Pharmaceutical strategies against amyloidosis: old and new drugs in targeting a "protein misfolding disease"

The group of diseases caused by abnormalities of the process of protein folding and unfolding is rapidly growing and includes diseases caused by loss of function as well as diseases caused by gain of function of misfolded proteins. Amyloidoses are caused by gain of function of certain proteins that lose their native structure and self-assemble into toxic insoluble, extracellular fibrils. This process requires the contribution of multiple factors of which only a few are established, namely the conformational modification of the amyloidogenic protein, protein's post-translational modifications and the co-deposition of glycosaminoglicans and of serum amyloid P component. In parallel with the exponential growth of biochemical data regarding the key events of the fibrillogenic process, several reports have shown that small molecules, through the interaction with either the amyloidogenic proteins or with the common constituents, can modify the kinetics of formation of amyloid fibrils or can facilitate amyloid reabsorption. These small molecules can be classified on the basis of their protein target and mechanism of action, according to the following properties. 1) molecules that stabilize the amyloidogenic protein precursor 2) molecules that prevent fibrillogenesis by acting on partially folded intermediates of the folding process as well as on low molecular weight oligomers populating the initial phase of fibril formation 3) molecules that interact with mature amyloid fibrils and weaken their structural stability 4) molecules that displace fundamental co-factors of the amyloid deposits like glycosaminoglycans and serum amyloid P component and favor the dissolution of the fibrillar aggregate.     

Inhibition of aggregate formation as therapeutic target in protein misfolding diseases: effect of tetracycline and trehalose

Importance of the field: The identification of molecules that inhibit protein deposition or reverse fibril formation could open new strategies for therapeutic intervention in misfolding diseases. Numerous compounds have been shown to inhibit amyloid fibril formation in vitro. Among these compounds, tetracycline and the disaccharide trehalose have been reported to inhibit or reverse amyloid aggregation but their efficiency as potential drugs is controversial.

Areas covered in this review: The results obtained using tetracycline and trehalose, reported in the last 15 years, are described and discussed.

What the reader will gain: The conclusions have important implications for the development of therapeutic agents for protein deposition diseases. If fibrillar proteins contribute to cell degeneration, then the disassembly of fibrils may reverse or slow down disease progression; however, if the action of therapeutic agents produces intermediates of fibrillation and/or products of fibril disaggregation, then their accumulation could be harmful.

Take home message: Care should be taken to ensure that strategies aimed at inhibiting fibril formation do not cause a corresponding increase in the concentration of toxic oligomeric species.     

Methods to evaluate the inhibition of TTR fibrillogenesis induced by small ligands

Transthyretin is an amyloidogenic protein associated with several amyloidosis, namely familial amyloidotic polyneuropathy, familial amyloidotic cardiomyopathy, and central nervous system selective amyloidosis, familial rare diseases caused by single point mutants, and senile systemic amyloidosis associated with wild-type TTR. The current model for amyloid fibril formation involves initial dissociation of the native TTR tetramer into non-native monomers which associate into soluble oligomers and protofibrils that evolve to mature amyloid deposits. A number of efforts are addressed to identify small molecules targeting the formation, clearance, or assembly of toxic aggregates as a promising therapeutic strategy to treat amyloidosis. This review classifies and summarizes the different strategies and assays that have been developed in vitro, ex vivo, and in vivo as tools to screen libraries of compounds or to test compounds from rational design in the search of drug candidates for the treatment of TTR-associated amyloidosis. Depending on the property they measure, the assays are classified as: a) in vitro assays that monitor protein aggregation and/or fibril formation, b) in vitro assays that monitor binding to native protein, c) ex vivo TTR plasma selectivity assays, d) in vitro assays for tetrameric TTR stabilization, e) cellular assays, and f) animal models to evaluate amyloidosis inhibitors.     

Therapeutic approaches against common structural features of toxic oligomers shared by multiple amyloidogenic proteins

Impaired proteostasis is one of the main features of all amyloid diseases, which are associated with the formation of insoluble aggregates from amyloidogenic proteins. The aggregation process can be caused by overproduction or poor clearance of these proteins. However, numerous reports suggest that amyloid oligomers are the most toxic species, rather than insoluble fibrillar material, in Alzheimer's, Parkinson's, and Prion diseases, among others. Although the exact protein that aggregates varies between amyloid disorders, they all share common structural features that can be used as therapeutic targets. In this review, we focus on therapeutic approaches against shared features of toxic oligomeric structures and future directions.     

Mishandling of the Therapeutic Peptide Glucagon Generates Cytotoxic Amyloidogenic Fibrils

PURPOSE: Some therapeutic peptides exhibit amyloidogenic properties that cause insolubility and cytotoxicity against neuronal cells in vitro. Here, we characterize the conformational change in monomeric therapeutic peptide to its fibrillar aggregate in order to prevent amyloidogenic formation during clinical application. METHODS: Therapeutic peptides including glucagon, porcine secretin, and salmon calcitonin were dissolved in acidic solution at concentrations ranging from 1 mg/ml to 80 mg/ml and then aged at 37 degrees C. Amyloidogenic properties were assessed by circular dichroism (CD), electron microscopy (EM), staining with beta-sheet-specific dyes, and size-exclusion chromatography (SEC). Cytotoxic characteristics were determined concomitantly. RESULTS: By aging at 2.5 mg/ml or higher for 24 h, monomeric glucagon was converted to fibrillar aggregates consisting of a beta-sheet-rich structure with multimeric states of glucagon. Although no aggregation was observed by aging at the clinical concentration of 1 mg/ml for 1 day, 30-day aging resulted in the generation of fibrillar aggregates. The addition of anti-glucagon serum significantly inhibited fibrillar conversion of monomeric glucagon. Glucagon fibrils induced significant cell death and activated an apoptotic enzyme, caspase-3, in PC12 cells and NIH-3T3 cells. Caspase inhibitors attenuated this toxicity in a dose-dependent manner, indicating the involvement of apoptotic signaling pathways in the fibrillar formation of glucagon. On the contrary to glucagon, salmon calcitonin exhibited aggregation at a much higher concentration of 40 mg/ml and secretin showed no aggregation at the concentration as high as 75 mg/ml. CONCLUSIONS: These results indicated that glucagon was self-associated by its beta-sheet-rich intermolecular structure during the aging process under concentrated conditions to induce fibrillar aggregates. Glucagon has the same amyloidogenic propensities as pathologically related peptides such as beta-amyloid (Abeta)1-42 and prion protein fragment (PrP)106-126 including conformational change to a beta-sheet-rich structure and cytotoxic effects by activating caspases. These findings suggest that inappropriate preparation and application of therapeutic glucagon may cause undesirable insoluble products and side effects such as amyloidosis in clinical application.     

Glycation,carbonyl stress and AGEs inhibitors: a patent review

Introduction: The glycation process, comprising a series of reactions, results in the formation of heterogeneous adducts, known as advanced glycation end products (AGEs). AGEs are involved in several pathologies, including diabetes-associated late complications, atherosclerosis, Alzheimer’s disease and inflammatory arthritis. Several inhibitors of AGEs and/or reactive carbonyl species have been identified from various sources, including natural products and synthetic molecules, and have been investigated for their mechanism of action.

Areas covered: This review covers the literature on AGEs inhibitors published as patents between 2001 and 2014. Initially, the earlier reported molecules with AGEs inhibitory properties, their mechanism of actions and reported adverse effects are discussed. The main focus has been on the chemical structures, methods for evaluation of the activity, modes of action, pharmacokinetics and therapeutic outcomes. The potential of these AGEs inhibitors in the treatment and management of a number of diseases are also discussed in this review.

Expert opinion: The reactive carbonyl species and AGEs have recently emerged as novel therapeutic targets for the prevention and treatment of several diseases. Currently, the major concerns with the use of AGEs inhibitors as therapeutic agents are low effectiveness, poor pharmacokinetics and undesirable side effects. Many of the AGEs inhibitors reviewed here possess potent antiglycation activity and are devoid of undesirable side effects. These small molecules inhibitors can, therefore, serve as scaffolds for the development and designing of new AGEs inhibitors as clinical agents.     

Towards understanding the structure-function relationship of human amyloid disease

Immunoglobulin light chain (LC) proteins exhibit the greatest sequence variability of all proteins associated with amyloid disease. The hallmark event in amyloidogenesis is a change in the secondary and/or tertiary structure of a normal, soluble protein, that fosters self-aggregation and fibril formation. The structural heterogeneity of light chain proteins has hampered understanding of the precise mechanisms involved in fibril formation. The development of effective therapeutics will be benefited by a fundamental understanding of mechanisms and structural prerequisites which govern amyloidogenesis. This review focuses on light chain (AL) amyloidosis resulting from the aggregation of kappa and lambda LCs. Specifically the thermodynamic and structural data of several WT and mutant amyloidogenic LCs have been carefully examined. Moreover, we discuss the importance of hydrophobic and ionic interactions on amyloidosis by comparing several available three-dimensional structures of amyloidogenic and highly homologous non-amyloidogenic proteins that can be destabilized to become amyloidogenic by site specific mutations.     

Benzofuranone derivatives as effective small molecules related to insulin amyloid fibrillation: a structure-function study

Amyloids are protein fibrils of nanometer size resulting from protein self-assembly. They have been shown to be associated with a wide variety of diseases such as Alzheimer's and Parkinson's and may contribute to various other pathological conditions, known as amyloidoses. Insulin is prone to form amyloid fibrils under slightly destabilizing conditions in vitro and may form amyloid structures when subcutaneously injected into patients with diabetes. There is a great deal of interest in developing novel small molecule inhibitors of amyloidogenic processes, as potential therapeutic compounds. In this study, the effects of five new synthetic benzofuranone derivatives were investigated on the insulin amyloid formation process. Protein fibrillation was analyzed by thioflavin-T fluorescence, Congo red binding, circular dichroism, and electron microscopy. Despite high structural similarity, one of the five tested compounds was observed to enhance amyloid fibrillation, while the others inhibited the process when used at micromolar concentrations, which could make them interesting potential lead compounds for the design of therapeutic antiamyloidogenic compounds.     

Syntheses and structure-activity relationships of seven manganese-salen derivatives as anti-amyloidogenic and fibril-destabilizing agents against hen egg-white lysozyme aggregation

Accumulation of intra- and/or extracellular misfolded proteins as amyloid fibrils is a key hallmark in more than 20 amyloid-related diseases. In that respect, blocking or reversing amyloid aggregation via the use of small compounds is considered as two useful approaches in hampering the development of these diseases. In this research, we have studied the ability of different manganese-salen derivatives to inhibit amyloid self-assembly as well as to dissolve amyloid aggregates of hen egg-white lysozyme, as an in vitro model system, with the aim of investigating their structure-activity relationships. By coupling several techniques such as thioflavin T and anilinonaphthalene-8-sulfonic acid fluorescence, congo red absorbance, far-UV circular dichroism, and transmission electron microscopy, we demonstrated that all compounds possessed anti-amyloidogenic activities and were capable of dispersing the fibrillar aggregates. In addition, MTT assay of the treated SK-N-MC cells with the preformed fibrils formed in the presence of compounds at a drug-to-protein molar ratio of 5:1, indicated a significant increase in the viability of cells, compared to the fibrils formed in the absence of each of the compounds. Our spectroscopy, electron microscopy, and cellular studies indicated that EUK-15, with a methoxy group at the para position (group R(5)), had higher activity to either inhibit or disrupt the β-sheet structures relative to other compounds. On the basis of these results, it can be concluded that in addition to aromatic rings of each of the derivatives, the type and position of the side group(s) contribute to lower lysozyme fibril accumulation.     

Synthetic strategies and medicinal properties of beta-lactams

More than five decades since the Discovery of Penicillin, the chemistry and biological activity of b-lactams continue to attract the wide spread attention of research workers. Owing to high efficacy and extremely safe toxicological profile, they are agents of choice in the current therapeutic index for the bacterial infectious diseases. Tremendous efforts have been made into synthesis and structural modification of the beta-lactam nucleus to increase antimicrobial activity and pharmacokinetic performance. These efforts resulted in the development of ampicillin, amoxicillin and a group of cephalosporins as clinically effective therapeutic agents. However the rapid emergence of bacterial strains resistant to most generally used members of this class of compound stimulated research for novel beta-lactams, stable to beta-lactamase and possess high potency, broad spectrum of activity both in vitro and in vivo. The mode of action of beta-lactams is to inhibit an enzyme transpeptidase , penicillin binding proteins, critical in the production of bacterial cell wall.     

Pharmacological modulation of microparticle release: new strategies for the management of atherothrombotic vascular disorders

Microparticles (MPs) are submicron vesicles (0.1-1 μm) shed from the membrane of platelets, monocytes, endothelial cells and other cell types. Abundant clinical evidence relates increased plasma levels of MPs with several cardiovascular and inflammatory diseases, being a topic of tremendous interest in recent years. MPs have been proposed as potential effectors in thrombosis, inflammation, vascular injury or angiogenesis. Although MPs were traditionally considered noxious actors, recent scientific advances revealed another layer of complexity with their diverse roles in the pathophysiology of thrombotic disorders. Therefore, whilst their impact on the evolution of the disease is indisputable, the milieu of factors regulating MP release is still an intriguing field. Since MPs have been shown to be involved in thrombosis and inflammatory diseases, modulation of their release might have important therapeutic applications and provide further insights into their (patho)physiological roles. In this regard, increasing clinical attention has been devoted to the effects of pharmacological agents on MP circulating levels and antigenic composition. This trend led to many recent studies with special focus on the pharmaceutical options to inhibit formation of procoagulant MPs. Thus, this review aims to summarize available clinical and in vitro literature on mechanisms triggering MP release and modulating their activity.     

Arylalkyl ketones, benzophenones, desoxybenzoins and chalcones inhibit TNF-α induced expression of ICAM-1: structure-activity analysis

The interaction between leukocytes and the vascular endothelial cells (EC) via cellular adhesion molecules plays an important role in the pathogenesis of various inflammatory and autoimmune diseases. Small molecules that block these interactions have been targeted as potential therapeutic agents against acute and chronic inflammatory diseases. In an effort to identify potent intercellular cell adhesion molecule-1 (ICAM-1) inhibitors, a large number of arylalkyl ketones, benzophenones, desoxybenzoins and chalcones and their analogs (54 in total) have been synthesized and screened for their ICAM-1 inhibitory activity. The structure-activity relationship studies of these compounds identified three potent chalcone derivatives and also demonstrated the possible mechanism for their ICAM-1 inhibitory activities. The most active compound was found to be 79.     

Zn finger containing proteins as targets for the control of viral infections

The zinc finger proteins have fascinated many research groups because of their modular assembly, broad range of biological functions and more recently because they are attractive targets for antiviral therapy. The zinc finger domain is a very stable structural element whose hallmark is the coordination of a zinc ion by several amino acid residues, usually cysteines and histidines. These structural motifs are associated with protein-nucleic acid recognition as well as protein-protein interactions. The biological function of the zinc finger proteins is strongly dependent on the zinc ion, which assure integrity and stability. Thus, the disruption of critical zinc finger viral proteins represents a fundamentally new approach to inhibit viral replication in the absence of mutations leading to drug resistance phenotypes. This review summarizes the drug design and potential therapeutic applications of viral zinc fingers disrupting agents for the control of viral diseases.     

Targeting T-cell adhesion molecules for drug design

Adhesion molecules participate in many stages of immune response; they regulate leukocyte circulation, lymphoid cell homing to tissues and inflammatory sites, migration across endothelial cells and T-cell stimulation. During T-cell immune response, adhesion molecules form a specialized junction between T-cell and the antigen presenting cell. Thus, many researchers have focused their attention on targeting adhesion molecules for developing therapeutic agents. Most of these efforts are intended to develop drugs for autoimmune and inflammatory diseases. Therapeutic agents like efalizumab and alefacept have been approved by the FDA for the treatment of inflammatory autoimmune diseases. This review focuses on some of the basic aspects and importance of adhesion molecules, recent understanding of the structure of adhesion molecules, and the targeted therapeutic agents.     

Antirheumatic agents and leukocyte recruitment. New light on the mechanism of action of oxaceprol.

Most anti-inflammatory agents used in the treatment of joint diseases exert inhibitory effects on leukocyte infiltration. Methotrexate, a disease-modifying drug, and corticosteroids also inhibit leukocyte accumulation during inflammation. However, the mechanisms of action of these different compounds on leukocytes vary and in the case of non-steroidal anti-inflammatory drugs (NSAIDs) the mechanism(s) may be indirect. No current drug for inflammatory or degenerative joint disease has been proposed to act specifically by an inhibitory action on neutrophilic leukocytes. Oxaceprol is an amino acid derivative that has been used for several years for the treatment of osteoarthritis and rheumatoid arthritis, ameliorating pain and stiffness and showing good gastrointestinal safety, particularly in comparison with NSAIDs. Recent experimental studies have shown that oxaceprol does not inhibit the synthesis of prostaglandins in vitro, but markedly inhibits neutrophil infiltration into the joints of rats with adjuvant arthritis. These results support earlier screening data showing inhibition by oxaceprol of leukocyte infiltration into sites of acute inflammation. In studies on surgical ischemia reperfusion in hamsters in vivo, oxaceprol was an effective inhibitor of leukocyte adhesion and extravasation. It is proposed that oxaceprol represents a therapeutic agent for degenerative and inflammatory joint diseases, which acts predominantly by inhibiting leukocyte adhesion and migration.     

Antiviral and immunomodulatory properties of new pro-glutathione (GSH) molecules

Reduced glutathione (GSH) is present in millimolar concentrations in mammalian cells. It is involved in many cellular functions such as detoxification, amino acid transport, production of coenzymes, and the recycling of vitamins E and C. GSH acts as a redox buffer to preserve the reduced intracellular environment. Decreased glutathione levels have been found in numerous diseases such as cancer, viral infections, and immune dysfunctions. Many antioxidant molecules, such as GSH and N-acetylcysteine (NAC), have been demonstrated to inhibit in vitro and in vivo viral replication through different mechanisms of action. Accumulating evidence suggests that intracellular GSH levels in antigen-presenting cells such as macrophages, influence the Th1/Th2 cytokine response pattern, and more precisely, GSH depletion inhibits Th1-associated cytokine production and/or favours Th2 associated responses. It is known that GSH is not transported to most cells and tissues in a free form. Therefore, a number of different approaches have been developed in the last years to circumvent this problem. This review discusses the capacity of some new molecules with potent pro-GSH effects either to exert significant antiviral activity or to augment GSH intracellular content in macrophages to generate and maintain the appropriate Th1/Th2 balance. The observations reported herein show that pro-GSH molecules represent new therapeutic agents to treat antiviral infections and Th2-mediated diseases such as allergic disorders and AIDS.     

Kinetic Profile of Amyloid Formation in the Presence of an Aromatic Inhibitor by Nuclear Magnetic Resonance

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