Urinary excretion of beta 2-glycoprotein-1 (apolipoprotein H) and other markers of tubular malfunction in "non-tubular" renal disease

Discovery and Validation of a Biomarker Model (PRESERVE) Predictive of Renal Outcomes After Liver Transplantation

BACKGROUND AND AIMS

A high proportion of patients develop chronic kidney disease (CKD) after liver transplantation (LT). We aimed to develop clinical/protein models to predict future glomerular filtration rate (GFR) deterioration in this population.

APPROACH AND RESULTS

In independent multicenter discovery (CTOT14) and single-center validation (BUMC) cohorts, we analyzed kidney injury proteins in serum/plasma samples at month 3 after LT in recipients with preserved GFR who demonstrated subsequent GFR deterioration versus preservation by year 1 and year 5 in the BUMC cohort. In CTOT14, we also examined correlations between serial protein levels and GFR over the first year. A month 3 predictive model was constructed from clinical and protein level variables using the CTOT14 cohort (n = 60). Levels of β-2 microglobulin and CD40 antigen and presence of hepatitis C virus (HCV) infection predicted early (year 1) GFR deterioration (area under the curve [AUC], 0.814). We observed excellent validation of this model (AUC, 0.801) in the BUMC cohort (n = 50) who had both early and late (year 5) GFR deterioration. At an optimal threshold, the model had the following performance characteristics in CTOT14 and BUMC, respectively: accuracy (0.75, 0.8), sensitivity (0.71, 0.67), specificity (0.78, 0.88), positive predictive value (0.74, 0.75), and negative predictive value (0.76, 0.82). In the serial CTOT14 analysis, several proteins, including β-2 microglobulin and CD40, correlated with GFR changes over the first year.

CONCLUSIONS

We have validated a clinical/protein model (PRESERVE) that early after LT can predict future renal deterioration versus preservation with high accuracy. This model may help select recipients at higher risk for subsequent CKD for early, proactive renal sparing strategies.

Urinary β-trace protein: A unique biomarker to screen early glomerular filtration rate impairment

The screening for chronic kidney disease (CKD) patients needs the measurement of serum markers like creatinine. Our previous results indicated that urinary excretion of β-trace protein (BTP), a low-molecular-weight protein (23-29 kDa), is increased in CKD patients from stage 2. The aim of this study was to assess the major determinants of urinary excretion of BTP and to evaluate its feasibility as noninvasive marker of glomerular filtration rate (GFR) impairment.We studied 355 CKD patients (198 males), aged 15 to 83 years, in stable clinical conditions, classified in the different stages of CKD on the basis of GFR (renal clearance of Tc-diethylenetriamine penta-acetic acid). At the same time, we measured serum and urinary creatinine and BTP, and urinary albumin. Urinary excretion of BTP and albumin was expressed as mg/g urinary creatinine. Fractional clearance of BTP was calculated as the ratio of BTP clearance to creatinine clearance (%).Urinary excretion of BTP is mainly determined by its serum concentration and by the level of GFR, and to a lower extent by urinary albumin excretion. In fact, urinary BTP (U-BTP) and fractional clearance of BTP progressively and significantly increased along with the reduction of GFR and the concurrent rise in serum BTP (S-BTP). The relationship of U-BTP with GFR was very similar to that of S-BTP with GFR: U-BTP mirrors S-BTP. The accuracy of U-BTP to screen patients with GFR <90 mL/min/1.73 m was good (area under the curve 0.833), its sensitivity was 76.9%, specificity 80%, and positive predictive value 84.9%. Sensitivity of U-BTP was quite similar to that of S-BTP and serum creatinine.The major determinants of urinary excretion of BTP are S-BTP and GFR. U-BTP may be a suitable noninvasive marker to screen the general population for detection of GFR <90 mL/min/1.73 m.

Urinary prognostic biomarkers in patients with focal segmental glomerulosclerosis

Background:

Focal segmental glomerulosclerosis (FSGS) is a type of nephrotic syndrome which is diagnosed by renal biopsy. Degree of the proteinuria, renal dysfunction, histologic findings and the response to therapy are some factors used for evaluating the prognosis of FSGS.

Objectives:

In the present study, we attempted to discover some protein candidates for disease prognosis related to glomerular filtration rate (renal dysfunction).

Patients and Methods:

Urine samples were collected from ten patients. Urine proteome was extracted and trypsinated. Digested peptides were separated and identified by nano-flow LC-MS/MS. Protein content were determined using label-free quantification method. Protein profiles were analyzed using supervised multivariate statistical method.

Results:

Output of a predictive model was 54 significant proteins of which ribonuclease 2 and haptoglobin had the greatest fold change in terms of overrepresentation and underrepresentation in patients with the best and worse prognosis, respectively. Complement and coagulation cascades were the only significant pathways which were impaired in FSGS.

Conclusions:

Urinary biomarkers can potentially be used as non-invasive prognostic markers. However these candidate biomarkers need further validation by an alternative method and in a larger cohort.

Increased urinary protein excretion in the "normal" range is associated with increased renin-angiotensin system activity

Increased levels of albuminuria and proteinuria, both linked to augmented renin-angiotensin system (RAS) activity, are associated with adverse kidney and cardiovascular events. However, the relationship between variations in urinary albumin excretion (UAE) and total protein excretion (UTPE) in the normal range and RAS activity is unclear. We examined the association between UAE and UTPE and the hemodynamic response to angiotensin II (ANG II) challenge, a well-accepted indirect measure of RAS activity, in healthy individuals with normal UAE and UTPE. Forty subjects (15 men, 25 women; age 38 ± 2 yr; UAE, 3.32 ± 0.55 mg/day; UTPE, 56.8 ± 3.6 mg/day) were studied in high-salt balance. Blood pressure (BP), arterial stiffness determined by applanation tonometry, and circulating RAS components were measured at baseline and in response to graded ANG II infusion. The primary outcome was the BP response to ANG II challenge at 30 and 60 min. UAE was associated with a blunted diastolic BP response to ANG II infusion (30 min, P = 0.005; 60 min, P = 0.17), a relationship which remained even after adjustment (30 min, P < 0.001; 60 min, P = 0.035). Similar results were observed with UTPE (30 min, P = 0.031; 60 min, P = 0.001), even after multivariate analysis (30 min, P = 0.008; 60 min, P = 0.001). Neither UAE nor UTPE was associated with systolic BP, circulating RAS components, or arterial stiffness responses to ANG II challenge. Among healthy individuals with UAE and UTPE in the normal range, increased levels of these measures were independently associated with a blunted diastolic BP response to ANG II, indicating increased vascular RAS activity, which is known to be deleterious to both renal and cardiac function.

Clinical and plasma proteomic markers correlating with chronic kidney disease after liver transplantation

Chronic kidney disease (CKD) occurs frequently after liver transplantation (LT) and is associated with significant morbidity and mortality. Thus, there is a pressing need to identify characteristics and biomarkers diagnostic of CKD to enable early diagnosis allowing preemptive interventions, as well as mechanistic insights into the progression from kidney injury to irreversible kidney failure. We analyzed 342 patients who had baseline glomerular filteration rate (GFR) >60 at the time of LT and are now >3 years post-LT. Risk factors for post-LT CKD were compared between three different groups defined by current GFR: >90 (n = 40), 60-90 (n = 146) and <60 (n = 156) mL/min. Age, cyclosporine use and pre-LT GFR were independently associated with new onset CKD. A subset (n = 64) without viral/immune disease or graft dysfunction underwent multianalyte plasma proteomic evaluations for correlation with CKD. Plasma proteomic analysis of two independent cohorts, test (n = 22) and validation (n = 42), identified 10 proteins highly associated with new onset CKD. In conclusion, we have identified clinical characteristics and a unique plasma proteomic signature correlating with new onset CKD after LT. These preliminary results are currently being validated in a prospective, multicenter study to determine if this signature precedes the onset of CKD and resolves with early interventions aimed at preserving kidney function.

Identification of diagnostic urinary biomarkers for acute kidney injury

Acute kidney injury (AKI) is an important cause of death among hospitalized patients. The 2 most common causes of AKI are acute tubular necrosis (ATN) and prerenal azotemia (PRA). Appropriate diagnosis of the disease is important but often difficult. We analyzed urine proteins by 2-dimensional gel electrophoresis from 38 patients with AKI. Patients were randomly assigned to a training set, an internal test set, or an external validation set. Spot abundances were analyzed by artificial neural networks to identify biomarkers that differentiate between ATN and PRA. When the trained neural network algorithm was tested against the training data, it identified the diagnosis for 16 of 18 patients in the training set and all 10 patients in the internal test set. The accuracy was validated in the novel external set of patients where conditions of 9 of 10 patients were correctly diagnosed including 5 of 5 with ATN and 4 of 5 with PRA. Plasma retinol-binding protein was identified in 1 spot and a fragment of albumin and plasma retinol-binding protein in the other. These proteins are candidate markers for diagnostic assays of AKI.

Phlorizin prevents glomerular hyperfiltration but not hypertrophy in diabetic rats

The relationships of renal and glomerular hypertrophies to development of hyperfiltration and proteinuria early in streptozotocin-induced diabetes were explored. Control, diabetic, phlorizin-treated controls, and diabetic male Fischer rats were used. Phlorizin (an Na⁺-glucose cotransport inhibitor) was given at a dose sufficient to normalize blood glucose. Inulin clearance (C_inulin) and protein excretion rate (PER) were measured. For morphometry, kidney sections were stained with periodic acid Schiff. At one week, diabetes PER increased 2.8-folds (P < .001), C_inulin increased 80% (P < .01). Kidney wet and dry weights increased 10%–12% (P < .05), and glomerular tuft area increased 9.3% (P < .001). Phlorizin prevented proteinuria, hyperfiltration, and kidney hypertrophy, but not glomerular hypertrophy. Thus, hyperfiltration, proteinuria, and whole kidney hypertrophy were related to hyperglycemia but not to glomerular growth. Diabetic glomerular hypertrophy constitutes an early event in the progression of glomerular pathology which occurs in the absence of mesangial expansion and persists even after changes in protein excretion and GFR are reversed through glycemic control.

Glomerular protein sieving and implications for renal failure in Fanconi syndrome

BACKGROUND

Glomerular sieving coefficients (GSCs) of proteins have been measured extensively in animals but not humans. We have studied the proteinuria of Fanconi syndrome, a "knock-out" of renal tubular protein reabsorption, to estimate GSCs and detect potential contributors to development of renal failure.

METHODS

Immunoassay of proteins and polypeptides in serum and urine of patients with early Dent's disease (mean GFR = 83 mL/min, range 60 to 101, N = 5), Lowe's syndrome (N = 3), and ADIF (N = 2) were used.

RESULTS

Twenty-one proteins, ranging in mass from insulin (5.1 kD) and parathyroid hormone (PTH; 9.4 kD) to transferrin (78 kD) and intact IgG (160 kD), were present in Fanconi urine at> 6 to 1000-fold normal. A simple model assuming complete "knock-out" of the reuptake of each protein filtered normally by the glomerulus was applied to protein excretion by Dent's patients. GSCs were estimated for 12 plasma proteins, including albumin (7.7 +/- 0.9 x 10-5) and IgG (4.2 +/- 0.28 x 10-5; mean +/- SEM). We calculated the albumin concentration in normal glomerular filtrate to be 3.5 +/- 0.41 mg/L (53 +/- 6.4 nmol/L), consistent with studies in rat and dog.

CONCLUSIONS

To our knowledge, this study provides the first estimates of human in vivo GSCs. Our model explains why tubular proteinuria of Fanconi syndrome includes proteins of mass of albumin and above as well as low-molecular-weight proteins, and further characterizes the endocytic pathway(s) believed defective in these syndromes. High urinary concentrations of potentially bioactive hormones such as PTH, insulin, IGF-1 and the chemokine monocyte chemoattractant protein-1 (MCP-1), were found; their presence in tubular fluid may contribute to the hypercalciuria, interstitial fibrosis, and the progressive renal failure of Fanconi syndromes.

Tubular proteinuria defined by a study of Dent's (CLCN5 mutation) and other tubular diseases

Tubular proteinuria defined by a study of Dent's ( CLCN5 mutation) and other tubular diseases.

BACKGROUND

The term "tubular proteinuria" is often used interchangeably with "low molecular weight proteinuria" (LMWP), although the former implies a definite etiology. A specific quantitative definition of tubular proteinuria is needed, and we address this by studying five different renal disorders.

METHODS

Tubular proteinuria was assessed by measuring urinary retinol-binding protein (RBP), beta2-microglobulin (beta2M), alpha1-microglobulin (alpha1M), and albumin in 138 patients: 26 affected males and 24 female carriers of the X-linked syndrome "Dent's disease," 6 patients with other Fanconi syndromes, 17 with distal renal tubular acidosis (dRTA), 39 with glomerulonephritis (GN), and 26 with Chinese herbs nephropathy (CHN).

RESULTS

RBP was better than beta2M or alpha1M in identifying the tubular proteinuria of Dent's disease. Median urinary RBP levels in mg/mmol creatinine were: affected male Dent's, 18.2, N = 26; carrier female Dent's, 0. 30, N = 24; dRTA, 0.027, N = 17; GN, 0.077, N = 39; and normal adults, 0.0079, N = 61. Elevated urinary RBP (>0.017) and albumin < (10 x RBP) + 2 identified all patients with the LMWP of Dent's disease and clearly distinguished their LMWP from that of dRTA and GN. This is a quantitative definition of tubular proteinuria. Consistent with this definition, 80% of those patients with CHN who had an elevated RBP had tubular proteinuria. Urinary RBP and albumin in carriers of Dent's disease were strikingly correlated over a 100-fold range (R = 0.933).

CONCLUSION

The combination of elevated urinary RBP (>0.017) and albumin < (10 x RBP) + 2 (mg protein/mmol creatinine) is a quantitative definition of tubular proteinuria. Furthermore, our findings suggest that a shared defect in tubular RBP and albumin reuptake causes this form of proteinuria.

Urinary alpha 1-microglobulin detects uropathy. A prospective study in 483 urological patients

PURPOSE

The aim of the study was to evaluate prospectively urinary alpha 1-microglobulin as a marker of proximal tubular damage following acute pyelonephritis and outflow disease of the upper urinary tract in a urological population with minimal exclusion criteria. We also measured the urinary gamma-glutamyltransferase activity, urinary albumin, urinary and serum creatinine, serum IgA and serum alpha 1-microglobulin.

PATIENTS AND METHODS

We studied 483 urological patients (age: 1 to 92 years, 297 men, 186 women) excluding patients receiving nephrotoxic drugs, or suffering from type 1 diabetes or renal diseases. There were 141 patients with urinary tract infection but no fever, 36 patients with high fever of non-renal origin, 51 patients with acute pyelonephritis and 156 patients with outflow disease of the upper tract, and 99 patients were included in the reference population.

RESULTS

For acute pyelonephritis, vesico-ureteral reflux, and ureteral obstruction, urinary alpha 1-microglobulin had a sensitivity of 94%, 90% and 63% respectively and a specificity of 67%, 77% and 76%. The area under the curve of the receiver operator characteristic curve was significantly (p < 0.001) higher for urinary alpha 1-microglobulin than for albumin or gamma-glutamyltransferase activity. Unexpected positive results were found in acute prostatitis. The urinary alpha 1-microglobulin was the only parameter which differentiated between acute prostatitis and pyelonephritis (p < 0.001). Creatinine clearance or age had little and gender had no influence on the urinary excretion of alpha 1-microglobulin. Urine production rate significantly increases the urinary alpha 1-microglobulin/creatinine ratio.

CONCLUSION

Our results suggest that the urinary alpha 1-microglobulin/creatinine ratio is a diagnostically useful marker of tubular damage in acute pyelonephritis and vesico-ureteral reflux in the urological population. Following renal colic and chronic ureteral obstruction, a significant increase in urinary alpha 1-microglobulin excretion was observed.

Beta 2-glycoprotein-1 (apolipoprotein H) excretion and renal tubular malfunction in diabetic patients without clinical proteinuria

AIM

To compare the urinary excretion of beta 2-glycoprotein-1 with that of two other markers of early tubular disorder in diabetic patients without clinical proteinuria.

METHODS

The urinary excretion of retinol binding protein, beta 2-glycoprotein-1, and N-acetyl-beta-D-glucosaminidase was measured in 90 known diabetic patients who had a negative reagent strip test for proteinuria.

RESULTS

Among 43 patients with urinary albumin excretion within the reference range, 23 (53%) had raised urinary N-acetyl-beta-D-glucosaminidase activity, five (12%) increased excretion of beta 2-glycoprotein-1, and five (12%) increased loss of retinol binding protein. Among 47 patients with an albumin excretion of 0.9-7.9 mg/mmol creatinine, 42 (89%) had increased urinary N-acetyl-beta-D-glucosaminidase, 23 (49%) an increased output of beta 2-glycoprotein-1, and 16 (34%) a raised excretion of retinol binding protein. The excretion of these markers of tubular defects seldom exceeded two and a half times the upper reference limit and the differences between the findings in the insulin dependent and non-insulin dependent patients with similar albumin excretion were small and insignificant.

CONCLUSIONS

In diabetic patients with a negative dipstick test for proteinuria: (a) assay of urinary beta 2-glycoprotein-1 may be a more sensitive test for the detection of impaired tubular reabsorption of protein than measurement of retinol-binding protein; (b) assay of N-acetyl-beta-D-glucosaminidase can detect tubular injury at a time when protein reabsorption remains normal; and (c) impaired renal tubular function may be present in the absence of evidence of glomerular malfunction.