Mechanisms and risk factors for the development of the proteinuria after kidney transplantation

Consequences of Nephrotic Proteinuria and Nephrotic Syndrome after Kidney Transplant

Proteinuria is the main predictor of kidney graft loss. However, there is little information regarding the consequences of nephrotic proteinuria (NP) and nephrotic syndrome (NS) after a kidney transplant. We aimed to describe the clinical and histopathological characteristics of kidney recipients with nephrotic-range proteinuria and compare the graft surveillance between those who developed NS and those who did not. A total of 204 patients (18.6% of kidney transplants in the study period) developed NP, and 68.1% of them had NS. Of the 110 patients who underwent a graft biopsy, 47.3% exhibited ABMR, 21.8% the recurrence of glomerulonephritis, 9.1% IFTA, and 7.3% de novo glomerulonephritis. After a median follow-up of 97.5 months, 64.1% experienced graft loss. The graft survival after the onset of NP declined from 75.8% at 12 months to 38% at 5 years, without significant differences between those with and those without NS. Patients who developed NS fewer than 3 months after the onset of NP exhibited a significantly higher risk of death-censored graft loss (HR: 1.711, 95% CI: 1.147-2.553) than those without NS or those with late NS. In conclusion, NP and NS are frequent conditions after a kidney transplant, and they imply extremely poor graft outcomes. The time from the onset of NP to the development of NS is related to graft survival.

Effect of earlier-proteinuria on graft functions after one-year living donor renal transplantation

BACKGROUND

Proteinuria is an indicator of subsequent renal function decline in most nephropathies and early proteinuria has been assumed to be a risk factor of poor kidney transplant outcomes. However, there is no information about the effect of earlier-proteinuria at the first week on short-term graft function after living donor renal transplantation.

METHODS

Retrospective cohort study of 439 living donor kidney transplants to analyze the effect of early proteinuria at 7-day post-transplantation on short-term prognosis of living donor renal transplantation. Patients were stratified into 2 groups according to the definition of earlier-proteinuria: Group A as proteinuria < 0.4 g/24h and Group B as proteinuria ≥ 0.4 g/24h, and differences over the first year post-transplantation were analyzed.

RESULTS

Patients with earlier-proteinuria ≥ 0.4 g/24h had a significantly higher 1-year proteinuria and lower 1-year graft function post-transplantation. Discrepancies of weight ratio of donor-recipient and mean artery pressure difference of recipient to donor influenced the urine protein excretion at the 7-day post-transplantation.

CONCLUSIONS

Earlier-proteinuria at 7-day after living donor renal transplantation was associated with short-term graft function. To eliminate the functional discrepancies between living donors and recipients could be viewed as a solution of reducing earlier-proteinuria.

Proximal Tubular Expression Patterns of Megalin and Cubilin in Proteinuric Nephropathies

Introduction

Receptor-mediated endocytosis is responsible for protein reabsorption in the proximal tubules. For albumin this process involves at least 2 interacting receptors, megalin and cubilin. Albumin is not usually present in the urine, indicating a highly efficient tubular reuptake under physiological conditions. However, early appearance of albuminuria may mean that the tubular system is overwhelmed by large quantities of albumin or that the function is impaired.

Methods

To better understand the physiological role of megalin and cubilin in human renal disease, renal biopsies from 15 patients with a range of albuminuria and 3 healthy living donors were analyzed for proximal tubular expression of megalin and cubilin using immunohistochemistry (IHC) and semiquantitative immune-electron microscopy. Their expression in proteinuric zebrafish was also studied.

Results

Megalin and cubilin were expressed in brush border and cytoplasmic vesicles. Patients with microalbuminuric IgA nephropathy and thin membrane disease had significantly higher megalin in proximal tubules, whereas those with macro- or nephrotic-range albuminuria had unchanged levels. Cubilin expression was significantly higher in all patients. In a proteinuric zebrafish nphs2 knockdown model, we found a dose-dependent increase in the expression of tubular megalin and cubilin in response to tubular protein uptake.

Discussion

Megalin and cubilin show different expression patterns in different human diseases, which indicates that the 2 tubular proteins differently cooperate in cleaning up plasma proteins in kidney tubules.