ALBERT

Description: We reported previously that exposure of normal human fibroblasts in G2 phase of the cell cycle to high-LET radiation produces a much higher frequency of isochromatid breaks than exposure to gamma rays. We concluded that an increase in the production of isochromatid breaks is a signature of initial high-LET radiation-induced G2-phase damage. In this paper, we report the repair kinetics of isochromatid breaks induced by high-LET radiation in normal G2-phase human fibroblasts. Exponentially growing human fibroblasts (AG1522) were irradiated with gamma rays or energetic carbon (290 MeV/nucleon), silicon (490 MeV/nucleon), or iron (200 MeV/nucleon) ions. Prematurely condensed chromosomes were induced by calyculin A after different postirradiation incubation times ranging from 0 to 600 min. Chromosomes were stained with Giemsa, and aberrations were scored in cells at G2 phase. G2-phase fragments, the result of the induction of isochromatid breaks, decreased quickly with incubation time. The curve for the kinetics of the rejoining of chromatid-type breaks showed a slight upward curvature with time after exposure to 440 keV/microm iron particles, probably due to isochromatid-isochromatid break rejoining. The formation of chromatid exchanges after exposure to high-LET radiation therefore appears to be underestimated, because isochromatid-isochromatid exchanges cannot be detected. Increased induction of isochromatid breaks and rejoining of isochromatid breaks affect the overall kinetics of chromatid-type break rejoining after exposure to high-LET radiation.

Description: No abstract available

Description: Although cells derived from Ataxia Telangiectasia (AT) patients are known to exhibit abnormal responses to ionizing radiations, its underlying mechanism still remains unclear. Previously, the authors reported that at the same gamma-irradiation dose AT cells show higher frequencies of misrepair and deletions compared to normal human fibroblast cells. In this study, we investigated the effects of heavy ions beams on chromosomal aberrations in normal and AT cells. Normal and AT fibroblast cells arrested at G0/G1 phase were irradiated with 2 Gy of X-rays, 490 MeV/u Silicon (LET 55 keV/m), 500 MeV/u Iron (LET 185 keV/m) and 200 MeV/u Iron (LET 440 keV/m) particles, and then cells were allowed to repair for 24 hours at 37 degrees before subculture. Calyculin-A induced PCC method was employed to collect G2/M chromosomes and whole DNA probes 1 and 3 were used to analyze chromosomal aberrations such as color-junctions, deletions, simple exchanges (incomplete and reciprocal exanges) and complex-type exchanges. The percentages of aberrant cells were higher when normal and AT cells were exposed to heavy ions compared to X-rays, and had a tendency to increase with increasing LET up to 185 keV/m and then decreased at 440 keV/m. When the frequency of color-junctions per cell was compared after X-ray exposure, AT cells had around three times higher frequency of color-junctions (mis-rejoining) than normal cells. However, at 185 keV/m there was no difference in the frequency of color-junctions between two cell lines. It was also found that the frequency of simple exchanges per cell was almost constant in AT cells regardless LET levels, but it was LET dependent for normal cells. Interestingly, the frequency of simple exchanges was higher for AT cells when it was compared at 185 keV/m but AT cells had more complex-type exchanges at the same LET levels. Heavy ions are more efficient in inducing chromosome aberrations in normal and AT cells compared to X-rays, and the aberration types between normal and AT fibroblast appeared different probably due to difference in the ATM gene function.

Description: We have determined the differences in the effects of continual prostaglandin E(sub 2) (PGE(sub 2) treatment in aged (non-growing) and young (growing) cancellous bone sites in 7-month-old Sprague-Dawley rats. The sites involved are the aged distal tibial metaphysis (DTM) with a closed epiphysis and the young proximal tibial metaphysis (PTM) with a slow growing, open epiphysis. The study involved rats treated with 0, 1, 3 or 6 mg PGE(sub 2)/kg/d for 60, 120 and 180 days. Static and dynamic histomorphometry of percent trabecular area, and tissue-referent bone formation rate (BFR/TV) were determined in both DTM and PTM. In pretreatment controls, the secondary spongiosa of the two metaphyses contain the same amount of cancellous bone (11% in DTM vs. 13% in PTM), but markedly less bone formation in DTM (0.6%/y in DTM vs. 41.5%/y in PTM). After 60 days of 6 mg PGE(sub 2)/kg/d treatment, %Tb.Ar was increased 607% in DTM and 199% in PTM, BFR/TV was increased to nearly 14 fold in DTM and only 5 fold in PTM. These results indicated the aged metaphysis of the DTM was much more responsive to PGE(sub 2) treatment than young, growing metaphysis of the PTM. The results of 120 and 180 days treatment did not significantly differ from 60 days treatment in both sites, indicating that the effect of continuous daily PGE2 treatment were in equilibrium after 60 days. We concluded that aged metaphysis was much more responsive to PGE(sub 2) treatment than young growing metaphysis.

Description: We have determined the differences in the effects of continual prostaglandin E2 (PGE2) treatment in aged (non-growing) and young (growing) cancellous bone sites in 7 month-old Sprague-Dawley rats. The sites involved are the aged Distal Tibial Metaphysis (DTM) with a closed epiphysis and the young Proximal Tibial Metaphysis (PTM) with a slow growing, open epiphysis. The study involved rats treated with 0, 1, 3 or 6 mg PGE2/kg/d for 60, 120 and 180 days. Static and dynamic histomorphometty of percent trabecular area, and tissue-referent bone formation rate (BFR/TV) were determined in both DTM and PTM. In pretreatment controls, the secondary spongiosa of the two metaphyses contain the same amount of cancellous bone (11% in DTM vs. 13% in PTM), but markedly less bone formation in DTM (0.6%/y in DTM vs. 41.5%/y in PTM). After 60 days of 6 mg PGE2/kg/d treatment, %Tb.Ar was increased 607% in DTM and 199% in PTM, BFR/TV was increased to nearly 14 fold in DTM and only 5 fold in PTM. These results indicated the aged metaphysis of the DTM was much more responsive to PGE2 treatment than young, growing metaphysis of the PTM. The results of 120 and 180 days treatment did not significantly differ from 60 days treatment in both sites, indicating that the effect of continuous daily PGE2 treatment were in equilibrium after 60 days. We concluded that aged metaphysis was much more responsive to PGE2 treatment than young growing metaphysis.

Description: Radiation-induced chromosome damage can be measured in interphase using the Premature Chromosome Condensation (PCC) technique. With the introduction of a new PCC technique using the potent phosphatase inhibitor calyculin-A, chromosomes can be condensed within five minutes, and it is now possible to examine the early damage induced by radiation. Using this method, it has been shown that high-LET radiation induces a higher frequency of chromatid breaks and a much higher frequency of isochromatid breaks than low-LET radiation. The kinetics of chromatid break rejoining consists of two exponential components representing a rapid and a slow time constant, which appears to be similar for low- and high- LET radiations. However, after high-LET radiation exposures, the rejoining process for isochromatid breaks influences the repair kinetics of chromatid-type breaks, and this plays an important role in the assessment of chromatid break rejoining in the G2 phase of the cell cycle.