Hydrogen Promotes the M1 Macrophage Conversion During the Polarization of Macrophages in Necrotizing Enterocolitis

Inhibition of Pck1 in intestinal epithelial cells alleviates acute pancreatitis via modulating intestinal homeostasis

Intestinal barrier dysfunction usually occurred in acute pancreatitis (AP) but the mechanism remains unclear. In this study, RNA sequencing of ileum in L-arginine-induced AP mice demonstrated that phosphoenolpyruvate kinase 1 (Pck1) was significantly up-regulated. Increased Pck1 expression in intestinal epithelial cells (IECs) was further validated in ileum of AP mice and duodenum of AP patients. In AP mice, level of Pck1 was positively correlated with pancreatic and ileal histopathological scores, serum amylase activity, and intestinal permeability (serum diamine oxidase (DAO), D-lactate, and endotoxin). In AP patients, level of Pck1 had a positive correlation with Ranson scores, white blood cell count and C-reactive protein. Inhibition of Pck1 by 3-Mercaptopicolinic acid hydrochloride (3-MPA) alleviated pancreatic and ileal injuries in AP mice. AP + 3-MPA mice showed improved intestinal permeability, including less epithelial apoptosis, increased tight junction proteins (TJPs) expression, decreased serum DAO, D-lactate, endotoxin, and FITC-Dextran levels, and reduced bacteria translocation. Lysozyme secreted by Paneth cells and mucin2 (MUC2) secretion in goblet cells were also partly restored in AP + 3-MPA mice. Meanwhile, inhibition of Pck1 improved intestinal immune response during AP, including elevation of M2/M1 macrophages ratio and secretory immunoglobulin A (sIgA) and reduction in neutrophils infiltration. In vitro, administration of 3-MPA dramatically ameliorated inflammation and injuries of epithelial cells in enteroids treated by LPS. In conclusion, inhibition of Pck1 in IECs might alleviate AP via modulating intestinal homeostasis.

Human milk-derived MANF, as an immuno-nutritional factor, maintains the intestinal epithelial barrier and protects against necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is a leading cause of death in preterm infants. Compared to formula milk, breastfeeding protects against NEC. However, the composition of breast milk is quite complicated, and many immunological compositions remain unknown. In this study, we aimed to investigate the concentration of a secreted protein, Mesencephalic astrocyte-derived neurotrophic factor (MANF), in breastmilk and evaluate its immune-regulatory function in protecting the intestinal epithelial barrier. Our data indicated that MANF was secreted in human milk but could not be detected in infant formulas. More importantly, the amount of MANF in colostrum was higher than that in mature milk. We also clarified that MANF was mainly expressed in intestinal macrophages and was capable of inducing apoptosis and decreasing the inflammation of pro-inflammatory macrophages in both NEC intestinal tissues and BMDMs. Mechanismly, MANF protein significantly inhibited the apoptosis of intestinal epithelial cells and protected epithelial tight junctions through downregulation of the NF-κB pathway in pro-inflammatory macrophages. These results reveal the crucial function of human milk-derived MANF in intestinal macrophages, which contributes to downregulating the intestinal inflammatory response and protecting the homeostasis of intestinal epithelial cells. Our study not only demonstrates a potential mechanism underlying breastfeeding protective effects in NEC but also, more importantly, enables clinical translation, facilitating new strategies for the development of nutritional interventions in the prevention of NEC.

New insights into intestinal macrophages in necrotizing enterocolitis: the multi-functional role and promising therapeutic application

Necrotizing enterocolitis (NEC) is an inflammatory intestinal disease that profoundly affects preterm infants. Currently, the pathogenesis of NEC remains controversial, resulting in limited treatment strategies. The preterm infants are thought to be susceptible to gut inflammatory disorders because of their immature immune system. In early life, intestinal macrophages (IMφs), crucial components of innate immunity, demonstrate functional plasticity and diversity in intestinal development, resistance to pathogens, maintenance of the intestinal barrier, and regulation of gut microbiota. When the stimulations of environmental, dietary, and bacterial factors interrupt the homeostatic processes of IMφs, they will lead to intestinal disease, such as NEC. This review focuses on the IMφs related pathogenesis in NEC, discusses the multi-functional roles and relevant molecular mechanisms of IMφs in preterm infants, and explores promising therapeutic application for NEC.

NAMPT inhibition relieves intestinal inflammation by regulating macrophage activation in experimental necrotizing enterocolitis

Nicotinamide phosphoribosyl transferase (NAMPT) is associated with various NAD+ -consuming enzymatic reactions. The precise role in intestinal mucosal immunity in necrotizing enterocolitis (NEC) is not well defined. Here, we examined whether NAMPT inhibition by the highly specific inhibitor FK866 could alleviate intestinal inflammation during the pathogenesis of NEC. In the present study, we showed that NAMPT expression was upregulated in the human terminal ileum of human infants with NEC. FK866 administration attenuated M1 macrophage polarization and relieved the symptoms of experimental NEC pups. FK866 inhibited intercellular NAD+ levels, macrophage M1 polarization, and the expression of NAD+ -dependent enzymes, such as poly (ADP ribose) polymerase 1 (PARP1) and Sirt6. Consistently, the capacity of macrophages to phagocytose zymosan particles, as well as antibacterial activity, were impaired by FK866, whereas NMN supplementation to restore NAD+ levels reversed the changes in phagocytosis and antibacterial activity. In conclusion, FK866 reduced intestinal macrophage infiltration and skewed macrophage polarization, which is implicated in intestinal mucosal immunity, thereby promoting the survival of NEC pups.

NF-κB inactivation attenuates the M1 macrophage polarization in experimental necrotizing enterocolitis by glutaredoxin-1 deficiency

The pathogenesis of necrotizing enterocolitis (NEC) is severe inflammatory injury in preterm infants, which resulted from macrophage polarization. Nuclear factor-κB (NF-κB) is implicated to be involved in macrophage polarization. We here evaluated the essential role of NF-κB in macrophage polarization in NEC in human samples from neonates with NEC and the mouse experimental NEC model. Enhanced intestinal macrophage (IM) infiltration was presented in human neonates with NEC, the majority of which were M1 macrophages. Meanwhile, NF-κB was activated in the IMs in human NEC samples. NF-κB inhibition by BAY promoted the M1 to M2 macrophage polarization. Furthermore, glutaredoxin-1 (Grx1) deficiency promoted M2 polarization via NF-κB inactivation from the lipopolysaccharide-induced proinflammatory macrophages. The IMs isolated from Grx1^{- / -} mice presented with decreases in total numbers and less macrophage differentiation. Grx1^{- / -} derived IM were effective in the increased survival in experimental NEC through inflammation blocking. Our study provides evidence that NF-κB inactivation by Grx1 depletion contributed to the alleviation of NEC via inhibiting M1 macrophage polarization. The modulation to alternative macrophages in the intestines may provide a promising benefits for NEC treatment.