Investigation of the effect of UV irradiation on DNA damage: comparison between skin cancer patients and normal volunteers

Hesperidin Attenuates Ultraviolet B-Induced Apoptosis by Mitigating Oxidative Stress in Human Keratinocytes

Human skin cells undergo pathophysiological processes via generation of reactive oxygen species (ROS) upon excessive exposure to ultraviolet B (UVB) radiation. This study investigated the ability of hesperidin (C₂₈H₃₄O₁₅) to prevent apoptosis due to oxidative stress generated through UVB-induced ROS. Hesperidin significantly scavenged ROS generated by UVB radiation, attenuated the oxidation of cellular macromolecules, established mitochondrial membrane polarization, and prevented the release of cytochrome c into the cytosol. Hesperidin downregulated expression of caspase-9, caspase-3, and Bcl-2-associated X protein, and upregulated expression of B-cell lymphoma 2. Hesperidin absorbed wavelengths of light within the UVB range. In summary, hesperidin shielded human keratinocytes from UVB radiation-induced damage and apoptosis via its antioxidant and UVB absorption properties.

Baicalin Protects Keratinocytes from Toll-like Receptor-4 Mediated DNA Damage and Inflammation Following Ultraviolet Irradiation

UVB radiation contributes to both direct and indirect damage to the skin including the generation of free radicals and reactive oxygen species (ROS), inflammatory responses, immunosuppression and gene mutations, which can ultimately lead to photocarcinogenesis. A plant-derived flavonoid, baicalin, has been shown to have antioxidant, anti-inflammatory and free radical scavenging activities. Previous studies from our laboratory have shown that in murine skin, Toll-like receptor-4 (TLR4) enhanced both UVB-induced DNA damage and inflammation. The aim of this study was to investigate the efficacy of baicalin against TLR4-mediated processes in the murine keratinocyte PAM 212 cell line. Our results demonstrate that treating keratinocytes with baicalin both before and after UV radiation (100 mJ cm(-2) ) significantly inhibited the level of intracellular ROS and decreased cyclobutane pyrimidine dimers and 8-Oxo-2'-deoxyguanosine (8-oxo-dG)-markers of DNA damage. Furthermore, cells treated with baicalin demonstrated an inhibition of TLR4 and its downstream signaling molecules, MyD88, TRIF, TRAF6 and IRAK4. TLR4 pathway inhibition resulted in NF-κB inactivation and down-regulation of iNOS and COX-2 protein expression. Taken together, baicalin treatment effectively protected keratinocytes from UVB-induced inflammatory damage through TLR pathway modulation.

Knowledge, attitudes and practices of the general public toward sun exposure and protection: A national survey in Saudi Arabia

Background: Many international studies have been conducted to assess the knowledge, attitudes and practices (KAP) of the public toward sun exposure and sun-protection measures. However, there are scarce data on these factors from the Middle East. Objectives: This study aimed to explore the KAP of the public toward sun exposure and sun-protection measures among Saudis. Methods: A cross-sectional survey using a specially designed questionnaire was conducted on a stratified random sample of the general population in the five geographical regions of Saudi Arabia (central, eastern, northern, southern, and western). Data were collected between October 2010 and March 2011. Multiple logistic regressions were applied to relate the use of sunscreen and skin cancer awareness with various socio-demographic variables. Results: The questionnaire was distributed to 2900 Saudis. A total of 2622 questionnaires were completed, returned, and included in the data analysis, corresponding to a response rate of 90.4%. The mean (SD) age of respondents was 27.8 ± 9.7 years. Fifty percent (1301/1601) of the respondents were males. Fifty-five percent (1406/2544) were aware of the association between sun exposure and skin cancer. Female, young and student respondents were more likely to be aware of the connection between sun exposure and skin cancer (p < 0.001). Likewise, respondents from the middle social class and those with higher education levels were more likely to be informed (p < 0.02). The prevalence of regular sunscreen use among study participants was only 23.7%, and female and employed respondents were more likely to use sunscreen (p < 0.001). Protective clothes were the most commonly used sun protection measure as reported by more than 90% of our participants. Conclusion: This study has shown that sun awareness and protection are generally inadequate in the Saudi population and suggests the need for health education programs.

Photobiological implications of melanin photoprotection after UVB-induced tanning of human skin but not UVA-induced tanning

Repetitive suberythemal UVA and/or UVB exposures were used to generate comparable UV-induced tans in human skin over the course of 2 weeks. To evaluate the potential photoprotective values of those UVA- and/or UVB- induced tans and to avoid the confounding issue of residual UV-induced DNA damage, we waited 1 week before challenging those areas with a 1.5 MED of UVA+UVB after which we measure DNA damage. The results show that the type of UV used to induce skin pigmentation affects the redistribution of melanin in the skin and/or de novo melanin synthesis. The UVA-induced tans failed to even provide a minimal SPF of 1.5, which suggests that producing a tan with UVA-rich sunlamps prior to a holiday or vacation is completely counterproductive.

Protective effect of trehalose-loaded liposomes against UVB-induced photodamage in human keratinocytes

Trehalose, a naturally occurring non-reducing disaccharide, is known to act as a major protein stabilizer that can reduce ultraviolet B (UVB)-induced corneal damage when topically applied to the eye. However, due to the low skin permeability of trehalose, which makes the development of topical formulations difficult, its use as a skin photoprotective agent has been limited. Previous findings demonstrated that liposomes may significantly improve the intracellular delivery of trehalose. Therefore, the present study aimed to assess the protective effects of trehalose-loaded liposomes against UVB-induced photodamage using the immortalized human keratinocyte cell line, HaCaT. The effects were also compared to those of the common skin photoprotective compounds, including L-carnosine, L-(+)-ergothioneine, L-ascorbic acid and DL-α-tocopherol. The levels of cyclobutane pyrimidine dimers, 8-hydroxy-2'-deoxyguanosine and protein carbonylation in HaCaT cells were used as biological markers of UVB-induced damage. Compared to other compounds, trehalose-loaded liposomes showed the highest efficacy in reducing the levels of the three markers following UVB irradiation of HaCaT cells (all P<0.001 when compared to each of the four other photoprotective compounds). Therefore, these findings indicate that there may be a clinical application for trehalose-loaded liposomes, and further studies should be performed to assess the potential usefulness in skin photoprotection and the prevention of non-melanoma skin cancer.

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.

The human health effects of ozone depletion and interactions with climate change

Depletion of the stratospheric ozone layer has led to increased solar UV-B radiation (280-315 nm) at the surface of the Earth. This change is likely to have had an impact on human exposure to UV-B radiation with consequential detrimental and beneficial effects on health, although behavioural changes in society over the past 60 years or so with regard to sun exposure are of considerable importance. The present report concentrates on information published since our previous report in 2007. The adverse effects of UV radiation are primarily on the eye and the skin. While solar UV radiation is a recognised risk factor for some types of cataract and for pterygium, the evidence is less strong, although increasing, for ocular melanoma, and is equivocal at present for age-related macular degeneration. For the skin, the most common harmful outcome is skin cancer, including melanoma and the non-melanoma skin cancers, basal cell carcinoma and squamous cell carcinoma. The incidence of all three of these tumours has risen significantly over the past five decades, particularly in people with fair skin, and is projected to continue to increase, thus posing a significant world-wide health burden. Overexposure to the sun is the major identified environmental risk factor in skin cancer, in association with various genetic risk factors and immune effects. Suppression of some aspects of immunity follows exposure to UV radiation and the consequences of this modulation for the immune control of infectious diseases, for vaccination and for tumours, are additional concerns. In a common sun allergy (polymorphic light eruption), there is an imbalance in the immune response to UV radiation, resulting in a sun-evoked rash. The major health benefit of exposure to solar UV-B radiation is the production of vitamin D. Vitamin D plays a crucial role in bone metabolism and is also implicated in protection against a wide range of diseases. Although there is some evidence supporting protective effects for a range of internal cancers, this is not yet conclusive, but strongest for colorectal cancer, at present. A role for vitamin D in protection against several autoimmune diseases has been studied, with the most convincing results to date for multiple sclerosis. Vitamin D is starting to be assessed for its protective properties against several infectious and coronary diseases. Current methods for protecting the eye and the skin from the adverse effects of solar UV radiation are evaluated, including seeking shade, wearing protective clothing and sunglasses, and using sunscreens. Newer possibilities are considered such as creams that repair UV-induced DNA damage, and substances applied topically to the skin or eaten in the diet that protect against some of the detrimental effects of sun exposure. It is difficult to provide easily understandable public health messages regarding "safe" sun exposure, so that the positive effects of vitamin D production are balanced against the negative effects of excessive exposure. The international response to ozone depletion has included the development and deployment of replacement technologies and chemicals. To date, limited evidence suggests that substitutes for the ozone-depleting substances do not have significant effects on human health. In addition to stratospheric ozone depletion, climate change is predicted to affect human health, and potential interactions between these two parameters are considered. These include altering the risk of developing skin tumours, infectious diseases and various skin diseases, in addition to altering the efficiency by which pathogenic microorganisms are inactivated in the environment.

Basal cell carcinoma: what's new under the sun

Basal cell carcinoma (BCC) is the most common skin cancer in white populations with an increasing incidence worldwide, thereby imposing an important public health problem. Its etiology is still unclear, but existing data indicate that the risk for BCC development is of multifactorial origin and results from the interplay of both constitutional and environmental factors. Yet, UV radiation (UVR) is believed to be the predominant causative risk factor in the pathogenesis of BCC. For years, BCC and squamous cell carcinoma (SCC) have been grouped together as "nonmelanoma skin cancer." However, it seems that there are considerable biologic differences between BCC and SCC, and thus each type of epithelial cancer should be addressed separately. The present review provides an overview of the intriguing etiologic link of BCC with UVR and attempts a comprehensive review of recent epidemiologic and molecular evidence that supports this association.