Pattern of chromosomal aberrations persisting over 30 years in a Chernobyl Nuclear Power Plant accident survivor: study using mFISH

The long-term in vivo cytogenetic effects of high-dose radiation exposure can be traced in accidentally irradiated persons, and particularly useful for developing strategies of monitoring and therapy of such patients, as well as for elucidating the fundamental aspects of hematopoiesis and radiobiology. Using 24-color fluorescent in situ hybridization (mFISH), we analysed the frequency and the spectrum of chromosomal aberrations (CA) in peripheral blood lymphocytes of the Chernobyl Nuclear Power Plant (NPP) accident victim 30, 31, 32 and 33 years after acute accidental exposure to high-dose gamma radiation of the whole body. Totally, 993 metaphase cells were analyzed (or 219, 272, 258, 244 cells each year), of which 297 were aberrant. Our study demonstrated a constant aberrant cell frequency at 28% in 2016-2018 years, while in 2019, a significant increase up to 35% occurred due to contribution of significantly elevated frequency of simple aberrations in the absence of evident recent genotoxic factors. Four clonal aberrations were detected, three of which persisted for more than one year at a frequency up to 2.5% of analyzed cells. The distribution of 731 breakpoints per individual chromosomes was nearly proportional to their physical length, excepting Chromosomes 13 and 20, which were significantly breakpoint-deficient compared to the genome median rate. Monitoring of the long-term effects on chromosomal instability caused by radiation exposure is important for understanding and predicting the long-term effects of ionizing radiation.

Improved harvest and fixation methodology for isolated human peripheral blood mononuclear cells in cytokinesis-block micronucleus assay

PURPOSE

In suspected radiation exposures, cytokinesis-block micronucleus (CBMN) assay is used for biodosimetry by detecting micronuclei (MN) in binucleated (BN) cells in whole blood and isolated peripheral blood mononuclear cell (PBMC) cultures. Standardized harvest protocols for whole blood were published by the International Atomic Energy Agency (IAEA) in 2001 (Technical report no. 405) and 2011 (EPR-Biodosimetry). For isolated PBMC harvest, cytocentrifugation of fresh cells is recommended to preserve cytoplasmic boundaries for MN scoring. However, cytocentrifugation utilizes specialized equipment and long-term cell suspension storage is difficult. In this study, an alternative CBMN harvest protocol is proposed for laboratories interested in culturing PBMCs and storing fixed cells with routine biodosimetry methods.

MATERIALS AND METHODS

Peripheral blood from 4 males (24, 34, 41, 51 y.o.) and females (26, 37, 44, 56 y.o.) was irradiated with 0 and 2 Gy X-rays. For cells harvested with IAEA 2001 and 2011 protocols, whole blood was used. For cells harvested with our protocol (CRG), isolated PBMCs were used. CRG protocol was validated in DAPI, acridine orange and Giemsa stain, and in three other laboratories. Cytoplasm status, nuclear division index (NDI) and induced MN frequency (MN frequency at 2 Gy - background MN frequency at 0 Gy) (MN/1000 BN) of Giemsa-stained BN cells were compared in IAEA 2001, IAEA 2011, IAEA 2011 + formaldehyde (FA) and CRG protocols. Effects of low and high humidity spreading were evaluated.

RESULTS

>94% of 1000 BN cells were scorable with clear cytoplasmic boundaries in all donors harvested with CRG protocol. FA addition in IAEA 2011 protocol reduced cell rupture in whole blood cultures, but cell rupture was affected by age, sex and humidity. Almost all cells harvested with IAEA 2001 protocol had cytoplasm loss. PBMCs harvested with CRG protocol stained well in DAPI, acridine orange and Giemsa, and showed high scorable BN frequency in all laboratories. A higher NDI and a lower induced MN frequency were seen in 2 Gy isolated PBMC than whole blood cultures.

CONCLUSION

This quick CBMN harvest protocol for isolated PBMCs is a viable alternative to cytocentrifugation, as many scorable BN cells were obtained with routine biodosimetry reagents and equipment. IAEA 2011 + FA protocol should be used to improve CBMN harvest in whole blood cultures. Humidity during spreading should be optimized depending on the harvest protocol. NDI and MN frequency should be separately evaluated for whole blood and isolated PBMC cultures.