Regulation of Intestinal Epithelial Cells Properties and Functions by Amino Acids

Table 1

The roles of amino acids (arginine, glutamine, and glycine) in several intestinal disorders.

Amino acid	Disorder	Model	Role (mechanism)	Reference
Arginine	IBD	DSS-induced mouse colitis	L-arginine supplementation improved responses to DSS-induced injury and inflammation (e.g., colonic permeability ↓, proinflammatory cytokine and chemokine expression ↓, wound repair capacity ↑).	[37]
			Dietary arginine supplementation had beneficial effects on clinical and biochemical parameters of colitis (e.g., changes in serum amino acids profile, colonic oxidative injury ↓, Claudin-1 ↑).	[59]
	Weaning-related GI infections	E. coli LPS challenged- weaned pigs	L-arginine supplementation improved intestinal mucosal immune function and maintained barrier integrity in response to LPS challenge (e.g., Intraepithelial lymphocytes ↑, IgA-secreting cells ↑, CD8(+) and CD4(+) T cells ↑, mast cells ↓, Peyer’s patch lymphocyte apoptosis ↓).	[36]
	Radiotherapy (cancer)	Abdominal irradiation rat model	Arginine supplementation had protective effect on maintaining the colonic wall of irradiated rats (maintaining the partial volume of the colonic epithelium, not the total volume of the wall).	[66]
Glutamine	Weaning-related GI infections	Weaned piglets of E. coli infection	L-Glutamine supplementation reduced the severity of infections by improving intestinal barrier function (e.g., potential difference and Isc ↑, junctional proteins expression ↑), and by reducing mucosal cytokine response (e.g., IL-1β, IL-6, and TGF-β ↓).	[32]
	Intestinal IR	IR injury rat model	Oral glutamine supplementation attenuated IR-induced mucosal injury and improved intestinal recovery (e.g., enterocytes proliferation ↑, bowel and mucosal weight, mucosal DNA, villus height, and crypt depth ↑).	[33]
	TBI-associated intestinal mucosal damage	TBI rat model	Glutamine supplementation ameliorated the TBI-caused intestinal structure damage (intestinal apoptosis ↓, NF-B activity ↓, IL-1β, IL-6, and TNF-α ↓).	[57]
	IBD	Human duodenal biopsies	Glutamine has favorable effects on cytokine responses in human intestine (IL-1β-induced IL-6 and IL-8 ↓, IL-10 ↑).	[46]
	IBD	DSS-induced mouse colitis	Dietary glutamine supplementation had beneficial effects on the clinical and biochemical parameters of colitis (e.g., changes in serum amino acids profile, NF-B activity ↓, PI3K-Akt signaling ↓).	[59]
	Radiotherapy (cancer)	Abdominal irradiation rat model	Glutamine supplementation had protective effect on maintaining the colonic wall of irradiated rats.	[65]
Glycine	IBD	TNBS- or DSS-induced rat colitis	Dietary glycine prevented TNBS- or DSS-induced colitis by inhibiting inflammatory cytokine and chemokine production (e.g., IL-1β, TNF-α, myeloperoxidase activities, cytokine-induced neutrophil chemoattractant, and macrophage inflammatory protein ↓).	[60]
	Radiotherapy (cancer)	Abdominal irradiation rat model	Glycine supplementation had protective effect on maintaining the colonic wall of irradiated rats (maintaining the thickness of colonic wall and mucosal epithelium).	[65, 66]

Note. (1) ↑: increased/upregulated; ↓: decreased/downregulated; (2) DSS: dextran sulfate sodium; GI: gastrointestinal; IBD: inflammatory bowel disease; IR: ischemia-reperfusion; TBI: traumatic brain injury; TNBS: 2,4,6-trinitro-benzene sulphonic acid.