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PubMed2006

Transformation of pyrene in aqueous chlorination in the presence and absence of bromide ion: kinetics, products, and their aryl hydrocarbon receptor-mediated activities.

To assess the endocrine-disrupting activity stemming from the presence of pyrene in drinking water, the kinetics of chlorination of pyrene was investigated at room temperature, the products of its aqueous chlorination with and without bromide ion were identified, and their aryl hydrocarbon receptor (AhR)-mediated activities were determined. It was found that the presence of bromide ion greatly promoted the reaction rate of chlorination of pyrene accompanied with the formation of brominated products. While the main product was 1-Cl-pyrene without the addition of bromide ion, di-Br-pyrene and 1-Br-pyrene became the main products in the presence of bromide ion. GC-MS and NMR analysis identified three structures of dibromopyrene in chlorination with the addition of bromide ion as 1,3-di-Br-pyrene, 1,6-di-Br-pyrene, and 1,8-di-Br-pyrene, and their molar ratio was determined to be approximately 0.3:1:1. Finally, 1-Br-pyrene, 1,3-di-Br-pyrene, a mixture of 1,6-di-Br-pyrene and 1,8-di-Br-pyrene (di-Br-pyrene), 1-Cl-pyrene, and a mixture of 1,6-di-Cl-pyrene and 1,8-di-Cl-pyrene (di-Cl-pyrene) were fractionated by HPLC, and their AhR-mediated activities were assessed by a yeast assay. It was found that the effective molar concentrations (or mass concentration) showing half-maximal transcriptional response, EC50, for pyrene, 1-Br-pyrene, 1-Cl-pyrene, di-Cl-pyrene, and di-Br-pyrene were 5632 (1.14), 3089 (0.86), 1942 (0.46), 597.2 (0.21), and 147.3 (0.04) nM (mg/L), respectively.

Bromides↗
PubMed1984

Importance of the route of administration for genetic differences in benzo[a]pyrene-induced in utero toxicity and teratogenicity.

C57BL/6N (Ahb/Ahb) mice have a high-affinity Ah receptor in tissues, whereas AKR/J and DBA/2N (Ahd/Ahd) mice have a poor-affinity Ah receptor. The cytochrome P1-450 induction response (enhanced benzo[a]pyrene metabolism) occurs much more readily in Ahb/Ahb and Ahb/Ahd than in Ahd/Ahd mice, at any given dose of the inducer benzo[a]pyrene. Embryos from the AKR/J X (C57BL/6N)(AKR/J)F1 and the reciprocal backcross were studied during benzo[a]pyrene feeding of the pregnant females. Oral benzo[a]pyrene (120 mg/kg/day) given to pregnant Ahd/Ahd mice between gestational day 2 and 10 produces more intrauterine toxicity and malformations in Ahd/Ahd than Ahb/Ahd embryos. This striking allelic difference is not seen in pregnant Ahb/Ahd mice receiving oral benzo[a]pyrene. Pharmacokinetics studies with [3H]benzo[a]pyrene in the diet and high-performance liquid chromatographic analysis of benzo[a]pyrene metabolism in vitro by the maternal intestine, liver, and ovary and the embryos of control and oral benzo[a]pyrene-treated pregnant females are consistent with "first-pass elimination" kinetics and differences in benzo[a]pyrene metabolism by the embryos and/or placentas versus maternal tissues. In the pregnant Ahd/Ahd mouse receiving oral benzo[a]pyrene, little induction of benzo[a]pyrene metabolism occurs in her intestine and liver; this leads to much larger amounts of benzo[a]pyrene reaching her embryos, and genetic differences in toxicity and teratogenesis are manifest. In the pregnant Ahb/Ahd mouse receiving oral benzo[a]pyrene, benzo[a]pyrene metabolism is greatly enhanced in her intestine and liver; this leads to less benzo[a]pyrene reaching her embryos, much less intrauterine toxicity and malformations, and no genetic differences are manifest. More toxic metabolites (especially benzo[a]pyrene 1,6- and 3,6-quinones) are shown to occur in Ahd/Ahd embryos than in Ahb/Ahd embryos. In additional studies, no prenatal or neonatal "imprinting" effect in C57BL/6N mice by 2,3,7,8-tetrachlorodibenzo-p-dioxin or Aroclor 1254 on benzo[a]pyrene metabolism later in life was detectable. These genetic differences in intrauterine toxicity and teratogenicity induced by oral benzo[a]pyrene are just opposite those induced by intraperitoneal benzo[a]pyrene [Shum et al., '79; Hoshino et al., '81). The data in the present report emphasize the importance of the route of administration when the teratogen induces its own metabolism.

Abnormalities, Drug-Induced↗
PubMed1983

Systemic excretion of benzo(a)pyrene in the control and microsomally induced rat: the influence of plasma lipoproteins and albumin as carrier molecules.

In vitro studies have previously indicated that benzo(a)pyrene distributes primarily into the plasma lipoprotein fraction when incubated with whole plasma. Hydroxylated metabolites of benzo(a)pyrene distribute increasingly into the albumin fraction as the degree of metabolite hydroxylation increases. This report assesses the influence of plasma lipoproteins and albumin as carriers for benzo(a)pyrene on carcinogen excretion in the control and microsomally induced rat. Male Sprague-Dawley rats cannulated in the bile duct received i.v. injections of radiolabeled benzo(a)pyrene noncovalently bound to the very-low-density, low-density, or high-density lipoproteins in equimolar amounts. Bile was collected and measured for radioactivity. Cumulative biliary excretions of benzo(a)pyrene complexed with rat lipoproteins were 39.6 +/- 9.7 (S.D.), 24.6 +/- 1.3, and 21.2 +/- 8.8% for very low-density, low-density, and high-density lipoprotein, respectively. Values for excretion of benzo(a)pyrene complexed with rat or human lipoproteins were comparable. These data suggest that the transport molecule can effect a 2-fold difference in benzo(a)pyrene excretion under conditions of the present study. We infer that metabolism of the plasma lipoprotein molecules determines, in part, the extent of benzo(a)pyrene excretion. Cumulative biliary excretions of albumin-bound benzo(a)pyrene, 3-hydroxybenzo(a)pyrene, benzo(a)pyrene 7,8-dihydrodiol, and benzo(a)pyrene-4,5-epoxide were 28.0 +/- 2.7, 39.8 +/- 0.5, 46.9 +/- 2.5, and 49.8 +/- 1.2%, respectively. Thus, excretion increased as the degree of benzo(a)pyrene hydroxylation increased. The effect of microsomal enzyme induction on excretion of lipoprotein-bound benzo(a)pyrene was also assessed. Contrary to expectation, excretion of benzo(a)pyrene bound to the very-low-density, low-density, or high-density lipoproteins in Aroclor-induced rats was not greater than that of control animals. Hence, under the conditions of the present study, 60 to 80% of the injected benzo(a)pyrene and 50 to 60% of the injected benzo(a)pyrene metabolites were not excreted immediately in control or microsomally induced animals. This benzo(a)pyrene may represent a carcinogen pool that is slowly excreted.

Animals↗
PubMed2001

Intestinal bioavailability and biotransformation of 3-hydroxybenzo(a)pyrene in an isolated perfused preparation from channel catfish, Ictalurus punctatus.

The intestinal bioavailability and biotransformation of 3-hydroxybenzo(a)pyrene, a major metabolite of benzo(a)pyrene in many animal species, was investigated in an in situ isolated intestinal preparation from the channel catfish, and in vitro with preparations of catfish intestine and blood. 3-Hydroxybenzo(a)pyrene was a good substrate for adenosine 3'-phosphate 5'-phosphosulfate (PAPS)-sulfotransferase and UDP-glucuronosyltransferase in cytosol or microsomes prepared from intestinal mucosa. The benzo(a)pyrene-3-glucuronide and 3-sulfate conjugates were only very slowly hydrolyzed by intestinal beta-glucuronidase and sulfatase. The K(m) values for PAPS-sulfotransferase and UDP-glucuronosyltransferase were 0.4 and 1 microM, respectively, and V(max) were 1.61 +/- 1.08 nmol benzo(a)pyrene-3-sulfate/min/mg of cytosolic protein and 1.08 +/- 0.54 nmol benzo(a)pyrene-3-glucuronide/min/mg of microsomal protein. Hydrolytic enzyme activities were three orders of magnitude slower. In the in situ intestinal preparation, [(3)H]3-hydroxybenzo(a)pyrene was readily metabolized to the glucuronide and sulfate conjugates. After 1 h of incubation of 2 or 20 microM [(3)H]3-hydroxybenzo(a)pyrene in the in situ preparation, the luminal contents contained 3-hydroxybenzo(a)pyrene, benzo(a)pyrene-3,6-dione, benzo(a)pyrene-3-sulfate, and benzo(a)pyrene-3-glucuronide. Mucosal samples contained these components, as well as some unextractable material. The blood contained mainly benzo(a)pyrene-3-sulfate and an as yet unidentified metabolite of 3-hydroxybenzo(a)pyrene bound to hemoglobin. Some, but not all, blood samples contained small amounts of 3-hydroxybenzo(a)pyrene, benzo(a)pyrene-3-glucuronide, and benzo(a)pyrene-3,6-dione. These studies demonstrate the rapid phase 2 conjugation of a phenolic benzo(a)pyrene metabolite in intestinal mucosa, and the transfer of the phase 2 sulfate and glucuronide conjugates to blood.

Animals↗
PubMed1975

Kinetic analysis of the metabolism of benzo(a)pyrene to phenols, dihydrodiols, and quinones by high-pressure chromatography compared to analysis by aryl hydrocarbon hydroxylase assay, and the effect of enzyme induction.

High-pressure liquid chromatography was used to analyze the rate of benzo(a)pyrene metabolite formation by liver microsomes from control and 3-methylcholanthrene-treated rats. The relative amounts of each metabolite formed were determined with several concentrations of microsomal mixed-function oxidases. The specific activity, i.e., amount formed per mg protein per min, was found to be constant for the formation of 3-hydroxybenzo(a)pyrene and 4,5-dihydro-4,5-dihydroxybenzo(a)pyrene. The specific activity for the formation of 9,10-dihydro-9,10-dihydroxybenzo(a)pyrene was higher at high microsomal enzyme concentration. The formation of 9-hydroxybenzo(a)pyrene, however, did not increase with greater amounts of microsomes. The data indicate that 9-hydroxybenzo(a)pyrene is a nonenzymatic product derived from a reactive intermediate, probably benzo(a)pyrene-9,10-oxide. The relatively constant specific activity for the formation of 4,5-dihydro-4,5-dihydroxybenzo(a)pyrene with several enzyme concentrations suggests that the K-region epoxide, benzo(a)pyrene-4,5-oxide, is the most stable of the benzo(a)pyrene epoxide intermediates. The relative percentages of each metabolite fraction found are as follows: 3-hydroxybenzo(a)pyrene, 36; 9-hydroxybenzo(a)pyrene, 3 to 13; 9,10-dihydro-9,10-dihydroxybenzo(a)pyrene, 15 to 25; 4,5-dihydro-4,5-dihydroxybenzo(a)pyrene, 8; 7,8-dihydro-7,8-dihydroxybenzo(a)pyrene, 12 to 14; benzo(a)pyrene quinones, 14 to 17. Induction of the enzyme system by 3-methylcholanthrene increases the amount of each metabolite formed to a different extent. The amount of 9,10-dihydro-9,10-dihydroxy- and 7,8-dihydro-7,8-dihydroxybenzo(a)pyrene formed are markedly increased relative to the increase in the other metabolites. Thus the induction of the enzyme may specifically alter pathways of metabolism relevant to carcinogenesis. This study also makes a detailed comparison between the results obtained by high-pressure liquid chromatography analysis and the standard aryl hydrocarbon hydroxylase assay and further develops the chromatographic analysis of benzo(a)pyrene metabolites.

Animals↗
PubMed2005

Effects of temperature and soil components on emissions from pyrolysis of pyrene-contaminated soil.

Effects of temperature and soil on yields and identities of light gases (H2, CH4, C2H2, C2H4, C2H6, CO, and CO2) and polycyclic aromatic hydrocarbons (PAH) from thermal treatment of a pyrene-contaminated (5 wt%) soil in the absence of oxygen were determined for a U.S. EPA synthetic soil matrix prepared to proxy U.S. Superfund soils. Shallow piles (140-170 mg) of contaminated soil particles and as controls, neat (non-contaminated) soil (140-160 mg), neat pyrene (10-15 mg), neat sand (230 mg), and pyrene-contaminated sand (160 mg), were heated in a ceramic boat inside a 1.65 cm i.d. pyrex tube at temperatures from 500 to 1100 degrees C under an axial flow of helium. Volatile products spent 0.2-0.4s at temperature before cooling. Light gases, PAH and a dichloromethane extract of the residue in the ceramic boat, were analyzed by gas chromatography or high pressure liquid chromatography (HPLC). Over 99% pyrene removal was observed when heating for a few tens of seconds in all investigated cases, i.e., at 500, 650, 750, 1000, and 1100 degrees C for soil, and 750 and 1000 degrees C for sand. However, each of these experiments gave significant yields (0.2-16 wt% of the initial pyrene) of other PAH, e.g., cyclopenta[cd]pyrene (CPP), which mutates bacterial cells and human cells in vitro. Heating pyrene-polluted soil gave pyrene conversions and yields of acetylene, CPP, and other PAH exceeding those predicted from similar, but separate heating of neat soil and neat pyrene. Up to 750 degrees C, recovered pyrene, other PAH, and light gases accounted for all or most of the initial pyrene whereas at 1000 and 1100 degrees C conversion to soot was significant. A kinetic analysis disentangled effects of soil-pyrene interactions and vapor phase pyrolysis of pyrene. Increase of residence time was found to be the main reason for the enhanced conversion of pyrene in the case of the presence of a solid soil or sand matrix. Light gas species released due to the thermal treatment, such as acetylene and methane, lead the formation of other, pyrene-derived PAH, e.g., methylpyrenes, cyclopenta[cd]pyrene, and benzo[a]pyrene. Implications of these findings for the chemistry of soil thermal decontamination and for diagnosing potential defects in soil thermal cleaning, e.g., incomplete elimination of targeted pollutants and formation of adverse by-products, are discussed.

Environmental Monitoring↗
PubMed2005

Biotransformation of the polycyclic aromatic hydrocarbon pyrene in the marine polychaete Nereis virens.

In vivo and in vitro biotransformation of the polycyclic aromatic hydrocarbon (PAH) pyrene was investigated in the marine polychaete Nereis virens. Assays were designed to characterize phase I and II enzymes isolated from gut tissue. High-pressure liquid chromatography measurement of 1-hydroxypyrene, pyrene-1-glucuronide, pyrene-1-sulfate, and pyrene-1-glucoside appeared to be a sensitive method for estimating the activity of pyrene hydroxylase, glucuronosyl transferase, and sulfotransferase. Total pyrene in gut tissue after a 5-d exposure to 10 microg/g dry weight pyrene constituted 65% pyrene-l-glucuronide, 12% pyrene-1-sulfate, 2% pyrene-1-glucoside, 4% 1-hydroxypyrene, and 17% pyrene, indicating that glucuronidation is the prominent phase II pathway in this organism. Only pyrene hydroxylase activity was induced significantly after pre-exposure to sediment-associated pyrene (10 microg/g dry wt). Apparent kinetic parameters were determined for all enzymatic reactions. Glucuronidation was confirmed as being the prominent phase II reaction, based on its high apparent maximum velocity (Vmax(a)). Sulfation had the lowest apparent Michaelis constant (Km(a)), indicating high specificity. Apparent kinetic parameters for pyrene hydroxylase activity were changed after induction with pyrene. Induced worms showed increased Vmax(a)) and decreased Km(a) compared to noninduced worms, indicating that the relative amount of the cytochrome P450 enzyme(s) responsible for pyrene hydroxylation is increased. Our findings show that N. virens has a high biotransformation capacity for PAHs, with inducible pyrene hydroxylase activity, and that the most prominent phase II pathway in this organism is glucuronidation.

Animals↗
PubMed1981

Reduction of tumorigenicity and of dihydrodiol formation by fluorine substitution in the angular rings of dibenzo(a,i)pyrene.

The tumor-initiating activities on mouse skin and in vitro metabolism of dibenzo(a,i)pyrene, 2-fluorodibenzo(a,i)pyrene, 3-fluorodibenzo(a,i)pyrene, and 2, 10-difluorodibenzo(a,i)pyrene were compared. After an initiating dose of 500 micrograms, followed by promotion with tetradecanoylphorbol acetate, dibenzo(a,i)pyrene induced skin tumors in 85% of the mice and caused 5.8 skin tumors/mouse. The corresponding tumorigenic activities for the fluorinated compounds were: 2-fluorodibenzo(a,i)pyrene (85%; 1.7 tumors/mouse); 3-fluorodibenzo(a,i)pyrene (80%; 3.1 tumors/mouse); and 2,10-difluorodibenzo(a,i)pyrene (10%; 0.1 tumors/mouse). After an initiating dose of 100 micrograms, only dibenzo(a,i)pyrene showed significant tumor-initiating activity. 3,4-Dihydro-3,4-dihydroxydibenzo(a,i)pyrene was identified as a metabolite of dibenzo(a,i)pyrene formed by the 9000 X g supernatant from the livers of Aroclor 1254-pretreated rats. Another dihydrodiol was tentatively identified as 1,2-dihydro-1,2-dihydroxydibenzo(a,i)pyrene. The formation of these angular ring dihdrodiols was inhibited in the metabolism of 2-fluorodibenzo(a,i)pyrene and 3-fluorodibenzo(a,i)pyrene. Angular ring dihydrodiols were not detected in the metabolism of 2,10-difluorodibenzo(a,i)pyrene. These results suggest that an angular ring dihydrodiol, 3,4-dihydro-3,4-dihydroxydibenzo(a,i)pyrene, which can form a bay-region dihydrodiol epoxide, may be a proximate carcinogen of dibenzo(a,i)pyrene.

Animals↗