Abstract
Introduction
It is shown that beta-D-glucan is an immunologic system booster with radioprotectory effects. Radioprotectors are chemical components that can alleviate biological damage produced by ionizing radiation.
Aim
This study was designed to investigate the synergistic radioprotectory effects of beta-D-glucan and vitamin E on irradiated mice with 60Co source.
Materials and Methods
A total of 240 female mice were arranged in four, equal population groups of control group (C), treated group with beta D-glucan (G), treated group with vitamin E (E), and treated group with both beta D-glucan and vitamin E (G+E). Each group was divided into three equal population groups of D6, D7 and D8 exposed to 60Co radiation with prescribed total body dose of 6, 7 and 8 Gray (Gy), respectively. After the exposure, the number of survived animals was counted by time, then Lethal Dose50/30 (LD50/30), Lethal Dose50/60 (LD50/60) and Dose Reduction Factor (DRF) were calculated in all groups and corresponding groups.
Results
Based on the results of current study, treatment of the animals with vitamin E did not change values of LD50/30 and LD50/60, in comparison to control group. LD50/30 and LD50/60 of treated groups with beta D-glucan and beta D-glucan + vitamin E showed significant difference with those of control group (p<0.01). The DRF values in groups E, G and G + E, were calculated respectively as 1, 1.25 and 1.375 based on LD50/30, and respectively as 1, 1.17 and 1.33 based on LD50/60. While values of DRF in groups G and G + E showed significant difference in comparison to that of control group (p<0.01), but the difference between DRF of groups G and G + E was not significant (p=0.395).
Conclusion
The findings of study obviously showed that, presence of beta D-glucan in the body of mice, during exposure to ionizing radiation, leads to DRF of higher than one, proving the radioprotectory effect of this agent. Also, we demonstrated that, while vitamin E had no radioprotectory effect on irradiated mice, beta D-glucan in combination with vitamin E increased resistance of mice against ionizing radiation.
Keywords: Ionizing radiation, Radioprotectors, Toxicity
Introduction
Radioprotectors are chemical components that can alleviate biological damage produced by ionizing radiation. The first evidence of agents that were used as radioprotectors to reduce harmful effect of radiation on the mammalian bodies dates back to several decades ago [1]. Radioprotectors can have a wide range of applications. For radiation technologists or those who may be subject of unwanted exposure to ionizing radiation, application of radioprotectors could be used with radiation protection purpose to effectively reduce biological side effects. In patients who undergo radiotherapy procedures as a treatment, absorption of high level of radiation may lead to post therapy complications in their blood, intestine and immunologic systems. Radioprotectors, here, may be used as an effective agent that could allow application of high dose to the tumour with minimum risk to normal tissues. Adverse effects of ionizing radiation in both groups, irradiated staff and treated patients with radiation, can be reduced using radioprotectors.
Up till now, several attempts have been done to introduce and study components that exhibit radioprotective properties [2–7], none of which meet the ideal radioprotector requirements and act perfectly. Most of the radioprotectors have cysteine amino acid and cysteine amine in their structures that are capable of blocking performance of free radicals in the body, however a vast majority of effective radioprotectors are toxic and there are continuous researches conducting to introduce new suitable radioprotectors with respect to properties such as efficiency, toxicity, manufacturing costs and duration of stability. One of these substances with potential radioprotective properties is beta D-glucan. Beta D-glucan is a polysaccharide which acts as an immune system booster and may improve recovery of patients after radiation therapy [8,9]. This agent is shown to have a good antioxidant activity by scavenging of hydroxyl radical [10]. It is also reported that, beta glucan of Ganoderma lucidum have significant DNA repairing ability [11]. This chemical component can reinforce immune system and protect body against ionizing radiation [12].
Molecular structure and chain conformations of D-glucan is well studied using infrared spectroscopy, Nuclear Magnetic Resonance (NMR) and laser scattering [13]. It is shown that, D-glucan is composed of main chain of 1-3 beta D-glucan and side chain of 1-6 beta-D glucopyranosyl, and can be extracted from mushroom, bacteria and plant [14,15]. Because of interesting properties of this component including anti-tumour and anti-osteoporosis effects, improvement of the immune system [13] and anti-infection properties [16,17], beta D-glucan, has drawn interest of researches as an effective radioprotector agent.
Similar to D-glucan, vitamin E is also known as anti-oxidant agent that can decrease radiation induced damage in vitro [18]. This agent is shown to reduce chromosomal aberrations as well as micronuclei in bone marrow of irradiated mouse with 1 Gy [19]. However, there is also evidence in which vitamin E has not protected chromosomes against X-ray photons [20].
Therefore, in current study we assessed radioprotectory effect of beta D-glucan, alone and in combination with vitamin E, on irradiated mice with gamma photons, using Dose Reduction Factor, Lethal Dose50/30 (LD50/30), Lethal Dose50/60 (LD50/60).
Materials and Methods
A total of 240 female mice were arranged in four, equal population, groups of control (C), treated with beta D-glucan (G), fed with 250 mg/body-weight, treated with vitamin E (E), fed with 1 mg/body-weight for one month, and treated with both beta D-glucan and vitamin E (G+E). Each group was then divided into three equal population groups of D6, D7 and D8 exposed to 60Co radiation with prescribed total body dose of 6, 7 and 8 Gy, respectively.
To assess response of the animals to ionizing radiation, three quantities of LD50/30, LD50/60 and DRF were calculated for each of groups. LD50/30 is a dose of radiation that can kill half of the irradiated animals within 30 days. Similarly, LD50/60 refers to the dose of radiation that can kill half of the animals within 60 days. DRF is another quantity to describe the effectiveness of a radioprotector and is defined as the ratio of the dose required to cause death in the presence of the component divided by the dose required to create the same effect in the absence of component.
Statistical Analysis
The analysis of variance (Kruskal–Wallis test) was used for each dose under four treatments. A p-value of less than 0.05 was considered to be statistically significant. The SPSS for Windows software package (Release 22, SPSS Inc., Chicago, Illinois) was applied for the statistical analysis.
Results
Surviving rate of animals, after exposure to the radiation doses of 6, 7 and 8 Gy, in control group and treated groups with vitamin E, beta D-glucan and vitamin E + beta D-glucan are given in [Table/Fig-1,2,3 and 4]. DRF of these groups, with respect to the LD50/30 and LD50/60, were also given in [Table/Fig-5]. In [Table/Fig-6], LD50/30 and LD50/60 of the control and treated groups are presented.
[Table/Fig-6]:
Group | LD50/30 (Gy) | DRF | LD50/60 (Gy) | DRF |
---|---|---|---|---|
Control (C) | 8 | - | 6 | - |
Vitamin E (E) | 8 | 1 | 6 | 1 |
Beta Glucan (G) | 10 | 1.25 | 7 | 1.17 |
Beta D-Glucan + Vitamin E (G+E) | 11 | 1.375 | 8 | 1.33 |
Based on the statistical analysis of the results;
The difference of DRF in group G in comparison with group C was significant at both LD50/30 (p= 0.005) and LD50/60 (p= 0.005).
The difference of DRF in group E in comparison with group C was insignificant at both LD50/30 (p= 1.000) and LD50/60 (p=1.000).
The difference of DRF in group E + G in comparison with group C was significant at both LD50/30 (p≤ 0.001) and LD50/60 (p≤ 0.001), but in comparison with group G it was insignificant at both LD50/30 (p=0.395) and LD50/60 (p=0.395).
According to [Table/Fig-6], in control group, LD50/30 and LD50/60 are 8 and 6 Gy, respectively. Values of LD50/30 and LD50/60 in the group treated with vitamin E were same as that of control group, which indicate that vitamin E, alone, did not have effect on the animal resistance against ionizing radiation. For groups G and G + E of animals, we observed that, at the end of 30 days, number of animals killed by radiation did not reached to the ratio of 50%, therefore, we had to increase radiation doses up to 9, 10 and 11 Gy. The LD50/30 values for group G and group G + E was found 10 Gy and 11 Gy, respectively. Both findings show significant difference with that of control group (p<0.001), which means that both beta D-glucan and combination of beta D-glucan with vitamin E has radioprotective effect on animals. Any difference between these two groups was not observed. Also, after exposure of animals of group G and G + E to dose of 6 Gy, half of the animals did not die within the 60 days and it took 66 days to reach to this number. For these groups, LD50/60 was determined 7 Gy for group G and 8 Gy for group G + E, both were significantly higher than that of control group (p<0.005).
Discussion
These finding was another evidence to confirm that, beta D-glucan and its combination with vitamin E exhibit radioprotective effect. Our results agree with previous findings in which radioprotective properties of beta-glucan on immune system of the body was studied [14,17,21]. In a study, anti-tumour and radioprotectoty properties of beta D-glucan was measured on mice, based on the tumour volume, Natural Killer (NK) and Lymphokine Activated Killer (LAK) [22]. It was shown in treated group with beta D-glucan, weight and survival rate of animals not just had significant difference with those of control group, but level of NK and LAK was also increased. In other similar study, it was reported that chronic treatment with beta D-glucan decreased growth rate of tumour [23]. The reason of increased radioprotectory effect after administration of beta D-glucan was mentioned the hematopoietic effect as a result of increase of leukocytes and lymphocytes. In another attempt, anti-tumour effect of beta D-glucan in combination of vitamin C on breast and lung tumours was reported [24]. Authors of that study concluded that simultaneous presence of these two components as wells as anti-tumour effect of beta D-glucan had been the reason for that finding. Synergistic effect of beta D-glucan in combination of resveratrol on the immune system has also been reported in similar studies [25,26].
Of the main findings of current study was the synergistic effect of beta D-glucan in combination with vitamin E to increase body radioprotective capability, which is in a good agreement with previous studies [21,26]. On the other hand, DRF of group G + E was higher than that of group E, which means beta D-glucan increased radioprotective effect of vitamin E. However, DRF of group G + E was not significantly higher than that of group G.
Because of the effectiveness of beta D-glucan and its combination with vitamin E as a radioprotective agent, this component could be used in clinical context for the patients that, because of treatment operations, their immune systems have been weakened. However, comprehensive studies are required to translate this compound from bench to beside. For this reason, we conducted another research project to assess effect of beta D-glucan in reduction of side effects of ionizing radiation on healthy tissues of patients undergoing radiation based therapy. Also, because of the positive effect of beta D-glucan on the immune system, another study was planned to evaluate the effect of this substance on mitigation of chemotherapy side effects.
Limitation
In this attempt we used a fixed dose of beta D-glucan at 250 mg/body weight that is a limitation to this study, therefore, it is recommended to assess a similar study at different doses of this component in order to reach to an optimum dose of beta D-glucan as a radioprotective agent in combination with vitamin E.
Conclusion
The findings obviously demonstrated that, presence of beta D-glucan in the body of mice, during exposure to ionizing radiation, leads to DRF of higher than one, proving the radioprotectory effect of this agent. Also, we depicted that, while vitamin E had no radioprotectory effect on irradiated mice, beta D-glucan in combination with vitamin E increased resistance of mice against ionizing radiation.
Financial or Other Competing Interests
None.
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