Niacinamide and 12-hydroxystearic acid prevented benzo(a)pyrene and squalene peroxides induced hyperpigmentation in skin equivalent.

Skin surface is constantly exposed to environmental and secreted stressors such as UV, air pollution and peroxidized sebum. The current study aims to use reconstructed human skin equivalents to demonstrate topical stressor-induced hyperpigmentation and evaluate bioactives' potential protective effect. Given that polycyclic aromatic hydrocarbons are representative airborne particle-bound organic compounds with known relevance to pigmentation pathways, benzo(a)pyrene was selected as surrogate environmental toxin. On the other hand, squalene monohydroperoxides are well-characterized sebum peroxidation product under UV and pollutant exposure, thus are used as another representative skin stressor. With 3-day continuous exposure, 30 pmol/cm2 of benzo(a)pyrene and 3.4 nmol/cm2 of squalene monohydroperoxides induced significant viability loss, inflammatory response, and approximately 10 shades of pigmentation increase in pigmented living skin equivalents. At the same time, pretreatment and co-treatment with 12-hydroxystearic acid (12-HSA, 20 μmol/L) or niacinamide (5 mmol/L) ameliorated such stressor-induced consequences. Niacinamide was particularly effective against benzo(a)pyrene damage, probably as a substrate for important NAD+ dependent detoxification pathways, while 12-HSA was potent against squalene monohydroperoxides through barrier enhancing, anti-inflammatory, and anti-oxidative mechanisms. In summary, topical stressor-induced hyperpigmentation was achieved in vitro, with known bioactives showing protective benefits.