Isoelectric points of urinary light chains in myelomatosis: analysis in relation to nephrotoxicity

Recent advances in the pathogenesis and management of cast nephropathy (myeloma kidney)

Multiple myeloma is an incurable plasma cell malignancy that is often accompanied by renal failure; there are a number of potential causes of this, of which cast nephropathy is the most important. Renal failure is highly significant in myeloma, as patient survival can be stratified by the severity of the renal impairment. Consequently, there is an ongoing focus on the pathological basis of cast nephropathy and the optimal treatment regimens in this setting, including effective chemotherapy regimens to reduce light chain production and emerging extracorporeal techniques to remove circulating light chains. This paper bridges recent advances in the pathogenesis and management of cast nephropathy in multiple myeloma.

Renal failure in myelomatosis

Renal failure is a common presenting feature in myelomatosis. This review offers a practical means for classifying renal failure in this disease. Three groups are identified: (1) those patients whose renal failure improves or is stable when they are maintained on a high fluid intake; (2) the minority of patients whose renal failure progresses despite high fluid intake; and (3) those patients who are fluid-intolerant due to oliguric renal failure or congestive cardiac failure. The difference between groups 1 and 2 is not simply due to differences in response to chemotherapy, for many group-1 patients achieve improvement in renal function without or before loss of light chain proteinuria. It is concluded that all patients with myelomatosis with excess monoclonal free light chain proteinuria are at risk from developing renal failure of the type associated with group 1. The chances of them doing so are diminished if they maintain a high fluid intake. Group 2 encompasses a range of conditions not all of which are clearly defined. There is generally a poor correlation between the physical characteristics of light chains and the presence of group-2 renal failure.

Renal manifestations of plasma cell dyscrasias: an appraisal from the patients' bedside to the research laboratory

One of the most prominent features of plasma cell dyscrasias is the frequent occurrence of renal dysfunction. Renal insufficiency is a common finding with elevated serum creatinine in more than 50% of patients with multiple myeloma at the time of diagnosis. Renal failure is the second most common cause of death in myeloma surpassed only by infections. The reasons for renal failure are multifactorial and early accurate diagnosis of the renal alterations may significantly impact morbidity and survival. Renal failure may result from selective glomerular, tubular interstitial, or vascular pathology or from a combination of pathologic events. The disorders associated with plasma cell dyscrasias include those characterized by monoclonal light chain deposition, encompassing AL-amyloidosis, in addition to the less well-characterized entities, such as heavy chain deposition disease and heavy chain amyloidosis. Therefore, it is more accurate to refer to them as monoclonal immunoglobulin deposition diseases. Staining of renal biopsy specimens for kappa and lambda light chains using immunofluorescence techniques and more sophisticated advanced diagnostic techniques such as immunoelectron microscopy permit detailed characterization of the various renal pathologic manifestations. Renal biopsies can identify monoclonal immunoglobulin deposition, and nephrologists have an opportunity to detect an underlying plasma cell dyscrasia early in its clinical course before overt hematologic alterations become manifest and irreversible renal damage has occurred. The overall spectrum of clinical and pathologic manifestations of monoclonal immunoglobulin deposition renal diseases has expanded considerably in recent years. Recent developments in the research arena promise new therapeutic interventions aimed at avoiding or ameliorating renal damage and even promoting reversal of some of the pathologic alterations. Currently, the 5-year survival rate in myeloma is 29% in white patients and 30% in African-American patients, a rather modest improvement from 24% in the 1970s. Bone marrow ablation followed by transplantation is available as an alternative mode of therapy that may be extraordinarily helpful in a subset of patients with early myeloma.

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.

Differential glycosylation of Bence Jones protein and kidney impairment in patients with plasma cell dyscrasia

Although Bence Jones protein (BJP) is generally accepted to be critically involved in the pathogenic process of kidney impairment in patients with myeloma, patients with BJP do not always have kidney dysfunction. As proteins often undergo glycosylation and alter their molecular nature, it is expected that the heterogeneity in kidney dysfunction can be explained at least partly by the differential affinity to the kidneys of BJP dependent on its glycosylation. Accordingly, we analyzed the structures of carbohydrates of urine BJP biochemically to correlate the structure with kidney function. BJP was obtained from 16 patients with myeloma, 2 patients with light chain amyloidosis, a patient with plasma cell leukemia, and a patient with Waldenstrom's macroglobulinemia. All BJP had five forms of oligosaccharides: three forms of biantennary oligosaccharides and two forms of triantennaries. The three biantennaries correspond to previously reported oligosaccharides on only lambda-type BJP, whereas the triantennaries are novel oligosaccharides found on BJP. Among the five oligosaccharides, the triantennary oligosaccharide Gal(beta)1-4GlcNAc(beta)1-2Man(alpha)1-6 [Gal(beta)1-GlcNA(beta)1-4(Gal(beta)1-4GlcNAc(beta) 1-2)Man(alpha)1-3]Man(beta)1-4GlcNAc(beta)1-4GlcNAc showed a significant negative correlation with the serum creatinine level (p = 0.015 by Spearman's correlation test, R = 0.744). Thus determination of BJP glycosylation may be useful for the evaluation of kidney impairment in patients with BJP.

Protease resistance and binding of Ig light chains in myeloma-associated tubulopathies

Kidney tubule dysfunction and lesions are frequent complications of myeloma, related to unknown properties of the monoclonal light chain. We have analyzed protease sensitivity and binding properties of urinary light chains from four patients with Fanconi's syndrome, 12 with cast nephropathy, and four control patients without myeloma-associated tubulopathy. All light chains were normal-sized, monomeric and/or dimeric, and none was N-glycosylated. Kinetic studies of light chain digestion by pepsin and the lysosomal enzyme cathepsin B showed the generation of a protease-resistant 12 kDa fragment, corresponding to the V domain of the kappa chain in the four Fanconi's syndrome patients; in two out of four the V domain was also completely resistant to trypsin. Western and dot blots revealed similar patterns of reactivity of light chains from patients with the Fanconi's syndrome towards other light chains. Properties of cast-nephropathy light chains were more heterogeneous but clearly differed from those of Fanconi's syndrome: (i) 9 out of 12 were of the lambda-type; (ii) only four yielded a transient 12 kDa fragment after cathepsin B digestion, but all showed some resistance to proteolysis of the entire molecule or a fragment thereof to at least one protease, at variance with control light chains; (iii) they displayed various patterns of reactivity with other light chains; (iv) 7 out of 12 reacted specifically with Tamm-Horsfall protein (THP) by ELISA, in contrast with those of Fanconi's syndrome. In one patient who presented with cast nephropathy and the Fanconi's syndrome, the light chain exhibited both partial resistance of the V kappa domain to cathepsin B and the highest reactivity with THP.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrophoretic study of the physico-chemical characteristics of Bence-Jones proteinuria and its association with kidney damage

AIM

To identify a physico-chemical criterion, or set of criteria, explaining and possibly predicting the nephrotoxic behaviour of Bence-Jones proteins (BJP).

METHODS

The electrophoretic mobility and isoelectric point (pI) of 92 BJP isolates were determined using various electrophoresis procedures on polyacrylamide gel. The proportions of monomers and dimers were determined using sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS PAGE) in 58 cases. PAGE data for 10 BJP isolates were used to construct Ferguson plots and titration curves.

RESULTS

The distribution of electrophoretic mobility and pI values was bimodal and showed a positive correlation when the pI was above 6. The values of these two parameters in 22 patients with renal impairment were not significantly different from those in the patients without renal impairment, and the statistical analysis showed no predictive value for the onset of renal impairment. However, patients excreting the lambda light chain isotype had a 2.8-fold higher risk of developing renal impairment compared with the other patients. Studies of the charge variation of the protein with pH indicated three types of behaviour, suggesting that the charge of BJP is highly variable at physiological pH.

CONCLUSION

It is important to study not only the positivity or negativity of the BJP charge at a given pH, but also its intensity. The study of the BJP titration curves in patients with renal impairment suggests that a low charge at physiological urinary pH could predict renal impairment.

Nephrotoxic potential of Bence Jones proteins

BACKGROUND

The renal manifestations of diseases associated with the production of monoclonal light chains--myeloma (cast) nephropathy, light-chain deposition disease, and amyloidosis AL--result from the deposition of certain Bence Jones proteins as tubular casts, basement-membrane precipitates, or fibrils, respectively. For unknown reasons, the severity of the renal manifestations of these diseases varies greatly from patient to patient. We employed an experimental in vivo model to determine the pathologic importance of various Bence Jones proteins.

METHODS

Mice were injected intraperitoneally with 300 mg of Bence Jones protein from 40 patients with multiple myeloma or amyloidosis AL and killed 48 hours later. The mouse kidneys were examined by light and electron microscopy, and light-chain deposits were identified immunohistochemically with highly specific antihuman light-chain antiserum.

RESULTS

Of the 40 different human Bence Jones proteins studied, 26 were deposited in the mouse kidneys predominantly as tubular casts, basement-membrane precipitates, or crystals; no light-chain deposits were detected in the kidneys of the mice that received the other 14 Bence Jones proteins. Of the 18 patients for whom renal tissue was available for study, the findings in 14 were comparable to those in the mice. Furthermore, the proteins obtained from 22 of the 27 patients whose serum creatinine concentrations equaled or exceeded 168 mumol per liter (1.9 mg per deciliter) were deposited in the mouse kidneys, whereas protein deposition occurred after the injection of proteins from only 4 of the 13 patients with serum creatinine concentrations below 168 mumol per liter. The repeated injection of Bence Jones proteins from two patients who had amyloidosis AL resulted in deposition of the protein in the mouse kidneys as amyloid.

CONCLUSIONS

Particular Bence Jones proteins are primarily responsible for producing the distinctive types of protein deposition in renal tissue and the clinical manifestations that occur in patients with light-chain-associated diseases. This experimental model has potential value for the identification of nephrotoxic or amyloidogenic light chains.

Renal impairment in myeloma: negative association with isoelectric point of excreted Bence-Jones protein

The isoelectric point (pI) of the major form of Bence-Jones protein excreted by 62 patients with myeloma and six with macroglobulinaemia was measured by combining isoelectric focusing with immunoblotting techniques. The distribution of the pI values for both kappa and lambda type proteins was bimodal, most falling in the ranges 5.0-6.0 and 7.0-7.5. Plasma creatinine and creatinine clearance and the urine excretion of alpha-1-microglobulin and beta-2-microglobulin were measured in 24 of the patients. These patients, who were free of additional factors known to have an association with the development of renal impairment, were followed up for a mean period of 16 months (range three to 28 months). It was found that renal impairment was not related to the pI of the Bence-Jones protein excreted.

Differential nephrotoxicity of low molecular weight proteins including Bence Jones proteins in the perfused rat nephron in vivo

To investigate the pathogenetic mechanisms of tubule nephrotoxicity of low molecular weight proteins (LMWP), proximal tubules (PT) of rats were perfused in vivo with artificial tubule fluid (ATF) containing one of five LMWPs: three human Bence Jones proteins (BJP), beta-lactoglobulin (BLG), and rabbit myoglobin (MYG). Volume (JV), chloride (JCl) and glucose (JG) fluxes in these perfused PTs were compared with those determined using ATF alone. In separate experiments, perfused nephrons were examined with electron and immunoelectron microscopy. After exposure to BJP1 or BLG, JV, JCl, and JG were less (P less than 0.05) than corresponding control fluxes. Cell damage of these perfused PTs, along with cellular debris in the distal tubules, was prominent. The PT lysosomes often appeared atypical and contained crystals. In contrast, perfusion with BJP2, BJP3, or MYG did not alter JV, JCl, or JG. These findings were corroborated by the normal ultrastructure of these PTs despite immunohistochemical evidence of endocytosis of the BJPs. Isoelectric point, molecular form, and isotype were not factors associated with PT damage. In addition, proteins with pI less than 7.4 precipitated in the distal nephron, forming acellular casts. Thus, certain nephrotoxic LMWPs damaged the PT, while others precipitated in the distal tubule, obstructing the nephron. These two pathogenetic mechanisms may independently be responsible for tubulointerstitial nephropathy of LMWPs in humans.

The clinical spectrum of pure Bence Jones proteinuria. A study of 66 patients

Sixty-six consecutive patients exhibiting isolated urinary excretion of monoclonal free light chains, i.e. Bence Jones protein (BJP), on screening investigation for serum and urine monoclonal immunoglobulins were studied in order to better define the spectrum of immunoproliferative disorders associated with such a protein abnormality. The typical plasma cell neoplasms accounted for only one third of the cases, multiple myeloma (MM) and systemic amyloidosis (AL) being diagnosed in 18% and 15% of the patients, respectively. Eighteen (27%) of the patients were recognized as having malignant nonHodgkin's lymphomas (NHL), 21 (32%) had chronic lymphocytic leukemia (CLL), and 2 (3%) had hairy cell leukemia (HCL). Three patients (5%) without apparent evidence of any malignant immunoproliferative disease were classified as having a monoclonal gammopathy of undetermined significance (MGUS). The greatest urinary concentrations of BJP were found in plasmacytic neoplasms, the daily excretion of MM patients being significantly higher than that of AL patients. Considerably lower BJP outputs were recorded in the other diseases, the lowest ones being associated with MGUS. NHL patients had a daily excretion four times higher as compared with that of CLL patients. The distribution of NHL by histologic type was: follicular center cell lymphomas (FCCL) 39%, small lymphocytic lymphoma (SLL) 33%, immunoblastic lymphoma (IBL) 17%, and plasmacytoid lymphocytic lymphoma (PLL) 11%. The highest BJP levels were found in PLL, and the lowest ones in FCCL. In CLL patients the amount of urinary BJP correlated significantly with the tumor load, as estimated by the number of enlarged lymphoid areas. The study suggests that detection and measurement of isolated urinary BJP may provide useful data for the clinical evaluation of a wide spectrum of immunoproliferative disorders.

Analysis of proteinuria using a commercial system for automated electrophoresis and isoelectric focusing

We describe an investigation of proteinuria using Pharmacia PhastSystemTM electrophoresis apparatus. The analysis of urinary proteins by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) of unconcentrated urine followed by silver staining took about 2 h and could clearly demonstrate tubular dysfunction or glomerular damage in urines with a negative or only trace-positive dip-stick test for protein. In addition, we show the identification of urinary proteins by immunoblotting from SDS-PAGE gels and the characterisation of Bence-Jones proteins by isoelectric focusing (IEF) and immunoblotting.

Human Bence Jones protein toxicity in rat proximal tubule epithelium in vivo

To investigate the direct toxicity of human Bence Jones protein (BJP), individual nephrons of male Sprague-Dawley rats were perfused in vivo at 20 nl/min with an artificial tubule fluid (ATF) that contained no protein, a human kappa BJP (5 g/dl), or bovine serum albumin (5 g/dl), and proximal convoluted tubule function and morphology were examined. Perfusion with BJP perfusate for less than or equal to 5 minutes produced no changes (P = NS) in absorption of water, Jv, (1.09 +/- 0.20 vs. 1.50 +/- 0.25 nl/min/mm), chloride, JCl, (95 +/- 47 vs. 123 +/- 41 pEq/min/mm), and glucose, JG, (39 +/- 3 vs. 40 +/- 5 pmol/min/mm) compared to perfusions with only ATF. However, perfusion for at least 20 minutes with the same BJP perfusate produced decreased (P less than 0.025) in Jv (0.58 +/- 0.12 vs. 1.15 +/- 0.14 nl/min/mm) and JG (27 +/- 3 vs. 38 +/- 3 pmol/min/mm) compared to perfusions with ATF alone; the decrease in JCl (64 +/- 47 vs. 119 +/- 27 pEq/min/mm) did not reach statistical significance. Perfusion for 20 minutes with ATF containing albumin resulted in no changes in Jv (1.22 +/- 0.21 vs. 1.15 +/- 0.14 nl/min/mm), JCl (207 +/- 29 vs. 119 +/- 27 pEq/min/mm), and JG (31 +/- 1 vs. 38 +/- 3 pmol/min/mm), when compared to the ATF perfusions. Immunocytochemistry, immunofluorescence and immunoelectron microscopy of the BJP-perfused tubules demonstrated the kappa light-chain protein in endosomes and activated lysosomes. In addition, cellular desquamation and fragmentation, prominent cytoplasmic vacuolation, and focal loss of the microvillus border were found in the BJP-perfused tubules, but not in the albumin-perfused tubules. In conclusion, these functional and morphologic data show that a human kappa light-chain is toxic to the proximal convoluted tubule of the rat. This toxicity occurred in a time-dependent fashion when the lysosomal system was markedly activated. Direct damage of the tubule epithelium by BJP's may be involved in the development of the tubulointerstitial nephropathy associated with multiple myeloma.

Immunoglobulin light-chain immunoblots of urine proteins from patients with tubular and Bence-Jones proteinuria

Immunoglobulin excretion by patients with monoclonal gammopathies and tubular proteinuria has been analysed by agarose gel isoelectricfocussing of untreated urine and immunoblotting. About three-quarters of the Bence-Jones proteins detected occurred as multiple bands on isoelectricfocussing; in about half of these cases the multiple forms were due to polymerisation or fragmentation of the light chains. In specimens with tubular proteinuria, a characteristic light chain pattern of three broad bands covering the pI ranges 7.1-7.3, 7.8-8.0 and 8.3-8.5 was found. This pattern also occurred in 53% of specimens with Bence-Jones proteinuria and was identical to that found in concentrated normal urine. Intact monoclonal immunoglobulin usually appeared as three or more evenly spaced bands of similar intensity whereas polyclonal intact immunoglobulins produced diffuse staining from pI 5.0-8.5. A scheme for the qualitative analysis of urinary immunoglobulin excretion using this technique has been developed.