Hypoxia, a common stressor with preterm birth, increases morbidity and mortality associated with prematurity. Glucocorticoids (GC) are administered to the preterm infant to improve oxygenation; prolonged use of GCs remains controversial. We evaluated a selective glucocorticoid receptor (GR) antagonist (CORT113176) in our neonatal rat model of human prematurity to assess how fasting and hypoxia-induced increases in neonatal corticosterone affects endogenous hormones and endocrine pancreas function. Neonatal rat pups at postnatal day (PD) 2, PD8, and PD15 were pretreated with CORT113176 and, after 60 min of separation and fasting, exposed to hypoxia (8% O2) or control (normoxia) for 30 or 60 minutes while fasting was continued. Plasma corticosterone, ACTH, glucose, and insulin were measured and fasting HOMA-IR (index of insulin resistance) calculated. Glucocorticoid and insulin receptor sensitive gene mRNAs were analyzed in liver, muscle, and adipose to evaluate target tissue biomarkers. CORT113176 pretreatment augmented baseline and hypoxia-induced increases in corticosterone and attenuated hypoxia-induced increases in insulin resistance at PD2. Normoxic and hypoxic stress increased the hepatic GR sensitive gene mRNAs, Gilz and Per1; this was eliminated by pretreatment with CORT113176. CORT113176 pretreatment decreased baseline insulin receptor sensitive gene mRNAs Akt2, Irs1, Pik3r1, and Srebp1c at PD2. We show that CORT113176 variably augments the stress-induced increases in corticosterone concentrations (attenuation of negative feedback) and that GR is critical for hepatic responses to stress in the hypoxic neonate. We also propose that measurement of Gilz and Per1 mRNA expression may be useful to evaluate the effectiveness of GR antagonism.
Premature birth is a major public health problem worldwide and can lead to transient adrenal insufficiency1,2. The stress of premature birth includes the inability to control blood glucose and maintain normal oxygenation leading to hypoxia3. Corticosteroid administration enhances surfactant production and improves oxygenation in preterm humans. However, corticosteroids can also have negative consequences4,5. We have validated a rat model of separation and hypoxia on post-natal day (PD) 2 that emulates the stress and treatment of hypoxia in the preterm human infant6,7. We hypothesized that the role of endogenous glucocorticoids in our neonatal rat model of preterm birth can be evaluated using the novel selective glucocorticoid receptor (GR) antagonist CORT113176 (Corcept) which is devoid of progesterone receptor effects8. Pups (PD 2, 8, or 15; N=6–8 per treatment/timepoint) were given CORT113176 (60 mg/kg IP) or vehicle, then placed into chambers in room air with mild warming to prevent hypothermia due to maternal separation. 60 min later, one group of pups was euthanized and trunk blood collected (baseline). The remaining pups were exposed to hypoxia (8% O2) or normoxia (time control) for 30 or 60 min at which times trunk blood was collected for the measurement of plasma glucose, insulin, ACTH, and corticosterone. Plasma ACTH, corticosterone, and insulin were measured by immunoassay. Glucose was measured by glucose oxidase method and insulin sensitivity calculated (HOMA-IR). Organs were frozen (brain, pituitary, adrenal glands, kidney, liver, muscle, fat) for future assessment of tissue-specific glucocorticoid-sensitive gene expression. In PD2 rats, basal and hypoxia-stimulated plasma ACTH and corticosterone were lower and basal HOMA-IR greater with CORT113176 pretreatment suggesting (unexpectedly) glucocorticoid agonist activity. In PD8 and PD15 rats, basal and hypoxia-stimulated plasma ACTH and corticosterone were augmented after CORT113176 pretreatment demonstrating classic antagonist activity. However, in PD8 rats, CORT113176 effects were tissue-specific acting as a classic antagonist on the HPA-axis, but as an agonist on whole-body insulin resistance. The differential effects of CORT113176 based on age and target tissue indicate that GR regulation changes in early development in our animal model of human prematurity. These findings may have significant implications in the treatment of hypoxia and transient adrenal insufficiency in the preterm infant1,2 as well as give insight into the nuances of the control of glucocorticoid receptor function. 1Lancet 392:1923–1994, 2018 2Curr Opin Endocrinol Diabetes Obes 17:8–12, 2010 3Compr Ther 13:14–19, 1987 4Int Immunopharmacol 66:242–250, 2019 5J Neuroendocrinol 27:468–480, 2015 6Am J Physiol 300:R708-715, 2011 7Am J Physiol 302:R627-R633, 2012 8Med Chem Lett 25:5720−5725, 2015
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% O2) 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.
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