Effect of various concentrations of lead nitrate on the induction of micronuclei in mouse bone marrow

The frequency of micronuclei was evaluated in the bone marrow of mice of either sex administered with 0, 0.625, 1.25, 2.5, 5, 10, 20, 40 and 80 mg/kg b.wt of lead nitrate at 12, 24 and 36 h post-treatment. The frequency of micronucleated polychromatic erythrocytes (MPCE) and micronucleated normochromatic erythrocytes (MNCE) increased significantly at 12, 24 and 36 h after treatment with lead nitrate compared to non-drug treated controls. The frequency of micronuclei did not show a dose related increase and the elevation in the frequency of micronuclei was fluctuating type. One important observation which emerged from this study was that the male mice were more sensitive to the induction of micronuclei compared to female mice. This was evidenced by higher frequencies of MPCE in males than females at all the doses for all the post-treatment time periods. The lead nitrate treatment resulted in a spurt in the erythropoiesis as is evidenced by a significant increase in the ratios of polychromatic to normochromatic erythrocytes (P/N ratio) compared to non-drug treated controls at 12, 24 and 36 h post-treatment. The P/N ratio was significantly higher in females than males at 12 and 24 h post-treatment.     

Genotoxicity and cytotoxicity in male B6C3F1 mice following exposure to mixtures of 1,3-butadiene and styrene

1,3-Butadiene and styrene are oxidized, in part, by cytochrome P450 2E1 and have been shown to metabolically interact in rodents exposed by inhalation to mixtures of both compounds. Because the reactive metabolites of butadiene and styrene are thought to be responsible for the toxicity of each compound, metabolic interactions may alter the response in animals exposed to mixtures of butadiene and styrene compared with the response in animals exposed to butadiene alone or styrene alone. The purpose of this study was to quantitate alterations in genotoxicity and cytotoxicity in male B6C3F1 mice exposed to mixtures of butadiene and styrene. Male B6C3F1 mice were exposed to 6.25, 62.5, 200, or 625 ppm butadiene alone, 50 ppm styrene alone, or mixtures of 6.25, 62.5, 200, or 625 ppm butadiene and 50 ppm styrene. Genotoxicity was assessed by quantitating the frequency of micronucleated polychromatic erythrocytes in bone marrow. Cytotoxicity was assessed by counting total spleen and thymus cells and by quantitating the frequency of polychromatic erythrocytes in the peripheral blood. Butadiene and mixtures of butadiene and styrene were genotoxic in mice, as shown by a significant increase in the frequency of micronucleated polychromatic erythrocytes. The increased frequency following exposure to mixtures of butadiene and styrene was not significantly different compared with the frequency following exposure to butadiene alone. Styrene and mixtures of butadiene and styrene were cytotoxic in mice, as shown by significantly decreased number of spleen cells. Exposure to mixtures of butadiene and styrene with butadiene concentrations of 62.5 or 625 ppm significantly reduced the number of thymus cells. Exposure to 200 ppm or 625 ppm butadiene alone, or to mixtures of 200 ppm or 625 ppm butadiene and 50 ppm styrene, significantly reduced the frequency of polychromatic erythrocytes in the peripheral blood. The results of the study demonstrate that exposure to mixture of butadiene and styrene does not reduce the respective genotoxicity of butadiene or cytotoxicity of styrene.     

The modulatory effect of aminothiols on the clastogenic activity of X-rays assayed by the vivo mouse micronucleus test

The modulatory effect of AET (S-2-aminoethylisothio-uronium bromide hydrobromide) and WR-2721 (S-2-/3-ami-nopropylamino/ethylphosphorothioic acid) on the clastogenic activity of X-rays was assessed by the in vivo mouse micronucleus test. The frequency of micronucleated polychromatic erythrocytes (MNPCEs) in the peripheral blood of adult male Swiss mice exposed to 5 Gy X-rays alone, or treated with AET or WR-2721, at a does of 200 mg/kg body weight, 15 or 30 minutes prior to X-irradiation, respectively, was determined during a fifteen-day period. The number of micronuclei increased on day 1 post-irradiation in X-irradiated mice and declined thereafter with the frequency of MNPCEs remaining lower in the thiol pre-treated mice. A more effective protection against the clastogenic activity of X-rays in the erythropoietic system was observed after WR-2721 administration than AET application.     

Hydroquinone increases the frequency of micronuclei in a dose-dependent manner in mouse bone marrow

The frequency of micronuclei (micronucleated polychromatic erythrocytes, MPCE and micronucleated normochromatic erythrocytes, MNCE) was studied at 12, 24 and 36 h post-treatment in the bone marrow of mice treated with 0, 0.78, 1.56, 3.125, 6.25, 12.5, 25, 50, 75 and 100 mg/kg body wt of hydroquinone (HQ). Treatment of mice with various doses of HQ resulted in a dose dependent increase in the frequency of both MPCE and MNCE at all the post-treatment time periods. The frequency of MPCE was significantly higher after administration of 3.125 mg/kg HQ at 24 h post-treatment, except 12 and 36 h, where a significant increase in the frequency of MPCE was observed only after administration of 6.25 mg/kg drug dose. Similarly, a significant increase in the frequency of MNCE was observed after 12.5 mg/kg HQ treatment at all the post-treatment time periods. The dose effect relationship between various HQ doses and MPCE and MNCE induction was linear and linear quadratic, respectively at all the post-treatment time periods. The PCE/NCE ratio declined in a dose dependent manner at all the post-treatment time periods and this decline was significant when compared to non-drug treated controls. The dose effect relationship was linear quadratic at all the post-treatment time periods studied.     

Rhodopsin mutations as the cause of retinal degeneration. Classification of degeneration phenotypes in the model system Drosophila melanogaster

The modifying effect of treatment with vitamins C, E and beta-carotene on the clastogenic activity of gamma rays was investigated in mice. Damage in vivo was measured by the micronucleus assay in bone marrow polychromatic erythrocytes and exfoliated bladder cells. The vitamins were administered orally, either for five consecutive days before or immediately after irradiation with 2 Gy of gamma rays. The results show that pretreatment with vitamin E (100-200 mg/kg/day) and beta-carotene (3-12 mg/kg/day) were effective in protecting against micronucleus induction by gamma rays. Vitamin C depending on its concentration enhanced the radiation effect (400 mg/kg/day), or reduced the number of micronucleated polychromatic erythrocytes (50-100 mg/kg/day). Such effect was weekly observed in exfoliated bladder cells. The most effective protection in both tissues was noted when a mixture of these vitamins was used as a pretreatment. Administration of the all antioxidant vitamins to mice immediately after irradiation was also effective in reducing the radiation-induced micronucleus frequency. The data from the in vitro experiments based on the comet assay show that the presence of the vitamins in culture medium influences the kinetic of repair of radiation-induced DNA damage in mouse leukocytes.     

Changes in hepatic enzyme activities related to ethanol metabolism in mice following chronic ethanol administration

Male mice of three strains, C57BL, DBA and C3H/He, were fed on commercial food with 10% (v/v) ethanol solution as drinking liquid ad libitum for eighty days, and the changes in the activities of enzymes in the metabolic pathway of ethanol in the liver were examined. C57BL and C3H/He mice showed a preference for drinking the 10% (v/v) ethanol solution, while DBA mice did not. The ethanol intake g/g of body weight of C3H/He mice showed the highest value among all three strains and that of C57BL mice tended to show higher value than that of DBA mice. The liver weights of C57BL and C3H/He mice increased significantly following chronic ethanol administration, but that of DBA did not. The cytosolic enzyme alcohol dehydrogenase (ADH) showed no changes in any of the strains following chronic ethanol administration. The microsomal ethanol-oxidizing system (MEOS) of C57BL mice exhibited approximately 2-fold higher activity compared to that of DBA and C3H/He mice but did not increase in any strain following chronic ethanol administration. However, the microsomal aniline hydroxylase activity in the liver increased significantly in C57BL and C3H/He mice following chronic administration of ethanol. The microsomal cytochrome P-450 content also tended to slightly increase in the same strains of mice. It seemed that cytochrome P-450IIE1 was induced in the liver microsomes of these strains. Total aldehyde dehydrogenase (ALDH) activities together with high-Km ALDH activity increased markedly in the microsomes of C57BL mice and tended to increase in C3H/He mice, while it did not change in DBA mice following chronic ethanol administration. In the mitochondria of C57BL, total ALDH activities increased slightly and high-Km ALDH activities tended to increase. These mitochondrial ALDH activities of C3H/He and DBA mice tended to increase following chronic ethanol administration. The cytosolic ALDH activity showed no changes in any strain of mice following chronic ethanol administration. It seemed that in the microsomes, the activities of enzymes related to oxidation of ethanol increased in C57BL and C3H/He mice, which tended to consume a large amount of ethanol, and did not in DBA mice which tended to consume a small amount of it. It seemed that the increases in activities of enzymes related to oxidation of acetaldehyde in the microsomes and in the mitochondria were responsible for the strain difference.     

Genotoxicity of Farbasol and its component: 4-ethyltoluene

A combination of assays for gene mutations in Salmonella typhimurium TA97a, TA98, TA100 and TA102 strains with and without rat liver activation, and for micronucleus and sister chromatid exchange (SCE) in bone marrow cells of Imp:Balb/c mice was used to provide data on the mutagenic and genotoxic properties of the mixture of aromatic solvents, known under the trade name of Farbasol. In addition, 4-ethyltoluene (the main ethylmethylbenzenic component of Farbasol) was also tested for muta- and genotoxicity. The results revealed that neither Farbasol nor 4-ethyltoluene induced an increased reverse mutation in bacterial cells or the formation of micronucleated polychromatic erythrocytes in bone marrow. However, those compounds were found to be active as sister chromatid exchange (SCE) agents.     

Respective roles of human cytochrome P-4502E1, 1A2, and 3A4 in the hepatic microsomal ethanol oxidizing system

The microsomal ethanol oxidizing system comprises an ethanol-inducible cytochrome P-4502E1, but the involvement of other P-450s has also been suggested. In our study, human CYP2E1, CYP1A2, and CYP3A4 were heterologously expressed in HepG2 cells, and their ethanol oxidation was assessed using a corresponding selective inhibitor: all three P-450 isoenzymes metabolized ethanol. Selective inhibitors-4-methylpyrazole (CYP2E1), furafylline (CYP1A2), and troleandomycin (CYP3A4)-also decreased microsomal ethanol oxidation in the livers of 18 organ donors. The P-450-dependent ethanol oxidizing activities correlated significantly with those of the specific monooxygenases and the immunochemically determined microsomal content of the respective P-450. The mean CYP2E1-dependent ethanol oxidation in human liver microsomes [1.41+/-0.11 nmol min(-1) (mg protein)(-1)] was twice that of CYP1A2 (0.61+/-0.07) or CYP3A4 (0.73+/-0.11) (p < 0.05). Furthermore, CYP2E1 had the highest (p < 0.05) specific activity [28+/-2 nmol min(-1) (nmol CYP2E1)(-1) versus 17+/-3 nmol min(-1) (nmol CYP1A2)(-1), and 12+/-2 nmol min(-1) (CYP3A4)(-1), respectively]. Thus, in human liver microsomes, CYP2E1 plays the major role. However, CYP1A2 and CYP3A4 contribute significantly to microsomal ethanol oxidation and may, therefore, also be involved in the pathogenesis of alcoholic liver disease.     

Comparison of glycoprotein components, tryptophan, lipid peroxidation and antioxidants in borderline and severe hypertension and myocardial infarction

Between 1957 and 1993, the Siberian Chemical Complex (Tomsk-7) located in the Tomsk region (Russia) regularly discharged radioactive liquid wastes into the Tom River which resulted in an extensive contamination of large territories with long lived radionuclides such as cesium-137 and strontium-90. In the summers of 1996 and 1997, Research Team of Siberian Medical University conducted biodosimetry and cytogenetic monitoring of pikes (Esox lucius) caught in the Tom River at various distances downstream from the Siberian Chemical Complex (SCC) using the micronucleus test and the gamma spectroscopy. Our findings demonstrated that the difference in frequency of micronucleated erythrocytes between the radiation-exposed fish caught downstream from the SCC and the controls was statistically significant (P < 0.01). Moreover, we found a good correlation between radiocesium concentration and micronucleated erythrocyte frequency in pikes. It was found that both the micronucleated erythrocyte frequency in pike blood and the level of the pike radiocesium concentration depended on the age of pikes. The micronucleated erythrocyte frequency gradually increased from the 1-year-old pikes to the over 20-year-old pikes. On the other hand, the average level of radiocesium concentration gradually increased from the 1-year-old pikes only up to the 10-year-old pikes. There is no correlation between radiocesium concentration and micronucleated erythrocyte frequency in the over 10-year-old pikes.     

Messenger RNA synthesis, transport, and storage in silkmoth ovarian follicles

The effect on liver microsomal enzyme activity of three steroid contraceptive drug (SCD) combinations was compared in rats, mice and guinea-pigs. Lynestrenol plus mestranol, norethisterone plus mestranol and norethynodrel plus mestranol were given orally for 4 consecutive days (acute treatment) or 30 days (chronic treatment) at various doses eliciting an experimentally controlled antifertility activity which varied in its extent. In rats and mice all the combined treatments (with the exception of norethynodrel plus mestranol in mice) were active as inducers of liver microsomal enzymes. This induction seems to be mediated mainly by the progestogenic compounds. Oestrogens showed a very poor effect bordering on significance only in a few cases. No effect on liver microsomal protein or cytochrome P 450 concentration was obtained after treatment with doses capable of increasing the microsomal enzyme activity. The activity of the liver microsomal enzymes did not appear to be reduced immediately (2 h) after the last administration of the SCD given during 4 or 30 days. Contraceptive treatments at doses capable of eliciting complete antifertility activity were inactive on liver microsomal enzyme activity in guinea-pigs.     

Effect of S-methyl cysteine sulphoxide and its metabolite methyl methane thiosulphinate, both occurring naturally in Brassica vegetables, on mouse genotoxicity

S-methyl cysteine sulphoxide (SMCSO) and its metabolite methyl methane thiosulphinate (MMTSO), both naturally occurring compounds present in Brassica vegetables, were investigated for their putative ability to inhibit benzo[a]pyrene (B[a]P)-induced genotoxicity in ICR mice. The mouse bone marrow micronucleus assay was used as an indicator of in vivo genotoxicity. Doses of 0.5 mmol SMCSO and 0.05mmol MMTSO per kg body weight significantly inhibited the formation of B[a]P-induced micronucleated polychromatic erythrocytes (MPCEs) by 31 and 33%, respectively, compared with control mice. Two higher doses of MMTSO (0.5 and 1.0 mmol/kg body weight) administered to mice displayed severe acute toxicity. The inhibition of experimental genotoxicity by these two organosulphur compounds present in Brassica may, in part, be responsible for the anticarcinogenic effect of these vegetables.     

Antimutagenicity of Tochu tea (an aqueous extract of Eucommia ulmoides leaves): 1. The clastogen-suppressing effects of Tochu tea in CHO cells and mice

The suppressing effect of crude extracts of Tochu tea, an aqueous extract of Eucommia ulmoides leaves and a popular beverage in Japan, on the induction of chromosome aberrations in CHO cells and mice was studied. When CHO cells were treated with Tochu tea crude extract after MMC treatment, the frequency of chromosome aberrations was reduced. Out of 17 Tochu tea components, 5 irridoids (geniposidic acid, geniposide, asperulosidic acid, deacetyl asperulosidic acid, and asperuloside) and 3 phenols (pyrogallol, protocatechuic acid, and p-trans-coumaric acid) were found to have anticlastogenic activity. Since the anticlastogenic irridoids had an alpha-unsaturated carbonyl group, this structure was considered to play an important role in the anticlastogenicity. The anticlastogenic effect of Tochu tea extracts was examined in mice using a micronucleus assay. When mice received 1.0 ml 4% Tochu tea extract by oral gavage 6 h before intraperitoneal injection of MMC, a decrease in the frequency of micronuclei was observed. This decrease was not due to a delay in the maturation of micronucleated reticulocytes.     

Chronic ethanol inhibits inositol metabolism in specific brain regions

Many neurotransmitters and hormones in the nervous system transmit signals through receptors coupled to the poly-phosphoinositide (PI) signaling pathway. In this study, an in vivo protocol with [3H]inositol was used to examine the effect of chronic ethanol administration on inositol metabolism and poly-PI turnover in the cerebral cortex, hippocampus, and cerebellum of mouse brain. C57BL/6 mice were given a nutritionally complete liquid diet containing either ethanol (5%, w/v) or isocaloric sucrose for 2 months. Mice were injected intracerebrally with [3H]inositol; after 16 or 24 hr, they were injected intraperitoneally with lithium (8 mEq/kg body weight) to inhibit the inositol monophosphatase (IP1) activity. All mice were decapitated 4 hr after lithium injection. Labeled inositol phospholipids accounted for 16 to 23% of total labeled inositol in different regions of control mouse brain, and the percentages in the hippocampus were consistently higher than the cerebral cortex and cerebellum. In control mice, the percentages of labeled IP1 after a 4-hr lithium treatment were 11.5%, 9.9%, and 3.7% for cerebral cortex, hippocampus, and cerebellum, respectively. Chronic ethanol feeding resulted in a significant (p < 0.05) decrease in the percent of labeled IP1 and inositol phospholipids, and this effect was observed in the cerebral cortex and, to a lesser extent, hippocampus but not cerebellum. When ratios of labeled IP1 were expressed against labeled inositol phospholipids as an index of the poly-PI turnover activity, significant decreases in IP/lipid ratios were observed in the cerebral cortex, but not the hippocampus or cerebellum. Although mice killed 24 + 4 hr after the last ethanol feeding would have experienced an 8-hr period of ethanol withdrawal, compared with the 16 + 4-hr group, no differences in IP/lipid ratios were observed between the two time groups. These results illustrate regional differences in the effect of chronic ethanol on inositol metabolism in the brain, but no difference in poly-PI turnover in brain due to ethanol withdrawal.     

Change in activity of microsomal cytochrome P-450-dependent monooxygenases from rat liver exposed to chronic low doses of radiation

The activity changes of cytochrome P-450-dependent monooxygenases of hepatic microsomal fraction were studied in, experimental animals after prolonged application (1 month) of low radiation doses (0.258 mkl/kg). The obtained results show the increase in catalytic activities of main forms of cytochrome P-450, participating in steroid hydroxylation, as well as the decrease in total content of cytochrome P-450 in hepatic microsomal fraction and the lowering of its demethylase activity.     

Ethanol modulates metastatic potential of B16BL6 melanoma and host responses

The experimental metastatic potential (lung-colonizing ability) of B16BL6 melanoma cells was examined in C57BL/6 mice after exposure to ethanol in vitro and in vivo. In vitro, tumor cells were cultured with ethanol (0.3% v/v), or medium alone, for three passages at 5-day intervals. In vivo, B16BL6 melanoma was exposed to ethanol by administering ethanol (10% or 20% w/v) to mice following subcutaneous inoculation of tumor cells into the dorsal hip. All tumor cells were subsequently inoculated intravenously into the lateral tail vein of water-drinking mice to assess changes in metastatic phenotype. Tumor cells cocultured in vivo with ethanol produced significantly higher numbers of superficial lung colonies, compared with tumor cells cultured in control medium. Experimental metastasis of tumor cells obtained from 20% w/v ethanol-consuming mice was also significantly increased, compared with cells obtained from water-drinking mice. Metastasis of B16BL6 melanoma cells previously obtained from mice consuming 10% w/v ethanol did not differ from controls. In other experiments, water-drinking and ethanol-consuming (2.5%, 10%, and 20% w/v) mice were inoculated subcutaneously into the dorsal hip with B16BL6 melanoma cells, and monitored for tumor growth rate and survival time. In these experiments, survival times were significantly shorter in mice consuming 20% ethanol, compared with all other groups. Subcutaneous tumor growth rate was unaffected by ethanol consumption. Lung metastasis resulting from subcutaneous tumor implantation of B16BL6 melanoma was respectively inhibited, or absent, in 10% and 20% ethanol-consuming groups. Thus, tumor growth rate and incidence of lung metastases were not apparent determinants of decreased survival in 20% ethanol-consuming mice. The results of this study indicate that the experimental metastatic potential of B16BL6 melanoma is increased during exposure to ethanol; however, metastasis from subcutaneous tumor-bearing mice is suppressed. This latter finding is consistent with previous results in which spontaneous metastasis was also suppressed after inoculation of the tumor into the pinna of the ear. Although ethanol increases the ability of B16BL6 melanoma to colonize the lung after intravenous inoculation, this effect is abated in the presence of host factors in ethanol-consuming mice.     

Microsomal function in biliary obstructed rats: effects of S-adenosylmethionine

BACKGROUND/AIMS: S-adenosylmethionine has been reported to have beneficial effects in the treatment of different chronic liver diseases and to protect against different hepatotoxic agents. The aim of this study was to investigate whether S-adenosylmethionine treatment might contribute to improved microsomal function in chronically biliary obstructed rats. METHODS: Secondary biliary cirrhosis was induced by 28 days of bile duct obstruction. Groups of control and cirrhotic animals received S-adenosylmethionine (10 mg/kg per day) through the experimental period. RESULTS: Bile duct obstruction resulted in a marked increase in lipid peroxidation levels and decreases in glutathione concentration, microsomal membrane fluidity, microsomal cytochrome P-450 content, NADPH-cytochrome P-450 reductase activity and the activities of the aniline hydroxylase, aminopyrine demethylase and ethoxycoumarin deethylase. Reductions in glutathione and cytochrome P-450 concentration were not corrected by S-adenosylmethionine, but lipid peroxidation, the decrease in the activities of the various microsomal monooxygenases and the reduction in microsomal membrane fluidity were partially prevented. A significant relationship was found between membrane fluidity and aniline hydroxylase, aminopyrine demethylase or ethoxycoumarin deethylase activities. CONCLUSIONS: S-adenosylmethionine administration partially preserves microsomal function. This effect could be associated to the protection of membrane function by restoring transmethylation reactions.     

Influence of serum micronutrients on the incidence of kinetochore-positive or -negative micronuclei in human peripheral blood lymphocytes

The possible contribution of some selected serum micronutrients (beta-carotene, vitamins B12 and C, folic acid and alpha-tocopherol) to spontaneous chromosomal damage was investigated in human peripheral blood lymphocytes from 33 non-smoking healthy donors by the cytokinesis-block micronucleus assay. Labelling of micronuclei with antikinetochore serum was used to discriminate between kinetochore-positive and -negative micronuclei and thus between micronuclei which arise from whole chromosome loss and those which arise from chromosome breaks. Simple correlation analysis showed that age was significantly associated with the increased frequency of micronucleated cells, and this age-related increase in these cells was due to the increase in cells with both kinetochore-positive and -negative micronuclei. Serum micronutrient levels had no apparent significant effects on incidence of micronucleated cells except for the weak positive correlation between vitamin B12 levels and frequency of kinetochore-positive micronucleated cells. Multiple regression analysis with age and serum micronutrient levels as independent variables showed that (a) age was the most influential variable for the frequency of micronucleated cells, (b) the serum vitamin C level was associated with increased frequency of spontaneous micronucleated cells, and this increase was mainly due to the increase in cells with kinetochore-positive micronuclei, and (c) the serum folic acid level was significantly and negatively related to the frequencies of cells with both kinetochore-positive and -negative micronuclei. To avoid the predominant age-effect, we also performed separate multiple regression analysis with age-adjusted frequency of micronucleated cells as dependent variable. The results from this analysis again showed a significant and positive effect of serum vitamin C level on age-adjusted frequency of kinetochore-positive micronucleated cells, while marginal negative effect of folic acid on age-adjusted frequency of total micronucleated cells (P < 0.06) and kinetochore-positive micronucleated cells (P < 0.051) was detected. These results suggest that age and serum vitamin C are definitely variables for frequencies of spontaneous chromosome loss, and that serum folic acid is perhaps another important micronutrient which influence the frequency of spontaneous chromosomal damage.     

Induction of micronuclei and of enzyme-altered foci in the liver of female rats exposed to progesterone and three synthetic progestins

Progesterone (PG) and three structurally similar synthetic progestins-norethisterone (NE), allylestrenol (AE), and dydrogesterone (DG)-have been compared for their ability to induce the formation of micronuclei and of enzyme-altered foci in the liver of female rats. In the micronucleus assay, carried out in rats given a single p.o. dose of 100 mg kg-1 3 days before partial hepatectomy and sacrificed for cell sampling 2 days later, the frequency of micronucleated hepatocytes was 3.5-fold higher than in controls with PG, 2.8-fold with DG, 2.2-fold with NE and 2.1-fold with AE, but the increase was statistically significant only for PG. In the liver foci assay, performed to evaluate the tumor initiating activity of p. o. dosing with 100 mg kg-1 once a week for 6 successive weeks, the values of the number and area of gamma-glutamyltranspeptidase-positive foci were, as compared to controls, 15.9- and 100-fold higher with NE, and 13.9- and 52-fold higher with AE, but only the increase of area produced by NE was statistically significant; PG and DG did not display in this test any activities. Considered together with previous findings, these results suggest that NE might be biotransformed in the liver into reactive species and thus behave as a weak genotoxic agent.     

Degradation studies on Escherichia coli capsular polysaccharides by bacteriophages

The mouse peripheral blood micronucleus assay, a measure of DNA damage in erythroblastic cells, was used to determine: (1) the incidence of spontaneously occurring micronucleated reticulocytes (MNRETs) as a function of age, and (2) the induction of micronuclei following treatment of young and old animals with mitomycin C. Male C57BL/6 mice, 92 weeks of age, exhibited a significantly higher frequency of spontaneously occurring peripheral blood MNRETs than mice that were 6 or 10 weeks of age. Mice that were 5-6 weeks or 91-92 weeks old were treated with one dose, or two consecutive doses of mitomycin C; this resulted in dose-related increases in the frequency of MNRETs. Mitomycin C, at a single dose of 1 or 2 mg/kg, induced one-third as many MNRETs in the older animals as compared to the younger animals. When treated with a split dose of mitomycin C (total dose 0.5 to 2 mg/kg), older animals displayed on average two-thirds the mutagenic response of the younger animals. However, analysis of variance performed on these data indicated that the age of the animals did not have a significant effect on their mutagenic response to mitomycin C at any dose level. It appears that aging mice may not be more sensitive to the mutagenic effects of chemically-induced DNA damage than younger mice, suggesting that the higher spontaneous mutation frequency in older mice could be the result of an increased load of accumulated DNA damage.