Induction of micronuclei in mouse bone-marrow erythrocytes in association with hypothermia after administration of the sigma receptor ligand E-5842

Hyperthermia-induced micronucleus formation in a human keratinocyte cell line

Elevated temperature can cause biological effects in vitro and in vivo. Many studies on effects of hypo- and hyperthermia have been conducted, but only few studies systematically investigated the formation of genomic damage in the micronucleus test in human cells in vitro as a consequence of different temperatures. In the present study, HaCaT human keratinocytes were exposed to different temperatures from 37°C to 42°C for 24h in a regular cell culture incubator. Micronucleus frequency as a marker of genomic damage was elevated in a temperature-dependent and statistically significant manner. Apoptosis occurred at temperatures of 39°C or higher. Cell proliferation was unaffected up to 40°C and decreased at 41°C and 42°C. Expression of the heat shock protein Hsp70 was elevated, particularly at temperatures of 40°C and higher. These findings are in agreement with several in vivo studies and some in vitro studies looking at single, specific temperatures, but a systematically investigated temperature-dependent increase of genomic damage in human keratinocytes in vitro is demonstrated for the first time here.

Micronucleus to distinguish adenocarcinoma from reactive mesothelial cell in effusion fluid

To evaluate the role of the scoring of micronucleated cell (MNC) to distinguish reactive mesothelial cells from adenocarcinoma cells in effusion fluid. A total of 20 cases of unequivocal metastatic adenocarcinoma and 15 controls with reactive mesothelial cell proliferation in ascetic fluid were selected for scoring of the MNC. The numbers of cells having micronuclei were counted per 1000 of the well-preserved cells in May Grunwald Giemsa stained slides in each case. The mean number of MNC in metastatic adenocarcinoma and reactive mesothelial cells were 21 + 6.53 and 2.93 + 2.63, respectively, per 1000 cells. Micronuclei frequency was significantly increased in adenocarcinoma patients compared with controls (Student's t-test, P < 0.001). The scoring of MNC can be used as an additional biomarker and to discriminate between benign reactive mesothelial cells versus metastatic adenocarcinoma in effusion fluids in difficult situation.

Induction of hypothermic conditions associated with increased micronuclei formation in sigma-1 receptor knockout mice after administration of the antipsychotic compound E-5842

The antipsychotic sigma-1 (sigma(1)) receptor ligand E-5842 has been shown to increase micronucleated polychromatic erythrocyte (MNPCE) frequency in mouse bone marrow secondary to compound-induced hypothermia. Interaction with sigma(1) receptor has been considered a plausible contributing factor for E-5842-induced hypothermia, raising concern for a possible class effect of sigma receptor ligands in the mouse micronucleus (MN) test. We assessed the potential of E-5842 (200 mg/kg, oral) to produce hypothermic conditions associated with increased micronuclei formation in sigma(1) receptor knockout (sigma(1)R-KO) and wild type (WT) mice. After administration, animal's rectal temperature was recorded and peripheral blood and bone marrow samples were obtained (48 hr) and assessed for induction of micronucleated reticulocytes (MNRET) and MNPCE, respectively. E-5842 administration produced marked hypothermia both in sigma(1)R-KO and WT mice. Maximum decreases from preadministration temperature were 12.2 and 13.5 degrees C in sigma(1)R-KO and WT mice, respectively. Temperature returned to normal approximately 32 hr after administration. Bone marrow examination revealed a statistical significant increase (P < 0.05) in MNPCE frequency both in sigma(1)R-KO and WT animals. Examination of peripheral blood samples showed a slight, although nonstatistical significant, increase in MNRET frequency in sigma(1)R-KO mice. No similar effect was observed among WT animals. The results obtained after E-5842 administration to sigma(1)R-KO mice indicate that induction of hypothermic conditions associated with increased MNPCE formation is not mediated by compound interaction with sigma(1) receptor, ruling out concern for a possible class effect of similar high affinity sigma(1) receptor ligands in the mouse MN test.

Formation of micronucleated erythrocytes in mouse bone-marrow under conditions of hypothermia is not associated with stimulation of erythropoiesis

Conditions of marked and long-lasting hypothermia have been shown to increase the formation of micronucleated polychromatic erythrocyte (MNPCE) in mouse bone-marrow. Stimulation of erythropoiesis as a consequence of anoxic conditions associated with decreased body temperature has been suggested as a possible mechanism for hypothermia-induced micronucleus formation. We examined whether chemically induced hypothermic conditions that produced increased MNPCE formation were associated with stimulation of erythropoiesis by measuring erythropoietin (EPO) concentrations in blood. Marked and long-lasting hypothermia was induced in male mice by oral administration of the antipsychotic compounds E-5842 (200 mg/kg) or chlorpromazine (100 mg/kg). Maximum decreases from the basal temperature, achieved 8 h after treatment, were 14.8 and 12.8 degrees C, respectively. A statistically significant increase in bone-marrow MNPCE frequency was observed 48 h after administration of E-5842 (p<0.01) or chlorpromazine (p<0.05). Mice made anaemic by retro-orbital bleeding (0.5 ml), which acted as positive control for stimulation of erythropoiesis, showed no relevant variation in mean rectal temperature and a slight non-statistically significant increase in MNPCE frequency after 48 h. Blood samples for determination of EPO levels were obtained 4 (bleed-control animals only), 8, 16 and 24 h after treatment. In spite of the induced hypothermia, no significant variation in EPO blood levels was observed after administration of E-5842 or chlorpromazine. Bleed-induced anaemic mice showed a clear increase in EPO blood levels at all sampled time points, differences from baseline values being statistically significant (p<0.001) at the 8-h samplings and beyond. These results indicate that induction of MNPCE secondary to chemically induced hypothermia is not mediated by stimulation of erythropoiesis.

Evaluation of the genotoxic potential of the natural neurotoxin Tetrodotoxin (TTX) in a battery of in vitro and in vivo genotoxicity assays

The genotoxic potential of the natural neurotoxin Tetrodotoxin (TTX) was evaluated in a battery of in vitro and in vivo genotoxicity assays. These comprised a bacterial reverse-mutation assay (Ames test), an in vitro human lymphocyte chromosome-aberration assay, an in vivo mouse bone-marrow micronucleus assay and an in vivo rat-liver UDS assay. Maximum test concentrations in in vitro assays were determined by the TTX limit of solubility in the formulation vehicle (0.02% acetic acid solution). In the Ames test, TTX was tested at concentrations of up to 200 microg/plate. In the chromosome-aberration assay human lymphocytes were exposed to TTX at concentrations of up to 50 microg/ml for 3 and 20 h in the absence of S9, and for 3h in the presence of S9. For the in vivo assays, maximum tested dose levels were determined by the acute lethal toxicity of TTX after subcutaneous administration. In the mouse micronucleus assay TTX dose levels of 2, 4 and 8 microg/kg were administered to male and female animals, and bone-marrow samples taken 24 and 48 h (high-dose animals only) after administration. In the UDS assay, male rats were given TTX on two occasions with a 14-h interval at dose levels of 2.4 and 8 microg/kg, the last dose being administered 2h before liver perfusion and hepatocyte culturing. Relevant vehicle and positive control cultures and animals were included in all assays. TTX was clearly shown to lack in vitro or in vivo genotoxic activity in the assays conducted in this study. The results suggest that administration of TTX as a therapeutic analgesic agent would not pose a genotoxic risk to patients.

Effect of staining procedures on the results of micronucleus assays with exfoliated oral mucosa cells

Micronuclei in exfoliated epithelial cells are widely used as biomarkers of cancer risk in humans. To elucidate the effect of different staining procedures on the outcome of such investigation, we conducted a study in which the micronuclei frequencies in oral mucosa cells of heavy smokers (n = 20) and nonsmokers (n = 10) were evaluated with nonspecific (Giemsa, May-Grünwald-Giemsa) and DNA-specific (4',6-diamidino-2-phenylindole, Feulgen, acridine orange) stains, whereas with Giemsa-based stains, the frequencies of micronuclei in smokers were significantly (4- to 5-fold) higher in the smokers group, no significant increase was observed with any of the DNA-specific stains. Furthermore, the evaluation of cells of the two study groups with Feulgen stain showed that oral mucosa cells from smokers had significantly increased levels of nuclear anomalies other than micronuclei. These anomalies are consequences of cell injury found in epithelial cells and are paralleled by formation of keratin bodies in the cytoplasm that resemble micronuclei. Correlation analyses showed that micronuclei frequencies scored in Giemsa-stained slides correlated significantly with karyorrhexis, karyolysis, condensed chromatin, and binucleates, whereas no such correlations were found with DNA-specific stains. These findings indicate that nuclear anomalies (and possibly keratin bodies) may be misinterpreted as micronuclei with nonspecific DNA stains and lead to false-positive results in studies with cells of epithelial origin. Furthermore, our results show that exposure of oral mucosa cells to genotoxic carcinogens contained in tobacco smoke does not lead to induction of micronuclei in these cells.

Report of the IWGT working group on strategies and interpretation of regulatory in vivo tests I. Increases in micronucleated bone marrow cells in rodents that do not indicate genotoxic hazards

In vivo genotoxicity tests play a pivotal role in genotoxicity testing batteries. They are used both to determine if potential genotoxicity observed in vitro is realised in vivo and to detect any genotoxic carcinogens that are poorly detected in vitro. It is recognised that individual in vivo genotoxicity tests have limited sensitivity but good specificity. Thus, a positive result from the established in vivo assays is taken as strong evidence for genotoxic carcinogenicity of the compound tested. However, there is a growing body of evidence that compound-related disturbances in the physiology of the rodents used in these assays can result in increases in micronucleated cells in the bone marrow that are not related to the intrinsic genotoxicity of the compound under test. For rodent bone marrow or peripheral blood micronucleus tests, these disturbances include changes in core body temperature (hypothermia and hyperthermia) and increases in erythropoiesis following prior toxicity to erythroblasts or by direct stimulation of cell division in these cells. This paper reviews relevant data from the literature and also previously unpublished data obtained from a questionnaire devised by the IWGT working group. Regulatory implications of these findings are discussed and flow diagrams have been provided to aid in interpretation and decision-making when such changes in physiology are suspected.

Assessment of the genotoxic potential of the antipsychotic sigma receptor ligand E-5842

The genotoxic potential of E-5842, a sigma ligand compound being developed as an antipsychotic drug, was evaluated by means of an extensive battery of in vitro and in vivo assays. Negative results were obtained in an Ames test (up to 5000 μg/plate), a mouse lymphoma assay (up to 535.1 μg/ml (-S9) and 891.8 μg/ml (+S9)), an in vivo rat hepatocyte micronucleus assay (up to 100 mg/kg/day on 2 days), and a two-dose mouse micronucleus assay (up to 40 mg/kg/day on 2 days). In a single-dose mouse bone-marrow micronucleus assay (up to 400 mg/kg; 24, 48 and 72 h sampling) a slight and non-statistically significant increase in the frequency of micronucleated polychromatic erythrocytes (MNPCE) was observed 48 h after administration of a 200 mg/kg dose, in the absence of bone-marrow toxicity. This minor increase in MNPCE frequency was considered of questionable biological relevance, because it was observed under conditions of marked animal toxicity including mortality. In addition, it occurred in association with a strong hypothermic effect produced by administration of E-5842. A clear increase in the frequency of structural chromosomal aberrations was observed in human lymphocytes at concentrations ≥350.6 and 1685.4 μg/ml in the presence and absence of S9, respectively. Mitotic accumulation was observed at those concentrations at which clastogenic effects were observed, a condition that may have masked toxicity. Concentrations lacking clastogenic effects in this chromosome aberration assay (300.7 and 173.2 μg/ml in the presence and absence of S9, respectively) were well in excess of maximum human plasma concentrations attained in clinical studies at the maximum tolerated dose (19.1 ng/ml). A weight-of-evidence analysis, taking into consideration the results obtained in the different in vitro and in vivo assays and the conditions of clinical use, suggest that E-5842 would not pose a genotoxic risk under clinical conditions.