The Effect of a Novel Glucocorticoid Receptor Antagonist (CORT113176) on Glucocorticoid and Insulin Receptor Sensitive Hepatic Gene (mRNA) Expression in a Neonatal Rat Model of Human Prematurity

Preterm birth is a global health problem the sequelae of which are not well understood. Hypoxia, a common stressor with prematurity, can affect blood glucose via stress-induced increases in glucocorticoids (GC). GCs are also administered to preterm infants to improve oxygenation; however, this is controversial. CORT113176 (Corcept Therapeutics) is a novel, selective glucocorticoid receptor (GR) antagonist that does not bind to the progesterone receptor. We have demonstrated that CORT113176 (in our rat model of preterm birth) increases baseline corticosterone (due to loss of GC negative feedback) and attenuates hypoxia-induced increases in insulin resistance implicating endogenous corticosterone in post-natal metabolic adaptations to stress. We now propose that CORT113176 is useful to evaluate the hepatic effects of endogenous GCs in our rat model of preterm birth by measuring critical GC and insulin receptor sensitive gene mRNAs. Postnatal day (PD) 2 rat pups of both sexes (N=5 per treatment/sex) were pretreated with CORT113176 (600 mg/kg IP) or vehicle. After 60 minutes, a group of pups were euthanized with livers collected and preserved in RNAlater (baseline). The remaining pups were separated from their dams, exposed to normoxia (control) or hypoxia (8% O(2)) for 60 minutes, and livers obtained. Total hepatic RNA was extracted, and mRNA expression was analyzed (RT-qPCR) for GC and insulin receptor sensitive genes: GC: Fkbp5, Gilz, Nr3c1 (Gr), Nr3c2 (Mr), Per1, Ttpa. INSULIN: Akt2, G6Pase, Igf1r, Insr, Irs1, Irs2, Pik3cb, Pik3r1, Srebp1c. CORT113176 decreased the expression of all baseline hepatic insulin receptor mRNAs in both sexes, except for G6Pase. Pik3r1 mRNA expression significantly decreased with 60 minutes of normoxic separation (fasting) in males and females compared to baseline and hypoxic separation; this was blocked by CORT113176. In the GC receptor sensitive panel, CORT113176 decreased basal Nr3c1 (Gr) mRNA. Normoxic and hypoxic separation increased Per1 and Gilz mRNA expression; this effect was blocked by CORT113176. Interestingly, Fkbp5 expression, a proposed clinical marker for GR antagonism, was not altered by CORT113176. The hepatic GC and insulin receptor sensitive gene mRNA panels we developed are sensitive to GR antagonism suggesting they may be a useful addition to Fkbp5. The increase in endogenous corticosterone, acting via GR, is critical in the hepatic response to stress in our neonatal rat model of hypoxia and prematurity.