Abstract:
Background and Aims: The human skin is constantly exposed to an array of external threats such as pollutants, toxins and UV-irradiation. These external factors are considered as the sources of reactive oxygen species (ROS) and exert oxidative stress to the skin. Many skin disorders and diseases are related to the oxidative stress, thus the application of antioxidant, serving as strong defence agent against oxidation, in dermatological health-care is of great interest. Catechin is a family of natural phenol compounds showing potential antioxidant properties. However, topical application of this antioxidant encounters several challenges. Firstly, the skin barrier which mostly lays in the stratum corneum (SC) prevents the transporting of external substance into the skin and thus limits the reservoir of the antioxidant in the deep layers. Moreover, the catechin group are chemically instable and easily undergoes degradation. Taking together, it would offer advantages if the antioxidant is incorporated into a lipid drug carrier to facilitate its transport across the skin and protect it from degradation. The carriers that are made up of non-ionic surfactants, having the similar bilayer structure to liposomes are niosomes. Theses carriers are widely used topically. Objective: The aim of this project was to design a niosome carrier system to deliver the antioxidant into the skin so that it exhibits the antioxidant effect. The drug candidates are two compounds from the catechin family, namely, (+)-catechin (C) and (-)-epigallocatechin gallate (EGCG). Methods: An HPLC method was developed and validated for the determination of the compounds; preformulation studies were performed to study the physicochemical properties of the two compounds, such as partition coefficient, aqueous solubility and forced stability. C-loaded niosomes and EGCG-loaded niosomes were prepared using film hydration technique. An experimental design strategy was applied for optimisation of the formulation parameters. The chemical and physical properties of drug-loaded niosomes such as morphology, particles size, entrapment efficiency, zeta potential and in vitro release profiles were characterised. The drug compatibility with the carrier was studied by differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR). The penetration of drug across the skin barrier and the drug deposition in the skin were determined using a Franz diffusion cell. The antioxidant effects of two drugs and the drug-loaded niosomes on the human skin fibroblasts (Fbs) were evaluated: the lipid peroxidation product malondialdehyde (MDA) and two antioxidant enzymes including superoxide dismutase (SOD) and glutathione peroxidase (GSH-px), which reflect the antioxidant capacity of Fbs in oxidative stress were evaluated. The interactions of niosomes with the skin fibroblasts were also explored using a fluorescence-labelled niosomes on the Fbs. Results and discussion: The preformulation studies showed that C and EGCG are slightly soluble in water and PBS. Compared to EGCG (Log P 1.23), C is more hydrophilic with a Log P value of 0.41. Both compounds were vulnerable to external stresses conditions such as base (0.5 mM NaOH), oxidation(0.01% v/v H2O2)and high temperature (70 °C). The optimum formulation was obtained at the following condition: the selected optimum condition for preparing drug-loaded niosomes were as the following: for C-niosome, Span 60 and cholesterol (CH) (total 150 μmol) at the molar ratio of 4:1 were used as vesicle components; dicetyl phosphate (DCP) (2 μmol) was added as a charge inducer; 10 mL of hydration medium containing 2 mg of C was used to hydrate the lipid film for two hours, allowing formation of C-niosomes. Regarding EGCG-niosome, Span 60 and CH (total 150 μmol) at the molar ratio of 10:9 were used as vesicle components; a DCP amount of 2 μmol was added as charge inducer; 10 mL of hydration medium containing 1.4 mg of EGCG was applied to hydrate the lipid film for two hours. Under such process conditions, the drug-loaded niosomes could be produced with an acceptable size in nano-scale (204 nm and 235 nm respectively) and high drug entrapment efficiency (49% and 53% respectively). The studies with FT-IR and DSC revealed that drug was entrapped in the niosomes in an amorphous state. In vitro release results indicated that C-niosome and EGCG-niosome could effectively sustain drug release for a prolonged time period. Besides, niosomes were demonstrated to have protective effect on the entrapped drug and niosome were relative stable under at 2-8 °C for at least one month. To apply the antioxidants on the skin models, the application with a niosomal formulation resulted in enhanced drug penetration across SC on both skin models. Drug deposition in epidermis and dermis was significantly enhanced with the use of a niosomal carrier (p < 0.05). The in vitro evaluation study on the human skin Fbs showed C and EGCG, particularly their niosomes significantly enhanced the cell viability. Compared to the pure drug, drug within niosome carrier had more favourable property on the protective effect on the Fbs. C and EGCG encapsulated in niosomes functioned as greater antioxidants than the drug solutions, most possibly in relation to the facilitated cellular uptake of the encapsulated drug by the carriers. Conclusion: This project has demonstrated that the developed niosomes were able to improve the physical and chemical stability of the antioxidants; impart a penetration-enhancing effect across skin SC, hence increase the drug deposition in the deep layer of the skin; and enhance antioxidant capacity on Fbs. The research highlighted that niosomes are potential topical carriers for dermal delivery of antioxidant such as the two compounds from the catechin family. The niosome carrier serves as an officious tool for topical drug delivery and could be potentially used in skin-health care and pharmaceutical products.