Cellulose acetate membrane electrophoresis in the analysis of urinary proteins in patients with tubulointerstitial nephritis

Rapid glycosylation analysis of mouse serum glycoproteins separated by supported molecular matrix electrophoresis

Previously, we developed a novel separation technique, namely, supported molecular matrix electrophoresis (SMME), which separates mucins on a PVDF membrane that impregnated with a hydrophilic polymer (such as polyvinyl alcohol), so it has the characteristics that are compatible with glycan analysis of the separated bands. Here, we describe the first instance of the application of SMME to mouse sera fractionation and demonstrate their differences from the pooled human sera fractionation by SMME. Furthermore, we have developed a fixation method for the lectin blotting of SMME-separated glycoproteins by immersing the SMME membranes into acetone solvent followed by heating. It showed that the amount of protein samples required for SMME were reduced more than 4-fold than that of the process of SDS-PAGE. We applied these techniques for the detection of glycosylation patterns of serum proteins from Fut8^+/+ and Fut8^-/- mice, further analyzed N-linked and O-linked glycans from the separated γ-bands by mass spectrometry, and demonstrated that there are α2,8-sialylated O-glycans contained in mouse sera glycoproteins. SMME can provide simple, rapid sera fractionation, glycan profiling differences between the bands of two samples and a new insight into the underlying mechanism that responsible for related diseases. SIGNIFICANCE: We describe that the first application of SMME can separate mouse serum proteins into six bands and identify the major protein components of each fraction in mouse serum separated by SMME. Furthermore, we successfully developed a fixation method for lectin blotting of SMME-separated glycoproteins and applied to the detection of glycosylation patterns of serum glycoproteins from Fut8^+/+ and Fut8^-/- mice, also, the method is promising for detecting glycan profiling differences between two samples in both research and clinical settings.

Cellulose Acetate Electrophoresis of Hemoglobin

The electrophoresis on cellulose acetate membrane is most widely used because of its simplicity, and is without the use of any sophisticated instrument other than electrophoresis apparatus and the cellulose acetate strip. Here we describe a modified version of cellulose acetate membrane electrophoresis for hemoglobin separation from blood sample. Sharp, clear bands without tailing effects can be obtained with this method. The method and apparatus described here would be appropriate to separate protein fractions under 1 h at voltages up to 60 V/cm measured between the electrodes.

Cellulose Acetate Membrane Electrophoresis Based Urinary Proteomics for the Identification of Characteristic Proteins

BACKGROUND

Analysis of urinary proteins using cellulose acetate membrane electrophoresis (CAME) is a useful and challenging method for the recognition of damaged sites in the kidney. However, protein content of each CAME fraction is still not completely understood.

METHODS

In this study, an effective method of protein extraction from each band fractionated by CAME was established, which enabled us to examine the extracted proteins by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and mass spectrometry.

RESULTS

Proteins were extracted from the gel and analyzed by mass spectrometry. In all, 31 proteins were identified, including 20 urinary proteins that were newly identified in the CAME-based analysis.

CONCLUSION

This methodology was useful for identifying the proteins responsible for creating unique bands on CAME in a urine sample of a patient with drug-induced interstitial nephritis. These findings provide in-depth characterization of urinary protein contents in each CAME fraction.

Biochemistry and Clinical Role of Human Cystatin C

Low molecular-mass plasma proteins play a key role in health and disease. Cystatin C is an endogenous cysteine proteinase inhibitor belonging to the type 2 cystatin superfamily. The mature, active form of human cystatin C is a single non-glycosylated polypeptide chain consisting of 120 amino acid residues, with a molecular mass of 13,343-13,359 Da, and containing four characteristic disulfide-paired cysteine residues. Human cystatin C is encoded by the CST3 gene, ubiquitously expressed at moderate levels. Cystatin C monomer is present in all human body fluids; it is preferentially abundant in cerebrospinal fluid, seminal plasma, and milk. Cystatin C L68Q variant is an amyloid fibril-forming protein with a high tendency to dimerize. It forms self-aggregates with massive amyloid deposits in the brain arteries of young adults, leading to lethal cerebral hemorrhage. The main catabolic site of cystatin C is the kidney: more than 99% of the protein is cleared from the circulation by glomerular ultrafiltration and tubular reabsorption. The diagnostic value of cystatin C as a marker of kidney dysfunction has been extensively investigated in multiple clinical studies on adults, children, and in the elderly. In almost all the clinical studies, cystatin C demonstrated a better diagnostic accuracy than serum creatinine in discriminating normal from impaired kidney function, but controversial results have been obtained by comparing this protein with other indices of kidney disease, especially serum creatinine-based equations. In this review, we present and discuss most of the available data from the literature, critically reviewing conclusions and suggestions for the use of cystatin C in clinical practice. Despite the multitude of clinical data in the literature, cystatin C has not been widely used, perhaps because of a combination of factors, such as a general diffidence among clinicians, the absence of definitive cut-off values, conflicting results in clinical studies, no clear evidence on when and how to request the test, the poor commutability of results, and no accurate examination of costs and of its routine use in a stat laboratory.

Increased urinary cystatin C reflects structural and functional renal tubular impairment independent of glomerular filtration rate

OBJECTIVES

The ratio of the urinary mass concentrations of cystatin C and creatinine (UcysC/Ucrea)>/=11.3 mg/mmol has recently been proposed as an accurate marker for the detection of GFR</=60 mL/min/1.73 m(2).

DESIGN AND METHODS

We prospectively evaluated the diagnostic performance of UcysC/Ucrea>/=11.3 mg/mmol and factors associated with increased UcysC/Ucrea in 72 children and adults with a wide variety of renal disorders. UcysC/Ucrea was calculated, and GFR wad estimated from serum creatinine and cystatin C by equations.

RESULTS

UcysC/Ucrea>/=11.3 mg/mmol had a low diagnostic value to detect GFR values</=60 mL/min/1.73 m(2) estimated by creatinine or cystatin-C-based equations with sensitivities of 72% and 63%, and specificities of 42% and 34%. ROC curves for UcysC/Ucrea to detect GFR</=60 mL/min/1.73 m(2) confirmed this with AUCs of 0.59 for creatinine and 0.57 for cystatin-C-based equations. Multivariate analysis identified tubular proteinuria, tubulointerstitial disease and heavy proteinuria, but not GFR</=60 mL/min/1.73 m(2), as factors independently associated with increased UcysC/Ucrea.

CONCLUSIONS

UcysC/Ucrea>/=11.3 mg/mmol is not an accurate marker to detect GFR</=60 mL/min/1.73 m(2), but reflects tubular dysfunction and proteinuria due to heavy proteinuria and tubulointerstitial disease.

Urinary Cystatin C as a Marker of Tubular Dysfunction

Cystatin C (CysC) is a nonglycosylated 13 KD protein that belongs to the type II cystatin gene family. It is a strong inhibitor of cysteine proteinases, freely filtered by the kidney glomerulus and reabsorbed by the tubulus, where it is almost totally catabolized. Remainder of the nonmetabolized CysC is eliminated in urine and may represent a useful marker of tubular dysfunction. The aim of the study was to confirm the clinical importance of the quantitative determination of CysC by an automated immunonephelometric method (DADE Behring). Two groups of patients were examined: one with glomerular (GD, n=36) and one with tubular dysfunction (TD, n=31), and compared with the control group (CG, n=31) of healthy males and females from laboratory personnel (n=11) and patients on routine systematic examination (n=20), from 25 to 58 years old. The patient groups were categorised according to the urine analysis of total proteins, creatinine and adequate proteins electrophoretic panel. CysC concentration in CG was in the range of 0.02-0.15 mg/L; 0.01-0.48 mg/L and 0.25-18 mg/L in GD and TD groups respectively. Values of means ± SD for patient groups (GD=0.11 ± 0.14; TD=3.92 ± 3.75 mg/L) showed statistical significance (p<0.001) in the TD group in relation to GD and CG groups. It confirms that quantitative determination of CysC in one urine portion, with a fast laboratory method, might be a useful marker of tubular dysfunction, especially in emergency situations, taking into account that there is no interference of circadian variation on its concentration.

Cystatin C as a Marker of Renal Function in Kidney Transplant Patients

INTRODUCTION

Serum creatinine (sCr) is the most commonly used biochemical parameter for gauging kidney function, but, due to its limitations, it is not the ideal marker for glomerular filtration rate (GFR). Cystatin C (sCyC) appears to be an endogenous marker of GFR.

AIM

To assess the use of sCyC as a marker of renal function in kidney transplant patients, we compared it with sCr and with creatinine clearance either in a 24-hour urine or calculated using the Cockroft-Gault formula.

METHODS

Among 78 patients (62.8% men, 37.2% women) undergoing kidney transplantation (average age 44.87 +/- 13.37 years) we determined at 2, 5, 7, 15, and 30 days, and 6, 12 and 18 months after kidney transplantation: sCr (using the Jaffé colorimetric method), sCyC (immunonephelometry), creatinine clearance with a 24-hour urine, creatinine clearance using the Cockroft-Gault formula.

RESULTS

During the first 30 days following transplantation, there was a progressive decline in sCr levels. sCyC increased up to the fifth day, coinciding with the highest doses of steroids, and then decreased. At 6, 12, and 18 months, there was a correlation between sCyC and sCr, creatinine clearance in a 24-hour urine or calculated with the Cockroft-Gault formula (R = 0.859; R = -0.713, and R = -0.684, respectively, P < .001.)

CONCLUSIONS

sCyC is an endogenous marker of GFR. Its limitations relate to its being affected by the high doses of steroids in the first days following transplantation. In the 18-month posttransplant period, it correlated with creatinine clearance in a 24-hour urine or calculated by the Cockroft-Gault formula.

Examination of the molecular diversity of alpha1 antitrypsin in urine: deficit of an alpha1 globulin fraction on cellulose acetate membrane electrophoresis

In the clinical field of nephrology, a noninvasive approach employing the analysis of electrophoretic patterns in urinary protein has been established. In this study a total of 52 urine samples with IgA nephropathy (IgAN), anti-neutrophil cytoplasmic antigen-associated crescentic glomerulonephritis (GN), and other types of GN were analyzed. Patients with high alpha1 globulin (alpha1G) fractions, which contained alpha1AT in cellulose acetate membrane electrophoresis (CAE), tended to have alpha1 antitrypsin (alpha1AT) of normal molecular weight (57 kDa and 49 kDa), while patients with a deficit alpha1G fraction tended to have alpha1AT of low molecular weight (<49 kDa) (P < 0.01). The alpha1G fraction was significantly higher in patients with IgAN, and there were significantly more patients with normal molecular weight alpha1AT compared to patients with other diseases (P < 0.01). The isoelectric point of alpha1AT with lower-weight molecules was more on the alkali side compared to higher-weight molecules in two-dimensional electrophoresis. Detecting changes in alpha1G fractions in CAE may support the differential diagnosis of IgAN from other types of GN.

Urinary protein fraction in healthy subjects using cellulose acetate membrane electrophoresis followed by colloidal silver staining

We previously reported a rapid and highly sensitive colloidal silver staining solution suitable for the cellulose acetate membrane. This method was useful for detecting even very small amounts of urinary protein. In the present study, we examined urinary protein fractions in healthy subjects, using cellulose acetate membrane electrophoresis (CAE) with a highly sensitive colloidal silver staining, in an attempt to determine the clinical relevance of urinary protein fractions. Sixty unconcentrated spot urine specimens were analyzed by CAE and calculated by densitometry. All of the samples were separated into five fractions by CAE. The mean +/- 1 SD of the percentage of five fractions was 28.37 +/- 8.51 in albumin, 4.30 +/- 4.19 in alpha1-globulin, 14.41 +/- 6.14 in alpha2-globulin, 19.45 +/- 7.10 in beta-globulin, and 33.46 +/- 8.24 in gamma-globulin. The albumin/globulin (A/G) ratio was 0.41 +/- 0.17. These six items and the concentrations of total protein, albumin, and beta-N-acetyl-D-glucosaminidase (NAG) did not significantly differ between males and females. NAG is the marker of tubulointerstitial nephropathy. The results suggest that there are no gender-dependent differences in the urinary protein fractions of healthy subjects.

Prognostic value of tubular proteinuria and enzymuria in nonoliguric acute tubular necrosis

BACKGROUND

Acute tubular necrosis (ATN) has high mortality, especially in patients who require renal replacement therapy (RRT). We prospectively studied the diagnostic accuracy of the urinary excretion of low-molecular-weight proteins and enzymes as predictors of a need for RRT in ATN.

METHODS

In 73 consecutive patients with initially nonoliguric ATN, we measured urinary excretion of alpha(1)- and beta(2)-microglobulin, cystatin C, retinol-binding protein, alpha-glutathione S-transferase, gamma-glutamyltransferase, lactate dehydrogenase, and N-acetyl-beta-D-glucosaminidase early in the course of ATN.

RESULTS

Twenty-six patients (36%) required RRT a median of 4 (interquartile range, 2-6) days after detection of proteinuria and enzymuria. Patients who required RRT had higher urinary cystatin C and alpha(1)-microglobulin [median (interquartile range), 1.7 (1.2-4.1) and 34.5 (26.6-45.1) g/mol of creatinine] than patients who did not require RRT [0.1 (0.02-0.5) and 8.0 (5.0-17.5) g/mol of creatinine]. Urinary excretion of cystatin C and alpha(1)-microglobulin had the highest diagnostic accuracies in identifying patients requiring RRT as indicated by the largest areas under the ROC curves: 0.92 (95% confidence interval, 0.86-0.96) and 0.86 (0.78-0.92), respectively. Sensitivity and specificity were 92% (95% confidence interval, 83-96%) and 83% (73-90%), respectively, for urinary cystatin C >1 g/mol of creatinine, and 88% (78-93%) and 81% (70-88%) for urinary alpha(1)-microglobulin >20 g/mol of creatinine.

CONCLUSION

In nonoliguric ATN, increased urinary excretion of cystatin C and alpha(1)-microglobulin may predict an unfavorable outcome, as reflected by the requirement for RRT.