Table 1.

Effects of intestinal microorganisms and metabolites on various indexes in vivo.

Metabolites	Targets	Biological effects (References)
SCFAs	Human	Bind-specific G protein-coupled receptor29,30 Activate T cells29,30 Reduce NF-κB protein expression29,30
	Mice	Increase calcium absorption 31 Stimulate intestinal serotonin synthesis31,32 Inhibition of osteoclast differentiation and bone resorption 31
Amino acid metabolites	Human	Serotonin production 36 Activate the TRPV1 receptor 37
	Mice	Activate G protein-coupled receptor 3535 Impaired tryptophan canine metabolic pathway35,40
LPS	Human	Reduce pain threshold 42 Increase inflammatory factor IL-1β, TNF-α, and IL-6 levels 42 Increase the expression of DRG neurons, TRPA1, and TRPV1 proteins 42
	Rat	Increase postoperative pain and delay wound growth 41 Increase inflammatory factor IL-1β, COX-2, and PGE2 levels 44
Succinic acid	Yolk	Inhibit the activity of PLA247
	Rat	Bind to GRP91 receptor and promote IL-1β and NO release 49

DRG, dorsal root ganglion; LPS, Lipopolysaccharide; NF-κB, nuclear factor kappa-B; SCFA, short-chain fatty acid