Premature chromosome condensation assay to study influence of high-level natural radiation on the initial DNA double strand break repair in human G0 lymphocytes.

The inherent capacity of individuals to efficiently repair ionizing radiation induced DNA double strand breaks (DSBs) may be inherited, however, it is influenced by several epigenetic and environmental factors. A pilot study tested whether chronic low dose natural radiation exposure influences the rejoining of initial DNA DSBs induced by a 2 Gy γ-irradiation in 22 individuals from high (>1.5 mGy/year) and normal (≤1.5 mGy/year) level natural radiation areas (H&NLNRA) of Kerala. Rejoining of DSBs (during 1 h at 37 °C, immediately after irradiation) was evaluated at the chromosome level in the presence and absence of wortmannin (a potent inhibitor of DSB repair in normal human cells) using a cell fusion-induced premature chromosome condensation (PCC) assay. The PCC assay quantitates DSBs in the form of excess chromosome fragments in human G0 lymphocytes without the requirement for cell division. A quantitative difference was observed in the early rejoining of DNA DSBs between individuals from HLNRA and NLNRA, with HLNRA individuals showing a higher (P = 0.05) mean initial repair ratio. The results indicate an influence of chronic low dose natural radiation on initial DNA DSB repair in inhabitants of HLNRA of the Kerala coast.

Radio-adaptive response in peripheral blood lymphocytes of individuals residing in high-level natural radiation areas of Kerala in the southwest coast of India.

The present study investigates whether the chronic low-dose radiation exposure induces an in vivo radio-adaptive response in individuals from high-level natural radiation areas (HLNRA) of the Kerala coast. Peripheral blood samples from 54 adult male individuals aged between 26 and 65 years were collected for the study with written informed consent. Each of the whole blood sample was divided into three, one was sham irradiated, second and third was exposed to challenging doses of 1.0 and 2.0 Gy gamma radiation, respectively. Cytokinesis-block micronucleus (CBMN) assay was employed to study the radio-adaptive response. Seventeen individuals were from normal-level natural radiation area (NLNRA ≤1.5 mGy/year) and 37 from HLNRA (> 1.5 mGy/year). Based on the annual dose received, individuals from HLNRA were further classified into low-dose group (LDG, 1.51-5.0 mGy/year, N = 19) and high-dose group (HDG >5.0 mGy/year, N = 18). Basal frequency of micronucleus (MN) was comparable across the three dose groups (NLNRA, LDG and HDG, P = 0.64). Age of the individuals showed a significant effect on the frequency of MN after challenging dose exposures. The mean frequency of MN was significantly lower in elder (>40 years) individuals from HDG of HLNRA as compared to the young (≤40 years) individuals after 1.0 Gy (P < 0.001) and 2.0 Gy (P = 0.002) of challenging doses. However, young and elder individuals within NLNRA and LDG of HLNRA showed similar frequency of MN after the challenging dose exposures. Thus, increased level of chronic low-dose radiation (>5.0 mGy/year) seems to act as a priming dose resulting in the induction of an in vivo radio-adaptive response in elder individuals of the Kerala coast.

Peripheral blood lymphocyte micronucleus frequencies in men from areas of Kerala, India, with high vs normal levels of natural background ionizing radiation.

We have measured the frequencies of micronuclei (MN) in adult male individuals living in areas of the Kerala coast, southwest India, with either high (HLNRA, >1.5mGy/year) or normal levels of natural ionizing radiation (NLNRA, ≤1.5mGy/year). Blood samples were obtained from 141 individuals, 94 from HLNRA and 47 from NLNRA, aged 18-72, and were subjected to the cytokinesis-block micronucleus (CBMN) assay. An average of 1835 binucleated (BN) cells per individual were scored. The overall frequency of MN (mean±SD) was 11.7±6.7 per 1000 BN cells. The frequencies of MN in the HLNRA (11.7±6.6) and NLNRA (11.6±6.7) were not statistically significantly different (P=0.59). However, a statistically significant (P<0.001) age-dependent increase in MN frequency was observed among individuals from both HLNRA and NLNRA. No natural background radiation dose-dependent increase in MN frequency was seen. MN frequency was not influenced by tobacco smoking or chewing but it was increased among individuals consuming alcohol. Chronic low-dose radiation in the Kerala coast did not have a significant effect on MN frequency among adult men.

Cytogenetic studies on newborns from high and normal level natural radiation areas of Kerala in southwest coast of India.

PURPOSE: To study, characterize and compare chromosome aberrations and karyotype anomalies among newborns from high (> 1.5 mGy/y) and normal (≤ 1.5 mGy/y) level natural radiation areas of monazite-sand bearing southwest coast of Kerala in India. MATERIALS AND METHODS: Cord blood samples from newborns were collected from selected Government hospitals in heparinized vials and cultures were set up employing standard microculture techniques, slides were prepared, coded and stained with giemsa. Well spread metaphases were analyzed for chromosome aberrations and karyotype anomalies. RESULTS: A total of 1,267,788 metaphases from 27,295 newborns of mothers aged 17-45 years (17,298 from high and 9,997 from normal level radiation areas) were analyzed during 1986-2007. Frequencies of dicentrics in high and normal level radiation areas were 1.90 ± 0.14 and 2.01 ± 0.26 per 10,000 cells, respectively (Relative frequency [RF] = 0.94; 95% CI: 0.71-1.26). Karyotype anomalies had a frequency of 5.49‰ and 6.7‰, respectively (RF = 0.82; 95% CI: 0.60-1.12). No dose-related trend was observed in chromosome aberrations or karyotype anomalies. CONCLUSION: Frequencies of chromosomal aberration and karyotype anomalies between the newborns from the high level natural radiation area (HLNRA) and normal level natural radiation areas (NLNRA) were very similar.

Spontaneous frequency of micronuclei among the newborns from high level natural radiation areas of Kerala in the southwest coast of India.

PURPOSE: The present study was an attempt to determine the spontaneous frequency of micronuclei (MN) in newborns from High Level Natural Radiation Areas (HLNRA) and the adjoining Normal Level Radiation Areas (NLNRA) of the monazite-bearing Kerala Coast in Southern West India using Cytochalasin Blocked Micronuclei (CBMN) assay. MATERIALS AND METHODS: Human umbilical cord blood samples were collected from a total number of 271 newborns (61 from NLNRA and 210 from HLNRA), born to mothers aged between 17 and 37 years (mean maternal age: 24.08 +/- 4.23 years). Lymphocyte cultures were set up following microculture techniques and cultures were terminated at 72 hours. Cytochalasin B at a concentration of 4.0 microg/ml was added to the lymphocyte cultures at 44 h. Enumeration of micronuclei was restricted to Cytochalasin Blocked binucleated (BN) cells only. RESULTS: The frequency of MN among the newborns from NLNRA (1.40 +/- 0.12) per 1000 BN cells was not statistically significant as compared to HLNRA newborns (1.33 +/- 0.04) per 1000 BN cells. Our data did not show any radiation dose response. Odds ratios (OR) and confidence intervals (CI) have been calculated to see statistical significance in the mean MN frequency among the newborns from various dose groups with respect to control and it did not reveal any significant difference (p > 0.05). A marginal increase in the frequency of micronuclei was observed among the female newborns as compared to males with increasing mothers' age groups except for the mothers aged > 30 years, though not statistically significant. CONCLUSION: The baseline frequency of micronuclei in HLNRA newborns is not statistically different from NLNRA newborns suggesting that elevated level of naturally occurring radiation has no significant effect on the induction of micronuclei frequency among the newborns.

Genetic monitoring of the human population from high-level natural radiation areas of Kerala on the southwest coast of India. II. Incidence of numerical and structural chromosomal aberrations in the lymphocytes of newborns.

Cytogenetic studies using cord blood samples from newborns from high-level natural radiation areas of the Kerala coast in Southwest India have been in progress since 1986. A total of 963,940 metaphases from 10,230 newborns have been screened for various types of chromosomal aberrations. Comparison of 8,493 newborns (804,212 cells) from high-level natural radiation areas (dose rate >1.5 mGy/year) and 1,737 newborns (159,728 cells) from normal-level natural radiation areas (