Lawrence W. Reiter

Incorporating new technologies into toxicity testing and risk assessment: moving from 21st century vision to a data-driven framework.

Based on existing data and previous work, a series of studies is proposed as a basis toward a pragmatic early step in transforming toxicity testing. These studies were assembled into a data-driven framework that invokes successive tiers of testing with margin of exposure (MOE) as the primary metric. The first tier of the framework integrates data from high-throughput in vitro assays, in vitro-to-in vivo extrapolation (IVIVE) pharmacokinetic modeling, and exposure modeling. The in vitro assays are used to separate chemicals based on their relative selectivity in interacting with biological targets and identify the concentration at which these interactions occur. The IVIVE modeling converts in vitro concentrations into external dose for calculation of the point of departure (POD) and comparisons to human exposure estimates to yield a MOE. The second tier involves short-term in vivo studies, expanded pharmacokinetic evaluations, and refined human exposure estimates. The results from the second tier studies provide more accurate estimates of the POD and the MOE. The third tier contains the traditional animal studies currently used to assess chemical safety. In each tier, the POD for selective chemicals is based primarily on endpoints associated with a proposed mode of action, whereas the POD for nonselective chemicals is based on potential biological perturbation. Based on the MOE, a significant percentage of chemicals evaluated in the first 2 tiers could be eliminated from further testing. The framework provides a risk-based and animal-sparing approach to evaluate chemical safety, drawing broadly from previous experience but incorporating technological advances to increase efficiency.

Behavioral effects of moderate lead exposure in children and animal models: Part 1, clinical studies

(1980). Behavioral effects of moderate lead exposure in children and animal models: Part 1, clinical studies. CRC Critical Reviews in Toxicology: Vol. 8, No. 1, pp. 43-99.

Trimethyltin disrupts acoustic startle responding in adult rats

Trimethyltin (TMT) is a limbic-system toxicant which also produces sensory dysfunction in adult animals. In the present experiment, we examined the effects of TMT on the acoustic startle response. Adult male, Long-Evans rats (N = 12/dose) received a single i.p. injection of either 0, 4.0, 5.0 or 6.0 mg/kg TMT hydroxide as the base. The number of responses, latency and peak amplitude of the startle response to a 13 kHz, 120 dB tone were measured 2 h, 2 weeks, and 4 weeks after dosing. For each test session, 10 stimuli were presented at each of three background noise levels (50, 65 and 80 dB). By 2 h after dosing, the number of responses and response amplitude were decreased following 4.0-6.0 mg/kg TMT; these treatment effects persisted through 4 weeks after dosing. Increases in latency were also seen following all dosages of TMT. These data suggest that TMT produces disruption of function within the acoustic-startle pathway.

Hyperactivity Induced by Triadimefon, a Triazole Fungicide

Triadimefon is an agriculturally important triazole fungicide. The present experiments were conducted to characterize the effects of triadimefon on a measure of motor activity. Dosage-effect, time-effect, and the effect of repeated dosing (7 days) were determined following triadimefon exposure. Male Long Evans hooded rats, approximately 70 days old, received triadimefon po in 2.0 ml/kg corn oil. Motor activity testing was conducted for 1 hr in figure-eight mazes. For the dosage-effect determination, triadimefon (50-400 mg/kg) was administered 1 hr prior to testing. In the time-course study, triadimefon (200 mg/kg) was administered either 0.5, 1, 2, 4, 8, or 24 hr prior to testing. In the repeated dosing experiment animals received triadimefon (100 mg/kg) daily for 7 days and were tested 24 hr after the last exposure. Triadimefon produced significant hyperactivity following dosages of 100 and 200 mg/kg. This hyperactivity was rapid in both onset (0.5 hr) and recovery (8.0 hr). Repeated dosing with 100 mg/kg/day revealed no cumulative effects nor tolerance. These results indicate that triadimefon produces a transient hyperactivity at dosages 17 to 33% of the reported LD50.

Acute behavioral toxicity of carbaryl and propoxur in adults rats

Motor activity and neuromotor function were examined in adult CD rats exposed to either carbaryl or propoxur, and behavioral effects were compared with the time course of cholinesterase inhibition. Rats received an IP injection of either 0, 2, 4, 6 or 8 mg/kg propoxur or 0, 4, 8, 16 or 28 mg/kg carbaryl in corn oil 20 min before testing. All doses of propoxur reduced 2 hr activity in a figure-eight maze, and crossovers and rears in an open field. For carbaryl, dosages of 8, 16 and 28 mg/kg decreased maze activity whereas 16 and 28 mg/kg reduced open field activity. In order to determine the time course of effects, rats received a single IP injection of either corn oil, 2 mg/kg propoxur or 16 mg/kg carbaryl, and were tested for 5 min in a figure-eight maze either 15, 30, 60, 120 or 240 min post-injection. Immediately after testing, animals were sacrificed and total cholinesterase was measured. Maximum effects of propoxur and carbaryl on blood and brain cholinesterase and motor activity were seen within 15 min. Maze activity had returned to control levels within 30 and 60 min whereas cholinesterase levels remained depressed for 120 and 240 min for propoxur and carbaryl, respectively. These results indicate that both carbamates decrease motor activity, but behavioral recovery occurs prior to that of cholinesterase following acute exposure.

Integrated Risk Assessment - Results from an International Workshop.

The World Health Organizations International Programme on Chemical Safety and international partners have developed a framework for integrated assessment of human health and ecological risks and four case studies. An international workshop was convened to consider how ecological and health risk assessments might be integrated, the benefits of and obstacles to integration, and the research and mechanisms needed to facilitate implementation of integrated risk assessment. Using the case studies, workshop participants identified a number of opportunities to integrate the assessment process. Improved assessment quality, efficiency, and predictive capability were considered to be principal benefits of integration. Obstacles to acceptance and implementation of integrated risk assessment included the disciplinary and organizational barriers between ecological and health disciplines. A variety of mechanisms were offered to overcome these obstacles. Research recommendations included harmonization of exposure characterization and surveillance methods and models, development of common risk endpoints across taxa, improved understanding of mechanisms of effect at multiple scales of biological organization, and development of methods to facilitate comparison of risks among endpoints.

Pattern recognition of behavioral events in the nonhuman primate

A computerized pattern recognition system has been developed that is capable of identifying 40 separate spontaneously occurring behavioral acts of the primateMacaca fascicularis. The system, called PROBE (pattern recognition of behavioral events), is described in detail. In its present stage of development, PROBE classifies behavioral activity with a reliability comparable to trained human observers. The potential applications for and improvements to the PROBE system are discussed.

Serotonergic modulation of the acoustic startle response in rats during preweaning development

The involvement of serotonin (5-HT) in modulating the acoustic startle response (ASR) is well established in adult rats, but 5-HT involvement during the preweaning period, when 5-HT neurons undergo extensive development, has not previously been described. Three 5-HT receptor subtypes are reported to modulate the ASR in adult rats: 5-HT1A and 5-HT2 receptor agonists facilitate the ASR, whereas 5-HT1B agonists decrease the response. In the present study, the effects of 5-HT agonists and generalized 5-HT depletion on the ASR were studied in preweanling animals, using independent groups of Long-Evans rats tested on postnatal day (PND) 13, 17 and 21. 8-Hydroxy-2-(di-n-propylamino) tetralin (8OHDPAT, 62-1000 micrograms/kg), a 5-HT1A receptor agonist, and 5-methoxy-N,N-dimethyl tryptamine (MeODMT, 2-4 mg/kg), a nonselective 5-HT agonist, had no effect on PND 13 and then increased the ASR on PND 17 and 21. The 5-HT2 receptor antagonists cyproheptadine (5 mg/kg) and ketanserin (5 mg/kg) blocked the effect of MeODMT at both ages, providing some evidence that MeODMT increased the ASR through 5-HT2 receptors. 1-(m-Chlorophenyl) piperazine (mCPP, 1-5 mg/kg), a 5-HT1B agonist, had no effect on ASR amplitude on PND 13 or 17 and then produced a dose-related decrease in the response on PND 21. Generalized depletion of 5-HT by 80-90% in whole-brain and spinal cord, using p-chlorophenylalanine (PCPA, 300 mg/kg 24 hr prior to testing), did not alter ASR amplitude at any age.(ABSTRACT TRUNCATED AT 250 WORDS)

A self-contained, regulated, burst-firing constant-current ac shock generator

A line- and load-regulated constant-current ac shock generator has been designed for animal behavior experiments. The self-contained unit has four operating modes, amplitude adjustment, and a leakage current detection circuit. A unique feature of this generator is that the good load regulation achieved by using a high-voltage source is preserved without such problems as arcing and high current density effects. Circuit schematics, along with a discussion of selected circuits, are included. Experimental data are presented to demonstrate the utility of the device.

Advancing Exposure Science and Its Applications

The mission of most environmental organizations around the world is to safeguard human health and the environment. In the United States, air quality management practice relies on the ambient concentrations of pollutants of concern and the success of a regulatory strategy is assessed by determining whether pollutant emissions have been reduced and ambient concentration levels have decreased. Some countries (e.g. United Kingdom) assess the success of their regulatory strategy by determining whether exposure reduction have occured. Exposure is defined as the contact of a stressor with a receptor for a given duration of time. It is now well-recognized that ambient concentrations and human exposure levels are not the same. Hence, it is important to better understand exposure levels since exposure is the link between environmental pollution and human and ecosystem health. Exposure science deals with comprehensive understanding of the relationship among pollutant emissions, pollutant transport and fate, pollutant levels that people breathe in and stressor levels to sensitive ecosystems, and associates health effects. Given the increasing complexity of current and emerging environmental problems, exposure science must play a pivotal role in developing and implementing most meaningfull and cost-effective emission control policies. Theis paper provides exposure framework to identify and minimize exposures to harmful pollutants, thereby better protectinf human ecosystem health.