Development of topical gel containing Capsicum oleoresin encapsulated Tamanu nanocarrier and its analgesic and anti-inflammatory activities

Capsicum oleoresin (CO), which consists capsaicin as the most effective component, has been used as a topical treatment of neuropathic pain. However, topical formulations with adequate concentrations of capsaicin, which are required to achieve effective pain relief, cause several local adverse skin reactions such as burning sensation, itching, skin redness, and pain. Tamanu oil (TO), a fatty oil containing both liquid lipids and solid lipids derived from Calophyllum inophyllum seeds, has emerged as a potential ingredient for the preparation of a nanostructured lipid carrier (NLC)-based gel formulation in order to reduce the local adverse skin reactions as well as enhance the analgesic effect of capsaicin topical. In this study, Tamanu oil-based NLC encapsulating Capsicum oleoresin (CO@TO) Gel was prepared using emulsification followed by homogenization methods. The results suggested the best formulation of the CO@TO was prepared from 20% Tamanu oil, 12% tween 80, 1% lecithin and 1.5% Capsicum oleoresin with homogenization at 20,000 rpm for 10 min. The CO@TO particles was sphere and unique with diameter of ~147 nm and zeta potential of − 76 mV. The capsaicin EE and LC of the CO@TO was ~99% and 0.15%, respectively. The CO@TO performed sustainable capsaicin release during 48 h, which fitted with Korsmeyer-Peppas kinetic model. The skin irritation test on rabbits demonstrated that the CO@TO Gel bearing 0.1% capsaicin caused no skin irritation. Meanwhile in vivo studies on mice illustrated that the CO@TO Gel performed similar analgesic and anti-inflammation effects as the commercial drugs Paracetamol/Codeine and diclofenac, respectively. The CO@TO Gel in this study would be a potential Tamanu oil-based nanostructured lipid carrier formulations for capsaicin topical products. [Display omitted] •Topical gel containing 0.1% capsaicin was successfully prepared from Tamanu oil and Capsicum oleoresin (CO@TO Gel).•The optimal formulation and technical parameters for CO@TO Gel preparation were determined.•The CO@TO particles was sphere with ~145 nm diameter and sustainable capsaicin release profile.•The CO@TO Gel performed no skin irritation but similar analgesic and anti-inflammatory effects as commercial drugs.