Photoreactivation of ultraviolet radiation-induced basic fibroblast growth factor (bFGF) and the role of bFGF in corneal lesion formation in Monodelphis domestica

Chronic ultraviolet radiation (UVR) exposure to the eyes of Monodelphis domestica causes corneal opacification, neovascularization, and fibrosarcoma induction. By immunohistochemistry and Western blotting, we have shown that one to four exposures of the eyes of this opossum to UVR enhances basic fibroblast growth factor (bFGF) expression by the corneal epithelium. Treatment with photoreactivating light, which selectively removes UVR-induced pyrimidine dimers, suppresses bFGF induction, indicating that UVR induction of bFGF is ultimately due to DNA damage. Furthermore, UVR-induced corneal tumors derived from corneal keratocytes express bFGF mRNA and protein, as determined by immunohistochemistry and in situ hybridization. Taken together, these findings suggest that bFGF acts in both an autocrine and a paracrine manner to stimulate corneal fibroplasia, neovascularization, and tumor development.

Dose response for ultraviolet radiation A-induced focal melanocytic hyperplasia and nonmelanoma skin tumors in Monodelphis domestica

Four groups of 30 dorsally shaved opossums (Monodelphis domestica) were exposed to graded doses of ultraviolet radiation A (UVA) (320-400 nm) three times per week for 90 weeks. Animals were monitored for the appearance of focal melanocytic hyperplasia (FMH) and nonmelanoma skin tumors (NMST) during the course of the exposures and for an additional 20 weeks following termination of exposures. FMH is the putative precursor for melanoma in the opossum. The lowest dose of UVA (2.5 x 10(3) J/m2) used in this study was selected based on the action spectrum for the induction of melanoma in a fish model. The prediction was that 2.5 x 10(3) J/m2 would induce FMH in the opossum if the action spectra for the induction of FMH in the opossum and melanoma in the fish were the same. The highest UVA dose was 2.5 x 10(5) J/m2. Only the highest dose of UVA gave a statistically significant induction of FMH and NMST in the opossum. As in previous studies, the FMH appeared earlier than the NMST during the course of exposures and the final prevalence of FMH was lower than the final prevalence of NMST. Overall, the results of this study indicate that the efficacy of UVA to induce FMH in the opossum is not as great as would be predicted from the action spectrum for melanoma induction in a fish model.

UVAI-induced edema and pyrimidine dimers in murine skin

The induction of edema and pyrimidine dimers in epidermal DNA was determined in the skin of SKH:HR1 mice exposed to graded doses of ultraviolet radiation AI (UVAI; 340-400 nm). Exposure to UVAI induced 1.6 +/- 0.08 x 10(-6) (mean +/- standard error of mean) pyrimidine dimers per 10(8) Da of DNA per J/m2. Edema in irradiated animals was determined as an increase in skinfold thickness. A dose of 1.8 x 10(6) J/m2 of UVAI that resulted in a 50% increase in skinfold thickness (SFT50%) would have induced 1.0 x 10(5) dimers per basal cell genome. A similar increase in SFT induced by full spectrum solar ultraviolet radiation (290-400 nm) would accompany the induction of 11.0 x 10(5) pyrimidine dimers per basal cell genome. These results support a hypothesis that UVAI-induced pathological changes of the skin are mediated through the formation of nondimer photoproducts.

Photobiology of Monodelphis domestica

The gray, short-tailed opossum, Monodelphis domestica, has been used for photobiologic studies since 1984. The presence of a light-activated DNA repair pathway in the tissues of Monodelphis has been used to identify pyrimidine dimers in DNA as initiating events for a number of ultraviolet radiation (UVR)-induced pathologies of the skin and cornea. Furthermore, Monodelphis, unlike common laboratory rodents, is susceptible to the induction of melanoma by UVR alone.

Cloning and characterization of the CDKN2A and p19ARF genes from Monodelphis domestica

The tumor suppressor gene, CDKN2A (p16), encodes a cyclin-dependent kinase inhibitor and functions as a negative regulator in the retinoblastoma pathway that blocks cell cycle progression from the G1 phase. The gene has been found to be deleted, truncated, mutated, or silenced by promoter methylation in a wide range of tumor types. Where melanoma CDKN2A mutations have been characterized, C --> T and CC --> TT transitions were found, indicating a direct role for ultraviolet radiation (UVR)-induced pyrimidine dimers in the formation of some tumors. The South American opossum, Monodelphis domestica, has been shown by our group and others to be susceptible to the induction of melanoma on chronic exposure to UVR alone. The CDKN2A gene and its exon 1beta alternate transcript p19ARF were cloned and sequenced from M. domestica to investigate the role of these genes in the development of UVR-induced melanoma and non-melanoma tumors. Both genes were first amplified by polymerase chain reaction (PCR) using cDNA from an opossum corneal-tumor cell-line library and degenerate primers based on human, mouse, and rat CDKN2A gene sequences. To verify these as normal sequences, both genes were then RT-PCR amplified from cultured normal opossum melanocyte mRNA. When comparing the tumor and melanocyte sequences, we found a UVR signature point mutation, a C --> T transition, within exon 2 in the corneal tumor cell line. The same mutation at this site in other tumors has been shown to alter the CDKN2A protein's ability to bind CDK4 kinase, which may lead to uncontrolled cell cycling. A comparison of the amino acid sequence of opossum CDKN2A showed identities relative to human, mouse, and rat between 57% and 63%, and when conserved amino acid substitutions are considered (similarity), the range is 63% to 67%. The amino acid identity and similarity for p19ARF ranged from 39% to 49%.

Ultraviolet A radiation (320-400 nm) protects hairless mice from immunosuppression induced by ultraviolet B radiation (280-320 nm) or cis-urocanic acid

T cell-mediated immune function, here measured as the contact hypersensitivity reaction, is readily suppressed by moderate exposure of mice to ultraviolet B (UVB) or solar-simulated radiation (SSUV), or by topical application of cis-urocanic acid. The effect of ultraviolet A (UVA) radiation on immune function has been unclear. Here we have demonstrated that when UVA radiation from a fluorescent tube source was rigorously filtered to remove contaminating UVB radiation, it was immunologically innocuous at physiologically relevant doses. Furthermore, we have found that mice exposed to UVA radiation, either immediately after, or up to 24 h before, immunosuppressive treatment with either UVB radiation, SSUV or cis-urocanic acid, became refractory to the immunosuppression and retained more normal contact hypersensitivity. A greater UVA exposure reversed the immunosuppression more effectively. The results suggest that there are immunologically significant interactions between UV wavebands, and that UVA exposure may induce a relatively long-lived immunoprotective photoproduct, as yet unidentified, that can inhibit the activity of epidermal cis-urocanic acid and thus provide protection from photoimmunosuppression.

H-ras oncogene activation in invasive UVR-induced corneal sarcomas of the opossum Monodelphis domestica

Chronic exposure to ultraviolet radiation (UVR) induces corneal sarcomas in the South American opossum Monodelphis domestica. Cell lines are readily established from these tumors. Northern blotting of mRNA from six such cell lines revealed high expression of the H-ras oncogene. H-ras cDNA from an eye tumor cell line was cloned and characterized; the germline sequence of codons 12, 13, and 61 was confirmed by examination of H-ras sequences amplified from liver DNA by the polymerase chain reaction. The Monodelphis H-ras coding sequence is 84-89% identical to that of other vertebrates at the nucleotide level, and the predicted 189-amino-acid sequence differs by 2-12 amino acids from that of other vertebrates. Analysis of 12 primary invasive corneal sarcomas induced by chronic UVR exposure revealed no evidence of H-ras gene amplification or rearrangement. One tumor was heterozygous for an activating point mutation in codon 61 of the H-ras gene; the tumor was also homozygous for a point mutation at an adjacent site in codon 62. These results provide additional evidence for the functional importance and consequent evolutionary conservation of the ras oncogenes.

Ultraviolet radiation A-induced precursors of cutaneous melanoma in Monodelphis domestica

Two groups of 30 dorsally shaved opossums (Monodelphis domestica) were exposed three times per week for 81 weeks to 250 J/m2 of UV radiation from FS40 sunlamps (approximately 150 J/m2 of UV radiation B; UV-B), or to 2.5 x 10(4) J/m2 of UV radiation A (UV-A) from filtered F40BLB fluorescent lamps (black lights). Animals were monitored for the appearance of nonmelanoma skin tumors (NMSTs) and melanocytic hyperplasia (MH). After 81 weeks of exposures, the prevalence of NMSTs was 71% and 4% for animals exposed to UV-B and UV-A, respectively. The difference between the treatment groups was statistically significant (P < 0.001). However, the prevalence of MH in the treatment groups, 31% for UV-B-exposed animals and 22% for UV-A-exposed animals, was not significantly different (P > 0.05). Thus, a dose of UV-A that was relatively ineffective in producing NMSTs, compared to UV-B, was as effective as UV-B in the induction of MH. If, as shown previously, MH is the precursor lesion for melanoma in this model, these results suggest that the action spectra for the induction of melanoma and NMSTs in the opossum are different.

S-100 immunoreactivity in melanomas of the South American opossum Monodelphis domestica

S-100 immunoreactivity was determined 1) in foci of melanocytic hyperplasia, 2) in naturally occurring, ultraviolet radiation-induced, and 9,10-dimethyl-1,2-benzanthracene (DMBA)-induced primary melanomas, and 3) in metastatic melanoma lesions in the South American opossum Monodelphis domestica. Preneoplastic lesions of melanocytic hyperplasia contained scattered cells with S-100-positive nuclei. All primary melanomas, with the exception of a single DMBA-induced tumor, contained cells with S-100-positive nuclei. The pattern of S-100 reactivity in tumors varied from large foci of S-100-positive cells to scattered individual S-100-positive cells. Lymph node metastases were S-100 positive, but metastatic masses in internal organs were usually S-100 negative. Although S-100 reactivity did not distinguish preneoplastic lesions from tumors or benign melanomas from malignant melanomas, identification of metastatic tumor cells clearly demonstrated malignancy.

Chemoprevention of ultraviolet radiation-induced skin cancer

The use of chemical and physical sunscreening agents has increased dramatically during the last two to three decades as an effective means of preventing sunbum. The use of high sunprotection factor sunscreens has also been widely promoted for the prevention of skin cancer, including melanoma. Whereas sunscreens are undoubtedly effective in preventing sunbum, their efficacy in preventing skin cancer, especially melanoma, is currently under considerable debate. Sunscreens have been shown to prevent the induction of DNA damage that presumably results from the direct effects of ultraviolet radiation (UVR) on DNA. DNA damage has been identified as an initiator of skin cancer formation. However, both laboratory and epidemiological studies indicate that sunscreens may not block the initiation or promotion of melanoma formation. These studies suggest that the action spectrum for erythema induction is different than the action spectrum for the induction of melanoma. Indeed, recent reports on the wavelength dependency for the induction of melanoma in a fish model indicate that the efficacy of ultraviolet A wavelengths (320-400 nm) to induce melanoma is orders of magnitude higher than would be predicted from the induction of erythema in man or nonmelanoma skin tumors in mice. Other strategies for the chemoprevention of skin cancer have also been reported. Low levels and degree of unsaturation of dietary fats protect against UVR-induced skin cancer in mice humens. Compounds with antioxidant activity, including green tea extracts (polyphenols), have been reported to inhibit UVR-induced skin carcinogenesis.

Sunscreen protection against ultraviolet radiation-induced pyrimidine dimers in mouse epidermal DNA

Pyrimidine dimers were measured in epidermal DNA of SKH:HR1 mice following exposure to solar-simulated UV radiation (SSUV, 290-400 nm) or to UVA (320-400 nm). Mice were exposed to SSUV or UVA after topical application (2 mg/cm2) of vehicle, a UVB absorber (5% 2-ethylhexyl p-methoxycinnamate [2-EHMC]), or a broad-spectrum UVA absorber (5% Mexoryl SX). The rates of induction of pyrimidine dimers in untreated animals were 5.4 +/- 0.57 x 10(-4) (mean +/- SEM) and 7.6 +/- 0.95 x 10(-6) dimers per 10(8) Da of epidermal DNA per J/m2 of SSUV and UVA, respectively. Topical application of Mexoryl SX reduced the rate of induction of pyrimidine dimers in SSUV-exposed animals to 4.7 +/- 0.44 x 10(-5) dimers per 10(8) Da per J/m2 for a dimer induction protection factor (PF) of 11.5 (5.4 x 10(-4)/4.7 x 10(-5). The rate of dimer induction in Mexoryl SX-treated, UVA-exposed mice was 0.95 +/- 0.2 x 10(-6) dimers per 10(8) Da per J/m2 (PF = 8.0). The 2-EHMC at a concentration of 5% (wt/wt) was significantly less effective than Mexoryl SX in preventing the induction of pyrimidine dimers in animals exposed to either SSUV or UVA. The rates of dimer induction in 2-EHMC-treated mice were 8.2 +/- 1.1 x 10(-5) and 3.8 +/- 0.33 x 10(-6) dimers per Da per J/m2 of SSUV (PF = 6.6) and UVA (PF = 2.0), respectively. Upon normalizing to the efficacy for edema induction, UVA induced approximately one-fourth the number of pyrimidine dimers per equivalent edematous response when compared to SSUV.

Cis-urocanic-acid-induced suppression of contact hypersensitivity in Monodelphis domestica is prevented by ultraviolet A radiation/photoreactivating light

The suppression of contact hypersensitivity by UVB (280-320 nm) radiation can be prevented by photoreactivating light (PRL; 320-400 nm) in the opossum Monodelphis domestica, implicating epidermal DNA lesions as the immunosuppressive impairment. However, contact hypersensitivity can also be suppressed in the opossum with exogenous cis-urocanic acid, a molecule which is produced in UVB-irradiated epidermis and is a second potential mediator of photo-immunosuppression apparently independent of UVB-induced DNA damage. Here we demonstrate that irradiation of opossums with PRL either before or following treatment with exogenous cis-urocanic acid, significantly reduced the degree of immunosuppression. This suggests that, in addition to its capacity to initiate post-UVB-exposure epidermal DNA repair, the PRL waveband can induce an immunoprotective product, as yet unidentified, in opossum epidermis.

Photorepair of ultraviolet radiation (UVR)-induced pyrimidine dimers in lens epithelial DNA of Monodelphis domestica

The repair of UV radiation-induced pyrimidine dimers has been measured in lens epithelial DNA of the marsupial Monodelphis domestica using a pyrimidine dimer-specific endonuclease from Micrococcus luteus. Approximately 40% of the initially induced dimers were repaired during 90 min exposures to photoreactivating light. This capacity of the lens epithelium to photorepair pyrimidine dimers may provide a means with which to determine whether pyrimidine dimers in lens epithelial DNA are involved in UV radiation-induced pathologic changes of the lens.

Effect of chronic exposure to ultraviolet radiation and photoreactivation on life span and tumor development in the marsupial Monodelphis domestica

The effect of exposure to chronic ultraviolet (UV) radiation on life span was examined in Monodelphis domestica, which is capable of photoreactivation repair of UV-radiation-induced pyrimidine dimers. Shaved Monodelphis were exposed to 500 J/m2 UV radiation, 500 J/m2 UV radiation then 90 min of photoreactivating light (PRL), or 90 min of PRL three times weekly for 104 weeks. Opossums were weighed weekly; samples for serum chemistry and hematology testing were obtained periodically. Complete postmortem examinations revealed a primary cause of death for each opossum. Meaningful differences among the groups in weight gain, serum chemistry values or hematology values were not seen. Significant life-shortening due to UV-radiation exposure was found for females but not males. Photoreactivation prolonged life only in the females exposed to UV radiation. Exposure to UV radiation was not associated with accelerated development of degenerative disease. Significant treatment-related mortality occurred in both male and female opossums exposed to UV radiation. Photoreactivation reduced the relative risk of skin tumors but not eye tumors in Monodelphis exposed to UV radiation. Eye and skin tumors were less likely to be a cause of death in UV-radiation-exposed opossums subsequently exposed to PRL than in opossums exposed to UV radiation alone. Females exposed only to UV radiation had an increased risk of skin tumor development relative to males.

Epidermal urocanic acid and suppression of contact hypersensitivity by ultraviolet radiation in Monodelphis domestica

A single specific epidermal photoreceptor for the immunosuppressive action of UV radiation has not been defined, although separate evidence is accruing in favour of each of two candidates, trans-urocanic acid and DNA. In Monodelphis domestica, specific photoreactivation repair of UV radiation-induced pyrimidine dimers has been shown to abrogate the suppression of contact hypersensitivity (CHS), thus suggesting that DNA is the target for this impairment. However, the both haired and hairless mice, immunosuppressive effects of UV radiation have been reproduced by the exogenous administration of the UV photoproduct of urocanic acid, cis-urocanic acid. We show here that the epidermis of M. domestica contains urocanic acid, that UV irradiation of the shaved dorsal skin has resulted in an increase in epidermal cis-urocanic acid and that the topical application of a cis-urocanic acid-containing lotion significantly depressed the capacity of Monodelphis to respond to contact sensitisers, in a manner analogous to these responses in the hairless mouse. Therefore in Monodelphis, suppression of CHS by UV irradiation appears to involve both urocanic acid photo-isomerisation and epidermal DNA damage.

Lack of correlation between suppression of contact hypersensitivity by UV radiation and photoisomerization of epidermal urocanic acid in the hairless mouse

The immunological consequences of exposure to UVA (320-400 nm) radiation are unclear. This study describes the relationship between the generation of epidermal cis-urocanic acid and the ability to respond to a contact-sensitizing agent, in hairless mice exposed to different UV radiation sources, which incorporate successively greater short-wavelength cutoff by filtration of the radiation from fluorescent UV tubes. Mice were exposed to these radiation sources at doses systematically varying in UVB radiation content but supplying increasing proportions of UVA radiation. All radiation sources were found to generate approximately 35% cis-urocanic acid in the epidermis, thus normalizing the sources for cis-urocanic acid production. However, only those sources richest in short-wavelength UVB resulted in suppression of the systemic contact hypersensitivity response. These sources also induced the greatest erythema reaction, measured as its edema component, in the exposed skin. A strong correlation was thus demonstrated between the induction of edema and the suppression of contact hypersensitivity, but there appeared to be no correlation between the generation of epidermal cis-urocanic acid and suppression of contact hypersensitivity. The sources richest in UVA content did not result in suppression of contact hypersensitivity; furthermore mice previously irradiated with such UVA-rich sources were refractory to the immunosuppressive action of exogenous cis-urocanic acid. A protective effect of the increased UVA content thus appeared to be inhibiting immunosuppression by the available endogenously generated or exogenously applied cis-urocanic acid.

Changing the risk spectrum of injury and the performance of sunscreen products throughout the day

Sunscreen products are tested normally against a defined solar simulator spectrum that, in ultraviolet (UVB), closely resembles the noontime spectral composition of summer sunlight. Although such a spectrum may define the product for use in the most adverse sunlight conditions, little attention has been given to how such products perform against other natural sunlight spectra. Outdoor clinical trials suggest that indoor testing of sunscreens may overestimate the performance of many products. In this study we compared the predicted efficacy of specific products to a variety of natural sunlight spectra taken at different solar angles and under different atmospheric conditions. We found that a standard product always provides less protection for a natural sunlight spectrum than its label value would suggest. The deviation from the labeled value is the greatest when the sun is low in the sky, i.e., close to the horizon. The deviation is due to the changing ratio of UVA to UVB radiation in natural sunlight. The deviation can be as large as a factor of 2.0.

Characterization of cDNA encoding basic fibroblast growth factor of the marsupial Monodelphis domestica

We have isolated and characterized a 1,593-bp cDNA containing the coding region of the basic fibroblast growth factor (BFGF) gene of a marsupial, the opossum Monodelphis domestica. The encoded protein is 156 amino acids long. The BFGF gene of M. domestica is 82-87% identical to the BFGF genes of placental mammals at the nucleotide level and 92-93% identical to these genes at the level of the amino acids encoded. Regions of the BFGF molecule important in heparin binding, high-affinity receptor binding, and biologic function are highly conserved between placental mammals and this marsupial. There are several AUG and CUG codons in the 5' region of the marsupial cDNA that may serve as alternate sites of translation initiation; use of these sites would produce amino-terminally extended BFGF proteins. Amino-terminal extensions of BFGF in other species serve as nuclear localization signals. Conserved A+T-rich motifs in the 3' untranslated region of the marsupial mRNA probably serve to regulate mRNA stability. The high degree of evolutionary conservation of BFGF in mammals suggests that the molecule plays an important role in normal growth and development and that stringent control of its activity is essential.

Enhanced pyrimidine dimer repair in cultured murine epithelial cells transfected with the denV gene of bacteriophage T4

The patch size for excision repair of ultraviolet radiation (UV)-induced pyrimidine dimers was determined in cultured murine epithelial cells with normal and enhanced pyrimidine dimer repair capabilities. Cells with enhanced pyrimidine dimer repair were produced by transfecting 308 cells with the denV gene of bacteriophage T4; this gene encodes the enzyme endonuclease V. Pyrimidine dimer repair following exposure to UV from an FS-40 sunlamp was determined by micrococcal dimer-specific nuclease digestion and alkaline sucrose ultracentrifugation. Patch size ws estimated based on the photolytic lability of bromodeoxyuridine-substituted DNA. Excision repair of UV-induced pyrimidine dimers in denV-transfected 308 cells was enhanced two- to threefold. Production of mRNA from the denV gene in cell lines with enhanced repair was confirmed by RNA blotting. In control cells, the patch size for excision repair of DNA photoproducts was estimated to be 34 nucleotides per photoproduct removed; in denV-transfected cells, a smaller average patch size of 10-16 nucleotides per photoproduct removed was calculated. Thus, endonuclease V activity appears to alter not only the extent, but also the nature of excision repair in UV-exposed mammalian epithelial cells.

Genetic analysis of ultraviolet radiation-induced skin hyperplasia and neoplasia in a laboratory marsupial model (Monodelphis domestica)

Monodelphis domestica, the laboratory opossum, develops hyperplasia and neoplasia of shaved skin after repeated exposure to ultraviolet radiation (UVR). We exposed Monodelphis from genetically diverse families within our colony to determine whether there are any heritable components to the risk of two distinct skin lesion phenotypes-melanocytic nevus (MN) and advanced hyperkeratosis (HK). From about 5 months of age, animals were shaved and exposed three times a week to a dose of about 125 J/m2 of UVR (spectral peak, 302 nm; range, 280-400 nm). Of 33 sibships (151 individuals) that completed at least 30 weeks of the protocol, 137 completed 45 weeks. For genetic analyses, each animal was classified at 30 and 45 weeks as affected with MN and HK or not affected. Heritabilities were estimated using a variance decomposition approach. Susceptibility to MN showed no significant evidence for a genetic component at 30 or 45 weeks. In sharp contrast, susceptibility to HK was under virtually complete genetic control (heritability, 0.999; P < 0.001) at 30 weeks, and had a moderately high heritability (0.702; P < 0.001) at 45 weeks. We conclude that this model has great potential for identifying genes that confer susceptibility to UVR-induced skin lesions and for investigating environmental factors that may contribute to the increasing incidence of skin cancer in human populations.

Frequency of ultraviolet radiation-induced mutation at the hprt locus in repair-proficient murine fibroblasts transfected with the denV gene of bacteriophage T4

The frequency of spontaneous and ultraviolet radiation (UVR)-induced mutation at the hprt locus was determined in control and denV-transfected, repair-proficient murine fibroblasts. Control cells removed an average of 25% of pyrimidine dimers induced by exposure to 150 J/m2 UVR from an FS40 sunlamp within 24 h; under the same conditions of induction and repair, denV-transfected cells removed an average of 71% of pyrimidine dimers. Control cells were somewhat more resistant than denV-transfected cells to killing by UVR. The average frequency of spontaneous mutation at the hprt locus for control and denV-transfected cells was 3 and 15 6-thioguanine (6-TG)-resistant colonies per 10(6) surviving cells, respectively; there was no statistically significant difference between control and denV-transfected cells. However, after exposure to 75 or 150 J/m2 UVR, denV-transfected cells had a significantly lower frequency of mutation to 6-TG resistance. After exposure to a fluence of 75 J/m2, the average frequency of UVR-induced mutation at the hprt locus was 166 mutant colonies per 10(6) surviving cells for control cells and 92 mutant colonies for denV-transfected cells; after 150 J/m2, control cells had 205 6-TG-resistant colonies per 10(6) cells, while denV-transfected cells had 61 mutant colonies. These results demonstrate that UVR-induced pyrimidine dimers are mutagenic photoproducts in mammalian cells.

Ultraviolet radiation-induced corneal tumours in the South American opossum, Monodelphis domestica

Chronic exposure of the South American opossum, Monodelphis domestica, to ultraviolet radiation (UVR) induced 154 primary tumours of the cornea in 152 eyes. Tumours developed gradually; frank neoplasia was preceded by non-neoplastic proliferation of corneal stromal fibroblasts (keratocytes) and extensive neovascularization. Histologically, the majority of tumours (134 of 154) appeared to be fibrosarcomas arising from keratocytes, but about 12 per cent of the tumours (18 of 154) had a highly vascular appearance, suggesting haemangiosarcoma. In two eyes, squamous cell carcinomas overlay mesenchymal tumours. Ultrastructural features of UVR-induced corneal tumours were consistent with tumours, and cultured skin fibroblasts expressed high content of messenger RNA for the intermediate filament vimentin; no cytokeratin messenger RNA was detected in these cells and cell lines. Based upon their light microscopic, ultrastructural, and intermediate filament biosynthetic characteristics, the majority of UVR-induced corneal tumours in M. domestica appeared to be fibrosarcomas. Haemangiosarcomas constituted a smaller proportion of the tumours, and squamous cell carcinomas were very rare.

Expression of fibroblast growth factors in ultraviolet radiation-induced corneal tumors and corneal tumor cell lines from Monodelphis domestica

Chronic exposure of the gray, short-tailed opossum, Monodelphis domestica, to ultraviolet radiation (UVR) induces highly vascularized mesenchymal tumors of the cornea. Cell lines derived from these UVR-induced corneal tumors and the corneal tumors themselves were examined for the presence of mRNA coding for basic and acidic fibroblast growth factors (FGF), transforming growth factors-beta and -alpha (TGF-beta and TGF-alpha), epidermal growth factor (EGF), and tumor necrosis factor-alpha (TNF-alpha). Basic FGF was expressed in the cell lines derived from corneal tumors and in the corneal tumors. Expression of basic FGF was high in one corneal tumor. Transcripts for acidic FGF were detected only in the corneal tumor cell lines, not in primary tumors. TGF-beta expression was detected in the corneal tumors and tumor-derived cell lines. TGF-alpha, EGF, and TNF-alpha transcripts were not detectable in any opossum material; however, homologous gene sequences for TGF-alpha and EGF were detected on Southern blots of opossum genomic DNA. Southern blot analysis revealed no evidence of amplification or rearrangement of the genes for basic FGF or acidic FGF in the UVR-induced corneal tumor that expressed high levels of basic FGF. Opossum basic FGF, which stimulated the proliferation of fetal bovine heart endothelial cells, was purified by heparin affinity chromatography from a UVR-induced corneal tumor and a corneal tumor cell line. Immunoblotting of opossum basic FGF from a corneal tumor cell line using antiserum to bovine basic FGF showed two prominent immunoreactive bands of 17.5 and 18.5 kDa. Expression of basic FGF and acidic FGF may play a role in the development and progression of UVR-induced corneal tumors in M. domestica.

Characterization of the K-ras gene of the marsupial Monodelphis domestica

A cDNA clone isolated from a plasmid library contains the complete coding sequence for the K-ras gene of the marsupial Monodelphis domestica, a South American opossum. The nucleotide sequence of the coding region of the opossum K-ras gene is very similar to the K-ras coding sequences of placental mammals. The coding region of the opossum gene is 95% identical to the human gene at the nucleotide level; the human and opossum genes are 99% identical at the level of encoded amino acids. Transcribed but untranslated regions of the opossum gene 3' and 5' to the coding region are similar to corresponding regions of the human and mouse genes, but are less highly conserved than translated sequences. Based on the nucleotide sequence of the opossum K-ras cDNA clone, primers were designed that allowed amplification of exons 1 and 2 of the gene from opossum genomic DNA by the polymerase chain reaction. When exons 1 and 2 of K-ras were amplified from DNA isolated from an ultraviolet radiation-induced eye tumor of M. domestica and the nucleotide sequence of amplified material was determined, a heterozygous mutation in codon 61 of the gene was detected. This T to A transversion resulted in a change in the amino acid encoded by the codon. The tumor from which DNA was isolated had previously been shown to contain a transforming K-ras oncogene. Thus, the opossum K-ras gene can be mutationally activated in a manner similar to the K-ras genes of placental mammals.

Specific chromosomal defects associated with ultraviolet radiation-induced cutaneous tumors in Monodelphis domestica (Marsupialia, mammalia)

Cytogenetic analysis of eight ultraviolet radiation (UVR)-induced cutaneous tumors and one spontaneously transformed fibroblast cell line of Monodelphis domestica showed that two of the tumor cell lines were of murine origin and that the remaining six marsupial tumor cell lines had hyperdiploid stemline numbers ranging from 21 to 31. Each tumor cell line showed structural and numerical abnormalities. The single transformed fibroblast cell line also showed a hyperdiploid chromosome number with structural and numerical defects. All M. domestica tumor cell lines and the fibroblast line showed a common structural abnormality: deletion of the short arm (p) of a chromosome 1. In some cell lines, the short arm of chromosome 1 was replaced by a translocation with the X chromosome. We suggest, based on the Giemsa-banding homology of chromosome 1p in M. domestica and human chromosome 6q involved in melanomas, that marsupial chromosome 1p may harbor tumor suppressor gene(s) that are associated with UVR-induced cutaneous tumors.

Cell cycle progression in denV-transfected murine fibroblasts exposed to ultraviolet radiation

Repair-proficient murine fibroblasts transfected with the denV gene of bacteriophage T4 repaired 70-80% of pyrimidine dimers within 24 h after exposure to 150 J/m2 ultraviolet radiation (UVR) from an FS-40 sunlamp. Under the same conditions, control cells repaired only about 20% of UVR-induced pyrimidine dimers. After UVR exposure, both control and denV-transfected cells exhibited some degree of DNA-synthesis inhibition, as determined by flow cytometric analysis of cell-cycle kinetics in propidium iodide-stained cells. DenV-transfected cells had a longer and more profound S phase arrest than control cells, but both control and denV-transfected cells had largely recovered from UVR effects on cell-cycle kinetics by 48 h after UVR exposure. Inhibition of DNA synthesis by UVR was also measured by determining post-UVR incorporation of bromodeoxyuridine (BrdU). The amount of BrdU incorporated was quantitated by determining with flow cytometry the quenching of Hoechst dye 33342 by BrdU incorporated in cellular DNA. DenV-transfected cells showed more marked inhibition of BrdU incorporation after low fluences of UVR than control cells. Differences between denV-transfected and control cells in cell-cycle kinetics following UVR exposure may be related to differences in mechanisms of repair when excision repair of pyrimidine dimers is initiated by endonuclease V instead of cellular repair enzymes.

In vivo exposure to ultraviolet radiation enhances pathogenic effects of murine leukemia virus, LP-BM5, in murine acquired immunodeficiency syndrome

LP-BM5 murine leukemia virus (MuLV) induces an immunodeficiency syndrome (MAIDS) in C57BL/6 mice which resembles immunological abnormalities observed in early stages of human AIDS. In our study, MAIDS virus-infected mice were exposed to low doses of ultraviolet radiation (UVR) before and after virus inoculation and compared with MAIDS-infected but not UVR-exposed mice. In all tested parameters (blood IgM levels; mitogenic responses to PHA, ConA, LPS and anti-mu; MLR; antigenic response to SRBC; enlargement and histopathologic changes of the spleen) we observed the same trend: changes due to MAIDS infection were more pronounced in the UVR-exposed group than in the unexposed group. Statistically significant differences between these two groups were seen for mitogenic responses at two different time points after virus inoculation. These results demonstrate that in vivo UVR exposure enhances the immunosuppressive effects of a retroviral infection. UVR exposure may affect the progression of AIDS in a similar manner.

Purification and characterization of fibroblast growth factors from the opossum, Monodelphis domestica, brain

An extract from the brain of the opossum Monodelphis domestica was fractionated by heparin affinity chromatography. A major peak of mitogenic activity (heparin binding growth factor 2, HBGF-2) eluted from heparin-Sepharose between 1.7 and 2.0 M NaCl. Antisera specific for bovine bFGF detected four polypeptides of 17.5-23 kDa in opossum brain HBGF-2 preparations. Opossum brain heparin binding growth factor 1 (HBGF-1), a minor peak of activity, eluted from heparin-Sepharose at 1.1 NaCl and contained a 16.2 kDa protein that cross-reacted with antiserum against bovine aFGF.

Identification of a transforming ras oncogene in an ultraviolet radiation-induced corneal tumor of Monodelphis domestica

Chronic exposure of the gray, short-tailed oppossum, Monodelphis domestica to ultraviolet radiation (UVR) induces mesenchymal tumors of the cornea. High molecular weight DNA samples from 6 UVR-induced corneal tumors were assayed for their ability to transform NIH 3T3 cells to tumorigenicity. NIH 3T3 cells transfected with DNA from 5 of the corneal tumors produced 14 tumors in nude mice. Cell lines were established from these tumors. DNA from 13 of 14 tumor cell lines contained repetitive opossum DNA sequences. Southern blot analysis revealed that DNA from 3 of 4 cell lines derived from tumorigenic NIH 3T3 cells transfected with DNA from a single oppossum tumor contained opossum Ki-ras oncogene sequences in addition to the murine Ki-ras gene. Northern blot analysis of mRNA from a mouse tumor cell line containing opossum Ki-ras gene sequences showed mRNA species identical in size to opossum Ki-ras mRNA, as well as murine Ki-ras mRNA species. These results suggest that an activated Ki-ras oncogene was present in one of the original opossum corneal tumors tested. Thus, activation of Ki-ras may play a role in the development of UVR-induced corneal tumors in Monodelphis domestica. Further characterization of ras oncogenes in these opossum tumors may provide information on the molecular mechanisms by which UVR induces corneal tumors in this species.

Proliferative responses of lymphocytes to mitogens in the gray, short-tailed opossum, Monodelphis domestica

A South American opossum (Monodelphis domestica) is a model animal for studies on the health effects of exposure to ultraviolet radiation (UVR). As part of a broad evaluation of immune function in this animal, we have tested in vitro mitogenic responses using whole blood cultures. Lymphocytes proliferated in the presence of phytohemagglutinin (PHA), concanavalin A (Con A), and pokeweed mitogen (PWM), but were unresponsive to bacterial lipopolysaccharide (LPS).

Photoreactivation of ultraviolet radiation-induced skin and eye tumors of Monodelphis domestica

Chronic exposure of the opossum Monodelphis domestica to UV radiation (UVR) leads to the formation of cutaneous and corneal tumors. Groups of shaved opossums were exposed 3 times/week to: (a) UVR alone; (b) UVR followed immediately by 1 h of photoreactivating light (PRL) (320-700 nm); (c) 1 h of PRL followed by UVR; and (d) 1 h of PRL alone. Exposures were terminated after 70 weeks of treatment. Analysis of data plotted as probability of tumor formation versus weeks from first exposure shows that post-UVR exposure to PRL significantly (P less than 0.005) delayed the time to appearance of cutaneous tumors from a 50% probability of tumor formation at 73 weeks for those animals exposed to UVR alone to 128 weeks for those animals exposed to PRL after UVR. Pre-UVR exposure to PRL delayed the appearance of tumors by 6 weeks when compared to the UVR alone group, but the difference between the two groups was not statistically significant. The yield (number of tumors/surviving animal) of cutaneous tumors at 70 and 110 weeks following initiation of treatments also was significantly less in those animals exposed to PRL after, but not before, UVR. Based on the specificity of the PR repair pathway to act only on pyrimidine dimers, these results suggest that dimers are involved in the induction of cutaneous tumors. The results obtained with the induction of corneal tumors are more difficult to interpret. While exposure to PRL significantly delayed the appearance of corneal tumors, the magnitude of the effect was the same regardless of whether the PRL was given before or after each UVR exposure.

Photoreactivation of ultraviolet radiation-induced release of arachidonic acid from marsupial cells

Exposure of an established marsupial cell line, PtK2 (Potorous tridactylus), to ultraviolet radiation (UVR) from an FS-40 sunlamp (280-400 nm) resulted in a fluence-dependent release of radiolabeled arachidonic acid (AA) from cell membranes. Post-UVR, but not pre-UVR, exposure to photoreactivating light reversed UVR-induced pyrimidine dimers in DNA and suppressed the UVR-induced release of AA. These data indicate that DNA damage contributes to the release of AA from membrane phospholipids.

Differential protection by two sunscreens from UV radiation-induced immunosuppression

A controversy has arisen concerning the ability of sunscreens to protect mice from the immunosuppressive effects of UV radiation. We have assessed the photoprotection in hairless mice of two sun protection factor (SPF)15 sunscreens containing different UVB (280-320-nm) absorbers, namely, octyl-N-dimethyl-p-aminobenzoate (o-PABA) or 2-ethylhexyl-p-methoxycinnamate (2-EHMC). Following three minimum erythemal exposures to UV radiation, both systemic suppression of contact hypersensitivity to 2,4-dinitrofluorobenzene and induction of susceptibility to transplanted UV radiation-induced tumor cells was established. Topically applied 2-EHMC sunscreen protected totally from both forms of immunosuppression, but the o-PABA sunscreen failed to protect, although both sunscreens were equally effective in protection from UV radiation-induced erythema and edema.

Enhanced pyrimidine dimer removal in repair-proficient murine fibroblasts transformed with the denV gene of bacteriophage T4

The denV gene of bacteriophage T4, which encodes the pyrimidine dimer-specific repair enzyme endonuclease V, was introduced into murine fibroblasts with normal rodent pyrimidine dimer repair capabilities. Endonuclease V recognizes ultraviolet radiation (UVR)-induced pyrimidine dimers and produces single-strand breaks adjacent to the dimers. These nicks may serve as substrates to initiate excision repair of pyrimidine dimers by endogenous enzymes. In the present study, murine fibroblasts stably transfected with denV were able to remove 50-80% of UVR-induced pyrimidine dimers, while control cells removed only about 20% of dimers under the same conditions of pyrimidine dimer induction and repair. For both control and denV-transfected cells, repair continued for at least 24 h after exposure. When removal of UVR-induced photoproducts was initiated by endogenous excision repair mechanisms, an average of 38 nucleotides were replaced per dimer removed, as determined by bromouracil photolysis; denV-initiated excision repair, on the other hand, resulted in removal of an average of 6 nucleotides per dimer repaired. The enhanced pyrimidine dimer repair capabilities conferred by denV gene expression did not appear to improve post-UVR survival.

DNA damage is involved in the induction of opacification and neovascularization of the cornea by ultraviolet radiation

Studies were conducted to examine ultraviolet radiation (UVR)-induced alterations of the cornea of the gray, short-tailed opossum. Monodelphis domestica, and the effect of post-UVR illumination to photoreactivation light (PRL, 320-500 nm). As photoreactivation treatment specifically monomerizes pyrimidine dimers, an amelioration of the UVR-induced biological end-point would implicate DNA as being a primary chromophore for induction of that end-point. Corneas of anesthetized, four-month-old, opossums were exposed to 250 J m-2 (0.025 J cm-2) from a Westinghouse FS20 sunlamp either one or three times a week for up to 13 exposures. The corneas of 4-5 animals received either: (a) 90 min of PRL immediately prior to UVR; (b) PRL immediately following UVR; (c) PRL alone; or (d) UVR alone. Eyes were examined with a slit lamp microscope 24 hr following each exposure and scored for the appearance of opacification and neovascularization of the cornea. In animals exposed to UVR alone, 2-5 exposures, depending on whether the exposures were given once or three times per week, were required to obtain opacification and neovascularization in 50% of the irradiated corneas. The onset of both opacification and neovascularization in 50% of the corneas required 8-11 exposures when the UVR was immediately followed by PRL. Based on the specificity of photoreactivation repair to act solely on pyrimidine dimers, these observations suggest that UVR-induced pyrimidine dimers in corneal DNA are involved in UVR-induced opacification and neovascularization of the cornea of Monodelphis domestica.

Ultraviolet radiation-induced skin tumors in a South American opossum (Monodelphis domestica)

A total of 19 male and 21 female South American opossums (Monodelphis domestica) were exposed to 250 J/m2 ultraviolet radiation from FS-40 sunlamps (280-400 nm) three times weekly for 70 weeks. The backs of the opossums were shaved as necessary to remove hair. In order to prevent photoreactivation of ultraviolet radiation-induced pyrimidine dimers by the light-dependent photolyase enzyme of the opossum, ultraviolet radiation-exposed opossums were housed under red lights (600-800 nm). The opossum photolyase requires light in the 320-450 nm range for its activity. Twenty-nine control opossums (14 males and 15 females) were irradiated by fluorescent lights with emission spectra primarily in the visible light range (320-700 nm); these control opossums were also housed under red lights, and their backs were also shaved to remove hair. No skin tumors were observed in control opossums, while ultraviolet radiation-exposed opossums developed a variety of hyperplastic and neoplastic skin lesions on the backs and on a single ear. Hyperplastic lesions included foci of epithelial hyperplasia, dermal fibroplasia, and focal proliferation of dermal melanocytes. A total of 20 ultraviolet radiation-exposed opossums (50%) developed skin tumors, and 13 opossums (32.5%) had more than a single tumor. Epithelial tumors included 25 papillomas, four keratoacanthomas, seven carcinomas in situ, three microinvasive squamous cell carcinomas, two invasive squamous cell carcinomas, and a single basal cell tumor. Ten dermal spindle cell tumors also occurred; most of these appeared to be fibrosarcomas. Two benign melanomas and one malignant melanoma were observed.

Spectral comparison of solar simulators and sunlight

In evaluating sunscreen efficacy, spectral distribution of the irradiation sources can influence the sun protection factor (SPF). The purpose of this investigation was to examine the uniformity of ultraviolet (UV) spectral irradiance of solar simulators used in various SPF testing laboratories, compare them with natural sunlight UV radiation (UVR), and recommend performance limits to ensure that the variability of radiation sources in the UVB region minimally affects SPF estimates. The critical portion of the solar erythemogenic spectrum was identified as the UVB portion, defined as the region between 280 and 320 nm. The spectral irradiance of 26 solar simulators and other UV sources was measured and compared with a summer noon solar spectrum measured in Albuquerque, NM. Proposed spectral limits were developed as a 6-nm "acceptance band" centered on this standard spectrum normalized at 320 nm. The results indicated that the xenon-arc solar simulators currently used in the United States in testing sunscreens either meet the proposed standard solar spectrum or can be readily modified with available UV filters to meet this standard. The devices that have spectral characteristics not resembling sunlight fail to meet the proposed standard and should not be used for sunscreen SPF testing.

Photoreactivation of cyclobutane dimers and (6-4) photoproducts in the epidermis of the marsupial, Monodelphis domestica

Radioimmunoassays were used to investigate the repair of cyclobutane pyrimidine dimers and pyrimidine (6-4)pyrimidone photoproducts ((6-4] photoproducts) in the epidermis of the South American opossum, Monodelphis domestica. In the absence of photoreactivating light, both types of photodamage were excised with similar kinetics, 50% of the damage remaining 8 h after UV irradiation in vivo. Exposure of UV-irradiated skin to photoreactivating light resulted in removal of most of the cyclobutane dimers and an enhanced rate of (6-4) photoproduct repair. Photoenhanced excision repair of non-dimer damage increases the range of biologically effective lesions removed by in vivo photoreactivation.

Hypersensitivity of skin fibroblasts from basal cell nevus syndrome patients to killing by ultraviolet B but not by ultraviolet C radiation

Basal cell nevus syndrome (BCNS) is an autosomal dominant genetic disorder in which the afflicted individuals are extremely susceptible to sunlight-induced skin cancers, particularly basal cell carcinomas. However, the cellular and molecular basis for BCNS is unknown. To ascertain whether there is any relationship between genetic predisposition to skin cancer and increased sensitivity of somatic cells from BCNS patients to killing by UV radiation, we exposed skin fibroblasts established from unexposed skin biopsies of several BCNS and age- and sex-matched normal individuals to either UV-B (280-320 nm) or UV-C (254 nm) radiation and determined their survival. The results indicated that skin fibroblasts from BCNS patients were hypersensitive to killing by UV-B but not UV-C radiation as compared to skin fibroblasts from normal individuals. DNA repair studies indicated that the increased sensitivity of BCNS skin fibroblasts to killing by UV-B radiation was not due to a defect in the excision repair of pyrimidine dimers. These results indicate that there is an association between hypersensitivity of somatic cells to killing by UV-B radiation and the genetic predisposition to skin cancer in BCNS patients. In addition, these results suggest that DNA lesions (and repair processes) other than the pyrimidine dimer are also involved in the pathogenesis of sunlight-induced skin cancers in BCNS patients. More important, the UV-B sensitivity assay described here may be used as a diagnostic tool to identify presymptomatic individuals with BCNS.

Identification of the molecular target for the suppression of contact hypersensitivity by ultraviolet radiation

This study was conducted to explore the involvement of DNA damage in the suppression of contact hypersensitivity (CHS) by UV irradiation. The opossum, Monodelphis domestica, was used because cells of these marsupials have an enzyme that is activated by visible light (photoreactivating enzyme) and repairs ultraviolet radiation (UVR)-induced pyrimidine dimers in DNA. A single dose of 1,500 J/m2 of UVB (280-320 nm) radiation, representing 2 minimal erythema doses, was administered to the dorsal skin of opossums. This treatment prevented the opossums from developing a CHS response to dinitrofluorobenze (DNFB) applied either at the site of irradiation or an unirradiated site. In addition, this dose of UVR decreased the number of ATPase+ epidermal Langerhans cells in the dorsal epidermis to approximately 3% of that in unirradiated skin at the time of DNFB application. Treatment of the animals with wavelengths that activate the repair enzyme (320-500 nm, photoreactivating light, PRL) for 120 min immediately after UV irradiation inhibited the UVR-induced suppression of CHS almost completely. Exposure to PRL before UVR did not prevent UVR-induced suppression of CHS. PRL treatment after UV irradiation also prevented the decrease in the number of ATPase+ Langerhans cells. Measurements of lesions in DNA indicated that PRL treatment removed around 85% of the UVR-induced pyrimidine dimers. These data provide direct evidence that DNA, and most likely, the pyrimidine dimer, is the primary molecular target for the UVB-induced suppression of contact hypersensitivity to haptens applied to irradiated or unexposed skin.

Ultraviolet radiation--induced malignant melanoma in Monodelphis domestica

Several lines of evidence support the hypothesis that ultraviolet radiation (UVR) is involved in the etiology of cutaneous melanoma in humans. However, progress in understanding the mechanisms involved in induction of melanotic tumors by UVR has been hindered by lack of a suitable animal model. During the course of multiple exposures (3 times/wk for 70 wk) of the South American opossum, Monodelphis domestica, to UVR, we first observed the appearance of areas of dermal melanocytic hyperplasia (MH) on the exposed skin. Post-UVR exposure to photoreactivating light (320-500 nm) suppressed the occurrence of MH. We also observed at 100 weeks from first exposure that 10 of 46 surviving animals had developed melanotic tumors which arose, presumably, from areas of MH. Tumors on three of the 10 animals have been classified as malignant melanomas based on metastasis to lymph nodes. We conclude from these results that UVR can act as a complete carcinogen for melanoma induction and, based on the photoreactivation of MH induction, that DNA damage is involved in melanoma formation.

Excision repair characteristics of denV-transformed xeroderma pigmentosum cells

Introduction of the denV gene of phage T4, encoding the pyrimidine dimer-specific endonuclease V, into xeroderma pigmentosum cells XP12RO(M1) was reported to result in partial restoration of colony-forming ability and excision repair synthesis. We have further characterized 3 denV-transformed XP clones in terms of rates of excision of pyrimidine dimers and size of the resulting resynthesized regions following exposure to 100 J/m2 from an FS-40 sunlamp. In the denV-transformed XP cells we observed 50% dimer removal within 3-6 h after UV exposure as compared to no measurable removal in the XP12RO(M1) line and 50% dimer excision after 18 h in the GM637A human, control cells. Dimer removal was assayed with Micrococcus luteus UV-endonuclease in conjunction with sedimentation of treated DNA in alkaline sucrose gradients. The size of the resulting repaired regions was determined by the bromouracil photolysis technique. Based on the photolytic sensitivity of DNA repaired in the presence of bromodeoxyuridine, we calculated that the excision of a dimer in the GM637A cells appears to be accompanied by the resynthesis of a region approximately 95 nucleotides in length. Conversely, the resynthesized regions in the denV-transformed clones were considerably smaller and were estimated to be between 13 and 18 nucleotides in length. These results may indicate that either the endonuclease that initiated dimer repair dictated the size of the resynthesized region or that the long-patch repair observed in the normal cells resulted from the repair of non-dimer DNA lesions.

Photoreversal of the ultraviolet radiation-induced disappearance of ATPase-positive Langerhans cells in the epidermis of Monodelphis domestica

The present study was undertaken to explore the possible causes of ultraviolet radiation (UVR)-induced disappearance of ATPase-positive, epidermal Langerhans cells (LC). Monodelphis domestica was used because it has the capacity for photoreactivation of UVR-induced pyrimidine dimers in epidermal DNA. Single, 330 J/m2 (ears) or 500 J/m2 (back) UVR exposures (FS-40 sunlamps) reduced the numbers of ATPase-positive epidermal LC in M. domestica ears to approximately 15% of those in unirradiated ears and approximately 37% of those in unirradiated dorsal skin. Immediate 90-minute exposures to photoreactivating light (PRL, 320-400 nm) post-UVR reversed the effects of UVR, resulting in ATPase-positive LC numbers not being significantly different from controls. Exposure to PRL immediately preceeding UVR did not prevent ATPase-positive LC disappearance. The photoreactivation of UVR-induced ATPase-positive LC disappearance indicates that DNA damage (pyrimidine dimers) is involved in the loss of ATPase-positive LC.

Sunscreen protection against UV-induced pyrimidine dimers in DNA of human skin in situ

We have determined the ability of a chemical sunscreen with a sun protection factor (SPF) of 15 to protect human skin from ultraviolet (UV) radiation-induced DNA damage. The DNA damage was susceptible to cleavage by Micrococcus luteus UV endonuclease, which recognizes pyrimidine dimers in DNA. An alkaline agarose gel electrophoresis method was used to quantify the number of pyrimidine dimers in nonradioactive DNA from skin biopsies of 5 individuals irradiated with UV from a solar simulator. After exposure to an equivalent dose of UV, the number of pyrimidine dimers was 0.8 per 10(7) bases in sunscreen-treated skin as compared with 32 dimers per 10(7) bases in untreated skin. This assay provides a means of determining the efficacy of sunscreens in protecting skin from UV-induced DNA damage.

Photorepair of ultraviolet radiation-induced pyrimidine dimers in corneal DNA

The induction and photorepair of pyrimidine dimers in DNA have been measured in the ultraviolet-irradiated, corneal epithelium of the marsupial, Monodelphis domestica, using damage-specific nucleases from Micrococcus luteus in conjunction with agarose gel electrophoresis. We observed that FS-40 sunlamps (280-400 nm) induced 7.2 +/- 1.0 X 10(-5) pyrimidine dimers per kilobase (kb) of DNA per J/m2. Following 100 J/m2, 50% and greater than 90% of the dimers were photorepaired during a 10- and 30-min exposure to photoreactivating light (320-400 nm), respectively. In addition, approximately 70% and approximately 60% of the dimers induced by 300 and 500 J/m2, respectively, were repaired by a 60-min exposure to photoreactivating light. The capacity of the corneal epithelium of M. domestica to photorepair pyrimidine dimers identifies this animal as a potentially useful model with which to determine whether pyrimidine dimers are involved in pathological changes of the irradiated eye.