Ascorbate exacerbates iron toxicity on intestinal barrier function against Salmonella infection

Abstract

Ascorbic acid is often used to enhance iron absorption in nutritional interventions, but it produces pro-oxidant effects in the presence of iron. This study aimed to evaluate ascorbate’s role in iron toxicity on intestinal resistance against foodborne pathogens during iron supplementation/fortification. In polarized Caco-2 cell monolayers, compared to the iron-alone treatment, the iron-ascorbate co-treatment caused more than 2-fold increase in adhesion, invasion and translocation of Salmonella enterica serovar Typhimurium. According to 3-(4,5-dimethylthiazol-2-yl)−2,5-diphenyltetrazolium bromide assay, lactate dehydrogenase release and transepithelial electrical resistance, the iron-ascorbate co-treatment resulted in reduced cell viability and increased impairment of cell membrane and paracellular permeability compared to the iron-alone treatment. Butylated hydroxytoluene protected cells against these prooxidant toxicities of ascorbate. Ascorbate completely restored iron-induced intracellular oxidant burst and depletion of cytosolic antioxidant reserve, according to dichlorodihydrofluorescein fluorescence and intracellular reduced glutathione levels. In Salmonella-infected C57BL/6 mice, iron-ascorbate co-supplementation resulted in greater loss of body weight and appetite, lower survival rate, shorter colon length, heavier intestinal microvilli damage, and more intestinal pathogen colonization and translocation than the iron-alone supplementation. Overall, ascorbate would exacerbate iron toxicity on intestinal resistance against Salmonella infection through pro-oxidant impairment of intestinal epithelial barrier from extracellular side and/or by facilitating intestinal pathogen colonization.