Association of inter- and intrachromosomal exchanges with the distribution of low- and high-LET radiation-induced breaks in chromosomes.

To study the effects of low- and high-linear energy transfer (LET) radiation on break locations within a chromosome, we exposed human epithelial cells in vitro to (137)Cs γ rays at both low and high dose rates, secondary neutrons at a low dose rate, and 600 MeV/u iron ions at a high dose rate. Breakpoints were identified using multicolor banding in situ hybridization (mBAND), which paints chromosome 3 in 23 different colored bands. For all four radiation scenarios, breakpoint distributions were found to be different from the predicted distribution based on band width. Detailed analysis of chromosome fragment ends involved in inter- or intrachromosomal exchanges revealed that the distributions of fragment ends participating in interchromosomal exchanges were similar between the two low-LET radiation dose rates and between the two high-LET radiation types, but the distributions were less similar between low- and high-LET radiations. For fragment ends participating in intrachromosomal exchanges, the distributions for all four radiation scenarios were similar, with clusters of breaks found in three regions. Analysis of the locations of the two fragment ends in chromosome 3 that joined to form an intrachromosomal exchange demonstrated that two breaks with a greater genomic separation can be more likely to rejoin than two closer breaks, indicating that chromatin folding can play an important role in the rejoining of chromosome breaks. Comparison of the breakpoint distributions to the distributions of genes indicated that the gene-rich regions do not necessarily contain more breaks. In general, breakpoint distributions depend on whether a chromosome fragment joins with another fragment in the same chromosome or with a fragment from a different chromosome.

Differences in heating methods may account for variation in reported effects on gammaH2AX focus formation.

Previously we have shown that heat shock cannot induce DNA damage in several mammalian cell lines, using gammaH2AX foci formation as an indicator for DNA damage. However, there have also been reports showing heat shock can induce DNA damage. In an effort to clarify why such differences exist among different studies, we examined the effects of five different heating methods, e.g., (1) heat block; (2) submerged in water bath; (3) half-submerged in water bath; (4) pre-heated medium; and (5) heating oven, on gammaH2AX foci formation in human amnion FL cells and Chinese hamster CHL cells. It was found that during a 24 h period, heating at 42 degrees C for 30 min showed no significant cytotoxicity, while 45 degrees C exhibited various degrees of cytotoxicity. The ability of these five methods to induce gammaH2AX foci was quite distinct, with only heat block inducing gammaH2AX foci at both 42 degrees C and 45 degrees C in both FL and CHL cells. The two cell types also responded differently to the different heating methods, with CHL being more sensitive to heat shock. Taken together, it is clear that certain heating methods can induce gammaH2AX foci formation; on the other hand, their effects differ in thermo-tolerant and non-tolerant cells. And the difference in gammaH2AX foci formation observed in different reports most likely is a consequence of the different heating methods used in the study. However, expression of gammaH2AX may not be used as a surrogate of cell killing.

Induction and transmission of wheat-Haynaldia villosa chromosomal translocations.

In order to develop more wheat-Haynaldia villosa translocations involving different chromosomes and chromosome segments of H. villosa, T. durum-H. villosa amphiploid was irradiated with 60Co gamma-rays at doses of 800, 1,200, and 1,600 rad. Pollen collected from the spikes 1, 2, and 3 days after irradiation were transferred to emasculated spikes of the common wheat cv. 'Chinese Spring'. Genomic in situ hybridization was used to identify wheat-H. villosa chromosome translocations in the M1 generation. Transmission of the identified translocation chromosomes was analyzed in the BC1, BC2, and BC3 generations. The results indicated that all three irradiation doses were highly efficient for inducing wheat-alien translocations without affecting the viability of the M1 seeds. Within the range of 800-1,600 rad, both the efficiency of translocation induction and the frequency of interstitial chromosome breakage-fusion increased as the irradiation dosage increased. A higher translocation induction frequency was observed using pollen collected from the spikes 1 day after irradiation over that of 2 or 3 days after irradiation. More than 70% of the translocations detected in the M1 generation were transmitted to the BC1 through the female gametes. All translocations recovered in the BC1 generation were recovered in the following BC2, and BC3 generations. The transmission ability of different translocation types in different genetic backgrounds showed an order of 'whole-arm translocation > small alien segment translocation > large alien segment translocation', through either male or female gametes. In general, the transmission ability through the female gametes was higher than that through the male gametes. By this approach, 14 translocation lines that involved different H. villosa chromosomes have been identified in the BC3 using EST-STS markers, and eight of them were homozygous.

Anticlastogenic effect of Ginkgo biloba extract in Graves' disease patients receiving radioiodine therapy.

BACKGROUND: Chromosomal damage, as assessed by clastogenic factors (CFs) and micronuclei (MN) appearance, after radioiodine therapy of Graves' disease has been reported. OBJECTIVE AND METHODS: Our objective was to evaluate the effect of Ginkgo biloba extract (EGb 761) supplementation on the time course (up to 120 d) of CFs and MN appearance in lymphocytes from patients with Graves' disease after iodine-131 ((131)I) therapy. Patients were randomly assigned to EGb 761 or placebo, in a blinded manner. RESULTS: In the placebo group, MN increased early (P < 0.001) after (131)I, peaking at the 21st day (P = 0.0003) and declining thereafter. In EGb 761-treated patients, MN increased early (P < 0.05), while returning toward baseline value thereafter. Therefore, mean MN increment was significantly higher in the placebo group as compared with EGb 761-treated patients (P < 0.01). Moreover, an early (P < 0.0001) and sustained (up to 35 d; P < 0.001) MN increase induced by CFs was observed in the placebo group. Conversely, in EGb 761-treated patients, MN increase induced by CFs never reached the statistical significance; therefore, the mean of the MN increments was significantly lower than in placebo (P < 0.05). A significant positive correlation between MN maximum increment and the bone marrow dose was observed in the placebo group only (P = 0.03). No significant difference was observed in clinical outcome between the two groups. CONCLUSIONS: EGb 761 supplementation neutralized genotoxic damage induced by radioiodine treatment, without affecting the clinical outcome. Although (131)I therapy is generally safe, our data suggest that Gingko biloba extracts may prevent genetic effects of radioiodine therapy for hyperthyroid Graves' disease.