Benzo[a]pyrene 4,5-oxide. Discrepancy between induction of sister chromatid exchange and binding to DNA in cultured human fibroblasts

Sister-chromatid exchange: second report of the Gene-Tox Program

This paper reviews the ability of a number of chemicals to induce sister-chromatid exchanges (SCEs). The SCE data for animal cells in vivo and in vitro, and human cells in vitro are presented in 6 tables according to their relative effectiveness. A seventh table summarizes what is known about the effects of specific chemicals on SCEs for humans exposed in vivo. The data support the concept that SCEs provide a useful indication of exposure, although the mechanism and biological significance of SCE formation still remain to be elucidated.

Serum- and plasma-dependent variations of benzo(a)pyrene-induced sister chromatid exchange in human lymphocytes

Sister chromatid exchange (SCE) is frequently used to assess the potential mutagenicity of chemical agents to human beings. We demonstrate here that levels of SCE induced by benzo(a)pyrene (BP) in the widely used blood lymphocyte assay are influenced by serum and plasma supplements. Sister chromatid exchange induction by BP was greatest when using fetal calf serum (FCS), intermediate with newborn calf serum (NCS), and lowest with autologous human plasma (AHP). This new finding adds to a growing list of factors capable of modulating the SCE response and underscores the need for researchers to consider serum and plasma supplements in the standardization of the SCE approach in human mutagen assessments. The data also demonstrate the potential of SCE to aid in the study of serum factors which modify the mutagen sensitivity of human cells towards environmental carcinogens.

Activation of polycyclic hydrocarbons in Reuber H4-II-E hepatoma cells. An in vitro system for the induction of SCEs

Activation of polycyclic aromatic hydrocarbons (PAHs) was examined in the Reuber H4-II-E established cell line without the use of exogenous enzyme preparations. Metabolism of PAHs to genotoxic products was determined by the induction of sister-chromatid exchanges (SCEs). The induction of SCEs followed a dose-response pattern with plateaus at high doses of PAH. The effects of metabolic enzyme inducers (3-methylcholanthrene, phenobarbital, Aroclor 1254) and the epoxide hydrase inhibitor 1,1,1-trichloropropylene oxide were assessed as changes in SCE induction and enhanced production of water-soluble metabolites. Results indicate that Reuber H4-II-E cells can be employed in the testing of carcinogens activated by the P1-450 monooxygenase system and would be a useful in vitro system for the study of mechanisms of metabolic induction and their effect on genetic toxicity.

Determination of epoxide hydrolase activity in whole cells (human lymphocytes) and activation by benzoflavones

Epoxide hydrolase (epoxide hydratase, epoxide hydrase, E.C. 3.3.2.3) activity so far has only been measured in subcellular preparations. We show here that, with the highly lipophilic substrate (3H)-benzo(a)pyrene 4,5-oxide, the activity can be determined in intact cells. Whole human lymphocytes hydrolyze it at a similar rate to that in lymphocyte homogenate. We have previously reported that cultivation of lymphocytes in a medium containing 5,6-benzoflavone leads to an increase in epoxide hydrolase activity. We now demonstrate that this stimulation is due to enzyme activation and that enzyme induction does not contribute to this increase to any measurable extent. Moreover, both 5,6-benzoflavone and 7,8-benzoflavone activate epoxide hydrolase. This activation occurs not only in cell homogenate, but also - with a similar concentration-response relationship - in whole lymphocytes. Hence measurement of epoxide hydrolase activity in subcellular preparations reflects the activity in these intact cells. Furthermore, insofar as a concentration of 1 microM of the benzoflavones is sufficient to cause a measurable (10 to 20%) activation, it appears likely that foreign compounds can activate epoxide hydrolase in man.

Sister chromatid exchange (SCE) and structural chromosome aberration in mutagenicity testing

Data from previous studies published on the induction by mutagens of sister chromatid exchanges (SCEs) and structural chromosome damage were compared qualitatively and quantitatively. Although a good correlation between the incidence of both cytogenetic phenomena has been pointed out in many previous publications, about 30% of the agents for which comparable data were available yielded non-corresponding qualitative results concerning both indicator effects. However, even in groups with good qualitative agreement distinct quantitative differences indicated different molecular mechanisms of the formation of SCEs and breaks. Additional information supporting the importance of these differences for the validity of both indicator systems has been derived from the results obtained using strong clastogens exhibiting a low or no SCE-inducing activity and vice versa, from special observations on chromosomal breakage syndromes, and from studies on the action of known co- and anti-clastogens on SCE-induction by chemical mutagens. As a result, it has been suggested that the SCE-technique should be considered as a valuable additional method for cytogenetic mutagenicity testing, which, however, is not adequate to replace the classical methods of analysis of structural chromosome damage.