Evaluation of the ToxRTool's ability to rate the reliability of toxicological data for human health hazard assessments.

Regulatory agencies often utilize results from peer reviewed publications for hazard assessments. A problem in doing so is the lack of well-accepted tools to objectively, efficiently and systematically assess the quality of published toxicological studies. Herein, we evaluated the publicly available software-based ToxRTool (Toxicological data Reliability assessment Tool) for use in human health hazard assessments. The ToxRTool was developed by the European Commission's Joint Research Center in 2009. It builds on Klimisch categories, a rating system established in 1997, by providing additional criteria and guidance for assessing the reliability of toxicological studies. It also transparently documents the study-selection process. Eight scientists used the ToxRTool to rate the same 20 journal articles on thyroid toxicants. Results were then compared using the Finn coefficient and "AC1" to determine inter-rater consistency. Ratings were most consistent for high-quality journal articles, but less consistent as study quality decreased. Primary reasons for inconsistencies were that some criteria were subjective and some were not clearly described. It was concluded, however, that the ToxRTool has potential and, with refinement, could provide a more objective approach for screening published toxicology studies for use in health risk evaluations, although the ToxRTool ratings are primarily based on study reporting quality.

Inter-laboratory control data for reproductive endpoints required in the OPPTS 870.3800/OECD 416 reproduction and fertility test.

BACKGROUND: The U.S. EPA revised the Reproduction and Fertility Effects Test Guideline (OPPTS 870.3800/OECD 416) in 1998, adding numerous endpoints in an effort to incorporate new methodologies, improve the sensitivity for detecting reproductive toxicants, and more efficiently utilize study animals. Many of these new endpoints have not been used in regulatory reproductive toxicology studies prior to their inclusion in the test guidelines; thus, the Health and Environmental Sciences Institute (HESI) of the International Life Sciences Institute (ILSI) initiated the Reproductive Endpoints Project to examine the utility of these new endpoints. METHODS: This report provides a retrospective analysis of 43 multi-generation studies (16 in Wistar rats, 27 in Sprague-Dawley rats) conducted according to the latest version of the test guidelines. It focuses on vehicle (negative) control values (means and ranges) for the various endpoints to examine inter-laboratory variability. RESULTS: Based on the compiled data, the most variable endpoints across laboratories and their associated coefficients of variation (CV) for each generation were: percent abnormal sperm (166-205%), testicular spermatid concentration (126-147%), postimplantation loss (97-104%), primordial follicle counts (69%, only measured in P2 females), and epididymal sperm concentration (52-57%). Absolute and relative prostate and thymus weights, weanling uterine weights, and anogenital distance had CVs of 25-50%. Sources of variability included procedural differences between laboratories, inherent biological variability, and/or small sample sizes for some endpoints. CONCLUSIONS: These inter-laboratory control data provide a means for laboratories to review their performance on reproductive toxicity measures, and provide perspective for interpreting their own control data and data from treated animals.

A qualitative retrospective analysis of positive control data in developmental neurotoxicity studies.

Testing for neurodevelopmental effects commonly involves both functional and neuropathological assessments in offspring during and following maternal exposure. The use of positive controls in neurotoxicity screening has been advocated by numerous expert groups. Evaluation of positive control data allows evaluation of laboratory proficiency in detecting changes in the structure and function of the developing nervous system and comparison of the sensitivity of assessments in different studies and laboratories. This project surveyed approaches taken in contract and industrial laboratories in generating and providing these data. Positive control data submitted in support of 34 developmental neurotoxicity (DNT) studies from 16 different laboratories were summarized by test method for information on the following: age relevance of test subjects, the presence of a dose-response relationship, gender, group size, statistics, report quality, quality assurance, and the year the study was conducted. Endpoints included the following: developmental landmarks, clinical observations (CO), motor activity, startle response, learning and memory, qualitative neuropathology, and quantitative brain morphometry (linear measurements of selected brain regions). Results ranged from no positive control data for three laboratories, to one laboratory that submitted 17 separate positive control reports. The qualitative range was similarly broad, from excellent to poor. Various problems were identified, including the following: inappropriate report structure (e.g., copies of poster presentations), lack of individual data, inadequate methodological details, submission of very old data (>10 years) or data from completely different laboratories, use of inappropriate positive control chemicals or doses that were without effect, lack of statistical analysis, use of only one sex, and use of incompatibly aged animals. Analyses revealed that there were only 3 out of 16 laboratories that had submitted positive control data adequate for proficiency purposes for all of the major endpoints in the DNT study. Adequate positive control data are very useful in a weight-of-evidence approach to help determine the biological significance of results, and also to increase the confidence in negative results from DNT studies.

Recent developments in regulatory requirements for developmental toxicology.

A number of legislative and regulatory changes have occurred over the past 5 years to prompt the re-evaluation of the regulatory requirements for developmental toxicity testing and use of the data for risk assessment. In particular, passage of the 1996 Food Quality Protection Act (FQPA) in the United States required the USEPA to evaluate children's health risks in a more rigorous fashion, and to apply an additional 10-fold safety factor if data were inadequate or children appeared to be more sensitive than adults. A review of the testing protocols required by USEPA led to extension of the dosing period to term in the prenatal developmental toxicity study and the addition of endpoints to the 2-generation reproduction study protocol as indicators of possible neurologic, reproductive, or immune alterations. Revised testing guidelines for pesticides and toxic substances were published by USEPA in 1998, including a developmental neurotoxicity testing protocol. Further review for FQPA implementation resulted in the proposal for a core set of required toxicology studies, including routine developmental neurotoxicity, adult neurotoxicity, and adult immunotoxicity studies. In addition, development of new testing guidelines in several areas was recommended, these guidelines to be used in conjunction with or as follow-up when indicated from standard testing: developmental immunotoxicity, carcinogenesis, specialized neurotoxicity studies, endocrine disruptor studies, pharmacokinetics, and direct dosing of neonates. The impact of these efforts on the policies for toxicity testing of pesticides are discussed, and these issues are currently being reviewed on a broader scale, in particular, by evaluating the adequacy of the methods used for reference values (e.g. chronic RfD, RfC). Three major areas of focus for this review include life stages evaluated, endpoints assessed, and the duration of exposure used in various studies. A major focus of these efforts is to ensure that children's health risks are being adequately addressed in the risk assessment process.

Methods to identify and characterize developmental neurotoxicity for human health risk assessment. III: pharmacokinetic and pharmacodynamic considerations.

We review pharmacokinetic and pharmacodynamic factors that should be considered in the design and interpretation of developmental neurotoxicity studies. Toxicologic effects on the developing nervous system depend on the delivered dose, exposure duration, and developmental stage at which exposure occurred. Several pharmacokinetic processes (absorption, distribution, metabolism, and excretion) govern chemical disposition within the dam and the nervous system of the offspring. In addition, unique physical features such as the presence or absence of a placental barrier and the gradual development of the blood--brain barrier influence chemical disposition and thus modulate developmental neurotoxicity. Neonatal exposure may depend on maternal pharmacokinetic processes and transfer of the xenobiotic through the milk, although direct exposure may occur through other routes (e.g., inhalation). Measurement of the xenobiotic in milk and evaluation of biomarkers of exposure or effect following exposure can confirm or characterize neonatal exposure. Physiologically based pharmacokinetic and pharmacodynamic models that incorporate these and other determinants can estimate tissue dose and biologic response following in utero or neonatal exposure. These models can characterize dose--response relationships and improve extrapolation of results from animal studies to humans. In addition, pharmacologic data allow an experimenter to determine whether exposure to the test chemical is adequate, whether exposure occurs during critical periods of nervous system development, whether route and duration of exposure are appropriate, and whether developmental neurotoxicity can be differentiated from direct actions of the xenobiotic.

Methods for assessing sperm motility, morphology, and counts in the rat, rabbit, and dog: a consensus report. ILSI Risk Science Institute Expert Working Group on Sperm Evaluation.

Reproductive toxicity studies are increasingly including assessments of sperm parameters including motility, morphology, and counts. While these assessments can provide valuable information for the determination of potential reproductive toxicity, the methods for conducting the assessments have not been well developed in all laboratories and are continually evolving. The use of different methods in different laboratories makes comparison of data among laboratories difficult. To address the differences in methods, a working group was convened to discuss methods currently in use, share data, and try to reach consensus about optimal methods for assessing sperm parameters in rats, rabbits, and dogs. This article presents the consensus report, as well as future research needs, with the hope that optimized common methods will aid in the detection of reproductive effects and enhance interlaboratory comparisons.

Teratology study in mice subjected to inhalation of diethylhydroxylamine, nitroethane, and diethylamine hydrogen sulfite.

Pregnant female mice were exposed from Days 6 to 17 of pregnancy to 8.9 +/- 2.0 ppm of diethylhydroxylamine and 14.3 +/- 2.0 ppm of nitroethane. Exposures were for 8.25 +/- 2.25 hours/day including weekends. The mice were also exposed continuously for 24 hours a day to the vapor of diethylamine hydrogen sulfite. The exposure produced no effect on the dams compared to the control group. There was no evidence of compound-induced terata, variation in sex ratio, embryotoxicity, or inhibition of fetal growth and development.