Molecular Aspects of Insulin Aggregation and Various Therapeutic Interventions

Insulin fibrillation under physicochemical parameters of bioprocessing and intervention by peptides and surface-active agents

Even after the centenary celebration of insulin discovery, there prevail challenges concerning insulin aggregation, not only after repeated administration but also during industrial production, storage, transport, and delivery, significantly impacting protein quality, efficacy, and effectiveness. The aggregation reduces insulin bioavailability, increasing the risk of heightened immunogenicity, posing a threat to patient health, and creating a dent in the golden success story of insulin therapy. Insulin experiences various physicochemical and mechanical stresses due to modulations in pH, temperature, ionic strength, agitation, shear, and surface chemistry, during the upstream and downstream bioprocessing, resulting in insulin unfolding and subsequent fibrillation. This has fueled research in the pharmaceutical industry and academia to unveil the mechanistic insights of insulin aggregation in an attempt to devise rational strategies to regulate this unwanted phenomenon. The present review briefly describes the impacts of environmental factors of bioprocessing on the stability of insulin and correlates with various intermolecular interactions, particularly hydrophobic and electrostatic forces. The aggregation-prone regions of insulin are identified and interrelated with biophysical changes during stress conditions. The quest for novel additives, surface-active agents, and bioderived peptides in decelerating insulin aggregation, which results in overall structural stability, is described. We hope this review will help tackle the real-world challenges of insulin aggregation encountered during bioprocessing, ensuring safer, stable, and globally accessible insulin for efficient management of diabetes.

Exploration of the influence of environmental changes on the conformational and amyloidogenic landscapes of the zinc finger protein DPF3a by combining biophysical and molecular dynamics approaches

In the past few years, the double PHD fingers 3 (DPF3) protein isoforms (DPF3b and DPF3a) have been identified as new amyloidogenic intrinsically disordered proteins (IDPs). Although such discovery is coherent and promising in light of their involvement in proteinopathies, their amyloidogenic pathway remains largely unexplored. As environmental variations in pH and ionic strength are relevant to DPF3 pathophysiological landscape, we therefore enquired the effect of these physicochemical parameters on the protein structural and prone-to-aggregation properties, by focusing on the more disordered DPF3a isoform. In the present study, we exploited in vitro and in silico strategies by combining spectroscopy, microscopy, and all-atom molecular dynamics methods. Very good consistency and complementary information were found between the experiments and the simulations. Acidification unequivocally abrogated DPF3a fibrillation upon maintaining the protein in highly hydrated and expanded conformers due to extensive repulsion between positively charged regions. In contrast, alkaline pH delayed the aggregation process due to loss in intramolecular contacts and chain decompaction, the extent of which was partly reduced thanks to the compensation of negative charge by arginine side chains. Through screening attractive electrostatic interactions, high ionic strength conditions (300 and 500 mM NaCl) shifted the conformational ensemble towards more swollen, heterogeneous, and less H-bonded structures, which were responsible for slowing down the conversion into β-sheeted species and restricting the fibril elongation. For defining the self-assembly pathway of DPF3a, we unveiled that the protein amyloidogenicity intimately communicates with its conformational landscape, which is particularly sensitive to modification of its physicochemical environment. As such, understanding how to modulate DPF3a conformational ensemble will help designing novel protein-specific strategies for targeting neurodegeneration.

BioJect: An in vitro platform to explore release dynamics of peptides in subcutaneous drug delivery

Predicting the release performance of subcutaneous (SC) drug formulations is challenging due to the complex interplay between physicochemical properties and the physiological microenvironment, which includes the extracellular matrix (ECM), fluid composition, and fluid availability, factors that collectively influence bioavailability and absorption rates. The ECM often acts as a bandpass filter modulated by local ion and protein content. In this study, we introduce the BioJect cell, a modern release test method based on the compendial flow-through cell, integrating a perfusion system with customizable biomatrix components. We systematically investigated the release mechanisms of four insulin formulations: regular human insulin, insulin aspart, insulin glulisine, and Neutral Protamine Hagedorn (NPH) insulin. A modified simulated subcutaneous interstitial fluid (mSSIF) comprising multiple components of the SC physiological environment was employed. It incorporates important ions and proteins (138.5 mM sodium, 10 mM potassium, 1.8 mM calcium, 0.8 mM magnesium, 111.3 mM chloride, 28 mM bicarbonate, 0.5 mM sulfate, 5 mM acetate, 4.2 mM phosphate, 30 g/L total protein added as bovine serum albumin). Our release test method discriminated the tested formulations under varying biorelevant conditions, demonstrating its biopredictive capabilities. Notably, we discovered a previously undocumented albumin binding affecting the release rate of insulin glulisine, likely occurring in the low-shear environment of SC tissue only. Additionally, the inclusion of biorelevant components like hyaluronic acid and collagen into the biomatrix of the BioJect cell provided profound insights into potential absorption and release mechanisms, supported by two in vitro-in vivo relationships (level C and level A). The BioJect cell represents a significant advancement in simulating the SC environment for drug release testing. Our findings highlight the importance of considering protein binding and ECM components in predicting drug absorption, offering a promising tool for the development and optimization of SC formulations.

Polyoxometalates as effective inhibitors of insulin amyloid fibrils: a promising therapeutic avenue

Insulin is listed on the WHO model list of essential medicines for a basic healthcare system. Due to its usage at regular intervals on diabetic patients, a disease condition called injection amyloidosis exists due to the propensity of insulin to form fibrils. Hence, it is essential to understand the aggregation of the protein insulin and understand the role of fibrillation of the protein insulin and possible inhibition. In this particular investigation, insulin fibrils were produced in a controlled environment. The study focused on exploring the potential of a special class of inorganic nanomaterials known as polyoxometalates (POMs) to inhibit the formation of these insulin amyloid fibrils. Four specific POMs-phosphomolybdic acid (PMA), silicomolybdic acid (SMA), tungstosilicic acid (TSA), and phosphotungstic acid (PTA)-were selected for assessing the inhibition of fibril formation by POMs using the Thioflavin T (ThT) assay. The molecular docking study also shows the binding sites of POMs with insulin. The results provided promising insights into the inhibitory effects of POMs on insulin amyloid fibrils. This investigation opens up potential avenues for exploring the application of Keggin POMs in the context of neurodegeneration.

An antireductant approach ameliorates misfolded proinsulin-induced hyperglycemia and glucose intolerance in male Akita mice

Protein folding in the endoplasmic reticulum (ER) requires a high ratio of oxidized to reduced glutathione (GSSG/rGSH). Since the GSSG/rGSH depends on total glutathione (tGSH = GSSG + rGSH) levels, we hypothesized that limiting GSH biosynthesis will ameliorate protein misfolding by enhancing the ER oxidative milieu. As a proof-of-concept, we used DL-buthionine-(S,R)-sulfoximine (BSO) to inhibit GSH biosynthesis in Akita mice, which are prone to proinsulin misfolding. We conducted a 2-week intervention to investigate if BSO was safe and a 6-week intervention to find its effect on glucose intolerance. In both cohorts, male heterozygous Akita (AK) and wild-type (WT) mice were continuously administered 15 mM BSO. No adverse effects were observed on body weight, food intake, and water intake in either cohort. Unaltered levels of plasma aspartate and alanine aminotransferases, and cystatin-C, indicate that BSO was safe. BSO-induced decreases in tGSH were tissue-dependent with maximal effects in the kidneys, where it altered the expression of genes associated with GSH biosynthesis, redox status, and proteostasis. BSO treatment decreased random blood glucose levels to 80% and 67% of levels in untreated mice in short-term and long-term cohorts, respectively, and 6-h fasting blood glucose to 82% and 74% of levels in untreated mice, respectively. BSO also improved glucose tolerance by 37% in AK mice in the long-term cohort, without affecting insulin tolerance. Neither glucose tolerance nor insulin tolerance were affected in WT. Data indicate that BSO might treat misfolded proinsulin-induced glucose intolerance. Future studies should investigate the effect of BSO on proinsulin misfolding and if it improves glucose intolerance in individuals with Mutant Insulin Diabetes of Youth.

Inhibitory effects of silver and copper oxide nanoparticles, synthesized using Juglans regia green husk aqueous extract, on human insulin fibrillation

Recent research indicates that nanoparticles can serve as tools for the diagnosis and treatment of diseases. This study investigates the inhibitory effects of silver and copper oxide nanoparticles, synthesized using Juglans regia green husk aqueous extract, on human insulin fibrillation. Initially, the formation of amyloid fibrils in recombinant human insulin protein was examined under various buffers and by altering physicochemical conditions, such as pH and temperature, identifying optimal conditions for fibril formation. The nanoparticles were synthesized and characterized for size using dynamic light scattering (DLS), morphology via scanning electron microscopy (SEM), and surface charge through zeta potential analysis. Utilizing biochemical and biophysical techniques, including turbidimetry, DLS, SEM, and fluorescence spectroscopy, we demonstrate that both nanoparticle types effectively inhibit insulin fibrillation, with copper nanoparticles exhibiting superior efficacy. Bioinformatics analyses, combined with zeta potential measurements, suggest that the inhibitory effects of the nanoparticles arise from interactions with charged regions of the insulin molecule. These findings highlight the critical role of nanoparticle characteristics in modulating protein aggregation and present promising therapeutic potential for addressing amyloid-related diseases. Future research should aim to optimize nanoparticle design and evaluate their pharmacokinetics to improve their clinical applicability.

Anti-diabetic Biologicals: Exploring the Role of Different Analytical Techniques

Antidiabetic biologicals (ADBs) have revolutionized the treatment of diabetes mellitus, once considered incurable through conventional medicine. These biological products, derived from natural sources via extraction, semi-synthesis, or recombinant DNA technology, include insulin and its analogs, GLP-1 receptor agonists, amylin analogs, and the recently approved monoclonal antibody teplizumab. Regulatory authorities worldwide have established QC parameters outlined in pharmacopoeias, alongside analytical techniques to ensure their safety and efficacy. This review focuses on the analytical techniques used to assess QC parameters of ADBs, including chromatographic methods, spectroscopic techniques, capillary electrophoresis, immunoassays, and endotoxin testing. Key parameters such as identification, potency, purity, and impurity profiling are thoroughly examined. The paper provides a comprehensive and up-to-date compilation of QC requirements and methodologies, along with a detailed comparison of analytical techniques. In doing so, it highlights their advantages and limitations, offering valuable insights for researchers and regulatory professionals involved in selecting suitable methods for QC assessment and understanding the complexities of ADBs evaluation. Furthermore, the article discusses the paramount importance of QC and future perspectives, emphasizing the transition to advanced versions of current techniques driven by the need for efficiency and reliability in quality testing.

Molecular puzzle of insulin: structural assembly pathways and their role in diabetes

Properly folded proteins are essential for virtually all cellular processes including enzyme catalysis, signal transduction, and structural support. The cells have evolved intricate mechanisms of control, such as the assistance of chaperones and proteostasis networks, to ensure that proteins mature and fold correctly and maintain their functional conformations. Here, we review the mechanisms governing the folding of key hormonal regulators or glucose homeostasis. The insulin synthesis in pancreatic β-cells begins with preproinsulin production. During translation, the insulin precursor involves components of the endoplasmic reticulum (ER) translocation machinery, which are essential for proper orientation, translocation, and cleavage of the signal peptide of preproinsulin. These steps are critical to initiate the correct folding of proinsulin. Proinsulin foldability is optimized in the ER, an environment evolved to support the folding process and the formation of disulfide bonds while minimizing misfolding. This environment is intricately linked to ER stress response pathways, which have both beneficial and potentially harmful effects on pancreatic β-cells. Proinsulin misfolding can result from excessive biosynthetic ER load, proinsulin gene mutations, or genetic predispositions affecting the ER folding environment. Misfolded proinsulin leads to deficient insulin production and contributes to diabetes pathogenesis. Understanding the mechanisms of protein folding is critical for addressing diabetes and other protein misfolding-related diseases.

Exploring Cimetidine as a Potential Therapeutic Attenuator against Amyloid Formation in Parkinson's Disease: Spectroscopic and Microscopic Insights into Alpha-Synuclein and Human Insulin

Neurodegenerative diseases, notably Alzheimer's and Parkinson's, hallmark their progression through the formation of amyloid aggregates resulting from misfolding. While current therapeutics alleviate symptoms, they do not impede disease onset. In this context, repurposing existing drugs stands as a viable therapeutic strategy. Our study determines the antihistamine drug Cimetidine's potential as an inhibitor using diverse spectroscopic and microscopic methods on alpha-synuclein and human insulin amyloid formation, unveiling its efficacy. The thioflavin T (ThT) assay illustrated a dose-dependent reduction in amyloid formation with escalating concentrations of Cimetidine. Notably, the antihistamine drug maintained a helical structure and showed no significant conformational changes in the secondary structure. Confocal microscopy validated fewer fibrils in the Cimetidine-treated samples. Remarkably, Cimetidine interacted with pre-existing fibrils, leading to their disintegration. Further analyses (ThT, circular dichroism, and dynamic light scattering) showcased the conversion of fibrils into smaller aggregates upon Cimetidine addition. These findings signify the potential of this antihistamine drug as a plausible therapeutic option for Parkinson's disease. This study may open avenues for deeper investigations and possible therapeutic developments, emphasizing Cimetidine's promising role in mitigating neurodegenerative diseases like Parkinson's.

Heat-Stable Insulins: Any Progress?

Millions of people with diabetes have no or only limited access to electricity that limits their ability to store insulin according to the recommendations of the insulin manufacturer in general. At the same time, environmental temperatures are increasing in many countries which have a negative impact on the glucose-lowering effect of insulin not stored adequately. Therefore, the availability of heat-stable insulin formulations that do not require constant cooling would be of help for many patients; however, despite this clinical need, apparently not many are in clinical development. This commentary discusses the different aspects and approaches that are of relevance in this context.

Lipid-polymer hybrid-vesicles interrupt nucleation of amyloid fibrillation

Solubility and aggregation of proteins are crucial factors for their functional and further biological roles. Aggregation of proteins in vivo, such as the amyloid beta (Aβ1-40) peptide into fibrils, is significantly modulated by membrane lipids, abundantly present in cells. We developed a model membrane system, composed of lipid hybrid-vesicles bearing embedded hydrophilic polymers to in vitro study the aggregation of the Aβ1-40 peptide. Focus is to understand and inhibit the primordial, nucleation stages of their fibrillation by added hybrid-vesicles, composed of a natural lipid and amphiphilic polymers. These designed hybrid-vesicles are based on 1-palmitoyl-2-oleoyl-glycero-3-phosphocholine (POPC), displaying embedded hydrophilic (EO) m P n A_EG polymers (m = 2 or 3; P n = 10 to 52 with M n = 2800-9950 gmol-1) in amounts ranging from 5-20 mol%, anchored to the POPC vesicles via hydrophobic hexadecyl-, glyceryl- and cholesteryl-moieties, affixed to the polymers as end-groups. All investigated hybrid-vesicles significantly delay fibrillation of the Aβ1-40 peptide as determined by thioflavin T (ThT) assays. We observed that the hybrid-vesicles interacted with early aggregating species of Aβ1-40 peptide, irrespective of their composition or size. A substantial perturbation of both primary (k + k n ) and secondary (k + k 2) nucleation rates of Aβ1-40 by the POPC-polymer vesicles compared to POPC vesicles was observed, particularly for the cholesteryl-anchored polymers, interfering with the fragmentation and elongation steps of Aβ1-40. Furthermore, morphological differences of the aggregates were revealed by transmission electron microscopy (TEM) images supported the inhibitory kinetic signatures.

Rapid Coaggregation of Proteins Without Sequence Similarity: Possible Role of Conformational Complementarity

Despite extensive research on the sequence-determined self-assembly of both pathogenic and nonpathogenic proteins, the question of how the sequence identity would influence the coassembly or cross-seeding of diverse proteins without distinct sequence similarity remains largely unanswered. Here, we demonstrate that the rapid coaggregation of proteins with negligible sequence similarity is fundamentally governed by preferred heteromeric interactions between their partially unfolded states via the gain of additional charge complementarity and hydrophobic interactions. The partial loss of intramolecular interactions and concurrent gain of non-native intrinsically disordered regions with sticky groups become crucial for both aggressive heteromeric primary nucleation and secondary nucleation events. The results signify the direct relevance of sequence-independent conformational cross-talk between diverse proteins to the foundational events required for the growth of biological multiprotein amyloid deposits.

Bioactive Carbon@CeO2 Composites as Efficient Antioxidants with Antiamyloid and Radioprotective Potentials

Blending carbon particles (CPs) and nanoscale bioactive cerium dioxide is a promising approach for designing composites for biomedical applications, combining the sorption and antioxidant potentials of each individual component. To address this issue, it is crucial to assess the correlation between the components' ratio, physicochemical parameters, and biofunctionality of the composites. Thus, the current research was aimed at fabricating C@CeO2 composites with different molar ratios and the examination of how the parameters of the composites affect their bioactivity. XRD, X-ray photoelectron spectroscopy, and electron microscopy data verified the formation of C@CeO2 composites. CeO2 nanoparticles (NPs) of 4-6 nm are highly dispersed on the surfaces of amorphous CPs. The presence of CeO2 NPs on the carbon surface decreased its adsorption potential in a dose-dependent manner. Besides, the coexistence of carbon and CeO2 in a single composite promotes some redox interactions between O-functionalities and Ce3+/Ce4+ species, resulting in changes in the chemical state of the surface of the composites. These observations suggest the strong connection between these parameters and the biofunctionality of the composites. The presence of CeO2 NPs on the surface of carbon led to a significant increase in the stability of the prepared composites in their aqueous suspensions. The enhancement of bioactivity of the newly prepared C@CeO2 compared to bare carbon and CeO2 was validated by testing their pseudomimetic (catalase/peroxidase-like and superoxide dismutase-like), antiamyloid, and radioprotective activities.

Fenfuro®-mediated arrest in the formation of protein-methyl glyoxal adducts: a new dimension in the anti-hyperglycemic potential of a novel fenugreek seed extract

The fenugreek plant (Trigonella foenum-graecum) is traditionally known for its anti-diabetic properties owing to its high content of furostanolic saponins, which can synergistically treat many human ailments. Non-enzymatic protein glycation leading to the formation of Advanced Glycation End products (AGE) is a common pathophysiology observed in diabetic or prediabetic individuals, which can initiate the development of neurodegenerative disorders. A potent cellular source of glycation is Methyl Glyoxal, a highly reactive dicarbonyl formed as a glycolytic byproduct. We demonstrate the in vitro glycation arresting potential of Fenfuro®, a novel patented formulation of Fenugreek seed extract with clinically proven anti-diabetic properties, in Methyl-Glyoxal (MGO) adducts of three abundant amyloidogenic cellular proteins, alpha-synuclein, Serum albumin, and Lysozyme. A 0.25% w/v Fenfuro® was able to effectively arrest glycation by more than 50% in all three proteins, as evidenced by AGE fluorescence. Glycation-induced amyloid formation was also arrested by more than 36%, 14% and 15% for BSA, Alpha-synuclein and Lysozyme respectively. An increase in MW by attachment of MGO was also partially prevented by Fenfuro® as confirmed by SDS-PAGE analysis. Glycation resulted in enhanced aggregation of the three proteins as revealed by Native PAGE and Dynamic Light Scattering. However, in the presence of Fenfuro®, aggregation was arrested substantially, and the normal size distribution was restored. The results cumulatively indicated the lesser explored potential of direct inhibition of glycation by fenugreek seed in addition to its proven role in alleviating insulin resistance. Fenfuro® boosts its therapeutic potential as an effective phytotherapeutic to arrest Type 2 diabetes.

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

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

Natural compound plumbagin based inhibition of hIAPP revealed by Markov state models based on MD data along with experimental validations

Human islet amyloid polypeptide (amylin or hIAPP) is a 37 residue hormone co-secreted with insulin from β cells of the pancreas. In patients suffering from type-2 diabetes, amylin self-assembles into amyloid fibrils, ultimately leading to the death of the pancreatic cells. However, a research gap exists in preventing and treating such amyloidosis. Plumbagin, a natural compound, has previously been demonstrated to have inhibitory potential against insulin amyloidosis. Our investigation unveils collapsible regions within hIAPP that, upon collapse, facilitates hydrophobic and pi-pi interactions, ultimately leading to aggregation. Intriguingly plumbagin exhibits the ability to bind these specific collapsible regions, thereby impeding the aforementioned interactions that would otherwise drive hIAPP aggregation. We have used atomistic molecular dynamics approach to determine secondary structural changes. MSM shows metastable states forming native like hIAPP structure in presence of PGN. Our in silico results concur with in vitro results. The ThT assay revealed a striking 50% decrease in fluorescence intensity at a 1:1 ratio of hIAPP to Plumbagin. This finding suggests a significant inhibition of amyloid fibril formation by plumbagin, as ThT fluorescence directly correlates with the presence of these fibrils. Further TEM images revealed disappearance of hIAPP fibrils in plumbagin pre-treated hIAPP samples. Also, we have shown that plumbagin disrupts the intermolecular hydrogen bonding in hIAPP fibrils leading to an increase in the average beta strand spacing, thereby causing disaggregation of pre-formed fibrils demonstrating overall disruption of the aggregation machinery of hIAPP. Our work is the first to report a detailed atomistic simulation of 22 μs for hIAPP. Overall, our studies put plumbagin as a potential candidate for both preventive and therapeutic candidate for hIAPP amyloidosis.

Converting Short-Acting Insulin into Thermo-Stable Longer-Acting Insulin Using Multi-Layer Detachable Microneedles

The detachable dissolving microneedles (DDMNs) feature an array of needles capable of being separated from the base sheet during administration. Here they were fabricated to address delivery efficiency and storage stability of insulin. The constructed insulin-DDMN is multi-layered, with 1) a hard tip cover layer; 2) a layer of regular short-acting insulin (RI) mixed with hyaluronic acid (HA) and sorbitol (Sor) which occupies the taper tip region of the needles; 3) a barrier layer situated above the RI layer; and 4) a fast-dissolving layer connecting the barrier layer to the base sheet. RI entrapped in DDMNs exhibited enhanced thermal stability; it could be stored at 40 °C for 35 days without losing significant biological activity. Differential scanning calorimetric analysis revealed that the HA-Sor matrix could improve the denaturation temperature of the RI from lower than room temperature to 186 °C. Tests in ex vivo porcine skin demonstrated RI delivery efficiency of 91±1.59 %. Experiments with diabetic rats revealed sustained release of RI, i.e., when compared to subcutaneous injection with the same RI dose, RI-DDMNs produced slower absorption of insulin into blood circulation, delayed onset of hypoglycemic effect, longer serum insulin half-life, and longer hypoglycemic duration.

Study of Insulin Aggregation and Fibril Structure under Different Environmental Conditions

Protein amyloid aggregation is linked with widespread and fatal neurodegenerative disorders as well as several amyloidoses. Insulin, a small polypeptide hormone, is associated with injection-site amyloidosis and is a popular model protein for in vitro studies of amyloid aggregation processes as well as in the search for potential anti-amyloid compounds. Despite hundreds of studies conducted with this specific protein, the procedures used have employed a vast array of different means of achieving fibril formation. These conditions include the use of different solution components, pH values, ionic strengths, and other additives. In turn, this variety of conditions results in the generation of fibrils with different structures, morphologies and stabilities, which severely limits the possibility of cross-study comparisons as well as result interpretations. In this work, we examine the condition-structure relationship of insulin amyloid aggregation under a range of commonly used pH and ionic strength conditions as well as solution components. We demonstrate the correlation between the reaction solution properties and the resulting aggregation kinetic parameters, aggregate secondary structures, morphologies, stabilities and dye-binding modes.

Improving the stability of insulin through effective chemical modifications: A Comprehensive review

Insulin, an essential peptide hormone, conjointly regulates blood glucose levels by its receptor and it is used as vital drug to treat diabetes. This therapeutic hormone may undergo different chemical modifications during industrial processes, pharmaceutical formulation, and through its endogenous storage in the pancreatic β-cells. Insulin is highly sensitive to environmental stresses and readily undergoes structural changes, being also able to unfold and aggregate in physiological conditions. Even; small changes altering the structural integrity of insulin may have significant impacts on its biological efficacy to its physiological and pharmacological activities. Insulin analogs have been engineered to achieve modified properties, such as improved stability, solubility, and pharmacokinetics, while preserving the molecular pharmacology of insulin. The casually or purposively strategies of chemical modifications of insulin occurred to improve its therapeutic and pharmaceutical properties. Knowing the effects of chemical modification, formation of aggregates, and nanoparticles on protein can be a new look at the production of protein analogues drugs and its application in living system. The project focused on effects of chemical modifications and nanoparticles on the structure, stability, aggregation and their results in effective drug delivery system, biological activity, and pharmacological properties of insulin. The future challenge in biotechnology and pharmacokinetic arises from the complexity of biopharmaceuticals, which are often molecular structures that require formulation and delivery strategies to ensure their efficacy and safety.

State of the Science on Brain Insulin Resistance and Cognitive Decline Due to Alzheimer's Disease

Type 2 diabetes mellitus (T2DM) is common and increasing in prevalence worldwide, with devastating public health consequences. While peripheral insulin resistance is a key feature of most forms of T2DM and has been investigated for over a century, research on brain insulin resistance (BIR) has more recently been developed, including in the context of T2DM and non-diabetes states. Recent data support the presence of BIR in the aging brain, even in non-diabetes states, and found that BIR may be a feature in Alzheimer's disease (AD) and contributes to cognitive impairment. Further, therapies used to treat T2DM are now being investigated in the context of AD treatment and prevention, including insulin. In this review, we offer a definition of BIR, and present evidence for BIR in AD; we discuss the expression, function, and activation of the insulin receptor (INSR) in the brain; how BIR could develop; tools to study BIR; how BIR correlates with current AD hallmarks; and regional/cellular involvement of BIR. We close with a discussion on resilience to both BIR and AD, how current tools can be improved to better understand BIR, and future avenues for research. Overall, this review and position paper highlights BIR as a plausible therapeutic target for the prevention of cognitive decline and dementia due to AD.

Amyloids, amorphous aggregates and assemblies of peptides - Assessing aggregation

Amyloid and amorphous aggregates represent the two major categories of aggregates associated with diseases, and although exhibiting distinct features, researchers often treat them as equivalent, which demonstrates the need for more thorough characterization. Here, we compare amyloid and amorphous aggregates based on their biochemical properties, kinetics, and morphological features. To further decipher this issue, we propose the use of peptide self-assemblies as minimalistic models for understanding the aggregation process. Peptide building blocks are significantly smaller than proteins that participate in aggregation, however, they make a plausible means to bridge the gap in discerning the aggregation process at the more complex, protein level. Additionally, we explore the potential use of peptide-inspired models to research the liquid-liquid phase separation as a feasible mechanism preceding amyloid formation. Connecting these concepts can help clarify our understanding of aggregation-related disorders and potentially provide novel drug targets to impede and reverse these serious illnesses.

Clues to the Design of Aggregation-Resistant Insulin from Proline Scanning of Highly Amyloidogenic Peptides Derived from the N-Terminal Segment of the A-Chain

Insulin aggregation poses a significant problem in pharmacology and medicine as it occurs during prolonged storage of the hormone and in vivo at insulin injection sites. We have recently shown that dominant forces driving the self-assembly of insulin fibrils are likely to arise from intermolecular interactions involving the N-terminal segment of the A-chain (ACC1-13). Here, we study how proline substitutions within the pilot GIVEQ sequence of this fragment affect its propensity to aggregate in both neutral and acidic environments. In a reasonable agreement with in silico prediction based on the Cordax algorithm, proline substitutions at positions 3, 4, and 5 turn out to be very effective in preventing aggregation according to thioflavin T-fluorescence-based kinetic assay, infrared spectroscopy, and atomic force microscopy (AFM). Since the valine and glutamate side chains within this segment are strongly involved in the interactions with the insulin receptor, we have focused on the possible implications of the Q → P substitution for insulin's stability and interactions with the receptor. To this end, comparative molecular dynamics (MD) simulations of the Q5P mutant and wild-type insulin were carried out for both free and receptor-bound (site 1) monomers. The results point to a mild destabilization of the mutant vis à vis the wild-type monomer, as well as partial preservation of key contacts in the complex between Q5P insulin and the receptor. We discuss the implications of these findings in the context of the design of aggregation-resistant insulin analogues retaining hormonal activity.

Synthetic macromolecular peptide-mimetics with amino acid substructure residues as protein stabilising excipients

The clinical use of protein and peptide biotherapeutics requires fabrication of stable products. This particularly concerns stability towards aggregation of proteins or peptides. Here, we tested a hypothesis that interactions between a synthetic peptide, which is an aggregation-prone region analogue, and its homologous sequence on a protein of interest, could be exploited to design excipients which stabilise the protein against aggregation. A peptide containing the analogue of lysozyme aggregation-prone region (GILQINSRW) was conjugated to a RAFT agent and used to initiate the polymerisation of N-hydroxyethyl acrylamide, generating a GILQINSRW-HEA90 polymer, which profoundly reduced lysozyme aggregation. Substitution of tryptophan in GILQINSRW with glycine, to form GILQINSRG, revealed that tryptophan is a critical amino acid in the protein stabilisation by GILQINSRW-HEA90. Accordingly, polymeric peptide-mimetics of tryptophan, phenylalanine and isoleucine, which are often present in aggregation-prone regions, were synthesized. These were based on synthetic oligomers of acrylamide derivatives of indole-3 acetic acid (IND), phenylacetic acid (PHEN), or 2-methyl butyric acid (MBA), respectively, conjugated with hydrophilic poly(N-hydroxyethyl acrylamide) blocks to form amphiphilic copolymers denoted as INDm-, PHENm- and MTBm-b-HEAn. These materials were tested as protein stabilisers and it was shown that solution properties and the abilities of these materials to stabilise insulin and the peptide IDR 1018 towards aggregation are dependent on the chemical nature of their side groups. These data suggest a structure-activity relationship, whereby the indole-based INDm-b-HEAn peptide-mimetic displays properties of a potential stabilising excipient for protein formulations.

A New Approach for Preparing Stable High-Concentration Peptide Nanoparticle Formulations

The subcutaneous administration of therapeutic peptides would provide significant benefits to patients. However, subcutaneous injections are limited in dosing volume, potentially resulting in high peptide concentrations that can incur significant challenges with solubility limitations, high viscosity, and stability liabilities. Herein, we report on the discovery that low-shear resonant acoustic mixing can be used as a general method to prepare stable nanoparticles of a number of peptides of diverse molecular weights and structures in water without the need for extensive amounts of organic solvents or lipid excipients. This approach avoids the stability issues observed with typical high-shear, high-intensity milling methods. The resultant peptide nanosuspensions exhibit low viscosity even at high concentrations of >100 mg/mL while remaining chemically and physically stable. An example nanosuspension of cyclosporine nanoparticles was dosed in rats via a subcutaneous injection and exhibited sustained release behavior. This suggests that peptide nanosuspension formulations can be one approach to overcome the challenges with high-concentration peptide formulations.

Revealing the interaction between peptide drugs and permeation enhancers in the presence of intestinal bile salts

Permeability enhancer-based formulations offer a promising approach to enhance the oral bioavailability of peptides. We used all-atom molecular dynamics simulations to investigate the interaction between two permeability enhancers (sodium caprate, and SNAC), and four different peptides (octreotide, hexarelin, degarelix, and insulin), in the presence of taurocholate, an intestinal bile salt. The permeability enhancers exhibited distinct effects on peptide release based on their properties, promoting hydrophobic peptide release while inhibiting water-soluble peptide release. Lowering peptide concentrations in the simulations reduced peptide-peptide interactions but increased their interactions with the enhancers and taurocholates. Introducing peptides randomly with enhancer and taurocholate molecules yielded dynamic molecular aggregation, and reduced peptide-peptide interactions and hydrogen bond formation compared to peptide-only systems. The simulations provided insights into molecular-level interactions, highlighting the specific contacts between peptide residues responsible for aggregation, and the interactions between peptide residues and permeability enhancers/taurocholates that are crucial within the mixed colloids. Therefore, our results can provide insights into how modifications of these critical contacts can be made to alter drug release profiles from peptide-only or mixed peptide-PE-taurocholate aggregates. To further probe the molecular nature of permeability enhancers and peptide interactions, we also analyzed insulin secondary structures using Fourier transform infrared spectroscopy. The presence of SNAC led to an increase in β-sheet formation in insulin. In contrast, both in the absence and presence of caprate, α-helices, and random structures dominated. These molecular-level insights can guide the design of improved permeability enhancer-based dosage forms, allowing for precise control of peptide release profiles near the intended absorption site.

A comparative study of the impacts of preparation techniques on the rheological and textural characteristics of emulsion gels (emulgels)

A subtype of soft solid-like substances are emulsion gels (emulgels; EGs). These composite material's structures either consist of a network of aggregated emulsion droplets or a polymeric gel matrix that contains emulsion droplets. The product's rheological signature can be used to determine how effective it is for a specific application. The interactions between these structured system's separate components and production process, however, have a substantial impact on their rheological imprint. Therefore, rational comprehension of interdependent elements, their structural configurations, and the resulting characteristics of a system are essential for accelerating our progress techniques as well as for fine-tuning the technological and functional characteristics of the finished product. This article presents a comprehensive overview of the mechanisms and procedures of producing EGs (i.e., cold-set and heat-set) in order to determine the ensuing rheological features for various commercial applications, such as food systems. It also describes the influence of these methods on the rheological and textural characteristics of the EGs. Diverse preparation methods are the cause of the rheological-property correlations between different EGs. In many ways, EGs can be produced using various matrix polymers, processing techniques, and purposes. This may lead to various EG matrix structures and interactions between them, which in turn may affect the composition of EGs and ultimately their textural and rheological characteristics.

Design of Magnetic Fe3O4/CeO2 "Core/Shell"-Like Nanocomposites with Pronounced Antiamyloidogenic and Antioxidant Bioactivity

"Core/shell" nanocomposites based on magnetic magnetite (Fe3O4) and redox-active cerium dioxide (CeO2) nanoparticles (NPs) are promising in the field of biomedical interests because they can combine the ability of magnetic NPs to heat up in an alternating magnetic field (AMF) with the pronounced antioxidant activity of CeO2 NPs. Thus, this report is devoted to Fe3O4/CeO2 nanocomposites (NCPs) synthesized by precipitation of the computed amount of "CeO2-shell" on the surface of prefabricated Fe3O4 NPs. The X-ray diffraction, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy data validated the formation of Fe3O4/CeO2 "core/shell"-like NCPs, in which ultrafine CeO2 NPs with an average size of approximately 3-3.5 nm neatly surround Fe3O4 NPs. The presence of a CeO2 "shell" significantly increased the stability of Fe3O4/CeO2 NCPs in aqueous suspensions: Fe3O4/CeO2 NCPs with "shell thicknesses" of 5 and 7 nm formed highly stable magnetic fluids with ζ-potential values of >+30 mV. The magnetization values of Fe3O4/CeO2 NCPs decreased with a growing CeO2 "shell" around the magnetic NPs; however, the resulting composites retained the ability to heat efficiently in an AMF. The presence of a CeO2 "shell" generates a possibility to precisely regulate tuning of the maximum heating temperature of magnetic NCPs in the 42-50 °C range and stabilize it after a certain time of exposure to an AMF by changing the thickness of the "CeO2-shell". A great improvement was observed in both antioxidant and antiamyloidogenic activities. It was found that inhibition of insulin amyloid formation, expressed in IC50 concentration, using NCPs with a "shell thickness" of 7 nm was approximately 10 times lower compared to that of pure CeO2. For these NCPs, more than 2 times higher superoxide dismutase-like activity was observed. The coupling of both Fe3O4 and CeO2 results in higher bioactivity than either of them individually, probably due to a synergistic catalytic mechanism.

An unnatural amino acid modified human insulin derivative for visual monitoring of insulin aggregation

Insulin often forms toxic fibrils during production and transportation, which are deposited as amyloids at repeated injection sites in diabetic patients. Distinguishing early fibrils from non-fibrillated insulin is difficult. Herein, we introduce a chemically modified human insulin derivative with a distinct visual colour transition upon aggregation, facilitating insulin quality assessment.

Structural, kinetic, and thermodynamic aspects of insulin aggregation

Given the significance of protein aggregation in proteinopathies and the development of therapeutic protein pharmaceuticals, revamped interest in assessing and modelling the aggregation kinetics has been observed. Quantitative analysis of aggregation includes data of gradual monomeric depletion followed by the formation of subvisible particles. Kinetic and thermodynamic studies are essential to gain key insights into the aggregation process. Despite being the medical marvel in the world of diabetes, insulin suffers from the challenge of aggregation. Physicochemical stresses are experienced by insulin during industrial formulation, storage, delivery, and transport, considerably impacting product quality, efficacy, and effectiveness. The present review briefly describes the pathways, mathematical kinetic models, and thermodynamics of protein misfolding and aggregation. With a specific focus on insulin, further discussions include the structural heterogeneity and modifications of the intermediates incurred during insulin fibrillation. Finally, different model equations to fit the kinetic data of insulin fibrillation are discussed. We believe that this review will shed light on the conditions that induce structural changes in insulin during the lag phase of fibrillation and will motivate scientists to devise strategies to block the initialization of the aggregation cascade. Subsequent abrogation of insulin fibrillation during bioprocessing will ensure stable and globally accessible insulin for efficient management of diabetes.

Polyampholytes and Their Hydrophobic Derivatives as Excipients for Suppressing Protein Aggregation

Protein aggregation, which occurs under various physiological conditions, can affect cell function and is a major issue in the field of protein therapeutics. In this study, we developed a polyampholyte composed of ε-poly-l-lysine and succinic anhydride and evaluated its protein protection efficacy. This polymer was able to protect different proteins from thermal stress and its performance significantly exceeded that of previously reported zwitterionic polymers. In addition, we synthesized derivatives with varying degrees of hydrophobicity, which exhibited remarkably enhanced efficiency; thus, the polymer concentration required for protein protection was very low. By facilitating the retention of protein enzymatic activity and stabilizing the higher-order structure, these polymers enabled the protein to maintain its native state, even after being subjected to extreme thermal stress. Thus, such polyampholytes are extremely effective in protecting proteins from extreme stress and may find applications in protein biopharmaceuticals and drug delivery systems.

Prevention of insulin fibrillation by biocompatible choline-amino acid based ionic liquids: Biophysical insights

We have synthesized biocompatible ionic liquids (ILs) with choline as cation and amino acids as anions to explore their potential towards prevention of fibrillation in insulin and the obtain corresponding mechanistic insights. This has been achieved by examining the effect of these ILs on insulin at the nucleation, elongation and maturation stages of the fibrillation process. A combination of high sensitivity isothermal titration calorimetry (ITC) and differential scanning calorimetry (DSC) have been employed along with spectroscopy and microscopy to evaluate interaction of the ILs at each stage of fibrillation quantitatively. Choline glycinate is observed to provide maximum stabilization to insulin compared to that provided by choline prolinate, choline leucinate, and choline valinate. This increased thermal stabilization has direct correlation with the extent of reduction in the fibrillation of insulin by ILs determined using Thioflavin T and 8-anilinonaphthalene sulfonate based fluorescence assays. ITC has permitted understanding nature of interaction of the ILs with the protein at different fibrillation stages in terms of standard molar enthalpy of interaction whereas DSC has enabled understanding the extent of reduction in thermal stability of the protein at these stages. These ILs are able to completely inhibit formation of insulin aggregates at a concentration of 50 mM. Stabilization of proteins by ILs could be explained based on involvement of preferential hydration process. The work provides biocompatible IL based approach in achieving stability and prevention of fibrillation in insulin.

The Strategies of Development of New Non-Toxic Inhibitors of Amyloid Formation

In recent years, due to the aging of the population and the development of diagnostic medicine, the number of identified diseases associated with the accumulation of amyloid proteins has increased. Some of these proteins are known to cause a number of degenerative diseases in humans, such as amyloid-beta (Aβ) in Alzheimer's disease (AD), α-synuclein in Parkinson's disease (PD), and insulin and its analogues in insulin-derived amyloidosis. In this regard, it is important to develop strategies for the search and development of effective inhibitors of amyloid formation. Many studies have been carried out aimed at elucidating the mechanisms of amyloid aggregation of proteins and peptides. This review focuses on three amyloidogenic peptides and proteins-Aβ, α-synuclein, and insulin-for which we will consider amyloid fibril formation mechanisms and analyze existing and prospective strategies for the development of effective and non-toxic inhibitors of amyloid formation. The development of non-toxic inhibitors of amyloid will allow them to be used more effectively for the treatment of diseases associated with amyloid.

Micelle Formation in Aqueous Solutions of the Cholesterol-Based Detergent Chobimalt Studied by Small-Angle Scattering

The structure and interaction parameters of the water-soluble cholesterol-based surfactant, Chobimalt, are investigated by small-angle neutron and X-ray scattering techniques. The obtained data are analyzed by a model-independent approach applying the inverse Fourier transformation procedure as well as considering a model fitting procedure, using a core-shell form factor and hard-sphere structure factor. The analysis reveals the formation of the polydisperse spherical or moderately elongated ellipsoidal shapes of the Chobimalt micelles with the hard sphere interaction in the studied concentration range 0.17-6.88 mM. The aggregation numbers are estimated from the micelle geometry observed by small-angle scattering and are found to be in the range of 200-300. The low pH of the solution does not have a noticeable effect on the structure of the Chobimalt micelles. The critical micelle concentrations of the synthetic surfactant Chobimalt in water and in H2O-HCl solutions were obtained according to fluorescence measurements as ~3 μM and ~2.5 μM, respectively. In-depth knowledge of the basic structural properties of the detergent micelles is necessary for further applications in bioscience and biotechnology.

Peptide Inhibitors of Insulin Fibrillation: Current and Future Challenges

Amyloidoses include a large variety of local and systemic diseases that share the common feature of protein unfolding or refolding into amyloid fibrils. The most studied amyloids are those directly involved in neurodegenerative diseases, while others, such as those formed by insulin, are surprisingly far less studied. Insulin is a very important polypeptide that plays a variety of biological roles and, first and foremost, is at the basis of the therapy of diabetic patients. It is well-known that it can form fibrils at the site of injection, leading to inflammation and immune response, in addition to other side effects. In this concise review, we analyze the current knowledge on insulin fibrillation, with a focus on the development of peptide-based inhibitors, which are promising candidates for their biocompatibility but still pose challenges to their effective use in therapy.

Dietary anthocyanins inhibit insulin fibril formation and cytotoxicity in 3T3-L1 preadipocytes

Insulin fibril formation decreases the effectiveness of insulin therapy and causes amyloidosis in diabetes. Studies suggest that phytochemicals are capable of inhibiting fibril formation. Herein, we investigated the inhibitory effects of anthocyanins, including cyanidin, cyanidin-3-glucoside (C3G), cyanidin-3-rutinoside (C3R), malvidin, and malvidin-3-glucoside (M3G) on fibril formation. Our results revealed that anthocyanins (50-200 μM) significantly reduced the formation of insulin fibrils by increasing lag times and decreasing ThT fluorescence at the plateau phase. These findings were confirmed by TEM images, which showed reduced fibril length and number. Furthermore, FTIR analysis indicated that anthocyanins reduced the secondary structure transition of insulin from α-helix to β-sheet. Anthocyanins interacted with monomeric insulin (residues B8-B30) via H-bonds, van der Waals, and hydrophobic interactions, covering the fibril-prone segments of insulin (residues B12-B17). Based on the structure-activity analysis, the presence of glycosides and hydroxyl groups on phenyl rings increased intermolecular interaction, mediating the inhibitory effect of anthocyanins on fibril formation in the order of malvidin < cyanidin < M3G < C3G < C3R. Moreover, anthocyanins formed H-bonds with preformed insulin fibrils, except for malvidin. In preadipocytes, C3R, C3G, and cyanidin attenuated insulin fibril-induced cytotoxicity. In conclusion, anthocyanins are effective inhibitors of insulin fibril formation and cytotoxicity.

Polyisobutylene-based glycopolymers as potent inhibitors for in vitro insulin aggregation

A family of amphiphilic diblock copolymers containing a hydrophobic polyisobutylene (PIB, M_n = 1000 g mol^-1) segment and a hydrophilic block with sugar pendants has been synthesized by combining living cationic and reversible addition-fragmentation chain transfer (RAFT) polymerization techniques; to explore their potential in insulin fibrillation inhibition. The glucose content in the hydrophilic segment has been tailor-made from 20 to 57 units to prepare block copolymers. The removal of the acetates from the pendent glucose units resulted in amphiphilic block copolymers that generated micellar aggregates in aqueous media. The treatment of insulin with these block copolymers affected the fibril formation process which was demonstrated using an array of biophysical techniques, namely, thioflavin T (ThT) fluorescence, tyrosine (Tyr) fluorescence, Nile red (NR) fluorescence, isothermal titration calorimetry (ITC), etc. The Tyr fluorescence assay and NR fluorescence study revealed the crucial role of hydrophobic interaction in the inhibition process, whereas ITC measurements confirmed the importance of polar interaction. Thus, the block copolymers exhibit potent inhibition of insulin fibrillation owing to hydrophobic (from PIB segment) and glycosidic cluster effect (from sugar pendant block).

Amyloid Fibrillation of Insulin: Amelioration Strategies and Implications for Translation

Insulin is a therapeutically relevant molecule with use in treating diabetes patients. Unfortunately, it undergoes a range of untoward and often unpredictable physical transformations due to alterations in its biochemical environment, including pH, ionic strength, temperature, agitation, and exposure to hydrophobic surfaces. The transformations are prevalent in its physiologically active monomeric form, while the zinc cation-coordinated hexamer, although physiologically inactive, is stable and less susceptible to fibrillation. The resultant molecular reconfiguration, including unfolding, misfolding, and hydrophobic interactions, often results in agglomeration, amyloid fibrillogenesis, and precipitation. As a result, a part of the dose is lost, causing a compromised therapeutic efficacy. Besides, the amyloid fibrils form insoluble deposits, trigger immunologic reactions, and harbor cytotoxic potential. The physical transformations also hold back a successful translation of non-parenteral insulin formulations, in addition to challenges related to encapsulation, chemical modification, purification, storage, and dosing. This review revisits the mechanisms and challenges that drive such physical transformations in insulin, with an emphasis on the observed amyloid fibrillation, and presents a critique of the current amelioration strategies before prioritizing some future research objectives.

Poly(trehalose methacrylate) as an Excipient for Insulin Stabilization: Mechanism and Safety

Insulin, the oldest U.S. Food and Drug Administration (FDA)-approved recombinant protein and a World Health Organization (WHO) essential medicine for treating diabetes globally, faces challenges due to its storage instability. One approach to stabilize insulin is the addition of poly(trehalose methacrylate) (pTrMA) as an excipient. The polymer increases the stability of the peptide to heat and mechanical agitation and has a low viscosity suitable for injection and pumps. However, the safety and stabilizing mechanism of pTrMA is not yet known and is required to understand the potential suitability of pTrMA as an insulin excipient. Herein is reported the immune response, biodistribution, and insulin plasma lifetime in mice, as well as investigation into insulin stabilization. pTrMA alone or formulated with ovalbumin did not elicit an antibody response over 3 weeks in mice, and there was no observable cytokine production in response to pTrMA. Micropositron emission tomography/microcomputer tomography of 64Cu-labeled pTrMA showed excretion of 78-79% ID/cc within 24 h and minimal liver accumulation at 6-8% ID/cc when studied out to 120 h. Further, the plasma lifetime of insulin in mice was not altered by added pTrMA. Formulating insulin with 2 mol equiv of pTrMA improved the stability of insulin to standard storage conditions: 46 weeks at 4 °C yielded 87.0% intact insulin with pTrMA present as compared to 7.8% intact insulin without the polymer. The mechanism by which pTrMA-stabilized insulin was revealed to be a combination of inhibiting deamidation of amino acid residues and preventing fibrillation, followed by aggregation of inactive and immunogenic amyloids all without complexing insulin into its hexameric state, which could delay the onset of insulin activity. Based on the data reported here, we suggest that pTrMA stabilizes insulin as an excipient without adverse effects in vivo and is promising to investigate further for the safe formulation of insulin.

The intriguing dose-dependent effect of selected amphiphilic compounds on insulin amyloid aggregation: Focus on a cholesterol-based detergent, Chobimalt

The amyloidogenic self-assembly of many peptides and proteins largely depends on external conditions. Among amyloid-prone proteins, insulin attracts attention because of its physiological and therapeutic importance. In the present work, the amyloid aggregation of insulin is studied in the presence of cholesterol-based detergent, Chobimalt. The strategy to elucidate the Chobimalt-induced effect on insulin fibrillogenesis is based on performing the concentration- and time-dependent analysis using a combination of different experimental techniques, such as ThT fluorescence assay, CD, AFM, SANS, and SAXS. While at the lowest Chobimalt concentration (0.1 µM; insulin to Chobimalt molar ratio of 1:0.004) the formation of insulin fibrils was not affected, the gradual increase of Chobimalt concentration (up to 100 µM; molar ratio of 1:4) led to a significant increase in ThT fluorescence, and the maximal ThT fluorescence was 3-4-fold higher than the control insulin fibril's ThT fluorescence intensity. Kinetic studies confirm the dose-dependent experimental results. Depending on the concentration of Chobimalt, either (i) no effect is observed, or (ii) significantly, ∼10-times prolonged lag-phases accompanied by the substantial, ∼ 3-fold higher relative ThT fluorescence intensities at the steady-state phase are recorded. In addition, at certain concentrations of Chobimalt, changes in the elongation-phase are noticed. An increase in the Chobimalt concentrations also triggers the formation of insulin fibrils with sharply altered morphological appearance. The fibrils appear to be more flexible and wavy-like with a tendency to form circles. SANS and SAXS data also revealed the morphology changes of amyloid fibrils in the presence of Chobimalt. Amyloid aggregation requires the formation of unfolded intermediates, which subsequently generate amyloidogenic nuclei. We hypothesize that the different morphology of the formed insulin fibrils is the result of the gradual binding of Chobimalt to different binding sites on unfolded insulin. A similar explanation and the existence of such binding sites with different binding energies was shown previously for the nonionic detergent. Thus, the data also emphasize the importance of a protein partially-unfolded state which undergoes the process of fibrils formation; i.e., certain experimental conditions or the presence of additives may dramatically change not only kinetics but also the morphology of fibrillar aggregates.

Orange G is a potential inhibitor of human insulin amyloid fibrillation and can be used as a probe to study mechanism of amyloid fibrillation and its inhibition

The extracellular insoluble deposits of highly ordered cross-β-structure-containing amyloid fibrils form the pathological basis for protein misfolding diseases. As amyloid fibrils are cytotoxic, inhibition of the process is a therapeutic strategy. Several small molecules have been identified and used as fibrillation inhibitors in the recent past. In this work, we investigate the effect of Orange G on insulin amyloid formation using fluorescence-based assays and negative-stain electron microscopy (EM). We show that Orange G effectively attenuates nucleation, thereby inhibiting amyloid fibrillation in a dose-dependent manner. Fluorescence quenching titrations of Orange G showed a reasonably strong binding affinity to native insulin. Binding isotherm measurements revealed the binding of Orange G to pre-formed insulin fibrils too, indicating that Orange G likely binds and stabilizes the mature fibrils and prevents the release of toxic oligomers which could be potential nuclei or templates for further fibrillation. Molecular docking of Orange G with native insulin and amyloid-like peptide structures were also carried out to analyse the contributing interactions and binding free energy. The findings of our study emphasize the use of Orange G as a molecular probe to identify and design inhibitors of amyloid fibrillation and to investigate the structural and toxic mechanisms underlying amyloid formation.

An amphiphilic small molecule drives insulin aggregation inhibition and amyloid disintegration

The aggregation of proteins into ordered fibrillar structures called amyloids, and their disintegration represent major unsolved problems that limit the therapeutic applications of several proteins. For example, insulin, commonly used for the treatment of diabetes, is susceptible to amyloid formation upon exposure to non-physiological conditions, resulting in a loss of its biological activity. Here, we report a novel amphiphilic molecule called PAD-S, which acts as a chemical chaperone and completely inhibits fibrillation of insulin and its biosimilars. Mechanistic investigations and molecular docking lead to the conclusion that PAD-S binds to key hydrophobic regions of native insulin, thereby preventing its self-assembly. PAD-S treated insulin was biologically active as indicated by its ability to phosphorylate Akt, a protein in the insulin signalling pathway. PAD-S is non-toxic and protects cells from insulin amyloid induced cytotoxicity. The high aqueous solubility and easy synthetic accessibility of PAD-S facilitates its potential use in commercial insulin formulations. Notably, PAD-S successfully disintegrated preformed insulin fibrils to non-toxic smaller fragments. Since the structural and mechanistic features of amyloids are common to several human pathologies, the understanding of the amyloid disaggregation activity of PAD-S will inform the development of small molecule disaggregators for other amyloids.

Progress in Simulation Studies of Insulin Structure and Function

Insulin is a peptide hormone known for chiefly regulating glucose level in blood among several other metabolic processes. Insulin remains the most effective drug for treating diabetes mellitus. Insulin is synthesized in the pancreatic β-cells where it exists in a compact hexameric architecture although its biologically active form is monomeric. Insulin exhibits a sequence of conformational variations during the transition from the hexamer state to its biologically-active monomer state. The structural transitions and the mechanism of action of insulin have been investigated using several experimental and computational methods. This review primarily highlights the contributions of molecular dynamics (MD) simulations in elucidating the atomic-level details of conformational dynamics in insulin, where the structure of the hormone has been probed as a monomer, dimer, and hexamer. The effect of solvent, pH, temperature, and pressure have been probed at the microscopic scale. Given the focus of this review on the structure of the hormone, simulation studies involving interactions between the hormone and its receptor are only briefly highlighted, and studies on other related peptides (e.g., insulin-like growth factors) are not discussed. However, the review highlights conformational dynamics underlying the activities of reported insulin analogs and mimetics. The future prospects for computational methods in developing promising synthetic insulin analogs are also briefly highlighted.

Using a Caenorhabditis elegans Parkinson's Disease Model to Assess Disease Progression and Therapy Efficiency

Despite Parkinson's Disease (PD) being the second most common neurodegenerative disease, treatment options are limited. Consequently, there is an urgent need to identify and screen new therapeutic compounds that slow or reverse the pathology of PD. Unfortunately, few new therapeutics are being produced, partly due to the low throughput and/or poor predictability of the currently used model organisms and in vivo screening methods. Our objective was to develop a simple and affordable platform for drug screening utilizing the nematode Caenorhabditis elegans. The effect of Levodopa, the "Gold standard" of PD treatment, was explored in nematodes expressing the disease-causing α-synuclein protein. We focused on two key hallmarks of PD: plaque formation and mobility. Exposure to Levodopa ameliorated the mobility defect in C. elegans, similar to people living with PD who take the drug. Further, long-term Levodopa exposure was not detrimental to lifespan. This C. elegans-based method was used to screen a selection of small-molecule drugs for an impact on α-synuclein aggregation and mobility, identifying several promising compounds worthy of further investigation, most notably Ambroxol. The simple methodology means it can be adopted in many labs to pre-screen candidate compounds for a positive impact on disease progression.