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N Harper

Publications and source records attributed to N Harper.

At least 19 recordsLinked to original sources
PubMed2000

Acid-base control for biocatalysis in organic media: new solid-state proton/cation buffers and an indicator

Although great care is generally taken to buffer aqueous enzyme reactions, active control of acid-base conditions for biocatalysis in low-water media is rarely considered. Here we describe a new class of solid-state acid-base buffers suitable for use in organic media. The buffers, composed of a zwitterion and its sodium salt, are able to set and maintain the ionisation state of an enzyme by the exchange of H+ and Na+ ions. Surprisingly, equilibrium is established between the different solid components quickly enough to provide a practical means of controlling acid-base conditions during biocatalysed reactions. We developed an organosoluble chromoionophore indicator to screen the behaviour of possible buffer pairs and quantify their relative H+/Na- exchange potential. The transesterification activity of an immobilised protease, subtilisin Carlsberg, was measured in toluene in the presence of a range of buffers. The large observed difference in rates showed good correlation with that expected from the measured exchange potentials. The maximum water activities accessible without formation of hydrates or solutions of the buffers are reported here. The indicator was also used to monitor, for the first time in situ, changes in the acid-base conditions of an enzyme-catalysed transesterification reaction in toluene. We found that even very minor amounts of an acidic by-product of hydrolysis were leading to protonation of the enzyme, resulting in rapid loss of activity. Addition of solid-state buffer was able to prevent this process, shortening reaction times and improving yields. Solid-state buffers offer a general and inexpensive way of precisely controlling acid-base conditions in organic solvents and thus also have potential applications outside of biocatalysis.

Journal Article↗
PubMed1999

Temporal constraints on visual learning: a computational model.

Given a constant stream of perceptual stimuli, how can the underlying invariances associated with a given input be learned? One approach consists of using generic truths about the spatiotemporal structure of the physical world as constraints on the types of quantities learned. The learning methodology employed here embodies one such truth: that perceptually salient properties (such as stereo disparity) tend to vary smoothly over time. Unfortunately, the units of an artificial neural network tend to encode superficial image properties, such as individual grey-level pixel values, which vary rapidly over time. However, if the states of units are constrained to vary slowly, then the network is forced to learn a smoothly varying function of the training data. We implemented this temporal-smoothness constraint in a backpropagation network which learned stereo disparity from random-dot stereograms. Temporal smoothness was formalized with the use of regularization theory by modifying the standard cost function minimised during training of a network. Temporal smoothness was found to be similar to other techniques for improving generalisation, such as early stopping and weight decay. However, in contrast to these, the theoretical underpinnings of temporal smoothing are intimately related to fundamental characteristics of the physical world. Results are discussed in terms of regularization theory and the physically realistic assumptions upon which temporal smoothing is based.

Depth Perception↗
PubMed1998

Immunogenic properties of an anti-DNA antibody-derived peptide, 88H.64-80: location of a dominant idiotope defined by T and B cells.

Immunization of normal (BALB/cxNZW)F1 H-2(dxu) mice with peptide 88H. 64-80 derived from the framework (FR) 3 VH region sequence of anti-DNA mAb, V-88, induces the production of IgG anti-peptide antibodies which cross-react specifically with the parent mAb. However, immunization of these normal mice with peptide 88H.64-80 sometimes provokes increased production of anti-dsDNA antibodies. A set of alanine substitute homologues of peptide 88H.64-80 were made to identify the amino acid residues that contribute to the antigenic status of the peptide. Peptide 88H.64-80 contained an antibody epitope at the carboxyl terminus of the peptide, while substitution of particular residues throughout the peptide had a significant inhibitory effect on T cell stimulation. Finally, subclass analysis of IgG anti-88H.64-80 peptide antibodies revealed a close correlation between the production of IgG2a anti-peptide antibodies (associated with a TH1 T cell response) and the production of IgG anti-dsDNA antibodies, but there was no correlation with any other antibody subclass. Despite the ability of peptide 88H.64-80 to provoke both the production of anti-dsDNA antibodies as well as anti-V region antibodies, the sequence of this peptide differs by only one amino acid residue from a number of murine germline gene-encoded homologues. Peptide 88H.64-80 probably represents an epitope whose appearance correlates with the level of expression of the VH genes that carry its sequence, and as such is characteristic of cross-reactive idiotypes associated with pathology.

Amino Acid Sequence↗
PubMed1998

Effects of induced mast cell activation on prostaglandin E and metalloproteinase production by rheumatoid synovial tissue in vitro.

OBJECTIVE: To determine whether induced mast cell activation/degranulation in rheumatoid synovial explants modulates the production of prostaglandin E (PGE2), and the matrix metalloproteinases (MMPs) collagenase 1, gelatinase A, and stromelysin 1. METHODS: Synovial explant cultures were treated either with rabbit IgG anti-human IgE as a mast cell (MC) secretagogue or with non-immune rabbit IgG as controls. After 20 hours conditioned medium was assayed for the release of MC tryptase, PGE2, collagenase 1, gelatinase A, and stromelysin 1 using radioimmunoassay, enzyme linked immunosorbent assay, western blot, and zymogram techniques; tissue explants were examined immunohistologically for the relative distributions of MC tryptase, collagenase 1, and stromelysin 1. RESULTS: Over a 20 hour incubation period the MC secretagogue treated explants showed a significant increase in the quantities of released tryptase and PGE2 compared with controls. By contrast, the three MMPs showed variable values between experiments in response to MC activation; no reproducible trend of either an increased or decreased production of each MMP over control values was evident. Each MMP initially appeared as an inactive precursor form; collagenase 1 and stromelysin 1 were more effectively processed to active forms in the MC activated cultures. Immunolocalisation studies of MC activated explants showed that areas of extracellular tryptase were commonly associated with the local production of both collagenase 1 and stromelysin 1. CONCLUSION: MC degranulation induced artificially in rheumatoid synovial explant cultures consistently resulted in an increased production of PGE2 but had variable effects on the quantification of released collagenase 1, gelatinase A, and stromelysin 1. Such observations support the concept that activated synovial MCs within their native environment stimulate the production of non-MC derived PGE2 and may contribute to the regulation and processing of specific MMPs; both aspects represent important components of the inflammatory and degradative processes of the rheumatoid lesion.

Arthritis, Rheumatoid↗
PubMed1997

Costello syndrome.

Explore the source record for details and available documents.

Abnormalities, Multiple↗
PubMed1996

Immunotoxicity of a reconstituted polynuclear aromatic hydrocarbon mixture in B6C3F1 mice.

Previous studies on the immunotoxicity of a complex mixture of polynuclear aromatic hydrocarbon (PAH) by-products from a manufactured gas plant indicated possible synergistic interactions which were investigated by determining the immunosuppressive effects of a reconstituted PAH mixture in female B6C3F1 mice challenged with TNP-haptenated sheep red blood cells (SRBCs) (T-cell-dependent) or trinitrophenyl-lipopolysaccharide (TNP-LPS) (T-cell-independent) antigens. The reconstituted PAH mixture contained the following 17 congeners: 2-rings (indan, naphthalene, 1- and 2-methylnaphthalene), 3-rings (acenaphthylene, acenaphthene, dibenzofuran, fluorene, phenanthrene and anthracene), and > or = 4-rings (pyrene, fluoranthene, benz[a]anthracene, chrysene, benzo[b]fluoranthene, benzo[k]fluoranthene and benzo[a]pyrene), and resembled mixtures identified as by-products from manufactured gas plants. The reconstituted mixture and the 2-, 3- and > or = 4-ring PAH fractions all caused a dose-dependent decrease in the splenic plaque-forming cell (PFC) response to SRBCs or TNP-LPS, and their ED50 values for the four treatment groups were 86, 354, 145, and 23 or 163, 439, 637 and 31 mg/kg, respectively. The corresponding ED50 values for decreased serum anti-TNP IgM levels for these same mixtures were (TNP-haptenated SRBCs, T-cell-dependent) 144, 231, 42 and 27 units, respectively, and (TNP-LPS, T-cell-independent) 161, 406, 312 and 69 units, respectively. The suppression of anti-TNP IgM titers was similar to the suppression of the PFC response and shows that antigen-specific immunoglobulin titer can be used as a biomarker of PAH exposure. A direct comparison of the immunotoxic responses of the reconstituted PAH mixture and the corresponding dose of the > or = 4-ring PAHs indicated that the latter fraction was primarily responsible for the activity of the reconstituted mixture.

Animals↗
PubMed1996

Mucosal tolerance and suppression of collagen-induced arthritis (CIA) induced by nasal inhalation of synthetic peptide 184-198 of bovine type II collagen (CII) expressing a dominant T cell epitope.

The purpose of the study was to map the dominant T cell epitope of the CB11 sequence of CII in RTlu haplotype rats and to determine if, when used as a synthetic peptide, it would induce tolerance to protect against CIA. A dominant epitope corresponding to residues 184-198 included in the sequence of the CB11 fragment of bovine CII was identified in proliferation assay using peptides in an epitope scanning system using synthetic peptides of 15 amino acids, overlapping by 12 amino acids. This epitope is bovine-specific, but cross-reacts with the corresponding rat peptide. Minor epitopes in the bovine CB11 sequence was also autoantigenic. Use of independently synthesized and purified 184-198 peptide confirmed its dominance in the T cell responses of arthritic rats. The peptide itself was not arthritogenic. Cells from lymph nodes draining arthritic feet were particularly responsive to the dominant peptide sequence, and showed evidence of epitope spreading to include reactions to at least four subdominant epitopes. Mucosal tolerance was successfully induced by instilling CII into the nose of rats before induction of CIA: this was found to delay the onset of disease, reduce mean disease severity, shift the anti-CII antibody response to favour antibodies of the IgG1, rather than the IgG2b isiotype, and to reduce T cell reactivity to both CII and to the 184-198 peptide. The dominant 184-198 peptide itself had the same tolerogenic effects when given nasally to rats daily, on the 4 days immediately preceding the induction of CIA. Two forms of CIA with acute and delayed disease onset were each modified by pre-treatment with the peptide. This study demonstrates that mucosal tolerance to CII can be induced by delivering it nasally in a way similar to that achieved previously by oral delivery, and that the use of an immunodominant epitope contained in a synthetic peptide will also suppress the immunologic and arthritic responses to collagen.

Administration, Inhalation↗
PubMed1995

Halogenated aromatic hydrocarbon-induced suppression of the plaque-forming cell response in B6C3F1 splenocytes cultured with allogenic mouse serum: Ah receptor structure activity relationships.

The immunosuppressive effects of halogenated aromatic hydrocarbons (HAHs) were investigated in B6C3F1 female mice and in mouse splenocytes cultured with allogenic mouse serum using the Mishell-Dutton model for in vitro immunization to trinitrophenyl-lipopolysaccharide (TNP-LPS). Exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 2,3,4,7,8-pentachlorodibenzofuran (PeCDF), 1,2,3,7,8-PeCDF, 1,3,6,8-tetrachlorodibenzofuran (TCDF), 3,3',4,4',5-pentachlorobiphenyl (pentaCB), or 3,3',4,4',5,5'-hexaCB resulted in a dose-dependent suppression of the splenic plaque-forming cell (PFC) response both in vivo and in vitro. The effective dose required to decrease 50% (ED50) of the response to 2,3,7,8-TCDD, 2,3,4,7,8-PeCDF, 1,2,3,7,8-PeCDF, 1,3,6,8-TCDF, 3,3',4,4',5-pentaCB, or 3,3',4,4',5,5'-hexaCB in vivo was 14.1, 5.5, 1695, 34,800, 21, and 19 nmol/kg, respectively, and in vitro was 7.0, 10.6, 149, 2325, 9.1 and 9.1 nM, respectively. There was an excellent rank order and linear correlation between the in vivo versus in vitro activities for these HAHs (r < 0.99) and the relative immunosuppressive potencies of these compounds paralleled their binding affinities for the aryl hydrocarbon (Ah) receptor. These results show that splenocytes cultured with allogenic mouse serum is an Ah-responsive in vitro assay which can be used for quantitating the immunosuppressive effects of HAHs.

Analysis of Variance↗
PubMed1995

Immunosuppressive activity of polychlorinated biphenyl mixtures and congeners: nonadditive (antagonistic) interactions.

The dose-response inhibition of the splenic plaque-forming cell (PFC) response and serum IgM units to the antigen, trinitrophenyl-lipopolysaccharide, was determined for several polychlorinated biphenyl (PCB) mixtures and congeners in female B3C3F1 mice. The ED50 values for Aroclor 1260-, 1254-, 1248-, and 1242-induced immunotoxicity varied by less than twofold from 355 to 699 mg/kg. The range of ED50 values for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 3,3',4,4'-tetrachlorobiphenyl, 3,3',4,4',5-pentaCB, 3,3',4,4',5,5'-hexaCB, 2,3,3',4,4'-pentaCB, 2,3',4,4',5-pentaCB, 2,3,3',4,4',5-hexaCB, 2,3,3',4,4',5,5'-heptaCB, 2,2',3,3',4,4',5-heptaCB, and 2,2',3,4,4',5,5'-heptaCB were 4.6 to 4.9, 134 to 245, 4.7 to 7.0, 6.9 to 11.1, 88,000 to 121,000, 122,000 to 132,000, 99,000 to 157,000, 89,000 to 129,000, 117,000 to 240,000, and 132,000 to 238,000 micrograms/kg, respectively. The immunotoxicity-derived toxic equivalency factors (TEFs) for these congeners could be calculated from the ED50 (TCDD)/ED50 (congener) ratios and the TEF values were within the range of those previously determined for other aryl hydrocarbon receptor-mediated responses. Based on the known concentrations of these congeners in the PCB mixtures, TCDD or toxic equivalents (TEQs) in the mixture were calculated [i.e., TEQ = sigma (PCBcongener x TEF)] using the immunotoxicity-derived TEFs (plaque-forming cells/10(6) viable cells). TEQ values for Aroclors 1260, 1254, 1248, and 1242 were 16.0, 54.4, 260.4, and 197 ppm, respectively. Based on the ED50 value for the immunosuppressive activity of TCDD (4.8 micrograms/kg), the calculated ED50 values for immune suppression by Aroclors 1260, 1254, 1248, and 1242 were 300, 88, 18, and 24 mg/kg, respectively. The ED50 (observed)/ED50 (calculated) ratios were 1.2, 5.9, 21, and 22.0 for Aroclors 1260, 1254, 1248 and 1242, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

An enzyme-linked immunosorbent assay (ELISA) specific for antibodies to TNP-LPS detects alterations in serum immunoglobulins and isotype switching in C57BL/6 and DBA/2 mice exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin and related compounds.

An enzyme-linked immunosorbent assay (ELISA) was developed to detect IgM and IgG antibodies specific for trinitrophenyl-lipopolysaccharide (TNP-LPS). Treatment of C57BL/6 and DBA/2 mice with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and other aryl hydrocarbon (Ah) receptor agonists followed by immunization with TNP-LPS resulted in a dose-dependent decrease in serum IgM which paralleled the decrease in the splenic PFC response. The ED50 values for the IgM and splenic PFCs in C57BL/6 mice for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 3,3',4,4',5-pentachlorobiphenyl (pentaCB) and 3,3',4,4',5,5'-hexaCB were 2.8 and 1.6, 11 and 14, and 25 and 20 micrograms/kg, respectively; in the less Ah-responsive DBA/2 mice, the ED50 values were 8.5 and 10, 61 and 69, and 73 and 71 micrograms/kg, respectively. In addition, treatment of C57BL/6 mice with TCDD resulted in alterations of serum IgG relative to IgM and a delay of isotype switching was observed after immunization and boosting with TNP-LPS. This ELISA may prove to be a useful tool in monitoring immune function during long-term exposure of mice to TCDD and related compounds and exploring the mechanism of Ah receptor-mediated immunosuppression.

Animals↗
PubMed1994

Relative sensitivities of 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced Cyp1a-1 and Cyp1a-2 gene expression and immunotoxicity in female B6C3F1 mice.

Improvements in risk assessment require better linkage of exposure to response by the determination of target tissue dose. The relative sensitivity of several responses in female B6C3F1 mice was compared on the basis of administered and target tissue dose spanning 3 orders of magnitude. Twenty-four hours after administration, [3H]TCDD was detected in the heart, spleen, kidney, uterus, thymus, lung, and liver, and the highest concentrations were noted in the liver, uterus, and lung. At doses from 5 to 25 ng/kg, hepatic [3H]TCDD levels associated with the cytosolic and nuclear subcellular fractions increased from 12 to 62% of the total liver levels and then decreased at higher doses. At the two lowest doses used in the enzyme induction study, 5 and 10 ng/kg, the levels of specifically bound nuclear Ah receptor complex liganded with [3H]TCDD were 2.3 and 2.5 fmol/mg protein. Slightly higher levels of nuclear Ah receptor complex were observed at doses between 25 and 100 ng/kg (i.e., 3.6 to 4.2 fmol/mg protein) and a steep dose-dependent increase in nuclear Ah receptor levels was noted at doses of 500, 1000, and 5000 ng/kg (8.0, 39.3, and 92.8 fmol/mg protein, respectively). The dose-dependent effects of [3H]TCDD on hepatic Cyp1a-1 and Cyp1a-2 mRNA levels, ethoxyresorufin O-deethylase (EROD) activity, and the splenic antibody plaque-forming cell (PFC) response to sheep red blood cells were also determined; the latter response was determined 9 days after administration of TCDD. Statistically significant induction of hepatic Cyp1a-1 was observed at lower doses (25 ng/kg) than any other marker, followed by induction of EROD and PFCs expressed per spleen or per 10(6) cells which was observed at 100 ng TCDD/kg and at higher doses. Cyp1a-2 was elevated significantly relative to control at doses > or = 1000 ng/kg. The ED50 value for PFCs/10(6) cells was the lowest of the variables analyzed and was not statistically significantly different from control (91 +/- 92 ng/kg). A 50% increase in Cyp1a-2 and Cyp1a-1 mRNA levels was observed at doses of 736 +/- 132 and 1630 +/- 431 ng/kg, respectively. Due to variability in response in PFCs/spleen and the submaximal induction of EROD activity, ED50 values could not be calculated for these responses. The analyses indicate that the immunosuppressive response (when normalized for the number of spleen cells) may be depressed by administered doses as low as 90 ng TCDD/kg body weight. A 50% increase in Cyp1a-1 or Cyp1a-2 was observed at higher administered doses (1630 or 736 ng/kg, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1994

Inhibition of estrogen-induced progesterone receptor in MCF-7 human breast cancer cells by aryl hydrocarbon (Ah) receptor agonists.

17 beta-Estradiol (E2) induces progesterone receptor (PR) binding, immunoreactive protein, nuclear PR formation and PR mRNA levels in MCF-7 human breast cancer cells. Gel mobility shift analysis of nuclear extracts from E2-treated cells also exhibited a higher intensity retarded band associated with formation of a PR complex with a consensus [32P]progesterone/glucocorticoid responsive element. In contrast, 1 nM 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) alone did not alter or decrease these same responses in MCF-7 cells; however, in cells co-treated with 1 nM TCDD plus 1 nM E2, TCDD significantly inhibited all the E2-induced responses. Scatchard analysis of PR binding demonstrated that TCDD decreased the number of E2-induced PR cellular binding sites but not the binding affinity of the PR for a radiolabeled promegestrone. In parallel studies, 3-methylcholanthrene, a prototypical polynuclear aromatic hydrocarbon, also inhibited E2-induced PR binding and immunoreactive protein. For a series of halogenated aromatics including 2,3,7,8- and 1,2,7,8-tetrachlorodibenzofuran, 1,3,7,8-TCDD and 6-methyl-1,3,8-trichlorodibenzofuran, their rank order potency for inhibiting E2-induced PR binding paralleled their rank order binding to the aryl hydrocarbon (Ah) receptor. These results support a role for the Ah receptor in mediating the antiestrogenic activity of polynuclear and halogenated aromatic hydrocarbons and illustrate cross-talk between the Ah and estrogen receptor signal transduction pathways.

Blotting, Northern↗
PubMed1993

Immunosuppressive effects of highly chlorinated biphenyls and diphenyl ethers on T-cell dependent and independent antigens in mice.

The dose-dependent effects of 2,2',3,3',4,4',5,5',6-nonachlorobiphenyl (nonaCB), 2,2',3,3',4,4',5,6,6'-nonaCB, 2,2',3,3',4,5,5',6,6'-nonaCB and decaCB on the suppression of the splenic plaque-forming cell (PFC) response to the T-cell-dependent antigen, sheep red blood cells (SRBCs) and the T-cell-independent antigen, trinitrophenyl-lipopolysaccharide (TNP-LPS), were determined in genetically inbred mice. In addition, the induction of hepatic microsomal ethoxyresorufin O-deethylase (EROD) activity was also measured. The highly chlorinated biphenyls suppressed the splenic PFC response to SRBCs in C57BL/6 and DBA/2 mice and were relatively more active in the former strain. The C57BL/6 mice are more responsive to aryl hydrocarbon (Ah) receptor agonists than DBA/2 mice and these data support a possible role for the Ah receptor in mediating this response. However, previous studies with polychlorinated biphenyls (PCBs) indicate that congeners with 3 or 4 ortho-chloro substituents are inactive as Ah receptor agonists and this was consistent with the minimal induction of hepatic microsomal EROD activity by the highly chlorinated biphenyls in both strains of mice. Thus, the results suggest that the inhibition of the splenic PFC response to SRBCs observed in this study was primarily an Ah receptor-independent response. Some of the highly chlorinated diphyenyl ethers namely decachlorodiphenyl ether and 2,2',3,3',4,4',5,6,6'-nonachlorodiphenyl ether, inhibited the antigenic response to TNP-LPS in C57 BL/6 mice. The results indicate that the suppression of the TNP-LPS-mediated immune response may be a more reliable indicator of the Ah receptor-dependent immunotoxicity of halogenated hydrocarbons.

Animals↗
PubMed1993

Immunotoxic potencies of polychlorinated biphenyl (PCB), dibenzofuran (PCDF) and dibenzo-p-dioxin (PCDD) congeners in C57BL/6 and DBA/2 mice.

The dose-dependent effects of a single acute exposure of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 2,3,4,7,8-pentachlorodibenzofuran (PeCDF), 1,2,3,7,9-PeCDF, 1,3,6,8-tetrachlorodibenzofuran (TCDF), 3,3',4,4',5-pentachlorobiphenyl (pentaCB), and 3,3,',4,4',5,5'-hexaCB on the suppression of the splenic plaque-forming cell (PFC) response to the T-cell-independent antigen trinitrophenyl-lipopolysaccharide were determined in C57BL/6 and DBA/2 mice. In addition, the induction of hepatic microsomal ethoxyresorufin O-deethylase (EROD) activity was also measured in these animals. 2,3,7,8-TCDD and 2,3,4,7,8-PeCDF were the most immunotoxic congeners in both strains of mice and with the exception of the latter congener, the ED50 values for each compound were lower in the C57BL/6 than the DBA/2 mice. 2,3,7,8-TCDD induced hepatic microsomal EROD activity in both strains of mice whereas the other congeners were considerably less active or inactive as inducers. The results of this study demonstrated that for the halogenated aromatic hydrocarbons the immunotoxic response was a more sensitive indicator of exposure than the induction of CYP1A1 activity. The rank order for the immunotoxic potencies of the chlorinated aromatic compounds used in this study was 2,3,7,8-TCDD approximately 2,3,4,7,8-PeCDF > 3,3',4,4',5-pentaCB approximately 3,3',4,4',5,5'-hexaCB > 1,2,3,7,9-PeCDF > 1,3,6,8-TCDF. The order of activity for these congeners was similar for other Ah receptor-mediated responses and these results coupled with the differential responsiveness of the C57BL/6 and DBA/2 mice confirms the role of aryl hydrocarbon (Ah) receptor in mediating the suppression of this T-cell-independent response.

Animals↗
PubMed1993

Immunosuppressive and monooxygenase induction activities of highly chlorinated diphenyl ether congeners in C57BL/6 and DBA/2 mice.

The dose-response effects of 2,2',3,3',4,5,5',6,6'-2,2',3,3',4,4',5,6,6'- and 2,2',3,3',4,4',5,5',6- nonachlorodiphenyl ether (non-aCDE) and decachlorodiphenyl ether (decaCDE) on the splenic plaque-forming cell (PFC) response to sheep red blood cells (SRBCs) and the induction of hepatic microsomal ethoxyresorufin O-deethylase (EROD) activity was determined in aryl hydrocarbon (Ah)-responsive C57BL/6 and less Ah-responsive DBA/2 mice. All the congeners exhibited immunotoxicity at doses between 2.5 and 10 mumol/kg in C57BL/6 mice whereas in DBA/2 mice doses > or = 25 mumol/kg were required to cause inhibition of the PFC response to SRBCs. The results also showed that the nonaCDE isomers and decaCDE were more active as inducers of hepatic EROD activity in C57BL/6 than DBA/2 mice; however, there was not a correlation between the induced EROD activity and the CYP1A1 and CYP1A2 mRNA levels in the C57BL/6 mice. These data suggested that the immunotoxicity of these compounds was mediated through the Ah receptor. However, the results showed that the immunotoxicity of the nonaCDE isomers and decaCDE was unexpectedly high compared to that of lower chlorinated diphenyl ethers and there were no apparent structure-activity relationships among the higher chlorinated congeners. This suggests that some of the immunosuppressive effects observed for the nonaCDE isomers and decaCDE may be Ah receptor-independent.

Animals↗
PubMed1993

Synergistic activity of polynuclear aromatic hydrocarbon mixtures as aryl hydrocarbon (Ah) receptor agonists.

The relative potencies of benzo[a]pyrene and a complex mixture of polynuclear aromatic hydrocarbons (PAHs) produced as by-products of manufactured gas plant (MGP) residues as inducers of hepatic microsomal ethoxyresorufin O-deethylase (EROD) activity were determined in the B6C3F1 mouse. The ED50 values for the induction response were 78 and 65 mg/kg for benzo[a]pyrene and the MGP-PAH mixture, respectively. Analysis of the MGP-PAH mixture indicated that benzo[a]pyrene and other compounds containing four or more rings and which are known to induce EROD activity were only present as trace components of this mixture. A comparison of the EROD induction potencies of benzo[a]pyrene and the MGP-PAH mixture showed that the mixture was approximately 706 times more potent than expected based on its benzo[a]pyrene content (0.17%). This induced P-450 activity could significantly increase the metabolism of the carcinogenic PAHs and thereby modulate the overall carcinogenicity of the mixture. The apparent synergistic activity of the MGP-PAH mixture was further investigated by comparing the activities of this mixture and benzo[a]pyrene for several other aryl hydrocarbon (Ah) receptor-mediated responses including (i) induction of hepatic CYP1A1 mRNA levels, (ii) transformation of the rat cytosolic Ah receptor to a complex which binds to a dioxin responsive element, (iii) induction of EROD activity and (iv) antiestrogenicity in MCF-7 human breast cancer cells, and (v) inhibition of the splenic plaque-forming cell (PFC) response to both T cell-dependent and independent antigens in B6C3F1 mice. For the EROD and CYP1A1 mRNA induction and cytosolic transformation activities and immunosuppressive effects, the MGP-PAH mixture was approximately 100-900 times more potent as an Ah receptor agonist than expected based on its benzo[a]pyrene content. The synergistic activity was lower (19-fold) for the antiestrogenic response in MCF-7 cells. The reason for the synergistic effects of the MGP-PAH mixture were not due to contamination of the mixture by 2,3,7,8-tetrachlorodibenzo-p-dioxin and related compounds and the results suggest that the enhanced potency of the mixture is due to unknown interactions between the individual PAHs present in the mixture.

Animals↗