Wavelength dependence of cellular responses in human melanocytes and melanoma cells following exposure to ultraviolet radiation.

PURPOSE: To examine the wavelength dependence of cellular responses in human melanocytes and human melanoma cells exposed to ultraviolet radiation (UVR). MATERIALS AND METHODS: Primary human melanocytes and G361 human melanoma cells were exposed to ultraviolet-C (UVC), ultraviolet-B (UVB), or ultraviolet-A (UVA) radiation. Dose-response relationships for clonal cell survival were assessed, and flow cytometry was used to monitor cell cycle distributions for up to one week post-irradiation. Chromosomal aberrations were scored in exposed and unexposed melanoma cells. RESULTS: G361 melanoma cells were more sensitive than melanocytes to killing by UVB and UVC radiation. This difference in sensitivity between cell types was much less marked following UVA irradiation. The melanoma cells showed a sustained, dose-dependent G2/M block following exposure with all wavelengths; in addition, transit through S phase was slowed following UVA irradiation. There was no apparent block to G1 cells entering S phase at any wavelength. Melanocytes, on the other hand, showed a marked G1 arrest, particularly following UVA irradiation. Cytogenetic results showed a dose-dependent increase in chromatid-type aberrations, mostly gaps, breaks and exchanges, in exposed melanoma cells. CONCLUSION: These results show that G361 malignant melanoma cells have lost the ability to regulate the cell cycle at the G1/S checkpoint and are more sensitive than melanocytes to cell killing by UVC and UVB but not UVA radiation. Similarly, exposure of these melanoma cells to UVC and UVB, and to a much lesser extent UVA, induced chromatid aberrations. UVA nevertheless induced strong cell cycle delays in both cell types, indicating that UVA exposure can significantly affect genome metabolism.

Dominant lethal studies in male mice after exposure to a 50 Hz magnetic field.

The potential mutagenicity of power frequency magnetic fields was investigated using a dominant lethal assay in mice. A total of 42 male mice were exposed for 8 weeks to a 50 Hz sinusoidal magnetic field at 10 mT (rms) and 47 males acted as simultaneous cage controls. Each male was subsequently mated with two females on weeks 1, 3, 5, 7, and 9 post-exposure. The numbers of pregnant females, corpora lutea, and live and dead implants were recorded. Multiple logistic regression analyses examined the effects of exposure on pregnancy rate, pre-implantation survival and post-implantation survival. There were no statistically significant differences in overall response between exposed and control groups, nor was there any significant effect of exposure in any post-exposure week. Thus, exposure to power frequency magnetic fields at 10 mT for the approximate period of spermatogenesis did not appear to induce dominant lethal mutation in the germ cells of male mice.

Effects of prenatal exposure to 50 Hz magnetic fields on development in mice: I. Implantation rate and fetal development.

Pregnant CD1 mice were exposed or sham-exposed from day 0 to day 17 of gestation to a 50 Hz sinusoidal magnetic field at 20 mT (rms). Preimplantation and postimplantation survival were assessed and fetuses examined for the presence of gross external, internal, and skeletal abnormalities. There were no statistically significant field-dependent effects on preimplantation or postimplantation survival, sex ratio, or the incidence of fetuses with internal or skeletal abnormalities. Magnetic field exposure was, however, associated with longer and heavier fetuses at term, with fewer external abnormalities. The results lend no support to suggestions of increased rates of spontaneous abortion or congenital malformation following prenatal exposure to power frequency magnetic fields.

Lack of acute effects of 20 mT, 50 Hz magnetic fields on murine haemopoiesis.

Some epidemiological studies have drawn attention to a possible association between exposure to extremely low-frequency (ELF) electromagnetic fields and the development of acute myeloid leukaemia (AML) in adults. At present there is no experimental evidence for such an association. We have investigated the acute effects of power frequency magnetic fields on haemopoiesis in CBA/H mice known to be susceptible to the induction of AML after exposure to ionizing radiation. Up to 19 days after exposure to 50 Hz fields at 20 mT for 7 days no significant effects on peripheral blood characteristics were observed. Assays of the bone marrow stem cells and myelomonocytic progenitor cells also failed to reveal significant effects. Our experiments cannot, however, rule out subtle effects on cell population dynamics, and further investigations, including long-term studies, are required to establish the extent to which ELF magnetic fields might affect the haemopoietic system.

Dominant lethal studies in male mice after exposure to a 50-Hz electric field.

Male C3H/He mice were sham-exposed or exposed continuously for 2 weeks to a vertical, 50-Hz, electric field at 20 kV/m rms. Densities of currents induced in the testes are estimated to be near 100 microA/m2. After the exposure, each male was mated with two different female mice each week during a period of 8 weeks. By this schedule, female mice were impregnated with sperm that had been exposed to the electric field at different stages of the spermatogenic cycle. No significant differences as a function of exposure condition were observed in pregnancy rates or in survival of embryos before or after implantation. The absence of effects was not due to insensitivity of assays; other mice that were exposed to X-rays (dose to testes = 1.5 Gy) presented reliable evidence of mutagenesis.

Studies of the induction of dominant lethals and translocations in male mice after chronic exposure to microwave radiation.

Male C3H mice were exposed to 100 W m-2 of 2.45 GHz continuous-wave microwave radiation for 6 h per day for a total of 120 h over an 8-week period. The exposure level was chosen so that the specific energy absorption rate (SAR) would be approximately equal to the level of 4 W kg-1 which is considered by a number of organizations to be a threshold for adverse biological effects. At the end of the treatment period the mice were mated with a different group of (C3H x 101) F1 hybrid females each week for the following 8 weeks. There was no significant reduction in pregnancy rate, preimplantation survival or postimplantation survival in the exposed group compared to sham-exposed controls. At the end of the mating period a cytogenetic analysis was carried out of meiotic chromosome preparations of testicular tissue, thus sampling cells that were stem cell spermatogonia during the treatment regime. The results showed no difference in the frequency of reciprocal translocations between the sham and treated groups, or in the frequency of cells with autosome or sex chromosome univalents. Low levels of fragments and exchanges were found in both groups. It is concluded that there is no evidence in this experiment to show that chronic exposure of male mice to 2.45 GHz microwave radiation induces a mutagenic response in male germ cells. This conclusion is in agreement with the observations of Berman et al. (1980), who reported a lack of male germ cell mutagenesis after repetitive or chronic exposure of rats to 2.45 GHz.

Cytogenetic effects of microwave irradiation on male germ cells of the mouse.

Hybrid male mice were exposed to 2.45 GHz microwaves for 30 min/day, 6 days a week for two consecutive weeks at power densities of 1.0, 100 or 400 W m-2, with sham-exposed controls. Rectal temperatures before and after exposure were measured on days 1, 6 and 12. Measurements made on day 1 were treated with caution because of heterogeneity in rectal temperatures taken before exposure between the groups of mice given different treatments. On days 6 and 12, rectal temperatures rose by approximately 1 degree C in mice sham exposed, or exposed to 1 W m-2 or 100 W m-2. Only in the group of mice exposed to 400 W m-2 was the mean rise in rectal temperature during exposure (about 3 degrees C) significantly increased above the sham value. In groups killed 2-3 days after treatment (mainly meiotic exposure) frequencies of chromosome aberrations in spermatocytes showed no significant heterogeneity although the highest frequency of 1.5 per cent was at the highest (400 W m-2) power density. Another group killed 30 days after 100 W m-2 exposures (spermatogonial sampling) showed no significant increase over controls in chromosome aberration frequency. There was a small but significant increase in sperm count with increasing power density in mice killed 12-13 days after exposure, but a non-significant one in those exposed as spermatogonia (killed 41 days later). Thus effects were markedly less severe than those reported previously by Manikowska-Czerska et al. (1985) with a very similar radiation regime and were probably caused by the temperature enhancement.

Absence of chromosomal damage in human lymphocytes exposed to microwave radiation with hyperthermia.

Specimens of human blood were exposed to 0, 4, 40, 100, and 200 Wkg-1 of 2.45 GHz microwave radiation for 20 minutes. The blood temperature was carefully controlled so that it rose from 37 to 40 degrees C. Cultured lymphocytes were examined for induced chromosomal damage but no effect in excess of background was observed.

No clastogenic effect from in vitro microwave irradiation of G0 human lymphocytes.

Specimens of human blood were exposed at specific energy absorption rates of 104 or 193 W kg-1 to 2.45 GHz microwave radiation at temperatures below 36 degrees C. Cultured lymphocytes were examined for induced unstable chromosome and chromatid aberrations and sister chromatid exchanges. The amount of chromosome damage observed did not exceed that found in controls.

Sperm count and sperm abnormality in male mice after exposure to 2.45 GHz microwave radiation.

Adult male mice had the posterior halves of their bodies exposed at 44 W/kg in a waveguide system to 2.45 GHz microwave radiation for 30 min. They were killed sequentially over 10 weeks and assessed for decreased sperm count and abnormal sperm morphology. The response in each assay was maximal 2-4 weeks after the exposure. This corresponds to microwaves having their greatest effect on spermatids and spermatocytes. Male fertility, assessed as the proportion of normal sperm per epididymis, was compared with results of an earlier study on dominant lethality. It is concluded that reduced male fertility correlates well with reduced pregnancy rate but less well with pre-implantation survival. Whilst microwaves clearly induced abnormally shaped sperm, those which achieved fertilization cannot have possessed a dominant mutation which would result in the post-implantation death of the embryo.

Dominant lethal studies in male mice after exposure to 2.45 GHz microwave radiation.

Adult male mice had the lower halves of their bodies exposed in a waveguide system to 2.45 GHz microwave radiation for 30 min. The half body dose-rate of 43 W kg-1 had been shown in a previous study [7] to deplete severely the heat-sensitive stages of sperm production. The males were mated at intervals to adult hybrid females over the following 8-10 weeks. There was no significant reduction in post-implantation survival, suggesting that the microwave exposure did not have a mutagenic effect on the male germ cells. However, pregnancy rate was significantly reduced in weeks 3, 4, 5 and 6; reaching a minimum of about 10% of the control value in weeks 4 and 5. The occurrence of low values in weeks 4 and 5 correlated well with the expected reductions in sperm count due to the pattern of depletion of the spermatogenic epithelium of the testes. Thus it was concluded that the reduced pregnancy rate resulted from reduced male fertility. Pre-implantation survival can also be affected by reduced sperm count [8] and was significantly reduced in this study but it correlated less well with the anticipated heat response. A further study is in progress looking at the contribution of sperm count and sperm abnormality to the results.

Effects of 2.45 GHz microwave radiation and heat on mouse spermatogenic epithelium.

The rear halves of the bodies of anaesthetized male C3H mice were exposed for 30 min to 2.45 GHz microwave radiation and the effects on the testes were compared to those produced by direct heating. Effects were observed which are consistent with the hypothesis that heat damage is the primary effect of microwave exposure. Damage measured six days after exposure ranged in severity from depletion of the spermatocytes to extensive necrosis of the germinal epithelium. Temperature-sensitive probes implanted in the testes revealed a threshold effect for depletion of the spermatocytes of approximately 39 degrees C and an LD50 6 (50 per cent cell death after 6 days) of about 41 degrees C after microwave exposure or direct heating. The corresponding effective threshold effect and LD50 6 expressed in terms of absorbed microwave power were 20 W kg-1 and 30 W kg-1. However, it is probable that a conscious animal is better able to regulate testicular temperature and hence adjust to higher dose-rates.

The effect of acute far field exposure at 2.45 GHz on the mouse testis.

Male C3H mice were exposed in an anechoic chamber to 2.45 GHz microwave radiation. The exposures ranged from 1000 Wm-2 for 5 min to 100 Wm-2 for 260 min, giving dose rates to the testis ranging from 66 Wkg-1 to 7 Wkg-1. The mice were killed six days later and the testes examined histologically. Quantitatively, no significant effects were seen on cells identified as X-ray sensitive (spermatogonia type B) or heat sensitive (early primary spermatocytes and late primary and secondary spermatocytes) or on the sperm count. Extrapolation of these results to man would suggest that acute exposure to the Maximum Permissible Exposure level of 100 Wm-2 has no effect on the testes in the ranges 1 to 3.5 MHz and 300 MHz to 100 GHz. There was insufficient data to comment on other frequencies.