The dynamic placenta: II. Hypothetical model of a fetus driven transplacental water balance mechanism producing low apparent permeability in a highly permeable placenta

In Vitro Human Placental Studies to Support Adenovirus-Mediated VEGF-DΔNΔC Maternal Gene Therapy for the Treatment of Severe Early-Onset Fetal Growth Restriction

Severe fetal growth restriction (FGR) affects 1 in 500 pregnancies, is untreatable, and causes serious neonatal morbidity and death. Reduced uterine blood flow (UBF) is one cause. Transduction of uterine arteries in normal and FGR animal models using an adenovirus (Ad) encoding VEGF isoforms increases UBF and improves fetal growth in utero. Understanding potential adverse consequences of this therapy before first-in-woman clinical application is essential. The aims of this study were to determine whether Ad.VEGF-D^ΔNΔC (1) transfers across the human placental barrier and (2) affects human placental morphology, permeability and primary indicators of placental function, and trophoblast integrity. Villous explants from normal term human placentas were treated with Ad.VEGF-D^ΔNΔC (5 × 10^7-10 virus particles [vp]/mL), or virus formulation buffer (FB). Villous structural integrity (hematoxylin and eosin staining) and tissue accessibility (LacZ immunostaining) were determined. Markers of endocrine function (human chorionic gonadotropin [hCG] secretion) and cell death (lactate dehydrogenase [LDH] release) were assayed. Lobules from normal and FGR pregnancies underwent ex vivo dual perfusion with exposure to 5 × 10¹⁰ vp/mL Ad.VEGF-D^ΔNΔC or FB. Perfusion resistance, para-cellular permeability, hCG, alkaline phosphatase, and LDH release were measured. Ad.VEGF-D^ΔNΔC transfer across the placental barrier was assessed by quantitative polymerase chain reaction in DNA extracted from fetal-side venous perfusate, and by immunohistochemistry in fixed tissue. Villous explant structural integrity and hCG secretion was maintained at all Ad.VEGF-D^ΔNΔC doses. Ad.VEGF-D^ΔNΔC perfusion revealed no effect on placental permeability, fetoplacental vascular resistance, hCG secretion, or alkaline phosphatase release, but there was a minor elevation in maternal-side LDH release. Viral vector tissue access in both explant and perfused models was minimal, and the vector was rarely detected in the fetal venous perfusate and at low titer. Ad.VEGF-D^ΔNΔC did not markedly affect human placental integrity and function in vitro. There was limited tissue access and transfer of vector across the placental barrier. Except for a minor elevation in LDH release, these test data did not reveal any toxic effects of Ad.VEGF-D^ΔNΔC on the human placenta.

Ex Vivo Dual Perfusion of the Human Placenta: Disease Simulation, Therapeutic Pharmacokinetics and Analysis of Off-Target Effects

In recent years ex vivo dual perfusion of the human placental lobule is seeing an international renaissance in its application to understanding fetal health and development. Here, we discuss the methods and uses of this technique in the evaluation of (1) vascular function, (2) transplacental clearance, (3) hemodynamic and oxygenation changes associated with pregnancy complications on placental structure and function, and (4) placental toxicology and post-perfusion evaluation of tissue architecture.

Responses of Preterm Pigs to an Oral Fluid Supplement During Parenteral Nutrition

BACKGROUND

Nutrients and electrolytes in amniotic fluid swallowed by fetuses are important for growth and development. Yet, preterm infants requiring parenteral nutrition (PN) receive minimal or no oral inputs. With the limited availability of amniotic fluid, we evaluated the responses of preterm pigs receiving PN to an oral fluid supplement (OFS) based on the electrolyte and nutrient composition of amniotic fluid.

MATERIALS AND METHODS

Preterm pigs (92% of term) received a combination of PN (6 mL/kg-h) and 4 mL/kg-h of supplemental fluid as an experimental OFS (n = 9), lactated Ringer's either enterally (n = 10) or intravenously (n = 8). Outcome measures after 96 hours were weight gain, blood chemistry, organ weights, and small intestine mass and brush-border membrane carbohydrases.

RESULTS

The OFS did not improve weight gain compared with providing lactated Ringer's orally or intravenously, or increase serum urea nitrogen values, but resulted in higher serum total and low-density lipoprotein cholesterol, as well as improved glucoregulation and heavier intestines, livers, kidneys, and brains and lighter lungs.

CONCLUSIONS

Providing supplemental fluid and electrolytes during PN either intravenously or orally increases weight gain after preterm birth. An oral fluid supplement based on amniotic fluid may accelerate development and maturation of organs critical for extrauterine life after preterm birth and may enhance neurodevelopment.

Placental lesions associated with oligohydramnios in fetal growth restricted (FGR) pregnancies

INTRODUCTION

Aim of the study was to investigate the association between placental pathology and oligohydramnios in pregnancies complicated by fetal growth restriction (FGR).

METHODS

Placentas from 221 consecutive FGR pregnancies and 63 healthy controls were studied. Pathological lesions were described according to consensus nomenclature and standardized criteria; both elementary lesions and constellations of lesions (patterns) were considered. Statistics included analysis of linear trends and multinomial logistic regression.

RESULTS

Amniotic fluid index (AFI) was normal in 56 (25.3%) FGR pregnancies, whereas mild, moderate and severe oligohydramnios were diagnosed in 32 (14.5%), 44 (19.9%) and 89 (40.3%) subjects, respectively. In FGR pregnancies, after adjustment for potential confounders, membrane meconium staining (chi-square = 28.6, p < 0.001), chronic villous hypoxia pattern (chi-square = 18.8, p < 0.001) and fetal thrombotic vasculopathy pattern (chi-square = 9.2, p = 0.002) were positively and linearly correlated to AFI decrease. Odds ratios of meconium and chronic villous hypoxia were 9.2 (95% CI = 2.6-32.9) and 4.2 (95% CI = 1.3-13.6) in FGR pregnancies with normal AFI and 25.2 (95% CI = 6.9-91.8) and 9.7 (95% CI = 3-31.5) in those with severe oligohydramnios (p = 0.005 and p = 0.023 compared to normal AFI, respectively).

DISCUSSION

In FGR pregnancies, reduction of amniotic fluid volume is directly correlated to histological features of placental under-perfusion, meconium staining of membranes and fetal vascular damage. These findings support the clinical notion that in FGR pregnancies oligohydramnios is a risk factor of fetal hypoxia and possibly of increased adverse neonatal outcomes.

Association of Doppler parameters with placental signs of underperfusion in late-onset small-for-gestational-age pregnancies

OBJECTIVE

To elucidate the association between Doppler parameters and histological signs of placental underperfusion in late-onset small-for-gestational-age (SGA) babies.

METHODS

Umbilical, fetal middle cerebral and uterine artery pulsatility indices and umbilical vein blood flow (UVBF), which had been recorded within 7 days prior to delivery, were analyzed from a cohort of SGA singleton pregnancies delivered after 34 weeks' gestation and confirmed as having a birth weight < 10(th) percentile by local standards. In each case, the placenta was histologically evaluated for signs of placental underperfusion using a hierarchical and standardized classification system. The independent association of the Doppler parameters with placental underperfusion was evaluated using logistic regression and decision tree analysis.

RESULTS

In 51 cases (53.7%), there were 61 placental histological findings indicative of placental underperfusion. These cases had a significantly higher incidence of Cesarean section for non-reassuring fetal status (52.1% vs 11.9%; P < 0.001) and neonatal metabolic acidosis at birth (21.6% vs 0%; P = 0.001). Significant and independent contributions to the presence of placental underperfusion lesions were provided by increased mean UtA pulsatility index (PI) (P = 0.018; odds ratio (OR) 2 (95% CI, 1.1-3.7)) and decreased UVBF normalized to estimated fetal weight (P = 0.027; OR 0.97 (95% CI, 0.95-0.99)). The combination of both parameters revealed three groups with differing risks for placental underperfusion: normalized UVBF > 82 mL/min/kg (risk 31.3%), normalized UVBF ≤ 82 mL/min/kg and mean UtA-PI ≤ 95(th) percentile (risk 65.5%), and normalized UVBF ≤ 82 mL/min/kg and UtA-PI > 95(th) percentile (risk 94.4%).

CONCLUSIONS

In late-onset SGA pregnancies, uterine Doppler and UVBF are surrogates for placental underperfusion. These findings facilitate phenotypic profiling of cases of fetal growth restriction among the general population of late-onset SGA babies.

Application of the magnitude-squared coherence function between uterine and umbilical flow velocity waveforms for predicting placental dysfunction: a preliminary study

To examine whether the magnitude-squared coherence between uterine and umbilical blood flow velocity waveforms can, in conjunction with estimated fetal weight, uterine and umbilical pulsatility indices, fetal and maternal heart rates, diastolic notching and the amniotic fluid index, create a sensitive and specific model for the prediction of placental dysfunction. Binary logistic prediction models are created for preeclampsia, pregnancy induced hypertension and intrauterine growth restriction in a study group of 284 unselected midtrimester pregnancies. In each study group, the median value of derived parameters were compared with the uncomplicated pregnancy control group. The magnitude-squared coherence function between the uterine and umbilical flow velocity waveforms was found to be a statistically significant predictor of preeclampsia during the midtrimester of pregnancy. The magnitude-squared coherence did not improve the prediction of intrauterine growth restriction or pregnancy induced hypertension. The inclusion of magnitude-squared coherence as one of the prediction parameters may improve the early identification of pregnancies subsequently complicated by preeclampsia.

Paroxysmal coughing, subdural and retinal bleeding: a computer modelling approach

Unexplained subdural and retinal haemorrhages in an infant are commonly attributed to 'shaking', the mechanism of which is believed to be traumatic venous rupture. However, the haemorrhagic retinopathy reported as a result of Valsalva manoeuvres and the subdural bleeding that is a rare complication of pertussis together demonstrate that if a sustained rise in intrathoracic pressure is transmitted to cerebral and retinal vessels, it may result in bleeding, similar to that reported in inflicted injury. Such haemorrhages would be expected to occur whenever severe paroxysmal coughing were induced, whatever the cause. This study used a computer modelling approach to investigate feeding accidents as the trigger for bleeding. A dynamic circulatory model of a 3-month-old infant was induced to 'cough', and the response to changes in physiological variables monitored. It showed that coughing causes intracranial pressures to build up exponentially to approach a maximum, proportional to the amount of pressure the musculature of the thorax can produce, as venous return is impeded. They do not have time to become dangerous during individual coughs, as blood quickly returns after the cough is over, reestablishing normal pressures. Paroxysmal coughing, however, does not allow blood to return between coughs, with the result that very high luminal pressures may be generated, sufficient to damage veins. A history of coughing, vomiting or choking is not uncommon in otherwise normal infants with retinal and subdural bleeding. Our findings suggest that paroxysmal coughing could account for such bleeding in some cases.

Hypoxemic Fetoplacental Vasoconstriction: A Graduated Response to Reduced Oxygen Conditions in the Human Placenta

We investigated the characteristics of hypoxemic fetoplacental vasoconstriction (HFPV) in the dual perfused, single isolated human placental cotyledon. Fetal arterial blood pressures (FAP) were measured in four cotyledons (Group 1) equilibrated with 21% oxygen (O2), 5% carbon dioxide (CO2), and nitrogen (N2) [control] followed by 5% CO2 in N2 for 30 min. FAP (mean +/- sd) increased from 69.8 (+/- 6.4) to 105 (+/- 3.0) mm Hg (P < 0.05), confirming the utility of HFPV in the human placenta. Eight more cotyledons (Group 2) were exposed sequentially and alternately at 15-min intervals to the control gases and to gas blends containing 15%, 12%, 5%, and 0% O2 with 5% CO2 and N2. FAP increased significantly (P < 0.05) in a stepwise fashion from 68.7 (+/- 3.7) to 70.5 (+/- 3.3) mm Hg with 15% O2; from 69.3 (+/- 3.8) to 72.4 (+/- 4.3) mm Hg with 12% O2; from 67.8 (+/- 3.2) to 74.5 (+/- 3.4) mm Hg with 5% O2; and from 69.7 (+/- 3.4) to 77.9 (+/- 5.9) mm Hg with 0% O2, suggesting that HFPV is a graduated response to reduced O2 conditions in the human placenta.

Regulation of transplacental water transfer: the role of fetoplacental venous tone

We used the in vitro dually perfused human placental lobule to test the hypothesis that known vasoconstrictors of the fetal placental circulation, angiotensin II and the thromboxane mimetic U46619 could induce fetomaternal water transfer. Secondly, we used a combination of vasoconstrictor and mechanically induced increases in fetal placental circulatory pressure to examine the role of the venous system in this context. Fetal-side administration of angiotensin II (A-II) and U46619 (n=6 and n=9, for A-II and U46619, respectively) induced dose dependent, recoverable elevations in fetal inflow hydrostatic pressure (HP; A-II: maximum contractility=83 mmHg, EC50=22.0 nM; U46619: maximum contractility was not achieved, but exceeded the A-II effect) and loss of perfusate from the fetal side (A-II: EC50=70.2 nM, maximum fetal-side solvent loss=1906 microl/min; U46619: maximum fetal-side solvent loss was not achieved, but exceeded the A-II effect). Fetal-side solvent loss, for both agonists, was correlated linearly with fetomaternal inflow HP (FMIHP) in a biphasic manner (between 0 and 30 mmHg the slopes (+/-S.E.) were 6.4+/-2.2 and 17.1+/-5.8 microl/(min mmHg) for A-II and U46619, respectively; between 30 and 70 mmHg the slopes (+/-S.E.) were 35.6+/-6.5 and 43.7+/-15.9 microl/(min mmHg) for A-II and U46619, respectively). Increasing fetal-side lumenal pressure (n=3) by raising the fetal outflow catheter caused a loss of perfusate from the fetal side which was reduced in the presence of U46619 (fetal solvent loss per unit increase in fetal-side inflow HP: slopes were 1.198+/-0.123 and 0.783+/-0.085 microl/(min mmHg mmHg), respectively). Notwithstanding the possibility of fetoplacental arterial constriction, we conclude that vasoconstrictive agonists in the fetoplacental circulation affect venous resistance, causing fetomaternal fluid loss. These observations could be relevant to the oligohydramnios associated with intrauterine growth restriction, a condition associated with increased resistance in the umbilical circulation.

The dynamic placenta: I. Hypothetical model of a placental mechanism matching local fetal blood flow to local intervillus oxygen delivery

The placenta can be severely infarcted and yet return well oxygenated blood in spite of the potential shunt paths produced. Optimisation of oxygen transport by some form of local flow matching has been suggested, either via a direct action of hypoxia on subchorial vessels, or indirectly by syncytiotrophoblastic metabolic products. Using casts of cotyledonal vessels and software modelling, a mechanism of hypoxic fetoplacental vasoconstriction could be demonstrated. A simple previously described passive placental model was extended to include hypoxic sensitive arteries and dependence of syncytio-trophoblastic metabolism on intervillus (maternal) blood oxygen content. Such a mechanism of placental flow matching could maintain fetal pO2 by reducing flow through inadequately oxygenated cotyledons, therefore optimising pO2 at the expense of flow. A further modification stabilising fetal water transfer was required to avoid changes in intervillus oxygen delivery producing changes in fetal water content via placental capillary pressure alterations. Intervillus/villus flow matching is likely in the human placenta and this study suggests probable biologically plausible mechanisms for such a phenomenon.