Kathy A. Brzak

Agreement of pesticide biomarkers between morning void and 24-h urine samples from farmers and their children.

In pesticide biomonitoring studies, researchers typically collect either single voids or daily (24-h) urine samples. Collection of 24-h urine samples is considered the “gold-standard”, but this method places a high burden on study volunteers, requires greater resources, and may result in misclassification of exposure or underestimation of dose due to noncompliance with urine collection protocols. To evaluate the potential measurement error introduced by single void samples, we present an analysis of exposure and dose for two commonly used pesticides based on single morning void (MV) and 24-h urine collections in farmers and farm children. The agreement between the MV concentration and its corresponding 24-h concentration was analyzed using simple graphical and statistical techniques and risk assessment methodology. A consistent bias towards overprediction of pesticide concentration was found among the MVs, likely in large part due to the pharmacokinetic time course of the analytes in urine. These results suggest that the use of single voids can either over- or under-estimate daily exposure if recent pesticide applications have occurred. This held true for both farmers as well as farm children, who were not directly exposed to the applications. As a result, single void samples influenced the number of children exposed to chlorpyrifos whose daily dose estimates were above levels of toxicologic significance. In populations where fluctuations in pesticide exposure are expected (e.g., farm families), the pharmacokinetics of the pesticide and the timing of exposure events and urine collection must be understood when relying on single voids as a surrogate for longer time-frames of exposure.

Potential mechanisms of tumorigenic action of diethanolamine in mice

Diethanolamine (DEA), a secondary amine found in a number of consumer products, reportedly induces liver tumors in mice. In an attempt to define the tumorigenic mechanism of DEA, N-nitrosodiethanolamine (NDELA) formation in vivo and development of choline deficiency were examined in mice. DEA was administered with or without supplemental sodium nitrite to B6C3F1 mice via dermal application (with or without access to the application site) or via oral gavage for 2 weeks. Blood levels of DEA reflected the dosing method used; oral greater than dermal with access greater than dermal without access. No NDELA was observed in the urine, blood or gastric contents of any group of treated mice. Choline, phosphocholine and glycerophosphocholine were decreased </=62-84% in an inverse relation to blood DEA levels. These data demonstrated a lack of NDELA formation in vivo at tumorigenic dosages of DEA but revealed a pronounced depletion of choline-containing compounds in mice. It is suggested that the latter effect may underlie DEA tumorigenesis in the mouse.

Mechanism of trifluralin-induced thyroid tumors in rats.

Trifluralin, an herbicide, has been reported to cause a significant increase in thyroid follicular cell tumors in male Fischer 344 rats. This study was designed to determine the mechanism of thyroid hyperactivity after trifluralin exposure. A group of 15 male Fischer 344 rats were exposed to trifluralin-fortified (6500 ppm) diet for 2 weeks. The time weighted average daily intake of trifluralin was 441+/-77 mg/kg/day. Ten rats of the group were sacrificed and the sera analyzed for T3, T4, and TSH levels. The livers were also analyzed for selected T4-specific UGT gene expression and total UGT enzyme activity. In the trifluralin treated rats, the serum T3 and T4 levels decreased by 17% and 90%, respectively and TSH increased by 37% more than the control rats. Trifluralin-induced total hepatic UGT enzymes (2.4-fold) and mRNA expression of selected hepatic UGT isozymes (UGT1A1, 1.4-fold; UGT1A6, 6.4-fold; UGT2B1, 3.7-fold). For the remaining 5 rats in the group, bile was collected for 2 h and analyzed for free and conjugated T3 and T4. The total amount of T4 in bile more than doubled in trifluralin treated rats. Trifluralin treatment increased bile flow, caused a 3.2-fold increase in biliary elimination of conjugated T4 and 63% increase in conjugated T3. Based on these data, the decrease in total serum T3 and T4 levels in the trifluralin treated rats was due to enhanced peripheral metabolism and an increase in bile flow that results in a compensatory increase in TSH synthesis and secretion. The increased levels of TSH with chronic exposure to trifluralin would exert a continuous stimulation of the thyroid gland leading to cellular hypertrophy and proliferation predisposing to the development of follicular cell tumors in rats.

Cholinesterase inhibition and toxicokinetics in immature and adult rats after acute or repeated exposures to chlorpyrifos or chlorpyrifos–oxon

The effect of age or dose regimen on cholinesterase inhibition (ChEI) from chlorpyrifos (CPF) or CPF-oxon (CPFO) was studied in Crl:CD(SD) rats. Rats were exposed to CPF by gavage in corn oil, rat milk (pups), or in the diet (adults) or to CPFO by gavage in corn oil. Blood CPF/CPFO levels were measured. With acute exposure, ChEI NOELs were 2 mg/kg CPF for brain and 0.5 mg/kg CPF for red blood cells (RBCs) in both age groups. In pups, ChEI and blood CPF levels were similar using either milk or corn oil vehicles. Compared to gavage, adults given dietary CPF (12 h exposure) had greater RBC ChEI, but lower brain ChEI at corresponding CPF doses, indicating an effect of dose rate. With repeated CPF exposures, ChEI NOELs were the same across ages (0.5 and 0.1 mg/kg/day for brain and RBCs, respectively). With CPFO dosing, the ChEI NOELs were 0.1 mg/kg (acute) and 0.01 mg/kg/day (repeated doses) for RBCs with no ChEI in brain at CPFO doses up to 0.5 (pup) or 10 mg/kg (adult) for acute dosing or 0.5 mg/kg/day for both ages with repeat dosing. Thus, there were no age-dependent differences in CPF ChEI via acute or repeated exposures. Pups had less ChEI than adults at comparable blood CPF levels. Oral CPFO resulted in substantial RBC ChEI, but no brain ChEI, indicating no CPFO systemic bioavailability to peripheral tissues.

Determination of ortho-phenylphenol in human urine by gas chromatography-mass spectrometry

A sensitive gas chromatographic-mass spectrometric method was developed to quantitate total o-phenylphenol (OPP) (free plus conjugates) in human urine. Conjugates of OPP were acid-hydrolyzed to free OPP, derivatized to the pentafluorobenzoyl ester derivative and analyzed via negative-ion chemical ionization gas chromatography-mass spectrometry. Two stable isotope analogs of OPP were shown to be suitable as internal standards for this method (D2-phenol ring, 13C6-phenyl ring). A synthetic method is presented for the preparation of the D2-OPP internal standard. The 13C6-OPP analog was also shown to be useful as an alternate test material for laboratory-based exposure studies. The limit of quantitation for this method was 1 ng OPP/ml urine. Calibration curves were linear for the analyte over the concentration range of 0.5-1117 ng OPP/ml urine. Relative recovery of OPP from urine ranged from 97.0 to 104.7%. Low levels of OPP (mean=6+/-7 ng/ml; n=22) were found in control human urine samples. The method was validated with urine samples obtained from human volunteers undergoing a dermal exposure study with 12C-/13C6-/14C-OPP. This method was developed to aid in assessments of human exposure to OPP during a variety of uses of the compound.

Role of iodine in the toxicity of diiodomethyl-p-tolylsulfone (DIMPTS) in rats: ADME

Metabolism of diiodomethyl-p-tolylsulfone (DIMPTS) was investigated in rats to determine the role of iodide in its toxicity. Fischer 344 (F-344) (5 or 50mg/kg) or Sprague Dawley (SD) (5mg/kg) rats were gavaged with (14)C-DIMPTS or dermally applied with 5mg/kg (F-344 only) and absorption, distribution, metabolism and excretion (ADME) determined. Additional experiments were conducted with its deiodinated analog (methyl-p-tolylsulfone, MPTS) in female F-344 rats (20mg/kg) for comparison. Orally administered (14)C-DIMPTS was rapidly absorbed and eliminated in urine (92%). The elimination t(½) was 1-4h. Dermally applied (14)C-DIMPTS remained undetectable in plasma with bioavailability ≈ 7%, only 5-7% of the dose was recovered in urine. DIMPTS liberated one or both of its iodine atoms upon absorption. The rate of elimination of the liberated iodide from the systemic circulation was 2- to 3-fold slower in SD than F-344 rats, which resulted in higher bioavailability of iodide to SD rats. DIMPTS was primarily oxidized at the benzylic methyl moiety forming the corresponding benzoic acid. Glutathione conjugation on the sulfonyl methyl group, via displacement of I(-) was also observed. Overall 67-80% of the total iodine atoms were metabolically released from DIMPTS. The MPTS was rapidly absorbed from the GI tract, metabolized and eliminated in urine similar to that of DIMPTS. These data were compared to iodide toxicokinetic results of a reproductive toxicity study for DIMPTS (80 mg/kg/day) and MPTS (32 mg/kg/day), where DIMPTS was toxic to dams and pups, while MPTS caused no toxicity. These data show that the liberated iodide is the ultimate toxicant of DIMPTS, which is readily transported to pups through milk, while the methyltolylsulfone backbone structure (MPTS) of DIMPTS is relatively nontoxic.

Oral absorption, metabolism and excretion of 1-phenoxy-2-propanol in rats

1. This study was designed to determine the absorption, metabolism and excretion of 1-phenoxy-2-propanol in Fischer 344 rats following oral administration in an effort to bridge data with other propylene glycol ethers. 2. Rats were administered a single oral dose of 10 or 100 mg kg−1 14C-1-phenoxy-2-propanol as a suspension in 0.5% methyl cellulose ether in water (w/w). Urine was collected at 0–12, 12–24 and 24–48 h and faeces at 0–24 and 24–48 h post-dosing and the radioactivity was determined. Urine samples were pooled by time point and dose level and analysed for metabolites using LC/ESI/MS and LC/ESI/MS/MS. 3. The administered doses were rapidly absorbed from the gastrointestinal tract and excreted. The major route of excretion was via the urine, accounting for 93 ± 5% of the low and 96 ± 3% of the high dose. Most of the urinary excretion of radioactivity occurred within 12 h after dosing; 85 ± 2% of the low and 90 ± 1% of the high dose. Total faecal excretion remained < 10%. Rats eliminated the entire administered dose within 48 h after dosing; recovery of the administered dose ranged from 100 to 106%. Metabolites tentatively identified in urine were conjugates of phenol (sulphate, glutathione) with very low levels (< 2%) of hydroquinone (glucuronide), conjugates of parent compound (glucuronide, sulphate) and a ring-hydroxylated metabolite of parent. There was no free parent compound or phenol in non-acid-hydrolysed urine. In acid-hydrolysed urine, 61% of the dose was identified as phenol and 13% as 1-phenoxy-2-propanol. Although the parent compound was stable to acid hydrolysis, some of the phenol in acid hydrolysed urine may have arisen from degradation of acid-labile metabolite(s) as well as hydrolysis of phenol conjugates. 4. Rapid oral absorption, metabolism and urinary excretion of 1-phenoxy-2-propanol in rats were similar to other propylene glycol ethers.

Pharmacokinetics and metabolism of 14C-1,3-dichloropropene in the Fischer 344 rat and the B6C3F1 mouse

1. 14C-1,3-dichloropropene (14C-DCP) is rapidly absorbed and eliminated in both the male F344 rat and B6C3F1 mouse following oral administration of 1 or 50 mg kg−1 (rat) or 1 or 100 mg kg−1 (mouse). 2. It is extensively metabolized in both species. Urinary excretion was the major route of elimination, accounting for 50.9–61.3 and 62.5–78.6% of the administered dose in rat and mouse, respectively. 3. Urinary elimination half-lives ranged from 5 to 6 h (rat) and from 7 to 10 h (mouse). Elimination via faeces or as 14CO2 accounted for 14.5–20.5 and 13.7–17.6% of the administered dose, respectively. 4. Metabolites arising from glutathione conjugation account for 36–55 and 48–50% of the administered dose in excreted from rats and mice, respectively. Hydrolysis of the 3-chloro moiety of DCP accounted for 24–37 and 29% of the dose administered to rats and mice, respectively. Two novel dimercapturic acid conjugates were also identified at low levels that might arise via initial hydrolysis of DCP or of epoxidation of DCP-glutathione conjugate or of DCP itself. Structural confirmation of these dimercapturates was obtained via analysis of deuterium retention from D4-DCP in the male F344 rat. 5. Only quantitative differences are seen between the overall metabolic profile of DCP in these two species.

Direct quantitation of hydroxyethylvaline in hemoglobin by liquid chromatography/positive electrospray tandem mass spectrometry

Hemoglobin adducts are often used as biomarkers of exposure to reactive chemicals in toxicology studies. Therefore rapid, sensitive, accurate, and reproducible methods for quantifying these globin adducts are key to evaluate test material dosimetry. A new, simple, fast, and sensitive LC/ESI-MS/MS methodology has been developed and validated for the quantitation of hydroxyethylvaline (HEVal) in globin samples isolated from rats, both control and exposed to ethylene. Globin samples were first hydrolyzed to amino acids (including HEVal), followed by direct LC/ESI-MS/MS analysis. The lower limit of quantitation was 0.0095 ng/mL (0.026 pmol/mg globin). Typical calibration curves obtained over three days were linear over a concentration range from 0.0095 to 9.524 ng/mL, with correlation coefficient R(2)>0.999. The intra-day assay precision RSD values for all QC samples were ≤11.2%, with accuracy values ranging from 90.6 to 105%. The inter-day assay precision RSD values for all QC samples were ≤8.73%, with accuracy values ranging from 89.3 to 104.5%. The stability of HEVal in three freeze-thaw cycles over 48 h and at room temperature over 24 h was also evaluated, and the measured concentrations of HEVal were compared to the nominal values, with accuracy ranging from 94.8% to 109%. In conclusion, this method provides results comparable to those obtained using the traditional and complex Edman degradation phenylthiohydantoin-related quantitation method, but is much simpler and faster to conduct.