Biphasic entry of glucocorticoids into cultured human skin keratinocytes and fibroblasts

The ATP-binding cassette proteins ABCB1 and ABCC1 as modulators of glucocorticoid action

Responses to hormones that act through nuclear receptors are controlled by modulating hormone concentrations not only in the circulation but also within target tissues. The role of enzymes that amplify or reduce local hormone concentrations is well established for glucocorticoid and other lipophilic hormones; moreover, transmembrane transporters have proven critical in determining tissue responses to thyroid hormones. However, there has been less consideration of the role of transmembrane transport for steroid hormones. ATP-binding cassette (ABC) proteins were first shown to influence the accumulation of glucocorticoids in cells almost three decades ago, but observations over the past 10 years suggest that differential transport propensities of both exogenous and endogenous glucocorticoids by ABCB1 and ABCC1 transporters provide a mechanism whereby different tissues are preferentially sensitive to different steroids. This Review summarizes this evidence and the new insights provided for the physiology and pharmacology of glucocorticoid action, including new approaches to glucocorticoid replacement.

In vitro penetration through the skin layers of topically applied glucocorticoids

Corticoids are actives widely used in the treatment of skin diseases. This work aims to study the penetration of 3 corticoids (betamethasone, clobetasol, and flurandrenolide), their relationship with their Log D values and the effects of the vehicles. The 3 compounds were applied on a Franz-type diffusion cell in propylene glycol solution and their respective commercial creams and ointments. The active amounts found in the stratum corneum, epidermal, and dermal layers of the skin were investigated. Their diffusions were greatly affected by the formulation; moreover higher amounts of substance in the epidermis and dermis were detected in ointments than in creams. The enhancement effect of propylene glycol was also observed. The differences between the 3 substances could be related to their lipophilicity, molecular structure, and molecular weight. The more hydrophobic compounds (clobetasol and betamethasone) are present in higher amounts in the epidermis and dermis, while the hydrophilic compound (flurandrenolide) is mostly present in the receptor fluid.

Effects of topical corticosteroids on cell proliferation, cell cycle progression and apoptosis: in vitro comparison on HaCaT

Topical-corticosteroids are mainly used for the treatment of inflammatory or hyperproliferative skin diseases. The in vivo assay to rank topical-corticosteroids potency, based on the skin blanching, is not adapted to compare their anti-proliferative efficacy. We have compared the antiproliferative effect of six topical-corticosteroids on a model of hyperproliferant keratinocytes (HaCaT). Betamethasone-dipropionate; clobetasol-propionate; betamethasone-valerate; desonide; hydrocortisone-butyrate and hydrocortisone-base, at different concentrations (10(-8)-10(-4)M) have been compared. HaCaT proliferation has been evaluated by MTT-assay and the mechanism of the death was evaluated by annexin V/propidium iodide staining and cell cycle phases analysis. Topical corticosteroids reduced cell growth in a dose-dependent manner. At 10(-4)M, betamethasone dipropionate was the most antiproliferative compound while hydrocortisone-butyrate was the less. Hydrocortisone-base which is usually considered as the less potent topical-corticosteroids showed a clear cytotoxic effect. Betamethasone-dipropionate and betamethasone-valerate induced more apoptosis than necrosis whereas the reverse has been observed for other topical-corticosteroids. All topical-corticosteroids, except clobetasol-propionate, arrested cell cycle mainly in G2-phase. Clobetasol-propionate arrested cell cycle in S-phase population. At 10(-8)M, topical-corticosteroids induced HaCaT proliferation. In terms of antiproliferative effect at 10(-4)M, we propose to rank topical corticosteroids as follow: betamethasone-dipropionate>desonide≥betamethasone-valerate=hydrocortisone-base=clobetasol-propionate>hydrocortisone-butyrate. This classification differs from the current ranking, based on the vasoconstrictive effect, but is more adapted for hyperproliferative disease treatment.

Prednicarbate versus conventional topical glucocorticoids: pharmacodynamic characterization in vitro

PURPOSE

Pharmacodynamic characterization of topical glucocorticoids as prednicarbate (PC), its metabolites prednisolone 17-ethylcarbonate (PEC) and prednisolone (PD), betamethasone 17-valerate (BMV), betamethasone (BM) and desoximetasone (DM) by evaluating their effects on epidermal and dermal cells. Synopsis of pharmacokinetic and pharmacodynamic studies, possibly explaining the improved benefit-risk ratio of prednicarbate.

METHODS

Isolated foreskin keratinocytes were used to investigate the influence on epidermal inflammatory processes, dermal fibroblasts of the same origin to study antiproliferative activities of glucocorticoids. Interleukins were measured by ELISA-assay, the influence on II-1 alpha-production also on mRNA-level by RNAse protection assay. Proliferation was assessed by 3H thymidine incorporation and biodegradation by HPLC/UV-absorption. Cell viability was controlled by MTT assay.

RESULTS

In keratinocytes, inflammation was induced by TNF alpha, resulting in an increased II-1 alpha synthesis. This cytokine was particularly suppressed by PC and BMV, whereas PEC, PD, DM and BM were less potent (p < or = 0.05). Since, however, the double ester PC is rapidly degraded in keratinocytes, a RNAse-protection assay of II-1 alpha mRNA was performed allowing short incubation times and thus minimizing biodegradation effects. In agreement with the previous experiment, the antiinflammatory potency of native PC was confirmed. In fibroblasts, II-1 alpha and II-6 synthesis indicate proliferation and inflammation respectively. Whereas PC inhibited II-1 alpha and II-6 production in fibroblasts to a minor extent only, it was strongly reduced by the conventional glucocorticoids and PEC (p < or = 0.05). The minor unwanted effect of PC on fibroblasts was also reflected by its low influence on cell proliferation as assayed by 3H thymidine incorporation. More pronounced antiproliferative features were observed with BM, PEC and especially BMV.

CONCLUSIONS

Correlating antiphlogistic effects in keratinocytes (suppression of II-1 alpha) with antiproliferative effects in fibroblasts (suppression of II-1 alpha and II-6), the improved benefit-risk ratio of PC compared to conventional glucocorticoids does not result only from distinct drug metabolism in the skin but also from a specific influence on the cytokine network.

Binding of drugs to human skin: influencing factors and the role of tissue lipids

For a series of ten drugs with different physicochemical properties, binding to human skin (epidermis and corium) was determined. Epidermis was obtained by suction blistering, and corium was sliced with a microtome (0.2 mm). Binding experiments were performed in dialysis chambers, containing labelled drug solutions. All drugs investigated were bound to epidermis and corium. With one exception, epidermal drug binding was significantly higher than corial binding. Nevertheless, a good correlation between binding of drugs to both skin fractions could be found. In a range from 10(-7) to 10(-3) mol L-1 binding of drugs to both skin fractions is linear and not saturable. A good correlation was found between binding and lipophilicity of drugs, determined as the partition coefficients between an organic phase (octanol or heptane) and phosphate buffer of pH 7.0. The results show that binding to epidermis and corium is not saturable and depends on lipophilicity of drugs, indicating unspecific binding. Further binding experiments were performed with lipid-depleted tissue. Since drug binding to lipid-depleted samples and control samples differ only to a moderate extent, it is suggested, that tissue lipids play a marginal role on drug binding. Hence, drugs are bound to human skin by other components like proteins.

Effect of dexamethasone on nuclear envelope nucleoside triphosphatase in fibroblasts 3T3 and melanoma cells MMLI

Glucocorticoids are known to influence DNA and RNA synthesis in skin fibroblasts. In a novel approach to study this effect, we investigated the influence of the hormone analogue dexamethasone on the activity of nuclear envelope-associated nucleoside triphosphatase (NTPase) in intact cell systems (3T3 fibroblasts and MMLI melanoma cells). The NTPase is thought to be responsible for regulation of nucleocytoplasmic transport of mRNA. [3H]Dexamethasone was found to bind to nuclear ghosts at a density comparable with that of nuclear pores in this cellular fraction. Incubation of the cells for 48 h in the presence of different concentrations of dexamethasone resulted in a marked decrease of NTPase activity. Already concentrations as low as 0.1 ng/ml (3T3) or 1 ng/ml (MMLI) reduced the NTPase activity by approximately 50%. These results suggest that nuclear envelope NTPase is a site at which glucocorticoids regulate gene expression.