Urinary thymidine dimer as a marker of total body burden of UV-inflicted DNA damage in humans

Urinary thymidine dimer excretion reflects personal ultraviolet radiation exposure levels

Exposure to ultraviolet radiation (UVR) leads to skin DNA damage, specifically in the form of cyclobutane pyrimidine dimers, with thymidine dimers being the most common. Quantifying these dimers can indicate the extent of DNA damage resulting from UVR exposure. Here, a new liquid chromatography-mass spectrometry (LC-MS) method was used to quantify thymidine dimers in the urine after a temporary increase in real-life UVR exposure. Healthy Danish volunteers (n = 27) experienced increased UVR exposure during a winter vacation. Individual exposure, assessed via personally worn electronic UVR dosimeters, revealed a mean exposure level of 32.9 standard erythema doses (SEDs) during the last week of vacation. Morning urine thymidine dimer concentrations were markedly elevated both 1 and 2 days post-vacation, and individual thymidine dimer levels correlated with UVR exposure during the last week of the vacation. The strongest correlation with erythema-weighted personal UVR exposure (Power model, r2 = 0.64, p < 0.001) was observed when both morning urine samples were combined to measure 48-h thymidine dimer excretion, whereas 24-h excretion based on a single sample provided a weaker correlation (Power model, r2 = 0.55, p < 0.001). Sex, age, and skin phototype had no significant effect on these correlations. For the first time, urinary thymidine dimer excretion was quantified by LC-MS to evaluate the effect of a temporary increase in personal UVR exposure in a real-life setting. The high sensitivity to elevated UVR exposure and correlation between urinary excretion and measured SED suggest that this approach may be used to quantify DNA damage and repair and to evaluate photoprevention strategies.

A randomized, placebo-controlled, trial to assess the photosensitizing, phototoxic and carcinogenic potential of hydrochlorothiazide in healthy volunteers

BACKGROUND AND AIMS

Pharmacovigilance reports, associating hydrochlorothiazide (HCT) with skin cancer, resulted in a significant decrease of HCT prescriptions for hypertension and heart failure. Whether HCT exhibits phototoxic properties thereby causing skin cancer remains unknown. This study aimed to examine the photosensitizing, phototoxic and carcinogenic potential of HCT in a randomized, placebo-controlled, double-blind trial in vivo and also in vitro .

METHODS

The trial assigned 30 healthy, normotensive adult volunteers in a 2:1 ratio to either HCT 25 mg/day or placebo for 15 days. Photosensitivity of the skin with and without the effect of HCT treatment were assessed. Following whole-body ultraviolet A (UVA) and B (UVB, 311 nm) irradiation, phototoxic and carcinogenic reactions by measuring urinary excretion of pyrimidine dimers were evaluated. For the in-vitro studies, human keratinocytes (HaCaT) were incubated with HCT, irradiated with UVB, and analysed for markers of inflammation, apoptosis and carcinogenesis.

RESULTS

Skin photosensitivity following exposure to UVA and UVB remained unchanged from baseline to 15-day follow-up in both groups (UVA change HCT 0.0 J/cm 2 vs. placebo 0.0 J/cm 2 ; P  = 0.99; UVB change HCT 0.0 J/cm 2 vs. placebo -0.2 J/cm 2 ; P  = 0.06). Pyrimidine dimers were not detected in either group. In vitro , combination of HCT and UVB irradiation did not induce the expression of oxidative stress marker proteins, inflammatory proteins, apoptotic proteins or activation of oncoproteins.

CONCLUSION

HCT did not increase photosensitivity for UVA or UVB in healthy volunteers compared with placebo, and was not associated with phototoxic or carcinogenic reactions. In vitro , HCT was also not associated with phototoxicity or carcinogenesis (NCT04654312).

Nuclear and Urinary Measurements Show the Efficacy of Sun-Protection Factor 50+ Sunscreen against DNA Photoproducts upon Real-Life Recreational Exposure

Sunscreens have been shown to protect against UVR-induced DNA damage in human skin under laboratory conditions. We presently extended these observations to real-life conditions in volunteers after their ordinary exposure habits during summer holidays. Volunteers were randomly assigned to a control group and an educated group supplied with a SPF ≥50 sunscreen and receiving instructions for use. A questionnaire was used to determine the extent of exposure. No difference in average solar UVR exposure was found between the two groups. DNA photoprotection was first assessed by, to our knowledge, a previously unreported noninvasive assay on the basis of the quantification of pyrimidine dimers released by DNA repair in urine. Damage was also quantified in the nuclear DNA extracted from the roof of suction blisters collected after recreational exposure. The urinary concentration of photoproducts was significantly higher in the control than in the educated group. The same trend was observed for the level of photoproducts in the DNA from suction blisters. The unambiguous observation of an efficient photoprotection against DNA damage afforded by sunscreen under real-life conditions provides strong support for the efficiency of the sunscreens. In addition, the results validate the use of urinary DNA photoproducts as a noninvasive assay applicable to photoprotection.

DNA Containing Cyclobutane Pyrimidine Dimers Is Released from UVB-Irradiated Keratinocytes in a Caspase-Dependent Manner

Solar radiation induces the formation of cyclobutane pyrimidine dimers (CPDs) and other UV photoproducts in the genomic DNA of epidermal keratinocytes. Although CPDs have been detected in urine from UV- and sun-exposed individuals, the pathway by which they arrive there and the mechanisms by which UV-induced DNA damage in the skin has systemic effects throughout the body are not clear. Consistent with previous reports that DNA associates with small extracellular vesicles that are released from a variety of cell types, we observed that a small fraction of CPDs formed in genomic DNA after UVB exposure can later be detected in the culture medium. These extracellular CPDs are found within large fragments of histone-associated DNA and are released in a time- and UVB dose‒dependent manner. Moreover, studies with both cultured cells and human skin explants revealed that CPD release into the extracellular environment is blocked by caspase inhibition, which indicates a role for apoptotic signaling in CPD release from UVB-irradiated keratinocytes. Finally, we show that this released CPD-containing DNA can be taken up by other keratinocytes. These results therefore provide possible mechanisms for the export of damaged DNA from UVB-irradiated cells and for systemic effects of UVB exposure throughout the body.

DNA photoproducts released by repair in biological fluids as biomarkers of the genotoxicity of UV radiation

UV-induced formation of photoproducts in DNA is a major initiating event of skin cancer. Consequently, many analytical tools have been developed for their quantification in DNA. In the present work, we extended our previous liquid chromatography-mass spectrometry method to the quantification of the short DNA fragments containing photoproducts that are released from cells by the repair machinery. We designed a robust protocol including a solid-phase extraction step (SPE), an enzymatic treatment aimed at releasing individual photoproducts, and a liquid chromatography method combining on-line SPE and ultra-high-performance liquid chromatography for optimal specificity and sensitivity. We also added relevant internal standards for a better accuracy. The method was validated for linearity, repeatability, and reproducibility. The limits of detection and quantification were found to be in the fmol range. The proof of concept of the use of excreted DNA repair products as biomarkers of the genotoxicity of UV was obtained first in in vitro studies using cultured HaCat cells and ex vivo on human skin explants. Further evidence was obtained from the detection of pyrimidine dimers in the urine of human volunteers collected after recreational exposure in summer. An assay was designed to quantify the DNA photoproducts released from cells within short fragments by the DNA repair machinery. These oligonucleotides were isolated by solid-phase extraction and enzymatically hydrolyzed. The photoproducts were then quantified by on-line SPE combined with UHPLC-MS/MS with isotopic dilution.

Damage removal and gap filling in nucleotide excision repair

The nucleotide excision repair (NER) system removes a variety of types of helix-distorting lesions from DNA through a dual incision mechanism, in which the damaged nucleotide bases are excised in the form of a small, excised, damage-containing single-stranded DNA oligonucleotide (sedDNA). Damage removal leaves a gap in the DNA template that must then be filled in by the action of a DNA polymerase and ligated to the downstream phosphodiester backbone in the DNA to complete the repair reaction. Defects in damage removal, sedDNA processing, or gap filling have the potential to be mutagenic and lethal to cells, and thus several human pathologies, including cancer and aging, are associated with defects in NER. This review summarizes our current understanding of NER with a focus on the enzymes that excise sedDNAs and restore the duplex DNA to its native state in human cells.

Children sustain high levels of skin DNA photodamage, with a modest increase of serum 25-hydroxyvitamin D3 , after a summer holiday in Northern Europe

BACKGROUND

Childhood solar ultraviolet radiation (UVR) exposure increases the risk of skin cancer in adulthood, which is associated with mutations caused by UVR-induced cyclobutane pyrimidine dimers (CPD). Solar UVR is also the main source of vitamin D, essential for healthy bone development in children.

OBJECTIVES

To assess the impact of a 12-day Baltic Sea (54° N) beach holiday on serum 25-hydroxyvitamin D₃ [25(OH)D₃ ] and CPD in 32 healthy Polish children (skin types I-IV).

METHODS

Blood and urine were collected before and after the holiday and assessed for 25(OH)D₃ and excreted CPD, respectively, and personal UVR exposure was measured. Diaries were used to record sunbathing, sunburn and sunscreen use. Before- and after-holiday skin redness and pigmentation were measured by reflectance spectroscopy.

RESULTS

The average ± SD daily exposure UVR dose was 2·4 ± 1·5 standard erythema doses (SEDs), which is borderline erythemal. The mean concentration of 25(OH)D₃ increased (× 1·24 ± 0·19) from 64·7 ± 13·3 to 79·3 ± 18·7 nmol L^-1 (P < 0·001). Mean CPD increased 12·6 ± 10·0-fold from 26·9 ± 17·9 to 248·9 ± 113·4 fmol μmol^-1 creatinine (P < 0·001). Increased 25(OH)D₃ was accompanied by a very much greater increase in DNA damage associated with carcinogenic potential. Overall, skin type had no significant effects on behavioural, clinical or analytical outcomes, but skin types I/II had more CPD (unadjusted P = 0·0496) than skin types III/IV at the end of the holiday.

CONCLUSIONS

Careful consideration must be given to the health outcomes of childhood solar exposure, and a much better understanding of the risk-benefit relationships of such exposure is required. Rigorous photoprotection is necessary for children, even in Northern Europe.

Insight in DNA Repair of UV-induced Pyrimidine Dimers by Chromatographic Methods

UV-induced formation of pyrimidine dimers in DNA is a major deleterious event in both eukaryotic and prokaryotic cells. Accumulation of cyclobutane pyrimidine dimers and pyrimidine (6-4) pyrimidone photoproducts can lead to cell death or be at the origin of mutations. In skin, UV induction of DNA damage is a major initiating event in tumorigenesis. To counteract these deleterious effects, all cell types possess DNA repair machinery, such as nucleotide excision repair and, in some cell types, direct reversion. Different analytical approaches were used to assess the efficiency of repair and decipher the enzymatic mechanisms. We presently review the information provided by chromatographic methods, which are complementary to biochemical assays, such as immunological detection and electrophoresis-based techniques. Chromatographic assays are interesting in their ability to provide quantitative data on a wide range of damage and are also valuable tools for the identification of repair intermediates.

PostExcision Events in Human Nucleotide Excision Repair

The nucleotide excision repair system removes a wide variety of DNA lesions from the human genome, including photoproducts induced by ultraviolet (UV) wavelengths of sunlight. A defining feature of nucleotide excision repair is its dual incision mechanism, in which two nucleolytic incision events on the damaged strand of DNA at sites bracketing the lesion generate a damage-containing DNA oligonucleotide and a single-stranded DNA gap approximately 30 nucleotides in length. Although the early events of nucleotide excision repair, which include lesion recognition and the dual incisions, have been explored in detail and are reasonably well understood, the fate of the single-stranded DNA gaps and excised oligonucleotide products of repair have not been as extensively examined. In this review, recent findings that address these less-explored aspects of nucleotide excision repair are discussed and support the concept that postincision gap and excised oligonucleotide processing are critical steps in the cellular response to DNA damage induced by UV light and other environmental carcinogens. Defects in these latter stages of repair lead to cell death and other DNA damage signaling responses and may therefore contribute to a number of human disease states associated with exposure to UV wavelengths of sunlight, including skin cancer, aging and autoimmunity.

The Growing Burden of Invasive Melanoma: Projections of Incidence Rates and Numbers of New Cases in Six Susceptible Populations through 2031

New melanoma therapies are being developed rapidly, complementing prevention and detection strategies for disease control. Estimating the future burden of melanoma is necessary for deciding how best to deploy limited resources to achieve effective melanoma control. Using three decades of cancer registry data (1982-2011) from six populations with moderate to high melanoma incidence (US whites and the populations of the United Kingdom, Sweden, Norway, Australia, New Zealand), we applied age-period-cohort models to describe current trends and project future incidence rates and numbers of melanomas out to 2031. Between 1982 and 2011, melanoma rates in US whites, and the populations of the United Kingdom, Sweden, and Norway increased at more than 3% annually and are projected to continue rising until at least 2022. Melanoma incidence in Australia has been declining since 2005 (-0.7% per year), and melanoma incidence in New Zealand is increasing but is projected to decline soon. The numbers of new melanoma cases will rise in all six populations because of aging populations and high age-specific rates in the elderly. In US whites, annual new cases will rise from around 70,000 in 2007-2011 to 116,000 in 2026-2031, with 79% of the increase attributable to rising age-specific rates and 21% to population growth and aging. The continued increases in case numbers in all six populations through 2031 will increase the challenges of melanoma control.

Sun and ski holidays improve vitamin D status, but are associated with high levels of DNA damage

Skin cancer is caused by solar UVR, which is also essential for vitamin D production. DNA damage (thymine dimers: T-T dimers) and vitamin D (25(OH)D) synthesis are both initiated by solar UVB. We aimed to investigate the simultaneous adverse and beneficial effects of solar UVB exposure in holidaymakers. Sun-seekers and skiers (n=71) were observed over 6 days through on-site monitoring, personal diary entries, and recording of personal UVB exposure doses with electronic dosimeters. Urine and blood samples were analyzed for T-T dimers and 25(OH)D, respectively. The volunteers had a statistically significant increase in vitamin D. There were strong associations between UVB exposure and post-holiday levels of T-T dimers and vitamin D, as well as between post-holiday T-T dimers and vitamin D. We conclude that UVB-induced vitamin D synthesis is associated with considerable DNA damage in the skin. These data, on two major health predictors, provide a basis for further field studies that may result in better understanding of the risks and benefits of "real life" solar exposure. However, vitamin D status can be improved more safely through the use of vitamin D dietary supplements.

The variety of UV-induced pyrimidine dimeric photoproducts in DNA as shown by chromatographic quantification methods

Induction of DNA damage is one of the major consequences of exposure to solar UV radiation in living organisms. UV-induced DNA photoproducts are mostly pyrimidine dimers, including cyclobutane pyrimidine dimers, pyrimidine (6-4) pyrimidone photoproducts and Dewar valence isomers. In the last few decades, a large number of methods have been developed for the quantification of these pyrimidine dimers. The present review emphasizes the contribution of chromatographic techniques to our better understanding of the basic DNA photochemistry and the better description of damage in cells.

On the origins and development of the (32)P-postlabelling assay for carcinogen-DNA adducts

The (32)P-postlabelling method for the analysis of carcinogen-DNA adducts originated 30years ago from Baylor College of Medicine in Houston and was the work of a team comprised of Kurt and Erica Randerath, Ramesh Gupta and Vijay Reddy. With subsequent modifications and developments, it has become a highly sensitive and versatile method for the detection of DNA adducts that has been applied in a wide range of human, animal and in vitro studies. These include monitoring human exposure to environmental and occupational carcinogens, investigating genotoxicity of chemicals, elucidating pathways of metabolic activation of carcinogens, mechanistic studies of DNA repair, analysing the genotoxicity of complex mixtures and in ecotoxicology studies. Its use has been instrumental in providing new clues to the aetiology of some cancers and in identifying a new human carcinogen.

Urinary levels of thymine dimer as a biomarker of exposure to ultraviolet radiation in humans during outdoor activities in the summer

The incidence of skin cancer is rising rapidly in many countries, presumably due to increased leisure time exposure to solar ultraviolet radiation (UVR). UVR causes DNA lesions, such as the thymine dimer (T=T), which have been causatively linked to the development of skin cancer. T=T is clearly detectable in urine and may, thereby, be a potentially valuable biomarker of UVR exposure. The objective of this study was to evaluate the relationship between UVR exposure and urinary levels of T=T in a field study involving outdoor workers. Daily ambient and personal exposure of 52 beach lifeguards and agricultural workers to UVR were determined (employing 656 personal polysulphone dosimeters). In 22 of these subjects, daily urinary T=T levels (120 samples) were measured, the area of skin exposed calculated and associations assessed utilizing mixed statistical models. The average daily UVR dose was approximately 600 J/m(2) (7.7 standard erythemal doses), i.e. about 20% of ambient UVR. T=T levels were correlated to UVR dose, increasing by about 6 fmol/µmol creatinine for each 100 J/m(2) increase in dose (average of the three preceding days). This is the first demonstration of a relationship between occupational UVR exposure and urinary levels of a biomarker of DNA damage. On a population level, urinary levels of T=T can be used as a biomarker for UVR exposure in the field.

Quantification of ultraviolet radiation-induced DNA damage in the urine of Swedish adults and children following exposure to sunlight

CONTEXT

DNA damage following exposure to ultraviolet radiation (UVR) is important in skin cancer development. The predominant photoproduct, cyclobutane thymine dimer (T=T), is repaired and excreted in the urine, where it provides a biomarker of exposure.

OBJECTIVE

To quantify urinary T=T levels after recreational sunlight exposure in adults and children.

METHODS

Average UVR doses were measured with personal dosimeters. Urinary T=T was analysed with (32)P-postlabelling.

RESULTS

Background levels of T=T increased significantly following exposure to sunlight. Amounts of T=T in urine of children and adults were not significantly different after adjusting for area of skin exposed and physiological differences. UVR dose and amounts of T=T correlated for both adults and children.

CONCLUSION

Recreational exposure to sunlight in Sweden induces levels of DNA damage, clearly detectable in urine.

The novel function of OCT4B isoform-265 in genotoxic stress

OCT4 is a key transcription factor in maintaining the pluripotency and self-renewal of embryonic stem cells (ESCs). Human OCT4 gene can generate three mRNA isoforms (OCT4A, OCT4B, and OCT4B1) by alternative splicing and four protein isoforms (OCT4A, OCT4B-265, OCT4B-190, and OCT4B-164) by alternative splicing or alternative translation initiation. OCT4A is a transcription factor responsible for the stemness of ESCs, while the function of OCT4B protein isoforms is still not clear. We have previously reported that OCT4B-190 functioned in cell stress response. Here, we present another product of OCT4 gene, OCT4B-265, which is upregulated under genotoxic stress in stem cells, and it may function in stress response through p53 signaling pathway. This work gives an insight into the novel function of OCT4B protein isoforms and helps us to understand the complex expression patterns and biological functions of OCT4 gene.

The 32P-postlabeling assay for DNA adducts

32P-postlabeling analysis is an ultrasensitive method for the detection and quantitation of carcinogen-DNA adducts. It consists of four principal steps: (i) enzymatic digestion of DNA to nucleoside 3'-monophosphates; (ii) enrichment of the adduct fraction of the DNA digest; (iii) 5'-labeling of the adducts by transfer of 32P-orthophosphate from [gamma-32P]ATP mediated by polynucleotide kinase (PNK); (iv) chromatographic or electrophoretic separation of the labeled adducts or modified nucleotides and quantitation by measurement of their radioactive decay. The assay requires only microgram quantities of DNA and is capable of detecting adducts at frequencies as low as 1 in 10(10) nt, making it applicable to the detection of events resulting from environmental exposures, or experiments using physiological concentrations of agents. It has a wide range of applications in human, animal and in vitro studies, and can be used for a wide variety of classes of compound and for the detection of adducts formed by complex mixtures. This protocol can be completed in 3 d.