Effects of glyceryl glucoside on AQP3 expression, barrier function and hydration of human skin.

BACKGROUND/AIM: Aquaporins (AQPs) present in the epidermis are essential hydration-regulating elements controlling cellular water and glycerol transport. In this study, the potential of glyceryl glucoside [GG; alpha-D-glucopyranosyl-alpha-(1->2)-glycerol], an enhanced glycerol derivative, to increase the expression of AQP3 in vitro and ex vivo was evaluated. METHODS: In vitro studies with real-time RT-PCR and FACS measurements were performed to test the induction by GG (3% w/v) of AQP3 mRNA and protein in cultured human keratinocytes. GG-containing formulations were applied topically to volunteer subjects and suction blister biopsies were analyzed to assess whether GG (5%) could penetrate the epidermis of intact skin, and subsequently upregulate AQP3 mRNA expression and improve barrier function. RESULTS: AQP3 mRNA and protein levels were significantly increased in cultured human keratinocytes. In the studies on volunteer subjects, GG significantly increased AQP3 mRNA levels in the skin and reduced transepidermal water loss compared with vehicle-controlled areas. CONCLUSION: GG promotes AQP3 mRNA and protein upregulation and improves skin barrier function, and may thus offer an effective treatment option for dehydrated skin.

Epidermal-skin-test 1,000 (EST-1,000)--a new reconstructed epidermis for in vitro skin corrosivity testing.

The determination of a possible corrosive or irritative potential of certain products and ingredients is necessary for their classification and labeling requirements. Reconstructed skin as a model system provides fundamental advantages to single cell culture testing and leads to promising results as shown by different validation studies (for review: Fentem, J.H., Botham, P.A., 2002. ECVAM's activities in validating alternative tests for skin corrosion and irritation. ATLA 30(Suppl. 2), 61-67). In this study we introduce our new reconstructed epidermis "Epidermal-Skin-Test" (EST-1,000). This fully grown epidermis consists of proliferating as well as differentiating keratinocytes. EST-1,000 shows a high comparability to normal human skin as shown by histological and immunohistochemical data. Characteristic markers (KI-67, CK 1/10/5/14, transglutaminase, collagen IV, involucrin, beta 1 integrin) can be identified easily. The main focus of this work was to characterize EST-1,000 especially with respect to its barrier function by testing several substances of known corrosive potential. Skin corrosion was detected by the cytotoxic effect of the substances on a reconstructed epidermis after short-term application to the stratum corneum. The effect was determined by standard MTT assay and accompanying histological analysis. Hence EST-1,000 shows a very high predictive potential and closes the gap between animal testing and the established full-thickness model Advanced-Skin-Test 2,000 (AST-2,000) (Noll, M., Merkle, M.-L., Kandsberger, M., Matthes, T., Fuchs, H., Graeve, T., 1999. Reconstructed human skin (AST-2,000) as a tool for pharmaco-toxicology. ATLA 27, 302).

Regulation of cholesterol synthesis by oleic and palmitic acid in keratinocytes.

Cholesterol synthesis is essential for homeostasis of the epidermis, being required for both cell division and differentiation, as well as maintenance of the epidermal permeability barrier. Cholesterol synthesis in keratinocytes has been demonstrated to be regulated by sterol levels and the barrier function of the stratum corneum. Cholesterol synthesis in the epidermis is correlated with changes in mRNA levels for key enzymes, such as HMG-CoA synthase and HMG-CoA reductase, which have been previously demonstrated to be coordinately regulated by the sterol regulatory element binding proteins (SREBPs). In this study we demonstrate that a functional sterol regulatory element is required for sterol regulation of HMG-CoA synthase in keratinocytes. We also investigate the regulation of cholesterol synthesis by fatty acids, which are another important constituent of the stratum corneum lipids. Palmitic and oleic acid inhibit 14C-labelled acetate incorporation into sterols in a similar manner to sterols. However, unlike sterols, 50 microM oleic acid increase the steady state mRNA levels of HMG-CoA synthase and the activity of the HMG-CoA synthase promoter. The addition of 50 microM oleic acid to 25-hydroxycholesterol results in an enhancement of the inhibitory effect of the sterol on promoter activity. The inhibition of acetate incorporation into sterols in human keratinocytes by 50 microM palmitic and 50 microM oleic acid is not due to regulation of HMG-CoA synthase at the level of transcription.

Regulation of HMG-CoA synthase and HMG-CoA reductase by insulin and epidermal growth factor in HaCaT keratinocytes.

Synthesis of cholesterol, via the isoprenoid/mevalonate pathway, is required for keratinocyte growth and differentiation, and maintenance of the stratum corneum lipid lamellae. 3-hydroxy-3-methylglutaryl coenzyme A synthase catalyzes the first step in isoprenoid/mevalonate synthesis and under some conditions controls the flux into the pathway. We have investigated whether selected growth factors and hormones could increase 3-hydroxy-3-methylglutaryl coenzyme A synthase mRNA in keratinocytes. Northern blotting was used to demonstrate that 10 microg per ml insulin and 0.1 microg per ml epidermal growth factor both increased steady-state levels of 3-hydroxy-3-methylglutaryl coenzyme A synthase mRNA by 2.5 and 6-fold, respectively. Epidermal growth factor and insulin also increased 3-hydroxy-3-methylglutaryl coenzyme A reductase enzyme activity. 3-hydroxy-3-methylglutaryl coenzyme A synthase promoter activity in a luciferase reporter construct was increased 2-fold by insulin and 2.9-fold by epidermal growth factor. When a mutation in the sterol regulatory element was introduced into the 3-hydroxy-3-methylglutaryl coenzyme A synthase promoter, activity was not increased by insulin, but was increased by epidermal growth factor. Mutation of an AP-1 site in the 3-hydroxy-3-methylglutaryl coenzyme A synthase promoter did not affect the increase in activity following treatment with insulin or epidermal growth factor. Therefore, 3-hydroxy-3-methylglutaryl coenzyme A synthase expression in keratinocytes is regulated by insulin and epidermal growth factor by different mechanisms. These results suggest a role for hormones and growth factors in the control of epidermal cholesterol synthesis.

Semiquantitative chemiluminescent detection of UV-B-induced point mutations in the p53 tumor-suppressor gene.

The technique of allele-specific PCR (AS-PCR) enables the detection of a small number of mutant alleles in a large number of wild-type (WT) alleles. We used the AS-PCR technique and Southern blotting, using a nonradioactive labeled probe to analyze the formation of point mutations in the tumor-suppressor gene p53 of primary keratinocytes after UV-B irradiation. These permanent mutations resulting from CC dimers occur at distinct "hot-spots", one of which is affected in the human keratinocyte cell line HaCaT. This enabled us to establish the method with a defined positive control template, which also allowed semiquantitative determination of the mutation frequency. This, and the determination of the detection limit, was done with the use of serial dilutions of WT genomic DNA from primary keratinocytes with mutant genomic HaCaT DNA in the AS-PCR assay.