Probiotic Supplementation in Preterm Infants Does Not Affect the Risk of Bronchopulmonary Dysplasia: A Meta-Analysis of Randomized Controlled Trials

The Role of the Airway and Gut Microbiome in the Development of Chronic Lung Disease of Prematurity

Chronic lung disease (CLD) of prematurity, a common cause of morbidity and mortality in preterm-born infants, has a multifactorial aetiology. This review summarizes the current evidence for the effect of the gut and airway microbiota on the development of CLD, highlighting the differences in the early colonisation patterns in preterm-born infants compared to term-born infants. Stool samples from preterm-born infants who develop CLD have less diversity than those who do not develop CLD. Pulmonary inflammation, which is a hallmark in the development of CLD, may potentially be influenced by gut bacteria. The respiratory microbiota is less abundant than the stool microbiota in preterm-born infants. There is a lack of clear evidence for the role of the respiratory microbiota in the development of CLD, with results from individual studies not replicated. A common finding is the presence of a single predominant bacterial genus in the lungs of preterm-born infants who develop CLD. Probiotic preparations have been proposed as a potential therapeutic strategy to modify the gut or lung microbiota with the aim of reducing rates of CLD but additional robust evidence is required before this treatment is introduced into routine clinical practice.

Effects of Probiotics on Preterm Infant Gut Microbiota Across Populations: A Systematic Review and Meta-Analysis

Microbiota in early life is closely associated with the health of infants, especially premature ones. Probiotics are important drivers of gut microbiota development in preterm infants; however, there is no consensus regarding the characteristics of specific microbiota in preterm infants receiving probiotics. In this study, we performed a meta-analysis of 5 microbiome data sets (1816 stool samples from 706 preterm infants) to compare the gut microbiota of preterm infants exposed to probiotics with that of preterm infants not exposed to probiotics across populations. Despite study-specific variations, we found consistent differences in gut microbial composition and predicted functional pathways between the control and probiotic groups across different cohorts of preterm infants. The enrichment of Acinetobacter, Bifidobacterium, and Lactobacillus spp and the depletion of the potentially pathogenic bacteria Finegoldia, Veillonella, and Klebsiella spp. were the most consistent changes in the gut microbiota of preterm infants supplemented with probiotics. Probiotics drove microbiome transition into multiple preterm gut community types, and notably, preterm gut community type 3 had the highest α-diversity, with enrichment of Bifidobacterium and Bacteroides spp. At the functional level, the major predicted microbial pathways involved in peptidoglycan biosynthesis consistently increased in preterm infants supplemented with probiotics; in contrast, the crucial pathways associated with heme biosynthesis consistently decreased. Interestingly, Bifidobacterium sp. rather than Lactobacillus sp. gradually became dominant in gut microbiota of preterm infants using mixed probiotics, although both probiotic strains were administered at the same dosage. Taken together, our meta-analysis suggests that probiotics contribute to reshaping the microbial ecosystem of preterm infants at both the taxonomic and functional levels of the bacterial community. More standardized and relevant studies may contribute to better understanding the crosstalk among probiotics, the gut microbiota, and subsequent disease risk, which could help to give timely nutritional feeding guidance to preterm infants. This systematic review and meta-analysis was registered at PROSPERO (https://www.crd.york.ac.uk/PROSPERO/) as CRD42023447901.

State of the Art of Probiotic Use in Neonatal Intensive Care Units in French-Speaking European Countries

The effectiveness of probiotics in reducing the incidence of necrotizing enterocolitis has been supported by a very large number of studies. However, the utilization of probiotics in preterm infants remains a topic of debate. This study aims to assess the rate of probiotic use in European neonatal intensive care units (NICUs), compare administration protocols, and identify barriers and concerns associated with probiotic use. An online questionnaire was distributed via email to European NICUs between October 2020 and June 2021. Different questions related to the frequency of probiotic use were proposed. Data on probiotic administration protocols and reasons for non-utilization were collected. The majority of responses were from France and Switzerland, with response rates of 85% and 89%, respectively. A total of 21% of French NICUs and 100% of Swiss NICUs reported routine probiotic use. There was significant heterogeneity in probiotic administration protocols, including variations in probiotic strains, administration, and treatment duration. The main obstacles to routine probiotic use were the absence of recommendations, lack of consensus on strain selection, insufficient scientific evidence, and concerns regarding potential adverse effects. The rate of routine probiotic administration remains low in European NICUs, with heterogeneity among protocols. Further trials are necessary to elucidate optimal treatment modalities and ensure safety of administration.

Microbial signatures in amniotic fluid at preterm birth and association with bronchopulmonary dysplasia

BACKGROUND

Microbiome dysbiosis can have long-lasting effects on our health and induce the development of various diseases. Bronchopulmonary dysplasia (BPD) is a multifactorial disease with pre- and postnatal origins including intra-amniotic infection as main risk factor. Recently, postnatal pathologic lung microbiota colonization was associated with BPD. The objectives of this prospective observational cohort study were to describe differences in bacterial signatures in the amniotic fluid (AF) of intact pregnancies without clinical signs or risk of preterm delivery and AF samples obtained during preterm deliveries and their variations between different BPD disease severity stages.

METHODS

AF samples were collected under sterile conditions during fetal intervention from intact pregnancies (n = 17) or immediately before preterm delivery < 32 weeks (n = 126). Metabarcoding based approaches were used for the molecular assessment of bacterial 16S rRNA genes to describe bacterial community structure.

RESULTS

The absolute amount of 16S rRNA genes was significantly increased in AF of preterm deliveries and detailed profiling revealed a reduced alpha diversity and a significant change in beta diversity with a reduced relative abundance of 16S rRNA genes indicative for Lactobacillus and Acetobacter while Fusobacterium, Pseudomonas, Ureaplasma and Staphylococcus 16S rRNA gene prevailed. Although classification of BPD by disease severity revealed equivalent absolute 16S rRNA gene abundance and alpha and beta diversity in no, mild and moderate/severe BPD groups, for some 16S rRNA genes differences were observed in AF samples. Bacterial signatures of infants with moderate/severe BPD showed predominance of 16S rRNA genes belonging to the Escherichia-Shigella cluster while Ureaplasma and Enterococcus species were enriched in AF samples of infants with mild BPD.

CONCLUSIONS

Our study identified distinct and diverse intrauterine 16S rRNA gene patterns in preterm infants immediately before birth, differing from the 16S rRNA gene signature of intact pregnancies. The distinct 16S rRNA gene signatures at birth derive from bacteria with varying pathogenicity to the immature lung and are suited to identify preterm infants at risk. Our results emphasize the prenatal impact to the origins of BPD.

Early gut microbiota intervention in premature infants: Application perspectives

BACKGROUND

Preterm birth is the leading cause of death in children under the age of five. One of the major factors contributing to the high risk of diseases and deaths in premature infants is the incomplete development of the intestinal immune system. The gut microbiota has been widely recognized as a critical factor in promoting the development and function of the intestinal immune system after birth. However, the gut microbiota of premature infants is at high risk of dysbiosis, which is highly associated with adverse effects on the development and education of the early life immune system. Early intervention can modulate the colonization and development of gut microbiota and has a long-term influence on the development of the intestinal immune system.

AIM OF REVIEW

This review aims to summarize the characterization, interconnection, and underlying mechanism of gut microbiota and intestinal innate immunity in premature infants, and to discuss the status, applicability, safety, and prospects of different intervention strategies in premature infants, thus providing an overview and outlook of the current applications and remaining gaps of early intervention strategies in premature infants.

KEY SCIENTIFIC CONCEPTS OF REVIEW

This review is focused on three key concepts. Firstly, the gut microbiota of premature infants is at high risk of dysbiosis, resulting in dysfunctional intestinal immune system processes. Secondly, contributing roles of early intervention have been observed in improving the intestinal environment and promoting gut microbiota colonization, which is significant in the development and function of gut immunity in premature infants. Thirdly, different strategies of early intervention, such as probiotics, fecal microbiota transplantation, and nutrients, show different safety, applicability, and outcome in premature infants, and the underlying mechanism is complex and poorly understood.

Rad1 attenuates DNA double-strand breaks and cell cycle arrest in type II alveolar epithelial cells of rats with bronchopulmonary dysplasia

BACKGROUND

Bronchopulmonary dysplasia (BPD) is the most common and serious chronic lung disease in preterm infants with pathological characteristics of arrested lung development. DNA double-strand breaks (DSBs) are a serious manifestation of oxidative stress damage, but little is known about the role of DSBs in BPD. The current study set out to detect DSB accumulation and cell cycle arrest in BPD and study the expression of genes related to DNA damage and repair in BPD through DNA damage signaling pathway-based PCR array to determine a suitable target to improve arrested lung development associated with BPD.

METHODS

DSB accumulation and cell cycle arrest were detected in a BPD animal model and primary cells, then a DNA damage signaling pathway-based PCR array was used to identify the target of DSB repair in BPD.

RESULTS

DSB accumulation and cell cycle arrest were shown in BPD animal model, primary type II alveolar epithelial cells (AECII) and cultured cells after exposure to hyperoxia. Of the 84 genes in the DNA damage-signaling pathway PCR array, eight genes were overexpressed and 11 genes were repressed. Rad1, an important protein for DSB repair, was repressed in the model group. Real-time PCR and western blots were used to verify the microarray results. Next, we confirmed that silencing Rad1 expression aggravated the accumulation of DSBs and cell cycle arrest in AECII cells, whereas its overexpression alleviated DSB accumulation and cell cycle arrest.

CONCLUSIONS

The accumulation of DSBs in AECII might be an important cause of alveolar growth arrest associated with BPD. Rad1 could be an effective target for intervention to improve this arrest in lung development associated with BPD.

The clinical value of lung ultrasound in premature infants with bronchopulmonary dysplasia

OBJECTIVE

This study aimed to explore the risk factors of bronchopulmonary dysplasia in premature infants and the clinical application value of lung ultrasound in the diagnosis of bronchopulmonary dysplasia.

METHODS

A total of 80 premature infants with a gestational age of <32 weeks or a birth weight of <1,500 g who were treated in our hospital from January to August 2021 were randomly divided into a bronchopulmonary dysplasia group (n=12) and a non-bronchopulmonary dysplasia group (n=62). The clinical data, lung ultrasound, and X-ray image characteristics of the two groups were compared.

RESULTS

Among the 74 preterm infants, 12 preterm infants were diagnosed with bronchopulmonary dysplasia, and 62 preterm infants were determined not to have bronchopulmonary dysplasia. There were significant differences in sex, severe asphyxia, invasive mechanical ventilation, premature membrane ruptures, and intrauterine infection between the two groups (p<0.05). Lung ultrasound showed abnormal pleural lines and alveolar-interstitial syndrome in all 12 patients with bronchopulmonary dysplasia and vesicle inflatable signs in 3 patients. Before clinical diagnosis, the accuracy, sensitivity, specificity, positive predictive value, and negative predictive value of lung ultrasound in the diagnosis of bronchopulmonary dysplasia were 98.65, 100, 98.39, 92.31, and 100%, respectively. The accuracy, sensitivity, specificity, positive predictive value, and negative predictive value of X-rays in the diagnosis of bronchopulmonary dysplasia were 85.14, 75.00, 87.10, 52.94, and 94.74%, respectively.

CONCLUSION

The diagnostic efficiency of lung ultrasound for premature bronchopulmonary dysplasia is better than that of X-rays. The application of lung ultrasound can screen patients with bronchopulmonary dysplasia early for timely intervention.

When inflammation meets lung development-an update on the pathogenesis of bronchopulmonary dysplasia

Even more than 50 years after its initial description, bronchopulmonary dysplasia (BPD) remains one of the most important and lifelong sequelae following premature birth. Tremendous efforts have been undertaken since then to reduce this ever-increasing disease burden but a therapeutic breakthrough preventing BPD is still not in sight. The inflammatory response provoked in the immature lung is a key driver of distorted lung development and impacts the formation of alveolar, mesenchymal, and vascular structures during a particularly vulnerable time-period. During the last 5 years, new scientific insights have led to an improved pathomechanistic understanding of BPD origins and disease drivers. Within the framework of current scientific progress, concepts involving disruption of the balance of key inflammatory and lung growth promoting pathways by various stimuli, take center stage. Still today, the number of efficient therapeutics available to prevent BPD is limited to a few, well-established pharmacological interventions including postnatal corticosteroids, early caffeine administration, and vitamin A. Recent advances in the clinical care of infants in the neonatal intensive care unit (NICU) have led to improvements in survival without a consistent reduction in the incidence of BPD. Our update provides latest insights from both preclinical models and clinical cohort studies and describes novel approaches to prevent BPD.

Endothelial dysfunction in preterm infants: The hidden legacy of uteroplacental pathologies

Millions of infants are born prematurely every year worldwide. Prematurity, particularly at lower gestational ages, is associated with high mortality and morbidity and is a significant global health burden. Pregnancy complications and preterm birth syndrome strongly impact neonatal clinical phenotypes and outcomes. The vascular endothelium is a pivotal regulator of fetal growth and development. In recent years, the key role of uteroplacental pathologies impairing endothelial homeostasis is emerging. Conditions leading to very and extremely preterm birth can be classified into two main pathophysiological patterns or endotypes: infection/inflammation and dysfunctional placentation. The first is frequently related to chorioamnionitis, whereas the second is commonly associated with hypertensive disorders of pregnancy and fetal growth restriction. The nature, timing, and extent of prenatal noxa may alter fetal and neonatal endothelial phenotype and functions. Changes in the luminal surface, oxidative stress, growth factors imbalance, and dysregulation of permeability and vascular tone are the leading causes of endothelial dysfunction in preterm infants. However, the available evidence regarding endothelial physiology and damage is limited in neonates compared to adults. Herein, we discuss the current knowledge on endothelial dysfunction in the infectious/inflammatory and dysfunctional placentation endotypes of prematurity, summarizing their molecular features, available biomarkers, and clinical impact. Furthermore, knowledge gaps, shadows, and future research perspectives are highlighted.

Necrotizing enterocolitis and the gut-lung axis

The recently recognized connection between the gut microbiota and pulmonary disease has been termed the gut-lung axis. However, broader connections link the gut and the lungs and these organ systems are tightly interrelated in both homeostasis and disease. This concept is often ignored in the compartmentalized treatment of pulmonary or gastrointestinal disease. In newborns, the most severe gastrointestinal complication of prematurity, necrotizing enterocolitis, and the most severe pulmonary complication, bronchopulmonary dysplasia, both produce significant systemic morbidity. In this review, we highlight the often neglected pathophysiology of the gut-lung axis contributes to increased risk of bronchopulmonary dysplasia in premature infants with necrotizing enterocolitis.

Association between probiotics and bronchopulmonary dysplasia in preterm infants

Bronchopulmonary dysplasia is a chronic pulmonary disease with a high incidence in premature infants, and there is still no effective treatment. The purpose of our study was to analyze the association between the use of probiotics and BPD in premature infants. We retrospectively collected clinical data of infants with gestational age < 32 weeks admitted to the NICU of The First Hospital of Jilin University from January 1, 2019 to March 31, 2020. Demographic and clinicopathological data of the inclusion population were collected. The outcome was the incidence of BPD or death. The χ² tests was used to compare the categorical variables. The t test and non-parametric Wilcoxon rank-sum test were used to compare the continuous data. Univariate and multivariate logistic regression were used to analyze the association between probiotics and BPD. A total of 318 newborns met the inclusion criteria, of which 94 received probiotics and 224 received no probiotics. There were 16 deaths and 115 newborns with BPD in the included population. The results of univariate analysis showed differences in the maternal diabetes, the proportion of systemic antibiotics given to mother within 24 h before birth, the receiving rate of invasive mechanical ventilation, the prevalence of BPD/death, PDA, RDS and Ivh between newborns with and without probiotics (p < 0.05); The results of unadjusted univariate logistic regression model showed that probiotic (OR 0.034, 95% CI 0.012-0.096) was the factor affecting BPD in preterm infants (p < 0.05). Multivariate logistic regression result (OR 0.037, 95% CI 0.013-0.105) was consistent with univariate analysis (P < 0.001). Probiotics are associated with a reduced risk of BPD in preterm infants < 32 weeks of age. More prospective studies with large samples are still needed.

Gut microbiota and bronchopulmonary dysplasia

Bronchopulmonary dysplasia is a relatively common and severe complication of prematurity, and its pathogenesis remains ambiguous. Revolutionary advances in microbiological analysis techniques, together with the growing sophistication of the gut-lung axis hypothesis, have resulted in more studies linking gut microbiota dysbiosis to the occurrence and development of bronchopulmonary dysplasia. The present article builds on current findings to examine the intrinsic associations between gut microbiota and bronchopulmonary dysplasia. Gut microbiota dysbiosis may insult the intestinal barrier, triggering inflammation, metabolic disturbances, and malnutrition, consequences of which might impact bronchopulmonary dysplasia by altering the gut-lung axis. By evaluating the potential mechanisms, new therapeutic targets and potential therapeutic modalities for bronchopulmonary dysplasia can be identified from a microecological perspective.

Malnutrition, poor post-natal growth, intestinal dysbiosis and the developing lung

In extremely preterm infants, poor post-natal growth, intestinal dysbiosis and bronchopulmonary dysplasia are common, and each is associated with long-term complications. The central hypothesis that this review will address is that these three common conditions are interrelated. Challenges to studying this hypothesis include the understanding that malnutrition and poor post-natal growth are not synonymous and that there is not agreement on what constitutes a normal intestinal microbiota in this evolutionarily new population. If this hypothesis is supported, further study of whether "correcting" intestinal dysbiosis in extremely preterm infants reduces postnatal growth restriction and/or bronchopulmonary dysplasia is indicated.

Enteral Vitamin A for Reducing Severity of Bronchopulmonary Dysplasia: A Randomized Trial

BACKGROUND AND OBJECTIVES

Evidence suggests that intramuscular vitamin A reduces the risk of bronchopulmonary dysplasia (BPD) in preterm infants. Our objective was to compare enteral water-soluble vitamin A with placebo supplementation to reduce the severity of BPD in extremely preterm infants.

METHODS

We conducted a double-blind randomized controlled trial in infants <28 weeks' gestation who were to receive either enteral water-soluble vitamin A (5000 IU per day) or a placebo. Supplementation was started within 24 hours of introduction of feeds and continued until 34 weeks' postmenstrual age (PMA). The primary outcome was the severity of BPD, assessed by using the right shift of the pulse oximeter saturation versus the inspired oxygen pressure curve.

RESULTS

A total of 188 infants were randomly assigned. The mean ± SD birth weight (852 ± 201 vs 852 ± 211 g) and gestation (25.8 ± 1.49 vs 26.0 ± 1.39 weeks) were comparable between the vitamin A and placebo groups. There was no difference in the right shift (median [25th-75th percentiles]) of the pulse oximeter saturation versus inspired oxygen pressure curve (in kilopascals) between the vitamin A (11.1 [9.5-13.7]) and placebo groups (10.7 [9.5-13.1]) (P = .73). Enteral vitamin A did not affect diagnosis of BPD or other clinical outcomes. Plasma retinol levels were significantly higher in the vitamin A group versus the placebo group on day 28 and at 34 weeks' PMA.

CONCLUSIONS

Enteral water-soluble vitamin A supplementation improves plasma retinol levels in extremely preterm infants but does not reduce the severity of BPD.

Probiotics and Human Milk Oligosaccharides in Premature Infants

Intestinal dysbiosis precedes and is a likely causative factor in necrotizing enterocolitis (NEC) and many cases of late-onset sepsis. Randomized controlled trials and observational cohort studies demonstrate decreased risk of NEC, sepsis, and death with the administration of probiotic microbes and decreased risk of NEC and sepsis with feeding of human milk. Animal studies suggest promising mechanisms by which probiotic microbes and human milk oligosaccharides alter the composition of the intestinal microbiota and may prevent disease in premature infants. Inclusion of parents in discussions of the risks and benefits of human milk and probiotics for premature infants is essential.

Safety and efficacy of probiotic administration to preterm infants: ten common questions

In spite of a large number of randomized placebo-controlled clinical trials and observational cohort studies including >50,000 preterm infants from 29 countries that have demonstrated a decrease in the risk of necrotizing enterocolitis, death, and sepsis, routine prophylactic probiotic administration to preterm infants remains uncommon in much of the world. This manuscript reflects talks given at NEC Society Symposium in 2019 and is not intended to be a state-of-the-art review or systematic review, but a summary of the probiotic-specific aspects of the symposium with limited additions including a recent strain-specific network analysis and position statement from the European Society for Paediatric Gastroenterology Hepatology and Nutrition (ESPGHAN). We address ten common questions related to the intestinal microbiome and probiotic administration to the preterm infant.

Probiotics' efficacy in paediatric diseases: which is the evidence? A critical review on behalf of the Italian Society of Pediatrics

During the last decade several paediatric studies have been published with different possible indications for probiotics, leading to a global increase of probiotics' market. Nevertheless, different study designs, multiple single/combined strains and small sample size still leave many uncertainties regarding their efficacy. In addition, different regulatory and quality control issues make still very difficult the interpretation of the clinical data. The objective of this review is to critically summarise the current evidence on probiotics' efficacy and safety on a different number of pathologies, including necrotizing enterocolitis, acute infectious diarrhoea, allergic diseases and functional gastrointestinal disorders in order to guide paediatric healthcare professionals on using evidence-based probiotics' strains. To identify relevant data, literature searches were performed including Medline-PubMed, the Cochrane Library and EMBASE databases. Considering probiotics strain-specific effects, the main focus was on individual probiotic strains and not on probiotics in general.

Bacterial Colonization within the First Six Weeks of Life and Pulmonary Outcome in Preterm Infants <1000 g

Bronchopulmonary dysplasia (BPD) is a multifactorial disease mainly provoked by pre- and postnatal infections, mechanical ventilation, and oxygen toxicity. In severely affected premature infants requiring mechanical ventilation, association of bacterial colonization of the lung and BPD was recently disclosed. To analyze the impact of bacterial colonization of the upper airway and gastrointestinal tract on moderate/severe BPD, we retrospectively analyzed nasopharyngeal and anal swabs taken weekly during the first 6 weeks of life at a single center in n = 102 preterm infants <1000 g. Colonization mostly occurred between weeks 2 and 6 and displayed a high diversity requiring categorization. Analyses of deviance considering all relevant confounders revealed statistical significance solely for upper airway colonization with bacteria with pathogenic potential and moderate/severe BPD (p = 0.0043) while no link could be established to the Gram response or the gastrointestinal tract. Our data highlight that specific colonization of the upper airway poses a risk to the immature lung. These data are not surprising taking into account the tremendous impact of microbial axes on health and disease across ages. We suggest that studies on upper airway colonization using predefined categories represent a feasible approach to investigate the impact on the pulmonary outcome in ventilated and non-ventilated preterm infants.

The association between the microbes in the tracheobronchial aspirate fluid and bronchopulmonary dysplasia in preterm infants

OBJECTIVE

The study aimed to evaluate the association between microbes in the lower respiratory tract (LRT) and the srisk for severe bronchopulmonary dysplasia (sBPD) in premature infants.

METHODS

We conducted a retrospective, single-center study of preterm infants who were admitted to the neonatal intensive care unit (NICU) of Southern Medical University Affiliated Maternal & Child Health Hospital of Foshan, China, between January 2015 and December 2017. The microbes in the LRT were screened by using tracheobronchial aspirate fluid (TAF) culture.

RESULTS

One hundred and fifty-five infants were included in the analysis. Among 155 infants, 41 were diagnosed with sBPD, and 114 were diagnosed without sBPD. There were significant differences between infants with and without sBPD in regard to birth weight (BW), gestational age (GA), the duration of endotracheal ventilation and supplemental oxygen. The incidence of retinopathy (ROP) and sepsis was higher in the sBPD infants than in the infants without sBPD. There was a difference in the detection rate of Gram-negative bacteria (GNB) between the two groups. Stenotrophomonas maltophilia and Klebsiella pneumoniae were mainly detected in TAF.

CONCLUSIONS

The LRT microbes were different between infants with and without sBPD, and GNB is more frequently detected in sBPD infants.

Nutrients and Microbiota in Lung Diseases of Prematurity: The Placenta-Gut-Lung Triangle

Cardiorespiratory function is not only the foremost determinant of life after premature birth, but also a major factor of long-term outcomes. However, the path from placental disconnection to nutritional autonomy is enduring and challenging for the preterm infant and, at each step, will have profound influences on respiratory physiology and disease. Fluid and energy intake, specific nutrients such as amino-acids, lipids and vitamins, and their ways of administration -parenteral or enteral-have direct implications on lung tissue composition and cellular functions, thus affect lung development and homeostasis and contributing to acute and chronic respiratory disorders. In addition, metabolomic signatures have recently emerged as biomarkers of bronchopulmonary dysplasia and other neonatal diseases, suggesting a profound implication of specific metabolites such as amino-acids, acylcarnitine and fatty acids in lung injury and repair, inflammation and immune modulation. Recent advances have highlighted the profound influence of the microbiome on many short- and long-term outcomes in the preterm infant. Lung and intestinal microbiomes are deeply intricated, and nutrition plays a prominent role in their establishment and regulation. There is an emerging evidence that human milk prevents bronchopulmonary dysplasia in premature infants, potentially through microbiome composition and/or inflammation modulation. Restoring antibiotic therapy-mediated microbiome disruption is another potentially beneficial action of human milk, which can be in part emulated by pre- and probiotics and supplements. This review will explore the many facets of the gut-lung axis and its pathophysiology in acute and chronic respiratory disorders of the prematurely born infant, and explore established and innovative nutritional approaches for prevention and treatment.

Perspectives on Probiotics and Bronchopulmonary Dysplasia

Bronchopulmonary dysplasia (BPD) is a chronic respiratory disease of preterm infants, associated with high morbidity and hospitalization expenses. With the revolutionary advances in microbiological analysis technology, increasing evidence indicates that children with BPD are affected by lung microbiota dysbiosis, which may be related to the illness occurrence and progression. However, dysbiosis treatment in BPD patients has not been fully investigated. Probiotics are living microorganisms known to improve human health for their anti-inflammatory and anti-tumor effects, and particularly by balancing gut microbiota composition, which promotes gut-lung axis recovery. The aim of the present review is to examine current evidence of lung microbiota dysbiosis and explore potential applications of probiotics in BPD, which may provide new insights into treatment strategies of this disease.

Tobacco Smoking During Pregnancy Is Associated With Increased Risk of Moderate/Severe Bronchopulmonary Dysplasia: A Systematic Review and Meta-Analysis

Epidemiological evidence and animal studies support that intrauterine exposure to tobacco smoke disturbs lung development and has a negative effect in the pulmonary health of the offspring. Individual studies suggest an association between fetal exposure to maternal smoking and risk of developing bronchopulmonary dysplasia (BPD). However, this association has not yet been systematically investigated. We aimed to conduct a systematic review of studies reporting on tobacco smoking during pregnancy as potential risk factor for BPD. PubMed/MEDLINE and EMBASE databases were searched. BPD was defined as requirement of supplemental oxygen on postnatal day 28 (BPD28; all BPD), at the postmenstrual age (PMA) of 36 weeks (BPD36; moderate/severe BPD), or as requirement of more than 30% oxygen and/or positive pressure at 36 weeks PMA (severe BPD). Pooled risk ratios (RR) and 95% confidence intervals (CI) were calculated using a random-effects model. Of 2,894 potentially relevant studies, 33 met the inclusion criteria. The included studies evaluated 171,772 infants and included 30,445 cases of exposure to maternal smoking and 25,340 cases of BPD of any severity. Meta-analysis showed a significant association between tobacco smoking during pregnancy and BPD36 (17 studies, RR 1.126, 95% CI 1.008-1.259, p = 0.036), but could not demonstrate a significant association between tobacco smoking during pregnancy and BPD28 (16 studies, RR 1.021, 95% CI 0.924-1.129, p = 0.681), or severe BPD (3 studies, RR 1.143, 95% CI 0.528-2.478, p = 0.734). In conclusion, our data suggest that tobacco smoking during pregnancy increases the risk of moderate/severe BPD. Our results highlight the detrimental effects of tobacco smoking and reinforce the hypothesis of the involvement of prenatal insults in the etiopathogenesis of BPD.

Association of Chorioamnionitis With Bronchopulmonary Dysplasia Among Preterm Infants: A Systematic Review, Meta-analysis, and Metaregression

Importance

Bronchopulmonary dysplasia (BPD), a chronic lung disease of prematurity, remains one of the major and most common complications of very preterm birth. Insight into factors associated with the pathogenesis of BPD is key to improving its prevention and treatment.

Objective

To perform a systematic review, meta-analysis, and metaregression of clinical studies exploring the association between chorioamnionitis (CA) and BPD in preterm infants.

Data Sources

PubMed and Embase were searched without language restriction (last search, October 1, 2018). Key search terms included bronchopulmonary dysplasia, chorioamnionitis, and risk factors.

Study Selection

Included studies were peer-reviewed studies examining preterm (<37 weeks' gestation) or very low-birth-weight (<1500 g) infants and reporting primary data that could be used to measure the association between exposure to CA and the development of BPD.

Data Extraction and Synthesis

The Meta-analysis of Observational Studies in Epidemiology (MOOSE) guideline was followed. Data were independently extracted by 2 researchers. A random-effects model was used to calculate odds ratios (ORs) and 95% CIs. Heterogeneity in effect size across studies was studied using multivariate, random-effects metaregression analysis.

Main Outcomes and Measures

The primary outcome was BPD, defined as supplemental oxygen requirement on postnatal day 28 (BPD28) or at the postmenstrual age of 36 weeks (BPD36). Covariates considered as potential confounders included differences between CA-exposed and CA-unexposed infants in gestational age, rates of respiratory distress syndrome (RDS), exposure to antenatal corticosteroids, and rates of early- and late-onset sepsis.

Results

A total of 3170 potentially relevant studies were found, of which 158 met the inclusion criteria (244 096 preterm infants, 20 971 CA cases, and 24 335 BPD cases). Meta-analysis showed that CA exposure was significantly associated with BPD28 (65 studies; OR, 2.32; 95% CI, 1.88-2.86; P < .001; heterogeneity: I2 = 84%; P < .001) and BPD36 (108 studies; OR, 1.29; 95% CI, 1.17-1.42; P < .001; heterogeneity: I2 = 63%; P < .001). The association between CA and BPD remained significant for both clinical and histologic CA. In addition, significant differences were found between CA-exposed and CA-unexposed infants in gestational age, birth weight, odds of being small for gestational age, exposure to antenatal corticosteroids, and early- and late-onset sepsis. Chorioamnionitis was not significantly associated with RDS (48 studies; OR, 1.10; 95% CI, 0.92-1.34; P = .24; heterogeneity: I2 = 90%; P < .001), but multivariate metaregression analysis with backward elimination revealed that a model combining the difference in gestational age and the odds of RDS was associated with 64% of the variance in the association between CA and BPD36 across studies.

Conclusions and Relevance

The results of this study confirm that among preterm infants, exposure to CA is associated with a higher risk of developing BPD, but this association may be modulated by gestational age and risk of RDS.

Probiotic mechanisms of action

Intestinal dysbiosis is associated with a large number of disease processes including necrotizing enterocolitis and late-onset sepsis in preterm infants and colic and antibiotic-associated diarrhea in term infants. Probiotic microbes are increasingly administered to infants with the intent of decreasing risk of these acute diseases as well as chronic diseases of childhood such as asthma and atopic disease. The mechanisms by which probiotics decrease inflammation, decrease intestinal permeability, alter the intestinal microbiota, and influence metabolism have been discovered through both in vitro studies and in vivo in animal models. We review key mechanisms by which probiotic microbes improve health with emphasis on recent discoveries in the field.

The future of probiotics in the preterm infant

Probiotic administration to preterm infants is not universal despite randomised trial data from >10,000 infants, significant observational data and multiple meta-analyses. Advocates point to reductions in necrotising enterocolitis and sepsis, 'sceptics' hold concerns over data quality/interpretation or risks. Issues revolve around different products, primary outcomes, uncertain dosing strategies and individual large 'negative' trials alongside probiotic associated sepsis and quality control concerns. We review concerns and how to move probiotic use forward. Surprisingly little is known about parental perspectives, vital to inform next steps. How to share information and decisions around probiotic use now, and how this impacts on future available strategies is discussed. We address placebo controlled trials and propose alternate designs, including head to head studies, using 'routine' data collection systems, opt out consents and 'learning technologies' embedded in health care systems. We also raise the importance of underpinning mechanistic work to inform future trials.

Dysbiosis and Prematurity: Is There a Role for Probiotics?

Healthy microbiota is a critical mediator in maintaining health and it is supposed that dysbiosis could have a role in the pathogenesis of a number of diseases. Evidence supports the hypothesis that maternal dysbiosis could act as a trigger for preterm birth; aberrant colonization of preterm infant gut might have a role in feeding intolerance and pathogenesis of necrotizing enterocolitis. Despite several clinical trials and meta-analyses, it is still not clear if modulation of maternal and neonatal microbiota with probiotic supplementation decreases the risk of preterm birth and its complications.

Arguments for routine administration of probiotics for NEC prevention

PURPOSE OF REVIEW

Probiotic administration to premature infants for the purpose of prevention of necrotizing enterocolitis is common in many parts of the world but uncommon in the United States. The present review will emphasize recent findings in support of routine administration of probiotics to this highly vulnerable population.

RECENT FINDINGS

Additional evidence from animal models describing mechanisms of protection of probiotics in the immature gut and updated meta-analyses of randomized placebo-controlled trials and observational cohorts are presented (now including more than 40 000 premature infants from countries across the globe).

SUMMARY

The preponderance of evidence suggests that probiotic administration to premature infants is well tolerated and decreases the risk of death, necrotizing enterocolitis, and sepsis. Further comparisons of probiotic administration to placebo are not likely to alter these conclusions. Rather, future work should focus on assurance of high-quality products with demonstrated purity and viability of probiotic microbes, and future clinical trials should focus on comparisons between high-quality products and doses.

Probiotic research in neonates with congenital gastrointestinal surgical conditions - Now is the time

Neonates with congenital gastrointestinal surgical conditions (CGISC) receive parenteral nutrition, get exposed to multiple courses of antibiotics, undergo invasive procedures, and are nursed in intensive care units. They do not receive early enteral feeding and have limited opportunities for skin to skin contact with their mothers. Many of these infants receive gastric acid suppression therapies. All these factors increase the risk of gut dysbiosis in these infants. Gut dysbiosis is known to be associated with increased risk of infections and other morbidities in ICU patients. Experimental studies have shown that probiotics inhibit gut colonization with pathogenic bacteria, enhance gut barrier function, facilitate colonization with healthy commensals, protect from enteropathogenic infection through production of acetate, reduce antimicrobial resistance, enhance innate immunity, and increase the maturation of the enteric nervous system and promote gut peristalsis. Through these mechanisms, probiotics have the potential to decrease the risk of sepsis and inflammation, improve feed tolerance and minimise cholestasis in neonates with CGISC. Among preterm non-surgical infants, evidence from more than 35 RCTs and multiple observational studies have shown probiotics to be safe and beneficial. A RCT in neonates (N=24) with gastroschisis found that probiotic supplementation partially attenuated gut dysbiosis. Two ongoing RCTs (total N=168) in neonates with gastrointestinal surgical conditions are expected to provide feasibility data to enable the conduct of large RCTs. Rigorous quality assurance of the probiotic product, ongoing microbial surveillance and clinical vigilance are warranted while conducting such RCTs.

Probiotics and the prevention of necrotizing enterocolitis

BACKGROUND

Immaturity of the host immune system and alterations in the intestinal microbiome appear to be key factors in the pathogenesis of necrotizing enterocolitis (NEC). The aim of this paper is to weigh the evidence for the use of probiotics to prevent NEC in premature infants.

METHODS

Animal studies, randomized controlled trials, observational cohort studies and meta-analyses involving administration of probiotic products for the prevention of NEC were reviewed. This review of the evidence summarizes the available preclinical and clinical data.

RESULTS

In animal models probiotic microbes alter the intestinal microbiome, decrease inflammation and intestinal permeability and decrease the incidence and severity of experimental NEC. In randomized, placebo-controlled trials and cohort studies of premature infants, probiotic microbes decrease the risk of NEC, death and sepsis.

CONCLUSION

Evidence is strong for the prevention of NEC with the use of combination probiotics in premature infants who receive breast milk. The potential risks and benefits of probiotic administration to premature infants should be carefully reviewed with parents.

TYPE OF STUDY

Therapeutic.

LEVEL OF EVIDENCE

I.

Predicting BPD: Lessons Learned From the Airway Microbiome of Preterm Infants

Bronchopulmonary dysplasia (BPD) is the chronic lung disease of prematurity with an operational definition, various different clinical phenotypes, and a complex, multifactorial etiology. Newer unbiased systems biology approaches have identified various "omic" factors associated with the pathogenesis and prediction of BPD. Recent microbi "omic" studies have discovered that airways of newborns harbor a low biomass but distinct microbiome signature as early as at the time of birth. This early airway microbiome may serve to prime the host immune system and may play a role in modulating the infant's future susceptibility to severe BPD development. Temporal changes are observed in airway microbiome of preterm infants from birth to the diagnosis of BPD, with an overall decrease in bacterial diversity, and development of a relative dysbiosis marked by increased Gammaproteobacteria and decreased Lactobacilli abundance. This review will summarize previous investigations of the airway microbiome in preterm infants, appraise the utility of using the airway microbiome to predict BPD development, discuss possible molecular mechanisms involved, and speculate on future microbiome-mediated therapeutics for BPD.

Somatic growth and the risks of bronchopulmonary dysplasia and pulmonary hypertension: connecting epidemiology and physiology 1

In the premature infant, poor growth in utero (fetal growth restriction) and in the first weeks of life (postnatal growth restriction) are associated with increased risk for bronchopulmonary dysplasia and pulmonary hypertension. In this review, we summarize the epidemiologic data supporting these associations, present a novel rodent model of postnatal growth restriction, and review 5 promising mechanisms by which poor nutrition may affect the developing lung. These observations support the hypothesis that nutritional and (or) pharmacologic interventions early in life may be able to decrease risk of the pulmonary complications of extreme prematurity.

Inherited nongenetic influences on the gut microbiome and immune system

The gut microbiome and the immune system codevelop around the time of birth, well after genetic information has been passed from the parents to the offspring. Each of these "organ systems" displays plasticity. The immune system can mount highly specific adaptive responses to newly encountered antigens, and the gut microbiota is affected by changes in the environment. Despite this plasticity, there is a growing appreciation that these organ systems, once established, are remarkably stable. In health, the immune system rapidly mounts responses to infections, and once cleared, resolves inflammatory responses to return to homeostasis. However, a skewed immune system, such as seen in allergy, does not easily return to homeostasis. Allergic responses are often seen to multiple antigens. Likewise, a dysbiotic gut microbiota is seen in multiple diseases. Attempts to reset the gut microbiota as a therapy for disease have met with varied success. Therefore, how these codeveloping "organ systems" become established is a central question relevant to our overall health. Recent observations suggest that maternal factors encountered both in utero and after birth can directly or indirectly impact the development of the offspring's gut microbiome and immune system. Here, we discuss how these nongenetic maternal influences can have long-term effects on the progeny's health.

Increased incidence of necrotizing enterocolitis associated with routine administration of Infloran™ in extremely preterm infants

We aimed to evaluate the isolation of strains contained in the Infloran™ probiotic preparation in blood cultures and its efficacy in reducing necrotizing enterocolitis (NEC) and late-onset sepsis (LOS) in extremely preterm infants. Routine use of probiotics was implemented in 2008. Infants born at <28 weeks gestational age were prospectively followed and compared with historical controls (HC) born between 2005 and 2008. Data on sepsis due to any of the two probiotic strains contained in Infloran and rates of LOS and NEC were analysed. A total of 516 infants were included. During the probiotic period (PC), none of the strains included in the administered probiotic product were isolated from blood cultures. Probiotic administration was associated with an increase in NEC stage II or higher (HC 10/170 [5.9%]; PC 46/346 [13.3%]; P=0.010). Surgical NEC was 12.1% in PC (42/346) versus 5.9% (10/170) in HC (P=0.029). Adjusting for confounders (sex, gestational age, antenatal steroids and human milk) did not change those trends (P=0.019). Overall, clinical LOS and the incidence of staphylococcal sepsis were lower in PC (172/342, 50.3, and 37%, respectively) compared with HC (102/169, 60.3 and 50.9%, respectively) (P=0.038 and P=0.003, respectively). No episodes of sepsis attributable to the probiotic product were recorded. The period of probiotic administration was associated with an increased incidence of NEC after adjusting for neonatal factors, but also with a reduction in the LOS rate.

Donor Human Milk Protects against Bronchopulmonary Dysplasia: A Systematic Review and Meta-Analysis

Bronchopulmonary dysplasia (BPD) is the most common complication after preterm birth. Pasteurized donor human milk (DHM) has increasingly become the standard of care for very preterm infants over the use of preterm formula (PF) if the mother's own milk (MOM) is unavailable. Studies have reported beneficial effects of DHM on BPD. We conducted a systematic review and meta-analysis of randomized controlled trials (RCTs) and observational studies on the effects of DHM on BPD and other respiratory outcomes. Eighteen studies met the inclusion criteria. Meta-analysis of RCTs could not demonstrate that supplementation of MOM with DHM reduced BPD when compared to PF (three studies, risk ratio (RR) 0.89, 95% confidence interval (CI) 0.60-1.32). However, meta-analysis of observational studies showed that DHM supplementation reduced BPD (8 studies, RR 0.78, 95% CI 0.67-0.90). An exclusive human milk diet reduced the risk of BPD, compared to a diet with PF and/or bovine milk-based fortifier (three studies, RR 0.80, 95% CI 0.68-0.95). Feeding raw MOM, compared to feeding pasteurized MOM, protected against BPD (two studies, RR 0.77, 95% CI 0.62-0.96). In conclusion, our data suggest that DHM protects against BPD in very preterm infants.