Milestones for clinical translation of the artificial placenta

β3-Adrenoceptor Agonism to Mimic the Biological Effects of Intrauterine Hypoxia: Taking Great Strides Toward a Pharmacological Artificial Placenta

At different stages of life, from embryonic to postnatal, varying oxygen concentrations modulate cellular gene expression by enhancing or repressing hypoxia-inducible transcription factors. During embryonic/fetal life, these genes encode proteins involved in adapting to a low-oxygen environment, including the induction of specific enzymes related to glycolytic metabolism, erythropoiesis, angiogenesis, and vasculogenesis. However, oxygen concentrations fluctuate during intrauterine life, enabling the induction of tissue-specific differentiation processes. Fetal well-being is thus closely linked to the physiological benefits of a dynamically hypoxic environment. Premature birth entails the precocious exposure of the immature fetus to a more oxygen-rich environment compared to the womb. As a result, preterm newborns face a condition of relative hyperoxia, which alters the postnatal development of organs and contributes to prematurity-related diseases. However, until recently, the molecular mechanism by which high oxygen tension alters normal fetal differentiation remained unclear. In this review, we discuss the research trajectory followed by our research group, which suggests that early exposure to a relatively hyperoxic environment may impair preterm neonates due to reduced expression of the β3-adrenoceptor. Additionally, we explore how these impairments could be prevented through the pharmacological stimulation of the remaining β3-adrenoceptors. Recent preclinical studies demonstrate that pharmacological stimulation of the β3-adrenoceptor can decouple exposure to hyperoxia from its harmful effects, offering a glimpse of the possibility to recreating the conditions typical of intrauterine life, even after premature birth.

Cardiorespiratory interactions during the transitional period in extremely preterm infants: a narrative review

We aimed to review the physiology and evidence behind cardiorespiratory interactions during the transitional circulation of extremely preterm infants with fragile physiology and to propose a framework for future research. Cord clamping strategies have a great impact on initial haemodynamic changes, and appropriate transition can be facilitated by establishing spontaneous ventilation before cord clamping. Mechanical ventilation modifies preterm transitional haemodynamics, with positive pressure ventilation affecting the right and left heart loading conditions. Pulmonary vascular resistances can be minimized by ventilating with optimal lung volumes at functional residual capacity, and other pulmonary vasodilator treatments such as inhaled nitric oxide can be used to improve ventilation/perfusion mismatch. Different cardiovascular drugs can be used to provide support during transition in this population, and it is important to understand both their cardiovascular and respiratory effects, in order to provide adequate support to vulnerable preterm infants and improve outcomes. Current available non-invasive bedside tools, such as near-infrared spectroscopy, targeted neonatal echocardiography, or lung ultrasound offer the opportunity to precisely monitor cardiorespiratory interactions in preterm infants. More research is needed in this field using precision medicine to strengthen the benefits and avoid the harms associated to early neonatal interventions. IMPACT: In extremely preterm infants, haemodynamic and respiratory transitions are deeply interconnected, and their changes have a key impact in the establishment of lung aireation and postnatal circulation. We describe how mechanical ventilation modifies heart loading conditions and pulmonary vascular resistances in preterm patients, and how hemodynamic interventions such as cord clamping strategies or cardiovascular drugs affect the infant respiratory status. Current available non-invasive bedside tools can help monitor cardiorespiratory interactions in preterm infants. We highlight the areas of research in which precision medicine can help strengthen the benefits and avoid the harms associated to early neonatal interventions.

Scaled-up Microfluidic Lung Assist Device for Artificial Placenta Application with High Gas Exchange Capacity

Premature neonates with underdeveloped lungs experience respiratory issues and need respiratory support, such as mechanical ventilation or extracorporeal membrane oxygenation (ECMO). The "artificial placenta" (AP) is a noninvasive approach that supports their lungs and reduces respiratory distress, using a pumpless oxygenator connected to the systemic circulation, and can address some of the morbidity issues associated with ECMO. Over the past decade, microfluidic blood oxygenators have garnered significant interest for their ability to mimic physiological conditions and incorporate innovative biomimetic designs. Achieving sufficient gas transfer at a low enough pressure drop for a pumpless operation without requiring a large volume of blood to prime such an oxygenator has been the main challenge with microfluidic lung assist devices (LAD). In this study, we improved the gas exchange capacity of our microfluidic-based artificial placenta-type LAD while reducing its priming volume by using a modified fabrication process that can accommodate large-area thin film microfluidic blood oxygenator (MBO) fabrication with a very high gas exchange surface. Additionally, we demonstrate the effectiveness of a LAD assembled by using these scaled-up MBOs. The LAD based on our artificial placenta concept effectively increases oxygen saturation levels by 30% at a flow rate of 40 mL/min and a pressure drop of 23 mmHg in room air, which is sufficient to support partial oxygenation for 1 kg preterm neonates in respiratory distress. When the gas ambient environment was changed to pure oxygen at atmospheric pressure, the LAD would be able to support premature neonates weighing up to 2 kg. Furthermore, our experiments reveal that the LAD can handle high blood flow rates of up to 150 mL/min and increase oxygen saturation levels by ∼20%, which is equal to an oxygen transfer of 7.48 mL/min in an enriched oxygen environment and among the highest for microfluidic AP type devices. Such performance makes this LAD suitable for providing essential support to 1-2 kg neonates in respiratory distress.

The artificial placenta and EXTEND technologies: one of these things is not like the other

The so called "Artificial Placenta" and "Artificial Womb" (EXTEND) technologies share a common goal of improving outcomes for extreme premature infants. Beyond that goal, they are very dissimilar and, in our view, differ sufficiently in their technology, intervention strategy, demonstrated physiology, and risk profiles that bundling them together for consideration of the ethical challenges in designing first in human trials is misguided. In this response to the commentary by Kukora and colleagues, we will provide our perspective on these differences, and how they impact ethical clinical study design for first-in-human trials of safety/feasibility, and subsequently efficacy of the two technologies.

Fetal Oxygenation from the 23rd to the 36th Week of Gestation Evaluated through the Umbilical Cord Blood Gas Analysis

The embryo and fetus grow in a hypoxic environment. Intrauterine oxygen levels fluctuate throughout the pregnancy, allowing the oxygen to modulate apparently contradictory functions, such as the expansion of stemness but also differentiation. We have recently demonstrated that in the last weeks of pregnancy, oxygenation progressively increases, but the trend of oxygen levels during the previous weeks remains to be clarified. In the present retrospective study, umbilical venous and arterial oxygen levels, fetal oxygen extraction, oxygen content, CO2, and lactate were evaluated in a cohort of healthy newborns with gestational age < 37 weeks. A progressive decrease in pO2 levels associated with a concomitant increase in pCO2 and reduction in pH has been observed starting from the 23rd week until approximately the 33-34th week of gestation. Over this period, despite the increased hypoxemia, oxygen content remains stable thanks to increasing hemoglobin concentration, which allows the fetus to become more hypoxemic but not more hypoxic. Starting from the 33-34th week, fetal oxygenation increases and ideally continues following the trend recently described in term fetuses. The present study confirms that oxygenation during intrauterine life continues to vary even after placenta development, showing a clear biphasic trend. Fetuses, in fact, from mid-gestation to near-term, become progressively more hypoxemic. However, starting from the 33-34th week, oxygenation progressively increases until birth. In this regard, our data suggest that the placenta is the hub that ensures this variable oxygen availability to the fetus, and we speculate that this biphasic trend is functional for the promotion, in specific tissues and at specific times, of stemness and intrauterine differentiation.

Fetal oxygenation in the last weeks of pregnancy evaluated through the umbilical cord blood gas analysis

Introduction

Embryo and fetus grow and mature over the first trimester of pregnancy in a dynamic hypoxic environment, where placenta development assures an increased oxygen availability. However, it is unclear whether and how oxygenation changes in the later trimesters and, more specifically, in the last weeks of pregnancy.

Methods

Observational study that evaluated the gas analysis of the umbilical cord blood collected from a cohort of healthy newborns with gestational age ≥37 weeks. Umbilical venous and arterial oxygen levels as well as fetal oxygen extraction were calculated to establish whether oxygenation level changes over the last weeks of pregnancy. In addition, fetal lactate, and carbon dioxide production were analyzed to establish whether oxygen oscillations may induce metabolic effects in utero.

Results

This study demonstrates a progressive increase in fetal oxygenation levels from the 37th to the 41st weeks of gestation (mean venous PaO₂ approximately from 20 to 25 mmHg; p < 0.001). This increase is largely attributable to growing umbilical venous PaO₂, regardless of delivery modalities. In neonates born by vaginal delivery, the increased oxygen availability is associated with a modest increase in oxygen extraction, while in neonates born by cesarean section, it is associated with reduced lactate production. Independently from the type of delivery, carbon dioxide production moderately increased. These findings suggest a progressive shift from a prevalent anaerobic metabolism (Warburg effect) towards a growing aerobic metabolism.

Conclusion

This study confirms that fetuses grow in a hypoxic environment that becomes progressively less hypoxic in the last weeks of gestation. The increased oxygen availability seems to favor aerobic metabolic shift during the last weeks of intrauterine life; we hypothesize that this environmental change may have implications for fetal maturation during intrauterine life.