Conversion of vitamin D3 to hormonally active 1alpha,25-dihydroxyvitamin D3 in cultured keratinocytes: relevance to cell growth and differentiation.

The regulatory potential of intracellularly generated calcitriol on growth and differentiation of cultured keratinocytes is determined by the degree of cell confluence and availability of the highly lipophilic substrate vitamin D3 to these cells. The enzymatic conversion of vitamin D3 to calcitriol is considerably elevated in the presence of the nontoxic surfactant copolymer pluronic F127 (120 microg/ml medium) compared to the control without this agent. We found a positive correlation between the formation rate of calcitriol and inhibition of the 3H-thymidine incorporation rate into the DNA of keratinocytes.

Vitamin D metabolism.

Irradiation of human skin with ultraviolet B (280-320 nm) initiates the photochemical conversion of 7-dehydrocholesterol via previtamin D3 to vitamin D3. Vitamin D3 needs for its activation two hydroxylation steps in the liver and kidney. The final product, hormonally active 1alpha,25-dihydroxyvitamin D3 (calcitriol), arrives via the circulation to its target tissues and acts in a genomic or nongenomic manner.

Fundamental questions to sun protection: A continuous education symposium on vitamin D, immune system and sun protection at the University of Zürich.

Since exposure to sunlight is a main factor in the development of non-melanoma skin cancer and there are associations between malignant melanoma and short-term intense ultraviolet (UV) exposure, particularly burning in childhood, strict protection from UV-radiation is recommended. However, up to 90% of all requisite vitamin D has to be formed within the skin through the action of the sun-a serious problem, for a connection between vitamin D deficiency, demonstrated in epidemiological studies, and various types of cancer and other diseases has been confirmed. A UVB-triggered skin autonomous vitamin D(3) synthesis pathway has recently been described, producing the active Vitamin D metabolite calcitriol.

Lipidome of narrow-band ultraviolet B irradiated keratinocytes shows apoptotic hallmarks.

Background: UV light triggers a variety of biological responses in irradiated keratinocytes that might be associated with global perturbation of their lipidome. However, lipids that are specifically affected and the exact molecular mechanisms involved remain poorly understood.

Objectives: To characterize time-dependent changes of the lipidome of cultured keratinocytes induced by narrow-band ultraviolet B (NB-UVB) irradiation.

Selection and validation of candidate housekeeping genes for studies of human keratinocytes--review and recommendations.

Gene expression analysis using real-time PCR has become an integral part of biomedical research. Appropriate data normalization based on stably expressed housekeeping genes is crucial for reliable results. Thus, candidate housekeeping genes require careful evaluation with regard to the individual experimental system before being selected for studies of human keratinocytes.

Role of the vitamin D3 pathway in healthy and diseased skin--facts, contradictions and hypotheses.

Irradiation of human keratinocytes with UVB (280-320 nm) in vitro and in vivo activates the metabolism of 7-dehydrocholesterol to hormonally active calcitriol. The production of calcitriol in the skin strongly depends on the photosynthesis of vitamin D(3) which is biologically inactive in the first instance. Vitamin D(3) serves as the starting substrate for two subsequent enzymatic hydroxylation steps in epidermal keratinocytes.

Structural alterations provoked by narrow-band ultraviolet B in immortalized keratinocytes: assessment by atomic force microscopy.

We applied atomic force microscopy (AFM) to visualize ultrastructural changes of the keratinocyte morphology after narrow-band ultraviolet B (NB-UVB) irradiation. Immortalized human keratinocytes were cultured under standard conditions, irradiated with NB-UVB light at doses ranging from 50 to 800 mJ/cm2 and imaged by AFM mounted on an inverted optical microscope. It was observed, that NB-UVB irradiation provoked dose-dependent alterations of the keratinocyte morphology.

The UVB-induced synthesis of vitamin D3 and 1alpha,25-dihydroxyvitamin D3 (calcitriol) in organotypic cultures of keratinocytes: effectiveness of the narrowband Philips TL-01 lamp (311 nm).

Both calcitriol and UVB radiation exert potent antipsoriatic effects. We hypothesize that the therapeutical effect of UVB radiation may be attributed at least in part to UVB-triggered cutaneous synthesis of calcitriol. The optimum wavelength for initiation of the vitamin D(3) pathway was found to be in the range of 300+/-5 nm in vitro and in vivo.

Wavelength-dependent induction of CYP24A1-mRNA after UVB-triggered calcitriol synthesis in cultured human keratinocytes.

Earlier investigations in our laboratory have demonstrated that UVB irradiation of cultured human keratinocytes induces the conversion of 7-dehydrocholesterol (7-DHC) to hormonally active 1alpha,25-dihydroxyvitamin D3 (calcitriol). In the research presented here, we have investigated the influence of UVB-triggered calcitriol production on gene expression of the vitamin D3 hydroxylating enzymes catabolic 25-hydroxyvitamin-D3-24-hydroxylase (CYP24A1), active vitamin-D3-25-hydroxylase (CYP27A1), and 25-hydroxyvitamin-D3-1alpha-hydroxylase (CYP27B1) using real-time PCR. Our results demonstrate a marked and wavelength-dependent induction of CYP24A1-mRNA in cultured human keratinocytes supplemented with 7-DHC, which parallels the spectral optimum at about 300 nm of calcitriol production as detected by HPLC and radioimmunoassay.

The vitamin D3 pathway in human skin and its role for regulation of biological processes.

The skin is the only tissue yet known in which the complete ultraviolet-B (UV-B)-induced pathway from 7-dehydrocholesterol to hormonally active calcitriol (1alpha,25-dihydroxyvitamin D(3)) occurs under physiological conditions. Epidermal synthesis of calcitriol could be of fundamental relevance because calcitriol regulates important cellular functions in keratinocytes and immunocompetent cells. Because of their antiproliferative and prodifferentiating effects, calcitriol and other vitamin D analogs are highly efficient in the treatment of psoriasis vulgaris.

Vitamin D and skin: new aspects for dermatology.

It has been shown that epidermal keratinocytes have the capacity for the UVB-induced photochemical conversion of 7-dehydrocholesterol to vitamin D3, and also for the enzymatically controlled hydroxylation of the photolysis product. This metabolic loop results in the formation of the biologically active final product 1alpha,25-dihydroxyvitamin D3 (1alpha,25(OH)2D3, calcitriol). The epidermal synthesis of calcitriol is of fundamental relevance because calcitriol regulates important cellular functions in keratinocytes and immunocompetent cells.

Role for tumor necrosis factor-alpha in UVB-induced conversion of 7-dehydrocholesterol to 1alpha,25-dihydroxyvitamin D3 in cultured keratinocytes.

UVB irradiation of cultured human keratinocytes induces both the conversion of 7-dehydrocholesterol (7-DHC) to calcitriol (1alpha,25(OH)(2)D(3)) and the release of tumor necrosis factor-alpha (TNF-alpha) in these cells. Calcitriol synthesis in human keratinocytes was reduced in the presence if a neutralizing polyclonal antibody directed against human TNF-alpha. On the other hand, we found a 1.

Extrarenal sites of calcitriol synthesis: the particular role of the skin.

Calcitriol (1alpha,25(OH)2D3), the hormonally active form of vitamin D3 (D3) is produced by a cascade of reactions, including photochemical D3 synthesis in the skin and subsequent hydroxylation at the C-25 atom in the liver and finally at C-1alpha position in the kidney. However, there is substantial evidence for additional extrarenal sites of calcitriol synthesis. In vitro, many nonrenal cells, including bone, placenta, prostata, keratinocytes, macrophages, T-lymphocytes and several cancer cells (e.