Patient-specific microheterogeneity patterns of monoclonal immunoglobulin light chains as revealed by high resolution, two-dimensional electrophoresis

Free light chains in plasma of patients with light chain amyloidosis and non-amyloid light chain deposition disease. High proportion and heterogeneity of disulfide-linked monoclonal free light chains as pathogenic features of amyloid disease

Immunoglobulin light chain amyloidosis (AL) and non-amyloid light chain deposition disease (NALCDD) are different forms of protein aggregation disorders accompanied by a monoclonal gammopathy. Monoclonal free light chains (FLCs) are precursors of the pathological light chain tissue deposits that are fibrillar in AL and granular in NALCDD. However, direct biochemical examination of plasma FLC precursors, which would allow comparison and better understanding of these two diseases, is still lacking. In this study, we examined FLCs in plasma of patients with AL and NALCDD by employing separation on Sep-PaK C18 cartridges, micro-preparative electrophoresis, Western blotting and mass spectrometry. Comparative analysis of AL versus NALCDD and control plasma samples showed new evidence of increased level and heterogeneity of circulating disulfide-bound FLC species in AL. In addition to full length monomers comprising the disulfide-linked FLCs, the monoclonal disulfide-bound FLC fragments were typically revealed in AL plasma. We hypothesized that enhanced disulfide binding of FLCs in AL interferes with their normal clearance and metabolism, which in turn might play a role in amyloid formation. The applied methods might be useful to diagnose or predict the pathological form of the disease and shed light on the mechanisms involved in light chain aggregation in tissues.

A better understanding of molecular mechanisms underlying human disease

This review summarises and discusses the degree to which proteomics is contributing to medical care, providing examples and signspots for future directions. Why do genomic approaches provide a limited view of gene expression? Because of the multifactorial nature of many diseases, proteomics enables us to understand the molecular basis of disease, not only at the organism, whole-cell or tissue levels, but also in subcellular structures, protein complexes and biological fluids. The application of proteomics in medicine is expected to have a major impact by providing an integrated view of individual disease processes. This review describes several proteomic platforms and examines the role of proteomics as a tool for clinical biomarker discovery, the identification of prognostic and earlier diagnostic markers, their use in monitoring the effects of drug treatments and eventually find more efficient and safer therapeutics for a wide range of pathologies.

Charge differences between in vivo deposits in immunoglobulin light chain amyloidosis and non-amyloid light chain deposition disease

Immunoglobulin light chain amyloidosis (AL) and non-amyloid light chain deposition disease (NALCDD) are different forms of protein aggregation disorders that may occur in plasma cell dyscrasias with dysproteinemia. In systemic AL, the deposits are fibrillar and patchy in distribution, within and amongst different organs, whereas in NALCDD, the deposits are granular and diffusely distributed in systemic basement membranes, suggesting different mechanisms of aggregation and deposition. Previous evidence, that charge differences between the light chains in AL and NALCDD might account for their different phenotypes, prompted the present study, which compared the isoelectric points (pIs) of AL and NALCDD protein deposits extracted from human tissues. The pI profiles (5.2-8.8) of polypeptides in AL deposits were heterogenous in four cases, with a spread of both anionic and cationic isoforms; in contrast, in three of NALCDD the pI profiles (8.2-8.8) were homogeneous and restricted in the cationic range. These in vivo findings in human disease, together with other reported in vitro and in vivo experimental data, suggest that the fibrillar deposits in AL may form by electrostatic interaction between oppositely charged polypeptides, whereas the granular deposits in NALCDD form by the binding of cationic polypeptides to anionic proteoglycans sites in basement membranes.

The human plasma proteome: history, character, and diagnostic prospects

The human plasma proteome holds the promise of a revolution in disease diagnosis and therapeutic monitoring provided that major challenges in proteomics and related disciplines can be addressed. Plasma is not only the primary clinical specimen but also represents the largest and deepest version of the human proteome present in any sample: in addition to the classical "plasma proteins," it contains all tissue proteins (as leakage markers) plus very numerous distinct immunoglobulin sequences, and it has an extraordinary dynamic range in that more than 10 orders of magnitude in concentration separate albumin and the rarest proteins now measured clinically. Although the restricted dynamic range of conventional proteomic technology (two-dimensional gels and mass spectrometry) has limited its contribution to the list of 289 proteins (tabulated here) that have been reported in plasma to date, very recent advances in multidimensional survey techniques promise at least double this number in the near future. Abundant scientific evidence, from proteomics and other disciplines, suggests that among these are proteins whose abundances and structures change in ways indicative of many, if not most, human diseases. Nevertheless, only a handful of proteins are currently used in routine clinical diagnosis, and the rate of introduction of new protein tests approved by the United States Food and Drug Administration (FDA) has paradoxically declined over the last decade to less than one new protein diagnostic marker per year. We speculate on the reasons behind this large discrepancy between the expectations arising from proteomics and the realities of clinical diagnostics and suggest approaches by which protein-disease associations may be more effectively translated into diagnostic tools in the future.

Electrophoretic characteristics of monoclonal immunoglobulin G of different subclasses

Monoclonal IgG are commonly observed in various B cell disorders, of which multiple myeloma is the most clinically relevant. In a series of serum samples, we identified by immunofixation 73 monoclonal IgG, including 63 IgG(1), 4 IgG(2), 5 IgG(3), and 1 IgG(4). The light chains were of kappa type in 45 cases, and of lambda type in 28 cases. These monoclonal IgG were further characterized by high resolution two-dimensional polyacrylamide gel electrophoresis (2-DE) in various isoelectric focusing conditions, as well as by 3-DE (2-DE of the proteins extracted from agarose after serum protein agarose electrophoresis). After 2-DE, 38 out of 73 monoclonal gamma chains (52%) were visualized using immobilized pH 3-10 gradients for isoelectric focusing. In 6 cases (8%), gamma chains were only detected using alkaline immobilized pH 6-11 gradients. In 3 cases (4%), 3-DE revealed monoclonal gamma chains hidden by polyclonal gamma chains. Finally, in 26 cases (36%), no monoclonal gamma chains were clearly visualized. Sixty-one monoclonal light chains (84%) were detected using immobilized pH 3-10 gradients, whereas 12 (16%) were not. Monoclonal gamma chains and light chains were highly heterogeneous in terms of pI and M(r). However, a statistically significant correlation (P<0.05) was observed between the position of the monoclonal IgG in agarose gel and the pI of their heavy and light chains (R=0.733, multiple linear regression). Because of the extreme diversity of their heavy and light chains, it appears that a classification of monoclonal IgG based only on their electrophoretic properties is not possible.

Electrophoretic analysis of Bence Jones proteinuria

The electrophoresis of Bence Jones proteinuria (BJP) by urinary protein electrophoresis (UPE), immunoelectrophoresis (IE), immunofixation electrophoresis (IFE), sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), isoelectric focusing (IEF), two-dimensional electrophoresis (2-DE) and capillary electrophoresis (CE) is described. UPE, IE and IFE are briefly discussed as clinical laboratory methods for the detection and typing of free light chain (LC) whilst the high resolution electrophoretic methods (SDS-PAGE, IEF, 2-DE and CE) are considered in greater detail as research tools for molecular characterisation of free LC and its association with nephrotoxicity. Refinements of sample processing designed to improve the standardisation of analysis of BJP by high resolution electrophoretic methods are reported.

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.

Analysis of Bence Jones proteinuria by high resolution two-dimensional electrophoresis

Analysis of Bence Jones proteinuria by high resolution two-dimensional electrophoresis (2-DE) and immunoblotting reveals a complex pattern of light chain (LC) isoforms corresponding to the free monoclonal Bence Jones protein and its fragments. Replica blotting gives duplicate blots for LC typing (lambda, chi) and, under the conditions employed, leaves sufficient protein for Coomassie Blue staining of the urinary protein profile and pIIMr determination of the LC isoforms. Carrier ampholytes (CAs, in our "simplified" 2-DE system) and immobilised pH gradients (IPGs, in the Multiphor 2-DE system) give similar LC isoform patterns. Artifacts, including cone-like distortions and trailing "piggyback" spots, are visualised with both 2-DE systems. IPGs are advantageous as they allow reproducible detection of strongly basic LC isoforms by isoelectric focusing (under equilibrium conditions) without recourse to CA nonequilibrium pH gradient electrophoresis.

A rapid ELISA test for detection of human paraproteins

A rapid ELISA test for detection, characterization and quantification of human paraproteins was developed. The proposed method is a sandwich ELISA, where the capture antibody is specific for a given heavy chain (gamma, alpha or mu) and the labelled antibody is specific either for kappa or for lambda light chain. Both standard and patient sera are tested with all six possible antibody combinations. Each paraprotein produces a significant increase in titre (as compared with standard) only when tested with the relevant pair of antibodies. This enables the determination of the isotype and light chain type of the paraprotein and the evaluation of its relative quantity in patient serum. The accuracy of the assay (relative deviation) varies from 0.04 for gamma lambda to 0.19 for alpha kappa. The cut-off values for each type of polyclonal immunoglobulin were determined with 200 healthy donor sera. 103 patient sera were analysed. ELISA data are in good agreement with M-component and other clinical data.

Clinical applications of two-dimensional electrophoresis

Two-dimensional electrophoresis is increasingly being used as an important tool for biological research although it continues to have few direct clinical applications. In the absence of simple systems to identify and quantify individual proteins or groups of proteins it is unlikely that clinical applications will increase. Measurement of some individual proteins, for example a single acute phase reactant, often yields as much clinically useful information as could be currently expected from quantitation of several proteins with the same physiological role. Cost-containment pressures within the clinical laboratory will prevent the technique from becoming widely used in the clinical laboratory until it can clearly demonstrate that it can produce clinically important and necessary information that can not be obtained by other means. We continue to believe that the technique's greatest potential lies in identifying a protein or proteins whose concentration can be correlated with a disease and whose concentration varies with the progress of the disease. Antibodies to such proteins can then be produced and used to quantify the disease-associated proteins by a simple procedure, such as nephelometry. In spite of our belief of the likely clinical application of the technique there appears to be no systematic use of two-dimensional electrophoresis for this purpose. With clinical specimens a few investigators still run gels of serum or urine from patients with apparently unusual disorders and compare them visually with gels from healthy individuals. Nevertheless, the technique continues to have considerable unmet promise for clinical applications.

Two-dimensional gel electrophoresis of four serum samples from patients with IgD myeloma

Sera containing IgD paraprotein present problems in identifying patients with monoclonal gammopathies because only a small or even no spike may be present on standard serum protein electrophoresis. We have detected heavy chains of IgD monoclonal protein by means of high resolution two-dimensional gel electrophoresis. Besides clearly identifying delta heavy chains in maps of serum proteins, we also found size and charge heterogeneity of monoclonal immunoglobulins. The results demonstrate the usefulness of two-dimensional gel electrophoresis in the analysis of selected cases of immunoglobulin malignancies.