Relations between feeding intolerance and stress biomarkers in preterm infants

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.

Effects of two different positions on stress, pain and feeding tolerance of preterm infants during tube feeding

AIMS

This study aims to investigate the effects of semi-elevated right lateral and semi-elevated supine positions on feeding tolerance, stress severity and pain levels among premature infants during tube feeding.

METHODS

This was a randomized cross-over clinical trial. A total of 34 premature infants who were fed via orogastric tube were included in this study. Feeding tolerance was assessed by abdominal circumference measurements and checking gastric residuals; this assessment was single blinded. Physiological values were evaluated before, during and after tube feeding. The stress severity and pain levels of the infants were also evaluated independently by the researchers before, during and after tube feeding. A significance level of .05 was accepted for all statistical analyses.

RESULTS

There were no difference between infants' vital signs, stress and pain scores according to feeding positions before tube feeding (p > .05). By feeding positions, a statistically significant difference was found between infants' vital signs, abdominal circumference and gastric residuals of infants during tube feeding. Pain and stress levels of infants were found to be significantly higher in the semi-elevated supine position during tube feeding (p < .05).

CONCLUSIONS

Use of the semi-elevated right lateral position during tube feeding was found to have a more helpful effect in reducing stress and pain among premature infants when compared with the use of the semi-elevated supine position.

A Behavioral Epigenetics Model to Predict Oral Feeding Skills in Preterm Infants

BACKGROUND

Preterm infants experience a multitude of prenatal and postnatal stressors, resulting in cumulative stress exposure, which may jeopardize the timely attainment of developmental milestones, such as achieving oral feeding. Up to 70% of preterm infants admitted to the neonatal intensive care unit experience challenges while initiating oral feeding. Oral feeding skills require intact neurobehavioral development. Evolving evidence demonstrates that cumulative stress exposure results in epigenetic modification of glucocorticoid-related genes. Epigenetics is a field of study that focuses on phenotypic changes that do not involve alterations in the DNA sequence. Epigenetic modification of glucocorticoid-related genes alters cortisol reactivity to environmental stimuli, which may influence neurobehavioral development, and is the essence of the evolving field of Preterm Behavioral Epigenetics. It is plausible that early-life cumulative stress exposure and the ensuing epigenetic modification of glucocorticoid-related genes impair neurobehavioral development required for achievement of oral feeding skills in preterm infants.

PURPOSE

The purpose of this article is to build upon the evolving science of Preterm Behavioral Epigenetics and present a conceptual model that explicates how cumulative stress exposure affects neurobehavioral development and achievement of oral feeding skills through epigenetic modification of glucocorticoid-related genes.

METHODS/RESULTS

Using the Preterm Behavioral Epigenetics framework and supporting literature, we present a conceptual model in which early-life cumulative stress exposure, reflected by DNA methylation of glucocorticoid-related genes and altered cortisol reactivity, disrupts neurobehavioral development critical for achievement of oral feeding skills.

IMPLICATIONS FOR PRACTICE AND RESEARCH

Future investigations guided by the proposed conceptual model will benefit preterm infant outcomes by introducing epigenetic-based approaches to assess and monitor preterm infant oral feeding skills. Furthermore, the proposed model can guide future investigations that develop and test epigenetic protective interventions to improve clinical outcomes, representing an innovation in neonatal care.

Oxidative Stress Levels Throughout Pregnancy, at Birth, and in the Neonate

BACKGROUND

Oxidative stress is associated with poor perinatal outcomes. Little is known regarding the longitudinal levels of oxidative stress in the perinatal period or the correlation between maternal and neonatal oxidative stress levels.

OBJECTIVE

Describe and compare oxidative stress, specifically superoxide, superoxide dismutase, catalase, and glutathione levels, over the perinatal period.

STUDY DESIGN

Longitudinal descriptive design using a convenience sample of medically high- and low-risk pregnant women (n = 140) from a maternal-fetal medicine and general obstetrics practice, respectively. Blood was obtained from women at 12-20 and 24-28 weeks' gestation and during labor, from the umbilical cord at birth, and from neonates at 24-72 hr after birth. Levels of superoxide were measured using electron paramagnetic resonance (EPR) spectroscopy; antioxidants (superoxide dismutase, catalase, and glutathione) were measured using commercial assay kits. Relationships between oxidative stress levels at different time points were examined using nonparametric methods. Pregnancy outcome was collected.

RESULTS

Demographic variables, outcome variables, and oxidative stress levels in maternal blood, cord blood, and infants differed between medically high- and low-risk women. Descriptive patterns for oxidative stress measures varied over time and between risk groups. Significant correlations between time points were noted, suggesting intraindividual consistency may exist throughout the perinatal period. However, these correlations were not consistent across each medical risk group.

CONCLUSION

EPR spectroscopy is a feasible method for the perinatal population. Results provide new information on perinatal circulating superoxide levels and warrant further investigation into potential relationships between prenatal and neonatal physiologic dysregulation of oxidative stress.

Assessment of oxidative damage and enzymatic antioxidant system activity on the umbilical cord blood and saliva from preterm newborns with risk factors for early-onset neonatal sepsis

BACKGROUND

To determine the concentration of the Lipid Peroxidation Marker: Malondialdehyde (MDA), and Antioxidant Markers: Superoxide Dismutase (SOD), Glutathione Peroxidase (GPX), Catalase (CAL) in umbilical cord blood and in unstimulated saliva in the first 24 and 48 hours of life in the PTNB of mothers with and without risk factors for early-onset neonatal sepsis.

METHODS

Cross-sectional study with the signing of informed consent by the pregnant women and application of a standard questionnaire classifying the PTNB in Group 1 or 2.

RESULTS

Twenty-one PTNB were studied. Regarding gender, birth weight, need for oxygen, use of phototherapy, diagnosis of assumed sepsis, presence of fetal distress, number of pregnancies, type of delivery, use of corticosteroids, premature rupture of membranes, maternal fever, chorioamnionitis, APGAR at the 5th and 10th minute of life. Statistical analysis was performed with the Mann-Whitney test (p = 0.019) on the GPX variable of umbilical cord blood in the group of mothers with risk factors for early-onset neonatal sepsis. There was no statistical difference in the MDA, SOD, and CAT variables of the group with risk factors and in any variable of the group without risk factors.

CONCLUSION

There was an increase of the GPX concentration in the blood from the umbilical vein in the group with risk factors for early-onset neonatal sepsis. There was no statistical significance in the comparison of saliva and umbilical cord blood. There was no statistically significant difference in MDA, SOD, CAT.

Allostatic Load and Biomarkers of Stress in the Preterm Infant: An Integrative Review

Background:

Every year, an estimated 15 million babies are born preterm (<37 weeks’ gestational age) globally. These preterm infants are exposed to repeated stressful and often painful procedures as part of routine life-saving care within the neonatal intensive care unit (NICU). Low thresholds for tactile and nociceptive input make it more difficult for neonates to discriminate between noxious and nonnoxious stimuli, which can result in continuous activation of stress responses in an attempt to achieve stability through adaptation, or allostasis. Rapidly reoccurring stressors can render stress-response systems over- or underactive, creating wear and tear, or allostatic load. A better understanding of biomarkers related to allostatic load might aid in early detection and prevention/alleviation of allostatic load in this population.

Purpose:

To identify stress biomarkers that have been studied in preterm infants at different time points in the NICU and as long-term outcome measures.

Method/search Strategy:

Systematic searches were conducted of PubMed, CINAHL, SCOPUS, and PsychInfo databases.

Findings/results:

Twenty-one studies met inclusion criteria for this review. Several putative biomarkers were identified, including cortisol levels, epigenetic markers, brain microstructure, markers of oxidative stress, and the brain–gut–microbiome axis.

Conclusion:

The interaction of disease with therapeutic interventions may inadvertently increase infant allostatic load. In addition to human studies, future research should leverage newly available large data sets to conduct additional analyses.

Splanchnic Oxygenation at First Enteral Feeding in Preterm Infants: Correlation With Feeding Intolerance

Preterm infants are at risk of developing gastrointestinal complications such as feeding intolerance and necrotizing enterocolitis. Near-infrared spectroscopy (NIRS) provides continuous monitoring of abdominal oxygenation (ArSO2) and could help to predict gastrointestinal complications in preterm neonates. In this prospective observational study, ArSO2 patterns at first enteral feed were evaluated by NIRS in 61 clinically stable preterm infants. Splanchnic-cerebral oxygenation ratio, which is a marker of gut hypoxia, was also calculated. ArSO2 and splanchnic-cerebral oxygenation ratio were significantly lower both at baseline and after feeding administration in infants who later developed feeding intolerance (n = 23). NIRS could help the early prediction of gastrointestinal complications in high-risk preterm infants.

Feeding intolerance, inflammation, and neurobehaviors in preterm infants

PURPOSE

Identifying relationships between feeding intolerance (FI), inflammation, and early measures of neurodevelopment may provide the basis for clinically relevant assessments for NICU clinicians and staff. The purpose of this secondary analysis was to examine the relationship of FI to inflammatory markers and/or neurobehaviors in the first week of life.

METHODS

This was a retrospective, matched case-control design with data drawn from 114 infants born at ≤32 weeks gestation.

RESULTS

Eight infants developed FI prior to full enteral feedings. These infants were more likely to have dysregulated levels of cytokines, specifically IL6, and lower neurodevelopmental scores compared to infants without FI.

CONCLUSIONS

Results suggest physiologic dysregulation and an immature nervous system may contribute to the phenomenon of FI in preterm infants. Further research to identify the role of the brain-gut-immune axis on FI and other GI complications in this population is warranted.

Maternal variables associated with physiologic stress and perinatal complications in preterm infants

OBJECTIVE

Complications of prematurity may be related to dysregulation of the hypothalamic-pituitary-adrenal axis in preterm infants. Increased intrauterine exposure to cortisol may be responsible for adverse prenatal programming and subsequent dysfunction of the infant's hypothalamic-pituitary-adrenal axis. The aim of the study was to describe maternal social variables and their association with infant cortisol levels and complications of prematurity.

METHODS

Preterm infants <32 weeks' gestation were recruited. Primary outcomes were development of complications of prematurity and physiologic stress response, represented by cord blood and salivary cortisol levels on first day of life. Descriptive statistics and comparative analyses were performed.

RESULTS

Fifteen of 31 infants enrolled developed a complication of prematurity. Infants of greater gestational age when prenatal care was established had lower cord blood cortisol (p = 0.009) and trended a higher risk of necrotizing enterocolitis (p = 0.069). Infants whose mothers smoked more showed significantly different salivary cortisol distributions on day 1 (p = 0.037), and were at greater risk for intraventricular hemorrhage (p = 0.018).

CONCLUSIONS

The association between maternal social variables, hypothalamic-pituitary-adrenal axis dysregulation, and complications of prematurity supports the research model of physiologic dysregulation/allostatic load as a mechanism for complications in preterm infants. More research is warranted to investigate associations between maternal social variables, maternal stress levels, and adverse prenatal programming of the infant hypothalamic-pituitary-adrenal axis.

Lung Disease, Oxidative Stress, and Oxygen Requirements in Preterm Infants

BACKGROUND

The role of oxidative stress remains unclear in the multifactorial pathophysiologic mechanism of lung disease in preterm infants.

AIMS

The aim of this study was to examine the associations among chronic lung disease (CLD), oxidative stress, and oxygen requirements in preterm infants.

DESIGN

Prospective, longitudinal, and correlational design.

SUBJECTS

Preterm infants born at <32 weeks' gestation (N = 31), median gestation of 29.0 weeks (range 24.9-31.7).

MEASUREMENTS

The diagnosis of CLD was obtained from the medical record. Oxidative stress was measured using 8-hydroxydeoxyguanosine (8-OHdG) in the cord blood at birth and urine on Days 1 and 7. Oxygen requirements were measured using fraction of inspired oxygen (FIO2) recorded in the first hour after birth/admission and the average FIO2 during the first 12 hr and 7 days after birth. Descriptive statistics are presented. Comparison analyses were performed using Kruskal-Wallis and Fisher's exact tests.

RESULTS

Infants with CLD (n = 12) had lower gestational age (p = .04) and weight (p = .04) at birth, more days on the ventilator (p = .004), and longer neonatal intensive care unit stay (p = .04) compared to infants without CLD (n = 19). CLD was associated with lower oxidative stress levels (p = .03) and higher oxygen requirements during the first 12 hr (p = .025) and on Day 7 (p = .001). Lower oxidative stress levels on Day 7 were associated with higher oxygen requirements in the first 12 hr (p = .01) and on Day 7 (p = .03).

CONCLUSION

Our results linking CLD and higher oxygen requirements with low oxidative stress contradict previous reports. Findings identify a gap in knowledge for postresuscitation oxygen therapy in preterm infants and expose the role of oxidative stress from inflammation and intermittent hypoxia in the etiology of CLD.

Comparison of cortisol samples in the first two weeks of life in preterm infants

BACKGROUND

Growing literature on negative childhood stress emphasizes the need to understand cortisol values from varying biomarker samples.

OBJECTIVE

This work aimed to examine cortisol samples for usability, associations, and individual stability in neonates.

SUBJECTS

The sample consisted of preterm infants (n=31).

MATERIALS AND METHODS

Analyses on cortisol collected from cord blood and from saliva and urine samples on days 1, 7, and 14 included Spearman correlations and paired t-tests.

RESULTS

Usability rates were 80.6% (cord blood), 85.9% (saliva), and 93.5% (urine). Salivary and urinary cortisol levels had significant correlation on day 1 only (p=0.004). Significant differences in individual stability of cortisol concentrations existed except in urine on days 1 and 7 and in saliva on days 7 and 14.

CONCLUSIONS

Usability was highest for urine samples. We found little correlation between cortisol sample levels at each time; individual stability of cortisol concentrations was minimal. Interpretation of cortisol findings in all studies should be performed cautiously.

Maternal breast milk transforming growth factor-beta and feeding intolerance in preterm infants

BACKGROUND

Feeding intolerance (FI) occurs commonly in the neonatal intensive care unit. Breast milk contains a large pool of transforming growth factor-beta (TGF-β). Few studies describe TGF-β levels in preterm milk, and the relationship to FI remains unexplored. We measured TGF-β levels in preterm breast milk to investigate a correlation with FI in preterm infants.

METHODS

Prospective observational trial of 100 mother-infant pairs, enrolling infants born below 32 wk gestation and less than 1,500 g, and mothers who planned to provide breast milk. TGF-β levels were measured using enzyme-linked immunosorbent assay. Infant charts were reviewed for outcomes.

RESULTS

TGF-β declined postnatally, most elevated in colostrum (P < 0.01). TGF-β2 levels were higher than TGF-β1 at all time points (P < 0.01). Colostrum TGF-β levels correlated inversely with birth weight (P < 0.01) and gestational age (P < 0.05). One-week TGF-β2 levels were reduced in growth-restricted infants with FI (P < 0.01). Of infants with necrotizing enterocolitis (NEC), TGF-β2 levels appeared to be low, but small sample size precluded meaningful statistical comparisons.

CONCLUSION

TGF-β levels decline temporally in preterm milk. TGF-β1 colostrum levels correlate inversely with birth weight and gestational age. TGF-β2 may play a role in FI in growth-restricted infants. The relationship of TGF-β2 and NEC merits future investigation.