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Nuclear retention of topical glucocorticoids and absence of cross-linking with DNA in cultured dermal fibroblasts Au, Diana Shu-Lian

Abstract

The principal mechanism by which glucocorticoids exert their physiological effects is by alterations of DNA metabolism. Studies have been done to clarify the nuclear sites of human and mouse L-929 fibroblasts, with which the topical glucocorticoids, hydrocortisone (HC) and triamcinolone acetonide (TA), are likely to interact for initiating the alterations in DNA reactions, especially DNA itself and chromatin proteins. Further, data have been added on the uptake and retention of TA in the nuclei of L-929 fibroblasts. All studies have been done using actively metabolizing cells in culture over extended periods of time of exposure to the steroids (0-96 hr). The possible direct glucocorticoid-DNA interaction - by cross-linking was investigated by hydroxyapatite chromatography and thermal scanning analysis, using DNA isolated from 8-methoxypsoralen treated and UV-A irradiated mouse L-929 fibroblasts as positive controls. Cross-linking was not detectable under widely varying experimental conditions. The fate of the glucocorticoid in nuclei was studied by measuring the amount of specifically retained TA. The specific retention of ³H-TA at a concentration of 10⁻⁸ M in cultures of L-929 fibroblasts was evaluated in intact nuclei, chromatin and deproteinized DNA. The distribution of specifically retained TA between cytoplasm and nuclei, and its intranuclear distribution between the nucleoplasm and chromatin also were determined as a function of time. Approximately, 10% of cytosol retained TA was translocated into the nucleus. The highest level, 0.4 fmole/ug nuclear protein or 2.8 fmole/ug DNA, was reached after 6 hours. Relatively constant levels, approximately half of , the highest level, were observed thereafter up to 96 hr. The majority of TA in the nucleus, 56-75%, was associated with chromatin. The level of TA retained in chromatin reached the highest level, 0.6 fmole/ug chromosomal protein or 1.1 fmole/ug DNA, after 6 hours of incubation. Relatively constant levels, approximately 60% of the highest level, were observed thereafter up to 96 hr. Alternative sites of subchromatin localization of the ³H-TA, in terms of various classes of histone and nonhistone proteins, were studied in a preliminary investigation by the selective dissociation method of immobilized chromatin on hydroxyapatite. The TA was located in unbound chromosomal proteins (75%), histone proteins (13%) and nonhistone proteins (12%). None of the glucocorticoid was found in fractions of nucleic acids, thus confirming the unlild-iness of direct glucocorticoid-DNA interactions, but indicating that the primary sites of TA-nuclear interactions reside in chromatin proteins. The suppressive effect of triamcinolone acetonide, at concentrations of 10⁻⁸ and 5.0 x 10⁻⁶ M in culture media, on nuclear proteins and DNA of mouse L-929 fibroblasts was determined for various incubation intervals. The suppression was demonstrated to be a late, 24 hours or longer, consequence of the treatment of TA. The chemical stability of the glucocorticoids used was examined in storage solutions and in media removed from test cultures by a gas-liquid chromatographic assay developed for the purpose. The assay involved double derivatization of the glucocorticoids with methoxyamine and N-trimethylsilyl imidazole, and is capable of detecting nangram quantities of hydrocortisone, triamcinolone acetonide and desonide.

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