Heat-killed<i> Lactiplantibacillus plantarum</i> N1487-7 induces IL-10 production and enhances skin barrier function

Background: Interleukin (IL)-10, an anti-inflammatory cytokine, suppresses the release of inflammatory cytokines, such as IL-6, and inhibits the decline in skin barrier function. Mice orally administered test substances by gavage are subjected to physical stress, which results in the secretion of stress hormones. Stress hormones cause inflammation and reduce skin barrier function. Objective: The effects of heat-killed Lactiplantibacillus (Lpb.) plantarum N1487-7 (N1487-7-HK) on IL-10 production in Caco-2 cells and macrophages, and skin barrier function in physically stressed mice was investigated. Methods: Lpb. plantarum N1487-7 was cultured in fermented barley extract medium at 30 °C for 22 h with shaking (100 rpm). The washed cells were killed by heating at 110 °C for 10 minutes. The cells were then dried in a centrifugal evaporator and ground to obtain the cell powder. The powder was administered to Caco-2 cells and macrophages, and IL-10 mRNA and IL-10 protein expressions were measured by real-time quantitative polymerase chain reaction and Western blotting, respectively. N1487-7-HK cells or distilled water were orally administered daily by gavage to Hos:HR-1 mice for 5 weeks (the N1487-7-HK group or the control group). During weeks 3 and 5 only, dextran sulfate sodium (DSS) was mixed into the drinking water of these groups to induce mild colitis. The normal group was not orally administered anything by gavage and was not given DSS. Serum IL-10 and the trans epidermal water loss (TEWL) of mice were measured. Results: N1487-7-HK promoted the expression of IL-10 mRNA and IL-10 protein in both Caco-2 cells and macrophages. In mice subjected to physical stress, serum IL-10 levels in the N1487-7-HK group were significantly increased compared to the control group. The transepidermal water loss (TEWL) in the control group was notably higher than that in the normal group during Weeks 1 and 2. In contrast, the N1487-7-HK group showed no significant difference in TEWL compared to the normal group. The N1487-7-HK group showed a significantly lower TEWL at Week 4 compared to Week 0. Conclusions: N1487-7-HK promoted IL-10 production from intestinal epithelial cells and macrophages. Intake of N1487-7-HK inhibited the decline in skin barrier function in mice subjected to physical stress. Keywords: Lactiplantibacillus plantarum, Interleukin (IL)-10, Caco-2, macrophages, skin barrier