INDUCTION OF SKIN TUMORS IN THE RAT BY SINGLE EXPOSURE TO ULTRAVIOLET RADIATION

Abstract— The dose response for tumor induction in albino rat skin by single exposures of UV radiation has been characterized. The shaved dorsal skin of 202 animals was exposed to either of two sources: one emitting a broad spectrum of wavelengths from 275 to 375 nm, and the other emitting at 254 nm. Skin tumors began to appear within 10 weeks of exposure and continued to appear for 70 weeks. The highest tumor yield was 5.5 tumors per rat and occurred when the rats were exposed to 13.0 times 10⁴ J/m² of the 275–375 nm UV. The 275–375 nm UV was about eight times as effective as the 254 nm UV for the induction of tumors throughout the exposure range from 0.8 times 10⁴ to 26.0 times 10⁴J/m². Tissue destruction and hair follicle damage was found at the highest exposure to 275–375 nm UV but at none of the exposures to 254 nm UV. Repeated weekly exposures to 275–375 nm UV proved less effective than an equivalent single exposure for inducing tumors, even though the multiple exposures caused more severe skin damage. The transmission of the UV through excised samples of rat epidermis indicated that the exposure to the basal cell layer was about 3% of the surface exposure at 254 nm and about 15% of the surface exposure between 275 and 320 nm. The dependence of tumor yield on UV exposure was linear for 254 nm UV but was more complex for the 275–375 nm UV. For the latter more tumors were produced per unit exposure at lower exposures than at higher exposures.     

THE EFFECTS OF ULTRAVIOLET RADIATION EXPOSURE OF ADJACENT CELLS ON PLAQUE FORMATION WITH Herpes simplex VIRUS TYPE I

African green monkey kidney cells (CV-1P) were exposed to low fluences of 254 nm germicidal radiation and then infected with Herpes simplex virus, type I. The result of this treatment was an increase in viral plaque development rate, the large plaque effect (LPE). A measurement of the kinetics of plaque development suggested that a large portion of the effect could be due to events occurring in those cells that are adjacent to the initially infected cell. An infectious center assay was employed in order to isolate the effects of ultraviolet radiation (UV) on the initially infected cells from those effects on the adjacent cells that became infected as the plaque spread radially outward. Plaque development began earlier in UV irradiated cells and progressed at a uniformly accelerated rate compared to untreated cells. Results indicate that although the initially infected cell contributes to the LPE, the major effect is due to events that occur in the adjacent cells. Each round of viral replication appears to contribute equally to the LPE. The virally induced rate of fusion of the initially infected cell with its immediate neighbors is not affected by UV.     

INHIBITION OF THE IMMUNE RESPONSE TO ALLOANTIGEN IN THE RAT BY EXPOSURE TO ULTRAVIOLET RADIATION

Exposure of mice to ultraviolet radiation (UV) followed by alloantigen sensitization can suppress the immune response to that alloantigen. In order to assess the applicability of using UV-induced immunosuppression in organ transplantation, the effectiveness of UV in prolonging the survival of vascularized organ allografts must be determined. Because, for technical reasons, rats are better suited than mice for such experiments, we first wanted to determine whether UV suppresses the immune response of inbred rats to alloantigens. The data presented here demonstrate that exposure of rats to UV (115-129 kJ/m2) prior to alloantigenic sensitization decreases the mixed lymphocyte response to alloantigen. The depression of the proliferative response to alloantigen was selective in that spleen cells from the UV-treated rats could respond to mitogenic stimulation. In contrast to previous results with mice, suppressor cells could not be demonstrated in the spleens of the UV-treated rats. In addition, UV treatment after sensitization inhibited the response to alloantigen. These data suggest that treatment of the recipient with UV before or after alloantigenic sensitization may provide a novel method of inhibiting immune responses to allogeneic antigens.     

SKIN DAMAGE IN ADULT AMPHIBIANS AFTER CHRONIC EXPOSURE TO ULTRAVIOLET RADIATION

Abstract— The effects of repeated UV exposure on the skin of the European crested newt, Triturus cristatus carnifex , have been investigated. The animals were irradiated 3 times per week with a Westing-house FS40T12 fluorescent sun lamp (wavelength spectrum 275–350 nm). Two groups of animals received the same total fluence of 1.3 × 10⁵ J/m² in single fluences of either 1570 J/m² (group A) or 9430 J/m² (group C), and one group received a total fluence of 2.6 × 10⁵ J/m² in single fluences of 4710 J/m² (group B). All the animals were killed 7 months after the first UV exposure, but at different intervals after the last exposure. Striking epidermal hyperplasia was found in the newts irradiated at the lower fluence rate (group A). In the animals given the higher total fluence (group B), the most prominent skin changes were dermal fibrosis and irregular thinning and thickening of the epidermis. No significant skin changes were found in group C., in which if there had been UV lesions, they had been repaired during the 5 month interval between the last irradiation and the killing of the animals. No skin tumors developed in any experimental group.     

ENHANCEMENT OF INTRINSIC ANTITUMOR ACTIVITY IN SPORE-ENDOTOXIN MIXTURES OF Bacillus thuringiensis BY EXPOSURE TO ULTRAVIOLET RADIATION

Abstract— Irradiation of spore-endotoxin mixtures from Bacillus thuringiensis cultures at 254 nm (60 μW cm^-2) enhances their intrinsic antitumor potency as well as that of either component. The extent of enhancement depends on the length of exposure (optimum: 35 min) and may thus be due to photochemical changes of the endotoxin protein or/and to photoproduction of additional compounds with antitumor activity. Antitumor effects, expressed as survival rates of C57BL/6 mice inoculated with Lewis' mouse lung carcinoma and subjected to treatments 24 h later, depended on the number of doses of preparations administered (mixture, separated components).     

A DOSIMETRIC TECHNIQUE FOR THE MEASUREMENT OF ULTRAVIOLET RADIATION EXPOSURE TO PLANTS

Abstract Due to the effects of geometry, orientation, atmospheric conditions and optical properties of leaves and soils, the UV exposure to a plant may differ significantly from that of ambient radiation. This paper presents a method utilizing a passive measuring technique with polysulfone dosimeters that provides the ability of measuring the UV exposure at a number of sites simultaneously. The UV exposures are measured at selected sites over models of three canopy shapes with a computer program interpolating and summing these to provide the total UV exposure incident on the canopy.     

EFFECTS OF in vitro EXPOSURE TO ULTRAVIOLET RADIATION ON THE FUNCTIONAL ACTIVITY OF LYMPHOCYTES, WITH EMPHASIS ON SUSCEPTIBILITY OF DIFFERENT SPECIES

Abstract In this study lymphocytes from blood and/or spleen of different species (rat, mouse, human) were exposed to different doses of ultraviolet radiation (UVR). The functional activity of these lymphocytes was determined using assays for mitogen proliferation and the mixed lymphocyte response (MLR). These experiments demonstrated that in vitro exposure to UVR causes a dose-dependent decrease of the MLR activity of the irradiated lymphocytes. Viability of lymphocytes and mitogen proliferation responses were also decreased by UVR exposure but less severe in comparison to the MLR. Lymphocytes of rats seem to be more sensitive to UVR as compared to lymphocytes of mice and humans.     

SUPPRESSION OF THE INDUCTION OF DELAYED-TYPE HYPERSENSITIVITY REACTIONS IN MICE BY A SINGLE EXPOSURE TO ULTRAVIOLET RADIATION

Abstract— After a single exposure of mice to UV radiation, their ability to generate a contact hypersensitivity (CHS) response to contact sensitizers applied epicutaneously to distant, unirradiated skin is severely impaired. It is not clear, however, if the classic delayed type hypersensitivity (DTH) reponse to exogenous antigens, injected into the subcutaneous (s.c.) space, can also be modulated by UV radiation. We report here that a single exposure of mice to UV radiation suppressed the induction of DTH to both erythrocyte and soluble protein antigens injected s.c., but did not suppress the elicitation of the response. The suppressive effect was abrogated by cyclophosphamide treatment. In addition, antigen-specific suppressor cells were found in the spleens of the mice with a decreased DTH response. Since the ability to mount a DTH response has been linked with the resistance to certain pathogenic microorganisms, we suggest that the suppression of DTH by UV radiation may have the potential to compromise host resistance to such infectious agents.     

EFFECTS OF ULTRAVIOLET RADIATION ON THE IMMUNE SYSTEM IN HUMANS

In experimental animals, exposure to UV-B radiation produces selective alterations of immune function which are mainly in the form of suppression of normal immune responses. This immune suppression is important in the development of nonmelanoma skin cancer, may influence the development and course of infectious disease and possibly protects against autoimmune reactions. The evidence that this form of immune suppression occurs in humans is less compelling and very incomplete. The wavelengths of radiation most affected by a depletion of the stratospheric ozone layer are those known to be most immunosuppressive in animals and it is likely that such depletion will increase any suppressive effect of sunlight on immunity in humans. In addition to establishing whether or not UV-B radiation can cause suppression of immune function in humans, studies are required to determine if melanin can provide protection against such suppression, the role of this suppression in the pathogenesis of skin cancer, the development of infectious disease and vaccine effectiveness, and the capacity for humans to develop adaptive, protective mechanisms which may limit damage from continued exposure to UV-B radiation.     

EXPOSURE TO LONG WAVELENGTH ULTRAVIOLET RADIATION DECREASES PROCESSING OF LOW DENSITY LIPOPROTEIN BY CULTURED HUMAN FIBROBLASTS

Exposure of MRC5 human fibroblasts to UVA radiation (365 nm) resulted in a dose-dependent decrease in low density lipoprotein (LDL) uptake and degradation by cells. Following a 25 J/cm² irradiation dose, about 45% and 70% reduction in ¹²⁵I-LDL uptake and degradation were observed, respectively. Under the same conditions, the ¹⁴C-sucrose uptake was also decreased to about the same extent as LDL uptake. Cell pretreatment with the antioxidants vitamin E and vitamin C did not prevent the UVA-induced fall in LDL degradation. These results point to the possible effects of UVA radiation on receptor-mediated and nonspecific uptake of exogenous molecules. With special regard to the alterations in receptor-mediated processing of exogenous ligands, such a phenomenon could be of importance in UVA-induced skin degenerative processes.     

ACTIVATION OF THE HUMAN IMMUNODEFICIENCY VIRUS PROMOTER BY UVA RADIATION IN COMBINATION WITH PSORALENS OR ANGELICINS

Abstract— The effects of mono- and bifunctional furocoumarins plus UVA radiation (PUVA and related treatments) on the human immunodeficiency virus-1 (HIV-1) promoter were studied using HeLa cells stably transfected with the chloramphenicol acetyl transferase gene under the control of the HIV-1 promoter. The experiments were performed with three psoralens (5-methoxypsoralen, 5-MOP; 8-methoxypsoralen, 8-MOP; and 4′-aminomethyl-4,8,5′-trimethyl-psoralen, AMT) and four angelicins (angelicin; 4,5′-diniethylangclicin, 4,5′-DMA; 6,4′-dimethylangelicin, 6,4′-DMA; and 4,6,4′-trimethylangelicin, TMA). The drugs alone and UVA radiation alone showed no erect on the HIV promoter. However, when the cells were incubated with the furocoumarins at 0.1–40 μg/mL and then irradiated. the HIV promoter was activated in distinct fluence ranges, i.e. (1) no promoter activity was discernible at low fluences (e.g. at 0.1 μg/mL of 8-MOP up to 100 kJ/m²), (2) as the fluence was increased, the promoter activity increased to reach a maximum (10–50-fold with respect to the unexposcd samples), and (3) as the fluence was further increased, the promoter activity decreased. Similar (although shifted on the fluence scale) pattcrns were observed with either > 340-nm UVA radiation or with UVA radiation contaminated with a small amount of UVB radiation (typical for PUVA lamps). The effective fluences were inversely related to the drug concentration. Experiments with 5-MOP and 8-MOP indicated reciprocity of the drug concentration and radiation hence. The HIV promoter response patterns were similar for monofunctional angelicins and bifunctional psoralens. This indicated that the furocoumarin-DNA crosslinks are not a prerequisite for the promoter activation and that the monoadducts suffice to elicit the HIV promoter response. The HIV promoter-activating effectiveness of diKcrent drugs correlated with their photosensitizing potential. Thus, among psoralens the effectiveness order was AMT >. 5-MOP >8-MOP, and among angelicins: TMA > 6,4′-DMA > 4,5′-DMA > angelicin. The ektiveness did not vary substantially for 5-MOP, 8-MOP, 4,5′-DMA, and 6,4′-DMA. The combined drug and UVA radiation doses were higher than those that elicit cellular responses or those that may be received by the human white blood cells during cxtracorporeal PUVA therapy (photopheresis).     

PHOTOREACTIVATION OF ICR 2A FROG CELLS AFTER EXPOSURE TO MONOCHROMATIC ULTRAVIOLET RADIATION IN THE 252–313 nm RANGE

Abstract— Exposure of ICR 2A frog cells to photoreactivating light after treatment with monochromatic ultraviolet (UV) radiation in the 252–313 nm range resulted in an increase in survival with similar photoreactivable sectors for each of the wavelengths tested. As photoreactivating enzyme is specific for the repair of pyrimidine dimers in DNA, these findings support the hypothesis that these are critical lesions responsible for killing of cells exposed to UV radiation in this wavelength range. The action spectra for cell killing and production of UV-endonuclease sensitive sites were similar to the DNA absorption spectrum though not identical. Because the number of endonuclease sensitive sites is a reflection of the yield of pyrimidine dimers, these data also suggest that the induction of dimers in DNA by UV radiation in the 252–313 nm range is the principal event leading to cell death.     

EVALUATION OF SKIN CANCER RISK RESULTING FROM LONG TERM OCCUPATIONAL EXPOSURE TO RADIATION FROM ULTRAVIOLET LASERS IN THE RANGE FROM 190 TO 400 nm

The relative risk of occupational exposure to radiation from UV lasers was estimated using a mathematical model based on both epidemiological data and animal experiments. Calculations were performed for the 193 nm ArF excimer laser cornea shaping, the 308 nm XeCl excimer laser for coronary angioplasty, and other UV lasers in a laboratory environment. The model included the effects of direct exposure and exposure to scattered radiation. The results show that for the two medical applications the increase in the relative risk is comparable to that of one additional day of sunbathing per year. For subjects exposed to UV lasers in a laboratory setting, the relative risk may increase to a value comparable to that of people with an outdoor profession.     

INHIBITION OF 12-O-TETRADECANOYLPHORBOL-13-ACETATE-INDUCED TUMOR PROMOTION IN MURINE SKIN BY SYSTEMIC EFFECTS OF ULTRAVIOLET IRRADIATION

Systemic effects of UVB irradiation (280-320 nm) have been shown to prevent subsequent chemical tumorigenesis induced by an initiation-promotion protocol. The present investigation was designed to determine whether initiation or promotion is prevented by UV irradiation. Groups of 25 B6D2F1/J mice received 12 weeks of intermittent dorsal UVB radiation treatments administered before, or 3 weeks after, initiation with a single application of 7,12-dimethylbenz[a]anthracene on the ventral skin. All mice were promoted ventrally with 5 micrograms 12-O-tetradecanoylphorbol-13-acetate (TPA) applied three times weekly throughout the experiment. UV irradiation consisted of five 30-min exposures per week to a bank of 6 Westinghouse FS40 sunlamps. UV irradiation applied before or after initiation resulted in a decrease of 18-16 tumors per group of 25 mice, for a reduction of 61 and 50%, respectively, at 24 weeks after the first TPA treatment. Thus, prevention of tumor development was similar whether the UV influence was present or not during initiation. This finding suggests that the UV prevention of promotion could account for UV inhibition of skin tumors induced by an initiation-promotion regimen. Consistent with this concept, pretreatment of mice with dorsal UVB radiation was found to reduce DNA synthesis after exposure to TPA by 46%, although it did not decrease tritiated benzo[a]pyrene binding to DNA, in ventral epidermis. Thus, UVB irradiation systemically reduced TPA-induced tumor promotion in murine skin.     

MINIMUM DOSES OF ULTRAVIOLET RADIATION REQUIRED TO INDUCE MURINE SKIN EDEMA and IMMUNOSUPPRESSION ARE DIFFERENT and DEPEND ON THE ULTRAVIOLET EMISSION SPECTRUM OF THE SOURCE*

Many photoimmunological studies have used UV radiation sources that emit nonsolar UV spectral energy and UV doses based on nonimmunological endpoints, e.g. erythema and skin edema. Interpretation of these data has led to misunderstanding when extrapolated to hypothetical effects in humans exposed to solar UV. The purpose of this study was to: (1) establish UV dose response relationships for murine skin edema and immunosuppression, and (2) determine how different UV spectra affect these relationships. Back skin and ear minimum edema doses (MEdD) for Kodacel-filtered FS20 sunlamp UV (290–400nm) were greater than two-fold higher than those for unfiltered FS20 sunlamp UV (250–400nm). Xenon arc solar simulator UV (295–400nm) MEdD were > 10-fold higher than those for unfiltered sunlamp UV. Back skin and ear MEdD differed two- to five-fold between C3H/ HeN, SWR/J and HRA/Skh-1 mice. The minimum immunosuppression doses (MISD) in C3H mice showed similar UV source spectrum dependence. The solar simulator UV MISD was 5.4- and 1.5-fold higher than for unfiltered and Kodacel-filtered sunlamp UV MISD, respectively. Furthermore, MISD were from 3- to 50-fold higher than the MEdD for the three UV sources. The UV bioeffectiveness spectra indicated that UVC energy (250–290nm) contributed 12% and 18%, respectively, of the total skin edema and immunosuppression UV energy. These data demonstrate the variability in UV sensitivity among mouse strains, the significant differences between murine MEdD and MISD and how these differences are influenced by nonsolar regions (below 295 nm) of the UV spectrum.     

IN ACTIVATION OF A STRAIN OF TOBACCO NECROSIS VIRUS AND OF THE RNA ISOLATED FROM IT, BY ULTRAVIOLET RADIATION OF DIFFERENT WAVE-LENGTHS

Abstract— A train of tobacco necrosis virus (TNV) and infective nucleic acid isolated from it (TNV-RNA) are equally susceptible to inactivation by U.V. radiation at all wave-lengths tested (230-290 m_μ) and can be photoreactivated to the same extent by exposing inoculated host plants to daylight. The shape of the action spectrum for inactivation by U.V. of TNV and of TNV-RNA follows that of the absorption spectrum of TNV-RNA. Thus, unlike the RNA of tobacco mosaic virus, the RNA of TNV behaves in all these respects in the same way irrespective of whether it is inside or outside the virus particle. To inactivate TNV or TNV-RNA to 50 per cent of their original infectivities, each mg of RNA must absorb about 0.27 joules of radiation energy of any wave-length between 230 and 290 mp, which corresponds to a quantum yield of about 0.65 ×10^-3 at 260 mμ.     

EFFECTS OF ULTRAVIOLET RADIATION ON THE MITOTIC CYCLE AND DNA, RNA AND PROTEIN SYNTHESIS IN MAMMALIAN EPIDERMIS IN VIVO

Abstract— Acute effects of ultraviolet radiation on the mitotic cycle and macromolecular synthesis were investigated on hairless mouse epidermis in vivo. Colcemid was used to arrest mitoses in metaphase and thus allow more accurate mitotic counts. The radioactive tracers, TdR-³H, cytidine-³H, and the amino acids, histidine-³H and methionine-³H were used to examine DNA, RNA and protein synthesis, respectively. Using these techniques, we found that wavelengths shorter than 320 nm markedly inhibited mitosis, increased the basal cell turnover time and depressed DNA, RNA and protein synthesis within the first few hours post-irradiation. By 24hr, recovery and acceleration of these functions were in progress, reaching a peak by 48–72 hr and persisting though to a lesser degree for 7 days. This stage of acceleration was associated with epidermal hyperplasia and most likely represented post-injury cell renewal.