Permeant lipophilicity and vehicle composition influence accumulation of dyes in hair follicles of human skin.

In skin and hair research drug targeting to the hair follicle is of great interest. Therefore the influence of permeant lipophilicity and vehicle composition on local accumulation has been examined using confocal laser scanning microscopy (CLSM). Formulations saturated with either Oregon Green 488, Bodipy FL C(5) or Bodipy 564/570 C(5) were prepared. The dyes were applied in citric acid buffer, 8% (w/v) surfactants in citric acid buffer or 8% (w/v) surfactants/20% (w/v) propylene glycol in citric acid buffer. Flow-through diffusion experiments were performed with fresh human scalp skin, after which the skin was imaged using CLSM. Diffusion studies showed for Oregon Green 488 (low lipophilicity) a higher flux when applied in citric acid buffer compared to surfactants. In contrast the fluxes of the more lipophilic dyes (Bodipy FL C(5) and Bodipy 564/570 C(5)) are highest when applied in surfactants/propylene glycol. CLSM studies revealed that follicular accumulation increased with (i) a lipophilic dye and (ii) application of lipophilic dyes in surfactants-propylene glycol. Therefore we conclude that targeting to the hair follicle can be increased by the use of lipophilic drugs in combination with surfactant solutions and propylene glycol.