Antipruritic effects of petals of Hibiscus syriacus L

In cases of allergic diseases with chronic and severe pruritus, such as atopic dermatitis, it is important to inhibit scratching of the lesion. We have searched for natural compounds with antipruritic activity using in vivo assay systems [1] and revealed the antipruritic activity of fresh petals of Hibiscus syriacus L. Dried petals of white-colored H. syriacus have been used in Chinese herbal medicine under the name of Mokukinka for detoxication, reducing fever, and treating athlete's foot. This was the first report of its antipruritic activity. Here we report the antipruritic effects of fresh petals of H. syriacus and its active compounds.

Fresh petals of three colors, white flower (WT), white flower with central pink color point (Mix), and pink flower (Red), were subjected to extraction with 35% EtOH. The antipruritic activity of the extract and compounds was measured using a previously reported method [1], which evaluates the inhibitory effect of compound 48/80 (COM, a mast cell degranulation agent)-induced scratching behavior (avoidance behavior from itching sensation) in mice.

Mix and Red significantly inhibited COM-induced scratching behavior, but WT significantly inhibited COM-induced scratching behavior. None of the extracts inhibited locomotive behavior. Activity-guided fractionation and purification yielded vitexin (1), isovitexin (2) and isovitexin 7-O-β-D-glucoside (3) from Mix. Compounds 2 and 3 significantly inhibited COM-induced scratching behavior, but did not inhibit locomotive behavior. HPLC analysis showed that Red contained rich colored anthocyans such as cyanidin (4), cyanidin 3-O-β-D-glucoside (5), and malvidin 3-O-β-D-glucoside (6) that were not found in the non-active WT. The antipruritic effects of compounds 4-6 are under investigation. This work showed that the petals of H. syriacus offer promise for the discovery of new antipruritic substances.

References: 1. Oku, H. et al., (2003) Biol. Pharm. Bull., 26:1031–1034.