Effects of antenatal glucocorticoids on cerebral substrate metabolism in the preterm ovine fetus

Antenatal corticosteroids-to-delivery interval associates cord blood S100B levels

AIM

Antenatal corticosteroids (ACS) are recommended for women at risk of preterm birth before 34 weeks' gestation. However, adverse effects of ACS on the fetal brain have also been reported. The time interval from ACS administration to delivery (ACS-to-delivery interval) might alter the effect of ACS on the fetal brain. This study aimed to evaluate the effect of ACS-to-delivery interval on cord blood S100 calcium-binding protein B (S100B) levels as a biomarker of brain damage.

METHODS

Women who delivered between 2012 and 2020 at a tertiary medical center were divided into three groups according to ACS use and ACS-to-delivery interval, retrospectively: non-ACS, ACS ≤7 days, and ACS >7 days. Patients who did not complete the ACS regimen were excluded. The primary outcome was cord blood S100B levels.

RESULTS

Cord blood S100B levels were significantly lower in the ACS ≤7 days group than in the non-ACS and ACS >7 days groups. In the multiple regression analysis, birth ≤7 days after ACS showed a significant negative association with S100B level (p < 0.001).

CONCLUSIONS

Reduced S100B levels were observed in infants born ≤7 days after ACS but not in infants born >7 days after ACS. These findings suggest the importance of ACS timing to optimize its effects on the fetal brain, although further studies are required to identify these mechanisms.

Antenatal betamethasone redistributes central blood flows and preferentially augments right ventricular output and pump function in preterm fetal lambs

The glucocorticosteroid betamethasone, which is routinely administered prior to anticipated preterm birth to enhance maturation of the lungs and the cardiovascular system, has diverse fetal regional blood flow effects ranging from increased pulmonary flow to decreased cerebral flow. The aim of this study was to test the hypothesis that these diverse effects reflect alterations in major central flow patterns that are associated with complementary shifts in left ventricular (LV) and right ventricular (RV) pumping performance. Studies were performed in anesthetized preterm fetal lambs (gestation = 127 ± 1 days, term = 147 days) with (n = 14) or without (n = 12) preceding betamethasone treatment via maternal intramuscular injection. High-fidelity central arterial blood pressure and flow signals were obtained to calculate LV and RV outputs and total hydraulic power. Betamethasone therapy was accompanied by 1) increased RV, but not LV, output; 2) a greater RV than LV increase in total power; 3) a redistribution of LV output away from the fetal upper body region and toward the lower body and placenta; 4) a greater proportion of RV output passing to the lungs, and a lesser proportion to the lower body and placenta; and 5) a change in the relative contribution of venous streams to ventricular filling, with the LV having increased pulmonary venous and decreased foramen ovale components, and the RV having lesser superior vena caval and greater inferior vena caval portions. Taken together, these findings suggest that antenatal betamethasone produces a widespread redistribution of central arterial and venous flows in the fetus, accompanied by a preferential rise in RV pumping performance.

The effects of dexamethasone on post-asphyxial cerebral oxygenation in the preterm fetal sheep

Exposure to clinical doses of the glucocorticoid dexamethasone increases brain activity and causes seizures in normoxic preterm fetal sheep without causing brain injury. In contrast, the same treatment after asphyxia increased brain injury. We hypothesised that increased injury was in part mediated by a mismatch between oxygen demand and oxygen supply. In preterm fetal sheep at 0.7 gestation we measured cerebral oxygenation using near-infrared spectroscopy, electroencephalographic (EEG) activity, and carotid blood flow (CaBF) from 24 h before until 72 h after asphyxia induced by 25 min of umbilical cord occlusion. Ewes received dexamethasone intramuscularly (12 mg 3 ml(-1)) or saline 15 min after the end of asphyxia. Fetuses were studied for 3 days after occlusion. During the first 6 h of recovery after asphyxia, dexamethasone treatment was associated with a significantly greater fall in CaBF (P < 0.05), increased carotid vascular resistance (P < 0.001) and a greater fall in cerebral oxygenation as measured by the difference between oxygenated and deoxygenated haemoglobin (delta haemoglobin; P < 0.05). EEG activity was similarly suppressed in both groups. From 6 to 10 h onward, dexamethasone treatment was associated with a return of CaBF to saline control levels, increased EEG power (P < 0.005), greater epileptiform transient activity (P < 0.001), increased oxidised cytochrome oxidase (P < 0.05) and an attenuated increase in [delta haemoglobin] (P < 0.05). In conclusion, dexamethasone treatment after asphyxia is associated with greater hypoperfusion in the critical latent phase, leading to impaired intracerebral oxygenation that may exacerbate neural injury after asphyxia.

Glucocorticoids and preterm hypoxic-ischemic brain injury: the good and the bad

Fetuses at risk of premature delivery are now routinely exposed to maternal treatment with synthetic glucocorticoids. In randomized clinical trials, these substantially reduce acute neonatal systemic morbidity, and mortality, after premature birth and reduce intraventricular hemorrhage. However, the overall neurodevelopmental impact is surprisingly unclear; worryingly, postnatal glucocorticoids are consistently associated with impaired brain development. We review the clinical and experimental evidence on how glucocorticoids may affect the developing brain and highlight the need for systematic research.

Oxidative stress after antenatal betamethasone: acute downregulation of glutathione peroxidase-3

BACKGROUND

Human and experimental data show that antenatal exposure to glucocorticoids (GC) temporarily reduces fetal well-being and impairs the fetal response to hypoxemia.

AIMS

We tested the hypothesis that antenatal betamethasone provokes transient oxidative stress, which may be triggered directly by the GC or indirectly by metabolic signals such as increased glucose and free fatty acid (FFA) concentrations.

STUDY DESIGN

Prospective (single center, 18 months) cohort study in newborns <34 weeks gestational age at birth.

METHODS

We studied 105 newborns and measured oxidative damage to lipids [malondialdehyde (MDA)] and proteins (protein carbonyls), as well as glutathione peroxidase-3 (GPx3), an important antioxidant enzyme, in umbilical vein (UV) plasma. In addition, we measured umbilical artery and UV blood gases, and metabolic indices (plasma glucose, FFA and insulin) in UV.

RESULTS

MDA but not protein carbonyl concentrations was inversely related to time elapsed since the first or last betamethasone administration (p=0.006); MDA remained elevated by 69-96% for at least 72 h after the last betamethasone. By contrast, GPx3 concentrations were repressed in newborns who received betamethasone < or =24h before birth. GPx3 and MDA concentrations were correlated (r=-0.38, p<0.001). Labor, GA, sex, size at birth, blood gases or metabolic indices did not explain the effects of betamethasone on MDA and GPx3.

CONCLUSIONS

Antenatal GC elicit a rapid suppression of the GPx3 antioxidant defense system which may contribute to a longer-lasting but also transient rise in lipid oxidative damage.

Antenatal glucocorticoid therapy increases glucose delivery to cerebral circulations during acute hypoxemia in fetal sheep during late gestation

OBJECTIVE

To determine the effects of 2 maternal injections with dexamethasone on the calculated oxygen and glucose deliveries to fetal cerebral and peripheral circulations during acute hypoxemia in sheep.

STUDY DESIGN

Beginning at 124 days, ewes received 2 intramuscular injections of either dexamethasone (2 x 12 mg, n = 10) or saline solution (2 x 2 mL, n = 12) 24 hours apart. Hypoxemia (1 hour) was induced 32 hours after the first injection (H1) and 3 days after the second (H2).

RESULTS

In saline solution-treated fetuses, glucose delivery was unchanged or increased in femoral and carotid circulations, respectively, during H1 and H2. In dexamethasone-treated fetuses, the increase in glucose delivery to the head tended to be greater during H1 and was significantly enhanced in dexamethasone- vs saline solution-treated fetuses during H2.

CONCLUSION

Two maternal injections with dexamethasone significantly enhanced glucose delivery to the head during acute hypoxemia in the ovine fetus.