In addition to the sunlight, the damaging effects of pollutants on human skin have been the subject of intense research recently. Particulate matter (PM) in air pollution is a mixture of particles suspended in the air. Major components of PM are metals, organic compounds, ions, and particle carbon core. Gases are also contained that are adsorbed onto the particles.
Recently, PM has been reported to be associated with increased risks of skin diseases. It demonstrates that chronic traffic-related PM exposure is associated with premature skin aging, with 20% increase in pigment spots on the forehead and cheeks. In addition, literatures showed that pollutants may increase the incidence of atopic dermatitis in young people and aggravate their symptoms, particularly the itching sense, and may also be the cause of increased urinary ROS in the children with atopic dermatitis. These epidemiologic reports suggest that PM may penetrate the skin barrier to increase ROS, which aggravates skin inflammation.
Since PM is a mixture of insoluble particles and soluble components such as gases or ions, PM might still induce harmful effects through soluble components, even though the particles cannot penetrate into the skin. Nevertheless, because there is no direct evidence whether particles can penetrate into the skin, we investigated if particles from locally collected PM penetrates into mice skin in vivo and if PM causes inflammation via ROS-dependent manner.
Keratinocyte cytotoxicity increased in a dose-dependent manner by PM treatment. IL-8 and MMP-1 mRNA expression and protein levels were significantly increased compared to control by qPCR and ELISA, respectively. Cellular ROS production was increased by PM treatment, and antioxidant N-acetyl cysteine pretreatment prevented induction of inflammatory cytokines IL-8 and MMP-1. In PM-treated keratinocytes, electron-dense subcellular particles were observed by transmission electron microscopy. PM was observed inside hair follicles in both intact and barrier-disrupted skin in vivo. Additionally, intercellular penetration of PM was seen in the barrier-disrupted skin. Repeated PM application induced epidermal thickening and dermal inflammation with neutrophil infiltration. Finally, N-acetyl cysteine could ameliorate skin inflammation induced by PM application.
In conclusion, PM penetrates into the barrier-disrupted skin, causing inflammation, demonstrating detrimental effects in the skin.
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