Topical Application of .GAMMA.-Tocopherol Derivative Prevents UV-Induced Skin Pigmentation

Antimelanogenic chemicals with in vivo efficacy against skin pigmentation in guinea pigs

Ultraviolet (UV) radiation under sunlight stimulates skin pigmentation through immediately affecting the oxidative modification of existing melanin pigments and the spatial redistribution of pigmented melanosomes followed by the up-regulation of melanogenic genes in delayed kinetics. However, abnormal accumulation and synthesis of melanin biopolymers are responsible for skin disorders with more pigmented patches. Chemical-based regulation of the hyperpigmented disorders has been a long-standing goal for cosmetic and pharmaceutical applications. A large number of the chemicals with antimelanogenic activity have met with limited or no success in the treatment of skin patients, since they may not overcome the challenge of penetrating the skin barrier. Guinea pig skin displays similar kinetic parameters to human skin in the transdermal absorption of numerous chemicals, thus can serve as the surrogate for human skin. Here, we provide a concise review of our current understanding of the chemical-based therapy against skin hyperpigmentation in UV-irradiated guinea pig models, suggest molecular mechanisms of the action and emphasize the translation from preclinical outcomes to skin patients.

Co-localization of inducible nitric oxide synthase and phosphorylated Akt in the lesional skins of patients with melasma

Activation of the inducible nitric oxide synthase (iNOS)/nitric oxide (NO) pathway in keratinocytes has been reported to be associated with the pathogenesis of melanogenesis. Akt activation plays an important role in the activation of the transcription factor nuclear factor (NF)-kappaB and subsequent elevation of iNOS expression. In the present study, we highly detected both iNOS protein and Akt phosphorylation in keratinocytes of the basal layer of the epidermis at the junction with the dermis of melasma skin biopsy specimens, but not in normal skin tissues, from nine patients using immunohistological analysis. iNOS protein and phosphorylated Akt were co-localized in the lesional skins, and their levels were highly correlated R2= 0.69). Furthermore, iNOS mRNA was also detected in an additional three skin biopsy specimens, but not in normal skin, by reverse transcription polymerase chain reaction. Our results describe that iNOS expression is elevated in human melasma lesions, probably via activation of the Akt/NF-kappaB pathway, indicating that NO production plays an important role in the mechanism of hyperpigmentation in human facial melasma.

Preparation and In Vivo Evaluation of a Water-Soluble Prodrug for 2R-γ-Tocotrienol and as a Two-Step Prodrug for 2,7,8-Trimethyl-2S-(β-carboxyethyl)-6-hydroxychroman (S-γ-CEHC) in Rat

2R-gamma-Tocotrienol (gamma-T3) is currently receiving attention because it has beneficial effects not observed with alpha-tocopherol. To achieve the effective delivery of gamma-T3, we synthesized three kinds of ester derivatives of gamma-T3 and evaluated their use as hydrophilic prodrugs for gamma-T3 in vitro and in vivo. 2R-gamma-Tocotrienyl N,N-dimethylamino-acetate hydrochloride (compound 3) was a solid compound, with high solubility and stability in water, and was converted to gamma-T3 by esterases in rat and human liver. Intravenous administration of 3 in rats led to a rapid increase in the plasma, liver, heart, and kidney levels of gamma-T3. The bioavailability (plasma level) after intravenous administration was 82.5 +/- 13.4% and 100 +/- 11.3% for 3 and gamma-T3 in surfactant, respectively, and the availability in liver was 213 +/- 47.6% and 100 +/- 4.8% for 3 and gamma-T3 in surfactant, respectively. Furthermore, the systemic availability of 2,7,8-trimethyl-2S-(beta-carboxyethyl)-6-hydroxychroman (S-gamma-CEHC), a metabolite of gamma-T3, was 78.6% for compound 3, 47.1% for gamma-T3 in surfactant, and 100% for racemic gamma-CEHC. Based on these results, we identified compound 3 as the most promising water-soluble prodrug of gamma-T3 and two-step prodrug of S-gamma-CEHC.

UVB-induced Skin Damage and the Protection/Treatment —Effects of a Novel, Hydrophilic γ-Tocopherol Derivative

Ultraviolet radiation is the major environmental cause of skin damage. Although only 0.5% of ultraviolet B (UVB) radiation reaches the earth, it is the main cause of sunburn and inflammation and the most carcinogenic constituent of sunlight. We investigated whether the topical application of a novel, water-soluble gamma-tocopherol (gamma-Toc) derivative, gamma-tocopherol-N,N-dimethylglycinate hydrochloride (gamma-TDMG), could protect against UV-induced skin damage. Topical pre- or postapplication of gamma-TDMG solution significantly prevented sunburn cell formation, lipid peroxidation, and edema/inflammation that were induced by exposure to a single dose of UV irradiation. Cyclooxygenase-2 (COX-2)-catalyzed synthesis of prostaglandin E(2) (PGE(2)) levels seen after UV exposure were significantly suppressed by pre- or posttreatment with gamma-TDMG. The increase in COX-2 activity was significantly inhibited by gamma-TDMG, suggesting that the reduction in PGE(2) concentration was due to the direct inhibition of COX-2 activity by gamma-TDMG. The derivative strongly inhibited inducible nitric oxide synthase mRNA expression and nitric oxide production. With the application of gamma-TDMG, the pigmentation in melanocytes was lightened and the increase melanin concentration was suppressed. Gamma-TDMG is converted to gamma-Toc in the skin and has higher bioavailability than gamma-Toc itself. These results suggest that gamma-TDMG-derived gamma-Toc acts as an antioxidant, antiinflammatory and antipigmentation agent. Our data further suggest that the topical application of gamma-TDMG may be efficacious in preventing and reducing UV-induced skin damage in humans.