Abstract
Although spearmint oil (SMO) has various pharmacological properties, especially for cancer treatment, its low water solubility results in poor bioavailability. This limits its application as a medicine. One possible solution is to the use of SMO in the form of nanoemulsion, which has already been shown to have anticancer effects. However, the mechanism of SMO nanoemulsion formation remains unclear. The objective of this study was to use molecular dynamics (MD) for clarifying the formation of SMO nanoemulsion with triglycerides (trilaurin, tripalmitin, and triolein) and Cremophor RH40 (PCO40). Nanoemulsions with different SMO:triglyceride ratios and triglyceride types were prepared and analyzed for anticancer activity, droplet size, droplet morphology, and stability. Despite switching the type of carrier oil, SMO nanoemulsions retained strong anticancer effects. A ratio of 80SMO:20triglycerides produced the smallest droplets (<100 nm) and exhibited excellent physical stability after a temperature cycling test. MD simulations showed that polyoxyethylenes of PCO40 are located at the water interface, stabilizing the emulsion structure in an egglike layer. Droplet size correlated with triglyceride concentration, which was consistent with the experimental findings. Decreasing triglyceride content, except for the 90SMO:10triglyceride ratio, led to a decrease in droplet sizes. Hydrogen bond analysis identified interactions between triglyceride-PCO40 and carvone-PCO40. Geometry analysis showed PCO40 had an "L-like" shape, which maximizes the hydrophilic interfaces. These findings highlight the value of MD simulations in understanding the formation mechanism of SMO and triglyceride nanoemulsions. In addition, it might also be beneficial to use MD simulations before the experiment to select the potential composition for nanoemulsions, especially essential oil nanoemulsions.