The phototoxicity action spectra of visible light in HaCaT keratinocytes

Photocarcinogenesis of the skin: Current status and future trends

Solar radiation is essential for life on Earth but is also a major contributor to skin carcinogenesis. Solar radiation, particularly ultraviolet (UV) B (280-320 nm) and UVA (320-400 nm), induces photocarcinogenesis via various pathways. UV light can directly cause DNA damage, resulting in genetic mutations if not repaired correctly. UV light can also induce photocarcinogenesis by generating reactive oxygen species, inducing immunosuppression and inflammation. Recently, visible light (400-760 nm) has been shown to contribute to photocarcinogenesis by activating oxidative pathways. In addition to the irradiation dose (fluence, J/m2), UVB irradiance (W/m2) is also considered a factor influencing photocarcinogenesis. In this review, we summarize the mechanisms of photocarcinogenesis and provide strategies to prevent skin cancer.

Comparative study of ergosterol and 7-dehydrocholesterol and their endoperoxides: Generation, identification, and impact in phospholipid membranes and melanoma cells

Melanoma is an aggressive cancer that has attracted attention in recent years due to its high mortality rate of 80%. Damage caused by oxidative stress generated by radical (type I reaction) and singlet oxygen, 1O2 (type II reaction) oxidative reactions may induce cancer. Thus, studies that aim to unveil the mechanism that drives these oxidative damage processes become relevant. Ergosterol, an analogue of 7-dehydrocholesterol, important in the structure of cell membranes, is widely explored in cancer treatment. However, to date little is known about the impact of different oxidative reactions on these sterols in melanoma treatment, and conflicting results about their effectiveness complicates the understanding of their role in oxidative damage. Our results highlight differences among ergosterol, 7-dehydrocholesterol (7-DHC), and cholesterol in membrane properties when subjected to distinct oxidative reactions. Furthermore, we conducted a comparative study exploring the mechanisms of cell damage by photodynamic treatment in A375 melanoma. Notably, endoperoxides from ergosterol and 7-DHC generated by 1O2 showed superior efficacy in reducing the viability of A375 cells compared to their precursor molecules. We also describe a step-by-step process to produce and identify endoperoxides derived from ergosterol and 7-DHC. While further studies are needed, this work provides new insights for understanding cancer cell death induced by different oxidative reactions in the presence of biologically relevant sterols.

Novel Exosomal miRNA Expression in Irradiated Human Keratinocytes

The epidermis, the outer layer of the skin, relies on a delicate balance of cell growth and keratinocyte differentiation for its function and renewal. Recent research has shed light on exosomes' role in facilitating skin communication by transferring molecules like miRNAs, which regulate gene expression post-transcriptionally. Additionally, these factors lead to skin aging through oxidative stress caused by reactive oxygen species (ROS). In this research project, experiments were conducted to study the impact of Sun2000 solar simulator irradiation on exosomal miRNA profiles in HEKa cells. We hypothesized that acute oxidative stress induced by solar simulator irradiation would alter the expression profile of exosomal miRNAs in HEKa cells. The cells were exposed to different durations of irradiation to induce oxidative stress, and the levels of reactive ROS were measured using the CellROX Deep Red flow cytometry assay kit. Exosomes were isolated from both control and irradiated cells, characterized using DLS and SEM techniques, and their miRNAs were extracted and analyzed using qPCR. Solar simulator irradiation led to a time-dependent increase in intracellular ROS and a decrease in cell viability. Exosomal size increased in irradiated cells. Fifty-nine exosomal miRNAs were differentially expressed in irradiated HEKa cells, including hsa-miR-425-5p, hsa-miR-181b-5p, hsa-miR-196b-5p, hsa-miR-376c-3p, and hsa-miR-15a-5p. This study highlights the significant impact of solar radiation on exosomal miRNA expression in keratinocytes, suggesting their potential role in the cellular response to oxidative stress.

Effect of Combination of Blue and Red Light with Terbinafine on Cell Viability and Reactive Oxygen Species in Human Keratinocytes: Potential Implications for Cutaneous Mycosis

Cutaneous mycoses are common infections whose treatment has become more complex due to increasing antifungal resistance and the need for prolonged therapies, hindering patient adherence and increasing the incidence of adverse effects. Consequently, the use of physical therapies, especially photodynamic therapy (PDT), has increased for the treatment of onychomycosis due to its antimicrobial capacity being mediated by the production of reactive oxygen species. This study investigates the in vitro effect of applying blue light (448 nm) or red light (645 nm), alone or together with terbinafine, on the viability of human keratinocytes and the production of reactive oxygen species. The combination of terbinafine and blue light significantly increases ROS production and caspase-3 expression, while red light together with terbinafine increases catalase, superoxide dismutase (SOD) and PPARγ expression, which reduces the amount of ROS in the cultures. The effect of both treatments could be useful in clinical practice to improve the response of cutaneous mycoses to pharmacological treatment, reduce their toxicity and shorten their duration.

Innovative Photoprotection Strategy: Development of 2-(Benzoxazol-2-Yl)[(2-Hydroxynaphthyl)Diazenyl] Phenol Derivatives for Comprehensive Absorption of UVB, UVA, and Blue Light

Overexposure to blue light due to the excessive use of electronic devices has been implicated in premature skin aging and eye damage, among other injuries to health. This study aimed to synthesize two azo derivatives of the 2-(amino-2'-hydroxyphenyl) benzoxazole and explore their potential as UV and blue light filters, proposing a new spectral profile. The synthesis of the heterocyclic compounds involved condensation reactions and diazotation. The derivatives 2-(benzoxazol-2-yl)-5-[(2-hydroxynaphthyl)diazenyl]phenol and 2-(benzoxazol-2-yl)-4-[(2-hydroxynaphthyl)diazenyl]phenol were synthesized with a yield greater than 70%. Solubility was evaluated in seven different solvents. The maximum absorption wavelengths (λmax) were determined using UV-Vis scanning spectrophotometry in the range of 200-600 nm. Photostability was assessed using a solar simulator and the Sun protection factor (SPF) was determined using in vitro methodology. Cytotoxicity was evaluated using the MTT assay in V79 cells. These compounds were able to absorb UVA, UVB, and blue light, with λmax ranging from 300 to 500 nm and demonstrated photostability after 3 h of exposure to solar simulator with an SPF higher than 45. The compounds exhibited solubility in all lipophilic solvents tested. Regarding cytotoxicity, IC50 values were comparable to other filters. These findings indicate that both compounds hold promise as potential organic filters.

Expression of opsin and visual cycle-related enzymes in fetal rat skin keratinocytes and cellular response to blue light

The mechanism by which the skin, a non-visual tissue, responds to light remains unknown. To date, opsin expression has been demonstrated in keratinocytes, melanocytes, and fibroblasts, all of which are skin-derived cells. In this study, we examined whether the visual cycle, by which opsin activity is maintained, is present in skin keratinocytes. We also identified the wavelengths of light to which opsin in keratinocytes responds and explored their effects on skin keratinocytes. The fetal rat skin keratinocytes used in this study expressed OPN2, 3, and 5 in addition to enzymes involved in the visual cycle, and all-trans-retinal, which is produced by exposure to light, was reconverted to 11-cis-retinal, resulting in opsin activation. Using the production of all-trans-retinal after light exposure as an indicator, we discovered that keratinocytes responded to light at 450 nm. Furthermore, actin alpha cardiac muscle 1 expression in keratinocytes was enhanced and cell migration was suppressed by exposure to light at these wavelengths. These results indicate that keratinocytes express various opsins and have a visual cycle that keeps opsin active. Moreover, keratinocytes were shown to respond to the blue/UV region of the light spectrum, suggesting that opsin plays a role in the light response of the skin.

Contribution of oxidation reactions to photo-induced damage to cellular DNA

This review article is aimed at providing updated information on the contribution of immediate and delayed oxidative reactions to the photo-induced damage to cellular DNA/skin under exposure to UVB/UVA radiations and visible light. Low-intensity UVC and UVB radiations that operate predominantly through direct excitation of the nucleobases are very poor oxidizing agents giving rise to very low amounts of 8-oxo-7,8-dihydroguanine and DNA strand breaks with respect to the overwhelming bipyrimidine dimeric photoproducts. The importance of these two classes of oxidatively generated damage to DNA significantly increases together with a smaller contribution of oxidized pyrimidine bases upon UVA irradiation. This is rationalized in terms of sensitized photooxidation reactions predominantly mediated by singlet oxygen together with a small contribution of hydroxyl radical that appear to also be implicated in the photodynamic effects of the blue light component of visible light. Chemiexcitation-mediated formation of "dark" cyclobutane pyrimidine dimers in UVA-irradiated melanocytes is a recent major discovery that implicates in the initial stage, a delayed generation of reactive oxygen and nitrogen species giving rise to triplet excited carbonyl intermediate and possibly singlet oxygen. High-intensity UVC nanosecond laser radiation constitutes a suitable source of light to generate pyrimidine and purine radical cations in cellular DNA via efficient biphotonic ionization.

Identification by methods of steady-state and kinetic spectrofluorimetry of endogenous porphyrins and flavins sensitizing the formation of reactive oxygen species in cancer cells

The question about acceptor molecules of optical radiation that determine the effects of photobiomodulation in relation to various types of cells still remains the focus of attention of researchers. This issue is most relevant for cancer cells, since, depending on the parameters of optical radiation, light can either stimulate their growth or inhibit them and lead to death. This study shows that endogenous porphyrins, which have sensitizing properties, may play an important role in the implementation of the effects of photobiomodulation, along with flavins. For the first time, using steady-state and kinetic spectrofluorimetry, free-base porphyrins and their zinc complexes were discovered and identified in living human cervical epithelial carcinoma (HeLa) cells, as well as in their extracts. It has been shown that reliable detection of porphyrin fluorescence in cells is hampered by the intense fluorescence of flavins due to their high concentration (micromolar range) and higher (compared to tetrapyrroles) fluorescence quantum yield. Optimization of the spectral range of excitation and the use of extractants that provide multiple quenching of the flavin component while increasing the emission efficiency of tetrapyrroles makes it possible to weaken the contribution of the flavin component to the recorded fluorescence spectra.

An important step towards the comprehensive sun protection: Blue-light exposure inhibits DNA repair in reconstituted human skin and a broadband sunscreen avoids this inhibition

The field of sun protection is quickly changing and the research article by Douki et al., published in the current issue of Photochemistry and Photobiology, reported key experimental data that will certainly help the development of better sun care products. Mutagenic photoproducts (CPDs, cyclobutane pyrimidine dimers and 6-4PPs, pyrimidine-6-4-pyrimidone photoproducts) were formed in the reconstructed human epidermis (RHE) by UVB (312 nm) irradiation, and their concentrations were detected by HPLC-MS/MS as a function of time after the UVB treatment. RHE had been previously exposed or not (control) to blue light (427 nm). Both CPDs and 6-4PPs were shown to last longer in blue-light irradiated RHE, proving the inhibition of the DNA repair by blue light exposure. This is a highly relevant information because sunscreens allow people to enjoy longer periods under the sun and consequently, to endure very high doses of blue light. The work also reported results obtained with RHEs previously treated with a sunscreen formulation containing a broadband filter that offers blue-light protection. Interestingly, authors observed that the DNA repair was not significantly inhibited in RHE previously treated with the sunscreen offering broadband protection. Readers will find a scientifically sound proof of the importance of blue-light protection in sun care products.

Blue light impairs the repair of UVB-induced pyrimidine dimers in a human skin model

In recent years, interest is growing in the biological cutaneous effects of high-energy visible light (400-450 nm). In the present study, we explored the impact of blue light (BL) on the repair of pyrimidine dimers, the major class of premutagenic DNA damage induced by exposure to sunlight. We unambiguously demonstrate that the exposure of in vitro reconstructed human epidermis to environmentally relevant doses of BL strongly decreases the rate of repair of cyclobutane pyrimidine dimers and pyrimidine (6-4) pyrimidone photoproducts induced by a subsequent UVB irradiation. Using the highly sensitive and specific liquid chromatography-tandem mass spectrometry assay, we did not observe induction of pyrimidine dimers by BL alone. Finally, we showed that application, during the BL exposure step, of a formula containing a new filter, named TriAsorB and affording BL photoprotection, prevented the decrease in DNA repair efficiency. These results emphasize the potential deleterious effects of BL on DNA repair and the interest in providing adequate skin protection against this wavelength range of sunlight.

Assays on 3D tumor spheroids for exploring the light dosimetry of photodynamic effects under different gaseous conditions

The multifaceted nature of photodynamic therapy (PDT) requires a throughout evaluation of a multitude of parameters when devising preclinical protocols. In this study, we constructed MCF-7 human breast tumor spheroid assays to infer PDT irradiation doses at four gradient levels for violet light at 408 nm and red light at 625 nm under normal and hypoxic oxygen conditions. The compacted three-dimensional (3D) tumor models conferred PDT resistance as compared to monolayer cultures due to heterogenous distribution of photosensitizers along with the presence of internal hypoxic region. Cell viability results indicated that the violet light was more efficient to kill cells in the spheroids under normal oxygen conditions, while cells exposed to the hypoxic microenvironment exhibited minimal PDT-induced death. The combination of 3D tumor spheroid assays and the multiparametric screening platform presented a solid framework for assessing PDT efficacy across a wide range of different physiological conditions and therapeutic regimes.