Nitric oxide and long-term outcomes after kidney transplantation: Results of the TransplantLines cohort study.

Impaired endogenous nitric oxide (NO) production may contribute to graft failure and premature mortality in kidney transplant recipients (KTR). We investigated potential associations of 24-h urinary NOx (NO3- + NO2-) excretion (uNOx) with long-term outcomes. uNOx was determined by HPLC and GC-MS in 698 KTR and in 132 kidney donors before and after donation. Additionally, we measured urinary nitroso species (RXNO) by gas-phase chemiluminescence. Median uNOx was lower in KTR compared to kidney donors (688 [393-1076] vs. 1301 [868-1863] before donation and 1312 [982-1853] µmol/24 h after donation, P < 0.001). During median follow-up of 5.4 [4.8-6.1] years, 150 KTR died (61 due to cardiovascular disease) and 83 experienced graft failure. uNOx was inversely associated with all-cause mortality (HR per doubling of uNOx: 0.84 [95% CI 0.75-0.93], P < 0.001) and cardiovascular mortality (HR 0.78 [95% CI 0.67-0.92], P = 0.002). The association of uNOx with graft failure was lost when adjusted for renal function (HR per doubling of uNOx: 0.89 [95% CI 0.76-1.05], P = 0.17). There were no significant associations of urinary RXNO with outcomes. Our study suggests that KTR have lower NO production than healthy subjects and that lower uNOx is associated with a higher risk of all-cause and cardiovascular mortality.

Meat intake and risk of mortality and graft failure in kidney transplant recipients.

BACKGROUND: It is unknown whether meat intake is beneficial for long-term patient and graft survival in kidney transplant recipients (KTR). OBJECTIVES: We first investigated the association of the previously described meat intake biomarkers 1-methylhistidine and 3-methylhistidine with intake of white and red meat as estimated from a validated food frequency questionnaire (FFQ). Second, we investigated the association of the meat intake biomarkers with long-term outcomes in KTR. METHODS: We measured 24-h urinary excretion of 1-methylhistidine and 3-methylhistidine by validated assays in a cohort of 678 clinically stable KTR. Cross-sectional associations were assessed by linear regression. We used Cox regression analyses to prospectively study associations of log2-transformed biomarkers with mortality and graft failure. RESULTS: Urinary 1-methylhistidine and 3-methylhistidine excretion values were median: 282; interquartile range (IQR): 132-598 µmol/24 h and median: 231; IQR: 175-306 µmol/24 h, respectively. Urinary 1-methylhistidine was associated with white meat intake [standardized ß (st ß): 0.20; 95% CI: 0.12, 0.28; P < 0.001], whereas urinary 3-methylhistidine was associated with red meat intake (st ß: 0.30; 95% CI: 0.23, 0.38; P < 0.001). During median follow-up for 5.4 (IQR: 4.9-6.1) y, 145 (21%) died and 83 (12%) developed graft failure. Urinary 3-methylhistidine was inversely associated with mortality independently of potential confounders (HR per doubling: 0.55; 95% CI: 0.42, 0.72; P < 0.001). Both urinary 1-methylhistidine and urinary 3-methylhistidine were inversely associated with graft failure independent of potential confounders (HR per doubling: 0.84; 95% CI: 0.73, 0.96; P = 0.01; and 0.59; 95% CI: 0.41, 0.85; P = 0.004, respectively). CONCLUSIONS: High urinary 3-methylhistidine, reflecting higher red meat intake, is independently associated with lower risk of mortality. High urinary concentrations of both 1- and 3-methylhistidine, of which the former reflects higher white meat intake, are independently associated with lower risk of graft failure in KTR. Future intervention studies are warranted to study the effect of high meat intake on mortality and graft failure in KTR, using these biomarkers.

Net Endogenous Acid Excretion and Kidney Allograft Outcomes.

BACKGROUND AND OBJECTIVES: High dietary acid load may accelerate a decline in kidney function. We prospectively investigated whether dietary acid load is associated with graft outcomes in kidney transplant recipients, and whether venous bicarbonate mediates this association. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: We used data from 642 kidney transplant recipients with a functioning graft ≥1 year after transplantation. Net endogenous acid production was estimated using food frequency questionnaires and, alternatively, 24-hour urinary urea and potassium excretion to estimate net endogenous acid production. We defined the composite kidney end point as a doubling of plasma creatinine or graft failure. Multivariable Cox regression analyses, adjusted for potential confounders, were used to study the associations of dietary acid load with the kidney end point. We evaluated potential mediation effects of venous bicarbonate, urinary bicarbonate excretion, urinary ammonium excretion, titratable acid excretion, and net acid excretion on the association between net endogenous acid production and the kidney end point. RESULTS: The median net endogenous acid production using food frequency questionnaires and net endogenous acid production using urinary excretion were 40 (interquartile range, 35-45) and 54 (interquartile range, 44-66) mEq/day, respectively. During a median follow-up of 5.3 years (interquartile range, 4.1-6.0), 121 (19%) participants reached the kidney end point. After multivariable adjustment, net endogenous acid production using food frequency questionnaires and net endogenous acid production using urinary excretion (per SD higher) were independently associated with higher risk for kidney end point (hazard ratio, 1.33; 95% confidence interval, 1.12 to 1.57, P=0.001 and hazard ratio, 1.44; 95% confidence interval, 1.24 to 1.69, P<0.001, respectively). Baseline venous bicarbonate mediated 20% of the association between net endogenous acid production using food frequency questionnaires and the kidney end point. Baseline venous bicarbonate, urinary ammonium excretion, and net acid excretion mediated 25%, -14%, and -18%, respectively, of the association between net endogenous acid production using urinary excretion and the kidney end point. CONCLUSIONS: Higher dietary acid load was associated with a higher risk of doubling of plasma creatinine or graft failure, and this association was partly mediated by venous bicarbonate, urinary ammonium, and net acid excretion.

The association between use of proton-pump inhibitors and excess mortality after kidney transplantation: A cohort study.

BACKGROUND: Chronic use of proton-pump inhibitors (PPIs) is common in kidney transplant recipients (KTRs). However, concerns are emerging about the potential long-term complications of PPI therapy. We aimed to investigate whether PPI use is associated with excess mortality risk in KTRs. METHODS AND FINDINGS: We investigated the association of PPI use with mortality risk using multivariable Cox proportional hazard regression analyses in a single-center prospective cohort of 703 stable outpatient KTRs, who visited the outpatient clinic of the University Medical Center Groningen (UMCG) between November 2008 and March 2011 (ClinicalTrials.gov Identifier NCT02811835). Independent replication of the results was performed in a prospective cohort of 656 KTRs from the University Hospitals Leuven (NCT01331668). Mean age was 53 ± 13 years, 57% were male, and 56.6% used PPIs. During median follow-up of 8.2 (4.7-9.0) years, 194 KTRs died. In univariable Cox regression analyses, PPI use was associated with an almost 2 times higher mortality risk (hazard ratio [HR] 1.86, 95% CI 1.38-2.52, P < 0.001) compared with no use. After adjustment for potential confounders, PPI use remained independently associated with mortality (HR 1.68, 95% CI 1.21-2.33, P = 0.002). Moreover, the HR for mortality risk in KTRs taking a high PPI dose (>20 mg omeprazole equivalents/day) compared with patients taking no PPIs (HR 2.14, 95% CI 1.48-3.09, P < 0.001) was higher than in KTRs taking a low PPI dose (HR 1.72, 95% CI 1.23-2.39, P = 0.001). These findings were replicated in the Leuven Renal Transplant Cohort. The main limitation of this study is its observational design, which precludes conclusions about causation. CONCLUSIONS: We demonstrated that PPI use is associated with an increased mortality risk in KTRs, independent of potential confounders. Moreover, our data suggest that this risk is highest among KTRs taking high PPI dosages. Because of the observational nature of our data, our results require further corroboration before it can be recommended to avoid the long-term use of PPIs in KTRs. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT02811835, NCT01331668.

Urinary sulfate excretion and risk of late graft failure in renal transplant recipients - a prospective cohort study.

Hydrogen sulfide (H2 S), produced from metabolism of dietary sulfur-containing amino acids, is allegedly a renoprotective compound. Twenty-four-hour urinary sulfate excretion (USE) may reflect H2 S bioavailability. We aimed to investigate the association of USE with graft failure in a large prospective cohort of renal transplant recipients (RTR). We included 704 stable RTR, recruited at least 1 year after transplantation. We applied log-rank testing and Cox regression analyses to study association of USE, measured from baseline 24 h urine samples, with graft failure. Median age was 55 [45-63] years (57% male, eGFR was 45 ± 19 ml/min/1.73 m2 ). Median USE was 17.1 [13.1-21.1] mmol/24 h. Over median follow-up of 5.3 [4.5-6.0] years, 84 RTR experienced graft failure. RTR in the lowest sex-specific tertile of USE experienced a higher rate of graft failure during follow-up than RTR in the middle and highest sex-specific tertiles (18%, 13%, and 5%, respectively, log-rank P < 0.001). In Cox regression analyses, USE was inversely associated with graft failure [HR per 10 mmol/24 h: 0.37 (0.24-0.55), P < 0.001]. The association remained independent of adjustment for potential confounders, including age, sex, eGFR, proteinuria, time between transplantation and baseline, BMI, smoking, and high sensitivity C-reactive protein [HR per 10 mmol/24 h: 0.51 (0.31-0.82), P = 0.01]. In conclusion, this study demonstrates a significant inverse association of USE with graft failure in RTR, suggesting high H2 S bioavailability as a novel, potentially modifiable factor for prevention of graft failure in RTR.

Clinical impression for identification of vulnerable older patients in the emergency department.

OBJECTIVES: To investigate whether the clinical impression of vulnerability and the Dutch Safety Management Program (VMS), a screening instrument on four geriatric domains (activities in daily living, falls, malnutrition, delirium) are useful predictors of 1-year mortality in older patients in the emergency department. METHODS: This was a prospective observational study in the emergency department of a tertiary care teaching hospital. Patients aged 65 years and older visiting the emergency department, and their attending physicians and nurses were included. Clinical impression of vulnerability appraised by physician and nurse and the VMS-screening were recorded. RESULTS: We included 196 patients of whom 64.8%, 61.7%, and 52.6% were considered vulnerable based on the clinical impression of vulnerability of physicians, nurses, and VMS-screening, respectively. Agreement between clinical impression of vulnerability of physicians and nurses, and VMS-screening were both fair (overall agreement 63.3% for both, and respectively kappa 0.32 and kappa 0.31). Clinical impression of vulnerability of physicians, nurses, and VMS-screening had a sensitivity of respectively 94%, 86%, and 73% for predicting 1-year mortality. A positive clinical impression of vulnerability was associated mostly with factors which can be observed directly during first patient contact after arrival to the emergency department, such as age, nutritional status, and functional impairment. CONCLUSION: The clinical impression of vulnerability is a simple dichotomous question which can be used as a first step in the identification of vulnerable older emergency department patients, whereas the more time-consuming VMS-screening is more specific for detection of vulnerability. The clinical impression of vulnerability is therefore useful in a busy emergency department environment where time and resources are limited.

Physical Activity and the Development of Post-Transplant Diabetes Mellitus, and Cardiovascular- and All-Cause Mortality in Renal Transplant Recipients.

(1) Background: Little is currently known about the health impacts of daily-life moderate-to-vigorous physical activity (MVPA) in relation to the development of post-transplant diabetes mellitus (PTDM) and the long-term survival of renal transplant recipients (RTRs). (2) Methods: We analyzed self-reported data on MVPA within non-occupational and occupational domains, estimated with the SQUASH questionnaire, from a prospective cohort study of RTRs (n = 650) with a functioning graft exceeding 1 year. PTDM diagnoses were based on plasma glucose levels (≥126 mg/dL), HbA1c (≥6.5%), and the use of antidiabetic medication. Mortality data were retrieved from patient files up to the end of September 2015. (3) Results: During a median follow-up period of 5.3 years, 50 patients (10%) developed PTDM and 129 (19.8%) died. Of these deaths, 53 (8.9%) were caused by cardiovascular disease. Cox regression analyses showed that higher MVPA levels among patients were associated with a lower risk of PTDM (hazard ratio (HR); 95% confidence interval (95%CI) = 0.49; 0.25-0.96, p = 0.04), cardiovascular- (0.34; 0.15-0.77, p = 0.01), and all-cause mortality (0.37; 0.24-0.58, p < 0.001) compared with No-MVPA patients, independently of age, sex, and kidney function parameters. Associations of MVPA with cardiovascular and all-cause mortality remained significant and materially unchanged following further adjustments made for transplant characteristics, lifestyle factors, metabolic parameters, medication use, and creatinine excretion (muscle mass). However, the association between MVPA and PTDM was no longer significant after we adjusted for metabolic confounders and glucose levels. (4) Conclusion: Higher MVPA levels are associated with long-term health outcomes in RTRs.

Female Specific Association of Low Insulin-Like Growth Factor 1 (IGF1) Levels with Increased Risk of Premature Mortality in Renal Transplant Recipients.

Associations between insulin-like growth factor 1 (IGF1) and mortality have been reported to be female specific in mice and in human nonagenarians. Intervention in the growth hormone (GH)-IGF1 axis may particularly benefit patients with high risk of losing muscle mass, including renal transplant recipients (RTR). We investigated whether a potential association of circulating IGF1 with all-cause mortality in stable RTR could be female specific and mediated by variation in muscle mass. To this end, plasma IGF1 levels were measured in 277 female and 343 male RTR by mass spectrometry, and their association with mortality was assessed by Cox regression. During a median follow-up time of 5.4 years, 56 female and 77 male RTR died. In females, IGF1 was inversely associated with risk (hazard ratio (HR) per 1-unit increment in log2-transformed (doubling of) IGF1 levels, 95% confidence interval (CI)) of mortality (0.40, 0.24-0.65; p < 0.001), independent of age and the estimated Glomerular filtration rate (eGFR). In equivalent analyses, no significant association was observed for males (0.85, 0.56-1.29; p = 0.44), for which it should be noted that in males, age was negatively and strongly associated with IGF1 levels. The association for females remained materially unchanged upon adjustment for potential confounders and was furthermore found to be mediated for 39% by 24 h urinary creatinine excretion. In conclusion, low IGF1 levels associate with an increased risk of all-cause mortality in female RTR, which may link to conditions of low muscle mass that are known to be associated with poor outcomes in transplantation patients. For males, the strongly negative association of age with IGF1 levels may explain why low IGF1 levels were not found to be associated with an increased risk of all-cause mortality.

Mediterranean Style Diet and Kidney Function Loss in Kidney Transplant Recipients.

BACKGROUND AND OBJECTIVES: Despite improvement of short-term graft survival over recent years, long-term graft survival after kidney transplantation has not improved. Studies in the general population suggest the Mediterranean diet benefits kidney function preservation. We investigated whether adherence to the Mediterranean diet is associated with kidney outcomes in kidney transplant recipients. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: We included 632 adult kidney transplant recipients with a functioning graft for ≥1 year. Dietary intake was inquired using a 177-item validated food frequency questionnaire. Adherence to the Mediterranean diet was assessed using a nine-point Mediterranean Diet Score. Primary end point of the study was graft failure and secondary end points included kidney function decline (doubling of serum creatinine or graft failure) and graft loss (graft failure or death with a functioning graft). Cox regression analyses were used to prospectively study the associations of the Mediterranean Diet Score with study end points. RESULTS: During median follow-up of 5.4 (interquartile range, 4.9-6.0) years, 76 participants developed graft failure, 119 developed kidney function decline, and 181 developed graft loss. The Mediterranean Diet Score was inversely associated with all study end points (graft failure: hazard ratio [HR], 0.68; 95% confidence interval [95% CI], 0.50 to 0.91; kidney function decline: HR, 0.68; 95% CI, 0.55 to 0.85; and graft loss: HR, 0.74; 95% CI, 0.63 to 0.88 per two-point increase in Mediterranean Diet Score) independent of potential confounders. We identified 24-hour urinary protein excretion and time since transplantation to be an effect modifier, with stronger inverse associations between the Mediterranean Diet Score and kidney outcomes observed in participants with higher urinary protein excretion and participants transplanted more recently. CONCLUSIONS: Adherence to the Mediterranean diet is associated with better kidney function outcomes in kidney transplant recipients.

Proton-Pump Inhibitors and Hypomagnesaemia in Kidney Transplant Recipients.

Proton-pump inhibitors (PPIs) are commonly used after kidney transplantation and there is rarely an incentive to discontinue treatment. In the general population, PPI use has been associated with hypomagnesaemia. We aimed to investigate whether PPI use is associated with plasma magnesium, 24-h urinary magnesium excretion and hypomagnesaemia, in kidney transplant recipients (KTR). Plasma magnesium and 24-h urinary magnesium excretion were measured in 686 stable outpatient KTR with a functioning allograft for ≥1 year from the TransplantLines Food and Nutrition Biobank and Cohort-Study (NCT02811835). PPIs were used by 389 KTR (56.6%). In multivariable linear regression analyses, PPI use was associated with lower plasma magnesium (ß: -0.02, P = 0.02) and lower 24-h urinary magnesium excretion (ß: -0.82, P < 0.001). Moreover, PPI users had a higher risk of hypomagnesaemia (plasma magnesium <0.70 mmol/L), compared with non-users (Odds Ratio (OR): 2.12; 95% confidence interval (CI) 1.43-3.15, P < 0.001). This risk tended to be highest among KTR taking high PPI dosages (>20 mg omeprazole Eq/day) and was independent of adjustment for potential confounders (OR: 2.46; 95% CI 1.32-4.57, P < 0.005). No interaction was observed between PPI use and the use of loop diuretics, thiazide diuretics, tacrolimus, or diabetes (Pinteraction > 0.05). These results demonstrate that PPI use is independently associated with lower magnesium status and hypomagnesaemia in KTR. The concomitant decrease in urinary magnesium excretion indicates that this likely is the consequence of reduced intestinal magnesium absorption. Based on these results, it might be of benefit to monitor magnesium status periodically in KTR on chronic PPI therapy.

Urinary Oxalate Excretion and Long-Term Outcomes in Kidney Transplant Recipients.

Epidemiologic studies have linked urinary oxalate excretion to risk of chronic kidney disease (CKD) progression and end-stage renal disease. We aimed to investigate whether urinary oxalate, in stable kidney transplant recipients (KTR), is prospectively associated with risk of graft failure. In secondary analyses we evaluated the association with post-transplantation diabetes mellitus, all-cause mortality and specific causes of death. Oxalate excretion was measured in 24-h urine collection samples in a cohort of 683 KTR with a functioning allograft ≥1 year. Mean eGFR was 52 ± 20 mL/min/1.73 m2. Median (interquartile range) urinary oxalate excretion was 505 (347-732) µmol/24-h in women and 519 (396-736) µmol/24-h in men (p = 0.08), with 302 patients (44% of the study population) above normal limits (hyperoxaluria). A consistent and independent inverse association was found with all-cause mortality (HR 0.77, 95% CI 0.63-0.94, p = 0.01). Cause-specific survival analyses showed that this association was mainly driven by an inverse association with mortality due to infection (HR 0.56, 95% CI 0.38-0.83, p = 0.004), which remained materially unchanged after performing sensitivity analyses. Twenty-four-hour urinary oxalate excretion did not associate with risk of graft failure, post-transplant diabetes mellitus, cardiovascular mortality, mortality due to malignancies or mortality due to miscellaneous causes. In conclusion, in KTR, 24-h urinary oxalate excretion is elevated in 44% of KTR and inversely associated with mortality due to infectious causes.

Urinary Taurine Excretion and Risk of Late Graft Failure in Renal Transplant Recipients.

Taurine is a sulfur containing nutrient that has been shown to protect against oxidative stress, which has been implicated in the pathophysiology leading to late graft failure after renal transplantation. We prospectively investigated whether high urinary taurine excretion, reflecting high taurine intake, is associated with low risk for development of late graft failure in renal transplant recipients (RTR). Urinary taurine excretion was measured in a longitudinal cohort of 678 stable RTR. Prospective associations were assessed using Cox regression analyses. Graft failure was defined as the start of dialysis or re-transplantation. In RTR (58% male, 53 ± 13 years old, estimated glomerular filtration rate (eGFR) 45 ± 19 mL/min/1.73 m2), urinary taurine excretion (533 (210-946) µmol/24 h) was significantly associated with serum free sulfhydryl groups (ß = 0.126; P = 0.001). During median follow-up for 5.3 (4.5-6.0) years, 83 (12%) patients developed graft failure. In Cox regression analyses, urinary taurine excretion was inversely associated with graft failure (hazard ratio: 0.74 (0.67-0.82); P < 0.001). This association remained significant independent of potential confounders. High urinary taurine excretion is associated with low risk of late graft failure in RTR. Therefore, increasing taurine intake may potentially support graft survival in RTR. Further studies are warranted to determine the underlying mechanisms and the potential of taurine supplementation.

High plasma guanidinoacetate-to-homoarginine ratio is associated with high all-cause and cardiovascular mortality rate in adult renal transplant recipients.

L-Arginine:glycine amidinotransferase (AGAT) is the main producer of the creatine precursor, guanidinoacetate (GAA), and L-homoarginine (hArg). We and others previously reported lower levels of circulating and urinary hArg in renal transplant recipients (RTR) compared to healthy subjects. In adults, hArg emerged as a novel risk factor for renal and cardiovascular adverse outcome. Urinary GAA was found to be lower in children and adolescents with kidney transplants compared to healthy controls. Whether GAA is also a risk factor in the renal and cardiovascular systems of adults, is not yet known. In the present study, we aimed to investigate the significance of circulating GAA and the GAA-to-hArg molar ratio (GAA/hArg) in adult RTR. We hypothesized that GAA/hArg represents a measure of the balanced state of the AGAT activity in the kidneys, and would prospectively allow assessing a potential association between GAA/hArg and long-term outcome in RTR. The median follow-up period was 5.4 years. Confounders and potential mediators of GAA/hArg associations were evaluated with multivariate linear regression analyses, and the association with all-cause and cardiovascular mortality or death-censored graft loss was studied with Cox regression analyses. The study cohort consisted of 686 stable RTR and 140 healthy kidney donors. Median plasma GAA concentration was significantly lower in the RTR compared to the kidney donors before kidney donation: 2.19 [1.77-2.70] µM vs. 2.78 [2.89-3.35] µM (P < 0.001). In cross-sectional multivariable analyses in RTR, HDL cholesterol showed the strongest association with GAA/hArg. In prospective analyses in RTR, GAA/hArg was associated with a higher risk for all-cause mortality (hazard ratio (HR): 1.35 [95% CI 1.19-1.53]) and cardiovascular mortality (HR: 1.46 [95% CI 1.24-1.73]), independent of potential confounders. GAA but not GAA/hArg was associated with death-censored graft loss in crude survival and Cox regression analyses. The association of GAA and death-censored graft loss was lost after adjustment for eGFR. Our study suggests that in the kidneys of RTR, the AGAT-catalyzed biosynthesis of GAA is decreased. That high GAA/hArg is associated with a higher risk for all-cause and cardiovascular mortality may suggest that low plasma hArg is a stronger contributor to these adverse outcomes in RTR than GAA.

Chronic Use of Proton-Pump Inhibitors and Iron Status in Renal Transplant Recipients.

Proton-pump inhibitor (PPI) use may influence intestinal iron absorption. Low iron status and iron deficiency (ID) are frequent medical problems in renal transplant recipients (RTR). We hypothesized that chronic PPI use is associated with lower iron status and ID in RTR. Serum iron, ferritin, transferrin saturation (TSAT), and hemoglobin were measured in 646 stable outpatient RTR with a functioning allograft for ≥ 1 year from the "TransplantLines Food and Nutrition Biobank and Cohort Study" (NCT02811835). Median time since transplantation was 5.3 (1.8-12.0) years, mean age was 53 ± 13 years, and 56.2% used PPI. In multivariable linear regression analyses, PPI use was inversely associated with serum iron (ß = -1.61, p = 0.001), natural log transformed serum ferritin (ß = -0.31, p < 0.001), TSAT (ß = -2.85, p = 0.001), and hemoglobin levels (ß = -0.35, p = 0.007), independent of potential confounders. Moreover, PPI use was independently associated with increased risk of ID (Odds Ratio (OR): 1.57; 95% Confidence Interval (CI )1.07-2.31, p = 0.02). Additionally, the odds ratio in RTR taking a high PPI dose as compared to RTR taking no PPIs (OR 2.30; 95% CI 1.46-3.62, p < 0.001) was higher than in RTR taking a low PPI dose (OR:1.78; 95% CI 1.21-2.62, p= 0.004). We demonstrated that PPI use is associated with lower iron status and ID, suggesting impaired intestinal absorption of iron. Moreover, we found a stronger association with ID in RTR taking high PPI dosages. Use of PPIs should, therefore, be considered as a modifiable cause of ID in RTR.

Plasma ADMA, urinary ADMA excretion, and late mortality in renal transplant recipients.

Cardiovascular disease (CVD) is the leading cause of death in renal transplant recipients (RTR). Elevated plasma asymmetric dimethylarginine (pADMA), an endogenous nitric oxide synthase inhibitor produced from the turnover of methylated arginine moieties in proteins, is a risk factor for CVD and mortality. It is unknown how urinary ADMA excretion (uADMA), one of the main ADMA elimination routes, is associated with long-term survival. Furthermore, the association of pADMA and uADMA with markers for turnover of arginine-methylated proteins is unknown. We analyzed ADMA using a validated GC-MS/MS method in plasma and 24-h urine samples of 685 RTR, included ≥ 1 year after transplantation. We also analyzed urine symmetric dimethylarginine (uSDMA) using the same method. Urinary creatinine and urea excretions were used as markers for turnover of muscle protein and amino acids, respectively. We applied Cox regression analyses to study associations of pADMA, uADMA, and uSDMA with all-cause and CVD mortality. Mean pADMA was 0.61 ± 0.12 µM, uADMA was 31 ± 13 µmol/24 h, and uSDMA was 52 ± 19 µmol/24 h. Over median follow-up of 5.4 [4.9-6.1] years, 147 RTR died, of which 58 (39%) from CVD. High pADMA was associated with high all-cause mortality (HR per SD [95% CI]: 1.45 [1.26-1.67], P < 0.001), while high uADMA was associated with low all-cause and CVD mortality (HR per SD [95% CI]: 0.57 [0.47-0.69], P < 0.001, and 0.55 [0.40-0.74], P < 0.001, respectively). The associations were independent of adjustment for potential confounders. Creatinine excretion was associated with both pADMA (st. ß:- 0.21, P = 0.003) and uADMA (st. ß: 0.49, P < 0.001), and urea excretion was associated with uADMA (st. ß: 0.56, P < 0.001). Associations of uSDMA with outcomes and with creatinine excretion and urea excretion were comparable to those of uADMA. The associations of pADMA, uADMA and uSDMA with mortality were strongly affected by adjustment for creatinine excretion and urea excretion. We found for the first time that high uADMA and high uSDMA are associated with less risk of all-cause and CVD mortality. The links of uADMA and uSDMA with markers of muscle protein and amino acid turnover may serve to further understand ADMA and SDMA homeostasis and their clinical implications.

Effect of renal function on homeostasis of asymmetric dimethylarginine (ADMA): studies in donors and recipients of renal transplants.

Asymmetric dimethylarginine (ADMA) is a methylated form of arginine and an endogenous nitric oxide synthase inhibitor. Renal function decline is associated with increase of plasma ADMA in chronic kidney disease populations. It is yet unknown how isolated renal function impairment affects ADMA homeostasis in healthy humans. Here, we measured plasma concentrations and urinary excretion of ADMA using GC-MS/MS in 130 living kidney donors before and at 1.6 (1.6-1.9) months after donation. We additionally analyzed 201 stable renal transplant recipients (RTR) that were included > 1 year after transplantation, as a model for kidney disease in the context of single kidney state. We measured true glomerular filtration rate (mGFR) using 125I-iothalamate. To study enzymatic metabolism of ADMA, we also measured L-citrulline as primary metabolite. Mean age was 52 ± 10 years in donors and 54 ± 12 years in RTR. Renal function was significantly reduced from pre- to post-donation (mGFR: 104 ± 17 vs. 66 ± 10 ml/min per 1.73 m2 BSA, - 36 ± 7%, P < 0.001). Urinary ADMA excretion strongly and significantly decreased from pre- to post-donation (60.6 ± 16.0 vs. 40.5 ± 11.5 µmol/24 h, - 31.5 ± 21.5%, P < 0.001), while plasma ADMA increased only slightly (0.53 ± 0.08 vs. 0.58 ± 0.09 µM, 11.1 ± 20.1%, P < 0.001). Compared to donors post-donation, RTR had significantly worse renal function (mGFR: 49 ± 18 ml/min/1.73 m2, - 25 ± 2%, P < 0.001) and lower urinary ADMA excretion (30.9 ± 12.4 µmol/24 h, - 23.9 ± 3.4%, P < 0.001). Plasma ADMA in RTR (0.60 ± 0.11 µM) did not significantly differ from donors post-donation (2.9 ± 1.9%, P = 0.13). Plasma citrulline was inversely associated with mGFR (st. ß: - 0.23, P < 0.001), consistent with increased ADMA metabolism to citrulline with lower GFR. In both groups, the response of urinary ADMA excretion to renal function loss was much larger than that of plasma ADMA. As citrulline was associated with GFR, our data indicate that with renal function impairment, a decrease in urinary ADMA excretion does not lead to a corresponding increase in plasma ADMA, likely due to enhanced metabolism, thus allowing for lower renal excretion of ADMA.

Author Correction: Circulating Haptoglobin and Metabolic Syndrome in Renal Transplant Recipients.

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper.

Renal sulfate reabsorption in healthy individuals and renal transplant recipients.

Inorganic sulfate is essential for normal cellular function and its homeostasis is primarily regulated in the kidneys. However, little is known about renal sulfate handling in humans and particularly in populations with impaired kidney function such as renal transplant recipients (RTR). Hence, we aimed to assess sulfate reabsorption in kidney donors and RTR. Plasma and urinary sulfate were determined in 671 RTR and in 251 kidney donors. Tubular sulfate reabsorption (TSR) was defined as filtered load minus sulfate excretion and fractional sulfate reabsorption (FSR) was defined as 1-fractional excretion. Linear regression analyses were employed to explore associations of FSR with baseline parameters and to identify the determinants of FSR in RTR. Compared to kidney donors, RTR had significantly lower TSR (15.2 [11.2-19.5] vs. 20.3 [16.7-26.3] µmol/min), and lower FSR (0.56 [0.48-0.64] vs. 0.64 [0.57-0.69]) (all P < 0.001). Kidney donation reduced both TSR and FSR by circa 50% and 25% respectively (both P < 0.001). In RTR and donors, both TSR and FSR associated positively with renal function. In RTR, FSR was independently associated with urinary thiosulfate (ß = -0.18; P = 0.002), growth hormone (ß = 0.12; P = 0.007), the intakes of alcohol (ß = -0.14; P = 0.002), methionine (ß = -0.34; P < 0.001), cysteine (ß = -0.41; P < 0.001), and vitamin D (ß = -0.14; P = 0.009). In conclusion, TSR and FSR are lower in RTR compared to kidney donors and both associated with renal function. Additionally, FSR is determined by various dietary and metabolic factors. Future research should determine the mechanisms behind sulfate handling in humans and the prognostic value of renal sulfate reabsorption in RTR.

Dietary Approach to Stop Hypertension (DASH) diet and risk of renal function decline and all-cause mortality in renal transplant recipients.

Renal transplant recipients (RTR) are at risk of decline of graft function and premature mortality, with high blood pressure as an important risk factor for both. To study the association of the Dietary Approach to Stop Hypertension (DASH) diet with these adverse events, we conducted a prospective cohort study of adult RTR. Dietary data were collected using a validated 177-item food frequency questionnaire and an overall DASH-score was obtained. We included 632 stable RTR (mean ± standard deviation age 53.0 ± 12.7 years, 57% men). Mean DASH score was 23.8 ± 4.7. During median follow-up of 5.3 (interquartile range, 4.1-6.0) years, 119 (18.8%) RTR had renal function decline, defined as a combined endpoint of doubling of serum creatinine and death-censored graft failure, and 128 (20.3%) died. In Cox-regression analyses, RTR in the highest tertile of the DASH score had lower risk of both renal function decline (hazard ratio [HR] = 0.57; 95% confidence interval [CI], 0.33-0.96, P = .03) and all-cause mortality (HR = 0.52; 95%CI, 0.32-0.83, P = .006) compared to the lowest tertile, independent of potential confounders. Adherence to a DASH-style diet is associated with lower risk of both renal function decline and all-cause mortality. These results suggest that a healthful diet might benefit long-term outcome in RTR.

Functional vitamin B-6 status and long-term mortality in renal transplant recipients.

Background: Low plasma concentrations of pyridoxal 5'-phosphate (PLP) are common in renal transplant recipients (RTRs) and confer increased risk of long-term mortality. To our knowledge, it is not known whether low plasma PLP concentrations have functional (i.e., intracellular) consequences and, if so, whether such consequences are associated with increased risk of mortality.Objectives: We assessed the association of plasma PLP with functional vitamin B-6 status and explored the potential association of functional vitamin B-6 status with long-term mortality in RTRs.Design: In a longitudinal cohort of 678 stable RTRs with a median follow-up of 5.3 y (IQR: 4.8-6.1 y) and 297 healthy controls, PLP, plasma 3-hydroxykynurenine (3-HK), and xanthurenic acid (XA) were analyzed via validated assays. PLP was used as direct biomarker for vitamin B-6 status, and the 3-HK:XA ratio was used as functional biomarker of vitamin B-6 status with a higher ratio reflecting worse functional vitamin B-6 status.Results: Median PLP, 3-HK, and XA concentrations were 41 nmol/L (IQR: 29-60 nmol/L), 40.1 nmol/L (IQR: 33.0-48.0 nmol/L), and 19.1 nmol/L (IQR: 14.5-24.9 nmol/L), respectively, in healthy controls compared with 29 nmol/L (IQR: 17-50 nmol/L), 61.5 nmol/L (IQR: 45.6-86.5 nmol/L), and 25.5 nmol/L (IQR: 17.2-40.0 nmol/L), respectively, in RTRs (all P < 0.001). RTRs had a higher median 3-HK:XA ratio (2.38; IQR: 1.68-3.49) than did healthy controls (2.13; IQR: 1.63-2.71) (P < 0.05). In RTRs, the 3-HK:XA ratio was inversely associated with plasma PLP (ß = -0.21, P < 0.001). Moreover, a higher 3-HK:XA ratio was independently associated with increased risk of all-cause mortality (HR per SD increment: 1.30; 95% CI: 1.13, 1.49), cancer mortality (HR per SD increment: 1.47; 95% CI: 1.12, 1.95), and infectious disease mortality (HR per SD increment: 1.50; 95% CI: 1.21, 1.86) in RTRs.Conclusions: Vitamin B-6-deficient RTRs have a worse functional vitamin B-6 status than do healthy controls and vitamin B-6-sufficient RTRs. Worse functional vitamin B-6 status in RTRs is independently associated with an increased risk of mortality particularly because of cancer and infectious disease. This trial was registered at clinicaltrials.gov as NCT02811835.