Nitrate reductase activity of bacteria in saliva of term and preterm infants

Prevalence and phylogenetic traits of nitrite-producing bacteria in raw ingredients and processed baby foods: Potential sources of foodborne infant methemoglobinemia

Nitrite, which has been mainly regarded as a chemical hazard, can induce infant methemoglobinemia. As for nitrite as a product of microbial metabolism, the contribution of the oral or gut microbiome has mostly received attention, whereas the role of nitrite-producing bacteria (NPBs) in food has been less elucidated. In this study, mesophilic NPBs were isolated from food samples (n = 320) composed of raw ingredients for weaning foods (n = 160; beetroot, broccoli, carrot, lettuce, rice powder, spinach, sweet potato, and honey) and processed baby foods (n = 160; cereal snack, cheese, yogurt, powdered infant formula, sorghum syrup, vegetable fruit juice, and weaning food). The phylogenetic diversity of the NPB strains was analyzed via 16S rRNA sequencing. All 15 food items harbored NPBs, with a prevalence of 71.9 % and 34.4 % for the raw ingredients and processed foods, respectively. The NPBs isolated from the foods were identified as Actinomycetota (Actinomycetes), Bacteroidota (Flavobacteriia, Sphingobacteriia), Bacillota (Bacilli), or Pseudomonadota (Alpha-, Beta-, and Gammaproteobacteria). Among the raw and processed foods, beetroot (85.0 %) and powdered infant formula (70.0 %) showed had the highest NPB prevalence (P > 0.05). Bacillota predominated in both types of food. The contamination source of Pseudomonadota, which was another major phylum present in the raw ingredients, was presumed to be the soil and endophytes in the seeds, whereas that of Bacillota was the manufacturing equipment used with the raw ingredients. Common species for probiotics, such as Lacticaseibacillus, Leuconostoc, Enterococcus, and Bacillus, were isolated and identified as NPBs. To our knowledge, this is the first study to reveal the taxonomical diversity and omnipresence of NPBs in food for babies. The results of this study highlight the importance of food-mediated microbiological risks of infant methemoglobinemia which are yet underrecognized.

Localisation of nitrate-reducing and highly abundant microbial communities in the oral cavity

The nitrate (NO3-) reducing bacteria resident in the oral cavity have been implicated as key mediators of nitric oxide (NO) homeostasis and human health. NO3--reducing oral bacteria reduce inorganic dietary NO3- to nitrite (NO2-) via the NO3--NO2--NO pathway. Studies of oral NO3--reducing bacteria have typically sampled from either the tongue surface or saliva. The aim of this study was to assess whether other areas in the mouth could contain a physiologically relevant abundance of NO3- reducing bacteria, which may be important for sampling in clinical studies. The bacterial composition of seven oral sample types from 300 individuals were compared using a meta-analysis of the Human Microbiome Project data. This analysis revealed significant differences in the proportions of 20 well-established oral bacteria and highly abundant NO3--reducing bacteria across each oral site. The genera included Actinomyces, Brevibacillus, Campylobacter, Capnocytophaga, Corynebacterium, Eikenella, Fusobacterium, Granulicatella, Haemophilus, Leptotrichia, Microbacterium, Neisseria, Porphyromonas, Prevotella, Propionibacterium, Rothia, Selenomonas, Staphylococcus, Streptococcus and Veillonella. The highest proportion of NO3--reducing bacteria was observed in saliva, where eight of the bacterial genera were found in higher proportion than on the tongue dorsum, whilst the lowest proportions were found in the hard oral surfaces. Saliva also demonstrated higher intra-individual variability and bacterial diversity. This study provides new information on where samples should be taken in the oral cavity to assess the abundance of NO3--reducing bacteria. Taking saliva samples may benefit physiological studies, as saliva contained the highest abundance of NO3- reducing bacteria and is less invasive than other sampling methods. These results inform future studies coupling oral NO3--reducing bacteria research with physiological outcomes affecting human health.

The Oral Microbiome as Mediator between Oral Hygiene and Its Impact on Nasopharyngeal Carcinoma

Oral hygiene and the alteration of the oral microbiome have been linked to nasopharyngeal carcinoma (NPC). This study aimed to investigate whether the oral microbiome plays a mediating role in the relationship between oral hygiene and NPC, and identify differential microbial taxonomies that potentially mediated this association. We conducted a case–control study that involved 218 NPC patients and 192 healthy controls. The 16S rRNA gene sequencing of the V4 region was performed to evaluate the composition of the oral microbiome. Mediation analysis was applied to explore the relationship among oral hygiene, the oral microbiome and NPC. We found that dental fillings and poor oral hygiene score were associated with increased risks of NPC (OR = 2.51 (1.52–4.25) and OR = 1.54 (1.02–2.33)). Mediation analysis indicated that dental fillings increased the risk of NPC by altering the abundance of Erysipelotrichales, Erysipelotrichaceae, Solobacterium and Leptotrichia wadei. In addition, Leptotrichia wadei also mediated the association between oral hygiene score and the risk of NPC. Our study confirmed that poor oral hygiene increased the risk of NPC, which was partly mediated by the oral microbiome. These findings might help us to understand the potential mechanism of oral hygiene influencing the risk of NPC via the microbiome.

Nitrite in breast milk: roles in neonatal pathophysiology

Dietary nitrate has beneficial effects on health maintenance and prevention of lifestyle-related diseases in adulthood by serving as an alternative source of nitric oxide (NO) through the enterosalivary nitrate-nitrite-NO pathway, particularly when endogenous NO generation is lacking due to vascular endothelial dysfunction. However, this pathway is not developed in the early postnatal period due to a lack of oral commensal nitrate-reducing bacteria and less saliva production than in adults. To compensate for the decrease in nitrite during this period, colostrum contains the highest amount of nitrite compared with transitional, mature, and even artificial milk, suggesting that colostrum plays an important role in tentatively replenishing nitrite, in addition to involving a nutritional aspect, until the enterosalivary nitrate-nitrite-NO pathway is established. Increasing evidence demonstrates that breast milk rich in nitrite can be effective in the prevention of neonatal infections and gastrointestinal diseases such as infantile hypertrophic pyloric stenosis and necrotizing enterocolitis, suggesting that breastfeeding is advantageous for newborns at risk, given the physiological role of nitrite in the early postnatal period. IMPACT: The aim of this review is to discuss the physiological roles of nitrite in breast milk and its implications for neonates. Nitrite in breast milk may compensate for the decrease in nitrite during the early neonatal period until the enterosalivary nitrate-nitrite-nitric oxide pathway is established. Breast milk rich in nitrite may be effective in the prevention of neonatal infections and gastrointestinal diseases by providing nitric oxide bioavailability.

Consumption pattern and genotoxic potential of various smokeless tobacco products in Assam, India: A public health concern

Smokeless tobacco (SLT) consumption is presumed to be one of the major causes of high incidence of oral cancer in India. The present study aimed to document various types of SLT products consumed and their potential impact on the genome instability on the population from Assam state in Northeast India. A cross-sectional study (n = 5000) showed that 60.56 % of the study population consumed at least one of the three forms (sadagura, zarda and khaini) of SLT of which 52.0 % were only sadagura users. Genotoxicity assessment using buccal cytome assay in 240 age and sex matched volunteers revealed that except for zarda, other forms of SLT induced significantly higher incidence micronuclei in the buccal epithelial cells compared to the control individuals. Similar effects were also observed in other cytome parameters related to cell proliferation, cytokinesis defects and cell death. Significantly higher incidence of micronucleus was observed among sadagura and khaini users in lymphocyte cytokinesis-blocked micronucleus assay. The addition of lime in sadagura increased the pH and anion levels which possibly result in higher absorption and may lead to the development of cellular anomalies.

Potential role for age as a modulator of oral nitrate reductase activity

Reduction of salivary nitrate to nitrite by oral nitrate reductase (NR) expressing bacteria has emerged as an integral pathway in regulating nitric oxide (NO) homeostasis and signaling. The oral microbiome is critical for this pathway. Variations in this pathway may underlie variable responses in the magnitude by which dietary or therapeutic nitrate modulates NO-signaling. The relationships between oral microbes and NR activity, and the factors that affect this relationship remain unclear however. Using a cross-sectional study design, the objective of this study was to determine the relationships between oral microbes and oral NR activity using a protocol that directly measures initial NR activity. Tongue swabs were collected from 28 subjects ranging in age from 21 to 73y. Initial NR activity showed a bell-shaped dependence with age, with activity peaking at ~40-50y and being lower but similar between younger (20-30y) and older (51-73) individuals. Microbiome relative abundance and diversity analyses, using 16s sequencing, demonstrated differences across age and identified both NR expressing and non-expressing bacteria in modulating initial NR activity. Finally, initial NR activity was measured in 3mo and 13mo old C57BL/6J mice. No differences in bacterial number were observed. However initial NR activity was significantly (80%) lower in 13mo old mice. Collectively, these data suggest that age is a variable in NR activity and may modulate responsiveness to dietary nitrate.

Bronchopulmonary dysplasia is associated with reduced oral nitrate reductase activity in extremely preterm infants

Oral microbiome mediated nitrate reductase (NR) activity regulates nitric oxide (NO) bioavailability and signaling. While deficits in NO-bioavailability impact several morbidities of extreme prematurity including bronchopulmonary dysplasia (BPD), whether oral NR activity is associated with morbidities of prematurity is not known. We characterized NR activity in extremely preterm infants from birth until 34 weeks' post menstrual age (PMA), determined whether changes in the oral microbiome contribute to changes in NR activity, and determined whether changes in NR activity correlated with disease. In this single center prospective cohort study (n = 28), we observed two surprising findings: (1) NR activity unexpectedly peaked at 29 weeks' PMA (p < 0.05) and (2) when infants were stratified for BPD status, infants who developed BPD had significantly less NR activity at 29 weeks' PMA compared to infants who did not develop BPD. Oral microbiota and NR activity may play a role in BPD development in extremely preterm infants, indicating potential for disease prediction and therapeutic targeting.

Nitrite-producing oral microbiome in adults and children

Recently, it was suggested that the nitrite (NO₂^-) produced from NO₃^- by oral bacteria might contribute to oral and general health. Therefore, we aimed to clarify the detailed information about the bacterial NO₂-production in the oral biofilm. Dental plaque and tongue-coating samples were collected, then the NO₂-producing activity was measured. Furthermore, the composition of the NO₂^--producing bacterial population were identified using the Griess reagent-containing agar overlay method and molecular biological method. NO₂^--producing activity per mg wet weight varied among individuals but was higher in dental plaque. Additionally, anaerobic bacteria exhibited higher numbers of NO₂^--producing bacteria, except in the adults' dental plaque. The proportion of NO₂^--producing bacteria also varied among individuals, but a positive correlation was found between NO₂^--producing activity and the number of NO₂^--producing bacteria, especially in dental plaque. Overall, the major NO₂^--producing bacteria were identified as Actinomyces, Schaalia, Veillonella and Neisseria. Furthermore, Rothia was specifically detected in the tongue coatings of children. These results suggest that dental plaque has higher NO₂^--producing activity and that this activity depends not on the presence of specific bacteria or the bacterial compositions, but on the number of NO₂^--producing bacteria, although interindividual differences were detected.

Nitric oxide metabolism in the human placenta during aberrant maternal inflammation

KEY POINTS

Nitric oxide (NO) is a gasotransmitter with important physiological and pathophysiological roles in pregnancy. There is limited information available about the sources and metabolism of NO and its bioactive metabolites (NOx) in both normal and complicated pregnancies. The present study characterized and quantified endogenous NOx in human and mouse placenta following determination of the stability of exogenous NOx in placental homogenates. NOx have differential stability in placental homogenates. NO and iron nitrosyl species (FeNOs), are relatively unstable in placental homogenates from normal placentas. Exogenous NO, nitrite and nitrosothiols react with placental homogenates to form iron nitrosyl complexes. FeNOs were also detected endogenously in mouse and human placenta. NOx levels in placental villous tissue are increased in fetal growth restriction vs. placentas from women with normal pregnancies, particularly in fetal growth restriction associated with pre-eclampsia. Villitis was not associated, however, with an increase in NOx levels in either normotensive or pre-eclamptic placentas. The results call for further investigation of FeNOs in normal and complicated pregnancies.

ABSTRACT

Nitric oxide (NO) is a gasotransmitter with important roles in pregnancy under both physiological and pathophysiological conditions. Although products of NO metabolism (NOx) also have significant bioactivity, little is known about the role of NO and NOx under conditions of aberrant placental inflammation during pregnancy. An ozone-based chemiluminescence approach was used to investigate the stability and metabolic fate of NOx in human placental homogenates from uncomplicated pregnancies in healthy mothers compared to that in placental tissue from normotensive and pre-eclamptic pregnancies complicated with fetal growth restriction (FGR) with and without villitis of unknown aetiology. We hypothesized that placental NOx would be increased in FGR vs. normal tissue, and be further increased in villitis vs. non-villitis placentas. Findings indicate that nitrate, nitrite and nitrosothiols, but not NO or iron nitrosyl species (FeNOs), are relatively stable in placental homogenates from normal placentas, and that NO, nitrite and nitrosothiols react with placental homogenates to form iron nitrosyl complexes. Furthermore, NOx levels in placental villous tissue are increased in FGR vs. placentas from women with normal pregnancies, particularly in FGR associated with pre-eclampsia. However, in contrast to our hypothesis, villitis was not associated with an increase in NOx levels in either normotensive or pre-eclamptic placentas. Our results also strongly support the involvement of FeNOs in both mouse and human placenta, and call for their further study as a critical mechanistic link between pre-eclampsia and fetal growth restriction.

Neonatal comorbidities and gasotransmitters

Hydrogen sulfide, nitric oxide, and carbon monoxide are endogenously produced gases that regulate various signaling pathways. The role of these transmitters is complex as constitutive production of these molecules may have anti-inflammatory, anti-microbial, and/or vasodilatory effects whereas induced production or formation of secondary metabolites may lead to cellular death. Given this fine line between friend and foe, therapeutic attenuation of these molecules' production has involved both inhibition of endogenous formation and therapeutic supplementation. All three gases have been implicated as regulators of critical aspects of neonatal physiology, and in turn, comorbidities including necrotizing enterocolitis, hypoxic ischemic encephalopathy, and pulmonary hypertension. In this review, we present current perspectives on these associations, highlight areas where insights remain sparse, and identify areas for potential for future investigations.

The role of gasotransmitters in neonatal physiology

The gasotransmitters, nitric oxide (NO), hydrogen sulfide (H₂S), and carbon monoxide (CO), are endogenously-produced volatile molecules that perform signaling functions throughout the body. In biological tissues, these small, lipid-permeable molecules exist in free gaseous form for only seconds or less, and thus they are ideal for paracrine signaling that can be controlled rapidly by changes in their rates of production or consumption. In addition, tissue concentrations of the gasotransmitters are influenced by fluctuations in the level of O₂ and reactive oxygen species (ROS). The normal transition from fetus to newborn involves a several-fold increase in tissue O₂ tensions and ROS, and requires rapid morphological and functional adaptations to the extrauterine environment. This review summarizes the role of gasotransmitters as it pertains to newborn physiology. Particular focus is given to the vasculature, ventilatory, and gastrointestinal systems, each of which uniquely illustrate the function of gasotransmitters in the birth transition and newborn periods. Moreover, given the relative lack of studies on the role that gasotransmitters play in the newborn, particularly that of H₂S and CO, important gaps in knowledge are highlighted throughout the review.

Oral microbial biofilms: an update

Human oral cavity (mouth) hosts a complex microbiome consisting of bacteria, archaea, protozoa, fungi and viruses. These bacteria are responsible for two common diseases of the human mouth including periodontal (gum) and dental caries (tooth decay). Dental caries is caused by plaques, which are a community of microorganisms in biofilm format. Genetic and peripheral factors lead to variations in the oral microbiome. It has known that, in commensalism and coexistence between microorganisms and the host, homeostasis in the oral microbiome is preserved. Nonetheless, under some conditions, a parasitic relationship dominates the existing situation and the rise of cariogenic microorganisms results in dental caries. Utilizing advanced molecular biology techniques, new cariogenic microorganisms species have been discovered. The oral microbiome of each person is quite distinct. Consequently, commonly taken measures for disease prevention cannot be exactly the same for other individuals. The chance for developing tooth decay in individuals is dependent on factors such as immune system and oral microbiome which itself is affected by the environmental and genetic determinants. Early detection of dental caries, assessment of risk factors and designing personalized measure let dentists control the disease and obtain desired results. It is necessary for a dentist to consider dental caries as a result of a biological process to be targeted than treating the consequences of decay cavities. In this research, we critically review the literature and discuss the role of microbial biofilms in dental caries.

Methemoglobinemia: Infants at risk

Methemoglobin is formed when the iron center in hemoglobin is oxidized from ferrous iron to ferric iron. The functional consequence of this change is that hemoglobin is transformed to methemoglobin and cannot oxygenate tissues adequately, causing hypoxia and cyanosis. Infants have unique physiology that increases their risk of developing methemoglobinemia. Infants drink more water per body weight compared to children and adults, have lower NADH cyb5r reductase activity that converts methemoglobin to hemoglobin, and have a higher percentage of fetal hemoglobin, which is easier to convert to methemoglobin. A well-studied exposure to a chemical that can cause methemoglobinemia in infants is nitrate in well water. For the first part specifically about methemoglobin in infants, articles that were recent (2015-now) were given preference over articles that were older. Search terms included: methemoglobin, methemoglobinemia, infant, acquired, congenital, and methylene blue. For the latter half of the paper on nitrate and methemoglobinemia, preference was given to articles that described regionally important cases. In addition, search terms were: Minnesota, methemoglobinemia, nitrate, well water, drinking water, and infant. Acquired methemoglobinemia is rare, yet can still be seen in medical settings, and when an infant is exposed to nitrate in well water above 10 mg/L. To prevent exposure, parents should have their water tested for nitrate before the baby comes home. Physicians should make it practice to ask what the source of drinking water is for newly pregnant women and urge them to test for nitrate and bacteria if using a well. Using bottled water to make formula is also an option, but the best option is still breastfeeding.

Measuring nitrate reductase activity from human and rodent tongues

Reduction of salivary nitrate to nitrite by oral microbes expressing nitrate-reductase has emerged as a crucial pathway in systemic NO homeostasis in humans and other mammals. Selective depletion of oral microbes prevents dietary nitrate-dependent lowering of blood pressure, inhibition of platelet aggregation and ischemic injury. To date, most studies interrogate enterosalivary nitrate reduction by following changes in saliva or plasma nitrite and NO-signaling (functional) end points. Little is known about whether, and if so how, nitrate-reductase enzymatic activity per se (i.e. independent of nitrate levels) is a variable and may account for any individual to individual variation. Here, we describe a minimally invasive protocol that allows for NR activity determination from human, rat and mouse tongue scrapes/swabs. We validate this method using selective application of antiseptic agents to the distal tongue surface which decreased NR activity by >80% and show that bacterial number is a significant variable in measured NR activities between males and females. Also, we show that NR activity is >80% lower in smokers (humans) and after bromine gas exposure (mice), suggesting that exposure to inhaled reactive substances inhibit NR activity identifying a potentially new mechanism by which environmental toxicants promote dysfunction in NO-bioavailability. The described method will facilitate studies testing whether NR specific activity is a variable in different pathophysiologic settings, and in turn how this activity modulates enterosalivary nitrate-reduction.

The oral cavity microbiota: between health, oral disease, and cancers of the aerodigestive tract

Many studies show that the human microbiome plays a critical role in the chronic pathologies of obesity, inflammatory bowel diseases, and diabetes. More recently, the interaction between cancer and the microbiome has been highlighted. Most studies have focused on the gut microbiota because it represents the most extensive bacterial community, and the body of evidence correlating it with gut syndromes is increasing. However, in the strict sense, the gastrointestinal (GI) tract begins in the oral cavity, and special attention should be paid to the specific flora of this cavity. This study reviewed the current knowledge about the various microbial ecosystems of the upper part of the GI tract and discussed their potential link to carcinogenesis. The overall composition of the microbial communities, as well as the presence or absence of "key species", in relation to carcinogenesis is addressed. Alterations in the oral microbiota can potentially be used to predict the risk of cancer. Molecular advances and the further monitoring of the microbiota will increase our understanding of the role of the microbiota in carcinogenesis and open new perspectives for future therapeutic and prophylactic modalities.

Oral microbiome and history of smoking and colorectal cancer

BACKGROUND

The equilibrium of oral microbiome may be altered by environmental factors, including cigarette smoking. Several recent studies also suggest that oral pathogens causing periodontal disease, such as Fusobacterium nucleatum, are involved in pathogenesis of colorectal cancer.

METHODS

For this study oral rinse DNA samples from 190 participants in a population-based case-control study for colorectal cancer were used to amplify a V3-V4 region of bacterial 16S rRNA gene. The amplicons were sequenced using Illumina MiSeq paired end chemistry on two runs, yielding approximately 35 million filtered reads which were assigned to bacterial phyla.

RESULTS

No association was found between Fusobacterium abundance or presence and colorectal cancer. However, adjusted for age and experimental batch, colorectal cancer history was associated with increased presence of genus Lactobacillus and increased relative abundance of Rothia by 28% and current smoking was associated with a 33% decrease in relative counts of Betaproteobacteria (primarily Neisseria) and 23% increase in relative abundance of Veillonellaceae family. We also found that smoking had significant effects on the 2^nd component scores and 2^nd coordinate distances in principal component and coordinate analyses.

CONCLUSIONS

It remains to be elucidated whether the observed differences can be translated into biochemical changes in oral environment, thus potentially affecting oral health.

Changes in plasma and urinary nitrite after birth in premature infants at risk for necrotizing enterocolitis

BACKGROUND

Plasma nitrite serves as a reservoir of nitric oxide (NO) bioactivity. Because nitrite ingestion is markedly lower in newborns than adults, we hypothesized plasma nitrite levels would be lower in newborns than in adults, and that infants diagnosed with necrotizing enterocolitis (NEC), a disease characterized by ischemia and bacterial invasion of intestinal walls, would have lower levels of circulating nitrite in the days prior to diagnosis.

METHODS

Single blood and urine samples were collected from 9 term infants and 12 adults, 72 preterm infants every 5 d for 3 wk, and from 13 lambs before and after cord occlusion.

RESULTS

Nitrite fell 50% relative to cord levels in the first day after birth; and within 15 min after cord occlusion in lambs. Urinary nitrite was higher in infants than adults. Plasma and urinary nitrite levels in infants who developed NEC were similar to those of preterm control infants on days 1 and 5, but significantly elevated at 15 and 20 d after birth.

CONCLUSION

Plasma nitrite falls dramatically at birth while newborn urinary nitrite levels are significantly greater than adults. Acute NEC is associated with elevated plasma and urinary nitrite levels.

Nitric oxide is a potent inhibitor of the cbb(3)-type heme-copper oxidases

C-type heme-copper oxidases terminate the respiratory chain in many pathogenic bacteria, and will encounter elevated concentrations of NO produced by the immune defense of the host. Thus, a decreased sensitivity to NO in C-type oxidases would increase the survival of these pathogens. Here we have compared the inhibitory effect of NO in C-type oxidases to that in the mitochondrial A-type. We show that O2-reduction in both the Rhodobacter sphaeroides and Vibrio cholerae C-type oxidases is strongly and reversibly inhibited by submicromolar NO, with an inhibition pattern similar to the A-type. Thus, NO tolerance in pathogens with a C-type terminal oxidase has to rely mainly on other mechanisms.

Dietary intake and bio-activation of nitrite and nitrate in newborn infants

Nitrate and nitrite are commonly thought of as inert end products of nitric oxide (NO) oxidation, possibly carcinogenic food additives, or well-water contaminants. However, recent studies have shown that nitrate and nitrite play an important role in cardiovascular and gastrointestinal homeostasis through conversion back into NO via a physiological system involving enterosalivary recirculation, bacterial nitrate reductases, and enzyme-catalyzed or acidic reduction of nitrite to NO. The diet is a key source of nitrate in adults; however, infants ingest significantly less nitrate due to low concentrations in breast milk. In the mouth, bacteria convert nitrate to nitrite, which has gastro-protective effects. However, these nitrate-reducing bacteria are relatively inactive in infants. Swallowed nitrite is reduced to NO by acid in the stomach, affecting gastric blood flow, mucus production, and the gastric microbiota. These effects are likely attenuated in the less acidic neonatal stomach. Systemically, nitrite acts as a reservoir of NO bioactivity that can protect against ischemic injury, yet plasma nitrite concentrations are markedly lower in infants than in adults. The physiological importance of the diminished nitrate→nitrite→NO axis in infants and its implications in the etiology and treatment of newborn diseases such as necrotizing enterocolitis and hypoxic/ischemic injury are yet to be determined.

Evidence-based feeding strategies before and after the development of necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is a devastating disease of premature infants and is associated with significant morbidity and mortality. While the pathogenesis of NEC remains incompletely understood, it is well established that the risk of disease is increased by the administration of infant formula and decreased by the administration of breast milk. This review will focus on the mechanisms by which breast milk may serve to protect against NEC, and will review the evidence regarding various feeding strategies that may be utilized before and after an episode of NEC.

Nitrite and nitrate concentrations and metabolism in breast milk, infant formula, and parenteral nutrition

Dietary nitrate and nitrite are sources of gastric NO, which modulates blood flow, mucus production, and microbial flora. However, the intake and importance of these anions in infants is largely unknown. Nitrate and nitrite levels were measured in breast milk of mothers of preterm and term infants, infant formulas, and parenteral nutrition. Nitrite metabolism in breast milk was measured after freeze-thawing, at different temperatures, varying oxygen tensions, and after inhibition of potential nitrite-metabolizing enzymes. Nitrite concentrations averaged 0.07 ± 0.01 μM in milk of mothers of preterm infants, less than that of term infants (0.13 ± 0.02 μM) (P < .01). Nitrate concentrations averaged 13.6 ± 3.7 μM and 12.7 ± 4.9 μM, respectively. Nitrite and nitrate concentrations in infant formulas varied from undetectable to many-fold more than breast milk. Concentrations in parenteral nutrition were equivalent to or lower than those of breast milk. Freeze-thawing decreased nitrite concentration ~64%, falling with a half-life of 32 minutes at 37°C. The disappearance of nitrite was oxygen-dependent and prevented by ferricyanide and 3 inhibitors of lactoperoxidase. Nitrite concentrations in breast milk decrease with storage and freeze-thawing, a decline likely mediated by lactoperoxidase. Compared to adults, infants ingest relatively little nitrite and nitrate, which may be of importance in the modulation of blood flow and the bacterial flora of the infant GI tract, especially given the protective effects of swallowed nitrite.