Topical retinoids and cutaneous biology

The Role of the Status of Selected Micronutrients in Shaping the Immune Function

OBJECTIVE

This narrative review gives an overview on the essential role of adequate nutrition to an optimally functioning immune defence. Micronutrients act as regulators of the immune response, with the focus of this review on the immunomodulatory effects of the trace elements iron, zinc and selenium, and the vitamins A, D, E, C, B6 and B12 and folic acid.

RESULTS

Iron deficiency especially impairs the Th1 cell-borne cellular immunity. T lymphocytes are also most affected by a deficiency of zinc, needed for their maturation and the balance between the different T cell subpopulations and acting as a redox signal in the regulation of many enzymes. Selenium is also involved in redox reactions as the glutathione peroxidases and other redox enzymes are selenoproteins. Selenium status has shown special effects on cellular immunity and resistance to viral infections. Vitamin A in the form of retinoic acid induces a humoral Th2 cell response via antigen-presenting cells and is involved in maintaining intestinal immune defence and tolerance through its nuclear receptor RAR and via kinase signalling cascades. Immune tolerance is particularly promoted by vitamin D acting through dendritic cells to stimulate the differentiation of regulatory T cells. Vitamin E has antiinflammatory effects and stimulates naïve T cells especially in the elderly. Besides its antioxidative properties, vitamin C has effects on cell signalling and epigenetic regulation. The B vitamins are required for cytotoxic cellular immunity and modulate T cell responses.

CONCLUSION

A diverse diet and regular exposure to sunlight are the best sources for a balanced nutrient supply to maintain an optimal immune defence.

In vivo long-term effects of retinoic acid exposure in utero on induced tumours in adult mouse skin

BACKGROUND

Retinoic acid (RA) and its analogues (retinoids) are promising agents in skin cancer prevention following either topical application or oral administration. However, long-term in vivo effects of RA on chemically induced hyperplastic epidermal foci in adult mouse skin have also been described, casting some doubt with regard to its chemopreventive activity.

HYPOTHESIS/OBJECTIVES

To characterize chemically induced skin tumours and to investigate the in vivo long-term action and preventive effect of RA on adult mouse skin carcinogenesis.

ANIMALS

Fifty-six adult Naval Medical Research Institute mice, exposed (n = 28) or not exposed (n = 28) to RA in utero.

METHODS

Mice were treated with a standard two-stage skin carcinogenesis protocol, which included an initiating application of 7,12-dimethylbenz(a)anthracene followed by promotion with 12-O-tetradecanoylphorbol 13-acetate.

RESULTS

Retinoic acid administered to pregnant mice showed a long-term inhibitory action on cell differentiation and development of chemically induced tumours on the adult skin of their offspring, as well as a stimulatory effect on cell proliferation and expression of an early marker of malignant progression (keratin 13).

CONCLUSIONS AND CLINICAL IMPORTANCE

The results suggest that RA exposure in utero confers long-lasting effects on adult mouse skin carcinogenesis. These include chemopreventive activity (reduced number of tumours), as well as enhancement of squamous papilloma progression, which appears to be due to enhanced keratinocyte proliferation and suppression of epidermal maturation. The clinical significance of these findings is not known for other routes of RA administration at this time.

In vivo long-term effects of retinoic acid exposure in utero on induced hyperplastic epidermal foci in murine skin

Adult Naval Medical Research Institute (NMRI) mice, after prenatal exposure to retinoic acid (RA), were treated with a standard two-stage skin carcinogenesis regime to characterize hyperplastic epidermal foci that precede the appearance of cutaneous papillomas, and to investigate the in vivo long-term action of RA on adult mouse skin treated with DMBA (7,12 dimethyl benz[a]anthracene) and TPA (12-O-tetradecanoylphorbol 13-acetate). The results demonstrate that RA administered to pregnant mice had a long-term inhibitory action on the cell differentiation and development of hyperplastic lesions occurring prior to cancer on the adult skin of their offspring as well as a stimulatory effect on cell proliferation of these hyperplastic lesions.

Effects of in utero retinoic acid exposure on mouse pelage hair follicle development

We investigated in vivo the histological and immunohistochemical responses of mouse hair pelage follicle morphogenesis to prenatal exposure to a potentially nonteratogenic dose of all-trans-retinoic acid (RA), as a basis studying the preventive effect of RA on adult mouse skin carcinogenesis. In pregnant mice, a single oral dose of RA at 30 mg kg-1 body weight given on day 11.5 of gestation caused no RA-induced changes in the morphology or temporal expression patterns of keratins during pelage hair follicle morphogenesis. The only differential effect of RA was a statistically significant increase in the number of BrdU-positive nuclei in hair bulbs from RA exposed fetuses compared with nonexposed mice. The absence of adverse RA effects suggests that this experimental design may represent a valuable protocol for use in studies on the in vivo effects of this retinoid on different skin diseases.

Effects of retinoic acid exposure in utero on mouse vibrissal follicle development

It is known that topical all-trans-retinoic acid (RA) modulates growth and differentiation of skin and its cutaneous appendages. To examine whether a pre-natal exposure to a potentially non-teratogenic dosage of all-trans-RA had any effect on vibrissal follicle development, the histologic and immunohistochemical responses to RA during its morphogenesis in NMRI mouse were investigated. After a single oral dose of 30 mg/kg body weight of all-trans-RA on day 11.5 of gestation, no fetal malformations were detected and the histological features and the distribution of keratin (K) proteins in comparable stages of vibrissal development were similar for the untreated, vehicle-treated and RA-treated mice. The absence of teratogenic response and of adverse effects on the vibrissae under the experimental conditions indicates that this protocol may be useful for investigation of the effects of pre-natal exposure to RA on the post-natal development of experimental tumours in the mouse skin.

Differential effect of etretinate on proliferation and extracellular matrix metabolism of human dermal fibroblasts from elderly and young individuals in a novel three-dimensional culture

The effect of etretinate on proliferation and biosynthesis of collagens and glycosaminoglycans (GAGs) were investigated using human dermal fibroblasts in a novel three-dimensional culture supplemented with L-ascorbic acid 2-phosphate. Fibroblasts from two young and two elderly individuals were studied at different concentrations of etretinate, 0.25, 1.0 and 2.5 microg/ml. Collagens (hydroxyproline) and GAGs (disaccharide units) extracted from the cell layer were analyzed and quantified biochemically by high-performance liquid chromatography (HPLC). Etretinate showed no significant effect on fibroblast proliferation either in the monolayer or the three-dimensional culture. Etretinate increased the collagen or GAGs content in the cell layer, which was prominent at etretinate concentrations of 1.0 and 2.5 or 0.25 microg/ml, respectively in fibroblasts from the elderly (P < 0.05). This effect was not seen in dermal fibroblast from the young. These results suggest that etretinate may have the differential effect on collagen and GAG metabolisms depending on the donor age of the cultured fibroblasts.