Evaluation of patterns of urinary proteins by SDS-PAGE in rats of different ages

Excessive amount of lactose in the diet of two-week-old calves induces urinary protein changes

Abstract. The present paper was undertaken to analyse and identify urinary proteins that were significantly altered in urine of calves in response to short-term administration of milk replacer with lactose addition. We used 2-D electrophoresis combined with matrix-assisted laser desorption/ionisation and time-of-flight (MALDI-TOF) mass spectrometry. Of all spots analysed, four showed significantly decreased abundance: alpha-1-antiproteinase (A1AT), serotransferrin (TF), sex hormone-binding globulin (SHBG) and cytochrome P450 2E1 (CYP2E1). One displayed an increased abundance: adenosine triphosphate (ATP)-citrate synthase. The changes in abundance of SHBG and CYP2E1 proteins were caused by the direct effect of an oversupply of sugar, while A1AT, TF and ATP-citrate synthase showed altered abundance probably due to indirect effects. The results of this study confirmed that calves' urine is a very precious biological material to evaluate the renal function, and it may be valuable in veterinary and zootechnical diagnostics.

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.

The human urinary proteome reveals high similarity between kidney aging and chronic kidney disease

Aging induces morphological changes of the kidney and reduces renal function. We analyzed the low molecular weight urinary proteome of 324 healthy individuals from 2-73 years of age to gain insight on human renal aging. We observed age-related modification of secretion of 325 out of over 5000 urinary peptides. The majority of these changes were associated with renal development before and during puberty, while 49 peptides were related to aging in adults. We therefore focussed the remainder of the study on these 49 peptides. The majority of these 49 peptides were also markers of chronic kidney disease, suggesting high similarity between aging and chronic kidney disease. Blinded evaluation of samples from healthy volunteers and diabetic nephropathy patients confirmed both the correlation of biomarkers with aging and with renal disease. Identification of a number of these aging-related peptides led us to hypothesize that reduced proteolytic activity is involved in human renal aging. Finally, among the 324 supposedly healthy individuals, some had urinary aging-related peptide excretion patterns typical of an individual significantly older than their actual age. In conclusion, these aging-related biomarkers may allow noninvasive detection of renal lesions in healthy persons and show high resemblance between human aging and chronic kidney disease. This similarity has to be taken into account when searching for biomarkers of renal disease.

Accelerated NaCl-induced hypertension in taurine-deficient rat: Role of renal function

Taurine modulates blood pressure and renal function. As the kidney plays a pivotal role in long-term control of arterial pressure, we tested the hypothesis that taurine-deficient rats display maladaptive renal and blood pressure responses to uninephrectomy. Control and taurine-deficient (i.e., beta-alanine-treated) rats with either one or two remaining kidneys were fed diets containing basal or high (8%) NaCl diet. Urine osmolality was greater in the taurine-deficient than controls fed a normal NaCl diet; proteinuria and blood pressure were unaffected by uninephrectomy. Following 6 weeks on an 8% NaCl diet, the uninephrectomized (UNX) animals developed significant hypertension, which was more severe in the taurine-deficient group; baroreflex function was unaffected. However, the UNX taurine-deficient rats displayed impaired ability to dispose of an acute isotonic saline volume load before a switchover to a high NaCl diet. Nonetheless, a more protracted exposure (i.e., 14 weeks) to dietary NaCl excess eliminated the blood pressure differential between the two groups; at this stage, renal excretory responses to an acute saline volume load or to atrial natriuretic peptide were similar in the two groups. Nonetheless, hypertensive taurine-deficient rats displayed greater proteinuria, although both groups excreted proteins of similar molecular weights ( approximately 15-66 kDa). Further, taurine-deficient kidney specimens displayed periarterial mononuclear cell infiltrates with strong immunoreactivity to the histiocyte marker CD68, suggestive of increased phagocytic activity. In conclusion, taurine deficiency modulates renal adaptation to combined uninephrectomy and dietary NaCl excess, resulting in an accelerated development of hypertension.

Glomerular hyperfiltration and hypertrophy in the rat hypoplastic kidney as a model of oligomeganephronic disease

BACKGROUND

Rat male hypogonadisim (hgn/hgn) is accompanied by bilateral hypoplastic kidney (HPK). The HPK contains a reduced number of nephrons that progress to chronic renal failure. In this study, we describe the renal pathophysiology in adult HPK rats as a potential model of oligomeganephronic disease.

METHODS

Urine and blood samples were collected from adult male HPK rats and phenotypically normal littermates at 70 days of age for measurements of urea-nitrogen and creatinine clearances (Cun and Ccr). Glomerular number (GN) and glomerular projective area were determined using the maceration method. Blood pressure was measured. Urinary protein and renal histology were examined. Urinary albumin concentration was determined at early postnatal ages.

RESULTS

Renal weight was significantly smaller in adult HPK males than in normal males. Polyuria and polydipsia were observed in HPK rats. Ccr and Cun were low in HPK rats compared with those in normal rats. The HPK contained only 20% of the nephrons present in normal kidneys. The Cun and Ccr divided by GN (average values of single nephron Cun and Ccr) of HPK rats were about two and four times greater than normal levels, respectively. This hyperfiltration was not accompanied by systemic hypertension, but was associated with marked glomerular hypertrophy and glomerulosclerosis, which were observed mainly in the inner cortex. A considerable heterogeneity of glomerular size was found in HPK and most glomeruli of surface nephrons retained normal size and histology. A remarkable leakage of albumin into urine was found at 35 and 70 days of age.

CONCLUSIONS

The HPK rat is a useful model for studying the pathophysiology of oligomeganephronic disease as well as glomerular hyperfiltration and hypertrophy induced by severe congenital reduction of nephrons.

On the nature of proteinuria with acute renal injury in patients with chronic kidney disease

Albuminuria is an excellent marker of cardiovascular and renal prognosis. Commercially available tests of immunodetectable albumin in the urine may not identify posttranslationally modified albumin that makes it undetectable to antibodies. Also, it is unclear whether albumin is degraded to smaller fragments, such as through proteolysis, in the course of acute renal injury. In 20 men with chronic kidney disease, we measured excretion rates of urinary protein (pyragallol red), immundetectable urinary albumin (immunoturbidimetry), and urinary total intact albumin (HPLC) after a single dose of 100 mg intravenous iron sucrose administered over 5 min. Fragmentation of urinary albumin and carbonylation of urinary proteins were assessed by immunoblotting. Results showed that iron infusion increased carbonylation of plasma and urinary proteins in a time-dependent manner. A transient increase in urinary excretion rates of total protein, immunodetectable urinary albumin, and total intact albumin was seen. Fragmentation and loss of immunoreactivity of albumin paralleled the changes in total protein excretion. In conclusion, fragmentation, loss of immunoreactivity, and oxidation of albumin in a time-dependent manner may underestimate the extent of injury with the immunoreactive microalbumin assay. Measurement of total intact albumin may better quantify acute renal injury.

Earlier detection of microalbuminuria in diabetic patients using a new urinary albumin assay

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.

Differences in urinary albumin detected by four immunoassays and high-performance liquid chromatography

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.

Albumin fragments in normal rat urine are derived from rapidly degraded filtered albumin

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.

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.

Post-translational modification of transthyretin in plasma

To determine the behavior of transthyretin (TTR) in blood circulation, TTR purified from normal subjects' plasma was injected to rats, and blood and urine were collected time dependently. Although TTR in plasma was proven to be a predominantly cysteine (Cys) conjugated form by electrospray ionization mass spectrometry (ESI-MS) analysis, it was gradually converted into free, 32 Da (dihydroxylation), 80 Da (phosphorylation), and 306 Da (glutathionylation), increased forms in molecular weight of TTR. The plasma levels of TTR were decreased in a time-dependent manner with the half life of 72.4 min. No secretion of TTR into the urine was observed by ESI-MS. In conclusion, this method can be simply performed without loading a radioactive molecule to the targeted protein. It offers a possibility to determine natural protein behaviors in the blood stream.