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

Taurine Deficiency Is a Hallmark of Injured Kidney Allografts

BACKGROUND

Taurine is one of the most abundant amino acids in humans. Low taurine levels are associated with cellular senescence, mitochondrial dysfunction, DNA damage, and inflammation in mouse, all of which can be reversed by supplementation. It is unknown whether taurine metabolism is associated with kidney allograft function and survival.

METHODS

We performed urine metabolomic profiling of kidney transplant recipients in the early and late phases after transplantation combined with transcriptomic analysis of human kidney allografts. Single-nucleus RNA sequencing data sets of mouse kidneys after ischemia-reperfusion injury were analyzed. We analyzed the association of urinary taurine levels and taurine metabolism genes with kidney function, histology, and graft survival.

RESULTS

Urine taurine concentrations were significantly lower in kidney transplant recipients who experienced delayed graft function. In a mouse model of ischemia-reperfusion injury, the taurine biosynthesis gene, CSAD, but not the taurine transporter SLC6A6, was repressed. In the late stage of transplantation, low level of taurine in urine was associated with impaired kidney function and chronic structural changes. Urine taurine level in the lowest tertile was predictive of graft loss. Expression of the taurine transporter SLC6A6 in the upper median, but not CSAD, was associated with chronic kidney injury and was predictive of graft loss.

CONCLUSIONS

Low urine taurine level is a marker of injury in the kidney allograft, is associated with poor kidney function, is associated with chronic histological changes, and is predictive of graft survival. The differential expression of CSAD and SLC6A6, depending on the time after transplantation and marks of injury, highlights different mechanisms affecting taurine metabolism.

Sex-specific metabolic risk factors and their trajectories towards the non-alcoholic fatty liver disease incidence

PURPOSE

Non-alcoholic fatty liver disease (NAFLD) is a common chronic liver disease. This study examined sex-specific associations between NAFLD and metabolic factors and investigated the trajectory of risk factors.

METHODS

We retrospectively investigated 16,140 individuals from Beijing Health Management Cohort. Univariate and multivariate time-dependent Cox regression analyses were performed to identify independent risk factors for new-onset NAFLD. The trajectory of risk factors was investigated using the latent growth curve model and growth mixture model.

RESULTS

Over a median follow-up of 3.15 years, 2,450 (15.18%) participants developed NAFLD. The risk factors for NAFLD in men were increased body mass index (BMI); waist circumference (WC); triglyceride (TG), low-density lipoprotein cholesterol (LDL-C), haemoglobin (Hb), and serum uric acid (SUA) levels; and platelet (PLT) count and decreased serum creatinine-to-body weight (sCr/bw) and high-density lipoprotein cholesterol (HDL-C) levels. In women, the risk factors were increased BMI, WC, and fasting plasma glucose (FPG), TG, LDL-C, SUA, white blood cell (WBC), and PLT and decreased sCr/bw and HDL-C levels. In addition, BMI, LDL-C, sCr/bw and PLT changing trajectories were associated with NAFLD in men; BMI, WC, TG, LDL-C, SUA and sCr/bw trends was associated with NAFLD risk in women.

CONCLUSIONS

Development of NAFLD is associated with BMI, LDL-C, sCr/bw and PLT changing trajectories in men; BMI, WC, TG, LDL-C, SUA and sCr/bw trends are associated an increased risk of NAFLD in women. Deterioration of metabolic risk factors status can be a predictor of NAFLD many years before its occurrence.

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.

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.

Dietary intake of specific amino acids and liver status in subjects with nonalcoholic fatty liver disease: fatty liver in obesity (FLiO) study

PURPOSE

Identification of dietary factors involved in the development and progression of nonalcoholic fatty liver disease (NAFLD) is relevant to the current epidemics of the disease. Dietary amino acids appear to play a key role in the onset and progression of NAFLD. The aim of this study was to analyze potential associations between specific dietary amino acids and variables related to glucose metabolism and hepatic status in adults with overweight/obesity and NAFLD.

METHODS

One hundred and twelve individuals from the Fatty Liver in Obesity (FLiO) study were evaluated. Liver assessment was carried out by ultrasonography, magnetic resonance imaging and analysis of biochemical parameters. Dietary amino acid intake (aromatic amino acids (AAA); branched-chain amino acids (BCAA); sulfur amino acids (SAA)) was estimated by means of a validated 137-item food frequency questionnaire.

RESULTS

Higher consumption of these amino acids was associated with worse hepatic health. Multiple adjusted regression models confirmed that dietary AAA, BCAA and SAA were positively associated with liver fat content. AAA and BCAA were positively associated with liver iron concentration. Regarding ferritin levels, a positive association was found with BCAA. Dietary intake of these amino acids was positively correlated with glucose metabolism (glycated hemoglobin, triglyceride and glucose index) although the significance disappeared when potential confounders were included in the model.

CONCLUSION

These findings suggest that the consumption of specific dietary amino acids might negatively impact on liver status and, to a lesser extent on glucose metabolism in subjects with overweight/obesity and NAFLD. A control of specific dietary amino acid composition should be considered in the management of NAFLD and associated insulin resistance. NCT03183193; June 2017.