Excess risk of leukemia and brain tumors after CT scans in children has been reported. We performed dicentric chromosome assay (DCAs) before and after CT scan to assess effects of low-dose ionizing radiation on chromosomes. Peripheral blood (PB) lymphocytes were collected from 10 patients before and after a CT scan. DCA was performed by analyzing either 1,000 or 2,000 metaphases using both Giemsa staining and centromere-fluorescence in situ hybridization (Centromere-FISH). The increment of DIC formation was compared with effective radiation dose calculated using the computational dosimetry system, WAZA-ARI and dose length product (DLP) in a CT scan. Dicentric chromosome (DIC) formation increased significantly after a single CT scan, and increased DIC formation was found in all patients. A good correlation between the increment of DIC formation determined by analysis of 2,000 metaphases using Giemsa staining and those by 2,000 metaphases using Centromere-FISH was observed. However, no correlation was observed between the increment of DIC formation and the effective radiation dose. Therefore, these results suggest that chromosome cleavage may be induced by one CT scan, and we recommend 2,000 or more metaphases be analyzed in Giemsa staining or Centromere-FISH for DCAs in cases of low-dose radiation exposure.
We recently reported an increase in dicentric chromosome (DIC) formation after a single computed tomography (CT) scan (5.78–60.27 mSv: mean 24.24 mSv) and we recommended analysis of 2000 metaphase cells stained with Giemsa and centromere-FISH for dicentric chromosome assay (DCA) in cases of low-dose radiation exposure. In the present study, we analyzed the frequency of chromosome translocations using stored Carnoy's-fixed lymphocyte specimens from the previous study; these specimens were from 12 patients who were subject to chromosome painting of Chromosomes 1, 2 and 4. Chromosomes 1, 2 and 4 were analyzed in ∼5000 cells, which is equivalent to the whole-genome analysis of almost 2000 cells. The frequency of chromosome translocation was higher than the number of DICs formed, both before and after CT scanning. The frequency of chromosome translocations tended to be higher, but not significantly higher, in patients with a treatment history compared with patients without such a history. However, in contrast to the results for DIC formation, the frequency of translocations detected before and after the CT scan did not differ significantly. Therefore, analysis of chromosome translocation may not be a suitable assay for detecting chromosome aberrations in cases of low-dose radiation exposure from a CT scan. A significant increase in the frequency of chromosome translocations was not likely to be detected due to the high baseline before the CT scan; the high and variable frequency of translocations was probably due to multiple confounding factors in adults.
To clarify the significance of peptidergic nerves in Hirschsprung's disease (aganglionosis), hypoganglionosis, and neuronal intestinal dysplasia (NID), we investigated enteric nerve responses in colonic tissues obtained from patients with these diseases. Colonic tissue specimens were obtained from 12 patients with aganglionosis, 8 patients with hypoganglionosis, and 6 patients with NID. Colon specimens from 20 patients without constipation were used as controls. A mechanograph was used to evaluate in vitro colonic responses to electrical field stimulation (EFS) of the adrenergic and cholinergic nerve blockers and gastrointestinal hormones. The following results were obtained: (1) Non-adrenergic inhibitory nerves were found to act on the normal human colon and to a lesser extent in colons with hypoganglionosis or NID, but had no effect on the enteric nerves in colons with aganglionosis. (2) Peptidergic neurotransmitters such as VIP, substance P, and neurotensin apparently act in the normal human colon, and to a lesser extent in the colons with hypoganglionosis or NID, but their effect was almost absent in aganglionosis. (3) VIP acts via neural mechanisms, while substance P and neurotensin may act both via nerves and also directly on the bowel smooth muscle. The diminution of action of non-adrenergic inhibitory nerves and peptidergic nerves may be largely related to the impaired motility observed in hypoganglionosis, NID and aganglionosis.
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