Proteinuria without albuminuria: urinary protein excretion by a subset of patients with burn injuries

Urine retinol-binding protein 4: a functional biomarker of the proximal renal tubule

Measurement of retinol-binding protein 4 in urine (uRBP4) is arguably the most sensitive biomarker for loss of function of the human proximal renal tubule. Megalin- and cubilin-receptor-mediated endocytosis normally absorbs > 99% of the approximately 1.5 g/24 h of protein filtered by the renal glomerulus. When this fails there is "tubular proteinuria," comprising uRBP4, albumin, and many other proteins and peptides. This tubular proteinuria is a consistent feature of the renal Fanconi syndrome (FS) and measurement of uRBP4 appears to be an excellent screening test for FS. FS occurs in rare inherited renal diseases including cystinosis, Dent disease, Lowe syndrome, and autosomal dominant FS. Acquired FS occurs in paraproteinemias, tubulointerstitial renal disease, oncogenic osteomalacia, Chinese herbs nephropathy, and Balkan endemic nephropathy. Though poorly understood, FS may be associated with HIV disease and antiretroviral treatment; cadmium poisoning may cause FS. In addition to FS, uRBP4 measurement has a different role: the early detection of acute kidney injury. Urine RBP4 comprises several isoforms, including intact plasma RBP4, MW 21.07 kDa, and C-terminal truncated forms, des-L- and des-LL-RBP4, also probably plasma derived. In FS, uRBP4 levels are about 104-fold above the upper limit of normal and small increments are frequently seen in carriers of some inherited forms of FS and in acquired disease. The very high levels in disease, frequent assay nonlinearity, lack of defined calibrants, and multiple uRBP4 isoforms make accurate assay challenging; top-down mass spectrometry has brought advances. Assays for uRBP4 with defined molecular targets allowing good interlaboratory comparisons are needed.

A form of apolipoprotein a-I is found specifically in relapses of focal segmental glomerulosclerosis following transplantation

Recurrence of idiopathic focal segmental glomerulosclerosis (FSGS) following kidney transplantation occurs in a large percentage of patients. Accurate prediction of recurrence and elucidation of its pathogenesis are major therapeutic goals. To detect differential proteins related to FSGS recurrence, proteomic analysis was performed on plasma and urine samples from 35 transplanted idiopathic FSGS patients, divided into relapsing and nonrelapsing. Several proteins were detected increased in urine of relapsing FSGS patients, including a high molecular weight form of apolipoprotein A-I, named ApoA-Ib, found exclusively in relapsing patients. This finding was verified by Western blot individually in the 35 patients and validated in an independent group of 40 patients with relapsing or nonrelapsing FSGS, plus two additional groups: FSGS-unrelated patients showing different proteinuria levels (n = 30), and familial FSGS transplanted patients (n = 14). In the total of 119 patients studied, the ApoA-Ib form was detected in 13 of the 14 relapsing FSGS patients, and in one of the 61 nonrelapsing patients. Only one of the 30 patients with FSGS-unrelated proteinuria tested positive for ApoA-Ib, and was not detected in familial patients. Urinary ApoA-Ib is associated with relapses in idiopathic FSGS and warrants additional investigation to determine its usefulness as biomarker of relapse following transplantation.

Relation between proteinuria and acute kidney injury in patients with severe burns

Introduction

Proteinuria in burn patients is common, and may be associated with acute kidney injury (AKI) and adverse outcomes. We evaluated the incidences, outcomes, characteristics and determinants of proteinuria and its influence on AKI and outcomes in burn patients.

Methods

This retrospective study was carried out in a hospital's burn department. The study population consisted of patients with burn injuries admitted during a five-year period. Positive urine dipstick readings were defined as mild (± or 1+) or heavy (≥ 2+) proteinuria, and AKI was diagnosed and staged according to the Risk, Injury, Failure, Loss, End Stage (RIFLE) classification system. Patient characteristics, management and outcomes were evaluated for associations with proteinuria using nonparametric tests, chi-square (χ²) tests and binary logistic regression.

Results

Of the patients admitted to the burn unit during the study period (n = 2,497), 865 (34.64%) were classified as having proteinuria. In the patients whose total burn surface areas (TBSA) were > 30% (n = 396), 271 patients (68.43%) had proteinuria and 152 of these patients (56.09%) met AKI criteria. No patients without proteinuria developed AKI. Intensive care unit (ICU) mortality rates were 0.8%, 16.67% and 30.77% (P < 0.001) in the groups with no, mild and heavy proteinuria, respectively. Logistic regression analysis identified proteinuria (OR 4.48; 95% CI, 2.824 to 7.108; P < 0.001) and sequential organ failure assessment (OR 1.383; 95% CI, 1.267 to 1.509; P < 0.001) as risk factors for AKI.

Conclusions

We observed a high prevalence of proteinuria in patients with severe burns (> 30% TBSA). Severely burned patients with proteinuria had a high risk of developing AKI and a poor prognosis for survival. This suggests that proteinuria should be used for identifying burn patients at risk of developing AKI.

Immunochemically unreactive albumin in urine: fiction or reality?

Urinary albumin measurements are currently not standardized due to a lack of a reference method and reference (primary and secondary [matrix]) material. Multiple molecular forms of albumin in urine are identified. Modification of albumin by proteolysis during passage through the urinary tract and chemical modification during specimen storage leads to the formation of albumin fragments. Multiple methods have been developed to quantify albuminuria and significant different results are reported dependent on the available assay. The current point of view of the National Kidney Disease Education Program - IFCC Working Group on Standardization of Albumin considers the immunoassay with polyclonal sera as the primary method of quantifying urine albumin. This article reviews the process of albumin fragmentation and focuses on the controversial topic of immuno-unreactive, nonimmunoreactive, or immunochemically nonreactive albumin fractions and its consequences for albumin analysis. We conclude that at present there are no hard arguments for measuring immunochemically unreactive albumin in urine. Immunoassays using polyclonal antisera for the detection of urinary albumin remain the gold standard. The development of a reference measurement procedure remains one of the challenges for the future.

Increased B-type natriuretic peptide and decreased proteinuria might reflect decreased capillary leakage and is associated with a better outcome in patients with severe burns

Introduction

It is difficult to adjust fluid balance adequately in patients with severe burns due to various physical changes. B-type natriuretic peptide (BNP) is emerging as a potential marker of hydration state. Proteinuria is used as a predictor of outcome in severe illness and might correlate to systemic capillary leakage. This study investigates whether combining BNP and proteinuria can be used as a guide for individualized resuscitation and as a predictor of outcome in patients with severe burns.

Methods

From 2006 to 2009, 38 consecutive patients (age 47 ± 15 years, 74% male) with severe burns were included and followed for 20 days. All had normal kidney function at admission. BNP and proteinuria were routinely measured. Ordered and actually administered fluid resuscitation volumes were recorded. The Sequential Organ Failure Assessment (SOFA) score was used as the measure of outcome.

Results

BNP increased during follow-up, reaching a plateau level at Day 3. Based on median BNP levels at Day 3, patients were divided into those with low BNP and those with high BNP levels. Both groups had comparable initial SOFA scores. Patients with high BNP received less fluid from Days 3 to 10. Furthermore, patients with a high BNP at Day 3 had less morbidity, reflected by lower SOFA scores on the following days. To minimize effects of biological variability, proteinuria on Days 1 and 2 was averaged. By dividing the patients based on median BNP at Day 3 and median proteinuria, patients with high BNP and low proteinuria had significantly lower SOFA scores during the entire follow-up period compared to those patients with low BNP and high proteinuria.

Conclusions

Patients with higher BNP levels received less fluid. This might be explained by a lower capillary leakage in these patients, resulting in more intravascular fluid and consequently an increase in BNP. In combination with low proteinuria, possibly reflecting minimal systemic capillary leakage, a high BNP level was associated with a better outcome. BNP and proteinuria have prognostic potential in severely burned patients and may be used to adjust individual resuscitation.

Urine Peptidomic and Targeted Plasma Protein Analyses in the Diagnosis and Monitoring of Systemic Juvenile Idiopathic Arthritis

PURPOSE: Systemic juvenile idiopathic arthritis is a chronic pediatric disease. The initial clinical presentation can mimic other pediatric inflammatory conditions, which often leads to significant delays in diagnosis and appropriate therapy. SJIA biomarker development is an unmet diagnostic/prognostic need to prevent disease complications. EXPERIMENTAL DESIGN: We profiled the urine peptidome to analyze a set of 102 urine samples, from patients with SJIA, Kawasaki disease (KD), febrile illnesses (FI), and healthy controls. A set of 91 plasma samples, from SJIA flare and quiescent patients, were profiled using a customized antibody array against 43 proteins known to be involved in inflammatory and protein catabolic processes. RESULTS: We identified a 17-urine-peptide biomarker panel that could effectively discriminate SJIA patients at active, quiescent, and remission disease states, and patients with active SJIA from confounding conditions including KD and FI. Targeted sequencing of these peptides revealed that they fall into several tight clusters from seven different proteins, suggesting disease-specific proteolytic activities. The antibody array plasma profiling identified an SJIA plasma flare signature consisting of tissue inhibitor of metalloproteinase-1 (TIMP1), interleukin (IL)-18, regulated upon activation, normal T cell expressed and secreted (RANTES), P-Selectin, MMP9, and L-Selectin. CONCLUSIONS AND CLINICAL RELEVANCE: The urine peptidomic and plasma protein analyses have the potential to improve SJIA care and suggest that SJIA urine peptide biomarkers may be an outcome of inflammation-driven effects on catabolic pathways operating at multiple sites. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s12014-010-9058-8) contains supplementary material, which is available to authorized users.