Sun Filters Research Articles

Patología de la vitamina D

There is an elevated prevalence of vitamin D deficiency in the general population. This is defined by levels under 20ng/ml. Standing out among its causes are deficit of its skin synthesis due to limited exposure to ultraviolet radiation due to atmospheric contamination, uses of sun filters, latitudes very far from the equator or aging. Other described causes are malabsorption, hepatic or renal diseases, cytochrome p450 system inductor drugs and obesity. The skeletal consequence of vitamin D deficiency is osteomalacia in adults and rickets in children. There are multiple extraskeletal consequences: muscular weakness and greater tendency to fall, psoriasis, some cancers, arterial hypertension, cardiovascular diseases, diabetes mellitus or greater mortality. There are several preparations on the market for supplements, it being recommendable to monitor the plasma concentration of the vitamin at 4-6 months to avoid reaching supraphysiological levels that have adverse consequences (hyperkalcemia, hypercalciuria, nephfrolithiasis, etc.).

Liposomes as Alternative Vehicles for Sun Filter Formulations

The aim of our study was to determine the influence of several types of liposomes with a different lipid composition on the percutaneous absorption of one conventional sun filter with a lipophilic character (ethyl hexyl methoxycinnamate) using both in vitro and in vivo methodologies. Three different liposomes were prepared with unsaturated and saturated phosphatidylcholine (PC, HPC) and with a wool lipid mixture (IWL) with a composition similar to that of the stratum corneum lipids. Results showed that the liquid crystalline state associated with PC liposomes plays a key role in enhancing skin penetration. When liposomes with a composition and structural organization similar to that of the stratum corneum lipids (HPC and IWL) are used, the skin penetration is retarded, suggesting a certain reinforcement of the stratum corneum barrier. These two types of liposomes could be regarded as alternatives to conventional oil/water emulsions in the formulations of lipidic sun filters. Finally, an acceptable correlation was obtained using both in vitro and in vivo methodologies to evaluate the corresponding skin absorption profile.

Toxicity and Phototoxicity of Chemical Sun Filters

Two chemical sun filters that are ingredients in sunscreen products have been tested for their dark toxicity and possible toxicity to mouse cells after UV irradiation. Increased toxicity as a result of breakdown of a UVB filter, octyl methoxycinnamate, was observed. UV radiation absorbed by the pure chemical sunscreen may lead to breakdown to more reactive chemical compounds than the unexposed sunscreen filter. The UVA filter included in our tests, butyl methoxydibenzoylmethane, was also toxic in the dark, however, it was the more photostable of the two and no additional significant toxicity was induced by UV irradiation. It can be concluded that the two sun filters are toxic to cells in the dark, but the biological role of this dark toxicity in the skin is not clear. Unstable sun filters may be broken down by UV to form photoproducts that are potentially toxic.

Development of assays for the detection of photomutagenicity of chemicals during exposure to UV light—I. Assay development

Two complementary assay systems have been adapted for the detection of compounds which may form mutagenic photoproducts during exposure to UV light from an Osram Ultra-Vitalux sunlamp as used in the evaluation of the effectiveness of sun filters. The effects of UVA and of UVB were evaluated. A bacterial plate test using Escherichia coli strain WP2 allowed the bacteria, co-plated with test chemical in soft agar, to be irradiated with various doses of UV light. Mutagenesis was assessed by scoring numbers of tryptophan-independent colonies. The chosen reference compound was 8-methoxypsoralen (8-MOP) which was non-mutagenic alone at the highest dose tested (1000 micrograms/plate). Following simultaneous exposure of bacteria to 8-MOP and doses of UV light which alone had little effect, large numbers of revertants were scored. Numbers of mutants were dependent upon the doses of both 8-MOP and of UV light. The second test system involved the exposure of Chinese hamster ovary cells to UV light in the presence of test chemical to determine the clastogenic effects of photoproducts. Treatment with 8-MOP alone up to 50 micrograms/ml was not clastogenic but concomitant exposure to non-damaging doses of UV light caused large increases in the incidence of chromosome aberrations of all types. Damage was again dependent on the doses of both components. Two additional photoactive compounds, para-aminobenzoic acid and chlorpromazine both show photoclastogenic but not photomutagenic properties. These two complementary assay systems take advantage of using no-effect levels of UV light as a baseline against which photomutagenicity readily can be compared.(ABSTRACT TRUNCATED AT 250 WORDS)