Inhibitory effect of lactoperoxidase on the secretion of proinflammatory cytokine interleukin-8 in human intestinal epithelial Caco-2 cells

The effect of lactoperoxidase (LPO) on the H2O2-induced interleukin-8 (IL-8) secretion in human intestinal epithelial Caco-2 cells was examined. LPO markedly suppressed the H2O2-induced IL-8 secretion in Caco-2 cells, accompanied by a decreased level of IL-8 mRNA expression. Since this suppression was only apparent when the cells were treated with LPO in the presence of H2O2, the mechanism is thought to involve the elimination of H2O2 by LPO. The suppressive effect on the IL-8 secretion and antioxidative activity of LPO were well correlated, supporting the proposition of this mechanism. The activity of LPO remained after treating with pepsin (at pH 3 or higher) and trypsin (at neutral pH), although peptic digestion at pH 2 completely eliminated the activity. LPO was also stable against a pasteurizing heat treatment. These properties would assure the suitability of LPO as a functional ingredient for food to attenuate the intestinal inflammation associated with oxidative stress.