The human skin is exposed to various environmental factors including solar radiation and ambient air pollutants. Although, due to its physical and biological properties, the skin efficiently protects the body against the harm of environmental factors, their excessive levels and possible synergistic action may lead to harmful effects. Among particulate matter present in ambient air pollutants, PM2.5 is of particular importance for it can penetrate both disrupted and intact skin, causing adverse effects to skin tissue. Although certain components of PM2.5 can exhibit photochemical activity, only a limited amount of data regarding the interaction of PM2.5 with light and its effect on skin tissue are available. This study focused on light-induced toxicity in cultured human keratinocytes, which was mediated by PM2.5 obtained in different seasons. Dynamic Light Scattering (DLS) and Atomic Force Microscopy (AFM) were employed to determine sizes of the particles. The ability of PM2.5 to photogenerate free radicals and singlet oxygen was studied using EPR spin-trapping and time-resolved singlet oxygen phosphorescence, respectively. Solar simulator with selected filters was used as light source for cell treatment to model environmental lightning conditions. Cytotoxicity of photoexcited PM2.5 was analyzed using MTT assay, PI staining and flow cytometry, and the apoptotic pathway was further examined using Caspase-3/7 assay and RT-PCR. Iodometric assay and JC-10 assay were used to investigate damage to cell lipids and mitochondria. Light-excited PM2.5 were found to generate free radicals and singlet oxygen in season-dependent manner. HaCaT cells containing PM2.5 and irradiated with UV-Vis exhibited oxidative stress features–increased peroxidation of intracellular lipids, decrease of mitochondrial membrane potential, enhanced expression of oxidative stress related genes and apoptotic cell death. The data indicate that sunlight can significantly increase PM2.5-mediated toxicity in skin cells.

Aging may significantly modify antioxidant and photoprotective properties of melanin in retinal pigment epithelium (RPE). Here, photoreactivity of melanosomes (MS), isolated from younger and older human donors with and without added zeaxanthin and α‐tocopherol, was analyzed by electron paramagnetic resonance oximetry, time‐resolved singlet oxygen phosphorescence, and protein oxidation assay. The phototoxic potential of ingested melanosomes was examined in ARPE‐19 cells exposed to blue light. Phagocytosis of FITC‐labeled photoreceptor outer segments (POS) isolated from bovine retinas was determined by flow cytometry. Irradiation of cells fed MS induced significant inhibition of the specific phagocytosis with the effect being stronger for melanosomes from older than from younger human cohorts, and enrichment of the melanosomes with antioxidants reduced the inhibitory effect. Cellular protein photooxidation was more pronounced in samples containing older melanosomes, and it was diminished by antioxidants. This study suggests that blue light irradiated RPE melanosomes could induce substantial inhibition of the key function of the cells—their specific phagocytosis. The data indicate that while photoreactivity of MS and their phototoxic potential increase with age, they could be reduced by selected natural antioxidants.

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Skin cancer is the most common cancer in the U.S.A. and Europe. Its subtype, squamous skin carcinoma (SCC), if allowed to grow, has the potential to metastasize and can become deadly. Currently, carbon nanomaterials are being developed to treat cancer due to their attractive physicochemical and biological properties such as an enhanced permeability effect and their ability to produce reactive oxygen species. Here, we describe the synthesis of two water-soluble aminofullerenes (MonoaminoC60 and HexakisaminoC60), which were evaluated as novel [60]­fullerene based photosentizers exhibiting anticancer properties. Moreover, the previously described neutral glycofullerene GF1 and its peracetylated lipophilic precursor MMS48 were compared with the aminofullerenes for their ability to generate reactive oxygen species and oxidize lipids. Remarkably, the generation of singlet oxygen and a superoxide radical by HexakisaminoC60 was found to be markedly elevated in the presence of bovine serum albumin and NADH, respectively. Mechanistic studies of lipid peroxidation using cholesterol as a unique reporter molecule revealed that although all four fullerene nanomaterials primarily generated singlet oxygen, superoxide anion was also formed, which suggest a mixed mechanism of action (in which Type I and Type II photochemistry is involved). The [60]­fullerene derivative HexakisaminoC60 was also studied for its phototoxicity in squamous skin cancer cell line (A431) using the MTT test and propidium iodide staining.