High Amounts of S100-Alarmins Confer Antimicrobial Activity on Human Breast Milk Targeting Pathogens Relevant in Neonatal Sepsis

Abstract

Sepsis is a leading cause of perinatal mortality worldwide. Breast milk (BM) feeding is protective against neonatal sepsis, but the molecular mechanisms remain unexplained. Despite various supplementations with potential bioactive components from BM formula feeding cannot protect from sepsis. S100-alarmins are important immunoregulators in newborns preventing excessive inflammation. At high concentrations, the S100A8/A9 protein complex also has antimicrobial properties due to its metal ion chelation capacity. To assess whether BM contains S100-alarmins that might mediate the sepsis-protective effect of BM 97 human BM samples stratified for gestational age, mode of delivery and sampling after birth were collected and analyzed. S100A8/A9 levels were massively elevated after birth (p < 0.0005). They slowly decreased during the first month of life, then reaching levels comparable to normal values in adult serum. The concentration of S100A8/A9 in BM was significantly higher after term compared with preterm birth (extremely preterm, p < 0.005; moderate preterm, p < 0.05) and after vaginal delivery compared with cesarean section (p < 0.0005). In newborn s100a9−/− mice, enterally supplied S100-alarmins could be retrieved systemically in the plasma. To explore the antimicrobial activity against common causal pathogens of neonatal sepsis, purified S100-alarmins and unmodified as well as S100A8/A9-depleted BM were used in growth inhibition tests. The high amount of S100A8/A9 proved to be an important mediator of the antimicrobial activity of BM, especially inhibiting the growth of manganese (Mn) sensitive bacteria such as Staphylococcus aureus (p < 0.00005) and group B streptococci (p < 0.005). Depletion of S100A8/A9 significantly reduced this effect (p < 0.05, respectively). The growth of Escherichia coli was also inhibited by BM (p < 0.00005) as well as by S100A8/A9 in culture assays (p < 0.05). But its growth in BM remained unaffected by the removal of S100A8/A9 and was neither dependent on Mn suggesting that the antimicrobial effects of S100A8/A9 in BM are primarily mediated by its Mn chelating capacity. In summary, the enteral supply of bioavailable, antimicrobially active amounts of S100-alarmins might be a promising option to protect newborns at high risk from infections and sepsis.

S100-Alarmins Are Essential Pilots of Postnatal Innate Immune Adaptation

“…Labor and birth are certainly one of the most exhausting conditions in life, imposing heavy stress on the mother as well as the newborn infant. Thus, birthrelated stress is probably the main trigger of perinatal S100A8/A9 release, and the gradual resolution of stress after birth well explains the postnatal decrease of S100A8/A9 in breast milk (56) and the infant's blood circulation (27). Therewith in line is a previous report that glucocorticoids can induce the expression of S100-alarmins (69).…”

“…Neonatal granulocytes probably also express S100A8 and S100A9 at high levels, but this still needs to be demonstrated. Secondly, human breast milk contains the highest amounts of S100A8/A9 hitherto found under physiologic conditions (56). In healthy term newborns, the levels in breast milk are in average at least six times higher than the already elevated S100A8/A9 serum levels.…”

“…In exclusively breast milk-fed human infants, fecal levels of S100A8/A9 were shown to be significantly higher than in formula-fed ones (57). In mice, enterally supplied S100A8/A9 was demonstrated to be systemically bioavailable in the blood circulation (56). In humans, the dependence of the height of S100A8/A9 levels in the serum on the supply by breast milk awaits quantification.…”

Protein Concentrations of Thrombospondin-1, MIP-1β, and S100A8 Suggest the Reflection of a Pregnancy Clock in Mid-Trimester Amniotic Fluid

“…S100-alarmins have also been described as essential immunoregulators in newborns, preventing excessive inflammation [54]. S100A8/A9 have been analyzed in breast milk; concentrations were significantly higher after term delivery, compared with PTD, and after vaginal delivery, compared with cesarean section [55]. Thrombospondin-1 is expressed in the placenta and has previously been reported in cases of small for gestational age (SGA) pregnancies and preeclampsia [56,57].…”

Breastfeeding for 3 Months or Longer but Not Probiotics Is Associated with Reduced Risk for Inattention/Hyperactivity and Conduct Problems in Very-Low-Birth-Weight Children at Early Primary School Age

“…One proposed mechanism is the stabilization of early immune-microbiome interaction by specific human milk abundant molecules such as alarmin S100 A8/A9. The latter has a pleiotropic effect on innate immunity including the prevention of gut dysbiosis and (sustained) inflammation [33][34][35]. A potential hallmark of children with hyperactivity/attention deficit problems is "mild inflammation", as characterized by increased interferon-gamma blood levels [36].…”