Influence of different penetration enhancers on in vitro skin permeation and in vivo photoprotective effect of flavonoids

In the present study the permeation of two flavonoids (naringenin and hesperetin) through excised human skin mounted in Franz diffusion cells and its possible optimization following skin pretreatment with two penetration enhancers (D-limonene and lecithin) were determined. Hesperetin and naringenin were able to permeate through excised human skin; moreover, skin pretreatment with D-lmonene and lecithin increased, to different degrees, their cutaneous permeation. On the basis of findings obtained in these in vitro experiments, we designed a schedule for a series of in vivo experiments, in which the protective effect of topically applied naringenin and hesperetin against UV-B-induced skin damage was assessed monitoring the extent of erythema in human volunteers by means of reflectance spectrophotometry. Hesperetin and naringenin from formulations containing the flavonoid alone were completely ineffective in decreasing UV-B-induced erythema. Furthermore, both D-limonene and lecithin have enhanced, to a significant extent, the photoprotective activity of naringenin and hesperetin. Taken together. these data :demonstrate that hesperetin and naringenin may be successfully employed as topical photoprotective agents. However their topical activity needs to be optimized by using suitable penetration enhancers. (C) 1998 Elsevier Science B.V. All rights reserved.