Activin a plasma levels at birth: an index of fetal hypoxia in preterm newborn

Brain Damage in Preterm and Full-Term Neonates: Serum Biomarkers for the Early Diagnosis and Intervention

The Brain is vulnerable to numerous insults that can act in the pre-, peri-, and post-natal period. There is growing evidence that demonstrate how oxidative stress (OS) could represent the final common pathway of all these insults. Fetuses and newborns are particularly vulnerable to OS due to their inability to active the antioxidant defenses. Specific molecules involved in OS could be measured in biologic fluids as early biomarkers of neonatal brain injury with an essential role in neuroprotection. Although S-100B seems to be the most studied biomarker, its use in clinical practice is limited by the complexity of brain damage etiopathogenesis and the time of blood sampling in relation to the brain injury. Reliable early specific serum markers are currently lacking in clinical practice. It is essential to determine if there are specific biomarkers that can help caregivers to monitor the progression of the disease in order to active an early neuroprotective strategy. We aimed to describe, in an educational review, the actual evidence on serum biomarkers for the early identification of newborns at a high risk of neurological diseases. To move the biomarkers from the bench to the bedside, the assays must be not only be of a high sensitivity but suitable for the very rapid processing and return of the results for the clinical practice to act on. For the best prognosis, more studies should focus on the association of these biomarkers to the type and severity of perinatal brain damage.

Serum Activin A as Brain Injury Biomarker in the First Three Days of Life. A Prospective Case-Control Longitudinal Study in Human Premature Neonates

Disruption of normal intrauterine brain development is a significant consequence of premature birth and may lead to serious complications, such as neonatal brain injury (NBI). This prospective case-control longitudinal study aimed at determining the levels and prognostic value of serum activin A during the first three days of life in human premature neonates which later developed NBI. It was conducted in a single tertiary hospital and eligible participants were live-born premature (<34 weeks) neonates. Each case (n = 29) developed NBI in the form of an intraventricular haemorrhage, or periventricular leukomalacia, and was matched according to birth weight and gestational age to one neonate with normal head ultrasound scans. Serum activin A levels in both groups showed a stable concentration during the first three days of life as no difference was observed within the two groups from the first to the third day. Neonates diagnosed with NBI had significantly higher activin A levels during the first two days of life compared to control neonates and its levels correlated to the severity of NBI during the second and third day of life. Although serum activin A on the second day was the best predictor for neonates at risk to develop NBI, the overall predictive value was marginally fair (area under the ROC-curve 69.2%). Activin A, in combination with other biomarkers, may provide the first clinically useful panel for the early detection of premature neonates at high risk of NBI.

Oxidative stress biomarkers in the preterm infant

Oxidative stress (OS) plays a key role in the pathophysiology of preterm infants. Accurate assessment of OS remains an analytical challenge that has been partially addressed during the last few decades. A plethora of approaches have been developed to assess preterm biofluids to demonstrate a link postnatally with preterm OS, giving rise to a set of widely employed biomarkers. However, the vast number of different analytic methods and lack of standardization hampers reliable comparison of OS-related biomarkers. In this chapter, we discuss approaches for the study of OS in prematurity with respect to methodologic considerations, the metabolic source of different biomarkers and their role in clinical studies.

Early predictors of perinatal brain damage: the role of neurobiomarkers

The early detection of perinatal brain damage in preterm and term newborns (i.e. intraventricular hemorrhage, periventricular leukomalacia and perinatal asphyxia) still constitute an unsolved issue. To date, despite technological improvement in standard perinatal monitoring procedures, decreasing the incidence of perinatal mortality, the perinatal morbidity pattern has a flat trend. Against this background, the measurement of brain constituents could be particularly useful in the early detection of cases at risk for short-/long-term brain injury. On this scenario, the main European and US international health-care institutions promoted perinatal clinical and experimental neuroprotection research projects aimed at validating and including a panel of biomarkers in the clinical guidelines. Although this is a promising attempt, there are several limitations that do not allow biomarkers to be included in standard monitoring procedures. The main limitations are: (i) the heterogeneity of neurological complications in the perinatal period, (ii) the small cohort sizes, (iii) the lack of multicenter investigations, (iv) the different techniques for neurobiomarkers assessment, (iv) the lack of consensus for the validation of assays in biological fluids such as urine and saliva, and (v), the lack of reference curves according to measurement technique and biological fluid. In the present review we offer an up-to-date overview of the most promising developments in the use of biomarkers in the perinatal period such as calcium binding proteins (S100B protein), vasoactive agents (adrenomedullin), brain biomarkers (activin A, neuron specific enolase, glial fibrillary acidic protein, ubiquitin carboxyl-terminal hydrolase-L1) and oxidative stress markers.

Activin A in Mammalian Physiology

Activins are dimeric glycoproteins belonging to the transforming growth factor beta superfamily and resulting from the assembly of two beta subunits, which may also be combined with alpha subunits to form inhibins. Activins were discovered in 1986 following the isolation of inhibins from porcine follicular fluid, and were characterized as ovarian hormones that stimulate follicle stimulating hormone (FSH) release by the pituitary gland. In particular, activin A was shown to be the isoform of greater physiological importance in humans. The current understanding of activin A surpasses the reproductive system and allows its classification as a hormone, a growth factor, and a cytokine. In more than 30 yr of intense research, activin A was localized in female and male reproductive organs but also in other organs and systems as diverse as the brain, liver, lung, bone, and gut. Moreover, its roles include embryonic differentiation, trophoblast invasion of the uterine wall in early pregnancy, and fetal/neonate brain protection in hypoxic conditions. It is now recognized that activin A overexpression may be either cytostatic or mitogenic, depending on the cell type, with important implications for tumor biology. Activin A also regulates bone formation and regeneration, enhances joint inflammation in rheumatoid arthritis, and triggers pathogenic mechanisms in the respiratory system. In this 30-yr review, we analyze the evidence for physiological roles of activin A and the potential use of activin agonists and antagonists as therapeutic agents.

Lutein levels in arterial cord blood correlate with neuroprotein activin A in healthy preterm and term newborns: A trophic role for lutein?

BACKGROUND

Lutein (LT) is a naturally occurring xanthophyll carotenoid most predominant in the central nervous system (CNS), but its neurotrophic role is still debated. We therefore investigated whether cord blood concentrations correlated with a well-established neurobiomarker, namely activin A.

METHODS

We conducted a prospective study on the distribution of LT and activin A in arterial cord blood of healthy preterm (n=50) and term (n=82) newborns according to weeks of gestational age (wGA) and gender.

RESULTS

LT and activin A showed a pattern of concentration characterized by higher levels (P<0.01, for all) at 33-36 wGA followed by a progressive decrease (P<0.01, for all) from 37 onwards with a dip at term. Both LT and activin A were gender-dependent with significantly (P<0.01, for all) higher levels in all recruited females and after sub-grouping for preterm and term births. LT (R=0.33; P<0.001) correlated with wGA at sampling. There were significant positive correlations between lutein and activin A in male (R=0.93; P<0.001) and female (R=0.89; P<0.001) groups.

CONCLUSIONS

The present data showing a correlation between LT and activin A support the notion of a neurotrophic role gender-dependent for LT and open the way to further investigations correlating LT with well-established biochemical markers of CNS development/damage.

Hypoxia-induced activin A diminishes endothelial cell vasculogenic activity

Acute ischaemia causes a significant loss of blood vessels leading to deterioration of organ function. Multiple ischaemic conditions are associated with up‐regulation of activin A, but its effect on endothelial cells (EC) in the context of hypoxia is understudied. This study evaluated the role of activin A in vasculogenesis in hypoxia. An in vitro vasculogenesis model, in which EC were cocultured with adipose stromal cells (ASC), was used. Incubation of cocultures at 0.5% oxygen led to decrease in EC survival and vessel density. Hypoxia up‐regulated inhibin B_A (monomer of activin A) mRNA by 4.5‐fold and activin A accumulation in EC‐conditioned media by 10‐fold, but down‐regulated activin A inhibitor follistatin by twofold. Inhibin B_A expression was also increased in human EC injected into ischaemic mouse muscles. Activin A secretion was positively modulated by hypoxia mimetics dimethyloxalylglycine and desferrioxamine. Silencing HIF1α or HIF2α expression decreased activin A secretion in EC exposed to hypoxia. Introduction of activin A to cocultures decreased EC number and vascular density by 40%; conversely, blockade of activin A expression in EC or its activity improved vasculogenesis in hypoxia. Activin A affected EC survival directly and by modulating ASC paracrine activity leading to diminished ability of the ASC secretome to support EC survival and vasculogenesis. In conclusion, hypoxia up‐regulates EC secretion of activin A, which, by affecting both EC and adjacent mesenchymal cells, creates a micro‐environment unfavourable for vasculogenesis. This finding suggests that blockade of activin A signalling in ischaemic tissue may improve preservation of the affected tissue.

Expression, localization and control of activin A release from human umbilical vein endothelial cells

Activin-A is a member of the TGFβ superfamily found in maternal and umbilical cord blood throughout gestation. We investigated whether human umbilical vein endothelial cells (HUVEC) express activin-A in vivo and tested the effects of vasoactive (endothelin-1), pro-inflammatory (interferon-γ, interleukin-8) and anti-inflammatory (dexamethasone, urocortin) factors on activin-A release by isolated HUVEC in vitro. Activin βA subunit protein and mRNA were strongly localized in the endothelial cells of umbilical veins and were also detectable in scattered cells of the cord connective tissue. Dimeric activin-A was detected in the HUVEC culture medium at picomolar concentrations. Activin-A release by HUVEC decreased after cell incubation with urocortin (p < 0.01), whereas no effect was observed with interleukin-8, interferon-γ, endothelin-1 or dexamethasone. In summary, activin-A is present in the human umbilical vein endothelium in vivo and is produced and released by isolated HUVEC. Activin-A secretion is inhibited in vitro by urocortin, a neuropeptide with predominantly anti-inflammatory action.

Activin-A exerts a crucial anti-inflammatory role in neonatal infections

BACKGROUND

Activin-A is a cytokine with a critical role in infections and associated inflammation in experimental models and humans. Still, the effects of activin-A on neonatal infections remain elusive. Here, we investigated the expression of activin-A in the serum of septicemic preterm and term neonates and in peripheral blood leukocytes stimulated with inflammatory agents in vitro. The role of activin-A in the regulation of inflammatory responses by neonatal leukocytes was delineated.

METHODS

Peripheral blood was obtained from 37 septicemic neonates between the first and fifth days postinfection and from 35 healthy controls. Isolated monocytes and lymphocytes were stimulated with lipopolysaccharide (LPS) or phytohemagglutinin (PHA) in vitro in the presence of activin-A. Cell proliferation, cytokine, and chemokine release were investigated.

RESULTS

Activin-A was significantly increased in the serum of preterm septicemic neonates. Neonatal leukocytes secreted copious amounts of activin-A following stimulation, pointing to these cells as an essential source of activin-A in the circulation. Of note, treatment of neonatal leukocytes with activin-A during PHA and LPS stimulation resulted in significantly decreased interleukin (IL)-1β, IL-6, and CXCL8 production, concomitant with a striking increase in the anti-inflammatory mediator, IL-10.

CONCLUSION

Our findings uncover activin-A as a novel immunomodulatory agent critical for the control of inflammatory responses in septicemic neonates.

Elevated Activin A urine levels are predictors of intraventricular haemorrhage in preterm newborns

AIM

Intraventricular haemorrhage (IVH) is the most common variety of cerebral haemorrhage and cause of neurological disabilities in preterm newborns. We evaluated the usefulness of urine Activin A concentrations for the early detection of perinatal IVH.

METHODS

We conducted a case-control study on 100 preterm newborns (20 with IVH and 80 without IVH) in whom urine Activin A was measured at five predetermined time-points in the first 72 h after birth. IVH diagnosis and the extension of the lesion were performed by ultrasound scanning within the first 72 h and at 1 week after birth, respectively.

RESULTS

Urine Activin A in infants who developed IVH was significantly higher than in controls at all monitoring time-points (p < 0.01 for all), increasing progressively from first urination to 24 h when it reached the highest peak (p < 0.001). At a cut-off 0.08 ng/L, at the first void, Activin A sensitivity and specificity were 68.7% (CI: 41.3-89%) and 84.5% (CI: 75-91.5%).

CONCLUSION

Activin A measurements in urine soon after birth can constitute a promising tool for identifying preterm infants at risk of IVH.

Nucleated red blood cells and early EEG: predicting Sarnat stage and two year outcome

AIMS

Hypoxic Ischaemic Encephalopathy (HIE) causes characteristic changes of the electroencephalogram (EEG), and a raised Nucleated Red Blood Cell (NRBC) count compared to controls. We wished to examine whether combining these markers could improve their ability to predict HIE severity in the first 24h.

METHODS

Term infants with HIE were recruited. NRBC count and continuous multi-channel EEG were recorded within the first 24h. Neurological assessment was carried out at 24 months. A control population with NRBC counts in the first 24h was recruited.

RESULTS

44 infants with HIE and 43 control infants were recruited. Of the HIE population 39 completed a 2 year follow-up. The median NRBC count differed significantly between the controls and those with HIE (3/100 WBC [range of 0-11] vs 12.3/100 WBC [0-240]) (p<0.001). Within the HIE population the median NRBC count was significantly greater in infants with moderate/severe HIE than mild (16/100 WBC [range of 0-240] vs 8/100 WBC [1-23]) (p=0.016), and among infants with abnormal outcome compared to normal (21.3/100 WBC [1-239.8] vs 8.3/100 WBC [0-50])(p=0.03). The predictive ability of EEG changed with time post-delivery, therefore results are given at both 12 and 24h of age. At both time points the combined marker had a stronger correlation than EEG alone; with HIE severity (12h: r=0.661 vs r=0.622), (24h: r=0.645 vs r=0.598), and with outcome at 2 years (12h: r=0.756 vs r=0.652), (24h: r=0.802 vs r=0.746).

CONCLUSION

Combining early EEG and NRBC count to predict HIE severity and neurological outcome, improved the predictive ability of either in isolation.

Perioperative Activin A Concentrations as a Predictive Marker of Neurologic Abnormalities in Children after Open Heart Surgery

Background: Ischemic-reperfusion injury of the brain is a major adverse event after cardiac surgery, especially when extracorporeal circuits are used. Because brain injury induces local overproduction of activin A, we measured plasma concentrations in children after open heart surgery with cardiopulmonary bypass (CPB) to investigate the potential of measuring activin A for early identification of infants at risk for brain damage.

Methods: We evaluated 45 infants (age &lt;1 year) with congenital heart defects: 36 without overt neurologic injury, and 9 with neurologic injury on day 7 after the surgical procedure. Blood samples were taken before surgery, during surgery before CPB, at the end of CPB, at the end of surgery, and at 12 h after surgery. Neurologic development was assessed before surgery and on postoperative day 7.

Results: Activin A concentrations increased significantly during surgery (P &lt;0.0001) to a maximum at the end of CPB. Infants who developed abnormal neurologic sequelae had concentrations significantly higher (P &lt;0.0001, all comparisons) than patients with normal neurologic outcome at all evaluated times, but not before surgery. Activin A had a sensitivity of 100% (95% CI, 66%–100%) and a specificity of 100% (95% CI, 90%–100%) as a single marker for predicting neurologic abnormalities (area under the ROC curve, 1.0).

Conclusions: Activin A increases in children who experience poor neurologic outcomes after open heart surgery, and its assay may help in early identification of infants at risk for brain damage.

High Urinary Concentrations of Activin A in Asphyxiated Full-Term Newborns with Moderate or Severe Hypoxic Ischemic Encephalopathy

Background: Hypoxic ischemic encephalopathy (HIE) is a major cause of permanent neurological disabilities in full-term newborns. We measured activin A in urine collected immediately after birth in asphyxiated full-term newborns, and assessed the ability of the measurements to predict the occurrence of perinatal encephalopathy.

Methods: We studied 30 infants with perinatal asphyxia and 30 healthy term neonates at the same gestational age. We recorded routine laboratory variables, cranial assessments by standard cerebral ultrasound, and the presence or absence of neurological abnormalities during the first 7 days after birth. Urinary activin A concentrations were measured at first urination and 12, 24, 48, and 72 h after birth.

Results: Asphyxiated infants were subdivided as follows: group A (n = 18): no or mild HIE with good prognosis and group B (n = 12): moderate or severe HIE with a greater risk of neurological handicap. Activin A concentrations in urine collected at birth (median collection time at first urination &lt;2 h) and at 12, 24, 48, and 72 h from birth were significantly (P &lt;0.0001) higher in asphyxiated newborns with moderate or severe HIE (Group B) than in those with absent of mild HIE (group A) and controls. Concentrations did not differ between group A and controls. Activin A concentrations were &gt;0.08 μg/L at first urination in 10 of 12 patients with moderate or severe HIE but in none of 18 patients with no or mild HIE.

Conclusions: Activin A measurements in urine soon after birth may be a promising tool to identify which asphyxiated infants are at risk of neurological sequelae.

Activin A In Brain Injury

Activin A is a growth factor composed of two betaA subunits belonging to the transforming growth factor beta (TGF-beta) superfamily of dimeric proteins. The biological activity of activin A is mediated by two different types of receptors, the type I (ARI and ARIB) and the type II receptors (ARII and ARIIB), and by two activin-binding proteins, follistatin and follistatin-related gene. These factors bind to activin A and thereby inhibit its biological effects. Activin A, its receptors, and binding proteins are widely distributed throughout the brain. Studies employing models of acute brain injury strongly implicate enhanced activin A expression as a common response to acute neuronal damage of various origins. Hypoxic/ischemic injury, mechanical irritation, and chemical damage of brain evoke a strong upregulation of activin A. Subsequent experimental studies have shown that activin A has a beneficial role to neuronal recovery and that, by activating different pathways, activin A has robust neuroprotective activities. Because activin A induction occurs early after brain injury, its measurement may provide a potential biochemical index of the presence, location, and extent of brain injury. This approach may also facilitate the diagnosis of subclinical lesions at stages when monitoring procedures are unable to detect brain lesion and furthermore establish a prognosis.

The Timing of Neonatal Brain Damage

Although neonatal morbidity and mortality are less than in the past, the risk of pre-natal and neonatal brain damage has not been eliminated. In order to optimize pre-natal, perinatal and neonatal care, it is necessary to detect factors responsible for brain damage and obtain information about their timing. Knowledge of the timing of asphyxia, infections and circulatory abnormalities would enable obstetricians and neonatologists to improve prevention in pre-term and full-term neonates. Cardiotocography has been criticized as being too indirect a sign of fetal condition and as having various technical pitfalls, though its reliability seems to be improved by association with pulse oximetry, fetal blood pH and electrocardiography. Neuroimaging is particularly useful to determine the timing of hypoxic-ischemic brain damage. Cranial ultrasound has been used to determine the type and evolution of brain damage. Magnetic resonance has also been used to detect antenatal, perinatal and neonatal abnormalities and timing on the basis of standardized assessment of brain maturation. Advances in the interpretation of neonatal electroencephalograms have also made this technique useful for determining the timing of brain lesions. Nucleated red blood cell count in cord blood has been recognized as an important indication of the timing of pre-natal hypoxia, and even abnormal lymphocyte and thrombocyte counts may be used to establish pre-natal asphyxia. Cord blood pH and base excess are well-known markers of fetal hypoxia, but are best combined with heart rate and blood pressure. Other markers of fetal and neonatal hypoxia useful for determining the timing of brain damage are assays of lactate and markers of oxidative stress in cord blood and neonatal blood. Cytokines in blood and amniotic fluid may indicate chorioamnionitis or post-natal infections. The determination of activin and protein S100 has also been proposed. Obstetricians and neonatologists can therefore now rely on various methods for monitoring the risk of brain damage in the antenatal and post-natal periods.

Increased Plasma Concentrations of Activin A Predict Intraventricular Hemorrhage in Preterm Newborns

Background: Intraventricular hemorrhage (IVH) is a major cause of neurologic disabilities in preterm newborns. We evaluated the use of plasma activin A concentrations to predict the development of perinatal IVH.

Methods: We measured nucleated erythrocyte (NRBC) counts, plasma activin A, hypoxanthine (Hyp), and xanthine (Xan) in arterial blood samples obtained from 53 preterm infants during the first hour after birth. Cerebral ultrasound was performed within 48 h of birth and repeated at 5- or 6-day intervals until the age of 4 weeks.

Results: Grade I or II IVH was detected during the first 10 days of life in 11 of 53 patients (21%). Activin A, Hyp, and Xan concentrations and NRBC counts were higher in preterm newborns who subsequently developed IVH than in those who did not (P &lt;0.0001, except P = 0.019 for Xan). Neonatal activin A was correlated (P &lt;0.0001) with Hyp (r = 0.95), Xan (r = 0.90), and NRBC count (r = 0.90) in newborns without later IVH and in those who developed IVH (Hyp, r = 0.89, P = 0.0002; Xan, r = 0.95, P &lt;0.0001; NRBC count, r = 0.90, P = 0.0002). At a cutoff of 0.8 μg/L activin A, the sensitivity and specificity were 100% [11 of 11; 95% confidence interval (CI), 71%–100%] and 93% (39 of 42; 95% CI, 81%–98%), and positive and negative predictive values were 79% (95% CI, 61%–100%) and 0% (95% CI, 0%–2%), respectively. The area under the ROC curve was 0.98.

Conclusions: Activin A concentrations at birth are increased in preterm newborns who later develop IVH and may be useful for early identification of infants with hypoxic-ischemic brain insults who are at high risk for IVH.

Umbilical Cord Serum Activin A Levels are Increased in Pre-eclampsia with Impaired Blood Flow in the Uteroplacental and Fetal Circulation

The aims of the present study were to evaluate the umbilical cord serum activin A concentrations in complicated pregnancies and also to explore the relationship between activin A levels and blood flow velocity in fetal arteries. Umbilical cord blood samples were obtained postpartum after a full term uneventful gestation (control group, n=40), and from pregnancies complicated by gestational diabetes (n=13), preterm labour (n=18), or pre-eclampsia (n=19). Cord serum activin A levels were three-fold higher in pregnancies complicated by pre-eclampsia (1.17+/-0.14 ng/ml, p<0.01) than in the control group (0.43+/-0.03 ng/ml), but were unaltered in the diabetes and preterm labour groups. The pre-eclampsia group had a marked increase of umbilical artery pulsatility index (PI) and also a decrease of middle cerebral artery PI (p<0.01). Furthermore, activin A concentration correlated directly with the umbilical artery PI (r=0.540, p=0.021), with the length of stay in the Neonatal Intensive Care Unit (r=0.857, p<0.001) and also with cord blood pH (r=-0.886, p<0.001). In conclusion, umbilical cord serum activin A levels are increased in the presence of pre-eclampsia and provide an indirect marker of impaired blood flow in the uteroplacental and fetal circulation.

Inhibins and activins in pregnancy

Human placenta, decidua, and fetal membranes are the major sites of production and secretion of inhibin A and activin A in maternal serum, amniotic fluid, and umbilical cord blood. These tissues also express follistatin-related gene and betaglycan, the binding proteins of activin A and inhibin A, respectively, recently identified. They show a different expression throughout pregnancy, suggesting new functional roles into gestational tissues. The availability of suitable assays for measuring inhibin A and activin A lead us the possibility to investigate their secretion in healthy pregnancy. In addition, several evidences underline the potential role and the clinical usefulness of their measurement in the diagnosis, prevention, prognosis and follow-up of different gestational pathologies such as: threatened abortion, placental tumors, hypertensive disorders of pregnancy, intrauterine growth restriction, fetal hypoxia. The measurement of inhibin A and activin A into the biological fluids of pregnancy will offer in the future further possibilities in early diagnosis, prediction, and monitoring pregnancy diseases.