Maternal sildenafil impairs the cardiovascular adaptations to chronic hypoxaemia in fetal sheep

Thrombopoietin exerts a neuroprotective effect by inhibiting the suppression of neuronal proliferation and axonal outgrowth in intrauterine growth restriction rats

Chronic hypoxia in utero causes intrauterine growth restriction (IUGR) of the fetus. IUGR infants are known to be at higher risk for neurodevelopmental disorders, but the mechanism is unclear. In this study, we analyzed the structure of the cerebral cortex using IUGR model rats generated through a reduced uterine perfusion pressure operation. IUGR rats exhibited thinner cerebral white matter and enlarged lateral ventricles compared with control rats. Expression of neuron cell markers, Satb2, microtubule-associated protein (MAP)-2, α-tubulin, and nestin was reduced in IUGR rats, indicating that neurons were diminished at various developmental stages in IUGR rats, from neural stem cells to mature neurons. However, there was no increase in apoptosis in IUGR rats. Cells positive for Ki67, a marker of cell proliferation, were reduced in neurons and all glial cells of IUGR rats. In primary neuron cultures, axonal elongation was impaired under hypoxic culture conditions mimicking the intrauterine environment of IUGR infants. Thus, in IUGR rats, chronic hypoxia in utero suppresses the proliferation of neurons and glial cells as well as axonal elongation, resulting in cortical thinning and enlarged lateral ventricles. Thrombopoietin (TPO), a platelet growth factor, inhibited the decrease in neuron number and promoted axon elongation in primary neurons under hypoxic conditions. Intraperitoneal administration of TPO to IUGR rats resulted in increases in the number of NeuN-positive cells and the area coverage of Satb2. In conclusion, suppression of neuronal proliferation and axonal outgrowth in IUGR rats resulted in cortical thinning and enlargement of lateral ventricles. TPO administration might be a novel therapeutic strategy for treating brain dysmaturation in IUGR infants.

Maternal tadalafil treatment does not increase uterine artery blood flow or oxygen delivery in the pregnant ewe

Increasing placental perfusion (PP) could improve outcomes of growth-restricted fetuses. One way of increasing PP may be by using phosphodiesterase (PDE)-5 inhibitors, which induce vasodilatation of vascular beds. We used a combination of clinically relevant magnetic resonance imaging (MRI) techniques to characterize the impact that tadalafil infusion has on maternal, placental and fetal circulations. At 116-117 days' gestational age (dGA; term, 150 days), pregnant ewes (n = 6) underwent fetal catheterization surgery. At 120-123 dGA ewes were anaesthetized and MRI scans were performed during three acquisition windows: a basal state and then ∼15-75 min (TAD 1) and ∼75-135 min (TAD 2) post maternal administration (24 mg; intravenous bolus) of tadalafil. Phase contrast MRI and T2 oximetry were used to measure blood flow and oxygen delivery. Placental diffusion and PP were assessed using the Diffusion-Relaxation Combined Imaging for Detailed Placental Evaluation-'DECIDE' technique. Uterine artery (UtA) blood flow when normalized to maternal left ventricular cardiac output (LVCO) was reduced in both TAD periods. DECIDE imaging found no impact of tadalafil on placental diffusivity or fetoplacental blood volume fraction. Maternal-placental blood volume fraction was increased in the TAD 2 period. FetalD O 2 ${D_{{{\mathrm{O}}_2}}}$ andV ̇ O 2 ${\dot V_{{{\mathrm{O}}_2}}}$ were not affected by maternal tadalafil administration. Maternal tadalafil administration did not increase UtA blood flow and thus may not be an effective vasodilator at the level of the UtAs. The increased maternal-placental blood volume fraction may indicate local vasodilatation of the maternal intervillous space, which may have compensated for the reduced proportion of UtAD O 2 ${D_{{{\mathrm{O}}_2}}}$ .

A liquid chromatographic-mass spectrometric procedure for analysis of pentaerythrityl tetranitrate metabolites - Development, validation and application to ovine serum and human plasma samples

Pentaerythrityl tetranitrate (PETN) is an established drug in the treatment of coronary heart disease and heart failure. It is assumed, that the vasodilative and vasoprotective effects of PETN also have a positive impact on pregnant patients with impaired placental perfusion and studies evaluating the effect of PETN in risk pregnancies have been carried out. In the context of these clinical trials, measuring of serum levels of PETN and its metabolites pentaerythrityl trinitrate (PETriN), pentaerythrityl dinitrate (PEDN), pentaerythrityl mononitrate (PEMN) and pentaerythritol (PE) were required. To evaluate the transfer of PETN and its metabolites (PEXN) from the mother to the fetus using samples from a human clinical trial and animal study, the present work aimed to develop a rapid and simple method to simultaneously analyze PEXN in human and ovine samples. A method employing a rapid and simple liquid-liquid extraction followed by reversed-phase (C18) liquid chromatography coupled to high-resolution mass spectrometry with negative electrospray ionization was developed and validated for the detection of PETN and PEXN in human and ovine samples. PE could only be qualitatively detected at higher concenrations. Method validation requirements, including accuracy, repeatability and intermediate precision were fulfilled in ovine and human samples for all other PEXN with exception PETriN in human samples. The recovery (RE) in ovine samples was 76.7 % ± 12 % for PEMN, 98 % ± 23 % for PEDN, 94 % ± 22 % for PETriN, in human samples RE was 59 % ± 16 % for PEMN, 67 % ± 19 % for PEDN, 71 % ± 17 %. The matrix effects (ME) in ovine samples were 90 % ± 11 % for PEMN, 70 % ± 30 % for PEDN, 107 % ± 17 % for PETriN, in human samples the ME were 93 % ± 13 % for PEMN, 84 % ± 17 % for PEDN, 98 % ± 16 % for PETriN. The limits of quantification (LOQ) in ovine samples were 1.0 ng/mL for PETriN and 0.1 ng/mL for PEMN and PEDN. The LOQs in human samples were 5.0 ng/mL for PETriN and 0.3 ng/mL for PEMN und PEDN. The newly developed method was used to analyze 184 ovine serum samples and 18 human plasma samples. In ovine maternal samples, the highest observed PEDN concentration was 3.5 ng/mL and the highest PEMN concentration was 10 ng/mL, the respective concentrations in fetal serum samples were 4.9 ng/mL for PEDN and 5.4 ng/mL for PEMN. PETriN was only detected in traces in maternal and fetal samples, whereas PETN could not be detected at all. In human maternal samples, the highest concentration for PEDN was 27 ng/mL and for PEMN 150 ng/mL. In umbilical cord plasma, concentrations of 2.3 ng/mL for PEDN and 73 ng/mL for PEMN were detected. Although the PEMN and PEDN concentrations in the human samples were several times higher than in ovine samples, neither PETN nor PETriN signals could be detected. These results demonstrated that the metabolites were transferred from mother to fetus with a slight time delay.

Sildenafil during the 2nd and 3rd Trimester of Pregnancy: Trials and Tribulations

Sildenafil, a phosphodiesterase 5 inhibitor with a vasodilatory and anti-remodeling effect, has been investigated concerning various conditions during pregnancy. Per indication, we herein review the rationale and the most relevant experimental and clinical studies, including systematic reviews and meta-analyses, when available. Indications for using sildenafil during the second and third trimester of pregnancy include maternal pulmonary hypertension, preeclampsia, preterm labor, fetal growth restriction, oligohydramnios, fetal distress, and congenital diaphragmatic hernia. For most indications, the rationale for administering prenatal sildenafil is based on limited, equivocal data from in vitro studies and rodent disease models. Clinical studies report mild maternal side effects and suggest good fetal tolerance and safety depending on the underlying pathology.

Size-dependent placental retention effect of liposomes in ICR pregnant mice: Potential superiority in placenta-derived disease therapy

The great challenge in developing safe medications for placenta-derived diseases is to reduce or eliminate fetal drug exposure while still providing the necessary therapeutic effect. Rapid advances in nanotechnology have brought opportunities for the therapy of placenta-derived disease through accumulating the drug in the placenta while reducing its placental penetration. Among various nanocarriers, liposomes are regarded as an ideal type of carrier for placental drug delivery due to their biosafety and biodegradability. However, their placental retention effect with different particle sizes has not been studied. This research aimed to explore a suitable size of liposomes for placenta drug delivery. Cy 5 dye was chosen as a model molecule for tracing the distribution of three different-sized liposomes (∼80 nm, 200 nm, and 500 nm) in ICR pregnant mice. The stability, cytotoxicity, and cellular uptake study of Cy 5-loaded liposomes were performed. The in vivo fluorescence studies on ICR pregnant mice suggested that the particle size of liposomes was positively correlated with the degree of liposome aggregation in the placenta. The ratio of fluorescence in the placenta and fetus section (P/F value) was proposed to evaluate the placental retention effect of different-sized liposomes. The results showed that the liposomes with 500 nm had the highest P/F value and thus exhibited the strongest placental retention effect and the weakest placental penetration ability. Moreover, liquid chromatography-mass spectrometry analysis confirmed the reliability of the fluorescence section analysis in exploring the placental retention effect of nanovehicles. In general, this study introduced a simple and intuitive method to evaluate the placental retention effect of nanoplatforms and defined a suitable size of liposomes for placenta-derived disease drug delivery.

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.

Pharmacokinetics and pharmacodynamics of sildenafil in fetal lambs on extracorporeal support

BACKGROUND

Maternal transplacental administration of sildenafil is being considered for a variety of fetal conditions. Clinical translation also requires evaluation of fetal safety in a higher species, such as the fetal lamb. Experiments with the pregnant ewe are curtailed by minimal transplacental transfer as well as limited access to the fetus. The EXTra-uterine Environment for Neonatal Development (EXTEND) model renders the isolated fetal lamb readily accessible and allows for direct fetal administration of sildenafil.

METHODS

Five fetal lambs were placed on extracorporeal support in the EXTEND device and received continuous intravenous (IV) sildenafil (0.3-0.5-0.7 mg/kg/24hr) for a duration of one to seven days. Plasma sildenafil concentrations were sampled at regular intervals to establish the pharmacokinetic profile using population pharmacokinetic modeling. Serial Doppler ultrasound examination, continuous non-invasive hemodynamic monitoring and blood gas analysis were done to evaluate the pharmacodynamic effects and fetal response.

FINDINGS

The target concentration range (47-500 ng/mL) was attained with all doses. Sildenafil induced an immediate and temporary reduction of pulmonary vascular resistance, mean arterial pressure and circuit flow, without change in fetal lactate levels and acid-base status. The duration of the systemic effects increased with the dose.

INTERPRETATION

Immediate temporary pulmonary vascular and systemic hemodynamic changes induced by sildenafil were biochemically well tolerated by fetal lambs on extracorporeal support, with the 0.5 mg/kg/24 h dose balancing rapid attainment of target concentrations with short-lived systemic effects.

RESEARCH IN CONTEXT

None.

SEARCH STRATEGY BEFORE UNDERTAKING THE STUDY

A literature review was conducted searching online databases (Medline, Embase and Cochrane), using search terms: fetal OR prenatal OR antenatal AND sildenafil, without time-limit and excluding human studies. Where relevant, investigators were contacted in order to avoid duplication of work.

EVIDENCE BEFORE THIS STUDY

Prenatal therapy with sildenafil, a phosphodiesterase-5 inhibitor with vasodilatory and anti-remodeling effects on vascular smooth muscle cells, has been considered for a variety of fetal conditions. One multicenter clinical trial investigating the benefit of sildenafil in severe intrauterine growth restriction (the STRIDER-trial) was halted early due to excess mortality in the sildenafil-exposed arm at one treatment site. Such findings demonstrate the importance of extensive preclinical safety assessment in relevant animal models. Transplacentally administered sildenafil leads to decreased pulmonary arterial muscularization, preventing or reducing the occurrence of pulmonary hypertension in rat and rabbit fetuses with diaphragmatic hernia (DH). Validation of these results in a higher and relevant animal model, e.g. fetal lambs, is the next step to advance clinical translation. We recently demonstrated that, in contrast to humans, transplacental transfer of sildenafil in sheep is minimal, precluding the in vivo study of fetal effects at target concentrations using the conventional pregnant ewe model.

ADDED VALUE OF THIS STUDY

We therefore used the extracorporeal support model for fetal lambs, referred to as the EXTra-uterine Environment for Neonatal Development (EXTEND) system, bypassing placental and maternal metabolism, to investigate at what dose the target concentrations are reached, and what the fetal hemodynamic impact and response are. Fetal hemodynamic and metabolic tolerance to sildenafil are a crucial missing element on the road to clinical translation. This is therefore the first study investigating the pharmacokinetics, hemodynamic and biochemical effects of clinical-range concentrations of sildenafil in fetal lambs, free from placental and maternal interference.

IMPLICATIONS OF ALL THE AVAILABLE EVIDENCE

We demonstrated self-limiting pulmonary vasodilation, a decrease of both systemic arterial pressures and circuit flows, induced by clinical range concentrations of sildenafil, without the development of fetal acidosis. This paves the way for further investigation of prenatal sildenafil in fetal lambs on extracorporeal support. A dose of 0.5 mg/kg/24 h offered the best trade-off between rapid achievement of target concentrations and shortest duration of systemic effects. This is also the first study using the EXTEND as a model for pharmacotherapy during pregnancy.

Decreased Cyclic GMP-protein Kinase G signaling impairs Angiogenesis in a Lamb Model of Persistent Pulmonary Hypertension of Newborn

Impaired angiogenesis function of pulmonary artery endothelial cells (PAEC) contributes to persistent pulmonary hypertension of the newborn (PPHN). Decreased nitric oxide (NO) levels in PPHN lead to impaired mitochondrial biogenesis and angiogenesis in the lung; the mechanisms remain unclear. We hypothesized that decreased cGMP-Protein kinase G (PKG) signaling downstream of NO leads to decreased mitochondrial biogenesis and angiogenesis in PPHN. PPHN was induced by ductus arteriosus constriction from 128-136d gestation in fetal lambs. Controls were gestation matched lambs without ductal constriction. PAEC isolated from PPHN lambs were treated with soluble guanylyl cyclase activator, cinaciguat, PKG activator, 8-Br-cGMP or phosphodiesterase-V inhibitor, sildenafil. Lysates were immunoblotted for mitochondrial transcription factors and electron transport chain (ETC) complex proteins I-V. In vitro angiogenesis of PAEC was evaluated by tube formation and scratch recovery assays. cGMP levels were measured by enzyme immunoassay. Fetal lambs with ductal constriction were given sildenafil or control saline by continuous infusion in utero and lung histology, capillary counts, vessel density and right ventricular pressure were assessed at birth. PPHN PAEC showed decreased mitochondrial transcription factors, ETC proteins, and in vitro tube formation and cell migration; these were restored by cinaciguat, 8-Br-cGMP and sildenafil. Cinaciguat and sildenafil increased cGMP levels in PPHN PAEC. Radial alveolar and capillary counts and vessel density were lower and RV pressure and Fulton index higher in PPHN lungs; these were improved by in utero sildenafil infusion. cGMP-PKG signaling is a potential therapeutic target to restore decreased mitochondrial biogenesis and angiogenesis in PPHN.

The cerebral haemodynamic response to somatosensory stimulation in preterm newborn lambs is reduced with dopamine or dobutamine infusion

BACKGROUND

In the adult brain, increases in neural activity lead to increases in local blood flow. However, in the preterm neonate, studies of cerebral functional haemodynamics have yielded inconsistent results, including negative responses suggesting decreased perfusion and localised tissue hypoxia, probably due to immature neurovascular coupling. Furthermore, the impact of vasoactive medications, such as dopamine and dobutamine used as inotropic therapies in preterm neonates, on cerebrovascular responses to somatosensory input is unknown. We aimed to characterise the cerebral haemodynamic functional response after somatosensory stimulation in the preterm newborn brain, with and without dopamine or dobutamine treatment.

METHODS

We studied the cerebral haemodynamic functional response in 13 anaesthetised preterm lambs, using near infrared spectroscopy to measure changes in cerebral oxy- and deoxyhaemoglobin (ΔoxyHb, ΔdeoxyHb) following left median nerve stimulation using stimulus trains of 1.8, 4.8 and 7.8 s. The 4.8 and 7.8 s stimulations were repeated during dopamine or dobutamine infusion.

RESULTS

Stimulation always produced a somatosensory evoked response. Majority of preterm lambs demonstrated positive functional responses (i.e. increased ΔoxyHb) in the contralateral cortex following stimulus trains of all durations. Dopamine increased baseline oxyHb and total Hb, whereas dobutamine increased baseline deoxyHb. Both dopamine and dobutamine reduced the evoked ΔoxyHb responses to 4.8 and 7.8 s stimulations.

CONCLUSIONS

Somatosensory stimulation increases cerebral oxygenation in the preterm brain, consistent with increased cerebral blood flow due to neurovascular coupling. Notably, our results show that dopamine/dobutamine reduces oxygen delivery relative to consumption in the preterm brain during somatosensory stimulations, suggesting there may be a risk of intermittent localised tissue hypoxia which has clear implications for clinical practice and warrants further investigation.

Adaptations of the human placenta to hypoxia: opportunities for interventions in fetal growth restriction

BACKGROUND

The placenta is the functional interface between the mother and the fetus during pregnancy, and a critical determinant of fetal growth and life-long health. In the first trimester, it develops under a low-oxygen environment, which is essential for the conceptus who has little defense against reactive oxygen species produced during oxidative metabolism. However, failure of invasive trophoblasts to sufficiently remodel uterine arteries toward dilated vessels by the end of the first trimester can lead to reduced/intermittent blood flow, persistent hypoxia and oxidative stress in the placenta with consequences for fetal growth. Fetal growth restriction (FGR) is observed in ∼10% of pregnancies and is frequently seen in association with other pregnancy complications, such as preeclampsia (PE). FGR is one of the main challenges for obstetricians and pediatricians, as smaller fetuses have greater perinatal risks of morbidity and mortality and postnatal risks of neurodevelopmental and cardio-metabolic disorders.

OBJECTIVE AND RATIONALE

The aim of this review was to examine the importance of placental responses to changing oxygen environments during abnormal pregnancy in terms of cellular, molecular and functional changes in order to highlight new therapeutic pathways, and to pinpoint approaches aimed at enhancing oxygen supply and/or mitigating oxidative stress in the placenta as a mean of optimizing fetal growth.

SEARCH METHODS

An extensive online search of peer-reviewed articles using PubMed was performed with combinations of search terms including pregnancy, placenta, trophoblast, oxygen, hypoxia, high altitude, FGR and PE (last updated in May 2020).

OUTCOMES

Trophoblast differentiation and placental establishment are governed by oxygen availability/hypoxia in early pregnancy. The placental response to late gestational hypoxia includes changes in syncytialization, mitochondrial functions, endoplasmic reticulum stress, hormone production, nutrient handling and angiogenic factor secretion. The nature of these changes depends on the extent of hypoxia, with some responses appearing adaptive and others appearing detrimental to the placental support of fetal growth. Emerging approaches that aim to increase placental oxygen supply and/or reduce the impacts of excessive oxidative stress are promising for their potential to prevent/treat FGR.

WIDER IMPLICATIONS

There are many risks and challenges of intervening during pregnancy that must be considered. The establishment of human trophoblast stem cell lines and organoids will allow further mechanistic studies of the effects of hypoxia and may lead to advanced screening of drugs for use in pregnancies complicated by placental insufficiency/hypoxia. Since no treatments are currently available, a better understanding of placental adaptations to hypoxia would help to develop therapies or repurpose drugs to optimize placental function and fetal growth, with life-long benefits to human health.

The reliance on α-adrenergic receptor stimuli for blood pressure regulation in the chronically hypoxaemic fetus is not dependent on post-ganglionic activation

KEY POINTS

Chronic hypoxaemia is associated with intrauterine growth restriction (IUGR) and a predisposition to the development of hypertension in adult life. IUGR fetuses exhibit a greater reliance on α-adrenergic activation for blood pressure regulation. The fetal blood pressure response to post-ganglionic blockade is not different between control and IUGR fetuses. The decrease in mean arterial pressure is greater in the IUGR sheep fetus after α-adrenergic receptor blockade at the level of the vasculature and this is inversely related to fetal P O 2 . The increased reliance that the IUGR fetus has on α-adrenergic activation for maintenance of mean arterial pressure is not a result of increased post-ganglionic sympathetic activation.

ABSTRACT

Intrauterine growth restriction (IUGR) is associated with an increased risk of cardiovascular disease in adult life. Placental restriction (PR) in sheep results in chronic hypoxaemia and early onset IUGR with increased circulating plasma noradrenaline concentrations. These IUGR fetuses exhibit a greater decrease in mean arterial pressure (MAP) during α-adrenergic blockade. We aimed to determine the role of post-ganglionic sympathetic activation with respect to regulating MAP in IUGR fetal sheep. PR was induced by carunclectomy surgery prior to conception. Fetal vascular catheterization was performed at 110-126 days gestational age (GA) (term, 150 days) in nine control and seven PR-IUGR fetuses. The fetal blood pressure response to both a post-ganglionic and an α-adrenergic receptor blocker was assessed at 116-120 days GA and/or 129-131 days GA. The effect of both post ganglionic and α-adrenergic blockade on fetal blood pressure was then compared between control and IUGR fetuses at both GAs. There was no difference in the effect of post-ganglionic blockade on MAP in control and IUGR fetal sheep at either 116-120 days GA or 129-131 days GA. α-adrenergic receptor blockade decreased MAP to the same extent in both control and IUGR fetuses at 116-120 days GA. At 129-131 days GA, the drop in MAP in response to α-adrenergic receptor blockade was greater in IUGR fetuses than controls. There was a significant inverse relationship between the drop in MAP in response to α-adrenergic receptor blockade at both GAs with fetal P O 2 . Thus, the increased dependence on α-adrenergic activation for blood pressure regulation in the chronically hypoxaemic IUGR fetus is not a result of increased post-ganglionic sympathetic activation.