A comparison of intraperitoneal injection and oral gavage in the micronucleus test with mitomycin C in mice

Suppressive role of vascular endothelial growth factor on intestinal apoptosis in induced necrotizing enterocolitis in rats

Purpose

Necrotizing enterocolitis (NEC) is a devastating disease that can cause mortality in preterm babies. NEC may develop through an apoptotic pathway that is known to be inhibited by vascular endothelial growth factor (VEGF). This study determined whether VEGF exerted a protective effect against the development of NEC and apoptosis in rats.

Methods

To determine the effect of VEGF in NEC rats, neonatal rats were randomized into 4 groups: the control group, the NEC group, the NEC + intraperitoneal VEGF (50 ng/kg) group (NEC + VEGF IP group), and the NEC + oral VEGF (50 ng/kg) group (NEC + VEGF OR group). NEC was induced by lipopolysaccharide/hypoxia and cold stress. The animals were sacrificed 72 hours later. After laparotomy, we obtained a region of the proximal small bowel from the ileocecal valve about 18 cm in length.

Results

The NEC histological grade, apoptosis histological score, and caspase-3 activity were lower in the NEC + VEGF IP and OR groups than in the NEC group. In the NEC + VEGF IP and OR groups, the messenger RNA expression of apoptotic and inflammatory genes, such as Bax, NF-κB, p53, Fas, FasL, and PAF-R, but not that of Bcl-2, was decreased, as was the Bax/Bcl-2 protein ratio. Histological analysis revealed that the apoptosis-blocking effect of VEGF was more effective in the NEC + VEGF IP group than in the NEC + VEGF OR group.

Conclusion

We identified apoptotic and inflammatory genes to confirm the preventive effect of VEGF pretreatment on NEC in rats. This study presents a novel approach to prevent apoptosis via VEGF pretreatment in rats with lipopolysaccharide/hypoxia-induced NEC.

Evaluation of the acute and 28-day sub-acute intravenous toxicity of α-l-guluronic acid (ALG; G2013) in mice

α-l-Guluronic acid (ALG; G2013) has been previously introduced as a new anti-inflammatory agent with promising therapeutic effects. Thus, in the present study, we aimed to evaluate the acute and sub-acute toxicity of ALG through intravenous (i.v.) administration in Balb/C mice. ALG was administrated i.v. to the mice with doses of 300, 600, and 1000 mg/kg of body weight to investigate acute toxicity (single dose) and with doses of 25, 50, and 100 mg/kg of body weight to sub-acute toxicity study (daily injections for a period of 28 days). The mortality rate, food and water intake, behavior, body weight, gross necropsy, hematological and biochemical parameters as well as histopathological presentations of the vital organs (kidneys, liver, lungs, spleen, and heart) were examined in treated groups and compared to the healthy controls. The results of both acute and sub-acute studies showed that i.v. administrations of ALG did not affect the investigated parameters in both sexes, indicating that the LD₅₀ of ALG was higher than 1000 mg/kg of body weight. As no difference was observed in toxicity profiles of investigated doses, no-observed-adverse-effect-level for i.v. administration of ALG in the sub-acute study was greater than 100 mg/kg body weight in both female and male mice. According to the finding, i.v. administration of ALG did not lead to any clinical sign in abovementioned doses, suggesting that ALG was well tolerated up to 1000 mg/kg. These pre-clinical findings support the application of ALG in the future clinical trials.

The rat gut micronucleus assay: a good choice for alternative in vivo genetic toxicology testing strategies

The in vivo bone marrow (BM) micronucleus assay is one of the three tests in the standard test battery to assess the genotoxic potential of a pharmaceutical candidate. In some cases, depending on results of in vitro studies, the route of administration or the degree of systemic exposure, in vivo assessment of genotoxicity in the BM alone may not be sufficient. Based on the potential for high gut exposures to orally administered compounds with low systemic exposures as well as the potential susceptibility of rapidly dividing cells of the intestinal tissues, we have developed a modified technique for evaluating micronuclei formation in both the duodenum and colon of rats based on earlier publications. Adult male Sprague Dawley rats were treated once daily for 2 days with either vehicle control or with the test articles acetyl salicylic acid (ASA), carbendazim (CAR), cyclophosphamide (CP), dimethylhydrazine (DMH), mitomycin C (MMC) or vinblastine sulfate (VIN). The duodenum, colon, and BM were harvested, processed, and analyzed for micronucleus induction. Results from these studies demonstrated differences in the susceptibility for different test compounds in the three tissues tested. When MMC and VIN were dosed by different routes at the same dose levels both compounds produced positive results in all three tissues by intraperitoneal injection but not oral administration. These studies suggest that overall the GI micronucleus assay might be a useful tool for clastogenic and aneugenic compounds that are expected to produce high sustained concentrations in the gastrointestinal tract with little systemic exposure.

Flow cytometric analysis of micronucleated reticulocytes: Time- and dose-dependent response of known mutagens in mice, using multiple blood sampling

According to the current Organization of Economic Cooperation and Development (OECD) and International Committee on Harmonization (ICH) guidelines for the mammalian erythrocyte micronucleus (MN) test, analysis of peripheral blood reticulocytes (RETs) for the presence of micronuclei can be performed using flow cytometry. The MicroFlow PLUS method (Litron Laboratories, Rochester, NY) for MN analysis by flow cytometry is based on the binding of FITC-labeled antibodies to the CD71 transferrin receptor of immature RETs, on parallel RNA degradation, and on propidium iodide staining of DNA present as micronuclei. The objective of this study was to assess the sensitivity of this flow cytometry method to detect time- and dose-dependent induction of micronuclei in mouse peripheral blood RETs after treatment with nine chemical agents. Five known clastogens, two known aneugens, and two compounds previously reported to be inactive in the mouse bone marrow MN test were evaluated at three dose levels. Multiple blood sampling of the same animal before and at two time points after treatment was conducted. All known mutagens produced a dose-dependent increase in micronucleated reticulocytes (MN-RETs); the compounds previously shown to be inactive in the in vivo MN test were also negative using the present methodology. The highest frequency of MN-RETs was observed at 48 hr after treatment, except for 5-fluorouracil, which had its peak response at 72 hr. The results indicate that micronuclei can be measured by multiple blood sampling of the same animal before and after treatment without altering the sensitivity of the assay. The results confirm that the flow cytometric assessment of MN-RETs in mouse peripheral blood using MicroFlow PLUS is a sensitive method with high analysis throughput, and robust quality control.

Micronucleus formation induced by the combination of low doses of X-rays and antineoplastic drugs in bone marrow of male mice

People are widely exposed during their lifetime to many biological, chemical, and physical agents in the environment and at work. In this paper the effects of combined exposures of nonmutagenic doses of X-rays and anticancer agents (cyclophosphamide, mitomycin C, and vinblastine) have been investigated on the induction of micronuclei in the bone marrow of laboratory mice. The combination of X-rays and anticancer drugs enhanced the frequency of micronuclei in some cases. The strongest effects were found after the combination of X-rays and cyclophosphamide at 24 h and 72 h. The combined treatment of X-rays and mitomycin C enhanced the mutagenic effect at 72 h. The combination of X-rays + vinblastine slightly potentiated the mutagenic effect at 24 h and 48 h.

Low dose effects of chemicals as assessed by the flow cytometric in vivo micronucleus assay

Using flow cytometric automation of the mouse in vivo, micronucleus assay increases the sensitivity of the test. This is achieved through a very large increase in the number of cells scored, by a factor of 100x, which in turn greatly reduces the sampling error. With this method, dose-response relationships of in vivo micronucleus induction for four model agents mitomycin C (MMC), diepoxybutane (DEB), cyclophosphamide (CPA), and colchicine (COL) were studied at low dose levels. For the three clastogens MMC, DEB and CPA, linear dose-response relationships were found over the dose ranges studied, even in the very low dose region (defined as the dose region where the frequency of micronucleated erythrocytes is less than twice the baseline frequency). This is consistent with the view that no threshold should exist for genotoxic agents which target DNA. For COL a dose range was found, in which the frequency of micronucleated erythrocytes did not increase with dose, possibly indicating an in vivo threshold. The flow cytometric in vivo micronucleus assay represents one possibility for in vivo low dose-response studies.

Achievements by CSGMT/JEMS.MMS: the Collaborative Study Group for the Micronucleus Test in the Mammalian Mutagenesis Study Group of the Environmental Mutagen Society of Japan

The Collaborative Study Group for the Micronucleus Test (CSGMT) is one of the task groups in the Mammalian Mutagenesis Study Group (MMS) of the Environmental Mutagen Society of Japan (JEMS). It was established in 1982 and has made efforts to understand what the micronucleus test is, what are the advantages and disadvantages of the test as an in vivo detection system for mutagens/carcinogens, and to establish a standard protocol applicable to numerous chemicals. Members of the CSGMT have published more than 75 papers as part of collaborative studies and have contributed to the understanding of the nature of the micronucleus test and to setting guidelines for testing of medicinal and other chemicals. The CSGMT held some workshops to share up-to-date knowledge and techniques on the micronucleus test. Through workshops and collaborative studies, the CSGMT contributed to the maintaining of a high standard of knowledge and techniques among Japanese researchers of the micronucleus test. This paper reviews achievements made by the CSGMT until now.

Bone marrow micronucleus assay: a review of the mouse stocks used and their published mean spontaneous micronucleus frequencies

We have examined published negative control data from 581 papers on micronucleated bone marrow polychromatic erythrocytes (mnPCE) for differences in mean frequency and the frequency distribution profile among the mouse stocks used with the bone marrow micronucleus assay. For the 55 mouse stocks with published micronucleus assay data, the overall mean frequency is 1.95 mnPCE/1,000 PCE (1.95 mnPCE/1,000); for the 13 stocks most commonly used in the assay, it is 1.88 mnPCE/1,000. During the last 5 years, the mnPCE rate for these 13 major stocks has been 1.74 mnPCE/1,000. This current mean frequency is a substantial decrease from the mean of 3.07 mnPCE/1,000 observed for these 13 stocks for data published prior to 1981. Of the major stocks, the highest mean mnPCE negative control frequencies were observed for MS/Ae > BALB/c > C57Bl/6, and the lowest for CD-1 < Swiss Webster. We note that hybrid mouse stocks appear to have lower and less variable negative control frequencies than either of their parent strains and that the negative control frequency for some progeny stocks have diverged significantly from that of the parent stocks. Overall mean negative control frequencies appear to be correlated with breadth of the frequency distribution profile of published mean negative control values. Furthermore, a possible correlation between negative control frequency in the micronucleus assay and sensitivity to clastogens of different mouse strains may be indicated. The databases generated here allow us to define a range of norms for both the historical mean frequency and individual experimental mean frequencies for most stocks, but in particular, for the more commonly used mouse stocks. Our analysis, for the most part, bears out the recommendation of the first Gene-Tox Report on the micronucleus assay that the historical negative control frequency for a mouse stock should fall between 1 and 3 mnPCE/1,000. Eighty-six percent of the most commonly used mouse stocks have historical mean frequencies within this range. Though individual experimental mean values would not necessarily be expected to fall within the 1-3.00 mnPCE/1,000 range, 65.3% of the 2,327 published negative control values do, and 83.5% are < 3 mnPCE/1,000. The frequency with which an individual experimental mean value lies outside the 1.00 to 3.00 mnPCE/1,000 range differs among stocks and appears related to the mouse mean frequency. We suggest that the recommended range for historical mean frequency be extended slightly, to approximately 3.4 mnPCE/1,000, to accommodate some commonly used strains with overall mean negative control frequencies just above 3.00 mnPCE/1,000.(ABSTRACT TRUNCATED AT 400 WORDS)