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Wayne D Comper

Publications and source records attributed to Wayne D Comper.

29 records · Page 2Linked to original sources
PubMed2003

High prevalence of immuno-unreactive intact albumin in urine of diabetic patients.

BACKGROUND: Intact albumin in urine may exist in two forms, immunoreactive and immuno-unreactive. Previous estimates of albuminuria in diabetic urine have only detected immunoreactive forms. METHODS: High performance liquid chromatography (HPLC) was used in this study to measure both forms of intact albumin (termed total intact albumin) to provide a more accurate measurement of albuminuria compared with radioimmunoassay (RIA) on 97 fresh urine samples from patients with diabetes. Eighty-six control urine samples from volunteers without diabetes were also tested. RESULTS: There was no significant difference between the two methods for nondiabetic controls. For diabetic urine samples, 91.6% of samples showed a greater concentration of albumin measured by HPLC than RIA. For normoalbuminuric diabetic samples, HPLC gave a mean albumin excretion rate of 12.5 +/- 4.4 microgram/min (SD), whereas RIA gave a rate of 8.0 +/- 6.7 microgram/min (P = 0.004; N = 28). For microalbuminuric samples, there also was a statistically significant difference: HPLC albumin excretion rate, 82.0 +/- 49.9 microgram/min, and RIA, 49.0 +/- 34.6 microgram/min (P = 0.004; N = 30). Thirty-two urine samples were normoalbuminuric by RIA (albumin, 11.4 +/- 3.9 microgram/min), but in the microalbuminuric range as determined by HPLC (albumin, 38.5 +/- 14.4 microgram/min). For urine samples in the macroalbuminuric range, there was no statistically significant difference between HPLC and RIA. Immuno-unreactive albumin was confirmed as albumin, analyzed by two-dimensional electrophoresis and matrix-assisted laser desorption ionization mass spectrometry. CONCLUSION: These studies show that to determine microalbuminuria accurately, there is a need to assess urinary total intact albumin, rather than simply immunoreactive albumin. Am J Kidney Dis 41:336-342.

Adult↗
PubMed2003

The effect of ramipril on albumin excretion in diabetes and hypertension: the role of increased lysosomal activity and decreased transforming growth factor-beta expression.

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.

Albuminuria↗
PubMed2003

Additive effects of hypertension and diabetes on renal cortical expression of PKC-alpha and -epsilon and alpha-tubulin but not PKC-beta 1 and -beta 2.

OBJECTIVE: This study examined the separate and combined effects of hypertension and diabetes on renal cortical expression of protein kinase C (PKC) isoforms -beta 1, -beta 2, -alpha and -epsilon, to determine whether albuminuria is the result of an increase in the expression of one or a combination of PKC isoforms. Corresponding changes in renal microtubules were also assessed. METHODS: Diabetes (D) was induced in Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR) by streptozotocin. After 24 weeks, PKC expression was determined by Western blot and microtubules were assessed by immunohistochemistry for alpha-tubulin protein. RESULTS: Diabetes was characterized by significant increases in glycated haemoglobin (HbA1c) as compared to controls (C). There was a significant increase of three- to four-fold in PKC protein content for all four isoforms in renal cortex from SHR-C and WKY-D, and similar and significant levels of albuminuria (approximately 10 mg/24 h) observed in these groups in comparison to WKY-C (approximately 1 mg/24 h). Interestingly, PKC-alpha and -epsilon but not PKC-beta 1 and -beta 2 protein content was doubled in SHR-D, and albuminuria increased tenfold (approximately 100 mg/24 h) in comparison to SHR-C and WKY-D. These changes were paralleled by a significant decrease in alpha-tubulin protein content of approximately 50% in SHR-C and approximately 33% in WKY-D compared to WKY-C, with a further decrease of approximately 67% in SHR-D compared to WKY-C. CONCLUSION: These findings indicate that PKC expression can be increased by either diabetes or hypertension, and that there are further specific increases in the expression of PKC isoforms -alpha and -epsilon in the model of combined diabetes and hypertension. In addition, the degree of disruption in microtubular cytoskeleton appears to be correlated with PKC activation and levels of albuminuria.

Albuminuria↗
PubMed2003

Reversible angiotensin II-mediated albuminuria in rat kidneys is dynamically associated with cytoskeletal organization.

Angiotensin II (ANG II) is intimately involved in normal renal function, and is estimated to exist at a normal physiological range of 6-10 nM within the renal tubules. The potential role that intrarenal ANG II may play in renal disease was assessed by perfusing isolated rat kidneys with or without excess intratubular levels of ANG II, which may mimic changes in the intrarenal RAS under pathological conditions. The effects of increased systemic ANG II were also determined by infusing rats with ANG II by osmotic pump. In isolated perfused kidneys, ANG II significantly and specifically increased the fractional clearance of albumin to clinical levels, as determined by using radiolabelled albumin. This effect was reversible, as removing ANG II from the perfusate caused the albumin fractional clearance to decrease to pre-ANG II exposure levels. The increase in fractional clearance of albumin was not correlated with renal hemodynamic changes, nor glomerular permeability alterations as measured by the fractional clearance of 36 A Ficoll and immunoglobulin G. Immunochemical analysis using anti-alpha-tubulin antibody of perfused kidney sections revealed that ANG II caused a marked disruption of tubular epithelial cytoskeletal components, through disassembly and reorganization of alpha-tubulin. This disruption was reversible. In vivo, osmotic pump delivery of ANG II at less potent dosage caused a proteinuria (Biuret) and an albuminuria (radioimmunoassay) in rats, from as early as 2 days after pump implantation. These results demonstrate that ANG II may reversibly induce clinical levels of albuminuria. These data point to an important role for renal tubules and the intratubular lumen concentrations of ANG II in the renal processing of albumin.

Albuminuria↗
PubMed2002

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.

Albumins↗
PubMed2002

Exogenous albumin peptides influence the processing of albumin during renal passage.

UNLABELLED: Exogenous albumin peptides influence the processing of albumin during renal passage. BACKGROUND/AIMS: This study investigates the hypothesis that there will be peptide regions in albumin that will effectively compete for the receptors associated with the renal processing of albumin. METHODS: We employ albumin peptides prepared from albumin by trypsin digestion. The presentation of the exogenous peptides along with intact [(3)H]albumin to the kidney was made by intravenous injection into rats. The excretion rate and integrity of urinary [(3)H]albumin was measured. Similar experiments were performed with the use of gelatin peptides produced by trypsin digestion as controls. The formation of [(3)H]albumin derived fragments by extrarenal sources was also examined in rats with nonfiltering kidneys. RESULTS: In the presence of exogenous albumin-derived peptides there was a significant increase in the proportion of larger [(3)H]albumin fragments in the urine. This is a reversible effect. There was no significant change when gelatin peptides were used. The albumin peptides also increase the fractional clearance of [(3)H]albumin. There were no [(3)H]albumin-derived fragments produced in plasma over a 4-hour circulation period in rats with nonfiltering kidneys. CONCLUSIONS: This study demonstrates that albumin fragments, which are produced by the kidney and not by extrarenal sources, are exclusively excreted in the urine. Exogenous albumin peptides were able to specifically exert a competitive effect on the renal enzyme cleavage of intact albumin.

Animals↗
PubMed2002

Albuminuria in hypertension is linked to altered lysosomal activity and TGF-beta1 expression.

Increased intraglomerular pressure is considered a major factor for increased albumin excretion in hypertension. However, other factors should also be considered because recent studies in both humans and rats have demonstrated that proteins undergoing filtration and renal passage are extensively modified by renal cell lysosomal processing; >95% of albumin is degraded to peptides that are not detected by routine immunochemical assays. Changes in postglomerular lysosomal processing may therefore be responsible for the increased intact albumin excreted in hypertension-related kidney disease. We hypothesize that transforming growth factor-beta, which is known to decrease lysosomal activity, may be upregulated in hypertension and may play a role in increased intact albumin excretion. The aims of this study were to determine the effect that hypertension has on (1) renal cell lysosomal processing of albumin and dextran sulfate, (2) glomerular permeability, and (3) renal transforming growth factor-beta(1) expression. Spontaneously hypertensive rats and Wistar-Kyoto rats were used at 8, 16, and 24 weeks. We demonstrate that albuminuria in hypertension is linked to an inhibition of lysosomal processing as determined by (1) size exclusion chromatography analysis of urinary [(14)C]albumin structural integrity and (2) ion exchange analysis of urinary [(3)H]dextran sulfate. This inhibition gives rise to an increased proportion of radioimmunoassay detectable (intact) albumin and intact dextran sulfate independent of changes in glomerular capillary wall permeability as determined by the fractional clearance of [(3)H]Ficolls of various radii. These changes may be correlated with increased renal transforming growth factor-beta(1) expression.

Albuminuria↗
PubMedDate not supplied

Nephrotic-like proteinuria in experimental diabetes.

AIMS/HYPOTHESIS: Streptozotocin (STZ) diabetic rats are characterized by the development of albuminuria. It is not known, however, whether the excess excretion of protein is primarily due to intact protein or protein fragments or whether it is specific for albumin or occurs for all high-molecular-weight plasma proteins. To test this we have measured the excretion rates and fractional clearances of [(14)C]albumin, [(3)H]immunoglobulin G and [(3)H]transferrin in diabetic rats. METHODS: The radiolabeled proteins were delivered to the circulation of conscious diabetic (STZ induced for 6 weeks) and control rats by ALZET osmotic pumps. The plasma level of the radiolabeled proteins reached steady-state levels by day 7. Urine and plasma samples from day 7 were used to determine the excretion rates of the proteins by radioactivity and radioimmunoassay. RESULTS: When excretion rates were determined by radioactivity it was apparent that only the albumin excretion rate increased significantly with STZ diabetes to a value of 354 +/- 166 microg/min which agrees with proteinuria determined by Biuret assay of 299.9 +/- 52.4 microg/min. The major proportion of protein being excreted was in the form of protein fragments which are not detected by conventional immmunochemical assays. CONCLUSION: The previously unrecognized nephrotic-like levels of proteinuria in experimental diabetes appears to be associated with an albumin-specific mechanism responsible for the increase in albumin peptides in urine. There was significant lowering of plasma albumin concentration but plasma concentrations of transferrin and immunoglobulin G remained unchanged. There was also no significant appearance of intact protein in urine that is normally found in nephrotic states.

Animals↗
PubMedDate not supplied

Renal processing of albumin in diabetes and hypertension in rats: possible role of TGF-beta1.

BACKGROUND/AIMS: Recent studies show that albuminuria may be the result of changes in post-glomerular cellular uptake and processing of albumin. This study aims to determine whether this processing is disrupted in diabetes and/or hypertension. METHODS: Diabetes (d) was induced using streptozotocin in spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto rats (WKY) and studied after 8, 16 and 24 weeks of disease. Intact albumin excretion was determined by radioimmunoassay. Total albumin was determined by [(14)C]albumin. Lysosomal activity was determined by dextran sulfate desulfation. Renal TGF-beta1 and transforming growth factor-beta1 inducible gene-h3 mRNA (betaig-h3) expression was determined by real time RT-PCR. RESULTS: SHR-c rats exhibited an increase in intact albuminuria without significant change in total albumin excretion (intact plus albumin-derived peptides). For WKY-d rats, intact albuminuria developed initially, followed by an increase in total albumin excretion primarily in the form of albumin peptides (peptiduria). SHR-d rats exhibited both increases in peptiduria and intact albuminuria. There was no increase in glomerular permeability at 24 weeks for polydisperse [(3)H]Ficoll in all groups. Increased renal TGF-beta1 and betaig-h3 expression was correlated with a decrease in dextran sulfate desulfation and increased intact albuminuria independent of peptiduria. CONCLUSION: Increased albumin excretion in hypertension and/or diabetes is manifested in different forms independent of glomerular permeability.

Albumins↗