Antenatal Glucocorticoid Therapy: Hormone Concentrations. Hormones and Lung Maturation. Berlin: Springer Berlin Heidelberg; 1986. pp. 173-96. [DOI: 10.1007/978-3-642-82483-8_6]

Cell selective glucocorticoid induction of caveolin-1 and caveolae in differentiating pulmonary alveolar epithelial cell cultures

Increased caveolin-1 expression is a marker of the differentiation of lung alveolar epithelial type II cells into a type I phenotype. Here, we show in both a primary differentiating rat alveolar culture, and a human alveolar cell line (A549) that caveolae formation and caveolin-1 expression are dependent upon dexamethasone Dex, and is inhibited by the glucocorticoid receptor (GR) antagonist, mifepristone. Study of a panel of 20 different cell types showed the effect of (Dex) upon caveolin-1 expression to be highly cell selective for lung alveolar epithelial cells. The actions of glucocorticoid upon caveolin-1 appear indirect acting via intermediary genes as evidenced by cycloheximide (CHX) abolition of Dex-induced increases in caveolin-1 mRNA and by recombinant transfection studies using the caveolin-1 promoter cloned upstream of a reporter gene. Treatment with actinomycin D (ACD) revealed that the effects of Dex are also, at least in part, mediated by stabilisation of caveolin-1 mRNA. Collectively, these results indicate that glucocorticoids modulate the expression of caveolin-1 and caveolae biogenesis within alveolar epithelial cells via both transcriptional and translational modifications. The cell-selective effects of glucocorticoid upon caveolin may represent a previously unrecognised mechanism by which glucocorticoids affect lung development.

Modeling glucocorticoid-mediated fetal lung maturation: II. Temporal patterns of gene expression in fetal rat lung

Our previous report described the temporal steroid patterns during pharmacokinetic (PK) studies with dexamethasone (DEX) where doses of six 1 micromol/kg injections were given during gestational ages 18 to 20 days in rats. DEX PK was used in conjunction with the endogenous corticosterone profile to understand the regulation of fetal lung pharmacodynamics (PD). Expression of the glucocorticoid receptor (GR) and surfactant proteins A and B mRNA were chosen as lung maturational markers. GR seemed to be insensitive to the circulating glucocorticoids, indicating that unlike the adult situation, GR was not under negative feedback control of its ligand. Surfactant protein B exhibited approximately 400-fold induction in control fetal lung during the last days of gestation, and the inductive effect was even greater in the treatment group. Surfactant protein A displayed approximately 100-fold induction in control fetal lung during late gestation. However, the treatment group exhibited biphasic stimulatory and inhibitory effects for surfactant protein A. The inhibitory effect indicated that the chosen dosing scheme for DEX was not an optimal regimen. These data were used to determine by simulation the DEX regimen that would reproduce the temporal pattern of lung maturation observed in control animals. PK/PD modeling indicated that maintaining steroid exposure at approximately twice the equilibrium dissociation constant for the steroid/receptor interaction should produce optimal stimulation of both surfactant proteins. The simulations illustrate that administering smaller quantities of steroids over extended periods that produce sustained steroid exposure might be the optimal approach for designing dose-sparing antenatal corticosteroid therapy.

Betamethasone pharmacokinetics after two prodrug formulations in sheep: implications for antenatal corticosteroid use

Maternal administration of betamethasone to enhance fetal lung maturation for women who threaten preterm labor is common clinical practice. However, recommendations regarding the choice of betamethasone formulations for perinatal use are vague. The disposition of betamethasone from two commonly used antenatal formulations is poorly understood. We therefore designed a study to capture the true pharmacokinetic profiles of betamethasone from these fast acting and dual-release formulations. Betamethasone in sheep plasma was measured by a newly designed, highly sensitive liquid chromatography/tandem mass spectrometry assay after intramuscular injection (n = 4) of 0.25 mg/kg betamethasone phosphate and 0.5 mg/kg betamethasone phosphate/acetate formulations. Compartmental modeling was performed using the ADAPT II program. Betamethasone pharmacokinetics could be captured for 24 h for the phosphate and for 5 days for the phosphate/acetate formulations. The phosphate formulation profile had the appearance of a traditional Bateman function with a terminal half-life of 4 h, whereas the phosphate/acetate formulation produced a biexponential decline with a terminal half-life of 14 h. The latter is much longer than is commonly reported and has been missed in the literature due to assay limitations. Extrapolations to humans indicate that although both formulations might have similar therapeutic indices, the dual formulation might be associated with a lower safety profile. In light of this newly identified long terminal half-life for the betamethasone dual formulation, dosing practices for betamethasone in pregnancy need to be reassessed.

Antenatal steroids: miracle drug for preemies

Antenatal corticosteroid administration has been unequivocally demonstrated to reduce neonatal morbidity and mortality. In addition to its well-documented role in reducing respiratory distress syndrome, evidence is accumulating indicating the global maturational effect of this therapy in the growing fetus. New data demonstrates, the hitherto relatively not well known, beneficial effects of this mode of therapy on renal, cardiovascular, gastrointestinal, endocrinal and cerebral maturation. Despite its well proven efficacy and safety, this therapy is used only in a small fraction of eligible mothers. In this article, biological basis of antenatal steroids use, clinical benefits including those to extremely premature infants, indications for their administration, treatment regimens, practice variations in their administration, cost analysis, and some directions for future research are reviewed. It is hoped that given the evidence reviewed in this article, the use of antenatal steroids administration in proper clinical settings will increase with a significant impact in reducing the neonatal morbidity and mortality.