Potent Carcinogenicity of Uncovered Halogen Lamps in Hairless Mice'

ICANCER RESEARCH54, 5081-5085, October 1, 1994 Potent Carcinogenicity of Uncovered Halogen Lamps in Hairless Mice'

Francesco D'Agostini and Silvio De Flora2 Instituteof Hygieneand PreventiveMedicine.Universityof Genoa.1-16132Genoa,Italy

ABSTRACT posed animals versus 0% of unexposed controls and of animals exposed to glass-covered lamps. Uncovered halogen quartz lamps, which are potently genotoxic both in prokaryotic and human cells due to the emission of far-UV radiation (UVB and UVC), were assayed for carcinogenicity In three strains of MATERIALS AND METHODS hairless mice (SKH-1, MF-1, and C3H) of both sexes. As assessed In 5 Independent experiments, no spontaneous skin tumor was observed, even Three strains of hairless mice, i.e., 5}CJ.I.1albino (Charles River Italia, after more than 2 years, in 49 animals used as unexposed controls or In 29 Calco, Como, Italy), MF-1/Ola/Hsd albino, and C3HTFif-pigmented mice animals exposed to halogen lamps equipped with a common glass cover. In (both from Nossan, Correzzana, Milano, Italy) were used. Four-week-old contrast, almost all of the 185 mice exposed to the light emitted by animals, weighing 25â€”30g, were acclimatized for 10 days and randomly divided into groups, as indicated in Table 1. They were housed 4â€”5/makrolon low-voltage (12 V) and low-power (SO W) tungsten bulbs, equipped with cage, given mouse chow and tap water ad libitum, and maintained dichroic diffusers, contracted multiple skin tumors of various histological under controlled temperature (27 Â±1Â°C)andrelative humidity (50 Â±5%) type, both benign and malignant Tumors were induced over a range of conditions. illuminance levels (1,000, 3,333, 5,000, and 10,000 lux) and daily exposure Control animals were kept under natural 12 h dark/12 h light cycle (win times (1.5, 3, 6, and 12 h). The tumor latency times were quite short and dow-filtered daylight). All remaining mice were exposed under the various significanfly correlated with the daily exposure limes, as well as with the experimental conditions detailed in Table 1 to the light emitted by spotlights square of the distance (46â€”194cm)from the illumination source. A equipped with dichroic diffusers incorporating tungsten halogen quartz lamps carcinogenic effect was even observed when exposure was discontinued (12 V, 50 W) Model M50; Thorn Lighting Ltd., United Kingdom). Each cage wellbefore the appearance of skin lesions.Both in vitrogenotoxicitydata was illuminated by a single spotlight. The halogen bulbs were replaced every and animal carcinogenkity data support the view that the light emitted by 6 months. The mice of three experimental groups were exposed to the light of uncovered halogen lamps, to which an enormous number of individuals quartz bulbs protected with a 2-mm-thick common glass cover, positioned 5 are exposed, may pose carcinogenic risks to humans. Without renouncing mm below the lamp in order to allow air circulation and to prevent overheating. the benefits of this modern illumination system, UV-blockingdevices illuminance levels, which were not modified by the glass cover, were meas should be compulsory. tired on the bottom of each cage by using an electronic luxmeter (Model 1300/V; ICE, Milano, Italy). The animals were examined daily for survival and once a week for the score INTRODUCTION of skin lesions. The skin tumor yield is reported both in terms of prevalence (i.e., the percentage of tumor-bearing mice among surviving animals) and Halogen lamps provide a modern and attractive illumination system multiplicity (i.e., the mean number of tumors/mouse). Representative skin which is used more and more extensively in many countries at home, lesions of mice, either dead as a consequence of the disease or killed in an in offices, and in shops. Therefore, humans may be heavily exposed advanced stage of development of tumors, were excised, fixed in 10% forma to the light emitted by this kind of lamp, often for several hours a day lin, and embedded in paraffin, and then tissue sections were stained with and at relatively high illuminance levels, e.g., when halogen quartz hematoxylin and eosin. The histological type of tumors was defined according bulbs are installed in desktop lamps or are incorporated into dichroic to the classification proposed by Gallagher et a!. (5). diffusers used as multiple spotlights. We demonstrated previously that The comparison of survival curves for the different experimental groups was made by x2 analysis on data recorded every 5 weeks. Correlation (r) the light emitted by uncovered halogen lamps is potently mutagenic in coefficients and their statistical significance were calculated for evaluating the hisSalmonella typhimurium strains (1) and genotoxic in Escherichia relationships between tumor formation and (a) dose of absorbed light (illumi coli strains lacking DNA repair mechanisms, especially excision nance), which varied depending on the distance from the halogen lamp, (b) repair and SOS repair pathways (2). A clastogenic effect was pro daily exposure time, and (c) duration of exposure. duced in vitro by halogen lamps in human cells, as shown by the Animal care was in accord with our national guidelines, and mice did not increase of micronucleus frequency in cultured peripheral blood lym receive any treatment other than exposure to the illumination system under phocytes (3). Moreover, the results of a small pilot study with 12 study. hairless mice suggested that halogen quartz bulbs are inducers of skin tumors (4). All the investigated genotoxic and carcinogenic effects RESULTS could be totally prevented by covering the quartz bulbs with common glass sheets (1â€”4). Table 1 summarizes the results of five independent experiments Here we report the results of extensive carcinogenicity assays, involving the use of a total of 243 hairless mice of 3 strains (SKH-1, providing sound evidence for the dose- and time-related skin carci MF-1, and C3H), both males and females, exposed to various light nogenicity of this illumination system, which induces multiple skin intensity and time conditions. The minimum, median, and maximum tumors of various histological types in hairless mice within a short latency periods, corresponding within each group to the lag times latency period and with a prevalence of virtually 100% among cx needed for the macroscopical appearance of tumors in the earliest animal, in 50% of the animals and in the last animal, respectively, are Received 4/18/94; accepted 8/1/94. also reported. The costs of publication of this article were defrayed in part by the payment of page No spontaneous skin tumor could be observed in our experiments, charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. as shown by the absolute lack of lesions in the 49 mice used as I This study was funded in part by the Italian Ministry for University and Scientific controls (4 SKH-1, 40 MF-1, and 5 C3H) and in the 29 mice exposed Technological Research (40 and 60% grants) and by the CNR Targeted Project â€œPreven to glass-covered halogen lamps (4 5KB-i, 20 MF-1, and 5 C3H), tion and Control of Disease Factors-FATMA.â€• 2 To whom requests for reprints should be addressed, at Institute of Hygiene and even after observation for more than 2 years since the start of the Preventive Medicine, University of Genoa, via Pastore 1, 1-16132Genoa, Italy. experiments. 5081

miceExperimentStrainMice Table 1Outline of thecarcinogenicitv experimentsperformedwith halogen lamps in hairless (weeks)Illuminance conditionsSkin tumorsLatencyperiod

Multiplicity Cycle (% of tumor- (mean no. of tumors/mice)MinimumMedianMaximumISKH-lFSexNo.Exposure (lux)Glass cover (h/day)Time(weeks)Prevalencebearing mice) 4 a 0 0 >122 4 10,000 Yes 12 122 0 0 >122 4 10,000 No 12 36 100 18.5 16 21 24 2 SKH-l F 5 10,000 No 12 35 100 20.2 20 23 26 5 10,000 No 6 52 100 15.0 28 39 41 5 10,000 No 3 63 100 11.0 40 45 58 5 10,000 No 1.5 63 100 3.4 52 58 66 3 SKH-l F 5 10,000 No 12 16 100 8.2 25 30 35 5 10,000 No 12 20 100 14.2 23 26 38 5 10,000 No 12 24 100 15.4 22 27 34 5 10,000 No 12 28 100 20.4 24 28 31 5 10,000 No 12 40 100 21.0 21 25 31 4 MF-I M 20 â€” 0 0 >121 20 10,000 No 12 39 100 15.6 23 29 34 MF-l F 20 â€” 0 0 >121 20 10,000 Yes 12 121 0 0 >121 40 10,000 No 12 52 100 11.8 23 29 51 20 3,333 No 12 102 100 10.9 58 75 93 20 1,000 No 12 121 66.7 1.3 101 107 >121 5 C3H F 5 - 0 0 >58 5 10,000 Yes 12 58 0 0 >58 8 10,000 No 12 46 100 6.4 29 34 44 8 5,000 No 12 58 100 10.0 41 45 50

a Dashes indicate non-exposure to halogen lamps. @@ In contrast, almost all of the 185 mice exposed to tungsten few regressions of lesions were noted. Fig. 2 shows an example @ halogen lamps at illuminance levels ranging between 1,000 and time-related evolution of skin lesions in a MF-1 mouse exposed 10,000 lux, for daily cycles ranging between 1.5 and 12 h, and for an uncovered halogen lamp. @@@@@ periods ranging between 16 and 121 weeks, contracted multiple As evaluated by x@analysis on data recorded every 5 L i @@@@@@@@@ skin tumors. Fig. 1 shows at a glance the striking difference in the was no statistically significant difference in survival between @ appearance of SKH-l mice exposed to the light of either uncovered mice and mice exposed to 10,000 lux with glass covers, or to I i@ @@@@ or covered halogen quartz bulbs. In general, the skin lesions were ered lamps at illuminance levels of 5,000, 3,333, or 1,000 lux. I) i @@@@@@ initially detected either as erythematous areas or directly as papu the massive occurrence of skin tumors, survival was i i tI I @@@@@@@@@@@@ lae and noduli, which in some cases tended to become eroded and decreased only in groups of mice exposed to 10,000 lux \ @@@@@ ulcerated. The tumors increased both in number and size with time lamps) for 12 h/day. Interim killings were also performed i and often became confluent, thereby hampering an accurate enu groups for histological analyses. @@@ meration in late stages. Skin tumors of large size (up to 4.1 cm in The histological nature of skin lesions in the three mouse i i i @@@@@@@@ diameter and 10.2 g in weight) were recorded in several cases. A was evaluated in experiments 1, 4, and 5. Some i

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Fig. 1. Appearance of skin lesions induced by uncovered halogen tungsten lamps in female SKH-1 hairless mice after 8 months of exposure, 12 h/day, to the light by dichroic lamp incorporating a 12 V. 50 W halogen quartz bulb, either uncovered (left) or covered (right) with a glass sheet (see Table 1; experiment 1). 5082

WEEK 29 \\kNK @1

@@@@ \\â€˜FiFIK:@ \\[1@K @5 \\â€˜[IIK Fig. 2. Time-related evolution of skin lesions in a MF-1 hairless mouse exposed 12 h/day to the light emitted by an uncovered dichroic lamp incorporating a 12 V, 50 W halogen quartz bulb.

recorded among SKH-1 (38 lesions analyzed after 36 weeks of expo the bottom of cages. It is evident, as also indicated in Table 1, that the sure), MF-1 (110 lesions after 40 weeks), and C3H mice (42 lesions latency tumor-induction time tended to increase by lowering the after 58 weeks). In particular, in these three mouse strains we ob illuminance levels. Moreover, after appearance of the earliest lesions, served epidermal hyperplasias (21.1, 31.9, and 38.1%), papillomas the growth of both tumor multiplicity and prevalence was slower in (3L6, 12.0, and 19.0%), actinic keratosis (2.6, 6.1, and 7.1%), kera the low-exposure groups. Some fluctuations in the curves represented toacanthoma-like tumors (5.3, 4.7, and 4.7%), appendage-basal tu mors (10.5, 8.1, and 16.6%), carcinomas in situ (5.3, 24.1, and 7.1%),

@ and squamocellular carcinomas (23.7, 12.9, and 7.1%), respectively. 14 Overlapping â€˜ , Overlapping Furthermore, a few areas of atypical melanocyte proliferation were 12 lesions I o 10,000lux 1 lesions also observed in C3H mice. @@ 10 3333lux@ A 100% prevalenceof tumorswas observed in all groups of mice C., 8 (totaling 69 animals) exposed to uncovered halogen lamps for 12 0@ h/day at an illuminance level of 10,000 lux. The rank of sensitivity of the three mouse strains was SKH-1 > MF-1 > C3H, as shown by multiplicity values of 18.5 (experiment 1), 20.2 (experiment 2), and 2 21.0 (experiment 3) tumors/mouse in female SKH-1 mice; of 15.6 (males) and 11.8 (females) tumors/mouse in MF-1 mice (experiment 4); and of 6.4 tumors/mouse in female C3H mice (experiment 5). Moreover, the latency period was shorter in SKH-1 mice (median C., C values of 21, 23, and 25 weeks; experiments 1, 2, and 3, respectively) a, than in MF-1 mice (29 weeks in both males and females; experiment > 4) and in C3H mice (45 weeks; experiment 5). The dose dependence was investigated in MF-1 (experiment 4) and 0@ 60 100 120 OH (experiment 5) mice. Fig. 3 reports in detail the time course of tumor yield in female MF-1 mice exposed for 12 h/day to three Time (weeks) different levels of intensity of illuminance, i.e., 10,000, 3,333, and Fig. 3. Time-related evolution of skin tumor yield in MF-1 female halrlcss mice exposed 12 h/day to the light emitted by an uncovered dichroic lamp incorporating a 12 1,000 lux. These illuminance levels were obtained by positioning the V, 50 W halogen quartz bulb, at three different illuminance levels (10,000, 3,333, and halogen lamps at distances of 46, 102, and 194 cm, respectively, from 1,000 lux). See Table 1 for details (experiment 4). 5083

DISCUSSION

@. 12 â€¢0 The results of the present study provide sound evidence that un 06 0 Minimum covered halogen lamps are potently carcinogenic in hairless mice by E L@ Median inducing skin tumors with a quite short latency period, a prevalence of virtually 100%, and a high multiplicity. As it will be described in 0 Maximum U, 0 more detail in a separate article3 in which the immunohistochemical 0. x 1.5 w detection of p53 protein in halogen-induced skin tumors will be also reported, the histological analysis revealed the presence of a variety of microscopic lesions, both benign and malignant. Compared to the results generated in animal studies with chemical carcinogens, gen erally requiring doses which are orders of magnitude higher than those c,J E expected following human exposure, it should be emphasized that the 0 10 C%J carcinogenic effect was also produced by moderate exposures to the 5@ C.) light sources. Even if we refrain from extrapolating down the regres sion lines reported in Fig. 4 because we do not know whether these Cl) lines may still be linear at exposure times or doses lower than those 20 40 60 80 100 120 tested, it is meaningful that skin tumors could be induced following Latency period (weeks) moderate daily exposures (1 .5 h) or moderate illuminance levels (1,000 lux), accounted for by a 50-W spotlight placed at about 2 m of Fig. 4. Latency periods needed for the formation of skin tumors induced by the light emitted by an uncovered dichroic lamp incorporating a 12 V, 50 W halogen quartz bulb, distance, i.e., under exposure conditions which are frequent in hu as related either to the square of the distance from the halogen lamp in MF-1 mice exposed mans. It is also noteworthy that tumors were even induced when 12 h/day (Lower Panel) (see Table 1; experiment 4) or to the daily exposure times in SKH-l hairless mice exposed to 10,000 lux (Upper Panel) (see Table 1; experiment 2). exposure to halogen lamps was discontinued well before the macro scopical appearance of skin lesions. However, the multiplicity of tumors was inversely related to the period of exposure. These data are in Fig. 3 depended on contingent factors, such as regression of some in agreement with findings concerning the development of skin tu lesions, interim deaths of animals bearing multiple tumors, or conflu mors induced by chemicals in mice, supporting the view that the ence of enlarging lesions. As shown in Fig. 4 (lower panel), the malignant conversion stage of tumor progression occurs spontane minimum, median, and maximum latency periods were inversely ously (6) but may be enhanced by treatment of animals with genotoxic related to the square of the distance from the illumination source, with agents (7). A decrease in the multiplicity of skin tumors was also high and significant correlation indices between the two parameters observed by discontinuing exposure of hairless mice to UV radiation (r 0.99, and 1.00 for minimum and median latency periods, respec in the 280â€”370nm range, but in this case the induction time was tively; both P < 0.01). An evident dose-related effect was also ob increased proportionally (8). served in C3H mice exposed to 10,000 lux (distance of 46 cm) and The comparative carcinogenesis action spectra in humans and hair 5,000 lux (79 cm) (Table 1; experiment 5). less mice, which have been used for 30 years as an experimental The time dependence was explored by varying the duration of the model for photocarcinogenesis, are not known. Nevertheless, it is daily exposure, i.e., 12, 6, 3, and 1.5 h/day, at an equivalent illumi noteworthy that acute responses to UV radiation, such as edema, were nance level (10,000 lux) (Table 1; experiment 2). Both prevalence and found to be very similar in albino SKH-1 hairless mice and humans multiplicity of skin tumors decreased by shortening the exposure (9). The responsibility of UV radiation in inducing skin tumors in times, and the curves indicating the development of lesions tended to humans and animal models is well established (10), and carcinoge become less steep (Fig. 5). Nevertheless, it is noteworthy that even in nicity patterns have been investigated in hairless mice with radiation the group exposed for only 1.5 h/day, the majority of animals devel of different wavelengths, i.e., UVA (315â€”380nm; Ref. 11), UVB oped skin lesions. By drawing the regression lines between the latency (280â€”315nm; Ref. 12), and UVC (100â€”280nm; Ref. 13). Uncovered periods and the daily exposure times, a linear correlation was pointed tungsten halogen lamps do emit UV light due to the permeability of out (Fig. 4, upper panel), and the correlation indices (r = 1.0 for the their quartz bulb to this kind of radiation, and the emission covers a minimum latency period; r = 0.99 for the median and maximum wavelength spectrum starting from the UVC region (14). The involve values) were highly significant (P < 0.01). ment of far-UV wavelengths in the genotoxicity of halogen lamps is In another experiment (Table 1; experiment 3), exposure of SKH-1 well supported by our experiments in S. zyphimurium, in which the female mice to halogen lamps (10,000 lux; 12 h/day), was either light was filtered through either color filters, cutting off certain continued until the end of the experiment (40 weeks) or discontinued spectral regions, or UV interference filters, selectively allowing trans after 16, 20, 24, or 28 weeks. All mice in these 5 groups developed mittance of UVA, UVB, or UVC radiation. While the mutagenicity of skin tumors, and the latency periods were just marginally increased by sunlight was distributed over a wide UV spectrum and the mutage stopping exposure to the carcinogenic agent. Interestingly enough, in nicity of fluorescent lamps was mainly due to UVB, the mutagenicity the first two groups the lesions appeared a few weeks after stopping of halogen lamps depended on UVB and UVC emissions (1). More the exposure. The five groups differed in the multiplicity of tumors, over, the spectrum of sensitivity of E. coli strains lacking a variety of which was inversely related to the exposure period to halogen lamps DNA repair mechanisms was quite similar by using halogen lamps (r 0.88, P < 0.05). Moreover, as estimated from our experience on and a monochromatic UVC source (2). It is noteworthy that at the histological classification of lesions as related to their macroscop equivalent radiant energy the mutagenic potency of a 254-nm UVC ical appearance, the proportion of malignant tumors was lower when source was 8400-fold higher than that of a 365-nm UVA source (1). exposure was stopped earlier, i.e., roughly 31% of lesions were malignant when exposure was discontinued after 16 weeks, 46% after 3 F. D'Agostini, P. Fiallo, C. Di Marco, and S. Dc Flora, Detection of p53 and 20 weeks, 49% after 24 weeks, 51% after 28 weeks, and 55% when histopathological classification ofskin tumors induced by halogen lamps in hairless mice, exposure was continued until the end of the experiment. manuscript in preparation. 5084

22 20 18 16

>@ 14 Fig. 5. Time-related evolution of skin tumor mul .2 12 tiplicityin SKH-1femalehairlessmiceexposed12, 0. @ 6, 3, or 1.5 h/day to the light emitted by an uncov 10 ered dichroic lamp incorporating a 12 V. 50 W halogen quartz bulb, at an illuminance level of 10,000 lux. See Table 1 for details (experiment 2). 6 4 2 0 10 15 20 25 30 35 40 45 50 55 60 65 70

Time (weeks)

This implies that the emission of even small amounts of UVC REFERENCES radiation from an illumination system is expected to produce 1. Dc Flora, S., Camoirano, A., Izzotti, A., and Bennicelli, C. Potent genotoxicity of biological effects, which apparently were thus far overlooked in halogen lamps, compared to fluorescent light and sunlight. Carcinogenesis (Land.), the case of halogen lamps. Far-UV radiation is likely to be the 11: 2171â€”2177,1990. 2. Dc Flora, S., Camoirano, A., Izzotti, A., and Bennicelli, C. A bacterial DNA repair range of wavelength inducing melanoma (15). test evaluating the genotoxicity of light sources. Toxicol. Methods, 1: 116â€”122, The bacterial genotoxicity of uncovered halogen lamps is remark 1991. ably higher, even at considerably lower illuminance levels, than that 3. D'Agostini, F., Izzotti, A., and Dc Flora, S. 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Cancer Res., 51: 979â€”984, illumination system, the carcinogenic hazard can be easily avoided by 1991. using common glass or suitable plastic covers that block UV radiation. 9. Cole, C. A., Davies, R. E., Forbes, P. D., and D'Aloisio, L C. Comparison of action In fact, all genotoxic and carcinogenic effects could be totally pre spectra for acute cutaneous responses to ultraviolet radiation: man and albino hairless mouse. Photochem. Photobiol., 37: 623â€”631,1983. vented by interposing silica glass covers between the quartz bulb and 10. International Agency for Research on Cancer. Solar and ultraviolet radiation. In: the biological target. In some countries, glass covers are already IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Vol. 55. compulsory in case of mains-operated halogen lamps [ones which are Lyons, France: International Agency for Research on Cancer, 1992. 11. Kelfkens, G., de Gruijl, F. R., and van der Leun, J. C. 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5085

Francesco D'Agostini and Silvio De Flora

Cancer Res 1994;54:5081-5085.

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