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Behavioral assessment of visual toxicity.

A wide variety of behavioral methods has been employed with animals to assess visual changes induced by drugs or toxicants. The methods range from simple to complex, from broad screening devices to narrowly focused techniques. Their relative advantages for the environmental toxicologist are discussed. Manipulation of stimulus values is an essential ingredient in the identification of specific sensory functions. The percentage of correct choices from a discrete-trial, multiple-choice discrimination procedure is to be preferred to measures of response rate, speed or reaction time when experiments require answers about specific visual functions.

Animals

Integrating structure and experimental data annotations with computational modeling framework for predicting micro-nanoplastics toxicities.

The wide use of plastic materials leads to increased emissions of micro-nanoplastics (MNPs) into the environment, raising significant concerns about their impact on human health. Traditional experimental approaches for assessing MNPs toxicity are costly, time-consuming, and there are no experimental protocols that are universally acceptable. Computational modeling using machine learning (ML) approaches provides an efficient alternative to MNP toxicity assessment. However, most modeling studies of MNPs are limited due to the lack of high-quality data and there are few previous modeling studies considering complex structures of MNPs for model training. To address this challenge, we constructed three MNP datasets with popular toxicity endpoints from various resources and used nanostructure annotation techniques to create virtual MNPs (vMNPs) for all MNP structures. The MNP structures were digitalized from annotated vMNPs, and geometrical descriptors were calculated using the Delaunay Tessellation approach. Moreover, important experimental information, such as concentrations and cell lines, were transformed into extra training variables. Partial least squares regression (PLSR) models were built using both experimental and geometrical descriptors and validated through a leave-one-out cross validation procedure. The resulting models showed reasonable performance in predicting toxicity potentials of MNPs for the three endpoints in the present datasets. Moreover, an additional library of vMNPs with their predicted properties and bioactivities was constructed, directing further research of new MNPs. This study provides three novel ML models for MNPs by integrating geometrical and experimental descriptors, which have the potential to assess new MNPs for their toxicity. The modeling strategy developed in this study can be easily expanded to model other MNP toxicity endpoints and create promising new models for MNP toxicity assessments.

Data annotation

Tissue distribution as a factor in species susceptibility to toxicity and hazard assessment. Example: methylmercury.

Data on the tissue distribution and pharmacokinetics of methylmercury(MeHg) in cats and humans were utilized as an example of how such data can assist in extrapolating toxicity data between animal species. These data demonstrate that the whole-body half-time for clearance of MeHg was the same for cats (76.2 +/- 1.6 days) and humans (78 +/- 5 days) and that the concentration of MeHg in the brain at comparable signs of toxicity were the same (10 ppm) in the two species. However, the blood:brain ratio of MeHg concentration was 10 times as high in cats (1:1) as humans (1:10). From these data it was hypothesised that the no-effect level of methylmercury intake in cats should be 10 times that for humans. This hypothesis was verified from data o MeHg toxicity in cats and humans which demonstrated that ataxia developed in cats at a minimum dose of 46 microgram MeHg/kg body wt/day with blood MeHg levels of 6 to 8 ppm; humans developed ataxia with blood MeHg levels of 0.6 to 0.8 ppm and an estimated intake of 4 microgram MeHg/kg body wt/day.

Animals

The assessment of efficacy, toxicity and quality of care in long-term drug treatment.

Drug studies in man are usually divided into four phases. The first phase is to establish that the drug has a pharmacological action in man and in which dose range it occurs. The second phase is a study of the therapeutic effect of the drug in small numbers of closely observed patients. The third phase consists of large-scale studies which may involve hundreds or thousands of patients; such studies are designed to accumulate less detailed information about efficacy and to provide information about low frequency toxic events. At the end of this stage the drug is submitted to a regulatory body for a license to market it. Information derived from these studies usually has several important deficiencies. There is unlikely to be much evidence about the efficacy of the drug in relation to that of other substances used to treat the same condition. The carefully regulated conditions of the clinical trial may bear little relationship to the way the drug will be used in practice. Most important, the evidence obtained on efficacy may relate chiefly to the pharmacological action of the drug, e.g. in lowering blood pressure or blood sugar, or reducing inflammation, and may not bear directly upon therapeutic outcome. For these reasons much attention is being focused on monitoring of the way drugs are used after marketing. To provide evidence of therapeutic efficacy may require studies of such large scale and high cost that they are beyond the research of individual pharmaceutical companies and will require national or international action. Monitoring of the way drugs are used inevitably means studying not just the performance of the drug but also of the doctors who prescribe it. Studies that have been made of the quality of care of patients treated with anti-hypertensive drugs and those requiring anticoagulants are not reassuring concerning the general level of such quality.

Cost-Benefit Analysis

An in vivo model for assessing effects of drugs and toxicants on immunocompetence.

An in vivo assessment of the capacity of exposed animals to respond to antigenic challenge is recommended as the first screening phase for detecting potential immunotoxicants, with subsequent in vitro functional tests utilized to pinpoint the site of induced cellular alteration. Risk assessment of a candidate toxicant is based on a comparison of immune profiles of exposed animals with those of animals treated with prototype immunotoxicants. Extrapolation to man is facilitated by the use of licensed vaccines for antigenic challenge and the selection of clinically useful pharmaceutical drugs as prototype immunotoxicants. Three chemically induced alterations in immune responses are presented: 1) Immunosuppression characterized by impaired capacity to produce IgG and IgM classes of antibody on stimulation, 2) chronic high levels of IgE antibody in response to commonly encountered antigens, 3) modification of the capacity to mount an inflammatory response to antigenic material.

Animals

Hazards from chemicals: scientific questions and conflicts of interest.

All substances are toxic when the dose is large enough. In order to regulate the use of chemicals, we need to measure the level at which toxic effects are found. Epidemiological evidence suggests that present levels of chemical use do not lead to widespread harmful contamination of the human environment. For chemicals, most of the problems of toxicity are found in the workplace, while the population at large gets most of its toxic effects from voluntary exposure to substances such as tobacco smoke and ethanol. The prevention and control of toxic effects depends on a series of steps. This begins with measurement of toxicity in model systems, such as laboratory animals, and the estimation of the likely exposure of workers or consumers. Reliable extrapolation of information gathered from animals to the diverse and biochemically differing human population depends on understanding mechanisms of toxic effects. The toxic effect and mechanisms of action of substances such as carbon tetrachloride or paracetamol have been extensively investigated, and our ability to predict toxicity or develop antidotes to poisoning has had some success, but epidemiology is still an essential part of assessment of toxic effects of new chemicals. The example of phenobarbitone shows how animal experiments may well lead to conclusions which do not apply to man. After measurement of toxicity and assessment of likely hazards in use comes the final evaluation of the use of a chemical. This depends not only on its toxicity, but also on its usefulness. The direct effects on health may be small in comparison with the indirect advantageous effects which a useful substance such as vinyl chloride may bring. The assessment of risks and benefits of new chemicals can be partly removed from a political style of discourse, but the evaluation of the relative weight to be attached to these risks and benefits is inescapably political. The scientific contribution must be to allow the debate to take place in the light of maximum clarity of information about the consequences of use of chemicals.

Acetaminophen

Models for assessing the effect of toxicants on immunocompetence in mice. II. Effect of cyclophosphamide on the antibody responses to type III pneumococcal polysaccharide and tetanus toxoid in BALB/c female mice.

A mixture of antigens was used to detect alterations in immunocompetence. Type III pneumococcal polysaccharide (S3) and tetanus toxoid (TT) stimulate different cellular components, and can therefore be used to assess different compartments of the immune mechanism. Cyclophosphamide (CP), a known immunosuppressant, had a potent effect upon the antibody responses to both S3 and tetanus toxoid. All doses of CP administered within 2 days of priming with S3 resulted in a dose-related immunosuppressive action which persisted even after reinjection of S3. 300 mg/kg of CP given up to 14 days prior to or following primary immunization resulted in a marked suppression of antibodies to S3. Doses of S3 which were partially tolerogenic were made even more so by injections of CP. The effect persisted over a 96 day experimental period. CP also suppressed the formation a memory cells necessary for induction of a secondary-type IgG response to TT. The time of injection for maximum suppression was days 10 to 14 after priming. Therefore, the suppression must involve cellular mechanisms different from those responsible for S3 antibody suppression. In addition, there was a difference in the degree and persistence of the suppressive effect, since the suppressed animals were able to mount an immune response to subsequent injections of TT. Double injections of a high dose (300 mg/kg) of CP 4 weeks after priming completely suppressed the acquired immunity to both S3 and TT. Low and moderate doses of CP appeared to induce a mild augmentation of S3 antibody response when given 4 weeks after priming. However, an immunosuppressive effect occurred if the primed animals were reinjected with S3 or challenged with TT within a period of 2 days prior to or after receiving the CP treatment. Doses of CP, injected prior to challenge and resulting in suppressed tetanus antitoxin production, elevated the titers of specific IgE antibody. This class of antibody is associated with adverse hypersensitivity reactions. These data provided background for the development of models to assess immunocompetence in mice, based on a study of immune profiles following exposure to selected T-dependent and T-independent antigens. Such models may be used to detect potentially hazardous chemicals found in the environment of incorporated into foods, drugs, or cosmetics.

Animals

[Use of structure-activity analysis in toxicology].

An account is given of principles and methods of quantitative structure-action analysis which have promising applications in toxicology. Particular reference is made to the development of active principles with low toxicity for warm-blooded animals, early assessment of toxicity of recently synthetised or envisaged compounds of one substance class of which the toxicity of some agents has already become known, and appraisal of unspecific toxic effects.

Animals

Evaluation of overall toxicity of high-dosage methotrexate regimens.

The occurrence of overall toxicity was analyzed for 43 patients with osteosarcoma who received 349 high-dosage courses of methotrexate (HD-MTX) with citrovorum factor (Leukovorin) "rescue" (CF). The dosages of HD-MTX ranged from 50 to 350 mg/kg. Overall toxicity was assessed on the basis of five manifestations of toxicity: stomatitis, dermatitis, myelosuppression, liver dysfunction, and kidney function abnormalities. The great majority (91.4%) of the infusions were well tolerated, but 8.6% were associated with moderate or severe toxicity. Stomatitis and serum glutamic-oxaloacetic transaminase (SGOT) changes were the most frequent postinfusion findings. Three patients died from causes related to MTX toxicity. Dose, age, sex, and number of prior infusions were investigated by logistic regression analysis for prognostic effect on frequency of moderate to severe overall toxicity. Age and number of prior infusions had significant (P less than 0.06) effects on overall toxicity. Patients older than 15 years with greater than 10 prior infusions constituted the "high risk" group with a risk of moderate to severe toxicity 6.3 times that of the younger patients with fewer than 10 infusions.

Adolescent

Preliminary assessment of the acute toxicity of malathion in animals.

Laboratory studies were conducted to acquire information concerning the acute toxicity of malathion in animals under various conditions of exposure. The responses in rabbits and quail exposed to aerosols generated from technical grade malathion (95%) and approximating an ultra-low volume ground spray were compared with those from a 6% malathion/No. 2 fuel oil mixture simulating a high volume spray. Results indicate that technical grade malathion (95%) as an ultra-low volume spray and at effective insecticidal concentrations in particle sizes having a mass median diameter of about 12 mu is relatively nonhazardous compared to the possible toxic fuel oil effects of a 6% malathion/No. 2 fuel oil mixture with a mass median diameter of 25 mu. Based on blood plasma cholinesterase activity analyses, quail were more sensitive to equivalent malathion exposure concentrations than were rabbits. Oral administration of technical grade malathion to rabbits resulted in reduction of plasma and erythrocyte cholinesterase activity at dosages of 120, 300, and 600 mg/kg with death resulting from 1200 mg/kg.

Aerosols