In periodontal diseases, nitric oxide can kill Porphytomonas gingivalis, the mechanism of which may involve combination of nitric oxide with key enzymes of microorganisms and inactivating them. High volume fraction of nitric oxide can cause blood vessels to dilate and lower platelet aggregation, causing gum bleeding. Carbon monoxide can inhibit the expression of intercellular adhesion molecule-1 and vascular cell adhesion molecule-1, reduce the activity of nuclear factor(NF)-κB predominately induced by intercellular adhesion molecule-1 and vascular cell adhesion molecule, as well as lower immune active cells to vascular endothelial cells and gingival fibroblast adhesion, thus controlling periodontitis pathological inflammation. Hydrogen sulfide promotes the occurrence of periodontal disease by increasing the expression of interleukin(IL)-8 in gingival epithelium. Overexpression of IL-8 promotes accumulation of neutrophils, which causes periodontal tissue damage. Hydrogen sulfide can cause alveolar bone absorption because hydrogen sulfide can upregulate the expression of the receptor activator of nuclear factor-κB ligand(RANKL), which promotes the differentiation of the osteoclast. Hydrogen sulfide increases the permeability of the mucosa, causing inflammation. The reason for this phenomenon is that hydrogen sulfide destroys the integrity of the periodontal tissue barrier, which increases mucous membrane permeability. Hydrogen sulfide inhibits synthesis of collagen and promotes its degradation. Hydrogen can relieve inflammation of periodontal tissue. The mechanism may reduce hydrogen and the volume fraction of reactive oxygen species, reduce the infiltration of neutrophils in organization and osteoclast differentiation, or reduce the activity of inflammatory signal transduction pathways, such as the mitogen-activated protein kinase signal transduction pathway. Hydrogen inhibits the combination of RANKL and NF-κB receptor activation factor by eliminating active oxygen, thus decreasing bone absorption by reducing the formation of actin in osteoclasts. Therefore, a study on gaseous molecules, such as nitric oxide, carbon monoxide, hydrogen sulfide and hydrogen, may lead to new insights for prevention and treatment of periodontal disease.
