Nanotechnology and infection: vancomycin–loaded dextran-shelled/perfluoropentane-containing nanobubbles as topical skin-friendly antibacterial vector.

Introduction. Vancomycin is a glycopeptide antibiotic used for treatment of infections caused by Gram-positive bacteria, which are unresponsive to other less toxic antibiotics. This drug is poorly adsorbed from the gastrointestinal tract and its systemic administration can be associated with severe adverse effects. Nanobubbles are small gas-filled nanospheres with sizes lower than 1 µm easily loadable with drugs and transcutaneously deliverable via ultrasound-induced sonophoresis. Here, vancomycin-loaded nanobubbles (VLNs) were compared to vancomycin alone for bacterial killing abilities on methicillin-resistant Staphylococcus aureus (MRSA) and for potential cytotoxicity on human keratinocytes (HaCaT cell line). Methods. Dextran-shelled/perfluoropentane-containing nanobubbles were prepared and characterized for physical-chemical properties by optical microscopy, laser light scattering, and drug release studies according to (1). Liquid formulations of vancomycin (in saline solution) and VLNs, both with a drug concentration = 1 mg/ml, were tested on MRSA (104 Colony Forming Units/ ml) after 2 h, 3 h, 4 h, 6 h and 24 h incubation. At each incubation time, from each sample serial 10-fold dilutions were prepared in saline solution (0.9% NaCl), 100 l of each dilution was spread on agar medium (TSA), so that the number of CFU/ml could be determined. Vancomycin and VLNs were also incubated with HaCaT cells in DMEM medium implemented with 10% fetal calf serum (FCS) for 24 h, and citotoxicity was evaluated by measuring lactate dehydrogenase (LDH) activity, whereas cell viability was checked by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Results. VNLs showed sizes less than 500 nm, a negative surface charge and a spherical shape. In vitro studies displayed prolonged drug release kinetics. Antibacterial efficiency was assessed for different formulations and their responses during time monitored and compared. Finally, no toxic effects were displayed on human keratinocytes, and cell viability was not significantly affected. Conclusion. VNLs proved to be effective in bacterial killing without showing toxic effects on human keratinocytes. Thus, they appear to be good therapeutic tools for treatment of infected chronic wounds. References. (1) Cavalli R, Bisazza A, Giustetto P, Civra A, Lembo D, Trotta G, Guiot C, Trotta M. Preparation and characterization of dextran nanobubbles for oxygen delivery. Int J Pharm. 2009;381:160-5. Acknowledgements. Work supported by funding from Ateneo-Compagnia di San Paolo (ORTO11CE8R 2011).