Charge-Converting Nanoemulsions as Promising Retinal Drug and Gene Delivery Systems

Nanostructured lipid carriers decorated with polyphosphate coated linear and loop cell-penetrating peptides

AIM

This study aimed to evaluate the cellular uptake of nanostructured lipid carriers (NLCs) decorated with polyphosphate coated linear and loop cell-penetrating peptides (CPPs).

METHODS

Linear-CPPs and loop-CPPs were synthesized via ring-opening polymerization and anchored on the surface NLCs, followed by coating with polyphosphate (PP). These nanocarriers (NCs) were characterized in terms of particle size, polydispersity index (PDI), and zeta potential. Cell viability and hemolysis, as well as enzyme-induced charge conversion via phosphate cleavage by free and membrane-bound intestinal alkaline phosphatase (IAP) were investigated. Cellular uptake studies by Caco-2 and HEK cells were quantitatively analyzed by flow cytometry and visualized by confocal microscopy.

RESULTS

A shift in charge from positive to negative was obtained for both linear- and loop-CPPs-NLCs by coating with PP. PP-linear-CPPs-NLCs and PP-loop-CPPs-NLCs exhibited a particle size < 270 nm and a PDI of approximately 0.3. They had a minor effect on cell viability and caused in a concentration of 0.1 % (m/v) around 10 % hemolysis within 24 h. IAP triggered the cleavage and release of monophosphate from the surface of NLCs causing charge conversion from -22.2 mV to + 5.3 mV (Δ27.5 mV) for PP-linear-CPPs-NLCs and from -19.2 mV to + 11.9 mV (Δ31.1 mV) for PP-loop-CPPs-NLCs. Inhibition of alkaline phosphatase activity on Caco-2 and HEK cells confirmed the involvement of this enzyme in charge conversion. PP-linear-CPPs-NLCs showed on Caco-2 cells a higher uptake than PP-loop-CPPs-NLCs, whereas on HEK cells uptake of both types of NLCs was on the same level. The results of cellular uptake were confirmed visually by confocal microscopy.

CONCLUSION

CPPs-NLCs coated with polyphosphate are a promising approach to overcome the polycationic dilemma and to enhance cellular uptake.

Smart Nanocarriers for the Treatment of Retinal Diseases

Retinal diseases, such as age-related macular degeneration, diabetic retinopathy, and retinoblastoma, stand as the leading causes of irreversible vision impairment and blindness worldwide. Effectively administering drugs for retinal diseases poses a formidable challenge due to the presence of complex ocular barriers and elimination mechanisms. Over time, various approaches have been developed to fabricate drug delivery systems for improving retinal therapy including virus vectors, lipid nanoparticles, and polymers. However, conventional nanocarriers encounter issues related to the controllability, efficiency, and safety in the retina. Therefore, the development of smart nanocarriers for effective or more invasive long-term treatment remains a desirable goal. Recently, approaches have surfaced for the intelligent design of nanocarriers, leveraging specific responses to external or internal triggers and enabling multiple functions for retinal therapy such as topical administration, prolonged drug release, and site-specific drug delivery. This Review provides an overview of prevalent retinal pathologies and related pharmacotherapies to enhance the understanding of retinal diseases. It also surveys recent developments and strategies employed in the intelligent design of nanocarriers for retinal disease. Finally, the challenges of smart nanocarriers in potential clinical retinal therapeutic applications are discussed to inspire the next generation of smart nanocarriers.

Charge-Reversible Nanoparticles: Advanced Delivery Systems for Therapy and Diagnosis

The past two decades have witnessed a rapid progress in the development of surface charge-reversible nanoparticles (NPs) for drug delivery and diagnosis. These NPs are able to elegantly address the polycation dilemma. Converting their surface charge from negative/neutral to positive at the target site, they can substantially improve delivery of drugs and diagnostic agents. By specific stimuli like a shift in pH and redox potential, enzymes, or exogenous stimuli such as light or heat, charge reversal of NP surface can be achieved at the target site. The activated positive surface charge enhances the adhesion of NPs to target cells and facilitates cellular uptake, endosomal escape, and mitochondrial targeting. Because of these properties, the efficacy of incorporated drugs as well as the sensitivity of diagnostic agents can be essentially enhanced. Furthermore, charge-reversible NPs are shown to overcome the biofilm formed by pathogenic bacteria and to shuttle antibiotics directly to the cell membrane of these microorganisms. In this review, the up-to-date design of charge-reversible NPs and their emerging applications in drug delivery and diagnosis are highlighted.

Lipid nanoparticles with PEG-variant surface modifications mediate genome editing in the mouse retina

Ocular delivery of lipid nanoparticle (LNPs) packaged mRNA can enable efficient gene delivery and editing. We generated LNP variants through the inclusion of positively charged-amine-modified polyethylene glycol (PEG)-lipids (LNPa), negatively charged-carboxyl-(LNPz) and carboxy-ester (LNPx) modified PEG-lipids, and neutral unmodified PEG-lipids (LNP). Subretinal injections of LNPa containing Cre mRNA in the mouse show tdTomato signal in the retinal pigmented epithelium (RPE) like conventional LNPs. Unexpectedly, LNPx and LNPz show 27% and 16% photoreceptor transfection, respectively, with striking localization extending from the photoreceptor synaptic pedicle to the outer segments, displaying pan-retinal distribution in the photoreceptors and RPE. LNPx containing Cas9 mRNA and sgAi9 leads to the formation of an oval elongated structure with a neutral charge resulting in 16.4% editing restricted to RPE. Surface modifications of LNPs with PEG variants can alter cellular tropism of mRNA. LNPs enable genome editing in the retina and in the future can be used to correct genetic mutations that lead to blindness.

Peptide Antibiotic-Polyphosphate Nanoparticles: A Promising Strategy to Overcome the Enzymatic and Mucus Barrier of the Intestine

The aim of this study was to develop peptide antibiotic-polyphosphate nanoparticles that are able to overcome the enzymatic and mucus barriers providing a targeted drug release directly on the intestinal epithelium. Polymyxin B-polyphosphate nanoparticles (PMB-PP NPs) were formed via ionic gelation between the cationic peptide and the anionic polyphosphate (PP). The resulting NPs were characterized by particle size, polydispersity index (PDI), zeta potential, and cytotoxicity on Caco-2 cells. The protective effect of these NPs for incorporated PMB was evaluated via enzymatic degradation studies with lipase. Moreover, mucus diffusion of NPs was investigated with porcine intestinal mucus. Isolated intestinal alkaline phosphatase (IAP) was employed to trigger the degradation of NPs and consequent drug release. PMB-PP NPs exhibited an average size of 197.13 ± 14.13 nm, a PDI of 0.36, a zeta potential of -11.1 ± 3.4 mV and a concentration and time-dependent toxicity. They provided entire protection toward enzymatic degradation and exhibited significantly (p < 0.05) higher mucus permeating properties than PMB. When incubated with isolated IAP for 4 h, monophosphate and PMB were constantly released from PMB-PP NPs and zeta potential raised up to -1.9 ± 0.61 mV. According to these findings, PMB-PP NPs are promising delivery systems to protect cationic peptide antibiotics against enzymatic degradation, to overcome the mucus barrier and to provide drug release directly at the epithelium.