[Show abstract][Hide abstract] ABSTRACT: This study was conducted to determine species differences in the metabolism of ethylbenzene (EB) in liver and lung. EB (0.22-7.0mM) was incubated with mouse, rat and human liver and lung microsomes and the formation of 1-phenylethanol (1PE), acetophenone (AcPh), 2-ethylphenol (2EP), 4-ethylphenol (4EP), 2,5-ethylquinone, and 3,4-ethylquinone were measured. Reactive metabolites (2,5-dihydroxyethylbenzene-GSH [2EP-GSH] and 3,4-dihydroxyethylbenzene-GSH [4EP-GSH]) were monitored via glutathione (GSH) trapping technique. None of the metabolites were formed at detectable levels in incubations with human lung microsomes. Percent conversion of EB to 1PE ranged from 1% (rat lung; 7.0mM EB) to 58% (mouse lung; 0.22 mM EB). More 1PE was formed in mouse lung than in mouse liver microsomes, although formation of 1PE by rat liver and lung microsomes was similar. Metabolism of EB to 1PE was in the order of mouse > rat > human. Formation of AcPh was roughly an order of magnitude lower than 1PE. Conversion of EB to ring-hydroxylated metabolites was much lower (0.0001% [4EP-GSH; rat lung] to 0.6% [2EP-GSH; mouse lung]); 2EP-GSH was typically 10-fold higher than 4EP-GSH. Formation of 2EP-GSH was higher by lung (highest by mouse lung) than liver microsomes and the formation of 2EP-GSH by mouse liver microsomes was higher than rat and human liver microsomes. Increasing concentrations of EB did lead to a decrease in amount of some formed metabolites. This may indicate some level of substrate- or metabolite-mediated inhibition. High concentrations of 2EP and 4EP were incubated with microsomes to further investigate their oxidation to ethylcatechol (ECat) and ethylhydroquinone (EHQ). Conversion of 2EP to EHQ ranged from 6% to 9% by liver (mouse > human > rat) and from 0.1% to 18% by lung microsomes (mouse > rat > human). Conversion of 4EP to ECat ranged from 2% to 4% by liver (mouse > human approximately rat) and from 0.3% to 7% by lung microsomes (mouse > rat > human). Although ring-oxidized metabolites accounted for a relatively small fraction of overall EB metabolism, its selective elevation in mouse lung microsomes is nonetheless consistent with the hypothesized mode of action for observed preferential toxicity of EB to the lung in this species.
Preview · Article · Dec 2008 · Toxicological Sciences
[Show abstract][Hide abstract] ABSTRACT: This study was designed to experimentally measure the assimilation efficiency of hexachlorobenzene (HCB) in a warm-water, benthic-feeding fish species, the channel catfish (Ictalurus punctatus). Catfish were exposed to (14)C-radiolabeled HCB in catfish food over a 28-day exposure period, followed by a 14-day clearance period. Over the experimental period, the total (14)C residues were measured in fish tissue and a simple two-box kinetic model was applied to the data to simulate uptake and clearance dynamics. No detectable metabolism of HCB by catfish was found. A two-box kinetic model effectively modeled the uptake and clearance of (14)C-HCB in catfish, with a calculated assimilation efficiency of the chemical into the whole catfish of 67% (growth corrected). The growth-corrected pseudo first-order elimination half-life of (14)C-HCB from whole catfish was determined to be 29 days (k(2)=0.024 day(-1)).
No preview · Article · Feb 2008 · Ecotoxicology and Environmental Safety
[Show abstract][Hide abstract] ABSTRACT: This study determined the oral and dermal ADME of 2-amino-2-methyl-1-propanol (AMP), a substituted aliphatic alcohol used in a number of industrial and consumer products. Groups of 4 male Fischer 344 rats received either a single bolus oral or dermal dose of 18 mg/kg (14)C-AMP in water. The dermal dose was applied to an area of 12 cm(2) on the back of the rats for 6h under semi-occluded conditions and fitted with rodent jackets to prevent grooming. Time-course blood and excreta were collected, radioactivity determined and blood and urine analyzed for AMP and metabolites. The orally administered (14)C-AMP was rapidly absorbed and eliminated in urine. Elimination of radioactivity from blood was biphasic with a rapid alpha phase (t(1/2 alpha) approximately 1h) followed by a slower beta phase (t(1/2 beta)=41+/-4h plasma and 69+/-34 h RBC). Total urinary elimination accounted for 87-93% of the dose, most (72-77%) within the first 48 h. Fecal elimination accounted for only 3-10%. Only 3-4% of the dose was found in tissues 168h post-dosing. The total dermal absorption of (14)C-AMP was 42% that included approximately 8% of the dose remaining at the application site 162 h after washing. Less than 1% of the applied dose remained in the stratum corneum and approximately 6% of the dose was found in tissues. Urinary elimination was 43% of the administered dose, most ( approximately 17%) within 48 h, and approximately 2% was eliminated in feces. It took much longer to reach plasma C(max) after dermal application (8.5+/-4.7 h in plasma and 4.0+/-2.8h in RBC) than the oral dose (0.3h) and the AUC(0-->alpha) for dermal dose was approximately 8-fold lower than with the oral dose. Again, elimination of the radioactivity from blood was biphasic with apparent t(1/2 alpha) of 9+/-6 and 2+/-1h for plasma and RBC, respectively. However, the alpha phase was "flipped-flopped" due to relatively slow dermal penetration and rapid elimination of the systemically absorbed dose, which was corrected to approximately 0.3 h after separating alpha elimination phase from the absorption. The slope of the beta phase became parallel to the oral route upon cessation of the absorption from the dose site skin, between 18 and 42 h post-washing. No metabolite of AMP was detected either in blood or excreta of any rat. Results of this study suggests that toxicologically significant concentrations of AMP are unlikely to be achieved in the systemic circulation and/or target tissues in humans as a result of dermal application of products containing AMP. Additionally, systemically absorbed dose will be rapidly eliminated from the body with little remaining at the application site.
No preview · Article · Feb 2008 · Food and Chemical Toxicology
[Show abstract][Hide abstract] ABSTRACT: A rapid and sensitive method for the analysis of 17alpha-ethinylestradiol (EE2) in environmental aqueous samples has been developed. Aquatic samples were extracted using liquid-liquid extraction, and organic phase extracts were concentrated and derivatized with dansyl chloride. Analysis was performed using high-performance liquid chromatography with positive electrospray ionization and tandem mass spectrometry (HPLC/ESI-MS/MS). Deuterated 17alpha-ethinylestradiol was used as internal standard and was added to samples before extraction. A limit of quantitation of 1 ng/L was obtained using a 25 mL aqueous sample. The average recovery of EE2 spiked into a 25 mL tapwater sample was 100%. This highly sensitive quantitation method is useful for measuring low levels of EE2 in aqueous environmental samples.
Full-text · Article · Nov 2004 · Rapid Communications in Mass Spectrometry