Isoflavonoid compounds from red clover (Trifolium pratense) protect from inflammation and immune suppression induced by UV radiation

Isoflavones derived from many edible plants have been reported to possess s ignificant antioxidant, estrogenic and tyrosine kinase inhibitory activity. Genistein has been found previously to provide protection from oxidative d amage induced by UV radiation both in vitro and following dietary administr ation. We have therefore examined the potential of a number of isoflavones from red clover (Trifolium pratense) and some metabolically related compoun ds to offer protection from UV irradiation in hairless mice by topical appl ication after UV exposure. We show that whereas the primary isoflavones, da idzein, biochanin A and formononetin, were inactive, 20 muM lotions of geni stein and the metabolites equol, isoequol and the related derivative dehydr oequol had powerful potential to reduce the inflammatory edema reaction and the suppression of contact hypersensitivity induced by moderate doses of s olar-simulated UV radiation. For equol the protection was concentration dep endent and 5 muM equol markedly reduced the UV-induced inflammation but abr ogated the UV-induced immunosuppression. Equol protected similarly from imm unosuppression induced by the putative epidermal mediator, cis-urocanic aci d (UCA), indicating a potential mechanism of action involving inactivation of this UV-photoproduct. Since immunosuppression induced by both UV radiati on and by cis-UCA appears to be an oxidant-dependent response our observati ons support the actions of these topically applied isoflavones and their me tabolites as antioxidants. They also indicate that lotions containing equol , unlike topical UV sunscreens, more readily protect the immune system from photosuppression than from the inflammation of the sunburn reaction, even when applied after exposure, and thus such compounds may have a future role as sun-protective cosmetic ingredients.