Kobayashi 10_10

The anti-allergic activity of the 50% methanol extract of Citrus unshiu powder (MEC) was examined. Fifty percent methanol extract of MEC powder showed potent inhibitory activity against histamine release from basophils of patients suffering from seasonal allergic rhinitis to ceder pollen. To examine this anti-allergic mechanism in detail, we next used rat basophlilic leukemia RBL-2H3 cells. MEC significantly inhibited IgE-induced histamine and ßhexosaminidase release from RBL-2H3 cells. Since MEC contains a variety of flavonoids, we selected nobiletin, hesperetin, and hesperidin (hesperetin glycoside) as representative compounds, and further evaluated these inhibitory activities. Among the flavonoids tested, hesperetin was the most potent, while hesperidin had far less, if any, inhibitory activity. The mechanism by which flavonoids inhibited the degranulation process was then examined. As a result, hesperetin and nobiletin suppressed the phosphorylation of Akt-1, direct downstream effector of phosphatidylinositol 3-kinase (PI3-K). Thus, it was assumed that these flavonoids suppressed IgEmediated stimulation of basophils through PI3-K pathway and that proper intake of Citrus unshiu would be favorable for managing seasonal allergic rhinitis to ceder pollen. Introduction Allergic rhinitis is a common allergic disease in industrialized nations, characterized by sneezing, water rhinorrhea, itching in the nose, eyes, and palate, and nasal congestion (1). Recently, the incidence of both perennial (2-5) and seasonal allergic rhinitis (6-10) has been increasing worldwide. Seasonal allergic rhinitis (SAR) may occur at any age and affects between 10 and 30% of children (6). It causes major discomfort in affected patients, such as fatigue, absenteeism, and irritability, adversely affecting the child's adjustment and achievement at school. Therefore, effective management should be directed not only towards rapid and adequate relief of the clinical symptoms but also towards a sustained improvement in the patient's daily life. While conventional therapies for allergic symptoms are advancing steadily, natural products such as phytochemicals and herbal extracts have been widely used by consumers as alternatives to prescription drugs without definitive clinical evidence. Recently, citrus flavonoids have been reported to possess various pharmacological effects, such as anti-inflammation and even anti-cancer activity (11-13). For these activities, nobiletin, a polymethoxy (5, 6, 7, 8, 3', 4'-hexamethoxy) flavone, is thought to be a responsible compound and has been paid much attention. Concerning the anti-allergic effect of citrus flavonoids, hesperidin is the most famous one. Park et al reported that orally administrated hesperidin, flavanone glycoside, inhibited the passive cutaneous anaphylaxis (PCA) reaction of mice, but exhibited no PCA-inhibitory activity when administered intraperitoneally (14). Another group also demonstrated that hesperidin did not inhibit histamine release in vitro (15). However, hesperetin, the flavanone aglycone, inhibited ß-hexosaminidase release in vitro (14). The antiallergic activities of hesperidin and hesperetin are controversial since the mechanisms by which these citrus flavonoids exert their activities have not been fully clarified yet. In addition, to our knowledge, the anti-allergic activity of nobiletin has not been examined in detail. For this study, we chose Citrus unshiu, belonging to the family, Rutaceae. It is one of the most popular citrus fruits and its well-known name is Satsuma Mandarin. The ripe fruits are a common food and the dried peels have been used not only in traditional Chinese medicine but also as a skinmoisturizing agent in Japanese folk medicine (16). Citrus INTERNATIONAL JOURNAL OF MOLECULAR MEDICINE 17: 511-515, 2006 511 Evaluation of the anti-allergic activity of Citrus unshiu using rat basophilic leukemia RBL-2H3 cells as well as basophils of patients with seasonal allergic rhinitis to pollen SHOKO KOBAYASHI1 and SOICHI TANABE2 1Department of Food and Life-Science, Takasaki University of Health and Welfare, Takasaki 370-0033; 2Graduate School of Biosphere Science, Hiroshima University, 1-4-4 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8528, Japan Received October 10, 2005; Accepted November 18, 2005 _________________________________________ Correspondence to: Dr Soichi Tanabe, Graduate School of Biosphere Science, Hiroshima University, 1-4-4 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8528, Japan E-mail: [email protected] Abbreviations: DMSO, dimethyl sulfoxide; DNP, dinitrophenyl; ELISA, enzyme-linked immunosorbent assay; HSA, human serum albumin; MEC, 50% methanol extract of Citrus unshiu powder; MT, modified Tyrode buffer; PBMC, peripheral blood mononuclear cell; PCA, passive cutaneous anaphylaxis; PI3-K, phosphatidylinositol 3-kinase; RBL-2H3, rat basophil leukemia; SAR, seasonal allergic