Increase In Micronucleus Frequency Research Articles

Neurotoxicological Profile Assessment of Lobeline after Acute Treatment in Mice

Lobeline is a natural alkaloid with high affinity for nicotinic acetylcholine receptors, and it is a promising candidate for addiction treatment in human beings. This work evaluated the toxicological profile of lobeline with different behavioural models and investigated its effect on DNA damage (comet assay and micronucleus test) in mice. Acute administration of lobeline (5 or 10 mg/kg; i.p.) did not impair the parameters measured in the habituation and inhibitory avoidance test, suggesting that it has no effect on memory acquisition in these tasks. Lobeline did not affect the number or the latency to the first head-dip in the hole board test, indicating that it was not anxiolytic/anxiogenic in this model. No genotoxic effects were observed in blood, liver and brain tissues collected 24 hr after the single injection of lobeline (both doses). There was no increase in micronucleus frequency in mice treated with lobeline, indicating the absence of toxicity in bone marrow of the animals. Therefore, the acute treatment with high doses of lobeline did not impair the behavioural parameters measured in this work. Additionally, the drug was not able to produce DNA damage.

Seed germination, root elongation, root-tip mitosis, and micronucleus induction of five crop plants exposed to chromium in fluvo-aquic soil.

The present study aimed to determine the toxic effects of chromium (Cr) on cabbage (Brassica oleracea), cucumber (Cucumis sativus), lettuce (Lactuca sativa), wheat (Triticum aestivum), and corn (Zea mays), and identify the sensitive plant species and appropriate bioassays for potential use in phytotoxicity assessment of Cr in soil. Results showed that seed germination might not be a sensitive assay for assessing Cr toxicity because at most of the Cr levels there were no toxic effects. Root elongation was more sensitive to Cr than seed germination. The lowest concentration of adverse effect (LOAEC) of lettuce was 20 mg Cr/kg(-1) soil, and that of the other 4 species was 50 mg Cr/kg(-1) soil. The mitotic index fluctuated with increasing Cr concentration, thus it was insufficient to assess toxicity of Cr in soil. However, micronucleus assay showed that 5 mg Cr/kg(-1) soil caused a significant increase in micronucleus frequency in cabbage, cucumber, and lettuce. For wheat and corn, however, the LOAEC was 20 and 50 mg/Cr/kg(-1) soil, respectively. Furthermore, the analysis of Cr accumulation showed that lettuce significantly accumulated Cr for all the tested concentrations. However, corn and wheat significantly accumulated Cr only with the highest tested dose. This may explain the higher inhibitory effects of Cr on root growth. It can be concluded that root elongation and micronucleus assay are good indicators to assess the phytotoxicity of Cr in soil. Lettuce is the most sensitive species for indicating the toxicity of Cr in soil.

Does bleeding induce micronuclei via erythropoietin in Han-Wistar rats?

The effects of both intravenous administration of recombinant human erythropoietin (rhEPO) and blood withdrawal, either individually or in combination, on the frequency of micronucleated immature erythrocytes (MIE) in the bone marrow were investigated in 10-week old male Han Wistar rats. Clear increases in MIE frequency and evidence of erythroid hyperplasia were seen in the bone marrow after 1350 IU kg−1 rhEPO but only marginal increases in MIE were seen at the lower dose of 135 IU kg−1. At the lower dose, blood levels of rhEPO were found to be approximately 120 pg mL−1 within one hour of dosing. Withdrawal of 5 blood samples of 0.45 mL on each occasion during 24 hours, the maximum allowed by the Home Office licence, did not increase MIE frequency but did result in levels of endogenous EPO of 15–19 pg mL−1 24 to 72 hours after the start of treatment, with some evidence of increased erythropoiesis. Although the increased plasma amounts of EPO, resulting from blood withdrawal, were lower than the blood levels achieved by the administration of exogenous rhEPO that were required to give increases in micronucleus frequency, the possibility that blood withdrawal might influence the MIE response to genotoxins cannot be totally excluded without further investigation.

Protective effects of curcumin against genotoxicity induced by 131-iodine in human cultured lymphocyte cells.

Background:131-radioiodine has been widely used as an effective radionuclide for treatment of patients with thyroid diseases. The purpose of the present study is to investigate the radioprotective effects of curcumin as a natural product that protects against the genotoxic effects of 131I in human cultured lymphocytes.Materials and Methods:Whole blood samples from human volunteers were incubated with curcumin at doses of 5, 10, and 50 μg/mL. After 1-hour incubation, the lymphocytes were incubated with 131I (100 μCi/1.5 ml) for 2 hours. The lymphocyte cultures were then mitogenically stimulated to allow for evaluation of the number of micronuclei in cytokinesis-blocked binucleated cells.Results:Incubation of lymphocytes with 131I at dose 100 μCi/1.5 mL induced genotoxicity shown by increase in micronuclei frequency in human lymphocytes. Curcumin at 5, 10, and 50 μg/mL doses significantly reduced the micronuclei frequency. Maximal protective effects and greatest decrease in micronuclei frequency were observed when whole blood was incubated with 50 μg/mL dose of curcumin with 52%.Conclusion:This study has important implications for patients undergoing 131I therapy. Our results indicate a protective role for curcumin against the genetic damage and side effects induced by 131I administration.

Elevated micronucleus frequencies in patients with pleural plaque secondary to environmental exposure to asbestos

We examined genotoxic damage and frequency of micronuclei in people living in the Bekilli and Suller districts of Denizli city who had been diagnosed with pleural plaques as a result of environmental exposure to asbestos. Peripheral blood samples were obtained from 30 volunteer patients 59-86 years old who did not smoke or consume alcohol and who were diagnosed with calcified pleural plaques. We also examined 30 healthy controls with similar features, who also lived in downtown Denizli. Micronucleus frequencies, nuclear division index, and mitotic index were determined. Micronucleus frequency, nuclear division index, and mitotic index were significantly higher in patients who had been exposed to asbestos than in the controls. We conclude that asbestos had a genotoxic effect, resulting in an increase in micronucleus frequency and other changes in patients diagnosed with pleural plaques secondary to asbestos exposure.

Xanthium strumarium L. extracts produce DNA damage mediated by cytotoxicity in in vitro assays but does not induce micronucleus in mice.

Xanthium strumarium L. is a member of the Asteraceae commonly used in Cuba, mainly as diuretic. Some toxic properties of this plant have also been reported and, to date, very little is known about its genotoxic properties. The present work aims was to evaluate the potential cytotoxic and genotoxic risk of whole extract from Xanthium strumarium L. whole extract of aerial parts. No positive response was observed in a battery of four Salmonella typhimurium strains, when exposed to concentrations up to 5 mg/plate, with and without mammalian metabolic activation (liver microsomal S9 fraction from Wistar rats). In CHO cells, high concentrations (25–100 μg/mL) revealed significant reduction in cell viability. Results from sister chromatid exchanges, chromosome aberrations, and comet assay showed that X. strumarium extract is genotoxic at the highest concentration used, when clear cytotoxic effects were also observed. On the contrary, no increase in micronuclei frequency in bone marrow cells was observed when the extract was orally administered to mice (100, 500, and 2000 mg/Kg doses). The data presented here constitute the most complete study on the genotoxic potential of X. strumarium L. and show that the extract can induce in vitro DNA damage at cytotoxic concentrations.

Micronuclei in bone marrow and liver in relation to hepatic metabolism and antioxidant response due to coexposure to chloroform, dichloromethane, and toluene in the rat model.

Genotoxicity in cells may occur in different ways, direct interaction, production of electrophilic metabolites, and secondary genotoxicity via oxidative stress. Chloroform, dichloromethane, and toluene are primarily metabolized in liver by CYP2E1, producing reactive electrophilic metabolites, and may also produce oxidative stress via the uncoupled CYP2E1 catalytic cycle. Additionally, GSTT1 also participates in dichloromethane activation. Despite the oxidative metabolism of these compounds and the production of oxidative adducts, their genotoxicity in the bone marrow micronucleus test is unclear. The objective of this work was to analyze whether the oxidative metabolism induced by the coexposure to these compounds would account for increased micronucleus frequency. We used an approach including the analysis of phase I, phase II, and antioxidant enzymes, oxidative stress biomarkers, and micronuclei in bone marrow (MNPCE) and hepatocytes (MNHEP). Rats were administered different doses of an artificial mixture of CLF/DCM/TOL, under two regimes. After one administration MNPCE frequency increased in correlation with induced GSTT1 activity and no oxidative stress occurred. Conversely, after three-day treatments oxidative stress was observed, without genotoxicity. The effects observed indicate that MNPCE by the coexposure to these VOCs could be increased via inducing the activity of metabolism enzymes.

Evaluation of N-acetyl-cysteine against tetrachlorobenzoquinone-induced genotoxicity and oxidative stress in HepG2 cells

Tetrachlorobenzoquinone (TCBQ) is an active metabolite of pentachlorophenol (PCP). Although the genotoxic effect of PCP has been comprehensively investigated, there is little known about TCBQ’s genotoxic effects. In the current study, TCBQ was tested for its genotoxicity using HepG2 cells as experimental model. To select the exposure concentration of interest, cell viability was measured and three concentrations were used for further investigation. In single cell gel electrophoresis (SCGE) assay, concentration-dependent increase in tail length, tail DNA percentage and tail moment were detected following TCBQ exposure. Micronucleus (MN) assay indicated TCBQ gradually increased MN frequency and decreased nuclear division index (NDI). Enzyme-linked immunosorbent assay (ELISA) and western blotting analyses both showed TCBQ caused histone H2AX phosphorylation (γ-H2AX). Furthermore, the elevation of 8-hydroxydeoxyguanosine (8-OHdG) and reactive oxygen species (ROS) level indicated TCBQ-induced genotoxicity is associated with oxidative stress. On the other hand, N-acetyl-cysteine (NAC) administration significantly protected cells from the genotoxic effect of TCBQ. Overall, our data suggested TCBQ exerted genotoxic effect possibly via an oxidative damage mechanism in HepG2 cells and this toxicity is prevented by pretreatment with NAC.

Lipid peroxidation, detoxification capacity, and genome damage in mice after transplacental exposure to pharmaceutical drugs

Data on genome damage, lipid peroxidation, and levels of glutathione peroxidase (GPX) in newborns after transplacental exposure to xenobiotics are rare and insufficient for risk assessment. The aim of the current study was to analyze, in an animal model, transplacental genotoxicity, lipid peroxidation, and detoxification disturbances caused by the following drugs commonly prescribed to pregnant women: paracetamol, fluconazole, 5-nitrofurantoin, and sodium valproate. Genome damage in dams and their newborn pups transplacentally exposed to these drugs was investigated using the in vivo micronucleus (MN) assay. The drugs were administered to dams intraperitoneally in three consecutive daily doses between days 12 and 14 of pregnancy. The results were correlated, with detoxification capacity of the newborn pups measured by the levels of GPX in blood and lipid peroxidation in liver measured by malondialdehyde (HPLC-MDA) levels. Sodium valproate and 5-nitrofurantoin significantly increased MN frequency in pregnant dams. A significant increase in the MN frequency of newborn pups was detected for all drugs tested. This paper also provides reference levels of MDA in newborn pups, according to which all drugs tested significantly lowered MDA levels of newborn pups, while blood GPX activity dropped significantly only after exposure to paracetamol. The GPX reduction reflected systemic oxidative stress, which is known to occur with paracetamol treatment. The reduction of MDA in the liver is suggested to be an unspecific metabolic reaction to the drugs that express cytotoxic, in particular hepatotoxic, effects associated with oxidative stress and lipid peroxidation.

Micronuclei in Cord Blood Lymphocytes and Associations with Biomarkers of Exposure to Carcinogens and Hormonally Active Factors, Gene Polymorphisms, and Gene Expression: The NewGeneris Cohort

Background: Leukemia incidence has increased in recent decades among European children, suggesting that early-life environmental exposures play an important role in disease development.Objectives: We investigated the hypothesis that childhood susceptibility may increase as a result of in utero exposure to carcinogens and hormonally acting factors. Using cord blood samples from the NewGeneris cohort, we examined associations between a range of biomarkers of carcinogen exposure and hormonally acting factors with micronuclei (MN) frequency as a proxy measure of cancer risk. Associations with gene expression and genotype were also explored.Methods: DNA and protein adducts, gene expression profiles, circulating hormonally acting factors, and GWAS (genome-wide association study) data were investigated in relation to genomic damage measured by MN frequency in lymphocytes from 623 newborns enrolled between 2006 and 2010 across Europe.Results: Malondialdehyde DNA adducts (M1dG) were associated with increased MN frequency in binucleated lymphocytes (MNBN), and exposure to androgenic, estrogenic, and dioxin-like compounds was associated with MN frequency in mononucleated lymphocytes (MNMONO), although no monotonic exposure–outcome relationship was observed. Lower frequencies of MNBN were associated with a 1-unit increase expression of PDCD11, LATS2, TRIM13, CD28, SMC1A, IL7R, and NIPBL genes. Gene expression was significantly higher in association with the highest versus lowest category of bulky and M1dG–DNA adducts for five and six genes, respectively. Gene expression levels were significantly lower for 11 genes in association with the highest versus lowest category of plasma AR CALUX® (chemically activated luciferase expression for androgens) (8 genes), ERα CALUX® (for estrogens) (2 genes), and DR CALUX® (for dioxins). Several SNPs (single-nucleotide polymorphisms) on chromosome 11 near FOLH1 significantly modified associations between androgen activity and MNBN frequency. Polymorphisms in EPHX1/2 and CYP2E1 were associated with MNBN.Conclusion: We measured in utero exposure to selected environmental carcinogens and circulating hormonally acting factors and detected associations with MN frequency in newborns circulating T lymphocytes. The results highlight mechanisms that may contribute to carcinogen-induced leukemia and require further research.Citation: Merlo DF, Agramunt S, Anna L, Besselink H, Botsivali M, Brady NJ, Ceppi M, Chatzi L, Chen B, Decordier I, Farmer PB, Fleming S, Fontana V, Försti A, Fthenou E, Gallo F, Georgiadis P, Gmuender H, Godschalk RW, Granum B, Hardie LJ, Hemminki K, Hochstenbach K, Knudsen LE, Kogevinas M, Kovács K, Kyrtopoulos SA, Løvik M, Nielsen JK, Nygaard UC, Pedersen M, Rydberg P, Schoket B, Segerbäck D, Singh R, Sunyer J, Törnqvist M, van Loveren H, van Schooten FJ, Vande Loock K, von Stedingk H, Wright J, Kleinjans JC, Kirsch-Volders M, van Delft JHM, NewGeneris Consortium. 2014. Micronuclei in cord blood lymphocytes and associations with biomarkers of exposure to carcinogens and hormonally active factors, gene polymorphisms, and gene expression: The NewGeneris Cohort. Environ Health Perspect 122:193–200; http://dx.doi.org/10.1289/ehp.1206324

Erythromycin‐induced genotoxicity and hepatotoxicity in mice pups treated during prenatal and postnatal period

The main aim of this study was to investigate the oxidative stress, genotoxicity and cytotoxicity of erythromycin (EMC) in pups of treated dams in gestation as well as the lactation period (LP). The two doses of EMC were compared using intraperitoneal (i.p.) route in two different periods, that is, in gestation period and in the LP. The rationale behind selection of i.p. route is because of the fact that EMC gets degrades in acidic pH of the stomach. The doses of EMC used were clinically equivalent dose (CED; EMC 14.2 mg/kg, i.p.) and a lower dose (EMC 10 mg/kg, i.p.) than CED. EMC toxicities in mice pups were evaluated using various parameters such as micronucleus (MN) test in peripheral blood and bone marrow, malondialdehyde (MDA) assay, glutathione (GSH reduced) assay and histopathological assessment in liver tissue. The CED of EMC led to a significant increase in MDA and decreased in GSH concentration in pups' liver tissue in both gestation and LPs and also to a significant increase in MN frequency in both peripheral blood and bone marrow cells of pups. There were no significant toxicities at a lower dose than CED. There were also some chronic findings with liver histopathological examination at CED. It is thus concluded that EMC accentuates the oxidative stress, cytotoxicity and DNA damage in pups of their postnatal life; hence, EMC should be avoided in the pregnancy and also in the LP.

Neurobehavioral alterations and histopathological changes in brain and spinal cord of rats intoxicated with acrylamide

The aim of this project was to study the clinical manifestations, neurobehavioral, hematobiochemical, oxidative stress, genotoxicity, and histopathological changes during acrylamide toxicity in rats. A total of 30 adult male Wistar rats were divided in 5 equal groups and received 0, 10, 15, and 20 mg/kg body weight acrylamide as oral gavage, while group 5 was micronucleus (MN) control. Functional observational battery (FOB) parameters were studied at the 28th day of post treatment. Toxicological manifestations were evident in acrylamide-treated rats from 14th day onward. FOB revealed a significant change in central nervous system, neuromuscular, and autonomic domains. The hematological changes include significant decrease in concentration of hemoglobin, total erythrocyte count, packed cell volume, and mean corpuscular volume. The biochemical parameters aspartate aminotransferases, alkaline phosphatase, and albumin showed significant increase, while the levels of serum globulin and glucose were found to decrease significantly. The MN assay revealed the significant increase in frequencies of micronuclei and number of polychromatic erythrocytes. The oxidative stress parameters revealed no significant difference as compared to control rats. Histopathological changes observed in brain include neuronal degeneration, edema, and congestion, while spinal cord revealed demyelination in low-dose group and bilateral necrosis with malacia, liquefaction of white matter, and loss of myelin from gray matter in high-dose groups. The result indicates pathological alterations in brain and spinal cord and is responsible for neurobehavioral changes in rats. The FOB changes and histopathological alterations in spinal cord are in dose dependent to acrylamide intoxication. Various toxicological effects observed in experiment direct us to focus on a deep study and evaluate the possible causes pertaining to toxicity of this chemical. It would furnish the scientists with better options that would help them to search for a median path regarding the use of this chemical and take preventive measures to save the living beings from the hidden disasters of this chemical.

Association between genetic polymorphisms in pre-miR-146a and pre-miR-196a2 and genetic damage levels among coke oven workers

To investigate the association of rs2910164 G > C polymorphism and rs11614913 T > C polymorphism in pre-miR-146a and pre-miR-196a2 with genetic damage levels in coke oven workers. A total of 575 nonsmoking workers who have worked for more than one year in a coke-oven plant at Wuhan, Hubei Province were enrolled in this study in September to October, 2010. The general characteristics as well as blood and urine samples were collected. The genetic damage levels were detected by cytokinesis-block micronucleus cytom assay and represented as micronucleus (MN) frequencies of binucleate cells in peripheral blood lymphocytes. The rs2910164 G > C polymorphisms in pre-miR-146a and rs11614913 T > C polymorphisms in pre-miR-196a2 were genotyped by using TaqMan assay. The plasma concentrations of benzo[a]pyrene-diolepoxide (BPDE)-albumin adducts were determined by using ELISA. All data were analyzed, the frequency ratio (FR) and 95%CI were calculated. Totally, 575 workers were taken into consideration. The rs2910164 C allele was associated with increased MN frequencies in the coke oven workers (P trend = 0.025), and the MN frequencies were higher in rs2910164 CC genotype carriers (4.38 ± 3.46) than in wild-type rs2910164 GG genotype carriers (4.02 ± 3.09) (FR = 1.18, 95%CI:1.04-1.34). The further stratified analyses by working years, gender, alcohol consumption, and the levels of BPDE-albumin adducts showed that the effects of rs2910164 C allele in increasing MN frequencies were robust in subjects who were males (FR = 1.11, 95%CI:1.02-1.20), nondrinkers (FR = 1.07, 95%CI:1.00-1.14), working years less than 20 (FR = 1.12, 95%CI:1.03-1.22), and workers with lower BPDE-albumin adducts levels (FR = 1.11, 95%CI:1.02-1.21) (P trend = 0.011, 0.044, 0.006 and 0.020, respectively). In addition, the MN frequencies were higher in workers with rs11614913 TC genotype (4.27 ± 2.91) than workers with rs11614913 TT genotype (3.90 ± 3.32) (FR = 1.12, 95%CI:1.02-1.23).Workers carried both rs2910164 GG and rs11614913 TT genotypes were set as a control, and the MN frequencies of workers with both rs2910164 CC and rs11614913 CC genotypes (5.32 ± 4.94) were 1.51 (1.21-1.89) times higher than the control (3.75 ± 3.01). The rs2910164 C allele in pre-miR-146a and rs11614913 C allele in pre-miR-196a2 were associated with increased genetic damage levels in coke oven workers.

In VivoGenotoxicity Assessment of Sertraline by Using Alkaline Comet Assay and the Cytokinesis‐Block Micronucleus Assay

Sertraline, a leading antidepressant in the selective serotonin reuptake inhibitor (SSRI) group of medicine, is the most frequently prescribed drug. In this study, the alkaline comet assay and the cytokinesis-block micronucleus (CBMN) assay were used to investigate genotoxicity potential of sertraline in the peripheral blood lymphocytes (PBLs) of acute and chronic sertraline-treated Wistar albino rats. Male Wistar albino rats (n=48) were administered low, medium and high doses of sertraline (10, 40, 80mg/kg) for acute and chronic treatment by employing the gavage method to investigate genotoxicity of the administered drug. The data (tail length, tail intensity and tail moment) were analysed and indicated that there was no statistically significant difference between sertraline-treated groups and the negative control group with respect to DNA damage (p>0.05). However, it was observed that acute sertraline administration had caused much more DNA damage in comparison with chronic treatment (p<0.05). According to the data obtained from the CBMN test, an increase in the micronucleus (MN) frequency was detected at chronic and high-dose acute sertraline treatment. Based on the outcome of comet assay, detection of statistically insignificant DNA damage may be due to the fact that sertraline did not cause damage on DNA. Also, increase in frequency of MN in chronic sertraline treatment suggests that chronic sertraline administration might influence some mechanisms of cell division. Therefore, dose adjustment in depressed patients seems significant as it may help prevent further prognosis of the diseases.

The chemoprotective effects of l-carnitine against genotoxicity induced by diazinon in rat blood lymphocyte

The purpose of this study was to assess the preventive effects of L-carnitine (LC) against DNA damage induced by diazinon (DZN) in rat blood lymphocytes. Animals were concurrently administered intraperitoneally with DZN in proper solvent (20 mg/kg body weight (b.w.)) and LC at three different doses (50, 100, and 150 mg/kg b.w.) for 30 consecutive days. The positive control group received DZN at the same dose without LC. Twenty-four hour after last injection, 0.5 ml blood of each rat was received and cultured in culture medium for 44 h. The lymphocyte cultures were mitogenically stimulated with cytochalasin B for the evaluation of the number of micronuclei (MNs) in cytokinesis-blocked binucleated cells. Incubation of lymphocytes with DZN induced additional genotoxicity and was shown by increase in MNs frequency in rat lymphocytes. LC at all doses had a protective effect and significantly reduced the MNs frequency in cultured lymphocytes (p < 0.0001-p < 0.05). The maximum effect was observed at 150 mg/kg that reduced the frequency of MN from 12.78 ± 0.24% for DZN group to 5.61 ± 0.17%. Our study revealed that LC has a potent antigenotoxic effect against DZN-induced toxicity in rats, which may be due to the scavenging of free radicals and increased antioxidant status. Since LC is a natural compound and is being safe, it is recommended as a daily supplement for body defense against side effects induced by chemical hazardous agents.

Potential chemoprotective effects of selenium on diazinon-induced DNA damage in rat peripheral blood lymphocyte

The purpose of this study was to investigate the protective effects of selenium (Se) against genotoxicity induced by diazinon (DZN) in rat peripheral blood lymphocytes by micronucleus (MN) test. Animals were concurrently administered intraperitoneally with DZN in proper solvent (20mg/kg body weight (b.w.)) and Se at three different doses (0.5, 1, and 2mg/kg b.w.) for 30 consecutive days. The positive control group received DZN at the same dose without Se. After 24h of last injection, 0.5ml blood of each rat was received and cultured in culture medium for 44h. The lymphocyte cultures were mitogenically stimulated with cytochalasin B to allow the evaluation of number of MNs in cytokinesis-blocked binucleated cells. Incubation of lymphocytes with DZN induced additional genotoxicity and is shown by increase in MNs frequency in human lymphocytes. Se at low dose of 0.5mg/kg had a maximum effect and significantly reduced the MNs frequency in cultured lymphocytes (p<0.0001) that reduced the frequency of MN from 12.78±0.24% for DZN group to 4.40±0.36. The present study revealed that Se particularly at low doses has a potent antigenotoxic effect against DZN -induced toxicity in rats, which may be due to the scavenging of free radicals and increased antioxidant status.

Genotoxicity Profile of Azidothymidine In Vitro

Azidothymidine (Zidovudine, AZT) is part of the standard care of treatment for acquired immunodeficiency syndrome since many years. A great number of studies on the genotoxic potential of AZT have been published, but no comprehensive hypothesis yet explains all observations. We investigated a multitude of genotoxic endpoints, both in vitro and in vivo, with the goal to complete the picture. The mutagenic potential of AZT in bacteria was found to be restricted to strains with an "ochre" target sequence and could be abrogated both by thymidine supplementation and rat liver S9 mix. Single-strand breaks in mammalian cells were detected in the comet assay after short-term treatment (3h) with AZT, which did not induce micronuclei. The latter were mainly seen after prolonged exposure (24 and 48h) and are probably not directly related to AZT incorporation into DNA. Our data demonstrate that short-term exposure to low AZT concentrations does not induce biologically relevant micronucleation. Only treatment with high concentrations of AZT for prolonged time periods manifests in substantial micronucleus induction. Furthermore, we found that high concentrations of thymidine have no effect in the comet assay but increase micronucleus frequency in a manner very similar to AZT. These results lead us to the following hypothesis: AZT is triphosphorylated and then incorporated into DNA strands, leading to mutations and cytotoxicity. Cellular attempts to repair these DNA lesions as well as stalled replication forks due to chain termination are detectable with the comet assay. Increased micronucleus frequency is likely related to nucleotide pool imbalance.

Assessment of genotoxic potential of the insecticide Dichlorvos using cytogenetic assay

The possible genotoxic activity of Dichlorvos (2,2-Dichlorovinyl-O,O-dimethyl phosphate/DDVP, CAS No. 62-73-7), an organophosphorus insecticide was investigated employing three cytogenetic end points, i.e. micronucleus (MN) assay, mitotic indices (MI) and chromosome abberation (CA) analysis in vivo. The assays were carried out in hematopoietic bone marrow cells of Mus musculus at concentrations of 10, 20 and 30% of LD50 for intraperitoneal (ip) administration, corresponding to 0.06, 0.08 and 0.13 mg/kg Bwt, respectively. The normal control group received single ip dose of distilled water (2 ml/100 g Bwt), while animals of the positive group were injected with cyclophosphamide, a model mutagen (40 mg/kg Bwt) under identical conditions. The animals were sacrificed 24, 48 and 72 hrs post treatment. Under the present experimental conditions, there was no evidence of significant increase of MN frequencies at any dose or sampling time in polychromatic (PCE) and normochromatic (NCE) erythrocytes. The PCE/NCE ratio was not notably affected; however, a slight depression in prolonged exposure (48, 72 hr) intervals and a slight increase at the 24 hr interval were observed. Cells with various structural chromosome aberrations were noted but no significant (p<0.05; Man-Whitney U-test) differences in the frequencies of CA or mitotic indices (p<0.05; χ2 test) were observed between Dichlorvos treated groups and the normal control group at doses or time intervals used. The results of the present investigation reflects a negative in vivo genotoxic potential of Dichlorvos at sublethal doses in bone marrow cells. Further studies are underway to confirm the presence or absence of genotoxic activity since compounds negative in genotoxic evaluation are susceptible of being carcinogens triggering cancer by genotoxic or non–genotoxic mechanisms.

Drinking Water Disinfection Byproduct Iodoacetic Acid Induces Tumorigenic Transformation of NIH3T3 Cells

Iodoacetic acid (IAA) and iodoform (IF) are unregulated iodinated disinfection byproducts (DBPs) found in drinking water. Their presence in the drinking water of China has not been documented. Recently, the carcinogenic potential of IAA and IF has been a concern because of their mutagenicity in bacteria and genotoxicity in mammalian cells. Therefore, we measured their concentrations in Shanghai drinking water and assessed their cytotoxicity, genotoxicity, and ability to transform NIH3T3 cells to tumorigenic lines. The concentrations of IAA and IF in Shanghai drinking water varied between summer and winter with maximum winter levels of 2.18 μg/L IAA and 0.86 μg/L IF. IAA with a lethal concentration 50 (LC50) of 2.77 μM exhibited more potent cytotoxicity in NIH3T3 cells than IF (LC50 = 83.37 μM). IAA, but not IF, induced a concentration-dependent DNA damage measured by γ-H2AX staining and increased tail moment in single-cell gel electrophoresis. Neither IAA nor IF increased micronucleus frequency. Prolonged exposure of NIH3T3 cells to IAA increased the frequencies of transformed cells with anchorage-independent growth and agglutination with concanavalin A. IAA-transformed cells formed aggressive fibrosarcomas after inoculation into Balb/c nude mice. This study demonstrated that IAA has a biological activity that is consistent with a carcinogen and human exposure should be of concern.

Effects of long term low dose acrylamide exposure on rat bone marrow polychromatic erythrocytes

I investigated whether long term low dose exposure to acrylamide increased micronucleus frequency in rat bone marrow polychromatic erythrocytes (PCEs). Twenty-five male and 25 female Wistar rats were used. Animals of each sex were segregated into two treatment groups and one control group. Each treatment group consisted of ten animals and each control group consisted of five animals. Acrylamide, 2 or 5 mg/kg/day, was administered to the treatment groups in their drinking water for 90 days. Twenty-four hours after the last treatment, bone marrow samples were obtained and analyzed for the frequency of micronucleated polychromatic erythrocytes (MNPCEs). The cytotoxic effect of acrylamide on bone marrow also was tested by assessing the polychromatic erythrocyte/normochromatic erythrocyte (PCE/NCE) ratio. Both doses of acrylamide significantly increased the frequency of MNPCEs in both male and female rats. Acrylamide also decreased the PCE/NCE ratio in both sexes compared to the control group. My study showed that chronic low dose exposure to acrylamide increased the formation of micronuclei in PCEs of male and female rat bone marrow.