Immunoglobulin and amyloid fibril proteins

Inhibition by small-molecule ligands of formation of amyloid fibrils of an immunoglobulin light chain variable domain

Overproduction of immunoglobulin light chains leads to systemic amyloidosis, a lethal disease characterized by the formation of amyloid fibrils in patients' tissues. Excess light chains are in equilibrium between dimers and less stable monomers which can undergo irreversible aggregation to the amyloid state. The dimers therefore must disassociate into monomers prior to forming amyloid fibrils. Here we identify ligands that inhibit amyloid formation by stabilizing the Mcg light chain variable domain dimer and shifting the equilibrium away from the amyloid-prone monomer.

DOI:http://dx.doi.org/10.7554/eLife.10935.001

Systemic light chain amyloidosis is a disease that occurs when individuals produce too much of an immune protein. The excess protein chains normally exist in the body as individual molecules called “monomers” or in pairs called “dimers,” and they can readily switch between these two forms. However, the monomers are also prone to forming amyloid fibrils, which are difficult to break down. Amyloid fibrils are often deposited in the heart and kidneys and can lead to organ failure and death.

Finding molecules that prevent the formation of amyloid fibrils could help to develop treatments for amyloidosis. Now, Brumshtein, Esswein et al. have screened 27 compounds to identify those that stabilize the dimer form of the protein. This would reduce the number of monomers in the body, and so reduce the number of immune proteins that can form amyloid fibrils.

The experiments identified four compounds that could stabilize the dimers, including one called methylene blue. Comparing the chemical structures of these compounds with the structures of drugs approved for medical use identified thirteen drugs. However, follow-up tests showed that only one, called sulfasalazine, reduced the formation of amyloid fibrils. Neither methylene blue nor sulfasalazine is likely to have a strong enough effect to treat amyloidosis, but they may serve as templates for future drug designs.

DOI:http://dx.doi.org/10.7554/eLife.10935.002

Formation of amyloid fibers by monomeric light chain variable domains

Systemic light chain amyloidosis is a lethal disease characterized by excess immunoglobulin light chains and light chain fragments composed of variable domains, which aggregate into amyloid fibers. These fibers accumulate and damage organs. Some light chains induce formation of amyloid fibers, whereas others do not, making it unclear what distinguishes amyloid formers from non-formers. One mechanism by which sequence variation may reduce propensity to form amyloid fibers is by shifting the equilibrium toward an amyloid-resistant quaternary structure. Here we identify the monomeric form of the Mcg immunoglobulin light chain variable domain as the quaternary unit required for amyloid fiber assembly. Dimers of Mcg variable domains remain stable and soluble, yet become prone to assemble into amyloid fibers upon disassociation into monomers.

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.

Multiple nodular pulmonary amyloidosis. A case report and comparison with diffuse alveolar-septal pulmonary amyloidosis

A case of multiple nodular pulmonary amyloidosis in a 54-year-old Caucasian man is presented. Discrete symptomless radiodensities had developed in this patient's lungs within a period of three years, leading to a suspicion of a neoplastic process. The amyloid nature of these nodules was demonstrated by biopsy. In this case, as in others previously reported, there was no evidence of systemic disease, and immunoglobulins were normal. Local factors probably play an important part in the pathogenesis of this disease. This entity is to be distinguished from the diffuse type of pulmonary amyloidosis, which has a far graver prognosis. Diffuse alveolar septal amyloidosis is usually associated with primary systemic amyloidosis or multiple myeloma and leads rapidly to respiratory distress.

Immunopathologic mechanisms of renal disease

Anti-GBM antibodies and glomerular deposition of circulating immune complexes are responsible for the immunopathogenesis of about 5% and 75% of human glomerulonephritides, respectively. Anti-GBM antibodies most frequently cause rapidly progressive glomerulonephritides, respectively in about half of the patients with pulmonary hemorrhage, the Goodpasture's syndrome. Immune complexes cause a wide variety of glomerulonephritides, including diffuse and focal proliferative, membranous, membranproliferative and rapidly progressive morphologic varieties often accompanied by nephrotic syndrome. Immune complexes cause a wide variety of glomerulonephritides, including diffuse and focal proliferative, membranous, membranoproliferative and rapidly progressive morphologic varieties often accompanied by nephrotic syndrome. Immunopathologic tubulo-interstitial renal injury can be caused by antibodies reacting with TBM or by deposition of immune complexes in tubulo-interstitial tissue. Immunofluorescence studies of renal tissue supplemented by detection of circulating anti-basement membrane antibodies and immune complexes are essential in differentiating the immunopathologic mechanisms of glomerular and tubular injury, and are necessary adjuncts in evaluating patients with glomerulo- and tubulo-interstitial nephritis.