Is Response to Genotoxic Stress Similar in Populations of African and European Ancestry? A Study of Dose-Response After in vitro Irradiation.

Background: Exposure to genotoxic stress such as radiation is an important public health issue affecting a large population. The necessity of analyzing cytogenetic effects of such exposure is related to the need to estimate the associated risk. Cytogenetic biological dosimetry is based on the relationship between the absorbed dose and the frequency of scored chromosomal aberrations. The influence of confounding factors on radiation response is a topical issue. The role of ethnicity is unclear. Here, we compared the dose-response curves obtained after irradiation of circulating lymphocytes from healthy donors of African and European ancestry. Materials and Methods: Blood samples from six Africans living in Africa, five Africans living in Europe, and five Caucasians living in Europe were exposed to various doses (0-4 Gy) of X-rays at a dose-rate of 0.1 Gy/min using an X-RAD320 irradiator. A validated cohort composed of 14 healthy Africans living in three African countries was included and blood samples were irradiated using the same protocols. Blood lymphocytes were cultured for 48 h and chromosomal aberrations scored during the first mitosis by telomere and centromere staining. The distribution of dicentric chromosomes was determined and the Kruskal-Wallis test was used to compare the dose-response curves of the two populations. Results: No spontaneous dicentric chromosomes were detected in African donors, thus establishing a very low background of unstable chromosomal aberrations relative to the European population. There was a significant difference in the dose response curves between native African and European donors. At 4 Gy, African donors showed a significantly lower frequency of dicentric chromosomes (p = 8.65 10-17), centric rings (p = 4.0310-14), and resulting double-strand-breaks (DSB) (p = 1.32 10-18) than European donors. In addition, a significant difference was found between African donors living in Europe and Africans living in Africa. Conclusion: This is the first study to demonstrate the important role of ethnic and environmental factors that may epigenetically influence the response to irradiation. It will be necessary to establish country-of-origen-specific dose response curves to practice precise and adequate biological dosimetry. This work opens new perspective for the comparison of treatments based on genotoxic agents, such as irradiation.

Biological Dosimetry Network in Africa: Establishment of a Dose-Response Curve Using Telomere and Centromere Staining.

PURPOSE: Biological dosimetry, based on the relationship between the absorbed dose after exposure to ionizing radiation and the frequency of scored aberrations, has been and continues to be an important tool for estimating the dose after exposure. Dicentric chromosomes are considered to be the most specific and sensitive aberration related to radiation exposure. Here, we established the dose-response curve following in vitro irradiation of circulating lymphocytes from healthy donors from three African countries after scoring unstable chromosomal aberrations. MATERIALS AND METHODS: Blood samples from 16 African donors were exposed to various doses (0 to 4 Gy) using an X-RAD320 x-ray system with a maximum photon energy of 250 kV at a dose rate of 0.1 Gy min. Blood lymphocytes were cultured for 48 h, and chromosomal aberrations were scored during the first mitosis by telomere and centromere staining. The distribution of dicentric chromosomes was determined. RESULTS: No dicentric chromosomes were found after the analysis of 2,669 first-division metaphases before in vitro exposure. We established a linear-quadratic dose-response curve based on the frequency of dicentric and ring chromosomes and calculated double-strand breaks, taking into account all scored aberrations. CONCLUSION: The generation of a specific dose-response curve for African donors will allow the practice of precise biological dosimetry in these countries. This work is the first step towards realizing an African biodosimetry network and the establishment of a biological dosimetry laboratory, which could play a major role in the application of radioprotection norms.

Telomere shortening and associated chromosomal instability in peripheral blood lymphocytes of patients with Hodgkin's lymphoma prior to any treatment are predictive of second cancers.

PURPOSE: To investigate a potential link between telomere length, chromosomal instability, and the advent of a second cancer (SC) in patients with Hodgkin's lymphoma (HL), who are known to be at risk for SCs. This study was premised on the finding that telomere dysfunction and DNA repair pathways were related to many pathologic conditions. METHODS AND MATERIALS: Three cohorts of patients with HL were studied: 73 who were prospectively followed >5 years after diagnosis (prospective HL cohort), 28 who developed a SC (SC HL cohort), and 18 long-term survivors with no evidence of disease or complication since their initial treatment (NED HL cohort). Telomere length was analyzed by a telomeric restriction fragment assay in peripheral blood lymphocytes. Thirty healthy donors and 70 patients with a newly diagnosed solid tumor were the control population. RESULTS: Compared with controls, patients from the prospective HL cohort, before any treatment, showed age-independent shorter telomeres (mean, 8.3 vs. 11.7 kb in healthy donors; <6 kb in 18% in HL patients), increased spontaneous chromosomal abnormalities, and increased in vitro radiation sensitivity (p < 10(-4) each). After treatment, telomere shortening was associated with cytogenetic profiles characterized by the persistence of complex chromosomal rearrangement and clonal aberrations. Moreover, the two cases of SC in the prospective HL patients had short telomeres and CCR initially. In addition, the SC HL cohort was characterized by markedly short telomeres (6.6 vs. 9.7 kb in the NED HL cohort), the presence of complex chromosome rearrangements, and increased in vitro radiation sensitivity. CONCLUSIONS: An intimate relationship between pre-treatment telomere shortening, chromosomal instability, radiation sensitivity and occurrence of SC was found in HL patients.

Chromosomal aberrations induced by chemotherapy and radiotherapy in lymphocytes from patients with breast carcinoma.

PURPOSE: Stable chromosomal aberrations (SCAs) have been found in circulating lymphocytes from patients treated for breast carcinoma. Therefore, we tried to define their incidence in such patients, to determine an in vitro dose-effect relationship, and to correlate these data with clinical parameters. METHODS AND MATERIALS: This prospective study included 25 patients who, after surgery, underwent either radiotherapy (RT) alone (n = 15) or RT combined with chemotherapy (n = 10). SCAs were scored using the fluorescent in situ hybridization technique before RT and 4 and 12 months after RT. Dose-effect curves were established by in vitro irradiation of blood samples with 2 and 4 Gy, before and after treatment. RESULTS: In all patients, the rate of SCAs increased significantly after external irradiation. No significant decrease in SCAs was observed during the first year after RT. RT and chemotherapy had no effect on the lymphocyte in vitro dose-effect relationship. No relationship was found in the distribution of patients between the yield of SCAs scored after external irradiation and after in vitro irradiation. SCAs after RT or in vitro irradiation did not correlate with family history of breast carcinoma or acute toxicity of treatment. More significantly, the yield of SCA after external irradiation was strongly related to the irradiation of the internal mammary chain and the supraclavicular lymph node area, suggesting that the volume of irradiated blood vessels was an essential parameter in determining the rate of SCAs. CONCLUSION: A high and stable yield of SCAs persisted at least 1 year after external irradiation. The nature of the volume irradiated containing large blood vessels was the major determinant of the observed biologic dose.

Sensitivity to radiation and alkylating agent of peripheral lymphocytes and fibroblasts in a Hoyeraal-Hreidarsson syndrome patient.

Hoyeraal-Hreidarsson syndrome (HHS) is a severe infantile variant of X-linked dyskeratosis congenita (DC). The authors report evidence of increased in vitro sensitivity to radiation and alkylating agent in circulating lymphocytes and fibroblasts obtained from a 7-year-old boy with HHS. A major telomere shortening was also found (3 kb) as compared to healthy donors (10 kb). The standard treatments, chemotherapy regimens, and radiation therapy were not possible. The data suggest that conditioning regimens including TBI should not be used when a bone marrow transplantation procedure is planned in these patients.