Analysis of selected aspects of inflammasome function in the monocytes from neonates born extremely and very prematurely

Bifidobacterium regulates premature infant gut metabolites, reducing serum inflammatory factors: a randomised controlled trial

BACKGROUND

Analyse the effects of Bifidobacterium BB-12 on intestinal metabolites and serum inflammatory factors in premature infants.

METHODS

71 premature infants at gestational age of ≤32 weeks were randomly divided into the probiotic (n = 36) and control (n = 35) groups. Faecal and blood samples were collected from the two groups of premature infants at the 2nd and 4th week of life for intestinal metabolite detection and assessment of the level of the serum inflammatory markers TLR4, NF- κ B, IL-1β, and TNF- α.

RESULTS

Compared to the control group, the probiotic group contained more amino acids, these elements were enriched on multiple amino acid metabolic pathways, and the probiotic group showed significantly lower levels of the serum inflammatory markers TLR4, NF-κB, IL-1β, and TNF-α. Finally, the probiotic group showed a lower incidence of feeding intolerance.

CONCLUSIONS

The administration of Bifidobacterium BB-12 is associated with increasing the levels of glutamine, glutamic acid, and kynurenine in the gut of premature infants, and associated with reducing the levels of TLR4 and NF-κB in the serum, further decreasing the secretion of the pro-inflammatory factors IL-1β and TNF-α, and alleviating systemic inflammatory reactions, thereby reducing the incidence of feeding intolerance.

IMPACT

1. The use of Bifidobacterium BB-12 in premature infants can increase the levels of amino acids in the intestine. 2. Increases in Bifidobacterium BB-12 may decrease the serum levels of TLR4, NF-κB, IL-1β, and TNF-α. 3. Kynurenine may improve the prognosis of preterm infants by reducing inflammation. 4. Bifidobacterium BB-12 may improve the feeding tolerance of premature infants, thus reducing the incidence of feeding intolerance.

Healthy preterm newborns: Altered innate immunity and impaired monocyte function

Birth prior to 37 completed weeks of gestation is referred to as preterm (PT). Premature newborns are at increased risk of developing infections as neonatal immunity is a developing structure. Monocytes, which are key players after birth, activate inflammasomes. Investigations into the identification of innate immune profiles in premature compared to full-term infants are limited. Our research includes the investigation of monocytes and NK cells, gene expression, and plasma cytokine levels to investigate any potential differences among a cohort of 68 healthy PT and full-term infants. According to high-dimensional flow cytometry, PT infants have higher proportions of CD56+/- CD16+ NK cells and immature monocytes, and lower proportions of classical monocytes. Gene expression revealed lower proportions of inflammasome activation after in vitro monocyte stimulation and the quantification of plasma cytokine levels expressed higher concentrations of alarmin S100A8. Our findings suggest that PT newborns have altered innate immunity and monocyte functional impairment, and pro-inflammatory plasmatic profile. This may explain PT infants' increased susceptibility to infectious disease and should pave the way for novel therapeutic strategies and clinical interventions.

Imbalanced Inflammatory Responses in Preterm and Term Cord Blood Monocytes and Expansion of the CD14+CD16+ Subset upon Toll-like Receptor Stimulation

Developmentally regulated features of innate immunity are thought to place preterm and term infants at risk of infection and inflammation-related morbidity. Underlying mechanisms are incompletely understood. Differences in monocyte function including toll-like receptor (TLR) expression and signaling have been discussed. Some studies point to generally impaired TLR signaling, others to differences in individual pathways. In the present study, we assessed mRNA and protein expression of pro- and anti-inflammatory cytokines in preterm and term cord blood (CB) monocytes compared with adult controls stimulated ex vivo with Pam3CSK4, zymosan, polyinosinic:polycytidylic acid, lipopolysaccharide, flagellin, and CpG oligonucleotide, which activate the TLR1/2, TLR2/6, TLR3, TLR4, TLR5, and TLR9 pathways, respectively. In parallel, frequencies of monocyte subsets, stimulus-driven TLR expression, and phosphorylation of TLR-associated signaling molecules were analyzed. Independent of stimulus, pro-inflammatory responses of term CB monocytes equaled adult controls. The same held true for preterm CB monocytes-except for lower IL-1β levels. In contrast, CB monocytes released lower amounts of anti-inflammatory IL-10 and IL-1ra, resulting in higher ratios of pro-inflammatory to anti-inflammatory cytokines. Phosphorylation of p65, p38, and ERK1/2 correlated with adult controls. However, stimulated CB samples stood out with higher frequencies of intermediate monocytes (CD14⁺CD16⁺). Both pro-inflammatory net effect and expansion of the intermediate subset were most pronounced upon stimulation with Pam3CSK4 (TLR1/2), zymosan (TR2/6), and lipopolysaccharide (TLR4). Our data demonstrate robust pro-inflammatory and yet attenuated anti-inflammatory responses in preterm and term CB monocytes, along with imbalanced cytokine ratios. Intermediate monocytes, a subset ascribed pro-inflammatory features, might participate in this inflammatory state.

Emerging Role of the NLRP3 Inflammasome and Interleukin-1β in Neonates

Infection and persistent inflammation have a prominent role in the pathogenesis of brain injury and cerebral palsy, as well as other conditions associated with prematurity such as bronchopulmonary dysplasia. The NLRP3 inflammasome-interleukin (IL)-1β pathway has been extensively studied in adults and pre-clinical models, improving our understanding of innate immunity and offering an attractive therapeutic target that is already contributing to clinical management in many auto-inflammatory disorders. IL-1 blockade has transformed the course and outcome of conditions such as chronic infantile neurological, cutaneous, articular (CINCA/NOMID) syndrome. Inflammasome activation and upregulation has recently been implicated in neonatal brain and lung inflammatory disease and may be a novel therapeutic target.

The Role of Connexin and Pannexin Channels in Perinatal Brain Injury and Inflammation

Perinatal brain injury remains a major cause of death and life-long disability. Perinatal brain injury is typically associated with hypoxia-ischemia and/or infection/inflammation. Both hypoxia-ischemia and infection trigger an inflammatory response in the brain. The inflammatory response can contribute to brain cell loss and chronic neuroinflammation leading to neurological impairments. It is now well-established that brain injury evolves over time, and shows a striking spread from injured to previously uninjured regions of the brain. There is increasing evidence that this spread is related to opening of connexin hemichannels and pannexin channels, both of which are large conductance membrane channels found in almost all cell types in the brain. Blocking connexin hemichannels within the first 3 h after hypoxia-ischemia has been shown to improve outcomes in term equivalent fetal sheep but it is important to also understand the downstream pathways linking membrane channel opening with the development of injury in order to identify new therapeutic targets. Open membrane channels release adenosine triphosphate (ATP), and other neuroactive molecules, into the extracellular space. ATP has an important physiological role, but has also been reported to act as a damage-associated molecular pattern (DAMP) signal mediated through specific purinergic receptors and so act as a primary signal 1 in the innate immune system inflammasome pathway. More crucially, extracellular ATP is a key inflammasome signal 2 activator, with purinergic receptor binding triggering the assembly of the multi-protein inflammasome complex. The inflammasome pathway and complex formation contribute to activation of inflammatory caspases, and the release of inflammatory cytokines, including interleukin (IL)-1β, tumor necrosis factor (TNF)-α, IL-18, and vascular endothelial growth factor (VEGF). We propose that the NOD-like receptor protein-3 (NLRP3) inflammasome, which has been linked to inflammatory responses in models of ischemic stroke and various inflammatory diseases, may be one mechanism by which connexin hemichannel opening especially mediates perinatal brain injury.

Inflammasome function in monocyte subsets and a risk of late-onset sepsis in preterm very low birth weight neonates

BACKGROUND

Immature immune systems predispose very low birth weight (VLBW) neonates to systemic infections in early life. Defective inflammasome function may increase a neonate's susceptibility to late-onset sepsis (LOS).

METHODS

Blood samples were taken on the 5^th day of life (DOL) for all VLBW neonates (non-LOS and before-LOS groups; N.=76), and within 24 hours of sepsis onset (LOS group; N.=39). Monocyte (MO) subsets and intracellular interleukin-1β (IL-1β) expression were analyzed using flow cytometry. Inflammasome function, defined as level of IL-1β and interleukin-18 (IL-18) was measured with enzyme-linked immunosorbent assay. IRA B cells were reported as a fraction of all B cells.

RESULTS

Stimulation of classical MO in non-LOS cells demonstrated a higher expression of intracellular IL-1β in comparison to MO from before LOS group. Serum from the LOS group revealed a higher level of IL-18. Stimulation of mononuclear cultures from samples taken during LOS resulted in significantly increased supernatant level of IL-1β and IL-18 in comparison to samples taken on 5^th DOL. No changes in the levels of IRA B cells were detected with the onset of sepsis.

CONCLUSIONS

We did not observe a difference in the functioning of the inflammasome within monocytes taken on 5^th DOL from premature VLBW neonates. Furthermore, there was no observable change in the IRA B cells of the septic and non-septic groups. The decreased expression of intracellular IL-1β within classical MO of the before-LOS group may be an independent risk factor for LOS development.

Sepsis-Induced Immunosuppression in Neonates

Neonates, especially those born preterm, are at increased risk of sepsis and adverse long-term effects associated with infection-related inflammation. Distinct neonatal immune responses and dysregulated inflammation are central to this unique susceptibility. The traditional separation of sepsis into an initial hyper-inflammatory response followed by hypo-inflammation is continually under review with new developments in this area of research. There is evidence to support the association of mortality in the early acute phase of sepsis with an overwhelming hyper-inflammatory immune response. Emerging evidence from adults suggests that hypo- and hyper-inflammation can occur during any phase of sepsis and that sepsis-immunosuppression is associated with increased mortality, morbidity, and risk to subsequent infection. In adults, sepsis-induced immunosuppression (SII) is characterised by alterations of innate and adaptive immune responses, including, but not limited to, a prominent bias toward anti-inflammatory cytokine secretion, diminished antigen presentation to T cells, and reduced activation and proliferation of T cells. It is unclear if sepsis-immunosuppression also plays a role in the adverse outcomes associated with neonatal sepsis. This review will focus on exploring if key characteristics associated with SII in adults are observed in neonates with sepsis.