Ultraviolet B-induced oxidative damage in human skin keratinocytes is alleviated by Pinus morrisonicola leaf essential oil through activation of the Nrf2-dependent antioxidant defense system.

Background: Ultraviolet B (UVB) radiation contributes to skin disorders such as photodamage, photoaging, and cancer. Natural antioxidants can mitigate UVB-induced damage. Pinus morrisonicola (Taiwan white pine), known for its anti-cancer, anti-inflammatory, and antioxidant properties, is used in health-promoting beverages, but its skin-protective effects remain underexplored.

Purpose: This study investigates the protective effects of P. morrisonicola leaf essential oil (PMLEO) against UVB-induced damage in HaCaT keratinocytes.

Methods: HaCaT cells were exposed to UVB and treated with PMLEO. Cell viability, reactive oxygen species (ROS) levels, and antioxidant enzyme expression were assessed. The role of Nrf2, a key antioxidant regulator, was evaluated through knockdown experiments. The effects on UVB-induced melanogenesis were examined via α-MSH secretion followed by p53-mediated POMC expression.

Results: PMLEO and P. morrisonicola bark essential oil (PMBEO) were non-cytotoxic up to 200 µg/mL. UVB reduced cell viability to 43%, but PMLEO co-treatment significantly restored viability and reduced ROS levels via Nrf2 activation, increasing NQO-1 and HO-1. Nrf2 knockdown impaired PMLEO's protection. PMLEO also inhibited UVB-induced α-MSH secretion by downregulating p53-mediated POMC expression, suggesting an anti-melanogenic effect.

Conclusion: PMLEO protects dermal keratinocytes against UVB-induced oxidative stress, cell death, and melanogenesis via Nrf2 activation, highlighting its potential as a natural skin protectant.