Evaluation of a new fluorescent dye method to measure urinary albumin in lieu of urinary total protein

How human serum albumin-selective DNA aptamer binds to bovine and canine serum albumins

Serum albumin (SA) is the most abundant carrier protein in blood. SA carries a diverse range of nutrients, drugs, and metal ions. It has wide clinical and biochemical applications. Human serum albumin (HSA) can be used as a biomarker for kidney and liver diseases. Aptasensor is one of potential HSA detection methods. HSA-specific aptamer was selected for HSA detection. In animals, bovine serum albumin (BSA) and canine serum albumins (CSA) share high sequence similarities to HSA. Thus, it is interesting to explore the possibility of using HSA-selective aptamer for BSA and CSA aptasensor. In this study, molecular dynamics (MD) simulations were initially employed to investigate the binding of aptamer to BSA and CSA in comparison to HSA. Like HSA, both BSA and CSA can bind aptamer, but different binding affinities are observed. BSA shows the tighter binding to aptamer than CSA. Domain III is found to be the aptamer-binding domain although no specific aptamer conformation is captured. However, in all cases, the aptamer utilizes the 3'-end to attach on an albumin surface. Both nucleobases and phosphate backbones on a DNA aptamer are important for albumin-aptamer complexation. Our results imply the possibility of using HSA-specific aptamer for BSA detection due to tighter binding observed, but may be less effective in CSA. However, the test in actual complicated condition must be further studied.

Development of enzyme-linked immunosorbent assay for estimation of urinary albumin

Yearly estimation of urinary albumin is a prerequisite for predicting renal status in Diabetes Type II patients with negative dipstick results for overt proteinuria. A simple, sensitive, and cost-effective enzyme linked immunosorbent assay (ELISA) for urinary albumin has been developed using human serum albumin antiserum (HSA-antiserum), HSA-biotin, and streptavidin-horseradish peroxidase (SA-HRP) conjugates. To the antibody-coated wells, 100 μL of HSA standards followed by 1:100 diluted urine samples in duplicate were added and then 50 μL of HSA-biotin conjugates was added in all the wells. 100 μL of SA-HRP was added after washing. Bound enzyme activity was measured by adding 100 μL TMB/H2O2. The analytical sensitivity and ED50 of the developed method was found to be 0.01 μg/mL and 0.35 μg/mL, respectively. The percent recovery of the HSA from exogenously spiked urine pools were in the range of 98.13-100.29%. The intra- and inter-assay coefficient of variation (CVs) ranged from 3.38-10.32 % and 4.22-11.01%, respectively. The antibody showed 4.4% and 3.2% cross reactivity with monkey and horse serum albumin, respectively. There was no cross reaction with human β2-microglobulin, γ-globulin, and haemoglobulin.

Culture of omentum-induced regenerating liver yielded hepatocyte-committed stem cells

Earlier we showed that when omentum, activated by inert particles, is allowed to fuse to a wedge cut in the liver, it induces stem cell proliferation in the liver resulting in massive liver regeneration. Here, we attempt to culture stem cells from the omentum-induced regenerating liver tissue. Cells from regenerating liver tissue were harvested and cultured. Cultured cells were characterized by immune staining, fluorescence activated cell sorting analysis, growth factor assay, in vitro differentiation, and their ability to engraft to injured sites in vivo. Culture yielded cells with a mesenchymal stem cell phenotype that could be maintained in culture indefinitely. These cells, called regenerating liver stem cells, expressed both adult and embryonic stem cell markers, secreted high levels of vascular endothelial growth factor, and expressed albumin. When grown on matrigel in the presence of hepatocyte growth factor, these cells differentiated into hepatocyte-like cells in culture, but they did not differentiate to adipogenic and osteogenic lineages when grown in specific differentiation medium. The differentiated cells expressed α-fetoprotein and secreted high levels of albumin and urea. After systemic injection, the undifferentiated cells engrafted only to the injured sites in the liver and not to the normal areas of the liver. In conclusion, omentum-induced regenerating liver yields hepatocyte-committed stem cells in culture. Such cells could prove to be useful in cell transplantation therapies.

On-chip immunoassay for determination of urinary albumin

An immunoassay performed on a portable microfluidic device was evaluated for the determination of urinary albumin. An increase in absorbance at 500 nm resulting from immunoagglutination was monitored directly on the poly(dimethylsiloxane) (PDMS) microchip using a portable miniature fibre-optic spectrometer. A calibration curve was linear up to 10 mg L(-1) (r(2) = 0.993), with a detection limit of 0.81 mg L(-1) (S/N = 3). The proposed system showed good precision, with relative standard deviations (RSDs) of 5.1%, when evaluated with 10 mg L(-1) albumin (n = 10). Determination of urinary albumin with the proposed system gave results highly similar to those determined by the conventional spectrophotometric method using immunoturbidimetric detection (r(2) = 0.995; n = 15).

Evidence for a need to mandate kidney transplant living donor registries

Kidney disease is a global public health problem of growing proportions. Currently the best treatment for end-stage renal failure is transplantation. Living organ donation remains a complex ethical, moral and medical issue. It is based on a premise that kidney donation is associated with short-term minimal risks to harm the donor, and is outweighed by the definite advantages to the recipient. A growing number of patients with end-stage renal disease and shortage of kidney donors poses a pressing need to expand the criteria needed to accept kidney donors. The current donor registries are structured and are driven to expand donor pool. As living kidney donation is not without risks, more attention should be given to protect the donor health. After kidney donation, mild to moderate renal insufficiency may occur. Renal insufficiency, even mild, is associated with increased risks of hypertension, proteinuria and cardiovascular morbidity. We, therefore, foresee a need to mandate the establishment of renal transplant donor registries at all transplanting programs as a prerequisite to protect the long-term well being of kidney donors. These registries can collect the database necessary to develop standards of practice and guidelines for future kidney donation.

Evaluation of proteinuria in healthy living kidney donor candidates

BACKGROUND

Evaluation of living kidney donor candidates includes careful assessment for the presence or absence of kidney disease. Kidney donation has been considered to be at least relatively contraindicated if urinary total protein excretion is above the normal range. However, at the present time, there is no uniformly accepted level of urine total protein excretion that would exclude donation. Albumin excretion instead of total protein excretion as a criterion has not previously been evaluated.

MATERIALS AND METHODS

This was a prospective observational study over a 3-year period in a single tertiary care center designed to assess current selection criteria for kidney donation with respect to urine total protein and albumin excretion.

RESULTS

Twenty four percent (25 of 105) of healthy adult kidney donor candidates had elevated urinary total protein excretion rates (150 to 292 mg/24 h). Of these 105 candidates, 39 had simultaneous measurements of both urinary total protein and albumin. Although one-third (13/39) had elevated 24-hour urine total protein values, none had elevated urine albumin excretion.

CONCLUSION

Measurement of albumin, the most common single protein found in urine, appears to be helpful in the evaluation of proteinuria in donor candidates. Many healthy adult kidney donor candidates have mildly elevated total protein excretion but normal albumin excretion. We believe that such patients should not be excluded from donation.

Microalbuminúria: fator de risco cardiovascular e renal subestimado na prática clínica

Embora de fácil determinação, a medida da excreção de albumina na urina tem sido pouco utilizada na identificação de indivíduos com diabetes tipo 2 (DM2), de maior risco para o desenvolvimento de doença renal e cardiovascular (CV). Tem sido demonstrado que as medidas das concentrações de albumina e creatinina (Cr) em amostras isoladas de urina, permitindo o cálculo da relação entre elas, podem ser suficientes para o rastreamento e mesmo para a avaliação da eficácia de medidas adotadas para a redução da microalbuminúria. Valores >30 mg/g de Cr ou 3,4 mg/mmol de Cr são indicativos de microalbuminúria e, em pacientes com DM2, a associação freqüente com a elevação dos níveis da pressão arterial representa condição de alto risco CV. Evidências epidemiológicas indicam que a presença de microalbuminúria prediz maior morbidade e mortalidade CV independente de outros fatores de risco. Por outro lado, a microalbuminúria mostra-se também freqüentemente associada a outros fatores de risco CV, sendo um dos componentes da síndrome metabólica. A capacidade de reduzir a pressão arterial, a pressão intraglomerular e a permeabilidade da membrana glomerular, fatores determinantes da progressão da lesão renal, explica o efeito renoprotetor dos inibidores da enzima conversora da angiotensina (IECAs) e dos bloqueadores dos receptores da angiotensina II (BRAs). No tratamento da nefropatia diabética, o uso de IECAs e BRAs associado ao controle rígido da pressão arterial, que deve ser mantida em níveis iguais ou inferiores a 130/80 mmHg, tem se mostrado como estratégia não só para promover proteção renal como também para promover proteção CV.

Degradation of albumin by the renal proximal tubule cells and the subsequent fate of its fragments

BACKGROUND

In view of recent reports of large amounts of albumin fragments present in normal urine we investigated the mechanism of albumin handling by the proximal tubule.

METHODS

We injected (125)I-albumin intravenously in rats and measured the excretion of intact and degraded (125)I-albumin in the urine by trichloroacetic acid (TCA) precipitation. The excretion rate of intact (125)I-albumin was compared to that obtained by routine radioimmunoassay (RIA). Human proximal tubular HK-2 cells were used to characterize the albumin receptor and study the degradation of albumin to peptides, establish their size by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and gel filtration chromatography, and determine the direction in which the degradation products are removed from the cell.

RESULTS

Following injection of (125)I-albumin intravenously into rats we recovered large quantities of (125)I-albumin fragments in urine and determined that 98% was in a highly degraded form and only 2% was intact. Only the intact albumin could be detected by RIA. We observed similar results in the urine of ex vivo kidneys perfused with (125)I-albumin. We found that (125)I-albumin was taken up by HK-2 cells via a receptor, degraded in the lysosomes and the peptides exocytosed to both the apical and basolateral sides of the cells.

CONCLUSION

We conclude that normally the kidney degrades large amounts of albumin and that the degradation fragments appear in the urine. These findings are in sharp contrast with the established view that degraded albumin is completely reabsorbed into the blood stream.

Decreased urinary peptide excretion in patients with renal disease

BACKGROUND

Normal urine contains low-molecular-weight peptides or protein fragments that have been poorly studied, primarily because of the technical difficulty of measuring peptides in the presence of proteins. We studied these substances in healthy subjects and patients with renal disease and varying degrees of proteinuria to understand the factors that determine their excretion.

METHODS

We estimated these substances as the difference between results using the Lowry method (which detects both proteins and peptides) and those obtained using the dye-binding Bradford (Biorad) method (Biorad Laboratories Inc, Hercules, CA; which detects only proteins).

RESULTS

We validated this 2-assay approach to measure peptide levels by showing that such proteins as immunoglobulin G, albumin, and lysozyme were measured equally by the Lowry and Biorad methods, whereas degraded proteins were recognized by the Lowry method only, but not by the Biorad method. We found that healthy subjects excreted less than 200 mg of protein, but 3 to 4 g of peptides/g creatinine; thus, peptides constituted approximately 95% of total protein material excreted in urine. Patients with renal disease and proteinuria had a progressive decrease in peptide excretion, ranging from 3 to 0 g/g creatinine. Twenty-five percent of nephrotic patients (18 of 72 patients) excreted very small amounts of peptides in urine (0% to 10% of total protein material).

CONCLUSION

We found that healthy persons excrete substantial amounts of peptides in urine, and this excretion decreases in the presence of proteinuric renal disease. It is possible that these peptides in urine arise from the tubular degradation of filtered proteins and exocytosis of protein fragments toward the urinary side, a process that becomes increasingly impaired as proteinuria increases.

Microalbuminuria in type 2 diabetics: an important, overlooked cardiovascular risk factor

The presence of microalbumin in the urine of persons with type 2 diabetes is perhaps the most important early signal heralding the onset of systemic vasculopathy and associated target organ damage to the brain, the heart, and the kidneys. It is easily measured and, unfortunately, frequently overlooked as a screening tool in clinical medicine. If present, it identifies patients at risk for early cardiovascular death and progressive renal disease. Microalbuminuria also identifies patients who need more rigorous cardiovascular risk management, especially more intensive blood pressure control, preferably below 130/80 mm Hg, and strict attention to glycemic control and lipid levels. Therapeutic strategies to facilitate better blood pressure control and reduce microalbuminuria likely will prove to be the most effective way to retard not only the progression of renal disease but also cardiovascular disease. Consequently, the identification and normalization of urine microalbumin excretion should be an important consideration in patients with diabetes.

Classification of renal proteinuria: a simple algorithm

Total protein, albumin, alpha1-microglobulin, and immunoglobulin G (IgG) were analyzed in 1,622 urine samples without Bence-Jones proteinuria or gross hematuria. There was correlation with the histological picture obtained on renal biopsy in 61 patients. We established 24-h reference intervals for alpha1-microglobulin and IgG on 659 urine samples with total protein and albumin excretion rates below 100 mg/24 h and 30 mg/24 h, respectively, and creatinine clearance above 80 ml/min. The central 95% reference interval was found to be between 4 and 17 mg/24 h for alpha1-microglobulin and between 3 and 8.5 mg/24 h for IgG. In 80 urine samples with albumin excretion rate above 30 mg/24 h and alpha1-microglobulin and IgG within their reference intervals, we analyzed the 95% central interval of the distribution of the IgG/albumin ratios, and it was found to be within 0.01 and 0.20 (0.90 confidence interval: 0.17-0.24). Proteinuria was considered to be of the selective glomerular type if the albumin excretion rate was abnormal and the IgG/albumin ratio was under 0.20, even when the IgG excretion was within a pathological range. For the classification of proteinuria as predominantly tubular, we estimated the alpha1-microglobulin/albumin ratio in 173 urine samples with normal excretion rates of albumin and IgG and pathological excretion of alpha1-microglobulin. The discriminating value of 0.91 (0.90 confidence interval: 0.78-1.08) was accepted in order to define proteinuria of a tubular origin in the presence of a pathological albumin excretion rate. The association between albumin and IgG excretion rates and tubular reabsorption of the alpha1-microglobulin normally filtered by the glomerulus was studied in 33 urine samples from patients with no histologically significant tubulo-interstitial or vascular disease and a serum creatinine concentration below 141 pmol/l. The optimal curve-fitting function between albumin plus IgG and alpha1-microglobulin excretion rates was of the quadratic type (r = 0.927). Mixed proteinuria was considered when both, albumin and alpha1-microglobulin excretion rates were pathological and could not be included in the previously described groups.

Renal handling of albumin: a critical review of basic concepts and perspective

Biochemical and physiological processes that underlie the mechanism of albuminuria are completely reassessed in this article in view of recent discoveries that filtered proteins undergo rapid degradation during renal passage and the resulting excreted peptide fragments are not detected by conventional urine protein assays. This means that filtered protein and/or albumin levels in urine have been seriously underestimated. The concept that albuminuria is a result of changes in glomerular permeability is questioned in light of these findings and also in terms of a critical examination of charge selectivity, shunts, or large-pore formation and hemodynamic effects. The glomerulus appears to function merely in terms of size selectivity alone, and for albumin, this does not change significantly in disease states. Intensive albumin processing by a living kidney occurs through cellular processes distal to the glomerular basement membrane. Failure of this cellular processing primarily leads to albuminuria. This review brings together recent data about urinary albumin clearance and current knowledge of receptors known to process albumin in both health and disease states. We conclude with a discussion of topical and controversial issues associated with the proposed new understanding of renal handling of albumin.