Sayanti Brahmachari

Peptide-based supramolecular assemblies are a promising class of nanomaterials with important biomedical applications, specifically in drug delivery and tissue regeneration. However, the intrinsic antibacterial capabilities of these assemblies have been largely overlooked. The recent identification of common characteristics shared by antibacterial and self-assembling peptides provides a paradigm shift towards development of antibacterial agents. Here we present the antibacterial activity of self-assembled diphenylalanine, which emerges as the minimal model for antibacterial supramolecular polymers. The diphenylalanine nano-assemblies completely inhibit bacterial growth, trigger upregulation of stress-response regulons, induce substantial disruption to bacterial morphology, and cause membrane permeation and depolarization. We demonstrate the specificity of these membrane interactions and the development of antibacterial materials by integration of the peptide assemblies into tissue scaffolds. This study provides important insights into the significance of the interplay between self-assembly and antimicrobial activity and establishes innovative design principles toward the development of antimicrobial agents and materials.

The phenomenon of protein aggregation into amyloid fibrils is associated with a large number of major diseases of unrelated etiology. Unraveling the mechanism of amyloid self-assembly and identifying therapeutic directions to control this process are of utmost importance. Research in this field has been hampered by several challenges, including reproducibility, low protein purification yields, and the inherent aggregation propensity of amyloidogenic proteins, making them extremely difficult to study. Herein, on the basis of the similarity in the assembly mechanism, as well as the physical, chemical, and biological characteristics, of diphenylalanine nanostructures and aromatic amino acid containing amyloid fibrils, we report a simple, yet robust peptide-based platform that could be used for screening of small molecules potentially capable of interfering with the aggregation process and for mechanistic exploration of their mode of action. The system was validated using four small-molecule inhibitors, and the effect was examined via turbidity assay, thioflavin T fluorescence, and electron microscopy. The aggregation profile of diphenylalanine was very similar to that of β-amyloid polypeptide in the presence of the modulators. Rosmarinic acid emerged as an extremely potent inhibitor and a destabilizer of the aggregates. The effect of stoichiometric variation of rosmarinic acid on the process of destabilization was also probed using a microfluidic technique. Finally, the formation of equimolar complexes of diphenylalanine and inhibitors was detected using mass spectrometry. This approach not only provides a system for high-throughput screening of possible inhibitor molecules from larger libraries of modulators, but is also highly useful for understanding the mechanistic aspects of the interactions leading to the process of inhibition.

Fibrillar deposits formed by the aggregation of the human islet amyloid polypeptide (hIAPP) are the major pathological hallmark of type 2 diabetes mellitus (T2DM). Inhibiting the aggregation of hIAPP is considered the primary therapeutic strategy for the treatment of T2DM. Hydroxylated carbon nanoparticles have received great attention in impeding amyloid protein fibrillation owing to their reduced cytotoxicity compared to the pristine ones. In this study, we investigated the influence of hydroxylated single-walled carbon nanotubes (SWCNT-OHs) on the first step of hIAPP aggregation: dimerization by performing explicit solvent replica exchange molecular dynamics (REMD) simulations. Extensive REMD simulations demonstrate that SWCNT-OHs can dramatically inhibit interpeptide β-sheet formation and completely suppress the previously reported β-hairpin amyloidogenic precursor of hIAPP. On the basis of our simulation results, we proposed that SWCNT-OH can hinder hIAPP fibrillation. This was further confirmed by our systematic turbidity measurements, thioflavin T fluorescence, circular dichroism (CD), transmission electron microscope (TEM), and atomic force microscopy (AFM) experiments. Detailed analyses of hIAPP-SWCNT-OH interactions reveal that hydrogen bonding, van der Waals, and π-stacking interactions between hIAPP and SWCNT-OH significantly weaken the inter- and intrapeptide interactions that are crucial for β-sheet formation. Our collective computational and experimental data reveal not only the inhibitory effect but also the inhibitory mechanism of SWCNT-OH against hIAPP aggregation, thus providing new clues for the development of future drug candidates against T2DM.

With the change in lifestyle and aging of the population, osteoarthritis (OA) is emerging as a major medical burden globally. OA is a chronic inflammatory and degenerative disease initially manifesting with joint pain and eventually leading to permanent disability. To date, there are no drugs available for the definitive treatment of osteoarthritis and most therapies have been palliative in nature by alleviating symptoms rather than curing the disease. This coupled with the vague understanding of the early symptoms and methods of diagnosis so that the disease continues as a global problem and calls for concerted research efforts. A cascade of events regulates the onset and progression of osteoarthritis starting with the production of proinflammatory cytokines, including interleukin (IL)-1β, IL-6, tumor necrosis factor (TNF)-α; catabolic enzymes, such as matrix metalloproteinases (MMPs)-1, -3, and -13, culminating into cartilage breakdown, loss of lubrication, pain, and inability to load the joint. Although intra-articular injections of small and macromolecules are often prescribed to alleviate symptoms, low residence times within the synovial cavity severely impair their efficacy. This review will briefly describe the factors dictating the onset and progression of the disease, present the current clinically approved methods for its treatment and diagnosis, and finally elaborate on the main challenges and opportunities for the application of nano/micromedicines in the treatment of osteoarthritis. Thus, future treatment regimens will benefit from simultaneous consideration of the mechanobiological, the inflammatory, and tissue degradation aspects of the disease. This article is categorized under: Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Implantable Materials and Surgical Technologies > Nanotechnology in Tissue Repair and Replacement.

Protein misfolding and aggregation have been associated with several human disorders, including Alzheimer's, Parkinson's and Huntington's diseases, as well as senile systemic amyloidosis and Type II diabetes. However, there is no current disease-modifying therapy available for the treatment of these disorders. In spite of extensive academic, pharmaceutical, medicinal and clinical research, a complete mechanistic model for this family of diseases is still lacking. In this review, we primarily discuss the different types of small molecular entities which have been used for the inhibition of the aggregation process of different amyloidogenic proteins under diseased conditions. These include small peptides, polyphenols, inositols, quinones and their derivatives, and metal chelator molecules. In recent years, these groups of molecules have been extensively studied using in vitro, in vivo and computational models to understand their mechanism of action and common structural features underlying the process of inhibition. A salient feature found to be instrumental in the process of inhibition is the balance between the aromatic unit that functions as the amyloid recognition unit and the hydrophilic amyloid breaker unit. The establishment of structure-function relationship for amyloid-modifying therapies by the various functional entities should serve as an important step toward the development of efficient therapeutics.