Applications of InVitro Test Methods

In-vitro toxicity methods were first developed to study the mechanisms of actions of chemical substances at the molecular and cellular levels [39]. Increasingly, in-vitro methods have been applied in many fields such as cancer biology, drug discovery and toxicology. Genotoxicity was the first field of toxicology in which in-vitro test methods have been used for toxicity testing to identify the mutagenic characteristics of chemicals [40, 41]. At present, in-vitro methods cover a broad range of techniques and models, and a standardized battery of in-vitro tests can be used to assess acute local and systemic toxicity. Cytotoxicity testing, reproductive toxicity, mutagenicity, irritancy testing, immunology and target organ toxicity are the main areas of in-vitro toxicology [32].

Meanwhile, the application of in-vitro methods in toxicology is also faced by a number of difficulties. One important shortcoming of this approach is the lack of complexity [42]. Although cells in culture represent the elementary living systems, as a very simplified system, they cannot represent the complexity of the entire organism. Hence, an in-vitro system cannot replicate exactly the biodynamics of the whole human body due to the lack of possible mitigating systems (e.g., hormones, nervous system and immunity), and the lack of biotransformation and excretion pathways for their elimination in vitro [35]. The challenge of how to relate in-vitro concentrations which produce cellular toxicity in vitro to equivalent in-vivo dosages may be improved by the development and application of predictive tools such as PBTK models [39]. The basic toxicology knowledge of absorption, distribution, metabolism and elimination (ADME) of chemicals is essential for the development of appropriate toxicokinetic models.

The next limitation of these methods is related to chronic toxicity testing. Although some studies have shown promise [43], in-vitro test systems are to date mainly focused on acute toxicity testing rather than on short-term or long-term repeated dose toxicity investigations [44]. More knowledge of the mechanisms of toxicity is still needed before in-vitro methods could broadly be implemented for repeated-dose toxicity testing [45]. The physico-chemical properties of test chemicals, including low water solubility or high vapor pressure, may also cause technical problems during the course of in-vitro tests [46-48].

Nevertheless, in-vitro toxicity test systems offer new advantages when compared to traditional in-vivo approaches [39, 42, 44, 49-52]. In-vitro test methods eliminate the interspecies extrapolation by using human cells and tissues, which may in turn help to generate more representative data for human toxicological risk assessments. These methods are comparatively simpler, faster and hence less time-consuming and more cost-efficient [50]. Moreover, they facilitate the application of biochemical, cellular and molecular biology techniques to study the underlying mechanism of toxic action [51, 53]. In-vitro models for organ toxicity evaluation which have been developed for many organs and tissues (such as nephrotoxic, neurotoxic and hematotoxic models) allow the study of components of potential target organs and target systems [52]. Despite the complex organization of cells, in-vitro methods are also being developed for respiratory toxicity assessment using relevant airway cells, lung cells or tissues and for the implementation of target-specific endpoints [17, 54].

0 0

Post a comment