Tsuneya Matsumoto

No Lengthening of Life Span in Mice Continuously Exposed to Gamma Rays at Very Low Dose Rates

Abstract Tanaka, S., Tanaka, I. B. III., Sasagawa, S., Ichinohe, K., Takabatake, T., Matsushita, S., Matsumoto, T., Otsu, H. and Sato, F. No Lengthening of Life Span in Mice Continuously Exposed to Gamma Rays at Very Low Dose Rates. Radiat. Res. 160, 376–379 (2003). Late effects of continuous exposure to ionizing radiation are potential hazards to workers in radiation facilities as well as to the general public. Recently, low-dose-rate and low-dose effects have become a serious concern. Using a total of 4000 mice, we studied the late biological effects of chronic exposure to low-dose-rate radiation as assayed by life span. Two thousand male and 2000 female 8-week-old specific-pathogen-free (SPF) B6C3F1 mice were randomly divided into four groups (one nonirradiated control and three irradiated). Irradiation was carried out for approximately 400 days using 137Cs γ rays at dose rates of 21 mGy day–1, 1.1 mGy day–1 and 0.05 mGy day–1 with total doses equivalent to 8000 mGy, 400 mGy and 20 mGy, respectively. All mice were kept under SPF conditions until they died spontaneously. Statistical analyses showed that the life spans of mice of both sexes irradiated with 21 mGy day–1 (P < 0.0001) and of females irradiated with 1.1 mGy day–1 (P < 0.05) were significantly shorter than those of the control group. Our results show no evidence of lengthened life span in mice continuously exposed to very low dose rates of γ rays.

Cause of Death and Neoplasia in Mice Continuously Exposed to Very Low Dose Rates of Gamma Rays

Abstract Tanaka, I. B., III, Tanaka, S., Ichinohe, K., Matsushita, S., Matsumoto, T., Otsu, H., Oghiso, Y. and Sato, F. Cause of Death and Neoplasia in Mice Continuously Exposed to Very Low Dose Rates of Gamma Rays. Radiat. Res. 167, 417–437 (2007). Four thousand 8-week-old SPF B6C3F1 mice (2000 of each sex) were divided into four groups, one nonirradiated (control) and three irradiated. The irradiated groups were exposed to 137Cs γ rays at dose rates of 21, 1.1 and 0.05 mGy day−1 for approximately 400 days with total doses equivalent to 8000, 400 and 20 mGy, respectively. All mice were kept until natural death, and pathological examination was performed to determine the cause of death. Neoplasms accounted for >86.7% of all deaths. Compared to the nonirradiated controls, the frequency of myeloid leukemia in males, soft tissue neoplasms and malignant granulosa cell tumors in females, and hemangiosarcoma in both sexes exposed to 21 mGy day−1 were significantly increased. The number of multiple primary neoplasms per mouse was significantly increased in mice irradiated at 21 mGy day−1. Significant increases in body weights were observed from 32 to 60 weeks of age in males and females exposed to 1.1 mGy day−1 and 21 mGy day−1, respectively. Our results suggest that life shortening (Tanaka et al., Radiat. Res. 160, 376–379, 2003) in mice continuously exposed to low-dose-rate γ rays is due to early death from a variety of neoplasms and not from increased incidence of specific neoplasms.

Gene Expression Profiles in Mouse Liver after Long-Term Low-Dose-Rate Irradiation with Gamma Rays

Abstract Changes in gene expression profiles in mouse liver induced by long-term low-dose-rate &ggr; irradiation were examined by microarray analysis. Three groups of male C57BL/6J mice were exposed to whole-body radiation at dose rates of 17–20 mGy/day, 0.86–1.0 mGy/day or 0.042–0.050 mGy/day for 401–485 days with cumulative doses of approximately 8 Gy, 0.4 Gy or 0.02 Gy, respectively. The gene expression levels in the livers of six animals from each exposure group were compared individually with that of pooled sham-irradiated animals. Some genes revealed a large variation in expression levels among individuals within each group, and the number of genes showing common changes in individuals from each group was limited: 20 and 11 genes showed more than 1.5-fold modulation with 17–20 mGy/day and 0.86–1.0 mGy/day, respectively. Three genes showed more than 1.5-fold modulation even at the lowest dose-rate of 0.04–0.05 mGy/day. Most of these genes were down-regulated. RT-PCR analysis confirmed the expression profiles of the majority of these genes. The results indicate that a few genes are modulated in response to very low-dose-rate irradiation. The functional analysis suggests that these genes may influence many processes, including obesity and tumorigenesis.

Transmission experiments of cilia-associated respiratory bacillus in mice, rabbits and guineapigs

Transmission experiments of cilia-associated respiratory (CAR) bacillus were performed in mice in order to clarify the principal route of the infection, and in rabbits and guineapigs in order to examine their susceptibility. Determination of the infection was evaluated serologically by the indirect immunofluorescence assay (IFA) technique and histologically by the presence of CAR bacillus in the airways. BALB/c mice were intranasally inoculated with the SMR strain of CAR bacillus. The IFA antibody to the bacteria in these mice rose to more than 1 : 160 at 4 weeks postinoculation (PI) and the mice were utilized as transmitters for the following experiments. One out of 15 uninfected mice kept in intracage contact with infected mice became infected from 4 weeks after contact. Incidence of contact infection increased thereafter. On the other hand, there was no evidence of infection in the uninfected mice housed in the separate cages from the cage in which infected mice were housed throughout the 12-week observation period. The primary method of CAR bacillus transmission seems to be direct contact with infected mice or fomites contaminated by infected mice; airborne transmission appears to be of little importance. Rabbits and guineapigs were also intranasally inoculated with the SMR strain of CAR bacillus. IFA antibodies were positively detected by 4 weeks PI, but no CAR bacillus nor histological changes relating to the infection were observed in the airways of either species. It is suggested that rat origin CAR bacillus can transmit to rabbits and guineapigs, and that the infection can spread to other species of rodents and rabbits.

Radiation Dose-Rate Effect on Mutation Induction in Spleen and Liver of gpt delta Mice

Abstract The effect of dose rate on radiation-induced mutations in two somatic tissues, the spleen and liver, was examined in transgenic gpt delta mice. These mice can be used for the detection of deletion-type mutations, and these are the major type of mutation induced by radiation. The dose rates examined were 920 mGy/min, 1 mGy/min and 12.5 µGy/min. In both tissues, the number of mutations increased with increasing dose at each of the three dose rates examined. The mutation induction rate was dependent on the dose rate. The mutation induction rate was higher in the spleen than in the liver at the medium dose rate but was similar in the two tissues at the high and low dose rates. The mutation induction rate in the liver did not show much change between the medium and low dose rates. Analysis of the molecular nature of the mutations indicated that 2- to 1,000-bp deletion mutations were specifically induced by radiation in both tissues after high- and low-dose-rate irradiation. The occurrence of deletion mutation without any sequence homology at the break point was elevated in spleen after high-dose-rate irradiation. The results indicate that the mutagenic effects of radiation in somatic tissues are dependent on dose rate and that there is some variability between tissues.

Significance of platelets in an antimetastatic activity of bacterial lipopolysaccharide

Recently we reported an antimetastatic activity of bacterial lipopolysaccharide (LPS) on a NK-cell-resistant murine fibrosarcoma (NFSa). Here we investigate and report the mechanistic significance of platelets in this activity. The number of circulating platelets was reduced to 63% of the control 3 days after an i.v. injection of 1.0 µg LPS, and then recovered to the level of control at day 10. Aggregation efficiency of platelets was impaired by LPS. The number of metastatic lung colonies after an i.v. injection of tumor cells was maximally reduced to 2.2% of the control at day 3 and increased in proportion to the recovery of platelet number. Neuraminidase (Ndase), which caused a non-immunological thrombocytopenia, also inhibited lung metastasis when injected prior to an i.v. tumor cell challenge. LPS and Ndase showed an identical pattern against five other syngeneic tumors; these agents inhibited lung metastases of the FSa fibrosarcoma and the SCC VII squamous cell carcinoma but failed to inhibit those of the NR-S1 squamous cell carcinoma, the MMCa#4 mammary adenocarcinoma and the NR-PG parotid gland tumor. All the three cells which were not responsive to any agents possessed a high aggregating activity of platelets while the other three tumors responsive to both agents did not show a detectable level of this activity. Platelet transfusion failed to modify the antimetastatic activity of LPS. These results suggest that platelets play an important role in the antimetastatic activity of LPS, though whether the role is principal or assistant remains to be seen.

Antimetastatic activity of lipopolysaccharide against a NK-resistant murine fibrosarcoma

An intravenous injection of bacterial lipopolysaccharide (LPS) into mice exerted prominent antimetastatic activities against a NK-resistant weakly immunogenic NFSa fibrosarcoma. The number of visible metastases in the lung was increased by a pretreatment of anti-asialoGM1 (asGM1) antibody or silica, but pretreatment of asGM1 antibody or silica scarcely affected the antimetastatic activities of LPS. The pulmonary retention of radiolabeled tumor cells showed that LPS accelerated the detachment of the tumor cells from the lung, and that this acceleration was not suppressed by anti-asGM1 antibody. Sialic acids of lung endothelial cell surface, essential components of various receptors, was diminished by the i.v. injection of LPS. These results suggested that the antimetastatic effect of LPS against NK-resistant NFSa cells was partly the result of modulations of lung endothelial cell surface.

Active components of intestinal bacteria for abdominal irradiation-induced inhibition of lung metastases

We have previously reported that abdominal irradiation of mice inhibited lung metastases of a weakly immunogenic fibrosarcoma, and that transmigration after the irradiation ofEnterobacter cloacae into mesenteric lymph nodes coincided with this phenomenon. In this paper, we show thatEscherichia coli as well asE. cloacae reduce the number of metastatic lung colonies when these bacteria were intravenously injected into mice prior to the tumour cell challenge. The inhibition was caused not only by the administration of living bacteria but also by that of killed bacteria. Bacterial lipopolysaccharide (LPS), a component of membrane, replaced at least in part the effect of whole bacteria. Transfer of spleen cells from LPS-treated mice into intact recipients prominently inhibited metastatic development in the recipient mice. ‘Cross transfer’ between LPS high responders and LPS low responders suggested an indirect activity of transferred spleen cells. The antimetastatic activity of LPS depended on the tumour cell type; metastasis of fibrosarcomas was extensively inhibited by LPS irrespective of tumour immunogenicity while that of adenocarcinomas was only slightly inhibited. These results suggest that non-immunological mechanisms are involved in the antimetastatic activity of LPS.

Spontaneous necrotic enteritis in young RFM/Ms mice

Fatal necrotic enteritis was observed in mice 24-52 days old in the RFM/Ms breeding colony maintained in a clean conventional condition in the National Institute of Radiological Sciences. Gross lesions included hyperaemia, petechiae, erosion and the occasional formation of pseudomembranes in the mucosa of the ileum and caecum. Histologically, there was necrotic enteritis with numerous Gram-positive bacilli-forming spores but no inflammatory cell reaction. Non-type-A Clostridium perfringens was isolated from the intestinal contents. This disease cleared after the addition of chlortetracycline hydrochloride (11 mg/I) to the drinking water.

Influence of Escherichia coli, Klebsiella pneumoniae and Proteus vulgaris on the mortality pattern of mice after lethal irradiation with γ rays

The mortality patterns and the LD50/30 for mice free from Enterobacteriaceae, mice contaminated with Enterohacter cloacae, and mice inoculated with Escherichia coli, Klebsiella pneumoniae or Proteus vulgaris were examined after whole-body irradiation with γ rays. No clear differences were observed among the infected groups, but there were clear differences between them and those negative for Enterobacteriaceae. The LD50/30 of Enterobacteriaceae-positive mice was similar to that for conventional mice. All 4 nonpathogenic Enterobacteriaceae had very similar detrimental effects on mice after lethal irradiation.