Sachin S. Thakur

Resveratrol nanoformulations: Challenges and opportunities

Resveratrol, a naturally occurring polyphenol and phytoalexin, has received significant attention in recent years due to its vast therapeutic effects including anticancer, antioxidant and anti-inflammatory effects. However, poor pharmacokinetic properties such as low aqueous solubility, low photostability and extensive first pass metabolism result in poor bioavailability, hindering its immense potential. Conventional dosage forms such as dry powder capsules and injections have met with limited success, demonstrating challenges faced in developing an effective formulation. Recently, nanotechnology-based formulations (nanoformulations) are being looked upon as a novel method for improving the pharmacokinetic properties, as well as enhancing targetability and bioavailability of resveratrol. This review outlines the therapeutic potential of resveratrol, explores its mechanisms of action and pharmacokinetic limitations, and discusses the success and challenges of resveratrol-encapsulated nanoparticles in the last decade. Potential techniques to improve encapsulation of the drug within nanoparticles, thereby enhancing its clinical potential are highlighted.

Enhancing delivery and cytotoxicity of resveratrol through a dual nanoencapsulation approach.

Despite the known anticancer potential of resveratrol, its clinical applications are often hindered by physicochemical limitations such as poor solubility and stability. The encapsulation of resveratrol in formulations such as polymeric nanoparticles and liposomes has shown limited success. This study aimed to develop and optimize a novel drug carrier by co-encapsulating pristine resveratrol alongside cyclodextrin-resveratrol inclusion complexes in the lipophilic and hydrophilic compartments of liposomes, respectively by using a novel dual carrier approach. The particle size, polydispersity index and zeta potential of the final formulation were 131±1.30nm, 0.089±0.005 and -2.64±0.51mV, respectively. Compared to free resveratrol and conventional liposomal formulations with drug release profile of 40-60%, our novel nanoformulations showed complete (100%) drug release in 24h. The formulation was stable for 14days at 4°C. We also studied the in vitro cytotoxicity of resveratrol encapsulated liposomes in HT-29 colon cancer cell lines. The cytotoxicity profile of our liposomes was observed to be dose dependent and enhanced in comparison to free resveratrol (in DMSO). Our study demonstrates that co-encapsulation of pristine resveratrol along with its cyclodextrin complex in liposomal formulations is a plausible option for the enhanced delivery of the hydrophobic chemotherapeutic agent.

Intravitreal drug delivery in retinal disease: are we out of our depth?

Introduction: With the ever-increasing global burden of retinal disease, there is an urgent need to vastly improve formulation strategies that enhance posterior eye delivery of therapeutics. Despite intravitreal administration having demonstrated notable superiority over other routes in enhancing retinal drug availability, there still exist various significant physical/biochemical barriers preventing optimal drug delivery into the retina. A further complication lies with an inability to reliably translate laboratory-based retinal models into a clinical setting. Several formulation approaches have recently been evaluated to improve intravitreal therapeutic outcomes, and our aim in this review is to highlight strategies that hold the most promise. Areas covered: We discuss the complex barriers faced by the intravitreal route and examine how formulation strategies including implants, nanoparticulate carriers, viral vectors and sonotherapy have been utilized to attain both sustained delivery and enhanced penetration through to the retina. We conclude by highlighting the advances and limitations of current in vitro, ex vivo and in vivo retinal models in use by researchers globally. Expert opinion: Various nanoparticle compositions have demonstrated the ability to overcome the retinal barriers successfully; however, their utility is limited to the laboratory setting. Optimization of these formulations and the development of more robust experimental retinal models are necessary to translate success in the laboratory into clinically efficacious outcomes.

Stably engineered nanobubbles and ultrasound - An effective platform for enhanced macromolecular delivery to representative cells of the retina

Herein we showcase the potential of ultrasound-responsive nanobubbles in enhancing macromolecular permeation through layers of the retina, ultimately leading to significant and direct intracellular delivery; this being effectively demonstrated across three relevant and distinct retinal cell lines. Stably engineered nanobubbles of a highly homogenous and echogenic nature were fully characterised using dynamic light scattering, B-scan ultrasound and transmission electron microscopy (TEM). The nanobubbles appeared as spherical liposome-like structures under TEM, accompanied by an opaque luminal core and darkened corona around their periphery, with both features indicative of efficient gas entrapment and adsorption, respectively. A nanobubble +/- ultrasound sweeping study was conducted next, which determined the maximum tolerated dose for each cell line. Detection of underlying cellular stress was verified using the biomarker heat shock protein 70, measured before and after treatment with optimised ultrasound. Next, with safety to nanobubbles and optimised ultrasound demonstrated, each human or mouse-derived cell population was incubated with biotinylated rabbit-IgG in the presence and absence of ultrasound +/- nanobubbles. Intracellular delivery of antibody in each cell type was then quantified using Cy3-streptavidin. Nanobubbles and optimised ultrasound were found to be negligibly toxic across all cell lines tested. Macromolecular internalisation was achieved to significant, yet varying degrees in all three cell lines. The results of this study pave the way towards better understanding mechanisms underlying cellular responsiveness to ultrasound-triggered drug delivery in future ex vivo and in vivo models of the posterior eye.

High-Resolution Single Particle Zeta Potential Characterisation of Biological Nanoparticles using Tunable Resistive Pulse Sensing

Physicochemical properties of nanoparticles, such as size, shape, surface charge, density, and porosity play a central role in biological interactions and hence accurate determination of these characteristics is of utmost importance. Here we propose tunable resistive pulse sensing for simultaneous size and surface charge measurements on a particle-by-particle basis, enabling the analysis of a wide spectrum of nanoparticles and their mixtures. Existing methodologies for measuring zeta potential of nanoparticles using resistive pulse sensing are significantly improved by including convection into the theoretical model. The efficacy of this methodology is demonstrated for a range of biological case studies, including measurements of mixed anionic, cationic liposomes, extracellular vesicles in plasma, and in situ time study of DNA immobilisation on the surface of magnetic nanoparticles. The high-resolution single particle size and zeta potential characterisation will provide a better understanding of nano-bio interactions, positively impacting nanomedicine development and their regulatory approval.

Development and Evaluation of Lipid Nanoparticles Containing Natural Botanical Oil for Sun Protection: Characterization and in vitro and in vivo Human Skin Permeation and Toxicity

The use of sunscreen products is widely promoted by schools, government agencies, and health-related organizations to minimize sunburn and skin damage. In this study, we developed stable solid lipid nanoparticles (SLNs) containing the chemical UV filter octyl methoxycinnamate (OMC). In parallel, we produced similar stable SLNs in which 20% of the OMC content was replaced by the botanical urucum oil. When these SLNs were applied to the skin of human volunteers, no changes in fluorescence lifetimes or redox ratios of the endogenous skin fluorophores were seen, suggesting that the formulations did not induce toxic responses in the skin. Ex vivo (skin diffusion) tests showed no significant penetration. In vitro studies showed that when 20% of the OMC was replaced by urucum oil, there was no reduction in skin protection factor (SPF), suggesting that a decrease in the amount of chemical filter may be a viable alternative for an effective sunscreen, in combination with an antioxidant-rich vegetable oil, such as urucum. There is a strong trend towards increasing safety of sun protection products through reduction in the use of chemical UV filters. This work supports this approach by producing formulations with lower concentrations of OMC, while maintaining the SPF. Further investigations of SPF in vivo are needed to assess the suitability of these formulations for human use.