Direct and bystander effects in human blood lymphocytes exposed to ²⁴¹Am alpha particles and the relative biological effectiveness using chromosomal aberration and micronucleus assay

Abstract

Purpose: It is important to understand the significance of alpha (α) radiation-induced bystander effects (RIBE) and its relative biological effectiveness (RBE); this is because the phenomenon is not universal and the mechanism is unclear and because the RBE is widely varying and projected to be very high.

Materials and methods: Isolated lymphocytes from healthy volunteers (n = 10) were exposed to either low fluence α-particles (²⁴¹Am), γ-rays (⁶⁰Co), or X-rays (225 kVp and 6 MV). Co-culture methodology was employed to investigate bystander effects (BEs). Chromosomal aberrations (CA) and micronucleus (MN) formation were used to study the BE and calculated RBE.

Results: Lymphocytes directly exposed to the types of radiation used showed a dose-dependent increase in the frequency of CA and MN; dose independent increases in the frequency of these chromosomal damages in co-cultured bystander cells, implies that all three types of radiation-induced a BE. The calculated RBE at the level of 5% induced aberrations varied between 9 and 20.

Conclusion: The magnitude of low fluence α-particle induced RIBE is higher than in low LET (linear energy transfer) radiation. The RBE also varies depending upon the endpoints used and adds up to targeted effects. Since the endpoint of CA is considered as an important and early marker of risk prediction, the RIBE and RBE using CA as a marker are relevant for radiation protection purposes.

Keywords:

• Relative biological effect
• radiation-induced bystander effect
• chromosomal aberration
• micronucleus
• 241Am α-particle

Acknowledgments

The authors thank Professor Edouard Azzam, Department of Radiology, New Jersey Medical School, for his technical input and editing the manuscript and Dr. Chinnadurai Mani, Department of Cell Biology and Biochemistry, Texas Tech University Health Sciences Centre, Lubbock, Texas, USA, for editing the manuscript.

Disclosure statement

All the authors declare that there is no conflict of interest.

Additional information

Funding

The authors sincerely acknowledge the financial assistance from Atomic Energy Regulatory Board Government of India [grant number AERB/CSRP/Proj. No. 58/04/2014].

Notes on contributors

K. Karthik

K. Karthik is a CSIR-Senior Research Fellow, currently working on the Relative Biological effects of High LET radiation using cytogenetics markers such as dicentric chromosomes, micronucleus, and gene expression.

Vasumathy Rajan

Vasumathy Rajan is a scientific assistant at BARC, Mumbai, currently working on alpha particle induced bystander effects.

Badri N. Pandey

Badri N. Pandey is scientist ‘G’, Head, Radiation Signalling and Cancer Biology Section, Radiation Biology and Health Sciences Division, Bhabha Atomic Research Centre. His area of work is on the effects of radiation on signalling in cancer cells.

K. Sivasubramanian

K. Sivasubramanian is scientist ‘F’ at IGCAR, Kalpakkam, his work is mainly focused on the chemical and biological dosimetry.

Solomon F.D. Paul

Solomon F. D. Paul is a Head, Department of Human Genetics, currently working on radiation biodosimetry and gene polymorphism responsible for diabetes.

P. Venkatachalam

P. Venkatachalam is a Professor in Human Genetics, currently working on Radiation biodosimetry, Biological effects of low dose radiation and RBE of alpha particle radiation.