Oligomeric forms of insulin amyloid aggregation disrupt outgrowth and complexity of neuron-like PC12 cells

Light and Shadow of Na-Glucose Cotransporter 2 Inhibitors in the Treatment of Diabetes Mellitus: Points for Improvement Based on Our Clinical Experience

We analyzed the effect of Na-glucose cotransporter 2 inhibitors (SGLT2-I) in diabetic patients visiting our hospital. The study included 236 patients treated with SGLT2-I alone or with codiabetic drugs for at least two years. We analyzed overtime changes in glycosylated hemoglobin A1c (HbA1c) in the patients by repeated analyses of variance (ANOVA) and evaluated the therapeutic effect. HbA1c levels decreased significantly in the first six months after treatment. Afterward, they leveled off and increased slightly over the next two years. Six months after treatment, the mean (SD) of HbA1c was 8.19 (1.46) %; the mean difference dropped by 0.91%, and HbA1c in mild DM2 did not drop by below 8.0%. Overall, there was only a slight improvement. We performed multivariate logistic regression analysis using a model with or without improvement as the objective variable and several explanatory variables. Na and Hct were significant factors. They increased considerably over six months and then leveled off. eGFR significantly reduced in the hyperfiltration group six months after treatment. The annual decline rate in eGFR was also faster, even in the nonhyperfiltration group than in the healthy subjects, which may be a characteristic of renal clearance in SGLT2-I treatment. In conclusion, SGLT2-I is an excellent antidiabetic, nephroprotective agent to eliminate hyperfiltration, but unfortunately, SGLT2-I alone does not have enough power to reduce blood glucose levels. SGLT2-I, with insulin or insulin secretagogues, enhances insulin resistance, induces hyperinsulinemia, and exacerbates type 2 DM. In contrast, SGLT2-I, with noninsulin antidiabetic agents and a low-carbohydrate diet, may bring better results.

Molecular mechanism of insulin aggregation in the presence of a cationic surfactant

Protein aggregation and amyloid fibrillation are connected with neurodegenerative disorders. Insulin, a small molecular weight protein related to type II diabetes, has been shown to self-assemble to form protein aggregates. In this work, we investigated the effects of cetyltrimethylammonium bromide (CTAB) of insulin on the in vitro aggregation process at pH 7.4 and 2.0. The aggregation tendency of insulin was measured using a variety of biophysical approaches, including turbidity measurements, light scattering, far UV-CD, ThT dye binding, and transmission electron microscopy. The turbidity results demonstrated that at pH 7.4, a low concentration of CTAB (30-180 μM) causes insulin aggregation but at higer concentration (>180 μM) aggregation was not seen. However, at pH 2.0, both low as well as high concentrations of CTAB were unable to promote insulin aggregation. The ThT dye binding and far-UV CD data suggest that aggregation induced by CTAB is not having an ordered structure. Insulin treated with higher concentrations (>180 μM) of CTAB, the insulin gained a secondary structure. The possible cause of inducing aggregation in insulin is electrostatic and hydrophobic interaction because insulin contains a net negative charge at pH 7.4 and no aggregation at pH 2.0 due to electrostatic repulsion.

Dual Role of a Fluorescent Small Molecule as a Sensor and Inhibitor of Protein Fibrillation

Ordered fibrillar aggregates of proteins, called amyloids, are prevalent in several diseases like Alzheimer's, Parkinson's, and Type II diabetes. The key challenge in the treatment of such diseases is the early detection of protein fibrillation and its effective inhibition using extrinsic agents. Thus, molecules that can both detect and inhibit protein fibril formation have great diagnostic and therapeutic utility. Using insulin as a model protein, we report the dual action of an isoquinoline based molecule, named MK14 which detects and prevents insulin fibrillation. Dose dependent inhibition of insulin fibrillation by MK14 gave an IC₅₀ value of 9 μM, and mechanistic investigations suggested that MK14 prevented the elongation of fibrils by interacting with pre-fibrillar intermediates. The fluorescence of MK14 enhanced upon binding to fibrils of insulin as well as those of α-synuclein, the protein involved in Parkinson's disease. MK14 is an environmentally sensitive fluorophore, which could also detect amorphous aggregates of insulin. The dual nature of MK14 as an inhibitor and detector of protein fibrillation makes it an attractive lead compound for monitoring and disrupting protein amyloidogenesis.

Current Insights on the Use of Insulin and the Potential Use of Insulin Mimetics in Targeting Insulin Signalling in Alzheimer's Disease

Alzheimer's disease (AD) and type 2 diabetes (T2D) are chronic diseases that share several pathological mechanisms, including insulin resistance and impaired insulin signalling. Their shared features have prompted the evaluation of the drugs used to manage diabetes for the treatment of AD. Insulin delivery itself has been utilized, with promising effects, in improving cognition and reducing AD related neuropathology. The most recent clinical trial involving intranasal insulin reported no slowing of cognitive decline; however, several factors may have impacted the trial outcomes. Long-acting and rapid-acting insulin analogues have also been evaluated within the context of AD with a lack of consistent outcomes. This narrative review provided insight into how targeting insulin signalling in the brain has potential as a therapeutic target for AD and provided a detailed update on the efficacy of insulin, its analogues and the outcomes of human clinical trials. We also discussed the current evidence that warrants the further investigation of the use of the mimetics of insulin for AD. These small molecules may provide a modifiable alternative to insulin, aiding in developing drugs that selectively target insulin signalling in the brain with the aim to attenuate cognitive dysfunction and AD pathologies.

Molecular Aspects of Insulin Aggregation and Various Therapeutic Interventions

Protein aggregation leading to the formation of amyloid fibrils has various adverse effects on human health ranging from fatigue and numbness to organ failure and death in extreme cases. Insulin, a peptide hormone commonly used to treat diabetes, undergoes aggregation at the site of repeated injections in diabetic patients as well as during its industrial production and transport. The reduced bioavailability of insulin due to aggregation hinders the proper control of glucose levels in diabetic patients. Thus, it is necessary to develop rational approaches for inhibiting insulin aggregation, which in turn requires a detailed understanding of the mechanism of fibrillation. Given the relative simplicity of insulin and ease of access, insulin has also served as a model system for studying amyloids. Approaches to inhibit insulin aggregation have included the use of natural molecules, synthetic peptides or small molecules, and bacterial chaperone machinery. This review focuses on insulin aggregation with an emphasis on its mechanism, the structural features of insulin fibrils, and the reported inhibitors that act at different stages in the aggregation pathway. We discuss molecules that can serve as leads for improved inhibitors for use in commercial insulin formulations. We also discuss the aggregation propensity of fast- and slow-acting insulin biosimilars, commonly administered to diabetic patients. The development of better insulin aggregation inhibitors and insights into their mechanism of action will not only aid diabetic therapies, but also enhance our knowledge of protein amyloidosis.

Structural Stability of Insulin Oligomers and Protein Association-Dissociation Processes: Free Energy Landscape and Universal Role of Water

Association and dissociation of proteins are important biochemical events. In this Feature Article, we analyze the available studies of these processes for insulin oligomers in aqueous solution. We focus on the solvation of the insulin monomer in water, stability and dissociation of its dimer, and structural integrity of the hexamer. The intricate role of water in solvation of the dimer- and hexamer-forming surfaces, in long-range interactions between the monomers and the stability of the oligomers, is discussed. Ten water molecules inside the central cavity stabilize the structure of the insulin hexamer. We discuss how different order parameters can be used to understand the dissociation of the insulin dimer. The calculation of the rate using a recently computed multidimensional free energy provides considerable insight into the interplay between protein and water dynamics.

Monitoring the surface tension by the pendant drop technique for detection of insulin fibrillogenesis

Monitoring the aggregation of amyloid-prone proteins is critical for understanding the mechanism of amyloid fibril formation. Insulin, when dissolved in low pH buffer, has a surface tension of 61-64 mN m^-1, as measured by the pendant drop technique. Formation of insulin amyloid fibrils resulted in the increase of the surface tension values up to 71.2-73.5 mN m^-1. The kinetics of fibril formation and fibril morphology were validated by ThT fluorescence and AFM, respectively. The results demonstrate that monitoring the surface tension by the pendant drop technique is a valuable tool for the detection of insulin amyloid aggregation.

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.

Amyloid Prefibrillar Oligomers: The Surprising Commonalities in Their Structure and Activity

It has been proposed that a “common core” of pathologic pathways exists for the large family of amyloid-associated neurodegenerations, including Alzheimer’s, Parkinson’s, type II diabetes and Creutzfeldt–Jacob’s Disease. Aggregates of the involved proteins, independently from their primary sequence, induced neuron membrane permeabilization able to trigger an abnormal Ca²⁺ influx leading to synaptotoxicity, resulting in reduced expression of synaptic proteins and impaired synaptic transmission. Emerging evidence is now focusing on low-molecular-weight prefibrillar oligomers (PFOs), which mimic bacterial pore-forming toxins that form well-ordered oligomeric membrane-spanning pores. At the same time, the neuron membrane composition and its chemical microenvironment seem to play a pivotal role. In fact, the brain of AD patients contains increased fractions of anionic lipids able to favor cationic influx. However, up to now the existence of a specific “common structure” of the toxic aggregate, and a “common mechanism” by which it induces neuronal damage, synaptotoxicity and impaired synaptic transmission, is still an open hypothesis. In this review, we gathered information concerning this hypothesis, focusing on the proteins linked to several amyloid diseases. We noted commonalities in their structure and membrane activity, and their ability to induce Ca²⁺ influx, neurotoxicity, synaptotoxicity and impaired synaptic transmission.

Synthesis and Evaluation of Arylamides with Hydrophobic Side Chains for Insulin Aggregation Inhibition

Insulin, a peptide hormone, forms fibrils under aberrant physiological conditions leading to a reduction in its biological activity. To ameliorate insulin aggregation, we have synthesized a small library of oligopyridylamide foldamers decorated with different combination of hydrophobic side chains. Screening of these compounds for insulin aggregation inhibition using a Thioflavin-T assay resulted in the identification of a few hit molecules. The best hit molecule, BPAD2 inhibited insulin aggregation with an IC₅₀ value of 0.9 μM. Mechanistic analyses suggested that BPAD2 inhibited secondary nucleation and elongation processes during aggregation. The hit molecules worked in a mechanistically distinct manner, thereby underlining the importance of structure-activity relationship studies in obtaining a molecular understanding of protein aggregation.

Blended polar/nonpolar peptide conjugate interferes with human insulin amyloid-mediated cytotoxicity

Insulin, a peptide hormone and a key regulator of blood glucose level, is routinely administered to type-I diabetic patients to achieve the required glycemic control. Insulin aggregation and ensuing amyloidosis has been observed at repeated insulin injection sites and in injectable formulations. The latter occurs due to insulin agglomeration during shipping and storage. Such insulin amyloid leads to enhanced immunogenicity and allow potential attachment to cell membranes leading to cell permeability and apoptosis. Small molecule inhibitors provide useful interruption of this process and inhibit protein misfolding as well as amyloid formation. In this context, we report the propensity of a palmitoylated peptide conjugate to inhibit insulin aggregation and amyloid-mediated cytotoxicity, via designed interference with polypeptide interfacial interactions.

Intranasal Insulin Enhances Intracerebroventricular Streptozotocin-Induced Decrease in Olfactory Discriminative Learning via Upregulation of Subventricular Zone-Olfactory Bulb Neurogenesis in the Rat Model

Olfactory perception and learning play a vital role in the animal's entire life for habituation and survival. Insulin and insulin receptor signaling is well known to modulate the olfactory function and is also involved in the regulation of neurogenesis. A very high density of insulin receptors is present in the olfactory bulb (OB), the brain area involved in the olfactory function, where active adult neurogenesis also takes place. Hence, our study was aimed to explore the effect of intranasal insulin treatment and the involvement of the subventricular zone-olfactory bulb (SVZ-OB) neurogenesis on olfactory discriminative learning and memory in intracerebroventricular streptozotocin (ICV STZ) rat model. Our findings revealed that intranasal insulin treatment significantly increased ICV STZ-induced decrease in the olfactory discriminative learning. No significant change was observed in the post-treatment olfactory memory upon ICV STZ and intranasal insulin treatment. ICV STZ also caused a substantial decline in the SVZ-OB neurogenesis, as indicated by the reduction in the number of 5-bromo-2'-deoxyuridine (BrdU+) cells, BrdU+ Nestin+ cells, and Doublecortin (DCX+) cells, which was reversed by intranasal insulin treatment. Intranasal insulin treatment also increased the number of immature neurons reaching the olfactory bulb (OB) as indicated by an increase in the DCX expression in the OB as compared to the ICV STZ administered group. ICV STZ administration also resulted in the modulation of the expression of the genes regulating postnatal SVZ-OB neurogenesis like Mammalian achaete scute homolog 1 (Mash 1), Neurogenin 2 (Ngn 2), Neuronal differentiation 1 (Neuro D1), and T box brain protein 2 (Tbr 2). Intranasal insulin treatment reverted these changes in gene expression, which might be responsible for the observed increase in the SVZ-OB neurogenesis and hence the olfactory discriminative learning.

The concept of protein folding/unfolding and its impacts on human health

Proteins have evolved in specific 3D structures and play different functions in cells and determine various reactions and pathways. The newly synthesized amino acid chains once depart ribosome must crumple into three-dimensional structures so can be biologically active. This process of protein that makes a functional molecule is called protein folding. The protein folding is both a biological and a physicochemical process that depends on the sequence of it. In fact, this process occurs more complicated and in some cases and in exposure to some molecules like glucose (glycation), mistaken folding leads to amyloid structures and fatal disorders called conformational diseases. Such conditions are detected by the quality control system of the cell and these abnormal proteins undergo renovation or degradation. This scenario takes place by the chaperones, chaperonins, and Ubiquitin-proteasome complex. Understanding of protein folding mechanisms from different views including experimental and computational approaches has revealed some intermediate ensembles such as molten globule and has been subjected to biophysical and molecular biology attempts to know more about prevalent conformational diseases.

Sensing and modulation of amyloid fibrils by photo-switchable organic dots

Abnormal aggregation of amyloidogenic proteins (like Aβ 42, amylin, α-synuclein, insulin) and the deposition of these aggregates is believed to be associated with several diseases known as amyloidosis. The pathway of aggregation involves three distinct phases: the oligomeric, elongation and plateau phases. Among them, the oligomeric phase of Aβ 42 and α-synuclein involves the generation of transient oligomeric species suspected to cause several neurological disorders, including Alzheimer's and Parkinson's diseases. Over the past few years, scientists have devoted much more effort to devising new fluorescent molecular probes to estimate the mechanisms of formation, and have gained vital information about possible therapeutic routes for amyloidosis. However, such fluorescent probes face serious limitations because of self-quenching at high concentrations of the probe; therefore, they are inappropriate for quantitative analysis and bio-imaging experiments. Hence, smart biocompatible fluorescent probes are indispensable, as they not only overcome the drawbacks of conventional fluorescent probes, but also have the potential ability to fight amyloidosis through modulation of the pathways involved. In this work, for the first time we introduce a series of promising photo-switchable aggregation-induced emission (AIE) dots (DPAPMI, CPMI) and aggregation caused quenching (ACQ) dots (DMAPMI) which can detect amyloid fibrils in terms of switching and enhancing their fluorescence emission. Interestingly, the organic dots enhance the aggregation rate of insulin by speeding up the microscopic processes, specifically secondary nucleation (with rate constant k2) and the elongation process (with rate constant k+). Moreover, the comparison of kinetics studies with ThT suggests that our organic dots can sense pre-fibrillar aggregates of insulin during the aggregation process, which may be beneficial for the early detection of amyloid fibrils. In summary, our study indicates that these organic dots can be used for the imaging and early stage detection of amyloid fibril formation and the modulation of amyloid formation pathways.

Small-Molecule Inhibitor Prevents Insulin Fibrillogenesis and Preserves Activity

Amyloidosis is a well-known but poorly understood phenomenon caused by the aggregation of proteins, often leading to pathological conditions. For example, the aggregation of insulin poses significant challenges during the preparation of pharmaceutical insulin formulations commonly used to treat diabetic patients. Therefore, it is essential to develop inhibitors of insulin aggregation for potential biomedical applications and for important mechanistic insights into amyloidogenic pathways. Here, we have identified a small molecule M1, which causes a dose-dependent reduction in insulin fibril formation. Biophysical analyses and docking results suggest that M1 likely binds to partially unfolded insulin intermediates. Further, M1-treated insulin had lower cytotoxicity and remained functionally active in regulating cell proliferation in cultured Drosophila wing epithelium. Thus, M1 is of great interest as a novel agent for inhibiting insulin aggregation during biopharmaceutical manufacturing.

De Novo designed 13 mer hairpin-peptide arrests insulin and inhibits its aggregation: role of OH–π interactions between water and hydrophobic amino acids

Background: Protein aggregation in the cellular systems can be highly fatal causing a series of diseases including neurodegenerative diseases like ALS, Alzheimer, Prion Diseases, Parkinson's and other diseases like type II diabetes. To date, there is no crucial mechanism invented that shows how a protein molecule unfolds or misfolds. Insulin fibrillation in type II diabetes is an alarming event that brings every year deaths of millions of people around the globe. Pharmaceutical companies are still in the cultivation of finding newer therapeutic agents which halt/impede insulin aggregation to combat diabetes II and improve the patient's life expectancy. Methods and Results: Here in this report, we have engineered four short 13 mer peptides (N-term-DMYY- N-term-DITT- N-term-DIFF- N-term-KVYY-) which target monomeric insulin in its globular form. The de Novo designed peptides are found to be non-cytotoxic in human HEK293 cells. Among these four peptides, only DITT- showed complete inhibition of insulin fibrillation, whereas DIFF- and DIYY- and KVYY- lost their functionality to impede insulin aggregation to a great extent. High-resolution multi-dimensional NMR experiments portrayed the 13 mer sequences of peptides in the beta-hairpin forms. A series of biophysical techniques like CD, ThT assay, DLS, SEM, ITC, size-exclusion chromatography, and molecular dynamics simulation strongly evidenced inhibition of insulin fibrillation by N-term-DITT- compared to those by the other peptides. Conclusion and significance: Here we tried to unravel how DITT- could impede insulin fibrillation.

Protein aggregation in the cellular systems can be highly fatal causing a series of diseases including neurodegenerative diseases like ALS, Alzheimer, Prion Diseases, Parkinson's and other diseases like type II diabetes.

Toxicity of insulin-derived amyloidosis: a case report

BACKGROUND

Insulin-derived amyloidosis is a skin-related complication of insulin therapy that interferes with insulin therapy. Although toxicities of in vitro-formed insulin amyloid fibrils have been well studied, the toxicity of insulin-derived amyloidosis remains to be clarified.

CASE PRESENTATION

A 58-year-old man with type 2 diabetes mellitus underwent a lower limb amputation due to diabetic gangrene. Several antibiotics including minocycline were administered for infection and sepsis. A hard mass at the insulin injection sites in the lower abdomen was discovered by chance four months later. Although no abnormal findings in the surface skin of the mass were observed, necrotic tissue was seen around the mass when a biopsy was performed. Histological and toxicity studies were performed for this patient and four other patients with abdominal masses at insulin injection sites. Histological and immunohistochemical studies showed that the masses had typical characteristics of amyloid deposits in all cases, whereas necrotic findings were seen adjacent to the amyloid deposit only in the case presented. Toxicity studies indicated that the amyloid tissue from the present case had significant cell toxicity compared to the control skin tissue or the amyloid tissues from the other four cases.

CONCLUSIONS

This report showed that toxic insulin-derived amyloidosis can occur. In addition, this report suggested that toxic insulin-derived amyloidosis may cause necrosis in the surrounding tissue. Although the toxic amyloid deposit of insulin-derived amyloidosis was found in only one patient, no structural differences between toxic and non-toxic deposits were seen on histological and immunohistochemical studies.

Surface tension and intrinsic amyloid fluorescence of serum and cerebrospinal fluid samples in Alzheimer´s disease

AIM

Surface tension of biological fluids can be influenced by changes in oligomerization or aggregation of surfactant peptides or proteins. Amphiphilic peptides of amyloid-β or other amyloidogenic peptides/proteins display properties of surfactants, oligomerization and aggregation increase also their fluorescence intensity compared with native structures. Results/methodology: We estimated surface tension and native/ThioflavinT-based/intrinsic amyloid fluorescence intensity in serum and cerebrospinal fluid samples for their evalution as diagnostic biomarkers for Alzheimer´s disease (AD).

DISCUSSION/CONCLUSION

Our results indicate that values of surface tension are not a suitable biomarker for AD. However, the ratio of ThioflavinT-based fluorescence to intrinsic amyloid fluorescence in cerebrospinal fluid appears to be an acceptable supportive diagnostic biomarker for AD (its sensitivity was 61.1%, and the specificity 70.8% when compared with aged controls).

Trodusquemine enhances Aβ42 aggregation but suppresses its toxicity by displacing oligomers from cell membranes

Transient oligomeric species formed during the aggregation process of the 42-residue form of the amyloid-β peptide (Aβ₄₂) are key pathogenic agents in Alzheimer's disease (AD). To investigate the relationship between Aβ₄₂ aggregation and its cytotoxicity and the influence of a potential drug on both phenomena, we have studied the effects of trodusquemine. This aminosterol enhances the rate of aggregation by promoting monomer-dependent secondary nucleation, but significantly reduces the toxicity of the resulting oligomers to neuroblastoma cells by inhibiting their binding to the cellular membranes. When administered to a C. elegans model of AD, we again observe an increase in aggregate formation alongside the suppression of Aβ₄₂-induced toxicity. In addition to oligomer displacement, the reduced toxicity could also point towards an increased rate of conversion of oligomers to less toxic fibrils. The ability of a small molecule to reduce the toxicity of oligomeric species represents a potential therapeutic strategy against AD.

Paclitaxel inhibited lysozyme fibrillation by increasing colloidal stability through formation of "off-pathway" oligomers

Protein fibrillation is a challenging issue in medicine, causing many diseases, and an impediment to pharmaceutics and protein industry. Many chemicals, especially polyphenol compounds and aromatic small molecules, have been widely used as an effective strategy to combat protein fibril formation. Hence, understanding mechanisms of fibrillation inhibition and contributing forces in this process are significant. In this study, the inhibitory effect of paclitaxel on lysozyme fibrillation was investigated with respect to thermal and colloidal stability. Fibrillation was monitored with ThT fluorescence, circular dichroism, and AFM; paclitaxel-lysozyme interaction with isothermal titration calorimetry and docking; thermal and colloidal stability with differential scanning calorimetry and zeta-pulse, respectively. Paclitaxel inhibited lysozyme fibrillation, and interacted with lysozyme through hydrogen bonds and van der Waals' interactions. The viability of PC12 cells retrieved as a result of fibrillation inhibition by paclitaxel. Hydrophobic forces dominantly shielded the aggregation-prone region of lysozyme and suppressed the effective interactions between lysozyme monomers. Although paclitaxel did not affect lysozyme's thermal stability, it increased lysozyme's colloidal stability by either increasing the surface charge density or charge distribution on lysozyme. In conclusion, our results suggest a model for paclitaxel's inhibitory role through two complementary steps driving to "off-pathway" oligomer formation and attenuation of fibril formation.

Interaction of iron nanoparticles with nervous system: an in vitro study

Nanoparticles (NPs) are one of the interesting and widely studying issues mainly because of their particular physico-chemical features and broad applications in the field of biomedical sciences, such as diagnosis and drug delivery. In this study, the interaction of iron nanoparticles (Fe-NPs) with Tau protein and PC12 cell, as potential nervous system models, was investigated with a range of techniques including dynamic light scattering, intrinsic fluorescence spectroscopy, circular dichroism, [(3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium-bromid] assay, and acridine orange/ethidium bromide (AO/EB) dual staining method. An inverse correlation between Stern and Volmer constant (K_SV) and temperature indicated a probable static quenching mechanism occurred between Tau protein and Fe-NPs. The number of binding site (n = 0.86) showed that there is almost one binding site of Fe-NP per protein. The negative values of ∆H (-53.21 kJ/mol) and T∆S (-42.44 kJ/mol) revealed that Fe-NPs interacts with Tau protein with dominate role of hydrogen bonds and van der Waals interactions and this interaction was spontaneous (∆G = -10.77 kJ/mol). Also, Fe-NPs stabilized the random coil structure of Tau protein. Moreover, Fe-NPs reduced PC12 cells viability by fragmentation of DNA in an apoptotic manner. In conclusion, induced conformational changes of Tau protein and cytotoxicity of PC12 cells by Fe-NP were revealed to be in a concentration and time-dependent manner.

Selective inhibition of aggregation/fibrillation of bovine serum albumin by osmolytes: Mechanistic and energetics insights

Bovine serum albumin (BSA) is an important transport protein of the blood and its aggregation/fibrillation would adversely affect its transport ability leading to metabolic disorder. Therefore, understanding the mechanism of fibrillation/aggregation of BSA and design of suitable inhibitor molecules for stabilizing its native conformation, are of utmost importance. The qualitative and quantitative aspects of the effect of osmolytes (proline, hydroxyproline, glycine betaine, sarcosine and sorbitol) on heat induced aggregation/fibrillation of BSA at physiological pH (pH 7.4) have been studied employing a combination of fluorescence spectroscopy, Rayleigh scattering, isothermal titration calorimetry (ITC), dynamic light scattering (DLS) and transmission electron microscopy (TEM). Formation of fibrils by BSA under the given conditions was confirmed from increase in fluorescence emission intensities of Thioflavin T over a time period of 600 minutes and TEM images. Absence of change in fluorescence emission intensities of 8-Anilinonaphthalene-1-sulfonic acid (ANS) in presence of native and aggregated BSA signify the absence of any amorphous aggregates. ITC results have provided important insights on the energetics of interaction of these osmolytes with different stages of the fibrillar aggregates of BSA, thereby suggesting the possible modes/mechanism of inhibition of BSA fibrillation by these osmolytes. The heats of interaction of the osmolytes with different stages of fibrillation of BSA do not follow a trend, suggesting that the interactions of stages of BSA aggregates are osmolyte specific. Among the osmolytes used here, we found glycine betaine to be supporting and promoting the aggregation process while hydroxyproline to be maximally efficient in suppressing the fibrillation process of BSA, followed by sorbitol, sarcosine and proline in the following order of their decreasing potency: Hydroxyproline> Sorbitol> Sarcosine> Proline> Glycine betaine.

Fluorescence monitoring of the effect of oxidized lipids on the process of protein fibrillization

The kinetics of lysozyme and insulin amyloid formation in the presence of the oxidized phospholipids (oxPLs) was investigated using Thioflavin T fluorescence assay. The kinetic parameters of fibrillization process (lag time and apparent rate constant) have been determined upon varying the following experimental parameters: the type of lipid assemblies (premicellar aggregates and lipid bilayer vesicles), pH, temperature and lipid-to-protein molar ratio. It was found that oxPLs premicellar aggregates induced the more pronounced increase of the maximum Thioflavin T fluorescence, which is proportional to the extent of fibril formation, compared to the vesicles composed of the oxidized and unoxidized lipids. In contrast, the oxPLs, used as dispersions or included into vesicles, inhibited fibril nucleation and elongation under near-physiological conditions in vitro compared to liposomes containing unoxidized lipids. The results obtained provide deeper insight into the molecular mechanisms of the oxidative stress-modulated conformational diseases, and could be employed for the anti-amyloid drug development.

Interaction of single and multi wall carbon nanotubes with the biological systems: tau protein and PC12 cells as targets

Subtle changes in the structure of nanoparticles influence their surface tension and corresponding interaction with cells and proteins. Here, the interaction of the single wall carbon nanotube (SWCNT) and multiwall carbon nanotube (MWCNT) with different surface tension with tau protein was evaluated using a variety of techniques including far and near circular dichroism, fluorescence spectroscopy, dynamic light scattering, Zeta potential, and TEM evaluation. Also the cytotoxicity of SWCNT and MWCNT on the PC12 cell line as a model of nervous system cell line was investigated by the MTT, LDH, acridine orange/ethidium bromide staining, flow cytometry, caspase 3 activity, cell and membrane potential assays. It was observed that SWCNT induced more structural changes of tau protein relative to MWCNT/tau protein interaction. It was also revealed that SWCNT and MWCNT impaired the viability and complexity of PC12 cells in different modes of cytotoxicity. Analysis of cellular outcomes indicated that MWCNT in comparison with SWCNT resulted in induction of necrotic modes of cell death, whereas apoptotic modes of cell death were activated in SWCNT-incubated cells. Together these findings suggest that surface tension may be used to determine how nanoparticle structure affects neurotoxicity and protein conformational changes.

Curcumin Protects β-Lactoglobulin Fibril Formation and Fibril-Induced Neurotoxicity in PC12 Cells

In this study the β-lactoglobulin fibrillation, in the presence or absence of lead ions, aflatoxin M1 and curcumin, was evaluated using ThT fluorescence, Circular dichroism spectroscopy and atomic force microscopy. To investigate the toxicity of the different form of β-Lg fibrils, in the presence or absence of above toxins and curcumin, we monitored changes in the level of reactive oxygen species and morphology of the differentiated neuron-like PC12 cells. The cell viability, cell body area, average neurite length, neurite width, number of primary neurites, percent of bipolar cells and node/primary neurite ratios were used to assess the growth and complexity of PC12 cells exposed to different form of β-Lg fibrils. Incubation of β-Lg with curcumin resulted in a significant decrease in ROS levels even in the presence of lead ions and aflatoxin M1. The β-Lg fibrils formed in the presence of lead ions and aflatoxin M1 attenuated the growth and complexity of PC12 cells compared with other form of β-Lg fibrils. However, the adverse effects of these toxins and protein fibrils were negated in the presence of curcumin. Furthermore, the antioxidant and inhibitory effects of curcumin protected PC12 cells against fibril neurotoxicity and enhanced their survival. Thus, curcumin may provide a protective effect toward β-Lg, and perhaps other protein, fibrils mediated neurotoxicity.

Structural, morphological, and functional diversity of amyloid oligomers

Protein misfolding and aggregation are known to play a crucial role in a number of important human diseases (Alzheimer's, Parkinson's, prion, diabetes, cataracts, etc.) as well as in a multitude of physiological processes. Protein aggregation is a highly complex process resulting in a variety of aggregates with different structures and morphologies. Oligomeric protein aggregates (amyloid oligomers) are formed as both intermediates and final products of the aggregation process. They are believed to play an important role in many protein aggregation-related diseases, and many of them are highly cytotoxic. Due to their instability and structural heterogeneity, information about structure, mechanism of formation, and physiological effects of amyloid oligomers is sparse. This review attempts to summarize the existing information on the major properties of amyloid oligomers.

Oligomers, protofibrils and amyloid fibrils from recombinant human lysozyme (rHL): fibrillation process and cytotoxicity evaluation for ARPE-19 cell line

Amyloid-associated diseases, such Alzheimer's, Huntington's, Parkinson's, and type II diabetes, are related to protein misfolding and aggregation. Herein, the time evolution of scattered light intensity, hydrophobic properties, and conformational changes during fibrillation processes of rHL solutions at 55 °C and pH 2.0 were used to monitor the aggregation process of recombinant human lysozyme (rHL). Dynamic light scattering (DLS), thioflavin T (ThT) fluorescence, and surface tension (ST) at the air-water interface were used to analyze the hydrophobic properties of pre-amyloid aggregates involved in the fibrillation process of rHL to find a correlation between the hydrophobic character of oligomers, protofibrils and amyloid aggregates with the gain in cross-β-sheet structure, depending on the increase in the incubation periods. The ability of the different aggregates of rHL isolated during the fibrillation process to be adsorbed at the air-water interface can provide important information about the hydrophobic properties of the protein, which can be related to changes in the secondary structure of rHL, resulting in cytotoxic or non-cytotoxic species. Thus, we evaluated the cytotoxic effect of oligomers, protofibrils and amyloid fibrils on the cell line ARPE-19 using the MTT reduction test. The more cytotoxic protein species arose after a 600-min incubation time, suggesting that the hydrophobic character of pre-amyloid fibrils, in addition to the high prevalence of the cross-β-sheet conformation, can become toxic for the cell line ARPE-19.

Valproic acid attenuates the suppression of acetyl histone H3 and CREB activity in an inducible cell model of Machado-Joseph disease

Machado-Joseph disease (MJD) is caused by a (CAG)n trinucleotide repeat expansion that is translated into an abnormally long polyglutamine tract. This disease is considered the most common form of spinocerebellar ataxia (SCA). In the present study, we developed stable inducible cell lines (PC12Tet-On-Ataxin-3-Q28/84) expressing ataxin-3 with either normal or abnormal CAG repeats under doxycycline control. The expression of acetyl histone H3 and the induction of c-Fos in response to cAMP were strongly suppressed in cells expressing the protein with the expanded polyglutamine tract. Treatment with valproic acid, a histone deacetylase inhibitor (HDACi), attenuated mutant ataxin-3-induced cell toxicity and suppression of acetyl histone H3, phosphorylated cAMP-responsive element binding protein (p-CREB) as well as c-Fos expression. These results indicate that VPA can stimulate the up-regulation of gene transcription through hyperacetylation. Thus, VPA might have a therapeutic effect on MJD.

Sodium dodecyl sulphate modulates the fibrillation of human serum albumin in a dose-dependent manner and impacts the PC12 cells retraction

Protein aggregation is impacted by many factors including temperature, pH, and the presence of surfactants, electrolytes, and metal ions. The addition of sodium dodecyl sulphate (SDS) at different concentrations may play a significant role in the human serum albumin (HSA) fibrillation pathway. Here the heat induction of HSA fibrillation incubated with different concentrations of SDS was evaluated using a variety of techniques. These included ThT fluorescence, Congo red absorbance, circular dichroism, dynamic light scattering, and atomic force microscopy (AFM). To explore HSA surface properties, the surface tension of solutions was measured using Du Noüy Ring method tensiometry. In addition, the criteria of neurite outgrowth and complexity were monitored by exposing PC12 cells to different forms of HSA amyloid intermediates. ThT fluorescence kinetic studies indicated that SDS at low concentrations induced more fibrillation of HSA, while SDS at high concentrations inhibited the fibrillation of HSA. At higher SDS concentrations hydrophobic forces had a significant role whereas at lower SDS concentrations electrostatic forces were dominant. The cell culture studies demonstrated the significant impact of SDS concentration on HSA fibrillation and subsequent neuronal cell morphology. The HSA incubated with low concentrations of SDS inhibited neurite outgrowth and complexity of the PC12 cells, whereas high concentrations of SDS had lesser effect. Thus, SDS acts as a salt at lower concentrations, while at higher concentrations acts as a chaperon, with significant impact on fibrillation of HSA.

Preconditioning of mesenchymal stem cells by sevoflurane to improve their therapeutic potential

Background

Bone marrow mesenchymal stem cells (MSCs) have been found to produce beneficial effects on ischemia-reperfusion injury. However, most of the MSCs died when transplanted into the ischemic tissue, which severely limit their therapeutic potential.

Methods

Using an in vitro model of hypoxia and serum deprivation (H/SD), we investigated the hypothesis that sevoflurane preconditioning could protect MSCs against H/SD-induced apoptosis and improve their migration, proliferation, and therapeutic potential. The H/SD of MSCs and neuron-like PC12 cells were incubated in a serum-free medium and an oxygen concentration below 0.1% for 24 h. Sevoflurane preconditioning was performed through a 2-h incubation of MSCs in an airtight chamber filled with 2 vol% sevoflurane. Apoptosis of MSCs or neuron-like PC12 cells was assessed using Annexin V-FITC/propidium iodide (PI). Furthermore, the mitochondrial membrane potential was assessed using lipophilic cationic probe. The proliferation rate was evaluated through cell cycle analysis. Finally, HIF-1α, HIF-2α, VEGF and p-Akt/Akt levels were measured by western blot.

Results

Sevoflurane preconditioning minimized the MSCs apoptosis and loss of mitochondrial membrane potential. Furthermore, it increased the migration and expression of HIF-1α, HIF-2α, VEGF, and p-Akt/Akt, reduced by H/SD. In addition, neuron-like PC12 cells were more resistant to H/SD-induced apoptosis when they were co-cultured with sevoflurane preconditioning MSCs.

Conclusion

These findings suggest that sevoflurane preconditioning produces protective effects on survival and migration of MSCs against H/SD, as well as improving the therapeutic potential of MSCs. These beneficial effects might be mediated at least in part by upregulating HIF-1α, HIF-2α, VEGF, and p-Akt/Akt.

Inhibition study on insulin fibrillation and cytotoxicity by paclitaxel

Alzheimer, a neurodegenerative disease, and a large variety of pathologic conditions are associated with a form of protein aggregation known as amyloid fibrils. Since fibrils and prefibrillar intermediates are cytotoxic, numerous attempts have been made to inhibit fibrillation process as a therapeutic strategy. Peptides, surfactants and aromatic small molecules have been used as fibrillation inhibitors. Here we studied the effects of paclitaxel, a polyphenol with a high tendency for interaction with proteins, on fibrillation of insulin as a model protein. The effects of paclitaxel on insulin fibrillation were determined by Thioflavin T fluorescence, Congo red absorbance, circular dichroism and atomic force microscopy. These studies indicated that paclitaxel considerably hindered nucleation, and therefore, fibrillation of insulin in a dose-dependant manner. The isothermal titration calorimetry studies showed that the interaction between paclitaxel and insulin was spontaneous. In addition, the van der Waal's interactions and hydrogen bonds were prominent forces contributing to this interaction. Computational results using molecular dynamic simulations and docking studies revealed that paclitaxel diminished the polarity of insulin dimer and electrostatic interactions by increasing the hydrophobicity of its dimer state. Furthermore, paclitaxel reduced disrupting effects of insulin fibrils on PC12 cell's neurite outgrowth and complexity, and enhanced their survival.

Inhibition of human and bovine insulin fibril formation by designed peptide conjugates

The aggregation of insulin, to afford amyloidogenic fibers, is a well-studied phenomenon, which has interesting biological ramifications and pharmaceutical implications. These fibers have been ascribed an intriguing role in certain disease states and stability of pharmaceutical formulations of this hormone. The present study describes the design and inhibitory effects of novel peptide conjugates toward fibrillation of insulin as investigated by thioflavin T assay, circular dichroism (CD), and atomic force microscopy (AFM). Possible interaction of insulin with peptide-based fibrillation inhibitors is also probed by other solution phase studies, which reveal an important role of aromatic π-π interactions in the inhibition process. CD studies suggest that a freshly prepared solution of insulin, rich in α-helices, transforms into a β-sheet structure upon aggregation, which gets perturbed in the presence of synthesized inhibitors. Therefore, these newly designed peptides could serve as potential leads as inhibitors of insulin aggregation.

An efficient combinatorial synthesis of allocolchicine analogues via a triple cascade reaction and their evaluation as inhibitors of insulin aggregation

A controlled cascade: A divergent, diastereoselective and efficient one-pot synthesis of allocolchicinoids via a cascade Suzuki-Michael addition-Carbocyclization sequence is described. The utility of the compounds as possible inhibitors of insulin aggregation is also presented.

Structural analysis and aggregation propensity of reduced and nonreduced glycated insulin adducts

The milieu within pancreatic β cells represents a favorable environment for glycation of insulin. Therefore, in this study, insulin samples were individually subjected to glycation under reducing and nonreducing conditions. As monitored by ortho-phthalaldehyde and fluorescamine assays, the reduced glycated insulin adduct demonstrates extensively higher level of glycation than the nonreduced glycated counterpart. Also, gel electrophoresis experiments suggest a significant impact of glycation under a reducing system on the level of insulin oligomerization. Furthermore, reduced and nonreduced glycated insulin adducts respectively exhibit full and partial resistance against dithiothreitol-induced aggregation. The results of thioflavin T and Congo red assays suggest the existence of a significant quantity of amyloid-like entities in the sample of reduced glycated insulin adduct. Both fluorescence and far-ultraviolet circular dichroism studies respectively suggest that the extents of unfolding and secondary structural alteration were closely correlated to the level of insulin glycation. Moreover, the surface tension of two glycated insulin adducts was inversely correlated to their glycation extents and to the quantity of exposed hydrophobic patches. Overall, the glucose-modified insulin molecules under reducing and nonreducing systems display different structural features having significant consequences on aggregation behaviors and surface tension properties. The particular structural constraints of glycated insulin may reduce the binding interaction of this hormone to its receptor which is important for both insulin function and clearance.