Nigella sativa seed extract and its bioactive compound thymoquinone: the new melanogens causing hyperpigmentation in the wall lizard melanophores

Abstract

The effects of the lyophilized seed extract of Nigella sativa and its active ingredient, thymoquinone, were studied on the isolated melanophores of the wall lizard to find the mechanism of skin darkening at the cellular level. The integumental melanophores of the wall lizard, Hemidactylus flaviviridis, were assayed using the mean melanophore size index and their responses were recorded in the presence of various concentrations of the plant extract, thymoquinone, specific antagonists and potentiator. Significant skin darkening activity of the extract of N. sativa and thymoquinone was observed on the isolated melanophores of the wall lizard. The pigment cells responded by distinct dispersion leading to skin darkening. The effect was physiologically significant as re-immersion in physiological saline made the melanophores return to their normal intermediate state. These melanin dispersal effects were antagonized by atropine as well as hyoscine and were also found to be highly potentiated by neostigmine, an anticholinesterase agent. These findings suggest that the extract of N. sativa, as well as its active principle, mimic the action of acetylcholine in melanin dispersion leading to skin darkening via stimulation of cholinergic receptors of muscarinic nature within the melanophores of wall lizard. This study opens new vistas for the use of N. sativa active ingredient, thymoquinone, as a novel melanogen for its clinical application in skin disorders such as hypopigmentation or vitiligo.