Cytotoxic effects of postharvest fungicides, ortho-phenylphenol, thiabendazole and imazalil, on isolated rat hepatocytes

Monitoring the behavior of imazalil and its metabolite in grapes, apples, and the processing of fruit wine at enantiomeric level

BACKGROUND

Imazalil is widely used in agriculture, which may pose a threat to food safety. This study aimed to investigate the fate of imazalil and its main metabolite, R14821 (imazalil-M), in field grapes and apples, and in the processing of fruit wine at the enantiomeric level.

RESULTS

Analysis method was established to determine imazalil and imazalil-M enantiomers in grape, apple, fruit wine and pomace. The method showed acceptable recoveries of 71.6-99.9% and precision with relative standard deviation of 0.3-11.7%. Processing factors (PFs) were 0.15-0.40 (for imazalil enantiomers) and <0.13-0.83 (for imazalil-M enantiomers) during the wine-making process. The PFs after individual steps including washing, peeling, fermentation, and clarification were all less than 1. No enantioselective dissipation of imazalil was found in grapes under field conditions with half-lives of 23.82-24.49 days. R-(-)-imazalil degraded slightly faster than S-(+)-imazalil in apples under field conditions with half-lives of 9.82-10.09 days. S-(+)-imazalil-M preferentially degraded in field grapes and apple. No significant enantioselectivity of imazalil and imazalil-M was observed during the wine-making process. The enantiomeric fraction (EF) values of imazalil were 0.484-0.511 and 0.509-0.522 in grape wine and cider, respectively. The EFs were 0.484-0.501(in grape wine) and 0.484-0.504 (in cider) for imazalil-M.

CONCLUSION

The results showed that the wine-making process could reduce imazalil and imazalil-M residues in grapes and apples. The finding of non-enantioselectivity of imazalil during the processing of fruit wine was useful for accurate risk assessment for imazalil in raw and processing fruits. © 2021 Society of Chemical Industry.

Prospective association between dietary pesticide exposure profiles and postmenopausal breast-cancer risk in the NutriNet-Santé cohort

BACKGROUND

Some pesticides, used in large quantities in current agricultural practices all over Europe, are suspected of adverse effects on human reproductive health (breast and prostate cancers), through mechanisms of endocrine disruption and possible carcinogenic properties, as observed in agricultural settings. However, evidence on dietary pesticide exposure and breast cancer (BC) is lacking for the general population. We aimed to assess the associations between dietary exposure to pesticides and BC risk among postmenopausal women of the NutriNet-Santé cohort.

METHODS

In 2014, participants completed a self-administered semi-quantitative food-frequency questionnaire distinguishing conventional and organic foods. Exposures to 25 active substances used in EU plant-protection products were estimated using a pesticide-residue database accounting for farming practices, from Chemisches und Veterinäruntersuchungsamt Stuttgart, Germany. Non-negative matrix factorization (NMF), adapted for data with excess zeros, was used to establish exposure profiles. The four extracted NMF components' quintiles were introduced into Cox models estimating hazard ratio (HR) and 95% confidence interval (95% CI), adjusted for known confounding factors.

RESULTS

A total of 13 149 postmenopausal women were included in the analysis (169 BC cases, median follow-up = 4.83 years). Negative associations between Component 3, reflecting low exposure to synthetic pesticides, and postmenopausal BC risk were found [HRQ5 = 0.57; 95% CI (0.34; 0.93), p-trend = 0.006]. Positive association between Component 1 score (highly correlated to chlorpyrifos, imazalil, malathion, thiabendazole) and postmenopausal BC risk was found specifically among overweight and obese women [HRQ5 = 4.13; 95% CI (1.50; 11.44), p-trend = 0.006]. No associations were detected for the other components.

CONCLUSION

These associations suggest a potential role of dietary pesticide exposure on BC risk. Further research is needed to investigate the mechanisms and confirm these results in other populations.

Cytogenetic and genotoxic assessment in Allium cepa exposed to imazalil fungicide

Imazalil (IMZ), a fungicide containing imidazole group, is extensively used for the prevention and treatment of fungal diseases in plants. Current study was performed to examine cyto-genotoxic potential of IMZ on Allium cepa roots by following Allium ana-telophase and single cell gel electrophoresis (comet) assays. The concentration which reduced the growth of the root tips of IMZ by 50% compared to the negative control group (EC₅₀) was found to be 1 μg/mL by Allium root growth inhibition test. 0.5, 1, and 2 μg/mL concentrations of IMZ were exposed to Allium roots for intervals of 24, 48, 72, and 96 h. 10 μg/mL of methyl methane sulfonate (MMS) and distilled water were used as control groups, both positive and negative. Statistical analysis was performed by using one-way ANOVA with Duncan's multiple comparison tests at p ≤ 0.05 and Pearson correlation test at p = 0.01. IMZ showed cytotoxic effect by statistically decreasing root growth and mitotic index (MI) and also genotoxic effect by statistically increasing chromosomal aberrations (CAs) and DNA damage compared to the negative control group. With these cyto-genotoxic effects, it should be used carefully and further cyto-genotoxic mechanisms should be investigated along with other toxicity tests.

Effects of the fungicide ortho-phenylphenol (OPP) on the early development of sea urchin eggs

In this study, we assessed the impact of imidazole fungicide ortho-phenylphenol (OPP) on the early development of a marine invertebrate, the sea urchin, a marine bioindicator. Fungicides are widely used and have been reported to accumulate not only in farm soil but also in freshwater and seawater sediments. Therefore, it is essential to clarify the effects of OPP on marine environments. Toxicity was estimated as the inhibition ratio of the 120 min-embryo and/or the 24 h-embryo development. The addition of OPP to embryos of the two sea urchin species, Scaphechinus mirabilis (S. mirabilis) and Strongylocentrotus nudus (S. nudus), at 0.1 mM or higher, resulted in acute toxicity (cell death). The IC₅₀ value of the 120 min-embryos or the 24 h-embryos for S. mirabilis and S. nudus with OPP was around 0.06 mM, indicating that fertilized eggs and embryos of the sea urchin are more sensitive to OPP than higher vertebrates. In addition, in the presence of OPP (0.005-0.05 mM), the proportion (%) of the gastrula keeping the fertilization membrane increased, suggesting that OPP (0.005-0.05 mM) inhibited the hatching process, possibly by affecting the hatching enzyme activity.

Case examples of an evaluation of the human relevance of the pyrethroids/pyrethrins-induced liver tumours in rodents based on the mode of action

Rodent carcinogenicity studies are useful for screening for human carcinogens but they are not perfect. Some modes of action (MOAs) lead to cancers in both experimental rodents and humans, but others that lead to cancers in rodents do not do so in humans. Therefore, analysing the MOAs by which chemicals produce tumours in rodents and determining the relevance of such tumour data for human risk are critical. Recently, experimental data were obtained as case examples of an evaluation of the human relevance of pyrethroid (metofluthrin and momfluorothrin)- and pyrethrins-induced liver tumours in rats based on MOA. The MOA analysis, based on the International Programme on Chemical Safety (IPCS) framework, concluded that experimental data strongly support that the postulated MOA for metofluthrin-, momfluorothrin- and pyrethrins-produced rat hepatocellular tumours is mediated by constitutive androstane receptor (CAR) activation. Since metofluthrin and momfluorothrin are close structural analogues, reproducible outcomes for both chemicals provide confidence in the MOA findings. Furthermore, cultured human hepatocyte studies and humanized chimeric mouse liver studies demonstrated species difference between human hepatocytes (refractory to the mitogenic effects of these compounds) and rat hepatocytes (sensitive to their mitogenic effects). These data strongly support the hypothesis that the CAR-mediated MOA for liver tumorigenesis is of low carcinogenic risk for humans. In this research, in addition to cultured human hepatocyte studies, the usefulness of the humanized chimeric liver mouse models was clearly demonstrated. These data substantially influenced decisions in regulatory toxicology. In this review I comprehensively discuss the human relevance of the CAR-mediated MOA for rodent liver tumorigenesis based on published information, including our recent molecular research on CAR-mediated MOA.

The fungicide thiabendazole causes apoptosis in rat hepatocytes

Many pharmaceutical drugs cause hepatotoxicity in humans leading to severe liver diseases, representing a serious public health issue. This study investigates the ability of the anthelmintic and antifungal drug thiabendazole to cause cell death by apoptosis and metabolic changes in primary cultures of rat hepatocytes. Thiabendazole (200-500 μM) induced apoptosis in hepatocytes after 1 to 24h, causing loss of mitochondrial membrane potential, cytochrome c release from mitochondria, Fas-associated death domain (FADD) translocation from the cytosol to membranes, and activation of caspases-3, -8 and -9. Thus, thiabendazole activated both the mitochondrial and death receptor pathways of apoptosis. Under these conditions, cell death by necrosis was not detected following exposure to thiabendazole (100-500 μM) for 24-48 h, measured by lactate dehydrogenase release and propidium iodide uptake. Furthermore, thiabendazole increased activities of cytochrome P450 (CYP) isoenzymes CYP1A and CYP2B after 24 and 48 h, determined by 7-ethoxyresorufin-O-deethylase (EROD) and 7-pentoxyresorufin-O-dealkylase (PROD) activities, respectively. An important finding is that thiabendazole can eliminate hepatocytes by apoptosis, which could be a sensitive marker for hepatic damage and cell death. This study improves understanding of the mode of cell death induced by thiabendazole, which is important given that humans and animals are exposed to this compound as a pharmaceutical agent and in an environmental context.

LC-MS-MS Analysis of Urinary Biomarkers of Imazalil Following Experimental Exposures

Imazalil (IMZ) is a fungicide used in the cultivation of vegetables, such as cucumbers, in green houses or post-harvest on fruit to avoid spoilage due to fungal growth. Agricultural workers can be occupationally exposed to IMZ and the general public indirectly by the diet. The purpose of this study was to develop and validate an LC-MS-MS method for the analysis of IMZ in human urine. The method used electrospray ionization and selected reaction monitoring in the positive mode. Excellent linearity was observed in the range 0.5-100 ng/mL. The limit of detection of the method was 0.2 ng/mL, and the limit of quantitation 0.8 ng/mL. The method showed good within-run, between-run and between-batch precision, with a coefficient of variation <15%. The method was applied to analyze urine samples obtained from two human volunteers following experimental oral and dermal exposure. The excretion of IMZ seemed to follow a two-compartment model and first-order kinetics. In the oral exposure, the elimination half-life of IMZ in the rapid excretion phase was 2.6 and 1.9 h for the female and the male volunteer, respectively. In the slower excretion phase, it was 7.6 and 13 h, respectively. In the dermal exposure, the excretion seemed to follow a single-compartment model and first-order kinetics. The elimination half-life was 10 and 6.6 h for the female and the male volunteer, respectively. Although the study is limited to two volunteers, some information on basic toxicokinetics and metabolism of IMZ in humans is presented.

The potential for chemical mixtures from the environment to enable the cancer hallmark of sustained proliferative signalling

The aim of this work is to review current knowledge relating the established cancer hallmark, sustained cell proliferation to the existence of chemicals present as low dose mixtures in the environment. Normal cell proliferation is under tight control, i.e. cells respond to a signal to proliferate, and although most cells continue to proliferate into adult life, the multiplication ceases once the stimulatory signal disappears or if the cells are exposed to growth inhibitory signals. Under such circumstances, normal cells remain quiescent until they are stimulated to resume further proliferation. In contrast, tumour cells are unable to halt proliferation, either when subjected to growth inhibitory signals or in the absence of growth stimulatory signals. Environmental chemicals with carcinogenic potential may cause sustained cell proliferation by interfering with some cell proliferation control mechanisms committing cells to an indefinite proliferative span.

High-throughput screening of FDA-approved drugs using oxygen biosensor plates reveals secondary mitofunctional effects

Repurposing of FDA-approved drugs with effects on mitochondrial function might shorten the critical path to mitochondrial disease drug development. We improved a biosensor-based assay of mitochondrial O2 consumption, and identified mitofunctional defects in cell models of LHON and FXTAS. Using this platform, we screened a 1600-compound library of clinically used drugs. The assay identified drugs known to affect mitochondrial function, such as metformin and decoquinate. We also identified several drugs not previously known to affect mitochondrial respiration including acarbose, metaraminol, gallamine triethiodide, and acamprosate. These previously unknown 'mitoactives' represent novel links to targets for mitochondrial regulation and potentially therapy, for mitochondrial disease.

Assessment of cytogenetic damage in bovine peripheral lymphocytes exposed to in vitro tebuconazole-based fungicide

The tebuconazole-based fungicide was tested in vitro for its potential genotoxic and cytotoxic effects on cultured bovine peripheral lymphocytes. Following 24h and 48 h of incubation, several cytogenetic endpoints were investigated such as: Chromosome Aberrations (CAs); Sister Chromatid Exchanges (SCEs); Micronuclei (MN); Mitotic Index (MI); Proliferation Index (PI); and Cytokinesis Block Proliferation Index (CBPI). The cultured lymphocytes were exposed to the fungicide formulation at concentrations of 3, 6, 15, 30 and 60 μg mL(-1). Statistical significant increases were seen in the CA assays at concentrations ranging from 6 to 30 μg mL(-1) for 24h. The higher doses caused a decrease or total inhibition of chromosome damages in comparison to the last active dose, or the control values. The Fluorescence in situ Hybridisation (FISH) technique was also used for the study of stable/unstable structural chromosomal aberrations and numerical aberrations of aneuploidy/polyploidy at the concentrations of 6 and 15 μg mL(-1). Under conditions of our study, no reciprocal translocations were detected. The more frequent types of aberrations were trisomies and monosomies; both have been identified in association with either bovine chromosome 5 or 7. No statistical significant value was seen in the induced MN; but, the clear, evident reduction of the CBPI was observed. Significant elevations of SCE were observed after the applications of the fungicide formulation at doses from 15 to 60 μg mL(-1) in each donor for 24h. The highest concentrations also caused a statistical significant decrease in the PI. The treatment for 48 h failed to exhibit any genotoxic activity of the fungicide.

An antidote for imazalil-induced genotoxicity in vitro: the lichen, Dermatocarpon intestiniforme (Körber) Hasse

Imazalil (IMA), a commonly used fungicide in both agricultural and clinical domains, is suspected to produce serious toxic effects in vertebrates. In recent years, a number of studies have suggested that lichens might be easily accessible sources of natural drugs that could be used as a possible food supplement. Extensive research is being performed to explore the importance of lichen species, which are known to contain a variety of pharmacological active compounds. In this context, the antigenotoxic effect of aqueous Dermatocarpon intestiniforme (Körber) Hasse. extract (DIE) was studied against the genotoxic damage induced by IMA on cultured human lymphocytes (n = 6) using chromosomal aberration (CA) and micronucleus (MN) as cytogenetic endpoints. Human peripheral lymphocytes were treated in vitro with varying concentrations of DIE (0, 25, 50 and 100 μg/ml), tested in combination with IMA (336 μg/ml). DIE alone were not genotoxic and when combined with IMA treatment, it reduced the frequency of CAs and the rate of MNs. A clear dose-dependent decrease in the genotoxic damage of IMA was observed, suggesting a genoprotective role of DIE. The results of the present study suggest that this plant extract per se does not have a genotoxic potential, but can alleviate the genotoxicity of IMA on cultured human lymphocytes. In conclusion our findings may have an important application for the protection of cultured human lymphocyte from the genetic damage and side effects induced by medical and agricultural chemicals hazardous for people.

Role of aqueous Bryoria capillaris (Ach.) extract as a genoprotective agent on imazalil-induced genotoxicity in vitro

In recent years, a number of studies have suggested that lichens might be the easily accessible sources of natural drugs that could be used as a possible food supplement. Extensive research is being carried out to explore the importance of lichen species, which are known to contain a variety of pharmacological active compounds. On the other hand, imazalil (IMA), a commonly used fungicide in both agricultural and clinical domains, is suspected to produce very serious toxic effects in vertebrates. In this context, the antigenotoxic effect of aqueous Bryoria capillaris (Ach.) extract (BCE) was studied against the genotoxic damage induced by IMA on cultured human lymphocytes using chromosomal aberrations (CA) and micronucleus (MN) as cytogenetic parameters. Human peripheral lymphocytes were treated in vitro with varying concentrations of BCE (5, 10, 25, 50 and 100 µg/mL), tested in combination with IMA (336 µg/mL). BCE alone was not genotoxic, and when combined with IMA treatment, it reduced the frequency of CAs and the rates of MN. A clear dose-dependent decrease in the genotoxic damage of IMA was observed, suggesting a genoprotective role of BCE. The results of the present study suggest that this plant extract per se do not have genotoxic potential, but can modulate the genotoxicity of IMA on peripheral human lymphocytes in vitro. In conclusion, our findings may have an important application in the protection of cultured human lymphocyte from the genetic damage and side effects induced by agricultural and medical chemicals that are hazardous to people.

Anti-genotoxic role of eicosapentaenoic acid against imazalil-induced DNA damage in vitro

Eicosapentaenoic acid (EPA) is a polyunsaturated n-3 fatty acid and is essential to the health of mammals. Recent data show that EPA can act as anti-mutagenic agent. On the other hand, pesticides comprise a new and important class of environmental pollutants nowadays. Imazalil (IMA), a commonly used fungicide in both agricultural and clinical domains is suspected to produce very serious toxic effects in vertebrates. The present study investigated the anti-genotoxic effect of EPA against the genotoxic damage induced by IMA on cultured human lymphocytes using chromosomal aberration (CA) and micronucleus (MN) tests as cytogenetic endpoints. Peripheral blood cells were treated in vitro with varying concentrations of EPA (2.5, 5, 10, 20 and 40 μg/ml), tested in combination with IMA (336 μg/ml). Our results revealed that the rates of CAs and MNs in lymphocytes were significantly (p < 0.05) increased by IMA as compared to the controls. The results also showed that EPA alone was not genotoxic. Moreover, when combined with IMA treatment, EPA reduced the frequencies of CAs and MNs. A clear dose-dependent decrease in the genotoxic damage of IMA was observed, suggesting a genoprotective role of EPA. In conclusion, our data may have an important application for the protection of cultured human lymphocyte from the genetic damage and repercussions induced by agricultural and industrial chemicals hazardous in people.

The protective role of ascorbic acid on imazalil-induced genetic damage assessed by the cytogenetic tests

Ascorbic acid (AA), known as vitamin C, has important antioxidant and metabolic functions, making its incorporation into the human diet essential. On the other hand, imazalil (IMA), a commonly used fungicide in both agricultural and clinical domains is suspected to produce very serious toxic effects in vertebrates. In this study, the antigenotoxic effects of AA were studied against the genotoxic damage induced by IMA on cultured human lymphocytes using chromosomal aberration (CA) and sister chromatid exchange (SCE) as genetic end points. Human peripheral lymphocytes were treated in vitro with varying concentrations of AA (25, 50, 100, 200, and 400 μg/ml), tested in combination with IMA (336 mg/L). AA alone was not genotoxic and when combined with IMA treatment, reduced the frequencies of CAs and SCEs. A clear dose-dependent decrease in the genotoxic damage of IMA was observed, suggesting a genoprotective role of AA. In conclusion, the preventive role of AA in alleviating IMA-induced DNA damage was indicated for the first time in the present study.

Role of Peltigera rufescens (Weis) Humb. (a lichen) on imazalil-induced genotoxicity: analysis of micronucleus and chromosome aberrations in vitro

Imazalil (IMA), a commonly used fungicide in both agricultural and clinical domains, is suspected to produce very serious toxic effects on vertebrates. On the other hand, in recent years, a number of studies have suggested that lichens might be easily accessible sources of natural drugs that could be used as a possible food supplement. Extensive research is being carried out to explore the importance of lichen species, which are known to contain a variety of pharmacological active compounds. In this context, the anti-genotoxic effects of aqueous Peltigera rufescens (Weis) Humb. extracts (PREs) were studied against the genotoxic damage induced by IMA on cultured human lymphocytes using chromosomal aberrations (CAs) and micronucleus (MN) as cytogenetic parameters. Human peripheral lymphocytes were treated in vitro with varying concentrations of PREs (0, 5, 10, 25, 50 and 100 mg/L), tested in combination with IMA (336 mg/L). PREs alone were not genotoxic and when combined with IMA treatment, reduced the frequency of CAs and the rates of MNs. A clear dose-dependent decrease in the genotoxic damage of IMA was observed, suggesting a genoprotective role of P. rufescens extract. The results of the present study indicate that this plant extract per se do not have genotoxic potential but can minimize the genotoxicity of IMA on human lymphocytes in vitro. In conclusion our findings may have an important application for the protection of human lymphocyte from the genetic damage and side effects induced by agricultural and medical chemicals hazardous in people.

Carbendazim combined with imazalil or cypermethrin potentiate DNA damage in hepatocytes of mice

Traces of pesticides imazalil, cypermethrin and carbendazim are detected in plants used for human consumption. To explore whether their application in oral combinations will induce DNA breaks in hepatocytes, a subchronic in vivo experiment was performed in Swiss mice. Doses of 10 mg kg(-1) of imazalil (im) and cypermethrin (cy), and 20 mg kg(-1) of carbendazim (car) and their combinations (im, 10 mg kg(-1) + cy, 10 mg kg(-1); im, 10 mg kg(-1) + car, 20 mg kg(-1); car, 20 mg kg(-1) + cy, 10 mg kg(-1)) were applied daily for 28 days. Afterward, DNA damage in hepatocytes was evaluated by comet assay. Individually, imazalil and cypermethrin damaged DNA at alkali-labile sites, while the tail moment (TM) of carbendazim alone was similar to control but with higher tail length. In combination with carbendazim clastogen, properties of imazalils and cypermethrins were potentiated compared to all other treatments and control. There were pronounced sex differences in pattern of fragmentation between treated groups. Higher long tail nuclei (LTN) in females indicate that certain cells in females were especially prone to total nucleus disintegration. Due to synergistic effects, low environmentally present concentrations of imazalil and cypermethrin in food, and especially their mixtures with carbendazim have genotoxic potential that could be particularly dangerous over prolonged exposure in mammalian organism.

Potential of an in vitro toolbox combined with exposure data as a first step for the risk assessment of dietary chemical contaminants

In vitro risk assessment of dietary contaminants has become a priority in human food safety. This paper proposes an in vitro approach associating different complementary tools in an original toolbox and aims to improve the assessment of the toxicological impact of dietary contaminants at realistic human exposure levels, with a special focus on the intestinal compartment. The system is based on the use of four complementary cellular tools, namely stress gene induction in transgenic strains of Escherichia coli, modulation of the activity of key biotransformation enzymes (cytochrome P-450 (CYP) 1A1 and 3A4) in a human intestinal cell line, and activation of aryl hydrocarbon receptor (AhR) and oestrogenic receptor (ER)-dependent genes in agonistic and antagonistic assays with luciferase reporter cells. It was applied to four chosen model molecules: ochratoxin A (OTA) and deoxynivalenol (DON), two common food-borne mycotoxins, and imazalil (IMA) and benomyl (BEN), two fungicides widely occurring in foodstuffs. All these assays were performed at or around a realistic intestinal concentration, determined through a deterministic approach based on the calculation of a theoretical maximum daily intake (TMDI). Using the four model molecules, it is clearly highlighted that induction of CYP1A1 activity and inhibition of CYP3A4 activity occurred in Caco-2 cells at a realistic intestinal concentration of IMA. Furthermore, some bacterial stress genes were induced in a range of realistic concentrations, following exposure to DON and IMA. In addition, BEN clearly provoked an ER agonistic activity in a human oestrogen sensitive reporter cell line. All these results are in accordance with the literature, suggesting that the in vitro toolbox constitutes an interesting approach in order to obtain a first 'fingerprint' of dietary contaminants at realistic human exposure for further risk assessment.

Toxicologic evaluation of imazalil with particular reference to genotoxic and teratogenic potentials

Imazalil (IMA) is a fungicide that is used extensively in fruit plantations and post-harvest treatments. IMA is suspected to produce craniofacial malformations in vertebrates and scarce data are available about its genotoxicity. Therefore, toxicity tests on embryogenesis of zebrafish (Danio rerio) and genotoxicity biomonitoring assays on human lymphocytes were performed to assess the effects of IMA. For this aim, zebrafish embryos were continually exposed, from 0.5 to 144 h post-fertilization, to a range of concentrations (5, 10, 20, 50 and 100 µM). IMA (0 to 672 µM) were also applied to the whole-blood cultures from two persons. We used chromosomal aberrations (CA) and micronucleus (MN) tests to examine DNA damage by IMA in human peripheral lymphocytes. The fungicide significantly altered zebrafish development even at low concentrations and its effects were dose-dependent. Results of the experiment indicated that IMA concentrations of 10 µM and above negatively affected embryo survival and hatching success. Morphological analysis uncovered a large suite of abnormalities such as less melanin pigmentation, wavy notochord, crooked trunk, tail defect and cardiac edema. The cytogenetic results clearly showed that IMA caused increases of the frequencies of the structural chromosomal aberrations and the rates of MN as compared to controls in a dose-dependent manner. In conclusion, the present findings are of importance in the assessment of the potential risk of fungicides as IMA on aquatic ecosystems and humans.

PROBLEMS OF POSITIVE LIST SYSTEM REVEALED BY SURVEY OF PESTICIDE RESIDUE IN FOOD

The positive list system became effective from May 29, 2006 to improve the regulation of residual agricultural chemicals (pesticides, feed additives and veterinary drugs) in foods. In accordance with the system, we investigated pesticide residues in 50 agricultural products purchased in Morioka city from March to November 2006. Analyses were performed according to the "Multiresidue Method for Agricultural Chemicals by GC/MS", the Notice of the Ministry of Health, Labour and Welfare. Five pesticides and two non-agricultural chemicals were detected from 16 samples. Ortho-phenylphenol (OPP) was detected from 8 samples: immature pea, snap bean, kiwi, plain-boiled bamboo shoot, mango, white asparagus, lemon and domestic shiitake mushroom. Maximum residue limits (MRLs) have not been established for these products, and they exceeded the uniform level of 0.01 ppm. DDT was detected from Philippines banana (0.30 ppm) and Korean paprika (0.45 ppm). The residual level in Philippines banana was lower than the MRL, but Korean paprika exceeded its MRL. Chlorpyrifos, Thiabendazole and Imazaril were detected from citrus imported from the U.S.A., but their residue levels were lower than the respective MRLs. Aniline and 2-pyrrolidone were detected from several imported products. These two may not be regulated by the positive list system because they are not agricultural chemicals, although their derivatives are used as pesticides or veterinary drugs. Three problems have been revealed from this survey: 1) application of the uniform level to minor agricultural products, 2) residues of non-agricultural chemicals whose toxicity is uncertain, 3) metabolites of agricultural chemicals, which are also regulated by the positive list system, have not been clearly defined.

Genotoxic and aneugenic properties of an imidazole derivative

To contribute to a more accurate characterization of the mutagenic and aneugenic effects of thiabendazole (TBZ), a widely used antiparasitic and food preservative drug, the induction of sister chromatid exchanges (SCEs) and mitotic spindle anomalies as cytogenetic end-points were investigated. Studies were carried out in Chinese hamster ovary (CHO) cells and human peripheral blood lymphocytes. A significant dose-dependent increase in SCE frequency was observed in CHO cells with S9-Mix (P < 0.01) in the 50-100 microg ml(-1) dose-range, while in the absence of S9-Mix, an enhancement of the SCE frequency was exhibited at the highest dose (P < 0.01). In CHO-K1 cells a significant increase in mitotic spindle anomalies (P < 0.01) was observed with the highest concentration assayed reflecting the specific effect of TBZ formulation at the microtubule level. Cell proliferation kinetics (CPK) were not modified by the addition of this pharmaceutical product. In human lymphocyte cultures, exposure to 100 microg ml(-1) TBZ formulation resulted in a significant decrease of the mitotic index (MI) (P < 0.003) and changes in the replication index (RI) (P < 0.05).

Marine sponges as pharmacy

Marine sponges have been considered as a gold mine during the past 50 years, with respect to the diversity of their secondary metabolites. The biological effects of new metabolites from sponges have been reported in hundreds of scientific papers, and they are reviewed here. Sponges have the potential to provide future drugs against important diseases, such as cancer, a range of viral diseases, malaria, and inflammations. Although the molecular mode of action of most metabolites is still unclear, for a substantial number of compounds the mechanisms by which they interfere with the pathogenesis of a wide range of diseases have been reported. This knowledge is one of the key factors necessary to transform bioactive compounds into medicines. Sponges produce a plethora of chemical compounds with widely varying carbon skeletons, which have been found to interfere with pathogenesis at many different points. The fact that a particular disease can be fought at different points increases the chance of developing selective drugs for specific targets.

Enantioseparation of imazalil residue in orange by capillary electrophoresis with 2-hydroxypropyl-beta-cyclodextrin as a chiral selector

Chiral resolution of imazalil, a fungicide, was performed by capillary electrophoresis (CE) using 2-hydroxypropyl-beta-cyclodextrin as a chiral selector. Factors affecting the chiral resolution and migration time of imazalil were studied. The optimum running conditions were found to be 5 mM ammonium dihydrogenphosphate-50 mM phosphate buffer (pH 3.0) containing 4 mM 2-hydroxypropyl-beta-cyclodextrin with an effective voltage of +25 kV at 20 degrees C using direct detection at 200 nm. Under these conditions, the resolution (Rs) of racemic imazalil was approximately 6. The extraction of imazalil from orange samples was done with acetonitrile under basic conditions. The extract was purified with a solid-phase extraction cartridge (Sep-Pak plus PS-2) and was analyzed by the above CE method. Eight orange samples were analyzed, and imazalil was detected in seven samples. In four of these seven oranges, the level of (-)-imazalil was the same as that of (+)-imazalil, but in the other three oranges, the level of (-)-imazalil was found to be lower than that of (+)-imazalil, suggesting that (-)-imazalil was degraded more quickly than (+)-imazalil in oranges.

The effects of mebendazole on P4501A activity in rat hepatocytes and HepG2 cells. Comparison with tiabendazole and omeprazole

Mebendazole is a benzimidazole anthelmintic widely used in veterinary and human therapy. Among benzimidazole derivatives, several drugs with inducing effect on cytochromes P450 can be found. However, the induction capacity of mebendazole on P450s has not been explored yet. In this study, the effects of mebendazole on P4501A activity was tested in primary cultures of rat hepatocytes and in human hepatoma HepG2 cell line. Two known P4501A inducers with benzimidazole structure, tiabendazole and omeprazole, were also included in the experiments with the aim of studying structure-induction relationships. After 24-, 48- and 72-h incubation of rat hepatocytes and HepG2 cells with drugs in various concentrations (0.1-100 microM), enzyme activity associated with P4501A1/2 (EROD, MROD) was measured. In addition, the P4501A1/2 protein levels in both in-vitro systems were determined by Western-blotting. Mebendazole provoked a significant increase in P4501A1/2 protein expression and P4501A activity in both in-vitro systems. Omeprazole caused a significant dose-dependent increase of P4501A activity only in HepG2 cells. Although tiabendazole treatment led to significant increase of P4501A protein level, no effect on P4501A activity was observed in either system. The results demonstrate that mebendazole possesses the ability to significantly induce P4501A. Thus, pharmacological and toxicological consequences of P4501A induction should be taken into account in human therapy. The structure-induction relationships and differences between in-vitro systems used are discussed.

O-phenylphenol and its sodium and potassium salts: a toxicological assessment

Ortho-phenylphenol (OPP) and its sodium (SOPP) and potassium (POPP) salts are used as fungicides and disinfectants. Due to the widespread use of especially OPP and SOPP, the potential for consumer exposure and some "critical" findings the toxicological database is quite extensive and complex. In experimental animals toxicity after single oral and dermal administration of these compounds is low. For the skin and mucous membranes, OPP has to be considered as irritating, and SOPP and POPP as corrosive. A large number of chronic toxicity and reproduction studies did not show any indication of oestrogen-like or other endocrine effects of OPP in the mammalian organism. No teratogenic effects were observed after the administration of OPP or SOPP in rats, mice, and rabbits. In two-generation studies in rats, OPP did not affect reproduction. The available data do not suggest a relevant potential for immunotoxic properties. The administration of high dietary concentrations of OPP to mice up to 2 years induced hepatocellular changes indicative of adaptations to metabolic demands, zonal degeneration, focal hepatocellular necrosis, and/or pigmentation of the liver. Only in male mice of one study, using a strain prone to develop hepatocellular tumors at high spontaneous incidences, the incidence of hepatocellular adenomas was increased. The incidence of hepatocellular carcinomas was not affected by treatment. The urothel of the urinary bladder (at very high doses also of the renal pelvis and the papilla) is the main target tissue after the repeated oral exposure of rats. The changes initially consist of increased mitosis, followed by simple epithelial hyperplasia, developing to a papillary and/or nodular form, later on to papillomas and transitional carcinomas. Crystals or stones in the bladder do not play a decisive role in this cascade. SOPP is more effective than OPP in this respect. Male rats are much more sensitive than females. In mice, hamsters, guinea pigs, and dogs, urothelial lesions do not develop even at very high oral dose levels. The findings in rats explain why there is a large genotoxicity/mutagenicity data base not only for OPP and SOPP but also for their metabolites on nearly all kinds of endpoints/targets. The weight of evidence suggests that genotoxicity of OPP/SOPP or their metabolites does not play a decisive role for the carcinogenicity at the urothel. Among them are lack of DNA binding of OPP to the rat bladder epithelium, the differences between OPP and SOPP, between male and female rats, between rats and mice (despite roughly comparable toxicokinetics), as well as the fact that tumors develop only at dose levels inducing hyperplasias. In addition, the strong dependence of the incidence and severity of the nonneoplastic and neoplastic bladder changes on urinary pH values (modified by feeding of ammonium chloride or sodium hydrogen carbonate) is consistent with the hypothesis of a nongenotoxic mode of action. Finally, there is no correlation between the urinary concentration of OPP or its metabolites and the incidence of hyperplasias/tumors in the urinary bladder. Both tumorigenic effects in rats and male mice are considered to represent high-dose, sex- and/or species-specific phenomena, based on nongenotoxic mechanisms of action and therefore allow the conclusion that the conventional margin of safety approaches are appropriate when assessing the risk of applications of OPP and its salts.

Flow cytometry analysis of changes in the DNA content of the polychlorinated biphenyl degrader Comamonas testosteroni TK102: effect of metabolites on cell-cell separation

Flow cytometry was used to monitor changes in the DNA content of the polychlorinated biphenyl (PCB)-degrading bacterium Comamonas testosteroni TK102 during growth in the presence or absence of PCBs. In culture medium without PCBs, the majority of stationary-phase cells contained a single chromosome. In the presence of PCBs, the percentage of cells containing two chromosomes increased from 12% to approximately 50%. In contrast, addition of PCBs did not change the DNA contents of three species that are unable to degrade PCBs. In addition, highly chlorinated PCBs that are not degraded by TK102 did not result in a change in the DNA content. These results suggest that PCBs did not affect the DNA content of the cells directly; rather, the intermediate metabolites resulting from the degradation of PCBs caused the increase in DNA content. To study the effect of intermediate metabolites on the DNA content of the cells, four bph genes, bphA1, bphB, bphC, and bphD, were disrupted by gene replacement. The resulting mutant strains accumulated intermediate metabolites when they were grown in the presence of PCBs or biphenyl (BP). When the bphB gene was disrupted, the percentage of cells containing two chromosomes increased in cultures grown with PCBs or BP. When grown with BP, cultures of this mutant accumulated two intermediate metabolites, 2-hydroxybiphenyl (2-OHBP) and 3-OHBP. Addition of 2- or 3-OHBP to a wild-type TK102 and non-PCB-degrading species culture also resulted in an increase in the percentage of cells containing two chromosomes. Electron microscopy revealed that cell-cell separation was inhibited in this culture. This is the first report that hydroxy-BPs can inhibit bacterial cell separation while allowing continued DNA replication.

Transcriptional organization and dynamic expression of the hbpCAD genes, which encode the first three enzymes for 2-hydroxybiphenyl degradation in Pseudomonas azelaica HBP1

Pseudomonas azelaica HBP1 degrades the toxic substance 2-hydroxybiphenyl (2-HBP) by means of three enzymes that are encoded by structural genes hbpC, hbpA, and hbpD. These three genes form a small noncontiguous cluster. Their expression is activated by the product of regulatory gene hbpR, which is located directly upstream of the hbpCAD genes. The HbpR protein is a transcription activator and belongs to the so-called XylR/DmpR subclass within the NtrC family of transcriptional activators. Transcriptional fusions between the different hbp intergenic regions and the luxAB genes of Vibrio harveyi in P. azelaica and in Escherichia coli revealed the existence of two HbpR-regulated promoters; one is located in front of hbpC, and the other one is located in front of hbpD. Northern analysis confirmed that the hbpC and hbpA genes are cotranscribed, whereas the hbpD gene is transcribed separately. No transcripts comprising the entire hbpCAD cluster were detected, indicating that transcription from P(hbpC) is terminated after the hbpA gene. E. coli mutant strains lacking the structural genes for the RNA polymerase sigma(54) subunit or for the integration host factor failed to express bioluminescence from P(hbpC)- and P(hbpD)-luxAB fusions when a functional hbpR gene was provided in trans. This pointed to the active role of sigma(54) and integration host factor in transcriptional activation from these promoters. Primer extension analysis revealed that both P(hbpC) and P(hbpD) contain the typical motifs at position -24 (GG) and -12 (GC) found in sigma(54)-dependent promoters. Analysis of changes in the synthesis of the hbp mRNAs, in activities of the 2-HBP pathway enzymes, and in concentrations of 2-HBP intermediates during the first 4 h after induction of continuously grown P. azelaica cells with 2-HBP demonstrated that the specific transcriptional organization of the hbp genes ensured smooth pathway expression.

Effects of thiabendazole (TBZ) on mitochondrial function in renal cortex of ICR mice

The effects of thiabendazole (TBZ) on mitochondrial function of the renal cortex were investigated in ICR mice. Mice were given 1000 or 2000 mg TBZ/kg body weight by gavage and mitochondria were isolated from the renal cortex for the measurement of respiratory rates. The state 3 and DNP-uncoupled respiratory rates of renal cortical mitochondria were dose-dependently depressed at 6 hours after dosing. The depression of these respiratory rates of renal cortical mitochondria was more marked at 16 hours after dosing. There was no depression in these respiratory rates of renal cortical mitochondria at 3 hours after dosing, although renal cortical concentrations of TBZ were higher than those at 6 or 16 hours after dosing. Histochemical examination revealed that NAD-linked isocitrate dehydrogenase, a marker enzyme of mitochondria, was inhibited in renal cortical tubules at 16 hours after dosing of 1000 or 2000 mg TBZ/kg body weight. Furthermore, renal cortical ATP level was significantly decreased at 16 hours after dosing of 1000 or 2000 mg TBZ/kg body weight. The results indicate that administration of TBZ caused mitochondrial dysfunction in renal cortical tubules of mice.

Mechanism of mitochondrial dysfunction and cytotoxicity induced by tropolones in isolated rat hepatocytes

The mechanism of mitochondrial dysfunction and toxicity induced by the tropolones, beta-thujaplicin (4-isopropyl tropolone), tropolone and tropone, has been studied in freshly isolated rat hepatocytes. Incubation of hepatocytes with beta-thujaplicin (1-4 mM) elicited a concentration and time-dependent cell killing. The toxicity was accompanied by losses of cellular ATP, total adenine nucleotides and glutathione, independently of lipid peroxidation and protein thiol oxidation. The beta-thujaplicin-induced cytotoxicity was enhanced by the pretreatment of hepatocyte suspensions with EDTA (4 mM), a hydrophilic chelator, or by incubation in Ca2+ and Mg2+-deficient Krebs-Henseleit buffer. The partition coefficient of beta-thujaplicin, which formed complex with the divalent cations in Krebs-Henseleit buffer, in n-octanol/buffer was increased either in the presence of EDTA or absence of divalent cations. Comparison of toxic effects based on cell viability and adenine nucleotide levels showed that beta-thujaplicin was more toxic than tropolone or tropone in Krebs-Henseleit buffer containing EDTA (4 mM). The addition of beta-thujaplicin to isolated hepatic mitochondria reduced state 3 respiration with NAD+-linked substrate (pyruvate plus malate) and/or with an FAD-linked substrate (succinate plus rotenone), whereas state 3 respiration of ascorbate plus tetramethyl-p-phenylenediamine (cytochrome oxidase-linked respiration) was not significantly affected by beta-thujaplicin. Further, the addition of these tropolones caused a concentration-dependent increase in the rate of state 4 oxygen consumption, indicating an uncoupling effect. These results indicate that beta-thujaplicin- and tropolone-induced cytotoxicity are associated with an acute ATP depletion via mitochondrial dysfunction related to oxidative phosphorylation and that the induction of cytotoxicity is affected by EDTA or divalent cations.

Purification and characterization of 2-hydroxybiphenyl 3-monooxygenase, a novel NADH-dependent, FAD-containing aromatic hydroxylase from Pseudomonas azelaica HBP1

2-Hydroxybiphenyl 3-monooxygenase (HbpA), the first enzyme of 2-hydroxybiphenyl degradation in Pseudomonas azelaica HBP1, was purified 26-fold with a yield of 8% from strain HBP1 grown on 2-hydroxybiphenyl. The enzyme was also purified from a recombinant of Escherichia coli JM109, which efficiently expressed the hbpA gene. Computer densitometry of scanned slab gels revealed a purity of over 99% for both enzyme preparations. Gel filtration, subunit cross-linking, and SDS-polyacrylamide gel electrophoresis showed that the enzyme was a homotetramer with a molecular mass of 256 kDa. Each subunit had a molecular mass of 60 kDa containing one molecule of noncovalently bound FAD. The monooxygenase had a pI of 6.3. It catalyzed the NADH-dependent ortho-hydroxylation of 2-hydroxybiphenyl to 2,3-dihydroxybiphenyl. Molecular oxygen was the source of the additional oxygen of the product. The enzyme hydroxylated various phenols with a hydrophobic side chain adjacent to the hydroxy group. All substrates effected partial uncoupling of NADH oxidation from hydroxylation with the concomitant formation of hydrogen peroxide. 2,3-Dihydroxybiphenyl, the product of the reaction with 2-hydroxybiphenyl, was a non-substrate effector that strongly facilitated NADH oxidation and hydrogen peroxide formation without being hydroxylated and also was an inhibitor. The apparent Km values (30 degrees C, pH 7.5) were 2.8 microM for 2-hydroxybiphenyl, 26.8 microM for NADH, and 29.2 microM for oxygen. The enzyme was inactivated by p-hydroxymercuribenzoate, a cysteine-blocking reagent. In the presence of 2-hydroxybiphenyl, the enzyme was partly protected against the inactivation, which was reversed by the addition of an excess of dithiothreitol. The NH2-terminal amino acid sequence of the enzyme contained the consensus sequence GXGXXG, indicative of the betaalphabeta-fold of the flavin binding site and shared homologies with that of phenol 2-hydroxylase from Pseudomonas strain EST1001 as well as with that of 2,4-dichlorophenol 6-hydroxylase from Ralstonia eutropha.

Cytotoxic effects of 2,6-di-tert-butyl-4-methylphenyl N-methylcarbamate (terbutol) herbicide on hepatocytes and mitochondria isolated from male rats

The cytotoxic effects of 2,6-di-tert-butyl-4-methylphenyl N-methylcarbamate (terbutol) and its major metabolites were investigated in freshly isolated rat hepatocytes. Terbutol and its metabolite, especially 2,6-di-tert-butyl-4-methylphenyl carbamate (N-demethylterbutol), at a concentration of 1.0 mM resulted in a time dependent cell killing accompanied by losses of intracellular ATP, protein thiols, and glutathione (GSH) and the accumulation of oxidized GSH. Supplementation of the hepatocyte suspension with 5 mM N-acetylcysteine, a precursor of intracellular GSH, inhibited the cytotoxicity of N-demethylterbutol. In mitochondria isolated from rat liver, terbutol and its metabolites impaired respiration related to oxidative phosphorylation and the potency of their toxicity is associated with impairment of mitochondrial respiration. These results indicate that N-demethylterbutol is the most cytotoxic followed by terbutol and other metabolites, and that both the mitochondrial respiratory system and protein thiols are important targets for these compounds.