Dietary protein, blood pressure and renal function in renal transplant recipients

The relation between dietary polysaccharide intake and urinary excretion of tetraglucoside

The urinary metabolite tetraglucoside (Glc4) is a potential biomarker for hepatic glycogen storage diseases (GSDs). Glc4 is believed to reflect body glycogen content and/or turnover. However, dietary polysaccharide intake may influence Glc4 excretion, potentially limiting the utility of Glc4 as a monitoring biomarker in hepatic GSDs. We aimed to investigate the association of dietary polysaccharide intake with Glc4 excretion. Urinary Glc4 excretion (mmol/mmol creatinine and mmol/24 h) was analyzed using a validated LC-MS/MS method. Data was analyzed from 65 kidney transplant recipients and 58 healthy kidney donors in the TransplantLines cohort study. Spearman's correlation and multivariable linear regression analyses were performed. In the multivariable analysis, dry lean body mass (DLBM), dietary polysaccharide intake, transplantation status, age, sex, and glycated hemoglobin (HbA1c) served as independent variables. Daily variation was examined in 21 healthy individuals of urinary Glc4 excretion in 2-h collections over a 24-h period. Mixed generalized additive models were built to study the association of prior polysaccharide intake with Glc4 excretion. No (univariate) associations were found between polysaccharide intake and Glc4 excretion. However, a significant interaction between DLBM and polysaccharide on 24 h Glc4 excretion was observed in the multivariate analysis. Glc4 excretion throughout the day exhibited no relationship to prior polysaccharide intake. Our findings suggest an indirect effect of polysaccharide intake on Glc4 excretion, potentially due to changes in muscle glycogen content and/or turnover. We have found no evidence that dietary polysaccharides under normal intakes increase urinary Glc4 directly.

Effect of an intensive nutrition intervention of a high protein and low glycemic load diet on weight of kidney transplant recipients: a randomized clinical trial

PURPOSE

The purpose of this study is to evaluate the effect of a high protein and low glycemic load diet in preventing weight gain after kidney transplantation.

METHODS

We designed a prospective, single-center, open-label, randomized controlled study to compare the efficacy of a high protein (1.3-1.4 g/kg/day) and low glycemic load diet versus a conventional diet (0.8-1.0 g/kg/day of protein and no recommendations on glycemic load) in preventing weight gain (ClinicalTrials.gov identifier: NCT02883777). A total of 120 patients were evaluated. Patients were followed for 12 months, and the primary outcome was weight maintenance or weight gain lower than 5%.

RESULTS

There were no differences in total energy intake, carbohydrates, and total fats between groups. Intervention group (IG) increased protein intake to 1.38 ± 0.56 g/kg/day and decreased the glycemic load to 87.27 ± 4.54 g/day, while control group (CG) had a dietary protein intake of 1.19 ± 0.43 g/kg/day and a glycemic load of 115.60 ± 7.01 g/day. Total fiber intake was greater and trans-fat was lower in IG. Dietetic cholesterol increased in IG over time and was significantly different between groups. Overall, patients had an increase in body weight over time, with a mean increment of 4.1 ± 5.5 kg (5.75%). The percentage of patients who achieved the primary outcome was 50% of sample size, without differences between groups. The glomerular filtration rate improved over time in both groups. Considering 24-h proteinuria and albuminuria, a similar rise was observed in both groups.

CONCLUSION

The present dietary intervention was safe, but had no effect on weight gain in kidney transplant subjects. Our findings suggest that other strategies, including alternative dietary and/or pharmacological and psychological interventions might be tested in randomized control trials in order to improve patients' body weight outcomes after transplant.

Creatine homeostasis and the kidney: comparison between kidney transplant recipients and healthy controls

Creatine is a natural nitrogenous organic acid that is integral to energy metabolism and crucial for proper cell functioning. The kidneys are involved in the first step of creatine production. With kidney transplantation being the gold-standard treatment for end-stage kidney disease, kidney transplant recipients (KTR) may be at risk of impaired creatine synthesis. We aimed to compare creatine homeostasis between KTR and controls. Plasma and urine concentrations of arginine, glycine, guanidinoacetate, creatine and creatinine were measured in 553 KTR and 168 healthy controls. Creatine intake was assessed using food frequency questionnaires. Iothalamate-measured GFR data were available in subsets of 157 KTR and 167 controls. KTR and controls had comparable body weight, height and creatine intake (all P > 0.05). However, the total creatine pool was 14% lower in KTR as compared to controls (651 ± 178 vs. 753 ± 239 mmol, P < 0.001). The endogenous creatine synthesis rate was 22% lower in KTR as compared to controls (7.8 ± 3.0 vs. 10.0 ± 4.1 mmol per day, P < 0.001). Despite lower GFR, the plasma guanidinoacetate and creatine concentrations were 21% and 41% lower in KTR as compared to controls (both P < 0.001). Urinary excretion of guanidinoacetate and creatine were 66% and 59% lower in KTR as compared to controls (both P < 0.001). In KTR, but not in controls, a higher measured GFR was associated with a higher endogenous creatine synthesis rate (std. beta: 0.21, 95% CI: 0.08; 0.33; P = 0.002), as well as a higher total creatine pool (std. beta: 0.22, 95% CI: 0.11; 0.33; P < 0.001). These associations were fully mediated (93% and 95%; P < 0.001) by urinary guanidinoacetate excretion which is consistent with production of the creatine precursor guanidinoacetate as rate-limiting factor. Our findings highlight that KTR have a disturbed creatine homeostasis as compared to controls. Given the direct relationship of measured GFR with endogenous creatine synthesis rate and the total creatine pool, creatine supplementation might be beneficial in KTR with low kidney function.Trial registration ID: NCT02811835.Trial registration URL: https://clinicaltrials.gov/ct2/show/NCT02811835 .

High-Density Lipoprotein Particles and Torque Teno Virus in Stable Outpatient Kidney Transplant Recipients

Torque teno virus (TTV) is emerging as a potential marker for monitoring immune status. In transplant recipients who are immunosuppressed, higher TTV DNA loads are observed than in healthy individuals. TTV load measurement may aid in optimizing immunosuppressive medication dosing in solid organ transplant recipients. Additionally, there is a growing interest in the role of HDL particles in immune function; therefore, assessment of both HDL concentrations and TTV load may be of interest in transplant recipients. The objective of this study was to analyze TTV loads and HDL parameters in serum samples collected at least one year post-transplantation from 656 stable outpatient kidney transplant recipients (KTRs), enrolled in the TransplantLines Food and Nutrition Cohort (Groningen, the Netherlands). Plasma HDL particles and subfractions were measured using nuclear magnetic resonance spectroscopy. Serum TTV load was measured using a quantitative real-time polymerase chain reaction. Associations between HDL parameters and TTV load were examined using univariable and multivariable linear regression. The median age was 54.6 [IQR: 44.6 to 63.1] years, 43.3% were female, the mean eGFR was 52.5 (±20.6) mL/min/1.73 m2 and the median allograft vintage was 5.4 [IQR: 2.0 to 12.0] years. A total of 539 participants (82.2%) had a detectable TTV load with a mean TTV load of 3.04 (±1.53) log10 copies/mL, the mean total HDL particle concentration was 19.7 (±3.4) μmol/L, and the mean HDL size was 9.1 (±0.5) nm. The univariable linear regression revealed a negative association between total HDL particle concentration and TTV load (st.β = -0.17, 95% CI st.β: -0.26 to -0.09, p < 0.001). An effect modification of smoking behavior influencing the association between HDL particle concentration and TTV load was observed (Pinteraction = 0.024). After adjustment for age, sex, alcohol intake, hemoglobin, eGFR, donor age, allograft vintage and the use of calcineurin inhibitors, the negative association between HDL particle concentration and TTV load remained statistically significant in the non-smoking population (st.β = -0.14, 95% CI st.β: -0.23 to -0.04, p = 0.006). Furthermore, an association between small HDL particle concentration and TTV load was found (st.β = -0.12, 95% CI st.β: -0.22 to -0.02, p = 0.017). Higher HDL particle concentrations were associated with a lower TTV load in kidney transplant recipients, potentially indicative of a higher immune function. Interventional studies are needed to provide causal evidence on the effects of HDL on the immune system.

Dietary protein intake and plant-dominant diets to mitigate risk of allograft dysfunction progression in kidney transplant recipients

PURPOSE OF REVIEW

There are limited studies on the benefits of low dietary protein intake (DPI) and plant-dominant diets to delay kidney allograft dysfunction. We evaluate evidence regarding the association or effects of the amount and type of DPI on allograft function.

RECENT FINDINGS

There is conflicting evidence regarding the benefits of low DPI and plant-dominant diet including PLADO and PLAFOND on kidney allograft function. Taking the strength of evidence including study design, sample size, and time to follow-up, the proposed amount of DPI to slow the progression of allograft dysfunction, avoid negative nitrogen balance, and skeletal muscle mass loss is 1.0-1.3 g/kg/day during an immediate posttransplant period or when high protein catabolic rate exists. The DPI may be 0.8-1.0 g/kg/day in patients with stable allograft function. Patients with chronic allograft rejection or estimated glomerular filtration rate <25 ml/min may benefit from the DPI of 0.55-0.60 g/kg/day, while those with failed allograft requiring transition to dialysis including incremental (twice-weekly) hemodialysis should consider increasing DPI to 1.0-1.2 g/kg/day.

SUMMARY

While there is a lack of strong evidence, individualized approaches based on the patient's comorbidities, net state of immunosuppression, and periods posttransplant may guide the appropriate amount and type of DPI to slow allograft dysfunction.

Current Evidence on Dietary Factors and Kidney Allograft Function in Kidney Transplant Recipients: A Systematic Review

BACKGROUND

Currently, there is no accounted-for consensus and practical standard when counseling diet modification for kidney transplant recipients (KTRs). There are many differences between transplant centers regarding what KTRs are needed to follow a diet, what dietary factors and supplements are allowed, and how long KTRs should follow a modified diet. Relatively few scatter data are available for dietary factors in KTRs. Thus, we aimed to systematically review the literature on the purported dietary factors for kidney function.

METHODS

A systematic literature search was performed between February and March 2022 and updated in February 2023 using PubMed, Scopus, Web of Science, and Google Scholar. We included human observational and interventional studies that evaluated a dietary factor on kidney function and graft survival in KTRs. Data were extracted, and the risk of bias was assessed using established tools relevant to the study design.

RESULTS

Of the 5341 citations retrieved, seven prospective cohorts, five cross-sectional, seventeen randomized, and ten non-randomized clinical trials were included that evaluated seven purported dietary factors. Almost half of the studies (n = 22; 56%) were classified as having a low degree of bias and sufficient support. Twenty-one studies (54%) reported a positive effect on KTRs. DASH and Mediterranean diets decreased graft failure, low-sodium diet reduced blood pressure, and antioxidants improved creatinine, GFR, and graft function. Of these, only twelve studies (31%) were at low risk of bias.

CONCLUSION

Some dietary factors, including DASH, Mediterranean, moderate protein, and low-- sodium diet, as well as antioxidants, may be associated with improved survival and kidney function in KTRs. However, more research is needed.

Urinary Copper Excretion Is Associated with Long-Term Graft Failure in Kidney Transplant Recipients

INTRODUCTION

In chronic kidney disease, proteinuria increases urinary copper excretion, inducing oxidative tubular damage and worsening kidney function. We investigated whether this phenomenon occurred in kidney transplant recipients (KTRs). In addition, we studied the associations of urinary copper excretion with the biomarker of oxidative tubular damage urinary liver-type fatty-acid binding protein (u-LFABP) and death-censored graft failure.

METHODS

This prospective cohort study was performed in the Netherlands between 2008 and 2017, including outpatient KTR with a functioning graft for longer than 1 year, who were extensively phenotyped at baseline. Twenty-four-hour urinary copper excretion was measured by inductively coupled plasma mass spectrometry. Multivariable linear and Cox regression analyses were performed.

RESULTS

In 693 KTR (57% men, 53 ± 13 years, estimated glomerular filtration rate [eGFR] 52 ± 20 mL/min/1.73 m2), baseline median urinary copper excretion was 23.6 (interquartile range 11.3-15.9) µg/24 h. Urinary protein excretion was positively associated with urinary copper excretion (standardized β = 0.39, p < 0.001), and urinary copper excretion was positively associated with u-LFABP (standardized β = 0.29, p < 0.001). During a median follow-up of 8 years, 109 (16%) KTR developed graft failure. KTR with relatively high copper excretion were at higher risk of long-term graft failure (hazard ratio [HR]: 1.57, 95% confidence interval [CI]: 1.32-1.86 per log2, p < 0.001), independent of multiple potential confounders like eGFR, urinary protein excretion, and time after transplantation. A dose-response relationship was observed over increasing tertiles of copper excretion (HR: 5.03, 95% CI: 2.75-9.19, tertile 3 vs. 1, p < 0.001). u-LFABP was a significant mediator of this association (74% of indirect effect, p < 0.001).

CONCLUSION

In KTR, urinary protein excretion is positively correlated with urinary copper excretion. In turn, higher urinary copper excretion is associated with an independent increased risk of kidney graft failure, with a substantial mediating effect through oxidative tubular damage. Further studies are warranted to investigate whether copper excretion-targeted interventions could improve kidney graft survival.

Plasma endotrophin, reflecting tissue fibrosis, is associated with graft failure and mortality in KTRs: results from two prospective cohort studies

BACKGROUND

Fibrosis is a suggested cause of graft failure and mortality among kidney transplant recipients (KTRs). Accumulating evidence suggests that collagen type VI is tightly linked to fibrosis and may be a marker of systemic fibrosis and ageing. We studied whether plasma endotrophin, a pro-collagen type VI fragment, is associated with graft failure and mortality among KTRs.

METHODS

In cohort A (57% male, age 53 ± 13 years), we measured plasma endotrophin in 690 prevalent KTRs ≥1 year after transplantation. The non-overlapping cohort B included 500 incident KTRs with serial endotrophin measurements before and after kidney transplantation to assess trajectories and intra-individual variation of endotrophin.

RESULTS

In cohort A, endotrophin was higher in KTRs compared with healthy controls. Concentrations were positively associated with female sex, diabetes, cardiovascular disease, markers of inflammation and kidney injury. Importantly, endotrophin was associated with graft failure {hazard ratio [HR] per doubling 1.87 [95% confidence interval (CI) 1.07-3.28]} and mortality [HR per doubling 2.59 (95% CI 1.73-3.87)] independent of potential confounders. Data from cohort B showed that endotrophin concentrations strongly decrease after transplantation and remain stable during post-transplantation follow-up [intra-individual coefficient of variation 5.0% (95% CI 3.7-7.6)].

CONCLUSIONS

Plasma endotrophin is strongly associated with graft failure and mortality among KTRs. These findings suggest a key role of abnormal extracellular matrix turnover and fibrosis in graft and patient prognosis among KTRs and highlight the need for (interventional) studies targeting the profibrotic state of KTRs. The intra-individual stability after transplantation indicates potential use of endotrophin as a biomarker and outcome measure of fibrosis.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02811835.

Plasma Copper Concentration Is Associated with Cardiovascular Mortality in Male Kidney Transplant Recipients

Kidney transplant recipients (KTR) are at increased risk of cardiovascular mortality. We investigated whether, in KTR, post-transplantation copper status is associated with the risk of cardiovascular mortality and potential effect modification by sex. In this cohort study, plasma copper was measured using mass spectrometry in extensively-phenotyped KTR with a functioning allograft >1-year. Cox regression analyses with the inclusion of multiplicative interaction terms were performed. In 660 KTR (53 ± 13 years old, 56% male), the median baseline plasma copper was 15.42 (IQR 13.53-17.63) µmol/L. During a median follow-up of 5 years, 141 KTR died, 53 (38%) due to cardiovascular causes. Higher plasma copper was associated with an increased risk of cardiovascular mortality in the overall KTR population (HR 1.37; 95% CI, 1.07-1.77 per 1-SD, p = 0.01). Sex was a significant effect modifier of this association (P_interaction = 0.01). Among male KTR, higher plasma copper concentration was independently associated with a two-fold higher risk of cardiovascular mortality (HR 2.09; 95% CI, 1.42-3.07 per 1-SD, p < 0.001). Among female KTR, this association was absent. This evidence offers a rationale for considering a sex-specific assessment of copper's role in cardiovascular risk evaluation. Further studies are warranted to elucidate whether copper-targeted interventions may decrease cardiovascular mortality in male KTR.

Effects of an individualized nutritional intervention on kidney function, body composition, and quality of life in kidney transplant recipients: Study protocol for a randomized clinical trial

Background

Proteinuria after kidney transplantation (KTx) has been a frequent problem due to several factors, high protein intake being one of them. Individualized nutritional intervention in the late post-KTx period can promote the improvement or the reduction of risks associated with the parameters of evaluation of kidney function, body composition, and quality of life in individuals submitted to KTx.

Methods

This is a single-center, randomized and stratified clinical trial. The study will be conducted in a university hospital in northeastern Brazil with 174 individuals aged ≥19 years submitted to KTx and followed up for 12 months. Assessments will take place at 3-month intervals (T0, T3, T6, T9, and T12). The patients will be allocated to intervention and control groups by random allocation. The intervention group will receive individualized nutritional interventions with normoproteic diets (1.0 g/kg) after 60 days of KTx whereas the controls will receive the standard nutritional guidance for the post-KTx period. The primary efficacy variable is the change from baseline in log proteinuria assessed with the urinary albumin/creatinine ratio. Secondary efficacy variables include body composition, anthropometry, quality of life assessment and physical activity, lipid profile and glycemic control. Ninety-two subjects per group will afford 70% power to detect a difference of 25% between groups in log proteinuria. Primary efficacy analysis will be on the modified intention-to-treat population with between-groups comparison of the change from baseline in log proteinuria by analysis of covariance.

Discussion

The study will assess the effects of an individualized nutritional intervention on proteinuria 12 months after KTx.

Trial registration

REBEC (RBR-8XBQK5).

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/24h 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.

Ultra-processed foods and risk of all-cause mortality in renal transplant recipients

BACKGROUND

Renal transplant recipients (RTRs) have a 6-fold higher risk of mortality than age- and sex-matched controls. Whether high consumption of ultra-processed foods is associated with survival in RTRs is unknown.

OBJECTIVES

We aimed to study the association between high consumption of ultra-processed foods and all-cause mortality in stable RTRs.

METHODS

We conducted a prospective cohort study in adult RTRs with a stable graft. Dietary intake was assessed using a validated 177-item FFQ. Food items were categorized according to the NOVA classification system and the proportion ultra-processed foods comprised of total food weight per day was calculated.

RESULTS

We included 632 stable RTRs (mean ± SD age: 53.0 ± 12.7 y, 57% men). Mean ± SD consumption of ultra-processed foods was 721 ± 341 g/d (28% of total weight of food intake), whereas the intake of unprocessed and minimally processed foods, processed culinary ingredients, and processed foods accounted for 57%, 1%, and 14%, respectively. During median follow-up of 5.4 y [IQR: 4.9-6.0 y], 129 (20%) RTRs died. In Cox regression analyses, ultra-processed foods were associated with all-cause mortality (HR per doubling of percentage of total weight: 2.13; 95% CI: 1.46, 3.10; P < 0.001), independently of potential confounders. This association was independent from the quality of the overall dietary pattern, expressed by the Mediterranean Diet Score (MDS) or Dietary Approaches to Stop Hypertension (DASH) score. When analyzing ultra-processed foods by groups, only sugar-sweetened beverages (HR: 1.21; 95% CI: 1.05, 1.39; P = 0.007), desserts (HR: 1.24; 95% CI: 1.02, 1.49; P = 0.03), and processed meats (HR: 1.87; 95% CI: 1.22, 2.86; P = 0.004) were associated with all-cause mortality.

CONCLUSIONS

Consumption of ultra-processed foods, in particular sugar-sweetened beverages, desserts, and processed meats, is associated with a higher risk of all-cause mortality after renal transplantation, independently of low adherence to high-quality dietary patterns, such as the Mediterranean diet and the DASH diet.This trial was registered at clinicaltrials.gov as NCT02811835.

Plasma neutrophil gelatinase-associated lipocalin and kidney graft outcome

BACKGROUND

Plasma neutrophil gelatinase-associated lipocalin (pNGAL) has been investigated extensively in acute kidney injury. This study investigated its pathophysiological significance and utility as marker for graft failure and mortality in stable kidney transplant recipients (KTR).

METHODS

Baseline pNGAL was measured in 698 KTR (58% male, age 53 ± 13 years, estimated glomerular filtration rate 52.4 ± 20.4 mL/min/1.73 m2) at median 5.4 (interquartile range 1.8-12.0) years after transplantation, enrolled in the prospective TransplantLines Food and Nutrition Biobank and Cohort Study.

RESULTS

pNGAL concentrations were higher in males, younger patients, patients with a deceased-donor kidney and higher serum creatinine. Independent of these, pNGAL was positively associated with urinary protein excretion, systemic inflammation parameters and calcineurin inhibitor use. During median follow-up of 5.3 (4.5-6.0) years, death-censored graft failure rates were 3.9%, 7.3% and 25.0% across increasing tertiles of pNGAL (Plog-rank < 0.001). Cox-regression analyses showed no independent associations of pNGAL with mortality, but strong associations with graft failure (hazard ratio, per doubling 4.16; 95% confidence interval 3.03-5.71; P < 0.001), which remained independent of adjustment for confounders. These associations were present only in patients with pre-existent proteinuria and poor kidney function.

CONCLUSIONS

pNGAL is associated with parameters of kidney graft damage and with graft failure. The latter association is particularly present in KTR with pre-existent poor kidney function and proteinuria. Trial Registration: ClinicalTrials.gov NCT02811835.

Urinary excretion of amino acids and their advanced glycation end-products (AGEs) in adult kidney transplant recipients with emphasis on lysine: furosine excretion is associated with cardiovascular and all-cause mortality

Arginine (Arg) and lysine (Lys) moieties of proteins undergo various post-translational modifications (PTM) including enzymatic N^G- and N^ε-methylation and non-enzymatic N^G- and N^ε-glycation. In a large cohort of stable kidney transplant recipients (KTR, n = 686), high plasma and low urinary concentrations of asymmetric dimethylarginine (ADMA), an abundant PTM metabolite of Arg, were associated with cardiovascular and all-cause mortality. Thus, the prediction of the same biomarker regarding mortality may depend on the biological sample. In another large cohort of stable KTR (n = 555), higher plasma concentrations of N^ε-carboxymethyl-lysine (CML) and N^ε-carboxyethyl-lysine (CEL), two advanced glycation end-products (AGEs) of Lys, were associated with higher cardiovascular mortality. Yet, the associations of urinary AGEs with mortality are unknown. In the present study, we measured 24 h urinary excretion of Lys, CML, and furosine in 630 KTR and 41 healthy kidney donors before and after donation. Our result indicate that lower urinary CML and lower furosine excretion rates are associated with higher mortality in KTR, thus resembling the associations of ADMA. Lower furosine excretion rates were also associated with higher cardiovascular mortality. The 24 h urinary excretion rate of amino acids and their metabolites decreased post-donation (varying as little as − 24% for CEL, and as much as − 62% for ADMA). For most amino acids, the excretion rate was lower in KTR than in donors pre-donation [except for S-(1-carboxyethyl)-l-cysteine (CEC) and N^G-carboxyethylarginine (CEA)]. Simultaneous GC–MS measurement of free amino acids, their PTM metabolites and AGEs in urine is a non-invasive approach in kidney transplantation.

Boron Intake and decreased risk of mortality in kidney transplant recipients

Purpose

In a search for potentially modifiable factors to improve long-term outcome among kidney transplant recipients (KTR), we hypothesized that boron exposure is associated with improved long-term outcome in KTR.

Methods

We determined 24 h urinary boron excretion using inductively coupled plasma mass spectrometry as a measure of boron exposure in 693 stable KTR (57% male, mean age 53y), enrolled in the TransplantLines Food and Nutrition Biobank and Cohort Study. Dietary intake was assessed using validated food-frequency questionnaires.

Results

Linear regression analyses showed that dietary intake of fruit, wine and nuts were key determinants of boron excretion. In addition, boron excretion was negatively correlated with homocysteine and inflammatory parameters. In total, 73 (32%), 47 (20%) and 30 (13%) KTR died among the lowest, middle and highest tertiles of 24 h urinary boron excretion, respectively (P_log-rank < 0.001). Cox regression analyses showed that high boron excretion was strongly associated with lower risk of mortality, independent of age, sex, estimated glomerular filtration rate and history of cardiovascular disease (HR per doubling: 0.51, 95% CI: 0.40 to 0.66, P < 0.001).

Conclusion

Boron may be an overlooked target to improve long-term survival among KTR and potentially other patients, likely through pathways other than inflammation or the methionine-homocysteine cycle that were previously suggested. Interventional trials are warranted to confirm the potential of dietary boron supplementation in KTR and other patient populations.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00394-021-02702-0.

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 β (st β): 0.20; 95% CI: 0.12, 0.28; P < 0.001], whereas urinary 3-methylhistidine was associated with red meat intake (st β: 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.

Kidney Function-Dependence of Vitamin K-Status Parameters: Results from the TransplantLines Biobank and Cohort Studies

High circulating dephosphorylated (dp) uncarboxylated (uc) matrix Gla protein (MGP) and uc osteocalcin (OC) concentrations are regarded as markers of vitamin K-deficiency. However, because MGP and OC are small molecules, they may potentially pass the glomerulus, and their blood concentrations may strongly depend on kidney function. However, many studies with vitamin K-status parameters do not structurally adjust for baseline kidney function, and detailed studies on kidney function-dependence of vitamin K-status markers are lacking. We therefore measured plasma dp-ucMGP using a chemiluminescent assay in 578 kidney transplant recipients (41% females, age 56 ± 13y, 7.5 (3.2 to 13.7)y after transplantation, eGFR 49 ± 17 mL/min/1.73 m2) participating in the prospective TransplantLines Cohort Studies. Additionally, dp-carboxylated MGP, ucOC and carboxylated OC were measured using ELISA in plasma of a subgroup of 60 participants. Finally, dp-ucMGP was measured in a separate cohort of 124 kidney transplant recipients before and three months after kidney transplantation. Dp-ucMGP positively correlated with creatinine, cystatin C, and negatively with eGFR (Spearman's ρ 0.54, 0.60, and -0.54, respectively, p < 0.001 for all), and each 10 mL/min/1.73 m2 increase in eGFR was associated with a 14.0% lower dp-ucMGP. Additionally, dp-ucMGP strongly declined after kidney transplantation (pretransplantation: 1252 (868 to 1744) pmol/L to posttransplantation: 609 (451 to 914) pmol/L, p < 0.001). Proportions of dp-ucMGP over total MGP and ucOC over total OC were not associated with eGFR. This study highlights that dp-ucMGP is strongly associated with kidney function, and that levels strongly decrease after kidney transplantation. We therefore propose adequate adjustment for kidney function, or the use of kidney function-independent parameters such as proportion of uncarboxylated MGP or OC in the assessment of vitamin K-status in clinical practice and research.

Urinary Carnosinase-1 Excretion is Associated with Urinary Carnosine Depletion and Risk of Graft Failure in Kidney Transplant Recipients: Results of the TransplantLines Cohort Study

Carnosine affords protection against oxidative and carbonyl stress, yet high concentrations of the carnosinase-1 enzyme may limit this. We recently reported that high urinary carnosinase-1 is associated with kidney function decline and albuminuria in patients with chronic kidney disease. We prospectively investigated whether urinary carnosinase-1 is associated with a high risk for development of late graft failure in kidney transplant recipients (KTRs). Carnosine and carnosinase-1 were measured in 24 h urine in a longitudinal cohort of 703 stable KTRs and 257 healthy controls. Cox regression was used to analyze the prospective data. Urinary carnosine excretions were significantly decreased in KTRs (26.5 [IQR 21.4–33.3] µmol/24 h versus 34.8 [IQR 25.6–46.8] µmol/24 h; p < 0.001). In KTRs, high urinary carnosinase-1 concentrations were associated with increased risk of undetectable urinary carnosine (OR 1.24, 95%CI [1.06–1.45]; p = 0.007). During median follow-up for 5.3 [4.5–6.0] years, 84 (12%) KTRs developed graft failure. In Cox regression analyses, high urinary carnosinase-1 excretions were associated with increased risk of graft failure (HR 1.73, 95%CI [1.44–2.08]; p < 0.001) independent of potential confounders. Since urinary carnosine is depleted and urinary carnosinase-1 imparts a higher risk for graft failure in KTRs, future studies determining the potential of carnosine supplementation in these patients are warranted.

Exhaled Hydrogen as a Marker of Intestinal Fermentation Is Associated with Diarrhea in Kidney Transplant Recipients

BACKGROUND

Diarrhea is common among kidney transplant recipients (KTR). Exhaled hydrogen (H2) is a surrogate marker of small bowel dysbiosis, which may drive diarrhea. We studied the relationship between exhaled H2 and diarrhea in KTR, and explored potential clinical and dietary determinants.

METHODS

Clinical, laboratory, and dietary data were analyzed from 424 KTR participating in the TransplantLines Biobank and Cohort Study (NCT03272841). Fasting exhaled H2 concentration was measured using a model DP Quintron Gas Chromatograph. Diarrhea was defined as fast transit time (types 6 and 7 according to the Bristol Stool Form Scale, BSFS) of 3 or more episodes per day. We studied the association between exhaled H2 and diarrhea with multivariable logistic regression analysis, and explored potential determinants using linear regression.

RESULTS

KTR (55.4 ± 13.2 years, 60.8% male, mean eGFR 49.8 ± 19.1 mL/min/1.73 m2) had a median exhaled H2 of 11 (5.0-25.0) ppm. Signs of small intestinal bacterial overgrowth (exhaled H2 ≥ 20 ppm) were present in 31.6% of the KTR, and 33.0% had diarrhea. Exhaled H2 was associated with an increased risk of diarrhea (odds ratio 1.51, 95% confidence interval 1.07-2.14 per log2 ppm, p = 0.02). Polysaccharide intake was independently associated with higher H2 (std. β 0.24, p = 0.01), and a trend for an association with proton-pump inhibitor use was observed (std. β 0.16 p = 0.05).

CONCLUSION

Higher exhaled H2 is associated with an increased risk of diarrhea in KTR. Our findings set the stage for further studies investigating the relationship between dietary factors, small bowel dysbiosis, and diarrhea after kidney transplantation.

Metabolic syndrome-related dietary pattern and risk of mortality in kidney transplant recipients

BACKGROUND AND AIMS

Presence of the metabolic syndrome (MetS) importantly contributes to excess mortality in kidney transplant recipients (KTRs). However, it is unclear which dietary factors drive the adverse role of MetS in KTRs. We aimed to define a dietary pattern that maximally explained the variation in MetS components, and to investigate the association between this MetS-related dietary pattern (MetS-DP) and all-cause mortality in KTRs.

METHODS AND RESULTS

We included 429 adult KTRs who had a functioning graft ⩾1 year. A MetS-DP was constructed using habitual dietary intake derived from a 177-item food frequency questionnaire. We used reduced rank regression (RRR), and defined the six components of MetS (waist circumference, systolic blood pressure, diastolic blood pressure, serum triglycerides, HbA1c, and HDL cholesterol) as response variables and 48 food groups as predictor variables. We evaluated the association between the MetS-DP and all-cause mortality using multivariable Cox regression analysis. The MetS-DP was characterized by high intakes of processed meat and desserts, and low intakes of vegetables, tea, rice, fruits, milk, and meat substitutes. During a mean follow-up of 5.3 ± 1.2 years, 63 KTRs (14.7%) died. Compared to the lowest tertile of the Mets-DP score, those with the greatest adherence had a more than 3-fold higher risk of all-cause mortality (hazard ratio [HR] = 3.63; 95% confidence interval [CI], 1.70-7.74, P < 0.001), independent of potential confounders.

CONCLUSIONS

We identified a MetS-related dietary pattern which was independently associated with all-cause mortality in KTRs. The association between this dietary pattern and all-cause mortality was mediated by MetS. Clinical trial reg. no. NCT02811835.

Urinary liver-type fatty acid-binding protein is independently associated with graft failure in outpatient kidney transplant recipients

Urinary liver-type fatty acid-binding protein (uL-FABP) is a biomarker of kidney hypoxia and ischemia, and thus offers a novel approach to identify early kidney insults associated with increased risk of graft failure in outpatient kidney transplant recipients (KTR). We investigated whether uL-FABP is associated with graft failure and whether it improves risk prediction. We studied a cohort of 638 outpatient KTR with a functional graft ≥1-year. During a median follow-up of 5.3 years, 80 KTR developed graft failure. uL-FABP (median 2.11, interquartile range 0.93-7.37 µg/24"/>h) was prospectively associated with the risk of graft failure (hazard ratio 1.75; 95% confidence interval 1.27-2.41 per 1-SD increment; P = .001), independent of potential confounders including estimated glomerular filtration rate and proteinuria. uL-FABP showed excellent discrimination ability for graft failure (c-statistic of 0.83) and its addition to a prediction model composed by established clinical predictors of graft failure significantly improved the c-statistic to 0.89 (P for F-test <.001). These results were robust to several sensitivity analyses. Further validation studies are warranted to evaluate the potential use of a risk-prediction model including uL-FABP to improve identification of outpatient KTR at high risk of graft failure in clinical care.

Whole-body arginine dimethylation is associated with all-cause mortality in adult renal transplant recipients

Arginine residues in proteins can be singly or doubly methylated post-translationally. Proteolysis of arginine-methylated proteins provides monomethyl arginine, asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA). ADMA and SDMA are considered cardiovascular risk factors, with the underlying mechanisms being not yet fully understood. SDMA lacks appreciable metabolism and is almost completely eliminated by the kidney, whereas ADMA is extensively metabolized to dimethylamine (DMA), with a minor ADMA fraction of about 10% being excreted unchanged in the urine. Urinary DMA and ADMA are useful measures of whole-body asymmetric arginine-dimethylation, while urinary SDMA serves as a whole-body measure of symmetric arginine-dimethylation. In renal transplant recipients (RTR), we previously found that higher plasma ADMA concentrations and lower urinary ADMA and SDMA concentrations were associated with a higher risk of all-cause mortality. Yet, in this RTR collective, no data were available for urinary DMA. For the present study, we additionally measured the excretion rate of DMA in 24-h collected urine samples of the RTR and of healthy kidney donors in the cohort, with the aim to quantitate whole-body asymmetric (ADMA, DMA) and symmetric (SDMA) arginine-dimethylation. We found that lower DMA excretion rates were associated with higher all-cause mortality, yet not with cardiovascular mortality. In the healthy donors, kidney donation was associated with considerable decreases in ADMA (by - 39%, P < 0.0001) and SDMA (by - 21%, P < 0.0001) excretion rates, yet there was no significant change in DMA (by - 9%, P = 0.226) excretion rate. Our results suggest that protein-arginine dimethylation is altered in RTR compared to healthy kidney donors and that it is pronouncedly shifted from symmetric to asymmetric arginine-dimethylation, with whole-body protein-arginine dimethylation being almost unaffected.

Food Literacy Is Associated With Adherence to a Mediterranean-Style Diet in Kidney Transplant Recipients

OBJECTIVES

Adherence to a Mediterranean-style diet is associated with improved health outcomes in kidney transplant recipients (KTR). However, poor dietary habits, including excessive sodium intake, are common in KTR, indicating difficulties with incorporating a healthy diet into daily life. Food literacy is identified as potential facilitator of a healthy diet, but the precise relationship between food literacy and dietary intake in KTR has not been investigated. This study examined food literacy levels in KTR and its association with adherence to a Mediterranean-style diet and sodium intake.

METHODS

This cross-sectional study is part of the TransplantLines Cohort and Biobank Study. Food literacy was measured with the Self-Perceived Food Literacy (SPFL) questionnaire. Dietary intake assessment with food frequency questionnaires was used to calculate the Mediterranean Diet Score. Sodium intake was based on the 24-hour urinary sodium excretion rate. Associations of SPFL with Mediterranean Diet Score and sodium intake were assessed with univariable and multivariable linear regression analyses.

RESULTS

In total, 148 KTR (age 56 [48-66]; 56% male) completed the SPFL questionnaire with a mean SPFL score of 3.63 ± 0.44. Higher SPFL was associated with a higher Mediterranean Diet Score in KTR (β = 1.51, 95% confidence interval 0.88-2.12, P ≤ .001). Although KTR with higher food literacy tended to have a lower sodium intake than those with lower food literacy (P = .08), the association of food literacy with sodium intake was not significant in a multivariable regression analysis (β = 0.52 per 10 mmol/24-hour increment, 95% confidence interval -1.79 to 2.83, P = .66).

CONCLUSIONS

Higher levels of food literacy are associated with better adherence to a Mediterranean-style diet in KTR. No association between food literacy and sodium intake was found. Further studies are needed to determine if interventions on improving food literacy contribute to a healthier diet and better long-term outcomes in KTR.

Association of Circulating Trimethylamine N-Oxide and Its Dietary Determinants with the Risk of Kidney Graft Failure: Results of the TransplantLines Cohort Study

Background. Due to the critical shortage of kidneys for transplantation, the identification of modifiable factors related to graft failure is highly desirable. The role of trimethylamine-N-oxide (TMAO) in graft failure remains undetermined. Here, we investigated the clinical utility of TMAO and its dietary determinants for graft failure prediction in renal transplant recipients (RTRs). Methods. We included 448 RTRs who participated in the TransplantLines Cohort Study. Cox proportional-hazards regression analyses were performed to study the association of plasma TMAO with graft failure. Net Benefit, which is a decision analysis method, was performed to evaluate the clinical utility of TMAO and dietary information in the prediction of graft failure. Results. Among RTRs (age 52.7 ± 13.1 years; 53% males), the baseline median TMAO was 5.6 (3.0–10.2) µmol/L. In multivariable regression analysis, the most important dietary determinants of TMAO were egg intake (Std. β = 0.09 [95%CI, 0.01; 0.18]; p = 0.03), fiber intake (Std. β = −0.14 [95%CI, −0.22, −0.05]; p = 0.002), and fish and seafood intake (Std. β = 0.12 [95%CI, 0.03,0.21]; p = 0.01). After a median follow-up of 5.3 (4.5–6.0) years, graft failure was observed in 58 subjects. TMAO was associated with an increased risk of graft failure, independent of age, sex, the body mass index (BMI), blood pressure, lipids, albuminuria, and the Estimated Glomerular Filtration Rate (eGFR) (Hazard Ratio per 1-SD increase of TMAO, 1.62 (95% confidence interval (CI): 1.22; 2.14, p < 0.001)). A TMAO and dietary enhanced prediction model offered approximately double the Net Benefit compared to a previously reported, validated prediction model for future graft failure, allowing the detection of 21 RTRs per 100 RTRs tested, with no false positives versus 10 RTRs, respectively. Conclusions. A predictive model for graft failure, enriched with TMAO and its dietary determinants, yielded a higher Net Benefit compared with an already validated model. This study suggests that TMAO and its dietary determinants are associated with an increased risk of graft failure and that it is clinically meaningful.

Urinary Excretion of N1-Methylnicotinamide and N1-Methyl-2-Pyridone-5-Carboxamide and Mortality in Kidney Transplant Recipients

It is unclear whether niacin nutritional status is a target for improvement of long-term outcome after renal transplantation. The 24-h urinary excretion of N¹-methylnicotinamide (N¹-MN), as a biomarker of niacin status, has previously been shown to be negatively associated with premature mortality in kidney transplant recipients (KTR). However, recent evidence implies higher enzymatic conversion of N¹-MN to N¹-methyl-2-pyridone-5-carboxamide (2Py) in KTR, therefore the need exists for interpretation of both N¹-MN and 2Py excretion for niacin status assessment. We assessed niacin status by means of the 24-h urinary excretion of the sum of N¹-MN and 2Py (N¹-MN + 2Py), and its associations with risk of premature mortality in KTR. N¹-MN + 2Py excretion was measured in a longitudinal cohort of 660 KTR with LS-MS/MS. Prospective associations of N¹-MN + 2Py excretion were investigated with Cox regression analyses. Median N¹-MN + 2Py excretion was 198.3 (155.9–269.4) µmol/day. During follow-up of 5.4 (4.7–6.1) years, 143 KTR died, of whom 40 due to an infectious disease. N¹-MN + 2Py excretion was negatively associated with risk of all-cause mortality (HR 0.61; 95% CI 0.47–0.79; p < 0.001), and infectious mortality specifically (HR 0.47; 95% CI 0.29–0.75; p = 0.002), independent of potential confounders. Secondary analyses showed effect modification of hs-CRP on the negative prospective association of N¹-MN + 2Py excretion, and sensitivity analyses showed negative and independent associations of N¹-MN and 2Py excretion with risk of all-cause mortality separately. These findings add further evidence to niacin status as a target for nutritional strategies for improvement of long-term outcome in KTR.

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

Hydrogen sulfide (H₂S), produced from metabolism of dietary sulfur‐containing amino acids, is allegedly a renoprotective compound. Twenty‐four‐hour urinary sulfate excretion (USE) may reflect H₂S 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 H₂S bioavailability as a novel, potentially modifiable factor for prevention of graft failure in RTR.

High-Density Lipoprotein Particles and Their Relationship to Posttransplantation Diabetes Mellitus in Renal Transplant Recipients

High concentrations of high-density lipoprotein (HDL) cholesterol are likely associated with a lower risk of posttransplantation diabetes mellitus (PTDM). However, HDL particles vary in size and density with yet unestablished associations with PTDM risk. The aim of our study was to determine the association between different HDL particles and development of PTDM in renal transplant recipients (RTRs). We included 351 stable outpatient adult RTRs without diabetes at baseline evaluation. HDL particle characteristics and size were measured by nuclear magnetic resonance (NMR) spectroscopy. During 5.2 (IQR, 4.1‒5.8) years of follow-up, 39 (11%) RTRs developed PTDM. In multivariable Cox regression analysis, levels of HDL cholesterol (hazard ratio [HR] 0.61, 95% confidence interval [CI] 0.40-0.94 per 1SD increase; p = 0.024) and of large HDL particles (HR 0.68, 95% CI 0.50-0.93 per log 1SD increase; p = 0.017), as well as larger HDL size (HR 0.58, 95% CI 0.36-0.93 per 1SD increase; p = 0.025) were inversely associated with PTDM development, independently of relevant covariates including, age, sex, body mass index, medication use, transplantation-specific parameters, blood pressure, triglycerides, and glucose. In conclusion, higher concentrations of HDL cholesterol and of large HDL particles and greater HDL size were associated with a lower risk of PTDM development in RTRs, independently of established risk factors for PTDM development.

Urinary Excretion of N1-methyl-2-pyridone-5-carboxamide and N1-methylnicotinamide in Renal Transplant Recipients and Donors

N¹-methylnicotinamide (N¹-MN) and N¹-methyl-2-pyridone-5-carboxamide (2Py) are successive end products of NAD⁺ catabolism. N¹-MN excretion in 24-h urine is the established biomarker of niacin nutritional status, and recently shown to be reduced in renal transplant recipients (RTR). However, it is unclear whether 2Py excretion is increased in this population, and, if so, whether a shift in excretion of N¹-MN to 2Py can be attributed to kidney function. Hence, we assessed the 24-h urinary excretion of 2Py and N¹-MN in RTR and kidney donors before and after kidney donation, and investigated associations of the urinary ratio of 2Py to N¹-MN (2Py/N¹-MN) with kidney function, and independent determinants of urinary 2Py/N¹-MN in RTR. The urinary excretion of 2Py and N¹-MN was measured in a cross-sectional cohort of 660 RTR and 275 healthy kidney donors with liquid chromatography-tandem mass spectrometry (LC-MS/MS). Linear regression analyses were used to investigate associations and determinants of urinary 2Py/N¹-MN. Median 2Py excretion was 178.1 (130.3–242.8) μmol/day in RTR, compared to 155.6 (119.6–217.6) μmol/day in kidney donors (p < 0.001). In kidney donors, urinary 2Py/N¹-MN increased significantly after kidney donation (4.0 ± 1.4 to 5.2 ± 1.5, respectively; p < 0.001). Smoking, alcohol consumption, diabetes, high-density lipoprotein (HDL), high-sensitivity C-reactive protein (hs-CRP) and estimated glomerular filtration rate (eGFR) were identified as independent determinants of urinary 2Py/N¹-MN in RTR. In conclusion, the 24-h urinary excretion of 2Py is higher in RTR than in kidney donors, and urinary 2Py/N¹-MN increases after kidney donation. As our data furthermore reveal strong associations of urinary 2Py/N¹-MN with kidney function, interpretation of both N¹-MN and 2Py excretion may be recommended for assessment of niacin nutritional status in conditions of impaired kidney function.

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.

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 (β: −0.02, P = 0.02) and lower 24-h urinary magnesium excretion (β: −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 (P_interaction > 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 Excretion of N1-Methylnicotinamide, as a Biomarker of Niacin Status, and Mortality in Renal Transplant Recipients

Renal transplant recipients (RTR) commonly suffer from vitamin B₆ deficiency and its functional consequences add to an association with poor long-term outcome. It is unknown whether niacin status is affected in RTR and, if so, whether this affects clinical outcomes, as vitamin B₆ is a cofactor in nicotinamide biosynthesis. We compared 24-h urinary excretion of N¹-methylnicotinamide (N¹-MN) as a biomarker of niacin status in RTR with that in healthy controls, in relation to dietary intake of tryptophan and niacin as well as vitamin B₆ status, and investigated whether niacin status is associated with the risk of premature all-cause mortality in RTR. In a prospective cohort of 660 stable RTR with a median follow-up of 5.4 (4.7-6.1) years and 275 healthy kidney donors, 24-h urinary excretion of N¹-MN was measured with liquid chromatography-tandem mass spectrometry LC-MS/MS. Dietary intake was assessed by food frequency questionnaires. Prospective associations of N¹-MN excretion with mortality were investigated by Cox regression analyses. Median N¹-MN excretion was 22.0 (15.8-31.8) μmol/day in RTR, compared to 41.1 (31.6-57.2) μmol/day in healthy kidney donors (p < 0.001). This difference was independent of dietary intake of tryptophan (1059 ± 271 and 1089 ± 308 mg/day; p = 0.19), niacin (17.9 ± 5.2 and 19.2 ± 6.2 mg/day; p < 0.001), plasma vitamin B₆ (29.0 (17.5-49.5), and 42.0 (29.8-60.3) nmol/L; p < 0.001), respectively. N¹-MN excretion was inversely associated with the risk of all-cause mortality in RTR (HR 0.57; 95% CI 0.45-0.71; p < 0.001), independent of potential confounders. RTR excrete less N¹-MN in 24-h urine than healthy controls, and our data suggest that this difference cannot be attributed to lower dietary intake of tryptophan and niacin, nor vitamin B₆ status. Importantly, lower 24-h urinary excretion of N¹-MN is independently associated with a higher risk of premature all-cause mortality in RTR.

Urinary Properdin and sC5b-9 Are Independently Associated With Increased Risk for Graft Failure in Renal Transplant Recipients

The pathophysiology of late kidney-allograft failure remains complex and poorly understood. Activation of filtered or locally produced complement may contribute to the progression of renal failure through tubular C5b-9 formation. This study aimed to determine urinary properdin and sC5b-9 excretion and assess their association with long-term outcome in renal transplant recipients (RTR). Methods: We measured urinary properdin and soluble C5b-9 in a well-defined cross-sectional cohort of RTR. Urinary specimens were taken from a morning urine portion, and properdin and sC5b-9 were measured using an enzyme-linked-immunosorbent assay (ELISA). Cox proportional hazard regression analyses were used to investigate prospective associations with death-censored graft failure. Results: We included 639 stable RTR at a median [interquartile range] 5.3 (1.8-12.2) years after transplantation. Urinary properdin and sC5b-9 excretion were detectable in 161 (27%) and 102 (17%) RTR, respectively, with a median properdin level of 27.6 (8.6-68.1) ng/mL and a median sC5b-9 level of 5.1 (2.8-12.8) ng/mL. In multivariable-adjusted Cox regression analyses, including adjustment for proteinuria, urinary properdin (HR, 1.12; 95% CI 1.02-1.28; P = 0.008) and sC5b-9 excretion (HR, 1.34; 95% CI 1.10-1.63; P = 0.003) were associated with an increased risk of graft failure. If both urinary properdin and sC5b-9 were detectable, the risk of graft failure was further increased (HR, 3.12; 95% CI 1.69-5.77; P < 0.001). Conclusions: Our findings point toward a potential role for urinary complement activation in the pathogenesis of chronic allograft failure. Urinary properdin and sC5b-9 might be useful biomarkers for complement activation and chronic kidney allograft deterioration, suggesting a potential role for an alternative pathway blockade in RTR.

Urinary Epidermal Growth Factor/Creatinine Ratio and Graft Failure in Renal Transplant Recipients: A Prospective Cohort Study

Graft failure (GF) remains a significant limitation to improve long-term outcomes in renal transplant recipients (RTR). Urinary epidermal growth factor (uEGF) is involved in kidney tissue integrity, with a reduction of its urinary excretion being associated with fibrotic processes and a wide range of renal pathologies. We aimed to investigate whether, in RTR, uEGF is prospectively associated with GF. In this prospective cohort study, RTR with a functioning allograft ≥1-year were recruited and followed-up for three years. uEGF was measured in 24-hours urine samples and normalized by urinary creatinine (Cr). Its association with risk of GF was assessed by Cox-regression analyses and its predictive ability by C-statistic. In 706 patients, uEGF/Cr at enrollment was 6.43 [IQR 4.07-10.77] ng/mg. During follow-up, 41(6%) RTR developed GF. uEGF/Cr was inversely associated with the risk of GF (HR 0.68 [95% CI 0.59-0.78]; P < 0.001), which remained significant after adjustment for immunosuppressive therapy, estimated Glomerular Filtration Rate, and proteinuria. C-statistic of uEGF/Cr for GF was 0.81 (P < 0.001). We concluded that uEGF/Cr is independently and inversely associated with the risk of GF and depicts strong prediction ability for this outcome. Further studies seem warranted to elucidate whether uEGF might be a promising marker for use in clinical practice.

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.

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 (β = 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.

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 (β = -1.61, p = 0.001), natural log transformed serum ferritin (β = -0.31, p < 0.001), TSAT (β = -2.85, p = 0.001), and hemoglobin levels (β = -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.

Fruit and Vegetable Intake and Risk of Posttransplantation Diabetes in Renal Transplant Recipients

OBJECTIVE

Posttransplantation diabetes mellitus (PTDM) contributes to risk for cardiovascular morbidity and mortality in renal transplant recipients (RTRs). In the general population, consumption of a diet containing few fruits and vegetables predisposes to type 2 diabetes. The role of diet as a potential modifiable risk factor for PTDM has not been explored. Our focus was to investigate the prospective associations of fruit and vegetable intake with risk of PTDM in stable RTRs.

RESEARCH DESIGN AND METHODS

We included 472 adult RTRs who had a functioning graft ≥1 year. Fruit and vegetable intake was assessed by using a 177-item food frequency questionnaire. PTDM was defined according the American Diabetes Association's diagnostic criteria for diabetes.

RESULTS

During 5.2 years of follow-up, 52 RTRs (11%) developed PTDM. Fruit intake was not associated with PTDM (hazard ratio [HR] 0.90 [95% CI 0.79-1.03] per ²log g/day; P = 0.13), whereas vegetable intake was inversely associated with PTDM (HR 0.77 [95% CI 0.63-0.94] per ²log g/day; P = 0.009). Mediation analyses revealed that ±50% of the association between vegetable intake and PTDM was mediated by variations in key components of the metabolic syndrome (i.e., HDL cholesterol, triglycerides, and waist circumference) as determined by the National Cholesterol Education Program's Adult Treatment Panel III Expert Panel.

CONCLUSIONS

In this study vegetable intake, but not fruit intake, was associated with lower risk of PTDM in RTRs, likely largely through beneficial effects on key components of the metabolic syndrome. These findings further support accumulating evidence that supports a recommendation of higher vegetable intake by RTRs.

Plasma Malondialdehyde and Risk of New-Onset Diabetes after Transplantation in Renal Transplant Recipients: A Prospective Cohort Study

New-onset diabetes after transplantation (NODAT) is a frequent complication in renal transplant recipients (RTR). Although oxidative stress has been associated with diabetes mellitus, data regarding NODAT are limited. We aimed to prospectively investigate the long-term association between the oxidative stress biomarker malondialdehyde (measured by high-performance liquid chromatography) and NODAT in an extensively phenotyped cohort of non-diabetic RTR with a functioning graft ≥1 year. We included 516 RTR (51 ± 13 years-old, 57% male). Median plasma malondialdehyde (MDA) was 2.55 (IQR, 1.92-3.66) µmol/L. During a median follow-up of 5.3 (IQR, 4.6-6.0) years, 56 (11%) RTR developed NODAT. In Cox proportional-hazards regression analyses, MDA was inversely associated with NODAT, independent of immunosuppressive therapy, transplant-specific covariates, lifestyle, inflammation, and metabolism parameters (HR, 0.55; 95% CI, 0.36-0.83 per 1-SD increase; p < 0.01). Dietary antioxidants intake (e.g., vitamin E, α-lipoic acid, and linoleic acid) were effect-modifiers of the association between MDA and NODAT, with particularly strong inverse associations within the subgroup of RTR with relatively higher dietary antioxidants intake. In conclusion, plasma MDA concentration is inversely and independently associated with long-term risk of NODAT in RTR. Our findings support a potential underrecognized role of oxidative stress in post-transplantation glucose homeostasis.

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 (β = -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.

Circulating Haptoglobin and Metabolic Syndrome in Renal Transplant Recipients

Haptoglobin (Hp) is an acute phase protein that has recently been linked to components of the metabolic syndrome (MetS). We aimed to evaluate Hp as marker of MetS, and to assess its association with long-term outcome in renal transplant recipients (RTR). We measured plasma Hp in a prospective cohort of 699 stable RTR and 149 healthy controls. Median plasma Hp concentration in RTR was 1.4 [interquartile range (IQR), 1.0–1.8] g/L, which was higher compared to 1.1 [0.9–1.4] g/L in controls (P < 0.001). Hp was independently associated with the MetS (β = 0.10) (P = 0.005). During follow-up of 5.4 [4.8–6.1] years, 150 (21%) recipients died, of whom 60 (9%) due to cardiovascular causes, and 83 (12%) RTR developed graft failure. High (≥2.0 g/L) and low (≤0.9 g/L) plasma Hp were associated with increased risk of mortality (HR’s 2.3 [1.3–4.1] and 1.9 [1.0–3.5], resp.), predominantly cardiovascular. The association of high Hp lost significance upon adjustment for inflammation markers (HR 1.5 [0.8–2.7]), while low Hp was independently associated with mortality (HR 2.2 [1.2–4.0]). Hp was not associated with graft failure (P = 0.49). In conclusion, plasma Hp is independently associated with MetS in RTR. Importantly, high and low Hp are associated with increased mortality risk, independent of MetS.

Lifestyle intervention to improve quality of life and prevent weight gain after renal transplantation: Design of the Active Care after Transplantation (ACT) randomized controlled trial

BACKGROUND

Low physical activity and reduced physical functioning are common after renal transplantation, resulting in a reduced quality of life. Another common post-transplantation complication is poor cardio-metabolic health, which plays a main role in long-term outcomes in renal transplant recipients (RTR). It is increasingly recognized that weight gain in the first year after transplantation, especially an increase in fat mass, is a highly common contributor to cardio-metabolic risk. The aim of this study is to compare the outcomes of usual care to the effects of exercise alone, and exercise combined with dietary counseling, on physical functioning, quality of life and post-transplantation weight gain in RTR.

METHODS

The Active Care after Transplantation study is a multicenter randomized controlled trial with three arms in which RTR from 3 Dutch hospitals are randomized within the first year after transplantation to usual care, to exercise intervention (3 months supervised exercise 2 times per week followed by 12 months active follow-up), or to an exercise + diet intervention, consisting of the exercise training with additional dietary counseling (12 sessions over 15 months by a renal dietician). In total, 219 participants (73 per group) will be recruited. The primary outcome is the subdomain physical functioning of quality of life, (SF-36 PF). Secondary outcomes include other evaluations of quality of life (SF-36, KDQOL-SF, EQ-5D), objective measures of physical functioning (aerobic capacity and muscle strength), level of physical activity, gain in adiposity (body fat percentage by bio-electrical impedance assessment, BMI, waist circumference), and cardiometabolic risk factors (blood pressure, lipids, glucose metabolism). Furthermore, data on renal function, medical history, medication, psychological factors (motivation, kinesiophobia, coping style), nutrition knowledge, nutrition intake, nutrition status, fatigue, work participation, process evaluation and cost-effectiveness are collected.

DISCUSSION

Evidence on the effectiveness of an exercise intervention, or an exercise + diet intervention on physical functioning, weight gain and cardiometabolic health in RTR is currently lacking. The outcomes of the present study may help to guide future evidence-based lifestyle care after renal transplantation.

TRIAL REGISTRATION

Number: NCT01047410 .

Effect of an intensive nutrition intervention of a high protein and low glycemic-index diet on weight of kidney transplant recipients: study protocol for a randomized clinical trial

BACKGROUND

Excessive weight gain is commonly observed within the first year after kidney transplantation and is associated with negative outcomes, such as graft loss and cardiovascular events. The purpose of this study is to evaluate the effect of a high protein and low glycemic-index diet on preventing weight gain after kidney transplantation.

METHODS

We designed a prospective, single-center, open-label, randomized controlled study to compare the efficacy of a high protein (1.3-1.4 g/kg/day) and low-glycemic index diet versus a conventional diet (0.8-1.0 g/kg/day of protein) on preventing weight gain after kidney transplantation. A total of 120 eligible patients 2 months after transplantation will be recruited. Patients with an estimated glomerular filtration rate through the modification of diet of renal disease (MDRD) formula < 30 mL/min/1.73 m2 or urinary albumin excretion > 300 mg/24 h will be excluded. Patients' diets will be allocated through simple sequential randomization. Patients will be followed-up for 12 months with nine clinic appointments with a dietitian and the evaluations will include nutritional assessment (anthropometrics, body composition, and resting metabolic rate) and laboratory tests. The primary outcome is weight maintenance or body weight gain under 5% after 12 months. Secondary outcomes include body composition, resting metabolic rate, satiety sensation, kidney function, and other metabolic parameters.

DISCUSSION

Diets with higher protein content and lower glycemic index may lead to weight loss because of higher satiety sensation. However, there is a concern about the association of high protein intake and kidney damage. Nevertheless, there is little evidence on the impact of high protein intake on long-term kidney function outcome. Therefore, we designed a study to test if a high protein diet with low-glycemic index will be an effective and safe nutritional intervention to prevent weight gain in kidney transplant patients.

TRIAL REGISTRATION

ClinicalTrials.gov identifier, NCT02883777 . Registered on 3 August 2016.

Vitamin B-6 deficiency is common and associated with poor long-term outcome in renal transplant recipients

Background: Previous studies have reported low circulating concentrations of pyridoxal-5-phospate (PLP) in renal transplant recipients (RTRs). It is unknown whether this is because of low intake or altered handling, and it is also unknown whether variation in circulating concentrations of PLP influences long-term outcome.Objective: We compared vitamin B-6 intake and circulating PLP concentrations of RTRs with those of healthy controls and investigated long-term clinical implications of vitamin B-6 deficiency in stable outpatient RTRs.Design: In a longitudinal cohort of 687 stable RTRs (57% male; mean ± SD age: 53 ± 13 y) with a median (IQR) follow-up of 5.3 y (4.8-6.1 y) and 357 healthy controls (47% male; age 54 ± 11 y), baseline vitamin B-6 was measured as plasma PLP by high-performance liquid chromatography (HPLC). Vitamin B-6 deficiency was defined as PLP <20 nmol/L, and insufficiency as PLP 20-30 nmol/L. Dietary intake was assessed by validated food-frequency questionnaires.Results: At inclusion [5.3 y (1.8-12.1 y) after transplantation], the mean vitamin B-6 intakes in RTRs and healthy controls were 1.77 ± 0.49 and 1.85 ± 0.56 mg/d, respectively (P = 0.23). In these groups, the median plasma PLP concentrations were 29 nmol/L (17-50 nmol/L) and 41 nmol/L (29-60 nmol/L), respectively (P < 0.001). Accordingly, deficiency was present in 30% of RTRs compared with 11% of healthy controls. PLP concentrations were inversely associated with glucose homeostasis variables and inflammation variables (all P < 0.01). During follow-up, 149 (21%) RTRs died and 82 (12%) developed graft failure. In RTRs, vitamin B-6 deficiency was associated with considerably higher mortality risk (HR 2.14; 95% CI: 1.48, 3.08) than a sufficient vitamin B-6 status, independent of potential confounders. No associations were observed for graft failure (P = 0.18).Conclusions: Vitamin B-6 deficiency is common in RTRs and does not seem to be a consequence of inadequate intake. In addition, this deficient state is clinically relevant and independently associated with an increased risk of mortality in RTRs. The cohort on which the study was based [TransplantLines Food and Nutrition Biobank and Cohort Study (TxL-FN)] was registered at clinicaltrials.gov as NCT02811835.