Tocotrienols improve urban particulate matter-induced skin damages by regulating skin barrier function and ROS/MAPK signalling pathway in keratinocytes

Abstract

Urban particulate matter (PM) is a major air pollutant that triggers molecular processes and is detrimental to the skin. We investigated the protective effects of tocotrienol-rich fraction (TRF) against urban PM-induced skin ageing, inflammation, and skin barrier dysfunction in human epidermal keratinocytes. Alpha-tocopherol (αTP) and retinoic acid (RA) were used as comparators. Our results showed that TRF significantly restored cell viability and alleviated increased intracellular reactive oxygen radicals in PM-treated keratinocytes. In addition, TRF significantly downregulated the activation of mitogen-activated protein kinases in PM-stimulated keratinocytes. This was substantiated by lower protein expression in the phosphorylation of extracellular signal-regulated kinase, Jun N-terminal kinase, and p38. This resulted in the inhibition of cyclooxygenase-2 expression, which is a downstream inflammatory mediator. TRF significantly protected skin barrier function upon exposure to PM by upregulating filaggrin, transglutaminase-1, and involucrin. In contrast, αTP and RA did not exhibit protective effects against skin damages in the PM-treated keratinocytes. Overall, this study suggests that TRF possesses antioxidant, anti-inflammatory, and skin barrier protective properties, and may serve as a potential ingredient in personal care and cosmeceutical industries to combat skin damage due to air pollution.