Polyhalogenated Aromatic Compounds Research Articles

A fast gas chromatography coupled with electron capture negative ion mass spectrometry in selected ion monitoring mode screening method for short-chain and medium-chain chlorinated paraffins.

Chlorinated paraffins (CPs) are a group of anthropogenic pollutants that consist of complex mixtures of polychlorinated n-alkanes of different chain lengths (~C10 to C30 ). Persistence, bioaccumulation, toxicity, and long-range transport of short-chain chlorinated paraffins (SCCPs, C10 - to C13 -CPs) have prompted their classification as persistent organic pollutants (POPs) by the Stockholm Convention in 2017. Due to the varying chain lengths and chlorination degrees, quantification of SCCPs and medium-chain chlorinated paraffins (MCCPs, C14 - to C17 ) using gas chromatography coupled with electron capture negative ion mass spectrometry in selected ion monitoring mode (GC/ECNI-MS-SIM) is not only challenging but also very time consuming. In particular, up to eight GC runs per sample are required for the comprehensive GC/ECNI-MS-SIM quantification of SCCPs and MCCPs. These efforts are high especially if the samples do not contain CPs above the limit of detection (LOD), subsequently. We developed a semi-quantitative and sensitive method for the examination of SCCPs and MCCPs in one GC run. This GC/ECNI-MS-SIM screening method was based on the recording of Cl- (m/z 35 and 37), Cl2 - (m/z 70 and 72), and HCl2 - (m/z 71 and 73) isotope ions and evaluation of the ratios between them. Correctness of the results of the screening method was verified by analysis of edible oils with and without CPs, CP standards, as well as a technical CP mixture. Polychlorinated biphenyls (PCBs) and other polyhalogenated aromatic compounds, as well as brominated flame retardants, do not form all of the fragment ions analyzed by the screening method. After the screening, only CP-positive samples may need to be measured in detail. Measurement time will already be gained in the case of ~10% samples without CPs.

Synthesis of Graphene-like Films by Electrochemical Reduction of Polyhalogenated Aromatic Compounds and their Electrochemical Capacitor Applications.

Graphene is a promising two-dimensional nanomaterial for many applications due to its exciting properties. In the past decade, a variety of techniques-each with its own set of advantages and disadvantages-have been developed to prepare graphene, and there are ongoing efforts to improve these techniques and to reveal new approaches. Here, we describe a simple and low-cost process for the bottom-up synthesis of graphene-like films. This new methodology involves a two-step procedure: (i) formation of polyaromatic ring structures by the repeated covalent coupling of aryl radicals generated from electrochemical reduction of polyhalogenated aromatic compounds in aprotic solvent, and (ii) production of carbon networks by heating of polyaromatic surface films. Accordingly, polymeric films were prepared on the electrodes by electrochemical reduction of polyhalogenated compounds such as hexafluorobenzene (HFB), hexachlorobenzene (HCB), and hexabromobenzene (HBB), and then polymer films were annealed at 400 °C for 30 min. The structure and surface characteristics of electrodeposited carbon films under self- and thermal-annealing conditions were studied by spectroscopic and morphological techniques. Also, the capacitance performance of the films was evaluated by means of cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy. Results indicate that graphene-like carbon films can be achieved by use of the electrochemical approach under mild conditions without expensive equipment, and also that these carbon materials are very promising for low-cost energy-storage devices.

The Unexpected and Exceptionally Facile Chemical Modification of the Phenolic Hydroxyl Group of Tyrosine by Polyhalogenated Quinones under Physiological Conditions.

The phenolic hydroxyl group of tyrosine residue plays a crucial role in the structure and function of many proteins. However, little study has been reported about its modification by chemical agents under physiological conditions. In this study, we found, unexpectedly, that the phenolic hydroxyl group of tyrosine can be rapidly and efficiently modified by tetrafluoro-1,4-benzoquinone and other polyhalogenated quinones, which are the major genotoxic and carcinogenic quinoid metabolites of polyhalogenated aromatic compounds. The modification was found to be mainly due to the formation of a variety of fluoroquinone-O-tyrosine conjugates and their hydroxylated derivatives via nucleophilic substitution pathway. Analogous modifications were observed for tyrosine-containing peptides. Further studies showed that the blockade of the reactive phenolic hydroxyl group of tyrosine in the substrate peptide, even by very low concentration of tetrafluoro-1,4-benzoquinone, can prevent the kinase catalyzed tyrosine phosphorylation. This is the first report showing the exceptionally facile chemical modification of the phenolic hydroxyl group of tyrosine by polyhalogenated quinones under normal physiological conditions, which may have potential biological and toxicological implications.

Low-Temperature Growth of Large-Area Heteroatom-Doped Graphene Film

Large-area heteroatom-doped graphene films are greatly attractive materials for various applications, such as electronics, fuel cells, and supercapacitors. Currently, these graphene films are prepared by the high-temperature chemical vapor deposition method, which produces a low doping level in N-doped graphene (NG) and fails in the synthesis of large-area S-doped graphene (SG) film. Here, we report a low-temperature method toward the synthesis of large-area heavily heteroatom-doped graphene on copper foils via a free radical reaction using polyhalogenated aromatic compounds. This low-temperature method allows the synthesis of single-layer NG film with a high nitrogen content, and the production of large-area SG film for the first time. Both doped graphenes show enhanced electrical properties in field effect transistors as well as high-performance electrocatalysts for fuel cells.

Studies on the preference of multiple coupling in the introduction of thiophene ring into poly-halogenated aromatic compounds with nickel NHC catalyst

Several thiophene derivatives can be deprotonated by the combination of ethyl magnesium chloride (EtMgCl) and a catalytic amount of 2,2,6,6-tetramethylpiperidine (TMP-H). The metalated 3-hexylthiophene reacts with 2,3- and 2,5-dibromothiophenes in the presence of a nickel catalyst bearing NHC ligand (IPr) to afford the di-coupled product exclusively along with recovery of dibromothiophene albeit the equimolar reaction. The 1:1 reaction of 3-hexylthiophene with dibrominated benzene derivatives also gives di-coupled product as a sole product.

Structural identification by differential mass spectrometry as a criterion for selecting the best quantum chemical calculation of formation enthalpy for tetrachlorinated biphenyls

The assignment of correct structures for isomers with similar mass spectra (e.g. polyhalogenated aromatic compounds) is not always successful when spectral libraries alone are employed or, even worse, when the compounds are not present in commercial spectral libraries. We present a computational method based on differential mass spectrometry (Diff-MS) for the validation of formation enthalpy (Δ(f)H) series calculated using quantum chemistry for the fragments produced in electron ionization (EI)-MS. The method simulates the chemical structure identification (CSI) of isomers with similar mass spectra using differential mass spectra and Δ(f)H series. The best Δ(f)H values were those from which the correct structures could be derived. We have used six tetrachlorinated biphenyl isomers (TeCBs 44, 46, 52, 66, 74, 77). Their EI mass spectra were acquired at 70 eV and, for the principal ions, five series of Δ(f) H values were computed by the semi-empirical methods, AM1, MINDO3, MNDO, PM3, and RM1. The generation of differential mass spectra and the correlation with the Δ(f)H series for the calculation of probabilities from the list of structural assignments were carried out with the ordering algorithm (ORD) of the CSI-Diff-MS Data Analysis 3.1.1 program. Intelligent software, used for structural elucidation based on MS and QCC, was employed to select the best values of the formation enthalpies of TeCBs. The advantages and disadvantages of the semi-empirical methods for the calculation of Δ(f)H values for different TeCB ions are critically presented. The best semi-empirical methods were RM1, AM1 and MINDO3, which can be used to calculate the Δ(f)H database necessary to identify TeCB isomers. This approach allowed the correct assignment of structures for isomers with very similar mass spectra and demonstrated the reliability of the correlation between differential mass spectra and the formation enthalpies of the fragment ions.

A Novel Mechanism for Metal-independent Hydroxyl Radical Production by Hydrogen Peroxide and Halogenated Quinones

The hydroxyl radical ((center dot)OH) has been considered to be one of the most reactive oxygen species that are produced in biological systems. Frequently, (center dot)OH formation is ascribed to the transition metal-catalyzed Fenton reaction. During the study of the molecular mechanism for the genotoxicity of the wood preservative pentachlorophenol (PCP), we found that (center dot)OH could be produced by H(2)O(2) and PCP metabolite tetrachloro-1,4-benzoquinone (TCBQ) independent of transition metal ions. Further studies showed that TCBQ, but not its corresponding semiquinone radical, is essential for (center dot)OH production. Metal-independent production of (center dot)OH could also be observed with other halogenated quinones and H(2)O(2). Based on these data, we propose that (center dot)OH production by TCBQ and H(2)O(2) is not through a semiquinone-dependent organic Fenton reaction, but rather through a novel nucleophilic substitution and homolytical decomposition mechanism. This represents a novel mechanism for (center dot)OH production not requiring the catalysis of redox-active transition metal ions, and may partly explain the potential carcinogenicity of the widely used biocides such as PCP and other polyhalogenated aromatic compounds.

Potential Mechanism for Pentachlorophenol-Induced Carcinogenicity: A Novel Mechanism for Metal-Independent Production of Hydroxyl Radicals

The hydroxyl radical ((*)OH) has been considered to be one of the most reactive oxygen species produced in biological systems. It has been shown that (*)OH can cause DNA, protein, and lipid oxidation. One of the most widely accepted mechanisms for (*)OH production is through the transition metal-catalyzed Fenton reaction. Pentachlorophenol (PCP) was one of the most widely used biocides, primarily for wood preservation. PCP is now ubiquitously present in our environment and even found in people who are not occupationally exposed to it. PCP has been listed as a priority pollutant by the U.S. Environmental Protection Agency (EPA) and classified as a group 2B environmental carcinogen by the International Association for Research on Cancer (IARC). The genotoxicity of PCP has been attributed to its two major quinoid metabolites: tetrachlorohydroquinone and tetrachloro-1,4-benzoquinone (TCBQ). Although the redox cycling of PCP quinoid metabolites to generate reactive oxygen species is believed to play an important role, the exact molecular mechanism underlying PCP genotoxicity is not clear. Using the salicylate hydroxylation assay and electron spin resonance (ESR) secondary spin-trapping methods, we found that (*)OH can be produced by TCBQ and H(2)O(2) independent of transition metal ions. Further studies showed that TCBQ, but not its corresponding semiquinone radical, the tetrachlorosemiquinone radical (TCSQ(*)), is essential for (*)OH production. The major reaction product between TCBQ and H(2)O(2) was identified to be trichloro-hydroxy-1,4-benzoquinone (TrCBQ-OH), and H(2)O(2) was found to be the source and origin of the oxygen atom inserted into this reaction product. On the basis of these data, we propose that (*)OH production by TCBQ and H(2)O(2) is not through a semiquinone-dependent organic Fenton reaction but rather through the following novel mechanism: a nucleophilic attack of H(2)O(2) to TCBQ, leading to the formation of an unstable trichloro-hydroperoxyl-1,4-benzoquinone (TrCBQ-OOH) intermediate, which decomposes homolytically to produce (*)OH. These findings represent a novel mechanism of (*)OH formation not requiring the involvement of redox-active transition metal ions and may partly explain the potential carcinogenicity of the widely used biocides such as PCP and other polyhalogenated aromatic compounds.

Possible mechanisms of thyroid hormone disruption in mice by BDE 47, a major polybrominated diphenyl ether congener

Polybrominated diphenyl ethers (PBDEs) are a class of polyhalogenated aromatic compounds commercially used as fire retardants in consumer products. These compounds have been shown to decrease thyroid hormone concentrations in rodents after acute exposures. This study examines the ability of 2,2′,4,4′-tetrabromodiphenyl ether (BDE 47) to decrease circulating thyroid hormone concentrations and pairs this with BDE 47-induced effects on genes involved in thyroid hormone homeostasis. Female C57BL/6 mice (9 weeks old) were orally administered 3, 10, or 100 mg/kg/day of BDE 47 for 4 days. Animals were euthanized 24 h after the final dose (day 5) and liver, kidney, and serum were collected for analysis. BDE 47 caused a significant 43% decrease at 100 mg/kg/day in serum total thyroxine (T 4) concentrations. There was no increase in hepatic T 4-glucuronidation activity, but significant increases in hepatic Ugt1a1, Ugt1a7, and Ugt2b5 mRNA expression accompany significant decreases in T 4 concentrations at 100 mg/kg/day of BDE 47. Induction of PROD activity occurred at the lowest dose (3 mg/kg/day). Cyp2b10 mRNA expression also increased significantly at 10 and 100 mg/kg/day. These key findings show that BDE activates the nuclear receptor, CAR. Decreases in Mdr1a mRNA expression also occurred at the lowest dose administered (3 mg/kg/day BDE 47). BDE 47 exposure also decreased hepatic transthyretin and monocarboxylate transporter 8 (Mct8) mRNA expression, suggesting that while induction of UGTs may be partly responsible for T 4 decreases, other mechanisms are also involved. No effects were seen in the kidney. We conclude that changes in hepatic UGTs and transporters may be involved in decreases in circulating T 4 following BDE 47 exposure.

Vapour pressures, aqueous solubilities, Henry’s Law constants, and octanol/water partition coefficients of a series of mixed halogenated dimethyl bipyrroles

Basic physical–chemical properties of five bromine and chlorine containing mixed halogenated dimethyl bipyrroles (HDBPs) were determined using established methods. Subcooled liquid vapour pressures ( P L , 25 o ) , aqueous solubilities ( S w,25), and octanol/water partition coefficients ( K ow) were determined using the gas chromatography-retention time, generator column, and slow-stirring methods, respectively. Henry’s Law constants ( H 25) were estimated using experimentally-derived P L o and S w,25 data. Values of all four properties were generally similar to those reported for other polyhalogenated aromatic compounds [ P L , 25 o = ( 7.55 – 191 ) × 10 - 6 Pa; S w,25 = (1.0–1.9) × 10 −5 g/l; log K ow=6.4–6.7; H 25 = 0.0020–0.14 Pa m 3/mol]. The effect of replacing a chlorine with a bromine atom significantly decreased P L , 25 o ( log P L , 25 o = - 0.4197 (# bromine atoms) − 2.643, p < 0.01) and H 25 (log H 25 = −0.508 (# bromine atoms) + 0.394, p < 0.02). There were no significant effects of bromine/chlorine substitution on S w,25 or K ow. A simple Level I equilibrium partitioning model predicted the environmental behaviour of HDBPs to be similar to a tetrabrominated diphenyl ether. Only slight differences in behaviour amongst HDBP congeners were predicted since substitution of a bromine for a chlorine (Cl/Br substitution) atom had less effect than H/Cl or H/Br substitution on P L , 25 o , S w,25, H 25, and K ow.

Evaluation of the Benchmark Dose Method for Dichotomous Data: Model Dependence and Model Selection

The benchmark dose (BMD) method was evaluated using the USEPA BMD software. Dose–response data on cleft palate and hydronephrosis for a number of related polyhalogenated aromatic compounds were obtained from the literature. According to χ 2 test statistics, each dichotomous USEPA model failed to adequately describe only 1 of 12 cleft palate data sets. For hydronephrosis, the models were discriminated to a higher extent according to global goodness-of-fit. NOAELs for cleft palate corresponded to BMDLs (the approximate lower confidence limit on the BMD) for extra risks in the range of 5% or below. Model dependence of the BMDL estimate was more pronounced at lower levels of benchmark response (BMR). A BMR of 5% (extra risk) is recommended for cleft palate since model differences at this level were limited for all data. In addition, at BMRs of 5–10% the BMDL for all models was little affected by the specified confidence limit size (in the 90–99% range). For BMDL determination a conservative model selection approach was applied. At the suggested level of BMR (5%) this procedure resulted in use of the same model (multistage model) for the cleft palate endpoint in general. Akaike's information criterion (AIC) was considered for comparison between models. Determination of appropriateness of use of such methods in dose–response applications requires further analysis.

Role of small differences in CYP1A2 in the development of uroporphyria produced by iron and 5-aminolevulinate in C57BL/6 and SWR strains of mice

Previous work has implicated CYP1A2 in experimental uroporphyria caused by polyhalogenated aromatic compounds, and in uroporphyria caused by iron and 5-aminolevulinate (ALA) in the absence of inducers of CYP1A2. Here we examined whether the different susceptibilities of SWR and C57BL/6 strains of mice to uroporphyria in the absence of inducers of CYP1A2 are related to different levels of CYP1A2. Enzymological assays (ethoxy- and methoxyresorufin dealkylases, and uroporphyrinogen oxidation) and immunoblots indicated that there was about twice the amount of hepatic CYP1A2 in SWR mice compared with C57BL/6 mice. Immunohistochemistry revealed that CYP1A2 was located centrilobularly in the liver, and the staining was more intense in SWR mice than in C57BL/6 mice. Hepatic non-heme iron was about double in SWR compared with C57BL/6 mice. In SWR mice given iron dextran, hepatic iron was 1.7-fold that of C57BL/6 mice given iron dextran. SWR mice administered ALA in the drinking water accumulated much less hepatic protoporphyrin than did C57BL/6 mice. To confirm the importance of small increases in CYP1A2, C57BL/6 mice were given a low dose of 3-methylcholanthrene (MC) (15 mg/kg), as well as iron and ALA. There was about a 5- to 6-fold increase in hepatic uroporphyrin accumulation after 32 days on ALA compared with animals not given MC. In these animals, CYP1A2 was increased by 10-fold at 2 days, but returned to basal levels by 14 days. We conclude that small and transient differences in CYP1A2 may be important in the development of uroporphyria.

Monooxygenase activities in carp as biochemical markers of pollution by polycyclic and polyhalogenated aromatic hydrocarbons: choice of substrates and effects of temperature, gender and capture stress

Cytochrome P450-dependent monooxygenase activities (7-ethoxyresorufin, 7-pentoxyresorufin and 7-ethoxycoumarin O-dealkylases and aminopyrine N-demethylase) were measured in hepatopancreatic microsomes of carp collected in one control and one polychlorinated biphenyl- and polycyclic aromatic hydrocarbon-polluted ponds in the Czech Republic. The magnitudes of responses of monooxygenase activities to the exposure to polycyclic and polyhalogenated aromatic compounds (PAC), namely polycyclic aromatic hydrocarbons and polychlorinated biphenyls, and effects of other factors including ambient temperature and stress associated with reduction of water volume at capture were assessed. An increase of the level of 7-ethoxyresorufin O-deethylase (EROD) i.e. the specific monooxygenase activity mediated by the cytochrome P4501A (CYP1A) isoenzymes, was the most sensitive biochemical marker of environmental pollution and exposure to PAC. Carp hepatic 7-pentoxyresorufin O-depentylase (PROD) was unsuitable as a specific indicator of elevation of cytochrome P4502B-like isoenzymes (and thus as a biomarker of presence of CYP2B-type of inducers e.g. organochlorine pesticides) due to a probable inducibility by CYP1A inducers. PROD, unlike aminopyrine N-demethylase, another mammalian CYP2B-dependent activity which was not increased by exposure to PAC, was strongly inhibited by CYP1A inhibitors, α-naphthoflavone and 9-hydroxyellipticine. The respective dose-response curves were related to the EROD inhibition. Chloramphenicol, an inhibitor of CYP2B enzymes. inhibited both activities only weakly or not at all. Adaptation of carp to lower ambient temperatures and to the stress associated with reduction of water volume and subsequent capture by netting proved to highly significantly inhibit levels of EROD and PROD activities. Summer appeared to be the most suitable season for the biochemical monitoring of contamination. Activity of 7-ethoxycoumarin O-deethylase (ECOD) was also markedly induced by PAC, but the enzyme was less responsive than the EROD activity. The ECOD activity was not significantly influenced by ambient temperature or by stress associated with capture and removal of fish. This probably reflected a modulation of partly different CYP enzymes other than EROD. Unlike in ECOD, the results confirmed the high specificity and sensitivity of induction of CYP1A-dependent EROD activity in carp (PAC in environmental exposure levels affected EROD highly significantly).

Subchronic effects of 2,3,7,8-TCDD or PCBs on thyroid hormone metabolism: use in risk assessment

Effects of 2,3,7,8-tetrachlorodibenzo- p -dioxin (TCDD), 3,3′,4,4′,5-pentachlorobiphenyl (PCB 126), 2,3,3′,4,4′,5-hexachlorobiphenyl (PCB 156) on thyroid hormone metabolism were studied in 13-week feeding studies in female Sprague-Dawley rats. The diets were supplemented with the compounds tested at concentrations ranging from 0.2 to 20 μg/kg diet for TCDD, 7 to 180 μg/kg diet for PCB 126, or 12 mg/kg diet for PCB 156, respectively. Significant correlations were found for all three compounds between reductions in plasma total thyroxine (TT 4 ) levels and inductions of the microsomal phase II enzyme UDP-glucuronosyltransferase by using T 4 as a substrate (T 4 UGT). Furthermore, the coinduction of certain phase I and II isozymes, i.c., cytochrome P450 1A1 (CYP1A1) and UGT1A1, by these compounds, clearly suggests the involvement of an Ah receptor-mediated mechanism in the disturbance of thyroid hormone metabolism by these polyhalogenated aromatic compounds. These results provide a mechanistic base for the use of certain effects on thyroid hormone metabolism by polyhalogenated aromatic compounds in risk assessment. By using these effects, potencies of PCB 126 and PCB 156 relative to TCDD ranged from 0.008 to 0.1 for PCB 126, and from 0.00007 to 0.004 for PCB 156, respectively. These values correspond very well with relative potencies of PCB 126 and PCB 156 by using some other well-known Ah receptor-mediated toxic and biochemical parameters.

Subchronic effects of 2,3,7,8-TCDD or PCBs on thyroid hormone metabolism: use in risk assessment

Effects of 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD), 3,3′,4,4′,5-pentachlorobiphenyl (PCB 126), 2,3,3′,4,4′,5-hexachlorobiphenyl (PCB 156) on thyroid hormone metabolism were studied in 13-week feeding studies in female Sprague-Dawley rats. The diets were supplemented with the compounds tested at concentrations ranging from 0.2 to 20 μg/kg diet for TCDD, 7 to 180 μg/kg diet for PCB 126, or 12 mg/kg diet for PCB 156, respectively. Significant correlations were found for all three compounds between reductions in plasma total thyroxine (TT 4) levels and inductions of the microsomal phase II enzyme UDP-glucuronosyltransferase by using T 4 as a substrate (T 4UGT). Furthermore, the coinduction of certain phase I and II isozymes, i.c., cytochrome P450 1A1 (CYP1A1) and UGT1A1, by these compounds, clearly suggests the involvement of an Ah receptor-mediated mechanism in the disturbance of thyroid hormone metabolism by these polyhalogenated aromatic compounds. These results provide a mechanistic base for the use of certain effects on thyroid hormone metabolism by polyhalogenated aromatic compounds in risk assessment. By using these effects, potencies of PCB 126 and PCB 156 relative to TCDD ranged from 0.008 to 0.1 for PCB 126, and from 0.00007 to 0.004 for PCB 156, respectively. These values correspond very well with relative potencies of PCB 126 and PCB 156 by using some other well-known Ah receptor-mediated toxic and biochemical parameters.

Analysis of sewage sludge for polyhalogenated dibenzo-p-dioxins, dibenzofurans, and diphenylethers

The content of polybrominated and mixed polyhalogenated dibenzo-p-dioxins (PBDD and PXDD) and dibenzofurans (PBDF and PXDF) as well as of other polyhalogenated aromatic compounds in a series of samples of sewage sludges from municipal waste water treatment plants in the Federal Republic of Germany has been investigated. The analytical procedure developed for the determination of PCDD and PCDF in our laboratory was extended to the determination of PXDD and PXDF in this matrix. In all samples PCDD, PCDF, PCB, chlorobenzenes and octachlorothianthrene could be detected. Mono- to pentabrominated dibenzofurans (PBDF) and, compared with PBDF, relatively high levels of tri- to heptabrominated diphenylethers (PBDPE) were detected. Polybrominated dibenzo-p-dioxins, mixed polyhalogenated PXDD and PXDF, though present in automobile exhaust, and mixed polyhalogenated diphenylethers were not found in the sewage sludge samples. The fact that only Mono- to PentaBDF but relatively high concentrations of PBDPE were found in the samples, strongly suggests that the main source of PBDF in sewage sludge are brominated flame retardants.

Uroporphyrin accumulation in cultured chick embryo hepatocytes: Comparison of 2,3,7,8-tetrachlorodibenzo- p-dioxin and 3,4,3′,4′-tetrachlorobiphenyl

Uroporphyrin (URO) accumulation caused by 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD) and 3,4,3′,4′-tetrachlorobiphenyl (TCB) in cultured chick embryo hepatocytes was found to depend on the concentration of the added polyhalogenated aromatic compound, and on either the addition of 5-aminolevulinic acid or the induction of 5-aminolevulinic acid synthase. TCDD alone did not cause more than a slight increase in uroporphyrin, whereas TCB alone caused considerable uroporphyrin accumulation associated with increased 5-aminolevulinic acid synthase activity. However, in the presence of exogenous 5-aminolevulinic acid, TCDD was more potent than TCB in causing uroporphyrin accumulation. The concentrations of TCDD or TCB which maximally induced ethoxyresorufin deethylase activity, an indicator of induced cytochrome P450 activity, were lower than those required for maximal uroporphyrin accumulation. Furthermore, ethoxyresorufin deethylase activity was found to decline at concentrations of TCDD or TCB which caused maximum uroporphyrin accumulation. Pretreatment with 3-methylcholanthrene enhanced uroporphyrin accumulation, whereas addition of inhibitors of cytochrome P450 decreased uroporphyrin accumulation. Uroporphyrin accumulation occurred without a decrease in uroporphyrinogen decarboxylase activity, and was unrelated to the degree of conversion of the polyhalogenated aromatic compounds to water-soluble metabolites. Our results indicate that URO accumulation caused by TCDD and TCB requires two separate actions; (1) induction of cytochrome P450 which occurs at low concentrations of the halogenated chemicals, and (2) increased uroporphyrinogen oxidation which is catalyzed by the induced cytochrome P450 and which occurs at higher concentrations of the halogenated chemicals.

Effects of polyhalogenated aromatic compounds on porphyrin metabolism.

Heme production is a vital metabolic process that occurs in the bone marrow and liver. Porphyrins are unused by-products of this biosynthetic process and normally occur in urine and other body fluids in low concentrations. Various disorders can disrupt the heme biosynthetic process, causing greater quantities of porphyrins in urine. The porphyrias are a group of diseases characterized by excessive porphyrins and other precursors in urine. Porphyrias may be either hereditary or acquired through exposure to certain drugs or chemicals. Porphyria cutanea tarda (PCT) is the disease associated with exposure to polyhalogenated aromatic compounds. The urinary porphyrin pattern is of great value in diagnosing PCT and defining the etiology of the disease. As this liver disease from chemical damage develops, the urinary pattern progressively changes. With the development of a rapid and sensitive high-performance liquid chromatography analysis, urinary porphyrin patterns can be easily monitored. All free porphyrin acids can be quantitatively analyzed in less than 15 min. In our studies of groups exposed to porphyrinogenic chemicals, we have not observed clear differences in the urinary porphyrin patterns of cases when compared with carefully selected controls. In animal studies, however, PCT was clearly associated with polybrominated biphenyl exposure. Future evaluation of the utility of urinary porphyrin patterns as a diagnostic tool will require a cohort that has received a recent, well-documented exposure and a comparable control population. Assay of erythrocyte uroporphyrinogen decarboxylase activity will also be needed to define the form of the PCT.

Effects of Polyhalogenated Aromatic Compounds on Porphyrin Metabolism

Heme production is a vital metabolic process that occurs in the bone marrow and liver. Porphyrins are unused by-products of this biosynthetic process and normally occur in urine and other body fluids in low concentrations. Various disorders can disrupt the heme biosynthetic process, causing greater quantities of porphyrins in urine. The porphyrias are a group of diseases characterized by excessive porphyrins and other precursors in urine. Porphyrias may be either hereditary or acquired through exposure to certain drugs or chemicals. Porphyria cutanea tarda (PCT) is the disease associated with exposure to polyhalogenated aromatic compounds. The urinary porphyrin pattern is of great value in diagnosing PCT and defining the etiology of the disease. As this liver disease from chemical damage develops, the urinary pattern progressively changes. With the development of a rapid and sensitive high-performance liquid chromatography analysis, urinary porphyrin patterns can be easily monitored. All free porphyrin acids can be quantitatively analyzed in less than 15 min. In our studies of groups exposed to porphyrinogenic chemicals, we have not observed clear differences in the urinary porphyrin patterns of cases when compared with carefully selected controls. In animal studies, however, PCT was clearly associated with polybrominated biphenyl exposure. Future evaluation of the utility of urinary porphyrin patterns as a diagnostic tool will require a cohort that has received a recent, well-documented exposure and a comparable control population. Assay of erythrocyte uroporphyrinogen decarboxylase activity will also be needed to define the form of the PCT.

Kinetic parameters of L-[ 125I]triiodothyronine degradation in rats pretreated with polyhalogenated biphenyls

These studies were designed to elucidate the effects on thyroid function and thyroid-hormone activity of the long-term administration of low doses of four polyhalogenated aromatic compounds. The compounds studied were the polychlorinated biphenyls (PCBs) Aroclor 1254 and Aroclor 1242, and the polybrominated biphenyls (PBBs) hexabromobiphenyl and octabromobiphenyl. Groups of eight female Sprague-Dawley rats, specified pathogen free, were fed a diet containing 50 ppm of one of the polyhalogenated biphenyls or control diet for 7 months. Significant effects on serum triiodothyronine (T 3) were observed in the group given Aroclor 1254. Analysis of kinetic data revealed a decrease in T 3 degradation rate and an increase of biological half-life after long-term exposure to Aroclor 1254. The T 3 distribution space was increased in both groups treated with PCB, suggesting that PCB intoxication may open additional fluid pools to T 3, possibly because of cell damage. Analysis of values for the same parameters for rats treated with PBBs showed less marked effects. The results of this study indicate that PCBs exert a direct effect on the thyroid gland and that the rate of synthesis of T 3 may be reduced, and suggest that the mechanism of thyroid-hormone synthesis may be impaired.