Date Published: February 26, 2019
Publisher: Public Library of Science
Author(s): Erik Tenland, Alexander Pochert, Nitya Krishnan, Komal Umashankar Rao, Sadaf Kalsum, Katharina Braun, Izabela Glegola-Madejska, Maria Lerm, Brian D. Robertson, Mika Lindén, Gabriela Godaly, Riccardo Manganelli.
Intracellular delivery of antimicrobial agents by nanoparticles, such as mesoporous silica particles (MSPs), offers an interesting strategy to treat intracellular infections. In tuberculosis (TB), Mycobacterium tuberculosis avoids components of the immune system by residing primarily inside alveolar macrophages, which are the desired target for TB therapy.
We have previously identified a peptide, called NZX, capable of inhibiting both clinical and multi-drug resistant strains of M. tuberculosis at therapeutic concentrations. In this study we analysed the potential of MSPs containing NZX for the treatment of tuberculosis. The MSPs released functional NZX gradually into simulated lung fluid and the peptide filled MSPs were easily taken up by primary macrophages. In an intracellular infection model, the peptide containing particles showed increased mycobacterial killing compared to free peptide. The therapeutic potential of peptide containing MSPs was investigated in a murine infection model, showing that MSPs preserved the effect to eliminate M. tuberculosis in vivo.
In this study we found that loading the antimicrobial peptide NZX into MSPs increased the inhibition of intracellular mycobacteria in primary macrophages and preserved the ability to eliminate M. tuberculosis in vivo in a murine model. Our studies provide evidence for the feasibility of using MSPs for treatment of tuberculosis.
Antimicrobial peptides (AMPs) have gained interest as potential host directed therapeutic strategies against various infections. Defensins comprise one of the largest groups of host defence peptides and are the best studied in infection models . These cysteine-rich, cationic peptides act through disruption of microbial membranes, although they may have additional host-related immune-modulating activities [2, 3]. Peptides are potentially easily degradable and need to be protected in order to safely reach the site of infection where they can exercise their mode of action . To overcome these challenges, peptides can be delivered efficiently by encapsulating them in carrier systems, such as nanoparticles. Nanoparticles can also be designed to allow sustained drug release from the matrix which could have an impact on the treatment time. In this context, mesoporous, amorphous silica nanoparticles (MSPs) represent a highly promising drug delivery platform. The development of MSPs for theranostic applications have been extensively reviewed [5–8], with most research concentrated on the therapeutic effect of small molecular drugs loaded into MSPs; the function of MSPs for intracellular infections is largely unexplored.
We have designed mesoporous nanoparticles containing the antimicrobial peptide NZX at therapeutic concentrations. These MSPs were non-toxic to mammalian cells at therapeutic concentrations but showed increased intracellular anti-mycobacterial activity. In a murine model of TB, we showed that NZX containing MSPs significantly decreased the bacterial load, at levels comparable to rifampicin treatment. The MSPs were synthesized with a mean diameter of ~200 nm in order to enable fast cellular internalization of the particles by alveolar macrophages . For MSPs, a recent study showed that HeLa cells favoured a particle size of 50–120 nm . In our study, the particles were taken up efficiently by the majority of the cells, with the most efficient engulfment by primary macrophages. This observation agrees with previous studies reporting that primary cells have increased uptake efficiency compared to cell-line [26, 27].