Modulation of trichloroethylene in vitro metabolism by different drugs in rats.

Trichloroethylene (TCE) is a widely used chemical to which humans are frequently exposed. Toxicological interactions with drugs are among factors having the potential to modulate the toxicity of TCE. The aim of this study was to identify metabolic interactions between TCE and 14 widely used drugs in rat suspended hepatocytes and characterize the strongest using microsomal assays (oxidation and/or glucuronidation). The concentrations of TCE and its metabolites, trichloroethanol (TCOH) and trichloroacetate (TCA), were measured by gas chromatography with injection headspace coupled to mass spectrometry (GC-MS). Results in hepatocyte incubations show that selected drugs can be segregated into four groups: group 1: drugs causing no significant interactions (five drugs: amoxicillin, carbamazepine, ibuprofen, mefenamic acid and ranitidine); group 2: increasing both TCE metabolites (two drugs: naproxen and salicylic acid); group 3: decreasing both TCE metabolites (five drugs: acetaminophen, gliclazide, valproic acid, cimetidine and diclofenac) and group 4: affecting only one (two drugs: erythromycin and sulphasalazine). Naproxen and salicylic acid (group 2) and acetaminophen, gliclazide and valproic acid (from group 3) presented the strongest interactions (i.e. drugs changing metabolite levels by 50% or more). For group 2 drugs, characterization in rat microsomes confirmed interaction with naproxen only, which was found to partially competitively inhibit TCOH glucuronidation (K(i) = 211.6 µM). For group 3 selected drugs, confirmation was positive only for gliclazide (K(i) = 58 µM for TCOH formation) and valproic acid (K(i) = 1215.8 µM for TCA formation and K(i) = 932.8 µM for TCOH formation). The inhibition was found to be partial non competitive for both drugs. Our results confirm the existence of interactions between TCE and a variety of widely used drugs. Further efforts are undertaken to determine if these interactions are plausible in humans and if they can impact the risk of toxicity of TCE in medicated population.

Mercury distribution and exchanges between the Amazon River and connected floodplain lakes.

This work presents the distribution and the partition of mercury (Hg) in the Curuai floodplain lakes along the Amazon River. The maximum Total Filtered Hg (T-FHg) concentrations in the floodplain lakes (28 to 52 pmol L(-1)) coincide with the maximum T-FHg concentrations of the Amazon River and are measured during the flooding period. The lowest T-FHg values (3 to 5 pmol L(-1)) are observed during the flood peak of the mainstream, during the rainy season, when waters are diluted by the local rainfall. In this system, Hg is mainly transported in the particulate phase, confirmed by elevated values of the Hg partition coefficient (4.77

Biomarkers of selenium status in the Amazonian context: blood, urine and sequential hair segments.

Selenium (Se) is an essential element and deficit or excess of dietary Se is associated with health disorders. Relatively elevated Se levels have been reported in the Brazilian Amazon, where there are also important annual variations in the availability of different foods. The present study was conducted among six riparian communities of the Tapajós River to evaluate seasonal variations in blood and sequential hair cm Se concentrations, and to examine the relationships between Se in blood and hair, and blood and urine. Two cross-sectional studies were conducted, at the descending water (DWS, n=259) and the rising water (RWS, n=137) seasons, with repeated measures for a subgroup (n=112). Blood Se (B-Se), hair Se (H-Se) and urine Se (U-Se) were determined. Match-paired analyses were used for seasonal comparisons and the method of best fit was used to describe the relationships between biomarkers. B-Se levels presented a very large range (142-2447 microg/l) with no overall seasonal variation (median 284 and 292 microg/l, respectively). Sequential analysis of 13 cm hair strands showed significant variations over time: Se concentrations at the DWS were significantly lower compared with the rising water season (medians: 0.7 and 0.9 microg/g; ranges: 0.2-4.3 microg/g and 0.2-5.4 microg/g, respectively). At both seasons, the relationships between B-Se and H-Se were linear and highly significant (r(2)=67.9 and 63.6, respectively), while the relationship between B-Se and U-Se was best described by a sigmoid curve. Gender, age, education and smoking did not influence Se status or biomarker relationships. Variations in H-Se suggest that there may be seasonal availability of Se sources in local food. For populations presenting a large range and/or elevated Se exposure, sequential analyses of H-Se may provide a good reflection of variations in Se status.

New evidence on the effects of tea on mercury metabolism in humans.

The authors present the results of an experiment in which they explored the role of tea in human metabolic processing of methylmercury (MeHg) from fish consumption. The experiment involved 50 scientists from the Collaborative Mercury Research Network (COMERN) who agreed to eat fish for 2 daily meals for 3 consecutive days. Half of the participants also drank 6 cups of tea daily, starting a week before and continuing through the experiment. The authors calculated the total amount of MeHg that each participant ingested from (1) the measured mercury (Hg) level in fish and (2) the quantity of fish eaten, and compared it with the total increases of Hg and MeHg levels in participants' blood. Results indicated that the control group metabolized roughly 100% of the available fish MeHg, whereas the tea-exposed group showed blood levels of MeHg at more than 40% than that available in the fish provided, suggesting that an external MeHg pool supplied part of the measured blood MeHg increase. The authors conclude that tea may accelerate the enterohepatic MeHg cycle and contribute to a temporary bioamplification of MeHg in the bloodstream.