Development, characterization and in vitro toxicity evaluation of nanoemulsion-loaded hydrogel based on copaiba oil and coenzyme Q10

Coenzyme Q10 (CQ10) is a lipophilic substance synthesized endogenously by the body that has antioxidant, photoprotective and wound-healing properties. However, when applied exogenously in topical preparations, there are obstacles to its permeation through the stratum corneum due to its high molar mass, low water solubility and susceptibility to photodegradation. In this case, permeation is desired for the substance to attain high levels of bioavailability in the lower levels of the epidermis, protecting keratinocytes against oxidative damages, and in the dermis to stimulate the proliferation of fibroblasts and collagen. In this work, we used copaiba oil, a vegetable oil with properties similar to those of CQ10, to compose oil-in-water (O/W) nanoemulsions with CQ10 (NECQ10) and without it (NECO), for comparative purposes, prepared by ultrasound processing. After adding the thickener ammonium acryloyldimethyltaurate/VP copolymer to the NECQ10 and NECO, the formulations NECQ10g and NECOg, respectively, were evaluated regarding the particle size distribution, which was monomodal with mean droplet size of about 60 nm and had mean polydispersity index (PDI) of 0.2. Furthermore, another formulation was obtained without using the ultrasound processor (ECQ10g), giving rise to an O/W emulsion (ECQ10 g) corresponding to NECQ10g, with dispersed droplet sizes of about 1.7 mu m, also for comparative purposes. The formulations were stable for 90 days, had pH compatible with the stratum corneum and were safe according to in vitro toxicity tests on fibroblasts and keratinocytes. The NE of interest incorporated in hydrogel (NECQ10 g) only weakened the gel's strength, while not affecting the rheological characteristics of a gel, thus having viscosity suitable for topical use. Furthermore, the NECQ10 g was able to improve the cell viability profile in fibroblasts when compared with the formulations NECOg and ECQ10 g, in the order NECQ10g > NECOg > ECQ10 g, due to the presence of CQ10 encapsulated in the nanoemulsion system.