Enhancing the Cellular Uptake and Antibacterial Activity of Rifampicin through Encapsulation in Mesoporous Silica Nanoparticles.

Paul Joyce,Santhni Subramaniam,Sajedeh Maghrebi,Hanna Ulmefors,Clive A Prestidge,Fredrik Höök,Silver Jõemetsa,Anthony Wignall

doi:10.3390/nano10040815

Abstract

An urgent demand exists for the development of novel delivery systems that efficiently transport antibacterial agents across cellular membranes for the eradication of intracellular pathogens. In this study, the clinically relevant poorly water-soluble antibiotic, rifampicin, was confined within mesoporous silica nanoparticles (MSN) to investigate their ability to serve as an efficacious nanocarrier system against small colony variants of Staphylococcus aureus (SCV S. aureus) hosted within Caco-2 cells. The surface chemistry and particle size of MSN were varied through modifications during synthesis, where 40 nm particles with high silanol group densities promoted enhanced cellular uptake. Extensive biophysical analysis was performed, using quartz crystal microbalance with dissipation (QCM-D) and total internal reflection fluorescence (TIRF) microscopy, to elucidate the mechanism of MSN adsorption onto semi-native supported lipid bilayers (snSLB) and, thus, uncover potential cellular uptake mechanisms of MSN into Caco-2 cells. Such studies revealed that MSN with reduced silanol group densities were prone to greater particle aggregation on snSLB, which was expected to restrict endocytosis. MSN adsorption and uptake into Caco-2 cells correlated well with antibacterial efficacy against SCV S. aureus, with 40 nm hydrophilic particles triggering a ~2.5-log greater reduction in colony forming units, compared to the pure rifampicin. Thus, this study provides evidence for the potential to design silica nanocarrier systems with controlled surface chemistries that can be used to re-sensitise intracellular bacteria to antibiotics by delivering them to the site of infection.

Highlights

Harmful pathogens, such as Staphylococcus aureus, have evolved a multitude of evasive and defensive mechanisms that promote their survival against conventional antimicrobial agents—one of which is their ability to be internalized within host cells, protecting them from immune responses and conventional antibiotics [1,2]
We investigate the ability for mesoporous silica nanoparticles (MSN) particles, with varying to surface chemistries and two different particle sizes, to be internalized by Caco-2 cells infected with SCV S. aureus, which serves as a model system simulating infected intestinal epithelial cells [25]
ATR-FTIR was performed to validate the removal of the cytotoxic templating surfactant, cetyltrimethylammonium bromide (CTAB) [34,35], from the MSN, which highlighted key differences in the surface chemistry of MSN treated with solvent extraction and calcination (Figure 1D,E)

Summary

Introduction

Harmful pathogens, such as Staphylococcus aureus, have evolved a multitude of evasive and defensive mechanisms that promote their survival against conventional antimicrobial agents—one of which is their ability to be internalized within host cells, protecting them from immune responses and conventional antibiotics [1,2]. In order to treat pathogens residing in the intracellular environment, antibacterial agents must be delivered to the site of infection. Conventional antibiotics, such as rifampicin, suffer from low solubilities and/or low permeabilities, which restricts their ability to diffuse or be actively transported across the cellular membrane [5]. It has been estimated that over two-thirds of prescribed antibiotics are ineffective against intracellular pathogens [6]. A growing urgency exists for the development of new classes of antibiotics capable of being efficiently internalized by infected cells

Methods

Results

Conclusion