Little Pro on 2018-02-11
Both in vitro and in vivo methods are routinely used by industries and regulatory authority in toxicity testing, GHS classification and chemical risk assessment. In this article, we will summarize the definition of in vitro and in vivo tests and provide a list of common validated in vitro toxicology test methods for chemicals. In the end we will explain some factors to consider when using in vitro toxicology methods for regulatory work.
An in vitro (latin: "in the glass") test is a study that is performed outside of a living organism (i.e, glass, petri dishes). The test usually involves the use of isolated tissues, organs or cells. In contrast, an in vivo (latin: "in the living") test is a study that is performed in living organisms (i.e, rat, rabbit).
Both in vitro and in vivo methods can be used to predict the inherent hazard properties of chemical substances. However, results obtained from in vitro studies cannot often be used directly to predict biological responses of organisms to chemical exposure in vivo.
That does not mean that in vitro data is of less value. In fact, in vitro test is gaining more attention in regulatory community since it can reduce the number of animals used significantly while offering reliable predictions for some toxicological endpoints. Take EU REACH for example, an in vivo eye irritation or skin irritation study shall only be considered in case the in vitro tests are not applicable for a substance or the results obtained are not adequate for classification and risk assessment.
The table below summarizes a list of common validated in vitro toxicology testing methods for chemicals. In vitro methods are mainly used for skin/eye irritation test, skin sensitisation test and genotoxicity tests. They cannot replace acute toxicity, repeated dose toxicity, development and reproductive toxicity, and carcinogenicity yet.
Endpoints | In vitro methods | |
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Skin Irritation |
Above methods may be used to replace the following traditional in vivo test.
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Serious Eye Damage/Eye Irritation |
Above methods may be used to replace the following traditional in vivo test.
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Sensitisation |
Any method above alone cannot replace the following traditional in vivo test.
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Genotoxicity |
The following in vitro studies are usually conducted first. If there is any positive response in the in vitro study, a follow-up in vivo study for the same endpoint is usually required.
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There are three factors to consider when using in vitro methods for regulatory work. Firstly, we need to know whether in vitro methods are accepted by regulatory authority in your jurisdiction or not. Some countries do not accept in vitro data at all while some countries/industries ban in vivo animal testing completely. Secondly, we need to consider animal welfare issue. In vitro methods should be used more to provide screening info for in vivo testing. Thirdly, we need to know the limitations of in vitro methods. For example, OECD TG 437 The Bovine Corneal Opacity and Permeability Test Method (BCOP) is an in vitro assay that can be used to identify chemicals (substances or mixtures) as either i) causing “serious eye damage” (Cat 1 ), or ii) not requiring classification at all. However, it cannot be used to determine if a chemical substance is an eye irritant or not (Cat 2).
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