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

Antigenotoxic effects of (-)-epigallocatechin-3-gallate (EGCG) and its relationship with the endogenous antioxidant system, 8-hydroxydeoxyguanosine adduct repair (8-OHdG), and apoptosis in mice exposed to chromium(VI)

This study aimed to investigate the relationship between endogenous antioxidant system, 8-hydroxydeoxyguanosine adduct (8-OHdG) repair, and apoptosis in mice treated with chromium(VI) alone and in the presence of the antigenotoxic compound (-)-epigallocatechin-3-gallate (EGCG). Groups of 5 Hsd:ICR male mice were divided and treated as follows: (1) control, vehicle only; (2) EGCG, 8.5 mg/kg by gavage alone; (3) CrO₃, 20 mg/kg intraperitoneally alone; and (4) EGCG combined with CrO₃, EGCG was administered 4 hr prior to CrO₃. Peripheral blood parameters were analyzed before treatment administration (time 0), and 48 hr after exposure. The administration of EGCG increased 8-OHdG levels and superoxide dismutase (SOD) activity. Treatment with CrO₃ increased number of micronucleus (MN) presence, elevated apoptotic/necrotic cells frequencies, decreased 8-OHdG levels, diminished total antioxidant capacity (TAC), increased glutathione (GSH) total levels, and lowered SOD activity. Administration of EGCG prior to treatment with CrO₃ resulted in lower concentrations of MN, reduced apoptotic and necrotic cell number, and restored TAC and SOD activity to control levels. It is conceivable that the dose of EGCG plays an important role in the genotoxic damage protection pathways. Thus, this study confirms the action of EGCG as an antigenotoxic agent against chromium(VI)-induced oxidative insults and demonstrates potential protective pathways for EGCG actions to counteract genotoxic damage induced by this metal.

The 10th anniversary of the publication of genes and environment: memoir of establishing the Japanese environmental mutagen society and a proposal for a new collaborative study on mutagenic hormesis

The Japanese Environmental Mutagen Society (JEMS) was established in 1972 by 147 members, 11 of whom are still on the active list as of May 1, 2016. As one of them, I introduce some historic topics here. These include 1) establishment of JEMS, 2) the issue of 2-(2-furyl)-3-(3-nitro-2-furyl)acrylamide (AF-2), 3) the Mammalian Mutagenicity Study Group (MMS) and its achievements, and 4) the Collaborative Study Group of the Micronucleus Test (CSGMT) and its achievements. In addition to these historic matters, some of which are still ongoing, a new collaborative study is proposed on adaptive response or hormesis by mutagens. There is a close relationship between mutagens and carcinogens, the dose-response relationship of which has been thought to follow the linear no-threshold model (LNT). LNT was fabricated on the basis of Drosophila sperm experiments using high dose radiation delivered in a short period. The fallacious 60 years-old LNT is applied to cancer induction by radiation without solid data and then to cancer induction by carcinogens also without solid data. Therefore, even the smallest amount of carcinogens is postulated to be carcinogenic without thresholds now. Radiation hormesis is observed in a large variety of living organisms; radiation is beneficial at low doses, but hazardous at high doses. There is a threshold at the boundary between benefit and hazard. Hormesis denies LNT. Not a few papers report existence of chemical hormesis. If mutagens and carcinogens show hormesis, the linear dose-response relationship in mutagenesis and carcinogenesis is denied and thresholds can be introduced.

Lack of micronuclei formation in bone marrow of rats after oral exposure to thiocyclam insecticide

In this study, a nereistoxin analogue insecticide, thiocyclam, was administered to adult male albino rats by gavage dose of 135, 270 and 540 mg/kg b.w. repeated for 5 days at 24 h intervals. Control animals received only water. Thiocyclam was tested for its potential to cause genotoxic effects in rat bone marrow cells using an in vivo micronucleus assay. After 24 h of the last treatment, rats from all dose levels were sacrificed. Bone marrow cells were collected and assayed for the presence of micronuclei. Thiocyclam did not cause any increase in the incidence of micronucleated polychromatic erythrocytes in rats bone marrow at any of the dose levels. The polychromatic erythrocytes/normochromatic erythrocytes (PCE:NCE) ratio was found to be in the range from 0.50 ± 0.11 to 0.55 ± 0.02. The results of this study demonstrate that the effect of thiocyclam is not significant in the rat in vivo micronucleus assay.

Strategies and testing methods for identifying mutagenic risks

The evolution of testing strategies and methods for identification of mutagenic agents is discussed, beginning with the concern over potential health and population effects of chemical mutagens in the late 1940s that led to the development of regulatory guidelines for mutagenicity testing in the 1970s and 1980s. Efforts to achieve international harmonization of mutagenicity testing guidelines are summarized, and current issues and needs in the field are discussed, including the need for quantitative methods of mutagenic risk assessment, dose-response thresholds, indirect mechanisms of mutagenicity, and the predictivity of mutagenicity assays for carcinogenicity in vivo. Speculation is offered about the future of mutagenicity testing, including possible near-term changes in standard test batteries and the longer-term roles of expression profiling of damage-response genes, in vivo mutagenicity testing methods, and models that better account for differences in metabolism between humans and laboratory model systems.

Effects of chronic exposure to coal in wild rodents (Ctenomys torquatus) evaluated by multiple methods and tissues

Rio Grande do Sul (RS) coal is low quality and typically obtained by strip mining. In a recent study concerning 2 years of biomonitoring in coal regions, we demonstrated the genotoxicity of coal and related products on blood cells of native rodents, from RS, Brazil. With the goal of studying the variations in the effects of RS coal on different tissues of the same rodent, we utilized, besides the single cell gel (SCG) and micronucleus (MN) assay on blood, histological analyses and SCG assay of bone marrow, spleen, kidney, liver and lung cells, and MN assay of bone marrow and spleen cells. In addition, to identify agents that can potentially influence the results, concentrations of several heavy metals were analyzed in livers and in soil, and the total concentration of hydrocarbons in the soil was determined. Rodents exposed to coal were captured at two different sites, Butiá and Candiota, in RS. Reference animals were obtained from Pelotas, where there is no coal mining. This report provides chemical and biological data from coal regions, indicating the possible association between Zn, Ni, Pb and hydrocarbons in the induction of DNA damage (e.g. single strand-breaks and alkali-labile sites) determined by the alkaline SCG assay in cells from Ctenomys torquatus. The results of the present SCG study indicate that coal and by-products not only induce DNA damage in blood cells, but also in other tissue cells, mainly liver, kidney and lung. Neither the MN assay nor histopathological observations showed significant differences; these analyses may be useful under circumstances where genotoxicity is higher. In conclusion we believe that the in vivo genotoxicity of coal can be biomonitored by the SCG assay, and our studies suggest that wild rodents, such as C. torquatus are useful for monitoring genotoxic damage by both methods, the SCG assay and the MN test.

Target organ and time-course in the mutagenicity of five carcinogens in MutaMouse: a summary report of the second collaborative study of the transgenic mouse mutation assay by JEMS/MMS

We studied five carcinogens for (a) organ-specific mutagenicity and expression time in the transgenic (TG) mouse mutation assay and (b) clastogenicity in the peripheral blood micronucleus assay in the same mice. Groups of mice were injected intraperitoneally (ip) with N-nitroso-di-n-propylamine (NDPA), propylnitrosourea (PNU), 7, 12-dimethylbenz[a]anthracene (DMBA), 4-nitroquinoline-1-oxide (4NQO), or procarbazine (PCZ); 4NQO was also administered orally. LacZ mutant frequencies (MF) of various organs, sampled 7, 14 and 28 days after treatment, were analyzed by galE positive selection. At least 5 organs were analyzed in each experiment. Bone marrow, liver, and testis were always analyzed, as were each chemical's target organs. All chemicals, except NDPA, induced micronuclei. All chemicals increased lacZ MF in all of their target organs for carcinogenesis and, to a lesser extent, in some non-target organs. That suggests that an organ that has a positive response to a chemical in the TG mouse mutation assay is likely to develop tumors on exposure to that chemical, but it does not always happen. The time-course of MF increases (7-28 days) differed among tissues. In general, time-dependent increase in MF occurred in organs with a low cell proliferation rate whereas no increase, or even a decrease, occurred in organs with a high proliferation rate. Our results demonstrated that the TG mouse mutation assay is effective for the detection of chemical mutagenesis in the target organs for carcinogenesis, and organ and time-course variations in chemical mutagenesis are important issues for the establishment of an optimal protocol for the assay.