between serum bicarbonate concentration and CVD and whether the effect of intensive blood pressure (BP) lowering on CVD outcomes is modified by serum bicarbonate level. METHODS: The Systolic Blood Pressure Intervention Trial (SPRINT) randomized participants to a systolic BP target <120 mmHg (intensive treatment) or <140 mmHg (standard treatment). The primary CVD outcome was a composite of nonfatal myocardial infarction (MI), acute coronary syndrome not resulting in MI, stroke, acute decompensated heart failure and CVD death. Cox proportional hazards models adjusted for demographic, clinical and laboratory characteristics were used to evaluate the association of interest in 9334 SPRINT participants (ClinicalTrials.gov: NCT01206062). RESULTS: Over a median follow-up of 3.33 years (interquartile range 2.87-3.87 years), 618 (6.6%) participants experienced a primary CVD outcome. Participants with serum bicarbonate <22 mEq/L had a significantly higher risk of the primary CVD outcome (hazard ratio 1.54; 95% confidence interval 1.11-2.14, P = 0.01), compared with participants with bicarbonate 22-26 mEq/L. The magnitude of the CVD risk reduction with intensive BP lowering was similar across bicarbonate strata (P-value for interaction = 0.97). CONCLUSIONS: In hypertensive individuals, serum bicarbonate level <22 mEq/L was associated with an increased CVD risk. The effect of intensive BP lowering on CVD outcomes was not modified by the serum bicarbonate level.

Contribution of 'clinically negligible' residual kidney function to clearance of uremic solutes.

BACKGROUND: Residual kidney function (RKF) is thought to exert beneficial effects through clearance of uremic toxins. However, the level of native kidney function where clearance becomes negligible is not known. METHODS: We aimed to assess whether levels of nonurea solutes differed among patients with 'clinically negligible' RKF compared with those with no RKF. The hemodialysis study excluded patients with urinary urea clearance >1.5 mL/min, below which RKF was considered to be 'clinically negligible'. We measured eight nonurea solutes from 1280 patients participating in this study and calculated the relative difference in solute levels among patients with and without RKF based on measured urinary urea clearance. RESULTS: The mean age of the participants was 57 years and 57% were female. At baseline, 34% of the included participants had clinically negligible RKF (mean 0.7 ± 0.4 mL/min) and 66% had no RKF. Seven of the eight nonurea solute levels measured were significantly lower in patients with RKF than in those without RKF, ranging from -24% [95% confidence interval (CI) -31 to -16] for hippurate, -7% (-14 to -1) for trimethylamine-N-oxide and -4% (-6 to -1) for asymmetric dimethylarginine. The effect of RKF on plasma levels was comparable or more pronounced than that achieved with a 31% higher dialysis dose (spKt/Vurea 1.7 versus 1.3). Preserved RKF at 1-year follow-up was associated with a lower risk of cardiac death and first cardiovascular event. CONCLUSIONS: Even at very low levels, RKF is not 'negligible', as it continues to provide nonurea solute clearance. Management of patients with RKF should consider these differences.

A Randomized Trial Comparing the Safety, Adherence, and Pharmacodynamics Profiles of Two Doses of Sodium Bicarbonate in CKD: the BASE Pilot Trial.

BACKGROUND: Oral sodium bicarbonate (NaHCO3) may preserve kidney function in CKD, even if initiated when serum bicarbonate concentration is normal. Adequately powered trials testing this hypothesis have not been conducted, partly because the best dose for testing is unknown. METHODS: This multicenter pilot trial assessed the safety, tolerability, adherence, and pharmacodynamics of two doses of NaHCO3 over 28 weeks in adults with eGFR 20-44 or 45-59 ml/min per 1.73 m2 with urinary albumin/creatinine (ACR) ≥50 mg/g and serum bicarbonate 20-28 meq/L. We randomly assigned 194 participants from ten clinical sites to receive higher-dose (HD-NaHCO3; 0.8 meq/kg of lean body wt per day; n=90) or lower-dose (LD-NaHCO3; 0.5 meq/kg of lean body wt per day; n=52) NaHCO3 or matching placebo (n=52). The dose was adjusted depending on side effects. The prescribed dose at week 28 was the primary outcome; a dose was considered acceptable for a full-scale trial if ≥67% of participants were on full-dose and ≥80% were on ≥25% of the per-protocol dose. RESULTS: Mean±SD baseline eGFR was 36±9 ml/min per 1.73 m2, serum bicarbonate was 24±2 meq/L, and median (IQR) ACR was 181 (25-745) mg/g. Both doses were well tolerated without significant changes in BP, weight, or serum potassium. The proportions of adverse events and hospitalizations were similar across the groups. Consequently, 87% in HD-NaHCO3, 96% in LD-NaHCO3, and 87% in placebo were on full dose at week 28; and 91% in HD-NaHCO3, 98% in LD-NaHCO3, and 92% in placebo were on ≥25% of the per-protocol dose. Mean urinary ammonium excretion was 25% lower and serum bicarbonate concentration was 1.3 meq/L higher in HD-NaHCO3 compared with LD-NaHCO3 at week 28. However, mean ACR increased by 12% in the lower-dose group and 30% in the higher-dose group. CONCLUSIONS: Both NaHCO3 doses were well tolerated over 28 weeks with no significant difference in adverse events or hospitalization compared with placebo. The higher dose lowered urinary ammonium excretion and increased serum bicarbonate more than the lower dose but was associated with a greater increase in ACR. The higher 0.8 meq/kg of lean body wt per day dose of NaHCO3 may be a reasonable choice for future trials.

Effects of Sodium Bicarbonate in CKD Stages 3 and 4: A Randomized, Placebo-Controlled, Multicenter Clinical Trial.

RATIONALE & OBJECTIVE: Metabolic acidosis associated with chronic kidney disease (CKD) may contribute to muscle dysfunction and bone disease. We aimed to test whether treatment with sodium bicarbonate improves muscle and bone outcomes. STUDY DESIGN: Multicenter, randomized, placebo-controlled, clinical trial. SETTING & PARTICIPANTS: 149 patients with CKD stages 3 and 4 between July 2011 and April 2016 at 3 centers in Cleveland, OH, and the Bronx, NY. INTERVENTION: Sodium bicarbonate (0.4 mEq per kg of ideal body weight per day) (n=74) or identical-appearing placebo (n=75). OUTCOMES: Dual primary outcomes were muscle function assessed using sit-to-stand test and bone mineral density. Muscle biopsies were performed at baseline and 2 months. Participants were seen at baseline and 2, 6, 12, and 24 months. RESULTS: Mean baseline serum bicarbonate level was 24.0±2.2 (SD) mEq/L and mean baseline estimated glomerular filtration rate was 36.3±11.2mL/min/1.73m2. Baseline characteristics did not differ between groups. Mean serum bicarbonate levels in the intervention arm during follow-up were 26.4±2.2, 25.5±2.3, 25.6±2.6, and 24.4±2.8 mEq/L (at 2, 6, 12, and 24 months). These were significantly higher than in the placebo group (P<0.001). Compared to the placebo group, participants randomly assigned to sodium bicarbonate treatment had no significant differences in sit-to-stand time (5 repetitions: P=0.1; and 10 repetitions P=0.07) or bone mineral density (P=0.3). Sodium bicarbonate treatment caused a decrease in serum potassium levels that was of borderline statistical significance (P=0.05). There were no significant differences in estimated glomerular filtration rates, blood pressure, weight, serious adverse events, or levels of muscle gene expression between the randomly assigned groups. LIMITATIONS: Initial mean serum bicarbonate level was in the normal range. CONCLUSIONS: Sodium bicarbonate therapy in patients with CKD stages 3 and 4 significantly increases serum bicarbonate and decreases potassium levels. No differences were found in muscle function or bone mineral density between the randomly assigned groups. Larger trials are required to evaluate effects on kidney function. FUNDING: National Institutes of Health grant. TRIAL REGISTRATION: Registered at ClinicalTrials.gov with study number NCT01452412.

Effect of continuous venovenous haemodialysis on outcome and pharmacokinetics of arsenic species in a patient with acute promyelocytic leukaemia and acute kidney injury.

This study presents outcome and pharmacokinetics of arsenic trioxide (ATO) metabolites in patients on continuous venovenous haemodialysis (CVVHD). Of 3 acute promyelocytic leukaemia patients receiving CVVHD in management of acute kidney injury, only 1 patient was included. The patient presented disseminated intravascular coagulation and acute kidney injury before induction therapy was conducted. CVVHD was performed and ATO was initiated. Species of ATO metabolites in plasma and effluent were analysed using high performance liquid chromatography-hydride generation-atomic fluorescence spectrometry. Plasma concentrations of AsIII , monomethylarsonic acid and dimethylarsinic acid with CVVHD were lower than those without CVVHD. Area under the concentration-time curve from 0 to the last sample with quantifiable concentration of AsIII without CVVHD was significantly higher than that with CVVHD (292.10 ng h/mL vs 195.86 ng h/mL, P = .037), which were not observed for monomethylarsonic acid and dimethylarsinic acid. Dialysate saturation of arsenic species was remarkable, especially for AsIII . Complete remission was achieved and renal function recovered. In this study, ATO can be used safely and effectively to treat acute promyelocytic leukaemia patients undergoing CVVHD without dose adjustment.