Differential radiation effects in smokers--culture time dependence of the yield of gamma ray-induced chromosome damage in first division metaphases.
OBJECTIVE
Telomeric associations (TA) and unstable chromosomal aberration (CA) transmission through M1-M4 metphases (first to fourth division) in gamma-ray irradiated G0 lymphocytes in 2 smokers were examined, since TA in conventionally stained chromosomes were reported earlier as a sensitive cytogenetic marker in mutagen-exposed populations. The purpose of the present study is an extension of our earlier studies on unstable CA transmission through successive mitotic divisions.


METHODS
The bromodeoxyuridine (BrdU) incorporation and fluorescence plus giemsa (FPG) method for M1-M5 metaphase analysis was carried out at 50, 72, 96 h to analyse TA and CA in conventionally and FPG stained chromosomes after irradiation of human blood samples with 3 Gy of gamma-rays. In situ hybridization (ISH) with enzymatic/fluorescence detection was used to analyse radiation-induced aneuploidy and TA. Analysis was carried out on sister chromatid exchanges (SCE) in M2 cells at 72 h and micronuclei (MN) at 24, 50, 72, 96 h.


RESULTS
TA, corroborated by the absence of acentric fragments, were not detected in conventional/FPG stained/ISH chromosomes. Chromosome 21 aneuploidy was observed. Significant differences in mean frequencies of dicentrics/micronuclei (MN)/SCE with high frequency cells (HFC) were found in smokers after irradiation compared to non-smokers. Higher radiation induced CA in M1 cells were found with extended culture time. Induction of giant cells with mirror dicentrics, tricentrics and rings were found.


CONCLUSIONS
TA in conventional or FPG stained metaphase chromosomes is not a sensitive cytogenetic marker for mutagen exposed population screening. Higher radiation induced CA frequencies in M1 cells with extended culture time were indicative of a delay in cell cycle progression of aberrant cells or different lymphocyte subset populations. Bridge-breakage-fusion (BBF) events due to dicentrics may be instrumental in the perpetuation of chromosomal instability. Differential effects were noted in radiation-induced dicentric, SCE and MN frequencies in smokers compared to non-smokers. Heavy smoking could be a confounding variable in chromosome-based biodosimetry and biomonitoring studies. Giant cells may denote a switch to amitotic modes of cell survival, providing additional mechanisms of genotoxic resistance.
Krishnaja
Ayyathan P
AP
Genetic Toxicology and Chromosome Studies Section, Radiation Biology and Health Sciences Division, Bhabha Atomic Research Centre, Mumbai, India. krishnja@apsara.barc.gov.in
Sharma
Narinder K
NK
D000328:Adult; D002478:Cells, Cultured; D002869:Chromosome Aberrations / Q000528:radiation effects*; D002875:Chromosomes / Q000528:radiation effects*; D004307:Dose-Response Relationship, Radiation; D005720:Gamma Rays; D006801:Humans; D008214:Lymphocytes / Q000528:radiation effects*; D008297:Male; D008677:Metaphase / Q000528:radiation effects*; D008875:Middle Aged; D011829:Radiation Dosage; D012907:Smoking / Q000235:genetics* / Q000378:metabolism*