Green and Lash (1999) commented, in a letter to the editor, on our paper reporting an increased incidence of renal cell cancer in workers exposed to high concentrations of trichloroethene over extended periods of time (Vamvakas et al. 1998). Unfortunately, because of irregular handling of the letter by the editorial management of the journal, we were not in a position to follow common practice, that is to respond immediately and in the same issue (see footnote).We do not accept the statement at the outset of Green and Lash's letter that signi®cant methodological¯aws make our results unreliable. Rather, we regard their criticism as unsubstantiated, for following reasons.

The mycotoxin ochratoxin A (OTA) and its metabolite ochratoxin alpha (OT-alpha) were investigated, to examine their potency to induce sister chromatid exchanges (SCE) in cultured porcine urinary bladder epithelial cells (PUBEC) (primary culture). Serum-free cultured PUBEC were incubated for 5 h with either OTA or OT-alpha, respectively, and subsequently cultured in the presence of 5-bromo-2-deoxyuridine (BrdU). After two cell cycles, mitosis was inhibited by the colchicine derivative Colcemid, cells were fixed and chromosomes were prepared for SCE analysis. For OTA, a dose-dependent increase in SCE frequency was measured in concentrations between 100 pM and 100 nM OTA. At 100 nM OTA, SCE frequency increased by about 41%, compared to the base SCE level (7.27 SCEs per chromosome set, solvent control). Higher concentrations of OTA were cytotoxic. The metabolite OT-alpha also increased SCE frequency, but at higher concentrations. At a concentration of 10 microM OT-alpha, an increase of about 55% was detected. OT-alpha showed no cytotoxic effect. These results indicate that OTA is genotoxic in this in vitro system, which represents the urinary bladder epithelium, a target organ of OTA in vivo. It could also be shown that OT-alpha, which is said to be non-toxic, is genotoxic in this assay at higher concentrations.

No abstract

Molecular epidemiological studies require high numbers of participants. The combination of an non-invasive access to human DNA with a rapid genotyping analysis, e.g. by use of LightCycler assisted real-time polymerase chain reaction (PCR), can be helpful in conducting such trials. The aim of our study was to define, for the first time, the use of LightCycler technology in analysis of non-invasively derived DNA. DNA extracted from blood, mouthwash and buccal cytobrush samples from 100 volunteers was analyzed for the genotypes of cytochrome P450 CYP1B1, and glutathione S-transferases GSTT1, GSTM1 and GSTP1. The median amounts of DNA isolated from blood, mouthwash and buccal cytobrush samples were 95, 11 and 8 microg, respectively. While genotyping for CYP1B1 codon 432 polymorphism and GSTP1 codon 105 polymorphism resulted in a complete correspondence for all three modes of sampling, the identification of individuals with null-genotype for GSTT1 or GSTM1 failed in some cases due to atypical courses of the corresponding melting curves, leading to high false-positive rates in the group of non-invasively derived samples. Thus, the results presented here call for caution in using LightCycler assisted real-time PCR in non-invasively collected samples, at least when appropriate control strategies are not implemented.