James D. McKinney

Neonatal effects of transplacental exposure to PCBs and DDE

Neonatal effects of transplacental exposure to polychlorinated biphenyls (PCBs) and dichlorodiphenyl dichloroethene (DDE) were examined in a study of 912 infants. Birth weight, head circumference, and neonatal jaundice showed no relationship to PCBs or DDE. We also administered the Brazelton Neonatal Behavioral Assessment Scales, which are psychologic and neurologic tests designed for use in newborn infants. The results of these tests showed that higher PCB levels were associated with hypotonicity and hyporeflexia and that higher DDE levels were associated with hyporeflexia.

Separation of pure polychlorinated biphenyl isomers into two types of inducers on the basis of induction of cytochrome P-450 or P-448

Abstract A number of isomerically pure polychlorinated biphenyls (PCBs) were tested as inducers of hepatic drug-metabolizing enzymes in the rat. The chlorinated biphenyl isomers can be categorized into two distinct groups of inducers, while commercial PCB mixtures have characteristics of both groups. Biphenyls chlorinated symmetrically in both the meta and para positions (3,4,3′,4′- and 3,4,5,3′,4′,5′-) increase the formation of cytochrome P-448, the ratio of the 455 to 430 peaks of the ethyl isocyanide difference spectrum, and aryl hydrocarbon hydroxylase and glucuronyl transferase activities, but decrease aminopyrine N-demethylase activity. These isomers are also the most toxic, as measured by weight loss. Biphenyl isomers chlorinated in both the para and ortho positions induce the formation of cytochrome P-450 rather than P-448, regardless of the chlorination of the meta position. These isomers, which include 2,4,2′,4′-tetra- and 2,4,5,2′,4′,5′-, 2,3,4,2′,3′,4′- and 2,4,6,2′,4′,6′-hexachlorobiphenyls, increase cytochrome P-450 and N-demethylase activity, but produce only a slight increase in aryl hydrocarbon hydroxylase activity, and do not alter the peak of the CO-difference spectrum or the ratio of the 455/430 peaks of the ethyl isocyanide difference spectrum. Isomers which are chlorinated in only one ring, or are chlorinated in both rings but not in the para positions, have very little activity as inducers of liver enzymes. Of the dichlorobiphenyls tested, 3,3′- and 4,4′-dichlorobiphenyls have very slight activity at extremely high doses.

Toxicological assessment of hexachlorobiphenyl isomers and 2,3,7,8 tetrachlorodibenzofuran in chicks. I. Relationship of chemical parameters.

Abstract Five hexachlorobiphenyl (HCB) isomers and 2,3,7,8-tetrachlorodibenzofuran (TCDF) were fed to chicks for 21 days. Liver weights increased, with the smallest increase produced by 2,3,6,2′,3′,6′-HCB and the largest by 2,4,6,2′,4′,6′-HCB. Weight gain was decreased by 2,3,4,2′,3′,4′-, 2,3,6,2′,3′,6′-, and 2,4,5,2′,4′,5′-HCB, while 1μg/kg of TCDF did not affect body weight or liver weight. Pathological changes in the liver were greatest in the 2,4,6,2′,4′,6′-HCB group, moderate in the 2,3,4,2′,3′,4′- and 2,3,6,2′,3′,6′-HCB groups, and mildest in the 3,4,5,3′,4′,5′-, 2,4,5,2′,4′,5′-HCB, and 5μg/kg TCDF groups, with no significant effect for the 1μg/kg TCDF group. Thymic involution and edema were observed with 3,4,5,3′,4′,5′ HCB and TCDF. 3,4,5,3′,4′,5′-HCB and 5μg/kg of TCDF were lethal. HCB retention indices from gas chromatography correlated well with adipose-tissue concentration, with the exception of the 2,4,6,2′,4′,6′-isomer, which had the smallest retention index but relatively high tissue accumulation. Extraction p -values correlated poorly, but the 2,3,6,2′,3′,6′-HCB gave the smallest p -value, whereas the 2,4,6,2′,4′,6′-HCB p -value was next to the highest. The HCB retention indices generally correlated with their overall biological response and were highest in isomers with 3,4-substitution.

Metabolism of symmetrical hexachlorobiphenyl isomers in the rat

The excretion and metabolism of four symmetrical hexachlorobiphenyl [14C] isomers 2,3,5,2′,3′,5′-hexa-; 2,3,6,2′,3′,6′-hexa-; 2,4,5,2′,4′,5′-hexa-; and 2,4,6,2′,4′,6′-hexachlorobiphenyl, have been studied in the rat. Excretion of these hexachlorobiphenyl prior to metabolism to more polar compounds was negligible. Of the four isomers studied, the three which do not have vicinal unsubstituted carbon atoms were metabolized and excreted quite slowly. One isomer, 2,3,6,2′,3′,6′-hexachlorobiphenyl, which does have vicinal unsubstituted carbon atoms, was rapidly metabolized and excreted. The results indicate that the rate of metabolism and excretion of these hexachlorobiphenyl isomers depends on the position rather than the degree of chlorine substitution on the biphenyl ring. Metabolites of these hexachlorobiphenyl isomers were isolated from rat feces and identified by comparison of their mass and NMR spectral and chromatographic properties with synthetic metabolites. The hexachlorobiphenyl metabolites showed evidence of dechlorination, chlorine shifts, and possible metabolism via the direct insertion of a hydroxyl group. The nature of the metabolites of these hexachlorobiphenyl isomers strongly supports the intermediacy of an arene oxide as the predominant mechanism of PCB metabolism. Metabolism by direct insertion of a hydroxyl group is of importance only in the absence of vicinal unsubstituted carbon atoms and is facilitated by the presence of unchlorinated meta positions.

Toxicological assessment of hexachlorobiphenyl isomers and 2,3,7,8-tetrachlorodibenzofuran in chicks: II. Effects on drug metabolism and porphyrin accumulation

Pure hexachlorobiphenyl (HCB) isomers induce a number of changes in parameters of drug metabolism in the chick including changes in cytochrome P-450, liver weight, and p-nitrophenol glucuronyl transferase, but not in testosterone glucuronyl transferase activity. The most active inducers of drug metabolism were 2,3,4,2′,3′,4′-HCB and 2,4,6,2′,4′,6′-HCB, while 2,4,5,2′,4′,5′-HCB produced intermediate effects and 2,3,6,2′,3′,6′-HCB was a poor inducer. All HCBs caused uroporphyrin accumulation and increased δ-aminolevulinic acid (ALA) synthetase activity, but only 3,4,5,3′,4′,5′-HCB, 2,3,4,2′,3′,4′-HCB, and 2,4,5,2′,4′,5′-HCB produced gross accumulation of hepatic porphyrins. Tissue HCB concentrations correlated well with hepatic effects. 2,3,7,8-Tetrachlorodibenzofuran (TCDF), a contaminant of commercial polychlorinated biphenyl (PCB) mixtures, had no effects on hepatic ALA synthetase activity, porphyrin accumulation, or glucuronyl transferase. TCDF did produce a slight increase in cytochrome P-450, but the increase was smaller than that produced by HCBs. Also, the cytochrome induced by TCDF appeared qualitatively different from the cytochrome induced by TCBs, differing by a shift in the peak of the CO-difference spectrum from 450 to 449 nm and by the ratio of absorbance at 455 to 430 nm of the ethyl isocyanide difference spectrum.

Toxicity of selected symmetrical hexachlorobiphenyl isomers in the mouse

Abstract Five-week-old male mice were given: 0.3, 1, 3, 10, 30, 100, or 300 ppm of 3,4,5,3′,4′,5′-hexachlorobiphenyl (HCB); 10, 30, 100 or 300 ppm of 2,4,5,2′,4′,5′-HCB, 2,3,6,2′,3′,6′-HCB, or 2,4,6,2′,4′,6′-HCB in feed daily for 28 days. HCB residue levels were determined in adipose tissue and liver. There were marked differences in dose response and severity of pathologic effects among the isomers. 3,4,5,3′,4′,5′-HCB was the most toxic isomer causing mortality, and body and organ weight effects at all dose levels, and was the only isomer which produced excess porphyrin accumulation. It was also the most concentrated isomer in fat and liver. 3,4,5,3′,4′,5′-HCB caused subcutaneous edema, enlargement of liver with accentuated hepatic lobular markings, fatty infiltration, hepatocellular swelling and necrosis, and atrophy of the thymus. 2,4,6,2′,4′,6′-HCB and 2,4,5,2′,4′,5′-HCB caused the same lesions but to a lesser degree. Slight cardiomyopathy was observed with 2,4,6,2′,4′,6′-HCB. The decreasing order of overall toxicity was 3,4,5-HCB >> 2,4,6-HCB > 2,4,5-HCB > 2,3,6-HCB.

Induction of different species of cytochrome P-450 by coplanar and noncoplanar isomers of hexachlorobiphenyl

Abstract The effects of coplanar+ 3,4,5,3′,4′,5′-hexachlorobiphenyl (HCB) and noncoplanar 2,4,5,2′,4′,5′-HCB, 2,3,5,2′,3′,5′-HCB, phenobarbitone (PB) and 3-methylcholanthrene (3-MC) on drug metabolizing enzymes have been studied 72 hr after dosing in male rat liver. 3-MC and 3,4,5,3′,4′,5′-HCB induced the activity of ethoxyresorufin deethylase dramatically. NADPH cytochrome P-450 reductase and benzphetamine N -demethylase were induced by PB and noncoplanar isomers and not by 3-MC or 3,4,5,3′,4′,5′-HCB. Sodium dodecyl sulfate polyacrylamide gel electrophoresis of the microsomes obtained from various groups showed that 3-MC and 3,4,5,3′,4′,5′-HCB induced the synthesis of a polypeptide of approximate 54,500 daltons which was absent in the microsomes obtained from control, PB or noncoplanar isomer treated animals. Noncoplanar isomers and PB induced the synthesis of a polypeptide of approximate 51,000 daltons. These results, along with the reduced, CO difference spectra, demonstrate that 3,4,5,3′,4′,5′-HCB induces the synthesis of cytochrome P-448 and resembled 3-MC in its mechanism of action, while noncoplanar isomers induced the synthesis of cytochrome P-450 and resembled PB in its mechanism of action. Further administration of various doses of 3,4,5,3′,4′,5′-HCB to genetically responsive mice (C57BL/6J), induced cytochrome P-450, caused one nm shift in the difference spectrum of reduced microsomes and induced the activity of ethoxyresorufin deethylase, whereas it did not induce the activity of ethoxyresorufin deethylase in non-responsive mice (DBA/2J) even at the highest dose studied. These studies indicate the fact that coplanar and noncoplanar isomers have differential interaction with Ah locus .

Effects of thyroid hormones on the induction of cleft palate by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in C57BL6N mice☆

Abstract The induction of cleft palate by 2,3,7,8-tetrachlorodibenzo- p -dioxin (TCDD) administered with thyroid hormones triiodothyronine (T 3 ) or thyroxine (T 4 ) was investigated in C57BL 6N mice. Timed-pregnant mice were treated with vehicle, TCDD, T 3 , T 4 , TCDD plus T 3 , or TCDD plus T 4 on Days 10 to 13 of gestation. No cleft palates were observed in any control fetuses in this study, nor have there been any cleft palates in 1193 fetuses or 154 control litters in the past 24 months. TCDD (3 μg/kg/day) caused about 8% cleft palates per litter, while T 3 (120, 240, 480 μg/kg/day) and T 4 (625, 1250, 2500 μg/kg/day) resulted in no more than 1.2% cleft palates per litter in any of the treatment groups and the incidence was not dose related. The combination of TCDD (3 μg/kg/day) plus T 3 at 120, 240, and 480 μg/kg/day resulted in 15.9, 20.6, and 31.4% cleft palates per litter, respectively. TCDD plus T 4 at 625, 1250 and 2500 μg/kg/day caused 15.1, 22.9, and 27.2% cleft palates per litter. No cleft palates were observed when large doses of T 3 were given in combination with T 4 . These data demonstrated that coadministration of T 3 or T 4 with TCDD increased the incidence of cleft palate to incidences greater than expected from the separate administration of the hormones plus TCDD.

Modulation of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-mediated myelotoxicity by thyroid hormones

Although binding by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) to the Ah receptor is a prerequisite for toxicity, the events responsible for subsequent TCDD effects are essentially unknown. Several lines of evidence have indicated that thyroid hormones share common molecular properties with TCDD and can modulate its toxicity. In the present studies we employed suppression of murine bone marrow hematopoiesis by TCDD as an in vitro model to study the relationship between thyroid hormones and TCDD toxicity. Supraphysiological levels of thyroid hormone mimicked TCDD myelotoxicity, in that both were inhibited by a common antagonist, 1-NH2-3,7,8-trichlorodibenzo-p-dioxin. Furthermore, myelotoxicity by both TCDD and thyroid hormone segregated with the Ah locus in congenic mice. These data provide evidence of a relationship between TCDD and thyroid hormones in that hormonal activity may help regulate TCDD toxicity.

Production and characterization of antisera specific for chlorinated biphenyl species: initiation of a radioimmunoassay for Aroclors.

Abstract Antisera to 4-amino-4′-monochlorobiphenyl, 2-amino-4,5,3′,4′-, and 3-amino-2,6,2′,6′-tetrachlorobiphenyl have been produced in rabbits by conjugating these compounds to proteins using the mixed anhydride method. Extensive characterization studies indicated the antisera were fairly specific to their nonaminated biphenyl analogs. Values for these isomers in Aroclors by radioimmunoassay and gas chromatography correlated well for several of the antisera. Suggestive evidence is presented indicating the feasibility of employing radioimmunoassays for determining the Aroclor product number and concentration in environmental samples. A feature of the assay is the use of nonionic detergents to solubilize the extremely hydrophobic chlorinated biphenyls in a manner permitting their binding to antibodies.