Biophysics of alpha particles in zebrafish embryos (in vivo)

Abstract

The biological effects and health risks induced by low dose radiation remain ambiguous [1] because the currently used linear no-threshold model (LNT) comes to a challenge by the radiation-induced effects such as bystander and hormetic effect in case of low dose radiation. For the radiation-induced bystander effect, evidence has proved that it results in supra-linear dose-response relationship. It means that the biological damage caused by ionizing radiation is not directly proportional to the dose. In addition, for the hormetic effect, it results in infra-linear dose-response relationship. In other words, a threshold exists, below which there would be no risk. Therefore, the bystander effect is considered to intensify the harmful consequences of irradiation whereas the hormetic effect is suggested to mitigate the stressful effects of radiation. It is essential to investigate and understand the radiation-induced effects in the view of protecting ourselves from low dose radiations. In the present study, zebrafish embryos are used as a vertebrate model to investigate both bystander and rescue effect. Zebrafish are commonly used to examine the environmental factors and pharmacological agents. This is because many soluble agents can pass through zebrafish via its skin [2]. Also, similar to humans, zebrafish have complex social interactions. Numerous research groups use zebrafish as a potential model to study human-related diseases especially in tumor-associated diseases. In this project, tricarbonylchloro(glycinato)ruthenium (II) (CORM-3) was employed to study the radiation-induced bystander and rescue effect. In fact, CORMs are regarded as a carbon monoxide releasing agent. Low concentration of exogenous carbon monoxide acts as an anti-inflammatory agent. Also, previous studies have shown that low concentration of carbon monoxide can attenuate radiation-induced bystander effect in vitro while it was found that the degree of attenuation is dependent on concentration [3]. Besides, previous experimental results showed that 20 μM of CORM-3 can completely suppress the bystander effect in vivo [4]. In this study, 20 μM of CORM-3 was used. In this project, we would like to investigate the relationship between the bystander and rescue effects when CORM-3 is employed compared with when no CORM-3 is used. In this study, a planar 241Am source with an activity of 0.1151μCi was used. 241Am source is an alpha-particle emitter with main energy of 5.49 MeV. It was found that the average radiation dose absorbed by each embryo was approximately 4.13 mGy. The numbers of apoptotic cells of the unirradiated (naïve) and irradiated embryos were counted when they were developed to 24 hours of fertilization (hpf) by the staining of the vital dye, that is acridine orange. Then, the apoptotic signals were captured under a fluorescent microscope. The present study revealed that the relationship between the radiation-induced bystander and rescue effect when 0 and 20 μM CORM-3 were used. In the absence of CORM-3, both bystander and rescue effects were observed and the apoptotic signals between irradiated embryos and naïve embryos showed no significant difference. For 20 μM CORM-3, no bystander effect was observed which is in agreement with the previous study by Choi et al. [4]. Interestingly, in the same study, it was found that the rescue effect was observed.