Polyhalogenated Hydrocarbons Research Articles

Biotransformation of short-chain chlorinated paraffins (SCCPs) with LinA2: A HCH and HBCD converting bacterial dehydrohalogenase

Short-chain chlorinated paraffins (SCCPs) are polyhalogenated hydrocarbons as are hexachlorocyclohexanes (HCHs) and hexabromocyclododecanes (HBCDs). They all have been classified as persistent organic pollutants (POPs) under the UN Stockholm Convention. Per se such compounds are transformed slowly in the environment, transported over long distances and accumulate in biota. Several Sphingomonadacea strains isolated from HCH dump sites have evolved to express enzymes that can transform HCHs and HBCDs. We hypothesized that LinA2, a dehydrohalogenase expressed in such bacteria, may also transform CPs to chlorinated olefins (COs). Three mixtures of penta- to deca-chlorinated undecanes (C11), dodecanes (C12) and tridecanes (C13) were exposed to LinA2. High-resolution full-scan mass spectra (R∼8′000) of CPs and COs were obtained applying a soft ionization method, enhancing chloride-adduct [M+Cl]- formation. A mathematical deconvolution procedure was used to separate interfering spectra to verify that LinA2 indeed catalyzed the conversion of CPs to COs. About 20–40% of the material was transformed in 24 h, about 50–70% was converted in 200 h. A bimodal first-order kinetic model could describe transformations of reactive and persistent CPs. Under the given conditions reactive CPs (τ1/2 = 1.4–6.9 h) were converted 30 to 190-times faster than the persistent ones (τ1/2 = 150–260 h). Proportions of persistent isomers (pp) varied from 60 to 80%. Lower chlorinated homologues contained higher proportions of persistent isomers. In conclusion, SCCP mixtures contain both, material that is readily converted by LinA2, and persistent material that is not or only slowly transformed.

Estimating the Physicochemical Properties of Polysubstituted Aromatic Compounds Using UPPER

The UPPER model (Unified Physicochemical Property Estimation Relationships) has been used to predict 9 essential physicochemical properties of pure compounds. It was developed almost 25 years ago and has been validated by the Yalkowsky group for almost 2000 aliphatic, aromatic, and polyhalogenated hydrocarbons. UPPER is based on a group of additive and nonadditive descriptors along with a series of well-accepted thermodynamic relationships. In this model, the 2-dimensional chemical structure is the only input needed. This work extends the applicability of UPPER to hydrogen bonding and non-hydrogen bonding aromatic compounds with several functional groups such as alcohol, aldehyde, ketone, carboxylic acid, carbonate, carbamate, amine, amide, nitrile as well as aceto, and nitro compounds. The total data set includes almost 3000 compounds. Aside from the enthalpies and entropies of melting and boiling, no training set is used for the calculation of the properties. The results show that UPPER enables a reasonable estimation of all the considered properties.

Synthesis and Supercapacitor Application of Alkynyl Carbon Materials Derived from CaC2 and Polyhalogenated Hydrocarbons by Interfacial Mechanochemical Reactions.

The discovery of new carbon materials and the reactive activation of CaC2 are challenging subjects. In this study, a series of alkynyl carbon materials (ACMs) were synthesized by the interfacial mechanochemical reaction of CaC2 with four typical polyhalogenated hydrocarbons. Their properties and structures were characterized, and their electrochemical performances were examined. The reaction was rapid and efficient arising from the intense mechanical activation of CaC2. The ACMs are micro-mesoporous materials with distinct layered structure, specific graphitization degree, and clear existence of sp-C. In addition, the ACMs exhibit high specific capacitance in the range of 57-133 F g-1 and thus can be ideal candidates for active materials used in supercapacitors. The results may imply an alternative synthesis of carbon allotropes, as well as an efficient approach for the activation of CaC2.

Learning about cognition risk with the radial-arm maze in the developmental neurotoxicology battery

Cognitive dysfunction has been found in epidemiological studies to be among the most sensitive impairments associated with developmental exposure to a variety of environmental contaminants from heavy metals to polyhalogenated hydrocarbons and pesticides. These chemicals have been also shown to impair cognitive function after developmental exposure in experimental animal models. The radial-arm maze (RAM) has proven to be a sensitive and reliable way to assess both learning and memory in a variety of species, most often in rats and mice. The RAM is a very adaptable test method that takes advantage of rodents' instinct to explore new places in the environment to forage. That is, rodents do not need to be trained to run through the maze; they will normally do this from the initial session of testing. Training with differential reinforcement for arm choices provides a more rigorous test of learning and memory. The RAM is quite adaptable for assessing various aspects of cognition. Although the RAM has been mostly used to assess spatial learning and memory, it can be configured to assess non-spatial memory as well. Both working and reference memory can be easily distinguished. The RAM can be run with both appetitive (food reinforced) and aversive (water escape) motivators. The RAM has been found to be sensitive to a wide variety of developmental toxicants including heavy metals such as mercury and pesticides such as chlorpyrifos. There is an extremely rich literature especially with rats showing the effects of many types of brain lesions and drug effects so that the participation of a wide variety of neural systems in RAM performance is known. These systems, notably the hippocampus and frontal cortex, and acetylcholine and glutamate neurotransmitter systems, are the same neural systems that have been shown in humans to be critical for learning and memory. This considerably aids the interpretation of neurobehavioral toxicity studies.

LinA2, a HCH-converting bacterial enzyme that dehydrohalogenates HBCDs

Hexabromocyclododecanes (HBCDs) and hexachlorocyclohexanes (HCHs) are lipophilic, polyhalogenated hydrocarbons with comparable stereochemistry. Bacterial evolution in HCH-contaminated soils resulted in the development of several Spingomonadaceae which express a series of HCH-converting enzymes. We showed that LinB, a haloalkane dehalogenase from Sphingobium indicum B90A, also transforms various HBCDs besides HCHs. Here we present evidence that LinA2, another dehalogenase from S. indicum also converts certain HBCDs to pentabromocyclododecenes (PBCDEs). Racemic mixtures of α-, β-, γ-HBCDs, a mixture of them, and δ-HBCD, a meso form, were exposed to LinA2. Substantial conversion of (−)β-HBCD was observed, but all other stereoisomers were not transformed significantly. The enantiomeric excess (EE) of β-HBCDs increased up to 60% in 32h, whereas EE values of α- and γ-HBCDs were not affected. Substrate conversion and product formation were described with second-order kinetic models. One major (P1β) and possibly two minor (P2β, P3β) metabolites were detected. Respective mass spectra showed the characteristic isotope pattern of PBCDEs, the HBr elimination products of HBCDs. Michaelis–Menten parameters KM=0.47±0.07μM and vmax=0.17±0.01μmoll−1h−1 were deduced from exposure data with varying enzyme/substrate ratios. LinA2 is more substrate specific than LinB, the latter converted all tested HBCDs, LinA2 only one. The widespread HCH pollution favored the selection and evolution of bacteria converting these compounds. We found that LinA2 and LinB, two of these HCH-converting enzymes expressed in S. indicum B90A, also dehalogenate HBCDs to lower brominated compounds, indicating that structural similarities of both classes of compounds are recognized at the level of substrate-protein interactions.

Polychlorinated Dibenzo-p-dioxins (PCDDs), Polychlorinated Dibenzofurans (PCDFs), and Polychlorinated Biphenyls (PCBs) in Olivaceous Cormorant (<i>Phalacrocorax brasilianus) </i>from Sepetiba Bay, Rio de Janeiro, Brazil

An expressive number of man-made chemicals have been introduced in the aquatic environment represent the major problems arising in the development worldwide. Many of these chemical contaminants are persistent polyhalogenated aromat ic hydrocarbons known to bioaccumu late and bio magnify as they move through the aquatic food web, effect ing spe- cies associated with aquatic systems. Concentrations of polychlorinated dibenzo-p-dio xins (PCDDs), polychlorinated dibenzofurans (PCDFs), and polychlorinated biphenyls (PCBs) were measured in Olivaceous Cormorant Phalacrocorax brasilianus collected fro m 2007 to 2011 on Sepetiba Bay, Rio de Janeiro, Brazil. Detectable hepatic concentrations of PCDD/Fs and PCBs were found in all samples analy zed. These data represent some of the first measurements of PCDD/ Fs and PCBs in seabirds from this area. While levels of these contaminants in the tested specie currently appear to fall belo w critical values, continued monitoring is warranted for these compounds, especially in this bay.

Biotransformation of Hexabromocyclododecanes (HBCDs) with LinB—An HCH-Converting Bacterial Enzyme

Hexabromocyclododecanes (HBCDs) and hexachlorocyclohexanes (HCHs) are polyhalogenated hydrocarbons with similar stereochemistry. Both classes of compounds are considered biologically persistent and bioaccumulating pollutants. In 2009, the major HCH stereoisomers came under regulation of the Stockholm convention. Despite their persistence, HCHs are susceptible to bacterial biotransformations. Here we show that LinB, an HCH-converting haloalkane dehalogenase from Sphingobium indicum B90A, is also able to transform HBCDs. Racemic mixtures of α-, β-, and γ-HBCDs were exposed to LinB under various conditions. All stereoisomers were converted, but (-)α-, (+)β-, and (+)γ-HBCDs were transformed faster by LinB than their enantiomers. The enantiomeric excess increased to 8 ± 4%, 27 ± 1%, and 20 ± 2% in 32 h comparable to values of 7.1%, 27.0%, and 22.9% as obtained from respective kinetic models. Initially formed pentabromocyclododecanols (PBCDOHs) were further transformed to tetrabromocyclododecadiols (TBCDDOHs). At least, seven mono- and five dihydroxylated products were distinguished by LC-MS so far. The widespread occurrence of HCHs has led to the evolution of bacterial degradation pathways for such compounds. It remains to be shown if LinB-catalyzed HBCD transformations in vitro can also be observed in vivo, for example, in contaminated soils or in other words if such HBCD biotransformations are important environmental processes.

Estimation of the ionization potential for polyhalogenated hydrocarbons by weakest bound potential method

The weakest bound potential method was proposed to estimate the ionization potential (IP) of polyhalogenated methanes, that is, the model IP = aχve + bPEIfi + c was developed, in which χve is molecular electronegativity calculated by valence electrons equilibration method, and polarizability effect index (PEI)fi is the influence of polarizability effect. The result indicates that the model is reasonable and effective to predict the IP for polyhalogenated methanes. Besides, the quantum chemistry method, the MOPAC AM1 method, and the density functional theory (B3LYP) method were employed to calculate the IP values of the same polyhalogenated methanes, and those results were less than that of the weakest bound potential method. Furthermore, the experimental values of 67 polyhalogenated hydrocarbons were correlated with the parameters χve and PEIfi. The regression results show a good correlation (R = 0.988), and the average absolute error between the experimental values and the calculated values is only 0.10 eV. Copyright © 2011 John Wiley & Sons, Ltd.

Human exposure to polyhalogenated hydrocarbons and incidence of selected malignancies – central European experience

This paper describes results of two ecological studies design to analyze the incidence of selected malignancies in two populations exposed to polychlorinated hydrocarbons, mostly PCBs and TCDDs/Fs by comparing data available in the National Cancer Registry of the Slovak Republic and National Oncological Registry of the Czech Republic databases for the Slovak Republic (approximately 5M inhabitants) and the Czech Republic (10,3 M inhabitants) to the data relevant for the population of Michalovce District, the Slovak Republic (approximately 112,000 inhabitants) and Uherske Hradiste, the Czech Republic (146,000 inhabitants). Those districts are recognized as PCB-contaminated areas due to production and industrial use of PCBs. Data were analyzed for the 10-year period 1987-1996. The age adjusted world standard ratio (WSR) incidence of thyroid, pancreatic, breast, ovarian, bladder, and brain tumors in females and thyroid, pancreatic, breast, bladder, brain, prostate and testicular tumors in males were compared. Neither PCBs nor TCDDs/Fs appear to contribute to the observed significantly lower incidence of breast and prostate cancer in the Michalovce District and lower bladder cancer incidence in Uherske Hradiste District. However, anti-estrogenic and anti-androgenic properties have been described for hydroxylated and methylsulfonyl PCB metabolites. These properties could contribute to a mechanism through which these metabolites might modulate the development of breast, prostate and bladder cancer. The results of our analysis points to substantial potential problems of risk assessment for cancer incidence in populations exposed to xenobiotics, or more generally, as it relates to a wide spectrum of confoundings of cancer risk factors.

Tissue-Specific Contaminant Accumulation and Associated Effects on Hepatic Serum Analytes and Cytochrome P450 Enzyme Activities in Hooded Seals (Cystophora cristata) from the Gulf of St. Lawrence

The current study aims to assess contaminant levels and tissue burdens in hooded seal (Cystophora cristata) blubber, liver, and blood in association with cytochrome P450 (CYP) enzymes (CYP1A and -3A) and serum analytes (hepatic enzymes like alanine aminotransferase [ALT], aspartate aminotransferase, alkaline phosphatase [AP], and gamma-glutamyltransferase [GGT], serum proteins, and creatine kinase). Contaminant accumulation levels and patterns of polychlorinated biphenyls, chlorinated pesticides, and polybrominated diphenyl ethers (PBDEs) differed between tissues and seal groups, with the highest levels in liver. Pups showed higher liver contaminant levels, especially for PBDEs, than adults. These high levels might be associated with the ingestion of large amounts of contaminated milk and subsequent accumulation in the liver. Adult males and females mainly differed in PBDE levels, which were higher in females, possibly due to a sex-specific diet. The association between blubber contaminant burdens and the diagnostic enzymes ALT, GGT, and AP, and serum albumin, was inconclusive. In contrast, several CYP isoenzymes showed a clear positive relationship with the overall blubber contaminant burden, indicating enzyme induction following exposure to polyhalogenated hydrocarbons. Therefore, liver CYP isoenzymes may serve as a sensitive biomarker for long-term exposure to polyhalogenated hydrocarbons.

Risk of Incidence of Selected Malignancies and Human Exposure to Polyhalogenated Hydrocarbons

ISEE-924 Objective: Findings regarding the carcinogenicity of polyhalogenated hydrocarbons are still inconclusive and even contradictory. We analyzed the incidence of selected malignancies in a population exposed to polychlorinated biphenyls (PCBs) by comparing data available in the Czech National Cancer Registry database for Czech Republic (∼10 million inhabitants), with data from the population of Uherské Hradišťe District (∼146,000 inhabitants). The District Uherské Hradišťe (UH) is recognized as the most heavily PCB-contaminated area in Czech Republic. Material and Methods: Cancer incidence data was analyzed for the 10-year period 1987–1996. The age adjusted world standard ratio (WSR), the over all (total) incidence of malignancies, and the incidence of thyroid, pancreatic, breast, ovarian, bladder, brain, prostate, and testicular tumors found in local populations were compared. Statistical significance was evaluated using two sample paired t-tests of the means in the STATISTICA 6.0 software. Results: The only statistically validated difference, between the UH District and the Czech Republic analyzed database, was a lower incidence of bladder malignancies both in men and women on the same level of significance (P < 0.01). This study does not confirm our previous experience from Eastern Slovakia. In a former study, which was respecting the same protocol in a population heavily exposed to PCBs, there was a lower incidence of breast (P < 0.01) and prostate malignancies (P < 0.03), in the local population (∼112,000 inhabitants), compared with the whole Slovakia (∼5 million inhabitants). Conclusions: Neither PCBs nor polychlorinated dibenzofurans (PCDFs) appear to contribute to the observed lower incidence of bladder cancer in men and women (P < 0.01) in the UH District. However, antiestrogenic and antiandrogenic properties have been described for hydroxylated and methylsulfonyl PCBs metabolites. Acknowledgement: This study is a continuation of the recently finished 5th FP PROJECT: Evaluating human health risk from low-dose and long-term PCB exposure QLK4-2000-00488 PCBRISK and currently supported by CASCADE NoE 6FP EC.

Perinatal TCDD exposure and the adult onset of autoimmune disease

Modulation of the developing immune system can occur following perinatal exposure to a number of immunotoxic compounds, including polyhalogenated hydrocarbons like 2,3,7,8-tetra-chlorodibenzo-p-dioxin (TCDD; dioxin), the most toxic of the congeners. Studies in rodents have shown immunologic effects from perinatal TCDD exposure are more severe and persistent than following exposure in the adult, and include what appears to be life-long immunosuppression. Whether prenatal TCDD exposure may predispose an individual to postnatal autoimmune disease remains largely unknown. TCDD crosses the placenta and alters normal prenatal thymocyte maturation, T-cell receptor expression and expression of thymic major histocompata-bility complex Class II molecules. During the juvenile stage, mice exposed to TCDD prenatally show increased peripheral T-cells possessing “autoreactive” variable-β receptors. These data suggest that gestational exposure to TCDD may interfere with normal development of central tolerance in the thymus. In possible support of this theory, when autoimmune disease-prone mice were treated with TCDD during gestation, postnatal autoimmunity had an accelerated onset and was exacerbated. This review provides an overview of the currently available information, which appears to support a hypothesis for increased risk of postnatal autoimmune responses as a result of TCDD exposure during the sensitive time of immune system establishment.

Identification of kaempferol as an inhibitor of cigarette smoke-induced activation of the aryl hydrocarbon receptor and cell transformation

The aryl hydrocarbon receptor (AHR) is a cytosolic receptor which upon activation by its agonists, translocates into the nucleus and forms a dimer with ARNT (aryl hydrocarbon nuclear translocator). The AHR/ARNT dimer regulates the expression of its target genes by binding to DNA recognition elements termed dioxin responsive elements (DREs). Many AHR agonists, like the polyaromatic hydrocarbons and polyhalogenated hydrocarbons are known human carcinogens. Human exposure to these compounds is common due to their presence in air pollution and cigarette smoke. Interestingly, many dietary constituents that have chemo preventative properties have been found to also act as antagonists of the AHR pathway. Thus, a chemopreventive approach that may be effective in decreasing the incidences of many human cancers may involve a dietary regimen that includes a number of these naturally occurring AHR antagonists. With this idea in mind, we have assayed the ability of 15 flavonoids to inhibit AHR activated reporter activity and selected kaempferol for further analysis. Kaempferol proved to be capable of inhibiting binding of agonist and agonist-induced formation of the AHR/ARNT DNA-binding complex and upregulation of the AHR target gene, CYP1A1. Using an in vitro paradigm of events that are thought to occur during cigarette-smoke-induced lung cancer, we found that kaempferol also inhibited the ability of cigarette smoke condensate to induce growth of immortalized lung epithelial (BEAS-2B) cells in soft agar. Taken together, these results illustrate the promise associated with the use of flavonoids, that inhibit both AHR signaling and the carcinogenic actions of AHR agonists, for chemopreventive purposes.

High plasma concentrations of polychlorinated biphenyls and phthalate esters in women with endometriosis: a prospective case control study

The objective of this study was to detect the probable association between polychlorinated biphenyls (PCBs) and phthalate esters (PEs), and the occurrence of endometriosis in a prospective case control study. We found that PCBs and PEs may be instrumental in the etiology of endometriosis.

HUMAN EXPOSURE TO POLYHALOGENATED HYDRO-CARBONS AND INCIDENCE OF SELECTED MALIGNANCIES

ISEE-158 Introduction: A population based cross sectional study (PCB Risk 5th FP) confirmed higher exposure of the local population of the Michalovce District, Eastern Slovakia region, to PCBs, due to the previous production of PCBs in a local chemical plant (1959 – 1983, 21 500 metric tons) (Koěan et al. 2001; Trnovec et al. 2004).Aim: Due to inconclusive and sometimes even contradictory findings concerning carcinogenicity of polyhalogenated hydrocarbons (Bencko 2003; Pavúk et al. 2004) we decided to analyze the incidence of selected malignancies in the exposed population, using data available in the Slovak National Cancer Registry database (established in 1975) for Slovakia (∼ 5 M inhabitants), in comparison with the population of Michalovce District (∼ 55 000 inhabitants). The Michalovce District is recognized as one of the world areas most heavily polluted with PCBs. The analyzed period represents 10year interval of 1987-1996. Methods: Age adjusted (world standard ratio – WSR) incidences of the following tumours were compared for the Michalovce District WSR and Slovakia data: thyroid, pancreas, breast, ovarium, bladder, and brain tumors (in females) and thyroid, pancreas, breast, bladder, brain, prostate and testes tumours (in males). Study base for Slovakia for the follow up period of 1987-1996 represents 50 M person-years and for Michalovce District ∼ 0.55 M person-years. For calculation of statistical significance, paired two sample t-test for means were used (STATISTICA 6.0 software). Results: PCBs or PCDFs do not appear to be likely causal agents for the observed lower incidence of breast and possibly prostate cancer in the Michalovce district. This, in spite of the higher PCB levels in this district. However, based on the anti-estrogenic properties described for hydroxylated and methylsulfonyl PCB metabolites, such a mechanism of action may be a feasible pathway for the observed lower incidence of breast tumours in the Michalovce district. Conclusion: Further studies on the occurrence of these metabolites in the blood of exposed populations could clarify a possible role for PCB metabolites as anti-estrogenic agents in humans. This study was supported by the 5th FP Project Evaluating Human Health Risk from Low-dose and Long-term PCB Exposure (PCBRISK) QLK4-2000-00488 and CASCADE NoE 6FP EC.

Metabolic activation of polycyclic aromatic hydrocarbons to carcinogens by cytochromes P450 1A1 and1B1

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitously distributed environmental chemicals. PAHs acquire carcinogenicity only after they have been activated by xenobiotic-metabolizing enzymes to highly reactive metabolites capable of attacking cellular DNA. Cytochrome P450 (CYP) enzymes are central to the metabolic activation of these PAHs to epoxide intermediates, which are converted with the aid of epoxide hydrolase to the ultimate carcinogens, diol-epoxides. Historically, CYP1A1 was believed to be the only enzyme that catalyzes activation of these procarcinogenic PAHs. However, recent studies have established that CYP1B1, a newly identified member of the CYP1 family, plays a very important role in the metabolic activation of PAHs. In CYP1B1 gene-knockout mice treated with 7,12-dimethylbenz[a]anthracene and dibenzo[a,l]pyrene, decreased rates of tumor formation were observed, when compared to wild-type mice. Significantly, gene expression of CYP1A1 and 1B1 is induced by PAHs and polyhalogenated hydrocarbons such as 2,3,7,8-tetrachlorodibenzo-p-dioxin through the arylhydrocarbon receptor. Differences in the susceptibility of individuals to the adverse action of PAHs may, in part, be due to differences in the levels of expression of CYP1A1 and 1B1 and to genetic variations in the CYP1A1 and 1B1 genes.

Nickel(0)/Imidazolium Chloride Catalyzed Reduction of Aryl Halides

Dehalogenation of aryl halides was efficiently performed in refluxing THF using a catalytic combination composed of Ni(0)/N-heterocyclic carbene (NHC)/β-hydrogen-containing alkoxide. IMes·HCl (1,3-bis(2,4,6-trimethylphenyl)imidazolium chloride) and Ni(acac)2 used respectively as carbene and Ni(0) precursors associated to in situ generated i-PrONa were found to be the most effective for the dehalogenation of functionalized aryl chlorides, bromides, iodides, and polyhalogenated hydrocarbons.

Reduced levels of 1,25-dihydroxyvitamin D(3) in rat dams and offspring after exposure to a reconstituted PCB mixture.

Previous studies revealed effects of polychlorinated biphenyls (PCBs) and other polyhalogenated hydrocarbons on steroid hormone levels and hormone-dependent functions including behavior. In the present study serum concentrations of the vitamin D(3) metabolites 25-hydroxycholecalciferol (25-D) and 1,25-dihydroxycholecalciferol (1,25-D) were determined in rat dams and offspring after exposure to a PCB mixture that was reconstituted according to the congener pattern found in human breast milk. Unmated females were exposed to diets adulterated with 0; 5; 20; or 40 mg PCBs/kg diet. Exposure started 50 days prior to mating and was terminated at birth. Gestational exposure reduced serum concentrations of 1,25-D in dams in a dose-dependent manner. Concentration of 25-D was also decreased at the time of delivery, but not at weaning. Determination of 1,25-D in offspring at weaning revealed reductions in both high-exposure groups. Levels of 25-D were diminished only at the highest exposure level. Internal PCB concentrations in adipose tissue and brains exhibited a linear relation to dosages in diet. Concentrations of PCBs in brains were similar in dams and offspring at birth, but decreased at the end of lactation in dams. In offspring, values increased during this period because of continued exposure via the milk. In the adipose tissue, PCB levels were much lower in offspring than in dams. To our knowledge, this is the first report of PCB-induced effects on vitamin D(3) metabolites. In dams, reductions were seen even at the lowest exposure level used. Further studies are needed to evaluate the biological significance of these reductions in pregnant dams and possible consequences for the developing offspring.

A cytochrome P4501B gene from a fish species

The cytochrome P4501A (CYP1A) gene products of vertebrates are the major catalysts of polyaromatic hydrocarbon (PAH) hydroxylation and are therefore critical determinants of the pathways leading to pollutant detoxification and excretion on the one hand, or DNA-adduct formation and carcinogenesis on the other. In addition, the levels of CYP1A transcripts and protein rise in response to PAH and polyhalogenated hydrocarbons and this phenomenon has led to the development of widely used biomonitoring tools to determine pollutant exposure in wild fish populations. Recently a second CYP1 family (CYP1B) of genes has been isolated from mammals and, in common with CYP1A genes, they are transcriptionally activated by PAH and their protein products metabolise PAH. Phylogenetic analyses of CYP1 family sequences show that the CYP1A and CYP1B genes diverged long before the evolutionary emergence of mammals, suggesting that CYP1B genes may exist in fish species. If this is true then there may be important implications, both for fish health and for biomonitoring programs. In order to test this hypothesis, a plaice ( Pleuronectes platessa) genomic DNA library was screened at low stringency with a plaice CYP1A6 cDNA. Amongst the resulting hybridising clones, a plaice CYP1B-related sequence was isolated. The structure, sequence and tissue expression profile of this sequence conclusively show it to be a plaice CYP1B gene.

Hearing loss following exposure during development to polychlorinated biphenyls: A cochlear site of action

Maternal exposure to polyhalogenated hydrocarbons results in early postnatal hypothyroxenemia and a low-frequency hearing loss in adult offspring (Goldey et al., 1995a. Toxicol. Appl. Pharmacol. 135, 67–76; Herr et al., 1996. Fundam. Appl. Toxicol. 33, 120–128). The purpose of the present work was to determine whether the site-of-action of this auditory impairment was within the cochlea. Primiparous Long–Evans rats were given daily oral doses of corn oil (control) or 8 mg/kg of the commercial PCB mixture Aroclor 1254 (A1254) from gestation day (GD) 6 through postnatal day (PND) 21. Auditory thresholds for 1-, 4-, 16-, and 40-kHz tones were assessed using reflex modification audiometry in young adult offspring on postnatal days (PND) 92–110. Approximately 6 weeks after auditory assessments, a subset of animals ( n=4 per group) were killed for histological assessment of the cochlea. Surface preparations of the organ of Corti were prepared from one cochlea per animal and modiolar sections were prepared from the opposite cochlea. Consistent with previous findings, auditory thresholds for 1-kHz tones were elevated by approximately 25 dB in the A1254-exposed animals. Thresholds for all higher frequencies were not different compared to controls. Surface preparations of the organ of Corti revealed a mild to moderate loss of outer hair cells in the upper-middle and apical turns. Inner hair cells were not affected. Modiolar sections failed to reveal alterations in any other cochlear structures. There was also no apparent loss of ganglion cells. These data clearly link the loss of low-frequency hearing caused by exposure during development to A1254 to a loss of outer hair cells in the organ of Corti. The mechanism that underlies this developmental ototoxicity remains to be determined. These data provide the first evidence of a structural deficit in the nervous system of adult animals exposed to PCBs during development.