Clinical Impact of Contouring Variability for Prostate Cancer Tumor Boost

PURPOSE/OBJECTIVE(S)

In the FLAME randomized phase III trial, adding a focal radiotherapy (RT) boost to tumors visible on MRI improved prostate cancer disease-free survival, local control, and regional/distant metastasis-free survival without increasing toxicity. In a prospective study (ReIGNITE RT Boost), we found substantial variability in radiation oncologists' attempts to contour prostate cancer tumors on MRI. Participants' accuracy and reliability improved when they used a quantitative MRI biomarker for cancer called the restriction spectrum imaging restriction score (RSIrs). Here, we measure the impact of radiation oncologists' tumor contour attempts on RT plans and predicted probability of biochemical failure.

MATERIALS/METHODS

A total of 44 radiation oncologists (participants) from multiple institutions contoured prostate tumors on 30 patient cases, some with only conventional MRI and some with conventional MRI plus RSIrs maps. We developed a knowledge-based planning automated algorithm to generate RT plans with focal tumor boost per the FLAME trial protocol: 77 Gy in 35 fractions to prostate and integrated boost up to 95 Gy to the focal target, provided no normal tissue constraints were violated. We applied this algorithm to each participant's tumor contour and compared dosimetric parameters to those achieved when using the expert-defined tumor (consensus of two radiologists and a radiation oncologist). The primary metric was dose covering 98% of the expert-defined tumor (D98%), which was associated with probability of biochemical failure in a model published with the FLAME trial.

RESULTS

In this preliminary analysis, 42 target volumes were analyzed from 20 participants and two patient cases: case 1 was contoured with conventional MRI alone and case 2 with RSIrs. All plans had adequate coverage of the prostate and met all key normal tissue constraints. For case 1 (without RSIrs), the expert's D98% was 87.1 Gy. By comparison, median D98% for participants was 82.2 Gy (IQR 77.8 - 84.6 Gy). Per the FLAME trial model, the predicted probability of biochemical failure at 7 years is 6% for the expert, but participants' plans yielded a median failure probability of 11% (IQR 18 - 9%). For case 2 (with RSIrs), the expert's D98% was 82.8 Gy, while median D98% for participants was 80.6 Gy (IQR 80.0 - 81.0 Gy). Predicted probability of biochemical failure is 12% for the expert-defined target and median 13% (IQR 14 - 13%) for participants.

CONCLUSION

Variability in radiation oncologists' prostate tumor contours can lead to clinically meaningful changes to focal RT boost plans. The probability of biochemical failure for one patient case increased from 6% to a median of 11% when using conventional MRI alone. Use of RSIrs may mitigate this problem by increasing the accuracy and reliability of radiation oncologists' tumor contours.

Tributyltin disrupts fin development in Fundulus heteroclitus from both PCB-sensitive and resistant populations: Investigations of potential interactions between AHR and PPARγ

Tributyltin (TBT) and dioxin-like polychlorinated biphenyls (PCBs) are environmental contaminants that are highly toxic to fish and co-occur in New Bedford Harbor (NBH), an estuarine Superfund site located in Massachusetts, USA. Atlantic killifish (Fundulus heteroclitus) that reside in NBH (and other highly contaminated sites along the east coast of the United States) have developed resistance to activation of the aryl hydrocarbon receptor (AHR) pathway and the toxicity of dioxin-like chemicals, such as 3,3',4,4',5-pentachlorobiphenyl, PCB126. In many biological systems, TBT disregulates adipose and bone development via the PPARγ-RXR pathway; AHR activation also disrupts adipose and bone homeostasis, potentially through molecular crosstalk between AHR and PPARγ. However, little is known about how co-exposure and the interaction of these pathways modulate the toxicological effects of these contaminants. Here, we tested the hypotheses that TBT would induce teratogenesis in killifish via activation of PPARγ and that PCB126 co-exposure would suppress PPARγ pathway activation in PCB-sensitive killifish from a reference site (Scorton Creek, SC, PCB-sensitive) but not in PCB-tolerant NBH killifish. Killifish embryos from both populations exposed to TBT (50 and 100 nM) displayed caudal fin deformities. TBT did not change the expression of pparg or its target genes related to adipogenesis (fabp11a and fabp1b) in either population. However, expression of osx/sp7, an osteoblast marker gene, and col2a1b, a chondroblast marker gene, was significantly suppressed by TBT only in SC killifish. An RXR-specific agonist, but not a PPARγ-specific agonist, induced caudal fin deformities like those observed in TBT-treated embryos. PCB126 did not induce caudal fin deformities and did not exacerbate TBT-induced fin deformities. Further, PCB126 increased expression of pparg in SC embryos and not NBH embryos, but did not change the expression of fabp1b. Taken together, these results suggest that in killifish embryos the PPARγ pathway is regulated in part by AHR, but is minimally active at least in this early life stage. In killifish, RXR activation, rather than PPARγ activation, appears to be the mechanism by which TBT induces caudal fin teratogenicity, which is not modulated by AHR responsiveness.

Estrogen receptor-related receptors in the killifish Fundulus heteroclitus: diversity, expression, and estrogen responsiveness

The estrogen receptor-related receptors (ERRs) are a group of nuclear receptors that were originally identified on the basis of sequence similarity to the estrogen receptors. The three mammalian ERR genes have been implicated in diverse physiological processes ranging from placental development to maintenance of bone density, but the diversity, function, and regulation of ERRs in non-mammalian species are not well understood. In this study, we report the cloning of four ERR cDNAs from the Atlantic killifish, Fundulus heteroclitus, along with adult tissue expression and estrogen responsiveness. Phylogenetic analysis indicates that F. heteroclitus (Fh)ERRalpha is an ortholog of the single ERRalpha identified in mammals, pufferfish, and zebrafish. FhERRbetaa and FhERRbetab are co-orthologs of the mammalian ERRbeta. Phylogenetic placement of the fourth killifish ERR gene, tentatively identified as FhERRgammab, is less clear. The four ERRs showed distinct, partially overlapping mRNA expression patterns in adult tissues. FhERRalpha was broadly expressed. FhERRbetaa was expressed at apparently low levels in eye, brain, and ovary. FhERRbetab was expressed more broadly in liver, gonad, eye, brain, and kidney. FhERRgammab was expressed in multiple tissues including gill, heart, kidney, and eye. Distinct expression patterns of FhERRbetaa and FhERRbetab are consistent with subfunctionalization of the ERRbeta paralogs. Induction of ERRalpha mRNA by exogenous estrogen exposure has been reported in some mammalian tissues. In adult male killifish, ERR expression did not significantly change following estradiol injection, but showed a trend toward a slight induction (three- to five-fold) of ERRalpha expression in heart. In a second, more targeted experiment, expression of ERRalpha in adult female killifish was downregulated 2.5-fold in the heart following estradiol injection. In summary, our results indicate that killifish contain additional ERR genes relative to mammals, including ERRbeta paralogs. In addition, regulation of ERRalpha expression in killifish apparently differs from regulation in mammals. Together, these features may facilitate determination of both conserved and specialized ERR gene functions.

Genetic and developmental influences on infant mouse ultrasonic calling. III. Patterns of inheritance in the calls of mice 3-9 days of age

Infant mice produce ultrasonic calls that may elicit retrieval by adult mice. Age-related differences and genetic effects, such as additivity and directional dominance, have been found for most call characteristics at 3 days of age. Significant maternal effects have been reported for calling rate. However, little is known about how the influence of these genetic effects changes with age. This study explored developmental-genetic patterns of inheritance of seven ultrasonic call characteristics at ages 3-9 days, from groups of mice derived from a complete 4 x 4 diallel cross. The results indicate that additive variance contributes significantly to all characteristics for all ages. Maternal effects have a small effect on call characteristics. Dominance effects decrease with age for rate, range, and length of calls, suggesting less selective pressure toward higher rates, greater range, and longer calls as pups become more competent thermoregulators.

A review of the methods of studies on infant ultrasound production and maternal retrieval in small rodents

Ultrasonic vocalizations or calls produced by young rodents have been associated with aspects of maternal behavior, in particular retrieving. We reviewed the methods of study used by investigators on each topic, focusing on intrinsic or subject variables and extrinsic or experimental variables. Intrinsic variables included the species studied, genotypes employed, number and sex composition of the litters, and the ages of mothers and pups. Extrinsic variables for studies on ultrasonic calling included: eliciting stimuli, test surroundings, and the length of observation. Extrinsic variables in studies of maternal retrieval included the testing procedure and the length of observation. The methods used in studies within each topic vary greatly. In an effort to facilitate progress in the areas, especially with respect to isolating individual genes with a contribution to ultrasonic call production or studying the effects of pharmaceutical agents on either behavior, we propose some standardization of nomenclature and/or procedure in four areas: (1) the stimuli or situations used to elicit ultrasonic calls, (2) the length of observation in ultrasonic call studies, (3) the number of pups per litter and the sex composition of litters in both ultrasonic call and maternal retrieval studies and finally, (4) the apparatus or testing situation used in studies of pup retrieval.

Biological activity and physicochemical parameters of marine halogenated natural products 2,3,3',4,4',5,5'-heptachloro-1'-methyl-1,2'-bipyrrole and 2,4,6-tribromoanisole

Physicochemical parameters (vapor pressure, water solubility, Henry's law constant) and biological activities of two halogenated natural products frequently detected in marine samples and food were determined. Synthetic 2,3,3',4,4',5,5'-heptachloro-1'-methyl-1,2'-bipyrrole (Q1) and 2,4,6-tribromoanisole (TBA) were available in pure form. The physicochemical parameters were in the range of anthropogenic chlorinated compounds of concern. The aqueous solubilities at 25 degrees C (S(w,25)) of Q1 and TBA were 4.6 microg/L and 12,200 microg/L, respectively, whereas subcooled liquid vapor pressures were 0.00168 Pa (Q1) and 0.06562 Pa (TBA) as measured by the gas chromatographic-retention time technique. Q1 was negative by established test systems for the determination of ethoxyresorufin-O-deethylase (EROD) induction and by sulforhodamine B assay. EROD induction potency was at least 10(-7) times lower than that of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). At a relatively high concentration (20 microM), Q1 inhibited specific binding of 2 nM [(3)H]TCDD to the in vitro-expressed human aryl hydrocarbon receptor (AHR) by 18%; lower concentrations showed no effect. Molecular modeling showed that Q1 is nonplanar, consistent with its relatively modest affinity as an AHR ligand. When tested for cell-growth inhibitory/cytocidal activity in human tumor cells, Q1 was only marginally, if at all, active with an IC(50) value >50 microM compared with five to ten times lower IC(50) values for potent cytotoxins tested in the test system used. Furthermore, standard pesticide tests on insecticidal, herbicidal, and fungicidal activity did not provide any significant activity at highest concentrations. For TBA, the results in all tests were comparable with Q1. The SRB assay was also applied to the halogenated natural product 4,6-dibromo-2-(2',4'-dibromo)phenoxyanisole, but no toxic response was found. Although it was apparent that Q1 and TBA had been proven to have relatively low biological activity in all tests performed, further research is necessary to clarify whether metabolites of the compounds eventually may possess a risk to humans or other living organisms. Nevertheless, the role of Q1 in nature remains uncertain.

[Radioulnar impingement after distal ulnar resection and ulnar head hemiresection interposition arthroplasty (Bowers procedure). An experimental biomechanical study]

Resection of the distal ulna (Darrach operation) and the ulnar head hemiresection interposition arthroplasty (Bowers procedure) are common methods of treating the arthrotic distal radioulnar joint (DRUJ). The purpose of this study was to evaluate the dynamic effects of both the Bowers operation and the resection of the distal ulna on radioulnar impingement and dorsal-palmar displacement and to compare their biomechanical performances. With a dynamic forearm simulator forearm rotation was performed with simultaneous loading of relevant muscles. Torque along the forearm axis was generated by simulated muscle action with loading of the relevant tendons while the wrist was constrained to prescribed ranges of motion. The instability of the radius relative to the ulna was evaluated using displacement data of digitized landmarks in an ulnar coordinate system. Seven fresh-frozen cadaver upper extremities were used. Resection of the distal ulna created a significant instability of the forearm with movement of the radius ulnarly. Anteroposterior translations in each loading condition could be detected as well but the magnitude of displacement was little and less predictable. The results of the Bowers operation demonstrated significantly less instability compared with the Darrach results. Our data demonstrates that the dynamic behavior of the Bowers procedure is superior to the mechanical performance of complete resection of the distal ulna.

The dynamic radioulnar convergence of the Darrach procedure and the ulnar head hemiresection interposition arthroplasty: a biomechanical study

Resection of the entire ulnar head (Darrach operation) and the hemiresection interposition arthroplasty are common methods of treating the arthritic distal radioulnar joint (DRUJ). Biomechnical investigation about both of these procedures is lacking. The purpose of this study was to evaluate the dynamic effects of both the hemiresection interposition arthroplasty and the Darrach procedure on radioulnar convergence and dorsal-palmar displacement and to compare their biomechanical behaviours. With a dynamic computer-controlled testing device, cadaveric forearm rotation was performed with simultaneous loading of relevant muscles. Torque along the forearm axis was generated by simulated muscle action through pneumoactuators attached to relevant tendons while the wrist was constrained to prescribed ranges of motion. The instability of the radius relative to the ulna was evaluated using displacement data of digitized landmarks in an ulnar coordinate system. Seven fresh-frozen cadaver upper extremities were used. The Darrach resection created an extreme instability of the forearm with movement of the radius ulnarly. Anteroposterior translations in each loading condition could also be detected, but the magnitude of displacement was small and less predictable. The results of the hemiresection interposition arthroplasty demonstrated significantly less instability compared with the Darrach results.

Dynamische radioulnare Konvergenz nach Darrach-Operation, Weichteilstabilisierungsoperationen der distalen Ulna und Ulnakopfprothesenimplantation - Eine experimentelle biomechanische Studie

The most common method of treating the arthrotic distal radioulnar joint (DRUJ) is resection of the entire ulnar head (Darrach procedure). Complications related to instability of the distal forearm resulting from loss of the ulnar head are usually manifested by pain and weak grip strength and have remained the drawbacks of this procedure. In an attempt to mechanically stabilize the distal forearm, an endoprosthesis was developed to replace the ulnar head after Darrach resection. The purpose of this study was to: 1) evaluate the dynamic effects of the Darrach procedure on radioulnar convergence; and 2) evaluate the mechanical efficacy of two soft tissue stabilizing techniques (Pronator quadratus advancement flap and ECU/FCU tenodesis) for the unstable distal ulnar stump and 3) the stability after the implantation of an ulnar head endoprosthesis following a Darrach resection on radioulnar convergence. With a dynamic PC-controled forearm simulator the rotation of 7 fresh-frozen cadaver upper extremities was actively and passively performed while loading relevant muscles. Resultant total forearm torque and the 3-dimensional kinematics of the ulna, radius and third metacarpal were recorded simultaneously. The implantation of the ulnar head endoprosthesis effectively restored the stability of the DRUJ. There were significantly better results after the implantation of the prosthesis compared with the Darrach and the soft tissue stabilization procedures. This study provides laboratory validity to the option of implanting an ulnar head endoprosthesis as an attempt to stabilize the distal forearm after Darrach resection in lieu of performing soft tissue stabilization techniques.

Prenatal cocaine exposure alters maternal retrieval behavior in mice

Previous studies have demonstrated alterations in maternal retrieval behavior as a result of direct cocaine exposure. To establish the influence of prenatal cocaine exposure on pup retrieval, we exposed pups of three F1 genotypes by injecting their mothers (all C57BL/10J strain) with 20 mg/kg cocaine hydrochloride or saline subcutaneously on gestation days 7 to 17. When those pups became adults, control and exposed females were mated with males of the same genotype and tested for pup retrieval on postpartum days 4 and 5. Because ultrasonic calls are known to be elicitors of maternal retrieval behavior, the rate of ultrasonic calling was measured. Prenatal cocaine exposure exerted a significant effect upon retrieval latency on day 4. No relationship was found between genotype and retrieval latency.

The effects of cold, rotation, and genotype on the production of ultrasonic calls in infant mice

There has been a revival of interest recently in the ultrasonic calls of infant rodents as investigators are using them to assess neurobehavioral development and animal models of anxiety. We compared the rates of ultrasonic calling of infant mice of two genotypes in two situations, cold and rotation. The subjects of study were 169 mouse pups from 29 litters and of two F1 genotypes, C57BL/10J x DBA/2J and C57BL/10J x SJL/J. Half of each litter was recorded in a cool situation for 20 seconds and the other half was recorded while rotating at 10 rpm for 20 seconds. All pups were recorded on days of age 2 to 8. Rotation elicited calling at about twice the rate as cool temperature on each day of age and on average across days; situation (cold or rotation) accounted for over 50% of the variation between litters. Genotype also altered call rate, and on some days situation and genotype interacted. In studies of neurobehavioral development and the effects of pharmacological agents on infant mice, it is particularly important to understand the roles of the stimuli and genotypes employed.

cDNA cloning and characterization of a high affinity aryl hydrocarbon receptor in a cetacean, the beluga, Delphinapterus leucas

Some cetaceans bioaccumulate substantial concentrations of planar halogenated aromatic hydrocarbons (PHAHs) in their tissues, but little is known about the effects of such burdens on cetacean health. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) and related PHAHs cause toxicity via activation of the aryl hydrocarbon receptor (AHR), a member of the bHLH-PAS family of transcription factors. Differences in AHR structure and function are known to contribute to species-specific differences in susceptibility to PHAH toxicity. To ascertain the potential for PHAH effects in a cetacean, we characterized an AHR from the beluga whale, Delphinapterus leucas. The 3.2 kb cDNA encodes an 845-amino acid protein with a predicted size of 95.5 kDa. Overall, the beluga AHR shares 85% amino acid sequence identity with the human AHR and 75% identity with the mouse AHR Ah(b-1) allele. Beluga AHR protein synthesized in a rabbit reticulocyte lysate system demonstrated specific, high-affinity [(3)H]TCDD binding. Saturation binding analysis was used to compare the [(3)H]TCDD binding affinity of the in vitro-expressed beluga AHR with affinities of in vitro-expressed AHRs from a dioxin-sensitive mouse strain (Ah(b-1) allele) and humans. The beluga AHR bound [(3)H]TCDD with an affinity (K(d)= 0.43 +/- 0.16 nM) that was at least as high as that of the mouse AHR (K(d)= 0.68 +/- 0.23 nM), and significantly greater than that of the human AHR (K(d)= 1.63 +/- 0.64 nM). In electrophoretic mobility shift assays, the beluga AHR exhibited sequence-specific, Arnt-dependent binding to a dioxin responsive enhancer (DRE). Upon transient transfection into mammalian cells, the beluga AHR activated transcription of a luciferase reporter under control of a DRE-containing fragment of the mouse Cyp1a1 promoter. These results show that in an in vitro system, the beluga AHR possesses characteristics similar to those of AHRs from other mammals that are considered sensitive to toxic effects of PHAHs. Together, these results demonstrate that the use of in vitro-expressed proteins is a promising approach for addressing molecular and biochemical questions concerning PHAH toxicity in endangered or protected species.

An aryl hydrocarbon receptor (AHR) homologue from the soft-shell clam, Mya arenaria: evidence that invertebrate AHR homologues lack 2,3,7,8-tetrachlorodibenzo-p-dioxin and beta-naphthoflavone binding

The aryl hydrocarbon receptor (AHR) mediates numerous toxic effects following exposure of vertebrate animals to certain aromatic environmental contaminants, including 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). To investigate possible effects of TCDD on invertebrates, a cDNA encoding an AHR homologue was cloned from the soft-shell clam, Mya arenaria. The predicted amino acid sequence contains regions characteristic of vertebrate AHRs: basic helix-loop-helix (bHLH) and PER-ARNT-SIM (PAS) domains and a glutamine-rich region. Phylogenetic analysis shows that the clam AHR sequence groups within the AHR subfamily of the bHLH-PAS family, in a clade containing AHR homologues from Drosophila melanogaster and Caenorhabditis elegans. AHR mRNA expression was detected in all tissue types tested: adductor muscle, digestive gland, foot, gill, gonad, mantle, and siphon. The in vitro-expressed clam AHR exhibited sequence-specific interactions with a mammalian xenobiotic response element (XRE). Velocity sedimentation analysis using either in vitro-expressed clam AHR or clam cytosolic proteins showed that this AHR homologue binds neither [(3)H]TCDD nor [(3)H]beta-naphthoflavone (BNF). Similarly, in vitro-expressed D. melanogaster and C. elegans AHR homologues lacked specific binding of these compounds. Thus, the absence of specific, high-affinity binding of the prototypical AHR ligands TCDD and BNF, is a property shared by known invertebrate AHR homologues, distinguishing them from vertebrate AHRs. Comparative studies of phylogenetically diverse organisms may help identify an endogenous ligand(s) and the physiological role(s) for this protein.

2,3,7,8-Tetrachlorodibenzo-p-dioxin induces apoptotic cell death and cytochrome P4501A expression in developing Fundulus heteroclitus embryos

Fundulus heteroclitus embryos were exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) during early development using nanoinjection or water bath exposure. TCDD caused developmental abnormalities that included hemorrhaging, loss of vascular integrity, edema, stunted development and death. The LC(50) and LD(50) of TCDD for Fundulus embryos were approximately 19.7+/-9.5 pg TCDD/microl (water bath) and 0.25+/-0.09 ng TCDD/g embryo (nanoinjection). To identify a possible cause for these developmental abnormalities we analyzed the effects of TCDD on apoptotic cell death and cytochrome P4501A (CYP1A) expression in the embryos. TCDD exposure increased apoptotic cell death in several tissues including brain, eye, gill, kidney, tail, intestine, heart, and vascular tissue. CYP1A expression was also increased in the TCDD-exposed embryos predominantly in liver, kidney, gill, heart, intestine, and in vascular tissues throughout the embryo. There was co-occurrence of TCDD-induced apoptosis and CYP1A expression in some, but not all, cell types. In addition the dose response relationships for apoptosis and mortality were similar, while CYP1A expression appeared more sensitive to TCDD induction.

Dioxin toxicology and the aryl hydrocarbon receptor: insights from fish and other non-traditional models

Fish are established models in biology. Recent findings suggest that fish and other nontraditional species also may serve as valuable model systems for understanding receptor-dependent signaling pathways and their interactions with environmental chemicals. Because they are highly sensitive to chlorinated dioxins and related halogenated aromatic hydrocarbons, fish are being used to elucidate the role of chemical signaling pathways in the developmental and molecular toxicology of dioxin-like compounds. Much of this work is focused on the aryl hydrocarbon receptor (AHR), a ligand-activated, bHLH-PAS transcription factor through which dioxins cause altered gene expression and toxicity. In contrast to mammals, which appear to express a single dioxin-binding AHR, many fish species possess at least two AHR genes. Studies of these two fish AHRs may help to reveal the multiple functions of the single mammalian "AHR," its physiological ligand, and the molecular mechanisms involved in differential sensitivity to dioxin-like compounds. In addition, fish have great potential as models for understanding the in vivo functions and interactions of bHLH-PAS proteins, the evolutionary history of their diversification in vertebrates, and their role in human physiology and disease.

Acquired resistance to Ah receptor agonists in a population of Atlantic killifish (Fundulus heteroclitus) inhabiting a marine superfund site: in vivo and in vitro studies on the inducibility of xenobiotic metabolizing enzymes

New Bedford Harbor (NBH), MA, is a federal Superfund site that is heavily contaminated with polychlorinated biphenyls (PCBs) and other halogenated aromatic hydrocarbons (HAHs), including some potent aryl hydrocarbon receptor (AhR) agonists. A population of Atlantic killifish (Fundulus heteroclitus) continues to inhabit this site, despite accumulating extraordinarily high concentrations of PCBs (272 microg/g dry weight). To determine if NBH killifish have developed resistance to HAHs that act through the AhR, we examined the inducibility of cytochrome P4501A1 (CYP1A1), UDP glucuronosyl transferase (UGT), and glutathione S-transferase (GST) in fish from NBH and a reference site, Scorton Creek (SC, Cape Cod, MA; PCB concentrations 0.177 microg/g dry weight). 2,3,7,8-Tetrachlorodibenzofuran (TCDF) induced CYP1A1 mRNA, protein, and activity in SC fish in all tissues examined (liver, heart, gut, gill, kidney, spleen, and gonad). In contrast, NBH fish expressed low levels of CYP1A1 and showed no induction of CYP1A1 mRNA, protein, or activity by TCDF, or induction that was lower in magnitude or required higher doses of inducer. p-Nitrophenol UGT activity was not induced by TCDF in either population, while GST activity with 1-chloro-2,4-dinitrobenzene as substrate was induced only in NBH fish in one experiment. Inducibility of CYP1A1 by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) or beta-naphthoflavone (BNF) was measured in primary hepatocyte cultures prepared from SC and NBH fish. TCDD induced CYP1A1 activity (ethoxyresorufin O-deethylase) to the same degree in hepatocytes from both populations, demonstrating the functionality of the AhR signaling pathway in NBH fish. However, hepatocytes from NBH fish were 14-fold less sensitive to TCDD than were those from SC fish. The nonhalogenated AhR agonist BNF also induced CYP1A1 in cells from both populations, although with only a 3-fold difference in sensitivity (NBH < SC). These results indicate that chronic exposure to high levels of HAHs has led to a reduction in the sensitivity of NBH killifish to AhR agonists. The resistance is systemic and pretranslational, and exhibits compound-specific differences in magnitude. These findings suggest an alteration in the AhR signal transduction pathway in NBH fish.

The effects of prenatal cocaine exposure and genotype on the ultrasonic calls of infant mice

Estimates are that as many as 44,000 humans are exposed to cocaine in utero per year. In this study we examined the effects of prenatal cocaine exposure on one aspect of the mother-infant relationship in mice, infant ultrasonic calls. We mated C57BL/10J female mice with males of three different inbred strains (producing pups of three different F(1) genotypes). We injected those females, subcutaneously, with saline or 20 mg/kg of cocaine hydrochloride on days 7-17 of gestation. That dosage did not compromise mother or pup viability, weight, or gestation length. On postnatal days 2-4, we recorded and measured the calls of pups while they were separated from their nest and slightly chilled. The results indicate changes in the ultrasonic calls as a function of cocaine and genotype. Overall, cocaine reduced the number of calls and increased the beginning pitch of calls. Pups of one genotype, a C57BL/10JxSJL/J hybrid were unaffected by cocaine exposure. The effects of cocaine, though reliable, were small, explaining only 1-2% of the total sum of squares. The size of the effect is in part due to the differential effect of cocaine on different genotypes.

Relative contributions of affinity and intrinsic efficacy to aryl hydrocarbon receptor ligand potency

Models of receptor action are valuable for describing properties of ligand-receptor interactions and thereby contribute to mechanism-based risk assessment of receptor-mediated toxic effects. In order to build such a model for the aryl hydrocarbon receptor (AHR), binding affinities and CYP1A induction potencies were measured in PLHC-1 cells and were used to determine intrinsic efficacies for 10 halogenated aromatic hydrocarbons (HAH): 2,3,7, 8-tetrachlorodibenzo-p-dioxin (TCDD), 2,3,7, 8-tetrachlorodibenzofuran (TCDF), and eight polychlorinated biphenyls (PCB). TCDD, TCDF, and non-ortho-substituted PCBs 77, 81, 126, and 169 behaved as full agonists and displayed high-intrinsic efficacy. In contrast, the mono- and di-ortho-substituted PCBs bound to the AHR but displayed lower or no intrinsic efficacy. PCB 156 was a full agonist, but with an intrinsic efficacy 10- to 50-fold lower than non-ortho-substituted PCBs. PCB 118 was a very weak partial agonist. PCBs 105 and 128 were shown to be competitive antagonists in this system. The model was then used to predict CYP1A induction by binary mixtures. These predictions were tested with binary mixtures of PCB 126, 128, or 156 with TCDD. Both PCB 156 (a low-intrinsic efficacy agonist) and PCB 128 (a competitive antagonist) inhibited the response to TCDD, while the response to TCDD and PCB126 was additive. These data support the following conclusions: 1) only 1-2% of the receptors in the cell need be occupied to achieve 50% of maximal CYP1A induction by one of the high-intrinsic efficacy agonists, demonstrating the existence of "spare" receptors in this system; 2) the insensitivity of fish to ortho-substituted PCBs is due to both reduced affinity and reduced intrinsic efficacy compared to non-ortho-substituted PCBs; 3) PCB congeners exhibit distinct structure-affinity and structure-efficacy relationships. Separation of AHR ligand action into the properties of affinity and intrinsic efficacy allows for improved prediction of the behavior of complex mixtures of ligands, as well as mechanistic comparisons across species and toxic endpoints.

Developmental and tissue-specific expression of AHR1, AHR2, and ARNT2 in dioxin-sensitive and -resistant populations of the marine fish Fundulus heteroclitus

Fundulus heteroclitus is a well-characterized marine fish model for studying aryl hydrocarbon toxicity. The F. heteroclitus population in New Bedford Harbor (NBH), a Superfund site in southeastern Massachusetts, exhibits heritable resistance to the toxic effects of planar halogenated aromatic hydrocarbons (PHAHs), including 2,3,7, 8-tetrachlorodibenzo-p-dioxin (TCDD) and polychlorinated biphenyls (PCBs). To investigate the role of the aryl hydrocarbon receptor (AHR) signal transduction pathway in PHAH resistance, we measured the relative levels of AHR1, AHR2, and ARNT2 mRNA in whole embryos at different developmental stages and in dissected tissues of adults, comparing expression of these genes in NBH fish with fish from a reference site (Scorton Creek, MA [SC]). Expression of both AHR1 and AHR2 mRNA increased during development, achieving maximum levels prior to hatching. Maximal embryonic expression of AHR1 was delayed relative to AHR2. Whole NBH and SC embryos exhibited no discernable differences in expression of these genes. As we have previously observed, adult SC fish expressed AHR2 and ARNT2 mRNA in all tissues examined, while AHR1 was expressed predominantly in brain, heart, and gonads. In contrast, AHR1 mRNA was widely expressed in NBH fish, appearing with unusual abundance in gill, gut, kidney, liver, and spleen. This AHR1 expression pattern was not observed in the lab-reared progeny of NBH fish, demonstrating that constitutive AHR1 expression in gill, gut, kidney, liver, and spleen is not a heritable phenotype. Furthermore, widespread AHR1 expression was not induced in reference-site fish by TCDD or PCB mixtures, suggesting that aberrant AHR1 expression is not simply a normal physiological response of contaminant exposure. These results identify ubiquitous AHR1 expression as an attribute unique to feral NBH F. heteroclitus, and they represent a first step in determining the regulatory mechanisms underlying this expression pattern and its possible role in TCDD resistance.

The bioflavonoid galangin blocks aryl hydrocarbon receptor activation and polycyclic aromatic hydrocarbon-induced pre-B cell apoptosis

Bioflavonoids are plant compounds touted for their potential to treat or prevent several diseases including cancers induced by common environmental chemicals. Much of the biologic activity of one such class of pollutants, polycyclic aromatic hydrocarbons (PAH), is mediated by the aryl hydrocarbon receptor/transcription factor (AhR). For example, the AhR regulates PAH immunotoxicity that manifests as pre-B cell apoptosis in models of B cell development. Because bioflavonoids block PAH-induced cell transformation and are structurally similar to AhR ligands, it was postulated that some of them would suppress PAH-induced, AhR-dependent immunotoxicity, possibly through a direct AhR blockade. This hypothesis was tested using a model of B cell development in which pre-B cells are cultured with and are dependent on bone marrow stromal or hepatic parenchymal cell monolayers. Of seven bioflavonoids screened, galangin (3,5,7-trihydroxyflavone) blocked PAH-induced but not C(2)-ceramide- or H(2)O(2)-induced pre-B cell apoptosis. Because galangin blocked AhR-dependent reporter gene expression, AhR complex-DNA binding, and AhR nuclear translocation, inhibition of a relatively early step in AhR signaling was implicated. This hypothesis was supported by the ability of galangin to bind the AhR and stabilize AhR-90-kDa heat shock protein complexes in the presence of AhR agonists. These studies demonstrate the utility of pre-B cell culture systems in identifying compounds capable of blocking PAH immunotoxicity, define at least one mechanism of galangin activity (i.e., repression of AhR activation), and motivate the use of this and similar dietary bioflavonoids as relatively nontoxic inhibitors of AhR agonist activity and as pharmacologic agents with which to dissect AhR signaling pathways.

In vitro metabolism of polychlorinated biphenyl congeners by beluga whale (Delphinapterus leucas) and pilot whale (Globicephala melas) and relationship to cytochrome P450 expression

We measured rates of oxidative metabolism of two tetrachlorobiphenyl (TCB) congeners by hepatic microsomes of two marine mammal species, beluga whale and pilot whale, as related to content of selected cytochrome P450 (CYP) forms. Beluga liver microsomes oxidized 3,3',4,4'-TCB at rates averaging 21 and 5 pmol/min per mg for males and females, respectively, while pilot whale samples oxidized this congener at 0.3 pmol/min per mg or less. However, rates of 3,3',4,4'-TCB metabolism correlated with immunodetected CYP1A1 protein content in liver microsomes of both species. The CYP1A inhibitor alpha-naphthoflavone inhibited 3,3',4,4'-TCB metabolism by 40% in beluga, supporting a role for a cetacean CYP1A as a catalyst of this activity. Major metabolites of 3,3',4,4'-TCB generated by beluga liver microsomes were 4-OH-3,3',4',5-TCB and 5-OH-3,3',4,4'-TCB (98% of total), similar to metabolites formed by other species CYP1A1, and suggesting a 4,5-epoxide-TCB intermediate. Liver microsomes of both species metabolized 2,2',5,5'-TCB at rates of 0.2-1.5 pmol/min per mg. Both species also expressed microsomal proteins cross-reactive with antibodies raised against some mammalian CYP2Bs (rabbit; dog), but not others (rat; scup). Whether CYP2B homologues occur and function in cetaceans is uncertain. This study demonstrates that PCBs are metabolized to aqueous-soluble products by cetacean liver enzymes, and that in beluga, rates of metabolism of 3,3',4,4'-TCB are substantially greater than those of 2,2',5,5'-TCB. These directly measured rates generally support the view that PCB metabolism plays a role in shaping the distribution patterns of PCB residues found in cetacean tissue.

The evolution of aryl hydrocarbon signaling proteins: diversity of ARNT isoforms among fish species

The aryl hydrocarbon receptor nuclear translocator (ARNT) mediates aryl hydrocarbon signaling and toxicity by dimerizing with the ligand-activated aryl hydrocarbon receptor (AHR), forming a complex that binds specific DNA elements and alters transcription of target genes. Two genes encode different forms of ARNT in rodents: ARNT1, which is widely expressed, and ARNT2, which exhibits a very restricted expression pattern. In an effort to characterize aryl hydrocarbon signaling mechanisms in fishes, we previously isolated an ARNT cDNA from Fundulus heteroclitus and discovered that this species expresses ARNT2 ubiquitously. This situation differs not only from mammals, but also from rainbow trout, which expresses a divergent ARNT gene that we hypothesized was peculiar to salmonids (rtARNTa/b). In this communication, we examine the ARNT sequences of multiple fish species, including a newly isolated cDNA from scup (Stenotomus chrysops). Our phylogenetic analysis demonstrates that zebrafish ARNT, like the Fundulus protein, is an ARNT2. Contrary to expectations, the scup ARNT is closely related to the rainbow trout protein, demonstrating that the existence of this ARNT isoform predates the divergence of salmonids from the other teleosts. Thus, different species of fish express distinct and highly conserved isoforms of ARNT. The number, type, and expression pattern of ARNT proteins may contribute to interspecies differences in aryl hydrocarbon toxicity, possibly through distinct interactions with additional PAS-family proteins.

Towards molecular understanding of species differences in dioxin sensitivity: initial characterization of Ah receptor cDNAs in birds and an amphibian

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) and related planar halogenated aromatic hydrocarbons (PHAHs) are highly toxic to most vertebrate animals, but there are dramatic species differences in sensitivity, both within and among vertebrate classes. For example, studies in cultured avian hepatocytes have revealed differential sensitivity of birds to PHAHs [Kennedy et al. (1996). Toxicol. Appl. Pharmacol., 141, 214-230]. Differences in the characteristics or expression of the aryl hydrocarbon receptor (AHR) could contribute to these species differences in PHAH responsiveness. To investigate the molecular mechanism of differential PHAH sensitivity, we have begun to characterize the AHR in white leghorn chicken (Gallus gallus), Pekin duck (Anas platyrhynchos), and common tern (Sterna hirundo), as well as an amphibian, mudpuppy (Necturus maculosus). Partial AHR cDNAs encompassing the helix-loop-helix and PAS domains were cloned and sequenced. Comparison of amino acid sequences in this region indicated a high degree of sequence conservation among the bird species (97% amino acid identity). The percent identity between bird sequences and either mouse or mudpuppy was lower (79%); the mudpuppy AHR was 74% identical to the mouse AHR. Phylogenetic analysis of these and other AHR amino acid sequences showed that the bird and mudpuppy AHRs were more closely related to mammalian and fish AHR1 forms than to fish AHR2. Future studies include the in vitro expression and functional characterization of AHRs from these and other non-mammalian vertebrates.

Serum alters the uptake and relative potencies of halogenated aromatic hydrocarbons in cell culture bioassays

The effects of many chemicals on cellular processes are governed by their ability to enter the cell, which is in turn a function of the composition of the cell's external environment. To examine this relationship, the effect of serum in cell culture medium on the bioavailability of cytochrome P450 1A (CYP1A)-inducing compounds was determined in PLHC-1 (Poeciliopsis lucida hepatocellular carcinoma) cells. The presence of 10% calf serum in the medium increased the EC50 (effective concentration to achieve 50% maximal response) for induction of ethoxyresorufin O-deethylase (EROD) activity by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) 20-fold as compared to treatment in serum-free medium. Measurement of [3H]TCDD uptake and Ah receptor binding indicated that the apparent difference in potencies was a result of decreased bioavailability in the presence of serum, effectively reducing the concentration of TCDD within the cells. Induction of EROD and CYP1A protein in response to treatment with each of three coplanar polychlorinated biphenyls (PCB congeners 77, 126, and 169) was similarly affected by serum, although the magnitude varied among inducers and assays. Relative potencies (calculated as EC50TCDD / EC50PCB) for EROD induction by the three PCBs were significantly higher in the absence of serum. However, serum showed no significant effect on the relative potencies for CYP1A protein induction. These results demonstrate that measured inducing potencies, and relative potencies for EROD induction, by halogenated aromatic hydrocarbons are strongly dependent on the composition of culture medium, which can lead to artificial differences in comparisons among cell types.

Cytochrome P4501A induction and porphyrin accumulation in PLHC-1 fish cells exposed to sediment and oil shale extracts

The present study describes the use of a fish hepatoma cell line (PLHC-1) in monitoring the biological effects of sediments collected from recipient waters of the oil shale industry. Sampling sites were located in River Purtse and River Kohtla in northeast Estonia. The effects of pure oil shale on the PLHC-1 cells were also studied. The cells were exposed to n-hexane-extracted samples in 48-well plates for 24 h, and 7-ethoxyresorufin O-deethylase (EROD) activity, total protein, and porphyrin content were measured in the exposed cells. Polycyclic aromatic hydrocarbon (PAH) contents in the samples were measured by high-performance liquid chromatography (HPLC). All the sediment and oil shale samples induced CYP1A activity and led to porphyrin accumulation in the cells. The most potent inducers were the sediments collected near the oil shale processing plants (site Lüganuse in River Purtse and Kohtla in River Kohtla), as well as those at the most downstream site in River Purtse (Purtse). These samples possessed high total PAH contents, ranging from 4,270 to nearly 150,000 microg/kg dry sediment. The presence of other lipophilic organic contaminants in the samples was not determined in this study. Both EROD activity and porphyrin content exhibited biphasic induction curves, and the ED(50)(1) values for EROD activity were lower than the ED(50)s for porphyrin content. 2,3,7, 8-Tetrachlorodibenzo-p-dioxin induction equivalents (TCDD-EQs) calculated from EROD induction potencies correlated well with total PAHs (r(2) = 0.827 and p = 0.003 for log-transformed data) and also with individual PAHs. TCDD-EQs for porphyrin content did not correlate significantly with total PAHs (log-log r(2) = 0.785, p = 0. 116). The biological potency and PAH contamination of the samples showed the same rank order, except at Lüganuse, where sediment extracts induced CYP1A and porphyrins more than could have been expected based on PAH contents. Bioassay-derived induction EQs (normalized to dibenz(a,h)anthracene) were 20- to 3,200-fold greater than EQs calculated from the concentrations of five PAHs, suggesting important contributions from other compounds or nonadditive effects. The PLHC-1 cells proved to be a sensitive bioanalytical tool for sediments contaminated with PAH-type pollutants in the oil shale processing area. We suggest further use of this bioassay in screening and monitoring waters with similar background of pollution as in northeast Estonia.

Identification and functional characterization of two highly divergent aryl hydrocarbon receptors (AHR1 and AHR2) in the teleost Fundulus heteroclitus. Evidence for a novel subfamily of ligand-binding basic helix loop helix-Per-ARNT-Sim (bHLH-PAS) factors

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor through which 2,3,7, 8-tetrachlorodibenzo-p-dioxin (TCDD) and related compounds cause altered gene expression and toxicity. The AHR belongs to an emerging multigene family of transcription factors possessing basic helix loop helix (bHLH) and Per-ARNT-Sim (PAS) domains. Most bHLH-PAS proteins occur as duplicates or "paralog groups" in mammals, but only a single mammalian AHR has been identified. Here we report the cDNA cloning of two distinct AHRs, designated FhAHR1 and FhAHR2, from a single vertebrate species, the teleost Fundulus heteroclitus (Atlantic killifish). Both Fundulus AHR proteins possess bHLH and PAS domains that are closely related to those of the mammalian AHR. FhAHR1 and FhAHR2 are highly divergent (40% overall amino acid identity; 61% identity in the N-terminal half), suggesting that they arose from a gene duplication predating the divergence of mammals and fish. Photoaffinity labeling with 2-azido-3-[(125)I]iodo-7, 8-dibromodibenzo-p-dioxin and velocity sedimentation analysis using 2,3,7,8-[1,6-(3)H]TCDD showed that both FhAHR1 and FhAHR2 exhibit specific, high-affinity binding of dioxins. Both AHRs also showed specific, TCDD- and ARNT-dependent interactions with a mammalian xenobiotic response element. The two Fundulus AHR genes displayed different tissue-specific patterns of expression; FhAHR1 transcripts were primarily expressed in brain, heart, ovary, and testis, while FhAHR2 transcripts were equally abundant in many tissues. Phylogenetic analysis demonstrated that Fundulus AHR1 is an ortholog of mammalian AHRs, while AHR2 forms in Fundulus and other fish are paralogous to Fundulus AHR1 and the mammalian AHRs and thus represent a novel vertebrate subfamily of ligand-binding AHRs.

The role of polycyclic aromatic hydrocarbon metabolism in dimethylbenz[a]anthracene-induced pre-B lymphocyte apoptosis

Previous studies indicated that two prototypic PAH, benzo[a]pyrene (B[a]P) and 7,12-dimethylbenz[a]anthracene (DMBA), suppress the developing immune system by inducing apoptosis in bone marrow pre-B lymphocytes. In bone marrow cultures consisting of pre-B cells growing on bone marrow stromal cell monolayers, pre-B cell apoptosis was shown to be dependent on the aryl hydrocarbon receptor/transcription factor (AhR) expressed in stromal cells. However, it was not determined if AhR activation alone is sufficient or if DMBA metabolism is required for induction of a stromal cell-derived apoptosis signal. To address these issues we assessed: 1) the ability of poorly metabolized AhR ligands to induce pre-B cell apoptosis and 2) the capacity for and the mechanism through which an early DMBA metabolite induces pre-B cell apoptosis. Three poorly metabolized AhR ligands, 2,3,7,8-tetrachlorodibenzo-p-dioxin, 3,3',4,4',5-pentachlorobiphenyl, and 3,3',4,4'-tetrachlorobiphenyl failed to induce pre-B cell apoptosis in bone marrow cultures, indicating that AhR activation alone is not sufficient to induce apoptosis and suggesting a role for PAH metabolism in induction of an apoptosis signal. Consistent with this hypothesis, DMBA-3, 4-dihydrodiol, an early DMBA metabolite, induced significant pre-B cell apoptosis. The ability of DMBA-3,4-dihydrodiol to activate the AhR, inhibition of DMBA-3,4-dihydrodiol-induced apoptosis by alpha-naphthoflavone, and the significantly lower levels of DMBA-3, 4-dihydrodiol-induced apoposis in pre-B cell populations maintained on AhR(-) stromal cells strongly support a role for the AhR in DMBA-3,4-dihydrodiol-induced apoptosis. Of two DMBA-metabolizing enzymes evaluated, CYP1A1 and CYP1B1, the latter appeared to be the more likely to play a role in DMBA-induced apoptosis. These data confirm a role for the AhR in PAH-induced pre-B cell apoptosis, indicate a role for DMBA metabolism, and suggest a feedback loop in which at least one product of DMBA metabolism augments AhR signaling, leading to induction of an apoptosis stimulus.

Two forms of aryl hydrocarbon receptor type 2 in rainbow trout (Oncorhynchus mykiss). Evidence for differential expression and enhancer specificity

Two aryl hydrocarbon receptors (AhRs), rtAhR2alpha and rtAhR2beta, were cloned from rainbow trout (rt) cDNA libraries. The distribution of sequence differences, genomic Southern blot analysis, and the presence of both transcripts in all individual rainbow trout examined suggest that the two forms of rtAhR2 are derived from separate genes. The two rtAhR2s have significant sequence similarity with AhRs cloned from mammalian species, especially in the basic helix-loop-helix and PAS functional domains located in the amino-terminal 400 amino acids of the protein. In contrast, the Gln-rich transactivation domain found in the carboxyl-terminal half of mammalian AhRs is absent from both rtAhR2s. Both clones were expressed by in vitro transcription/translation and proteins of approximately 125 kDa were produced. These proteins bind 2,3,7, 8-tetrachlorodibenzo-p-dioxin (TCDD) and are able to bind dioxin response elements in gel shift assays. rtAhR2alpha and rtAhR2beta are expressed in a tissue-specific manner with the highest expression of rtAhR2beta in the heart. Expression of rtAhR2alpha and rtAhR2beta mRNAs is positively regulated by TCDD. Both rtAhR2alpha and rtAhR2beta produced TCDD-dependent activation of a reporter gene driven by dioxin response elements. Surprisingly, the two receptors showed distinct preferences for different enhancer sequences. These results suggest that the two receptor forms may regulate different sets of genes, and may play different roles in the toxic responses produced by AhR agonists such as TCDD.

Functional diversity of vertebrate ARNT proteins: identification of ARNT2 as the predominant form of ARNT in the marine teleost, Fundulus heteroclitus

The aryl hydrocarbon receptor nuclear translocator (ARNT) is a member of the bHLH/PAS protein superfamily. ARNT dimerizes with several PAS superfamily members, including the ligand-activated aryl hydrocarbon receptor (AHR), forming a complex that alters transcription by binding specific elements within the promoters of target genes. Two genes encode different forms of the protein in rodents: ARNT1, which is widely expressed, and ARNT2, which is limited to the brain and kidneys of adults and specific neural and branchial tissues of embryos. In an effort to characterize aryl hydrocarbon signaling mechanisms in Fundulus heteroclitus, a marine teleost that can develop heritable xenobiotic resistance, we have isolated a liver cDNA encoding an ARNT homolog. The protein exhibits AHR-dependent DNA binding capability typical of other vertebrate ARNTs. Unexpectedly, phylogenetic analysis reveals that the cDNA encodes an ARNT2. This is the only detectable ARNT sequence in Fundulus liver, gill, ovary, and brain, suggesting that ARNT2 is the predominant form of ARNT in this species. Also surprising is the relative lack of sequence identity with another fish ARNT protein, rainbow trout ARNTb, which we show forms a distinct branch outside the ARNT1 and ARNT2 clades in phylogenetic analyses. Functional diversity of ARNT proteins in fish may have important implications for the assessment of aryl hydrocarbon effects on natural populations. The increasing use of fish models in developmental and toxicological studies underscores the importance of identifying taxon-specific roles of ARNT proteins and their potential dimeric partners in the PAS superfamily.

The aryl hydrocarbon receptor: a comparative perspective

The aryl hydrocarbon receptor (Ah receptor or AHR) is a ligand-activated transcription factor involved in the regulation of several genes, including those for xenobiotic-metabolizing enzymes such as cytochrome P450 1A and 1B forms. Ligands for the AHR include a variety of aromatic hydrocarbons, including the chlorinated dioxins and related halogenated aromatic hydrocarbons whose toxicity occurs through activation of the AHR. The AHR and its dimerization partner ARNT are members of the emerging bHLH-PAS family of transcriptional regulatory proteins. In this review, our current understanding of the AHR signal transduction pathway in non-mammalian and other non-traditional species is summarized, with an emphasis on similarities and differences in comparison to the AHR pathway in rodents and humans. Evidence and prospects for the presence of a functional AHR in early vertebrates and invertebrates are also examined. An overview of the bHLH-PAS family is presented in relation to the diversity of bHLH-PAS proteins and the functional and evolutionary relationships of the AHR and ARNT to the other members of this family. Finally, some of the most promising directions for future research on the comparative biochemistry and molecular biology of the AHR and ARNT are discussed.

Genetic and developmental influences on infant mouse ultrasonic calling. II. Developmental patterns in the calls of mice 2-12 days of age

Infant house mice, Mus musculus, produce ultrasonic calls that reliably lead to retrieval by adult mice. While individual differences in calls have been demonstrated both among and within species, the influences of age and sex on call characteristics have not been systematically investigated in mice. This study examined the influences of age, sex, and genotype (inbred versus hybrid) on the rate, length, and frequency characteristics of the calls of 486 male and female mice from 2 to 12 days of age. Rate of calling followed a shallow inverted U-shaped function across days. Call lengths decreased and call frequency characteristics increased, in a linear manner, with age. Females emitted fewer calls, with a smaller bandwidth, at some ages than males. Hybrid pups produced more calls of greater length and a lower frequency than inbred pups. These results indicate the presence of cues that could allow adult mice to behave differentially toward pups as a function of their age and sex.

Aryl hydrocarbon receptor function in early vertebrates: inducibility of cytochrome P450 1A in agnathan and elasmobranch fish

The mammalian aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that controls the expression of cytochrome P450 1A (CYP1A) genes in response to halogenated aromatic hydrocarbons such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The natural ligand and normal physiologic function of this protein are as yet unknown. One approach to understanding AHR function and significance is to determine the evolutionary history of this receptor and of processes such as CYP1A induction that are controlled by the AHR in mammals. In these studies, AHR function was evaluated in representative cartilaginous fish (little skate, Raja erinacea) and jawless fish (sea lamprey, Petromyzon marinus and Atlantic hagfish, Myxine glutinosa), using CYP1A induction as a model AHR-dependent response. Treatment of skate with beta-naphthoflavone (BNF) caused an 8-fold increase in hepatic ethoxyresorufin O-deethylase (EROD) activity as well as a 37-fold increase in the content of immunodetectable CYP1A protein. Evidence of CYP1A inducibility was also obtained for another cartilaginous fish, the smooth dogfish Mustelus canis. In contrast, hepatic EROD activity was not detected in untreated lamprey nor in lamprey treated with 3,3'4,4'-tetrachlorobiphenyl (TCB), a potent AHR agonist in teleosts. A possible CYP1A homolog was detected in lamprey hepatic microsomes by one of three antibodies to teleost CYP1A, but expression of this protein was not altered by TCB treatment. CYP1A protein and catalytic activity were measurable in hagfish, but neither was induced after treatment with TCB. These results suggest that the AHR-CYP1A signal transduction pathway is highly conserved in gnathostomes, but that there may be fundamental differences in AHR signaling or AHR-CYP1A coupling in agnathan fish. Agnathan fish such as hagfish and lamprey may be interesting model species for examining possible ancestral AHR functions not related to CYP1A regulation.

A fish hepatoma cell line (PLHC-1) as a tool to study cytotoxicity and CYP1A induction properties of cellulose and wood chip extracts

Cytotoxicity and CYP1A induction properties of celluloses and wood chips were studied with a teleost liver cell line, PLHC-1. Cells were exposed to acetone extracts of celluloses produced using new bleaching techniques (elemental chlorine free, ECF; totally chlorine free, TCF) in two sulphate mills or without any bleaching (unbleached, UB) in a sulphite mill. In another set of exposures, celluloses (ECF and TCF bleached) and wood chips (from pine and birch) were collected from a sulphate mill, extracted with acetone, and the extracts used to treat the cells. After exposure, O-deethylation of 7-ethoxyresorufin (EROD, a measure of cytochrome P4501A (CYP1A) catalytic activity), and total protein content, a measure of cytotoxicity, were assayed. The presence of the CYP1A protein in the exposed cells was assessed by immunoblotting. The cellulose and wood chip extracts were able to cause both cytotoxicity and EROD induction in the PLHC-1 cells. In the exposures conducted with the material from three different mills, the celluloses made of birch were more cytotoxic and more potent inducers of EROD activity than were the celluloses of pine. Further, UB celluloses increased EROD activity and caused cytotoxicity at lower doses than material bleached with modern bleaching techniques. In the exposures made with material from one single mill, there were no clear trends between the celluloses made of pine or birch. Wood chips of pine, however, were more cytotoxic than wood chips of birch. Especially with pine wood chips, cytotoxicity interfered with the induction of EROD activity, thus complicating the evaluation of CYP1A induction. CYP1A protein content was not detected in cells exposed to extracts of celluloses or wood chips, possibly due to low amounts of protein available for the assay. Wood and pulp processing, like bleaching, may change the chemical composition of the raw material in a way that reduces the potency for biological effects of the final product, cellulose. This could explain why both UB celluloses and wood chips were more potent in the cells than ECF or TCF bleached celluloses. In this study the PLHC-1 cell line showed its potential for use in evaluating the biological activity existing in pulp and paper mill products and raw materials. The identity and source of the compounds that were able to affect the PLHC-1 cell line remain to be determined.

Low inducibility of CYP1A activity by polychlorinated biphenyls (PCBs) in flounder (Platichthys flesus): characterization of the Ah receptor and the role of CYP1A inhibition

Several studies have reported a low inducibility of hepatic cytochrome P4501A (CYP1A) activity in European flounder (Platichthys flesus) following exposure to mixtures of polychlorinated biphenyls (PCBs). Here we report on mechanistic studies toward understanding this low CYP1A inducibility of flounder, involving molecular characterization of the Ah receptor (AhR) pathway as well as inhibition of the CYP1A catalytic activity by PCB congeners. Hepatic cytosolic AhR levels in flounder were determined using hydroxylapatite, protamine sulfate adsorption analysis, or velocity sedimentation on sucrose gradients. AhR levels in flounder (approximately 2-7 fmol/mg protein) were much lower than observed generally in rodents (approximately 50-300 fmol/mg protein). Molecular characterization of the flounder AhR was provided by first-strand cDNA synthesis and amplification of flounder hepatic poly(A)+ RNA using RT-PCR. A 690-bp product was found, similar in size to a Fundulus AhR cDNA. The specificity of the 690-bp band was established by Southern blotting and hybridization with a degenerate AhR oligonucleotide. The deduced amino acid sequence of the flounder AhR fragment was 59-60% identical to mammalian AhR sequences. Although the AhR is present in flounder cytosol, we were unable to demonstrate detectable amounts of inducible TCDD-AhR-DRE complex in gel-retardation assays. High induction levels of CYP1A protein and associated EROD activity have been previously found in flounder following exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). In contrast, the induction of CYP1A catalytic activity by PCB mixtures remains unexpectedly low. Therefore, we further characterized the inhibitory potential of PCB congeners on CYP1A activity in flounder and compared this with inhibitory effects of PCB congeners on rat CYP1A activity. Analysis in vitro demonstrated that 3,3',4,4'-tetraCB, 3,3',4,4',5-pentaCB, 2,2',4,4',5,5'-hexaCB, 3,3',4,4',5,5'-hexaCB, and the commercial PCB mixture Clophen A50 are potent competitive inhibitors of hepatic microsomal CYP1A catalytic activity in flounder and rat. The K(m) for ethoxyresorufin (0.095 microM) in flounder is strikingly close to Ki's found for the tested PCBs. This emphasizes the possible involvement of PCB congeners in inhibition of EROD activity in PHAH exposed fish. Finally, our data indicate that flounder CYP1A is more efficient in metabolizing ethoxyresorufin than that of rat CYP1A.

Molecular evolution of two vertebrate aryl hydrocarbon (dioxin) receptors (AHR1 and AHR2) and the PAS family

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor through which halogenated aromatic hydrocarbons such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) cause altered gene expression and toxicity. The AHR belongs to the basic helix-loop-helix/Per-ARNT-Sim (bHLH-PAS) family of transcriptional regulatory proteins, whose members play key roles in development, circadian rhythmicity, and environmental homeostasis; however, the normal cellular function of the AHR is not yet known. As part of a phylogenetic approach to understanding the function and evolutionary origin of the AHR, we sequenced the PAS homology domain of AHRs from several species of early vertebrates and performed phylogenetic analyses of these AHR amino acid sequences in relation to mammalian AHRs and 24 other members of the PAS family. AHR sequences were identified in a teleost (the killifish Fundulus heteroclitus), two elasmobranch species (the skate Raja erinacea and the dogfish Mustelus canis), and a jawless fish (the lamprey Petromyzon marinus). Two putative AHR genes, designated AHR1 and AHR2, were found both in Fundulus and Mustelus. Phylogenetic analyses indicate that the AHR2 genes in these two species are orthologous, suggesting that an AHR gene duplication occurred early in vertebrate evolution and that multiple AHR genes may be present in other vertebrates. Database searches and phylogenetic analyses identified four putative PAS proteins in the nematode Caenorhabditis elegans, including possible AHR and ARNT homologs. Phylogenetic analysis of the PAS gene family reveals distinct clades containing both invertebrate and vertebrate PAS family members; the latter include paralogous sequences that we propose have arisen by gene duplication early in vertebrate evolution. Overall, our analyses indicate that the AHR is a phylogenetically ancient protein present in all living vertebrate groups (with a possible invertebrate homolog), thus providing an evolutionary perspective to the study of dioxin toxicity and AHR function.

Genetic and developmental influences on infant mouse ultrasonic calling. I. A diallel analysis of the calls of 3-day olds

Ultrasonic calls produced by young mice reliably elicit investigation and retrieval by adults. While there are large individual differences in the characteristics of these calls, little work has been done to partition that variation. We completed a 4 x 4 diallel cross and Hayman analyses on several characteristics of these cries. The major result was the detection of directional dominance toward a higher rate of calling, longer calls, and calls of lower overall frequency with a greater bandwidth. Within the context of biometrical genetic theory, we conclude that calls with such characteristics may have important fitness value. Extending this idea, we propose that within the population sampled for this study (the animals of the four inbred strains and 12 F1 hybrid groups), the calls most effectively eliciting investigation and retrieval would be calls with the average hybrid values of the diallel cross.

Halogenated aromatic hydrocarbon-mediated porphyrin accumulation and induction of cytochrome P4501A in chicken embryo hepatocytes

Concentration-dependent induction of cytochrome P4501A (CYP1A) and intracellular porphyrin accumulation were observed following treatment of chicken embryo hepatocyte (CEH) cultures with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 2,3,7,8-tetrachlorodibenzofuran (TCDF), 3,3',4,4'-tetrachlorobiphenyl (PCB 77, IUPAC nomenclature), 2,3',4,4',5-pentachlorobiphenyl (PCB 118), 3,3',4,4',5-pentachlorobiphenyl (PCB 126), 3,3',4,4',5,5'-hexachlorobiphenyl (PCB 169), and a commercial mixture of PCBs (Aroclor 1254). For these halogenated aromatic hydrocarbons (HAHs), or mixture, maximal CYP1A activity [measured as ethoxyresorufin-O-deethylase (EROD) activity] and immunodetectable protein were observed at concentrations just prior to, or coincident with, the concentrations at which porphyrin accumulation became evident. Both immunodetectable CYP1A protein and catalytic activity decreased at high concentrations of these compounds, but the rate and extent of decrease of immunodetectable CYP1A protein varied. Time-course studies with PCB 77 indicated a decrease in potency and an increase in maximal CYP1A induction between 24 and 48 hr of exposure which may indicate in vitro metabolism of this HAH. Intracellular accumulation of total porphyrins without CYP1A induction, was observed for 2,2',5,5'-tetrachlorobiphenyl (PCB 52), 2,2',6,6'-tetrachlorobiphenyl (PCB 54), 2,2',3,5',6-pentachlorobiphenyl (PCB 95), 2,2',4,5,5'-pentachlorobiphenyl (PCB 101), 2,2',3,3',6,6'-hexachlorobiphenyl (PCB 136), and 2,2',4,4',5,5'-hexachlorobiphenyl (PCB 153). Overall, these results are consistent with a role for CYP1A induction and/or Ah receptor activation in porphyrin accumulation mediated by HAHs with a planar configuration, whereas those that are not planar may mediate porphyrin accumulation by a mechanism not involving induction of CYP1A.

Cytochrome P4501A induction in avian hepatocyte cultures: a promising approach for predicting the sensitivity of avian species to toxic effects of halogenated aromatic hydrocarbons

Concentration-dependent effects of halogenated aromatic hydrocarbons (HAHs) on cytochrome P4501A (CYP1A) induction in primary hepatocyte cultures prepared from embryos of chickens (four breeds), pheasants, turkeys, ducks (three breeds), and herring gulls were determined. CYP1A activity was estimated by measuring ethoxyresorufin O-deethylase (EROD) activity and the concentration of immunodetectable CYP1A was estimated using mouse monoclonal antibody 1-12-3 that was prepared against scup (Stenotomus chrysops) CYP1A1. The HAHs studies were 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 2,3,7,8-tetrachlorodibenzofuran (TCDF), 3,3',4,4'-tetrachlorobiphenyl (PCB 77, IUPAC nomenclature), 3,4,4',5-tetrachlorobiphenyl (PCB 81), 3,3',4,4',5-pentachlorobiphenyl (PCB 126), 3,3',4,4',5,5'-hexachlorobiphenyl (PCB 169), 2,3,3',4,4'-pentachlorobiphenyl (PCB 105), and 2,3',4,4',5-pentachlorobiphenyl (PCB 118). Two general types of comparisons were made: (1) relative potencies of compounds within a species (expressed relative to TCDD as induction equivalency factors, IEFs) and (2) relative sensitivity of each species to EROD induction by each compound. Three methods for estimating potency were compared. These were: (1) the concentration of inducer that produced a half-maximal (EC50) EROD response, (2) the concentration producing a response equivalent to 10% of the maximal response produced by TCDD (ECTCDD 10%), and (3) a slope ratio method. For each method, the rank order in potency was TCDD > or = TCDF > PCB 126 > PCB 81 > PCB 77 > PCB 169 in chicken, pheasant, and turkey hepatocytes. The rank order was similar in duck and herring gull hepatocytes with the following exceptions: TCDF was approximately 2- to 4-fold more potent than TCDD in duck hepatocytes; PCB 169 induced EROD in gulls, but PCB 77 had no measurable effect in this species. PCB 118 was a relatively weak EROD inducer in most species/breeds, but it did not induce EROD in Pekin ducks or gulls. PCB 105 was a weak inducer in White Leghorn chicken and turkey hepatocytes, but it did not induce EROD in other species. The EC50, ECTCDD10% and slope ratio methods for estimating potencies generally gave similar IEFs for compounds that produced a maximal response that was at least 60% of the maximal response produced by TCDD. For compounds that caused a response that was 50% or lower than that produced by TCDD, EC50-based IEFs were greater (10- to 100-fold) than ECTCDD10%-based IEFs or slope-ratio-based IEFs. Among species, the rank order in sensitivity to EROD induction was chicken > pheasant > turkey > or = duck > or = herring gull. The relative sensitivity of avian hepatocyte cultures to EROD induction by PCB 77 was similar to the relative sensitivity of these species (reported elsewhere) to lethality after in ovo injection of PCB 77. Chicken hepatocyte cultures were 5-10 times more sensitive to EROD induction by TCDD than were pheasant hepatocyte cultures, which is identical to the difference in sensitivity of these species to the lethal effect of TCDD after in ovo injection. Measuring the sensitivity of hepatocyte cultures to EROD induction might be useful for estimating the sensitivity of avian species (including rare or endangered species, where it is impossible to conduct in vivo studies) to the embryotoxic effects of TCDD, non-ortho substituted PCBs, and other aryl hydrocarbon receptor agonists.

Issues in the genetics of social behavior: revisited

Though social behavior has not been overlooked by behavior geneticists, the number of studies is small when compared to those on individual traits. One reason for the neglect may be the difficulty of making connections between genes and social behaviors, which by definition involve the interaction of two or more organisms. Fuller and Hahn (1976) addressed this issue and described three means of establishing social groups that would facilitate genetic analysis. We survey the literature on agonistic behavior in mice from 1976 through 1994 and describe interesting uses of those three methods. One of those methods (the standard tester design) often employs a "noninteractive" social partner. We present data showing that the standard tester design may be more valuable when using an evocative and interactive standard tester.

Uroporphyrin accumulation associated with cytochrome P4501A induction in fish hepatoma cells exposed to aryl hydrocarbon receptor agonists, including 2,3,7,8-tetrachlorodibenzo-p-dioxin and planar chlorobiphenyls

Hepatic uroporphyria is a well-known effect of halo- genated aromatic hydrocarbons in mammalian and avian systems, including primary cell cultures, but attempts to produce uroporphyria in vertebrate (mammalian) hepatoma lines have been unsuccessful. In this study, the ability of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 2,3,7,8-tetrachlorodibenzofuran (TCDF), and selected chlorobiphenyl congeners to cause uroporphyria was examined in a fish hepatoma cell line (PLHC-1) that expresses aryl hydrocarbon (Ah) receptors and an inducible cytochrome P4501A (CYP1A). Dose-dependent accumulation of porphyrins was observed in cells treated for 48 h with TCDD or 3,3',4,4'-tetrachlorobiphenyl (3,3',4,4'-TCB; IUPAC 77) when the heme precursor delta-aminolevulinic acid (ALA) was present during the last 5 h of treatment. HPLC analysis identified the porphyrins as uroporphyrin (approximately 80%) and heptacarboxylporphyrin (approximately 20%). Uroporphyria did not occur in cells treated with TCDD or 3,3',4,4'-TCB in the absence of added ALA. ALA-dependent porphyrin accumulation was also seen following treatment of PLHC-1 cells with TCDF or with the non-ortho-substituted chlorobiphenyls 3,4,4',5-tetrachlorobiphenyl (IUPAC 81) and 3,3',4,4',5-pentachlorobiphenyl (IUPAC 126). Neither of the mono-ortho-substituted chlorobiphenyls 2,3,3',4,4'-pentachlorobiphenyl (IUPAC 105) or 2,3',4,4'5-pentachlorobiphenyl (IUPAC 118) increased the porphyrin content of PLHC-1 cells. The ability of the PCB congeners to cause porphyria correlated with their ability to induce the CYP1A catalytic activity ethoxyresorufin 0-deethylase (EROD) and immunodetectable CYP1A protein in these cells, suggesting direct or indirect regulation of porphyrin accumulation via the Ah receptor and/or the induced CYP1A. Induction of EROD activity by TCDD, TCDF, and the planar polychlorinated biphenyls was biphasic, with increases at lower concentrations of inducer followed by decreased induction at higher concentrations, as seen previously. EC50 values for porphyrin accumulation were similar to, or slightly higher than, the concentrations at which peak EROD activities were obtained, suggesting a relationship between the decline in EROD activity and enhanced porphyrin accumulation. alpha-Naphthoflavone inhibited TCDD-induced EROD activity and porphyrin accumulation, providing further evidence for the involvement of a fish CYP1A in the mechanism of this prophyria. Addition of 3,3',4,4'-TCB to TCDD-treated cells also inhibited EROD activity, but enhanced porphyrin accumulation, suggesting that an interaction between the halogenated inducer and the induced CYP1A is necessary for the porphyrogenic response. PLHC-1 cells grown in medium supplemented with ALA may be a useful model System for studying mechanisms of chemical uroporphyria induced by Ah receptor agonists.

Cytochromes P450 (CYP) in the Poeciliopsis lucida hepatocellular carcinoma cell line (PLHC-1): dose- and time-dependent glucocorticoid potentiation of CYP1A induction without induction of CYP3A

Glucocorticoids are being found to influence expression of cytochrome P450 (CYP) genes in multiple subfamilies in mammals (J.S. Sidhu, and C.J. Omiecinski (1995) Pharmacogenetics 5, 24--36). In the present study we investigated CYP1A and CYP3A expression in the fish Poeciliopsis lucida hepatocellular carcinoma cell line (PLHC-1) after coadministration of CYP1A and CYP3A inducers, including glucocorticoids. A putative CYP3A protein is expressed in PLHC-1 cells but its content was not altered by exposure of cultures to the prototypical mammalian CYP3A inducers dexamethasone (DEX), pregnenolone-16 alpha-carbonitrile (PCN), or rifampicin (RIF). However, when coadministered with 3,3', 4,4'-tetrachlorobiphenyl or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), DEX but not PCN or RIF caused increases in the degree of CYP1A induction by these aryl hydrocarbon receptor (AHR) agonists. This increase was seen both in CYP1A protein content and rates of ethoxyresorufin-O-deethylase (EROD) activity. DEX alone caused no induction of CYP1A, indicating that the enhancement of CYP1A induction caused by DEX + AHR agonists was not an additive effect but rather a potentiation. The dose of DEX required for maximal potentiation was three orders of magnitude greater at 48 h than the dose required at 24 h. Moreover, the degree of potentiation of CYP1A induction was much greater at the lower doses than at the highest doses of TCDD. There was up to 20-fold potentiation of EROD induction in cultures exposed to 0.1 nM TCDD. Two other glucocorticoid receptor (GR) agonists, cortisol and prednisone, also produced a strong potentiation of CYP1A induction, but other mammalian CYP3A inducers that are not GR agonists, such as the anti-glucocorticoid PCN, the anti-mineralocorticoid spironolactone, or the macrolide antibiotics RIF and troleandomycin, did not potentiate the CYP1A induction in PLHC-1 cells. Addition of the mammalian GR antagonists PCN or RU 38486 reduced the DEX-mediated potentiation of CYP1A induction, whereas spironolactone had no effect on the potentiation. RU 38486 also potentiated the induction of EROD activity by the TCDD, which suggests that RU 38486 acts as a partial GR agonist in PLHC-1 cells. These results suggest that potentiation of CYP1A induction in this nonmammalian cell line proceeds by a classical GR-mediated pathway, independently of the expression of CYP3A. However, the complex interaction between doses of both GR and AHR agonists and duration of exposure, suggests that additional processes influence this potentiation. The unusually strong potentiation at lower doses of TCDD may make PLHC-1 cells particularly suitable in exploring further the consequences of this potentiation.

Evolutionary conservation of the vertebrate Ah (dioxin) receptor: amplification and sequencing of the PAS domain of a teleost Ah receptor cDNA

The PAS domain of a teleost Ah receptor was amplified using reverse transcription-PCR with degenerate primers containing inosine. The deduced amino acid sequence of the amplified cDNA fragment was 62-64% identical with the PAS domains of mammalian Ah receptors. These data demonstrate the homology of Ah receptors in mammals and fish, and reveal regions of this protein that are highly conserved between these diverse vertebrate groups.

Induction of cytochrome P4501A1 by aryl hydrocarbon receptor agonists in porcine aorta endothelial cells in culture and cytochrome P4501A1 activity in intact cells

Endothelium is a single-cell layer lining blood vessels and constituting capillaries and could be a primary site of chemical effects in the cardiovasculature and systemically. Cytochrome P4501A1 (CYP1A1) is strongly inducible in vertebrate endothelium in vivo by aryl hydrocarbon receptor (AhR) agonists [Mol. Pharmacol. 36:723-729 (1989); Mol. Pharmacol. 41:1039-1046 (1992)]. We investigated CYP1A expression and activity in porcine aorta endothelial cells (PAEC) exposed in culture to the AhR agonists 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 3,3',4,4'-tetrachlorobiphenyl (TCB), benzo[a]pyrene (BP), or beta-naphthoflavone (BNF). Immunoblotting with monoclonal anti-CYP1A1 and polyclonal anti-CYP1A1 and anti-CYP1A2 antibodies showed that CYP1A1 was induced in cultures exposed to TCDD, TCB, BP, or BNF but was not detectable in untreated or dimethylsulfoxide-exposed cultures. CYP1A1 was strongly induced at intermediate concentrations (0.1 microM or 1.0 microM) of TCB, BP, or BNF, but induction was suppressed by higher concentrations, a response not due to general toxicity; cell viability (trypan blue exclusion) was > 97% with BNF or TCB at up to 10 microM. CYP1A1 induction by TCDD was maximal at 0.3-1.0 nM. ED50 values for induction of CYP1A1 by TCDD, TCB, and BP were 0.016 nM, 3-10 nM, and 180 nM, respectively. Immunohistochemical analysis confirmed CYP1A1 induction in PAEC but also showed that only some cells in the cultures were induced. Subcellular fractionation, marker enzyme analysis, and immunoblot analysis showed that PAEC had a typical complement of microsomal electron-transport components. NADPH-cytochrome P450 reductase showed comparable rates (approximately 40 nmol/min/mg) in induced and control cultures. Cultures maximally induced by 0.1 microM TCB had microsomal CYP1A1 [ethoxyresorufin-O-deethylase (EROD)] activity averaging 25 pmol/min/mg. Addition of purified rat reductase to PAEC microsomes increased the EROD rates 3-fold. EROD rates measured in intact cells maximally induced by BP, TCB, or TCDD ranged from 15 to 30 pmol/min/mg of whole-cell protein. Methoxyresorufin O-demethylase activity induced by TCDD was 2 pmol/min/mg, i.e., < 10% of the EROD activity. In cultures in which CYP1A1 was strongly induced, CYP1A2 was not detectably expressed. The CYP1A2 inducer acenaphthylene did not induce EROD or methoxyresorufin O-demethylase in intact cells. The results show that CYP1A1 but not CYP1A2 is strongly induced in mammalian endothelial cells in culture and that CYP1A1 is active in intact cells, although the catalytic rates are low.(ABSTRACT TRUNCATED AT 400 WORDS)

Regulation of cytochrome P4501A1 in teleosts: sustained induction of CYP1A1 mRNA, protein, and catalytic activity by 2,3,7,8-tetrachlorodibenzofuran in the marine fish Stenotomus chrysops

Cytochrome P4501A1 (CYP1A1) is known to play important roles in the activation and detoxification of carcinogens and other toxicants in vertebrate animals, including fish. Although extensively studied in mammalian systems, the regulation of CYP1A forms in other vertebrates is less well understood. We examined the time course and dose-response relationships for induction of CYP1A1 mRNA, protein, and catalytic activity by 2,3,7,8-tetrachlorodibenzofuran (TCDF) in the marine fish Stenotomus chrysops (scup). The time course of CYP1A1 induction was determined following a single ip dose (10 nmol/kg) of 2,3,7,8-TCDF. Hepatic ethoxyresorufin O-deethylase activity was increased after 1 day, reached a maximum by 8 days, and was still elevated 14 days after treatment. The content of immunodetectable CYP1A1 protein in liver was elevated on Day 1 and continued to increase through 14 days. CYP1A1 protein content was also strongly induced in heart and gill beginning at 2 days after treatment and extending through Day 14. Hepatic CYP1A1 mRNA was strongly induced by 1 day after dosing and remained elevated through 14 days. The sustained induction of CYP1A1 mRNA by 2,3,7,8-TCDF contrasts with the transient induction seen previously in fish treated with nonhalogenated inducers and most likely reflects differences in persistence of the inducers. Dose-response studies indicated that induction of CYP1A1 mRNA, protein, and catalytic activity occurred following doses of 2,3,7,8-TCDF as low as 0.4 nmol/kg (120 ng/kg), within the range of whole-body contents of this congener measured in fish from contaminated environments. The estimated dose producing half-maximal CYP1A1 induction in scup was approximately 2-10 nmol/kg, suggesting that the sensitivity of these fish to induction may be as great as or greater than that of rats. In contrast to previous results obtained with 3,3',4,4'-tetrachlorobiphenyl (TCB) and beta-naphthoflavone, which appear to inhibit or inactivate CYP1A1 in fish and other vertebrates, there was a good correlation among levels of CYP1A1 mRNA, protein, and catalytic activity in individual fish following various doses of 2,3,7,8-TCDF. The difference in response to 2,3,7,8-TCDF versus 3,3',4,4'-TCB may reflect differences in the inducing potencies of the two compounds relative to their similar potencies as inhibitors of CYP1A1 catalytic activity. In additional studies to evaluate structure-activity relationships for CYP1A1 induction by chlorinated dibenzofurans in fish, scup were treated with 2,3,6,8-tetrachlorodibenzofuran (2,3,6,8-TCDF). At 10 or 50 nmol/kg, 2,3,6,8-TCDF was inactive as an inducer of CYP1A1 mRNA, protein, or catalytic activity.(ABSTRACT TRUNCATED AT 400 WORDS)