Glucocorticoid treatment does not alter early cardiac adaptations to growth restriction in preterm sheep fetuses

Prenatal interventions for fetal growth restriction in animal models: A systematic review

Fetal growth restriction (FGR) in human pregnancy is associated with perinatal mortality, short- and long-term morbidities. No prenatal therapy is currently established despite decades of research. We aimed to review interventions in animal models for prenatal FGR treatment, and to seek the next steps for an effective clinical therapy. We registered our protocol and searched MEDLINE, Embase, and The Cochrane Library with no language restrictions, in accordance with the PRISMA guideline. We included all studies that reported the effects of any prenatal intervention in animal models of induced FGR. From 3257 screened studies, 202 describing 237 interventions were included for the final synthesis. Mice and rats were the most used animals (79%) followed by sheep (16%). Antioxidants (23%), followed by vasodilators (18%), nutrients (14%), and immunomodulators (12%) were the most tested therapy. Two-thirds of studies only reported delivery or immediate neonatal outcomes. Adverse effects were rarely reported (11%). Most studies (73%), independent of the intervention, showed a benefit in fetal survival or birthweight. The risk of bias was high, mostly due to the lack of randomization, allocation concealment, and blinding. Future research should aim to describe both short- and long-term outcomes across various organ systems in well-characterized models. Further efforts must be made to reduce selection, performance, and detection bias.

Effect of Preterm Birth on Cardiac and Cardiomyocyte Growth and the Consequences of Antenatal and Postnatal Glucocorticoid Treatment

Preterm birth coincides with a key developmental window of cardiac growth and maturation, and thus has the potential to influence long-term cardiac function. Individuals born preterm have structural cardiac remodelling and altered cardiac growth and function by early adulthood. The evidence linking preterm birth and cardiovascular disease in later life is mounting. Advances in the perinatal care of preterm infants, such as glucocorticoid therapy, have improved survival rates, but at what cost? This review highlights the short-term and long-term impact of preterm birth on the structure and function of the heart and focuses on the impact of antenatal and postnatal glucocorticoid treatment on the immature preterm heart.

Myocardial function in late preterm infants during the transitional period: comprehensive appraisal with deformation mechanics and non-invasive cardiac output monitoring

BACKGROUND

There is a paucity of functional data on mid-to-late preterm infants between 30+0 and 34+6 weeks gestation. We aimed to characterise transitional cardiopulmonary and haemodynamic changes during the first 48 hours in asymptomatic mid-to-late preterm infants.

METHODS

Forty-five healthy preterm newborns (mean ± standard deviation) gestation of 32.7 ± 1.2 weeks) underwent echocardiography on Days 1 and 2. Ventricular mechanics were assessed by speckle tracking-derived deformation, rotational mechanics, tissue Doppler imaging, and right ventricle-focused measures (tricuspid annular plane systolic excursion, fractional area change). Continuous haemodynamics were assessed using the NICOM™ system to obtain left ventricular output, stroke volume, heart rate, and total peripheral resistance by non-invasive cardiac output monitoring.

RESULTS

Right ventricular function increased (all measures p < 0.005) with mostly stable left ventricular performance between Day 1 and Day 2. NICOM-derived left ventricular output [mean 34%, 95% confidence interval 21-47%] and stroke volume [29%, 16-42%] increased with no change in heart rate [5%, -2 to 12%]. There was a rise in mean blood pressure [11%, 1-21%], but a decline in total peripheral resistance [-14%, -25 to -3%].

CONCLUSION

Left ventricular mechanics remained persevered in mid-to-late premature infants, but right ventricular function increased. Non-invasive cardiac output monitoring is feasible in preterm infants with an increase in left ventricular output driven by an improvement in stroke volume during the transitional period.

Expression of eight glucocorticoid receptor isoforms in the human preterm placenta vary with fetal sex and birthweight

INTRODUCTION

Administration of betamethasone to women at risk of preterm delivery is known to be associated with reduced fetal growth via alterations in placental function and possibly direct effects on the fetus. The placental glucocorticoid receptor (GR) is central to this response and recent evidence suggests there are numerous isoforms for GR in term placentae. In this study we have questioned whether GR isoform expression varies in preterm placentae in relation to betamethasone exposure, fetal sex and birthweight.

METHODS

Preterm (24-36 completed weeks of gestation, n = 55) and term placentae (>37 completed weeks of gestation, n = 56) were collected at delivery. Placental GR expression was examined using Western Blot and analysed in relation to gestational age at delivery, fetal sex, birthweight and betamethasone exposure. Data was analysed using non-parametric tests.

RESULTS

Eight known isoforms of the GR were detected in the preterm placenta and include GRα (94 kDa), GRβ (91 kDa), GRα C (81 kDa) GR P (74 kDa) GR A (65 kDa), GRα D1-3 (50-55 kDa). Expression varied between preterm and term placentae with a greater expression of GRα C in preterm placentae relative to term placentae. The only sex differences in preterm placentae was that GRα D2 expression was higher in males than females. There were no alterations in preterm placental GR expression in association with betamethasone exposure.

DISCUSSION

GRα C is the isoform involved in glucocorticoid induced apoptosis and suggests that its predominance in preterm placentae may contribute to the pathophysiology of preterm birth.

Effects of intrauterine growth restriction on sleep and the cardiovascular system: The use of melatonin as a potential therapy?

Intrauterine growth restriction (IUGR) complicates 5-10% of pregnancies and is associated with increased risk of preterm birth, mortality and neurodevelopmental delay. The development of sleep and cardiovascular control are closely coupled and IUGR is known to alter this development. In the long-term, IUGR is associated with altered sleep and an increased risk of hypertension in adulthood. Melatonin plays an important role in the sleep-wake cycle. Experimental animal studies have shown that melatonin therapy has neuroprotective and cardioprotective effects in the IUGR fetus. Consequently, clinical trials are currently underway to assess the short and long term effects of antenatal melatonin therapy in IUGR pregnancies. Given melatonin's role in sleep regulation, this hormone could affect the developing infants' sleep-wake cycle and cardiovascular function after birth. In this review, we will 1) examine the role of melatonin as a therapy for IUGR pregnancies and the potential implications on sleep and the cardiovascular system; 2) examine the development of sleep-wake cycle in fetal and neonatal life; 3) discuss the development of cardiovascular control during sleep; 4) discuss the effect of IUGR on sleep and the cardiovascular system and 5) discuss the future implications of melatonin therapy in IUGR pregnancies.

Exposure to intrauterine inflammation leads to impaired function and altered structure in the preterm heart of fetal sheep

Intrauterine inflammation gives rise to a reduction in the number and an increase in maturity of cardiac cells in the hearts of fetal lambs. This was accompanied by suppression of contractile function and enhanced vulnerability of the heart to reperfusion injury and stress.

Maternal melatonin administration mitigates coronary stiffness and endothelial dysfunction, and improves heart resilience to insult in growth restricted lambs

Intrauterine growth restriction (IUGR) is associated with impaired cardiac function in childhood and is linked to short- and long-term morbidities. Placental dysfunction underlies most IUGR, and causes fetal oxidative stress which may impact on cardiac development. Accordingly, we investigated whether antenatal melatonin treatment, which possesses antioxidant properties, may afford cardiovascular protection in these vulnerable fetuses. IUGR was induced in sheep fetuses using single umbilical artery ligation on day 105-110 of pregnancy (term 147). Study 1: melatonin (2 mg h(-1)) was administered i.v. to ewes on days 5 and 6 after surgery. On day 7 fetal heart function was assessed using a Langendorff apparatus. Study 2: a lower dose of melatonin (0.25 mg h(-1)) was administered continuously following IUGR induction and the ewes gave birth normally at term. Lambs were killed when 24 h old and coronary vessels studied. Melatonin significantly improved fetal oxygenation in vivo. Contractile function in the right ventricle and coronary flow were enhanced by melatonin. Ischaemia-reperfusion-induced infarct area was 3-fold greater in IUGR hearts than in controls and this increase was prevented by melatonin. In isolated neonatal coronary arteries, endothelium-dependent nitric oxide (NO) bioavailability was reduced in IUGR, and was rescued by modest melatonin treatment. Melatonin exposure also induced the emergence of an indomethacin-sensitive vasodilation. IUGR caused marked stiffening of the coronary artery and this was prevented by melatonin. Maternal melatonin treatment reduces fetal hypoxaemia, improves heart function and coronary blood flow and rescues cardio-coronary deficit induced by IUGR.

Short- and long-term effects of exposure to natural and synthetic glucocorticoids during development

1.Glucocorticoids (GCs) are necessary for fetal development, but clinical and experimental studies suggest that excess exposure may be detrimental to health in both the short and longer term. 2.Exposure of the fetus to synthetic GCs can occur if the mother has a medical condition requiring GC therapy (e.g. asthma) or if she threatens to deliver her baby prematurely. Synthetic GCs can readily cross the placenta and treatment is beneficial, at least in the short term, for maternal health and fetal survival. 3.Maternal stress during pregnancy can raise endogenous levels of the natural GC cortisol. A significant proportion of the cortisol is inactivated by the placental 'GC barrier'. However, exposure to severe stress during pregnancy can result in increased risk of miscarriage, low birth weight and behavioural deficits in children. 4.Animal studies have shown that excess exposure to both synthetic and natural GCs can alter normal organ development, including that of the heart, brain and kidney. The nature and severity of the organ impairment is dependent upon the timing of exposure and, in some cases, the type of GC used and the sex of the fetus. 5.In animal models, exposure to elevated GCs during pregnancy has been associated with adult-onset diseases, including elevated blood pressure, impaired cardiac and vascular function and altered metabolic function.

Placental P-glycoprotein is unaffected by timing of antenatal glucocorticoid therapy but reduced in SGA preterm infants

INTRODUCTION

The beneficial effects of antenatal glucocorticoid therapy on fetal lung maturation require their passage across the placental glucocorticoid barrier, composed of glucocorticoid metabolising enzymes, such as 11 beta hydroxysteroid dehydrogenase (11βHSD), and proteins that efflux glucocorticoids, such as P-glycoprotein (P-gp). We have shown that 11βHSD2 activity is responsive to antenatal glucocorticoids, however the effect on placental P-gp remains unknown. Since antenatal glucocorticoids have a greater prophylactic effect in females compared to males, we also assessed whether this therapy induced sexually dimorphic effects on P-gp expression, as well as on placental inflammatory processes mediated by corticosteroids.

METHODS

Placentas were collected from 53 women presenting in threatened preterm labour, and processed to assess cytokine and P-gp mRNA expression, as well as P-gp localisation using immunohistochemistry.

RESULTS

Placental cytokine, P-gp mRNA and protein expression were not altered by timing of antenatal glucocorticoids or fetal sex. However, both P-gp mRNA and protein expression were significantly reduced in placentas from infants born small for gestational age (SGA) compared to appropriately grown infants (p < 0.05), suggesting a role for P-gp in its pathogenesis via the provision of a net increase in fetal exposure to bioactive exogenous glucocorticoids.

CONCLUSIONS

While this study identified no change in placental P-gp following antenatal glucocorticoids, it has provided evidence that P-gp plays an important role in cases of SGA. This supports the known mechanistic relationship between antenatal glucocorticoids, fetal development and the postnatal phenotype. Given that P-gp also confers fetal protection from a number of drugs, this finding warrants further investigation to improve clinical management of the SGA fetus.