Apoptosis may contribute to false-positive results in the in vitro micronucleus test performed in extreme osmolality, ionic strength and pH conditions

Conditions in which clastogens produce positive responses have been increasingly challenged, and several situations have been described in which clastogenic responses would be considered not to be relevant. For example, extreme culture conditions lead to high variations of pH, osmolality or ionic strength. Apoptosis is induced in extreme culture conditions and contributes to false-positive results in the in vitro micronucleus test performed with CTLL-2 cells. These cells can enter apoptosis when exposed to apoptosis stimuli or after IL-2 deprivation, whereas the CTLL-2 1362 cell line is protected from apoptosis due to the over-expression of the apoptosis inhibitor Bcl2 in bcl2-transfected CTLL-2 cells. The two cell lines were treated in extreme culture conditions of either pH or osmolality or were submitted to high ionic strength. The apoptosis level was measured in parallel with the in vitro micronucleus test using the annexin V-FITC method. Data obtained in the two cell lines suggested that apoptosis caused by extreme culture condition induces the formation of micronucleated cells, which leads to false-positive results in the in vitro micronucleus test. (C) 2004 Elsevier B.V. All rights reserved.