l-Arginine supplementation prevents intestinal epithelial barrier breakdown under heat stress conditions by promoting nitric oxide synthesis.

Heat stress (HS) induced by exposure to high ambient temperatures or prolonged excessive physical activities is known to primarily induce deleterious effects on the intestinal integrity by disrupting junctional complexes. Considering the association of l-arginine (l-Arg) with the improvement of gut function, the hypothesis of this study was to assess whether l-Arg supplementation can prevent the intestinal barrier disruption under HS conditions and to understand whether the l-Arg-induced effects are associated with maintaining nitric oxide (NO) as the major product of l-Arg metabolism. For this study, human colorectal adenocarcinoma (Caco-2) cells grown on Transwell inserts were pretreated with different l-Arg concentrations (0.4, 1, and 4 mmol/L), and after exposure to HS, markers of intestinal barrier integrity, stress-related markers, and NO levels were determined. l-Arg deprivation markedly increased the mRNA expression of heat shock protein 70 and heme-oxygenase-1 under HS conditions. The HS-induced drop in transepithelial electrical resistance values and increase in Lucifer Yellow permeability could be prevented by 4 mmol/L l-Arg supplementation. In turn, l-Arg mitigated the downregulation and delocalization of adherens junction protein E-cadherin in HS-exposed cells. NO and inducible NO synthase levels were significantly decreased in HS-exposed cells, whereas pretreatment with 4 mmol/L l-Arg prevented this decrease. Inhibition of inducible NO synthase by the NO synthase inhibitor l-NG-nitroarginine methyl ester abrogated the effect of l-Arg on preserving intestinal integrity under HS conditions as measured by transepithelial electrical resistance, Lucifer Yellow flux, and E-cadherin expression. In summary, l-Arg supplementation protects the intestinal epithelial integrity, at least partly, by maintaining NO synthesis under HS conditions.