Clonal immunoglobulin light chain variable region germline gene use in AL amyloidosis: association with dominant amyloid-related organ involvement and survival after stem cell transplantation

Native State Stabilization of Amyloidogenic Proteins by Kinetic Stabilizers: Inhibition of Protein Aggregation and Clinical Relevance

Proteinopathies or amyloidoses are a group of life-threatening disorders that result from misfolding of proteins and aggregation into toxic insoluble amyloid aggregates. Amyloid aggregates have low clearance from the body due to the insoluble nature, leading to their deposition in various organs and consequent organ dysfunction. While amyloid deposition in the central nervous system leads to neurodegenerative diseases that mostly cause dementia and difficulty in movement, several other organs, including heart, liver and kidney are also affected by systemic amyloidoses. Regardless of the site of amyloid deposition, misfolding and structural alteration of the precursor proteins play the central role in amyloid formation. Kinetic stabilizers are an emerging class of drugs, which act like pharmacological chaperones to stabilize the native state structure of amyloidogenic proteins and to increase the activation energy barrier that is required for adopting a misfolded structure or conformation, ultimately leading to the inhibition of protein aggregation. In this review, we discuss the kinetic stabilizers that stabilize the native quaternary structure of transthyretin, immunoglobulin light chain and superoxide dismutase 1 that cause transthyretin amyloidoses, light chain amyloidosis and familial amyotrophic lateral sclerosis, respectively.

Role of the mechanisms for antibody repertoire diversification in monoclonal light chain deposition disorders: when a friend becomes foe

The adaptive immune system of jawed vertebrates generates a highly diverse repertoire of antibodies to meet the antigenic challenges of a constantly evolving biological ecosystem. Most of the diversity is generated by two mechanisms: V(D)J gene recombination and somatic hypermutation (SHM). SHM introduces changes in the variable domain of antibodies, mostly in the regions that form the paratope, yielding antibodies with higher antigen binding affinity. However, antigen recognition is only possible if the antibody folds into a stable functional conformation. Therefore, a key force determining the survival of B cell clones undergoing somatic hypermutation is the ability of the mutated heavy and light chains to efficiently fold and assemble into a functional antibody. The antibody is the structural context where the selection of the somatic mutations occurs, and where both the heavy and light chains benefit from protective mechanisms that counteract the potentially deleterious impact of the changes. However, in patients with monoclonal gammopathies, the proliferating plasma cell clone may overproduce the light chain, which is then secreted into the bloodstream. This places the light chain out of the protective context provided by the quaternary structure of the antibody, increasing the risk of misfolding and aggregation due to destabilizing somatic mutations. Light chain-derived (AL) amyloidosis, light chain deposition disease (LCDD), Fanconi syndrome, and myeloma (cast) nephropathy are a diverse group of diseases derived from the pathologic aggregation of light chains, in which somatic mutations are recognized to play a role. In this review, we address the mechanisms by which somatic mutations promote the misfolding and pathological aggregation of the light chains, with an emphasis on AL amyloidosis. We also analyze the contribution of the variable domain (V_L) gene segments and somatic mutations on light chain cytotoxicity, organ tropism, and structure of the AL fibrils. Finally, we analyze the most recent advances in the development of computational algorithms to predict the role of somatic mutations in the cardiotoxicity of amyloidogenic light chains and discuss the challenges and perspectives that this approach faces.

Dissecting the Molecular Features of Systemic Light Chain (AL) Amyloidosis: Contributions from Proteomics

Amyloidoses are characterized by aggregation of proteins into highly ordered amyloid fibrils, which deposit in the extracellular space of tissues, leading to organ dysfunction. In AL (amyloid light chain) amyloidosis, the most common form in Western countries, the amyloidogenic precursor is a misfolding-prone immunoglobulin light chain (LC), which, in the systemic form, is produced in excess by a plasma cell clone and transported to target organs though blood. Due to the primary role that proteins play in the pathogenesis of amyloidoses, mass spectrometry (MS)-based proteomic studies have gained an established position in the clinical management and research of these diseases. In AL amyloidosis, in particular, proteomics has provided important contributions for characterizing the precursor light chain, the composition of the amyloid deposits and the mechanisms of proteotoxicity in target organ cells and experimental models of disease. This review will provide an overview of the major achievements of proteomic studies in AL amyloidosis, with a presentation of the most recent acquisitions and a critical discussion of open issues and ongoing trends.

Genetic pathogenesis of immunoglobulin light chain amyloidosis: basic characteristics and clinical applications

Immunoglobulin light chain amyloidosis (AL) is an indolent plasma cell disorder characterized by free immunoglobulin light chain (FLC) misfolding and amyloid fibril deposition. The cytogenetic pattern of AL shows profound similarity with that of other plasma cell disorders but harbors distinct features. AL can be classified into two primary subtypes: non-hyperdiploidy and hyperdiploidy. Non-hyperdiploidy usually involves immunoglobulin heavy chain translocations, and t(11;14) is the hallmark of this disease. T(11;14) is associated with low plasma cell count but high FLC level and displays distinct response outcomes to different treatment modalities. Hyperdiploidy is associated with plasmacytosis and subclone formation, and it generally confers a neutral or inferior prognostic outcome. Other chromosome abnormalities and driver gene mutations are considered as secondary cytogenetic aberrations that occur during disease evolution. These genetic aberrations contribute to the proliferation of plasma cells, which secrete excess FLC for amyloid deposition. Other genetic factors, such as specific usage of immunoglobulin light chain germline genes and light chain somatic mutations, also play an essential role in amyloid fibril deposition in AL. This paper will propose a framework of AL classification based on genetic aberrations and discuss the amyloid formation of AL from a genetic aspect.

IGVL gene region usage correlates with distinct clinical presentation in IgM vs non-IgM light chain amyloidosis

Patients with immunoglobulin M (IgM) light chain (AL) amyloidosis have a distinct clinical presentation compared with those with non-IgM amyloidosis. We hypothesized that differential immunoglobulin light-chain variable region (IGVL) gene usage may explain the differences in organ involvement, because IGVL usage correlates with organ tropism. IGVL usage was evaluated by mass spectrometry of amyloid deposits (IgM, n = 45; non-IgM, n = 391) and differed across the 2 groups. In the λ family, LV2-08 (13% vs 2%; P < .001) and LV2-14 (36% vs 10%; P < .001) usage was more common in IgM vs non-IgM amyloidosis, whereas LV1-44 (0% vs 10%; P = .02) and LV6-57 (2% vs 18%; P = .004) usage was less common. In the κ family, there was a trend toward higher KV4-01 (11% vs 4%; P = .06) usage in IgM amyloidosis. IGVL usage correlated with disease characteristics/organ tropism. LV2-14 (more common in IgM amyloidosis) has historically been associated with peripheral nerve involvement and lower light chain burden, which were more frequent in IgM amyloidosis. LV1-44 (less common in IgM), associated with cardiac involvement, was less frequent in IgM patients. LV6-57 (less common in IgM) is associated with t(11;14), which was less frequent in IgM patients. In conclusion, IGVL gene usage differs in patients with IgM vs non-IgM amyloidosis and may explain the distinct clinical presentation.

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.

Solid Organ Transplantation in Amyloidosis

Amyloidosis comprises a diverse group of diseases characterized by misfolding of precursor proteins which eventually form amyloid aggregates and preceding intermediaries, which are deposited in target tissues causing progressive organ damage. In all forms of amyloidosis, vital organs may fail; depending on the specific amyloidosis type, this may occur rapidly or progress slowly. Beyond therapies to reduce the precursor protein (chemotherapy for light chain [AL] amyloidosis, anti-inflammatory therapy in serum A amyloid-osis [AA], and antisense RNA therapy in transthyretin amyloidosis [ATTR]), organ transplantation may also be a means to reduce amyloidogenic protein, e.g., in types of amyloid-osis in which the variant precursor is produced by the liver. Heart transplantation is a life-saving approach to the treatment of patients with advanced cardiac amyloidosis; however, amyloidosis may still be considered a contraindication to the procedure despite data supporting improved outcomes, similar to patients with other indications. Kidney transplantation is associated with particularly favorable outcomes in patients with amyloidosis, especially if the precursor protein has been eliminated. Overall, outcomes of solid organ transplantation are improving, but more data are needed to refine the selection criteria and the timing for organ transplantation, which should be performed in highly experienced centers involving multidisciplinary teams with close patient follow-up to detect amyloid recurrence.

Supportive Care in AL Amyloidosis

Immunoglobulin light-chain (AL) amyloidosis is a systemic disease characterized by the production and deposition of light chain-derived amyloid fibrils in different organs. Prompt treatment directed to the underlying plasma cell clone is crucial in order to achieve a rapid, deep and durable hematologic response. The decrease in the production of the amyloidogenic light chains is a required condition to obtain the organ response, which is commonly delayed. Meanwhile, supportive treatment is aimed to maintain quality of life of these patients and preserve their involved organs' function. From simple measures, such as salt restriction or compressive stockings, to very complex interventions, such as heart transplantation in very selected patients with isolated severe cardiac involvement, this supportive care is essential and has to be necessarily included in the multidisciplinary management of this disease.

Inherent Biophysical Properties Modulate the Toxicity of Soluble Amyloidogenic Light Chains

In light chain amyloidosis (AL), fibrillar deposition of monoclonal immunoglobulin light chains (LCs) in vital organs, such as heart, is associated with their severe dysfunction. In addition to the cellular damage caused by fibril deposition, direct toxicity of soluble prefibrillar amyloidogenic proteins has been reported, in particular, for cardiotoxicity. However, the molecular bases of proteotoxicity by soluble LCs have not been clarified. Here, to address this issue, we rationally engineered the amino acid sequence of the highly cardiotoxic LC H6 by introducing three residue mutations, designed to reduce the dynamics of its native state. The resulting mutant (mH6) is less toxic than its parent H6 to human cardiac fibroblasts and C. elegans. The high sequence and structural similarity, together with the different toxicity, make H6 and its non-toxic designed variant mH6 a test case to shed light on the molecular properties underlying soluble toxicity. Our comparative structural and biochemical study of H6 and mH6 shows closely matching crystal structures, whereas spectroscopic data and limited proteolysis indicate that H6 displays poorly cooperative fold, higher flexibility, and kinetic instability, and a higher dynamic state in its native fold. Taken together, the results of this study show a strong correlation between the overall conformational properties of the native fold and the proteotoxicity of cardiotropic LCs.

MAGE genes: Prognostic indicators in AL amyloidosis patients

A high frequency of MAGE-CT (cancer testis) antigens are expressed in Multiple Myeloma (MM) patients; however, in other plasma cell dyscrasias, their potential function remains unclear. We measured the expression of MAGE-CT genes (MAGE-C1/CT7, MAGE-A3, MAGE-C2/CT10) in 105 newly diagnosed amyloid light-chain (AL) amyloidosis patients between June 2013 and January 2018 at Peking University People's Hospital using real-time quantitative polymerase chain reaction. In the newly diagnosed AL patients, the positive expression rates of patients with MAGE-C1/CT7, MAGE-C2/CT10 and MAGE-A3 were 83.8% (88/105), 56.71% (38/67) and 22.0% (13/59) respectively. There was no significant correlation between organ propensity and MAGE-CT gene expression. Changes in the MAGE-C1/CT7 levels were consistent with a therapeutic effect. The expression levels of MAGE-C1/CT7, MAGE-C2/CT10 and MAGE-A3 provide potentially effective clinical indicators for auxiliary diagnoses and monitoring treatment efficacy in AL amyloidosis patients.

The CDR1 and Other Regions of Immunoglobulin Light Chains are Hot Spots for Amyloid Aggregation

Immunoglobulin light chain-derived (AL) amyloidosis is a debilitating disease without known cure. Almost nothing is known about the structural factors driving the amyloidogenesis of the light chains. This study aimed to identify the fibrillogenic hotspots of the model protein 6aJL2 and in pursuing this goal, two complementary approaches were applied. One of them was based on several web-based computational tools optimized to predict fibrillogenic/aggregation-prone sequences based on different structural and biophysical properties of the polypeptide chain. Then, the predictions were confirmed with an ad-hoc synthetic peptide library. In the second approach, 6aJL2 protein was proteolyzed with trypsin, and the products incubated in aggregation-promoting conditions. Then, the aggregation-prone fragments were identified by combining standard proteomic methods, and the results validated with a set of synthetic peptides with the sequence of the tryptic fragments. Both strategies coincided to identify a fibrillogenic hotspot located at the CDR1 and β-strand C of the protein, which was confirmed by scanning proline mutagenesis analysis. However, only the proteolysis-based strategy revealed additional fibrillogenic hotspots in two other regions of the protein. It was shown that a fibrillogenic hotspot associated to the CDR1 is also encoded by several κ and λ germline variable domain gene segments. Some parts of this study have been included in the chapter “The Structural Determinants of the Immunoglobulin Light Chain Amyloid Aggregation”, published in Physical Biology of Proteins and Peptides, Springer 2015 (ISBN 978-3-319-21687-4).

Novel Therapies in Light Chain Amyloidosis

Light chain (AL) amyloidosis is the most common form of amyloidosis involving the kidney. It is characterized by albuminuria, progressing to overt nephrotic syndrome and eventually end-stage renal failure if diagnosed late or ineffectively treated, and in most cases by concomitant heart involvement. Cardiac amyloidosis is the main determinant of survival, whereas the risk of dialysis is predicted by baseline proteinuria and glomerular filtration rate, and by response to therapy. The backbone of treatment is chemotherapy targeting the underlying plasma cell clone, that needs to be risk-adapted due to the frailty of patients with AL amyloidosis who have cardiac and/or multiorgan involvement. Low-risk patients (∼20%) can be considered for autologous stem cell transplantation that can be preceded by induction and/or followed by consolidation with bortezomib-based regimens. Bortezomib combined with alkylators, such as melphalan, preferred in patients harboring t(11;14), or cyclophosphamide, is used in most intermediate-risk patients, and with cautious dose escalation in high-risk subjects. Novel, powerful anti-plasma cell agents, such as pomalidomide, ixazomib, and daratumumab, prove effective in the relapsed/refractory setting, and are being moved to upfront therapy in clinical trials. Novel approaches based on small molecules interfering with the amyloidogenic process and on antibodies targeting the amyloid deposits gave promising results in preliminary uncontrolled studies, are being tested in controlled trials, and will likely prove powerful complements to chemotherapy. Finally, improvements in the understanding of the molecular mechanisms of organ damage are unveiling novel potential treatment targets, moving toward a cure for this dreadful disease.

Concurrent structural and biophysical traits link with immunoglobulin light chains amyloid propensity

Light chain amyloidosis (AL), the most common systemic amyloidosis, is caused by the overproduction and the aggregation of monoclonal immunoglobulin light chains (LC) in target organs. Due to genetic rearrangement and somatic hypermutation, virtually, each AL patient presents a different amyloidogenic LC. Because of such complexity, the fine molecular determinants of LC aggregation propensity and proteotoxicity are, to date, unclear; significantly, their decoding requires investigating large sets of cases. Aiming to achieve generalizable observations, we systematically characterised a pool of thirteen sequence-diverse full length LCs. Eight amyloidogenic LCs were selected as responsible for severe cardiac symptoms in patients; five non-amyloidogenic LCs were isolated from patients affected by multiple myeloma. Our comprehensive approach (consisting of spectroscopic techniques, limited proteolysis, and X-ray crystallography) shows that low fold stability and high protein dynamics correlate with amyloidogenic LCs, while hydrophobicity, structural rearrangements and nature of the LC dimeric association interface (as observed in seven crystal structures here presented) do not appear to play a significant role in defining amyloid propensity. Based on the structural and biophysical data, our results highlight shared properties driving LC amyloid propensity, and these data will be instrumental for the design of synthetic inhibitors of LC aggregation.

Stability and aggregation propensity do not fully account for the association of various germline variable domain gene segments with light chain amyloidosis

Variable domain (VL) gene segments exhibit variable tendencies to be associated with light chain amyloidosis (AL). While few of them are very frequent in AL and give rise to most of the amyloidogenic light chains compiled at the sequence databases, other are rarely found among the AL cases. To analyze to which extent these tendencies depend on folding stability and aggregation propensity of the germline VL protein, we characterized VL proteins encoded by four AL-associated germline gene segments and one not associated to AL. We found that the AL-associated germline rVL proteins differ widely in conformational stability and propensity to in vitro amyloid aggregation. While in vitro the amyloid formation kinetics of these proteins correlate well with their folding stabilities, the folding stability does not clearly correlate with their germline's frequencies in AL. We conclude that the association of the VL genes segments to amyloidosis is not determined solely by the folding stability and aggregation propensity of the germline VL protein. Other factors, such as the frequencies of destabilizing mutations and susceptibility to proteolysis, must play a role in determining the light chain amyloidogenicity.

Addressing Common Questions Encountered in the Diagnosis and Management of Cardiac Amyloidosis

Advances in cardiac imaging have resulted in greater recognition of cardiac amyloidosis in everyday clinical practice, but the diagnosis continues to be made in patients with late-stage disease, suggesting that more needs to be done to improve awareness of its clinical manifestations and the potential of therapeutic intervention to improve prognosis. Light chain cardiac amyloidosis, in particular, if recognized early and treated with targeted plasma cell therapy, can be managed very effectively. For patients with transthyretin amyloidosis, there are numerous therapies that are currently in late-phase clinical trials. In this review, we address common questions encountered in clinical practice regarding etiology, clinical presentation, diagnosis, and management of cardiac amyloidosis, focusing on recent important developments in cardiac imaging and biochemical diagnosis. The aim is to show how a systematic approach to the evaluation of suspected cardiac amyloidosis can impact the prognosis of patients in the modern era.

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.

Amyloidosis: Insights from Proteomics

Amyloidoses are a spectrum of disorders caused by abnormal folding and extracellular deposition of proteins. The deposits lead to tissue damage and organ dysfunction, particularly in the heart, kidneys, and nerves. There are at least 30 different proteins that can cause amyloidosis. The clinical management depends entirely on the type of protein deposited, and thus on the underlying pathogenesis, and often requires high-risk therapeutic intervention. Application of mass spectrometry-based proteomic technologies for analysis of amyloid plaques has transformed the way amyloidosis is diagnosed and classified. Proteomic assays have been extensively used for clinical management of patients with amyloidosis, providing unprecedented diagnostic and biological information. They have shed light on the pathogenesis of different amyloid types and have led to identification of numerous new amyloid types, including ALECT2 amyloidosis, which is now recognized as one of the most common causes of systemic amyloidosis in North America.

Beyond the plasma cell: emerging therapies for immunoglobulin light chain amyloidosis

Systemic immunoglobulin light chain (LC) amyloidosis (AL) is a potentially fatal disease caused by immunoglobulin LC produced by clonal plasma cells. These LC form both toxic oligomers and amyloid deposits disrupting vital organ function. Despite reduction of LC by chemotherapy, the restoration of organ function is highly variable and often incomplete. Organ damage remains the major source of mortality and morbidity in AL. This review focuses on the challenges posed by emerging therapies that may limit the toxicity of LC and improve organ function by accelerating the resorption of amyloid deposits.

Immunoglobulin Light-Chain Amyloidosis: From Basics to New Developments in Diagnosis, Prognosis and Therapy

Immunoglobulin amyloid light-chain (AL) amyloidosis is the most common form of systemic amyloidosis, where the culprit amyloidogenic protein is immunoglobulin light chains produced by marrow clonal plasma cells. AL amyloidosis is an infrequent disease, and since presentation is variable and often nonspecific, diagnosis is often delayed. This results in cumulative organ damage and has a negative prognostic effect. AL amyloidosis can also be challenging on the diagnostic level, especially when demonstration of Congo red-positive tissue is not readily obtained. Since as many as 31 known amyloidogenic proteins have been identified to date, determination of the amyloid type is required. While several typing methods are available, mass spectrometry has become the gold standard for amyloid typing. Upon confirming the diagnosis of amyloidosis, a pursuit for organ involvement is essential, with a focus on heart involvement, even in the absence of suggestive symptoms for involvement, as this has both prognostic and treatment implications. Details regarding initial treatment options, including stem cell transplantation, are provided in this review. AL amyloidosis management requires a multidisciplinary approach with careful patient monitoring, as organ impairment has a major effect on morbidity and treatment tolerability until a response to treatment is achieved and recovery emerges.

[Optimization of the immunohistochemical diagnosis of AL amyloidosis using novel antibodies]

OBJECTIVE

to improve the immunohistochemical diagnosis of AL amyloidosis, by generating novel peptide antibodies against the variable and constant regions of the κ-light chains.

MATERIAL AND METHODS

All amyloidogenic κ-light chains were sought in the scientific literature and the database of the National Center for Biotechnology Information. On the basis of the findings, a chain was formed from the most common amino acid residues that were used to choose peptide regions for immunization. Four antibodies were generalized via immunization of rabbits with two peptides that corresponded to the variant or constant regions of κ-light chains.

RESULTS

The specificity of the obtained antibodies was confirmed using a series of 222 biopsy specimens from 193 patients with AL, AA, transthyretin, or insulin amyloidosis. All the novel polyclonal peptide antibodies produced positive staining in cases of ALκ amyloidosis.

CONCLUSION

The generated polyclonal peptide antibodies against the variable and constant regions of κ-light chains are able to improve the immunohistochemical diagnosis of amyloidosis.

Inhibition of Light Chain 6aJL2-R24G Amyloid Fiber Formation Associated with Light Chain Amyloidosis

Light chain amyloidosis (AL) is a deadly disease characterized by the deposition of monoclonal immunoglobulin light chains as insoluble amyloid fibrils in different organs and tissues. Germ line λ VI has been closely related to this condition; moreover, the R24G mutation is present in 25% of the proteins of this germ line in AL patients. In this work, five small molecules were tested as inhibitors of the formation of amyloid fibrils from the 6aJL2-R24G protein. We have found by thioflavin T fluorescence and transmission electron microscopy that EGCG inhibits 6aJL2-R24G fibrillogenesis. Furthermore, using nuclear magnetic resonance spectroscopy, dynamic light scattering, and isothermal titration calorimetry, we have determined that the inhibition is due to binding to the protein in its native state, interacting mainly with aromatic residues.

Proteomic detection of immunoglobulin light chain variable region peptides from amyloidosis patient biopsies

Immunoglobulin light chain (LC) amyloidosis (AL) is caused by deposition of clonal LCs produced by an underlying plasma cell neoplasm. The clonotypic LC sequences are unique to each patient, and they cannot be reliably detected by either immunoassays or standard proteomic workflows that target the constant regions of LCs. We addressed this issue by developing a novel sequence template-based workflow to detect LC variable (LCV) region peptides directly from AL amyloid deposits. The workflow was implemented in a CAP/CLIA compliant clinical laboratory dedicated to proteomic subtyping of amyloid deposits extracted from either formalin-fixed paraffin-embedded tissues or subcutaneous fat aspirates. We evaluated the performance of the workflow on a validation cohort of 30 AL patients, whose amyloidogenic clone was identified using a novel proteogenomics method, and 30 controls. The recall and negative predictive values of the workflow, when identifying the gene family of the AL clone, were 93 and 98%, respectively. Application of the workflow on a clinical cohort of 500 AL amyloidosis samples highlighted a bias in the LCV gene families used by the AL clones. We also detected similarity between AL clones deposited in multiple organs of systemic AL patients. In summary, AL proteomic data sets are rich in LCV region peptides of potential clinical significance that are recoverable with advanced bioinformatics.

Systemic AL amyloidosis with unusual cutaneous presentation unmasked by carotenoderma

We present a case study of an elderly woman with systemic lambda-type AL amyloidosis that featured unusually extensive cutaneous involvement. The case initially presented with a sudden hyper β-carotenemia with carotenoderma that instigated the clinical examination including skin biopsy. A diagnosis of systemic amyloidosis was made. Immunohistochemistry and Western-blot analysis indicated the presence of lambda light chain proteins in skin amyloid deposits. However, notable co-deposition of wild-type apoA-I and transthyretin was observed which caused initial diagnostic confusion. Proteomic analysis of microdissected skin amyloid deposits by mass spectrometry confirmed lambda light chain proteins in amyloid deposits and co-deposition of apolipoprotein A-IV and serum amyloid P-component. The patient died from renal failure caused by amyloid nephropathy combined with analgesic nephropathy. The autopsy disclosed vascular, cardiac, renal and pulmonary amyloid deposition. While all amyloid deposits were positive for lambda light chain proteins, the immunodetection of apoA-I and transthyretin varied significantly among the visceral amyloid deposits. Although the patient exhibited a 1000-fold increase in serum β-carotene levels, only a mild increase in retinol and lutein concentrations was observed. Increased β-carotene values were also found in the liver and the skin. The mechanisms underlying this hyper β-carotenemia remain undetermined.

Immunoglobulin light chain amyloidosis

Primary light chain amyloidosis is the most common form of systemic amyloidosis and is caused by misfolded light chains that cause proteotoxicity and rapid decline of vital organ function. Early diagnosis is essential in order to deliver effective therapy and prevent irreversible organ damage. Accurate diagnosis requires clinical skills and advanced technologies. The disease can be halted and the function of target organs preserved by the prompt reduction and elimination of the plasma cell clone producing the toxic light chains in the bone marrow. Heart damage is the major determinant of survival, and staging with cardiac biomarkers guides treatment. Two-thirds of patients can benefit from treatment with improved quality of life and extended survival. Future efforts should be directed at early diagnosis, improving the tolerability and efficacy of anti-plasma cell therapy, accelerating recovery of organ function via promoting resorption of amyloid deposits, and developing novel approaches to counter light chain proteotoxicity.

Systemic amyloidoses: what an internist should know

Systemic amyloidoses are rare, complex diseases caused by misfolding of autologous proteins. Although these diseases are fatal, effective treatments exist that can alter their natural history, provided that they are started before irreversible organ damage has occurred. The cornerstones of the management of systemic amyloidoses are early diagnosis, accurate typing, appropriate risk-adapted therapy, tight follow-up, and effective supportive treatment. Internists play a key role in suspecting the disease, thus allowing early diagnosis, starting the diagnostic workup and selecting patients that should be referred to specialized centers, judiciously titrating supportive measures, and following patients throughout the course of the disease. Here we review the pathogenesis, diagnosis and treatment of the most common forms of systemic amyloidoses.

Systemic light chain amyloidosis: an update for treating physicians

In immunoglobulin light chain amyloidosis a small, indolent plasma cell clone synthesizes light chains that cause devastating organ damage. Early diagnosis, based on prompt recognition of "red-flags" before advanced cardiomyopathy ensues, is essential for improving outcomes. Differentiation from other systemic amyloidoses may require advanced technologies. Prognosis depends on the extent of cardiac involvement, and cardiac biomarkers guide the choice of therapy. The protean clinical presentation requires individualized treatment. Close monitoring of clonal and organ response guides therapy changes and duration. Conventional or high-dose alkylator-based chemotherapy is effective in almost two-thirds of patients. Combinations of proteasome inhibitors, dexamethasone, and alkylators achieve high response rates, although controlled studies are needed. Risk-adapted stem cell transplant and consolidation with novel agents may be considered in selected patients. Immune-modulatory drugs are good options for refractory/relapsed patients. Novel agents and therapeutic targets are expected to be exploited, in an integrated, more effective and less toxic treatment strategy.

What do I need to know about immunoglobulin light chain (AL) amyloidosis?

Immunoglobulin light chain (AL) amyloidosis is the most common acquired systemic amyloidoses. Its presentation is often insidious and progressive, which may delay diagnosis. The interval between first symptoms and actual diagnosis along the intrinsic heterogeneity of tissue tropism create a wide spectrum of presentations, both in terms of scope and depth of symptoms and signs and functional status of patients. In this review, the authors review the pathogenesis, diagnosis and differential diagnosis of AL amyloidosis along with the prognosis and state-of-the-art management for patients with this affliction.

The challenge of systemic immunoglobulin light-chain amyloidosis (Al)

The cardiac involvement and associated mortality that occur in systemic AL amyloidosis remain among the most challenging aspects of the systemic amyloid-related diseases. Monoclonal immunoglobulin light chains produced by a clone of plasma cells are usually the cause of symptoms and organ dysfunction via both poorly understood toxic effects of misfolded species and accumulation of interstitial amyloid fibrils in key viscera. Treatment is aimed at eliminating the clonal cells in order to eliminate toxic light chain production. Recent advances in therapy have helped many patients with AL achieve complete hematologic responses and significant reversal of organ damage but these benefits do not extend to that 10-15 % who present with advanced cardiac involvement. Even with cardiac transplant followed by effective therapy such as stem cell transplant, outcomes for these patients remain promising at best.

The repertoire of λ light chains causing predominant amyloid heart involvement and identification of a preferentially involved germline gene, IGLV1-44

Monoclonal Ig light chains (LC) can be responsible for pathologic conditions in humans, as in systemic amyloid light amyloidosis. Protean clinical manifestations characterize this disorder with the most varied combination of symptoms generated by different degrees of diverse organ involvement. Kidney and heart are most frequently interested, with major heart involvement as the most relevant prognostic factor. The identification of the underlying mechanism involved in organ targeting is of major relevance for the pathobiology of this disorder. To this aim, we characterized the repertoire of variable region germline genes of λ LC preferentially targeting the heart and compared it with the repertoire of LC that do not in a case-control study. We found that the repertoires were highly restricted, showing preferential use of the same few germline genes but with a different frequency pattern. A single gene, IGVL1-44, was found associated with a 5-fold increase in the odds of dominant heart involvement (after adjusting for confounders in a multivariable logistic model). These results support an involvement of LC genetics in the determination of organ targeting. Study of the characteristics of IGVL1-44-LC with, and of the minority without, heart involvement might lead to identification of LC/tissue interactions.

Amyloidosis: pathogenesis and new therapeutic options

The systemic amyloidoses are a group of complex diseases caused by tissue deposition of misfolded proteins that results in progressive organ damage. The most common type, immunoglobulin light chain amyloidosis (AL), is caused by clonal plasma cells that produce misfolded light chains. The purpose of this review is to provide up-to-date information on diagnosis and treatment options for AL amyloidosis. Early, accurate diagnosis is the key to effective therapy, and unequivocal identification of the amyloidogenic protein may require advanced technologies and expertise. Prognosis is dominated by the extent of cardiac involvement, and cardiac staging directs the choice of therapy. Treatment for AL amyloidosis is highly individualized, determined on the basis of age, organ dysfunction, and regimen toxicities, and should be guided by biomarkers of hematologic and cardiac response. Alkylator-based chemotherapy is effective in almost two thirds of patients. Novel agents are also active, and trials are ongoing to establish their optimal use. Treatment algorithms will continue to be refined through controlled trials. Advances in basic research have led to the identification of new drug targets and therapeutic approaches, which will be integrated with chemotherapy in the future.

Utility of Doppler myocardial imaging, cardiac biomarkers, and clonal immunoglobulin genes to assess left ventricular performance and stratify risk following peripheral blood stem cell transplantation in patients with systemic light chain amyloidosis (Al)

BACKGROUND

Cardiac dysfunction is a well-recognized complication of light chain amyloidosis (AL). Autologous stem cell transplant (auto-SCT) has emerged as a successful treatment modality for AL patients. In this study, we examined the effect of clonal immunoglobulin light chain genes (VL), which encodes the immunoglobulin light chain protein that ultimately forms amyloid, on cardiac function, in the context of auto-SCT and its impact on overall survival.

METHODS

Longitudinal Doppler myocardial imaging parameters along with cardiac biomarkers were used to assess for cardiac function pre and post auto-SCT.

RESULTS

VL gene analysis revealed that Vl genes, in particular VlVI, were associated with worse cardiac function parameters than Vk genes. Clonal VL genes appeared to have an impact on left ventricular (LV) function post-transplant and also influenced mortality, with specific VL gene families associated with lower survival. Another key predictor of mortality in this report was change in tricuspid regurgitant flow velocity following auto-SCT. Correlations were also observed between systolic strain rate, systolic strain and VL genes associated with amyloid formation.

CONCLUSIONS

Clonal VL gene usage influences global cardiac function in AL, with patients having VlVI and VlII-III-associated amyloid more severely affected than those having Vk or VlI amyloid. Pulsed wave tissue Doppler imaging along with immunoglobulin gene analysis offers novel insights into prediction of mortality and cardiac dysfunction in AL after auto-SCT.

The critical role of the constant region in thermal stability and aggregation of amyloidogenic immunoglobulin light chain

Light chain (LC) amyloidosis (AL) is a fatal disease in which immunoglobulin LC deposit as fibrils. Although the LC amyloid-forming propensity is attributed primarily to the variable region, fibrils also contain full-length LC comprised of variable-joining (V(L)) and constant (C(L)) regions. To assess the role of C(L) in fibrillogenesis, we compared the thermal stability of full-length LC and corresponding V(L) and C(L) fragments. Protein unfolding and aggregation were monitored by circular dichroism and light scattering. A full-length λ6 LC purified from urine of a patient with AL amyloidosis showed irreversible unfolding coupled to aggregation. The transition temperature decreased at slower heating rates, indicating kinetic effects. Next, we studied five recombinant λ6 proteins: full-length amyloidogenic LC, its V(L), germline LC, germline V(L), and C(L). Amyloidogenic and germline proteins showed similar rank order of stability, V(L) < LC < C(L); hence, in the full-length LC, V(L) destabilizes C(L). Amyloidogenic proteins were less stable than their germline counterparts, suggesting that reduction in V(L) stability destabilizes the full-length LC. Thermal unfolding of the full-length amyloidogenic and germline LC required high activation energy and involved irreversible aggregation, yet the unfolding of the isolated V(L) and C(L) fragments was partially reversible. Therefore, compared to their fragments, full-length LCs are more likely to initiate aggregation during unfolding and provide a template for the V(L) deposition. The kinetic barrier for this aggregation is regulated by the stability of the V(L) region. This represents a paradigm shift in AL fibrillogenesis and suggests C(L) region as a potential therapeutic target.

Structural alterations within native amyloidogenic immunoglobulin light chains

Amyloid diseases are characterized by the misfolding of a precursor protein that leads to amyloid fibril formation. Despite the fact that there are different precursors, some commonalities in the misfolding mechanism are thought to exist. In light chain amyloidosis (AL), the immunoglobulin light chain forms amyloid fibrils that deposit in the extracellular space of vital organs. AL proteins are thermodynamically destabilized compared to non-amyloidogenic proteins and some studies have linked this instability to increased fibril formation rates. Here we present the crystal structures of two highly homologous AL proteins, AL-12 and AL-103. This structural study shows that these proteins retain the canonical germ line dimer interface. We highlight important structural alterations in two loops flanking the dimer interface and correlate these results with the somatic mutations present in AL-12 and AL-103. We suggest that these alterations are informative structural features that are likely contributing to protein instability that leads to conformational changes involved in the initial events of amyloid formation.

Mutations in specific structural regions of immunoglobulin light chains are associated with free light chain levels in patients with AL amyloidosis

Background

The amyloidoses are protein misfolding diseases characterized by the deposition of amyloid that leads to cell death and tissue degeneration. In immunoglobulin light chain amyloidosis (AL), each patient has a unique monoclonal immunoglobulin light chain (LC) that forms amyloid deposits. Somatic mutations in AL LCs make these proteins less thermodynamically stable than their non-amyloidogenic counterparts, leading to misfolding and ultimately the formation of amyloid fibrils. We hypothesize that location rather than number of non-conservative mutations determines the amyloidogenicity of light chains.

Methodology/Principal Findings

We performed sequence alignments on the variable domain of 50 κ and 91 λ AL light chains and calculated the number of non-conservative mutations over total number of patients for each secondary structure element in order to identify regions that accumulate non-conservative mutations. Among patients with AL, the levels of circulating immunoglobulin free light chain varies greatly, but even patients with very low levels can have very advanced amyloid deposition.

Conclusions

Our results show that in specific secondary structure elements, there are significant differences in the number of non-conservative mutations between normal and AL sequences. AL sequences from patients with different levels of secreted light chain have distinct differences in the location of non-conservative mutations, suggesting that for patients with very low levels of light chains and advanced amyloid deposition, the location of non-conservative mutations rather than the amount of free light chain in circulation may determine the amyloidogenic propensity of light chains.

AL-Base: a visual platform analysis tool for the study of amyloidogenic immunoglobulin light chain sequences

AL-Base, a curated database of human immunoglobulin (Ig) light chain (LC) sequences derived from patients with AL amyloidosis and controls, is described, along with a collection of analytical and graphic tools designed to facilitate their analysis. AL-Base is designed to compile and analyse amyloidogenic Ig LC sequences and to compare their predicted protein sequence and structure to non-amyloidogenic LC sequences. Currently, the database contains over 3000 de-identified LC nucleotide and amino acid sequences, of which 433 encode monoclonal proteins that were reported to form fibrillar deposits in AL patients. Each sequence is categorised according to germline gene usage, clinical status and sample source. Currently, tools are available to search for sequences by various criteria, to analyse the biochemical properties of the predicted amino acids at each position and to display the results in a graphical fashion. The likelihood that each sequence has evolved through somatic hypermutation can be predicted using an automated binomial or multinomial distribution model. AL-Base is available to the scientific community for research purposes.

Thermodynamic and kinetic characterization of a germ line human lambda6 light-chain protein: the relation between unfolding and fibrillogenesis

Proteins encoded by the gene segment 6a of the lambda variable light-chain repertoire are strongly associated with amyloid deposition. 6aJL2 is a model protein constructed with the predicted sequences encoded by the 6a and JL2 germ line genes. In this work, we characterized the urea- and temperature-induced unfolding of 6aJL2. In the short time scale, spectroscopic, hydrodynamic and calorimetric experiments were compatible with a two-state transition. Furthermore, DeltaG, m and the midpoint urea concentration obtained from equilibrium experiments were compatible with those obtained from kinetic experiments. Since fibril formation is a slow process, samples were also incubated for longer times. After incubation for several hours at 37 degrees C, spectroscopic, hydrodynamic and calorimetric experiments revealed the presence of a partially unfolded off-pathway intermediate around the midpoint urea concentration (1.5-3.0 M urea). In vitro fibrillogenesis assays show that the maximum growth rate for fibril formation and the minimum lag time were obtained at urea concentrations where the partially unfolded state was populated (2.5 M urea at 37 degrees C). This indicates that this partially unfolded state is critical for in vitro fibril formation. Concentration-dependent kinetics and hydrodynamic properties of the intermediate were consistent with a soluble oligomeric state. The intermediate is formed around the midpoint urea concentration, where the native and unfolded states are equally populated and their rate of interconversion is the slowest. This situation may promote the slow accumulation of an intermediate state that is prone to aggregate.

Evidence for the significant role of immunoglobulin light chains in antigen recognition and selection in chronic lymphocytic leukemia

We analyzed somatic hypermutation (SHM) patterns and secondary rearrangements involving the immunoglobulin (IG) light chain (LC) gene loci in 725 patients with chronic lymphocytic leukemia (CLL). Important differences regarding mutational load and targeting were identified in groups of sequences defined by IGKV/IGLV gene usage and/or K/LCDR3 features. Recurrent amino acid (AA) changes in the IGKV/IGLV sequences were observed in subsets of CLL cases with stereotyped B-cell receptors (BCRs), especially those expressing IGHV3-21/IGLV3-21 and IGHV4-34/IGKV2-30 BCRs. Comparison with CLL LC sequences carrying heterogeneous K/LCDR3s or non-CLL LC sequences revealed that distinct amino acid changes appear to be "CLL-biased." Finally, a significant proportion of CLL cases with monotypic LC expression were found to carry multiple potentially functional LC rearrangements, alluding to active, (auto)antigen-driven receptor editing. In conclusion, SHM targeting in CLL LCs is just as precise and, likely, functionally driven as in heavy chains. Secondary LC gene rearrangements and subset-biased mutations in CLL LC genes are strong indications that LCs are crucial in shaping the specificity of leukemic BCRs, in association with defined heavy chains. Therefore, CLL is characterized not only by stereotyped HCDR3 and heavy chains but, rather, by stereotyped BCRs involving both chains, which generate distinctive antigen-binding grooves.

Structural insights into the role of mutations in amyloidogenesis

Mechanisms of amyloidogenesis are not well understood, including potential structural contributions of mutations in the process. Our previous research indicated that the dimer interface of amyloidogenic immunoglobulin light chain protein AL-09 is twisted 90 degrees relative to the protein from its germline sequence, kappaI O18/O8. Here we report a systematic restoration of AL-09 to its germline sequence by mutating the non-conservative somatic mutations located in the light chain dimer interface. Among these mutants, we find a correlation between increased thermodynamic stability and an increase in the lag time for fibril formation. The restorative mutant AL-09 H87Y completes the trifecta and restores the dimer interface observed in kappaI O18/O8, emphasizing the potential importance of the structural integrity of these proteins to protect against amyloidogenicity. We also find that adding amyloidogenic mutations into the germline protein illustrates mutational cooperativity in promoting amyloidogenesis.

Restrictive usage of monoclonal immunoglobulin λ light chain germline in POEMS syndrome

POEMS syndrome is a rare plasma cell disorder characterized by peripheral neuropathy, monoclonal gammopathy, and high levels of serum vascular endothelial growth factor, the pathogenesis of which remains unclear. A unique feature of this syndrome is that the proliferating monoclonal plasma cells are essentially λ-restricted. Here we determined complete nucleotide sequences of monoclonal immunoglobulin λ light chain (IGL) variable regions in 11 patients with POEMS syndrome. The V-region of the Igλ gene of all 11 patients was restricted to the Vλ1 subfamily. Searching for homologies with IGL germlines revealed that 2 germlines, IGLV1-44*01 (9/11) and IGLV1-40*01 (2/10), were identified, with an average homology of 91.1%. The IGLJ3*02 gene was used in 11 of 11 re-arrangements with an average homology of 92.2%. These data suggest that the highly restricted use of IGL Vλ1 germlines plays an important role in the pathogenesis of POEMS syndrome.

Risk-adapted autologous stem cell transplantation with adjuvant dexamethasone +/- thalidomide for systemic light-chain amyloidosis: results of a phase II trial

High-dose melphalan (MEL) with autologous stem cell transplant (SCT) is an effective therapy for systemic AL amyloidosis (AL), but treatment-related mortality (TRM) has historically been high. We performed a phase II trial of risk-adapted SCT followed by adjuvant dexamethasone (dex) and thalidomide (thal) in an attempt to reduce TRM and improve response rates. Patients (n = 45) with newly diagnosed AL involving < or =2 organ systems were assigned to MEL 100, 140, or 200 mg/m(2) with SCT, based on age, renal function and cardiac involvement. Patients with persistent clonal plasma cell disease 3 months post-SCT received 9 months of adjuvant thal/dex (or dex if there was a history of deep vein thrombosis or neuropathy). Organ involvement was kidney (67%), heart (24%), liver/GI (22%) and peripheral nervous system (18%), with 31% having two organs involved. TRM was 4.4%. Thirty-one patients began adjuvant therapy, with 16 (52%) completing 9 months of treatment and 13 (42%) achieving an improvement in haematological response. By intention-to-treat, overall haematological response rate was 71% (36% complete response), with 44% having organ responses. With a median follow-up of 31 months, 2-year survival was 84% (95% confidence interval: 73%, 94%). Risk-adapted SCT with adjuvant thal/dex is feasible and results in low TRM and high haematological and organ response rates in AL patients.

Dangerous small B-cell clones

The detection of a monoclonal immunoglobulin in serum or urine usually raises concerns about the size of the underlying B-cell-derived clone and possible systemic effects caused by its expansion. However, a small clone can synthesize a very toxic protein, producing devastating systemic damage and protean clinical presentations. The resulting "monoclonal component-related diseases," although difficult to diagnose, may be progressive and even fatal. The monoclonal protein can aggregate and deposit systemically as occurs in light-chain amyloidosis, monoclonal immunoglobulin deposition disease, crystal-storing histiocytosis, and monoclonal cryoglobulinemia. Alternatively, some monoclonal proteins possess antibody activity toward autogenous antigens and cause chronic cold agglutinin disease, mixed cryoglobulinemia, and peripheral neuropathies. Other humoral mediators may contribute to neuropathy in variant disorders such as the POEMS (polyneuropathy, organomegaly, endocrinopathy, M protein, and skin changes) syndrome. The clone synthesizing the noxious monoclonal proteins is often small, and sensitive techniques may be required to detect these immunoglobulins. A delay in diagnosis can allow irreversible organ damage and dramatically shorten survival. Prompt recognition of suggestive signs and symptoms should trigger a thorough diagnostic approach to reach the correct diagnosis quickly, because this is the key to effective therapy. Although the treatment of these conditions is not optimal, significant advances have been made, improving the duration and quality of life.