Encapsulation of Peppermint essential oil in nanostructured lipid carriers: In-vitro antibacterial activity and accelerative effect on infected wound healing

Despite the use of essential oils for wound healing, their application is compromised due to their hydrophobic and volatile nature. This study was conducted to evaluate the efficiency of peppermint essential oil (PEO) loaded into nanostructured lipid carriers (PEO-NLC) on In-vitro antibacterial activity and In-vivo infected wound healing in mice model. The PEO-NLC was prepared using hot melt homogenization technique. Then, the morphology and size of PEO-NLC were determined by using Zeta potential (ZP) and Scanning Electron Microscopy (SEM) analyses. For in vitro study, PEO and PEO-NLC were tested for antibacterial activities against Escherichia coli, Salmonella typhimurium, Pseudomonas aeruginosa, Staphylococcus aureus, Staphylococcus epidermidis, Bacillus anthracis, Staphylococcus pneumonia, and Listeria monocytogenes Species. In order to perform an in vivo study, two full-thickness wounds with the size of 5 mm were induced in each mouse and inoculated with Pseudomonas aeruginosa and Staphylococcus aureus. The animals were divided into four groups as control, Mupirocin®, PEO, and PEO-NLC. Wound contraction, bacterial count, histological examinations, and molecular analyses were performed on these mice. Particle size analyses showed that all the fabricated PEO-NLC were in the range from 40 to 250 nm with narrow PDI∼0.4. The ZP value of the all fabricated PEO-NLC was found to be -10 to -15mv. SEM analysis indicated that the particles had a smooth surface, spherical and uniformly distributed around. In vitro analysis showed that PEO and PEO-NLC have similar antibacterial activities against S. epidermidis, S. aureus, L. monocytogenes, E. coli, and P. aeruginosa species. In vivo analysis showed that wound contraction rate, fibroblast infiltration, collagen deposition, and re-epithelialization were increased in PEO and PEO-NLC-treated animals compared to the control group. Also, it indicated positive effects on the FGF-2 and EGF mRNA levels expressions. Our results suggest the efficacy of PEO-NLC in order to treat an infected wound model and can provide an appropriate strategy for producing topical formulations.