Polymer formation during the degradation of human light chain and Bence-Jones proteins by an extrct of the lysosomal fraction of normal human kidney

Understanding Mesangial Pathobiology in AL-Amyloidosis and Monoclonal Ig Light Chain Deposition Disease

Patients with plasma cell dyscrasias produce free abnormal monoclonal Ig light chains that circulate in the blood stream. Some of them, termed glomerulopathic light chains, interact with the mesangial cells and trigger, in a manner dependent of their structural and physicochemical properties, a sequence of pathological events that results in either light chain–derived (AL) amyloidosis (AL-Am) or light chain deposition disease (LCDD). The mesangial cells play a key role in the pathogenesis of both diseases. The interaction with the pathogenic light chain elicits specific cellular processes, which include apoptosis, phenotype transformation, and secretion of extracellular matrix components and metalloproteinases. Monoclonal light chains associated with AL-Am but not those producing LCDD are avidly endocytosed by mesangial cells and delivered to the mature lysosomal compartment where amyloid fibrils are formed. Light chains from patients with LCDD exert their pathogenic signaling effect at the cell surface of mesangial cells. These events are generic mesangial responses to a variety of adverse stimuli, and they are similar to those characterizing other more frequent glomerulopathies responsible for many cases of end-stage renal disease. The pathophysiologic events that have been elucidated allow to propose future therapeutic approaches aimed at preventing, stopping, ameliorating, or reversing the adverse effects resulting from the interactions between glomerulopathic light chains and mesangium.

Renal crystal-storing histiocytosis involving glomeruli - A comprehensive clinicopathologic analysis

Crystal-storing histiocytosis (CSH) is a rare manifestation of monoclonal gammopathy in which histiocytes containing monoclonal proteins in their cytoplasm are found in various organs of the body including the kidney. Within the kidney, these monoclonal crystal-laden histiocytes have been described to occur in the interstitium (most commonly) or in the glomerular mesangium. CSH within glomerular capillary loops has rarely been reported. We describe three cases of CSH primarily affecting the glomerular capillaries and review the literature of CSH in general. Twenty cases of CSH involving the kidney are present in the literature; three describe CSH in glomeruli, only one of which showed histiocytes predominantly in glomerular capillary loops, while 15 had predominantly or solely interstitial CSH. Most cases involve IgG kappa crystals with only one case involving lambda light chain. Patients with CSH predominantly involving the glomerular capillaries showed a trend toward lower serum creatinine and proteinuria at presentation, and several patients with CSH lacked a definitive diagnosis of a monoclonal gammopathy at the time of diagnosis, emphasizing the role that kidney biopsy and particularly electron microscopy play in diagnosis of this entity.

Light chain amyloidosis: Where are the light chains from and how they play their pathogenic role?

Amyloid light-chain (AL) amyloidosis is a plasma-cell dyscrasia, as well as the most common type of systematic amyloidosis. Pathogenic plasma cells that have distinct cytogenetic and molecular properties secrete an excess amount of amyloidogenic light chains. Assisted by post-translational modifications, matrix components, and other environmental factors, these light chains undergo a conformational change that triggers the formation of amyloid fibrils that overrides the extracellular protein quality control system. Moreover, the amyloidogenic light-chain itself is cytotoxic. As a consequence, organ dysfunction is caused by both organ architecture disruption and the direct cytotoxic effect of amyloidogenic light chains. Here, we reviewed the molecular mechanisms underlying this sequence of events that ultimately leads to AL amyloidosis and also discuss current in vitro and in vivo models, as well as relevant novel therapeutic approaches.

Role of mutations in the cellular internalization of amyloidogenic light chains into cardiomyocytes

Light chain (AL) amyloidosis is characterized by the misfolding of immunoglobulin light chains, accumulating as amyloid fibrils in vital organs. Multiple reports have indicated that amyloidogenic light chains internalize into a variety of cell types, but these studies used urine-derived proteins without indicating any protein sequence information. As a result, the role of somatic mutations in amyloidogenic protein internalization has not been yet studied. We characterized the internalization of AL-09, an AL amyloidosis protein into mouse cardiomyocytes. We also characterized the internalization of the germline protein κI O18/O8, devoid of somatic mutations, and three AL-09 restorative mutations (I34N, Q42K, and H87Y) previously characterized for their role in protein structure, stability, and amyloid formation kinetics. All proteins shared a common internalization pathway into lysosomal compartments. The proteins caused different degrees of lysosomal expansion. Oregon green (OG) labeled AL-09 showed the most rapid internalization, while OG-Q42K presented the slowest rate of internalization.

Plasma exchange in rapidly progressive renal failure due to multiple myeloma. A retrospective case series

BACKGROUND/AIMS

To evaluate the effect of plasma exchange on renal function in patients with rapidly progressive renal failure secondary to multiple myeloma.

METHODS

The study was done through a retrospective chart review using a standardized form at a tertiary care centre in southwestern Ontario. Patients were included in the study if they had a diagnosis of multiple myeloma and rapidly progressive renal failure. Multiple myeloma was defined by a bone marrow aspirate >15% plasma cells plus one of the following: serum monoclonal paraproteins, monoclonal light-chain excretion, or lytic lesions. Patients were excluded if they had evidence of chronic renal failure or failed to complete three plasma exchanges. Twenty-six patients were reviewed; of these 24 were followed up to 1 year. All patients received hydration, standard chemotherapy, and plasma exchange. The plasma exchange volume was 50 ml/kg of 50% normal saline and 50% human serum albumin. Primary outcome measures included (1) prevention of acute dialysis and (2) prevention of progression from acute to chronic dialysis; secondary end points included (1) a decrease in creatinine of 25% or more within 3 months of the last plasma exchange and (2) survival at 1 year.

RESULTS

Sixteen of 24 patients, followed up to 1 year, did not require dialysis. Two patients required dialysis initially, but were able to come off dialysis after 3 months. Fourteen patients were alive at 1 year, 13 of whom were dialysis independent. Twelve of 13 dialysis-independent patients had a >25% reduction in creatinine at 3 months. Two patients were lost to follow-up after discharge and were not included in the analysis.

CONCLUSIONS

This retrospective study suggests that plasma exchange may offer some benefit in preventing the initiation or continuation of dialysis in patients with rapidly progressive renal failure secondary to multiple myeloma. A randomized controlled prospective study is needed to determine whether plasma exchange should be recommended as a standard treatment for patients with rapidly progressive renal failure due to multiple myeloma.

Binding of nascent collagen by amyloidogenic light chains and amyloid fibrillogenesis in monolayers of human fibrocytes

Light (L) chain dimers expressed by multiple myeloma cells and collected as Bence-Jones proteins from the urine of human subjects were tested for their ability to form deposits in fibroblast monolayer cell cultures. Bence-Jones proteins from subjects with primary amyloidosis associated with L chains were shown to form fibrillar deposits by the in vitro assay introduced in this report. Filaments interspersed with nascent collagen could be detected after only 48 h. Deposition of L chains continued over a period of 72 h culminating in the appearance of dense fibrils with widths of 80-100 A and a variety of lengths. Formation of amyloid-like fibrils was accompanied by interference with the maturation of the collagen produced by the fibroblast cells. Fibrils composed of the Mcg lambda-type L chain were deposited between collagen fibers, thus expanding them laterally and leading to their partial disintegration. Mature collagen was completely missing from fibroblast monolayers exposed to the Sea lambda chain and the Jen kappa chain. Collagen with the characteristic striped pattern matured normally in control samples, such as those not dosed with amyloid precursors or those treated with a non-amyloidogenic Bence-Jones protein (e.g., the Hud lambda chain dimer). By immunochemical techniques using fluorescein- and gold-labeled anti-L chain antibodies, amyloidogenic L chains were shown to decorate the strands of nascent collagen. This observation suggests that amyloidogenic L chains are concentrated in the extracellular matrix by monovalent antigen-antibody type reactions. The capacity of the Mcg L chain dimer to bind collagen-derived sequences was tested by soaking crystals with a collagenase substrate, PZ-Pro-Leu-Gly-Pro-D-Arg. Difference Fourier analysis at 2.7 A resolution indicated that the PZ-peptide is a site-filling ligand. It could not be removed from the active site by perfusion of the crystal with ammonium sulfate crystallizing media. Similar experiments with the collagen-derived peptide (Pro-Pro-Gly)(5) showed substantial hysteresis effects extending from one end of the Mcg dimer to the other. After the ligand was withdrawn, the active site of the Mcg dimer could no longer bind the PZ-peptide. However, if the active site was first blocked by the PZ-peptide and subsequently exposed to the (Pro-Pro-Gly)(5) peptide, the difference Fourier map was indistinguishable from that obtained with the PZ-peptide alone. We concluded that amyloidogenic L chains such as the Mcg dimer could be concentrated in the perivascular space by binding to normal tissue constituents. These components include nascent collagen, which can be deterred from maturing as a result of this binding. Participation in such pathological activity is also self-destructive to the amyloidogenic L chains, which lose their binding capabilities for collagen-derived peptides and also become susceptible to irreversible conversion to amyloid fibrils. All of these events may be prevented by prior treatment of the amyloidogenic L chains with site-filling ligands. (c) 2000 John Wiley & Sons, Ltd.

Physicochemical consequences of amino acid variations that contribute to fibril formation by immunoglobulin light chains

The most common form of systemic amyloidosis originates from antibody light chains. The large number of amino acid variations that distinguish amyloidogenic from nonamyloidogenic light chain proteins has impeded our understanding of the structural basis of light-chain fibril formation. Moreover, even among the subset of human light chains that are amyloidogenic, many primary structure differences are found. We compared the thermodynamic stabilities of two recombinant kappa4 light-chain variable domains (V(L)s) derived from amyloidogenic light chains with a V(L) from a benign light chain. The amyloidogenic V(L)s were significantly less stable than the benign V(L). Furthermore, only the amyloidogenic V(L)s formed fibrils under native conditions in an in vitro fibril formation assay. We used site-directed mutagenesis to examine the consequences of individual amino acid substitutions found in the amyloidogenic V(L)s on stability and fibril formation capability. Both stabilizing and destabilizing mutations were found; however, only destabilizing mutations induced fibril formation in vitro. We found that fibril formation by the benign V(L) could be induced by low concentrations of a denaturant. This indicates that there are no structural or sequence-specific features of the benign V(L) that are incompatible with fibril formation, other than its greater stability. These studies demonstrate that the V(L) beta-domain structure is vulnerable to destabilizing mutations at a number of sites, including complementarity determining regions (CDRs), and that loss of variable domain stability is a major driving force in fibril formation.

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.

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.

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.

Renal lesions in plasma cell dyscrasias: ultrastructural observations

The renal biopsies from 47 patients with plasma cell dyscrasias were studied by light and electronmicroscopy, and by immunohistochemical methods. This report is primarily concerned with the ultrastructural features of 24 cases of Bence Jones cast nephropathy and of ten cases of light chain deposit disease. In Bence Jones cast nephropathy, crystals derived from light chain proteins were detected in the majority of cases within the casts or in tubular cells and appeared to be related to the "hard" and "fractured" appearance of the casts as well as to the presence of foreign body type giant cells, the latter probably being of monocyte-macrophage origin. In light chain deposit disease, linear deposits of light chain proteins (eight kappa and two lambda) were present in a subendothelial position along the glomerular basement membrane and along the outer aspect of the tubular basement membranes in all cases, quite often in the mesangial matrix, but much less commonly in the interstitium and in the wall of small arteries. The light and electronmicroscopic features of both Bence Jones cast nephropathy and light chain deposit disease can be considered diagnostic for plasma cell dyscrasia. The possible pathogenetic mechanisms of these two different forms of renal involvement are discussed briefly.

Renal cell carcinoma and systemic amyloidosis: demonstration of AA protein and review of the literature

A case of renal cell carcinoma associated with systemic amyloidosis in a patient with nephrotic syndrome is presented. Amyloid deposits were present in the resected tumor, ipsilateral kidney, and spleen. Potassium permanganate treatment of histologic sections as well as immunoperoxidase staining identified AA protein within the amyloid. Surgical removal of the tumor caused marked remission of the patient's proteinuria. Thirty-nine previously reported cases of renal cell carcinoma with amyloidosis are reviewed. Most tumors have clear cell histologic features, and the amyloid distribution follows the "secondary" pattern. A possible mechanism of amyloid production in renal cell carcinoma is presented in which the tumor directly or indirectly participates in the modification of SAA protein into a precipitable form.

Proliferative glomerulonephropathy in multiple myeloma

A case of multiple myeloma with intra- and extracapillary proliferative glomerulonephropathy and other unusual morphologic and clinical manifestations is described. The probable role of light chain proteins in the pathogenesis of the glomerular lesions is discussed. Evidence is presented documenting the beneficial effects of appropriate therapy on the activity and progression of the renal lesions.

The clinical spectrum of light chain myeloma. A study of 35 patients with special reference to the occurrence of amyloidosis

During a 40 month interval, 35 patients were seen with a plasma cell dyscrasia in which the only detectable monoclonal immunoglobulin abnormality consisted of excess production of either type kappa or type lambda light chains (Bence Jones protein). This group constituted 17.3 per cent of the total number of patients with plasma cell dyscrasias and 25.7 per cent of the patients with myeloma identified during the same period. Variable initial clinical presentation, the absence of a typical monoclonal serum spike and the unreliability of commonly used urine protein tests made recognition of the disorder difficult in many patients. Sulfosalicylic acid and p-toluene sulfonic acid proved valuable in screening for ueine protein. Definition of "proteinuria" by quantitative, electrophoretic and immunochemical studies was essential for diagnosis. Bence Jones proteinemia was present in 80 per cent of the patients; panhypogammaglobulinemia and lytic bone lesions were demonstrable in more than 60 per cent. Although no specific morphologic abnormality of marrow plasma cells was evident by light microscopy, the absence of rouleau on peripheral blood smear was a helpful diagnostic clue. Although patients with lambda light chains presented with more Bence Jones proteinuria, this did not correlate with the severity of initial renal functional impairment or with survival when compared to patients with kappa light chains. No other clinical or laboratory observation differentiated the groups with kappa light chains from those with lambda light chains. Amyloid was identified in seven patients. Their course was dominated by the features of primary systemic amyloidosis instead of the usual findings of classic myeloma. Patients with amyloidosis had lower initial serum albumin levels, fewer lytic bone lesions and reduced survival compared to patients without amyloidosis.