Recent evidence from the study of different amyloidogenic proteins challenges the dogma that tissue damage is solely the result of amyloid fibril deposition. To examine whether amyloidogenic human immunoglobulin light chains (LCs) may cause acute toxic effects prior to the development of fibrillar tissue deposits in vivo, we have generated amyloidogenic LC-expressing cell lines and transplanted them into mice. A full length lambda-6 light chain was cloned from cDNA prepared from bone marrow of a patient with aggressive multi-organ AL amyloidosis. The LC was subcloned into an expression vector with a CMV promoter and transfected into SP2/0 plasmacytoma cells. Stably transfected cells were injected into syngeneic Balb/c and RAG−/− mice. Four-six weeks later, echocardiograms were performed and the mice were euthanized and serum, urine, and tissues were collected. Mice injected with LC-producing cells, but not control untransfected SP2/0 cells, had detectable circulating human LC in their serum, and 6 of 9 RAG−/− mice excreted LC and albumin in the urine. These mice had evidence of bradycardia by echocardiography, with 4 of 12 mice having heart rates lower than 500 bpm while no controls had heart rates that low, and upregulation of markers of cell stress in the heart. In the kidney, there was evidence of amorphous protein deposits and early glomerulopathy by electron microscopy in two mice examined, but no fibril deposition. Thus, short-term expression of human amyloidogenic LC in mice in vivo produces alterations in heart and kidney function prior to the development of fibrillar deposits.

The structural heterogeneity exhibited by immunoglobulin light chains (LC) involved in amyloidosis has been a subject of interest in establishing a pathogenesis of the disease. Dimerization of the light chain is hypothesized to be the first step in the polymerization of the protein to amyloid fibrils. The use of reduction agents in the purification and/or sample preparation of light chain proteins for structural analysis may destroy relevant post-translational modifications. The mass spectrometry methods presented here enable high-sensitivity determination of post-translational modifications. Post-translational modifications, such as cysteinylation, of these amyloidogenic LCs may have been altered. The use of reduction agents in the purification and/or sample preparation of light chain proteins for structural analysis may destroy relevant post-translational modifications.

Proteoglycans are associated with amyloid fibrils in patients with systemic amyloidosis. There is extensive data implicating heparan sulfate proteoglycans (HSPGs) in the genesis of amyloid. This chapter aim is to evaluate the response of primary cardiac fibroblasts to exogenous amyloidogenic light chains (LCs) and to correlate the localization of LCs with expression and localization of heparan sulfate proteoglycans. The response of cells to 11 urinary IgG LCs of kappa1, lambda 6 and 3 subtypes was evaluated and compared to a urinary LC from a patient with multiple myeloma and no amyloid. As the length of exposure to LC increased there was a transition from a punctate pattern to a filamentous appearance. The extensiveness of the filaments within the cells varied with the specific LCs and did not co-localize with F-actin. Cells displayed a transition from a fibroblast to myofibroblast morphology with extensive actin filaments. This change has been noted in other fibroblast cells in response to injury.