Solar UV exposure and mortality from skin tumors

A comprehensive and mechanistic review on protective effects of kaempferol against natural and chemical toxins: Role of NF-κB inhibition and Nrf2 activation

Different toxins, including chemicals and natural, can be entered from various routes and influence human health. Herbal medicines and their active components can attenuate the toxicity of agents via multiple mechanisms. For example, kaempferol, as a flavonoid, can be found in fruits and vegetables, and has an essential role in improving disorders such as cardiovascular disorders, neurological diseases, cancer, pain, and inflammation situations. The beneficial effects of kaempferol may be related to the inhibition of oxidative stress, attenuation of inflammatory factors such as tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), cyclooxygenase-2 (COX-2) and nuclear factor ĸB (NF-ĸB) as well as the modulation of apoptosis and mitogen-activated protein kinase (MAPK) signaling pathways. This flavonoid boasts a wide spectrum of toxin targeting effects in tissue fibrosis, inflammation, and oxidative stress thus shows promising protective effects against natural and chemical toxin induced hepatotoxicity, nephrotoxicity, cardiotoxicity, neurotoxicity, lung, and intestinal in the in vitro and in vivo setting. The most remarkable aspect of kaempferol is that it does not focus its efforts on just one organ or one molecular pathway. Although its significance as a treatment option remains questionable and requires more clinical studies, it seems to be a low-risk therapeutic option. It is crucial to emphasize that kaempferol's poor bioavailability is a significant barrier to its use as a therapeutic option. Nanotechnology can be a promising way to overcome this challenge, reviving optimism in using kaempferol as a viable treatment agent against toxin-induced disorders.

Tanning benefits, seasonal effects, and concerns about sunscreen: Measuring health beliefs about UV among college students

Objective: To develop and validate a scale measuring health beliefs about UV in cloudy climates that may impact UV exposure behaviors. Participants: Students at a large university in Oregon completed pilot (N = 115) and final (N = 335) scales online March-July, 2016. Five participants underwent cognitive interviews. Methods: Expert feedback, cognitive interviews, and pilot data guided item development and refinement. We conducted factor analysis and invariance testing. Results: The final four-factor model fit well (χ² = 37.97, df = 37, RMSEA = 0.000, CFI = 1.000). HBAU subscales are Sunscreen Toxicity, Seasonal Effects, Health Benefits of Tanning, and Tanning Through the Winter. Invariance testing supported strong invariance across sex and tanning status. Conclusion: The HBAU measures beliefs that encourage UV exposure and discourage protection (eg, the belief that sunscreen ingredients are toxic). This scale will enable more comprehensive measurement of cognitive predictors of UV exposure for student health, clinical, and research purposes.

Understanding Ultraviolet Radiation Dorsal Foot Injury at the Beach

BACKGROUND

Efforts made to protect the dorsal aspect of the foot are currently unknown. We sought to determine whether beachgoers protect the dorsal aspect of their feet as frequently as other anatomic sites.

METHODS

A convenience sample of Galveston, Texas, beachgoers completed anonymous surveys to assess whether the dorsal foot was at risk for ultraviolet radiation (UV-R) injury. Additional information collected included demographics and general knowledge about skin cancer to determine if these variables were significantly correlated with dorsal foot protection from UV-R injury.

RESULTS

Of 216 respondents, only 103 used a topical UV-R barrier on their dorsal feet, while 183 applied sunscreen to the body and 133 applied sunscreen to the legs. Eighty-seven of 113 nonusers explained, "I did not think about it." The average number of applications of sunscreen per person to the dorsal feet was less than other anatomical body sites (1.19 body applications, 0.86 leg applications, and 0.58 dorsal feet applications per person; P < .001). 58.0% of females applied sunscreen to the dorsal feet compared with only 36.5% of males (P = .001). Self-identifying Fitzpatrick skin type 5 or 6 individuals did not apply sunscreen to the dorsal foot as regularly as individuals with types 1 to 4 (84.6% versus 47.6%; P = .0001).

CONCLUSIONS

Current skin cancer epidemiology pairs the feet and the legs together as "lower extremity." For epidemiologic purposes, however, feet and legs should be considered distinct areas in UV-R research because they may use different photoprotection strategies.

Label-free electrochemical sensor to investigate the effect of tocopherol on generation of superoxide ions following UV irradiation

Background

Generation of reactive oxygen species (ROS), triggered by ultraviolet radiation (UVR), is associated with carcinogenesis of the skin. UV irradiation induced superoxide anion (O2^•−) is the key ROS involved in the cellular damage. The cytoprotective efficacy of an unknown anti-oxidant compound can be evaluated by analyzing the production of O2^•− from treated cells.

Methods

In this study, a glass carbon electrode functionalized with nanotube@DNA-Mn3(PO4)2 composite was applied to quantitative determination of generation of highly unstable O2^•− from the melanoma A375 cell line following UVR(UV, UVA and UVB). In addition, the cytoprotective efficacy of anti-oxidant α-tocopherol was evaluated by quantifying the production of O2^•−.

Results

The results showed that, UVR triggers generation of O2^•− in melanoma A375 cells, and α-tocopherol is effective in diminishing the production of O2^•− following UV irradiation. By comparing the conventional cell-survival assays results, we found that our simple and quick electrochemical sensing method can quantify O2^•− generation through the biological activity of an anti-oxidant compound (α-tocopherol).

Conclusion

Our label-free electrochemical quantification method for ROS (O2^•− major) in cells facing UVR stress demonstrates its potential application for high-throughput screening of anti-oxidation compounds.

Effects of Radon and UV Exposure on Skin Cancer Mortality in Switzerland

BACKGROUND

Skin cancer incidence in Switzerland is among the highest in the world. In addition to exposure to ultraviolet (UV) radiation, radon alpha particles attached to aerosols can adhere to the skin and potentially cause carcinogenic effects.

OBJECTIVES

We investigated the effects of radon and UV exposure on skin cancer mortality.

METHODS

Cox proportional hazard regression was used to study the association between exposures and skin cancer mortality in adults from the Swiss National Cohort. Modeled radon exposure and erythemal-weighted UV dose were assigned to addresses at baseline. Effect estimates were adjusted for sex, civil status, mother tongue, education, job position, neighborhood socioeconomic position, and UV exposure from outdoor occupation.

RESULTS

The study included 5.2 million adults (mean age 48 y) and 2,989 skin cancer deaths, with 1,900 indicating malignant melanoma (MM) as the primary cause of death. Adjusted hazard ratios (HR) for MM at age 60 were 1.16 (95% CI: 1.04, 1.29) per 100 Bq/m3 radon and 1.11 (1.01, 1.23) per W/m2 in UV dose. Radon effects decreased with age. Risk of MM death associated with residential UV exposure was higher for individuals engaged in outdoor work with UV exposure (HR 1.94 [1.17, 3.23]), though not statistically significantly different compared to not working outdoors (HR 1.09 [0.99, 1.21], p=0.09).

CONCLUSIONS

There is considerable variation in radon and UV exposure across Switzerland. Our study suggests both are relevant risk factors for skin cancer mortality. A better understanding of the role of the UV radiation and radon exposure is of high public health relevance. https://doi.org/10.1289/EHP825.

TRAF1 Is Critical for DMBA/Solar UVR-Induced Skin Carcinogenesis

TRAF1 is a member of the TRAF protein family, which regulates the canonical and noncanonical NF-κB signaling cascades. Although aberrant TRAF1 expression in tumors has been reported, the role of TRAF1 remains elusive. Here, we report that TRAF1 is required for solar UV-induced skin carcinogenesis. Immunohistochemical analysis showed that TRAF1 expression is up-regulated in human actinic keratosis and squamous cell carcinoma. In vivo studies indicated that TRAF1 expression levels in mouse skin are induced by short-term solar UV irradiation, and a long-term skin carcinogenesis study showed that deletion of TRAF1 in mice results in a significant inhibition of skin tumor formation. Moreover, we show that TRAF1 is required for solar UV-induced extracellular signal-regulated kinase-5 (ERK5) phosphorylation and the expression of AP-1 family members (c-Fos/c-Jun). Mechanistic studies showed that TRAF1 expression enhances the ubiquitination of ERK5 on lysine 184, which is necessary for its kinase activity and AP-1 activation. Overall, our results suggest that TRAF1 mediates ERK5 activity by regulating the upstream effectors of ERK5 and also by modulating its ubiquitination status. Targeting TRAF1 function might lead to strategies for preventing and treating skin cancer.

The Potential of Plant Phenolics in Prevention and Therapy of Skin Disorders

Phenolic compounds constitute a group of secondary metabolites which have important functions in plants. Besides the beneficial effects on the plant host, phenolic metabolites (polyphenols) exhibit a series of biological properties that influence the human in a health-promoting manner. Evidence suggests that people can benefit from plant phenolics obtained either by the diet or through skin application, because they can alleviate symptoms and inhibit the development of various skin disorders. Due to their natural origin and low toxicity, phenolic compounds are a promising tool in eliminating the causes and effects of skin aging, skin diseases, and skin damage, including wounds and burns. Polyphenols also act protectively and help prevent or attenuate the progression of certain skin disorders, both embarrassing minor problems (e.g., wrinkles, acne) or serious, potentially life-threatening diseases such as cancer. This paper reviews the latest reports on the potential therapy of skin disorders through treatment with phenolic compounds, considering mostly a single specific compound or a combination of compounds in a plant extract.

Topical treatment with pterostilbene, a natural phytoalexin, effectively protects hairless mice against UVB radiation-induced skin damage and carcinogenesis

The aim of our study was to investigate in the SKH-1 hairless mouse model the effect of pterostilbene (Pter), a natural dimethoxy analog of resveratrol (Resv), against procarcinogenic ultraviolet B radiation (UVB)-induced skin damage. Pter prevented acute UVB (360 mJ/cm(2))-induced increase in skin fold, thickness, and redness, as well as photoaging-associated skin wrinkling and hyperplasia. Pter, but not Resv, effectively prevented chronic UVB (180 mJ/cm(2), three doses/week for 6 months)-induced skin carcinogenesis (90% of Pter-treated mice did not develop skin carcinomas, whereas a large number of tumors were observed in all controls). This anticarcinogenic effect was associated with (a) maintenance of skin antioxidant defenses (i.e., glutathione (GSH) levels, catalase, superoxide, and GSH peroxidase activities) close to control values (untreated mice) and (b) an inhibition of UVB-induced oxidative damage (using as biomarkers 8-hydroxy-2'-deoxyguanosine, protein carbonyls, and isoprostanes). The molecular mechanism underlying the photoprotective effect elicited by Pter was further evaluated using HaCaT immortalized human keratinocytes and was shown to involve potential modulation of the Nrf2-dependent antioxidant response.

Low serum 25-hydroxyvitamin d concentrations are associated with increased risk for melanoma and unfavourable prognosis

Background

Low vitamin D status (serum 25(OH)D concentration) is associated with increased incidence and unfavourable outcome of various types of cancer. However, there are limited data on influence of serum 25(OH)D on risk and prognosis of malignant melanoma.

Methods

Basal serum 25(OH)D concentrations were retrospectively analyzed in a cohort of melanoma patients (n = 324) and healthy controls (n = 141). We tested the hypothesis that serum 25(OH)D concentrations are predictive of melanoma risk, thickness of primary melanomas, and overall survival (OS).

Results

Median serum 25(OH)D concentrations were significantly lower (p = 0.004) in melanoma patients (median = 13.6 ng/ml) as compared to controls (median = 15.6 ng/ml). Primary tumors of patients with low serum 25(OH)D concentrations (<10 ng/ml) had significantly (p = 0.006) greater Breslow thickness (median: 1.9 mm) as compared to patients with higher levels (>20 ng/ml; median: 1.00 mm). Patients with 25(OH)D serum concentrations in the lowest quartile had inferior overall survival (median: 80 months) comparing with the highest quartile (median: 195 months; p = 0.049).

Conclusions

Our data support the concept that serum 25(OH)D concentrations are associated with risk and prognosis of melanoma. Whether normalizing serum 25(OH)D concentrations in these patients improves outcomes will require testing in future clinical trials.

Caffeic acid directly targets ERK1/2 to attenuate solar UV-induced skin carcinogenesis

Caffeic acid (3,4-dihydroxycinnamic acid) is a well-known phenolic phytochemical present in coffee and reportedly has anticancer activities. However, the underlying molecular mechanisms and targeted proteins involved in the suppression of carcinogenesis by caffeic acid are not fully understood. In this study, we report that caffeic acid significantly inhibits colony formation of human skin cancer cells and EGF-induced neoplastic transformation of HaCaT cells dose-dependently. Caffeic acid topically applied to dorsal mouse skin significantly suppressed tumor incidence and volume in a solar UV (SUV)-induced skin carcinogenesis mouse model. A substantial reduction of phosphorylation in mitogen-activated protein kinase signaling was observed in mice treated with caffeic acid either before or after SUV exposure. Caffeic acid directly interacted with ERK1/2 and inhibited ERK1/2 activities in vitro. Importantly, we resolved the cocrystal structure of ERK2 complexed with caffeic acid. Caffeic acid interacted directly with ERK2 at amino acid residues Q105, D106, and M108. Moreover, A431 cells expressing knockdown of ERK2 lost sensitivity to caffeic acid in a skin cancer xenograft mouse model. Taken together, our results suggest that caffeic acid exerts chemopreventive activity against SUV-induced skin carcinogenesis by targeting ERK1 and 2.

Kaempferol targets RSK2 and MSK1 to suppress UV radiation-induced skin cancer

Solar UV (SUV) irradiation is a major factor in skin carcinogenesis, the most common form of cancer in the United States. The MAPK cascades are activated by SUV irradiation. The 90 kDa ribosomal S6 kinase (RSK) and mitogen and stress-activated protein kinase (MSK) proteins constitute a family of protein kinases that mediate signal transduction downstream of the MAPK cascades. In this study, phosphorylation of RSK and MSK1 was upregulated in human squamous cell carcinoma (SCC) and SUV-treated mouse skin. Kaempferol, a natural flavonol, found in tea, broccoli, grapes, apples, and other plant sources, is known to have anticancer activity, but its mechanisms and direct target(s) in cancer chemoprevention are unclear. Kinase array results revealed that kaempferol inhibited RSK2 and MSK1. Pull-down assay results, ATP competition, and in vitro kinase assay data revealed that kaempferol interacts with RSK2 and MSK1 at the ATP-binding pocket and inhibits their respective kinase activities. Mechanistic investigations showed that kaempferol suppresses RSK2 and MSK1 kinase activities to attenuate SUV-induced phosphorylation of cAMP-responsive element binding protein (CREB) and histone H3 in mouse skin cells. Kaempferol was a potent inhibitor of SUV-induced mouse skin carcinogenesis. Further analysis showed that skin from the kaempferol-treated group exhibited a substantial reduction in SUV-induced phosphorylation of CREB, c-Fos, and histone H3. Overall, our results identify kaempferol as a safe and novel chemopreventive agent against SUV-induced skin carcinogenesis that acts by targeting RSK2 and MSK1.

(+)-2-(1-Hydroxyl-4-oxocyclohexyl) ethyl caffeate suppresses solar UV-induced skin carcinogenesis by targeting PI3K, ERK1/2, and p38

For decades, skin cancer incidence has increased, mainly because of oncogenic signaling pathways activated by solar ultraviolet (UV) irradiation (i.e., sun exposure). Solar UV induces multiple signaling pathways that are critical in the development of skin cancer, and therefore the development of compounds capable of targeting multiple molecules for chemoprevention of skin carcinogenesis is urgently needed. Herein, we examined the chemopreventive effects and the molecular mechanism of (+)-2-(1-hydroxyl-4-oxocyclohexyl) ethyl caffeate (HOEC), isolated from Incarvillea mairei var. grandiflora (Wehrhahn) Grierson. HOEC strongly inhibited neoplastic transformation of JB6 Cl41 cells without toxicity. PI3K, ERK1/2, and p38 kinase activities were suppressed by direct binding with HOEC in vitro. Our in silico docking data showed that HOEC binds at the ATP-binding site of each kinase. The inhibition of solar UV-induced PI3K, ERK1/2, and p38 kinase activities resulted in suppression of their downstream signaling pathways and AP1 and NF-κB transactivation in JB6 cells. Furthermore, topical application of HOEC reduced skin cancer incidence and tumor volume in SKH-1 hairless mice chronically exposed to solar UV. In summary, our results show that HOEC exerts inhibitory effects on multiple kinase targets and their downstream pathways activated by solar UV in vitro and in vivo. These findings suggest that HOEC is a potent chemopreventive compound against skin carcinogenesis caused by solar UV exposure.

Preventing skin cancer through reduction of indoor tanning: current evidence

Exposure to ultraviolet radiation from indoor tanning devices (tanning beds, booths, and sun lamps) or from the sun contributes to the risk of skin cancer, including melanoma, which is the type of skin cancer responsible for most deaths. Indoor tanning is common among certain groups, especially among older adolescents and young adults, adolescent girls and young women, and non-Hispanic whites. Increased understanding of the health risks associated with indoor tanning has led to many efforts to reduce use. Most environmental and systems efforts in the U.S. (e.g., age limits or requiring parental consent/accompaniment) have occurred at the state level. At the national level, the U.S. Food and Drug Administration and the Federal Trade Commission regulate indoor tanning devices and advertising, respectively. The current paper provides a brief review of (1) the evidence on indoor tanning as a risk factor for skin cancer; (2) factors that may influence use of indoor tanning devices at the population level; and (3) various environmental and systems options available for consideration when developing strategies to reduce indoor tanning. This information provides the context and background for the companion paper in this issue of the American Journal of Preventive Medicine, which summarizes highlights from an informal expert meeting convened by the CDC in August 2012 to identify opportunities to prevent skin cancer by reducing use of indoor tanning devices.

Sunlight UV-induced skin cancer relies upon activation of the p38α signaling pathway

The activation of cellular signal transduction pathways by solar ultraviolet (SUV) irradiation plays a vital role in skin tumorigenesis. Although many pathways have been studied using pure ultraviolet A (UVA) or ultraviolet B (UVB) irradiation, the signaling pathways induced by SUV (i.e., sunlight) are not understood well enough to permit improvements for prevention, prognosis, and treatment. Here, we report parallel protein kinase array studies aimed at determining the dominant signaling pathway involved in SUV irradiation. Our results indicated that the p38-related signal transduction pathway was dramatically affected by SUV irradiation. SUV (60 kJ UVA/m(2)/3.6 kJ UVB/m(2)) irradiation stimulates phosphorylation of p38α (MAPK14) by 5.78-fold, MSK2 (RPS6KA4) by 6.38-fold, and HSP27 (HSPB1) by 34.56-fold compared with untreated controls. By investigating the tumorigenic role of SUV-induced signal transduction in wild-type and p38 dominant-negative (p38 DN) mice, we found that p38 blockade yielded fewer and smaller tumors. These results establish that p38 signaling is critical for SUV-induced skin carcinogenesis.

UVA, UVB and UVC induce differential response signaling pathways converged on the eIF2α phosphorylation

It is clear that solar UV irradiation is a crucial environmental factor resulting in skin diseases partially through activation of cell signaling toward altered gene expression and reprogrammed protein translation. Such a key translational control mechanism is executed by the eukaryotic initiation factor 2α subunit (eIF2α) and the downstream events provoked by phosphorylation of eIF2α at Ser(51) are clearly understood, but the upstream signaling mechanisms on the eIF2α-Ser(51) phosphorylation responses to different types of UV irradiations, namely UVA, UVB and UVC, are still not well elucidated. Herein, our evidence reveals that UVA, UVB and UVC all induce a dose- and time-dependent phosphorylation of eIF2α-Ser(51) through distinct signaling mechanisms. UVA-induced eIF2α phosphorylation occurs through MAPKs, including ERKs, JNKs and p38 kinase, and phosphatidylinositol (PI)-3 kinase. By contrast, UVB-induced eIF2α phosphorylation is through JNKs and p38 kinase, but not ERKs or PI-3 kinase, whereas UVC-stimulated response to eIF2α phosphorylation is via JNKs alone. Furthermore, we have revealed that ATM is involved in induction of the intracellular responses to UVA and UVB, rather than UVC. These findings demonstrate that wavelength-specific UV irradiations activate differential response signaling pathways converged on the eIF2α phosphorylation. Importantly, we also show evidence that a direct eIF2α kinase PKR is activated though phosphorylation by either RSK1 or MSK1, two downstream kinases of MAPKs/PI-3 kinase-mediated signaling pathways.

Time trends and latitude dependence of uveal and cutaneous malignant melanoma induced by solar radiation

In order to evaluate the role of solar radiation in uveal melanoma etiology, the time and latitude dependency of the incidence rates of this melanoma type were studied in comparison with those of cutaneous malignant melanoma (CMM). Norway and several other countries with Caucasian populations were included. there is a marked north-south gradient of the incidence rates of CMM in Norway, with three times higher rates in the south than in the north. No such gradient is found for uveal melanoma. Similar findings have been published for CMM in other Caucasian populations, with the exception of Europe as a whole. In most populations the ratios of uveal melanoma incidence rates to those of CMM tend to decrease with increasing CMM rates. This is also true for Europe, in spite of the fact that in this region there is an inverse latitude gradient of CMM, with higher rates in the north than in the south.In Norway the incidence rates of CMM have increased until about 1990 but have been constant or even decreased (for young people) after that time, indicating constant or decreasing sun exposure. The uveal melanoma rates have been increasing after 1990. In most other populations the incidence rates of CMM have been increasing until recently while those of uveal melanoma have been decreasing. These data generally support the assumption that uveal melanomas are not generated by ultraviolet (UV) radiation and that solar UV, via its role in vitamin D photosynthesis, may have a protective effect.

Promoter polymorphisms in matrix metallopeptidase 1 and risk of cutaneous melanoma

Matrix metallopeptidase 1 (MMP1) is one of the interstitial collagens in the extracellular matrix metalloproteinase family and involved in tumour behaviours. However, there is no report on the role of genetic variation in MMP1 in risk of cutaneous melanoma (CM). We investigated the association between genotypes and haplotypes of seven reported MMP1 promoter polymorphisms [-1607G ins/del (2G/1G), -839G>A, -755T>G, -519A>G, -422A>T, -340A>G and -320T>C, genotyped by the TaqMan assay] and CM risk in 872 patients and 873 cancer-free controls. These seven polymorphisms were not in linkage disequilibrium among each other (r(2)<0.63). Compared to their common homozygous genotypes, the variant -519GG was associated with significantly decreased CM risk [adjusted odds ratio (OR)=0.71, 95% confidence interval (CI)=0.52-0.99], whereas variants -422TT and -320CC were associated with significantly increased CM risk (OR=1.50, 95% CI=1.11-2.03 and OR=1.72, 95% CI=1.05-2.81, respectively) after adjustment for age, sex, family history and sun-exposure-related risk factors. The number of risk alleles of these three polymorphisms was associated with CM risk in a dose-response manner (P(trend)=0.0002). In the stratification analysis, we found that the associations of these polymorphisms with CM risk were modified by some of the risk factors. Furthermore, the haplotypes Gdel-A-G-A-T-G-T and G-G-G-A-T-A-T were associated with significantly increased CM risk (ORs=1.56 and 2.13, 95% CIs=1.02-2.38 and 1.22-3.70, respectively). These findings suggest that MMP1 promoter polymorphisms may individually or jointly play roles in the development of CM.

Latitude gradient for melanoma incidence by anatomic site and gender in Norway 1966-2007

Latitude gradients and time trends for cutaneous malignant melanoma (CMM) were analyzed using incident cases from the Norwegian Cancer Registry for the period 1966-2007. Sex and various anatomic regions of the body were taken into account, for better understanding of the role of ultraviolet radiation in CMM etiology. There is a latitude gradient for CMM on all body sites included in the present study, with 2-2.5 times higher incidence rates in the south. The latitude gradients seem to be largest for the trunk. Melanomas on sites intermittently exposed to the sun (like the trunk) dominate both in the north and in the south and this distribution has not changed over the years. A leveling off of the incidence rates are observed for both sexes and for all sites studied, after 1985-1995, slightly more in the south than in the north, except for the head and neck where the incidence rates have continued to increase slowly in the north as well as in the south. The leveling off of melanoma trend is probably associated with melanoma prevention campaigns and with increasing awareness, although vitamin D could play a role.