350 - The diurnal timing of antenatal steroids affects the circadian and functional development of fetal lung, placenta, and hypothalamus tissues

Publication Number: 1334.350

Lynn Mercer, Harbor UCLA/ Cedars-Sinai Fellowship, Torrance, CA, United States; Gourav Chandan, Lundquist Institute at Harbor UCLA, Torrance, CA, United States; Siddarth Amuthan, Harbor- UCLA Cedar sinai, Torrance, CA, United States; Ying Wang, The Lundquist Institute, Torrance, CA, United States; Jie Liu, Lundquist Institute, Torrance, CA, United States; Celia Yu, The Lundquist Institute for Biomedical Innovation, Torrance, CA, United States; Virender K.. Rehan, Lundquist Institute for Biomedical Innovation at Harbor-UCLA Medical Center, Torrance, CA, United States

Background: Antenatal steroids given to women at risk for premature delivery accelerate lung maturation in the fetus, significantly improving outcomes by accelerating lung development. The appropriate dosing regimen, optimal timing, and selection of patients who will benefit are still not fully established.

Objective: Although it is known that steroids interact with the circadian clock at transcriptional, translational, and posttranslational levels, the effect of diurnal timing of antenatal steroids administration on fetal lung maturity have not been examined. We hypothesized that administering antenatal glucocorticoids ‘in phase’ with the normal peak endogenous glucocorticoid activity may increase the fetal lung maturation response but may be associated with increased neurotoxicity.

Design/Methods: Pregnant Sprague-Dawley rat dams were given dexamethasone on embryonic day (e)18 and 19. The groups were given the medication either at 08:00 hr during their normal sleep cycle (AM group) or 20:00 hr during the normal wake cycle (PM group). The pregnant dams were sacrificed and fetal tissues were collected 48 hr after the initial treatment. Real time qRT-PCR was performed on lung tissue to evaluate relative fold-change of gene transcripts associated with lung maturation and circadian clock. Western blot analysis was used to evaluate changes to protein quantities of key lung development markers. The placenta and hypothalamus were evaluated to determine if peripheral clocks in these key fetal tissues are similarly responsive and to evaluate for apoptosis in the hypothalamus.

Results: There was upregulation of transcription of surfactant proteins and other markers of fetal lung development in the PM group compared to the AM group (p < 0.05). These responses were also confirmed at the protein level. The basal expression of clock genes (CLOCK, ARNTL, Per, Cry, NR1D1) were significantly higher in the PM group compared to the AM group in the lung tissue but did not change with steroid administration. Placental clocks showed statistically significant difference in AM and PM transcription of Per2 and NR1D2, suggesting that placental tissue also has diurnal variation.

Conclusion(s): Fetal lungs showed enhanced expression of genes consistent with maturation when antenatal corticosteroids were administered in alignment with the natural diurnal variation of endogenous steroids. Circadian variation in clock genes may drive the differential response to antenatal steroids based on the timing of administration. Our data demonstrates that the time of day when steroids are administered may influence their effectiveness.