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Vuchkova J, Comper WD. Inhibition of the metabolic degradation of filtered albumin is a major determinant of albuminuria. PLoS One 2015; 10:e0127853. [PMID: 26010895 PMCID: PMC4444184 DOI: 10.1371/journal.pone.0127853] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2015] [Accepted: 04/20/2015] [Indexed: 02/03/2023] Open
Abstract
Inhibition of the degradation of filtered albumin has been proposed as a widespread, benign form of albuminuria. There have however been recent reports that radiolabeled albumin fragments in urine are not exclusively generated by the kidney and that in albuminuric states albumin fragment excretion is not inhibited. In order to resolve this controversy we have examined the fate of various radiolabeled low molecular weight protein degradation products (LMWDPs) introduced into the circulation in rats. The influence of puromycin aminonucleoside nephrosis on the processing and excretion of LMWDPs is also examined. The status and destinies of radiolabeled LMWDPs in the circulation are complex. A major finding is that LMWDPs are rapidly eliminated from the circulation (>97% in 2 h) but only small quantities (<4%) are excreted in urine. Small (<4%) but significant amounts of LMWDPs may have prolonged elimination (>24 h) due to binding to high molecular weight components in the circulation. If LMWDPs of albumin seen in the urine are produced by extra renal degradation it would require the degradation to far exceed the known catabolic rate of albumin. Alternatively, if an estimate of the role of extra renal degradation is made from the limit of detection of LMWDPs in plasma, then extra renal degradation would only contribute <1% of the total excretion of LMWDPs of albumin. We confirm that the degradation process for albumin is specifically associated with filtered albumin and this is inhibited in albuminuric states. This inhibition is also the primary determinant of the massive change in intact albuminuria in nephrotic states.
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Affiliation(s)
- Julijana Vuchkova
- Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria 3800, Australia
| | - Wayne D. Comper
- SalAqua Diagnostics Inc., Suite 258, 888c 8 Ave, New York, New York, 10019, United States of America
- * E-mail:
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2
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Cho YT, Chen CW, Chen MP, Hu JL, Su H, Shiea J, Wu WJ, Wu DC. Diagnosis of albuminuria by tryptic digestion and matrix-assisted laser desorption ionization/time-of-flight mass spectrometry. Clin Chim Acta 2013; 420:76-81. [DOI: 10.1016/j.cca.2012.12.016] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2012] [Accepted: 12/17/2012] [Indexed: 11/25/2022]
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3
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The study of interferences for diagnosing albuminuria by matrix-assisted laser desorption ionization/time-of-flight mass spectrometry. Clin Chim Acta 2012; 413:875-82. [DOI: 10.1016/j.cca.2012.01.029] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2011] [Revised: 01/25/2012] [Accepted: 01/26/2012] [Indexed: 11/20/2022]
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Weyer K, Nielsen R, Christensen EI, Birn H. Generation of urinary albumin fragments does not require proximal tubular uptake. J Am Soc Nephrol 2012; 23:591-6. [PMID: 22282591 DOI: 10.1681/asn.2011101034] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Abstract
Urinary albumin excretion is an important diagnostic and prognostic marker of renal function. Both animal and human urine contain large amounts of albumin fragments, but whether these fragments originate from renal tubular degradation of filtered albumin is unknown. Here, we used mice with kidneys lacking megalin and cubilin, the coreceptors that mediate proximal tubular endocytosis of albumin, to determine whether proximal tubular degradation of albumin forms the detectable urinary albumin fragments. After intravenous administration of (125)I-labeled mouse albumin to knockout and control mice, we examined kidney uptake of albumin and urinary excretion of both intact albumin and its fragments using size exclusion chromatography. In control mice, all labeled albumin eluted as albumin fragments in the urine. In megalin/cubilin-deficient mice, we observed decreased uptake and degradation of albumin and increased urinary excretion of intact albumin; we did not, however, detect a decrease in the excretion of albumin fragments. These results show that the generation of urinary albumin fragments occurs independently of renal tubular uptake and degradation of albumin, suggesting that the pathophysiological implications of changes in urinary albumin fragments require reevaluation.
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Affiliation(s)
- Kathrin Weyer
- Department of Biomedicine, Aarhus University, Aarhus, Denmark.
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Speeckaert MM, Speeckaert R, Van De Voorde L, Delanghe JR. Immunochemically unreactive albumin in urine: fiction or reality? Crit Rev Clin Lab Sci 2011; 48:87-96. [PMID: 21871001 DOI: 10.3109/10408363.2011.591366] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
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.
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Affiliation(s)
- Marijn M Speeckaert
- Department of Clinical Chemistry, University of Ghent, Faculty of Medicine, Belgium
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6
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Sviridov D, Hortin GL. Urine albumin measurement: Effects of urine matrix constituents. Clin Chim Acta 2009; 404:140-3. [DOI: 10.1016/j.cca.2009.03.034] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2008] [Revised: 03/13/2009] [Accepted: 03/16/2009] [Indexed: 10/21/2022]
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7
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Nakayama A, Sakatsume M, Kasama T, Kawara T, Gejyo F, Isobe M, Sato K, Shiba K. Molecular heterogeneity of urinary albumin in glomerulonephritis: Comparison of cardiovascular disease with albuminuria. Clin Chim Acta 2009; 402:94-101. [DOI: 10.1016/j.cca.2008.12.026] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2008] [Revised: 12/19/2008] [Accepted: 12/19/2008] [Indexed: 10/21/2022]
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8
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Shiea J, Cho YT, Lin YH, Chang CW, Lo LH, Lee YC, Ke HL, Wu WJ, Wu DC. Using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry to rapidly screen for albuminuria. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2008; 22:3754-3760. [PMID: 18980259 DOI: 10.1002/rcm.3792] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) is used as an alternative method for the rapid diagnosis of albuminuria. This technique requires no further sample pretreatment than simply mixing the urine sample with a MALDI matrix and drying under ambient conditions. The resulting MALDI mass spectra reveal albumin ions having charges ranging from +1 to +5. The detection of albumin is possible using any of the three most common MALDI matrices - sinapinic acid (SA), 2,5-dihydroxybenzoic acid (2,5-DHB), or 4-hydroxy-alpha-cyanocinnamic acid (alpha-CHC). Using this analytical approach, the limit of detection for albumin in urine is 10(-6) M, approximately 5 to 10 times lower than that detectable through conventional chemical testing.
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Affiliation(s)
- Jentaie Shiea
- Department of Chemistry, National Sun Yat-Sen University, Kaohsiung, Taiwan.
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Miller WG, Bruns DE, Hortin GL, Sandberg S, Aakre KM, McQueen MJ, Itoh Y, Lieske JC, Seccombe DW, Jones G, Bunk DM, Curhan GC, Narva AS. Current issues in measurement and reporting of urinary albumin excretion. Clin Chem 2008; 55:24-38. [PMID: 19028824 DOI: 10.1373/clinchem.2008.106567] [Citation(s) in RCA: 234] [Impact Index Per Article: 14.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
BACKGROUND Urinary excretion of albumin indicates kidney damage and is recognized as a risk factor for progression of kidney disease and cardiovascular disease. The role of urinary albumin measurements has focused attention on the clinical need for accurate and clearly reported results. The National Kidney Disease Education Program and the IFCC convened a conference to assess the current state of preanalytical, analytical, and postanalytical issues affecting urine albumin measurements and to identify areas needing improvement. CONTENT The chemistry of albumin in urine is incompletely understood. Current guidelines recommend the use of the albumin/creatinine ratio (ACR) as a surrogate for the error-prone collection of timed urine samples. Although ACR results are affected by patient preparation and time of day of sample collection, neither is standardized. Considerable intermethod differences have been reported for both albumin and creatinine measurement, but trueness is unknown because there are no reference measurement procedures for albumin and no reference materials for either analyte in urine. The recommended reference intervals for the ACR do not take into account the large intergroup differences in creatinine excretion (e.g., related to differences in age, sex, and ethnicity) nor the continuous increase in risk related to albumin excretion. DISCUSSION Clinical needs have been identified for standardization of (a) urine collection methods, (b) urine albumin and creatinine measurements based on a complete reference system, (c) reporting of test results, and (d) reference intervals for the ACR.
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Affiliation(s)
- W Greg Miller
- Department of Pathology, Virginia Commonwealth University, Richmond, VA, USA.
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Candiano G, Bruschi M, Petretto A, Santucci L, Del Boccio P, Urbani A, Bertoni E, Gusmano R, Salvadori M, Scolari F, Ghiggeri GM. Proteins and protein fragments in nephrotic syndrome: Clusters, specificity and mechanisms. Proteomics Clin Appl 2008; 2:956-63. [DOI: 10.1002/prca.200780157] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2007] [Indexed: 11/06/2022]
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11
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Hortin GL, Sviridov D. Analysis of molecular forms of albumin in urine. Proteomics Clin Appl 2008; 2:950-5. [DOI: 10.1002/prca.200780145] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2007] [Indexed: 11/10/2022]
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12
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Nakayama A, Ida T, Hatano Y, Oohara K, Yoshida H, Baba T, Sakamoto H, Shiba K. Presence of immunounreactive albumin in the urine of diabetic patients. J Clin Lab Anal 2007; 20:29-36. [PMID: 16538642 PMCID: PMC6807341 DOI: 10.1002/jcla.20100] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
Recent studies have demonstrated that conventional immunochemical assays underestimate urinary albumin concentration because of the presence of immunounreactive albumin. It has been reported that intact urinary albumin in 24-hr diabetic urine samples could be detected as total concentration (immunoreactive+immunounreactive) by an HPLC method based on size exclusion chromatography. The aim of this study was to investigate urinary albumin concentration in diabetic spot urine samples by comparing the HPLC method with several other methods. The albumin concentrations on 80 diabetic spot urine specimens were measured by turbidimetric immunoassay (TIA), high performance liquid chromatography (HPLC), and a dipstick method. In addition, they were also analyzed by reducing sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS PAGE) and native polyacrylamide gel electrophoresis (Native PAGE). The albumin concentrations derived from diabetic spot urine samples measured by the HPLC method were higher than those of the other methods except for five of 80 samples. Furthermore, the albumin concentrations analyzed by Native PAGE were higher than SDS PAGE in 61 (76.2%) of 80 samples. This study suggests the need for evaluating diabetes not only by HPLC, but also by combining it with another method.
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Affiliation(s)
- Aki Nakayama
- Analytical Laboratory Chemistry, Graduate School of Allied Health Sciences, Tokyo Medical and Dental University, Bunkyo‐ku, Tokyo, Japan
| | - Takashi Ida
- Department of Internal Medicine, Nakano General Hospital, Nakano‐ku, Tokyo, Japan
| | - Yoshiji Hatano
- Department of Laboratory Medicine, Nakano General Hospital, Nakano‐ku, Tokyo, Japan
| | - Kayoko Oohara
- Department of Laboratory Medicine, Nakano General Hospital, Nakano‐ku, Tokyo, Japan
| | - Hiroshi Yoshida
- Research & Development Laboratory, NIPRO CORPORATION, Kusatsu, Shiga, Japan
| | - Toshiaki Baba
- Research & Development Laboratory, NIPRO CORPORATION, Kusatsu, Shiga, Japan
| | - Hisashi Sakamoto
- Division of Point of Care, ARKRAY Inc., Higashi‐kujo, Kyoto, Japan
| | - Kiyoko Shiba
- Analytical Laboratory Chemistry, Graduate School of Allied Health Sciences, Tokyo Medical and Dental University, Bunkyo‐ku, Tokyo, Japan
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McQueen MJ, Gerstein HC, Pogue J, Mann JFE, Yusuf S. Reevaluation by High-Performance Liquid Chromatography: Clinical Significance of Microalbuminuria in Individuals at High Risk of Cardiovascular Disease in the Heart Outcomes Prevention Evaluation (HOPE) Study. Am J Kidney Dis 2006; 48:889-96. [PMID: 17162143 DOI: 10.1053/j.ajkd.2006.09.003] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2006] [Accepted: 09/05/2006] [Indexed: 11/11/2022]
Abstract
BACKGROUND In the Heart Outcomes Prevention Evaluation Study, microalbumin and albumin levels measured by using radioimmunoassay (RIA) and less than the microalbuminuria threshold in baseline urine samples were associated independently with cardiovascular (CV) events. Conventional immunoassays may underestimate albuminuria by not detecting a mildly denatured unfragmented form of albumin, immunounreactive to conventional antibodies. METHODS Microalbuminuria was reanalyzed in baseline samples stored at -70 degrees C for 5,358 North American participants, 1,992 with diabetes mellitus, by using a high-performance liquid chromatography (HPLC) system that also detects immunochemically nonreactive urinary albumin. RESULTS The HPLC compared with RIA method identified microalbuminuria in 1,585 versus 719 participants, 809 versus 423 patients with diabetes, by using a conventionally accepted albumin-creatinine ratio (ACR) of 29 mg/g or greater (>or=3 mg/mmol) as a cutoff value. HPLC-detected microalbuminuria increased risk for the primary outcome (a composite of myocardial infarction, stroke, and CV death); unadjusted hazard ratio, 1.85 (95% confidence interval, 1.57 to 2.19). Receiver operating characteristic analysis did not differentiate between HPLC- and RIA-detected microalbuminuria as predictors of CV outcomes. CONCLUSION The prevalence of microalbuminuria is 2 to 3 times greater with HPLC than RIA using an ACR of 29 mg/g or greater (>or=3 mg/mmol). The optimal cutoff value for detecting CV risk in the entire study population by means of RIA was 9 mg/g (0.9 mg/mmol), and with HPLC, 32 mg/g (3.4 mg/mmol). Results from this study also show different ACR cutoff values for individuals with diabetes: RIA, 13 mg/g or greater (>or=1.4 mg/mmol); HPLC, 44 mg/g or greater (>or=5.2 mg/mmol) and without diabetes: RIA, 7 mg/g or greater (>or=0.7 mg/mmol); HPLC, 29 mg/g or greater (>or=3/1 mg/mmol). Results highlight the importance of method-dependent cutoff values in the prediction of CV events.
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Affiliation(s)
- Matthew J McQueen
- Hamilton Regional Laboratory Medicine Program, Department of Pathology, Population Health Research Institute, McMaster University, Hamilton, Ontario, Canada.
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Comper WD, Osicka TM, Clark M, MacIsaac RJ, Jerums G. Earlier detection of microalbuminuria in diabetic patients using a new urinary albumin assay. Kidney Int 2004; 65:1850-5. [PMID: 15086926 DOI: 10.1111/j.1523-1755.2004.00585.x] [Citation(s) in RCA: 93] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
BACKGROUND Microalbuminuria is regarded as the most important predictor of high risk for the development of diabetic nephropathy. Early detection may allow treatment to prevent progression to persistent albuminuria and renal failure. Recent studies have shown that conventional immunoassays underestimate urinary albumin concentration, as albumin in urine may exist in two forms, immuno-reactive and immuno-unreactive. The present study examines the differential lead-time for the development of microalbuminuria as measured by both conventional radioimmunoassay (RIA; measures immuno-reactive) and high-performance liquid chromatography (HPLC; measures total albumin = immuno-reactive plus immuno-unreactive) analysis in both type 1 and type 2 diabetic patients. METHODS Analysis was performed on 511 stored urine samples collected over the last 13 years from type 1 diabetic patients who either progressed from normo- to microalbuminuria (progressors, N= 17), or who remained normoalbuminuric (nonprogressors, N= 25) as defined by RIA, and on 634 urine samples collected from patients with type 2 diabetes defined as either progressors (N= 24) or nonprogressors (N= 25). RESULTS For type 1 progressors, the mean lead-time for the HPLC assay versus the RIA was 3.9 years, with a 95% CI of 2.1 to 5.6 years. For type 2 progressors, the mean lead-time was 2.4 years with a 95% CI of 1.2 to 3.5 years. There was no significant difference between the lead-time analysis between type 1 and type 2 diabetic patients. CONCLUSION These results demonstrate that measurement of total albumin may allow earlier detection of microalbuminuria associated with diabetic nephropathy.
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Affiliation(s)
- Wayne D Comper
- Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria, Australia.
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16
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Abstract
BACKGROUND Conventional immunoassays underestimate the urinary albumin concentration because intact albumin in urine exists in two forms, immunoreactive and immunochemically nonreactive. METHODS Urinary albumin concentration measured by HPLC (which measures total albumin, i.e., the sum of immunoreactive albumin + immunochemically nonreactive albumin) or RIA was compared with densitometric analysis of albumin bands in diabetic urine samples separated by either native polyacrylamide gel electrophoresis (PAGE) or reducing sodium dodecyl sulfate (SDS)-PAGE. Immunochemically nonreactive albumin was also isolated from diabetic urine (relative amount detected, 70-80% of the expected) and was tested for contamination by common urinary proteins by native PAGE, ELISA, and capillary electrophoresis. RESULTS Urinary albumin concentrations measured by native PAGE and HPLC were better correlated (r(2) = 0.83) than concentrations measured by native PAGE and RIA (r(2) = 0.62) because under native conditions both native PAGE and HPLC detect total albumin and not only the immunoreactive albumin alone that is measured by RIA. Urinary albumin concentrations measured by reducing SDS-PAGE and RIA were better correlated (r(2) = 0.84) than concentrations measured by reducing SDS-PAGE and HPLC (r(2) = 0.65) because under reducing conditions immunochemically nonreactive albumin is unstable and fragments into many smaller peptides. The partially purified preparation was found to contain <1% contamination by common urinary proteins and is stable to freezing and frequent freeze/thaw cycles. CONCLUSIONS The results are consistent with the interpretation that immunochemically nonreactive albumin has a limited number of polypeptide chain scissions and is held together by noncovalent intrachain bonding and disulfide bonds. Detection of this molecule is likely to be of clinical importance in diagnosing kidney disease as well as cardiovascular disease.
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Affiliation(s)
- Tanya M Osicka
- Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria, Australia
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Comper WD, Jerums G, Osicka TM. Differences in urinary albumin detected by four immunoassays and high-performance liquid chromatography. Clin Biochem 2004; 37:105-11. [PMID: 14725940 DOI: 10.1016/j.clinbiochem.2003.10.008] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
OBJECTIVES To compare the analysis of urinary albumin from diabetic patients by four conventional immunoassays including radioimmunoassay (RIA), immunonephelometry (IN), and two different methods of immunoturbidimetry (IT), as well as by high-performance liquid chromatography (HPLC). DESIGN AND METHODS Urines were collected over a 24-h period and stored at -20 degrees C until assay. Urinary albumin concentration was determined by an in-house RIA, by IN using a Beckman Array Analyser with reagents from Beckman Diagnostics (Sydney, Australia), by IT using a Dade-Behring Turbitimer with reagents from Dade-Behring (Marburg, Germany), by IT using a Dade-Behring Dimension R x L Chemistry Analyser with reagents from DiaSorin (Stillwater, OK, USA), and by HPLC using a Zorbax Bio series preparative GF-250 column. Regression lines were calculated using a least squares method to determine the correlation between the assays studied. Bland-Altman bias plots including limits of agreement were also calculated. RESULTS The correlation coefficients calculated were high (>0.85) indicating a strong linear relationship between all assays studied. The slopes calculated for the comparisons demonstrate that each assay can vary from one another (up to threefold) and have a slope significantly different from an ideal slope of 1 (P < 0.001). These results were confirmed by Bland-Altman bias plots and calculation of the limits of agreement that were all large. CONCLUSIONS At this time, there is no global standard by which urinary albumin assays may be standardized. This study suggests the need for such standards.
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Affiliation(s)
- Wayne D Comper
- Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria 3800, Australia.
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Clavant SP, Greive KA, Nikolovski J, Reeve S, Smith AI, Comper WD. Albumin fragments in normal rat urine are derived from rapidly degraded filtered albumin. Nephrology (Carlton) 2003; 8:72-9. [PMID: 15012737 DOI: 10.1046/j.1440-1797.2003.00136.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Filtered albumin is excreted as a heterogeneous population of albumin-derived molecules resulting from degradation during renal passage. In order to understand the dynamics of this degradation process, albumin clearance was studied over a short-term (minutes) and a long-term (7 days) by both radioactivity and radioimmunoassay. The radiolabelled material in the urine was also analysed extensively by using size exclusion chromatography, size selective filtration and high performance liquid chromatography. These studies demonstrate that during renal passage, albumin degradation to fragments in the size range of 500-10,000 occurs in a matter of minutes. The fragments are not detected by using radioimmunoassay. Steady state excretion rates or fractional clearance of radiolabelled albumin occur over a similar time period. Both rates of degradation and approach to steady-state clearance, while rapid, were considerably slower than the transit time for molecules in the Bowman's capsule and early tubular lumen. The results are consistent with an extremely rapid lysosomal uptake of filtered albumin, and degradation and regurgitation of the albumin-derived peptide fragments into the tubular lumen prior to excretion.
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Affiliation(s)
- Steven P Clavant
- Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria, Australia
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Russo LM, Brammar GC, Jerums G, Comper WD, Osicka TM. The effect of ramipril on albumin excretion in diabetes and hypertension: the role of increased lysosomal activity and decreased transforming growth factor-beta expression. J Hypertens 2003; 21:419-28. [PMID: 12569274 DOI: 10.1097/00004872-200302000-00035] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
OBJECTIVES Albumin excretion is modulated post-filtration by lysosomal processing that produces a spectrum of albumin-derived material in urine, much of which is not detected by conventional immunoassays. This study aimed to determine the efficacy of ramipril treatment (+ RAM) after 24 weeks on total albumin excretion (intact plus albumin-derived peptides) in spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats with (d) and without (c) diabetes. METHODS Intact albumin excretion was analysed by radioimmunoassay and total albumin excretion was analysed by measuring radioactivity derived from circulating [ C]albumin. Renal lysosomal activity was determined by urinary [ H]dextran sulphate desulphation. Renal transforming growth factor-beta 1 (TGF-beta 1), TGF-beta inducible gene-h3 (beta ig-h3) and angiotensinogen mRNA production were analysed by real time reverse transcriptase-polymerase chain reaction. RESULTS Hypertension (SHR-c and SHR-d) resulted in a significant increase in intact albumin excretion, which was significantly reduced by ramipril treatment (P < 0.05 for SHR-c + RAM and 0.001 for SHR-d + RAM compared to non-treated). This was accompanied by a significant decrease in blood pressure (P < 0.001 for SHR-c + RAM and SHR-d + RAM), renal beta ig-h3 mRNA production (P < 0.05 for SHR-c + RAM and SHR-d + RAM), and an increase in lysosomal activity. Diabetes (WKY-d and SHR-d) primarily caused a significant increase in total albumin excretion, predominantly in the form of albumin-derived fragments in the WKY-d group and intact albumin in the SHR-d group. Ramipril treatment reduced total albumin excretion in the WKY-d + RAM group (P < 0.001). CONCLUSIONS Ramipril prevents increases in both intact albumin and total albumin excretion in hypertensive and diabetic states, respectively.
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Affiliation(s)
- Leileata M Russo
- Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria, Australia
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Marshall T, Williams KM. Clinical analysis of human urinary proteins using high resolution electrophoretic methods. Electrophoresis 1998; 19:1752-70. [PMID: 9719556 DOI: 10.1002/elps.1150191037] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The application of isoelectric focusing (IEF), sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), two-dimensional electrophoresis (2-DE) and capillary electrophoresis (CE) for high resolution electrophoretic analysis of human urinary proteins is reviewed. In each case, the information is tabulated chronologically with details of sample preparation, electrophoretic system, detection method and clinical application. The text includes an historical perspective of the use of each method for urinalysis and a detailed review of the application of the methods to the investigation of renal disease, renal transplantation, Bence Jones proteinuria (BJP), diabetes mellitus, cadmium toxicity, nephrolithiasis and cancers of the urogenital tract.
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Affiliation(s)
- T Marshall
- Analytical Biochemistry Group, School of Health Sciences, The University of Sunderland, Great Britain.
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