Implementation of New Test Methods into Practical Testing

New toxicology test methods, especially those using in vitro methods, are continually being developed. Some are used by industry for screening purposes; others are eventually validated for regulatory use. However, for a new test method to be firmly adopted by industry it must be readily available, generally through an in-house industry laboratory, an academic laboratory, or a contract research organization. Regardless of the type of laboratory which intends to implement the test method, certain steps must be taken to ascertain that the method that is put into place is reproducible and performs identically to the test method that was published or has undergone validation. This involves developing protocols and standard operating procedures, training staff, developing historic positive and negative control data, establishing acceptable performance with proficiency chemicals, and addressing all the safety concerns that may accompany the assay. From experience within a contract research laboratory, we provide guidance on how to most efficiently accomplish these tasks.

Diagnosis: Toxic! – Trying to Apply Approaches of Clinical Diagnostics and Prevalence in Toxicology Considerations

The assessment of relevance of toxicological testing was compared with approaches of diagnostic medicine, a discipline that faces a comparable situation. Considering the work of a toxicologist as setting a diagnosis for compounds, assessment tools for diagnostic tests were transferred to toxicological tests. In clinical diagnostics, test uncertainty is well accepted and incorporated in this assessment. Furthermore, prevalence information is considered to evaluate the gain in information resulting from the application of a test. Several common toxicological scenarios, in which test uncertainty and prevalence are combined, are discussed including the interdependence of test accuracy, prevalence and predictive values or the sequential application of a screening and a confirmatory test. In addition, real prevalences derived from prevalences determined by an imperfect test are presented. We conclude that information on prevalences of toxic health effects is required to allow a complete assessment of the relevance of toxicological test. In this process, lessons can be learned from evidence-based approaches in clinical diagnostics.

Extent of initial corneal injury as the mechanistic basis for ocular irritation: key findings and recommendations for the development of alternative assays

Currently, there are no recognized alternative tests to eliminate the use of animals in ocular irritation testing. A major reason no replacement alternatives have been developed is that the current in vivo data set provides no perspective regarding the critical cellular and molecular changes involved in initial ocular injury, subsequent responses, and repair processes in standard in vivo tests. Without this perspective, mechanistically based replacement tests cannot be developed and validated. We have proposed that the level of ocular irritation is related to the extent of initial injury, and that regardless of the processes leading to tissue damage, the extent of initial injury is the principal factor determining the outcome of ocular irritation. This article summarizes the results from our studies of various surfactants and nonsurfactants of differing irritancy that support our hypothesis. Our findings indicate that a mechanistically based alternative to in vivo ocular irritation tests would be the microscopic or biochemical measurement of initial injury using either ex vivo or in vitro corneal equivalent systems composed of corneal epithelial, stromal keratocyte, and corneal endothelial cell layers. This work also provides a well-characterized panel of materials of varying types and irritation for use in developing and validating alternative tests.

An investigation of new toxicity test method performance in validation studies: 1. Toxicity test methods that have predictive capacity no greater than chance

An approach commonly used to measure new toxicity test method (NTM) performance in validation studies is to divide toxicity results into positive and negative classifications, and the identify true positive (TP), true negative (TN), false positive (FP) and false negative (FN) results. After this step is completed, the contingent probability statistics (CPS), sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) are calculated. Although these statistics are widely used and often the only statistics used to assess the performance of toxicity test methods, there is little specific guidance in the validation literature on what values for these statistics indicate adequate performance. The purpose of this study was to begin developing data-based answers to this question by characterizing the CPS obtained from an NTM whose data have a completely random association with a reference test method (RTM). Determining the CPS of this worst-case scenario is useful because it provides a lower baseline from which the performance of an NTM can be judged in future validation studies. It also provides an indication of relationships in the CPS that help identify random or near-random relationships in the data. The results from this study of randomly associated tests show that the values obtained for the statistics vary significantly depending on the cut-offs chosen, that high values can be obtained for individual statistics, and that the different measures cannot be considered independently when evaluating the performance of an NTM. When the association between results of an NTM and RTM is random the sum of the complementary pairs of statistics (sensitivity + specificity, NPV + PPV) is approximately 1, and the prevalence (i.e., the proportion of toxic chemicals in the population of chemicals) and PPV are equal. Given that combinations of high sensitivity-low specificity or low specificity-high sensitivity (i.e., the sum of the sensitivity and specificity equal to approximately 1) indicate lack of predictive capacity, an NTM having these performance characteristics should be considered no better for predicting toxicity than by chance alone.

Comprehensive outlook of in vitro tests for assessing skin irritancy as alternatives to Draize tests

In vitro alternative methods have been verified for the possibility to assess cutaneous irritancy because humans cannot be direct initial experimental subjects and animal experimentation could be forbidden in the near future. Many kinds of cell cytotoxicity assays have been tried, revealing their own advantages and limitations. Cell function-based tests have been used less frequently than cytotoxicity assays. Three-dimensional culture systems are promising because they are closer to the actual in vivo skin, and some of them are commercialized nowadays. The ultimate objective of in vitro irritancy tests, which is the high degree of correlation with human in vivo test results, has been accomplished in many experimental settings. Before applying these in vitro methods we must consider several points, including cell sources, irritant characteristics, exposure time, endpoint of experiment, extrinsic factors affecting irritation, etc. In vitro skin irritancy tests have been developed continuously, and in the future they could assume a heavy responsibility of estimating the irritancy in human skin in vivo.