Tubular and Glomerular Proteinuria in Diagnosing Chronic Allograft Nephropathy With Relevance to the Degree of Urinary Albumin Excretion

Association of urinary non-albumin protein with the different urinary marker for glomerular and tubular damage in patients with type 2 diabetes

BACKGROUND/AIM

In recent years, the diagnostic utility of urinary protein levels has been demonstrated for the early detection and progression of kidney disease. This study aimed to evaluate the associations of the non-albumin protein (NAP) with different urinary marker for tubular and glomerular damage in patients with type 2 diabetes (T2D).

METHODS

In this observational cross-sectional study, 424 patients with T2D duration > 10 years were classified into two groups according to estimated glomerular filtration rate (eGFR). The ratios of different urinary markers (albumin, NAP, total protein, transferrin, retinol-binding protein (RBP), and neutrophil gelatinase-associated lipocalin (NGAL) to creatinine were analyzed.

RESULTS

The levels of urinary biomarkers increased significantly with decrease in eGFR levels. In the group with moderately decreased eGFR, the albumin to-creatinine ratio (ACR), non-albumin protein-to-creatinine ratio (NAPCR), and total protein-to-creatinine ratio (PCR) were independently associated with all urinary markers after being adjusted for risk factors. The area under the receiver operating characteristics (ROC) curve for ACR and PCR had a better diagnostic value than other urinary biomarkers. Comparing ROC curve of NAPCR with other urinary biomarkers, it was significantly better than NGAL/Cr (p = 0.033).

CONCLUSIONS

The findings of the present study confirm that ACR and PCR are diagnostic biomarkers in T2D patients with decreased eGFR. NAPCR in these patients diagnostically only outperformed NGAL/Cr.

Association between nonalbumin proteinuria and renal tubular damage of N-acetyl-β-d-glucosaminidase and its clinical relevance in patients with type 2 diabetes without albuminuria

AIM

Although albuminuria and urinary N-acetyl-β-d-glucosaminidase (uNAG) are known as progression markers of diabetic kidney disease, there is limited information regarding the association between urinary nonalbumin proteinuria (NAP) and uNAG and the clinical relevance thereof in patients without albuminuria.

METHODS

This cross-sectional study included samples from 244 consecutive patients with type 2 diabetes mellitus (T2D) without albuminuria. Proteinuria and albuminuria were defined according to protein-to-creatinine ratio (uPCR) and albumin-to-creatinine ratio (uACR), respectively. NAP was indirectly calculated by the difference between uPCR and uACR.

RESULTS

NAP and uNAG excretion were significantly correlated (r = 0.525, P < 0.001). Individuals whose NAP levels were in the highest tertile had a longer duration of diabetes, uncontrolled hyperglycemia, and impaired insulin stimulation (all P < 0.05), although more patients in the highest NAP tertile were prescribed insulin and sulfonylurea. Multiple linear regression analyses revealed associations among uNAG, diabetes duration, and waist circumference.

CONCLUSIONS

T2D patients without albuminuria excrete proteinuria and that presence of the protein in urine is associated with uNAG. NAP was positively correlated with T2D duration and waist circumference, but negatively correlated with body mass index. Lean, but centrally obese, T2D patients in late diabetes experience more tubular damage, regardless of the presence of albuminuria.

Nonalbumin proteinuria is a simple and practical predictor of the progression of early-stage type 2 diabetic nephropathy

AIMS

Multiple biomarkers have emerged as a reliable predictor of the progression of diabetic nephropathy. The aim of this study was to pursue a more simple and practical predictor that can be applied in clinical practice.

METHODS

The urine albumin-to-creatinine ratio (ACR), the nonalbumin protein-to-creatinine ratio (NAPCR), and the levels of six biomarkers were measured in 73 patients with type 2 diabetes and estimated glomerular filtration rates (eGFRs)≥60mL/min/1.73m². The renal outcomes were the annual decline in eGFR and the development of chronic kidney disease (CKD) of stage 3 or greater.

RESULTS

The average rate of eGFR decline over a median of 50months of follow-up was -2.48mL/min/1.73m²/year. After adjusting for nine clinical parameters, only the NAPCR showed a significant association with the annual eGFR decline (adjusted R²=0.139, P=0.042). The NAPCR predicted a higher probability of the development of CKD of stage 3 or greater and was more effective than any of the six urinary biomarkers in this respect (C-index 82.7, sensitivity 92.3, specificity 81.7).

CONCLUSIONS

The NAPCR is a better and more practical predictor of the development and progression of CKD than are other urinary biomarkers in patients with early-stage type 2 diabetic nephropathy.

Nonalbuminuric proteinuria as a biomarker for tubular damage in early development of nephropathy with type 2 diabetic patients

AIM

The aim of this study was to evaluate the association between urinary nonalbumin protein (NAP) and urinary tubular markers in early diabetic nephropathy.

METHODS

Urinary NAP was measured in 118 patients with type 2 diabetes with estimated glomerular filtration rates (eGFR) ≥60 mL/min/1.73 m². Urine levels of tubular markers [kidney injury molecule (KIM)-1, neutrophil gelatinase-assoicated lipocalin (NGAL) and liver-type fatty acid-binding protein (L-FABP)] were measured by using an Enzyme-linked immunosorbent assay (ELISA). Patients were divided into three groups according to urinary NAP values.

RESULTS

The urine levels of KIM-1, NGAL and L-FABP were significantly higher in the third tertile group than in the first tertile group (all p < 0.001). There was a significant positive correlation between NAP and each tubular marker (KIM-1, NGAL and L-FABP) in univariate analysis (all p < 0.001). Urinary NAP was positively correlated with all urinary tubular markers after adjustment for age, duration of diabetes, systolic blood pressure, eGFR, low-density lipoprotein cholesterol, HbA1c and albumin-to-creatinine ratio (KIM-1 r = 0.170, p < 0.001; NGAL r = 0.142, p < 0.015 and L-FABP r = 0.262, p < 0.001). In normoalbuminuric patients (n = 58), urinary NAP was also significantly correlated with NGAL and L-FABP in multivariate regression analyses (r = 0.302, p = 0.030 and r = 0.430, p = 0.001).

CONCLUSIONS

These findings suggest that urinary NAP reflects tubular damage in the early-stage type 2 diabetic nephropathy (eGFR ≥ 60 mL/min/1.73 m²). We suggest that urinary NAP could be used as a biomarker for tubular damage in clinical practice.

Respective predictive role of urinary albumin excretion and nonalbumin proteinuria on graft loss and death in renal transplant recipients

Proteinuria is constituted by urinary albumin (UAE) and nonalbumin proteins (NAP). UAE was shown to predict ESRD and death. Whether NAP predicts graft or patient outcome is unknown in renal transplantation. We retrospectively analyzed the impact of UAE and NAP respectively on end-stage renal disease (ESRD) and death in 616 renal transplant recipients. In subjects with proteinuria <0.25 g/day, 76% of urine proteins were NAP; in those with >1 g/day, 44% of the urine proteins were NAP. Determinants of UAE and NAP were partly different: fasting glucose, body weight, donor cause of death and cyclosporine were significantly associated with NAP (but not UAE); panel reactive antibodies (PRA) and rapamycine were significantly associated with UAE (but not with NAP). NAP expressed as a continuous (HR: per g/day: 4.00 [2.85-5.63], p < 0.0001) or a categorical (presence vs. absence, HR = 29.09[8.80-96.20], p < 0.0001) parameter and UAE (per g/day, HR = 1.86 [1.24-2.78], p < 0.0001) were risk factors for graft loss in univariate analyses. NAP remained significant even after adjustment on UAE. The presence of NAP (HR: 5.37 [2.55-11.34], p < 0.0001) and macroalbuminuria (HR: 4.12 [1.65-10.29], p = 0.0024) were risk factors for death. Proteinuria is made of various proportions of UAE and NAP in renal transplantation; these two parameters provide different information on graft/patient survival.

Combination of Angiotensin-Converting Enzyme and Methylenetetrahydrofolate Reductase Gene Polymorphisms as Determinant Risk Factors for Chronic Allograft Dysfunction

OBJECTIVE

The aim of this study was to investigate the frequency of gene angiotensin-converting enzyme insertion/deletion (ACE I/D) and methylenetetrahydrofolate reductase (MTHFR C677T and A1298C) variants, as well as to evaluate the plasma homocysteine concentrations in 217 patients who underwent renal transplantation at least 12 months prior to define risk factors for chronic allograft dysfunction.

METHODS

The presence of the polymorphism ACE deletion was assessed by polymerase chain reaction (PCR) analysis. MTHFR polymorphisms were determined by PCR and restriction fragment length polymorphism (RFPL) techniques. The restriction enzymes were Hinf I and Mbo II for MTHFR variants C677T and A1298C, respectively. Plasma homocysteine concentrations were measured by liquid chromatography-tandem mass spectrometry (LS-MS/MS).

RESULTS

Hyperhomocysteinemias were more common in patients with chronic allograft dysfunction (P = .004). No statistically significant differences were observed between the allelic and genotypic distributions of MTHFR and ACE polymorphisms. An effective risk factor was found when the polymorphisms of the ACE and MTHFR genes and hyperhomocysteinemia were associated (odds ratio 2.51; 95% confidence interval 1.19-5.28). In conclusion, our study identified that the presence of hyperhomocysteinemia in combination with unfavorable genotypes contributes to an increased risk for development of chronic allograft dysfunction.