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Effects of 2,4,5-trichlorophenoxyacetic acid, pentachlorophenol, methylprednisolone, and Freund's adjuvant on 2-hydroxyethylnitrosourea carcinogenesis in MRC-Wistar rats.

A link was proposed between human non-Hodgkin's lymphoma and exposure to 2,4,5-trichlorophenoxyacetic acid (245T) and pentachlorophenol (PCP). To test this view and the hypothesis that immune suppression or stimulation could affect B-cell lymphoma (BCL) induction, we administered chronically to MRC-Wistar (MRC-W) rats of both sexes 98% pure 245T (600 mg/kg diet), 86% pure PCP (500 mg/kg diet), methylprednisolone (20 mg/kg ip weekly), and Freund's adjuvant (0.5 ml im every 3-6 wk) for 40 wk, together with 75 mg 2-hydroxyethylnitrosourea (HENU)/l drinking water, a system known to induce B-cell lymphoma. The 245T was shown to contain only 1-4 micrograms/kg each of 2,3,7,8-tetrachlorodibenzodioxin (TCDD) and 2,3,7,8-tetrachlorodibenzofuran (TCDF), but the PCP contained 25 micrograms TCDD and 670 micrograms TCDF/kg. HENU given alone induced B-cell lymphoma and osteosarcoma as before, with higher incidences of both tumors in males than in females. The B-cell lymphoma diagnosis was confirmed by immunologic typing of cell-surface markers and by probes for gene rearrangements. Coadministration with HENU of three of the four test agents did not affect tumor incidence, but PCP acted synergistically with HENU to induce acute myelocytic leukemia. PCP given alone or with HENU induced a 40-67% incidence of liver cell adenomas in the female rats. These effects were probably not due to TCDD in the PCP. HENU induced acute myelocytic leukemia and lung tumors in Wistar rats and n-butylnitrosourea induced acute myelocytic leukemia in MRC-Wistar rats, indicating that B-cell lymphoma induction was specific to the HENU-MRC-Wistar rat model.

2,4,5-Trichlorophenoxyacetic Acid↗

Pentachlorophenol, an assessment of the occupational hazard.

Pentachlorophenol (PCP) is used primarily as a wood preservative. It can be absorbed into the body by all the routes of occupational exposure. It causes local irritation to the eyes and nose, as well as systemic effects that result from its ability to uncouple mitochondrial oxidative phosphorylation. Also, it is fetotoxic and teratogenic during early gestation. Commercial PCP is contaminated with chlorinated dioxins and dibenzofurans, tetrachlorophenols, and hydroxychlorodiphenyl ethers. Some of these impurities are capable of causing chloracne and chronic liver damage. Several areas in PCP's toxicological profile, such as carcinogenesis and mutagenesis, are incomplete. With regard to occupational exposures, precautions should be taken to avoid direct contact and air levels should be kept within acceptable levels.

Abnormalities, Drug-Induced↗

Permeation through five commercially available glove materials by two pentachlorophenol formulations.

Five glove materials were tested for permeation by two commonly used formulations of pentachlorophenol (PCP). Permeation was conducted using the method used in two prior studies by NIOSH. The lower limit of PCP quantitation in the receiving side of the permeation cell was 70 parts per billion (ppb). When challenged with a 4.3% PCP in diesel oil solution, both the Dayton Flexible Products Triflex (PVC) and the Best 64 NFW (natural rubber) gloves exhibited breakthrough times thirty seconds after exposure. The Playtex #835 (latex/neoprene) glove exhibited breakthrough after sixty minutes, but showed a five fold greater rate of permeation than the Dayton and the Best glove. Neither the Edmont Sol-Vex (nitrile rubber) nor the Granet Glo-Gluv (PVC) gloves had been permeated after testing for 8 and 16 hours respectively. Following challenge with a 4.2% sodium pentachlorophenate solution, only the Best (natural rubber) glove allowed breakthrough; this only thirty seconds after exposure. Neither the Dayton (5 hours), Playtex (7.5 hours), Edmont (15.5 hours), nor Granet (15.5 hours) gloves had been permeated following completion of testing after the listed duration. This study has shown that different gloves offer differing resistance to permeation by PCP based upon the composition of the glove and the PCP formulation tested.

Chlorophenols↗

Occupational exposure of electrical utility linemen to pentachlorophenol.

Occupational exposure to pentachlorophenol (PCP) for a crew of electrical utility linemen was monitored over a 6-month period by using total PCP in urine per gram of creatinine as a biological monitoring parameter. Urine samples were collected from three groups: A, B, and control, at a 4-week frequency during 1989. Group A was required to use new gloves after each 4-week work period; Group B changed gloves on a need basis as per normal operating procedure. The control group consisted of members of the administrative office staff who were not occupationally exposed. The used gloves returned by Group A were monitored for contamination. On the basis of analysis of the collected data the following conclusions were noted. (1) The linemen experienced a seasonal exposure pattern with exposures peaking in July and August. This seasonal effect was also observed with glove contamination data. (2) The glove contamination levels were significantly associated with urine PCP concentrations when both these variables were expressed as geometric means for the individuals in Group A. Inclusion of work experience as an additional variable enhances this association. Less experienced linemen tended to perform more activities with higher current exposure and had higher urine and glove PCP measurements and higher correlations between these variables than more experienced linemen. (3) Over the study period, the difference in long-term exposures of Group A and Group B linemen was not statistically significant. (4) The long-term individual exposures, calculated as the geometric mean of each individual's sequential sample readings, were all below the biological monitoring guideline value of 1000 micrograms PCP/g creatinine.

Creatinine↗

Assessment of the rhizosphere competency and pentachlorophenol-metabolizing activity of a pesticide-degrading strain of Trichoderma harzianum introduced into the root zone of corn seedlings.

To develop a dependable approach to introduce laboratory selected, pesticide-degrading microorganisms into soil environments for the purpose of in situ bioremediation, we tested the possibility of utilizing plant rhizospheres as the vehicle. We first established the rhizosphere competency of a strain of the soil fungus Trichoderma harzianum, a biocontrol species well studied by plant pathologists to colonize plant rhizosphere in many parts of the world. The strain we chose, T.h.2023 is resistant to many fungicides, and it has been shown to metabolize several pesticides. Second, we found that it readily metabolized pentachlorophenol (PCP), which is quickly and stochiometrically converted to pentachloroanisole (PCA) in liquid culture. Taking advantage of this specific feature, we have developed a sensitive metabolic marker approach that allowed us to monitor for the continuous presence and activity of this fungal strain in the corn rhizosphere soil in situ over time.

Biodegradation, Environmental↗

Temporal changes in the toxicity of pentachlorophenol to Chlorella pyrenidosa algae.

The toxicity of pentachlorophenol (PCP) on Chlorella pyrenidosa algae was investigated with specific attention given to possible variation of toxic effects with time. A concentration-effect relationship was observed in which there was significant inhibition of PCP on cell density and chlorophyll A content. The inhibition rate of PCP on cell density was dependent on exposure time. The IC50 values after exposure times of 2, 4 and 6 days for cell growth were 4.18 +/- 0.49, 3.49 +/- 0.40 and 3.30 +/- 0.26 mg/L, respectively. There was also inhibition of chlorophyll A production, which appeared to increase marginally with exposure time for a given concentration of PCP. The corresponding IC50 values on day 2, 4 and 6 were 2.30 +/- 0.12, 2.63 +/- 0.38 and 3.30 +/- 0.34 mg/L, respectively. The effect of PCP on nitrate reductase (NR), was first stimulation followed by an inhibition phase. It is postulated that the observed temporal changes in the activity of nitrate reductase (NR) may occur through the addition or loss of phosphorus in the NR protein.

Biomass↗

Photodegradation of pentachlorophenol by sunlight in aquatic surface microlayers.

Photodegradation of pentachlorophenol (PCP) in aquatic surface microlayer (SM) was examined under natural sunlight. SM samples were collected using a glass plate, along with corresponding subsurface waters. PCP was added to samples of the SM and subsurface water. When all samples were exposed to the same natural sunlight conditions, the first order photodegradation rates of PCP in the SM water samples were different from those of PCP in corresponding subsurface water samples. The difference was correlated with the enrichment of dissolved organic carbon (DOC) in SM compared to the corresponding subsurface waters. Enhanced photodegradation in SM may be due to increased abundance of photoreactants related to the UV-absorbing properties of dissolved organic materials in the SM as the result of photo-induced reactions. Effects of environmental factors, pH and salinity, on photodegradation process of PCP in SM were also evaluated.

Environmental Monitoring↗

Evidence from 32P-postlabeling and the use of pentachlorophenol for a novel metabolic activation pathway of diethylstilbestrol and its dimethyl ether in mouse live: likely alpha-hydroxylation of ethyl group(s) followed by sulfate conjugation.

Diethylstilbestrol (DES), a synthetic stilbene estrogen, is a potent development toxin and carcinogen in humans and rodents. A number of 32P-postlabeling studies suggest that genotoxic effects of DES substantially contribute to these biological effects. The mechanisms involved in DES-mediated genotoxicity are not completely understood, however. As reported here, the structural resemblance of tamoxifen to DES led to the hypothesis that DES may be hydroxylated and sulfated at the allylic C2 and/or C5 of the ethyl side chains in analogy to alpha-hydroxylation and sulfation of and DNA adduct formation by tamoxifen. Female ICR mice were administered 500 mumol/kg DES or its dimethyl ether derivative (DiMeDES), either alone or in combination with the sulfotransferase inhibitor pentachlorophenol (PCP) (75 mumol/kg), once daily for 4 days. Liver DNA adducts were measured 24 h after the last dose by dinucleotide/monophosphate 32P-postlabeling. Administration of DES or DiMeDES led to the formation of a unique and novel pattern of several major DNA adducts which were absent in vehicle controls. With minor exceptions the pattern was qualitatively similar for the two compounds, suggesting rapid O-demethylation of DiMeDES to DES in vivo followed by metabolic activation. Adducts formed in vivo did not chromatographically match DES quinone adducts synthesized in vitro. Co-administration of PCP with DES or DiMeDES significantly decreased adduct formation from either compound, by 33-61%. Taken together, these results are consistent with a hitherto unrecognized pathway of metabolic activation and DNA adduct formation by DES involving the putative hydroxylation of the allylic alpha-carbon of the ethyl side chain(s), followed by formation of DNA-reactive sulfuric acid esters. DES is now known to induce DNA damage in vivo by at least four different mechanisms. It is postulated that this multiplicity of mechanisms in itself explains why this drug elicits such a plethora of unique and complex pathophysiological effects in adults and off-spring of different species.

Animals↗

Pentachlorophenol (PCP) produces liver oxidative stress and promotes but does not initiate hepatocarcinogenesis in B6C3F1 mice.

To elucidate the mechanism of hepatocarcinogenesis of pentachlorophenol (PCP) in mice, critical effects related to carcinogenicity were studied in the livers of B6C3F1 male mice administered PCP at concentrations of 600 and 1200 p.p.m. in the diet for 8 weeks. Oxidative stress was assessed by measurements of 8-oxodeoxyguanosine (8-oxodG) in the liver nuclear DNA and hepatocyte cell proliferation was quantified by bromodeoxyuridine incorporation. Also, initiation and promotion were assessed in a two-stage hepatocarcinogenesis model in which one group of mice was given PCP at concentrations of 600 and 1200 p.p.m. as initiator for the first 13 weeks with subsequent administration of phenobarbital (PB) as promoter at a concentration of 500 p.p.m. in the drinking water for 29 weeks. A second group was initiated with diethylnitrosamine (DEN) at 20 p.p.m. in the drinking water for the first 13 weeks followed after a 4 week recovery interval by PCP at concentrations of 300 and 600 p.p.m. in the diet for 25 weeks. Significant elevations in 8-oxodG levels and cell proliferation were observed in a dose-dependent manner. Incidences and multiplicities of hepatocellular tumors in mice treated with PCP after DEN initiation were increased compared with those in mice given initiation only. In contrast, in mice given PCP as initiator followed by PB no enhancement of neoplastic lesions occurred. These findings are interpreted to demonstrate that PCP exerts a promoting action, but not an initiating effect on liver carcinogenesis and that the promoting action is related to oxidative stress and compensatory hepatocellular proliferation.

8-Hydroxy-2'-Deoxyguanosine↗

Prevention of the down-regulation of gap junctional intercellular communication by green tea in the liver of mice fed pentachlorophenol.

Much evidence has been documented supporting the hypothesis that the down-regulation of gap junctional intercellular communication (GJIC) is a cellular event underlying the tumor promotion process and that treatment to prevent the down-regulation or to up-regulate GJIC is important in preventing tumor promotion. We explored the potential preventive effects of green tea against the promoting action of pentachlorophenol (PCP) in mouse hepatocarcinogenesis, examining whether drinking green tea prevents the down-regulation of GJIC inhibition in the liver caused by tumorigenic doses of PCP. We used a modified in vivo GJIC assay, the incision loading/dye transfer method. Male B6C3F1 mice were given a green tea infusion for 1 week and then PCP was fed at a dose of 300 or 600 p.p.m. in the diet for the following 2 weeks, along with green tea treatment. A dose-related inhibition of GJIC in the hepatocytes was evident in the mice treated with PCP alone that was associated with a reduction in connexin32 (Cx32) plaques in the plasma membrane and an increase in the cell proliferation index. Drinking green tea significantly protected mice against GJIC inhibition, the reduction in Cx32 and the elevation of the labeling index. These findings suggest that green tea might act as an anti-promoter against PCP-induced mouse hepatocarcinogenesis via its ability to prevent down-regulation of GJIC.

Animals↗

Analysis of DNA adducts in rats exposed to pentachlorophenol.

Pentachlorophenol (PCP) is a widely used biocide that has been reported to be hepatocarcinogenic in mice. Its effects in rats are equivocal, but the liver clearly is not a target organ for carcinogenesis. The carcinogenic effects of PCP in mice may relate to reactive oxygen species generated during metabolism. PCP is known to increase the hydroxyl radical-derived DNA lesion, 8-oxodeoxyguanosine (ohdG), in the liver of exposed mice. To investigate whether the generation of oxidative DNA damage and direct DNA adducts may explain the species difference in carcinogenicity, we have analyzed ohdG in hepatic DNA from PCP-exposed rats. Rats were exposed acutely to PCP for 1 or 5 days. Tissues also were obtained from a 27 week interim sacrifice of the 2 year National Toxicology Program carcinogenesis bioassay. We used HPLC with electrochemical array detection for ohdG analysis. Single or 5 day exposure to PCP (up to 120 or 60 mg/kg/day, respectively) did not increase ohdG. Dietary exposure to 1000 p.p.m. PCP (equivalent to 60 mg/kg/day) for 27 weeks induced a 2-fold increase in ohdG (1.8 versus 0.91x10(-6) in controls). In parallel, formation of direct DNA adducts was analyzed by 32P-post-labeling following nuclease P1 adduct enrichment. We detected two major DNA adducts with relative adduct labeling of 0.78x10(7) adducts per total nucleotides. One of these adducts was found to co-migrate with the adduct induced by the metabolite, tetrachloro-1,4-benzoquinone. We observed differences in DNA adduct formation between acute and chronic studies, with acute studies not inducing any detectable amount of DNA adducts. These results indicated that chronic, but not acute exposure to PCP increased ohdG and direct adducts in hepatic DNA. As the same exposure conditions that enhanced ohdG did not produce liver cancer in rats, the generation of reactive oxygen species, oxidative DNA damage and direct DNA adducts is not sufficient for the induction of hepatocarcinogenesis by PCP in the rat.

8-Hydroxy-2'-Deoxyguanosine↗

Inhibition by pentachlorophenol of the initiating and promoting activities of 1'-hydroxysafrole for the formation of enzyme-altered foci and tumors in rat liver.

The hepatocarcinogen 1'-hydroxysafrole (HOS) exhibited weak initiating activity and strong promoting activity for the induction of enzyme-altered foci and tumors in rat liver. Thus, administration of a single dose of HOS to rats 18 h after a 70% hepatectomy, followed by administration of phenobarbital (PB) in the diet for 6 months, induced a low, but statistically significant, number of foci of enzyme-altered cells. This treatment did not result in gross liver tumors, even when the PB treatment was continued for 16 months. Large numbers of enzyme-altered foci developed when HOS was administered in the diet at levels of 0.05-0.25% to rats previously administered a single dose of N,N-diethylnitrosamine (DEN) 24 h after a 70% hepatectomy. Similarly, rats given a single dose of DEN 24 h after a partial hepatectomy and then fed 0.10 or 0.25% of HOS in the diet for 10 months developed a high incidence of hepatocellular carcinomas. In the absence of pretreatment with DEN, dietary administration for at least 4 months of 0.10 or 0.25% of HOS induced significant numbers of enzyme-altered foci; these data and liver tumor induction by continuous feeding of HOS, in the absence of pretreatment with DEN, provide additional evidence for an initiating, as well as a promoting, activity of HOS in rat liver. Concurrent administration of the hepatic sulfotransferase inhibitor pentachlorophenol with HOS in each of the above assays almost completely inhibited the initiating and promoting activities of HOS for the formation of enzyme-altered foci and tumors; these data strongly suggest that both the initiating and promoting activities are mediated by the sulfuric acid ester, 1'-sulfooxysafrole. HOS also exhibited initiating activity in adult mouse liver. Thus, dietary administration of 0.25% of HOS for only 1 month, followed by administration of the hepatic tumor promoter 1,4-bis[2-(3,5-dichloropyridyloxy)]benzene resulted in a high incidence and multiplicity of hepatomas by 10 months. In the absence of the promoter, administration of HOS for only 1 month induced no hepatomas; 1,4-bis[2-(3,5-dichloropyridyloxy)]benzene alone induced only a low incidence. In mice not given the promoter, continuous administration of HOS for 3-6 months was required for hepatoma development by 16 months.

Animals↗

Autoradiographic studies on in vivo covalent binding of N-hydroxy-2-acetylaminofluorene in rat liver containing gamma-glutamyltranspeptidase-positive foci. The effect of the sulfation-inhibitor pentachlorophenol.

The role of sulfation in the covalent binding of [ring-3H]-N-hydroxy-2-acetylaminofluorene (N-OH-AAF) in rat liver containing gamma-glutamyltranspeptidase-positive (GGT+) foci was studied in vivo by autoradiography. GGT+ foci were induced by initiation with diethylnitrosamine, followed by a selection protocol consisting of a 2-week exposure to 2-aminofluorene in the drinking water and a single administration of CCl4. Both surrounding ('normal') liver tissue and, to a lesser extent, GGT+ foci covalently bound N-OH-AAF, administered 10 days after selection. The sulfation inhibitor, pentachlorophenol (PCP), reduced the covalent binding of N-OH-AAF in cells surrounding the foci. However, PCP had no effect on binding of radiolabel in GGT+ foci. Thus, reduced sulfotransferase activity may contribute to the resistance of GGT+ preneoplastic lesions to carcinogen cytotoxicity. The results suggest also, that cells in GGT+ foci are able to bind N-OH-AAF covalently by a sulfotransferase-independent pathway.

2-Acetylaminofluorene↗

Prevention of dual promoting effects of pentachlorophenol, an environmental pollutant, on diethylnitrosamine-induced hepato- and cholangiocarcinogenesis in mice by green tea infusion.

In order to explore a possibility that the custom of drinking green tea infusion is efficacious for reducing the carcinogenic risk of environmental exposure to pentachlorophenol (PCP), we examined the effects in a hepato- and cholangiocarcinogenesis model in mice exposed to diethylnitrosamine (DEN). In the first experiment, groups of 15 male mice were initially treated with DEN at a dose of 20 p.p.m. in the drinking water for the first 8 weeks followed by a 4 week recovery interval by PCP at concentrations of 0 (basal diet), 300 or 600 p.p.m. in the diet for 23 weeks. Further groups of animals were treated with DEN and PCP in the same manner and received 2% green tea infusion (GT) instead of the drinking water from week 10 until death. PCP exposure at the high dose promoted DEN-induced hepatocarcinogenesis, and also caused progression of cystic hyperplasias of the intrahepatic bile ducts to cholangiocellular tumors. Co-administration of GT was able to prevent the increases of incidences and multiplicities of DEN-induced hepatocellular tumors and also arrest the progression of cholangiocellular tumors. In the second experiment, co-treatment with GT in the drinking water from 1 week before 300 or 600 p.p.m. PCP treatment in the diet to the end of the experiment at week 3 in B6C3F1 male mice suppressed increases of serum ALT activities, 8-oxodeoxyguanosine levels in liver DNA and bromodeoxyuridine labeling indices of hepatocytes and intrahepatic biliary epithelial cells induced by PCP. These findings suggest that regular intake of green tea may reduce the carcinogenic risk posed by an environmental pollutant, PCP, presumably due to effects on oxidative stress.

Animals↗

Determination of pentachlorophenol and 2,3,4,6-tetrachlorophenol in human urine by high resolution gas chromatography.

A method for the determination of pentachlorophenol, 2,3,4,6-tetrachlorophenol, and their salts or hydrolyzable biological conjugates in urine, water, serum, or fish tissue is reported. The method utilizes fused silica capillary gas chromatography (GC) with electron capture detection of the free phenols following hydrolysis and extraction into toluene. A recovery standard (4-chloro-2-nitrophenol) and an internal standard for GC (1-nitro-2,3,5,6-tetrachlorobenzene) are used to monitor recovery and GC performance. The detection limit for TCP and PCP is 0.5 ppb and the precision observed for each sample in the 1- to 100-ppb range is between 3 and 12% relative standard deviation for both components.

Chlorophenols↗

Normal values for pentachlorophenol in urine samples collected from a general population.

Aliquots of urine samples collected over a 24-h period from normal individuals were analyzed for pentachlorophenol (PCP). Urine samples were taken from subjects living in various regions (both rural and urban) throughout the province of Saskatchewan. Urinary PCP concentrations were determined with gas chromatography-mass spectrometry and stable isotope dilution. The normal PCP concentrations were found to range from 0.05 to 3.6 ng/mliters. Because the aliquots analyzed were taken from 24-h sample collections, the normal range of PCP excreted on a daily basis was determined. A total of 69 samples taken from 26 males and 43 females who ranged in age from 6 to 87 years were analyzed. The average amount of excreted PCP was determined to be 4.3 nmol/day.

Adolescent↗

Determination of phenol and pentachlorophenol in plasma and urine samples by gas liquid chromatography.

Gas chromatographic methods have been developed using a Supelco 1240-DA column for the determination of pentachlorophenol (PCP) in plasma and urine samples, and phenol in urine samples. These methods required no derivatization. Electron capture detection has been used for PCP determination, while flame ionization detection has been used to determine urinary phenol. The proposed phenol method avoids the use of perchloric acid, a safety hazard, as well as the formation of interfering compounds, which may be read as phenol if column resolution is inadequate.

Chlorophenols↗

Dose-specific production of chlorinated quinone and semiquinone adducts in rodent livers following administration of pentachlorophenol.

Production of chlorinated quinoid metabolites was investigated in the livers of Sprague-Dawley rats and B6C3F1 mice following single oral administration of pentachlorophenol (PCP) (0-40 mg/kg body weight) and in male Fischer 344 rats, following chronic ingestion of PCP at 1,000 ppm in the diet for 6 months (equivalent to 60 mg PCP/kg body weight/day). Analyses of the rates of adduction in the livers of Sprague-Dawley rats and B6C3F1 mice suggested that the production of tetrachloro-1,2-benzosemiquinone (Cl4-1,2-SQ) adducts was proportionally greater at low doses of PCP (less than 4-10 mg/kg body weight) and was 40-fold greater in rats than in mice. Production of tetrachloro-1,4-benzoquinone (Cl4-1,4-BQ) adducts, on the other hand, was proportionally greater at high doses of PCP [greater than 60-230 mg/kg body weight] and was 2- to 11-fold greater in mice than in rats over the entire range of dosages. A mathematical model employed these data to predict the rates of daily adduct production and steady state levels of PCP-derived quinone and semiquinone adducts in rats and mice. To evaluate predictions of the model, levels of PCP-derived adducts at steady state were investigated in the livers of male Fischer 344 rats chronically ingesting 60 mg PCP/kg body weight/day. Levels of total Cl4-1,4-BQ-derived adducts in liver cytosolic proteins (Cp) (22.0 nmol/g) and in liver nuclear proteins (Np) (3.07 nmol/g) were comparable to those of model predictions (15.0 and 3.02 nmol/g for Cp and Np, respectively). Overall, these results suggest that species differences in the metabolism of PCP to semiquinones and quinones were, in part, responsible for the production of liver tumors in mice but not rats in chronic bioassays.

Animals↗