Human hair follicle pigmentary unit as a direct target for modulators of melanogenesis, as studied by [14C]-2-Thiouracil incorporation

The purpose of this study was to evaluate human hair follicle melanogenic activity using the [C-14]-2-thiouracil, which was known to incorporate into nascent melanins. Results obtained on pigmented, grey and non-pigmented hair follicles demonstrated that [C-14]-2-TU incorporation was restricted to the melanogenic compartment with a strong accumulation located around dermal papilla and within the fibre of pigmented hair follicles. Quantitative analysis of [C-14]-2-TU incorporation showed a significant increase in pigmented hair follicles upon stimulation with 1 mu m forskolin concomitant to an increase in tyrosinase levels. A strong significant decrease in [C-14]-2-TU incorporation was noted, when hair follicles were incubated with the tyrosinase competitive inhibitor kojic acid (200 mu m). Incubation with the MC1-R agonist alpha-MSH (0.2 mu m) did not induce a significant stimulation of hair melanogenesis. The present model could thus represent a useful new tool to identify modulators of human hair pigmentation.