Conclusion
Addition of glutathione in EGCG formulations significantly reduces its photodegradation. Skin microporation with maltose microneedles facilitates the penetration of EGCG across the stratum corneum into the deeper skin layers - viable epidermis and dermis.
Methods
Effect of l-glutathione on photodegradation of EGCG was investigated by exposing samples to ultraviolet irradiation for 1 h using a solar simulator. Hydrogels with varying concentrations of Carbopol 980 (0.5-2% w/v) as an gelling agent were prepared, and their rheological properties were evaluated using a rheometer. Skin microporation was confirmed by assessing the skin resistance, transepidermal water loss and calcein imaging of the microchannels created by the microneedles. Permeation of EGCG from aqueous solution as well as the rheologically optimized hydrogel through the dermatomed porcine skin (untreated and microneedle treated) was evaluated using static vertical Franz diffusion cells.
Objective
Epigallocatechin-3-gallate (EGCG) is the physiologically most active and abundant flavanol, accounting for 50-80% of green tea catechins. It is an anti-inflammatory, antioxidant, chemopreventive and skin photoprotective agent. However, light sensitivity and low permeability of EGCG across the stratum corneum due to its high molecular weight as well as strong binding to the lipid bilayers in the skin make it difficult to be used as a key ingredient in cosmetic products. This study aimed to formulate a photostable hydrogel of EGCG with good rheological properties for dermal application and investigate the effect of skin microporation using maltose microneedles on its permeation through dermatomed porcine skin.
Results
l-glutathione acting as a co-antioxidant and photostabilizer significantly (P < 0.05) reduced the degradation of EGCG from 21.53 ± 2.78% to 1.0 ± 0.68% after 1 h of ultraviolet irradiation. Rotational and oscillatory rheological tests indicated that the hydrogel containing 1.5% Carbopol 980 is acceptable for topical application in terms of flow behaviour, elasticity, spreadability, structural stability and thixotropy. Microneedle-treated skin showed significant enhancement (P < 0.05) in the delivery of EGCG to viable epidermis and dermis from the aqueous solution (38.67 ± 2.96 μg cm(-2) ) as well as hydrogel (24.60 ± 2.62 μg cm(-2) ) in comparison with the untreated skin (24.16 ± 2.11 and 15.62 ± 0.24 μg cm(-2) for aqueous solution and hydrogel, respectively).