Crocin Ameliorates Atopic Dermatitis Symptoms by down Regulation of Th2 Response via Blocking of NF-κB/STAT6 Signaling Pathways in Mice

Abstract

Crocin, a major constituent of Gardenia jasminoides, is a natural colorant carotenoid compound that has been reported to have anti-inflammatory effects. This study investigated the therapeutic effects of crocin on mice with atopic dermatitis induced by Dermatophagoides farinae crude extract, which is a common environmental allergen in house dust that causes atopic dermatitis in humans. Crocin application ameliorated Dermatophagoides farinae crude extract-induced atopic dermatitis symptoms by inhibiting the dermatitis severity score, ear thickness, and serum immunoglobulin E levels in NC/Nga mice. The increases in epidermal thickness and dermal inflammatory cells (eosinophil and mast cells) infiltrations observed on the dorsal back skin of atopic dermatitis control mice were inhibited in a dose-dependent manner by topical application of crocin in atopic dermatitis treatment mice. Crocin inhibited the Dermatophagoides farinae crude extract-induced increase of thymus and activation-regulated chemokines, interleukin (IL)-4, and IL-13 on the dorsal skin of mice. Crocin also inhibited Dermatophagoides farinae crude extract-induced activation of nuclear factor-κB (NF-κB) and signal transducer and activator of transcription (STAT) 6. These results show that crocin ameliorates atopic dermatitis symptoms by down regulation of the Th2 cells-mediated immune response via blocking of NF-κB/STAT6 signaling pathways.

Keywords: Gardenia jasminoides; Immunoglobulin E; NC/Nga; eosinophils; thymus and activation-regulated chemokine.

Figure 1

(a) Chemical structure of crocin and (b) experimental scheme for induction of atopic dermatitis (AD) and treatment of drugs in NC/Nga mice.

Figure 2

(a) Clinical features; (b) dermatitis severity score; (c) ear thickness; and (d) total immunoglobulin E (IgE) levels in serum. Results are expressed as mean ± standard error of the mean (S.E.M.) for six mice. Groups: Normal, no treatment group; Control, DfE-treated group; Crocin, 0.1%- or 0.3%-treated group; and TAC, tacrolimus-treated group. Key: ^### p < 0.001 versus Normal group; * p < 0.05, ** p < 0.01, and *** p < 0.001 versus Control group.

Figure 3

Histopathology and histomorphometrical analysis of the ear and back skin tissues. (a) Ear and back skin sections were stained with hematoxylin and eosin (H&E; original magnification ×200). Back skin sections were stained with Congo red (CR; ×400) or toluidine blue (TB; ×200). (b) Full ear thickness in the ear, epidermal thickness, inflammatory cells number, eosinophils number, and mast cells number in the back skin. Results are expressed as mean ± standard error of the mean (S.E.M.) for six mice. Groups: Normal, no treatment group; Control, DfE-treated group; Crocin, 0.1%- or 0.3%-treated group; TAC, tacrolimus-treated group. Key: ^## p < 0.01 and ^### p < 0.001 versus Normal group; * p < 0.05, ** p < 0.01, and *** p < 0.001 versus Control group.

Figure 4

Effects of crocin on Dermatophagoides farinae extract (DfE)-induced NF-κB and signal transducer and activator of transcription 6 (STAT6) activation in the back skin tissues. Expression of IκBα, p-IκBα, p-STAT6, STAT6, and β-actin protein were evaluated by measuring protein levels in the total extracts using Western blotting (a). The relative abundance of proteins was calculated for the p-STAT6/STAT6, p-IκBα/β-actin, and IκBα/β-actin ratios (b). Values represent the mean ± standard error of the mean (S.E.M) of three independent experiments. ^# p < 0.05 and ^### p < 0.001 versus Normal group; * p < 0.05, ** p < 0.01 and *** p < 0.001 versus Control group.