|Year : 2021 | Volume
| Issue : 1 | Page : 23-26
Synergistic interaction of heavy metal salts with hyperthermia or ionizing radiation
Mariia Tolkaeva1, Kaushala Prasad Mishra2, Ekaterina Evstratova3, Vladislav Petin1
1 A. Tsyb Medical Radiological Research Center – Branch of the National Medical Research Radiological Center of the Ministry of Health of the Russian Federation, Obninsk, Russia
2 Bhabha Atomic Research Center, Mumbai, Maharashtra, India
3 National Medical Research Radiological Center of the Ministry of Health of the Russian Federation, Obninsk, Russia
|Date of Submission||02-Dec-2020|
|Date of Acceptance||02-Feb-2021|
|Date of Web Publication||25-Mar-2021|
Ms. Mariia Tolkaeva
A. Tsyb Medical Radiological Research Center – Branch of the National Medical Research Radiological Center of the Ministry of Health of the Russian Federation, Obninsk
Source of Support: None, Conflict of Interest: None
Background: One of the ways to enhance the effectiveness of radiation therapy or sterilization of objects of various origins is to use chemical agents in combination with hyperthermia and ionizing radiation. Some drugs commonly used in medicine include heavy metals. However, the study of their synergistic interaction with other agents is fragmentary. The purpose of this study was to establish a general pattern of synergistic interaction of heavy metal salts with hyperthermia or ionizing radiation. Materials and Methods: Bacterial and diploid yeast cells were used in the experiments. To quantify the synergistic effect, cell survival was determined after individual effects of heavy metal salts, hyperthermia, ionizing radiation, and their simultaneous action. The following heavy metal salts were used: lead iodide, potassium dichromate, cisplatin, and zinc sulfate. Results: For all analyzed cases, optimal conditions of interacting agents were observed under which the greatest synergistic effect was achieved. Conclusion: Comparison of the results obtained with previously published data indicates general patterns of synergistic effect display that are independent of acting agents, biological objects, and tests.
Keywords: Combined action, heavy metals, hyperthermia, ionizing radiation, synergistic effect
|How to cite this article:|
Tolkaeva M, Mishra KP, Evstratova E, Petin V. Synergistic interaction of heavy metal salts with hyperthermia or ionizing radiation. J Radiat Cancer Res 2021;12:23-6
|How to cite this URL:|
Tolkaeva M, Mishra KP, Evstratova E, Petin V. Synergistic interaction of heavy metal salts with hyperthermia or ionizing radiation. J Radiat Cancer Res [serial online] 2021 [cited 2021 Jun 25];12:23-6. Available from: https://www.journalrcr.org/text.asp?2021/12/1/23/311946
| Introduction|| |
Synergistic interaction means that the final effect of two agents exceeds independent summation of the effects from each agent., The term “independent summation” determines by the product of probabilities of the effects from each agent. Some general patterns of synergistic effects were revealed, which were independent of agents applied together, biological objects, and effects observed. Some actively used drugs in medicine include heavy metals.,,,, However, the study of their synergistic interaction with hyperthermia or ionizing radiation is fragmented. Therefore, the study of interaction of heavy metals with hyperthermia or ionizing radiation is an urgent task.
| Materials and Methods|| |
Main experimental results were obtained with diploid Saccharomyces cerevisiae yeast cells (strain XS800) in the stationary phase of growth. Response of yeast cells to various impacts is qualitatively similar to that of mammalian cells. Cells were incubated before exposures for 35 days at 30°C on a complete nutrient agar media. To identify common patterns of synergistic effects, we obtained data with Escherichia coli bacterial cells (strain B/r) and cultured mammalian cells CHO. The following solutions of heavy metal salts were used in the experiments: lead iodide PbI2 at a concentration of 2.5 and 5 mg/ml, potassium dichromate K2Cr2O7 0.5 and 5 mg/ml, cisplatin Pt(NH3)2Cl2 0.25 and 0.5 mg/ml, and zinc sulfate ZnSO4 0.01 M. Hyperthermia was achieved in a water bath (43°C–56°C) where the desired temperature of ±0.1°C was maintained. To have the simultaneous action of hyperthermia and heavy metals, the time interval between introduction of the cells into preheated water and the beginning of exposure was about 0.1–0.3 min, which was significantly less than the total treatment time. At the end of the treatment, samples were rapidly cooled to room temperature. Therefore, high-temperature durations and chemical agents' exposure were identical. The 60Co γ-ray source was “Issledovatel” (Radon, Russia), dose rate (20 Gy/min) was determined by ferrous sulfate dosimeter.
After treatment with each heavy metal applied alone or combined simultaneously with heat or ionizing radiation, a known number of cells were plated so that 150–200 colonies per dish would form by the surviving cells after 5–7 days of yeast cells or 1 day of bacteria incubation at 30°C and 37°C, respectively. All experiments were performed with three replicates in each series. Error bars in all figures presented below indicate inter-experimental standard errors.
Synergistic interaction of two agents means that the recorded biological effect is greater than that expected for independent addition of the effects caused by each agent. It is known that under independent action probability of the total effect, in accordance with the well-known statement of the probability theory,, is determined by the product of the probabilities of the effects induced by each agent separately. Then for cell survival, we have
Where SΣ is probability of cell survival after simultaneously combined exposure, and S1 and S2 are probabilities of survival after the action (in our case) of heavy metal salts and hyperthermia separately. Then after the logarithm of equation (1), we have
lnS = l nS1+ l nS2 or l gS = l gS1+ l gS2(2)
This means that independent action of two agents is characterized by summing of logarithms of survival after the action of heavy metals and hyperthermia. According to Poisson statistics,, the number of damages induced by the acting factor is described by the expression
N = l nS(3)
Then, equation (2) means that the total number of damages caused by the independent action of interacting factors is determined by the sum of the damages produced by each agent. Details of materials and methods are described in our previous publications.,,
| Results|| |
[Figure 1]a, [Figure 1]b, [Figure 1]c, [Figure 1]d comprises data pertaining to survival curves of diploid yeast cells of S. cerevisiae after separate action of 2.5 mg/ml PbI2 solution (curves 1) and hyperthermia – 50°C [Figure 1]a, 52°C [Figure 1]b, 53°C [Figure 1]c, and 54°C [Figure 1]d (curves 2) as well as after simultaneous application of these agents (curves 4). Curves 3 reflect theoretical curves calculated under the condition of independent summation of the effects induced by the factors used (Eqs. 1). Four types of survival curves presented in [Figure 1]a were obtained in all experiments described below to calculate the dependence of synergistic enhancement ratio on acting temperature or concentration of a salt solution.
|Figure 1: Survival curves of diploid yeast cells of S. cerevisiae after simultaneous and separate applications of hyperthermia (a–50°C, b–52°C, c–53°C, d–54°C) and PbI2 solution|
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To quantify the effectiveness of synergistic interaction, the synergistic enhancement ratio was determined by the ratio of isoeffective exposure durations on theoretical and experimental survival curves.,
k = t2/t1.(4)
An example of k calculation is shown in [Figure 1]a by arrows for 10% survival. This ratio shows how many times the effect intensified compared to independently summation of the effects from each agent. Note that this ratio for exponential survival curves observed in all our experiments does not depend on cell survival for which it is calculated.
[Figure 2] shows dependences of the synergistic enhancement ratio on current temperature after its simultaneous action with heavy metals solution: PbI2-2.5 mg/ml [Figure 2]a, 5 mg/ml [Figure 2]b or K2Cr2O7-0.5 mg/ml [Figure 2]c, and 5 mg/ml [Figure 2]d on survival diploid yeast cells of S. cerevisiae (strain XS800). It can be seen that all these dependencies are bell shaped when the synergistic enhancement ratio initially increases, reaches the greatest value, and then declines. The greatest synergistic effect for PbI2 is observed at a temperature of 53°C and concentration of 2.5 mg/ml shifting to 54°C for 5 mg/ml. A similar shift in temperature and concentration is also observed for K2Cr2O7 – the greatest synergistic effect for this compound observed at a temperature of 47°C and concentration of 0.5 mg/ml shifted to 50°C for 5 mg/ml. Obviously, the lower the acting temperature, the lower the concentration of the solution provides the greatest synergistic effect.
|Figure 2: The dependence of the synergistic enhancement ratio on the current temperature after its simultaneous action with heavy metals solution: PbI2 (a – 2.5 mg/ml, b – 5 mg/ml), K2Cr2O7 (c – 0.5 mg/ml, d – 5 mg/ml) on survival of Saccharomyces cerevisiae diploid yeast cells|
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[Figure 3]a and [Figure 3]b show dependences of the synergistic enhancement ratio on the temperatures used, acting simultaneously with cisplatin – 0.05 mg/ml [Figure 3]a and 0.25 mg/ml [Figure 3]b on the survival of diploid yeast cells. It is seen that bell-shaped dependence is again observed when the synergistic enhancement ratio gradually increases to its greatest value and then decreases with an increase in acting temperature. It is also obvious that optimal temperature providing the greatest synergistic effect should be shifted to lower temperature with a decrease in cisplatin concentration. The same patterns were described for the data shown in [Figure 2]. Taking these data as a whole, one can conclude that the synergistic effect may be observed at a low concentration of harmful chemical agents interacting with the environmental temperature.
|Figure 3: The dependence of the synergistic enhancement ratio on the current temperature after its simultaneous action with cisplatin on survival of S. cerevisiae yeast cells (a– 0.05 mg/ml, b–0.25 mg/ml), ZnSO4 on survival of Escherichia coli (c) and cisplatin on survival of Chinese hamster cells (d)|
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It would be of interest to check whether the revealed patterns will be preserved for other biological objects. [Figure 3]c and [Figure 3]d show the dependence of synergistic enhancement ratio on current temperature after its simultaneous action with 0.01 M ZnSO4 [Figure 3]c on the survival of E. coli bacterial cells (strain B/r) and 3 μM cisplatin [Figure 3]d on the survival of Chinese hamster cells CHO. These data also demonstrate a bell-shaped dependence of synergistic enhancement ratio on acting temperature. Any deviation of acting temperature from the optimal value, at which the greatest synergistic enhancement ratio is achieved, leads to a decrease in the effectiveness of synergistic interaction.
[Figure 4] depicts the dependence of synergistic enhancement ratio on the concentration of heavy metal solutions K2Cr2O7 [Figure 4]a and PbI2 [Figure 4]b after their simultaneous irradiation with ionizing radiation (60Co, 10.8 Gy/min) on the survival of diploid yeast cells S. cerevisiae (strain XS800). A bell-shaped pattern is observed here again. In other words, there is an optimal concentration of chemical compounds that maximizes synergistic interaction.
|Figure 4: The dependence of the synergistic enhancement ratio on the concentration of heavy metal solutions: K2Cr2O7 (a), PbI2 (b) after their simultaneous action with ionizing radiation (60Co, 10.8 Gy/min) on the survival of diploid yeast cells Saccharomyces cerevisiae (strain XS800)|
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| Discussion|| |
The results described in this article for simultaneous action of heavy metal salts with hyperthermia or ionizing radiation together with our data published earlier for combination of hyperthermia with various physical and chemical agents denote universality of synergistic effects display. Indeed, the results presented in this article, as well as published in many of our earlier articles, indicate that regardless of agents applied and biological objects used,,,,,, a bell-shaped dependence of synergistic enhancement ratio on acting temperature or salt concentration is observed. In other words, the optimum effective temperature or concentration of the agents used is recorded, at which the greatest synergistic effect is achieved.
To interpret these dependencies, we use previously proposed and detailed mathematical model of synergistic interactions., The model suggests that synergism is caused by additional effective damage arising from interaction of sublesions induced by each agent. These sublesions are considered to be ineffective if each agent is taken individually. The remarkable feature of this model is that it does not operate with a real amount of effective damage, which would not be evaluated directly but only with nondimensional ratio of effective damage produced by the agents under consideration that can be estimated from experimental results. The model describes quantitatively synergistic interaction and predicts its greatest value and the condition under which it can be achieved. In addition, the model also predicts that the rate of exposure to physical agents or the concentration of chemical agents strongly influences synergy. It is these patterns that are described in this work.
| Conclusion|| |
Existence of certain temperature ranges and concentrations of heavy metal salts, within which synergistic effects are observed, has been demonstrated. Within these ranges, there are optimal values of operating temperatures or concentrations of chemical compounds, at which the greatest synergistic effect is achieved. These data, together with the results described in our previous publications,,,,,, indicate universality of synergistic effects display and demonstrate possibility of mutual amplification of harmful effects of environmental agents at intensities and concentrations actually encountered in the biosphere.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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