Dicentrics

The nucleus of all eucariotic cells contains the carrier of the genetic information in the chromosomes. It is possible to visualize the chromosomes and analyze their number and pattern during a special period of cell division (the metaphase). Alterations from their normal shapes are observed as structural chromosome aberrations. These are chromosome type aberrations (terminal and interstitial deletions, dicentrics and rings), chromatid aberrations (gaps, breaks and exchanges) and sister chromatid exchanges. Spontanous frequencies of such chromosome... 

Figure 1. Total chromosome type aberration frequencies (sum of dicentrics, terminal and interstitial deletions) in the population of Badgastein.

Vulpis (1973) added pure natural boron as H3B03, which contains about 19% B-10, to the blood culture. It was then irradiated with thermal neutrons from a reactor. The reaction of B-10(n,a)Li-7 within the culture served as alpha source. The dose range was 35 to 195 mGy according to her dose estimation which was complicated by subtracting the dose due to the reactor radiation alone. The dicentric chromosomes appeared to follow a linear response up to about 0.18 Gy and then leveled off to a plateau due to a "saturation effect. The relative biological efficiency (RBE) with respect to X-rays with the doses up to 5f1 Gy was found to be 23. v... 

Edwards et al. (1980) used a Cm-242 source to irradiate externally a thin film of blood. The energy of 4 9 MeV of the alpha particles were almost entirely absorbed by the blood. The dicentrics yield was linear from 0.11 to 4 2 Gy. From this resulted a RBE of 17.9 with respect to Co-60 gamma rays. It was, however, only 6.0 at the initial slope. To explain this RBE, which was low compared to that expected from neutron experiments, a model is presented taking into account cell killing and mitotic delay. 

Occupational exposure of 20 workers to pentachlorophenol at concentrations that ranged from 1.2 to ISOpg /m for 3-34 years did not result in any increased incidence of sister chromatid exchanges or chromosomal aberrations. In another report, significant increases in the incidence of dicentric chromosomes and acentric fragments were detected in the peripheral lymphocytes of exposed workers the frequency of sister chromatid exchanges was not increased." ... 

Examples of sublesions are single chromosome breaks that combine to produce a dicentric aberration or single-strand DNA breaks, which, when in close proximity, result in double-stranded DNA breaks. The expression, Eq. (35), provides the link between the micro-dosimetric quantity z, and the dose-effect coefficients a and p. 

Fig. 7.2 Frequency of rings and dicentrics in Chinese hamster liver cells following acute (50-150 mGy min 5-15 rad min- ) or protracted in viix) exposures to Co gamma radiation (from Brooks et al., 1971).

Julg, A. New procedure for the semi-theoretical calculation of mono- and dicentric coulombic integrals. J. Chim. Phys. 55, 413 (1958). 

Blazak WF, Stewart BE, Galperin I, et al. 1986. Stable dicentric chromosomes induced by chemical mutagens in L4178Y mouse lymphoma cells. Mutat Res 173 263-266. 

Chromosome changes Increase in dicentric chromosomes and chromosome fragments noted. 

In a study involving 43 gas-exposed females and 40 gas-exposed males 3 years after the disaster, a signiflcant increase in chromosomal aberration was reported these aberrations included breaks, gaps, and dicentric rings, which were more marked in females than in males (Ghosh et al, 1990). Chromosomal aberrations (Goswami et al, 1985, 1990 Ghosh et al, 1990) and cell cycle abnormalities have been identifled in Bhopal victims (Deo et al, 1987). 

Miller, A.C., Xu, J., Stewart, M., Brooks, K., Hodge, S., Shi, L., Page, N., McClain, D. (2002h). Observation of radiation-specific damage in human cells exposed to depleted uranium dicentric frequency and neoplastic transformation as endpoints. Radiat. Prot. Dosimetry 99 275-8. 

In a series of in vitro experiments on a human lymphocyte culture system, it was reported that chlorine induced chromatid and chromosome breaks, translocations, dicentric chromosomes, and gaps. 

Alpha radiation from plutonium produces cytotoxic and genotoxic effects in cultured cells. These can include cell death, chromosomal aberrations (dicentrics, translocations, and complex exchanges), and pretransformation molecular alterations such as upregulation of oncogene products coupled with inactivation of tumor suppressor genes. 

Figure 8.8 Human metaphase figure showing a dicentric chromosome (a) and an acentric fragment (b).

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