Tetrachlorodibenzo-p-dioxin Research Articles

Effects of 2,3,7,8 tetrachlorodibenzo-p-dioxin (TCDD) on lipid synthesis and lipogenic enzymes in the rat

A single intraperitoneal administration of 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) caused within 1 week of exposure, a dose dependent progressive inhibition of liver fatty acid synthetic rate with concomitant decreases in hepatic fatty acid synthetase (FAS) and acetyl coenzyme A carboxylase (ACX) activities. Similarly, hepatic cholesterol synthetic rate was markedly inhibited with increasing dosage of TCDD although the corresponding decrease in 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) activity was of lesser magnitude. Linear regression analyses of the reciprocals of the responses versus the dose revealed that the TCDD concentration which caused 50% inhibition (ED 50) of the activities of various lipogenic enzymes and of lipid synthetic rates ranged from 11 to 20 ug/kg (34 to 67 nmoles/kg) with an average value of 15 ug/kg (47 nmoles/kg). Significantly, the adipose tissue was found to be more sensitive than the liver with respect to inhibition of fatty acid synthesis by increasing dosage of TCDD. Thus, the biochemical mechanism of loss of adipose mass caused by TCDD exposure may well be mediated by strong inhibition of lipid synthesis in the adipose tissue coupled with increased mobilization of depot fat.

GC/MS and GC/MS/MS: complimentary techniques for the quantitation of tetrachlorodibenzo-p-dioxin in soils & sediments from industrial sites

The complimentary nature of GC/MS and GC/MS/MS in the analysis of industrial soils and sediments for tetrachlorodibenzo-p-dioxin (TCDD) has been demonstrated. Low resolution GC/MS provides the ability for fast screening of samples, while GC/MS/MS gives fast and specific confirmation of samples found to contain TCDD in the presence of interferences. In analyses where TCDD surrogates are used, the GC/MS/MS instrument precision was found to be ± 15% as compred to a GC/MS instrument precision of ± 2%. Utilization of an internal standard in the GC/MS/MS analysis improves the precision to ± 5%. The sensitivity of the GC/MS/MS was found to be at least a factor of three better due to an improved signal to noise level.

Interactions of rutaecarpine alkaloids with specific binding sites for 2,3,7,8-tetrachlorodibenzo-p-dioxin in rat liver.

Rutaecarpine alkaloids have the capacity to inhibit specific 2,3,7,8-[1,6-3H]tetrachlorodibenzo-p-dioxin (TCDD) binding in rat liver cytosol, as analysed by electrofocusing in polyacrylamide gel. The IC50 value for binding of 7,8-dehydrorutaecarpine was estimated to approximately 7 nM indicating a high-affinity interaction, whereas rutaecarpine appeared less active (IC50 approximately 110 nM). These findings are of interest in view of the fact that analogues to these compounds may be formed following UV-irradiation of tryptophan and that such photo-products have been suggested to constitute (the) endogenous ligand(s) for the TCDD receptor. As further support of this notion, the rutaecarpine alkaloids investigated could be fitted into a rectangle of 6.8 x 13.7 A, a characteristic common for most high affinity ligands of the TCDD receptor hitherto studied. In view of their structural similarity to dehydrorutaecarpine and the agreement of their mol. wt with that of the photoproduct with the highest affinity for the TCDD receptor, we suggest deaza-analogues of dehydrorutaecarpine to represent possible candidates for the endogenous TCDD receptor ligand.

Elucidation of cellular targets responsible for tetrachlorodibenzo-p-dioxin (TCDD)-induced suppression of antibody responses: I. The role of the B lymphocyte

The objective of these studies was to identify the primary cellular target(s) responsible for TCDD (tetrachlorodibenzo-p-dioxin)-induced suppression of antibody production. Responses to T-independent and T-dependent antigens (administered in vivo or directly to splenic culture) were suppressed in a dose-related fashion in female B6C3F1 mice dosed for 5 consecutive days with 0.1, 1.0 and 10.0 μg/kg of 2,3,7,8-TCDD. When nonadherent (B and T) and adherent (macrophage) cells from vehicle- and TCDD-treated mice were combined in various combinations and immunized with either DNP-Ficoll (T-independent) or sRBCs (T-dependent), it was demonstrated that nonadherent cells, but not adherent cells, were functionally affected by TCDD. Similarly, as various combinations of B + macrophage and T + macrophage populations were immunized with sRBCs, the B cell was shown to be the primary target. Using LPS as the stimulus, an inhibition of the antibody response with no effect on the mitogenic response further indicated that the primary target of the TCDD-induced suppression of IgM antibody production is the B lymphocyte at the level of cell differentiation.

Radioligand-dependent differences in the molecular properties of the mouse and rat hepatic aryl hydrocarbon receptor complexes

A comparison of the molecular properties of the male Long-Evans rat and male C57BL/ 6 mouse hepatic cytosolic aryl hydrocarbon (Ah) receptor complex was determined using 2,3,7,8-[ 3H]tetrachlorodibenzo- p-dioxin (TCDD) and 2,3,7,8-[ 3H]tetrachlorodibenzofuran (TCDF) as radioligands. In low salt buffer, the sedimentation coefficients, Stokes radii, relative molecular masses, frictional ratios, axial ratios and gel permeation chromatographic properties of the rat receptor complexes were ligand independent. In contrast, there were several ligand-dependent differences in the mouse Ah receptor complexes formed after incubation in low salt buffer and these include: sucrose density gradient analysis of the 2,3,7,8-[ 3H]TCDF receptor complex gave a 9.5 S specifically bound peak and a 2.6 S nonspecifically bound peak whereas the corresponding 2,3,7,8-[ 3H]TCDD receptor complex gave a single 9.6 S specifically bound peak; sucrose density gradient analysis of the two major peaks eluted from a Sephacryl S-300 column chromatographie separation of the 2,3,7,8-[ 3H]TCDF receptor complex gave two specifically bound peaks at 9.2 and 5.1 S. The molecular properties of the rat hepatic cytosolic receptor complexes incubated in high salt (0.4 m KCl) buffer were ligand independent with one exception, namely the significant difference in the sedimentation coefficient of the specifically bound disaggregated 2,3,7,8-[ 3H]TCDD receptor complex (6.8 S) and the corresponding 2,3,7,8-[ 3H]TCDF receptor complex (5.0 S). The major ligand-dependent differences in the mouse receptor complexes incubated in high salt (0.4 m KCl) were associated with the sedimentation coefficients of the complexes derived after direct incubation and after gel permeation chromatography. For example, both ligands gave two specifically bound complexes after chromatography on Sephacryl S-300 column and centrifugation of these fractions gave both the ~9 and ~5 S peaks; this suggested that there was some equilibration between the aggregated and disaggregated receptor complexes. The behavior of the 2,3,7,8-[ 3H]TCDF mouse receptor complex was similar after incubation in low or high salt buffer except that sucrose density gradient analysis of the gel permeation Chromatographic fractions gave an additional specifically bound peak which sedimented at 7.2 S. These studies demonstrate that the molecular properties of the Ah receptor were dependent on the source of the cytosolic receptor preparation, the ionic strength of the incubation media, and the structure of the radioligand.

Human dioxin-inducible cytosolic NAD(P)H:menadione oxidoreductase. cDNA sequence and localization of gene to chromosome 16.

NAD(P)H:menadione oxidoreductase (NMOR1) is a flavoprotein that catalyzes the two-electron reduction of various redox dyes and quinones. It has been proposed that this enzyme may have a protective effect against cancer caused by quinones and their metabolic precursors. We show that tetrachlorodibenzo-p-dioxin (TCDD) treatment of the human hepatoblastoma cell line Hep-G2 produces a 5-fold induction of NMOR activity. Several overlapping human NMOR1 cDNAs were isolated from a human liver lambda gt 11 expression library, and their composite sequence corresponds to an mRNA of 2448 nucleotides containing a continuous open reading frame encoding a protein of 274 residues (molecular weight, 30,880). The corresponding human NMOR1 mRNA has an unusually long 3'-untranslated region (1679 base pairs) with four potential polyadenylation signals (I-IV) at positions 986, 1460, 1838, and 2419 and a single copy of human Alu repetitive sequence between polyadenylation sites II and III. Southern blot analysis of human genomic DNA suggests the presence of a single NMOR1 gene approximately 10 kilobases (KB) in length. The use of three of the aforementioned polyadenylation signals is likely to account for the three different species (2.7, 1.7, and 1.2 kb) of mRNA hybridizing to NMOR1 cDNA in Hep-G2 cells. Indeed several partial cDNA clones were isolated that corresponded to the mRNA derived by use of the proximal polyadenylation signal. Interestingly, the longest (2.7 kb) mRNA species was induced severalfold by TCDD, whereas the other two mRNAs (1.7 and 1.2 kb) were induced to a much lesser extent by TCDD treatment. The human NMOR1 cDNA and protein are 83 and 85% similar to rat liver cytosolic NMOR1 cDNA and protein, respectively. Southern analysis of DNA from 54 human x mouse and 39 human x hamster somatic cell hybrids shows that the NMOR1 gene resides on human chromosome 16.

Pentachlorodibenzo-p-dioxin Isomer Differentiation by Capillary Gas Chromatography Fourier Transform Infrared Spectroscopy

Reference infrared vapor-phase spectra of the 14 pentachlorodibenzo-p-dioxin (PnCDD) isomers were recorded at low microgram concentrations. A unique infrared spectrum corresponding to each chromatographically separated or spectrally subtracted mixture component was observed. The structures for individual isomers in each isomer pair were assigned by qualitative valence-bond evaluations and empirically derived quantitative estimations of ether linkage asymmetric stretching frequencies [ vcoc(asym)] Correlations between calculated ether linkage (C-O-C) bond angles and vcoc(asym) indicate the existence of buttressed 1,6 and 1,9 nonbonded interactions not observed in tetrachlorodibenzo- p-dioxin (TCDD) isomers.

Molecular Geometry Approximations for Chlorinated Dibenzodioxins by Fourier Transform Infrared Spectroscopy

Reference infrared vapor-phase spectra of 15 polychlorinated dibenzodioxin- p-dioxin (PCDD) isomers were recorded at low microgram concentrations. Ether linkage (COC) bond angles for these isomers and for the 22 tetrachlorodibenzodioxin (TCDD) isomers were calculated from infrared data, with the use of mass approximations for the terminal atom in a nonlinear XY2 model and by neglecting the valence force equation symmetric stretch bending term. Calculated bond angles show a good correlation with x-ray diffraction (XRD) and carbon-13 nuclear magnetic resonance (13C NMR) relaxation results. Molecular geometries in PCDD isomers, as defined by the COC bond angle and the COC stretching frequencies, were found to range from near planar, in laterally substituted isomers with high electron withdrawing capacity aromatic rings, to tetrahedral, for isomers with low electron withdrawing capacity rings. Non-bonded interactions were also found to influence molecular geometry. Molecular geometry was used to assign structures for the 1,2,3,6,7,8- and 1,2,3,7,8,9-hexachlorodibenzodioxin isomer mixture and was found to be an important factor in estimations of COC bond strength from empirical data. Correlations between infrared data and PCDD LD50 values suggest that molecular geometry, polarizability, and steric PCDD/receptor interactions are associated with isomer toxicity.

Transplacental induction of cytochromes P-450IA1 and P-450IA2 by polycyclic aromatic carcinogens: TCDD-binding protein level as the rate-limiting step.

Induction of cytochromes P-450c and P-450d have been compared in fetal and adult rat liver. A single dose of 3-methylcholanthrene (MC) 16 h before death, resulted in a pronounced accumulation of both mRNAs in adult liver. In contrast, treatment of fetuses with a single dose of MC did not increase the hepatic content in P-450c and P-450d mRNAs, whereas a 3-day treatment gave rise to a considerable accumulation of mRNAs. The fetal rat liver content in 2,3,7,8 tetrachlorodibenzo-p-dioxin (TCDD)-binding protein was extremely low compared to the adult content. Pretreatment of fetuses with phenobarbital potentiated the inducing effect of MC upon P-450c and P-450d mRNA accumulation in relation to the duration of pretreatment, as well as increasing the hepatic content in TCDD-binding protein. Data strongly suggest that the hepatic TCDD-binding protein level is the rate-limiting step in MC induction of P-450c and P-450d in fetal but not in adult rat liver. In addition, phenobarbital and MC are potent inducers of the TCDD-binding protein in the fetal rat liver.

Synthesis and aryl hydrocarbon receptor binding properties of radiolabeled polychlorinated dibenzofuran congeners

Microchlorination of 1,4,9[ 3H]dibenzofuran gave several polychlorinated dibenzofuran (PCDF) products and 2,3,7,8-[ 3H]tetrachlorodibenzofuran (TCDF), 1,2,3,7,8-[ 3H]pentachlorodibenzofuran (PeCDF), and 1,2,3,6,7,8-/1,2,3,4,7,8-hexachloro-dibenzofuran (HCDF) of high specific activity (57, 34, and 32.5 Ci/mmol, respectively) were purified by preparative high-pressure liquid chromatography. These compounds were investigated as radioligands for the rat liver cytosolic aryl hydrocarbon (Ah) receptor protein. Like 2,3,7,8-[ 3H]tetrachlorodibenzo- p-dioxin (TCDD), the radiolabeled PCDF congeners exhibited saturable binding with the receptor protein and sucrose density gradient analysis of the radiolabeled ligand-receptor complexes gave specific binding peaks with comparable sedimentation profiles. The rank order of radioligand binding affinities ( K d values) was 2,3,7,8-TCDD > 2,3,7,8-TCDF > 1,2,3,6,7,8-HCDF > 1,2,3,7,8-PeCDF and the maximum difference in K d values for the four radioligands was less than 13-fold (0.44-5.9 n m). The interactions of the PCDF radioligands with the cytosolic receptor all exhibited saturable binding curves and linear Scatchard plots and the slopes of their Hill plots were in the range 1.0–1.1, thus indicating that cooperativity was not a factor in these binding interactions. The relative stabilities and dissociation kinetics of the radioligand-receptor complexes were highly dependent on the structure of the radioligand. The dissociation curves of the 2,3,7,8-[ 3H]TCDD and PCDF receptor complexes were biphasic and this suggests that there may be a temporal shift in ligand binding affinities. However, the rates of dissociation did not correlate with the rank order of ligand binding affinities. The stabilities of the radioligand-receptor complexes were also dependent on the structures of the radioligands; for example, the 2,3,7,8-[ 3H]TCDD-receptor complex degraded more rapidly than the PCDF-receptor complex and these relative stabilities were clearly not related to the K d values or the relative in vivo or in vitro biologic potencies of these halogenated aryl hydrocarbons.

Disposition of toxic PCB congeners in snapping turtle eggs: expressed as toxic equivalents of TCDD.

Studies of snapping turtles, taken from the region of the Upper Hudson River, in New York State, revealed exceedingly high levels of PCBs in the adipose tissue. There is evidence to suggest that large reserves of fat provide protection against chlorinated hydrocarbon toxicity. Such storage may protect snapping turtle eggs from disposition of toxic PCB congeners and account for the apparent absence of reports regarding detrimental effects on the hatchability of eggs from turtles living in the vicinity of the upper Hudson River. The present study was undertaken to determine if indeed these eggs are protected against disposition of toxic PCB congeners by the presence of large reserves of fat. Although tissue volumes play an important role in determining the initial site of disposition, the major factor controlling the elimination of these compounds involves metabolism. For simple halogenated benzenes as well as for more complex halogenated biphenyls, oxidative metabolism catalyzed by P-448, occurs primarily at the site of two adjacent unsubstituted carbon atoms via arene oxide formation leading to the formation of water soluble metabolites. Toxicological studies have demonstrated that the most toxic PCB congeners, isosteriomers of tetrachlorodibenzo-p-dioxin (TCDD), require no metabolic activation. These compounds have chlorine atoms in themore » meta and para positions of both rings. It may be concluded that the structures of PCB congeners and isomers which favor induction of cytochrome P-448 are also those which are toxic and resist metabolism. It is the objective of the present study to determine if the heavy fat bodies of the female turtle provide a sufficiently large sink to retain the toxic congeners and prevent their incorporation into the eggs.« less

Tetrachlorodibenzo-p-Dioxin Isomer Differentiation by Capillary Gas Chromatography Fourier Transform-Infrared Spectroscopy

Reference infrared vapor-phase spectra of the 22 tetrachlorodibenzo-dioxin (TCDD) isomers were recorded at low microgram concentrations. These reference spectra of synthetic mixture components separated chromatographically or by spectral subtraction exhibit distinct infrared spectra for each isomer. The infrared frequencies are delineated in correlation tables and are interpreted in terms of substitution patterns which determine the strength of the ether linkage. Absorbance values in the 1330–1280 cm−1 (C-O-C asymmetric stretch) region correlate with specific substitution patterns and molecular geometry. Relative electron-withdrawing capacities for chlorinated aromatic rings in TCDD isomers were estimated on the basis of relative capacities determined for model compounds. Qualitative correlations were established between electron-withdrawing capacities and the effects of resonance and field interactions on the ether linkage absorption frequencies of individual TCDD isomers. Gas chromatography Fourier transform infrared (GC/FT-IR) isomer assignments are generally consistent with those obtained by proton Fourier transform nuclear magnetic resonance (1H FT/NMR) and flame ionization gas chromatography (GC/FID). A chromatographically independent method of assigning TCDD isomer structures on the basis of ether linkage asymmetric stretching frequencies was established by utilization of valence-bond approximations. GC/FT-IR assignments for several TCDD isomers differ from isomer assignments in previously published results. A user-generated, vapor-phase reference library, containing individual TCDD spectra and spectra of isomer pairs that are incompletely resolved on chromatographic columns, correctly identified each isomer in variety of mixtures by means of a software algorithm.

Health effects in family pets and 2,3,7,8-TCDD contamination in Missouri: a look at potential animal sentinels.

In 1971, waste oils containing 2,3,7,8:tetrachlorodibenzodioxin (TCDD) were sprayed in Missouri for dust control. To determine if pets could serve as sentinels of human health risks associated with this contamination, we asked pet owners in a pilot study of exposed human populations about their pets' illnesses. Of 13 pets with owner-reported illnesses, 8 had potential TCDD exposures and 5 did not (p less than .05 by Mantel-Haenzel chi-square analysis stratified by age). Owner-reported illnesses in 2 of 8 illness categories were associated with TCDD contamination after adjusting for age. Although these findings suggest that pets in TCDD-contaminated areas may have greater health risks, the small sample size, unlikely pathologic groupings, and unconfirmed nature of the data fail to support a relationship between pet illnesses and possible TCDD exposure and thus make extrapolation to human populations inappropriate. The limited validity found for owner-reported pet illnesses should caution against using such data in future environmental health studies.

Comparison of human mouse P1450 upstream regulatory sequences in liver- and nonliver-derived cell lines.

The foreign chemical tetrachlorodibenzo-p-dioxin (TCDD) is known to interact with the aromatic hydrocarbon receptor and, in turn, activate transcription of the mouse P1450 and P3450 genes. Various lengths of DNA upstream from the human P1450 gene were inserted into the promoterless pSVO-cat prokaryotic expression vector and compared with mouse P1450 upstream sequences similarly treated. The constructs were cotransfected with pSV2-neo into human, mouse, and monkey liver- and nonliver-derived cell lines. After selection in G418, the transformed colonies were treated with control medium, TCDD, or, in some cases, cycloheximide. Pooled transformants were then assayed for chloramphenicol acetyltransferase activity. The data are consistent with the presence of several functional regulatory regions within the upstream DNA: a promoter region, a region that is negatively autoregulated, and a region further upstream that activates transcription and is dependent upon a functional aromatic hydrocarbon receptor. Compared with 1604 base pairs of human P1450 upstream sequences, 1646 base pairs of mouse P1450 upstream sequences exhibit an increased sensitivity to TCDD; this effect was found to require both trans-acting protein factors and cis-acting DNA elements. Our results demonstrate the successful interaction of mouse trans-acting factors with human P1450 upstream sequences and human trans-acting factors with mouse P1450 upstream sequences.

A critical evaluation of the use of mutagenesis, carcinogenesis, and tumor promotion data in a cancer risk assessment of 2,3,7,8-tetrachlorodibenzo- p-dioxin

Regulatory agencies in the Western Hemisphere are currently assessing the potential human health risks of environmental contamination by 2,3,7,8 tetrachlorodibenzo- p-dioxin (TCDD). Some U.S. agencies such as the Environmental Protection Agency (EPA) and Centers for Disease Control (CDC) have assumed that TCDD behaves as a tumor initiator in animals and have used linear low-dose mathematical extrapolation models for estimating any human risk. In contrast, the Ontario Ministry of the Environment, the State Institute of National Health of The Netherlands, and the Federal Environmental Agency of the Federal Republic of Germany have concluded that TCDD does not have initiator activity; these agencies have advocated a risk extrapolation approach which applies a safety factor to a no-observable-effect level. Estimations of the potential risk obtained by these two approaches can differ by three to four orders of magnitude and have a major impact on the allocation of resources within the affected countries. This paper critically reviews the TCDD bacterial, animal, and human data on mutagenesis, carcinogenesis, and tumor promotion and concludes that the scientific evidence does not support risk estimations which are based on TCDD as a tumor initiator. Rather, the animal data overwhelmingly support TCDD as a tumor promoter. Risk estimations which incorporate tumor promotion activity more accurately reflect the scientific understanding of TCDD's mechanism of action and provide better estimates of its risk.

Effects of induction of rat liver cytosolic aldehyde dehydrogenase on the oxidation of biogenic aldehydes

Phenobarbital and tetrachlorodibenzo- p-dioxin (TCDD) induce two different forms of aldehyde dehydrogenase (EC 1.2.1.3, ALDH), designated φ and τ respectively, in the rat liver cytosol. The physiological substrates for these enzymes are as yet unknown. In this study we investigated whether the induction of these enzymes forms affected the metabolism of dopamine and norepinephrine in rat liver slices. A 10-fold increase in φ-ALDH produced by phenobarbital treatment resulted in small increases in the formation of 3,4-dihydroxyphenylacetic acid and 3,4-dihydroxymandelic acid from the biogenic amines. The 50- to 100-fold elevation of the τ-isozyme did not alter the rate of formation of the acids. When liver slices were incubated with 40 mM ethanol, the formation of the reduced products of dopamine and norepinephrine, 3,4-dihydroxyphenylethanol and 3,4-dihydroxyphenylglycol, respectively, was favored. Under these conditions, the induction of the φ-isoenzyme again produced only a small increase in the formation of the acid products, whereas the induction of the τ-isoenzyme had no effect on acid production from biogenic amine metabolism. The results suggest that neither the φ- nor the τ-forms of ALDH are involved in the hepatic metabolism of dopamine or norepinephrine and support the conclusion that the oxidation of the aldehyde derived from dopamine occurs in mitochondria.

Intracellular location of the Ah receptor.

The subcellular distribution of the Ah receptor from the mouse hepatoma line, Hepa-1, was investigated following cytochalasin B treatment and cell enucleation. Probing the resultant cytoplast and nucleoplast fractions with radiolabelled tetrachlorodibenzo-p-dioxin (TCDD) revealed the presence of a specifically bound peak of receptor only in the cytoplast fraction. However, the quantity of receptor recovered in these experiments was only 10-12% of the expected value. We therefore undertook an investigation to determine the fate of the Ah receptor in the presence of cytochalasin B. Incubation of Hepa-1 cells with this compound resulted in a rapid loss or inactivation of cytosolic binding activity with a concomitant decrease in the amount of receptor partitioned into the nucleus at all time periods examined. Control experiments indicated that cytochalasin B did not compete with TCDD for binding to the Ah receptor and furthermore, that its mechanism of action could not be attributed to a non-specific effect on all cytosolic proteins. The results obtained are discussed in relation to the proposed models for induction by the estrogen and glucocorticoid binding receptors.

Micro-Diffuse Reflectance and Matrix Isolation Fourier Transform Infrared Techniques for the Identification of Tetrachlorodibenzodioxins

Micro-diffuse reflectance Fourier transform infrared (DRIFT) and matrix isolation (MI) Fourier transform infrared spectra of the 22 tetrachlorodibenzodioxin (TCDD) isomers have been recorded. The DRIFT and MI techniques required about four minutes and one-half minute, respectively, of signal averaging to produce high signal-to-noise (S/N) spectra on low-nanogram-level samples. Spectral subtraction was employed to remove DRIFT solvent impurity interferences. The validity of the DRIFT subtraction technique was demonstrated by comparison of the corrected DRIFT, with the chromatographically pure, MI spectra. The reproducibility of DRIFT frequencies and intensities was tested by comparison of the 1,3,7,8-TCDD spectra from samples independently prepared by two analysts. The MI technique successfully identified 2,3,7,8 in environmental samples. MI spectral subtraction was applied to one sample to remove a coeluting impurity. The DRIFT and MI spectral techniques, used in conjunction with modern chromatographic separation and spectral subtraction, are very promising for the on-line or off-line differentiation of low-level toxic isomeric compounds.

Liver alterations as a result of the 90-day continuous feeding of 2,3,7,8-tetrachlorodibenzo-p-dioxin

Chlorinated hydrocarbons are a highly toxic, ubiquitous class of environmental toxins of which 2,3,7,8- tetrachlorodibenzo-p-dioxin (TCDD) is the most toxic. PCB pyrolysates contain a complex mixture of these chemicals and have been shown to produce extensive alterations in the liver of guinea pig hepatocytes, including proliferated smooth endoplasmic reticulum (SER), concentric membrane arrays (CMA) which are a condensation of proliferated SER, and cytoplasmic vacuoles. A mechanism of membrane excretion into the bile canaliculi and sinusoids has been proposed to account for these alterations and their relationship to each other. This report demonstrates the proposed mechanism for a purified compound (TCDD) fed continuously for 90 days and further elucidates the role of the cytoplasmic vacuoles which are observed for dose levels at which no other alteration is present.

The Diagnosis of Dioxin-Associated Illness

The clinical recognition of dioxin-associated illness can be extremely difficult for the physician. After analyzing the relative sensitivity and specificity of reported manifestations of exposure to 2,3,7,8 tetrachlorodibenzo-p-dioxin (TCDD), we suggest criteria for the diagnosis of dioxin toxicity. Exposure to higher doses of 2,3,7,8-TCDD may lead to the appearance of chloracne and the increased excretion of porphyrins and porphyria cutanea tarda. Liver function abnormalities, peripheral neuropathy, hyperlipidemia, and evidence of weakness and depression may occur following exposure; however, these findings are less specific since diseases such as diabetes or alcoholism could cause several of these problems. The long-term effects of exposure to low-dose TCDD are currently uncertain.