The use of historical data for identifying biologically unimportant but statistically significant results in genotoxicity assays

Abstract

The definition of a negative result is a problem in genetic toxicology. Here we suggest that a result may be considered biologically unimportant (negative) if it falls within the limits of variation usually found in the negative controls of the particular test. To determine 'usual' variation, we have set 95% confidence limits on three indices of variation, calculated from historical values for duplicate negative control data from several genotoxicity tests. These tests showed four characteristic types of response and the appropriate index of variability was determined for each. Where there was little test-to-test variation in true mean (micronucleus test and metaphase analysis), confidence limits set on the overall distribution of negative controls were the best index of variability. In other assays (Ames, yeast and mouse lymphoma), there was considerable test-to-test variation so that differences between, or ratios of, the members of control duplicates were the preferred measure of variability. This approach can define what is biologically unimportant in terms of the test system. However, no inference can be drawn as to potential importance. Thus the main use is the removal of the positive 'label' from statistically significant results which fall within the usual range of spontaneous variation for the assay under consideration.

Screening and Testing for Endocrine Disruption in Fish—Biomarkers As “Signposts,” Not “Traffic Lights,” in Risk Assessment

“…The same approach exists in other areas of ecotoxicology and mammalian toxicology (Dave 1993; Environment Canada 1990; Mitchell et al 1990). Relative to this point, the OECD (2003) guidance document on the validation of test methods defines the following terms (with the current addition of the last point on interassay comparability):…”

Evaluation of the reproductive effects of tamoxifen citrate in partial and full life‐cycle studies using fathead minnows (Pimephales Promelas)

“…Concomitant with such extensive biological studies is the need to evaluate data from both statistical and biological perspectives. This is widely recognized in mammalian toxicology studies, where consideration of the reversibility of responses, their mechanistic plausibility, and historical databases are important adjuncts to statistical analyses of individual studies [29–32]. This mammalian approach has been used successfully in previous fish full life‐cycle testing of a pharmaceutical product [4].…”

“…The FFLC study was started using embryos Ͻ24 h postfertilization collected from at least three spawnings. The partial life-cycle study was conducted between September 27 and November 8, 2002, and the FFLC study was conducted between March 5 and December 29,2003.…”

Regulatory immunotoxicology: does the published evidence support mandatory nonclinical immune function screening in drug development?

“…(b) As already discussed, the relevance of up to a 4-fold increase in total serum IgM, only at the low dose, as an indicator of immunosuppressive potential is highly disputable.For compounds with well characterised immunomodulatory properties, consistent increases in serum IgM have been observed in rats for immunostimulants such as HCB (Ezendam et al, 2003;Michielsen et al, 1977;Michielsen et al, 1999;Schielen et al, 1995;Schulte et al, 2002) and silica in an experimental model of silicosis (Huang et al, 2001), and decreases in serum IgM for the immunosuppressant benzo[a]pyrene . (c) The majority of the salmeterol data indicate an absence of effects on immune function.The two affected parameters, splenic B cells and levels of the T. spiralis-specific IgG are only marginally reduced, and several lines of evidence, already discussed, suggest that both findings could have been chance events.Interpretation criteria in immunotoxicology should be no different from those employed in mainstream toxicology; in the case of clinical pathology (or genotoxicity) data for instance, it is accepted that all statistically significant differences do not necessarily represent true or toxicologically significant effects (Carakostas and Banerjee, 1990;Carakostas, 1992;Mitchell et al, 1990).Assessment of biological importance relies in immunotoxicology as in general toxicology, on corroborative evidence from a variety of endpoints (CDER, 2002;Descotes, 2004;Lewis et al, 2002;.…”