Effect of betamethasone treatment on brain cell death and neurosteroidogenic pathways in a guinea pig model of growth restriction

Objectives: Neurosteroids have potent neuroprotective actions in the fetal and adult brain. We have shown that key neurosteroidogenic enzyme, 5α reductase (5αR), is upregulated in response to acute hypoxia in the late gestation fetus and the resultant increase in 5α-reduced steroids reduces hypoxia-induced apoptotic cell death in the hippocampus (Yawno et al, 2007 Neurosci 146: 1726). Repeated treatment with betamethasone, a synthetic corticosteroid, may interfere with these processes and adversely affect the fetal brain. The aim of this study was to determine the effect of repeated betamethasone treatment on the expression of key enzymes in the neurosteroid synthetic pathway and on the level of apoptotic brain cell death in normal and growth restricted fetuses. Methods: Placental insufficiency in guinea pigs was produced by the ablation of uterine artery branches at mid gestation (term 68d) in order to induce fetal growth restriction (GR). Sham and GR fetuses were treated with vehicle or betamethasone (1mg/kg/day) for 4 days prior to sacrifice (65d). Western blot and real time PCR were used to quantify the effects on key neurosteroidogenic enzymes (5αR and P450scc) in fetal brain, adrenal glands and placenta. Apoptotic cell death was assessed by the measurement of activated caspase-3 by immunohistochemistry in the fetal brain. Results: Betamethasone treatment resulted in decreased placental weight as a proportion to body weight in normal pregnancies and reduced brain weight (inhibiting brain sparing) when administered during compromised pregnancies. This treatment also reduced 5αR expression in the placenta by 51% (P=0.029), but not in the brain. Activated caspase-3 staining was not affected by betamethasone alone however, a marked increase in staining was seen in the cortex and hippocampus of GR fetuses receiving betamethasone. Conclusions: These findings indicate betamethasone treatment while not affecting apoptotic cell death in normal fetuses, causes a potentially detrimental increase in cell death in fetuses already compromised. The placental deficit, due to betamethasone treatment, in the capacity to synthesize protective neurosteroids may contribute to these effects