Exposure of human skin to ultraviolet (UV) radiation may cause skin damage such as erythema and pigmentation, and acceleration of skin aging.1) Hyperpigmentation including melasma, freckles and senile lentiginoses is caused by the over-production of melanin, a pigment in the human skin acting as a major defense mechanism against UV light.2) However, hyperpigmentation on faces is a high anxiety-producing symptom for people from the aspect of beauty appearance. Nowadays, skin whitening agents, particularly natural antioxidants such as flavonoids, are receiving increasing attention because such flavonoids possess potential antioxidant activity and are claimed to be free of toxicity and side effects.3) Recently, much research has been focused on the potential use of flavonoids for preventive oxidative skin damage. [4][5][6] For skin bleaching, the topical delivery system is the considered administration route. Nevertheless, the most difficult aspect of a transdermal delivery system is to overcome the barrier of stratum corneum against foreign substances. Use of penetration enhancers is valuable and important for improving drug permeation, 7-9) but attention must be paid to the extensive damage to the skin caused by such enhancers, although the large increase in permeation rate is a positive. Therefore, optimal formulation design is important for topical application of pharmaceutical products.Flavanone compounds such as hesperetin (and its glycoside hesperidin) are a kind of flavonoid and have been reported to possess a wide range of pharmacological properties such as being anti-inflammatory and possessing enzymes (including hyaluronidase and xanthine oxidase) inhibitors, antimicrobial activity, UV protecting activity, along with analgesic and antioxidant effects.10) Moreover, hesperidin is extremely safe and without side effects even during pregnancy.10) The molecular weight of hesperetin is about 302, which makes it a good candidate for topical application. Therefore, the aim of this study was to design an optimal hesperetin cream which is the most common dosage forms for topical application. The in vitro permeation study was used to evaluate the effect of the composite on permeability of the drug through rat skin. In vivo studies such as skin whitening and irritation tests were used to assess the clinical usability of hesperetin cream.
ExperimentalMaterials The following reagents were used: hesperetin, naringenin, menthol, linoleic acid, azone, methyl paraben, stearic acid and PEG-30 dipolyhydroxystearate (Tokyo Chemical Industry, Japan), cetyl alcohol (Acros, Belgium), lecithin (Wako, Japan), propylene glycol (PG), polyethylene glycols 400 (PEG 400) (Merck Chemicals, U.S.A.). Plush blush ® cream containing 1% ascorbyl magnesium phosphate (UNT, Taiwan). All other chemicals and solvents were of analytical reagent grade.Solubility Measurement An excess of hesperetin was placed in sealed glass tubes containing 2 ml of solvent. The tubes were shaken occasionally on a vortex mixer and were maintained at room temperatur...