Does circulating erythropoietin reflect progression of IgA nephropathy? Comparison with urinary N-acetyl-beta-D-glucosaminidase

Urinary N-Acetyl-Beta-D-Glucosaminidase levels predict immunoglobulin a nephropathy remission status

BACKGROUND

Tubulointerstitial lesions play a pivotal role in the progression of IgA nephropathy (IgAN). Elevated N-acetyl-beta-D-glucosaminidase (NAG) in urine is released from damaged proximal tubular epithelial cells (PTEC) and may serve as a biomarker of renal progression in diseases with tubulointerstitial involvement.

METHODS

We evaluated the predictive value of urinary NAG (uNAG) for disease progression in 213 biopsy-proven primary IgAN patients from January 2018 to December 2019 at Zhongshan Hospital, Fudan University. We compared the results with those of serum cystatin C (sCysC).

RESULTS

Increased uNAG and sCysC levels were associated with worse clinical and histological manifestations. Only uNAG level was independently associated with remission status after adjustment. Patients with high uNAG levels (> 22.32 U/g Cr) had a 4.32-fold greater risk of disease progression. The combination of baseline uNAG and clinical data may achieve satisfactory risk prediction in IgAN patients with relatively preserved renal function (eGFR ≥ 60 ml/min/1.73 m2, area under the curve [AUC] 0.760).

CONCLUSION

Our results suggest that uNAG is a promising biomarker for predicting IgAN remission status.

DCR2, a Cellular Senescent Molecule, Is a Novel Marker for Assessing Tubulointerstitial Fibrosis in Patients with Immunoglobulin A Nephropathy

BACKGROUND/AIMS

Stress-induced cell senescence, which contributes to cell cycle arrest and is independent of age, plays an important role in chronic kidney disease (CKD) progression. DcR2, as a senescent marker, exclusively expressed in senescent tubular epithelia. The objective of this study was to examine whether urinary DcR2 (uDcR2) could be a potential biomarker for tubulointerstitial fibrosis (TIF) in patients with immunoglobulin A nephropathy (IgAN).

METHODS

This study included 210 IgAN patients and 80 healthy volunteers, with uDcR2 levels measured using enzyme-linked immunosorbent assay. We examined the relationship among uDcR2/Cr levels, renal function, and pathological parameters, using regression analysis to identify risk factors for TIF and the area under the curve (AUC) approach to predict TIF. Renal DcR2 expression was quantified by immunohistochemistry. Co-expression of DcR2 with fibrotic markers (α-smooth muscle actin [α-SMA], collagen III) was analyzed by confocal microscopy.

RESULTS

Levels of uDcR2/Cr were significantly higher in IgAN patients and in those with more severe TIF, compared with healthy controls. Serum DcR2 levels were similar across groups. The proportion of IgAN patients with stages 1-2 CKD and T0 was highest among those with uDcR2/Cr <130 ng/g. In contrast, the majority of those with uDcR2/Cr >201 ng/g had stages 4-5 CKD and T2. Levels of uDcR2/Cr were positively associated with urinary albumin to creatinine ratio (ACR), urinary N-acetyl-β-D-glucosaminidase (uNAG)/Cr, and TIF scores and negatively associated with estimated glomerular filtration rate (eGFR). uDcR2/Cr, uNAG, ACR, and eGFR were independent predictors for TIF, with AUC of 0.907 for uDcR2/Cr. This AUC value was higher than that observed for eGFR, uNAG/Cr, or ACR. The sensitivity and specificity of uDcR2/Cr in predicting TIF were 87.0 and 80.5%, respectively. Moreover, uDcR2/Cr levels were positively associated with the percentage of renal DcR2 expression. Renal DcR2 co-localized with α-SMA and collagen III in the kidneys of IgAN patients.

CONCLUSIONS

Levels of uDcR2/Cr were closely associated with the severity of TIF and renal function parameters. uDcR2/Cr represents a potential biomarker for predicting TIF in IgAN patients.

Dopamine-Induced Changes in Serum Erythropoietin and Creatinine Clearance Reflect Risk Factors for Progression of IgA Nephropathy

INTRODUCTION

The infusion of low-dose dopamine is normally associated with an increase in creatinine clearance, thereby allowing one to assess renal functional reserve. Increased renal blood flow is also associated with a reduction in erythropoietin (EPO) levels.

OBJECTIVES

We evaluated the use of dopamine infusion in subjects with IgA nephropathy to determine if these functional changes correlate with risk factors for progression and compared this to the renal biopsy findings.

PATIENTS AND METHODS

Changes in creatinine clearance and EPO levels were determined in 46 non-nephrotic IgA patients with relative preserved renal function after the infusion of low dose dopamine. Control subjects (n = 15) were evaluated using similar protocols.

RESULTS

Subjects with IgA nephropathy could be separated into those who showed a fall in EPO levels (n = 24) and those who showed no change or a rise in EPO levels (n = 22). Subjects showing the expected fall in EPO demonstrated a higher increase in creatinine clearance, similar to that observed in control subjects. Most importantly, subjects who showed a fall in EPO had less proteinuria, less N-acetyl-β-D-glucosaminidase excretion, lower serum uric acid, blood pressure, and less features of metabolic syndrome despite similar inflammation and fibrosis on biopsy as compared to the others.

CONCLUSIONS

A decrease in EPO in response to dopamine is associated with a clinical phenotype that is less likely to develop progressive renal disease. These studies suggest that a fall in EPO in response to dopamine likely reflects preserved tubulointerstitial function that cannot be assessed by renal biopsy alone.

Diagnosis and monitoring of IgA nephropathy: the role of biomarkers as an alternative to renal biopsy

IgA nephropathy (IgAN) is the most prevalent form of chronic glomerulonephritis in the world. The underlying pathogenesis of this autoimmune disease comprises the formation of immune complexes, including glycan-specific IgA1 or IgG antibodies and an aberrant glycosylation of IgA1. Until now, anatomopathological analysis of renal biopsies is essential for the diagnosis of IgAN and different histological classification systems have been proposed, e.g. the Oxford classification. However, a percutaneous renal biopsy is frequently not performed for several reasons and the Oxford classification system has some limitations. Since the poor prognosis of IgAN patients is partly the result of a delayed diagnosis, there is an urgent need for reliable noninvasive biomarkers that might be applicable in routine clinical practice. This article reviews the advances on the understanding of the underlying pathophysiological mechanisms of IgAN and discusses in depth the recent development of new biomarkers, including the use of proteomics and microRNAs.

Clinicopathological role of kidney injury molecule-1 in immunoglobulin A nephropathy

BACKGROUND

Urinary kidney injury molecule-1 (KIM-1) is an early and sensitive biomarker of acute kidney injury, but it is unclear if it is a biomarker of chronic glomerulonephritis. We evaluated whether urinary KIM-1 levels in patients with immunoglobulin A (IgA) nephropathy can be a marker to reflect clinicopathological severity and predict the prognosis.

METHODS

We measured urinary KIM-1 levels in 40 patients (15 males; mean age 36.6±12.9 years) with IgA nephropathy and 10 healthy people (5 males; mean age 37.3±9.6 years) as controls. The correlation of urinary KIM-1 levels with patients' clinical parameters, histological grades, and follow-up data were analyzed using the modified H. S. Lee grading system and tubulointerstitial change scores.

RESULTS

Urinary KIM-1 levels were higher in patients with IgA nephropathy than healthy controls (P=0.001). Univariate and multivariate regression analyses showed that urinary KIM-1 levels had a direct correlation with H. S. Lee grade and tubulointerstitial inflammation (P=0.004 and P=0.011, respectively).

CONCLUSION

In patients with IgA nephropathy, urinary KIM-1 has a significant correlation with histopathologic severity.

Tubular damage in chronic systolic heart failure is associated with reduced survival independent of glomerular filtration rate

BACKGROUND

The prognostic impact of reduced glomerular filtration rate (GFR) in chronic heart failure (CHF) is increasingly recognised, but little is known about tubular damage in these patients.

OBJECTIVE

To investigate the prevalence of tubular damage, and its association with GFR, and prognosis in patients with CHF.

METHODS AND RESULTS

In 90 patients with CHF, GFR and effective renal plasma flow (ERPF) were measured ([(125)I]iothalamate and [(131)I]hippuran clearances). The tubular markers neutrophil gelatinase-associated lipocalin (NGAL), N-acetyl-beta-D-glucosaminidase (NAG) and kidney injury molecule 1 (KIM-1) as well as urinary albumin excretion were determined in 24 h urine collections. Mean GFR was 78+/-26 ml/min/1.73 m(2). Urinary NGAL (175 (70-346) microg/g creatinine (gCr)), NAG (12 (6-17) U/gCr) and KIM-1 (277 (188-537) ng/gCr) levels were increased compared with 20 healthy controls (all p<0.001). Urinary NAG, but not NGAL or KIM-1 correlated with GFR (r=-0.34, p=0.001) and ERPF (r=-0.29, p=0.006). Both NAG (r=0.21, p=0.048) and KIM-1 (r=0.23, p=0.033) correlated with plasma N-terminal pro-brain natriuretic peptide levels. Both urinary KIM-1 (HR=1.15 (95% CI 1.02 to 1.30) per 100 ng/gCr increase, p=0.025) and NAG (HR=1.42 (95% CI 1.02 to 1.94) per 5 U/gCr increase, p=0.039), were associated with an increased risk of death or heart failure hospitalisations, independent of GFR.

CONCLUSION

Tubular damage, as indicated by increased urinary concentrations of NGAL, NAG and KIM-1 is common in patients with CHF and mildly reduced GFR. Both urinary KIM-1 and NAG showed prognostic information additional to GFR. These findings suggest an important role for tubular damage and tubular markers in cardiorenal interaction in heart failure.

Neutrophil gelatinase-associated lipocalin (NGAL): a new marker of cyclosporine nephrotoxicity?

The aim of work was to investigate whether serum and urinary neutrophil gelatinase-associated lipocalin(sNGAL and uNGAL, respectively) are potential biomarkers of early cyclosporine A (CsA) nephrotoxicity in steroid-dependent nephrotic children (SDNS). The study group (I) consisted of 19 children with SDNS aged 9.46+/-5.52 years treated with CsA. The children were examined four times: at proteinuria relapse, prior to CsA treatment,then after 3, 6, and 12 months of CsA treatment. The control group (II) consisted of 18 healthy children aged 3-15 years. A commercial enzyme-linked immunosorbent assay method was used to measure NGAL concentration.The sNGAL level in SDNS children prior to the administration of CsA was similar to that in the healthy controls (p>0.05), but it increased significantly during the course of treatment (p<0.01). The uNGAL/creatinine (cr) ratio in SDNS patients was higher before the withdrawal of CsA therapy (p<0.05), and was also increased at the consecutive examinations (p<0.01). There was a positive correlation between both sNGAL and uNGAL levels and CsA serum level. However, based on the serum and urinary NGAL/cr receiver operating characteristic curve and area under the curve (AUC) analysis, it remains uncertain whether uNGAL is a good predictor of cyclosporine nephropathy. Both sNGAL and uNGAL concentrations increased during the course of CsA treatment. Further studies in larger groups of patients are therefore necessary to confirm our experimental data that increased NGAL levels may be a non-invasive marker for the early detection of tubulointerstitial damage in CsA nephrotoxicity.

N-acetyl-beta-D-glucosaminidase index as an early biomarker for chronic kidney disease in cats with hyperthyroidism

BACKGROUND

Hyperthyroid cats are at risk of developing azotemic chronic kidney disease (CKD) and diagnostic tools currently used to screen for CKD in hyperthyroid cats are either unreliable or impractical.

HYPOTHESIS

Urine N-acetyl-beta-D-glucosaminidase index (NAG(i)) is a good biomarker for azotemic CKD in hyperthyroid cats.

ANIMALS

Twenty-four newly diagnosed nonazotemic hyperthyroid cats and 10 healthy cats.

METHODS

All cats were evaluated for hyperthyroidism at baseline. Hyperthyroid cats were treated with methimazole and reevaluated once euthyroid. At the end of the study, cats were divided into 3 groups: healthy cats, nonazotemic, and azotemic euthyroid cats. Baseline group characteristics were compared to predict azotemic CKD. The influence of treatment on NAG(i) was evaluated.

RESULTS

Baseline NAG(i) was significantly different among groups (P= .004). Azotemic cats had a higher median value (13.12 U/g) when compared with healthy cats (1.38 U/g). With NAG(i) >2.76 U/g, negative and positive predictive values for development of azotemia were 77.7 and 50%, whereas the combination of a urine specific gravity (USG) <or=1.035 and T(4) >7.80 microg/dL enhanced predictive values to 88.9 and 83.3%, respectively. NAG(i) values decreased significantly over time in treated nonazotemic cats.

CONCLUSIONS AND CLINICAL RELEVANCE

Baseline NAG(i) did not differentiate azotemic from nonazotemic euthyroid cats. NAG(i) could be used to assess renal function during medical therapy allowing the clinician to adjust methimazole dosage accordingly. The combination of USG and T(4) could optimize identification of appropriate candidates for permanent treatment of hyperthyroidism.

Urinary neutrophil gelatinase-associated lipocalin (NGAL) is an early biomarker for renal tubulointerstitial injury in IgA nephropathy

Renal tubulointerstitial injury plays an important role in the development of IgA nephropathy (IgAN), the most common form of glomerulonephritis. Few currently in use biomarkers can sensitively detect the earliest signs of renal tubular injury, hindering our efforts to launch preventive and therapeutic measures for this disorder in a timely manner. Neutrophil gelatinase-associated lipocalin (NGAL) is an acute phase protein that is rapidly released from not only neutrophils but also a variety of cell types upon inflammation and tissue injury. Its small molecular size and protease resistance could render it an excellent biomarker of renal injury in IgAN. In this study, we tested this hypothesis by measuring urinary levels of NGAL, creatinine and N-acetyl-beta-D-glucosaminidase (NAG) in 40 healthy individuals and 70 IgAN patients with various disease severities. The urinary NGAL levels and NGAL/creatinine values were significantly upregulated in Lee grade III IgAN patients, in correlation with progressive glomerular mesangial proliferation and tubulointerstitial injury. Compared with urinary NAG levels, the urinary NGAL levels elevated much more drastically and can be readily detected even in Lee grade II IgAN patients when their NAG levels showed almost no change. Our findings suggest the promising use of urinary NGAL as an early biomarker for tubulointerstitial injury of IgA nephropathy and perhaps other types of renal disease in general.

Relationship between renal anemia and prognostic stages of IgA nephropathy

In 2002, the Joint Committee of the Special Study Group on Progressive Glomerular Diseases, Ministry of Health, Labor and Welfare of Japan newly revised the clinical guidelines for IgA nephropathy (Sakai et al.: Jpn J Nephrol 37:417-421, 1995; Tomino and Sakai: Clin Exp Nephrol, 7, 93-97, 2003). The prognostic stages were classified into four groups: the good prognosis group (Group I), relatively good prognosis group (Group II), relatively poor prognosis group (Group III), and poor prognosis group (Group IV). The relationship between the levels of Hb, Ht, and RBC in peripheral blood and the renal prognostic stages was determined in 62 patients with IgA nephropathy in the present study. The mean levels of Hb, Ht, and RBC were significantly lower in Group IV than in Group I (P<0.05). However, there were no significant changes in the levels of serum creatinine (s-Cr) or creatinine clearance (CCr) among these four groups. It appears that the levels of Hb, Ht, and RBC in peripheral blood may be important clinical parameters for the evaluation of prognostic stages in patients with IgA nephropathy.