Exposure Rate as a Determinant of the Synergistic Interaction of Heat Combined with Ionizing or Ultraviolet Radiation in Cell Killing

Abstract

A synergistic interaction of hyperthermia with ionizing or UV light (254 nm) radiation was analyzed in experiments with yeast cells. For a fixed dose rate of radiation, the synergism was shown to be observed only within a definite temperature range (40-45 degrees C), inside of which there was an optimal temperature to achieve the highest synergism. The effectiveness of the synergistic interaction was smaller for haploid cells than for diploid cells. Experimental data from diploid yeast cells evidenced the significance of the exposure rate in the synergistic interaction of heat combined with ionizing or ultraviolet radiation. The data show that the less is the intensity of radiation, the lower is the temperature that should be used to provide some definite, or highest, synergistic interaction with the radiation. To demonstrate the significance of this rule for other cellular systems, the results of other authors published for bacterial spores and mammalian cells are discussed. Calculations from these results have confirmed the revealed relationship between the dose rate and the exposure temperature. On this basis, it is inferred that synergism may take place at small intensities of harmful environmental factors existing in the biosphere. Hence, any assessment of the health or environmental risks should take into account synergistic interactions between harmful agents.

Thermoluminescence in Sintered CaF2:Tb

“…The intensity of 458 K glow peak of Tb 4 O 7 sample sintered at 1473 K is 1.9 times that of the sample sintered at 1373 K. It can be seen fromFig. 1that the intensity of 378 K glow peak of the codoped sample (curve a) is 12.9 times that of 458 K glow peak of Tb4 O 7 doped sample sintered at 1473 K. *Corresponding author: Phone: +81-72-875-3001 Fax: +81-72-871-1259 E-mail: fukuda@due.osaka-sandai.ac.jp 1 Department of Urban Environment, Osaka Sangyo University, Nakagaito 3-1-1, Daito, Osaka, 574-8530, Japan. YASUNORI FUKUDA S68…”

“…Therefore, the biological effectiveness induced by UV radiation (UV-B, UV-C) has been studied [1][2][3][4] . And this situation has been driving the development of an effective sensor of practical use for UV radiation.…”

Survival and Recovery of Yeast Cells After Simultaneous Treatment of UV Light Radiation and Heat¶

“…Error bars in all the figures show interexperimental errors. The details were described elsewhere (10,12). Some preliminary results have been published in Russian (20).…”

“…The hyperthermia and UV radiation interacted additively for the induction of the reproductive death in cultured mammalian cells (2,3). There is information concerning the synergistic interaction between UV radiations of different energies (4), UV (5,6), UV radiation and chemicals (7,8), UV radiation and hyperthermia (9)(10)(11)(12)(13). It seems widely accepted now that the synergistic interaction of the W light combined with another agent is displayed by decreased repair rates at molecular and cellular levels (1,8,14,15).…”

The Fluence Rate Determines the Synergistic Interaction of UV Radiation and Heat for Mitotic Recombination and Cell Inactivation in Yeasts

“…The only possibility important for the problem of low doses and UV light safety is the case when a decreased fluence rate must be accompanied by a decrease in the intensity of another factor used in combination to provide the same level of synergism. Appropriate data of a combined action of ionizing radiation and heat have revealed that the dose rate can be considered a determinant of synergy (8,9). The decrease in the dose rate of the ionizing radiation required a decrease in the temperature at which the irradiation was carried out to preserve a definite effect of a simultaneous thermoradiation action on T4 bacteriophage (10), dry Bacillus subtilis spores (11), attenuated poliovirus (12), mammalian (13) and yeast (14) cells.…”