Fish acute toxicity syndromes and their use in the QSAR approach to hazard assessment.

Implementation of the Toxic Substances Control Act of 1977 creates the need to reliably establish testing priorities because laboratory resources are limited and the number of industrial chemicals requiring evaluation is overwhelming. The use of quantitative structure activity relationship (QSAR) models as rapid and predictive screening tools to select more potentially hazardous chemicals for in-depth laboratory evaluation has been proposed. Further implementation and refinement of quantitative structure-toxicity relationships in aquatic toxicology and hazard assessment requires the development of a "mode-of-action" database. With such a database, a qualitative structure-activity relationship can be formulated to assign the proper mode of action, and respective QSAR, to a given chemical structure. In this review, the development of fish acute toxicity syndromes (FATS), which are toxic-response sets based on various behavioral and physiological-biochemical measurements, and their projected use in the mode-of-action database are outlined. Using behavioral parameters monitored in the fathead minnow during acute toxicity testing, FATS associated with acetylcholinesterase (AChE) inhibitors and narcotics could be reliably predicted. However, compounds classified as oxidative phosphorylation uncouplers or stimulants could not be resolved. Refinement of this approach by using respiratory-cardiovascular responses in the rainbow trout, enabled FATS associated with AChE inhibitors, convulsants, narcotics, respiratory blockers, respiratory membrane irritants, and uncouplers to be correctly predicted.

A computationally based identification algorithm for estrogen receptor ligands: part 2. Evaluation of a hERalpha binding affinity model.

The objective of this study was to evaluate the capability of an expert system described in the previous paper (S. Bradbury et al., Toxicol. Sci. 58, 253-269) to identify the potential for chemicals to act as ligands of mammalian estrogen receptors (ERs). The basis of the expert system was a structure activity relationship (SAR) model, based on relative binding affinity (RBA) values for steroidal and nonsteroidal chemicals derived from human ERalpha (hERalpha) competitive binding assays. The expert system enables categorization of chemicals into (RBA ranges of < 0.1, 0.1 to 1, 1 to 10, 10 to 100, and >150% relative to 17ss-estradiol. In the current analysis, the algorithm was evaluated with respect to predicting RBAs of chemicals assayed with ERs from MCF7 cells, and mouse and rat uterine preparations. The best correspondence between predicted and observed RBA ranges was obtained with MCF7 cells. The agreement between predictions from the expert system and data from binding assays with mouse and rat ER(s) were less reliable, especially for chemicals with RBAs less than 10%. Prediction errors often were false positives, i.e., predictions of greater than observed RBA values. While discrepancies were likely due, in part, to species-specific variations in ER structure and ligand binding affinity, a systematic bias in structural characteristics of chemicals in the hERalpha training set, compared to the rodent evaluation data sets, also contributed to prediction errors. False-positive predictions were typically associated with ligands that had shielded electronegative sites. Ligands with these structural characteristics were not well represented in the training set used to derive the expert system. Inclusion of a shielding criterion into the original expert system significantly increased the accuracy of RBA predictions. With this additional structural requirement, 38 of 46 compounds with measured RBA values greater than 10% in hERalpha, MCF7, and rodent uterine preparations were correctly categorized. Of the remaining 129 compounds in the combined data sets, RBA values for 65 compounds were correctly predicted, with 47 of the incorrect predictions being false positives. Based upon this exploratory analysis, the modeling approach, combined with a high-quality training set of RBA values derived from a diverse set of chemical structures, could provide a credible tool for prioritizing chemicals with moderate to high ER binding affinity for subsequent in vitro or in vivo assessments.

Comparative toxicology of the pyrethroid insecticides.

The toxic effects elicited by synthetic pyrethroids in animals are varied in degree and nature. Their relative safety to birds and mammals contrasts sharply with their acute effects on fish and arthropods. Explantation of their differences in toxicity depends on examination of all factors of their comparative toxicology. Routes of exposure are important, as are metabolism and elimination rates, especially for mammals and birds with their considerable capabilities for biotransformation. Significant differences in sensitivity at the sites of toxic action may also play a role in differential responses to these insecticides. Finally, physical properties that influence the environmental disposition and subsequently affect bioavailability of the compounds in water, soil, air, produce, and nontarget species are also instrumental in determining the impact of current and future synthetic pyrethroid insecticides.

Quantitative structure-activity relationships and ecological risk assessment: an overview of predictive aquatic toxicology research.

In the field of aquatic toxicology, quantitative structure-activity relationships (QSARs) have developed as scientifically credible tools for predicting the toxicity of chemicals when little or no empirical data are available. A fundamental understanding of toxicological principles has been considered an important component to the acceptance and application of QSAR approaches as biologically relevant in ecological risk assessments. As a consequence, there has been an evolution of QSAR development and application from that of a chemical-class perspective to one that is more consistent with assumptions regarding modes of toxic action. In this review, techniques to assess modes of toxic action from chemical structure are discussed, with consideration that toxicodynamic knowledge bases must be clearly defined with regard to exposure regimes, biological models/endpoints and compounds that adequately span the diversity of chemicals anticipated for future applications. With such knowledge bases, classification systems, including rule-based expert systems, have been established for use in predictive aquatic toxicology applications. The establishment of QSAR techniques that are based on an understanding of toxic mechanisms is needed to provide a link to physiologically based toxicokinetic and toxicodynamic models, which can provide the means to extrapolate adverse effects across species and exposure regimes.

Predicting modes of toxic action from chemical structure: an overview.

In the field of environmental toxicology, and especially aquatic toxicology, quantitative structure activity relationships (QSARs) have developed as scientifically-credible tools for predicting the toxicity of chemicals when little or no empirical data are available. A basic and fundamental understanding of toxicological principles has been considered crucial to the continued acceptance and application of these techniques as biologically relevant. As a consequence, there has been an evolution of QSAR development and application from that of a chemical-class perspective to one that is more consistent with assumptions regarding modes of toxic action. The assessment of a compound's likely mode of toxic action is critical for a correct QSAR selection; incorrect mode of action-based QSAR selections can result in 10- to 1000-fold errors in toxicity predictions. The establishment of toxicologically-credible techniques to assess mode of toxic action from chemical structure requires toxicodynamic knowledge bases that are clearly defined with regard to exposure regimes and biological models/endpoints and based on compounds that adequately span the diversity of chemicals anticipated for future applications. With such knowledge bases classification systems, including rule-based experts systems, have been established for use in predictive aquatic toxicology applications.

Use of knowledge bases and QSARs to estimate the relative ecological risk of agrichemicals: a problem formulation exercise.

Ecological risk assessments can be used to establish the likelihood that an adverse effect will result from exposure to one or more chemicals. When evaluating contaminated sites with many chemicals present, risk assessors must grapple with the problem of quickly identifying the chemicals that are most likely to be of concern, based on effect and exposure assessment information. Many times data gaps exist and the risk assessor is left with decisions on which models to use to estimate the parameter of concern. In the present paper, a procedure is presented for ranking agrichemicals, utilizing the ASTER (ASsessment Tools for the Evaluation of Risk) system. The procedure was employed to rank the relative ecological risk of forty-nine pesticides historically used in agricultural sites in the Walnut Creek watershed near Ames, lowa, USA. Empirical data from the ASTER system were used when available in the associated databases, and quantitative structure-activity relationships and expert systems were invoked when data were lacking. Separate rankings were conducted based on major species taxonomic groupings. Resulting toxic effects thresholds were compared to surface water concentrations.

Reactivity profiles of ligands of mammalian retinoic acid receptors: a preliminary COREPA analysis.

Retinoic acid and associated derivatives comprise a class of endogenous hormones that bind to and activate different families of retinoic acid receptors (RARs, RXRs), and control many aspects of vertebrate development. Identification of potential RAR and RXR ligands is of interest both from a pharmaceutical and toxicological perspective. The recently developed COREPA (COmmon REactivity PAttern) algorithm was used to establish reactivity profiles for a limited data set of retinoid receptor ligands in terms of activation of three RARs (alpha, beta, gamma) and an RXR (alpha). Conformational analysis of a training set of retinoids and related analogues in terms of thermodynamic stability of conformers and rotational barriers showed that these chemicals tend to be quite flexible. This flexibility, and the observation that relatively small energy differences between conformers can result in significant variations in electronic structure, highlighted the necessity of considering all energetically reasonable conformers in defining common reactivity profiles. The derived reactivity patterns for three different subclasses of the RAR (alpha, beta, gamma) were similar in terms of their global electrophilicity (nucleophilicity) and steric parameters. However, the profile of active chemicals with respect to interaction with the RXR-alpha differed qualitatively from that of the RARs. Variations in reactivity profiles for the RAR versus RXR families would be consistent with established differences in their affinity for endogenous retinoids, likely reflecting functional differences in the receptors.

Recovery of cholinesterase activity in mallard ducklings administered organophosphorus pesticides.

Oral doses of the organophosphorus pesticides acephate, dicrotophos, fensulfothion, fonofos, malathion, and parathion were administered to mallard ducklings (Anas platyrhynchos), and brain and plasma cholinesterase (ChE) activities were determined for up to 17 d after dosing. In vivo recovery of brain ChE activity to within 2 standard deviations of the mean activity of undosed birds occurred within 8 d, after being depressed an average of 25-58% at 24 h after dosing. In vivo recovery of plasma ChE appeared as fast as or faster than that of brain, but the pattern of recovery was more erratic and therefore statistical comparison with brain ChE recovery was not attempted. In vitro tests indicated that the potential for dephosphorylation to contribute to in vivo recovery of inhibited brain ChE differed among chemical treatments. Some ducklings died as a result of organophosphate dosing. In an experiment in which ducklings within each treatment group received the same dose (mg/kg), the brain ChE activity in birds that died was less than that in birds that survived. Brain ChE activities in ducklings that died were significantly different among pesticide treatments: fensulfothion greater than parathion greater than acephate greater than malathion (p less than or equal to 0.05).

Toxicity of fenvalerate to bobwhite quail (Colinus virginianus) including brain and liver residues associated with mortality.

The toxicity of the synthetic pyrethroid fenvalerate to bobwhite quail (Colinus virginianus) was examined. The acute oral LD50 to adult (19-wk-old) male and female birds was in excess of 4000 mg/kg. The LD50 to immature (5-wk-old) birds was 1785 mg/kg. Dietary toxicity testing with 2-wk-old chicks indicated an 8-d LC50 in excess of 15,000 ppm. Observed signs of intoxication included hyperactivity, irregular locomotion, ataxia, spastic muscle contraction, and, preceding death, sternal recumbency with muscle flaccidity. Significant weight loss (adult birds) or reduction in rate of weight gain (immature birds and chicks) was note generally at all dose levels in the acute testing, but only at the highest level in the dietary test. Brain residue levels associated with mortality increased with the dose (means of 0.10-1.26 ppm), whereas liver residues remained constant (overall mean of 0.74 ppm).

Influence of cytochrome P450 mixed-function oxidase induction on the acute toxicity to rainbow trout (Salmo gairdneri) of primary aromatic amines.

The influence of enzyme induction on the acute toxicity of aniline and 4-chloroaniline to rainbow trout (Salmo gairdneri) was investigated. For these two xenobiotics, bioactivation reactions are known to occur in mammals. Induction of cytochrome P450 mixed-function oxidase was obtained by intraperitoneal (ip) injection of trout with a mixture of polychlorinated biphenyls (Aroclor 1254). Five days after ip injection with three different doses of Aroclor 1254 (50, 100, and 200 mg/kg), benzo[a]pyrene hydroxylase activity in trout liver microsomes increased five- to sixfold. Cytochrome P450 concentrations in the microsomes were slightly, but significantly, enhanced in two of the three dose levels. The 96-hr LC50's of aniline and 4-chloroaniline were not affected by pretreatment with Aroclor 1254, suggesting that metabolic activation does not necessarily play a role in the acute toxicity of aromatic amines to fish.

Respiratory symptoms and pulmonary impairment in male and female subjects with pottery workers' silicosis.

Respiratory symptoms, smoking habit, lung function and radiological category of silicosis were assessed in 276 present and former pottery workers who were receiving industrial disablement benefit for silicosis. There were 140 females and 136 males. The proportion with conglomerate disease (massive fibrosis) was similar in both sexes. The FEV1 declined with increasing X-ray category of silicosis irrespective of smoking habit and was most marked in subjects with symptomatic chronic bronchitis. In females who had never smoked the average decline of FEV1 in those with simple silicosis was 18 ml year-1 and for those with conglomerate disease 38 ml year-1. Symptomatic chronic bronchitis was common and only partly related to smoking, occurring in 69% of 101 nonsmoking female silicotic patients. No significant changes were observed in vital capacity, lung volume or transfer factor for carbon monoxide.

Principals of design and evaluation of an information system for a department of respiratory medicine.

OBJECTIVES: To evaluate a departmental computer system. DESIGN: a. Direct comparison of the time taken to use a manual system with the time taken to use a computer system for lung function evaluation, loan of equipment and production of correspondence. b. Analysis of the accuracy of data capture before and after the introduction of the computer system. c. Analysis of the comparative running costs of the manual and computer systems. SETTING: Within a department of respiratory medicine serving a hospital of 1323 beds. MAIN OUTCOME MEASURES: a. Time taken to perform functions with the assistance of computerised methods, in comparison to the manual method used alone. b. Accuracy of data capture. c. Relative running costs. RESULTS: a. The computer system (CS) was significantly faster than the manual system (MS) for lung function evaluation (CS = 7.63 min/test, MS = 12.25 min/test), loan of equipment (CS = 0.40 min/loan, MS = 2.07 min/loan), and checking for overdue equipment (CS = 0.49 s/record, MS = 9 s/record). The production of correspondence was slightly slower with the computer (CS = 9.30 min/letter, MS = 8.54 min/letter). b. All outpatient episodes, but only 43 of 65 (66%) of in-patient episodes, were captured. Lung function and managerial report data were accurate using both manual and computerised methods. The manual system for equipment loans was inefficient, and use of the computer resulted in the recovery of 221 nebulisers. c. Development costs for 1988-1990 were high (72,178 pounds). Only 1200 pounds to 1845 pounds per year was recovered directly from staff time saved by the computer but larger savings resulted from changes in work practice (4049-4765 pounds). After 10 years the projected deficit is 10,000 pounds per annum in running costs. CONCLUSIONS: In comparison with the manual methods, the computer system has shown significant advantages which provide accurate information, with significant favourable effects on working practices. In evaluating computer systems used in clinical practice it is essential to ensure that the projected work practice benefits are achieved without unacceptable costs in staff time, inaccurate data and high financial outlay.

Hepatic microsomal N-hydroxylation of aniline and 4-chloroaniline by rainbow trout (Onchorhyncus mykiss).

1. N-Hydroxylation of aniline and 4-chloroaniline was quantified in rainbow trout microsomal preparations using h.p.l.c.-liquid scintillation methods. Radioactive phenylhydroxylamine and 4-chlorophenylhydroxylamine metabolites were identified by co-elution with non-labelled standards. The method provided resolution of metabolite standards, and quantification of both N-hydroxylated metabolites was achieved without derivatization. 2. The maximum velocities at 25 degrees C were 33.8 +/- 1.40 and 22.0 +/- 0.98 pmol/min per mg for aniline and 4-chloroaniline N-hydroxylation, respectively. The Km values were 1.0 +/- 0.11 and 0.8 +/- 0.11 mM for aniline and 4-chloroaniline N-hydroxylation, respectively. These activities were not induced by treatment of the trout with Aroclor 1254 under the conditions of this study. 3. When incubations were performed at 11 degrees C, the physiological temperature of rainbow trout in this study, the Vmax for 4-chloroaniline N-hydroxylation decreased from 22.0 to 6.4 pmol/min per mg and the Km decreased from 0.8 to 0.5 mM. 4. The pH optimum for 4-chloroaniline N-hydroxylation was 8.0 while the pH optimum for aniline N-hydroxylation ranged from 7.4 to 8.0, suggesting the possible contribution of different isoenzymes. 5. The demonstration of aniline and 4-chloroaniline N-hydroxylation by rainbow trout microsomes provides further insight into the high acute:subchronic toxicity ratios observed in fish exposed to these compounds.

Toxicokinetics and metabolism of aniline and 4-chloroaniline in medaka (Oryzias latipes).

The in vivo toxicokinetics and in vitro hepatic microsomal metabolism of [14C]aniline and [14C]4-chloroaniline in medaka (Oryzias latipes) were investigated to provide a basis upon which to interpret the toxicological responses of small aquarium fish to aniline derivatives. During static aqueous exposures of up to 320 min, parent equivalents failed to reach steady state and results from depuration studies clearly demonstrated biphasic elimination. Due to low elimination rates, 40 to 20% of absorbed aniline and 4-chloroaniline doses, respectively, remained within the fish through 330 min postexposure. Based on an analysis of excreted metabolites, N-acetylation was the dominant route of in vivo metabolism for 4-chloroaniline, with no indication of ring hydroxylation, while the evidence suggested that polar conjugates were the dominant in vivo aniline metabolites. The toxicokinetics and in vivo metabolism of both aniline and 4-chloroaniline were best described by a two-compartment model that was consistent with the assumption that metabolites of the parent amines were accumulating in the fish. In partial support of the hypothesis that these amines are being metabolically activated in medaka, N-hydroxylation of aniline and 4-chloraniline to phenylhydroxylamine and 4-chlorophenylhydroxylamine were quantified in hepatic microsomal preparations.