Luteolin, a flavonoid abundant in plants worldwide, demonstrates a spectrum of biological activities. This study is aimed at evaluating its inhibiting effects on inflammatory responses in vivo. We investigated the anti-inflammatory activity of luteolin in acute and chronic models in mice. We found that oral administration of luteolin (10 and 50 mg/kg) efficiently suppressed paw edema when induced by injecting carrageenan, and a similar tendency was also observed in the cotton pellet granuloma test. In the air pouch test, luteolin markedly reduced the number of infiltrated leukocytes and the elevated level of 6-keto-prostaglandin F1alpha (6-keto-PGF1alpha) in the exudate. The results derived from the whole blood assay for cyclooxygenase (COX) and from the reverse transcription-polymerase chain reaction (RT-PCR) assay indicate that luteolin may be a potent selective inhibitor of cyclooxygenase-2 (COX-2) and that the inhibition is attributable to its down-regulation of the mRNA expression of COX-2 in inflammatory responses.

The present study is aimed at evaluating the effects of luteolin on the scratching behavior associated with an allergic cutaneous reaction in mice. Elicitation of passive cutaneous anaphylaxis, and intradermal injections of compound 48/80, histamine or serotonin induced scratching behavior in ICR mice. Models of irritant contact dermatitis and allergic contact dermatitis were prepared by the topical application of 2,4-dinitrochlorobenzene (DNCB) on the ears of mice. Topical application of luteolin at concentrations of 20 and 100 mug/site significantly inhibited the number of scratching incidents associated with passive cutaneous anaphylaxis, and a similar tendency was also observed in histamine-, serotonin- and compound 48/80-evoked cutaneous reactions. The vascular permeability increase induced by passive cutaneous anaphylaxis or histamine injection was also significantly reduced by luteolin. Luteolin showed a potent inhibition on the ear thickness increase in models of irritant contact dermatitis and allergic contact dermatitis. In conclusion, luteolin significantly inhibited the scratching behavior associated with allergic cutaneous anaphylaxis. Its effects against pruritus are mainly attributed to its inhibition of mediator release from activated mast cells and direct antagonist effects on the released mediators which may act as local pruritogens.