Genetic Toxicology

When testing the potential DNA-damaging effects by pharmaceutical drugs and other chemicals, the test systems are generally based on experimental animals, bacteria or various kinds of transformed cells. We measure DNA-damage using the so called Comet Assay, which is a relatively quick, simple and cheap method for evaluating DNA-strand breaks in individual cells. The major objective of our in vitro studies is to improve the risk assessment regarding exposures to genotoxic agents. One example of this is our recent study (Durling et al., 2009) on the DNA damaging effect of 5-hydroxy-methylfurfural (HMF), a heat-induced food toxicant present in a vast number of food items. Since HMF has been suggested to be genotoxic after being bioactivated by the sulfotransferase SULT1A1, the comet assay was used to evaluate the DNA damaging effect of HMF in cell lines with different activities of SULT1A1. We found that HMF induced significant DNA damage in all cell lines independent of the activity of SULT1A1 in the cells, and that the HMF-induced DNA damage was observed only at rather high concentrations, which in most cases were associated with a concomitant decrease in cell viability.

From point of view of risk assessment, it is important to differ between genotoxic carcinogens and other substances that increase the risk of cancer by other mechanisms. In the case of drug-induced oxidative DNA-changes, for instance, one can distinguish two different main groups of substances: those who cause various types of reactive oxygen radicals in the cells directly and those who cause oxidative stress indirectly, as a consequence of general cytotoxicity. The research of recent years has also shown that the DNA repair has a great impact on whether the DNA-damage is manifested as a mutation or not, and there is reason to believe that there is a great variation in individual sensitivity to genotoxic agents, due to individual differences in DNA repair, metabolic bioactivation/detoxification pattern and/or other defense mechanisms in the cells. All those aspects are studied in this project.

In a recent project, supported by SIDA/SAREC, we are currently also evaluating the genotoxic and antigentoxic effects of some plant extracts used in traditional medicine in Ethiopia, and in these studies we also include fractions of extracts and/or pure compounds from extracts. One example of this is our recent study on plumbagin (Demma et al., 2009), a naphtoquinone present in the roots of Plumbago zeylanica, a traditionally used medicinal plant which has been reported to have many beneficial effects but also many side effects. The potential genotoxicity and antigenotoxicity of plumbagin was evaluated in mouse lymphoma L5178Y cells. Without affecting the cell viability, plumbagin itself induced significant DNA damage at concentrations as low as 0.25 ng/ml. When the cells were exposed to non-DNA damaging concentrations of plumbagin, together with NQNO (known to interact with DNA in many different ways) or catechol (known to induce oxidative DNA damage), plumbagin was found to significantly reduce the catechol-induced DNA damage, but to be without protective effect against the NQNO-induced damage. These findings provides further support for the idea that plumbagin may act as an antioxidative agent at low non-DNA damaging concentrations.

Principal investigator: Björn Hellman