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.