Selecting the best non-invasive matrix to measure mercury exposure in human biomonitoring surveys.

Exposure to mercury, even at low doses, can affect human health, well-being and life quality at a broad scale. Human biomonitoring is the most straightforward approach to measure and quantify mercury exposure in humans. The objective of the present study is to compare and discuss the relationships between Hg levels in the most used matrices, hair, urine and blood, with the aim to ascertain to what extent mercury exposure and internal mercury levels could be predicted by monitoring non-invasive matrices. The study population (n = 527) is a subsample from Spanish BIOAMBIENT. ES study (18-65 y, both sexes), with data of Hg levels in blood, hair, and urine from the same individuals. We found strong inter-matrix Spearman correlations between blood and hair mercury (r2 = 0.84), while the correlations for urine and blood mercury (r2=0.64) and urine and hair mercury (r2=0.65) were weaker. The geometric mean of the ratios between matrices were (GM, 95%CI): Hair/Blood 280 (271-290), Urine/Blood 0.174 (0.163-0.186) and Hair/Urine 2070 (1953-2194) and Urine/Blood 0.135 (0.128-0.144) for urine corrected by creatinine. High individual variation was observed particularly in those ratios involving urine. Considering the wide range of values observed in the ratios, we do not recommend applying them at individual level. The predictive models indicate that hair Hg was a more accurate predictor than urine. The inclusion of urine values did not increase the predictive accuracy, so, we recommend a cautious interpretation of urine mercury levels. Our study presents clear evidence that in a population highly exposed to food-borne mercury, a large portion of urinary mercury primarily emanates from methylmercury demethylation. We conclude that urine, as a non-invasive matrix, can be used as a reliable qualitative biomarker for Hg exposure when hair measurements not are available. For quantitative individual assessments, still blood measurements are to be preferred.

Procedures for the reconstruction, primary culture and experimental use of rainbow trout gill epithelia.

This protocol describes how to reconstruct and culture the freshwater rainbow trout gill epithelium on flat permeable membrane supports within cell culture inserts. The protocol describes gill cell isolation, cultured gill epithelium formation, maintenance, monitoring and preparation for use in experimental procedures. To produce a heterogeneous gill epithelium, as seen in vivo, seeding of isolated gill cells twice over a 2-d period is required. As a consequence, this is termed the double-seeded insert technique. Approximately 5-12 d after cell isolation and seeding, preparations develop electrically tight gill epithelia that can withstand freshwater on the apical cell surface. The system can be used to study freshwater gill physiology, and it is a humane alternative for toxicity testing, bioaccumulation studies and environmental water quality monitoring.

Fish consumption patterns and hair mercury levels in children and their mothers in 17 EU countries.

The toxicity of methylmercury (MeHg) in humans is well established and the main source of exposure is via the consumption of large marine fish and mammals. Of particular concern are the potential neurodevelopmental effects of early life exposure to low-levels of MeHg. Therefore, it is important that pregnant women, children and women of childbearing age are, as far as possible, protected from MeHg exposure. Within the European project DEMOCOPHES, we have analyzed mercury (Hg) in hair in 1799 mother-child pairs from 17 European countries using a strictly harmonized protocol for mercury analysis. Parallel, harmonized questionnaires on dietary habits provided information on consumption patterns of fish and marine products. After hierarchical cluster analysis of consumption habits of the mother-child pairs, the DEMOCOPHES cohort can be classified into two branches of approximately similar size: one with high fish consumption (H) and another with low consumption (L). All countries have representatives in both branches, but Belgium, Denmark, Spain, Portugal and Sweden have twice as many or more mother-child pairs in H than in L. For Switzerland, Czech Republic, Hungary, Poland, Romania, Slovenia and Slovakia the situation is the opposite, with more representatives in L than H. There is a strong correlation (r=0.72) in hair mercury concentration between the mother and child in the same family, which indicates that they have a similar exposure situation. The clustering of mother-child pairs on basis of their fish consumption revealed some interesting patterns. One is that for the same sea fish consumption, other food items of marine origin, like seafood products or shellfish, contribute significantly to the mercury levels in hair. We conclude that additional studies are needed to assess and quantify exposure to mercury from seafood products, in particular. The cluster analysis also showed that 95% of mothers who consume once per week fish only, and no other marine products, have mercury levels 0.55 µg/g. Thus, the 95th percentile of the distribution in this group is only around half the US-EPA recommended threshold of 1 µg/g mercury in hair. Consumption of freshwater fish played a minor role in contributing to mercury exposure in the studied cohort. The DEMOCOPHES data shows that there are significant differences in MeHg exposure across the EU and that exposure is highly correlated with consumption of fish and marine products. Fish and marine products are key components of a healthy human diet and are important both traditionally and culturally in many parts of Europe. Therefore, the communication of the potential risks of mercury exposure needs to be carefully balanced to take into account traditional and cultural values as well as the potential health benefits from fish consumption. European harmonized human biomonitoring programs provide an additional dimension to national HMB programs and can assist national authorities to tailor mitigation and adaptation strategies (dietary advice, risk communication, etc.) to their country's specific requirements.

Transcriptomics and proteomics. Applications to ecotoxicology.

Researchers from Europe and the USA met at the Joint Research Center (JRC) of the European Commission to discuss how to integrate gene and protein expression analyses with bioinformatic tools in the field of ecotoxicology and how this new approach could be translated in improved risk assessment procedures. The measurements of gene and/or protein expression levels, upon exposure to a chemical or a stressor, can be used to develop robust molecular biomarkers that will allow the early detection of environmental stress, study long-term exposure and infer the mechanism of action. These molecular biomarkers should be linked to phenotypic end points of exposure such as adverse effects in growth and reproduction in single organisms and populations. At environmentally realistic exposure levels there could be "non-linear" dose-response curves, which should be accounted for in the experimental design and in the analyses of microarray and proteomic data. The application of gene and protein expression profiling in ecotoxicology will have a significant impact on the ecotoxicology field in the near future and international collaborations will play an important role in accelerating the application of those techniques.

Effects of copper on CYP1A activity and epithelial barrier properties in the rainbow trout gill.

The effects of copper on beta-naphthoflavone (betaNF)-induced ethoxyresorufin O-deethylase (EROD) activity were studied in rainbow trout (Oncorhynchus mykiss) gill filaments (after in vivo exposure) and in gill cells cultured as both primary cultures and as polarised epithelia, i.e. with water in the apical compartment and culture medium in the basolateral compartment. In the in vivo study betaNF and copper were added to the water, in primary cultures both chemicals were added to the culture medium and in cultured epithelia copper was added to the apical water whilst betaNF was added to the basolateral culture medium. In primary cultures this investigation was repeated with and without foetal bovine serum (FBS) supplementation of the culture media. Gill barrier properties, specifically polyethylene glycol (PEG-4000) permeability (i.e. paracellular permeability), sodium efflux and transepithelial electrical resistance (TER) were also investigated in cultured gill cell epithelia after apical treatment with copper. Two micromolar copper had no effect on EROD activity in gill filaments in vivo irrespective of whether EROD was induced by 0.01, 0.1 or 1.0 microM betaNF. Similarly, 0.5-100 microM copper had no effect on EROD induction in cultured epithelia. In primary cultures copper did reduce EROD induction but the effective concentration was dependent on whether the cells were supplemented with FBS, i.e. EROD activity was reduced by all copper concentrations of 5 and above if FBS was included, but only by 1000 microM if FBS was omitted. In cultured epithelia PEG-4000 permeability increased, whilst sodium efflux and TER were unaffected following treatment with 75 microM copper. Based on these results we conclude that the branchial monooxygenase system is a less sensitive target for copper than the barrier properties of the gill. Indeed, these data suggest the apical membrane of the gill epithelial cells minimises the uptake of waterborne copper and therefore protects the intracellular environment, including the CYP1A system. This could enable the freshwater fish gill to retain their potential of first-pass metabolism of waterborne organic compounds whilst simultaneously being exposed to waterborne copper.

Apolipoprotein AI could be a significant determinant of epithelial integrity in rainbow trout gill cell cultures: a study in functional proteomics.

The freshwater fish gill forms a barrier against an external hypotonic environment. By culturing rainbow trout gill cells on permeable supports, as intact epithelia, this study investigates barrier property mechanisms. Under symmetrical conditions the apical and basolateral epithelial surfaces contact cell culture media. Replacing apical media with water, to generate asymmetrical conditions (i.e. the situation encountered by the freshwater gill), rapidly increases transepithelial resistance (TER). Proteomic analysis revealed that this is associated with enhanced expression of pre-apolipoprotein AI (pre-apoAI). To test the physiological relevance, gill cells were treated with a dose of 50 microg ml(-1) human apolipoprotein (apoAI). This was found to elevate TER in those epithelia which displayed a lower TER prior to apoAI treatment. These results demonstrate the action of apoAI and provide evidence that the rainbow trout gill may be a site of apoAI synthesis. TER does not differentiate between the trans-cellular (via the cell membrane) and para-cellular (via intercellular tight junctions) pathways. However, despite the apoAI-induced changes in TER, para-cellular permeability (measured by polyethylene glycol efflux) remained unaltered suggesting apoAI specifically reduces trans-cellular permeability. This investigation combines proteomics with functional measurements to show how a proteome change may be associated with freshwater gill function.

Cultured gill epithelia as models for the freshwater fish gill.

We review recent progress in the development of models for the freshwater teleost gill based on reconstructed flat epithelia grown on permeable filter supports in primary culture. Methods are available for single-seeded insert (SSI) preparations consisting of pavement cells (PVCs) only from trout and tilapia, and double-seeded insert (DSI) preparations from trout, containing both PVCs (85%) and mitochondria-rich cells (MRCs, 15%), as in the intact gill. While there are some quantitative differences, both SSI and DSI epithelia manifest electrical and passive permeability characteristics typical of intact gills and representative of very tight epithelia. Both preparations withstand apical freshwater exposure, exhibiting large increases in transepithelial resistance (TER), negative transepithelial potential (TEP), and low rates of ion loss, but there is only a small active apical-to-basolateral "influx" of Cl(-) (and not of Na(+)). Responses to various hormonal treatments are described (thyroid hormone T3, prolactin, and cortisol). Cortisol has the most marked effects, stimulating Na(+),K(+)-ATPase activity and promoting active Na(+) and Cl(-) influxes in DSI preparations, and raising TER and reducing passive ion effluxes in both epithelia via reductions in paracellular permeability. Experiments using DSI epithelia lacking Na(+) uptake demonstrate that both NH(3) and NH(4)(+) diffusion occur, but are not large enough to account for normal rates of branchial ammonia excretion, suggesting that Na(+)-linked carrier-mediated processes are important for ammonia excretion in vivo. Future research goals are suggested.