Thomas H. Umbreit

Physiological implications of estrogen receptor modulation by 2,3,7,8-tetrachlorodibenzo-p-dioxin

The interactions of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) with hormones and hormone receptors have important implications for TCDD toxicity. Evidence suggests that TCDD modulates receptors for glucocorticoids, prolactin, thyroxine, low density lipids, epidermal growth factor, and estrogens. Estrogen receptor modulation and the animals physiological responses to this modulation appear to be particularly important effects and can explain much of the toxicity observed in TCDD-treated animals. Susceptibility of different species to TCDD correlates with their steroid glucuronidation capacity. Because of the close interactions and interdependent regulation of hormonal systems, other hormones may have a similar role in TCDD toxicity.

Reproductive toxicity in female mice of dioxin-contaminated soils from a 2,4,5-trichlorophenoxyacetic acid manufacturing site

Reproduction in female C57B/6 mice treated with contaminated soils from a 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) manufacturing site and a metal scrap yard in Newark, New Jersey was studied. Soils contained a wide variety of contaminants, including halogenated dibenzodioxins and dibenzofurans, benzene, alkylbenzenes, chlorobenzenes, polyaromatic hydrocarbons, phenolics, phenoxy acids and other compounds. Acute and reproductive toxicity (primarily fewer live pups born and fewer pups surviving until weaning) was observed from the manufacturing site soil (soil A; with 2,050 μg 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD)/kg soil and 18 mg total dibenzodioxins and dibenzofurans/kg soil); the scrap yard soil (soil B; with 230 (μg 2,3,7,8-TCDD/kg soil) had no observable effect. Soil recontaminated with 2,3,7,8-TCDD, or 2,3,7,8-TCDD in corn oil interfered with estrus cycling and completely prevented reproduction. If 2,3,7,8-TCDD treatment was terminated, estrus cycling resumed within four weeks, but reproduction was still unsuccessful for these mice. The results suggest that 1) the manufacturing site soil (soil A) is toxic but the signs of toxicity cannot be solely attributed to the 2,3,7,8-TCDD content; 2) even though the bioavailability of 2,3,7,8-TCDD from this soil is low (Umbreitet al. 1986), other reproductive toxins are bioavailable or the low doses of 2,3,7,8-TCDD that are bioavailable may be sufficient to be reproductive toxins; 3) 2,3,7,8-TCDD blocks estrus in mice and (as previously reported) interferes with reproduction; and 4) after cessation of dosing, thein situ concentrations of 2,3,7,8-TCDD that block estrus are decreased below an effective level within four weeks.

Alteration of the acute toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) by estradiol and tamoxifen

We have hypothesized that part of the toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is mediated by interaction with the estrogen receptor complex. The experiments reported here investigate the interactions of TCDD with agonists and antagonists of the estrogen receptor. CD-1 female mice were observed for 2 months after treatment with various combinations of corn oil, estradiol, or tamoxifen, and/or TCDD in corn oil on 3 consecutive days. Estradiol had little effect on acute TCDD lethality but increased severity of TCDD-induced ascites and antagonized TCDD-induced uterine suppression. Severe liver damage did occur in TCDD and estradiol:TCDD treatment groups. Tamoxifen, a competitive inhibitor and a mixed agonist of the mouse estrogen receptor, antagonized the estrogenic effects of estradiol and estradiol:TCDD. Tamoxifen or tamoxifen:TCDD treatment greatly slowed body weight gain in comparison to controls and estrogen-treated animals. While the dose of tamoxifen used was otherwise non-toxic, tamoxifen greatly increased toxicity of TCDD as measured by time to death and percent lethality while having no effect on relative liver weight or relative uterine weight changes induced by TCDD. These findings are consistent with the hypothesis that a portion of the toxicity of TCDD is manifest through activity of the estrogen receptor complex.

Pulmonary bioavailability and fine particle enrichment of 2,3,7,8-tetrachlorodibenzo-p-dioxin in respirable soil particles

The pulmonary bioavailability of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and the enrichment of polychlorinated dioxins (PCDDs) and furans (PCDFs) in fine particles were evaluated to assess the implications that these factors have on risk and exposure assessments. Respirable subfractions of PCDD-contaminated soil from a former 2,4,5-trichlorophenoxyacetic acid manufacturing site were isolated by chemical dispersion and gravity sedimentation. Analysis of the subfractions revealed that there was a size-dependent enrichment of PCDDs and PCDFs, with smaller particles more highly contaminated. TCDD was enriched up to 33-fold as compared to unfractionated soil. Soil and laboratory-recontaminated gallium oxide, which served as the positive control, were administered by intratracheal instillation to female Sprague-Dawley rats. Animals were terminated up to 28 days following treatment and pulmonary bioavailability of TCDD was assessed by hepatic enzyme induction and TCDD concentration. Enzyme induction was dependent on the duration of exposure with up to 56 and 918% increases in cytochrome P450 and aryl hydrocarbon hydroxylase (AHH) activity, respectively, following exposure to PCDD-contaminated soil. There was no significant difference in AHH induction between animals which received contaminated soil and those treated with the positive control. Hepatic concentration of TCDD in soil-exposed rats was 115, 101, and 179% of positive controls at 1, 7, and 28 days post-treatment, suggesting that the soil or cocontaminants influenced retention of TCDD in the liver. These data indicate that the relative pulmonary bioavailability of TCDD on respirable soil particles is 100% as compared to laboratory-recontaminated gallium oxide and that PCDDs and PCDFs are highly enriched on respirable particles.(ABSTRACT TRUNCATED AT 250 WORDS)

Bioavailability and cytochrome P-450 induction from 2,3,7,8-tetrachlorodibenzo-P-dioxin contaminated soils from Times Beach, Missouri, and Newark, New Jersey

Bioavailability of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) from contaminated soils from Times Beach, Missouri and Newark, New Jersey, was examined using liver concentrations and toxicity in guinea pigs observed up to 60 days following a single oral administration, and induction of cytochrome P-450 in rats sacrificed 24 hours after a single oral dose as endpoints. Both soils are contaminated with several chlorinated dioxins and numerous other compounds. Times Beach soil resulted in greater TCDD concentration in liver and TCDD was considerably more bioavailable from Times Beach soil than from Newark soil. However, both soils induced cytochrome P-450 activity to approximately the same extent. Moreover, similar banding patterns of microsomal proteins were seen on polyacrylamide electrophoretic gels. The many other compounds present in the soils, particularly in Newark, may account for the similar protein bands and levels of cytochrome P-450 observed.

Comparative toxicity of TCDD contaminated soil from Times Beach, Missouri, and Newark, New Jersey

Abstract Conflicting results have been obtained when examining the toxicity of soils from TCDD contaminated sites. We have made a direct comparison of soils from two sites: Times Beach, Missouri, and Newark, New Jersey; previously reported as highly toxic and slightly toxic, respectively. Guinea pigs were treated by gavage with TCDD contaminated soils at 1–10 ug/kg and with appropriate controls. Two groups of guinea pigs received a single dose and were observed for toxic signs. One group was sacrificed and autopsied after the first death attributable to TCDD occurred, and the second group was sacrificed 60 days after treatment. The Times Beach soil was highly toxic to guinea pigs and produced the typical TCDD syndrome; Newark soil was much less toxic to guinea pigs. These results indicate that bioavailability of TCDD from soil varies between sites, and that TCDD content alone may not be indicative of potential human hazard from contaminated environmental materials. (Supported by USEPA cooperative agreement #CR812114-01-0).

Hepatic Aryl Hydrocarbon Hydroxylase and Cytochrome P450 Induction following the Transpulmonary Absorption of TCDD from Intratracheally Instilled Particles

Inhalation of particles contaminated with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) will be an increasingly important route of human exposure in light of the increased utilization of municipal waste incineration and the resultant emission of contaminated materials into the environment. The potential for pulmonary absorption of the compound from respirable particles was assessed in the present study following the intratracheal instillation of TCDD (1) as a contaminant of gallium oxide particles and (2) in a corn oil vehicle. Groups of five female Sprague-Dawley rats received 0, 0.005, 0.055, 0.55, or 5.5 micrograms/kg TCDD in a single instillation and were euthanized 4 days later. Absorption was characterized by enzyme induction [aryl hydrocarbon hydroxylase (AHH) activity and total cytochrome P450] and histopathological examination of the liver. Induction of hepatic enzymes was dose-dependent with both treatment regimes. Up to an 18-fold increase in AHH and an 80% increase in cytochrome P450 were observed in treated animals. Induction was slightly higher when animals received TCDD in corn oil than when animals received TCDD-contaminated particles and was relatively comparable to induction following oral exposure. Similar results were obtained when animals were treated with particles contaminated up to 4 weeks prior to instillation. Characteristics of TCDD-induced hepatotoxicity, including enlarged hepatocytes and fatty infiltration, were apparent in treated rats, but were not present in vehicle-instilled animals. These results indicate that systemic effects occur following pulmonary exposure to TCDD and that inhalation may be an important route of exposure for TCDD.

Bioavailability of lead and chromium from encapsulated pigment materials

Bioavailability is a major factor in determining toxicity of compounds taken into a human or animal. If an ingested compound is unable to cross the wall of the gut and enter into the body, then (except in very specialized cases) its capacity to cause systemic toxicity is small. Therefore, bioavailability is an important factor in determining the true exposure level for use in risk assessment models. The results of a study of relative oral bioavailability of lead and chromium from pigment materials in both natural and encapsulated forms are reported. The levels of lead and chromium were measured in the blood after 2 and 4 weeks of treatment and after a further 2 weeks of recovery. Blood levels were used as an index of metal uptake into the body. After the recovery period, both blood levels and tissue levels in the kidneys were measured.

Species comparison of steroid UDP-glucuronyl transferase: Correlation to TCDD sensitivity

Estradiol glucuronidation via steroid UDP-glucuronyl transferase (sUDPGT) was examined in 2,3,7,8-te trachlorodibenzo-p-dioxin (TCDD) sensitive and resistant species and strains. Steroid UDPGT was not induced by treatment with TCDD or estradiol. The most sensitive species to TCDD lethality, the guinea pig, had relatively high steroid UDPGT activity, while the hamster, the most resistant species, and rats had low levels of activity; no differences in sUDPGT activities were observed between mouse or rat strains differing in susceptibility to TCDD intoxication. These results suggest a role for differences in steroid physiology in the determination of species susceptibility to TCDD, but also demonstrate that other factors are involved.

Reproductive studies of C57B/6 male mice treated with TCDD-contaminated soils from a 2,4,5-trichlorophenoxyacetic acid manufacturing site

Reproduction was studied in male C57B/6 mice treated with contaminated soils from a 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) manufacturing site in Newark, New Jersey, and a metal scrap yard where equipment from the manufacturing site was recycled. The soils contained a wide variety of contaminants including 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD). Treated males were mated to females given decontaminated soil. No acute toxicity was observed in treated males. 2,3,7,8-TCDD (up to 90 μg/kg) or 2,3,7,8-TCDD from the contaminated soils (up to 288 μg/kg) had no adverse effect on reproduction when the male mouse was treated. However, treatment of males with soil from the 2,4,5-T manufacturing site was associated with a marked decrease in viable litters at whelping and a decrease in pup survival. This toxicity may be associated with TCDD in combination with other toxic compounds that are present on the soil.