Prediction of tissue and urine concentrations of 2-phenoxyethanol and its metabolite 2-phenoxyacetic acid in rat and human after oral and dermal exposures via GastroPlusTM physiologically based pharmacokinetic modelling

A physiologically based pharmacokinetic (PBPK) model for the important chemical phenoxyethanol (PhE) and its metabolite phenoxyacetic acid (PhAA) was built via GastroPlus^TM software (version 9.0) using currently available analytically measured plasma and urinary time-courses of both PhE and its metabolite PhAA. This model was validated and used to predict tissue and urine concentrations of PhE and its metabolite PhAA in rats and humans after oral and dermal exposures. The prediction results showed that most predicted tissue concentrations of PhE or PhAA were lower than the experimental tissue concentrations based on total radioactivity. The predicted cumulative excretion of PhAA in both rats and humans fits very well with most experimental data. With this GastroPlus^TM-based model, the margins of exposure (MOE) of PhE and PhAA were also calculated as 194 and 73.7, respectively. The predicted MOE of PhE is two-fold higher than the previous PBPK model built using total radioactivity-based tissue time courses, and the predicted MOE of PhAA was comparable to the previous PBPK model. These data indicate that for chemicals like PhE, GastroPlus^TM can integrate multiple data sets into PBPK models to predict PK parameters for parent and metabolites in both rats and humans following intravenous, dermal, or oral exposures.

Beta-amyloid burden predicts poorer mnemonic discrimination in cognitively normal older adults

One of the earliest indicators of Alzheimer's disease pathology is the presence of beta-amyloid (Αβ) protein deposition. Significant amyloid deposition is evident even in older adults who exhibit little or no overt cognitive or memory impairment. Hippocampal-based processes that help distinguish between highly similar memory representations may be the most susceptible to early disease pathology. Amyloid associations with memory have been difficult to establish, possibly because typical memory assessments do not tax hippocampal operations sufficiently. Thus, the present study utilized a spatial mnemonic discrimination task designed to tax hippocampal pattern separation/completion processes in a sample of cognitively normal middle-aged and older adults (53-98 years old) who underwent PET ¹⁸F-Florbetapir Αβ scanning. The degree of interference between studied and new information varied, allowing for an examination of mnemonic discrimination as a function of mnemonic similarity. Results indicated that greater beta-amyloid burden was associated with poorer discrimination across decreasing levels of interference, suggesting that even subtle elevation of beta-amyloid in cognitively normal adults is associated with impoverished performance on a hippocampally demanding memory task. The present study demonstrates that degree of amyloid burden negatively impacts the ability of aging adults to accurately distinguish old from increasingly distinct new information, providing novel insight into the cognitive expression of beta-amyloid neuropathology.

Longitudinal validity of PET-based staging of regional amyloid deposition

Positron emission tomography (PET)-based staging of regional amyloid deposition has recently emerged as a promising tool for sensitive detection and stratification of pathology progression in Alzheimer's Disease (AD). Here we present an updated methodological framework for PET-based amyloid staging using region-specific amyloid-positivity thresholds and assess its longitudinal validity using serial PET acquisitions. We defined region-specific thresholds of amyloid-positivity based on Florbetapir-PET data of 13 young healthy individuals (age ≤ 45y), applied these thresholds to Florbetapir-PET data of 179 cognitively normal older individuals to estimate a regional amyloid staging model, and tested this model in a larger sample of patients with mild cognitive impairment (N = 403) and AD dementia (N = 85). 2-year follow-up Florbetapir-PET scans from a subset of this sample (N = 436) were used to assess the longitudinal validity of the cross-sectional model based on individual stage transitions and data-driven longitudinal trajectory modeling. Results show a remarkable congruence between cross-sectionally estimated and longitudinally modeled trajectories of amyloid accumulation, beginning in anterior temporal areas, followed by frontal and medial parietal areas, the remaining associative neocortex, and finally primary sensory-motor areas and subcortical regions. Over 98% of individual amyloid deposition profiles and longitudinal stage transitions adhered to this staging scheme of regional pathology progression, which was further supported by corresponding changes in cerebrospinal fluid biomarkers. In conclusion, we provide a methodological refinement and longitudinal validation of PET-based staging of regional amyloid accumulation, which may help improving early detection and in-vivo stratification of pathologic disease progression in AD.

Associations of the Top 20 Alzheimer Disease Risk Variants With Brain Amyloidosis

Importance

Late-onset Alzheimer disease (AD) is highly heritable. Genome-wide association studies have identified more than 20 AD risk genes. The precise mechanism through which many of these genes are associated with AD remains unknown.

Objective

To investigate the association of the top 20 AD risk variants with brain amyloidosis.

Design, Setting, and Participants

This study analyzed the genetic and florbetapir F 18 data from 322 cognitively normal control individuals, 496 individuals with mild cognitive impairment, and 159 individuals with AD dementia who had genome-wide association studies and 18F-florbetapir positron emission tomographic data from the Alzheimer's Disease Neuroimaging Initiative (ADNI), a prospective, observational, multisite tertiary center clinical and biomarker study. This ongoing study began in 2005.

Main Outcomes and Measures

The study tested the association of AD risk allele carrier status (exposure) with florbetapir mean standard uptake value ratio (outcome) using stepwise multivariable linear regression while controlling for age, sex, and apolipoprotein E ε4 genotype. The study also reports on an exploratory 3-dimensional stepwise regression model using an unbiased voxelwise approach in Statistical Parametric Mapping 8 with cluster and significance thresholds at 50 voxels and uncorrected P < .01.

Results

This study included 977 participants (mean [SD] age, 74 [7.5] years; 535 [54.8%] male and 442 [45.2%] female) from the ADNI-1, ADNI-2, and ADNI-Grand Opportunity. The adenosine triphosphate-binding cassette subfamily A member 7 (ABCA7) gene had the strongest association with amyloid deposition (χ2 = 8.38, false discovery rate-corrected P < .001), after apolioprotein E ε4. Significant associations were found between ABCA7 in the asymptomatic and early symptomatic disease stages, suggesting an association with rapid amyloid accumulation. The fermitin family homolog 2 (FERMT2) gene had a stage-dependent association with brain amyloidosis (FERMT2 × diagnosis χ2 = 3.53, false discovery rate-corrected P = .05), which was most pronounced in the mild cognitive impairment stage.

Conclusions and Relevance

This study found an association of several AD risk variants with brain amyloidosis. The data also suggest that AD genes might differentially regulate AD pathologic findings across the disease stages.

Association Between Midlife Vascular Risk Factors and Estimated Brain Amyloid Deposition

IMPORTANCE

Midlife vascular risk factors have been associated with late-life dementia. Whether these risk factors directly contribute to brain amyloid deposition is less well understood.

OBJECTIVE

To determine if midlife vascular risk factors are associated with late-life brain amyloid deposition, measured using florbetapir positron emission tomography (PET).

DESIGN, SETTING, AND PARTICIPANTS

The Atherosclerosis Risk in Communities (ARIC)-PET Amyloid Imaging Study, a prospective cohort study among 346 participants without dementia in 3 US communities (Washington County, Maryland; Forsyth County, North Carolina; and Jackson, Mississippi) who have been evaluated for vascular risk factors and markers since 1987-1989 with florbetapir PET scans in 2011-2013. Positron emission tomography image analysis was completed in 2015.

EXPOSURES

Vascular risk factors at ARIC baseline (age 45-64 years; risk factors included body mass index ≥30, current smoking, hypertension, diabetes, and total cholesterol ≥200 mg/dL) were evaluated in multivariable models including age, sex, race, APOE genotype, and educational level.

MAIN OUTCOMES AND MEASURES

Standardized uptake value ratios (SUVRs) were calculated from PET scans and a mean global cortical SUVR was calculated. Elevated florbetapir (defined as a SUVR >1.2) was the dependent variable.

RESULTS

Among 322 participants without dementia and with nonmissing midlife vascular risk factors at baseline (mean age, 52 years; 58% female; 43% black), the SUVR (elevated in 164 [50.9%] participants) was measured more than 20 years later (median follow-up, 23.5 years; interquartile range, 23.0-24.3 years) when participants were between 67 and 88 (mean, 76) years old. Elevated body mass index in midlife was associated with elevated SUVR (odds ratio [OR], 2.06; 95% CI, 1.16-3.65). At baseline, 65 participants had no vascular risk factors, 123 had 1, and 134 had 2 or more; a higher number of midlife risk factors was associated with elevated amyloid SUVR at follow-up (30.8% [n = 20], 50.4% [n = 62], and 61.2% [n = 82], respectively). In adjusted models, compared with 0 midlife vascular risk factors, the OR for elevated SUVR associated with 1 vascular risk factor was 1.88 (95% CI, 0.95-3.72) and for 2 or more vascular risk factors was 2.88 (95% CI, 1.46-5.69). No significant race × risk factor interactions were found. Late-life vascular risk factors were not associated with late-life brain amyloid deposition (for ≥2 late-life vascular risk factors vs 0: OR, 1.66; 95% CI, 0.75-3.69).

CONCLUSIONS AND RELEVANCE

An increasing number of midlife vascular risk factors was significantly associated with elevated amyloid SUVR; this association was not significant for late-life risk factors. These findings are consistent with a role of vascular disease in the development of Alzheimer disease.

PET Imaging of Tau Deposition in the Aging Human Brain

Tau pathology is a hallmark of Alzheimer's disease (AD) but also occurs in normal cognitive aging. Using the tau PET agent (18)F-AV-1451, we examined retention patterns in cognitively normal older people in relation to young controls and AD patients. Age and β-amyloid (measured using PiB PET) were differentially associated with tau tracer retention in healthy aging. Older age was related to increased tracer retention in regions of the medial temporal lobe, which predicted worse episodic memory performance. PET detection of tau in other isocortical regions required the presence of cortical β-amyloid and was associated with decline in global cognition. Furthermore, patterns of tracer retention corresponded well with Braak staging of neurofibrillary tau pathology. The present study defined patterns of tau tracer retention in normal aging in relation to age, cognition, and β-amyloid deposition.

Bactericidal Dendritic Polycation Cloaked with Stealth Material via Lipase-Sensitive Intersegment Acquires Neutral Surface Charge without Losing Membrane-Disruptive Activity

Net cationicity of membrane-disruptive antimicrobials is necessary for their activity but may elicit immune attack when administered intravenously. By cloaking a dendritic polycation (G2) with poly(caprolactone-b-ethylene glycol) (PCL-b-PEG), we obtain a nanoparticle antimicrobial, G2-g-(PCL-b-PEG), which exhibits neutral surface charge but kills >99.9% of inoculated bacterial cells at ≤8 μg/mL. The observed activity may be attributed PCL's responsive degradation by bacterial lipase and the consequent exposure of the membrane-disruptive, bactericidal G2 core. Moreover, G2-g-(PCL-b-PEG) exhibits good colloidal stability in the presence of serum and insignificant hemolytic toxicity even at ≥2048 μg/mL. suggesting good blood compatibility required for intravenous administration.

Study the pharmacokinetics of AV-45 in rat plasma and metabolism in liver microsomes by ultra-performance liquid chromatography with mass spectrometry

An ultra-performance liquid chromatography-tandem mass spectrometric (UPLC-MS/MS) method was developed and validated to determine AV-45 in rat plasma. After the addition of the internal standard benzophenone, plasma samples were pretreated by protein precipitation. Chromatographic separation was achieved on an Acquity UPLC BEH C₁₈ column (50 × 2.1 mm, 1.7 µm) by gradient elution at a flow rate of 0.4 mL/min. Detection of analytes and internal standard (IS) was done by tandem mass spectrometry, operating in positive-ion and multiple reaction monitoring mode. The method was fully validated for its sensitivity, selectivity, accuracy and precision, matrix effect and stability study. The calibration curve showed good linearity over the concentration range 2.00-1000 ng/mL for AV-45. Intra- and inter-day precisions were less than 7.6%, and accuracy ranged from 100.6 to 107.8%. There was no matrix effect. The validated method was successfully applied to a pharmacokinetic study of AV-45 in rats. Additionally, the metabolism of AV-45 in rat liver microsomes was also studied by ultra-performance liquid chromatography combined with time-of-flight mass spectrometry (UPLC/TOF-MS). With the help of chromatographic behavior and accurate mass measurements, the metabolites were characterized.

Uptake and elimination, and effect of estrogen-like contaminants in estuarine copepods: an experimental study

BACKGROUND, AIM, AND SCOPE

In recent years, anthropogenic chemicals which can disrupt the hormonal systems of both humans and wildlife have been raised to a major cause of concern. The aim of the present work was to determine the bioconcentration factors of the two major alkylphenols (AP) of the Seine Estuary [4-nonylphenol (4 NP) and nonylphenol acetic acid (NP1EC)] and of the synthetic estrogen, estrogen ethinylestradiol (EE2), in Eurytemora affinis after exposure in a continuous flow-through system under environmental realistic conditions. Moreover, the elimination of these compounds in copepods from the Seine Estuary has been investigated by measuring concentrations after 1 week in clean water in comparison to background levels.

MATERIALS AND METHODS

In this study, the dominant copepod species of the Seine Estuary, E. affinis, was exposed at environmental relevant concentrations under laboratory-controlled conditions to selected waterborn contaminants, a mixture of 4 NP/NP1EC, and a synthetic EE2. The uptake and the elimination of these contaminants by E. affinis have been studied.

RESULTS

The results show that, at the end of the uptake period, both 4 NP and NP1EC, and also EE2 were accumulated in exposed copepods with respective concentration factors of 324, 3,020, and 5,383. A rapid elimination of these compounds was also observed in copepods placed in clean water since 54% of total NP1EC and 100% of EE2 amounts have been lost after 3 days. Pregnenolone was synthesized after exposure to EE2 and AP mixture.

DISCUSSION

These results demonstrate that E. affinis has the potency to accumulate but also to eliminate endocrine disrupters which suggests a non-negligible role of this copepod species in the biogeochemical cycles of these contaminants in estuarine ecosystems. Hence, these results also suggest that a transfer of 4 NP, NP1EC, and EE2 to copepod predators and subsequently that secondary poisoning of these organisms might be possible. Estrogen-like contaminants can induce pregnenolone synthesis and affect the reproduction of E. affinis.

CONCLUSIONS

These results suggest the important role of this copepod species in biogeochemical cycles of non-ionic surfactants as well as synthetic steroids in estuarine ecosystems.

RECOMMENDATIONS AND PERSPECTIVES

E. affinis could be a non-negligible route of exposure for juvenile fish and underline the potential for deleterious effects on copepod predators.

Florbetapir (18F), a PET imaging agent that binds to amyloid plaques for the potential detection of Alzheimer's disease

Florbetapir (18F), being developed by Avid Radiopharmaceuticals, is an 18F-labeled PET tracer binding to amyloid-β (Aβ) plaques for the potential detection of Alzheimer's disease (AD). Preclinical studies indicated high binding affinity of florbetapir (18F) to Aβ fibrils and specific labeling of Aβ plaques in the cortical regions and hippocampus. In phase I and II clinical trials, florbetapir (18F) clearly differentiated patients with AD from healthy controls and uptake was most prominent in the precuneus. The neocortical-to-cerebellar tracer uptake ratio reached a plateau within 50 min post-injection and high-quality images were acquired with 5 to 10 min image acquisition time with 370 MBq of florbetapir (18F). Results from an ongoing phase III clinical trial confirmed a strong correlation between florbetapir (18F) PET images and postmortem assessment of Aβ deposition. No serious adverse events were reported in any of the clinical trials of florbetapir (18F). At the time of publication, a marketing application for florbetapir (18F) had been submitted to the US FDA. The fast kinetics and strong evidences of radiological-pathological correlation are advantages of florbetapir (18F) over other 18F-labeled amyloid PET tracers. This tracer has a potential to serve as an agent for preclinical detection of AD-related pathology in the large elderly population.

In vivometabolism and kinetics of ethylene glycol monobutyl ether and its metabolites, 2-butoxyacetaldehyde and 2-butoxyacetic acid, as measured in blood, liver and forestomach of mice

1. Ethylene glycol monobutyl ether (EGBE) causes forestomach hyperplasia and neoplasia in mice when administered chronically by inhalation. 2. The study was initiated to test the physiologically based pharmacokinetic (PBPK) model prediction that 2-butoxyacetaldehyde (BAL), a transient, labile intermediate in the oxidation of EGBE to butoxyacetic acid (BAA), is unlikely to achieve concentrations sufficient to cause DNA damage in target tissues. 3. Male and female B6C3F1 mice were administered a high oral dose of EGBE (600mgkg(-1)), and tissues were collected at 5, 15, 45 and 90min following the dose. The tissues were processed for determination of EGBE, BAL and BAA by gas chromatography-mass spectrometry. 4. BAL was detected at low concentrations in all tissues sampled and at all time points following EGBE administration (about 0.3-33 microM). BAL concentrations were highest in the initial samples (5 min) in all tissues and declined from that point. 5. BAL concentrations in liver and forestomach tissues corresponded to the peak concentrations predicted by an already published PBPK model, and are higher than BAL concentrations that could be achieved by inhalation exposure to EGBE. 6. Mouse inhalation exposure to EGBE is therefore unlikely to generate BAL concentrations in tissues sufficient to initiate a carcinogenic response.

Priming dose of phenylhydrazine protects against hemolytic and lethal effects of 2-butoxyethanol

Protection against a high dose of a toxicant by prior exposure to another toxicant is called heteroprotection. Our objective was to establish a heteroprotection model in RBCs. Female Sprague Dawley rats treated with an LD90 dose of 2-butoxyethanol (BE, 1500 mg/kg in water, 5 ml/kg po) 14 days after priming with 0.9% NaCl suffered 90% mortality by 15 days, whereas all rats receiving the LD90 dose of BE 14 days after priming with phenylhydrazine (PHZ, 125 mg/kg in 0.9% NaCl, 3 ml/kg po) survived. Hematocrit decreased from normal 45% to 24% by day 3 after PHZ priming and improved thereafter. Increasing the time interval between the priming and LD90 dose to 21 days abolished the heteroprotection. RBCs obtained on days 7 and 14 after PHZ priming unlike those on day 21 were resilient to the hemotoxic metabolite of BE, butoxyacetic acid (BAA). Unaltered hepatic alcohol and aldehyde dehydrogenase activities upon PHZ priming suggested that bioactivation of BE to BAA was unaffected. Lower renal (6 and 12 h) and hepatic (12 h) BAA levels and 3 fold higher excretion of BAA in PHZ-primed rat urine suggested a protective role of toxicokinetics. Higher erythropoietin, reticulocytes, and resiliency of PHZ-primed rat RBCs indicated that newly formed RBCs are resilient to hemolytic BAA. The antioxidant levels in the PHZ-primed rat RBCs did not indicate a protective role in heteroprotection. In conclusion, the resistance of PHZ-primed rats against BE-induced hemotoxicity and lethality is mediated by a combination of altered toxicokinetics, robust erythropoiesis, and resiliency of new RBCs.

Discrepancies between different rat models for the assessment of percutaneous penetration of hazardous substances

By regulatory authorities the rat is considered to be a suitable animal model to predict the percutaneous absorption of hazardous substances in humans. In our study, the percutaneous penetration of 2-butoxyethanol (BE) and toluene was compared in different rat models. Intradermal microdialysis and static diffusion cells were used in in vivo and in vitro experiments with haired Wistar and hairless Lewis rats. Microdialysis experiments showed a steady-state penetration for BE and a penetration maximum for toluene in both rat strains at approximately 60 min after beginning of exposure. However, in diffusion cell experiments the penetration of the test compounds in both rat strains increased until the end of exposure (4 h). Additionally, in microdialysis experiments BE penetrated in hairless rats in a higher amount than in haired rats (factor: 1.4; P < 0.01), for toluene it was just the opposite (factor: 1.9; P < 0.001). In diffusion cell experiments, the penetrated amounts of both compounds were higher in hairless rats compared to haired rats. The fluxes for BE were in diffusion cell experiments at a factor of 14.5 (haired rat) and 18.1 (hairless rat) higher than in microdialysis experiments, the difference factor for toluene was 2.6 (haired rat) and 12.9 (hairless rat). The lag times indicate a significantly faster penetration in microdialysis experiments compared with diffusion cell experiments (P < 0.001). There are great differences in percutaneous penetration behaviour between the techniques and the rat strains. The diffusion cell method has difficulties to describe the percutaneous penetration kinetics, whereas microdialysis describes it more reliable. Due to these differences the reliability of a conversion factor for the transfer of percutaneous absorption data from rat to human skin, as proposed in the literature, is questionable.

The influence of water mixtures on the dermal absorption of glycol ethers

Glycol ethers are solvents widely used alone and as mixtures in industrial and household products. Some glycol ethers have been shown to have a range of toxic effects in humans following absorption and metabolism to their aldehyde and acid metabolites. This study assessed the influence of water mixtures on the dermal absorption of butoxyethanol and ethoxyethanol in vitro through human skin. Butoxyethanol penetrated human skin up to sixfold more rapidly from aqueous solution (50%, 450 mg/ml) than from the neat solvent. Similarly penetration of ethoxyethanol was increased threefold in the presence of water (50%, 697 mg/ml). There was a corresponding increase in apparent permeability coefficient as the glycol ether concentration in water decreased. The maximum penetration rate of water also increased in the presence of both glycol ethers. Absorption through a synthetic membrane obeyed Fick's Law and absorption through rat skin showed a similar profile to human skin but with a lesser effect. The mechanisms for this phenomenon involves disruption of the stratum corneum lipid bilayer by desiccation by neat glycol ether micelles, hydration with water mixtures and the physicochemical properties of the glycol ether-water mixtures. Full elucidation of the profile of absorption of glycol ethers from mixtures is required for risk assessment of dermal exposure. This work supports the view that risk assessments for dermal contact scenarios should ideally be based on absorption data obtained for the relevant formulation or mixture and exposure scenario and that absorption derived from permeability coefficients may be inappropriate for water-miscible solvents.

Multifunctional polymeric nanoparticles from diverse bioactive agents

We present a rational approach for assembling diverse bioactive agents, such as DNA, proteins, and drug molecules, into core-shell multifunctional polymeric nanoparticles (PNPs) that can be internalized in human breast cancer cells. Using ring-opening metathesis polymerization (ROMP), block copolymers containing small-molecule drug segments (>50% w/w) and tosylated hexaethylene glycol segments were prepared and assembled into PNPs that allowed for the surface conjugation of single-stranded DNA sequences and/or tumor-targeting antibodies. The resulting antibody-functionalized particles were readily uptaken by breast cancer cells that overexpressed the corresponding antigens.

Physiologically based pharmacokinetic modelling of human exposure to 2-butoxyethanol

A physiologically based pharmacokinetic (PBPK) model describing the disposition of 2-butoxyethanol (2-BE) was developed in order to predict the urinary concentration of its major metabolite, butoxyacetic acid (BAA) under a range of exposure scenarios. Based on Corley et al. [Corley, R.A., Bormett, G.A., Ghanayem, B.I., 1994. Physiologically based pharmacokinetics of 2-butoxyethanol and its major metabolite, 2-butoxyacetic acid, in rats and humans. Toxicol. Appl. Pharmacol. 129, 61-79], the model included such features as multiple entry routes into the body, varying workload conditions, metabolism in the liver and elimination of free BAA in urine by glomerular filtration and acid transport. A bladder compartment simulating the fluctuations in metabolite concentration in urine caused by micturition formed a novel aspect of the model. Good agreement between model predictions and existing experimental data of total BAA levels in the blood and urine over various exposure conditions were observed. The mechanistically based PBPK model allowed comparison of disparate studies and also enabled the prediction of urinary concentrations of BAA post-shift. By calculating the total amount of BAA, any inter-individual variability in conjugation is taken into account. This led us to conclude that a biological monitoring guidance value should be proposed for total rather than free BAA with a value of 250 mmol/mol of creatinine (post-shift), based on an 8h exposure to 25 ppm 2-BE at resting working conditions.

The mechanism of ethylene glycol ether reproductive and developmental toxicity and evidence for adverse effects in humans

Numerous experimental studies have established that only a few among the large family of ethylene glycol ethers (EGEs) elicit toxicity on reproduction in either gender. Notable are the monomethyl (EGME) and monoethyl (EGEE) ethers and their respective acetate esters whose production volumes have dramatically declined. Oxidation to the respective monoalkoxy acids is a prerequisite for toxicity. The most potent EGE reproductive toxicant is EGME (via 2-methoxyacetic acid; MAA), which elicits developmental phase-specific insults on either conceptus or on testes. Toxicity at either target site is markedly attenuated by simple physiological compounds such as acetate, formate, glycine, D-glucose and serine. Lack of solid EGME occupational exposure data and the need to improve the scientific foundations for animal data extrapolations, prompted the development of physiologically based pharmacokinetic (PBPK) models for pregnancy application. Interspecies (mouse-rat) and different exposure routes (including inhalation) were experimentally validated. Such PBPK models were then extrapolated to potential occupational exposures, using rather limited human MAA pharmacokinetic data. PBPK model predictions of human blood levels upon simulated inhalation exposure to the 5 ppm threshold limit value (TLV) for 8 h were approximately 60 microM were well below those causing adverse effects in pregnant mice or rats. This conclusion concurs with the lack of objective analytical chemistry data for EGME/MAA in occupational settings, regardless of the potential route of exposure. There are no exposure data that can be linked in a cause-and-effect association to adverse human reproductive outcomes.

Determination of age and gender differences in biochemical processes affecting the disposition of 2-butoxyethanol and its metabolites in mice and rats to improve PBPK modeling

2-Butoxyethanol (BE) is the most widely used glycol ether solvent. BEs major metabolite, butoxyacetic acid (BAA), causes hemolysis with significant species differences in sensitivity. Several PBPK models have been developed over the past two decades to describe the disposition of BE and BAA in male rats and humans to refine health risk assessments. More recent efforts by Lee et al. [Lee, K.M., Dill, J.A., Chou, B.J., Roycroft, J.H., 1998. Physiologically based pharmacokinetic model for chronic inhalation of 2-butoxyethanol. Toxicol. Appl. Pharmacol. 153, 211-226] to describe the kinetics of BE and BAA in the National Toxicology Program (NTP) chronic inhalation studies required the use of several assumptions to extrapolate model parameters from earlier PBPK models developed for young male rats to include female F344 and both sexes of B6C3F1 mice and the effects of aging. To replace these assumptions, studies were conducted to determine the impact of age, gender and species on the metabolism of BE, and the tissue partitioning, renal acid transport and plasma protein binding of BAA. In the current study, the Lee et al. PBPK model was updated and expanded to include the further metabolism of BAA and the salivary excretion of BE and BAA which may contribute to the forestomach irritation observed in mice in the NTP study. The revised model predicted that peak blood concentrations of BAA achieved following 6 h inhalation exposures are greatest in young adult female rats at concentrations up to 300 ppm. This is not the case predicted for old (> or =18 months) animals, where peak blood concentrations of BAA in male and female mice were similar to or greater than female rats. The revised model serves as a quantitative tool for integrating an extensive pharmacokinetic and mechanistic database into a format that can readily be used to compare internal dosimetry across dose, route of exposure and species.

Is the permeability coefficient Kp a reliable tool in percutaneous absorption studies?

In percutaneous absorption studies the potency of penetration of chemical substances is often described by the permeability coefficient Kp. The experimentally determined Kp is characterized according to Fick's first law of diffusion by the ratio of flux and the concentration of the test compound (Kp=Flux/C). This equation implies that in percutaneous absorption studies Kp is theoretically a more reliable parameter than flux taking the concentration into consideration, and should remain constant for each compound independent from the grade of dilution. In our study we evaluated the course of the percutaneous absorption parameters flux and Kp of neat and of 50% aqueous solution of 2-butoxyethanol (BE). An infinite dose of neat and 50% aqueous solution of non-radiolabeled BE were applied on excised human skin from two donors in static diffusion cells in parallel (for each test setting n=21). The flux of 50% aqueous BE (0.704+/-0.152 mg/cm2/h) was about 15-fold higher than that of neat BE (0.045+/-0.014 mg/cm2/h). The comparison of the Kp values of both test settings showed with a factor of about 31 (Kp=1.563 x 10(-3) cm/h) much higher values for 50% aqueous BE and Kp=0.050 x 10(-3) cm/h for neat BE. Although the flux does not consider the chemical concentration, it showed a smaller difference in both test settings as Kp; however, the flux remains a non-specific parameter for the description of percutaneous absorption. The results of our experiments showed that the permeability coefficient Kp was not able to adjust the flux of BE to the concentration. This is in agreement with the evaluation of Kp from BE data described in the literature.

Cutaneous metabolism of glycol ethers

The toxicity of glycol ethers is associated with their oxidation to the corresponding aldehyde and alkoxyacetic acid by cytosolic alcohol dehydrogenase (ADH; EC 1.1.1.1.) and aldehyde dehydrogenase (ALDH; 1.2.1.3). Dermal exposure to these compounds can result in localised or systemic toxicity including skin sensitisation and irritancy, reproductive, developmental and haemotological effects. It has previously been shown that skin has the capacity for local metabolism of applied chemicals. Therefore, there is a requirement to consider metabolism during dermal absorption of these compounds in risk assessment for humans. Cytosolic fractions were prepared from rat liver, and whole and dermatomed skin by differential centrifugation. Rat skin cytosolic fractions were also prepared following multiple dermal exposure to dexamethasone, ethanol or 2-butoxyethanol (2-BE). The rate of ethanol, 2-ethoxyethanol (2-EE), ethylene glycol, 2-phenoxyethanol (2-PE) and 2-BE conversion to alkoxyacetic acid by ADH/ALDH in these fractions was continuously monitored by UV spectrophotometry via the conversion of NAD+ to NADH at 340 nm. Rates of ADH oxidation by rat liver cytosol were greatest for ethanol followed by 2-EE >ethylene glycol >2-PE >2-BE. However, the order of metabolism changed to 2-BE >2-PE >ethylene glycol >2-EE >ethanol using whole and dermatomed rat skin cytosolic fractions, with approximately twice the specific activity in dermatomed skin cytosol relative to whole rat skin. This suggests that ADH and ALDH are localised in the epidermis that constitutes more of the protein in dermatomed skin than whole skin cytosol. Inhibition of ADH oxidation in rat liver cytosol by pyrazole was greatest for ethanol followed by 2-EE >ethylene glycol >2-PE >2-BE, but it only inhibited ethanol metabolism by 40% in skin cytosol. Disulfiram completely inhibited alcohol and glycol ether metabolism in the liver and skin cytosolic fractions. Although ADH1, ADH2 and ADH3 are expressed at the protein level in rat liver, only ADH1 and ADH2 are selectively inhibited by pyrazole and they constitute the predominant isoforms that metabolise short-chain alcohols in preference to intermediate chain-length alcohols. However, ADH1, ADH3 and ADH4 predominate in rat skin, demonstrate different sensitivities to pyrazole, and are responsible for metabolising glycol ethers. ALDH1 is the predominant isoform in rat liver and skin cytosolic fractions that is selectively inhibited by disulfiram and responds to the amount of aldehyde formed by the ADH isoforms expressed in these tissues. Thus, the different affinity of ADH and ALDH for alcohols and glycol ethers of different carbon-chain length may reflect the relative isoform expression in rat liver and skin. Following multiple topical exposure, ethanol metabolism increased the most following ethanol treatment, and 2-BE metabolism increased the most following 2-BE treatment. Ethanol and 2-BE may induce specific ADH and ALDH isoforms that preferentially metabolise short-chain alcohols (i.e. ADH1, ALDH1) and longer chain alcohols (i.e. ADH3, ADH4, ALDH1), respectively. Treatment with a general inducing agent such as dexamethasone enhanced ethanol and 2-BE metabolism suggesting induction of multiple ADH isoforms.

Percutaneous absorption of 5 glycol ethers through human skin in vitro

Absorption across full thickness human skin was evaluated in vitro for five selected glycol ethers. Skin membranes were settled on static diffusion cells and both neat and 50% water diluted glycol ethers were applied on the donor chamber for 8 h. The amount of glycol ethers permeated into the receptor fluid was measured by gas chromatograph equipped with flame ionization detector (GC-FID). For neat solvents, permeation coefficient Kp ranged from 0.06 to 0.83 cm h(-1) 10(-3) respectively for DEGBEA and EGMEA while for 50% v/v diluted glycol ethers it varied from 0.08 to 1.81 cm h(-1) 10(-3) respectively for DPGME and EGMEA. These experiments show a statistically significant (Student's t-test, P <0.05) increase in permeation coefficients from neat to 50% water diluted glycol ethers and the same trend can be observed in fluxes and lag times. Only DPGME show an opposite behaviour. These results confirm the good ability of these solvents of permeating the skin and show that they could represent a risk for their potential dermal absorption both for workers and for occasional exposures, since the average lag time is 1.57 h.

Percutaneous penetration and metabolism of 2-butoxyethanol

2-Butoxyethanol (2-BE) is widely used as an industrial solvent, which may result in human dermal exposure within the workplace. This study compares in vivo and in vitro skin absorption of 2-BE using similar application regimes and determines the potential of skin to metabolise this chemical prior to entering the systemic blood circulation. Following topical application of undiluted [1-14C] 2-BE to occluded rat skin in vivo, 28% of the dose was absorbed after 24 h. The major routes of excretion included the urine (19%), expiration as carbon dioxide (6%) and faeces (0.4%) whilst little of the dose remained in the carcass (1.3%). Free 2-BE (0.5%), butoxyacetic acid (8%), glucuronide conjugate (3%), sulphate conjugates (0.7%) and ethylene glycol (0.6%) were detected in urine. Permeation rates of 2-BE through unoccluded rat dermatomed skin (16%) were greater than rat whole skin (8%) whilst absorption through human dermatomed skin (4%) was lower than the rat. Absorption of undiluted 2-BE through occluded rat dermatomed skin in vitro (18%) most accurately predicted absorption through rat skin in vivo. However, 2-BE absorption (23%) was enhanced by application in methanol. Distribution analysis and microautoradiography demonstrated the lack of 2-BE accumulation within the skin in vitro or in vivo. This was reflected in the absence of first pass metabolism of 2-BE during percutaneous penetration through viable human or rat skin in vitro or rat skin in vivo, despite rat skin cytosol having the potential to metabolise 2-BE. In conclusion, the in vitro system provided a reasonable estimate of dermal absorption in vivo for the rat. Therefore, by extrapolation of the comparative in vitro data for human and rat skin in vitro, dermal absorption of 2-BE in man was about one-fifth of that in the rat. However, the rapid penetration through skin in vitro prevented local metabolism and systemic exposure after skin contact with 2-BE in vivo was likely to be to the parent compound. Thus, in vitro skin systems can be used to model dermal absorption of volatile glycol ethers, to predict how much compound enters the circulation and allows the toxicologist to evaluate the body burden of a chemical and potential systemic toxicity.

A human exposure study to investigate biological monitoring methods for 2-butoxyethanol

2-Butoxyethanol is a glycol ether widely used in printing inks, varnishes and cleaning fluids. As skin absorption can be significant, biological monitoring is useful in monitoring worker exposure. A number of analytes and matrices have been used previously, including 2-butoxyethanol in blood and free and total 2-butoxyacetic acid in urine. Using a combination of a volunteer study and samples from exposed workers, we compared the applicability of some of the biological monitoring markers available. We conclude that 2-butoxyethanol in blood is not a suitable marker for biological monitoring due to sampling problems. In view of the low-level exposures reported in occupational surveys, 2-butoxyethanol in breath is also unsuitable because of a lack of sensitivity. Measuring 2-butoxyacetic acid in blood is possible, although non-invasive urine samples are preferred. Free 2-butoxyacetic acid in urine has previously been widely used; however, we found that the extent of conjugation of 2-butoxyacetic acid in urine varied from 0 to 100% both within and between individuals and is not related to time, concentration or urine pH. Data from 48 exposed workers suggested that an estimated 57% (95% confidence interval 44-70%) of the total 2-butoxyacetic acid is excreted in the conjugated form, and that conjugation may be activated above a certain exposure level. Using total 2-butoxyacetic acid significantly reduced inter-individual variation. Elimination half-lives for free and total 2-butoxyacetic acid were similar ( approximately 6 h) and there was no delay in excretion of the conjugated metabolite (peak excretion for both free and total was between 6 and 12 h after the end of exposure). In conclusion, we propose that total butoxyacetic acid (after acid hydrolysis) in urine is the biomarker of choice for monitoring exposure to 2-butoxyethanol. Urine samples should be collected post-shift towards the end of the working week.

Percutaneous absorption of neat and aqueous solutions of 2-butoxyethanol in volunteers

OBJECTIVES

To study the influence of the presence of water on the dermal absorption of 2-butoxyethanol (BE) in volunteers.

METHODS

Six male volunteers were dermally exposed to 50%, 90% or neat w/w BE for 4 h on the volar forearm over an area of 40 cm(2). An inhalation exposure with a known input rate and duration served as a reference dosage. The dermal absorption parameters were calculated from 24-h excretion of total (free + conjugated) butoxyacetic acid (BAA) in urine and BE in blood, measured after both inhalation and dermal exposure.

RESULTS

The dermal absorption of BE from aqueous solutions was markedly higher than that of neat BE. The time-weighted average dermal fluxes were calculated from the urine and blood data and expressed in milligrammes per square centimetre per hour. The dermal fluxes obtained from cumulative 24-h excretion of BAA amounted to 1.34+/-0.49, 0.92+/-0.60 and 0.26+/-0.17 mg cm(-2) h(-1 )for 50%, 90% and neat BE, respectively. The dermal fluxes calculated from the BE blood data amounted to 0.92+/-0.34 and 0.74+/-0.25 mg cm(-2) h(-1 )for 50% and 90% BE, respectively. The permeation rates into the blood reached a plateau between 60 and 120 min after the start of exposure, indicating achievement of steady-state permeation. The apparent permeability coefficient K(p), was 1.75+/-0.53x10(-3) and 0.88+/-0.42x10(-3) cm h(-1 )for 50% and 90% BE, respectively.

CONCLUSION

The percutaneous absorption of BE from aqueous solution increased markedly when compared with neat BE. Even water content as low as 10% led to an approximate fourfold increase in the permeation rates. These findings are important for the health risk assessment of occupational exposure to BE, since BE is commonly used in mixtures that contain water. Exposure to aqueous solutions of 50% and 90% of BE may result in substantial skin absorption: if a 60-min skin contact of 1,000 cm(2) is assumed, dermal uptake would be four-times higher than the pulmonary uptake of an 8-h occupational exposure at a TLV of 100 mg m(-3). This clearly justifies the skin notation for BE. For the purpose of biological monitoring, both BE in blood and BAA in urine were shown to be reliable indicators of exposure.

Percutaneous toxicokinetic and repeated cutaneous contact studies with ethylene glycol monohexyl ether

Ethylene glycol monohexyl ether (EGHE; CAS no. 112-54-4) is a liquid industrial chemical with a potential for skin contact. The toxicokinetics of EGHE was investigated in Fischer 344 rats and New Zealand White rabbits by intravenous (i.v.) and 48-h occluded epicutaneous dosing. Given i.v. to male rats (2.5-25 mg kg(-1)) [(14)C]EGHE demonstrated fi rst-order kinetics. Carbon-14 was eliminated mainly in urine (68-74%) as metabolites, with no free EGHE. The plasma free EGHE concentration declined rapidly post-dosing and was not detectable by 8 h. Similar results were obtained for [(14)C]EGHE given i.v. to male rabbits in the dosage range 1-10 mg kg(-1), except that the metabolism of EGHE was more rapid, with no free EGHE being detectable in plasma by 1 h post-dosing. After cutaneous dosing of male and female rats with 25 mg kg(-1), there was rapid percutaneous absorption, with >95% of the radiochemical dose being recovered. Percutaneous bioavailability was >75%. Carbon-14 was excreted in urine (21-33%) to a lesser extent than by the i.v. route, and (14)CO(2) and volatiles accounted for 15-18%. Carbon-14 recovery was low from tissues and organs (0.39-0.46%), with no preferential accumulation. Extensive metabolism was indicated by the rapid decline in plasma free EGHE, with none being detectable by 48 h. Free EGHE was not present in urine, and urinary radioactivity was associated with up to seven metabolites. After cutaneous dosing of male and female rabbits (10 mg kg(-1)) ca. 75% of the dose was recovered, most (14)C being in urine (58-60%). Urine radioactivity was associated with up to nine metabolite peaks, but no free EGHE. The toxicokinetic findings indicate a significant percutaneous absorption of EGHE across both rat and rabbit skin, which is rapidly and extensively metabolized, with renal excretion being the principal route of elimination of metabolites. A 9-day repeated skin contact study in the male and female New Zealand White rabbit, using a dosage range of 44-444 mg kg(-1) day(-1), did not show any evidence for percutaneous systemic toxicity.

Surfactant-free microspheres of poly(epsilon-caprolactone)/poly (ethylene glycol)/poly(epsilon-caprolactone) triblock copolymers as a protein carrier

The aim of this study is to prepare biodegradable microspheres without the use of surfactants or emulsifiers for a novel sustained delivery carriers of protein drugs. A poly(epsilon-caprolactoney poly(ethylene glycol)/poly(epsilon-caprolactone) (CEC) triblock copolymer was synthesized by the ring-opening of epsilon-caprolactone with dihydroxy poly (ethylene glycol) to prepare surfactant-free microspheres. When dichloromethane (DCM) or ethyl formate (EF) was used as a solvent, the formation of microspheres did not occur. Although the microspheres could be formed prior to lyophilization under certain conditions, the morphology of microspheres was not maintained during the filtration and lyophilization process. Surfactant-free microspheres were only formed when ethyl acetate (EA) was used as the organic solvent and showed good spherical microspheres although the surfaces appeared irregular. The content of the protein in the microsphere was lower than expected, probably because of the presence of water channels and pores. The protein release kinetics showed a burst release until 2 days and after that sustained release pattern was showed. Therefore, these observations indicated that the formation of microsphere without the use of surfactant is feasible, and, this the improved process, the protein is readily incorporated in the microsphere.

Repeated ingestion of 2-butoxyethanol: case report and literature review

BACKGROUND

Ethylene glycol monobutyl ether (2-butoxyethanol) is not commonly associated with significant human poisoning. Exposures are usually through occupational contact and typically involve inhalation injury. Animal studies report severe hemolysis occurring in rats and mice. Rare published human cases give varied descriptions of the clinical course associated with 2-butoxyethanol poisoning including reports of metabolic acidosis, ethylene glycol production, oxaluria, renal failure, and anemia. We report a case of two separate ingestions (80 to 100 grams) of a glass cleaner concentrate containing 22% 2-butoxyethanol, and its primary metabolite butoxyacetic acid.

CASE REPORT

An 18-year-old male ingested 360-480 mL of 22% 2-butoxyethanol on two separate occasions. Approximately 10hours after the first ingestion, the patient developed severe CNS depression, metabolic acidosis, hematuria, and mild elevation of hepatic enzymes. He was treated initially with ethanol therapy but continued to deteriorate and was started on hemodialysis. Approximately 10 days after discharge, the patient ingested 480 mL of the same product and received ethanol and hemodialysis within four hours of ingestion. During his second admission the patient did not develop the delayed severe CNS depression or profound metabolic acidosis. Clinically significant hemolytic anemia, oxaluria, ethylene glycol production, and renal failure were not noted in either episode. The patient recovered on both occasions without sequelae.

CONCLUSION

Hemodialysis may be an effective treatment intervention for managing severe acute 2-butoxyethanol intoxication, however, further investigation is warranted.

Factors affecting the extent of dermal absorption of solvent vapours: a human volunteer study

OBJECTIVES

We have previously reported that solvent vapours can be absorbed through the skin and that the extent varies markedly and depends on the chemical. For some chemicals, the extent of absorption is significant, e.g. for 1-methoxy-2-propanol dermal absorption accounts for up to 14% of the total absorbed dose after 8 h exposure at the OES. We have conducted a second study using 2-butoxyethanol to investigate the influence of temperature, humidity and clothing on the dermal absorption of vapours. As for the first study, the extent of dermal absorption was determined by biological monitoring to measure the resultant body burden of the chemical.

METHODS

Four volunteers were exposed on nine occasions. For eight of these exposures they wore air-fed half-masks to supply clean air for the inhalation route. The 'baseline' conditions (one 'whole body' and one 'skin only' exposure) were 25 degrees C, 40% relative humidity with volunteers wearing shorts and T-shirt. For each subsequent exposure, a single parameter was changed: humidity (60%, 65%), temperature (20 degrees C, 30 degrees C) or clothing (minimal and overalls). Finally, a 'industrial scenario' was conducted where volunteers wore overalls over their shorts and T-shirts and environmental conditions reflected high temperature and high humidity (30 degrees C, 60%), such as might be encountered in a tank-cleaning operation or similar.

RESULTS

Results show that 'baseline' dermal absorption of 2-butoxyethanol vapour was, on average, 11% of the total absorbed dose. Higher temperature (30 degrees C, mean 14%, P = 0.03) and greater humidity (65% RH, mean 13%, P = 0.1) increased dermal absorption. The wearing of whole-body overalls did not attenuate absorption (mean 10%). By combining several factors together in the 'industrial scenario', dermal absorption of vapours was significantly increased with a mean of 39% of the total absorbed dose.

CONCLUSIONS

The work has shown that dermal absorption of vapours can be significant and that environmental conditions may affect the absorption. Some types of protective clothing may not be suitable to reduce absorption. The possibility of dermal absorption of vapours should be considered particularly for workers in high vapour concentration conditions where control of exposure relies on respiratory protection.

Mode of action and pharmacokinetic studies of 2-butoxyethanol in the mouse with an emphasis on forestomach dosimetry

Chronic inhalation studies with 2-butoxyethanol (BE) conducted by the National Toxicology Program identified the forestomach and liver of B6C3F1 mice as target organs for tumorigenicity (NTP, 2000). Previous studies have shown that the liver tumors likely resulted from chronic hemolysis-induced oxidative stress. For the forestomach lesions seen in mice, chronic contact irritation (cytotoxicity) and regenerative hyperplasia are hypothesized to result in forestomach tumor development. To test this hypothesis, several experiments were conducted to address the sensitivity of the mouse forestomach to BE administered by various routes. Oral administration of undiluted BE was shown to cause irritation and a compensatory proliferative response in the mouse forestomach, confirming that direct contact between the forestomach and BE, which can occur via grooming of BE condensed on the fur during inhalation exposures, can cause irritation. However, only small amounts of BE (<10 mg/kg) were detected on the fur of mice at the end of 6-h, whole-body or nose-only inhalation exposures to the highest concentration used in the NTP chronic inhalation studies (250 ppm). Furthermore, no significant differences were detected in the end-exposure blood concentrations of BE and butoxyacetic acid (BAA) between these types of exposures. In addition, parenteral administration of BE (ip and sc injection) also resulted in forestomach lesions, indicating that there may be sources other than grooming for BE- or BAA-induced forestomach irritation. In the pharmacokinetic study, BE and, to a lesser extent, BAA was eliminated more slowly from the forestomach tissue of mice than from blood or other tissues, following either oral gavage or ip injection. The forestomach was the only tissue with detectable levels of BE at 24 h. BE and BAA were both excreted in the saliva and were present in stomach contents for a prolonged period of time following these routes of exposure, which may further contribute to forestomach tissue dosimetry. Thus, there appear to be multiple mechanisms behind the increased levels of BE and BAA in the forestomach tissue of mice, which together can contribute to a prolonged contact irritation, compensatory hyperplasia, and tumorigenicity in mice. The relevance of these effects in humans, who lack a forestomach, is questionable.

Effects of experimental conditions on absorption of glycol ethers through human skin in vitro

OBJECTIVES

To determine effects of experimental variables on the dermal absorption of 2-ethoxyethanol (EE), 2-butoxyethanol (BE) and 1-methoxy-2-propanol (M2P) through human skin in vitro.

METHODS

Percutaneous absorption of EE, BE and M2P, in aqueous solution (3 mg ml(-1), 200 microl) or undiluted (10.5 microl), though full thickness or dermatomed human breast skin (0.64 cm(2) exposed area) was measured for 24 h using flow-through diffusion cells. Tissue culture medium was used as receptor fluid, with 2% (w/v) bovine serum albumin (BSA) or 2%-6% (w/v) polyethylene glycol 20 oleyl ether (PEG 20) added for some studies. Volatilised test compounds were trapped on charcoal filters placed above cells.

RESULTS

In aqueous solution, steady-state flux of BE (544+/-64 nmol cm(-2) h(-1)) exceeded that of EE (143+/-19 nmol cm(-2) h(-1)) and M2P (48+/-6 nmol cm(-2) h(-1)). Reducing the dose volume to 100 microl decreased the steady-state flux of BE by about 55%, though the flux of EE was approximately doubled. Doubling the dose concentration of EE increased the flux by about eight-fold. Using full thickness skin increased tau of both EE and BE and reduced the steady-state flux of BE. Absorption rates of undiluted solvents in finite doses exceeded those measured with aqueous solutions, though the apparent permeability coefficient was higher with aqueous doses. Addition of BSA or PEG 20 to receptor fluid markedly increased absorption in both aqueous and undiluted doses.

CONCLUSIONS

The dermal absorption potential of M2P from a liquid application was markedly lower than from EE or BE in all but infinite undiluted doses. The influence of receptor fluid on dermal absorption of glycol ethers could be relevant to prediction of absorption in vivo.

Butoxyethoxyacetic acid, a biomarker of exposure to water-based cleaning agents

The aim of the study was to investigate the suitability of butoxyethoxyacetic acid (BEAA) as a biomarker of exposure to water-based cleaning agents containing diethylene glycol mono butyl ether (DEGBE). The study was performed in two printing plants where water-based products containing 10-15% DEGBE were used for rubber and blanket washes. Thirty nine newspaper pressroom workers (exposed) and 19 employees of newspaper despatch departments (controls) were investigated. By questionnaire, the workers were asked about the use of personal protective measures. BEAA was determined in post-shift urine using GC-MS. The BEAA concentration in the urine of exposed workers ranged up to 75.1 mg/l (median 6.3 mg/l), whereas in urine samples of the controls the BEAA level was below or around the determination limit of 0.5 mg/l. A protective effect on DEGBE uptake was observed with the use of protective gloves. This observation implies that dermal penetration of DEGBE may be important in exposure monitoring.

Use of 2% 2-phenoxyethanol and 0.1% octenidine as antiseptic in premature newborn infants of 23-26 weeks gestation

In preterm newborn infants, topical iodine-containing antiseptics disturb thyroid hormone regulation while alcohol-based disinfectants may cause local burns. We therefore investigated the use of an aqueous solution containing 0.1% octenidine and 2% 2-phenoxyethanol for skin disinfection during the first seven days of life in premature newborns with a gestational age <27 weeks who were consecutively admitted to our level III neonatal intensive care unit between November 1, 2000 and December 31, 2001 (N=24). In boys. (N=13) the renal excretion of absorbed 2-phenoxyethanol and its metabolite 2-phenoxyacetic acid was quantitated by high-pressure liquid chromatography. In the most immature newborn (gestational age 23 6/7 weeks), a transient erythematous reaction was observed following application of the octenidine/phenoxyethanol solution prior to umbilical vessel catheterization. No other local reactions were observed. The urinary concentration of 2-phenoxyethanol was <2 ppm in all samples, while urinary 2-phenoxyacetic acid concentrations reached 5-95 ppm (median 24 ppm). One infant had a culture-proven septicaemia (Bacillus species) during the first seven days of life. We conclude that, in contrast to alcohol-based antiseptics, an aqueous solution of 0.1% octenidine and 2-phenoxyethanol does not cause major skin damage in premature newborn infants <27 weeks' gestation. 2-Phenoxyethanol is readily absorbed by the newborn's skin but apparently undergoes extensive oxidative metabolization to 2-phenoxyacetic acid.

Use of sensitivity analysis to assess reliability of metabolic and physiological models

Because ethical considerations often preclude directly determining the human health effects of treatments or interventions by experimentation, such effects are estimated by extrapolating reactions predicted from animal experiments. Under such conditions, it must be demonstrated that the reliability of the extrapolated predictions is not excessively affected by inherent data limitations and other components of model specification. This is especially true of high-level models composed of ad hoc algebraic equations whose parameters do not correspond to specific physical properties or processes. Models based on independent experimental data restricting the numerical space of parameters that do represent actual physical properties can be represented at a more detailed level. Sensitivities of the computed trajectories to parameter variations permit more detailed attribution of uncertainties in the predictions to these low-level properties. S-systems, in which parameters are estimated empirically, and physiological models, whose parameters can be estimated accurately from independent data, are used to illustrate the applicability of trajectory sensitivity analysis to lower-level models.

Percutaneous penetration and metabolism of 2-ethoxyethanol

Percutaneous absorption and cutaneous metabolism of 2-ethoxyethanol were assessed in vivo and with an in vitro flow-through diffusion system. Topical application of undiluted (14)C-ethoxyethanol to occluded rat skin in vivo resulted in 25% of the dose being absorbed after 24 h. The major routes of excretion included the urine (15%), expiration as carbon dioxide (6%), and feces (1.2%), while little of the dose remained in the carcass (1.3%). Free ethoxyethanol, ethoxyacetic acid, and glycine conjugate were detected in urine. Permeation rates of ethoxyethanol through unoccluded rat split skin (20%) were greater than rat whole skin (11%), while absorption through human split skin (8%) was lower than the rat. Absorption of undiluted ethoxyethanol through occluded rat split skin in vitro (22%) most accurately predicted absorption through rat skin in vivo. However, ethoxyethanol absorption (29%) was enhanced by application in methanol. First pass metabolism of ethoxyethanol was not detected during percutaneous penetration through viable human or rat skin in vitro or rat skin in vivo. However, rat skin cytosol had the potential to metabolize ethoxyethanol, suggesting that the rapid penetration through skin in vivo prevented metabolism and that systemic exposure after skin contact with 2-ethoxyethanol is likely to be to the parent compound. In conclusion, the in vitro system provided a reasonable estimate of dermal absorption for the rat in vivo and comparison of human and rat skin in vitro indicated 2-ethoxyethanol absorption in humans is about one-third of that in the rat.

Alkylphenolic compounds in edible molluscs of the Adriatic Sea (Italy)

This paper reports the first group of results on alkylphenol (APE) contamination of seafood in the Adriatic Sea, in the framework of a national project on the quality of this Sea (PRISMA 2). Nonylphenol (NP), octylphenol (OP), and their ethoxylates (NPE and OPE) were detected in edible molluscs, either filter feeders or predators (clams, mussels, cuttlefishes, and squids), caught from 15 harbors along the Italian coast in the Adriatic Sea in 1997. NP was the compound found always at levels much higher than the other APEs in all the examined species. It reached the maximum concentration of 696 ng/g fresh weight in the squids from the central Adriatic Sea. OP generally occurred at levels 30 times lower than NP. OP was found up to a level of 18.6 ng/g in squids from central Adriatic Sea. OPE was the compound always spotted at the lowest concentrations, up to 0.43 ng/g. NPE was always below the detection limit. The pattern of contamination in the three areas examined was different between bivalve and cephalopod species. No exhaustive risk assessment for marine organisms and human health can be conducted on the basis of these results because data are insufficient. Yet, the occurrence of NP suggests a negligible risk for mussels, which represent the only molluscs for which data are adequate. As to the possible human health implications, the consumption of molluscs of the Adriatic Sea implies APE intakes that are some orders of magnitude lower than those responsible for toxic effects in laboratory animals. Despite these apparently low risks for mussels and human health, the reasons for concern still remain because the levels of alkylphenols found in this study indicate a general contamination of the Adriatic Sea even far from the cost. Furthermore, these levels might represent an unacceptable hazard for other marine organisms. Finally, they contribute to the general environmental estrogen pool.

Investigation of the utility of an in vitro release test for optimizing semisolid dosage forms

Current literature indicates that an in vitro release test (IVRT) can serve as a research tool during the course of developing topical formulations. The purpose of this study was therefore to investigate the ability of an IVRT to select the topical semisolid formulations with the most rapid release rate of the model drug ketoprofen from two closely related hydrogels in a simulated product development process. Two glycols with distinct differences in their physical-chemical properties, Transcutol P (ethoxydiglycol) and propylene glycol, were incorporated into Carbopol 980 and Poloxamer 407 formulations. The release rate of ketoprofen was determined utilizing different receptor media and conditions, i.e., phosphate buffer pH 7.4, isopropyl myristate (IPM), and a combination of an IPM soaked membrane and phosphate buffer (pH 7.4) as receptor fluid. The results indicated that the conditions chosen could affect greatly the conclusions concerning the formulations. The only observable trend was that Transcutol P-containing formulations tended to permit a faster ketoprofen release than propylene glycol-containing formulations when utilizing IPM as a receptor component. This was attributed to the mutual miscibility of Transcutol P in IPM. It can be concluded that, for the purpose of formulation screening in the early phases of product development, an IVRT will only be useful for predicting the amount of drug available for absorption if the receptor medium has properties that closely mimic human skin. These results illustrate the importance of selecting suitable receptor components and indicate that it may be necessary to consider alternatives to the commonly used synthetic membranes.

Proposed occupational exposure limits for select ethylene glycol ethers using PBPK models and Monte Carlo simulations

Methoxyethanol (ethylene glycol monomethyl ether, EGME), ethoxyethanol (ethylene glycol monoethyl ether, EGEE), and ethoxyethyl acetate (ethylene glycol monoethyl ether acetate, EGEEA) are all developmental toxicants in laboratory animals. Due to the imprecise nature of the exposure data in epidemiology studies of these chemicals, we relied on human and animal pharmacokinetic data, as well as animal toxicity data, to derive 3 occupational exposure limits (OELs). Physiologically based pharmacokinetic (PBPK) models for EGME, EGEE, and EGEEA in pregnant rats and humans have been developed (M. L. Gargas et al., 2000, Toxicol. Appl. Pharmacol. 165, 53-62; M. L. Gargas et al., 2000, Toxicol. Appl. Pharmacol. 165, 63-73). These models were used to calculate estimated human-equivalent no adverse effect levels (NAELs), based upon internal concentrations in rats exposed to no observed effect levels (NOELs) for developmental toxicity. Estimated NAEL values of 25 ppm for EGEEA and EGEE and 12 ppm for EGME were derived using average values for physiological, thermodynamic, and metabolic parameters in the PBPK model. The uncertainties in the point estimates for the NOELs and NAELs were estimated from the distribution of internal dose estimates obtained by varying key parameter values over expected ranges and probability distributions. Key parameters were identified through sensitivity analysis. Distributions of the values of these parameters were sampled using Monte Carlo techniques and appropriate dose metrics calculated for 1600 parameter sets. The 95th percentile values were used to calculate interindividual pharmacokinetic uncertainty factors (UFs) to account for variability among humans (UF(h,pk)). These values of 1.8 for EGEEA/EGEE and 1.7 for EGME are less than the default value of 3 for this area of uncertainty. The estimated human equivalent NAELs were divided by UF(h,pk) and the default UFs for pharmacodynamic variability among animals and among humans to calculate the proposed OELs. This methodology indicates that OELs (8-h time-weighted average) that should protect workers from the most sensitive adverse effects of these chemicals are 2 ppm EGEEA and EGEE (11 mg/m(3) EGEEA, 7 mg/m(3) EGEE) and 0.9 ppm (3 mg/m(3)) EGME. These recommendations assume that dermal exposure will be minimal or nonexistent.

2-Methoxyethanol metabolism, embryonic distribution, and macromolecular adduct formation in the rat: the effect of radiofrequency radiation-induced hyperthermia

Exposure of pregnant rats to the solvent 2-methoxyethanol (2ME) and radiofrequency (RF) radiation results in greater than additive fetal malformations (Nelson, B.K., Conover, D.L., Brightwell, W.S., Shaw, P.B., Werren, D.W., Edwards, R.M., Lary, J.M., 1991. Marked increase in the teratogenicity of the combined administration of the industrial solvent 2-methoxyethanol and radiofrequency radiation in rats. Teratology 43, 621-34; Nelson, B.K., Conover, D.L., Shaw, P.B., Werren, D.W., Edwards, R.M., Hoberman, A.M., 1994. Interactive developmental toxicity of radiofrequency radiation and 2-methoxyethanol in rats. Teratology 50, 275-93). The current study evaluated the metabolism of 14C-labeled 2ME and the distribution of methoxyacetic acid (MAA) in maternal and embryonic tissues of pregnant Sprague-Dawley rats either exposed to 10 MHz RF radiation or sham conditions. Additionally, adduct formation for both plasma and embryonic protein was tested as a possible biomarker for the observed 2ME/RF teratogenicity. Rats were administered [ethanol-1,2-(14)C]-2ME (150 mg/kg, 161 microCi/rat average) by gavage on gestation day 13 immediately before RF radiation sufficient to elevate body temperature to 42 degrees C for 30 min. Concurrent sham- and RF-exposed rats were sacrificed at 3, 6, 24 or 48 h for harvest of maternal blood, urine, embryos and extra-embryonic fluid. Tissues were either digested for determination of radioactivity or deproteinized with TCA and analyzed by HPLC for quantification of 2ME metabolites. Results show the presence of 2ME and seven metabolites, with the major metabolite, MAA, peaking at 6 h in the tissues tested. MAA, the proximal teratogen, was detectable in maternal serum, urine, embryo and extraembryonic fluid 48 h after dosing. Clearance of total body 14C was significantly reduced for the RF-exposed animals (P<0.05) for the 24-48 h period, but MAA values for serum, embryos and extraembryonic fluid were similar for both sham- and RF-exposed rats. Additionally, no difference was noted for 2ME metabolite profiles in urine or tissue for sham- or RF-exposed rats, thus eliminating an effect of RF radiation on MAA production as a possible explanation for the reported RF-2ME synergism. Subsequently, serum and embryo protein-bound adducts were evaluated by analysis of covalently bound radioactivity. Serum protein binding was significantly higher for sham than RF rats at 3- and 6-h - highest for sham rats at 6 h (519+/-95 microg as parent 2ME/g of protein) whereas RF serum values were highest at 24 h (266+/-79 microg/g protein). Embryonic protein binding was significantly higher for sham rats at 6 h, but binding was highest for both groups at 24 h (sham=229+/-71 microg/g, RF=185+/-48 microg/g). Formation of protein adducts after 2ME is thought to be related to levels of methoxyacetaldehyde, a reactive intermediate in the formation of MAA. These results suggest that no direct relationship exists for covalent binding in the embryo which would explain RF-2ME synergistic malformations. In comparison with urinary metabolites, the relatively slow elimination of adducted serum 2ME indicates that analysis of protein-bound concentrations could be a potential tool for long- term biomonitoring of worker exposure.

Butoxyethanol ingestion with prolonged hyperchloremic metabolic acidosis treated with ethanol therapy

BACKGROUND

Severe toxic ingestions of butoxyethanol (CAS No. 111-76-2) are rare despite the prevalence of this glycol ether in products such as glass and surface cleaners. Manifestations of acute butoxyethanol toxicity include metabolic acidosis, hemolysis, hepatorenal dysfunction, and coma, but vary widely in reported cases. Furthermore, the optimal therapeutic approach is not yet established. Much of the toxicity of butoxyethanol has been ascribed to its aldehyde and acid metabolites which are similar to those produced by oxidative metabolism of methanol and ethylene glycol. Although the roles of alcohol dehydrogenase inhibition with ethanol or fomepizole and hemodialysis are clear in the case of toxic ingestions of methanol and ethylene glycol, they remain poorly defined for butoxyethanol poisoning.

CASE REPORT

We report the case of a 51-year-old female who ingested up to 8 ounces of Sanford Expo White Board Cleaner (butoxyethanol and isopropanol). She developed prolonged hyperchloremic metabolic acidosis and mental status depression and was treated with ethanol therapy but not hemodialysis. This patient recovered without apparent sequelae. The kinetics of butoxyethanol metabolism in this case are described and the potential therapeutic options are discussed.

Mass spectrometric study of persistent acid metabolites of nonylphenol ethoxylate surfactants

A mass spectrometric study was carried out on two nonylphenoxycarboxylic acids, NP1EC and NP2EC (where 1 and 2 indicate the number of ethoxylate units attached to the nonylphenoxy moiety), that are persistent metabolites of widely used nonionic surfactant nonylphenol ethoxylates. In a gas chromatographic/mass spectrometric (GC/MS) study of the methyl esters of NP1EC and NP2EC, two series of fragment ions were observed in electron ionization (EI) mass spectra; m/z (179 + 14n, n = 0-7) and m/z (105 + 14n, n = 0-4) for NP1ECMe and m/z (223 + 14n, n = 0-7) and m/z (107 + 14n, n = 0-5) for NP2ECMe. Similarity indices were used to compare quantitatively the mass spectra of isomers. The mass spectra of two isomers were found to be similar whereas those of the remaining isomers were readily distinguishable from each other. The abundant fragment ions of the two NPECMes were investigated further by GC/MS/MS; product ions resulting from cleavage in the alkyl moiety, cleavage in the ECMe moiety and cleavage in both moieties were detected. Possible structures of the nonyl groups in the two esters were inferred. GC/chemical ionization (CI) mass spectra of the NPECMes with isobutane as reagent gas showed characteristic hydride ion-abstracted fragment ions shifted by 1 Da from those in the corresponding EI mass spectra. The sensitivity of a selected ion monitoring quantitation method for the NPECMes is enhanced under CI conditions compared with that under EI conditions. With electrospray ionization MS/MS, [M - H](-) ions of NP1EC (m/z 277) and NP2EC (m/z 321) were observed and, upon collision-induced dissociation of [M - H](-) of each of the two acids, fragment ions of m/z 219 corresponding to deprotonated nonylphenol, were observed in each case. Based on this observation, a rapid, simple and reliable selected product ion quantitation method is proposed for NP1EC and NP2EC.

A new technology to measure skin absorption of vapors

Skin vapor absorption is one of the major exposure routes for some widely used chemicals (e.g., 2-methoxy ethanol), but a good apparatus with which exposure can be measured is currently unavailable. In this study, a polished stainless-steel chamber-combined with computer-controlled auto-feedback software and hardware, real-time gas sensors, and an auto-injection microsyringe-was proposed as new technology. In addition, the machines had activated-charcoal tubes and cold traps, both of which simulated the skin uptake and validated the reliability of the proposed system. The exposure concentrations, relative humidity, and temperature were effectively controlled at 25+/-0.5 ppm (or 300+/-10 ppm), 80+/-2%, and 27.5+/-0.5 degrees C, respectively. The relative errors between the quantity of 2-methoxy ethanol collected in either the charcoal tubes or the cold traps and the quantity of ME injected to maintain a constant exposure were less than 5%. The authors also used this new technology to successfully measure skin absorption of ME vapor in 6 volunteers. The authors concluded that this new technology is a direct, continuous, noninvasive, and simple tool with which to measure skin absorption of vapors.

A toxicokinetic study of inhaled ethylene glycol monomethyl ether (2-ME) and validation of a physiologically based pharmacokinetic model for the pregnant rat and human

Exposures to sufficiently high doses of ethylene glycol monomethyl ether (2-methoxyethanol, 2-ME) have been found to produce developmental effects in rodents and nonhuman primates. The acetic acid metabolite of 2-ME, 2-methoxyacetic acid (2-MAA), is the likely toxicant, and, as such, an understanding of the kinetics of 2-MAA is important when assessing the potential risks to humans associated with 2-ME. A previously described physiologically based pharmacokinetic (PBPK) model of 2-ME/2-MAA kinetics for rats exposed via oral or iv administration was extended and validated to inhalation exposures. Pregnant Sprague-Dawley rats were exposed for 5 days (gestation days 11-15), 6 h/day, to 2-ME vapor at 10 and 50 ppm. Validation consisted of comparing model output to maternal blood and fetal 2-ME and 2-MAA concentrations during and following 5 days of exposure (gestation days 11-15). These concentrations correspond to a known no observed effect level (NOEL) and a lowest observed effect level (LOEL) for developmental effects in rats. The rat PBPK model for 2-ME/2-MAA was scaled to humans and the model (without the pregnancy component) was used to predict data collected by other investigators on the kinetics of 2-MAA excretion in urine following exposures to 2-ME in human volunteers. The partially validated human model (with the pregnancy component) was used to predict equivalent human exposure concentrations based on 2-MAA dose measures (maximum blood concentration, C(max), and average daily area under the 2-MAA blood concentration curve, AUC, during pregnancy) that correspond to the concentrations measured at the rat NOEL and LOEL exposure concentrations. Using traditional PBPK scale-up techniques, it was calculated that pregnant women exposed for 8 h/day, 5 days/week, for the duration of pregnancy would need to be exposed to 12 or 60 ppm 2-ME to produce maternal 2-MAA blood concentrations (C(max) or average daily AUC) equivalent to those in rats exposed to the NOEL (10 ppm) or LOEL (50 ppm), respectively.

A toxicokinetic study of inhaled ethylene glycol ethyl ether acetate and validation of a physiologically based pharmacokinetic model for rat and human

The solvents ethylene glycol monoethyl ether acetate (EGEEA) and ethylene glycol monoethyl ether (EGEE), at sufficiently high doses, are known to be rodent developmental toxicants, exerting their toxic effects through the action of their metabolite 2-ethoxyacetic acid (2-EAA). Thus risks associated with exposure to these compounds are best evaluated based on a measure of the internal dose of 2-EAA. The goals of the work reported here were to develop physiologically based pharmacokinetic (PBPK) models of EGEEA and EGEE for pregnant rats and humans. These models were used to identify human exposure levels (ppm in air) equivalent to the rat no observed effect level (NOEL) and lowest observed effect level (LOEL) for developmental effects (Hanley et al., 1984). We exposed pregnant Sprague-Dawley rats to concentrations of EGEEA corresponding to the NOEL and LOEL. Maternal blood, urine, and fetal tissue concentrations of EGEE and 2-EAA measured in these experiments were used to validate the rat EGEEA and EGEE models. Data collected by other researchers were used to validate the capabilities of the rodent EGEEA and EGEE models to predict the kinetics in humans. The models for estimating circulating blood concentrations of 2-EAA were considered valid based on the ability of the model to accurately predict 2-EAA concentrations in rat blood, urine, and fetal tissue. The human inhaled concentration equivalent to the rat NOEL for EGEEA (50 ppm) was predicted to be 25 ppm using the maternal blood average daily area under the curve (AUC) and 40 ppm using the maximum concentration achieved in maternal blood (C(max)). The human inhaled concentration equivalent to the rat LOEL for EGEEA (100 ppm) was determined to be 55 ppm using the maternal blood average daily AUC and 80 ppm using the maternal blood C(max).

Toxicity review of ethylene glycol monomethyl ether and its acetate ester

Ethylene glycol monomethyl ether (EGME) and its acetate ester (EGMEA) are highly flammable, colorless, moderately volatile liquids with very good solubility properties. They are used in paints, lacquers, stains, inks and surface coatings, silk-screen printing, photographic and photo lithographic processes, for example, in the semiconductor industry, textile and leather finishing, production of food-contact plastics, and as an antiicing additive in hydraulic fluids and jet fuel. EGME and EGMEA are efficiently absorbed by inhalation as well as via dermal penetration. Dermal absorption may contribute substantially to the total uptake following skin contact with liquids or vapours containing EGME or EGMEA. EGMEA is rapidly converted to EGME in the body and the two substances are equally toxic in animals. Therefore, the two substances should be considered as equally hazardous to man. Effects on peripheral blood, testes, and sperm have been reported at occupational exposure levels ranging between 0.4 and 10 ppm EGME in air, and with additional, possibly substantial, dermal exposure. Severe malformations and disturbed hematopoiesis have been linked with exposure to EGME and EGMEA at unknown, probably high, levels. Embryonic deaths in monkeys and impaired spermatogenesis in rabbits have been reported after daily oral doses of 12 and 25 mg per kg body weight, respectively. In several studies, increased frequency of spontaneous abortions, disturbed menstrual cycle, and subfertility have been demonstrated in women working in the semiconductor industry. The contribution of EGME in relation to other exposure factors in the semiconductor industry is unclear.

Measurement of percutaneous uptake of 2-methoxy ethanol vapor in humans

Absorption of vapors through skin has been largely ignored in occupational health, although for ethylene glycol ethers this route of exposure could be more important than inhalation. We used an automated concentration and humidity controlled system to measure real-time percutaneous absorption of 2-methoxy ethanol (ME) vapor in seven volunteers. The exposure concentration (300 +/- 10 ppm or 25 +/- 0.5 ppm), humidity (80 +/- 2%), and temperature (27.5 +/- 0.5 degrees C) were controlled throughout the experiments. Uptakes during 4-hour single-arm exposure at 25 ppm and 300 ppm were 7.0 mg and 65.3 +/- 25.0 mg, respectively, with corresponding uptake rates of 1.36 micrograms/cm2/hr and 13.2 +/- 5.0 micrograms/cm2/hr. Percutaneous absorption was consistent and unsaturated during exposure. Because the permeability constant of ME vapor (14.0 +/- 5.3 cm/hr) was much higher than that of many widely used organic chemicals, we concluded that vapor absorption through skin is a significant contributor to overall ME exposure.

Development of a physiologically based pharmacokinetic model of 2-methoxyethanol and 2-methoxyacetic acid disposition in pregnant rats

An accurate description of developing embryos' exposure to a xenobiotic is a desirable component of mechanism-based risk assessments for humans exposed to potential developmental toxicants during pregnancy. 2-Methoxyethanol (2-ME), a solvent used in the manufacture of semiconductors, is embryotoxic and teratogenic in all species tested including nonhuman primates. 2-Methoxyacetic acid (2-MAA) is the primary metabolite of 2-ME and the proximate embryotoxic agent. The objective of the work described here was to adapt an existing physiologically based pharmacokinetic (PBPK) model for 2-ME and 2-MAA kinetics during midorganogenesis in mice to rats on gestation days (GD) 13 and 15. Blood and tissue data were analyzed using the extrapolated PBPK model that was modified to simulate 2-ME and 2-MAA kinetics in maternal plasma and total embryo tissues in pregnant rats. The original mouse model was simplified by combining the embryos and placenta with the richly perfused tissue compartment. The model includes a description of the growth of the developing embryo and changes in the physiology of the dam during pregnancy. Biotransformation pathways of 2-ME to either ethylene glycol (EG) or to 2-MAA were described as first-order processes based on the data collected from rats by Green et al., (Occup. Hyg. 2, 67-75, 1996). Tissue partition coefficients (PCs) for 2-ME and 2-MAA were determined for a variety of maternal tissues and the embryos. Model simulations closely reflected the biological measurement of 2-ME and 2-MAA concentrations in blood and embryo tissue following gavage or iv administration of 2-ME or 2-MAA. The PBPK model for rats as described here is well suited for extrapolation to pregnant women and for assessment of 2-MAA dosimetry under various conditions of possible human exposure to 2-ME.