FORMULATED EXTRACT FROM MULTIPLE CITRUS PEELS IMPAIRS DENDRITIC CELL FUNCTIONS AND ATTENUATES ALLERGIC CONTACT HYPERSENSITIVITY

Chi-Chen Lin¹, Yi-Che Chen¹,Michiko Suzawa², Shiming Li³, Chi-Tang Ho³

¹Institute of Biomedical Science, National Chung-Hsing University, Taichung, Taiwan, Republic of China; ²Miyauchi Citrus Research Center, Shigoka-Machi, Takasaki, Gunma, 370-0845, Japan; ³Department of Food Science, Rutgers University, New Brunswick, NJ 08901, USA

Keywords: Citrus peels, dendritic cells (DCs), T cells, contact hypersensitivity

Background: Gold lotion (GL), a formulated product made from the peels of six citrus fruits (navel orange, citrus hassaku, citrus limon, citrus natsudaidai, citrus miyauchi iyo, and Satsuma), was initially marketed as cosmetics in Japan to protect skin from ultraviolet (UV) light irradiation. Chemical analysis of GL has revealed the abundant existence of flavonoids with a total measured content of at least 450 ppm or 0.45 mg/mL and PMFs content is as high as 106 ppm or 0.1 mg/mL. Evidence showed that GL has anti-inflammatory and immunomodulatory effects. However, to the best of our knowledge, the cellular and molecular targets of GL in the immune system have remained unclear.

Objective: In this study, we investigated the ability of GL on the maturation and functional properties of dendritic cells (DCs), which are potent antigen presenting cells that control both of the innate and adaptive immune systems.

Methods: Bone marrow-derived DCs treated with various concentrations of GL for 1 h followed by stimulation with or without 100 ng/mL lipopolysaccharide (LPS) in vitro. The functions of DCs, including cytokine and chemokine production, costimulatory molecules, and antigen-specific T cell activation, were analyzed. To investigate the molecular mechanisms of GL-mediated inhibitory effect of BMDCs maturation, the levels of phosphorylated MAPKs and nuclear NF-κB were also measured. Moreover, contact hypersensitivity (CHS) is a typical dendritic cell mediated T cell-dependent cutaneous immune response to reactive haptens. CHS can be induced by epicutaneous immune sensitization and subsequently challenged with haptens, such as DNFB. We also used this model to examine the in vivo effect of GL on DNFB hapten-loaded, DC-mediated CHS immune responses.

Results: Upon exposure of LPS-stimulated BMDCs to GL in vitro, the expression of cytokines/chemokines and maturation surface markers (CD40, CD80, CD86, MHC class I/II) and the ability of DCs to stimulate the proliferation of antigen specific T-cells were down regulated in a dose-dependent manner. In addition, GL attenuates MAPK-JNK, p3, and NF-κB signaling pathways in LPS-treated DCs. Moreover, oral administration of 200 μL GL showed significantly less DNFB-induced ears swelling, less CD4⁺ and CD8⁺ T cells infiltrating, and less expression levels of inflammatory marker, including IL-1 beta, IL-6, TNF-alpha, IFN-gamma, and Cc12 (a monocyte-attracting chemokine) IFN-gamma cytokines production in the ear than that of DNFB (0.2%) challenged alone group.

Conclusion: Our study suggests that GL significantly influences the important pro-inflammatory signaling cascades and impairs the phenotype and function of mice DCs, making it an attractive therapeutic agent in chronic inflammatory and autoimmune disease.