Intrapartum magnesium sulfate exposure attenuates neutrophil function in preterm neonates

Antenatal Magnesium Sulfate and adverse gastrointestinal outcomes in Preterm infants-a systematic review and meta-analysis

INTRODUCTION

To evaluate the effect of antenatal magnesium sulfate (MgSO4) on mortality and morbidity outcomes related to the gastrointestinal system (GI) in preterm infants.

METHODS

Data sources: A systematic literature search was conducted in November 2022. PubMed, CINAHL Plus with Full Text (EBSCOhost), Embase (Elsevier), and CENTRAL (Ovid) were searched. There were 6695 references. After deduplication, 4332 remained. Ninety-nine full-text articles were assessed and forty four articles were included in the final analysis.

STUDY ELIGIBILITY CRITERIA

Randomized or quasi-randomized clinical trials and observational studies that evaluated at least one of the pre-specified outcomes were included. Preterm infants whose mothers were given antenatal MgSO4 were included and whose mothers did not receive antenatal MgSO4 were the comparators. The main outcomes and measures were: Necrotizing enterocolitis (NEC) (stage ≥ 2), surgical NEC, spontaneous intestinal perforation (SIP), feeding intolerance, time to reach full feeds, and GI-associated mortality.

STUDY APPRAISAL AND SYNTHESIS METHODS

A random-effects model meta-analysis was performed to yield pooled OR and its 95% CI for each outcome due to expected heterogeneity in the studies. The analysis for each predefined outcome was performed separately for adjusted and unadjusted comparisons. All included studies were assessed for methodological quality. The risk of bias was assessed using elements of the Cochrane Collaboration's tool 2.0 and the Newcastle-Ottawa Scale for randomized controlled trials (RCTs) and non-randomized studies (NRS), respectively. The study findings were reported as per PRISMA guidelines.

RESULTS

A total of thirty-eight NRS and six RCTs involving 51,466 preterm infants were included in the final analysis. There were no increased odds of stage ≥2 NEC, (NRS : n = 45,524, OR: 0.95; 95% CI: 0.84-1.08, I2- 5% & RCT's: n = 5205 OR: 1.00; 95% CI: 0.89-1.12, I2- 0%), SIP (n = 34,186, OR: 1.22, 95% CI: 0.94-1.58, I2-30%), feeding intolerance (n = 414, OR: 1.06, 95% CI: 0.64-1.76, I2-12%) in infants exposed to antenatal MgSO4. On the contrary, the incidence of surgical NEC was significantly lower in MgSO4 exposure infants (n = 29,506 OR:0.74; 95% CI: 0.62-0.90, ARR: 0.47%). Studies assessing the effect on GI-related mortality were limited to make any conceivable conclusion. The certainty of evidence (CoE) for all outcomes was adjudged as 'very low' as per GRADE.

CONCLUSION

Antenatal magnesium sulfate did not increase the incidence of gastrointestinal-related morbidities or mortality in preterm infants. With the current evidence concerns, regarding the adverse effects of MgSO4 administration leading to NEC/SIP or GI-related mortality in preterm infants should not be a hurdle in its routine use in antenatal mothers.

Targeting Neutrophil β2-Integrins: A Review of Relevant Resources, Tools, and Methods

Neutrophils are important innate immune cells that respond during inflammation and infection. These migratory cells utilize β₂-integrin cell surface receptors to move out of the vasculature into inflamed tissues and to perform various anti-inflammatory responses. Although critical for fighting off infection, neutrophil responses can also become dysregulated and contribute to disease pathophysiology. In order to limit neutrophil-mediated damage, investigators have focused on β₂-integrins as potential therapeutic targets, but so far these strategies have failed in clinical trials. As the field continues to move forward, a better understanding of β₂-integrin function and signaling will aid the design of future therapeutics. Here, we provide a detailed review of resources, tools, experimental methods, and in vivo models that have been and will continue to be utilized to investigate the vitally important cell surface receptors, neutrophil β₂-integrins.

Effects of Antenatal Magnesium Sulfate on the Gut Function of Preterm (<32 weeks) Very Low Birth Weight Neonates: Experience from a Tertiary Institute in South India

OBJECTIVE

Antenatal magnesium sulfate (MgSO4) is found to have various adverse effects in newborn, but the effect on preterm gut is still unclear. This study aimed to evaluate the effects of antenatal MgSO4 on preterm gut function by assessing the clinical outcomes and mesenteric blood flow.

METHODS

This was a prospective cohort study on all preterm very low birth weight (VLBW) neonates born at a tertiary care center in South India from November 2016 to August 2017. Neonates with antenatal magnesium (Mg) exposure were compared with those with no exposure for various neonatal outcome variables like time to reach full feeds, feed intolerance, necrotizing enterocolitis (NEC) and other preterm complications, serial serum Mg levels and superior mesenteric artery (SMA) Doppler velocity measurements at two time points (24-48 h and 4-5 days after birth).

RESULTS

Out of 84 neonates, 56 neonates were exposed to antenatal Mg with a median cumulative maternal dose of 28 g and the rest 28 neonates had no exposure. The mean time to reach full feeds was the same in both groups (10.5 days). Feed intolerance episodes were similar in the first week of life between the exposed and unexposed groups (48.2% vs. 46.4%; p = 0.88). Univariate analysis revealed no difference between groups concerning rates of NEC (p = 0.17) or mortality (p = 0.39). There was no significant difference in SMA Doppler parameters and hypermagnesemia between the two groups.

CONCLUSION

Our study found no significant impact on postnatal feed tolerance and mesenteric blood flow among preterm VLBW neonates with antenatal MgSO4 exposure.

Granulocytic Myeloid-Derived Suppressor Cells in Breast Milk (BM-MDSC) Correlate with Gestational Age and Postnatal Age and Are Influenced by Infant's Sex

BACKGROUND

Infections are the main cause of death in preterm infants. Causative agents often descend from the intestinal flora of the infected neonate, indicating insufficient protection by the mucosal barrier. Breast milk (BM) contains different subsets of immune cells. We recently showed that BM contains significant numbers of myeloid-derived suppressor cells (MDSC)-immune cells that actively suppress pro-inflammatory immune responses-and hypothesized that the transfer of BM-MDSC may modulate the mucosal immunity of the newborn.

METHODS

Percentages of MDSC in the BM from mothers of 86 preterm infants between 23 + 0 and 36 + 6 weeks of gestation during their first five postnatal weeks were analyzed by flow cytometry and correlated with maternal and infant characteristics.

RESULTS

Percentages of BM-MDSC positively correlated with gestational age and postnatal age. The expression of activation markers on BM-MDSC did not change with gestational age, but it decreased with postnatal age. Mothers who received antepartum tocolytics had lower percentages of BM-MDSC, and infant's sex strongly influenced percentages of BM-MDSC.

CONCLUSION

Our results point toward a role of BM-MDSC for immune regulation in the neonatal gut, making them a potential target of immune-based therapies shortly after birth.

Dichotomous development of the gut microbiome in preterm infants

BACKGROUND

Preterm infants are at risk of developing intestinal dysbiosis with an increased proportion of Gammaproteobacteria. In this study, we sought the clinical determinants of the relative abundance of feces-associated Gammaproteobacteria in very low birth weight (VLBW) infants. Fecal microbiome was characterized at ≤ 2 weeks and during the 3rd and 4th weeks after birth, by 16S rRNA amplicon sequencing. Maternal and infant clinical characteristics were extracted from electronic medical records. Data were analyzed by linear mixed modeling and linear regression.

RESULTS

Clinical data and fecal microbiome profiles of 45 VLBW infants (gestational age 27.9 ± 2.2 weeks; birth weight 1126 ± 208 g) were studied. Three stool samples were analyzed for each infant at mean postnatal ages of 9.9 ± 3, 20.7 ± 4.1, and 29.4 ± 4.9 days. The average relative abundance of Gammaproteobacteria was 42.5% (0-90%) at ≤ 2 weeks, 69.7% (29.9-86.9%) in the 3rd, and 75.5% (54.5-86%) in the 4th week (p < 0.001). Hierarchical and K-means clustering identified two distinct subgroups: cluster 1 started with comparatively low abundance that increased with time, whereas cluster 2 began with a greater abundance at ≤ 2 weeks (p < 0.001) that decreased over time. Both groups resembled each other by the 3rd week. Single variants of Klebsiella and Staphylococcus described variance in community structure between clusters and were shared between all infants, suggesting a common, hospital-derived source. Fecal Gammaproteobacteria was positively associated with vaginal delivery and antenatal steroids.

CONCLUSIONS

We detected a dichotomy in gut microbiome assembly in preterm infants: some preterm infants started with low relative gammaproteobacterial abundance in stool that increased as a function of postnatal age, whereas others began with and maintained high abundance. Vaginal birth and antenatal steroids were identified as predictors of Gammaproteobacteria abundance in the early (≤ 2 weeks) and later (3rd and 4th weeks) stool samples, respectively. These findings are important in understanding the development of the gut microbiome in premature infants.

Neutrophil chemotaxis and transcriptomics in term and preterm neonates

Neutrophils play a crucial role in combating life-threatening bacterial infections in neonates. Previous studies investigating neonatal cell function have been limited because of restricted volume sampling. Here, using novel microfluidic approaches, we provide the first description of neutrophil chemotaxis and transcriptomics from whole blood of human term and preterm neonates, as well as young adults. Ex vivo percent cell migration, neutrophil velocity, and directionality to N-formylmethionyl-leucyl-phenylalanine were measured from whole blood using time-lapse imaging of microfluidic chemotaxis. Genome-wide expression was also evaluated in CD66b⁺ cells using microfluidic capture devices. Neutrophils from preterm neonates migrated in fewer numbers compared to term neonates (preterm 12.3%, term 30.5%, P = 0.008) and at a reduced velocity compared to young adults (preterm 10.1 μm/min, adult 12.7 μm/min, P = 0.003). Despite fewer neutrophils migrating at slower velocities, neutrophil directionality from preterm neonates was comparable to adults and term neonates. 3607 genes were differentially expressed among the 3 groups (P < 0.001). Differences in gene expression between neutrophils from preterm and term neonates were consistent with reduced pathogen recognition and antimicrobial activity but not neutrophil migration, by preterm neonates. In summary, preterm neonates have significant disturbances in neutrophil chemotaxis compared to term neonates and adults, and these differences in phenotype appear at the transcriptional level to target inflammatory pathways in general, rather than in neutrophil migration and chemotaxis.

Age-Appropriate Functions and Dysfunctions of the Neonatal Neutrophil

Neonatal and adult neutrophils are distinctly different from one another due to well-defined and documented deficiencies in neonatal cells, including impaired functions, reduced concentrations of microbicidal proteins and enzymes necessary for pathogen destruction, and variances in cell surface receptors. Neutrophil maturation is clearly demonstrated throughout pregnancy from the earliest hematopoietic precursors in the yolk sac to the well-developed myeloid progenitor cells in the bone marrow around the seventh month of gestation. Notable deficiencies of neonatal neutrophils are generally correlated with gestational age and clinical condition, so that the least functional neutrophils are found in the youngest, sickest neonates. Interruption of normal gestation secondary to preterm birth exposes these shortcomings and places the neonate at an exceptionally high rate of infection and sepsis-related mortality. Because the fetus develops in a sterile environment, neonatal adaptive immune responses are deficient from lack of antigen exposure in utero. Newborns must therefore rely on innate immunity to protect against early infection. Neutrophils are a vital component of innate immunity since they are the first cells to respond to and defend against bacterial, viral, and fungal infections. However, notable phenotypic and functional disparities exist between neonatal and adult cells. Below is review of neutrophil ontogeny, as well as a discussion regarding known differences between preterm and term neonatal and adult neutrophils with respect to cell membrane receptors and functions. Our analysis will also explain how these variations decrease with postnatal age.

[Need for resuscitation in preterm neonates less than 32 weeks treated with antenatal magnesium sulphate for neuroprotection]

INTRODUCTION

Magnesium sulphate administration is recommended for foetal neuroprotection in pregnant women at imminent risk of early preterm birth.

OBJECTIVE

To evaluate the relationship between intrapartum magnesium sulphate for foetal neuroprotection and delivery room resuscitation of preterm infants less 32 weeks.

PATIENTS AND METHOD

A prospective observational study was conducted on preterm infants less 32 weeks exposed to magnesium sulphate for neuroprotection, and a comparison made with another historic group immediately before starting this treatment. Cases in both groups that had not reached lung maturity with corticosteroids were rejected. The rates of resuscitation, morbidity and mortality for each of the groups were analysed and compared.

RESULTS

There was a total of 107 preterm, with 56 exposed to magnesium sulphate. Rate of advanced resuscitation were similar between the two groups. There were no other differences in mortality, invasive mechanical ventilation, time to first stool, and other comorbidities.

CONCLUSIONS

Intrapartum magnesium sulphate for foetal neuroprotection was not associated with an increased need for intensive delivery room resuscitation and other morbidities in these cohorts of less than 32 weeks preterm infants.

Ionized magnesium and gestational age

OBJECTIVE

Investigation of magnesium (Mg) homeostasis has re-emerged as an area of interest in preterm born neonates who are at risk for brain pathology. However, data regarding the association between the biologically active ionized form of Mg and gestational age (GA) at an early stage of life in newborn infants are controversial.

METHODS

We evaluated the total and ionized Mg electrolyte (TMg and IMg) as well as the calcium (TCa and ICa) and pH in the cord blood and on day 2 of life in 22 neonates born at different gestational ages (< 32, 32-34 and > or =35 week) without magnesium tocolysis and absence of serious complications during pregnancy and delivery.

RESULTS

The IMg fraction that accounted for 68.1+/-5.1% of the TMg in the cord blood and 67.9+/-4.5% of the TMg on day 2 of life, was significantly higher in very preterm infants (GA< 32 week) as compared to neonates with GA > 35 week. Higher IMg levels were correlated with the lower pH that was recorded in the cord blood of the very preterm infants (correlation coefficient, r=-0.80, p< 0.0001) and ICa (r = -0.52, P< 0.01). Lower pH also was correlated with the GA (P< 0.0001). However, standard multiple regression analysis showed significant association between IMg levels and decreased pH but not the gestational age or ICa (beta=-1.10+/-0.21, p< 0.00009).

CONCLUSION

Extremely preterm infants even without additional exposure to tocolytic magnesium are at risk for the lower pH associated elevation of ionized Mg, which should be considered during the management of these infants in order to prevent hypermagnesemia-related pathology.

Dysfunction of innate immunity and associated pathology in neonates

The neutrophils and complement system are the critical elements of innate immunity mainly due to participation in the first line of defense against microorganisms by means of phagocytosis, lysis of bacteria and activation of naive B-lymphocytes. In this report we provide an overview of the up to date information regarding the neutrophil and complement system's functional ability in newborn infants in association with the maternal conditions that exist during the intrauterine stage, gestational age and post-neonatal pathology. The neonates' capacity to control the neutrophil and complement protein activation process has also been discussed because of the evidence that uncontrolled activation of these immune elements provides a significant contribution to the tissue damage and subsequent pathology. The authors are confident that despite the many unanswered questions this review updates their knowledge and points the need for further research to clarify the role of the age-associated dysfunction of neutrophils and complement system in the infection and inflammation related pathology of newborn infants.