Comet-assay parameters as rapid biomarkers of exposure to dietary/environmental compounds - An in vitro feasibility study on spermatozoa and lymphocytes

Twelve chemical compounds have been selected for the European NewGeneris study on the basis of their potential to damage DNA, in order to establish adequate and reliable biomarkers of exposure. These genotoxic chemicals include heterocyclic amines, organochlorines, polycyclic aromatic hydrocarbons, mycotoxins, lipid peroxidation products and alcohol. Damage in somatic cells such as lymphocytes could give rise to cancer, while damage in germ cells could not only give rise to cancer but also to heritable defects. The alkaline Comet assay, with and without metabolic activation, as well as the neutral Comet assay were used to assess DNA integrity in spermatozoa and lymphocytes after in vitro treatment with low, middle and high doses of each chemical. DNA-reactive aldehydes generated by lipid peroxidation, food mutagens such as heterocyclic amines, nitrosamine and benzo[a]pyrene produced the highest amounts of DNA damage, even without metabolic activation. Damage seen with the neutral Comet assay – detecting primarily double-strand breaks – was lower than with the alkaline assay. In general, there was increased damage in the spermatozoa by comparison with the lymphocytes, with altered slopes in the dose–response curves. The Comet assay with sperm was generally very sensitive in assessing genotoxic damage, with the Comet parameters being good biomarkers of induced DNA damage. Establishing reliable biomarkers of exposure for the evaluation of dietary/environmental carcinogens is of utmost importance to protect our health and the health of our offspring

In vitro evaluation of baseline and induced DNA damage in human sperm exposed to benzo[a]pyrene or its metabolite benzo[a]pyrene-7,8-diol-9,10-epoxide, using the comet assay

Exposure to genotoxins may compromise DNA integrity in male reproductive cells, putting future progeny at risk for developmental defects and diseases. To study the usefulness of sperm DNA damage as a biomarker for genotoxic exposure, we have investigated cellular and molecular changes induced by benzo[a]pyrene (B[a]P) in human sperm in vitro, and results have been compared for smokers and non-smokers. Sperm DNA obtained from five smokers was indeed more fragmented than sperm of six non-smokers (mean % Tail DNA 26.5 and 48.8, respectively), as assessed by the alkaline comet assay (P < 0.05). B[a]P-related DNA adducts were detected at increased levels in smokers as determined by immunostaining. Direct exposure of mature sperm cells to B[a]P (10 or 25 μM) caused moderate increases in DNA fragmentation which was independent of addition of human liver S9 mix for enzymatic activation of B[a]P, suggesting some unknown metabolism of B[a]P in ejaculates. In vitro exposure of samples to various doses of B[a]P (with or without S9) did not reveal any significant differences in sensitivity to DNA fragmentation between smokers and non-smokers. Incubations with the proximate metabolite benzo[a]pyrene-r-7,t-8-dihydrodiol-t9,10-epoxide (BPDE) produced DNA fragmentation in a dose-dependent manner (20 or 50 μM), but only when formamidopyrimidine DNA glycosylase treatment was included in the comet assay. These levels of DNA fragmentation were, however, low in relation to very high amounts of BPDE–DNA adducts as measured with 32P postlabelling. We conclude that sperm DNA damage may be useful as a biomarker of direct exposure of sperm using the comet assay adapted to sperm, and as such the method may be applicable to cohort studies. Although the sensitivity is relatively low, DNA damage induced in earlier stages of spermatogenesis may be detected with higher efficiencies

Parallel evaluation of Doxorubicin inducing Genetic damage in human lymphocytes and sperm using the Comet assay and spectral karyotyping

NoIn recent years, two techniques for detecting genetic damage in the whole genome have gained importance: the alkaline comet assay, to detect DNA damage such as strand breaks and alkali-labile sites, and a multicolour FISH method, spectral karyotyping (SKY), to identify chromosomal aberrations simultaneously in all metaphase chromosomes. In the present study, the induction of DNA damage in human sperm and lymphocytes in vitro has been studied employing an anticancer drug, doxorubicin (DX). An increase in DNA damage was observed with the comet assay as the median per cent head DNA of sperm significantly decreased from 82.07 and 85.14% in the untreated control groups to 63.48 and 72.52% at doses of 0.8 µM DX. At 1.6 µM the percentage declined to 60.96% (the corresponding tail moment increased from 4.42 to 12.19). In stimulated lymphocytes, a significant increase was observed in tail moment, from 0.72 and 0.53 in controls to 15.17 and 12.10 at 0.2 µM DX, continuing at the same level to a final concentration of 1.6 µM. Structural aberrations found in the parallel SKY study in stimulated lymphocytes at 0.2 µM DX consisted of 14% chromatid-type and 2% chromosome-type aberrations; none were found in controls. The SKY results correlate very well with the findings of the comet assay in lymphocytes where DNA damage was observed at similar doses. This study is the first reporting use of the comet assay and SKY analysis in parallel after chemical treatment. The potential of the two techniques together is evident, as they represent a set of assays feasible for evaluating damage in human somatic and germ cells after chemical treatment (i) by direct observation of two different end-points, detecting general DNA damage and chromosomal aberrations and (ii) by extrapolation from lymphocytes to sperm, which provides a `parallelogram¿ approach in human cells

Assessment of cellular and molecular toxicity by in vitro tests: the okadaic acid toxin case

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