Shishihakuhito, a traditional Chinese medicine for atopic dermatitis, inhibits IgE-mediated histamine release from rat RBL-2H3 basophilic leukocyte cells

梔子柏皮湯は,山梔子,黄柏,甘草の3つの構成生薬より熱水抽出した水製乾燥エキスであり,アトピー性皮膚炎の有効な漢方治療薬である。本研究では,梔子柏皮湯の作用メカニズムを解明するため,ラット好塩基球性白血病細胞(RBL-2H3)において,アレルギー反応のケミカルメデイエーターであるヒスタミン遊離への梔子柏皮湯の影響を検討した。さらに,COX-2などの炎症性遺伝子の転写誘導において中心的な役割を演じるNF-κB依存的転写活性に対する梔子柏皮湯の効果について検討した。その結果,RBL-2H3細胞において梔子柏皮湯は濃度依存的にIgEが仲介するヒスタミン遊離を抑制した。また,その構成生薬エキスの一味抜き漢方エキスについてヒスタミン遊離抑制活性を検討したところ,黄柏を抜いた一味抜き漢方エキスでのみ顕著な抑制活性の低下が認められた。さらに,C6ラットグリオーマ細胞において,梔子柏皮湯と各一味抜き漢方エキスによるLPS誘導性NF-κB依存的転写の抑制が認められた。これらの結果より,梔子柏皮湯はヒスタミン遊離および炎症性遺伝子の転写誘導に関与するNF-κB依存的転写を抑制する薬効により,抗アトピー性皮膚炎作用を示すことが示唆された。

Shishihakuhito is a traditional Chinese medicine that is effective in the treatment of pruritic skin diseases of the elderly and atopic dermatitis. However, the molecular mechanism of such a beneficial action of shishihakuhito on the dermatologic disorders is unknown. In the present study, we for the first time examined whether shishihakuhito extract exhibits the inhibitory action on IgE-mediated histamine release from the rat basophilic leukocyte cell line, RBL-2H3 cells. The extract decreased IgE-mediated histamine release at 30μg/ml, and more potently inhibited the histamine release at the concentrations of more than 100μg/ml, with almost abolishing it at 200-400μg/ml. Shishihakuhito consists of Gardenia Fruit, Phellodendron Bark and Glycyrrhiza. Next, to address the question of which crude drug components of shishihakuhito are responsible for the inhibitory action on IgE-mediated histamine release from RBL-2H3 cells, the activity of the Kampo preparations excluding each bulk extract of the shishihakuhito to inhibit the histamine release from RBL-2H3 cells was examined. The Kampo preparations without Gardenia Fruit or Glycyrrhiza at 100μ/ml still prevented the histamine release, whereas that without Phellodendron Bark failed to inhibit the histamine release, demonstrating that Phellodendron Bark extract is mainly involved in the inhibitory action of shishihakuhito extract. In addition, shishihakuhito extract and the Kampo preparations excluding each bulk extract of the Kampo medicine inhibited lipopolysaccharide (LPS)-induced stimulation of NF-κB-dependent transcription in C6 rat glioma cells. These results suggest that shishihakuhito may exhibit the in vivo antagonistic action on allergic inflammation by inhibition of histamine release as well as LPS-induced stimulation of NF-κB-dependent transcription.