N-acetylmuramic acid triggers anti-inflammatory capacity in LPS-induced RAW 264.7 cells and mice

• Phagocytosis of PGN from L. acidophilus was enhanced in LPS-induced macrophages.
• PGN fragment exerts anti-inflammatory response in mice small intestine.
• NAM has a potential pharmaceutical application in anti-inflammatory drugs.

Lactic acid bacteria (LAB) have long been used in the manufacture of yogurt and cheese. LAB inhabit the human gastrointestinal tract alongside dozens of varieties of gut bacteria, which play an essential role in modulating the innate immune response to gastrointestinal disorders. This research sought to provide a basis for the investigation of peptidoglycan (PGN) from Lactobacillus acidophilus (L. acidophilus) by macrophages phagocytosis related to the anti-inflammatory effect both in vitro and vivo. Results show that PGN, PGN hydrolysate and PGN monomer N-acetylmuramic acid (NAM) from L. acidophilus were found to have an anti-inflammatory effect on LPS-induced inflammation in RAW 264.7 cells, the profiling of iNOS mRNA levels was also inhibited in NAM-treated (100–300 µg/mL) group. The activation of the Nuclear factor κB (NF-κB) pathway is regulated by the cellular kinase p38 in mitogen-activated protein kinases (MAPK) upon NAM treatment (300 µg/mL). These findings were further supported in Escherichia coli (E. coli)-stimulated ICR mice, in which we found that oral administration of free L. acidophilus PGN and NAM from L. acidophilus exerted a potential anti-inflammatory response. NAM, as the main components of the LAB cell wall, will be a candidate for pharmaceutical application of anti-inflammatory drugs.