Molecular basis of the inhibition and disaggregation of thermally-induced amyloid fibrils of human serum albumin by an anti-Parkinson's drug, benserazide hydrochloride

Bioflavonoids ameliorate crowding induced hemoglobin aggregation: a spectroscopic and molecular docking approach

The cellular environment is densely crowded, confining biomacromolecules including proteins to less available space. This macromolecular confinement may affect the physiological conformation of proteins in long-term processes like ageing. Changes in physiological protein structure can lead to protein conformational disorders including neurodegeneration. An intervention approach using food and plant derived bioflavonoids offered a way to find a treatment for these enervating pathological conditions as there is no remedy available. The bioflavonoids NAR (naringenin), 7HD (7 hydroxyflavanone) and CHR (chrysin) were tested for their ability to protect Hb (hemoglobin) against crowding-induced aggregation. Morphological and secondary structural transitions were studied using microscopic and circular dichroism experiments, respectively. The kinetic study was carried out using the relative thioflavin T assay. Molecular docking, AmylPred2, admetSAR and FRET were applied to understand the binding parameters of bioflavonoids with Hb and their drug likeliness. Isolated human lymphocytes were used as a cellular system to study the toxic effects of Hb aggregates. Redox perturbation and cytotoxicity were evaluated by DCFH-DA and MTT assays, respectively. This study suggests that bioflavonoids bind to Hb in the vicinity of aggregation prone amino acid sequences. Binding of the bioflavonoids stabilizes the Hb against crowding-induced structural alterations. Therefore, this study signifies the potential of bioflavonoids for future treatment of many proteopathies including neurodegeneration.Communicated by Ramaswamy H. Sarma.

Antiglycation, antifibrillation and antioxidative effects of para coumaric acid and vitamin D; an in-vitro and in-silico comparative-cum-synergistic approach

Diabetes Mellitus is a metabolic disorder that results in impaired utilization of carbohydrates, lipids, and proteins. Severe hyperglycemia is its principal clinical symptom. Human serum albumin (HSA) is used as a model protein since it is viewed as a sign of glycaemic management because it is more likely to get glycated in diabetic people than other proteins. Para-coumaric acid (pCA), a phenolic acid, and Vitamin D (vit-D) are used as protective agents. In the present work, we deduce a synergistic-cum-comparative effect of pCA and vit-D, expecting some improvement in the efficacy of pCA when combined with vit-D. Methods employed are DPPH radical scavenging activity, In-vitro glycation of HSA, UV-vis spectroscopy, fluorescence analysis, and circular dichroism measurement. After treatment, increasein the absorbance and fluorescence intensity were reduced along with normalization of CD value. . The glycation-mediated fibrillation assessed by Congo-Red and Thioflavin T (ThT) were found to be diminishedwhen HSA was treated with equimolar concentration of p-CA and vit-D- treatment. Fructosamine adduct formation and lysine modificationwas also decreased, while inhibition to hemolysis and lipid peroxidation was found to increase upon treatment. The reactive oxygen species generation detection was also performed in lymphocytes treated with various protein samples. Docking results further confirmed theblocking some glycation-prone amino acids by both compounds. The study shows that the combination in the ratio of 1:1 has provided higher overall protection comparable to aminoguanidine (AG), the molecule which is utilized as a positive control.

β-Carboline Alkaloids Resist the Aggregation and Cytotoxicity of Human Islet Amyloid Polypeptide

β-Carboline alkaloids have a variety of pharmacological activities, such as antitumor, antibiosis and antidiabetes. Harmine and harmol are two structurally similar β-carbolines that occur in many medicinal plants. In this work, we chose harmine and harmol to impede the amyloid fibril formation of human islet amyloid polypeptide (hIAPP) associated with type 2 diabetes mellitus (T2DM), by a series of physicochemical and biochemical methods. The results indicate that harmine and harmol effectively prevent peptide fibril formation and alleviate toxic oligomer species. In addition, both small molecules exhibit strong binding affinities with hIAPP mainly through hydrophobic and hydrogen bonding interactions, thus reducing the cytotoxicity induced by hIAPP. Their distinct binding pattern with hIAPP is closely linked to the molecular configuration of the two small molecules, affecting their ability to impede peptide aggregation. The study is of great significance for the application and development of β-carboline alkaloids against T2DM.

The inhibitory effect of Sunset Yellow on thermally induced Human Serum Albumin aggregates: Possible role in naturopathy

Intensive research in the field of protein aggregation confirmed that the deposition of amyloid fibrils of proteins are the major cause for the development of various neurotoxic and neurodegenerative diseases, which could be controlled by ensuring the efficient inhibition of aggregation using anti aggregation strategies. Herein, we elaborated the anti amyloidogenic potential of Sunset Yellow (SY) dye against Human Serum Albumin (HSA) fibrillogenesis utilising different biophysical, computational and microscopic techniques. The inhibitory effect of sunset yellow was confirmed by Rayleigh Light Scattering (RLS) measurements along with different dye binding assays (ANS, ThT and CR) by showing concentration dependent reduction in scattering intensity and fluorescence intensity respectively. Further, destabilization and anti fibrillation activity of HSA aggregates were characterized through spectroscopic techniques like Circular Dichroism (CD) and other microscopic techniques like Transmission Electron Microscopy (TEM) for elucidating the structural properties. The SDS-PAGE was also carried out that render the disaggregation effect of the dye on the protein. Moreover, Molecular Docking studies revealed the binding parameters justifying the stable protein-dye complex. Simulation studies were also performed accordingly. Thus, this dye which is used as food additive can serve as a potential aggregation inhibiting agent that can aid in the prevention of amyloidogenic diseases.

Triterpenoids impede the fibrillation and cytotoxicity of human islet amyloid polypeptide

The inhibition of human islet amyloid polypeptide (hIAPP) deposition to block its toxicity is an important strategy for the prevention and treatment of type II diabetes mellitus (T2DM).Natural compounds with pharmacological properties and low toxicity can serve as a good point to discover potential inhibitors of protein misfolding, which may be useful for the treatment of various amyloidosis-related diseases. Previous studies have reported that triterpenoids, such as maslinic acid (MA) and momordicin I (MI), can modulate glucose metabolism partially by reducing insulin resistance. However, the internal antidiabetic mechanism of these triterpenoids remains unclear. In this study, we examined the inhibition and disaggregation of MAandits isomer MI on the fibrillation of hIAPP using various experimental and computational approaches. The assembly behaviors and peptide-induced cytotoxicity of hIAPP could be effectively resisted by MA and MI. Moreover, the interaction of the two triterpenoids with hIAPP displayed a spontaneous and exothermic process. Moreover, molecular dynamics simulation results of different peptides revealed that MA and MI could bind to Asn and other non-polar residues near the core C-terminal region and reduce the oligomerization of hIAPP. The binding affinity was predominantly contributed by hydrophobic, electrostatic and hydrogen bonding interactions. The present work provides valuable data for MA and MI to treat T2DM and amyloidosis-related diseases.

Unusual human serum albumin fibrillation inhibition by ketoprofen and fenoprofen: Mechanistic insights

Development of efficient therapeutic strategies to combat protein misfolding and fibrillation is of great clinical significance. In the current study, efforts have been made to obtain qualitative and quantitative insights into interactions of anti-inflammatory drugs; ketoprofen and fenoprofen with the transport protein HSA and their inhibitory action on fibrillation by employing a combination of calorimetric, spectroscopic, microscopic, and molecular docking methods. Interestingly, both ketoprofen and fenoprofen are able to completely inhibit fibrillation of HSA when added at a concentration of 0.5 mM for fenoprofen or 1 mM ketoprofen. Further, no amorphous aggregates are formed. Isothermal titration calorimetric studies highlight the predominant role of polar interactions of these drugs with protein in prevention of fibrillation. The role of conformational flexibility of benzoyl and phenoxy groups of drugs has been correlated with inhibition efficiency. Such studies highlight the role of functionality required for an inhibitor in addressing neurodegenerative diseases.

Modification with N-benzylisatin restricts stress-induced aggregation of hen egg white lysozyme: Anti-amyloidogenic property of isatin derivative with possible clinical implications

Hen egg white lysozyme (HEWL) is a structural homolog of human lysozyme and is widely used as a model protein to investigate protein aggregation. The effect of N-benzylisatin on stress-induced aggregation of HEWL has been investigated in the present study. Interaction of the isatin derivative with HEWL induced changes in protein secondary and tertiary structural conformation as evident from different biophysical and spectroscopic studies. In addition, modification with N-benzylisatin was found to increase the conformational stability of HEWL and afford considerable resistance to the protein to stress-induced aggregation as indicated from subsequent experimental studies, including thioflavin T fluorescence, microscopic imaging and dynamic light scattering analysis. Protein modification was analysed and confirmed by MALDI-TOF and ESI-MS studies. The results highlight possible clinical implications of isatin derivative in the treatment of protein misfolding and conformational disorders.

Evaluation of ThT augmentation and RLS inner filter effect caused by highly fluorescent coumarin derivative and establishing it as true inhibitor of amyloid fibrillation

Screening of inhibitors that slow down or suppress amyloid fibrils formation relies on some simple but sensitive spectroscopy techniques. Thioflavin T (ThT) fluorescence assay is one of the most common, amyloid specific and sensitive method. However, if an inhibitor is itself fluorescent in the ThT fluorescence range, its screening becomes complicated and require complementary assays. One of such molecules, 6, 7-dihydroxycoumarin (6, 7-DHC, also known as aesculetin, esculetin, and cichorigenin) is fluorescent in the ThT emission range and absorbs in the ThT excitation range. Therefore, it can produce a subtractive effect attributed to primary inner filter effect and/or additive effect due to its self-fluorescence in ThT assay. Our study shows that 6, 7-DHC produces an additive effect in ThT fluorescence, which is minimized at high concentration of ThT and decrease in ThT fluorescence is solely due to its inhibitory effect against HSA fibrillation. These ThT fluorescence-based results are verified through other complementary assays, such as Rayleigh and dynamic light scattering and amyloid-specific Congo red binding assay. Furthermore, hydrophobicity reduction is studied through Nile red (NR) and kinetics through far-UV circular dichroism (far-UV CD) in place of the most commonly employed ThT assay owing to extremely high fluorescence of 6, 7-DHC during initial incubation period.

On the binding reaction of loratadine with human serum acute phase protein alpha 1-acid glycoprotein

Loratadine is an important anti-allergic drug. It is a second generation antihistamine drug used to treat allergic rhinitis, hay fever and urticaria. Human serum alpha 1-acid glycoprotein (AG) is an important acute phase protein and its serum concentration is found to increase in inflammation and acute response.The binding interaction between loratadine and AG is studied using spectroscopy and molecular docking techniques. The results obtained from fluorescence quenching experiments demonstrated that the fluorescence intensity of AG is quenched by loratadine. Loratadine was found to bind AG with the binding constant of ≈10⁴ at 298 K. The Gibb's free energy change was found to be negative for the interaction of loratadine with AG indicating the binding process is spontaneous. Binding of loratadine with AG induced ordered structures in the protein. Hydrogen bonding and hydrophobic interactions were the main bonding forces between AG-loratadine as revealed by molecular docking results. This study suggests the importance of binding of anti-allergic drug to AG spatially in the diseases where the plasma concentration of AG increases many folds and interaction with this protein becomes significant. This study will help in design of drug dosage and adjustment accordingly to achieve optimal treatment outcome. Communicated by Ramaswamy H. Sarma.

Probing the Nongeneralized Amyloid Inhibitory Mechanism of Hydrophobic Chaperone

Increasing prevalence of protein misfolding disorders urges the search for effective therapies. Although several antiaggregation molecules have been identified, their molecular process of aggregation and clinical trials are underway. The present study is focused on the mechanism through which phenyl butyrate (PB), a chemical chaperone, triggers inhibition of human serum albumin (HSA) fibrillation. Turbidity and Rayleigh light scattering (RLS) measurements reveal the marked presence of aggregates in HSA that were confirmed as amyloid fibrils by thioflavin T (ThT) and Congo red (CR) and were subsequently inhibited by PB in a dose dependent manner. ThT fluorescence kinetics reveals a decrease in the apparent rate constant, K_app, in the presence of PB without triggering a lag phase in HSA suggesting PB's interference with the elongation phase. Dynamic light scattering (DLS) results display a reduction in the aggregate size in the presence of PB. Isothermal titration calorimetry (ITC) data reveals strong binding of PB at site II both at 25 °C (K_b ≈ 1.94 × 10⁵ M^-1) and 65 °C (K_b ≈ 2.90 × 10⁴ M^-1), mediated by hydrogen bonding. Overall, our finding establishes that PB stabilizes partially unfolded HSA molecules through hydrogen bonding, thereby preventing establishment of hydrogen bonds between them and hindering their progression into amyloid fibrils. This is in contrast to its chaperone effect manifested with other proteins.

An insight into the inhibition of fibrillation process verses disaggregation of preformed fibrils of bovine serum albumin by isoprenaline hydrochloride

This study is based on the analysis of the recent trend of medication in neurodegenerative diseases. Due to the asymptomatic nature of the diseases, medication delays. Therefore, mechanism of medication assists in removal of the symptoms. Therefore, in order to find out remedy for complete prevention of the disease we have considered "inhibition verses disaggregation" study. Various biophysical techniques such as turbidity measurement (TM), Thioflavin T (ThT) binding assays, circular dichroism (CD), transmission electron microscopy (TEM) etc. has been performed. Isoprenaline hydrochloride (ISO) was a good candidate for inhibition and disaggregation of preformed fibrils of BSA. Therefore, it is concluded that inhibition of fibrillation process was more momentous, effective procedure in restricting the aggregation by stabilizing the native conformation of BSA than the removal of preformed amyloid fibrils under in vitro condition. Forwarding ahead, to understand the efficiency of the two processes under in vivo condition, this study can be applied on animal models so that we can look forward on human beings as well for the development of vaccines. This study is concerned about the applied aspect of research in future so that we can hope for prevention of the disease instead of only removal of the symptoms.

The triphenylmethane dye brilliant blue G is only moderately effective at inhibiting amyloid formation by human amylin or at disaggregating amylin amyloid fibrils, but interferes with amyloid assays; Implications for inhibitor design

The development of inhibitors of islet amyloid formation is important as pancreatic amyloid deposition contributes to type-2 diabetes and islet transplant failure. The Alzheimer's Aβ peptide and human amylin (h-amylin), the polypeptide responsible for amyloid formation in type-2 diabetes, share common physio-chemical features and some inhibitors of Aβ also inhibit amyloid formation by h-amylin and vice versa. Thus, a popular and potentially useful strategy to find lead compounds for anti-amylin amyloid agents is to examine compounds that have effects on Aβ amyloid formation. The triphenylmethane dye, brilliant blue G (BBG, Sodium;3-[[4-[(E)-[4-(4-ethoxyanilino)phenyl]-[4-[ethyl-[(3-sulfonatophenyl)methyl]azaniumylidene]-2-methylcyclohexa-2,5-dien-1-ylidene]methyl]-N-ethyl-3-methylanilino]methyl]benzenesulfonate) has been shown to modulate Aβ amyloid formation and inhibit Aβ induced toxicity. However, the effects of BBG on h-amylin have not been examined, although other triphenylmethane derivatives inhibit h-amylin amyloid formation. The compound has only a modest impact on h-amylin amyloid formation unless it is added in significant excess. BBG also remodels preformed h-amylin amyloid fibrils if added in excess, however BBG has no significant effect on h-amylin induced toxicity towards cultured β-cells or cultured CHO-T cells except at high concentrations. BBG is shown to interfere with standard thioflavin-T assays of h-amylin amyloid formation and disaggregation, highlighting the difficulty of interpreting such experiments in the absence of other measurements. BBG also interferes with ANS based assays of h-amylin amyloid formation. The work highlights the differences between inhibition of Aβ and h-amylin amyloid formation, illustrates the limitation of using Aβ inhibitors as leads for h-amylin amyloid inhibitors, and reinforces the difficulties in interpreting dye binding assays of amyloid formation.

Metal Chelation Therapy and Parkinson's Disease: A Critical Review on the Thermodynamics of Complex Formation between Relevant Metal Ions and Promising or Established Drugs

The present review reports a list of approximately 800 compounds which have been used, tested or proposed for Parkinson's disease (PD) therapy in the year range 2014-2019 (April): name(s), chemical structure and references are given. Among these compounds, approximately 250 have possible or established metal-chelating properties towards Cu(II), Cu(I), Fe(III), Fe(II), Mn(II), and Zn(II), which are considered to be involved in metal dyshomeostasis during PD. Speciation information regarding the complexes formed by these ions and the 250 compounds has been collected or, if not experimentally available, has been estimated from similar molecules. Stoichiometries and stability constants of the complexes have been reported; values of the cologarithm of the concentration of free metal ion at equilibrium (pM), and of the dissociation constant Kd (both computed at pH = 7.4 and at total metal and ligand concentrations of 10-6 and 10-5 mol/L, respectively), charge and stoichiometry of the most abundant metal-ligand complexes existing at physiological conditions, have been obtained. A rigorous definition of the reported amounts is given, the possible usefulness of this data is described, and the need to characterize the metal-ligand speciation of PD drugs is underlined.

Unravelling the interaction mechanism between clioquinol and bovine serum albumin by multi-spectroscopic and molecular docking approaches

Clioquinol has recently been proposed for the treatment of Alzheimer's disease. It is able to diminish β-amyloid protein aggregation and to restore cognition of Alzheimer's mice. However, its therapeutic benefits for Alzheimer's disease in human remain controversy and need further confirmation. Herein, we have explored the interaction mechanism of clioquinol toward bovine serum albumin (BSA) by means of multi-spectroscopic and docking simulation approaches. Clioquinol interacts with BSA by a combined mechanism of static and dynamic processes. Application of the Hill's equation to fluorescence quenching experiment revealed that the binding constant of the BSA-clioquinol complex is extremely high at 10⁸ M^-1 level. Competitive displacement and docking analysis consistently suggested that there are the multiple binding modes of clioquinol toward BSA. Competitive binding study showed that clioquinol shares the binding sites with ibuprofen and digitoxin on albumin, referring to be site II and site III binding compounds. Besides, partial binding in site I was also observed. Docking simulation confirmed that clioquinol favors to bind in site I, site II, site III, fatty acid binding site 5, and the protein cleft between subdomain IB and IIIB of the BSA. Due to its small size and electric dipole property, clioquinol may easily fit in multiple pockets of the BSA. Our finding suggests the potential role of BSA as a clioquinol carrier in the vascular system. Nonetheless, clioquinol-induced BSA aggregation has been observed by the three-dimensional fluorescence technique. This phenomenon may not only impair the BSA, but may also affect other endogenous proteins, which eventually causes adverse effects to human. Therefore, the redesigned or modified molecular structure of clioquinol may reduce its toxicity and improve its bioavailability.