Mechanistic study of the anti-melanogenic property of tetrahyrocurcumin and evaluation of its bioaccessibilty through topical route and oral route
Creators: name: Tang, Xudong
Publisher: name: No Publisher Supplied
Year: 2021

description: Tetrahydrocurcumin (THC) is one of the major metabolites of curcumin, and it possess a variety of health-related benefits, such as anti-cancer, antioxidant, anti-inflammation, etc., Skin hyperpigmentation could be induced and severed by the aggressive accumulation of reactive oxygen species (ROS) generated by the external stresses such as constant exposure to UV, air pollution etc., Based on the anti-oxidant properties of THC, it might help to protect skin from any deleterious effects associated with ROS. However, because of its hydrophobic chemical structure and low aqueous solubility, its application has been quite limited. In order to solve this, two innovative formulation strategies were used including nanoemulsion and polymer conjugate. The objective is to solve the aqueous solubility challenge for THC and enhance its bioaccessibility through both the topical and oral route respectively.In the first part of this work, efficacy of THC as an anti-melanogenic agent was explored. In vitro tyrosinase activity method was utilized in order to study the efficacy of THC on the inhibition of tyrosinase, the key enzyme involved in the melanogenesis process. Later in vitro B16F10 melanoma cell model was studied, the data confirmed that THC is capable of reducing the α-MSH (melanocyte-stimulating hormone) induced production of melanin. Additionally, the protective role of THC on the keratinocytes was also investigated using the in vitro H2O2 induced oxidative stress model. Through this study, the data showed that THC could significantly reduce the ROS level after the oxidative stress. In addition, THC was able to reduce the production of α-MSH in the H2O2 induced oxidative stress keratinocytes model. As this hormone is the messenger between keratinocytes and melanocytes controlling the melanogenic process. Therefore, THC’s anti-melanogenic property and its mechanism was confirmed. Secondly, phospholipid based nanoemulsion was designed to enhance topical delivery efficacy of THC. The solubility of THC in three different carrier oils were determined. Medium Chain Triglyceride (MCT) showed the maximum solubility for THC, which is around 9.4 mg/mL compared to 1.2 mg/mL in sunflower oil and 0.6 mg/mL in argan oil. Later, a penetration enhancer, Diethylene Glycol Monomethyl Ether (DEGEE, commercial name: Transcutol®), was introduced and combined with MCT in order to find the optimized solubility for THC as well as reasonable solvent-solute effect. Last, the final formula was composed of MCT, Diethylene Glycol Monomethyl Ether, water and phospholipids. The stability of the formula was monitored at 50°C and room temperature. The permeation performance of this nanoemulsion vs. THC suspension was conducted using in vitro Franz diffusion cell model. This study confirmed that delivery efficacy for THC in the optimized phospholipid based nanoemulsion vesicle could be significantly increased compared to the free THC suspension. Thirdly, tetrahydrocurcumin-hyaluronic acid (THC-HA) conjugate was synthesized for the purpose of increasing the bioaccessibility of THC through oral route. Characterizations including 1H-Nuclear Magnetic Resonance (1H-NMR), differential scanning calorimetry (DSC) and x-ray diffraction (XRD) were used to confirm the formation of the conjugate. In vitro dissolution drug release in both simulated gastric fluids (SGF) and simulated intestinal fluids (SIF) was studied to evaluate the stability and integrity of the conjugate in the gastrointestinal tract. The result concluded that the conjugate remained stable with less than 10% w/w THC released from the conjugated form in both of the conditions up to 4 h. Later, the bioaccessibility was evaluated using ex vivo Franz cell model using small intestine from porcine and in vitro TNO dynamic gastrointestinal model-1 (TIM-1). Both models confirmed that THC-HA conjugate was able to enhance the overall bioaccessibility for THC. This could be explained by both the solubility enhancement and mucoadhesive property from hyaluronic acid that contribute directly to the bioaccessibility enhancement.