Preparation of tea tree oil nanoemulsion: Characterisation, antibacterial mechanism and evaluation of apoptosis

Abstract

Tea tree oil (TTO) is a natural plant essential oil that has strong bactericidal properties and low toxicity. However, owing to its irritability, volatility, instability under light/oxygen and hydrophobicity, the application of TTO in pharmaceutical production technology and the food industry is limited. To overcome these problems, TTO nanoemulsions (TTONs) were prepared using a high-speed shearing method. The mean droplets size of TTON was measured. TTON droplets were observed using confocal laser scanning microscopy and analysed using a Turbiscan scanning spectrum. The most suitable nanoemulsion formula was obtained as follows: TTO content, 10% (w/w); Tw-40 content, 8% (w/w); deionised water content, 82% (w/w); shearing time, 5 minutes. The antibacterial effect of TTON was studied, and it was found that its antibacterial activity against Escherichia coli was more potent than that against Staphylococcus aureus. The antibacterial mechanism of TTON was also investigated by observing bacterial morphology using scanning electron microscopy and testing the levels of bacterial reactive oxygen species. The effect of TTON on L-02 cells was evaluated. The results showed that the cell survival rates of L-02 cells treated with TTON at 0.05-0.25 μg/μL were all >90%. At each concentration, the total apoptosis rate of L-02 cells was <10%. These results indicated the high biocompatibility and biological safety of TTON. Therefore, the preparation of TTO into a nanoemulsion can improve its bioavailability, which has positive implications for further applications of TTO.

Progress of nanopreparation technology applied to volatile oil drug delivery systems

“…Frankincense oil NE were found to be effective in inducing apoptosis in cancer cells with minimal cytotoxic effects on normal lung cells, demonstrating the potential of frankincense oil NE to enhance the activity of systemic anti-lung cancer drugs [ 22 ]. In addition, many other volatile oils and their important constituents, including buckwheat flavonoids [ 23 ], limonene [ 24 ], cinnamon oil, coconut oil, sunflower oil, olive oil, palm oil, jojoba [ 25 ], red raspberry seed [ 26 ], peppermint [ 27 ], tea tree [ 28 ], clove [ 29 , 30 ], oregano [ 31 ], chilli pepper [ 32 ], and citrus [ 33 ], linseed [ 34 ], cinnamon [ 23 ], bitter fennel [ 24 ], thyme [ 35 , 36 ], Carlina acaulis L. [ 37 ], fritillary [ 38 ], lemongrass [ 39 , 40 ], cumin [ 41 ], lemon [ 42 ], peppermint [ 43 ], black pepper [ 44 ], cloves [ [45] , [46] , [47] ], lemon [ 48 ], fennel [ 49 , 50 ], Cinnamon [ [51] , [52] , [53] ], Lavender [ 54 , 55 ], Laurel [ 56 ], Peppermint [ 49 ], Thyme [ 57 ], Astragalus [ 58 ], Celandine [ 59 ], Cumin [ 60 ], Nettle [ 46 ] and other volatile oils of TCM, were loaded in NE to improve solubility, solubility and bioavailability. NE have extraordinary properties and are expected to be nanocarriers for hydrophobic drugs.…”

“…The speed gradually increases from the inside to the outside, and the materials are crushed by more intense shear, friction, impact, and collision during the movement to the outer ring, and their particle sizes are getting smaller and smaller so as to achieve the purpose of NE. For example, Liu Qi et al [ 27 ] and Han Rui et al [ 28 ] successfully prepared NE of peppermint and tea tree volatile oils with small particle sizes and good stability using HSS technology. However, most of the energy of HSS high shear is consumed in the form of frictional heat generation, so HSS has little advantage in terms of PDI and particle size [ 136 ].…”

“… Volatile oil nanopreparation Advantages Disadvantages Examples (partial) Microemulsion (ME) Thermodynamically stable system, infinitely dilutable, small particle size, high practical application value Liquid formulations with low viscosity cannot be dosed. Cinnamon [ 17 ] Clove [ 18 ] Garlic [ 19 ] Nanoemulsion (NE) Dynamically stable system with multiple routes of administration Unclear release mechanism, high cost, and cytotoxicity issues with excipients Jojoba [ 25 ], Red raspberry seed [ 26 ], Peppermint [ 27 ], Tea tree [ 28 ], Clove [ 29 , 30 ], Oregano [ 31 ], Chilli pepper [ 32 ], Citrus [ 33 ], Linseed [ 34 ], Bitter fennel [ 24 ], Thyme [ 35 , 36 ], Carlina acaulis L. [ 37 ], Fritillary [ 38 ], Lemongrass [ 39 , 40 ], Cumin [ 41 ], lemon [ 42 ], Peppermint [ 43 ], Black pepper [ 44 ], Lemon [ 48 ], Fennel [ 49 , 50 ], Cinnamon [ [51] , [52] , [53] ], Lavender [ 54 , 55 ], Laurel [ 56 ], Peppermint [ 49 ], Thyme [ …”

“…Jojoba [ 25 ], Red raspberry seed [ 26 ], Peppermint [ 27 ], Tea tree [ 28 ], Clove [ 29 , 30 ], Oregano [ 31 ], Chilli pepper [ 32 ], Citrus [ 33 ], Linseed [ 34 ], Bitter fennel [ 24 ], Thyme [ 35 , 36 ], Carlina acaulis L. [ 37 ], Fritillary [ 38 ], Lemongrass [ 39 , 40 ], Cumin [ 41 ], lemon [ 42 ], Peppermint [ 43 ], Black pepper [ 44 ], Lemon [ 48 ], Fennel [ 49 , 50 ], Cinnamon [ [51] , [52] , [53] ], Lavender [ 54 , 55 ], Laurel [ 56 ], Peppermint [ 49 ], Thyme [ 57 ], Astragalus [ 58 ], Celandine [ 59 ], Cumin [ 60 ], Nettle [ 46 ]…”