Inhibition of metabolic cooperation in vitro and enhancement of enzyme altered foci incidence in rat liver by the pyrethroid insecticide fenvalerate

Earthworm biomarker responses on exposure to commercial cypermethrin

Cypermethrin is a synthetic pyrethroid insecticide used worldwide in agriculture, home pest control, disease vector control, and food safety. It accumulates in soil. Therefore, traces of cypermethrin may frequently appear in vegetables grown in contaminated soil. There is a push now to develop biomarkers as early warning indicators of environmental pollution. In this study, DNA damage (tail DNA%, tail length, and olive tail moment), the micronucleus, neutral red retention (NRR) time, and pinocytic adherence ability of coelomocytes were investigated in Pheretima peguana earthworms exposed to cypermethrin in filter paper tests. The NRR time of earthworm coelomocytes decreased significantly at a concentration of 3.5 × 10(-3) µg · cm(-2) (1/100 LC50 ) after 48 h exposure, with a highly negative correlation with cypermethrin concentration. Pinocytic adherence ability of coelomocytes also declined significantly at a cypermethrin concentration of 3.5 × 10(-2) µg · cm(-2) (1/10 LC50 ). The DNA damage to earthworm coelomocytes (tail DNA%, tail length, and olive tail moment) increased considerably at the highest concentration (3.5 × 10(-1) µg · cm(-2) ) although the correlation between tail DNA% and cypermethrin concentration was low. Thus, physiological biomarkers were more sensitive than the genotoxic effects in earthworms exposed to commercial cypermethrin. Although a suite of earthworm biomarkers could be used to evaluate cypermethrin terrestrial pollution, the NRR test is easier to conduct and a more sensitive indicator.

A current review of cypermethrin-induced neurotoxicity and nigrostriatal dopaminergic neurodegeneration

Cypermethrin, a class II pyrethroid pesticide, is used to control insects in the household and agricultural fields. Despite beneficial roles, its uncontrolled and repetitive applications lead to unintended effects in non-target organisms. Cypermethrin crosses the blood-brain barrier and induces neurotoxicity and motor deficits. Cypermethrin prolongs the opening of sodium channel, a major site of its action, leading to hyper-excitation of the central nervous system. In addition to sodium channel, cypermethrin modulates chloride, voltage-gated calcium and potassium channels, alters the activity of glutamate and acetylcholine receptors and adenosine triphosphatases and induces DNA damage and oxidative stress in the neuronal cells. Cypermethrin also modulates the level of neurotransmitters, including gamma-aminobutyric acid and dopamine. It is one of the most commonly used pesticides in neurotoxicology research not only because of its variable responses depending upon the doses, time and routes of exposure and strain, age, gender and species of animals used across multiple studies but also owing to its ability to induce the nigrostriatal dopaminergic neurodegeneration. This article describes the effect of acute, chronic, developmental and adulthood exposures to cypermethrin in experimental animals. The article sheds light on cypermethrin-induced changes in the central nervous system, including its contribution in the onset of specific features, which are associated with the nigrostriatal dopaminergic neurodegeneration. Resemblances and dissimilarities of cypermethrin-induced nigrostriatal dopaminergic neurodegeneration with sporadic and chemicals-induced disease models along with its advantages and pitfalls are also discussed.

Veterinary Pesticides

Veterinary pesticides are used to treat a range of parasitic conditions in companion and farm animals. These products are based on a number of different compounds with different modes of action and different spectra of toxicity. The older agents include the synthetic pyrethroids and organophosphorus compounds, while the newer examples include, for example, representatives of the insect growth promoters, the neonicotinoids, and the oxadiazones. For many of these compounds, toxicity is associated with their pharmacological activity or mode of action. Thus the synthetic pyrethroids and the organophosphorus compounds exert neurotoxic effects. For others, toxicity may be associated with mechanisms that are independent of their mode of action. When used according to the manufacturer's instructions, these products are generally safe and efficacious. However, accidental contamination and misuse can lead to toxicity in operators and treated animals. These compounds are important in the treatment of parasitic disease in animals and their regulation and uses are based on favourable risk-benefit outcomes.

Protective effect of curcumin on cypermethrin-induced oxidative stress in Wistar rats

The aim of present study was to investigate the protective effect of curcumin on cypermethrin-induced changes in blood biochemical markers and tissue antioxidant enzyme in rats. Rats were divided into six groups of six each: group I used as control and II and III groups were used as vehicle control. While, groups IV, V and VI were orally treated with curcumin (100 mg/kg body weight), cypermethrin (25 mg/kg body weight) and cypermethrin plus curcumin, respectively for 28 days. Serum biochemical markers were measured in the serum, and the levels of lipid peroxidation and antioxidant enzyme activity were determined in the liver, kidney and brain. Cypermethrin administration caused elevated level of blood biochemical markers in serum and lipid peroxidation in liver, kidney and brain. While the activities of non-enzymatic and enzymatic antioxidants levels were decreased except superoxide dismutase in liver, kidney and brain tissues. The presence of curcumin with cypermethrin significantly decreased the blood biochemical markers and lipid peroxidation but significantly increased the reduced glutathione, catalase and glutathione peroxidase level and preserved the normal histological architecture of the liver, kidney and brain. Our results indicate that curcumin can be potent protective agent against cypermethrin-induced biochemical alterations and oxidative damage in rats.

Induction of oxidative stress and lipid peroxidation in rats chronically exposed to cypermethrin through dermal application

Present study was undertaken to study the effect of cypermethrin on oxidative stress after chronic dermal application. The insecticide was applied dermally at 50 mg/kg body weight in different groups of Wistar rats of either sex weighing 150~200 g. Significant (p < 0.05) increase in catalase activity was observed after 30 days of exposure. However, the superoxide dismutase activity declined significantly after 60 days of exposure. The activity of glutathione peroxidase and blood glutathione levels declined significantly (p < 0.05) after 30 days of cypermethrin dermal application. However, the activity of glutathione S-transferase increased significantly (p < 0.05) in all groups after 60 days of dermal exposure. Significant increase in lipid peroxidation was observed from 30 days onwards and reached a peak after 120 days of application.

Pulmonary effects of deltamethrin inhalation: an experimental study in rats

Deltamethrin is a synthetic pyrethroid widely used as the insecticide of choice especially for local vector mosquitoes in most countries. The application is mostly by cold aerosol spraying using vehicle-mounted equipment with a duration of 3-4 months during the summer. This experimental study aimed to evaluate the morphologic changes in the lungs caused by the inhalation of this insecticide. The study was performed on 30 mature male Wistar rats. While 10 of the rats were used as control group, 20 rats, separated into two groups, were exposed to 1:10 dilution of deltamethrin aerosol spray for 30 min each day for 45 days in doses of 6.0 and 12.0 mg/m3. The animals were sacrificed and tissue samples taken from the lungs were processed for both light microscopy and transmission electron microscopy. Light microscopic examination revealed heavy congestion, marked perivascular edema, and lymphoplasmocytic infiltration with focal nonspecific interstitial pneumonia, foamy macrophage accumulation, emphysema, peribronchial lymphoid tissue hyperplasia, and focal hemorrhage. Ultrastructurally, the ciliated cells of the airways appeared swollen with a few structurally abnormal cilia. Alveolar lining cells revealed mild degeneration and a slight hyperplasia in type II cells. Increases in the number of collagen bundles and edema in the alveolar septa were also noted.

Fenvalerate-induced oxidative damage in rat tissues and its attenuation by dietary sesame oil

The primary objective of this study was to investigate the propensity of Fenvalerate (FEN), a synthetic pyrethroid to induce oxidative stress (OS) in various tissues of growing male rats following a short-term (28 days) dietary regimen and its possible attenuation by dietary (10%) sesame oil (SO). FEN incorporated diet was fed to weanling male rats at the dosages of 0, 250, 500 and 1000 ppm. Terminally, significant induction of OS in liver, thymus, spleen and erythrocytes was noticed at higher doses as evidenced by the elevated levels of lipid peroxidation (LPO). Significant dose-dependent depletion of GSH levels, perturbations in antioxidant enzymes, and enhanced protein carbonyls further confirmed the potential of FEN to induce OS in hepatic tissue. In addition, FEN also caused significant increases in activities of hepatic transaminases, ALP and LDH. Interestingly, dietary SO significantly attenuated FEN-induced oxidative damage in liver and other tissues. The degree of protection was remarkably high, since LPO and GSH status, protein carbonyl content and antioxidant defenses in liver and other tissues were brought down to basal levels in the SO + FEN1ooo group. These results clearly indicate the potential of FEN to induce oxidative damage in vivo and also suggest the ability of SO, a dietary fat to significantly offset the oxidative damage which may related to the presence of antioxidant compounds in the oil.

Fenvalerate-induced chromosome aberrations and sister chromatid exchanges in the bone marrow cells of mice in vivo

Fenvalerate, a synthetic pyrethroid insecticide, is commonly used in agriculture and other domestic applications due to its high insecticidal activity and low mammalian-, avian- and phyto-toxicities. However, the genotoxic effect of fenvalerate is highly equivocal. In the present study the genotoxic effects of fenvalerate was evaluated using structural chromosome aberration (CA) and sister chromatid exchange (SCE) assays in mice. Out of the three doses (5, 10 and 20 mg/kg) tested, statistically significant increase in CA was found following intra peritoneal (i.p.) treatment of 2 0 mg/kg of fenvalerate for 24 h (P<0.01) and 48 h (P<0.05) only. Neither the acute doses of 5 and 10 mg/kg, nor the sub-acute dose (5x4 mg/kg) of fenvalerate could induce any significant effect. All the three acute doses induced significant increase in the frequency of SCEs (P<0.01) in the bone marrow cells, which showed a significant dose-response correlation (r=0.9541, P<0.05). With certain reservations to possible impurities, from the present findings technical grade fenvalerate may be considered as a weak clastogen and a potent inducer of SCEs in mice.

Use of a cell transformation assay with established cell lines, and a metabolic cooperation assay with V79 cells for the detection of tumour promoters: a review

Extensive studies on the safety evaluation of chemicals have indicated that a considerable number of non-genotoxic chemicals are carcinogenic. Tumour promoters are likely to be among these non-genotoxic carcinogens, and their detection is considered to be an important approach to the prevention of cancer. In this review, the results are summarised for in vitro transformation assays involving established cell lines, and for an assay for inhibition of gap junctional intercellular communication for the detection of tumour promoters, which involves V79 cells. Although the number of chemicals examined is still too small to permit a full evaluation of the correlation between in vitro cell transformation and in vivo carcinogenicity, it is clear that the sensitivity of the focus formation assay is very high. In the case of the metabolic cooperation assay, the sensitivity appears to be rather poor, but the assay can be considered to be useful because of its simple procedure and its considerable database. These in vitro assays for tumour promoters are recommended as useful tools for the detection of non-genotoxic carcinogens.

Contribution of planar (0-1 ortho) and nonplanar (2-4 ortho) fractions of Aroclor 1260 to the induction of altered hepatic foci in female Sprague-Dawley rats

The hepatic tumor promoting activity of the planar 0-1 ortho ( approximately 9.7% w/w) and the nonplanar 2-4 ortho ( approximately 90.3% w/w) fraction of the commercial PCB mixture Aroclor 1260 was studied using a medium-term two-stage initiation/promotion bioassay in female Sprague-Dawley rats. Fractionation was carried out on an activated charcoal column. The composition of the effluent from the column was tested by GC-ECD. The absence of planar compounds in the 2-4 ortho fraction was confirmed by GC-MS analysis. The dioxin-like toxic potency of the fractions was determined with the DR-CALUX assay. The animal experiment was started with the initiation procedure (diethylnitrosamine injection, 30 mg/kg body wt ip, 24 h after (2)/(3) hepatectomy), followed 6 weeks later by the promotion treatment, which consisted of a weekly subcutaneous injection during 20 weeks. Exposure groups (n = 10) received the following treatments (dose/kg body wt/week): Aroclor 1260 (10 mg), 0-1 ortho fraction (0.97 mg), 2-4 ortho fraction (1, 3, or 9 mg), a reconstituted 0-4 ortho fraction (9.97 mg), 2,2',4,4',5,5'-hexachlorobiphenyl (PCB 153; 1 or 9 mg), 2,3,7,8-TCDD (1 microg; positive control) or corn oil (1 ml; vehicle control). One group did not receive a promotion treatment. All exposure groups exhibited a significantly increased volume fraction of the liver occupied by hepatic foci positive for the placental form of glutathione-S-transferase-p compared to the corn oil control, except for the groups treated with 0-1 ortho fraction and 1 mg PCB 153/kg body wt/week. Approximately 80% of the total tumor promoting capacity of the reconstituted 0-4 ortho fraction could be explained by the 2-4 ortho PCB fraction while the 0-1 ortho fraction had only a negligible contribution. These results suggest that the majority of the tumor promotion potential of PCB mixtures resides in the non-dioxin-like fraction, which is not taken into account in the toxic equivalency factor (TEF) approach for risk assessment of PCBs. This may result in an underestimation of the tumor promotion potential of environmental PCB mixtures.

Induction of altered hepatic foci by a mixture of dioxin-like compounds with and without 2,2',4,4',5,5'-hexachlorobiphenyl in female Sprague-Dawley rats

The hepatic tumor-promoting activity of a mixture of polyhalogenated aromatic hydrocarbons (PHAHs) was studied in a medium term two-stage initiation/promotion bioassay in female Sprague-Dawley rats. The PHAH mixture contained 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 1, 2,3,7,8-pentachlorodibenzo-p-dioxin (PeCDD), 2,3,4,7, 8-pentachlorodibenzofuran (PeCDF), 3,3',4,4',5-pentachlorobiphenyl (PCB 126), 2,3',4,4',5-pentachlorobiphenyl (PCB 118), 2,3,3',4,4', 5-hexachlorobiphenyl (PCB 156), 2,2',4,4',5,5'-hexachlorobiphenyl (PCB 153) and covered >90% of the total toxic equivalents (TEQ) present in Baltic herring. To determine possible interactive effects of di-ortho-substituted PCBs, the PHAH mixture was tested with (PHAH+) and without (PHAH-) PCB 153. Rats were initiated by a diethylnitrosamine injection (30 mg/kg body wt i.p.) 24 h after a partial 23 hepatectomy. Six weeks after initiation, the PHAH mixtures were administered once a week by subcutaneous injections for 20 weeks. Treatment with the PHAH mixtures caused liver enlargement and an increased activity of the hepatic cytochrome P4501A1/2 and P4502B1/2. All PHAH exposure groups exhibited an increased occurrence of hepatic foci positive for the placental form of glutathione-S-transferase. In the PHAH-group dosed 1 microgram TEQ/kg body wt/week, the volume fraction of the liver occupied by foci was significantly lower compared to the TEQ equivalent dosed TCDD group (3.8 vs 8.7%). The volume fraction was significantly increased in the groups treated with 0.5, 1, or 2 micrograms TEQ/kg body wt/week of the PHAH+ mixture (4.5, 5.2, and 6.6%, respectively) compared to the corn oil group (2.0%), but to a lower extent than expected on basis of the TEQ doses. Overall, the TEQ-based administered dose overestimated the observed tumor-promoting effects of this PHAH mixture. The applicability of the toxic equivalency factor concept, the role of differences in toxicokinetic properties and interactive effects of PCB 153 on hepatic deposition of the dioxin-like congeners are discussed.

In vitro genotoxic effects of the insecticide deltamethrin in human peripheral blood leukocytes: DNA damage ('comet' assay) in relation to the induction of sister-chromatid exchanges and micronuclei

Deltamethrin, a synthetic dibromo-pyrethroid insecticide, is extensively used in agriculture, forestry and in household products because of its high activity against a broad spectrum of insect pests (both adults and larvae), its low animal toxicity and its lack of persistence in the environment. Data on the genotoxicity and carcinogenicity of deltamethrin are rather controversial, depending on the genetic system or the assay used. The aim of this study was to further evaluate the potential genotoxic activity of deltamethrin. The in vitro genotoxicity of deltamethrin has been evaluated by assessing the ability of the insecticide to damage DNA (as evaluated using the single-cell microgel-electrophoresis or 'comet' assay) or induce sister-chromatid exchanges (SCE) and micronuclei (MN) in human peripheral blood leukocytes. All treatments were conducted with and without the presence of an external bioactivation source (+/- S9mix). The results indicate that deltamethrin, in the presence of metabolic activation (+ S9mix), is able to induce DNA damage (double- and single-strand breaks, alkali-labile sites and open excision repair sites) as revealed by the increasing tail moment values observed with increasing doses. The frequency of SCE and MN were not statistically increased in deltamethrin-treated cells as compared to controls, both with and without S9mix. However, lower deltamethrin doses were tested, as compared to 'comet' assay, because of cytotoxicity.

Interactive effects of three structurally different polychlorinated biphenyls in a rat liver tumor promotion bioassay

Interactive effects between the non-ortho-substituted 3,3', 4,4', 5-pentachlorobiphenyl (PCB126), the mono-ortho-substituted 2,3,3',4, 4'-pentachlorobiphenyl (PCB105), and the di-ortho-substituted 2,2',4, 4',5,5'-hexachlorobiphenyl (PCB153) were studied in an initiation/promotion bioassay. Female Sprague-Dawley rats were injected with 30 mg/kg ip of N-nitrosodiethylamine 24 h after partial hepatectomy. Five weeks later, weekly sc administrations of the three PCBs in 15 systematically selected dose combinations started. After 20 weeks of administration, the animals were killed and the livers were analyzed for areas expressing placental glutathione-S-transferase as a marker of preneoplastic foci. In addition, concentration of liver and kidney retinoids and plasma retinol was analyzed, as well as body and organ weights, plasma transaminases, and induction of hepatic cytochrome P450 1A1/2 (CYP1A1/2) and CYP2B1/2 activities. Data were analyzed with a multivariate method. At the doses applied in this study, weak antagonism was observed between PCB126 and PCB153 for effects on volume fraction of foci, number of foci/cm3, concentration of plasma retinol and liver retinoids, relative liver weight, and induction of CYP2B1/2 activity. Weak antagonism was also observed between PCB126 and PCB105 for effects on volume fraction of foci, number of foci/cm3, and plasma retinol concentration. No interactions other than pure additivity were observed between PCB105 and PCB153. Synergism was not observed within the dose ranges investigated in this study. Knowledge of interactive effects is important for risk assessment of environmental mixtures of dioxin-like compounds. Antagonism between congeners generally results in risk assessments that overestimate human risk. The significance to human risk assessment of the relatively weak antagonism observed in this study is however unclear, considering many other uncertainties involved in the toxic equivalency factor (TEF) concept. A change of the TEF concept for risk assessments of dioxin-like substances is not motivated based on the results of this study.

Initiation and promotion of altered hepatic foci in female rats and inhibition of cell-cell communication by the imidazole fungicide prochloraz

The imidazole fungicide prochloraz (1-[N-propyl-N-2-(2,4,6-trichlorophenoxy) ethyl carbamoyl] imidazole) was investigated for its ability to inhibit gap junctional intercellular communication in the scrape-loading/dye-transfer assay in IAR 20 rat liver epithelial cells and for effects on the initiation and promotion stages of hepatocarcinogenesis. Female Sprague-Dawley rats initiated with N-nitrosodiethylamine 24-hr after partial hepatectomy were administered prochloraz five days a week by oral gavage (30 or 150 mg/kg) for 10 weeks. Altered hepatic foci (AHF) were analyzed by quantitative stereology from liver sections stained for gamma-glutamyltranspeptidase (GGT) and glutathione S-transferase P (GST-P). The fungicide was also studied for its ability to initiate the development of GGT-positive AHF in rat liver. The in vitro studies showed prochloraz to be an inhibitor of cell-cell communication in the test system used. In the in vivo studies, prochloraz showed no effect on the initiation of GGT-positive foci. However, significant increases in the percentage of liver tissue occupied by GGT-positive AHF and the number of GST-P-positive AHF per cm3 in initiated animals were recorded in the low dose group. The present data suggest that prochloraz acts as a weak tumour promoter of hepatocarcinogenesis but does not initiate this process.

Cypermethrin increases apo A-1 and apo B mRNA but not hyperlipidemia in rats

The hepatotoxic effect of cypermethrin and the expression of hepatic genes at the mRNA level, as molecular markers of liver damage, were evaluated in rats following exposure to cypermethrin. The expression of hepatic genes was compared with conventional liver functional tests, and correlations were made by studying the liver at the ultrastructural level. Cypermethrin treated rats presented a significant decrease, of 79% and 22%, on the expression of albumin and apo E genes at 5 days, respectively. The levels of apo A-1 and apo B mRNA were increased up to four- and fivefold, respectively. This increase did not correlate with the serum values of HDL and VLDL lipoprotein particles. Intracytoplasmic lipid droplets were observed after the first 2 days following cypermethrin administration, suggesting that apo A-1 and B mRNA were translated but not secreted. There were significant correlations between the low values of the albumin gene expression, the decrease in the HDL concentrations, and the ultrastructural alterations, respectively. These alterations were mainly a large amount and increased size of mitochondria in the animals exposed to cypermethrin. It is concluded that under the experimental conditions used, cypermethrin may alter the metabolism of lipids and proteins in rat liver.

Promotion of enzyme altered foci in female rat 2,3,3',4,4',5-hexachlorobiphenyl

The tumor promoting activity of 2,3,3',4,4',5-hexachlorobiphenyl (PCB 156) was studied in an initiation/promotion bioassay in female Sprague-Dawley rats initiated with N-nitrosodiethylamine after partial hepatectomy. PCB 156 (50, 300, 1500, or 7500 microg/kg body weight/week) was administered by once-weekly subcutaneous injections for 20 weeks. Some high dose animals were left without treatment for an additional 20 weeks to study posttreatment effects. The volume fraction of the liver occupied by glutathione S-transferase P-positive foci was significantly increased to 2.9, 3.3, and 12% at 300, 1500, and 7500 microg/kg body weight/week, respectively, compared to 1.2% in the controls. The volume fraction was 43% in the high dose group 20 weeks after treatment was stopped, probably reflecting the slow body clearance of PCB 156 as indicated by the sustained liver and adipose tissue concentrations. Treatment with PCB 156 following initiation caused decreased body weight gain, thymic atrophy, liver enlargement, induction of hepatic cytochrome P450 1A1/2 (CYP1A1/2) and CYP2B1/2 activities, histopathological effects, and increased activities of aspartate aminotransferase and gamma-glutamyltransferase in plasma. These results show that PCB 156 can enhance the growth of altered foci in rat liver and probably act as a tumor promoter of hepatocarcinogenesis. Based on promotional activity a relative potency of PCB 156 to 2,3,7, 8-tetrachlorodibenzo-p-dioxin of 0.0001-0.001 is proposed.

The ability to alter the gap junction protein expression outside GST-P positive foci in liver of rats was associated to the tumour promotion potency of different polychlorinated biphenyls

The results demonstrate different modes of action by a dioxin-like polychlorinated biphenyl (PCB 126) and a non dioxin-like PCB (PCB 153) in the alteration of connexin (cx) 26 and cx 32 expression outside GST-P positive foci in liver of female Sprague-Dawley rats, treated according to an initiation-promotion protocol. A decreased relative amount of immunopositive cx 26 and cx 32 spots in the parenchymal cell plasma membranes was observed after treatment with the potent tumour promoters PCB 126 or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). No reduction of cx 26 or cx 32 was noted after administration with the weaker tumour promoters PCB 153 or PCB 118 (PCB 118; both dioxin- and non dioxin-like). Additionally, we found that the down-regulation of connexins also occurred in rats treated with PCB 126 or TCDD without partial hepatectomy and initiation with nitrosodiethylamine. In summary, the results indicate that the ability to reduce the gap junction protein level in liver of rats can be associated to the tumour promotive potency of the different PCB-congeners and TCDD.

Interaction of 3,4,5,3',4'-pentachlorobiphenyl and 2,4,5,2',4',5'-hexachlorobiphenyl in promotion of altered hepatic foci in rats

This study was undertaken to investigate tumour promoting interactions of 2,4,5,2',4',5'-hexachlorobiphenyl (PCB 153) and 3,4,5,3',4'-pentachlorobiphenyl (PCB 126) in female Sprague-Dawley rats. Five weeks before the promotion treatment, the rats were partially hepatectomized and initiated with nitrosodiethylamine. The test substances were administered by weekly, subcutaneous injections for 20 weeks. The results from this study suggest that treatment with a combination of these two congeners causes a more than additive effect on the formation of gamma-glutamyltranspeptidase-positive hepatic foci. Co-exposure to PCB 126 and PCB 153 caused a dose-dependent reduction of the PCB 153-induced CYP2B1/B2-activity in these livers.

Liver tumour promoting activity of 3,4,5,3',4'-pentachlorobiphenyl and its interaction with 2,3,7,8-tetrachlorodibenzo-p-dioxin

This study was undertaken to compare the tumour promoting effects induced by 3,4,5,3',4'-pentachlorobiphenyl (PCB 126) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). In addition, interactive effects in rats treated with combinations of PCB 126 and TCDD were studied. Partially hepatectomized female Sprague-Dawley rats were initiated with nitrosodiethylamin. After 5 weeks of recovery the promotion treatment started and continued for 20 weeks. The results from the present study demonstrate that PCB 126 elicit approximately 10% of TCDD's tumour promoting activity measured as enhancement of the development of gamma-glutamyl-transpeptidase-positive altered hepatic foci in the liver. The factor required for the PCB to match the response of TCDD was adopted as a toxic equivalency factor and was in this case 0.1, which is the same as the factor suggested by Ahlborg et al. (1994). In the groups treated with a mixture of PCB 126 and TCDD the tumour promoting effect indicated an additive response. This result suggests that PCB 126 and TCDD act by the same mechanistical pathway, which in turn, supports that the toxic equivalency factor-concept can be used for TCDD-like tumour promoters.

Induction of micronuclei by five pyrethroid insecticides in whole-blood and isolated human lymphocyte cultures

Five pyrethroid insecticides: cypermethrin, deltamethrin, fenpropathrin, fenvalerate and permethrin, were tested for their ability to induce micronuclei in both whole-blood (WB; three donors) and isolated human lymphocyte (IL, 2 donors) cultures, by using the cytokinesis-block method with 6 micrograms/ml cytochalasin B (Cyt-B). Fenvalerate and permethrin were tested with two different concentrations of Cyt-B (3 and 6 micrograms/ml). At the concentration ranges tested, all the five pyrethroids induced clear dose dependent cytotoxic effects, fenpropathrin being the most toxic. Nuclear division index (NDI) and the newly introduced index of cytotoxicity, the cytokinesis block proliferation index (CBPI), reflected the dose dependency more accurately than the percentage of binucleated cells did. CBPI is similar to NDI except that it estimates the average number of cell divisions that the cell population has gone through, and, therefore, classifies both trinucleate and tetranucleate cells into the same category. Cypermethrin and fenpropathrin slightly increased the number of MN and micronucleated cells in WB lymphocyte cultures from two out of the three donors. Deltamethrin produced a positive response only in WB cultures of one donor and in IL cultures of another donor. Permethrin gave mostly negative results, although it increased the MN frequency in WB cultures of one donor when 6 micrograms/ml Cyt-B was used. Fenvalerate did not significantly induce MN. With certain reservations to the purity and isomer composition of each pesticide, the existing information appears to support the idea that pyrethroid insecticides have a weak (cypermethrin, deltamethrin and fenpropathrin) or nule (fenvalerate and permethrin) genotoxic activity in vitro.

Cell culture assays for chemicals with tumor-promoting or tumor-inhibiting activity based on the modulation of intercellular communication

The ability of chemicals with tumor-promoting or tumor-inhibiting activity to modulate gap junctional intercellular communication is reviewed. The two most extensively used types of assays for screening tests are (1) metabolic cooperation assays involving exchange between cells of precursors of nucleic acid synthesis and (2) dye-transfer assays that measure exchange of fluorescent dye from loaded cells to adjacent cells. About 300 substances of different biological activities have been studied using various assays. For tumor promoters/epigenetic carcinogens, metabolic cooperation assays have a sensitivity of 62% and dye-transfer assays 60%. Thirty percent of DNA-reactive carcinogens also possess the ability to uncouple cells. The complete estimation of the predictive power of these assays could not be made because the majority of the substances studied for intercellular communication effects in vitro have not yet been studied for promoting activity in vivo. Both metabolic cooperation assays and dye transfer assays respond well to the following classes of substances: phorbol esters, organochlorine pesticides, polybrominated biphenyls, promoters for urinary bladder, some biological toxins, peroxisome proliferators, and some complex mixtures. Results of in vitro assays for such tumor promoters/nongenotoxic carcinogens, such as some bile acids, some peroxides, alkanes, some hormones, mineral dusts, ascorbic acid, okadaic acid, and benz(e)pyrene, do not correlate with the data of in vivo two-stage or complete carcinogenesis. Enhancement of intercellular communication was found for 18 chemicals. Among these, cAMP, retinoids, and carotenoids have demonstrated inhibition of carcinogenesis. We examine a number of factors that are important for routine screening, including the requirement for biotransformation for some agents to exert effects on gap junctions. We also discuss the mechanisms of tumor promoter and tumor inhibitor effects on gap junctional permeability, including influences of protein kinase activation, changes in proton and Ca2+ intracellular concentrations, and effects of oxy radical production.

Relative tumour promoting activity of three polychlorinated biphenyls in rat liver

The relative tumour promoting activity of three structurally and toxicologically diverse polychlorinated biphenyls (3,4,5,3',4'-penta- 2,3,4,3',4'-penta- and 2,4,5,2',4',5'-hexachlorobiphenyl) was measured in an initiation/promotion assay in nitrosodiethylamine-initiated female Sprague-Dawley rats. The congeners under study were administered by once-weekly subcutaneous injections for 20 weeks. Evaluation of the development of gamma-glutamyl transpeptidase (GGT)- and glutation transferase P (GST-P)-positive hepatic foci showed that all congeners promoted altered hepatic foci, although 3,4,5,3',4'-pentachlorobiphenyl was far more potent. The volume fraction of the liver occupied by GGT-positive tissue in the 3,4,5,3',4'-pentachlorobiphenyl-treated animals (100 micrograms/kg per week) was 23%, while the volume fractions of altered liver tissue in the rats treated with 2,3,4,3',4'-pentachlorobiphenyl (5000 micrograms/kg per week) and 2,4,5,2',4',5'-hexaCB (20,000 micrograms/kg per week) were 1.2 and 2.3, respectively. The enhancement of GGT- and GST-P-positive foci was accompanied by an increased incidence of histological changes in the livers.

Effects of pyrethroid insecticides on gap junctional intercellular communications in Balb/c3T3 cells by dye-transfer assay

The effects of fenvalerate, esfenvalerate, permethrin, cypermethrin, deltamethrin, p-chlorophenylisovaleric acid (CPIA, major metabolite of fenvalerate) and DDT, a liver tumor promoter, on gap junctional intercellular communication (GJIC) were examined in Balb/c3T3 cells by dye-transfer assay. Separate groups of Balb/c3T3 cells were exposed to the chemicals for 1 day. On the following day, GJIC was measured by counting the number of dye-transferring cells per injection of Lucifer Yellow under a fluorescent microscope. Fenvalerate, esfenvalerate, permethrin, cypermethrin, deltamethrin and DDT inhibited GJIC at noncytotoxic concentrations, while CPIA did not inhibit GJIC even at a cytotoxic concentration. It is concluded that the examined pyrethyroid insecticides, but not a metabolite, have inhibitory effects on GJIC in Balb/c3T3 cells.

Effects of fenvalerate and esfenvalerate on hepatic gap junctional intercellular communication in rats

Effects of in vivo exposure with fenvalerate, esfenvalerate and DDT on hepatic gap junctional intercellular communication (GJIC) in Sprague-Dawley (SD) rats were examined by in vivo/in vitro dye-transfer assay and by immunohistochemical staining of connexin 32 (Cx32, major liver gap junction protein). Fenvalerate (75 mg/kg/day), esfenvalerate (25 mg/kg/day), DDT (50 mg/kg/day) and corn oil (vehicle control, 5 ml/kg/day) were administered orally once a day. Animals were killed at weeks 1, 2, 4 and 6 after starting the experiment. In the fenvalerate- and esfenvalerate-groups, no compound-related changes in GJIC and Cx32 expression were observed. On the contrary, in the DDT-group, average sizes of the dye spread after injection of Lucifer Yellow decreased at weeks 1, 2 and 4, and the area per GJ spot shown by Cx32-immunohistochemical staining decreased at weeks 4 and 6. It is concluded that neither fenvalerate nor esfenvalerate inhibits hepatic GJIC with in vivo exposure.

Rat liver foci study on coexposure with 50 Hz magnetic fields and known carcinogens

A study was performed to investigate possible interactions by magnetic fields (MF) with the processes of initiation and promotion of chemically induced preneoplastic lesions in rat liver. Male Sprague-Dawley rats were subjected to a 70% partial hepatectomy followed after 24 h by i.p. injection of diethylnitrosamine (DENA) as a tumour initiator. Starting one week after the DENA-treatment phenobarbital (PB) was given to promote growth of enzymatically altered foci of liver cells. MF was applied immediately after the partial hepatectomy and continued until sacrifice after 12 weeks of PB exposure. Homogenous horizontal AC magnetic fields with a frequency of 50 Hz and flux densities of 0.5 mu T or 0.5 mT were used. The rats coexposed with MF and DENA plus PB did not gain weight as much as the rats exposed to the chemical agents only. The MF-exposure also resulted in a slight reduction in size and numbers of the focal lesions. The results suggest an interaction of MF with the processes of chemical carcinogenesis either as a result of stress or depending on effects on the proliferation of preneoplastic cells.

Relative liver tumour promoting activity and toxicity of some polychlorinated dibenzo-p-dioxin- and dibenzofuran-congeners in female Sprague-Dawley rats

The polychlorinated dibenzo-p-dioxins/dibenzofurans 1,2,3,7,8-pentachlorodibenzo-p-dioxin (PeCDD), 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and 2,3,4,7,8-pentachlorodibenzofuran (PeCDF) were studied for liver tumour promoting activity in a medium-term altered foci assay in nitrosamine-initiated female Sprague-Dawley rats. The congeners under study were administered by weekly subcutaneous injections at three dose levels for 20 weeks. Evaluation of gamma-glutamyltranspeptidase (GGT+), altered hepatic foci development, showed that all congeners studied acted as potent promoters of hepatocarcinogenesis. TCDD and PeCDD were virtually equipotent as enhancers of foci development while PeCDF displayed approximately ten per cent of the activity of the dioxins. Analysis of the dioxin- and furan-congeners by gas chromatography/mass spectroscopy (GC/MS) technique showed that the retention of PeCDD and PeCDF in liver tissue was approximately 7 and 20 times, respectively, as high as the retention of TCDD. Based on the concentration of the respective congener in liver tissue, PeCDD and PeCDF were 0.14 and 0.007 times as active as TCDD as promoters of foci development. The dose related enhancement of GGT+ foci development induced by the PCDD/PCDF congeners was accompanied by an increased incidence of histological changes in the liver.

Intercellular contacts in the media of the thoracic aorta of rat fetuses treated with beta-aminopropionitrile

Beta-aminopropionitrile (BAPN) alters the scleroproteins of the arterial media in a way which permits an increase in the stress (force/unit area) applied to smooth muscle cells at a given pressure. Pregnant Sprague-Dawley rats were treated with BAPN and the thoracic aortas of exposed fetuses were studied by electron microscopy and image analysis. Transmission electron microscopy of the media of the thoracic aorta revealed that the types of intercellular contacts seen in the controls and in the BAPN group were intermediate junctions (IJs), nexus junctions (NJs), simple appositions (SAs), and interdigitations (Ids) as in adult vessels. The BAPN-treated animals showed an increased density of IJs, SAs, and Ids when compared with controls but the NJs demonstrated no change. Load-sensitive intercellular contacts have been considered to be the major route by which stress is applied across cells, and the increased number in the BAPN group probably represents a response of the vessel wall to increased tangential tension.

Lack of enhancing effects of fenvalerate and esfenvalerate on induction of preneoplastic glutathione S-transferase placental form positive liver cell foci in rats

The modifying effects of fenvalerate and esfenvalerate administration on liver carcinogenesis were investigated in male F344/DuCrj rats initially treated with N-nitrosodiethylamine (DEN). Two weeks after a single dose of DEN (200 mg/kg, intraperitoneally), rats were given fenvalerate at dietary levels of 1500, 500, 150, 50 and 15 parts per million (ppm), esfenvalerate at 500 ppm, or 2-acetylamino-fluorene (2-AAF) at 200 ppm and sodium phenobarbital (PB) at 500 ppm as positive controls for 6 weeks. At week 3 following DEN administration, all animals were subjected to partial hepatectomy. Prominent neurologic signs and moderate retardation of body weight were observed in the groups given 1500 ppm fenvalerate and 500 ppm esfenvalerate, although no adverse effects on survival were evident. While statistically significant increases in relative liver weights were noted in rats given fenvalerate at doses of 1500 or 500 ppm, no toxic hepatocyte lesions were found. Neither fenvalerate nor esfenvalerate significantly increased the numbers or areas of glutathione S-transferase placental form (GST-P) positive liver cell foci observed after DEN initiation, in clear contrast to the positive controls, 2-AAF and PB. The results thus demonstrated that fenvalerate and esfenvalerate are non-toxic for rat hepatocytes and lack modifying potential for liver carcinogenesis in our medium-term bioassay system.

Carcinogenicity studies with deltamethrin in mice and rats

The pesticide Deltamethrin, a synthetic pyrethroid, was studied for carcinogenicity in long-term experiments in mice and rats. Mice were given Deltamethrin by gavage in arachis oil at 0, 1, 4 or 8 mg/kg body wt for 2 years. A group of untreated controls was also available. Rats received 0, 3 or 6 mg/kg body wt. Deltamethrin in arachis oil for 2 years. In mice, an increased incidence of lymphomas was observed in the groups receiving 1 and 4 mg/kg body wt., but not in the group treated with 8 mg/kg body wt. Deltamethrin. In rats, an increased incidence of thyroid tumours was noted, but, no clear dose-response relationship was shown. Deltamethrin does not appear to be carcinogenic in mice or rats, but further studies are needed on the group of compounds to which this substance belongs.

Carcinogenicity study of the pesticide fenvalerate in mice

Fenvalerate is a widely used pesticide, which has been shown recently to be nonmutagenic. We studied its carcinogenicity in a long-term experiment in inbred C57Bl/6 mice given 0, 40 and 80 mg/kg body weight fenvalerate (99% pure) by gavage on 5 days/week for 104 weeks. Survival was decreased especially among females receiving the high dose. Exposure to fenvalerate resulted in a slight increase in the incidence of liver-cell tumours over that in controls only in male mice receiving the high dose. No significant difference in the incidence of other types of tumours was observed in treated groups when compared with controls. Fenvalerate-induced microgranulomas occurred concomitantly in the liver, spleen and lymph nodes of male and female mice, but their overall incidence did not increase with dose. In a separate experiment, groups of SJL/ola female mice were administered two different samples of fenvalerate (92% and 99% pure) once per week for 12 weeks. In animals that received 92% pure compound, the latent period for induction of lymphomas was shortened and their incidence increased, when compared with the group receiving 99% pure fenvalerate and with controls.

Effects of tetradecanoyl phorbol acetate, pyrethroids and DDT in the V79

The effects of the pyrethroids flucythrinate, cyfluthrin, bioallethrin and resmethrin on metabolic cooperation between V79 cells were investigated. Addition of flucythrinate to cocultures of 6-thioguanine-resistant and 6-thioguanine-sensitive V79 cells significantly increased the mutant cell recovery, indicating inhibition of intercellular communication. No such effect was observed by the other pyrethroids tested. To compare the modes of action of TPA-, DDT-, and pyrethroid-induced inhibition of intercellular communication, co-exposure experiments were undertaken. Addition of TPA, together with increasing doses of fenvalerate or flucythrinate, produced a synergistic response. Various combinations of fenvalerate-, flucythrinate- and DDT-exposure gave results in accordance with an additive response. The result suggest different pathways of action for TPA and the insecticides investigated in this study.

Chlorobenzilate-induced effects on enzyme-altered foci in rat liver and intercellular communication in rat liver WB-F344 epithelial cells

The mouse liver carcinogen chlorobenzilate (CB), a DDT-related pesticide, was investigated for enhancement of enzyme altered foci incidence in partially hepatectomized, diethyl-nitrosamine-initiated rats. In this in vivo experiment, CB administered per os (25 or 100 mg/kg per day for 10 weeks) enhanced foci incidence at the high dose level. In order to study potential mechanisms involved, CB was investigated for inhibition of gap-junctional intercellular communication in rat liver epithelial WB-F344 cells and Chinese hamster V79 cells in vitro. CB abolished dye transfer in WB-F344 cells and inhibited metabolic cooperation in V79 cells. Two CB metabolites were unable to induce such tumor promotion related effects. The results of this investigation provide support for the involvement of an epigenetic, tumor promoting mechanism in CB-induced liver tumors in laboratory animals.

Tumour promotion related effects by the cyclodiene insecticide endosulfan studied in vitro and in vivo

The cyclodiene insecticide endosulfan is structurally related to the tumour promoting pesticides chlordane and heptachlor. Divergent conclusions have been reported regarding the carcinogenic activity of endosulfan. In this study we have investigated if endosulfan and four of its metabolites possess tumour promotion related effects. Two in vitro test systems detecting inhibition of intercellular communication were used; the Chinese hamster lung fibroblast (V79) metabolic cooperation assay and a scrape loading/dye transfer assay using rat liver WB epithelial cells. At non-cytotoxic concentrations, technical grade endosulfan, analytical grade endosulfan (alpha- and beta-isomers and an alpha beta-isomer mixture) and endosulfan-sulfate inhibited gap junctional communication in both assay systems. In addition, the metabolite endosulfan-ether was effective in the rat liver WB epithelial cells. Endosulfan was also studied for enhancement of gamma-glutamyl transpeptidase positive enzyme altered foci incidence in partially hepatectomized, nitrosodiethylamine-initiated male Sprague-Dawley rats. However, endosulfan administered orally (1 or 5 mg/kg/day) five days a week for ten weeks did not enhance enzyme altered foci incidence. These apparently contradictory results with regard to possible tumour promoting activity of endosulfan are discussed in relation to metabolism, systemic toxicity and tissue/species specificity in tumour promotion.