"In vitro" rodent models as alternative methods in assessing cytotoxicity and carcinogenic potential of metal compounds.

Student thesis: Doctoral thesis

Abstract

n vitro morphological cell transformation tests encompass the multi-step process from neoplastic conversion to the established tumorigenic phenotype. In the present PhD thesis the in vitro Balb/3T3 assay, an immortalised mouse fibroblast cell line, was applied for assessing cytotoxicity and carcinogenic potential of selected metal compounds of environmental, occupational and biomedical interest by adopting a specific multi-stage work strategy. This has involved a very accurate protocol optimisation in order to assess intralaboratory reproducibility of the test protocol and to assure stability of the experimental conditions in which the Balb/3T3 assay was applied.<br/>Therefore, after optimisation of the adopted protocol the present PhD project was carried out following a "four steps approach": a) determination of cytotoxicity at a fixed concentration exposure (100 µM, 65 individual metal compounds). This allowed the selection of metal compounds to which priority is given for subsequent investigations; b) setting of dose-effect relationships for 35 metal compounds identified as first priority in step (a), in order to establish the corresponding IC50 values and a suitable exposure range of concentrations to be used in the subsequent steps; c) determination of carcinogenic potential of selected metal compounds from step (b); d) mechanistic studies on transforming metal species as identified in step (c). In this context, an initial mechanistic approach was the evaluation of the apoptotic response induced by selected metal compounds on the Balb/3T3 cells. This study on apoptosis has shown that more than one assay should be used in order to establish unequivocally the induction of apoptosis by a metal compound on the selected test system. This is due to the complexity of the problem and the difficulties to interpret the experimental data. Moreover, the findings on the apoptotic response induced by As(III), Cr(VI) and some Pt-compounds suggest the hypothesis of an existing relationship among apoptotic, genotoxic and carcinogenic processes.<br/>With regard to mechanistic studies and metal metabolism, the results obtained applying unique and peculiar analytical techniques like the use of radiotracers, Inductively Coupled Plasma-Mass Spectrometry and Nuclear Magnetic Resonance have made possible to get interesting metabolic data on uptake and intracellular repartition of metals incorporated into cells. This is an aspect generally neglected in in vitro studies although it is a key point for mechanistic interpretation of cytotoxicity and transforming activity induced by chemicals.<br/>In addition, a good level of concordance was achieved by comparing the results obtained from the application of the Balb/3T3 assay with selected in vitro rodent and human models.<br/>In conclusion, the present PhD project represents an important contribution to make the Balb/3T3 cell line as a valuable in vitro model to investigate correlation between uptake, biotransformation, cytotoxicity and carcinogenic potential of metal compounds. It is to state that the Balb/3T3 assay has the potential to be suitable for a future validation study.
Date of Award21 Jul 2003
Original languageEnglish
SupervisorEnrico Sabbioni (Director) & Ricardo Marcos Dauder (Tutor)

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