NOS2 and gastric ulcer: The expression of inflammatory mediators can directly reflect the degree of damage to the gastric mucosa, so when gastric ulceration occurs there will be a decrease in the levels of NO, iNOS, PGE2 and MTL, and an increase in the levels of TNF-α, IL-6 and MDA, and the significant changes in the levels of these inflammatory factors will directly lead to a significant decrease in the abundance of some oral and intestinal bacteria (e.g., Rothia, Corynebacterium, Streptococcus, Globicatella, Lactobacillus, Romboutsia).