Biomedical subjects
Publications and source records attributed to J Kiefer.
Dry eggs of Artemia salina were exposed to 80 KV-X-rays and Kr-Ions (energy: 11.75 MeV/u; LET: 3500 KeV/microns). Emergence, hatching and survival were determined. The results demonstrate a very high resistance both to sparsely and ionizing radiation.
Mutation induction (resistance to 6-thioguanine) in Chinese hamster fibroblasts (V79) by exposure to accelerated heavy ions (O, Ne, Ca, Ti, Ni, Xe, Pb and U with energies between 5 and 14.8 MeV/u) was investigated, covering a range of LET from 300 to about 15,700 KeV/micron. The LET-dependence of the mutation induction cross-section (sigma m) has, in a similar way to inactivation (sigma i), to be described by separate curves for each ion. Both sigma m and mutagenicity (sigma m/sigma i) decrease with increasing specific energy for any given ion. Relative biological effectiveness for mutation induction was found to be significantly smaller than unity for the ions and energies investigated.
The instruction to preservation of health especially the popularization of the personal hygiene are demanded a serious place from the medicine in the Age of Englightment. In reference to the salubrious influence of the bath and the warning against the use of unhealthy, metallic make-ups the purposive efforts of the physicians are illustrated.
Diploid wild-type yeast cells were exposed to beams of heavy ions covering a wide range of linear energy transfer (LET) (43-13,700 keV/microns). Synthesis of ribosomal RNA (rRNA) was assessed as a functional measure of damage produced by particle radiation. An exponential decrease of relative rRNA synthesis with particle fluence was demonstrated in all cases. The inactivation cross sections derived were found to increase with LET over the entire range of LET studied. The corresponding values for relative biological effectiveness were slightly less than unity. Maximum cross sections measured were close to 1 micron 2, implying that some larger structure within the yeast nucleus (e.g., the nucleolus) might represent the target for an impairment of synthetic activity by very heavy ions rather than the genes coding for rRNA. Where tested, an oxygen effect for rRNA synthesis could not be demonstrated.
Chinese hamster V79-S cells capable of growing in suspension culture were exposed to 60Co gamma rays at a high dose rate (84 Gy/h), low dose rates (200, 50, and 39 mGy/h), and a spectrum of very low dose rates (between 29 and 4.5 mGy/h). Following time for appropriate expression the cultures were assayed for the induction of 6-thioguanine-resistant mutants. For a given dose, a decrease in mutation induction occurred as the dose rate was reduced from high dose rates to low dose rates. However, further reduction in dose rate resulted in a reverse dose-rate effect, and an increase in the frequency of mutants was observed. The contribution of background mutation frequency to this reverse dose-rate effect was studied, both by examining fluctuations of mutation frequency in nonirradiated culture and by its impact upon the dose-rate-independent nature of the reversed effect, and it was found to be negligible. The physiological state of the suspension culture under periods of protracted exposure to very low dose rates was also investigated. The effect of doubling time, plating efficiency, cell cycle distribution, and sensitivity on survival and mutation were examined. In no case was a change apparent during the very low-dose-rate exposures. The results are discussed in terms of the possible expression of cryptic radiation damage after prolonged culture times and/or the involvement of an error-free repair system which requires a certain amount of radiation damage to become active.
The discussion on the possible increase of solar UV on earth due to the destruction of the stratospheric ozone has led to a renewed interest in the action of ultraviolet radiation on biological systems. The paper deals with changes at the cellular level stressing particularly molecular alterations in deoxyribonucleic acid, the carrier of genetic information. The most important repair processes by which lesions are removed or bypassed are described. It is also discussed whether the effectivity of a complex spectrum can be predicted on the basis of measurements with monochromatic radiation. Furthermore, possible consequences on human health are outlined which may be derived from cellular studies.
Mutation induction was investigated in wild-type haploid yeast Saccharomyces cerevisiae after split-dose UV-irradiation. Cells were exposed to fractionated 254 nm-UV-doses separated by intervals from 0 to 6 h with incubation either on non-nutrient or nutrient agar between. The test parameter was resistance to canavanine. If modifications of sensitivity due to incubation are appropriately taken into account there is no change of mutation frequency.
Heavy ions are an important part of space radiation. Although they contribute only about 1 percent in number the fraction in terms of energy deposited is much higher. Also the quality of radiation is different from the other components since the LET is generally quite high. This poses the problem of Relative Biological Effectiveness (RBE). It is considerably more important in space than on earth because shielding measures are costly and sometimes not even feasible. Radiation hazards appear to be the limiting factor In long term space flights and their evaluation constitutes a major task. There is still no general agreement about RBE of earthbound radiation, and even less concerning the biological weighting of very heavy and very energetic ions in space. Because of the lack of experimental data--particularly for risk estimates in humans-- theoretical approaches may be very helpful in this respect and provide the only means to judge the radiation protection situation in outer space. In order to be useful careful checks of their consistency are necessary. This paper summarizes some of the more common approaches in a critical manner. The unhappy conclusion at the end will be that at present it is not possible to understand even heavy ion action on survival quantitatively with an acceptable precision.
Radium contents of commercially obtained beer, wine, milk and mineral waters were measured. All distributions were log-normal with the following geometrical mean values: beer: 2.1 X 10(-2) Bq L-1; wine: 3.4 X 10(-2) Bq L-1; milk: 3 X 10(-3) Bq L-1; normal mineral water: 4.3 X 10(-2) L-1; medical mineral water: 9.4 X 10(-2) Bq L-1.
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Haploid yeast cells possess two different mating types which are controlled genetically by the MAT locus. Information of the opposite mating type is stored on the same chromosome but not expressed. Radiation may initiate a gene conversion event leading to 'mating-type switching'. This was studied by using X-rays and 254 nm ultraviolet light. X-ray-induced mating type switching shows an oxygen enhancement ratio of 2.9 which is higher than that for survival (1.8) and equals that for double-strand break induction. Mating-type switching by UV is not photoreactivable and depends on a functioning excision repair system. The results are compatible with the interpretation that mating type switching is initiated by a double-strand break in the MAT coding region.
Survival and mutation induction in a human lymphoblastoid cell line ('TK6'), after acute X- and low dose rate continuous gamma-irradiation, were investigated using the hypoxanthine guanine phosphoribosyl transferase (HGPRT)- and the thymidine kinase (TK)-mutation assay. The surviving fraction after acute exposure decreased exponentially (D0 = 0.47 Gy). The HGPRT- and TK-mutation frequencies after acute X- and continuous gamma-irradiation (2.7 and 27 mGy/h) showed linear responses and no dose-rate dependence.
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A diploid yeast strain heterozygous at the canavanine locus was subjected to long-term gamma exposure in continuous chemostat cultures. Radiation induces canavanine resistance presumably by mitotic recombination. The efficiency of this process increased with lower dose rate. Experiments using a split-dose protocol showed that radiation possibly induces a recombinogenic activity.
The survival of the yeast mutant rad 54-3, which is temperature-conditional for the repair of double-strand breaks, was measured after exposure to UV-light (254 nm) and incubation at 23 degrees C and 36 degrees C. It was found that survival was drastically reduced with incubation at the restrictive temperature. Temperature-shift experiments indicated that repair of UV-induced damage which is controlled by the rad 54 gene proceeds with a half-value-time of about 7 h.
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