Modeling acute and cumulative erythemal sun exposure on vulnerable body sites during beach vacations utilizing behavior-encoded 3D body models.

Vacationers in a high-solar-intensity beach setting put themselves at risk of ultraviolet radiation (UV) over-exposure that can lead to acute and chronic health consequences including erythema, photoaging, and skin cancer. There is a current gap in existing dosimetry work on capturing detailed time-resolved anatomical distributions of UV exposure in the beach vacation setting. In this study, a radiative transfer model of the solar conditions of Tampa Bay, St. Petersburg, Florida, USA (27.8°N, 82.8°W) is combined with an in silico three-dimensional body model and data on typical beach vacation behaviors to calculate acute and cumulative body-site-specific UV exposure risk during a beach vacation. The resulting cumulative UV exposure calculated for a typical mix of clothing choices, settings, and activities during a week-long (7-day) beach vacation is 172.2 standard erythemal doses (SED) at the forearm, which is comparable with the average total annual UV exposure of European and North American residents and consistent with existing dosimetry studies. This model further estimates that vacationers choosing to spend a full day exclusively in the beach or pool setting can experience UV exposure in excess of 50 SED a day at multiple body sites. Such exposure indicates that significant sun protective measures would be required to prevent sunburn across all skin types in this setting. This work clarifies the significant role that beach vacations play in UV exposure and corresponding acute and cumulative health risks and highlights the importance of behavioral choices (including clothing, activity and photoprotection) as crucial factors in differentiating personal solar exposure risks.

Greater efficacy of SPF 100+ sunscreen compared with SPF 50+ in sunburn prevention during 5 consecutive days of sunlight exposure: A randomized, double-blind clinical trial.

BACKGROUND: Beach vacations are high-risk settings for overexposure to ultraviolet radiation. OBJECTIVE: To compare the sunburn protective efficacy of SPF 50+ and SPF 100+ sunscreens under actual use at the beach. METHODS: A prospective, randomized, double-blind, single-center, split-body/face study of 55 healthy individuals. Each participant applied both sunscreens to randomized sides of the face/body for up to 5 consecutive days. Blinded clinical evaluation of erythema by a single grader and objective instrumental assessments, colorimetry, and diffuse reflectance spectroscopy were performed the morning after each sun exposure. RESULTS: After 5 days, 31 (56%) participants had more sunburn on the SPF 50+ side compared to 4 (7%) on the SPF 100+ side. Overall, mean erythema intensity showed statistically significantly less erythema on the SPF 100+ side compared with the SPF 50+ side. The first observation of sunburn exclusively on the SPF 50+ side occurred after 1 day of sun exposure, whereas that for SPF 100+ occurred after 3 days of sun exposure. LIMITATIONS: Only initial sunscreen application was monitored, only 1 participant with skin phototype I was recruited, and participants were recruited from a local beach area. CONCLUSION: SPF 100+ was significantly more effective in protecting against ultraviolet radiation-induced erythema and sunburn than SPF 50+ in actual use in a beach vacation setting.

SPF 100+ sunscreen is more protective against sunburn than SPF 50+ in actual use: Results of a randomized, double-blind, split-face, natural sunlight exposure clinical trial.

BACKGROUND: The value of additional photoprotection provided by use of high-sun protection factor (SPF) sunscreens is controversial, and limited clinical evidence exists. OBJECTIVE: To compare the sunburn protection provided by SPF 100+ and SPF 50+ sunscreen in conditions of actual use. METHODS: A total of 199 healthy men and women (≥18 years) participated in a natural sunlight, single-exposure, split-face, randomized, double-blind study in Vail, Colorado. Each participant wore both sunscreens simultaneously during activities, with no use restrictions other than designation of the treatment area. Erythema was clinically assessed on the day following exposure. Comparative efficacy was evaluated through bilateral comparison of sunburn between treatment areas and erythema score, as evaluated separately for each treatment area. RESULTS: Following an average 6.1 ± 1.3 hours of sun exposure, investigator-blinded evaluation identified 55.3% of the participants (110 of 199) as more sunburned on the SPF 50+ protected side and 5% (10 of 199) on the SPF 100+ protected side. After exposure, 40.7% of the participants (81 of 199) exhibited increased erythema scores (by ≥1) on the SPF 50+ protected side as compared with 13.6% (27 of 199) on the SPF 100+ protected side. LIMITATIONS: Single-day exposure may not extrapolate to benefits of longer-term protection. CONCLUSION: SPF 100+ sunscreen was significantly more effective in protecting against sunburn than SPF 50+ sunscreen in actual use conditions.

The B6 -vitamer Pyridoxal is a Sensitizer of UVA-induced Genotoxic Stress in Human Primary Keratinocytes and Reconstructed Epidermis.

UVA-driven photooxidative stress in human skin may originate from excitation of specific endogenous chromophores acting as photosensitizers. Previously, we have demonstrated that 3-hydroxypyridine-derived chromophores including B6 -vitamers (pyridoxine, pyridoxamine and pyridoxal) are endogenous photosensitizers that enhance UVA-induced photooxidative stress in human skin cells. Here, we report that the B6 -vitamer pyridoxal is a sensitizer of genotoxic stress in human adult primary keratinocytes (HEKa) and reconstructed epidermis. Comparative array analysis indicated that exposure to the combined action of pyridoxal and UVA caused upregulation of heat shock (HSPA6, HSPA1A, HSPA1L, HSPA2), redox (GSTM3, EGR1, MT2A, HMOX1, SOD1) and genotoxic (GADD45A, DDIT3, CDKN1A) stress response gene expression. Together with potentiation of UVA-induced photooxidative stress and glutathione depletion, induction of HEKa cell death occurred only in response to the combined action of pyridoxal and UVA. In addition to activational phosphorylation indicative of genotoxic stress [p53 (Ser15) and γ-H2AX (Ser139)], comet analysis indicated the formation of Fpg-sensitive oxidative DNA lesions, observable only after combined exposure to pyridoxal and UVA. In human reconstructed epidermis, pyridoxal preincubation followed by UVA exposure caused genomic oxidative base damage, procaspase 3 cleavage and TUNEL positivity, consistent with UVA-driven photooxidative damage that may be relevant to human skin exposed to high concentrations of B6 -vitamers.

The Tryptophan-Derived Endogenous Aryl Hydrocarbon Receptor Ligand 6-Formylindolo[3,2-b]Carbazole Is a Nanomolar UVA Photosensitizer in Epidermal Keratinocytes.

Endogenous UVA chromophores may act as sensitizers of oxidative stress underlying cutaneous photoaging and photocarcinogenesis, but the molecular identity of non-DNA key chromophores displaying UVA-driven photodyamic activity in human skin remains largely undefined. Here we report that 6-formylindolo[3,2-b]carbazole (FICZ), a tryptophan photoproduct and endogenous high-affinity aryl hydrocarbon receptor (AhR) agonist, acts as a nanomolar photosensitizer potentiating UVA-induced oxidative stress irrespective of AhR ligand activity. In human HaCaT and primary epidermal keratinocytes, photodynamic induction of apoptosis was elicited by the combined action of solar-simulated UVA and FICZ, whereas exposure to the isolated action of UVA or FICZ did not impair viability. In a human epidermal tissue reconstruct, FICZ/UVA cotreatment caused pronounced phototoxicity inducing keratinocyte cell death, and FICZ photodynamic activity was also substantiated in a murine skin exposure model. Array analysis revealed pronounced potentiation of cellular heat shock, endoplasmic reticulum stress, and oxidative stress response gene expression observed only upon FICZ/UVA cotreatment. FICZ photosensitization caused intracellular oxidative stress, and comet analysis revealed introduction of formamidopyrimidine-DNA glycosylase (Fpg)-sensitive oxidative DNA lesions suppressible by antioxidant cotreatment. Taken together, our data demonstrate that the endogenous AhR ligand FICZ displays nanomolar photodynamic activity representing a molecular mechanism of UVA-induced photooxidative stress potentially operative in human skin.

Focal activation of cells by plasmon resonance assisted optical injection of signaling molecules.

Experimental methods for single cell intracellular delivery are essential for probing cell signaling dynamics within complex cellular networks, such as those making up the tumor microenvironment. Here, we show a quantitative and general method of interrogation of signaling pathways. We applied highly focused near-infrared laser light to optically inject gold-coated liposomes encapsulating bioactive molecules into single cells for focal activation of cell signaling. For this demonstration, we encapsulated either inositol trisphosphate (IP3), an endogenous cell signaling second messenger, or adenophostin A (AdA), a potent analogue of IP, within 100 nm gold-coated liposomes, and injected these gold-coated liposomes and their contents into the cytosol of single ovarian carcinoma cells to initiate calcium (Ca(2+)) release from intracellular stores. Upon optical injection of IP3 or AdA at doses above the activation threshold, we observed increases in cytosolic Ca(2+) concentration within the injected cell initiating the propagation of a Ca(2+) wave throughout nearby cells. As confirmed by octanol-induced inhibition, the intercellular Ca(2+) wave traveled via gap junctions. Optical injection of gold-coated liposomes represents a quantitative method of focal activation of signaling cascades of broad interest in biomedical research.

Malondialdehyde-derived epitopes in human skin result from acute exposure to solar UV and occur in nonmelanoma skin cancer tissue.

Cutaneous exposure to solar ultraviolet radiation (UVR) is a causative factor in photoaging and photocarcinogenesis. In human skin, oxidative stress is widely considered a key mechanism underlying the detrimental effects of acute and chronic UVR exposure. The lipid peroxidation product malondialdehyde (MDA) accumulates in tissue under conditions of increased oxidative stress, and the occurrence of MDA-derived protein epitopes, including dihydropyridine-lysine (DHP), has recently been substantiated in human skin. Here we demonstrate for the first time that acute exposure to sub-apoptogenic doses of solar simulated UV light (SSL) causes the formation of free MDA and protein-bound MDA-derived epitopes in cultured human HaCaT keratinocytes and healthy human skin. Immunohistochemical staining revealed that acute exposure to SSL is sufficient to cause an almost twenty-fold increase in general MDA- and specific DHP-epitope content in human skin. When compared to dose-matched solar simulated UVA, complete SSL was more efficient generating both free MDA and MDA-derived epitopes. Subsequent tissue microarray (TMA) analysis revealed the prevalence of MDA- and DHP-epitopes in nonmelanoma skin cancer (NMSC). In squamous cell carcinoma tissue, both MDA- and DHP-epitopes were increased more than threefold as compared to adjacent normal tissue. Taken together, these date demonstrate the occurrence of MDA-derived epitopes in both solar UVR-exposed healthy human skin and NMSC TMA tissue; however, the potential utility of these epitopes as novel biomarkers of cutaneous photodamage and a functional role in the process of skin photocarcinogenesis remain to be explored.

Photobiological implications of folate depletion and repletion in cultured human keratinocytes.

Folate nutrition is critical in humans and a high dietary folate intake is associated with a diminished risk of many types of cancer. Both synthetic folic acid and the most biologically abundant extracellular reduced folate, 5-methyltetrahydrofolate, are degraded under conditions of ultraviolet radiation (UVR) exposure. Skin is a proliferative tissue with increased folate nutrient demands due to a dependence upon continuous epidermal cell proliferation and differentiation to maintain homeostasis. Regions of skin are also chronically exposed to UVR, which penetrates to the actively dividing basal layer of the epidermis, increasing the folate nutrient demands in order to replace folate species degraded by UVR exposure and to supply the folate cofactors required for repair of photo-damaged DNA. Localized folate deficiencies of skin are a likely consequence of UVR exposure. We report here a cultured keratinocyte model of folate deficiency that has been applied to examine possible effects of folate nutritional deficiencies in skin. Utilizing this model, we were able to quantify the concentrations of key intracellular folate species during folate depletion and repletion. We investigated the hypotheses that the genomic instability observed under conditions of folate deficiency in other cell types extends to skin, adversely effecting cellular capacity to handle UVR insult and that optimizing folate levels in skin is beneficial in preventing or repairing the pro-carcinogenic effects of UVR exposure. Folate restriction leads to rapid depletion of intracellular reduced folates resulting in S-phase growth arrest, increased levels of inherent DNA damage, and increased uracil misincorporation into DNA, without a significant losses in overall cellular viability. Folate depleted keratinocytes were sensitized toward UVR induced apoptosis and displayed a diminished capacity to remove DNA breaks resulting from both photo and oxidative DNA damage. Thus, folate deficiency creates a permissive environment for genomic instability, an early event in the process of skin carcinogenesis. The effects of folate restriction, even in severely depleted, growth-arrested keratinocytes, were reversible by repletion with folic acid. Overall, these results indicate that skin health can be positively influenced by optimal folate nutriture.

A topical lipophilic niacin derivative increases NAD, epidermal differentiation and barrier function in photodamaged skin.

The effects of myristyl nicotinate (MN), a nicotinic acid derivative designed to deliver nicotinic acid to skin without vasodilatation, on subjects with photodamaged skin have been studied. MN increased skin cell nicotinamide adenine dinucleotide (NAD) by 25% (P = 0.001) demonstrating effective delivery of nicotinic acid to skin. Relative to placebo, MN treatment of photodamaged facial skin increased stratum corneum thickness by approximately 70% (P = 0.0001) and increased epidermal thickness by approximately 20% (P = 0.001). In two separate studies, MN treatment increased rates of epidermal renewal by 6% (P = 0.003) to 11% (P = 0.001) and increased the minimal erythemal dose by 8.9 (P = 0.07) and 10% (P = 0.05) relative to placebo. MN treatment resulted in reductions in the rates of transepidermal water loss (TEWL) of approximately 20% relative to placebo on cheeks (P = 0.012) and arms (P = 0.017) of study subjects. Results of a tape stripping challenge before and after MN treatment demonstrated a significant correlation (P = 0.03) between increased skin NAD content and resistance to changes in TEWL for MN treated but not placebo subjects. Rates of TEWL changed more rapidly and to a greater extent in atopic subjects compared with normal subjects. The results indicate that MN enhances epidermal differentiation and barrier function in skin, suggesting that this method of nicotinic acid delivery may prove useful in limiting progression of actinic skin damage and possibly in treating other conditions involving skin barrier impairment.

Analysis and stability study of myristyl nicotinate in dermatological preparations by high-performance liquid chromatography.

Myristyl nicotinate is an ester prodrug under development for delivery of nicotinic acid to skin for treatment and prevention of conditions that involve skin barrier impairment such as chronic photodamage and atopic dermatitis or for mitigating skin barrier impairment that results from therapy such as retinoids or steroids. The formulation stability of myristyl nicotinate is crucial because even small amounts of free nicotinic acid cause skin flushing, an effect that is not harmful but would severely limit tolerability. We report here reversed-phase HPLC methods for the rapid analysis of myristyl nicotinate and nicotinic acid in dermatological preparations. Because of the large differences in polarity, myristyl nicotinate and nicotinic acid were analyzed by different chromatographic conditions, but they can be rapidly extracted from cream formulations using HPLC mobile phase as a solvent followed by HPLC analysis in less than 10 min. The methods were validated in terms of linearity, precision and accuracy and mean recovery of myristyl nicotinate from topical creams ranged from 97.0-101.2%. Nicotinic acid at levels of 0.01% in the formulations could be quantified. Stability studies show that myristyl nicotinate formulations are stable at room temperature for 3 years with less than 0.05% conversion to nicotinic acid. These methods will be effective for routine analysis of myristyl nicotinate stability in dermatological formulations.