Microelectrophoresis in the differential diagnosis of proteinuric diseases

Microelectrophoresis and auxilary micromethods

In this retrospect of approximately 30 years of work with micromethods, some of them developed in our own laboratory, their principles and application to different separation problems are described, such as one- and two-dimensional microelectrophoresis in capillaries and microslab gels, isoelectric focusing in capillaries or microslab gels, microchromatography, microphotometry, and microfluorometry for qualitative and quantitative evaluation of separation patterns. In addition, some useful auxiliary methods are also described, e.g., a method for quantitative protein determination in a microliter volume when neither the volume nor the protein content in that volume are known, and methods for the determination of glycoproteins, amino acids, and sugars in the picomole range.

Clinical analysis of human urinary proteins using high resolution electrophoretic methods

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.

The relationship between urinary Tamm-Horsfall glycoprotein excretion and urinary activity of glycosidases in normal pregnancy and pre-eclampsia

Electrophoretic analyses of the urinary proteins of pre-eclamptic patients revealed a decrease in the staining intensity of the protein band representing the Tamm-Horsfall glycoprotein (THP). In the present study the quantitative analysis of the THP excretion rate and the urinary activity of THP oligosaccharide metabolizing glycosidases were investigated. The median THP excretion rate of non-pregnant women (n = 24) was 20 mg/g creatinine (crea.). An increase in the THP excretion rate was seen in pregnancy to a level between 43 mg/g crea. (II. trimester) and 32 mg/g crea. (III. trimester) (n = 29). Hypertension in pregnancy was associated with a decrease in the THP excretion rate to 9 mg/g crea. (n = 85). Post partum, a transient elevated THP excretion rate up to 109 mg/g crea was recorded in the group of hypertensive patients. The urinary activities of the lysosomal beta-mannosidase, alpha-fucosidase, alpha-mannosidase (pH 4.5) and beta-galactosidase increased in normal pregnancy. This effect was most pronounced in the beta-galactosidase activity which increased from 50 U/mg crea. before pregnancy to 280 U/mg crea. at term. Hypertension in pregnancy was associated with a further increase in the activities of the lysosomal glycosidases. In the case of the beta-galactosidase a significant rise from 68 to 310 U/mg crea. was found. The urinary activity of the alpha-mannosidase (pH 5.5) originating from the Golgi apparatus was only elevated in patients with severe pre-eclampsia. Casuistic post partum recordings demonstrated that an elevation of the lysosomal glycosidases activities was followed by a transient increase in the THP excretion rate.

Elevated plasma levels of the immunosuppressive complement fragment Ba in renal failure

The complement fragment Ba is a 33 kD activation product of factor B which suppresses human B-lymphocyte functions in vitro. We report that plasma levels of Ba are highly elevated in patients with chronic renal failure (4.84 +/- 3.58 micrograms/ml) and in patients with end-stage renal disease undergoing regular hemodialysis (16.1 +/- 6.1 micrograms/ml) as compared to normals (1.01 +/- 0.30 micrograms/ml). Ba levels were strictly correlated with the creatinine clearance. The urinary excretion of Ba was 165-fold higher in patients with tubular proteinuria than in normals. These results indicate that the kidney is the major catabolic site for Ba. In addition, direct evidence was obtained for an enhanced turnover of the alternative pathway of complement in renal failure that, although it appears to be less important than the renal retention of Ba, contributes to elevated Ba plasma levels in these patients. Ba concentrations in dialysis patients who responded to hepatitis B vaccination were significantly lower than in non-responders. Furthermore, the in vitro IgM synthesis by purified mononuclear cells was negatively correlated with Ba concentrations determined in the plasma of these patients. These results suggest that the accumulation of Ba contributes to the defective immune response in patients with renal failure.

Sodium dodecyl sulphate electrophoresis of urinary proteins

The analysis of urinary proteins and their identification are discussed, particularly in regard to the technique of sodium dodecyl sulphate electrophoresis in polyacrylamide gradient gels. Urine collection, storage and preparation are evaluated, especially in regard to problems connected with concentration and dialysis of such samples. The instrumental approach to sodium dodecyl sulphate polyacrylamide gel electrophoresis represented by the Phast System appears to be particularly valuable in routine clinical analysis of urine specimens, since no sample pretreatment is required. The following types of proteinurias are evaluated: (a) orthostatic proteinurias; (b) post-renal proteinurias; (c) Bence-Jones proteinuria; (d) lower and upper urinary tract infection (cystitis and pyelonephritis) and (e) diabetes mellitus proteinurias.

Postischemic diagnostic localization of tubular lesions

Several functional parameters were applied in an experimental model of ischemia to test the ability to localize the distribution of tubular lesions. Canine kidneys were perfused with protective solutions and rendered ischemic for definite periods. Renal function was determined during a subsequent 3-h reperfusion. The pattern and the extent of renal injury were influenced by varying the duration of ischemia and by modifying the protective solution used. The results suggest that by employing an appropriate selection of parameters it is possible to allocate renal injury to definite sections of the tubules. According to such an evaluation, under protection with HTK-solution, the proximal tubule limits the tolerance of renal ischemia. The thick ascending limb shows some vulnerability that is aggravated by disadvantageous modifications of the protective solution and that may become more pronounced in the course of reperfusion. In contrast, more distal parts of the nephron retain a remarkable reserve transport capacity after a tolerable level of ischemia.

Essential problems in quantification of proteins following colloidal staining with coomassie brilliant blue dyes in polyacrylamide gels, and their solution

Quantitative determination of stained proteins following polyacrylamide gel electrophoresis (PAGE) is of increasing interest especially since computer-aided densitometers have become available as well as recipes for sensitive and background-free staining with Coomassie Brilliant Blue dyes. However, avoidance of separation artifacts is not the only essential prerequisite for quantitative evaluation. The local particle density of a protein in a given gel is of critical importance since it determines its stainability. Depending on local protein concentration, the dye binding to the same amount of a given protein differs considerably. Since the stainability of proteins using colloidal staining procedures, as with Coomassie Brilliant Blue dyes, is time-dependent and, in addition, also dependent on the pore size of a given polyacrylamide gel used for PAGE, calibration curves for quantitative determinations have to be prepared in polyacrylamide gels of the same composition as used for PAGE. Staining conditions also have to be identical for calibration gels and gels under analysis. If, however, a set of calibration curves is prepared for different staining times, it is possible to calculate a generalized calibration curve, allowing for quantitative evaluation with flexible staining time. Furthermore, and in consequence of the implications due to particle density, quantitative determination via densitometry is only possible by determining the protein amount of each single measuring point (pixel) via its absorbance on the basis of a calibration curve. Since the particle density is inherent in a calibration curve, the final summation of the protein amount per pixel will give values close to reality.

Early detection of renal dysfunction: practical recommendations

Test programmes for early detection of renal dysfunction are urgently needed. They should be adapted to the population under investigation, whether the general population or an occupationally or medically exposed population. At present, there is no clinically relevant definition of renal dysfunction on the basis of pathological test results. Due to the complex function and structure of the kidney, measurement of a single parameter is not sufficient for early detection of renal dysfunction. However, any prophylactic and prospective protocol should take into account the sensitivity and specificity of the applied tests, the amount of work involved and the possible positive effects for the population at risk.

Urinary protein electrophoresis profile in normal and hypertensive pregnancies

By using of modified urine preparation and a highly sensitive SDS-polyacrylamide gel electrophoresis (SDS-PAGE) we determined the urinary protein profile in 21 healthy males, 25 healthy females, 64 patients with uncomplicated pregnancy and 110 hypertensive pregnant women. The urinary protein patterns were similar in controls and in women with a normal pregnancy. There were no increase in the number of protein bands from the 1st trimester to term, and the electrophoresis pattern did not change in the postpartum period. In both groups, an intensively stained protein band with an apparent molecular weight of 105 kD was detected. The 105 kD band was significantly reduced or completely absent in 91 (83%) out of 110 hypertensive pregnant women. The urinary protein electrophoresis profile correlated significantly with the severity of the disease. The 105 kD band disappeared just before or simultaneously with the onset of clinical symptoms in 18 out of 32 hypertensive pregnant women followed throughout pregnancy. Postpartum the 105 kD in urine reappeared at 2 to 14 days after delivery in 49 of the 53 patients. Using a silver staining and Western blot, the 105 kD band was identified as Tamm-Horsfall protein, which is identical to the immunosuppressive glycoprotein uromodulin. The findings in the SDS-PAGE may reflect a transitory tubular dysfunction in cases of pre-eclampsia, which is usually reversible after delivery. The results of our study support the hypothesis of an immunological basis for this disorder.

[Urinary proteins as indicators of diabetic nephropathy]

During the last ten years, several studies proved the applicability of urinary albumin quantification in the early diagnosis of diabetic nephropathy. Owing to its high accuracy and its comparable low methodological effort, only the albumin determination was emphasised. Parallel studies of urinary protein patterns, however, using sodium dodecylsulfate-polyacrylamide gel-electrophoresis demonstrated the increased excretion of other high- and low-molecular mass proteins in different stages of diabetic nephropathy. Consequently an extension of the mere albumin assay including a macromolecular (e.g. transferrin) and a micromolecular (e.g. alpha-1-microglobulin) protein seems meaningful. According to this study, both methodological lines (combined quantitative and qualitative analysis, respectively) are useful tools in the early detection and the follow up of diabetic nephropathy.

Urinary protein analysis

The differentiation and analysis of urinary proteins has substantially contributed to our knowledge of physiological and pathophysiological processes during glomerular filtration and tubular catabolism of plasma constituents. By use of high-resolution biochemical separation techniques, several urinary polypeptides could be identified as plasma proteins, tissue antigens, tubular enzymes and protein breakdown products. With regard to clinical application, the separation results of conventional gel chromatography and agarose electrophoresis were surpassed by fast protein liquid chromatography and polyacrylamide electrophoresis in one- and two-dimensional systems. In contrast to early one-dimensional polyacrylamide gel electrophoresis (PAGE) methods using homogeneous gels on a macro scale, modern gradient slab gels achieve better resolution over the entire relative molecular mass range of urinary proteins. For clinical demands, the use of micro-scale gradient gels, either laboratory-made or pre-cast, together with an improved Coomassie Brillant Blue staining, offers several advantages, including rapidity, sensitivity and economy. Isoelectric focusing and two-dimensional PAGE, combined with sensitive silver staining and immunoblotting methods, have proved to be valuable tools for the identification and characterization of urinary proteins in defined renal and extra-renal diseases. The quantitative determination of urinary indicator proteins such as albumin and alpha 1- and beta 2-microglobulin can be regarded as a reasonable complement to the pattern diagnosis, especially in the long-term course of renal diseases.