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.

Effect of low and chronic radiation exposure: a case-control study of mental retardation and cleft lip/palate in the monazite-bearing coastal areas of southern Kerala.

A population-based 1:3 age-matched case-control study was conducted during 2006-2009 to assess the role of high-level natural radiation (>1 mSv/year) on congenital mental retardation and cleft lip/palate in the southwest coastal area of Kerala. Dosimetry was carried out in the house where parents resided during conception and the subsequent two trimesters of pregnancy of the study subject. Conditional logistic regression did not suggest any statistically significant association of either mental retardation (n = 445) or cleft lip/palate (n = 116) with high-level natural radiation. The odds of mental retardation and cleft lip/palate among those exposed to high-level natural radiation relative to normal levels of natural background radiation (≤1 mSv/year) were 1.26 (95% CI: 0.91-1.73) and 0.56 (95% CI: 0.31-1.02), respectively, after controlling for gender and maternal age at birth of the study subject. The data did not suggest any dose-related trend in the risk of either mental retardation (P = 0.113) or cleft lip/palate (P = 0.908). Notwithstanding the use of a single dose estimate to reconstruct past radiation exposure and the complex etiology of congenital malformations, it may reasonably be concluded that the prevailing high-level natural radiation in the study area does not appear to increase the risk of either mental retardation or cleft lip/palate among offspring of parents staying in the area.

Evaluation of spontaneous DNA damage in lymphocytes of healthy adult individuals from high-level natural radiation areas of Kerala in India.

Inhabitants of the high-level natural radiation areas (>1 mSv year(-1)) of Kerala in southwest India were evaluated for basal damage (spontaneous DNA strand breaks and alkali-labile sites) by the alkaline comet assay and oxidative DNA damage (ENDO III- and hOGG1-sensitive sites) by the enzyme-modified comet assay. Of the 67 adult male subjects studied, 45 were from high-level natural radiation areas and 22 subjects were from a nearby normal-level natural radiation area (≤1 mSv year(-1)). Basal damage due to the age and residential area (normal-level natural radiation area/high-level natural radiation areas) of the donors showed significant interaction (P < 0.001) when all subjects were analyzed using a general linear model (GLM). In subgroup analysis, basal damage increased with age in subjects from the normal-level natural radiation area (P = 0.02), while a significant negative correlation (P = 0.002) was observed in subjects from high-level natural radiation areas. Further, basal damage in elderly subjects from high-level natural radiation areas was significantly (P < 0.001) lower compared to the subjects from the normal-level natural radiation area. Oxidative DNA damage was not influenced by age, smoking habit or residential area in the entire sample. However, in a subgroup analysis, hOGG1-sensitive sites showed a significant increase with age in subjects from high-level natural radiation areas (P = 0.005). ENDO III-sensitive sites increased with natural radiation exposure in subjects from high-level natural radiation areas (P = 0.02), but when stratified according to smoking, a significant increase was observed only in smokers (P = 0.01). To the best of our knowledge, this is the first study on basal and oxidative DNA damage in healthy adults of this population. However, our findings need more validation in a larger study population.

Could a strong alkali deproteinization replace the standard lysis step in alkaline single cell gel electrophoresis (comet) assay (pH>13)?

The alkaline version of single cell gel electrophoresis (comet) assay is widely used for evaluating DNA damage at the individual cell level. The standard alkaline method of the comet assay involves deproteinization of cells embedded in agarose gel using a high salt-detergent lysis buffer, followed by denaturation of DNA and electrophoresis using a strong alkali at pH>13 [N.P. Singh, M.T. McCoy, R.R. Tice, E.L. Schneider, A simple technique for quantitation of low levels of DNA damage in individual cells, Exp. Cell. Res. 175 (1988) 184-191]. However, a recent report showed that a strong alkali treatment results in simultaneous deproteinization of cells and denaturation of genomic DNA [P. Sestili, C. Martinelli, V. Stocchi, The fast halo assay: an improved method to quantify genomic DNA strand breakage at the single cell-level, Mutat. Res. 607 (2006) 205-214]. This study was carried out to test whether the strong alkali deproteinization of cells could replace the high salt-detergent lysis step used in the standard method of the alkaline comet assay. Peripheral blood lymphocytes from 3 healthy individuals were irradiated with gamma rays at doses varying between 0 and 10 Gy. Following irradiation, the comet assay was performed according to the standard alkaline method (pH>13) and a modified method. In the modified method, agarose embedded cells were treated with a strong alkali (0.3M NaOH, 0.02 M Trizma and 1mM EDTA, pH>13) for 20 min to allow deproteinization of cells and denaturation of DNA. This was followed by electrophoresis using the same alkali solution to obtain comets. DNA damage expressed in terms of comet tail length, percentage of DNA in comet tail and tail moment obtained by the standard alkaline method and the modified method were compared. In both methods, DNA damage showed a good correlation with the dose of gamma ray. The results indicate a satisfactory sensitivity of the modified method in detecting radiation-induced DNA damage in human peripheral blood lymphocytes.

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 (