Proteinuria and Outcome After Renal Transplantation: Ratios or Fractions?

Fractional excretion of total protein predicts renal prognosis in Japanese patients with primary membranous nephropathy

Background

Primary membranous nephropathy (pMN) is one of the most common types of glomerulonephritis, with a third of patients progressing to renal insufficiency. Various prognostic factors have been reported, of which urinary protein and renal function are the most critical parameters. Fractional excretion of total protein (FETP) indicates protein leakage that accounts for creatinine kinetics and serum protein levels. In this study, we investigated the association between FETP and renal prognosis in pMN.

Methods

We retrospectively identified 150 patients with pMN. FETP was calculated as follows: (serum creatinine × urine protein)/(serum protein × urine creatinine) %. We divided the patients into three groups according to FETP values and compared the clinicopathological findings. The primary outcome was an estimated glomerular filtration rate (eGFR) decrease of ≥30% from the baseline level.

Results

FETP was associated with urinary protein and renal function, Ehrenreich and Churg stage, and global glomerulosclerosis. The primary outcome was observed in 38 patients (25.3%), and the frequency of the primary outcome was higher in the high FETP group (P = .001). FETP is higher than protein-creatinine ratio (PCR) in the area under the curve. In the multivariate analysis adjusted for age, eGFR, PCR and treatment, FETP was significantly associated with primary outcome (adjusted hazard ratio, 8.19; P = .019).

Conclusions

FETP is a valuable indicator that can reflect the pathophysiology and is more useful than PCR as a predictor of renal prognosis in patients with Japanese pMN.

High Albumin Clearance Predicts the Minimal Change Nephrotic Syndrome Relapse

Key Points

Albumin kinetics not only reflected the pathophysiology of minimal change nephrotic syndrome but was also a predictor of relapse. The high estimated 24-hour albumin clearance predicts the minimal change nephrotic syndrome relapse. The 24-hour albumin clearance can easily be calculated from only serum albumin and urinary protein excretion, which are routine laboratory measurements.

Background

Although albuminuria leakage that occurs in minimal change nephrotic syndrome (MCNS) may be related to the disease state, albumin kinetics in MCNS has never been evaluated. In this study, we investigated albumin kinetics in adult Japanese patients with MCNS by the estimated 24-hour albumin clearance (eCALB) and examined the association between eCALB and relapse.

Methods

We retrospectively identified 103 adult patients with a histological diagnosis of MCNS from four hospitals in Japan (2010–2020). The primary outcome is the first relapse in 2 years after complete remission after corticosteroid therapy. The eCALB [µ l/min] was defined as (2.71828(0.0445+0.9488×log(urinary protein) [g/24 hours])/(serum albumin [g/dl]×1440 [min/24 hours]) for women and (2.71828(-0.1522+0.9742×log(urinary protein) [g/24 hours])/(serum albumin [g/dl]×1440 [min/24 hours]) for men.

Results

Relapse was observed in 44 patients (103 kidney biopsy samples; 42.7%). The mean patient age was 41.0 years. Patients had an eGFR of 71.0 ml/min per 1.73 m2, urinary protein excretion of 6.8 g/d, serum albumin of 1.4 g/dl, and eCALB of 2.27 μ l/min. eCALB was strongly associated with hypoalbuminemia, severe proteinuria, lipid abnormalities, and coagulopathy. In the multivariable analysis, a high eCALB was significantly associated with relapse after adjusting for age, eGFR, time to complete remission, and urinary protein excretion (adjusted hazard ratio, 5.027; 95% confidence interval, 1.88 to 13.47; P = 0.001).

Conclusions

This study revealed that eCALB, which could substitute albumin kinetics, reflected the severity of MCNS, and a high eCALB was associated with recurrence.

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.

24-Hour Proteinuria Versus Spot Protein-Creatinine Ratio for Kidney Transplant Management in Clinical Practice

BACKGROUND

24-hour proteinuria (24h-P) has been the most widespread test for clinical follow-up of proteinuria after kidney transplantation (KT), but urine collection is often not properly collected. Spot protein-creatinine ratio (P/Cr) has become the alternative to 24h-P for proteinuria evaluation in many KT units. However, its reliability, equivalence to 24h-P, and prognostic value regarding allograft outcome remain unknown. Therefore, the aim of this study was to evaluate the correlation and agreement between both methods for assessing proteinuria and to analyze which of them is a better predictor of graft survival.

METHODS

We collected proteinuria measurements from KT patients in our center. 24h-P was adjusted for body surface area. Pearson correlation test and the Bland-Altman method were used to analyze correlation and agreement. Survival analysis was performed with the use of the Kaplan-Meier method and multivariate Cox proportional hazard model.

RESULTS

A total of 8,549 urine samples were analyzed from 472 patients in whom 24h-P and P/Cr were simultaneously measured. A significant correlation was observed between 24h-P and P/Cr (r = .76; P < .001); however, the agreement between methods showed that P/Cr overestimated proteinuria compared with 24h-P, particularly when the latter was >1 g/24 h. The Cox regression multivariate model showed an increased risk of graft loss associated with proteinuria when assessed by either 24h-P (hazard ratio [HR] 6.53, 95% confidence interval [CI] 2.49-17.1) or P/Cr (HR 3.34, 95% CI 1.04-10.7).

CONCLUSIONS

P/Cr is an method interchangeable with 24h-P for detecting proteinuria after KT. When proteinuria increases, the P/Cr overestimates 24h-P, even though it also has a significant and similar prognostic value for predicting graft survival.

Deleterious effects of phosphate on vascular and endothelial function via disruption to the nitric oxide pathway

Background

Hyperphosphataemia is an independent risk factor for accelerated cardiovascular disease in chronic kidney disease (CKD), although the mechanism for this is poorly understood. We investigated the effects of sustained exposure to a high-phosphate environment on endothelial function in cellular and preclinical models, as well as in human subjects.

Methods

Resistance vessels from rats and humans (± CKD) were incubated in a normal (1.18 mM) or high (2.5 mM) phosphate concentration solution and cells were cultured in normal- (0.5 mM) or high-phosphate (3 mM) concentration media. A single-blind crossover study was performed in healthy volunteers, receiving phosphate supplements or a phosphate binder (lanthanum), and endothelial function measured was by flow-mediated dilatation.

Results

Endothelium-dependent vasodilatation was impaired when resistance vessels were exposed to high phosphate; this could be reversed in the presence of a phosphodiesterase-5-inhibitor. Vessels from patients with CKD relaxed normally when incubated in normal-phosphate conditions, suggesting that the detrimental effects of phosphate may be reversible. Exposure to high-phosphate disrupted the whole nitric oxide pathway with reduced nitric oxide and cyclic guanosine monophosphate production and total and phospho endothelial nitric oxide synthase expression. In humans, endothelial function was reduced by chronic phosphate loading independent of serum phosphate, but was associated with higher urinary phosphate excretion and serum fibroblast growth factor 23.

Conclusions

These directly detrimental effects of phosphate, independent of other factors in the uraemic environment, may explain the increased cardiovascular risk associated with phosphate in CKD.

Early introduction of oral paricalcitol in renal transplant recipients. An open-label randomized study

In stable renal transplant recipients with hyperparathyroidism, previous studies have indicated that vitamin D agonist treatment might have anti-proteinuric effects. Animal studies indicate possible anti-fibrotic and anti-inflammatory effects. Early introduction of paricalcitol in de novo renal transplant recipients might reduce proteinuria and prevent progressive allograft fibrosis. We performed a single-center, prospective, randomized, open-label trial investigating effects of paricalcitol 2 μg/day added to standard care. Participants were included 8 weeks after engraftment and followed for 44 weeks. Primary end point was change in spot urine albumin/creatinine ratio. Exploratory microarray analyses of kidney biopsies at study end investigated potential effects on gene expression. Secondary end points included change in glomerular filtration rate (GFR), pulse wave velocity (PWV), and endothelial function measured by peripheral arterial tonometry as reactive hyperemia index (RHI). Seventy-seven de novo transplanted kidney allograft recipients were included, 37 receiving paricalcitol. Paricalcitol treatment lowered PTH levels (P = 0.01) but did not significantly reduce albuminuria (P = 0.76), change vascular parameters (PWV; P = 0.98, RHI; P = 0.33), or influence GFR (P = 0.57). Allograft gene expression was not influenced. To summarize, in newly transplanted renal allograft recipients, paricalcitol reduced PTH and was well tolerated without negatively affecting kidney function. Paricalcitol did not significantly reduce/prevent albuminuria, improve parameters of vascular health, or influence allograft gene expression.

Cardiovascular complications after transplantation: treatment options in solid organ recipients

Premature cardiovascular disease is the commonest cause of death in solid organ transplant recipients, with coronary artery disease, sudden cardiac death and heart failure being highly prevalent. There are unique factors leading to CV disease in organ transplant recipients that include underlying comorbidities, and metabolic effects of immunosuppression. As a consequence management strategies developed in the general population may have limited benefit. In this review, we will focus on renal transplantation, where most research has been carried out and, despite incomplete understanding of the disease process, the incidence of cardiovascular disease appears to be falling.