Cystatin C and albuminuria as predictors of long-term allograft outcomes in kidney transplant recipients

Association Between Graft Function and Urine CXCL10 and Acylcarnitines Levels in Kidney Transplant Recipients

OBJECTIVE

To evaluate post-transplantation graft functions noninvasively by using urine C-X-C motif chemokine 10 (CXCL10) and metabolome analysis.

METHODS

The 65 living-donor kidney-transplant recipients in our cohort underwent renal biopsy to investigate possible graft dysfunction. The patients were divided into 2 groups, according to pathology reports: chronic allograft dysfunction (CAD; n = 18) and antibody-mediated/humoral allograft rejection (AMR; n = 16). The control group was composed of renal transplant recipients with stable health (n = 33). We performed serum creatinine, blood urea nitrogen (BUN), cystatin C, urine protein, CXCL10, and metabolome analyses on specimens from the patients.

RESULTS

BUN, creatinine, cystatin C, urine protein, leucine + isoleucine, citrulline, and free/acetyl/propionyl carnitine levels were significantly higher in patients with CAD and AMR, compared with the control individuals. CXCL10 levels were significantly elevated in patients with AMR, compared with patients with CAD and controls. CXCL10 (AUC = 0.771) and cystatin C (AUC = 0.746) were significantly higher in the AMR group, compared with the CAD group (P<.02).

CONCLUSIONS

CXCL10 and metabolome analyzes are useful for evaluation of graft functions. Also, CXCL10 might be useful as a supplementary noninvasive screening test for diagnosis of allograft rejection.

Urinary Spermidine Predicts and Associates with In-Hospital Acute Kidney Injury after Cardiac Surgery

Acute Kidney Injury (AKI) affects up to 30% of the patients who undergo cardiac surgery (CVS) and is related to higher mortality. We aim to investigate molecular features associated with in-hospital AKI development and determine the predictive value of these features when analyzed preoperatively. This is a case-control study. From an initial cohort of 110 recruited subjects, a total of 60 patients undergoing cardiac surgery were included: 20 (33%) developed in-hospital AKI (CVS-AKI) and 40 did not (controls, CVS-C). Pre- and post-surgery samples were collected and a prospective study was carried out. A total of 312 serum samples and 258 urine samples were analyzed by nuclear magnetic resonance, mass spectrometry and ELISA. Six features predicted AKI development in pre-surgery samples: urinary kidney functional loss marker kidney injury molecule-1 (uKIM-1), 2-hydroxybutyric acid, 2-hydroxyphenylacetic acid, hippuric acid, phosphoethanolamine and spermidine. Two of them stood out as powerful predictors. Pre-surgery uKIM-1 levels were increased in CVS-AKI vs. CVS-C (AUC = 0.721, p-value = 0.0392) and associated strongly with the outcome (OR = 5.333, p-value = 0.0264). Spermidine showed higher concentration in CVS-AKI (p-value < 0.0001, AUC = 0.970) and had a strong association with the outcome (OR = 69.75, p-value < 0.0001). uKIM-1 and particularly spermidine predict in-hospital AKI associated with CVS in preoperative samples. These findings may aid in preventing postoperative AKI and improve prognosis of CVS.

Cystatin C: A Primer for Pharmacists

Pharmacists are at the forefront of dosing and monitoring medications eliminated by or toxic to the kidney. To evaluate the effectiveness and safety of these medications, accurate measurement of kidney function is paramount. The mainstay of kidney assessment for drug dosing and monitoring is serum creatinine (SCr)-based estimation equations. Yet, SCr has known limitations including its insensitivity to underlying changes in kidney function and the numerous non-kidney factors that are incompletely accounted for in equations to estimate glomerular filtration rate (eGFR). Serum cystatin C (cysC) is a biomarker that can serve as an adjunct or alternative to SCr to evaluate kidney function for drug dosing. Pharmacists must be educated about the strengths and limitations of cysC prior to applying it to medication management. Not all patient populations have been studied and some evaluations demonstrated large variations in the relationship between cysC and GFR. Use of eGFR equations incorporating cysC should be reserved for drug management in scenarios with demonstrated outcomes, including to improve pharmacodynamic target attainment for antibiotics or reduce drug toxicity. This article provides an overview of cysC, discusses evidence around its use in medication dosing and in special populations, and describes practical considerations for application and implementation.

Filtration Markers, Cardiovascular Disease, Mortality, and Kidney Outcomes in Stable Kidney Transplant Recipients: The FAVORIT Trial

Cystatin C and beta-2-microglobulin (B2M) are filtration markers associated with adverse outcomes in nontransplant populations, sometimes with stronger associations than for creatinine. We evaluated associations of estimated glomerular filtration rate from cystatin C (eGFR_cys ), B2M (eGFR_B2M ), and creatinine (eGFR_cr ) with cardiovascular outcomes, mortality, and kidney failure in stable kidney transplant recipients using a case-cohort study nested within the Folic Acid for Vascular Outcome Reduction in Transplantation (FAVORIT) Trial. A random subcohort was selected (N = 508; mean age 51.6 years, median transplant vintage 4 years, 38% women, 23.6% nonwhite race) with enrichment for cardiovascular events (N = 306; 54 within the subcohort), mortality (N = 208; 68 within the subcohort), and kidney failure (N = 208; 52 within the subcohort). Mean eGFR_cr , eGFR_cys , and eGFR_B2M were 46.0, 43.8, and 48.8 mL/min/1.73m² , respectively. After multivariable adjustment, hazard ratios for eGFR_cys and eGFR_B2M <30 versus 60+ were 2.02 (95% confidence interval [CI] 1.09-3.76; p = 0.03) and 2.56 (1.35-4.88; p = 0.004) for cardiovascular events; 3.92 (2.11-7.31) and 4.09 (2.21-7.54; both p < 0.001) for mortality; and 9.49 (4.28-21.00) and 15.53 (6.99-34.51; both p < 0.001) for kidney failure. Associations persisted with additional adjustment for baseline eGFR_cr . We conclude that cystatin C and B2M are strongly associated with cardiovascular events, mortality, and kidney failure in stable kidney transplant recipients.

Serum uromodulin predicts graft failure in renal transplant recipients

OBJECTIVE AND METHODS

Test the ability of serum uromodulin concentrations 1-3 months after renal transplantation to predict all-cause mortality (ACM) and graft loss (GL) in 91 patients.

RESULTS

uromodulin predicted GL equivalently to the other markers studied: the risk for GL was reduced by 0.21 per one standard deviation (SD) increase (cystatin C: hazard ratio [HR] 4.57, creatinine: HR 4.53, blood-urea-nitrogen [BUN]: HR 2.50, estimated glomerular filtration rate [eGFR]: HR 0.10). In receiver-operating-characteristic (ROC) analysis, uromodulin predicted GL with an area-under-the curve of 0.782 at an optimal cut-off (OCO) of 24.0 ng/ml with a sensitivity of 90.0% and a specificity of 70.2%.

CONCLUSION

Serum uromodulin predicted GL equivalently compared to conventional biomarkers of glomerular filtration.

Early postoperative C-terminal agrin fragment (CAF) serum levels predict graft loss and proteinuria in renal transplant recipients

BACKGROUND

C-terminal agrin fragment (CAF), cleavage product of agrin, was previously correlated with kidney function in renal transplant patients. This article studies the predictive value of CAF for long-term outcomes in renal transplant recipients.

METHODS

In this observational cohort study, serum CAF, creatinine and blood-urea-nitrogen (BUN) concentrations and eGFR (CKD-EPI) were assessed 1-3 months after transplantation in 105 patients undergoing kidney transplantation. Cox regression models were used to analyse the predictive value of all parameters concerning all-cause mortality (ACM), graft loss (GL), doubling of creatinine/proteinuria at the end of follow-up.

RESULTS

Median follow-up time was 3.1 years. The mean concentrations were 191.9±152.4 pM for CAF, 176±96.8 μmol/L for creatinine, 12.6±6.2 mmol/L for BUN and 44.9±21.2 mL/min for CKD-EPI formula, respectively. In univariate analysis CAF and BUN concentrations predicted ACM (CAF: HR=1.003, 1.1-fold risk, p=0.043; BUN: HR=1.037, 1.3-fold risk, p=0.006). Concerning GL, CAF (HR=1.006, 3.1-fold risk, p<0.001), creatinine (HR=2.396, 2.6-fold risk, p<0.001), BUN (HR=1.048, 1.7-fold risk, p=0.001) and eGFR (CKD-EPI) (HR=0.941, 0.45-fold risk reduction, p=0.006) showed a statistically significant association. CAF was the only parameter significantly associated with doubling of proteinuria (HR=1.005, 1.7-fold risk, p<0.001). In multiple regression analysis (CAF only) the association remained significant for GL and doubling of proteinuria but not ACM.

CONCLUSIONS

Early postoperative serum CAF appears to be a useful tool for the assessment of long-term outcomes in renal transplant recipients. Most importantly it represents a promising predictor for the development of proteinuria.

A high sodium intake reduces antiproteinuric response to renin-angiotensin-aldosterone system blockade in kidney transplant recipients

BACKGROUND

Post-transplant proteinuria is associated with lower graft and patient survival. Renin-angiotensin-aldosterone system blockers are used to reduce proteinuria and improve renal outcome. Although it is known that a high salt intake blunts the antiproteinuric effect of ACEI and ARB drugs in non-transplant patients, this effect has not been studied in kidney transplant recipients.

OBJECTIVE

To analyse the relationship between sodium intake and the antiproteinuric effect of ACEI/ARB drugs in kidney transplant recipients.

METHODS

We selected 103 kidney transplant recipients receiving ACEI/ARB drugs for more than 6 months due to proteinuria>1 g/day. Proteinuria was analysed at baseline and at 6 months after starting ACEI/ARB treatment. Salt intake was estimated by urinary sodium to creatinine ratio (uNa/Cr).

RESULTS

Proteinuria fell to less than 1g/day in 46 patients (44.7%). High uNa/Cr was associated with a smaller proteinuria decrease (r=-0.251, P=.011). The percentage proteinuria reduction was significantly lower in patients in the highest uNa/Cr tertile [63.9% (IQR 47.1%), 60.1% (IQR 55.4%), 38.9% (IQR 85.5%), P=.047]. High uNa/Cr independently relates (OR 2.406 per 100 mEq/g, 95% CI: 1.008-5.745, P=.048) to an antiproteinuric response <50% after renin-angiotensin-aldosterone system blockade.

CONCLUSIONS

A high salt intake results in a smaller proteinuria decrease in kidney transplant recipients with proteinuria treated with ACEI/ARB drugs.

Estimating glomerular filtration rate in kidney transplantation: Still searching for the best marker

Kidney transplantation is the treatment of choice for end-stage renal disease. The evaluation of graft function is mandatory in the management of renal transplant recipients. Glomerular filtration rate (GFR), is generally considered the best index of graft function and also a predictor of graft and patient survival. However GFR measurement using inulin clearance, the gold standard for its measurement and exogenous markers such as radiolabeled isotopes ((51)Cr EDTA, (99m)Tc DTPA or (125)I Iothalamate) and non-radioactive contrast agents (Iothalamate or Iohexol), is laborious as well as expensive, being rarely used in clinical practice. Therefore, endogenous markers, such as serum creatinine or cystatin C, are used to estimate kidney function, and equations using these markers adjusted to other variables, mainly demographic, are an attempt to improve accuracy in estimation of GFR (eGFR). Nevertheless, there is some concern about the inability of the available eGFR equations to accurately identify changes in GFR, in kidney transplant recipients. This article will review and discuss the performance and limitations of these endogenous markers and their equations as estimators of GFR in the kidney transplant recipients, and their ability in predicting significant clinical outcomes.

Cystatin C and serum creatinine as predictors of kidney graft outcome

PURPOSE

Serum cystatin C (Cys C) was evaluated as a predictor of kidney graft failure progression, and its predictive ability was compared to other markers of graft function.

METHODS

The following kidney graft markers were determined in 91 patients who came for regular checkups of kidney graft function to our outpatient service in February 2008: Cys C, serum creatinine (sCr), 24-h proteinuria and 24-h urinary creatinine clearance (CCr). Glomerular filtration rate (eGFR) was estimated using sCr-based and Cys C formula. Patients were regularly monitored until February 2013 or to graft failure.

RESULTS

During follow-up, graft failure occurred in 21 recipients. The Cys C ≥2.65 mg/l discriminated patients with and without graft failure (sensitivity of 80.95% and specificity of 92.86%). According to c statistic, the highest performance was achieved for Cys C (0.874). In addition, Cys C area under the curve (AUC) was significantly better than CCr AUC (p = 0.007), 24-h proteinuria AUC (p = 0.03), eGFR estimated by the chronic kidney disease epidemiology collaboration (EPI) AUC (p = 0.05), but not better than sCr or eGFR AUCs calculated by other formulas. In the multivariable model, sCr, CCr, Cys C and eGFRs were predictors of graft failure. Combination of Cys C, sCr and logarithm of 24 h proteinuria (0.883) or Cys C, CCr and logarithm of 24-h proteinuria (0.884) had the highest AUC for predicting graft outcome that exceed insignificantly Cys C or sCr areas.

CONCLUSIONS

The most reliable predictors of graft outcome were Cys C, sCr and proteinuria. Because Cys C is unavailable in many transplant centers, from the practical point of view, sCr remains the most sensitive predictor of graft outcome.