In vivo toxicity testing

Replacements are in vitro tests able to completely replace the use of in vivo toxicity test in a specific area of toxicity testing. 

Complex Mixtures Methods for In Vivo Toxicity Testing. Complex Mixture Committee, National Research Council, National Academy Press, 1988. 

Arnold, D.L., Grice, H.C. and Krewski, D.R. (1990). Handbook of In Vivo Toxicity Testing. Academic Press, San Diego, CA. 

Sediment assessment with cultivated organisms for use in in vivo toxicity testing... 

A variety of in vitro toxicity tests have been developed to model the effects of toxins on living cells or tissues. In these tests, a carrier medium (such as fetal bovine serum) containing given concentrations, or doses, of a particular toxin are added to cell cultures (cell lines). Various indicators of toxicity, cell morphology transformation, or cell prohferation are then measured after specified periods of time. The cell types used in a particular study can be chosen to approximate the types of cells that would be affected during acmal exposure, such as respiratory cells or tissues. Toxicity indicators include, for example, measures of the percent of viable cells remaining at the end of the test (compared to a control line with no added toxin), and the concentrations various cytokines or other cytoplasmic enzymes induced from the cells by the toxin. Uncertainties with the in vitro toxicity tests include how comparable their results are to those of in vivo toxicity tests, and how well they reproduce actual physiological conditions and processes in the human body (Johnson and Mossman, 2001). 

In vivo toxicity tests involve the direct exposure (via appropriate exposure routes) of hving animals to variable doses of toxins over time, followed by measurement of toxic effects or exposure indicators. Inhalation tests either expose the subject animals to known concentrations of particles in an airstream, or utihze direct intratracheal implantation of the particles in the subject animals (e.g., studies summarized in Johnson and... 

Fieldent MR, Kolaja KL. The role of early in vivo toxicity testing in drug discovery toxicology. Expert Opin Drug Saf. 2008 7(2) 107-110. 

Toxicologists must rely on results obtained from an alternative method if it is to serve as a replacement for an in vivo toxicity test. Two measures of alternative method performance must be known in order to define reliability from a test user s point of view. First, a toxicologist must know it is possible to consistently reproduce the data obtained from the alternative method over long periods of time. A test that does not provide the same results on the same test substance repeatedly would not be useful in the safety assessment process. Second, it must be possible to consistently predict in vivo toxicity endpoints at a known level of accuracy and precision. These measures of reliability are objective endpoints that can be measured experimentally. The part of the validation process that provides the data needed to confirm the reliability of an alternative method as proposed by its developers is the validation study. 

In practical terms, the assessment of relevance addresses the following question Given the information known about the alternative method, are the data provided by the assay good enough to allow its acceptance as a replacement for a given in vivo test In order to answer this question, all of the available information related to performance, operation, and mechanistic basis of an alternative method and the in vivo toxicity test it is intended to replace must be thoroughly reviewed. The benefits and risks associated with the adoption of the new method must also be defined. Once this information is available, it must be synthesized in a manner that allows those involved in a validation process to render a judgment that the performance of the alternative method is acceptable or not as a replacement for the in vivo toxicity test. 

Once estimates of the best possible performance of the methods are defined, another useful benchmark that can be used to assess the relevance of an alternative method is to compare its performance against that of the in vivo toxicity test it will replace. If the capability of the alternative method to predict an in vivo toxicity endpoint was at least equivalent to the capability of the in vivo test to predict its own result, then it would provide strong evidence supporting the relevance of the alternative method. 

Next, it is important to consider whether the width of the 95% CIpred from the alternative method is small enough to provide an acceptably precise prediction of in vivo toxicity. The analysis presented earlier demonstrated that the 95% CIpred from an alternative method might be large. A benchmark that can be used to assess the acceptability of a large 95% CIpred could be derived from an examination of the precision of toxicity measurements obtained from the in vivo toxicity test. If an alternative method provides predictions as precise as those obtained from the in vivo method it is intended to replace, then it would provide evidence that the 95% CIpred alternative method is acceptable (for more information on the utility of the 95% CIpred)-... 

In only a few cases have pure substances been isolated and identified (Fig. 8). In vitro and in vivo toxicity tests have been performed using middle molecular fraction of varying purity to demonstrate biological activity (B32, N5). Various fractions have decreased 59Fe incorporation into heme, inhibited lymphocyte proliferation, impaired glucose utilization, decreased motor nerve conduction velocity... 

Most previous studies are based on the assumption that the toxicity of snake toxins is induced by a narrowly defined active region. As a consequence, single amino acid residues vere chemically modified and the effects of the modification assayed by in vivo toxicity tests (11,14,18). However, it was found that the derivatives modified at all those positions believed to be important still have significant activity. Instead, as has been previously shown by Karlsson (1 1), there is a gradual decrease of, but never a complete reduction in toxicity ( affinity of binding). 

National Research Council (1988) Complex mixtures, methods for in vivo toxicity testing. National Academy, Washington DC, p 523... 

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