Chromosomal damage and ageing: effect on micronuclei frequency in peripheral blood lymphocytes

BACKGROUND

Instability in the organization and expression of the genetic material has been hypothesized as the basic mechanism of ageing.

OBJECTIVE

To quantify the effect of ageing on chromosomal damage as measured by spontaneous micronuclei (MN) frequency in peripheral blood lymphocytes.

METHOD

Analysis of a large population sample from two laboratories applying the cytokinesis-block technique and a third using traditional interphase analysis. The age-related effect on baseline level of micronuclei frequency and on cell proliferation measures was further investigated in a study of peripheral blood samples from healthy subjects.

RESULTS

There was an increase of MN frequency with age. The regression lines showed a positive slope and were statistically significant (P< 0.01) with a steeper trend for cytochalasin B-treated samples. An inverse correlation with age was detected for the percentage of binucleated cells in laboratories using cytochalasin B. This study confirms the increase of basal level of MN with age. A decrease by age in proliferation efficiency measured by the percentage of binucleated cells suggests an interference of age-related factors on cell division.

CONCLUSION

There is an increase in MN frequency with increasing age.

Genotoxicity biomarkers in the assessment of heavy metal effects in mussels: experimental studies

Heavy metals are stable and persistent environmental contaminants. The range of metal concentrations is generally below acute thresholds in coastal areas, where recognition of chronic sublethal effects is more relevant. Evidence of long-term adverse effects, such as cancer, due to heavy metals in marine animals comes from a number of field and experimental studies. The mechanism of metal carcinogenicity remains largely unknown, although several lines of experimental evidence suggest that a genotoxic effect may be involved. The aim of our study was to evaluate the sensitivity of genotoxicity tests, alkaline elution and micronucleus test, as biomarkers for the detection of heavy metals in mussels as the sentinel species. Experimental studies were carried out on Mytilus galloprovincialis exposed in aquarium (5 days) to different concentrations of three selected metal salts, CuCl2 (5, 10, 20, 40, 80 micrograms/l/a), CdCl2 (1.84, 18.4, 184 micrograms/l/a), and HgCl2 (32 micrograms/l/a), and to a mixture of equimolar doses of the three metals to study the results of their joint action. Metallothionein quantitation was used as a marker of metal exposure. Lysosomal membrane stability was applied to evaluate the influence of physiological status on genotoxic damage. The ranking of genotoxic potential was in decreasing order: Hg > Cu > Cd. Cu and Hg caused an increase of DNA single-strand breaks and micronuclei frequency. Cd induced a statistical increase of DNA damage, but gave negative results with the micronucleus test. A relationship between genotoxic effects and metallothionein content was observed. Reduction in lysosomal membrane stability with the increasing concentration of heavy metals was also evident.

32P-postlabeling detection of DNA adducts in mice treated with the herbicide Roundup

Roundup is a postemergence herbicide acting on the synthesis of amino acids and other important endogenous chemicals in plants. Roundup is commonly used in agriculture, forestry, and nurseries for the control or destruction of most herbaceous plants. The present study shows that Roundup is able to induce a dose-dependent formation of DNA adducts in the kidneys and liver of mice. The levels of Roundup-related DNA adducts observed in mouse kidneys and liver at the highest dose of herbicide tested (600 mg/kg) were 3.0 +/- 0.1 (SE) and 1.7 +/- 0.1 (SE) adducts/10(8) nucleotides, respectively. The Roundup DNA adducts were not related to the active ingredient, the isopropylammonium salt of glyphosate, but to another, unknown component of the herbicide mixture. Additional experiments are needed to identify the chemical specie(s) of Roundup mixture involved in DNA adduct formation. Findings of this study may help to protect agricultural workers from health hazards and provide a basis for risk assessment.

In vivo studies on genotoxicity of a soil fumigant, dazomet

Dazomet is a soil fumigant effective against germinating weed seeds, nematodes, soil fungi, and soil insects. Dazomet is primarily used for preplanting control in tobacco and forest nursery crops and is now marketed for a wider range of open field and greenhouse crops (e.g., vegetables, fruits, ornamental plants, lawns, and turfs). Swiss CD1 male and female mice were intraperitoneally treated with dazomet in order to evaluate its potential genotoxicity. DNA damage activity, namely, DNA single-strand breaks, DNA adducts, and increased micronuclei frequency due to treatment with the soil fumigant was observed in the experimental animals. Dose-dependent DNA adduct formation was detected in the liver, kidneys, and lungs of mice. DNA adduct levels in these three organs were 6.0 +/- 0.4 (SD), 4.8 +/- 0.1 (SD), and 2.2 +/- 0.4 (SD) adducts/10(8) nucleotides, respectively, at the highest dose of the soil fumigant tested (90 mg/kg). No adduct formation was observed in control mice. A significant increase in DNA single-strand breaks was detected in the liver and kidneys of mice treated with 100 mg/kg of dazomet (P < 0.05). A significant increase in micronuclei frequency was observed in the bone marrow of mice treated with 100 mg/kg of dazomet (P < 0.05).

Sister chromatid exchange induction in peripheral blood lymphocytes of traffic police workers

Traffic police workers, as a population exposed to urban atmosphere, were compared with a control population exposed to indoor air pollution levels. Sister chromatid exchanges (SCEs) as a biomarker of effect were measured in peripheral blood lymphocytes of 54 exposed subjects and 35 controls, and environmental concentration of polynuclear aromatic hydrocarbon (PAH) tracer compounds was detected by personal air samplers. The mean exposure level to benzo[a]pyrene in our group of traffic policemen (3.4 mg/m3) was in the range that has been estimated in urban areas in Europe during the last 10 years. No difference in SCE levels was found between exposed workers (7.36, SD 1.35) and controls (7.47, SD 1.28). No correlation was observed between SCE/cell and airborne PAH concentration in the traffic worker population. A positive regression of SCE on exposure estimate was found only in the non-smoking group of police workers. Our findings suggest that exposure to urban air pollution does not induce relevant cytogenetic effects.

Effect of a diet high in vegetables, fruit, and nuts on serum lipids

We assessed the effect of a diet high in leafy and green vegetables, fruit, and nuts on serum lipid risk factors for cardiovascular disease. Ten healthy volunteers (seven men and three women aged 33 +/- 4 years [mean +/- SEM]; body mass index, 23 +/- 1 kg/m2) consumed their habitual diet (control diet, 29% +/- 2% fat calories) and a diet consisting largely of leafy and other low-calorie vegetables, fruit, and nuts (vegetable diet, 25% +/- 3% fat calories) for two 2-week periods in a randomized crossover design. After 2 weeks on the vegetable diet, lipid risk factors for cardiovascular disease were significantly reduced by comparison with the control diet (low-density lipoprotein [LDL] cholesterol, 33% +/- 4%, P < .001; ratio of total to high-density lipoprotein [HDL] cholesterol, 21% +/- 4%, P < .001; apolipoprotein [apo] B:A-I, 23% +/- 2%, P < .001; and lipoprotein (a) [Lp(a)], 24% +/- 9%, P = .031). The reduction in apo B was related to increased intakes of soluble fiber (r = .84, P = .003) and vegetable protein (r = -.65, P = .041). On the vegetable compared with the control diet, the reduction in total serum cholesterol was 34% to 49% greater than would be predicted by differences in dietary fat and cholesterol. A diet consisting largely of low-calorie vegetables and fruit and nuts markedly reduced lipid risk factors for cardiovascular disease. Several aspects of such diets, which may have been consumed early in human evolution, have implications for cardiovascular disease prevention.

Age-related increase of baseline frequencies of sister chromatid exchanges, chromosome aberrations, and micronuclei in human lymphocytes

Intra- and interindividual variations of baseline frequencies of cytogenetic end points in lymphocytes of human populations have been reported by various authors. Personal characteristics seem to account for a significant proportion of this variability. Several studies investigating the role of age as a confounding factor in cytogenetic biomonitoring found an age-related increase of micronucleus (MN) frequency, whereas contradictory results were reported for chromosomal aberrations (CAs) and sister chromatid exchanges (SCEs). We have quantitatively evaluated the effect of age on SCE, CA, and MN through the analysis of a population sample that included data from several biomonitoring studies performed over the last few decades in 12 Italian laboratories. The large size of the data set, i.e., more than 2000 tests for each end point, allowed us to estimate the independent effect of age, taking into account other covariates, such as sex, smoking habits, occupational exposure, and inter- and intralaboratory variability. A greater frequency of the mean standardized values by increasing of age was observed for all of the end points. A leveling off was evident in the last age classes in the trend of MN frequencies. Frequency ratios (FRs), which express the increase of the cytogenetic damage with respect to the first age classes, i.e., 1-19 years, were estimated using Poisson regression analysis after adjustment for the potential confounding factors and confirmed the increasing trend by age class for all three end points. The most dramatic increase was observed for MN, with a FR that approaches the value of 2 at the age class 50-59 (FR, 1.97; 95% confidence interval, 1.43-2.71) and remains substantially unchanged thereafter. The trend of FRs for CA is more homogeneous, with a constant rise even in the older classes, whereas the frequency of SCE increases with age to a lesser extent, reaching a plateau in the age class 40-49 and the maximum value of FR in the age class over 70 (FR, 1.14; 95% confidence interval, 1.07-1.23). In conclusion, our results point to an age-related increase of the chromosome damage in lymphocytes and emphasize the need to take into account the potential confounding effect of this variable in the design of biomonitoring studies based on chromosome damage.

Airborne levels of polycyclic aromatic hydrocarbons: 32P-postlabeling DNA adducts and micronuclei in white blood cells from traffic police workers and urban residents

An epidemiologic study on 94 traffic police officers exposed to airborne polycyclic aromatic hydrocarbons (PAH) and 52 age-matched urban residents working in confined spaces considered as referent subjects without occupational exposure to PAH was conducted to characterize individual exposure to benzo(a)pyrene (BaP), benzo(b)-, and benzo(k)fluoranthene (BbF and BkF) and the occurrence of DNA adducts and micronuclei in white blood cells (WBC). The study's findings indicated that mean concentrations of PAH in the city air were 10 to 30 times higher among the traffic police officers compared with referent subjects (4.55 +/- 3.44 ng/m3 and 0.15 +/- 0.30 ng/m3 of BaP among police officers and referents, respectively). 32P-postlabeling DNA adducts in WBC obtained from police officers (1.48 +/- 1.35 RAL/10(8)) were significantly higher than in referent subjects (1.01 +/- 0.63 RAL/10(8), P = 0.007), suggesting a possible role of exposure to airborne PAH in the DNA damage. The frequency of micronuclei was significantly increased (P = 0.02) in referent subjects (4.49 +/- 2.0% cells) compared with police officers (3.75 +/- 1.65% cells) due to the large proportion of females in the former group. Comparison of the mean micronuclei frequencies among 82 male police officers (3.73 +/- 1.6% cells) and referents (4.03 +/- 1.61% cells) failed to reveal a statistically significant difference (P = 0.38). Our findings support the evidence of a noxious effect of the exposure to airborne PAH found in large cities on the occurrence of DNA adducts in WBC, whereas there seems to be no effect on the cytogenetic risk assessed as micronuclei frequency.

Cytogenetic biomonitoring in traffic police workers: micronucleus test in peripheral blood lymphocytes

Atmospheric pollution represents a relevant environmental hazard which has been associated with considerable excess mortality, morbidity, and increased rates of respiratory diseases in humans. To date, more than 3,000 environmental chemical compounds have been identified in the ambient atmosphere, including a variety of mutagenic and/or carcinogenic agents, such as polycyclic aromatic hydrocarbons (PAHs), aromatic amines, and heterocyclic compounds. Positive associations between cytogenetic markers and airborne levels of PAHs have been reported by experimental and human studies. Traffic has been implicated as the major determinant for the concentration of PAHs and, therefore, for the genotoxic activity of urban air. A biomonitoring study has been conducted in 82 italian traffic police workers exposed to air pollutants and 34 control subjects (matched by age, gender, and smoking habits) not exposed to traffic pollutants. The aim of this study was to assess the cytogenetic effects, such as micronucleus frequency in peripheral blood lymphocytes, and to estimate the association with individual exposure to PAH. Statistical analysis of the frequency of micronuclei in binucleated cells showed higher mean levels in referent subjects (4.03%) than in traffic police officers (3.73%). Smoking showed no effect on the frequency of micronuclei. The study failed to detect any association between micronucleus frequency and individual level of benzo(a)pyrene, considered a marker of exposure to PAHs. These findings indicate that exposure to urban air pollutants does not result in increased levels of micronuclei in peripheral white blood cells.

Prediction of glucose and insulin responses of normal subjects after consuming mixed meals varying in energy, protein, fat, carbohydrate and glycemic index

To see if both the amount and source of carbohydrate consumed determined postprandial glucose and insulin responses of mixed meals, eight nondiabetic subjects took five different mixed meals containing variable energy (1650-2550 kJ), fat (8-24 g), protein (12-25 g) carbohydrate (38-104 g) and glycemic index (43-99). Incremental glucose and insulin responses for the five meals varied over a 2.3-fold range. Amount of carbohydrate alone was not significantly related to the mean glucose and insulin responses. However, using previously derived equations, amount of carbohydrate and glycemic index explained approximately 90% of the variability of the observed mean glucose and insulin responses (P = 0.01). We conclude that both amount and source of carbohydrate determine the glucose and insulin responses of lean, young, nondiabetic subjects after different mixed meals with variable glycemic index. Variation in protein and fat intake, over the range tested here, appears to have a negligible effect on postprandial glucose and insulin.

Source and amount of carbohydrate affect postprandial glucose and insulin in normal subjects

To determine if source and amount of carbohydrate affected postprandial glucose and insulin responses, seven nondiabetic subjects consumed 0, 25, 50, 75 or 100 g carbohydrate (total carbohydrate minus total dietary fiber) portions of barley, spaghetti, bread or potato. By ANOVA, both source and amount of carbohydrate had significant effects on incremental response areas for capillary glucose (P = 0.001), plasma glucose (P = 0.01) and plasma insulin (P = 0.03), but there was no source x amount interaction. By regression analysis, source of carbohydrate explained a similar amount of the variability of glucose and insulin responses, 46-64%, as the amount of carbohydrate, 47-57%. Together, carbohydrate source and amount accounted for 85-94% of the variability of mean glucose and insulin responses. We conclude that, for individual foods with different glycemic indices, both source and amount of carbohydrate influence the postprandial glucose and insulin responses of nondiabetic subjects.

(32)P-postlabeling detection of DNA adducts in peripheral white blood cells of greenhouse floriculturists from western Liguria, Italy

Pesticides are widely used in agriculture to enhance crop yields and to control disease vectors. Floriculturists work frequently in greenhouses and may be exposed to high levels of pesticides, which may result in adverse health effects. To evaluate the relationship between exposure to pesticides and DNA adduct formation in peripheral WBCs of Italian floriculturists, the nuclease P1 modification of a (32)P-postlabeling assay was used to analyze WBC DNA from floriculturists (n = 26) and matched controls (n = 22). DNA adduct-positive samples were more frequent in floriculturists (11/26; 42%) than in matched controls (2/22; 9%) (P < 0.01). Slightly higher frequencies of DNA adduct-positive samples were observed in floriculturists > or = 44 years of age (53%) and in female floriculturists (57%). Floricultural practice was found to be associated with a significantly higher DNA adduct-positive rate in WBCs (rate ratio, 5.12; 95% confidence interval, 1.1-23.7) after allowing for the effects of age and gender. These two latter covariates were not significantly associated with DNA adduct-positive rates. The quantitative levels of DNA adducts were significantly higher in floriculturists than in matched controls according to the Mann-Whitney nonparametric statistic (P = 0.0052). The median adduct level for positive samples among floriculturists was 1.5/10(8) bases. A specific, well-visible spot, named alpha adduct, was detected in 7 out of the 11 DNA adduct-positive samples from floriculturists but in none of the (22 + 20) referent samples (P = 0.0004). The presence of pesticide-related DNA adducts was confirmed clearly using the butanol extraction procedure. Six of 8 floriculturists and 0 of 10 referents were found positive with this method. The median adduct level for positive samples was 6.0/10(8) bases. Two strong spots close to the origin could be identified in all six positive floriculturists, using the butanol extraction procedure. No association between DNA adducts and use of specific pesticides was observed.

Influence of sex on cytogenetic end points: evidence from a large human sample and review of the literature

The planning and evaluation of human cytogenetic studies should contemplate various confounders and effect modifiers, among these, sex and sex-related factors. The association between this variable and cytogenetic damage has been extensively studied, but conclusive evidence has thus far not been reached, especially for the most recent assays, such as the micronucleus test (MN). In the attempt to quantitatively estimate the sex effect on sister chromatid exchange (SCE), chromosomal aberration (CA), and MN in peripheral blood lymphocytes, we reanalyzed the original data sets of several biomonitoring studies performed over the last decades in 10 Italian laboratories. This approach yielded a very large database, namely 2140, 2495, and 2131 subjects screened for SCE, CA, and MN, respectively. Differences between sexes were expressed in terms of relative risk (RR) of females versus males, after adjustment for age, smoking habits, occupation exposure and inter- and intralaboratory variation. No difference between sexes was found for the frequency of SCE [RR = 1.01; 95% confidence interval (CI) = 0.99-1.03] and CA (RR = 1.00; 95% CI = 0.92-1.08) even if the CI of the RR for SCE includes the 3% excess in females frequently reported by the literature. Conversely, a 29% overall increase of the MN rate in females was observed in the whole data set (RR = 1.29; 95% CI = 1.20-1.38). Different trends by age of the MN rate are described in the two sexes, focusing on the peak observed in females in the menopausal period and on the subsequent decrease.

[Genotoxic damage in subjects exposed to automobile exhaust: preliminary results]

The associations between selected biomarkers of biologically effective dose (32P-post-labelling-DNA adducts), early biological effects (Micronuclei, MN) and sister chromatid exchanges (SCE) and individual measurements of exposure to benzo(a)pyrene (a surrogate index of exposure to polynuclear aromatic hydrocarbons, PAHs) are investigated in a study being conducted among traffic police workers and referent subjects in the City of Genova, Italy. Preliminary findings show B(a)P mean values of 1.33 ng/m3, SD = 1.35 ng/m3 and 0.06, SD = 0.17 in traffic police workers and referent subjects, respectively. Micronuclei mean levels in peripheral blood lymphocytes of 26 traffic police workers and 25 referents were 3.30, DS = 1.24 e 3.90, DS = 1.50 (per 1,000 binucleated cells). Eleven subjects (61%) out of 18 had detectable levels of DNA adducts (32P-post-labelling technique, range 1.8-9.0 Relative Adduct Level (RAL) per 10(9) nucleotides).

Chemical hazard evaluation: the use of factual health and safety databanks

The usefulness of factual health and safety databanks is discussed in this paper. Four databanks have been selected for this study: HSDB (Hazardous Substances Data Bank), ECDIN (Environmental Chemicals Data Information Network), RTECS (Registry of the Toxic Effects of Chemical Substances) and CCRIS (Chemical Carcinogenesis Research Information). The quality of the information available in the databanks considered was examined for five different chemical compounds and the completeness of the information available was carried out by an analysis of carcinogenic and mutagenic data.

Genotoxic effects of the carbamate insecticide methomyl. I. In vitro studies with pure compound and the technical formulation "Lannate 25"

The carbamate insecticide methomyl and the methomyl-containing technical formulation "Lannate 25" were tested on whole blood human lymphocyte cultures. Both products induced dose-dependent increases in chromosome aberrations and micronuclei. Lannate 25 induced DNA damage as measured by the alkaline elution assay and hydroxylation of guanine at the C8 position. Sister chromatid exchanges were not increased significantly with either product. Overall, the technical formulation was more active than the pure compound, when compared at similar concentrations of active principle. Moreover, a different ratio of CREST-positive/CREST-negative micronuclei was observed with the two products, pure methomyl being relatively more active than Lannate 25 in the induction of CREST-positive micronuclei. On the basis of these results, previous evaluations of methomyl as a nongenotoxic compound should be reconsidered.

Genotoxic effects of the carbamate insecticide, methyomyl. II. In vivo studies with pure compound and the technical formulation, "Lannate 25"

The carbamate insecticide, methomyl, and the methomyl-containing technical formulation, "Lannate 25", were tested for the induction of DNA damage in vivo. Swiss CD1 mice were treated intraperitoneally with test substances and the following tests were performed: alkaline elution of liver and kidney DNA, 8-hydroxyguanosine detection in liver DNA, and 32P-postlabelling analysis of DNA adducts in liver DNA. The clastogenic activity of the two pesticide preparations was also evaluated as micronucleus frequency in bone marrow. No DNA adducts were detected in liver DNA of mice treated with pure methomyl, while a dose-related increase in DNA adducts was found in Lannate 25-treated animals. All other tests were positive with both methomyl and Lannate 25. A summary of genotoxic activity of methomyl is also presented. The hypothesis that the observed genotoxic effects of methomyl are induced indirectly, through formation of active oxygen species, is discussed.

Frequency of micronuclei in lymphocytes from a group of floriculturists exposed to pesticides

A large part of the commercial flower production in Italy is located in the located in the western part of the Liguria region, near the French border. The use of pesticides in this area has been much higher than the national average. The frequency of micronuclei in peripheral blood lymphocytes was evaluated in a group of 71 floriculturists working in this area and in a control group of 75 healthy blood donors living in the same area. A significant increase of micronucleated lymphocytes was observed in floriculturists as compared to unexposed subjects (8.57 vs. 6.67, p < .05). Females showed a marked increase in MN frequency (45% higher than males) independently of the exposure. A dose-response relationship was observed between duration of exposure and MN frequency. The condition of exposure was also found to influence the micronuclei frequency. Increased relative risks in greenhouse workers (RR = 1.31) and in people working alternately in the greenhouse and in the open field (RR = 1.46) was observed with respect to the reference population.

Relationship between poly(ADP-ribose) polymerase activity and DNA damage induced by zinc dithiocarbamates in mouse and rat liver

The genotoxic effects due to in vivo treatment with zinc dithiocarbamates were evaluated in rat and mouse liver. The two pesticides Zineb and Ziram, belonging to this chemical class, induced an increase in single-strand DNA breaks, as measured by the alkaline elution technique. The nuclear enzyme poly(ADP-ribose) polymerase (pADPRP), a chromatin-bound catalytic protein, utilizing NAD+ as a substrate, was tested by a radiometric procedure. A close relationship between the increased extent of DNA damage and the enhanced level of endogenous pADPRP activity was obtained in rat liver, whereas both parameters remained unchanged in mouse liver.

Cytogenetic analysis of a human population occupationally exposed to pesticides

A great deal of the flower cultivation in Italy is carried out in the western part of the Region of Liguria. The extensive use of pesticides professionally exposes floriculturists operating in this area to a complex mixture of compounds. The frequency of micronuclei in peripheral lymphocytes has been evaluated in 71 floriculturists and in a control group of 75 healthy blood donors living in the area. No correlation between age and micronucleus frequency was found in peripheral lymphocytes of the controls while an increase in this parameter was observed in the elderly of the exposed group. Our data suggest a sex-related effect in the induction of micronuclei. The frequencies of micronucleated lymphocytes were significantly higher in females than in males in both exposed and control groups (RR = 1.45, 95% C.I. 1.25-1.67). The main result of this study, however, is the observation of a significant increase in micronucleated lymphocyte frequency in people occupationally exposed to pesticides. The micronucleus frequency was 8.57/1000 for exposed persons and 6.67/1000 for controls (p < 0.05). A dose-response relationship with duration of exposure was apparent with a maximum increment of 71% in the frequency of micronuclei in subjects exposed for over 30 years.

Biomonitoring of workers exposed to pesticides

The potential clastogenic effects of pesticides was investigated in 71 floriculturists exposed to complex chemical mixtures. Exposed and referent subjects were selected from the same geographical area located in north western Italy. A significant association between micronuclei frequency and occupational exposure to pesticides was found (RR = 1.25). A positive dose-response gradient was observed with years of employment (used as an index of cumulative exposure) as a floriculturist. Individuals working exclusively in greenhouses (confined spaces) showed higher micronuclei levels than subjects working in open fields. The study supports the hypothesis that human exposure to pesticides causes a clastogenic damage.

Modulation of DNA damage by vitamin A in developing Sprague-Dawley rats

Prenatal and neonatal Sprague-Dawley rats were given a diet deficient in or with an excess of Vitamin A and at the age of 55 days female progeny were treated with a single i.g. dose of 80 mg/kg DMBA or 50 mg/kg MNU. Under these experimental conditions it was found that the exposure of perinatal rats to a diet containing an excess of Vitamin A caused a decrease in the amount of DMBA- and MNU-induced DNA damage in the mammary gland and the liver of the female offspring. When diets were deficient in Vitamin A there was a dual effect in terms of DNA damage detected in the same organs, namely DMBA caused an amount of DNA damage comparable to controls, while the extent of DNA damage induced by MNU greatly increased in both organs. These results indicate that Vitamin A can permanently change the sensitivity of adult progeny to chemically induced DNA damage when it is given to pregnant and lactating females.

DNA damage induced by 7,12-dimethylbenz[a]anthracene in the liver and the mammary gland of rats exposed to polycyclic aromatic hydrocarbon enzyme inducers during perinatal life

The long-lasting modulating effect induced by the prenatal or neonatal exposure to phenobarbital (PB) and aroclor on the genotoxic activity of 7,12-dimethylbenz[a]anthracene (DMBA) in female Sprague-Dawley rats was studied. The effect was measured as DNA damage evaluated in the liver and in the mammary gland of 55-day-old animals, 4 and 24 h after an i.g. injection of 80 mg/kg of DMBA. PB was given per os, i.g. or in drinking water to pregnant females and by i.g. only to neonates or in adult progeny. Aroclor was injected i.g. in prenatal and in neonatal life, and a second dose was given in adult life. Under these experimental conditions it was shown that DNA damage kinetics caused by DMBA are modulated by exposure to PB and, to a minor extent, by aroclor. The amount and persistence of DNA damage were highest when PB was administered to neonates. An average 2-fold increase in the elution constants (K) of DNA in the liver and the mammary gland was observed 4 h after DMBA treatment, as compared to uninduced animals. Repeated enzyme induction by PB seems to reduce DMBA genotoxicity, as shown by a decrease in DNA damage and persistence in the liver and mammary gland. The inducibility of the monooxygenase enzyme system in perinatal life favouring metabolic activation or inactivation of polycyclic aromatic hydrocarbons might be critical in determining individual susceptibility of adult progeny to chemical carcinogenesis by DMBA.

[Induction of micronuclei in polychromatic erythrocytes from mouse bone marrow following intraperitoneal administration of halogenated benzenes]

The mutagenicity of halogenated benzenes, including three isomers of tri- and tetrachlorobenzenes (TCB, TeCB) was studied on male Swiss CD1 mice by MN test. The data presented show that all the halogenated benzenes tested were found to be clastogenic apart from 1,2,3,5-TeCB. No significant differences were observed in the clastogenic activities of TCB-isomers and TeCB-isomers.

Target tissue DNA damage in inbred mouse strains with different susceptibility to the colon carcinogen 1,2-dimethylhydrazine

We have compared liver, kidney and colon DNA damage, as single strand breaks, in mice with different strain-dependent susceptibility to the colon-specific carcinogen 1,2-dimethylhydrazine (DMH). The mouse strains studied were: AKR/J, DBA2 totally resistant; CD1, C57BL/6N moderately susceptible; SWR/J very susceptible to DMH-induced carcinogenesis. DNA breaks were estimated from the elution rate constant (K) according to the alkaline elution technique. At 4 h after carcinogen administration a substantial and comparable DNA damage was found in liver and kidney in all the strains examined. The DNA fragmentation index, however, reached a maximum value at 2 h after treatment in the liver of the most susceptible strain (SWR/J). About 50% of the liver DNA damage detected in all five strains 4 h after DMH administration persisted at 24 h after treatment and was totally repaired at 72 h. Kidney DNA damage decreased in 48 h toward the range of control values. In colon epithelial cells (the carcinogen target tissue) 2 and 4 h after DMH administration the amount of DNA single strand breaks was correlatable with the strain sensitivity to the carcinogen. In the time interval studied (2-72 h after DMH administration) the decrease of colon DNA damage was linear in the resistant strains. In contrast, in the more susceptible strain (SWR/J), the amount of DNA breaks remained high up to 24 h after treatment and returned to background level at 72 h.

A new method to reveal the genotoxic effects of N-nitrosodimethylamine in pregnant mice

DNA damage and repair in kidney and liver of mouse fetuses exposed to selected doses of N-nitrosodimethylamine (NDMA) (CAS No. 62.75.9) were studied using the alkaline elution technique. CD1 female mice (15 days pregnant) were treated i.p. with 2 and 10 mg/kg b.w. of NDMA; a slight increase in DNA damage was observed in their fetuses compared to untreated controls. A 2-fold higher extent of DNA damage was induced when mice were treated by intrafetal injections of a rat S9 activating fraction (S9) immediately before exposure to the same dose of NDMA by transplacental means. The DNA-strand breaks disappeared as a function of time in animals treated with NDMA alone. In contrast, a significant persistence of DNA damage was detected in the liver and lung of fetuses which were treated with S9 and NDMA in sequence. These experiments demonstrate the metabolic immaturity of unborn mice as far as the carcinogenic activation of NDMA is concerned and show the high susceptibility of fetal tissues to DNA-damaging agents. The alkaline elution applied in vivo by the transplacental route combined with the intrafetal injection of an exogenous activating microsomal fraction allow to extend our knowledge on the interaction of metabolism-dependent chemicals with fetal tissues.

Specific targets of alkylating agents in nuclear proteins of cultured hepatocytes

We have established a specific correlation between the carcinogenic potency of a series of alkylating agents, with a mechanism of reaction ranging between Ingold's SN1-SN2 (ENU greater than MNU = MNNG greater than EMS greater than DMS = MMS) (Vogel et al., 1979; Bartsch et al., 1983) and specific target sites in the amino acids of nuclear proteins of cultured hepatocytes. More potent carcinogens, that react predominantly with an Ingold's SN1 mechanism, mainly alkylate the amino group of lysine and the guanido group of arginine. Weaker carcinogens, reacting with a mechanism closely resembling an Ingold's SN2, mainly alkylate the sulfhydryl group of the cysteine and the 3 position of the imidazolic ring of histidine. A compound with an intermediate type of reactivity alkylates, to a comparable extent, all 4 of the above-described positions. Although stable DNA damage brought about by alkylating carcinogens is considered to be the most likely cause of neoplastic transformation, epigenetic modifications may also play an important role in the process, especially because of their extreme stability. We have verified the existence of a linear correlation between the Swain-Scott substrate constant (S) of each compound and the amount of alkylation produced at the specific target sites. This type of correlation could be the basis of a 'short-term' genotoxicity assay in a battery of complementary tests.

Quantitative predictivity of carcinogenicity of the autoradiographic repair test (primary hepatocyte cultures) for a group of 80 chemicals belonging to different chemical classes

In this work we have investigated the correlation existing between a short-term genotoxicity test (DNA repair in rat liver cells) and carcinogenicity in rodents. The work is in the framework of a line of thinking that considers as a possibility the utilization of the quantitative component of the information obtained from genotoxicity tests. In a preliminary report for 25 compounds belonging to different chemical classes, a correlation coefficient of 0.36 was found between carcinogenic potency in small rodents and potency in autoradiographic repair. This level of correlation is comparable with similar levels found for many other short-term tests: Ames test, alkaline DNA fragmentation in vivo, DNA adducts in vivo, morphological transformation in vitro and SCE induction in vivo. Obviously, since only 25 compounds were examined, assessment was rather uncertain, and the subdivision of the set into subsets for different chemical classes would have generated groups too small for a meaningful statistical analysis. With a much larger set (80 compounds) we hoped to be able to discriminate different predictivities for different chemical classes. This seems important because the test could be much more suitable for one given class than for another. Previous investigations with different short-term tests have shown that these differences can indeed exist and be very great. In this respect it is potentially very encouraging that the test considered here showed a fair correlation with carcinogenic potency for aromatic amines. Many other tests that we have examined so far have shown little or no predictivity for this important class of chemicals.

In vitro DNA and nuclear proteins alkylation by 1,2-dimethylhydrazine

The methylating carcinogen 1,2-dimethylhydrazine (DMH) CAS 540.73.8 is highly organ-specific and, under certain experimental conditions, produces a high incidence of adenocarcinoma in the colon of rodents. We have tried to assess the possibility that part of the organ-specifity in the carcinogenic effect of DMH could be attributed to its metabolism by specific microsomal enzymes. In particular, we compared the in vitro effects of DMH in the presence of either colon or liver microsomes from animals that had been treated with microsomal enzyme inducers. V79 Chinese hamster cells were used as the target to evaluate the damage to the genetic material, as judged by (1) formation of adducts of DNA bases and (2) amino acid modifications in nuclear proteins using [Me-14C]DMH and appropriate analytical detection systems. Our results tend to support the above postulated hypothesis.

Correlation between incidence of 1,2-dimethylhydrazine-induced colon carcinomas and DNA damage in six genetically different mouse strains

Mice from strains with different susceptibility to the colon-specific carcinogen 1,2-dimethylhydrazine (DMH) were tested for DNA damage in liver, kidney and colon after administration of the compound at a dosage that has been reported to induce a high incidence of adenocarcinoma in the colon of rodents. DNA breaks were evaluated from their elution rate constant according to the alkaline elution technique. We found that 4 h after administration of the carcinogen there was a substantial and comparable DNA damage in liver and kidney of all strains examined. Conversely, colon DNA damage was hardly above control levels in the carcinogen-resistant strains. The highest DNA damage was detected in the most susceptible strain and was slightly lower in the two other susceptible strains. We propose that the extent of DNA breakage in a target organ could be one of the factors determining organ-specific and strain-specific susceptibility to DMH.

Nuclear proteins damage by alkylating agents with different degrees of carcinogenicity

We have tried to establish a correlation between the carcinogenic potency of two alkylating compounds and specific target sites in chromatin. We have therefore compared the nuclear metabolism of radioactively-labelled methylmethanesulfonate (MMS), a relatively weak carcinogen and N-methylnitrosourea (MNU), a highly potent carcinogen in cultured primary hepatocytes which have, high microsomal drug-metabolizing activity and in V79 Chinese hamster cells which have low microsomal enzymatic activity. The modification of specific amino acid residues in acid-soluble nuclear proteins (H) and non-histone nuclear proteins (NH) was studied after exposing the cells to various doses of alkylating agents overnight. We found that at all doses, mainly the cysteine (Cys), but also to a lower extent the histidine (His) residues are methylated in both H and NH protein fractions by MMS. At high doses of MMS, traces of methylarginine and methylated lysines could be detected. MNU predominantly methylates lysine and arginine residues, the former being found mostly in H, the latter in NH. Although both hepatocytes and V79 cells metabolized radioactively-labelled carcinogen, a higher percentage of counts were incorporated by the hepatocytes; 'unusually' methylated amino acids were detectable in the hepatocyte proteins with relatively low doses of the alkylating agents but not in V79 cells. In the presence of exogenous microsomes, during exposure of V79 cells to the alkylating agents, the amount of amino acid methylation is qualitatively and quantitatively similar to that found in hepatocytes. Our data suggest a specific mechanism of protein methylation, at the level of target amino acids, for carcinogens with different potencies similar to what has been found for DNA bases. A component of the microsomal fraction (S9) may be able to enhance this effect.

Methylating agents: their target amino acids in nuclear proteins

We have tried to establish a correlation between the carcinogenic potency of four methylating compounds and their specific target sites in chromatin. We have therefore compared the nuclear metabolism of two relatively weak carcinogens radioactively labelled: dimethyl sulphate (DMS) and methyl methanesulphonate (MMS), and two potent carcinogens: N-methyl-N-nitrosourea (MNU) and N-methyl-N'-nitro-N-nitrosoguanosine (MNNG) in cultured primary hepatocytes and the V79 Chinese hamster cell line. Cysteine (when present), and to a lesser extent histidine, were methylated by MMS and DMS not only in the total acid-soluble nuclear protein (H) but also in purified histones H1 and H3. These compounds had the same effect not only on total non-histone nuclear protein (NH) but also on purified HMG1 and HMG2 (nuclear non-histone proteins with high electrophoretic mobility). Traces of methylarginine and methylated lysine could be detected in all samples. MNU and MNNG predominantly methylated lysine and arginine residues, the former being found mostly in acid soluble, the latter in non-histone nuclear protein. Methylated cysteine and histidine were present in trace amounts. Our preliminary data suggest specific amino acid methylation at the nuclear protein level for carcinogens with different potencies, similar to what has been found for DNA bases.

Benzo[a]pyrene-induced DNA damage in mouse fetal tissues

We have studied the occurrence and persistence of DNA damage in the hepatic and pulmonary tissues of fetal, newborn and adult CD1 mice exposed to selected doses of benzo[a]pyrene (BP) by utilizing the alkaline elution technique. Firstly 12-, 15- and 18-day pregnant and 1-, 7- and 82 to 85-day-old mice were treated i.p. with 10 mg/kg BP and the DNA fragmentation evaluated 4 h later. This approach indicated that, among the ages considered, 15-day-old fetuses were the most sensitive to BP genotoxicity. Therefore we concentrated on this intrauterine stage and evaluated the role of the maternal and fetal environment on the induction and the kinetics of disappearance of DNA damage by BP. BP at the dose levels of 0, 2 and 10 mg/kg was injected i.p. into pregnant females or directly into single fetuses and the fetal livers and lungs recovered 2, 4, 24 and 48 h later. According to the above protocol other 12-day-pregnant mice were treated i.p. with 500 mg/kg arochlor and their 15-day-old fetuses directly injected with the same doses of BP. The results showed that the maximum DNA damage is present at 4 h following BP treatment and it almost disappeared at 48 h irrespective of the route of BP administration. However, the decrease was not uniform and while at 48 h the lesion reached the control level in the liver, it remained slightly higher in the lung. The effects where markedly magnified in the arochlor-induced groups where the intrafetal injection of BP caused an average 2-fold increase and an earlier appearance of DNA damage in both liver and lung compared with uninduced animals. The amplified BP activity induced by arochlor was particularly evident in the lung where at 48 h there was still a significant amount of DNA damage. Since the lung is a preferential site of transplacental carcinogenic effects in CD1 mice, our results favor the conclusion that a correlation exists between DNA damage and tumor induction in the fetuses of this mouse strain.

DNA damage induced in vivo in various tissues by nitrochlorobenzene derivatives

Mono-, di-, and trinitrochlorobenzenes were injected i.p. into albino Swiss CD1 mice. Their effects were evaluated, in brain, liver and kidney, as single-strand DNA breaks. DNA damage was recognizable 4 h after administration in vivo, and its increment seemed to be related to the number of nitro groups contained in the chlorobenzene molecule. The simple and accurate microfluorometric procedure for DNA assay associated to the alkaline elution technique improved the application in vivo, avoiding the radiolabeling of DNA.

Evaluation of DNA damage by alkaline elution technique after in vivo treatment with aromatic amines

The time course of DNA damage induced by in vivo administration of benzidine, 1- and 2-naphthylamine or dimethylnaphthylamine has been evaluated using an alkaline elution technique. The organs damaged by the active ultimate metabolites, produced in mice treated with aromatic amines, appear to be, in decreasing order of susceptibility, liver, kidney and lung. Single-stranded DNA breaks are still evident 12 h after a single administered dose of the compounds. A direct dose-response relationship has been obtained using increasing concentrations of aromatic amines.

[Renal and hepatic toxicity studies in mice treated with sodium saccharin: breaks in single-stranded DNA]

The renal and hepatic effects of in vivo treatment with saccharin have been determined as increased DNA elutability on filter. A direct dose-damage relationship was not observed in the kidney and in the liver DNA of treated mice. Doses of 50, 100 and 200 mg/Kg seem to induce in almost all the experiments the same level of single-stranded breaks. The DNA elutability is increased in the range 130-210 % if compared with controls.

[Influence of the chemical structure of aromatic amines on alkaline elution of DNA]

The DNA damage induced by in vivo administration of: 2,4-dinitroaniline, ortho-toluidine and para-toluidine, was determined using alkaline filter elution of DNA. The target organs for ultimate carcinogens produced in mice appear to be the liver and the kidney. The damage was evident 4 hours after administration of a single dose of ortho- and para-toluidine. The values obtained after treatment with 2,4-dinitroaniline fall in the range of control mice.

[Fluorometric DNA assay at nanogram levels in biological material]

A high degree of reproducibility was obtained using a simple and rapid microfluorimetric method of DNA determination. The described method evaluates the increased fluorescence after reaction of 33258 Hoechst fluorochrome with calf thymus DNA and mouse liver chromatin preparations. The routinely used preparation reagents and the subcellular components do not interfere with the reaction.

[DNA damage and repair induced in vivo by benzidine treatment]

DNA damage was evaluated in kidney and liver of mice treated with benzidine at the dose of 150 mg/Kg. The data presented show that the liver can be considered as the target tissue more influenced by the benzidine metabolites. The maxima of DNA fragmentation in the liver and kidney were at 4 and 2 hours respectively after treatment. Moreover the induced DNA damage in kidney and liver of mice treated was evaluated in the time depending from the rate of repair synthesis.

[Influence of structure and physico-chemical properties of chemical agents in the induction of DNA alterations: nitrochlorobenzenes]

The DNA damage induced by mono-, di-, and trinitrochlorobenzenes has been evaluated in brain of male Swiss CD1 mice. The effect seems to be related to the increased content of nitro groups substituents on the chlorobenzene molecule. This class of compounds shows a high degree of specificity for the nervous tissue if compared to well-known carcinogens as NMU and NDMA.

[Role of aromatic amines in the induction of tumors of the urinary tract. Experimental evaluation of the DNA damage induced with naphthylamines]

DNA damage induced by 1-Naphtylamine and 2-Naphtylamine has been verified using alkaline elution technique. Single-stranded DNA breaks were evident in the liver and kidneys of mice treated within 4 hours from the injection. A difference in the organotropism of the two aromatic amines has been observed. These results improve the applicability of the technique and are interesting in order to obtain predictive evaluations on the carcinogenicity of the aromatic amines.

DNA damage and repair induced by diazoacetyl derivatives of amino acids with different mechanism of cytotoxicity. Correlations with mutagenicity and carcinogenicity

Eight synthetic N-diazoacetyl amino acids, prepared by inserting a diazoacetyl group onto the alpha-nitrogen of a natural amino acid, and two natural diazoazetyl amino acids, azaserine (9-diazoacetyl-L-serine) and DON (6-diazo-5-oxo-L-norleucine), have been studied by autoradiography for their capacity to induce DNA repair synthesis in mouse cells cultivated "in vitro". Dose-dependent unscheduled DNA synthesis was present in cells treated with the eight N-diazoacetyl derivatives, and was absent in cells exposed to approximately equitoxic concentrations of azaserine and DON. Azaserine and DON, unlike N-diazoacetyl derivatives, did not alkylate gamma-(4-nitrobenzyl) pyridine at an appreciable extent. When DNA damage (single stranded breaks or weak points in alkali) was measured by the sensitive technique of alkaline elution, DGA was found about 4 times as potent as azaserine and about 12 times as DON on a molar basis, but about 800 and 17,000 times as potent as azaserine and DON respectively by extrapolating to equitoxic concentrations. Carcinogenicity and mutagenicity seem to follow mainly the capability of inducing DNA damage.

DNA fragmentation in some organs of rats and mice treated with cycasin

Cycasin (methylazoxymethanol-beta-D-glucoside) is carcinogenic in several animal species. It produces a variety of malignant tumours, mainly in the liver of mice, and in the liver, kidney and large intestine in rats. It does not appear to be mutagenic in the Ames test, even in the presence of liver microsome fraction, and it is among those carcinogens (less than 10%) ranked as "false negatives" in this test. The ability of cycasin to damage in vivo liver, kidney, lung and colonic DNA of Wistar rats and C57BL/L mice was investigated by means of alkaline elution technique. Oral single-dose administration of cycasin, in the range of 50-400 mg/kg body weight, produced in the rat a clearly evident dose-dependent DNA fragmentation in the liver, and less marked damage to DNA from kidney and colon mucosa. In mice, the same treatment produced dose-dependent DNA damage only in the liver. DNA repair up to 18 h appeared to be incomplete both in mice and rats. Methylazoxymethanol acetate is considered to be an active form of cycasin. While in vivo methylazoxymethanol acetate caused DNA damage, in vitro it appeared inactive and required metabolic activation, possibly consisting in its hydrolysis by esterase activity, to be able to cause DNA fragmentation.