Endocrine disruptors

Many contaminants occurring in the food chain can be considered as endocrine disruptors: certain pesticides, POPs and metabolites thereof, phytoestrogens (present in fruit and vegetables and soy products), hormones like estradiol endogenously present in cow's milk and eggs, and residues of illegally applied hormones. Several synthetic endocrine disruptors are actually POPs and suspect for carcinogenity; information related to phytoestrogens is rather contradictory in this respect: both protection and promotion of cancers is claimed in literature [17]. The main classes of phytoestrogens are isoflavones, lignans, coumestans and natural stilbenes, and show structural similarities with potent estrogens. Their consumption by healthy adults may be without risk but the problem might be totally different when exposure occurs at critical stages of development, i.e., at foetal and prepubertal children. Soy-milk-based baby-food is especially relevant to check for adverse effects of phytoestrogens [18]. Cow's milk on the other hand should be checked for both estradiol and phytoestrogens. For an adequate risk assessment it is crucial to know how much phytoestrogens (or endocrine disruptors in general) are added to the "diet" of vulnerable consumers. Apart from endocrine disruptor analyses in the diet a clear insight into the endogenous estrogen background levels is needed. Recently, new data were presented using sensitive gas chromatography high-resolution mass spectrometry (GC/HRMS) down to the 2ng/L level in plasma samples [19]. It was shown that the endogenous levels in prepubertal children are much lower than previously thought based on less specific immunoassays; as a result the diet-contribution to the total exposure becomes much more critical and relevant. Within the scope of the EU project BioCop (phyto)estrogen levels have been assessed both in soy and cow's milk products [20].

Several bioactivity-based approaches are feasible for the screening of endocrine disruptors in the food chain. Apart from the SPR biosensor assay based on binding with specific human transport proteins already mentioned [12], robust transcription activation bioassays are available for estrogens [21]. The performance of the latest generation based on recombinant yeast cells fulfilled all validation and ISO 17025 accreditation requirements and the results obtained compared very well with GC/MS data [22]. Also a highly challenging transcriptomics approach is being explored within BioCop [20]. An MCF7 cell line is exposed to sample extracts. Next the messenger RNA (mRNA) is extracted from the cells and the cDNA is hybridized on a microarray carrying 47,000 human transcripts. Up and down regulation of specific transcripts was observed which will allow the design of dedicated microarrays having a limited number of transcripts for endocrine disruptor fingerprinting. A major challenge will be to ensure compatibility of real sample extracts with the cells, overall robustness and validation issues.

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