Article: Diesel Particulate Matter Permeation into Normal Human Skin and Intervention Using a Topical Ceramide Formulation
Authors: Kyong-Oh Shin, Kenya Ishida, Hisashi Mihara, Yerim Choi, Jae-Ho Park, Soo-Hyun Park, Jin-Taek Hwang, Joan S. Wakefield, Yasuko Obata, Yoshikazu Uchida, Kyungho Park
Journal: Skin Pharmacology and Physiology
Year: 2024
DOI: 10.1159/000539291
We are exposed to various pollutants and irritants on a daily basis. One such pollutant that we frequently encounter is particulate matter (PM), which is composed of microscopic solids and liquids that float through the air. This PM often includes dust, soot, smoke, and chemical pollutants from industrial emissions, vehicle exhaust, and some natural sources like wildfires. We are directly exposed to such irritants through our airway and skin, and they can penetrate deep into the skin and disrupt its barrier function. Research has shown that prolonged exposure to PM can trigger inflammatory responses, oxidative stress, and immune system dysregulation, all of which contribute to the development or worsening of skin conditions such as eczema and psoriasis. By aggravating inflammation and impairing the skin’s natural defenses, air pollution can lead to increased dryness, irritation, and flare-ups in individuals predisposed to these dermatological disorders.
A more specific type of PM is diesel particulate matter (DPM), which comes from diesel engines commonly used in cars, boats, electrical generators, and other vehicles and machines. It is primarily composed of carbon and involves polycyclic aromatic hydrocarbons (PAHs), which are a group of organic compounds composed of multiple fused benzene rings.
Our skin’s natural defense against DPM and other airborne pollutants is primarily comprised of layers of fatty molecules known as lipid-dominant lamellar structures. These play a crucial role in maintaining the skin’s barrier function and preventing excessive water loss. The outermost layer of our skin consists of dead, flattened skin cells embedded in a lipid matrix, forming a structure often compared to a “brick-and-mortar” system. The “mortar” is comosed primarily of lipids, including cholesterol, free fatty acids, ceramides, and other minor lipid components. These lipids organize into lamellar (layered) structures, which regulate the permeability of the skin and ensure its protective function against environmental pollutants. Ceramides, in particular, are essential for maintaining hydration and structural integrity, while cholesterol and fatty acids contribute to the fluidity and stability of the lipid layers. Disruptions in these lipid structures can lead to increased dryness and heightened sensitivity to DPM, ultimately compromising the skin’s overall health and function.
Fig 1: Stereo isomers of N-acyl-dihydrosphingosine (a ceramide). The long “tail” of the chemical structures cluster together in biological membranes and help form our skin barrier.
Our skin barrier’s ability to protect us from airborne pollutants was recently studied by Shin et. al., who investigated the extent to which DPM can permeate through the skin. They did so by using organ-cultured human skin, which they first treated with a topically-applied formulation containing a mixture of several types of fatty molecules including cholesterol, polyglycerol, and ceramides, which overall approximated the components of our natural skin barrier. Once the skin samples were treated with the formulation, DPM was applied and the skin was incubated for 24 hours. In order to assess the permeation of DPM into the skin, PAHs were extracted from the skin and analyzed with liquid chromatography electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS). LC-ESI-MS/MS is an analytical technique used to identify and quantify complex chemical compounds by separating compounds in a sample based on differences in their chemical properties, converting them into electrically charged ions using a fine mist and high-voltage field, then breaking these ions into smaller pieces, or fragmenting them, to measure their weight and ultimately identify molecules with high precision.
Through their analysis, Shin et. al. found three PAHs which permeated through the skin: 2-methylnaphthalene, triphenylene, and benzo(a)pyrene. These PAHs are common environmental pollutants which can be found in cigarette smoke, vehicle exhaust, and industrial emissions. Due to their chemical stability, they often persist in the environment long after they are emitted and can pose health risks through long-term exposure.
After finding that PAHs permeated normal human skin, the researchers then repeated the process, but with a pre-treatment formulation that contained significantly greater fatty compounds, and found that the use of the more robust topical formula decreased the amount of PAHs found in the skin. This suggested that the use of skin care compounds which can bolster our natural defenses with lipids may be useful to not only people with weakened skin barriers due to conditions like eczema or psoriasis, but also people with normal, barrier competent skin, as the PAHs were able to penetrate even the control samples.
