D-galactose Intake Alleviates Atopic Dermatitis in Mice by Modulating Intestinal Microbiota

Abstract

Atopic dermatitis (AD) is one of the most prevalent, chronic and persistent inflammatory skin diseases closely associated with intestinal microbiota. To evaluate the effect of D-galactose intake on AD, we orally administered D-galactose to BALB/c mice whose ears and skin were treated with 2,4-dinitrochlorobenzene (DNCB). D-galactose alleviated DNCB-induced AD-like phenotypes such as redness, scaling/dryness and excoriation. Ear thickness was also decreased by D-galactose administration. Histopathological analysis revealed decreased epidermal thickening, infiltration of immune cells, especially mast cells, in the dermis. Total levels of serum IgE representing the immunological response of AD were decreased by D-galactose administration. Microbiota analysis showed that D-galactose administration restored gut microbiota profiles, which were altered in AD mice, characterized by increased abundance of Bacteroidetes and decreased abundance of Firmicutes. The increased abundance of Bacteroides and the decreased abundance of Prevotella and Ruminococcus were reversed by D-galactose treatment, following improvement of AD. Our results suggest the possible use of D-galactose as a prebiotic to alleviate AD by altering gut microbiota.

Keywords: D-galactose; atopic dermatitis; inflammation; microbiota; nutrition.

Figure 1

Protective effects of D-galactose on DNCB-induced atopic dermatitis in mice. (A) Schematic diagram showing the experimental design of DNCB-induced AD mouse model. Mice were divided to six groups (n = 7/group). (B) AD-like skin lesions were evaluated by visual observation. (C) The dermatitis index was scored as described in the materials and methods. (D) Ear thickness was measured before sacrificing. Values are means ± SD. The significance of differences between the groups was assessed using Mann-Whitney U-test, with the level of significance set at *P < 0.05, **P < 0.01, ***P < 0.001.

Figure 2

Effects of D-galactose on spleen and axillary lymph nodes of mice with DNCB-induced atopic dermatitis. Size comparison of (A) spleen and (C) axillary lymph node with or without D-galactose treatment (Scale bars, 1 mm). Comparison of (B) spleen weight and (D) axillary lymph node weight. Values are means ± SD. Significant differences between the data were assessed using Mann-Whitney U-test, with the level of significance set at *P < 0.05, **P < 0.01, ***P < 0.001.

Figure 3

Effects of D-galactose on DNCB-induced serum IgE levels in mice. Blood was collected on the day of sacrifice in the experiment (day 14). The level of serum IgE was measured with ELISA. Values are means ± SD. Significant differences between the groups were assessed using Mann-Whitney U-test, with the level of significance set at *P < 0.05, **P < 0.01, ***P < 0.001.

Figure 4

Effect of D-galactose on cutaneous histopathological observations of DNCB-induced atopic dermatitis in mice. Representative histological findings of cutaneous tissue sections stained with (A) hematoxylin and eosin or toluidine blue staining (Scale bars, 100 μm). Histological evaluation of (B) cutaneous tissue sections and (C) epidermal thickness. (D) Mast cell infiltration was quantified and compared among the groups. Values are means ± SD. The significance of differences between the group was assessed using Mann-Whitney U-test, with the level of significance set at *P < 0.05, **P < 0.01, ***P < 0.001.

Figure 5

Effects of D-galactose on alpha and beta diversity. Alpha and beta diversity of intestinal microbiota in vehicle-treated and DNCB-treated mice with or without D-galactose treatment was evaluated. (A,B) Richness of intestinal microbiota in indicated by Shannon diversity and Inverse Simpson Diversity (C,D) Beta diversity 2D and 3D patterns were determined by principal coordinate analysis. PBS + Vehicle (Red), D-galactose + Vehicle (Blue), PBS + DNCB (Yellow), D-galactose + DNCB (Green). The significance of differences between the groups was assessed using Mann-Whitney U-test, with the level of significance set at *P < 0.05, **P < 0.01, ***P < 0.001.

Figure 6

Effects of D-galactose on intestinal microbiota composition in mice with DNCB-induced atopic dermatitis. (A) Relative abundance of bacterial phyla in the intestinal microbiota of mice. The color of each cell indicates the relative abundance of bacterial phyla. (B) Relative abundance of intestinal microbiota at the genus level in mice, which showed a significant difference between DNCB-induced AD groups. (C–E) Relative abundance of Bacteroides, Prevotella and Ruminococcus among the intestinal microbiota of mice. Values are means ± SD. Significant differences between the groups were assessed using Mann-Whitney U-test, with the level of significance set at *p < 0.05, **p < 0.01, ***p < 0.001.