Characteristics of an extraction and purification procedure for chlorinated dibenzo-p-dioxins and dibenzofurans in soil and liver

Liver is extracted with chloroform-methanol to give essentially quantitative transfer of endogenous chlorinated dibenzo-p-dioxins (CDDs) and dibenzofurans (CDFs) into the organic phase. A new procedure involving LH-20 Sephadex is used to remove most of the lipids from the extract. Soil is extracted by a simple, rapid and economical procedure giving very high recoveries of CDDs and CDFs from sandy soil, various types of clay, and humus-rich loam. Subsequent cleanup on basic and acidic alumina complete the preparation for gas chromatography-mass spectrometric analysis. The use of propylene glycol as a "keeper" and of 2,3,7-trichlorodibenzo-p-dioxin as a carrier minimizes losses during evaporation of solvents and on glass surfaces. Interactions of 2,3,7,8-CDD with organic material in loam slightly reduce recovery but there is no indication of high affinity binding sites, the losses being apparently associated with simple distribution coefficients. Special precautions needed to avoid losses of CDFs on alumina chromatography are described, and the effect of "aging" spiked soil is discussed.

In vitro metabolism of mono-2-ethylhexyl phthalate by microsomal enzymes. Similarity to omega- and (omega-1) oxidation of fatty acids

Mono-2-ethylhexyl pthalate (MEHP) is oxidized to omega-, omega-1-, and omega-2-hydroxylation products as well as (very slightly) to a dicarboxylic acid by washed microsomes from rat liver and kidney, and rabbit but not rat lung. The reactions involve molecular oxygen, are strongly inhibited by carbon monoxide and oxidized cytochrome c, and NADPH is preferred over NADH. Piperonyl butoxide inhibits hydroxylation of MEHP, but clofibrate does not. The differential effects of inducers (phenobarbital and clofibrate) and inhibitors (sodium laurate, n-decane, metyrapone) on terminal and subterminal hydroxylation as well as differences in apparent Km for the two suggest that rat liver contains at least two different MEHP hydroxylases. Comparisons of tissue distribution, susceptibility to inhibitors, and induction properties suggest that the hydroxylation of MEHP is more likely to be mediated by the P-450 isozymes associated with omega- and (omega-1)-hydroxylation of fatty acids than with those that utilize hydrocarbons as substrates.

Urinary metabolites of orally administered di-(5-hexenyl) phthalate and di-(9-decenyl) phthalate in the rat

Di-(5-hexenyl)- and di-(9-decenyl) phthalates were administered to male CD rats by gavage. The urinary metabolites retaining the phthalate moiety were identified by chromatographic and mass-spectrometric techniques. Di-(5-hexenyl) phthalate gave rise to epoxide and vicinal diol metabolites not previously seen with phthalic acid esters of saturated alcohols. Neither epoxide nor diol were detected when di-(9-decenyl) phthalate was fed. The distributions of carboxyl-terminated metabolites suggested that somewhat different pathways were followed for the two test compounds. The formation of epoxides from these unsaturated phthalate esters may have relevance to their potential toxicities. Like the metabolites of di-n-butyl phthalate, the metabolites of di-(5-hexenyl) phthalate included glucuronide conjugates; like the metabolites of di-(2-ethylhexyl) phthalate, those of di-(9-decenyl) phthalate did not.

Metabolism of methyl n-amyl ketone (2-heptanone) and its binding to DNA of rat liver in vivo and in vitro

Methyl n-amyl ketone (2-heptanone), a reported metabolite of 2-ethylhexanol which in turn is a primary metabolite of plasticizers such as di-(2-ethylhexyl) phthalate, is metabolized in male Fischer 344 rats to CO2, acetate and a variety of compounds that could be either anabolic or catabolic or a combination of the two. A significant percentage of the radioactivity given orally (gavage) as [2-14C]-2 heptanone, at least 10%, was not excreted from the body in 48 h. Radioactivity was incorporated into liver protein in the form of three unidentified products as well as [14C]arginine, and into DNA both as 14C-labeled normal nucleosides (50-75%) and as presently unidentified hydrophobic materials (25-50%). Urea and cholesterol were significantly labeled, indicative of anabolic reutilization of [2-14C]-2-heptanone breakdown products. The 2-heptanone also bound to DNA spontaneously in vitro, to the extent of 400 pmol/mg DNA.

Heterogeneity of hepatic aryl hydrocarbon hydroxylase activity in feral winter flounder: relevance to carcinogenicity testing

Hepatic microsomes from winter flounder (Pseudopleuronectes americanus), treated with polycyclic aromatic hydrocarbon (PAH) inducers, had elevated activities of benzo[alpha]pyrene hydroxylase (AHH) and 7-ethoxyresorufin deethylase (7-ERD). When electrophoresed, they showed a novel or enriched polypeptide species with a monomeric molecular weight of approximately 57,000. These results are consistent with inductive responses already well-characterized in several mammalian and fish species. However, when we studied the urinary clearance of 4-chlorobiphenyl in untreated flounder, wide variations (up to twentyfold) among fish were noted. Subsequent in vitro analysis of AHH and 7-ERD activities in liver demonstrated wide variations in these monooxygenase activities in flounder caught near Mount Desert Island, Maine. In some instances, AHH activities in these feral flounder were as high as those in PAH-induced fish. Based on the response of AHH activity to 7,8-benzoflavone (ANF) added in vitro, flounder could be divided into 2 groups; one had high hepatic AHH activity which was inhibited by ANF, the other had low AHH activity which was enhanced by ANF. Examination of a large number of winter flounder (greater than 400 total) over 4 experimental seasons demonstrated this variability of hepatic AHH activity to be a recurrent characteristic of the flounder population in waters around Mount Desert Island. The hepatic AHH activities did not correlate well with any physical parameter of the fish (e.g., liver, gonad or body weight, length, or sex) or the cytochrome P-450 content of the hepatic microsomes. Our attempt to evaluate the AHH activity (high vs. low) of individual fish in vivo by urinary clearance of antipyrine was unsuccessful, due to the excretion of large amounts of unchanged antipyrine through the gills. Similar studies were performed with another marine teleost, Fundulus heteroclitus. Of the approximately 200 Fundulus examined, almost all had AHH activity inhibited by ANF; in some experiments, hepatic 7-ERD activities were further increased after treatment with the potent PAH-type inducer 3,4,5,3',4',5'-hexachlorobiphenyl but only about twofold. Collectively, these data are consistent with PAH-type induction of the hepatic cytochrome P-450-dependent monooxygenase system in some feral marine teleosts (in winter flounder and Fundulus) from Maine by environmental contaminants or food constituents. It is not known whether these chemicals are of natural or anthropogenic origin. The variation in the response appears to be related to individual exposure level (dose) or sensitivity, or both.(ABSTRACT TRUNCATED AT 400 WORDS)

Dioxin in soil: bioavailability after ingestion by rats and guinea pigs

Soil environmentally contaminated with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was given by gavage to guinea pigs and rats. The development of a characteristic clinicopathologic syndrome in guinea pigs, the induction of aryl hydrocarbon hydroxylase in rats, and the presence of TCDD in the livers of both species show that TCDD in soil exhibits high biological availability after ingestion.

A screening assay for the tetrachlorodibenzo-p-dioxin receptor using the [125I]iodovaleramide derivative of trichlorodibenzo-p-dioxin as the binding ligand

A relatively simple assay method for the putative cytosolic 'receptor' that binds 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and related compounds is described. The assay is based on specific binding of [125I]dioxin to cytosol 'receptor' protein. Saturation is ensured by competition experiments in which unlabeled TCDD and other competitors displace the radiolabeled ligand from specific binding sites. This assay has been applied to estimation of levels of 'receptor' in cytosol.

Interactions between xenobiotics that increase or decrease the levels of cytochrome P-450 isozymes in rabbit lung and liver

Isozyme-specific enzymatic activities, radial immunodiffusion, and Western blotting were used to study the effects of phenobarbital, Aroclor 1260, and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on microsomal levels of cytochrome P-450 forms 2, 5, and 6. The pulmonary concentration of form 2 was decreased to trace levels by the administration of Aroclor 1260 but not TCDD; co-administration of phenobarbital did not mitigate the decrease. The pulmonary concentration of form 5 was not significantly changed following treatment with Aroclor 1260, phenobarbital, or TCDD. The pulmonary content of form 6 was increased 5- and 10-fold by administration of Aroclor 1260 and TCDD, respectively, and decreased 2-fold by treatment with phenobarbital. Further, phenobarbital antagonized the induction of form 6 by Aroclor 1260 but not by TCDD. In the liver, increases and decreases in form 2-mediated benzphetamine N-demethylation were observed following treatment with Aroclor 1260 depending on the time after dose and individual rabbit response. Hepatic induction of form 2 by phenobarbital was significantly decreased by co-administration of Aroclor 1260. However, form 5 was induced in the liver by either Aroclor 1260 or phenobarbital or both. Thus, the effect of Aroclor 1260 on the control of the concentration of form 2 is independent of that of form 5 in the lung and liver. Fractionation of the Aroclor 1260 to remove co-planar polychlorinated biphenyls and dibenzofurans was useful in demonstrating that the pulmonary induction of form 6 was dependent on these components and unrelated to the repression of form 2 in the lung and liver. The apparent repressive effect of phenobarbital on form 6 in the lung is interesting as it suggests an interaction between phenobarbital and polycyclic hydrocarbon-mediated induction.

Polar metabolites of di-(2-ethylhexyl)phthalate in the rat

Di-(2-ethylhexyl)phthalate (DEHP) is an important industrial chemical widely used as a plasticizer for vinyl and other plastics. DEHP is extensively metabolized by mammals, different species showing dramatic differences in metabolite distributions. Previous studies of the metabolism in rats led to the suggestion that the enzymatic processes normally associated with omega-, omega-1, alpha-, and beta-oxidation of fatty acids could account for the known metabolites of DEHP found in the urine. Several additional metabolites of DEHP have been identified in the present study. Their formation requires that the initial hydroxylation process be less specific than fatty acid omega- and omega-1 oxidation are thought to be. Furthermore, it is necessary to postulate either that the aliphatic chain of mono-(2-ethylhexyl)phthalate can be oxidized at two sites simultaneously, or that oxidation products can be recycled for a second hydroxylation prior to excretion.

Hepatic microsomal NADPH-cytochrome P-450 reductase from little skate, Raja erinacea. Comparison of thermolability and other molecular properties with a mammalian enzyme

Components of little skate (an elasmobranch) and rabbit hepatic microsomal cytochrome P-450 dependent monooxygenase systems were examined for differences which might explain the decreasing xenobiotic-metabolizing activity of little skate microsomes assayed at temperatures above 30 degrees C. The proportion of saturated fatty acids in microsomal lipids and the habitat temperature are both lower in skate as compared to rabbit, which is consistent with the known adaptive pattern. The more thermolabile enzyme of the skate system in microsomal preparations is NADPH-cytochrome P-450 reductase. The optimal assay temperature for purified skate reductase (30 degrees C) is 10 degrees C lower than that for the purified rabbit reductase. The purified skate reductase differs from rabbit reductase in monomeric molecular weight, in peptides produced by partial proteolysis, in immunochemical properties, but not in flavin content.

Incorporation of radioactivity from labeled Di-(2-ethylhexyl)phthalate into DNA of rat liver in vivo

Di-(2-ethylhexyl)phthalate (DEHP), when fed at high levels in the diet for two years, is reportedly an hepatocarcinogen to rats and mice. Radioactivity from ethylhexyl-labeled, but not from phthalate-labeled, [14C]-DEHP is associated with highly purified DNA from the livers of treated rats and this radioactivity is not accounted for by assumptions of adsorption, intercalation, attachment to RNA or histones, an impurity in the labeled DEHP, or artifactual binding during sample workup. Spontaneous binding of radioactivity to DNA from either ethylhexyl-labeled DEHP or its total urinary metabolites could not be detected. Although rat liver slices generated all of the known metabolites of DEHP in vitro, no binding to DNA occurred. Administration of dual 3H/14C-labeled DEHP to rats yielded liver DNA whose 3H/14C ratio was inconsistent with the attachment of any reasonable multi-carbon fragment from the ethylhexyl portion to the DNA. The observation that roughly 100 times as high a percentage of the 14C administered was found in urea as in total DNA suggests that the 14C entered DNA through carbamyl phosphate, a precursor of both urea and pyrimidine bases. If this is the case, the association of C-1 from the ethylhexyl portion of DEHP with DNA may not involve alteration of the DNA or genetic damage.

Chromatographic evidence of polychlorinated biphenyl exposure from a spill

Women who were part of a study in which polychlorinated biphenyls (PCBs) were measured in breast milk were exposed accidentally to a PCB spill. While the overall level of PCBs found in their milk was not different from background levels, the chromatograms showed unusual peaks that indicate the presence of heavily chlorinated PCBs of the kind that were spilled.

Toxic potential of the plasticizer Di(2-ethylhexyl) phthalate in the context of its disposition and metabolism in primates and man

Although human toxicity from exposure to the plasticizer di(2-ethylhexyl) phthalate (DEHP) is unknown, reports of animal toxicity from DEHP have stimulated extensive toxicological studies. In the absence of direct toxicity data, information on the disposition and metabolism of DEHP in primates and man may enhance our assessment of the toxic potential of DEHP in man. Studies of DEHP disposition and metabolism in the African Green monkey and man show that the compound is rapidly and extensively metabolized. It is excreted largely in the urine (greater than 90%) as conjugated (glucuronide) oxidation products of mono(2-ethylhexyl) phthalate; excretion in feces accounts for the other 10% of the administered DEHP. Plasma disappearance of parenterally administered DEHP is equally rapid so that by 24 hr following DEHP administration, plasma DEHP concentrations are virtually undetectable, while greater than 70% of the dose has been excreted in urine and stool. The transience of DEHP in primates and the extent to which it is metabolized and conjugated may play a role in the observed lack of toxicity.

Pharmacokinetics, interactions with macromolecules and species differences in metabolism of DEHP

The recent long-term carcinogenesis bioassay of di(2-ethylhexyl) phthalate (DEHP) in rats and mice reported by the National Toxicology Program was the first such bioassay to implicate DEHP as a hepatocarcinogen. At the levels of DEHP fed (up to 1.2% of the diet for two years), the livers of the rats would have been exposed to unhydrolyzed diester; this would not have been the case at lower dosages. Extrapolation to lower dosages is therefore questionable. We do not have sufficient pharmacokinetic data in mice to evaluate the dose relationships as yet. Rodents differ conspicuously from primates in their manner of metabolizing DEHP, both in terms of the demand made on the oxidation potential of the liver and in the chemical properties of the major metabolites. The relevance of these differences must be determined before rodent species can be considered models for the effects of DEHP in humans. Radioactivity from carbonyl-labeled DEHP did not associate with purified protein, RNA or DNA from rat liver in vivo. Label from 2-ethyl-(1-14C)-hexyl-labeled DEHP or mono(2-ethylhexyl) phthalate (MEHP) did appear to associate strongly with purified DNA, but label from free 14C-labeled 2-ethylhexanol did not. The apparent binding from DEHP and MEHP was not exchangeable, but was not proven to be covalent. This phenomenon needs additional study.

Chromatographic separation and quantitative determination of the metabolites of di-(2-ethylhexyl) phthalate from urine of laboratory animals

Free, glycine-conjugated, and glucuronide-conjugated metabolites of di-(2-ethylhexyl) phthalate may be stripped from urine with XAD-2 resin, derivatized, and quantitatively analyzed by liquid chromatography on a nitrile column with UV and/or radioactivity monitors. One class of metabolites requires reversed-phase chromatography or gas-liquid chromatography for its resolution. Relative molar responses of the hydrogen flame-ionization detector to these metabolites have been determined. Packed gas chromatography columns (OV-3, OV-210, cyclohexanedimethanol succinate) and fused-silica capillary columns (SP2100 and FFAP) are useful for quantitative analysis under appropriate conditions. The simplest gas chromatographic procedure permitting complete quantitative analysis requires hydrolysis of conjugates, formation of methyl esters of carboxyl groups, butyration of hydroxyl groups and chromatography on OV-3. Typical distributions of di-(2-ethylhexyl) phthalate metabolites in urine from mice, hamsters, and guinea pigs are presented.

The relationship between metabolism of 2,3,4,5,3',4',5'-heptachlorobiphenyl and its ability to induce both cytochromes P-448 and P-450

Male CD rats received i.p. injections of 2,3,4,5,3',4',5'-heptachlorobiphenyl (7CB) under conditions resulting in induction of both benzphetamine demethylase (cytochrome P-450-dependent) and ethoxyresorufin deethylase (cytochrome P-448-dependent) activities. To test the possibility that one class of induction (P-450) was due to the parent compound and the other (P-448) to a metabolite, liver, adipose, bile, urine and feces were analyzed for the presence of 3,4,5,3',4',5'-hexachlorobiphenyl (6CB) (the major photolysis product of 7CB) and/or 3-hydroxy-3,4,5,3',4',5'-hexachlorobiphenyl (OH-6CB), another known P-448 inducer. To allow for the possibility that 6CB might be a transient intermediate. The results supported the hypothesis that 7CB is a true 'mixed inducer', nor requiring metabolic alteration for its dual activity.

Applications of isotope differentiation for metabolic studies with di-(2-ethylhexyl) phthalate

The pervasiveness of the plasticizer di-(2-ethylhexyl) phthalate (DEHP) in the environment and especially in the laboratory results in a background that may cause severe interference with analytical studies. Animal-to-animal variability in the distribution of DEHP metabolites in excreta normally makes it necessary to use large groups of animals when different treatments are compared. Finally, radioactive tracers are usually considered undesirable for metabolic studies involving human subjects. All of these problems can be overcome through the use of multiple isotopic labels, especially 12C/13C/14C. Examples are given involving rats and monkeys, and applicability to humans is discussed. The principles involved are not limited to any particular class of test compounds. In rats, the competing pathways for metabolism of phthalate esters produce a different distribution of metabolites from a small intravenous dose of DEHP than from a large oral dose.

A new synthesis of tetrachlorofluorodibenzo-p-dioxin

The 1,2,3,4-tetrachloro-7-fluorodibenzo-p-dioxin has been synthesized via condensation of 4-fluorocatechol and pentachloronitrobenzene. This compound could be used as an internal standard for the analysis of 2,3,7,8-tetrachlorodibenzo-p-dioxin by chromatographic methods.

Identification of the metabolites of di-(2-ethylhexyl) phthalate in urine from the African green monkey

The metabolites of di-(2-ethylhexyl) phthalate (DEHP) found in urine from African Green monkeys after intravenous administration of the 14C-labeled parent compound were isolated and identified. Criteria of identification included cochromatography with rat-derived standards on direct-phase HPLC and a variety of gas-chromatographic columns, as well as correspondence of mass spectra (70-eV electron impact and methane positive chemical ionization) with those of known standards. Approximately 80% of the urinary metabolites were excreted in the form of glucuronide conjugates. This is analogous to what has been reported for the urinary metabolites of DEHP from humans, but in clear contrast to the metabolites found in rat urine. Rat urinary metabolites of DEHP are excreted unconjugated, and consist primarily of derivatives more highly oxidized than the major metabolites produced by monkey or human. It is suggested that the African Green monkey may be a better model for human metabolism of DEHP than is the rat.