Recent updates on guar gum derivatives in colon specific drug delivery.

Colon specific delivery of therapeutics have gained much attention of pharmaceutical researchers in the recent past. Colonic specific targeting of drugs is used not only for facilitating absorption of protein or peptide drugs, but also localization of therapeutic agents in colon to treat several colonic disorders. Among various biopolymers, guar gum (GG) exhibits pH dependent swelling, which allows colon specific release of drug. GG also shows microbial degradation in the colonic environment which makes it a suitable excipient for developing colon specific drug delivery systems. The uncontrolled swelling and hydration of GG can be controlled by structural modification or by grafting with another polymeric moiety. Several graft copolymerized guar gum derivatives are investigated for colon targeting of drugs. The efficacy of various guar gum derivatives are evaluated for colon specific delivery of drugs. The reviewed literature evidenced the potentiality of guar gum in localizing drugs in the colonic environment. This review focuses on the synthesis of several guar gum derivatives and their application in developing various colon specific drug delivery systems including matrix tablets, coated formulations, nano or microparticulate delivery systems and hydrogels.

Interaction of TGFß3 ligand with its receptors type II (TßRII) and type I (TßRI): A unique mechanism of protein-protein association.

The proper orchestration of transforming growth factor beta (TGFß) mediated signal transduction depends upon a delicate set of interactions between specific ligands and their receptors. Here we present an in-depth profiling of the binding mechanism of TGFß3 ligand with its type II and type I receptors (TßRII and TßRI) using isothermal titration calorimetry (ITC). Studies were carried out in acidic pH as it has great physiological relevance for TGFß3 activity. Our findings reveal an unusual positive enthalpy (∆H) compensated by a large favourable entropy (∆S) during TGFß3-TßRII interaction. In addition to the hydrophobic effect, we propose that a distinct conformational switch from "closed" to "open" form as experienced by TGFß3 on binding to TßRII is contributing significantly to the increase in overall entropy of the system. Binding studies of TGFß3 and TßRII were carried out at different pH values and salt concentrations to gain further insight into the thermodynamics of the interaction. Furthermore, the importance of hydrophobic interactions on the binding affinity of TßRII with TGFß3 was confirmed by two TßRII variants (interfacial). Finally, a distinct shift from entropy to enthalpy dominated interaction was observed upon recruitment of TßRI to the binary complex forming the ternary complex.

Exploring the potency of the naturally occurring polyphenol curcumin as a probe for protein aggregation in crowded environments.

Conventional dyes such as thioflavin T, ANS, and Congo Red etc. have mostly been used to monitor protein aggregation. In this work, we have tried the naturally occurring polyphenol, curcumin, for probing the aggregation of the serum protein bovine serum albumin (BSA) in crowded environments. The distinctive spectral profile of this polyphenol in response to varying aggregating scenario is indicative of its high sensitivity towards detection of aggregates. We have also gained possible insights into the heterogeneity of the aggregation mixture, that is, the different species that are present simultaneously at any instant of time by fitting curcumin's emission spectra to a sum of Gaussians in diverse aggregating conditions. SEM study reveals that the morphology of aggregates formed in presence of different crowding agents became independent of the nature of the crowder on prolonged incubation. To overcome the aqueous insolubility barrier of the molecular probe (curcumin), ß-cyclodextrin, which is known to complex with curcumin, was also added to the reaction mixture.

Crowder induced structural modulation of a multi-domain protein during its early stages of aggregation: A FRET-based and protein solvation study.

Protein aggregation has been known for long to be the prime cause for several neurological disorders in human beings. While protein aggregation is itself a complex process, understanding the same in the context of a crowded cellular medium remains a challenge. In this work, using Förster resonance energy transfer (FRET) and solvation dynamics, we have tried to gain important insights into the structural rearrangements, during the early stages of aggregation of the multidomain protein bovine serum albumin (BSA) in presence of a range of synthetic macromolecular crowding agents. FRET studies show that there is an initial compaction in the domain size (domain I) at the early time points of incubation followed by an increase in the distance between the donor-acceptor pair. Analyses of the solvent correlation traces of BADAN (labeled at free Cys-34 in domain I of BSA) reveal that the same domain becomes rigid during the initial phase of the aggregation process subsequent to which there was a gradual increase in flexibility, the latter we propose being a necessary step that allows facile addition of more protein units.

Polyphenols in combination with ß-cyclodextrin can inhibit and disaggregate α-synuclein amyloids under cell mimicking conditions: A promising therapeutic alternative.

Parkinson's disease is characterized by the presence of insoluble and neurotoxic aggregates (amyloid fibrils) of an intrinsically disordered protein α-synuclein. In this study we have examined the effects of four naturally occurring polyphenols in combination with ß-cyclodextrin (ß-CD) on the aggregation of α-synuclein in the presence of macromolecular crowding agents. Our results reveal that even at sub-stoichiometric concentrations of the individual components, the polyphenol-ß-CD combination(s) not only inhibited the aggregation of the proteins but was also effective in disaggregating preformed fibrils. Curcumin was found to be the most efficient, followed by baicalein with (-)-epigallocatechin gallate and resveratrol coming in next, the latter two exhibiting very similar effects. Our results suggest that the efficiency of curcumin results from a balanced composition of the phenolic OH groups, benzene rings and flexibility. The latter ensures proper positioning of the functional groups to maximize the underlying interactions with both the monomeric form of α-synuclein and its aggregates. The uniqueness of ß-CD was reinforced by the observation that none of the other cyclodextrin variants [α-CD and HP-ß-CD] used was as effective, in spite of these possessing better water solubility. Moreover, the fact that the combinations remained effective under conditions of macromolecular crowding suggests that these have the potential to be developed into viable drug compositions in the near future. MTT assays on cell viability independently confirmed this hypothesis wherein these combinations (and the polyphenols alone too) appreciably impeded the toxicity of the prefibrillar α-synuclein aggregates on the mouse neuroblastoma cell lines (N2a cells).

Modulation of Self-Assembly Process of Fibroin: An Insight for Regulating the Conformation of Silk Biomaterials.

Controlling the mechanism of self-assembly in proteins has emerged as a potent tool for various biomedical applications. Silk fibroin self-assembly consists of gradual conformational transition from random coil to ß-sheet structure. In this work we elucidated the intermediate secondary conformation in the presence of Ca(2+) ions during fibroin self-assembly. The interaction of fibroin and calcium ions resulted in a predominantly α-helical intermediate conformation, which was maintained to certain extent even in the final conformation as illustrated by circular dichroism and attenuated total reflectance-Fourier transform infrared spectroscopy. Further, to elucidate the mechanism behind this interaction molecular modeling of the N-terminal region of fibroin with Ca(2+) ions was performed. Negatively charged glutamate and aspartate amino acids play a key role in the electrostatic interaction with positively charged calcium ions. Therefore, insights about modulation of self-assembly mechanism of fibroin could potentially be utilized to develop silk-based biomaterials consisting of the desired secondary conformation.

Unusual effects of crowders on heme retention in myoglobin.

Myoglobin (Mb) undergoes pronounced heme loss under denaturing conditions wherein the proximal histidine gets protonated. Our data show that macromolecular crowding agents (both synthetic and protein based) can appreciably influence the extent of heme retention in Mb. Interestingly, glucose and sucrose, the monomeric constituents of dextran and ficoll-based crowders were much more effective in preventing heme dissociation of Mb, albeit, at much higher concentrations. The protein crowders BSA and lysozyme show very interesting results with BSA bringing about the maximum heme retention amongst all the crowding agents used while lysozyme induced heme dissociation even in the native state of Mb. The stark difference that these protein crowders exhibit when interacting with the heme protein is a testament to the varied interaction potentials that a test protein might be exposed to in the physiological (crowded) milieu.

ß-cyclodextrin and curcumin, a potent cocktail for disaggregating and/or inhibiting amyloids: a case study with α-synuclein.

Aggregation of α-synuclein has been implicated in Parkinson's disease (PD). While many compounds are known to inhibit α-synuclein aggregation, dissolution of aggregates into their constituent monomers cannot be readily achieved. In this study, using a range of techniques, we have shown that an optimized cocktail of curcumin and ß-cyclodextrin, at appreciably low concentrations, not only inhibited aggregation but also broke up the preformed aggregates almost completely. We propose that these compounds exhibit synergy in their action and thus provide us with the exciting prospect of working toward the development of a suitable drug candidate for prevention and treatment of PD.