Investigation of the absorption of hypericin into the skin of hairless mice

The skin absorption of hypericin was evaluated in hairless mice to develop an optimised hypericin topical formulation that could be used in the clinic al study of psoriasis. Hypericin (0.01-1.0%) in Beeler basis, polyethylene glycol ointment, carbop ol gel, cetomacrogol cream, petrolatum or emulsifying ointment, with and wi thout skin-absorption enhancers (isopropylidene glycerol and diethylene gly col monoethyl ether), was tested in-vivo on hairless mice skin. Using a ski n-stripping technique and the intrinsic fluorescence of hypericin under sta ndardised UV365 irradiation, it was demonstrated that the absorption of hyp ericin very much depended on the vehicle used. The concentrations of hyperi cin in the skin were then estimated by HPLC analysis. For this purpose, two vehicles were employed, with which hypericin penetrated the skin of hairle ss mice well (emulsifying ointment with isopropylidene glycerol) or very po orly (polyethylene glycol ointment). In the case of emulsifying ointment wi th isopropylidene glycerol (0.05% hypericin), a substantial concentration o f hypericin (8.6 +/- 32 mu g g(-1)) (mean +/- s.d., n = 5) was found in the skin. With polyethylene glycol ointment, however, only a limited hypericin skin concentration (0.38 +/- 0.34 mu g g(-1), n = 5) was achieved. These results show that emulsifying ointment with polyethylene glycol holds promise as an effective topical vehicle for the treatment of skin diseases , such as psoriasis, with hypericin.