Targeting SDF‐1 as an efficient strategy to resolve skin hyperpigmentation issues with Himanthalia elongata extract

BACKGROUND: During aging, human skin is facing hyperpigmentation disorders: senile lentigo (chronobiologic aging) leads to loss of melanogenesis' control while solar lentigo (UV exposure) promotes an increase of oxidized proteins, melanogenesis, and lipofuscin. AIMS: Stromal‐cell‐derived‐factor‐1 (SDF‐1) was identified as key regulator of hyperpigmentation and its expression is reduced in senescent fibroblasts, highlighting this protein as new target for skin hyperpigmentation. MATERIALS: We developed two skin explant models mimicking of senile and solar lentigo, based on H(2)O(2) systemic treatment and UV irradiation, respectively. We evaluated Himanthalia elongata extract (HEX) on these models after 5 days of treatment and analyzed SDF‐1 expression and skin pigmentation. For solar lentigo, we also analyzed oxidized proteins and lipofuscin accumulation. Finally, we evaluated HEX in vivo on nearly 100 multi ethnicities' volunteers. RESULTS: SDF‐1 expression decreased in senile lentigo model, associated with hyperpigmentation. HEX application restored SDF‐1 expression, leading to skin pigmentation decrease. For solar lentigo, we showed an impact of UVs on SDF‐1 expression linked to hyperpigmentation, while the application of HEX restored SDF‐1 expression and reduced skin pigmentation. On same model, HEX reduced oxidized proteins quantity and lipofuscin which increased after UV exposure. Clinically, HEX reduced dark spot pigmentation on Caucasian volunteers' hands and on Asian and African volunteers' face after 28 days. DISCUSSION: We have developed ex vivo models mimetic of senile and solar lentigo and showed for a very first time that SDF‐1 can be also a key regulator for UV‐induced hyperpigmentation. CONCLUSION: Our ex vivo and clinical studies highlighted the power of HEX with strong reduction of dark spots regardless of volunteers' ethnicities.