Synthesis and evaluation of styrene-maleic acid copolymer conjugated amphotericin B.

Amphotericin B (AmB), which plays a central role in the treatment of systemic fungal infections, is difficult to formulate because it's sparingly soluble in water and organic solvents. We previously prepared AmB-loaded micelles using styrene-maleic acid copolymer (SMA). Although solubilization was achieved by this formulation, stability in the blood circulation was as insufficient as that of Fungizone®, which is a conventional formulation of AmB. Meanwhile, it is well known that polymer-drug conjugates are more stable in circulation than drug-loaded micelles. Therefore, in this study, we developed covalently conjugated SMA-AmB (SMA-AmB conjugate). The SMA-AmB conjugate was found to be soluble and present as micelles in aqueous solution. Furthermore, it was revealed that this micelle behaves as a larger molecule by forming a complex with albumin. The circulation in the blood increased significantly compared to that of Fungizone®, which was suggested to be due to this complex-forming ability. Although in vitro and in vivo antifungal activity of the SMA-AmB conjugate against Saccharomyces cerevisiae was reduced by 1/3 compared to that of Fungizone®, hemolysis decreased to 1/40 or less, and the LD50 decreased to 1/10. In conclusion, it is expected that the SMA-AmB conjugate can be a polymer-therapeutic agent with high antifungal selectivity.

Human plasma and liver concentrations of styrene estimated by combining a simple physiologically based pharmacokinetic model with rodent data.

Long-term exposure to certain volatile organic compounds is a significant public health concern. A variety of food containers and drinking cups prepared from polystyrene or polystyrene-related plastics could contain styrene monomer. In the current study, the concentrations of styrene in plasma and liver were surveyed and determined after oral doses of 25 mg/kg to rats and 200 mg/kg to control and humanized-liver mice. Plasma concentrations of styrene in rats were still detected 2 hr after 10-25 mg/kg oral doses. In contrast, after an order of magnitude higher oral dose of styrene (200 mg/kg) to mice, styrene in mouse plasma was rapidly cleared within 15 min to the limit-of-detection level. However, unmetabolized styrene was detected in mouse liver 24 hr after oral treatment. A simple physiologically based pharmacokinetic (PBPK) model capable of estimating blood and liver concentrations of styrene was established for rats. A human PBPK model was then set up for styrene by using the same intrinsic hepatic clearances in rats and humans and by applying allometric scaling to rat parameters obtained from the plasma concentrations of styrene in rats. By reverse dosimetry analysis (from concentrations to doses), we found that the 95th percentile values of styrene concentrations (0.132 ng/mL) reported in United States biomonitoring data of more than 1000 human blood samples may imply exposure to repeated oral doses of styrene of 2.89 µg/kg/day. These results suggest that styrene biomonitoring data in human blood samples imply exposures roughly similar to or lower than the established tolerable daily intake level of 7.7 µg/kg/day.

Based on an analysis of mode of action, styrene-induced mouse lung tumors are not a human cancer concern.

Based on 13 chronic studies, styrene exposure causes lung tumors in mice, but no tumor increases in other organs in mice or rats. Extensive research into the mode of action demonstrates the key events and human relevance. Key events are: metabolism of styrene by CYP2F2 in mouse lung club cells to ring-oxidized metabolites; changes in gene expression for metabolism of lipids and lipoproteins, cell cycle and mitotic M-M/G1 phases; cytotoxicity and mitogenesis in club cells; and progression to preneoplastic/neoplastic lesions in lung. Although styrene-7,8-oxide (SO) is a common genotoxic styrene metabolite in in vitro studies, the data clearly demonstrate that SO is not the proximate toxicant and that styrene does not induce a genotoxic mode of action. Based on complete attenuation of styrene short-term and chronic toxicity in CYP2F2 knockout mice and similar attenuation in CYP2F1 (humanized) transgenic mice, limited metabolism of styrene in human lung by CYP2F1, 2 + orders of magnitude lower SO levels in human lung compared to mouse lung, and lack of styrene-related increase in lung cancer in humans, styrene does not present a risk of cancer to humans.

Significant association between decreased ALDH2 activity and increased sensitivity to genotoxic effects in workers occupationally exposed to styrene.

ALDH2 is involved in the metabolism of styrene, a widely used industrial material, but no data are available regarding the influence of this enzyme on the metabolic fate as well as toxic effects of this chemical. In this study, we recruited 329 workers occupationally exposed to styrene and 152 unexposed controls. DNA strand breaks, DNA-base oxidation in leukocytes and urinary 8-hydroxydeoxyguanosine (8-OH-dG) were assayed as biomarkers to measure genotoxic effects. Meanwhile, we examined the genetic polymorphisms, including ALDH2, EXPH1, GSTM1, GSTT1 and CYP2E1, and also analyzed the levels of styrene exposure through detecting urinary styrene metabolites and styrene concentration in air. In terms of DNA damage, the three genotoxic biomarkers were significantly increased in exposed workers as compared with controls. And the styrene-exposed workers with inactive ALDH2 *2 allele were subjected to genotoxicity in a higher degree than those with ALDH2 *1/*1 genotype. Also, lower levels of urinary styrene metabolites (MA + PGA) were observed in styrene-exposed workers carrying ALDH2 *2 allele, suggesting slower metabolism of styrene. The polymorphisms of other enzymes showed less effect. These results suggested that styrene metabolism and styrene-induced genotoxicity could be particularly modified by ALDH2 polymorphisms. The important role of ALDH2 indicated that the accumulation of styrene glycoaldehyde, a possible genotoxic intermediate of styrene, could account for the genotoxicity observed, and should be taken as an increased risk of cancer.

An evaluation of concentrations of styrene-7,8-oxide in rats and humans resulting from exposure to styrene or styrene-7,8-oxide and potential genotoxicity.

There is potential for oral exposure of humans to styrene (ST) such as from migration of residual levels in polystyrene food containers. After absorption, ST is metabolised to styrene-7,8-oxide (SO), an alkylating epoxide. Hence, a comparison of blood burdens of SO resulting from oral exposures to ST was made with SO burdens possibly warranting genotoxic concern. A validated physiological toxicokinetic model was used for the assessment. Model calculations predicted for exposures to ST that maximum concentrations of SO in venous blood of rats and humans should not exceed 0.33 µg/ml and 0.036 µg/ml, respectively, because of saturation of the SO formation from ST. The daily area under the concentration-time curve of SO in venous blood (AUCSO) was directly proportional to the dose of ST (mg/kg body weight; BW), independent of the exposure route (inhalation or oral exposure). In resting humans, the daily AUCSO was about half that in rats at the same amount of ST/kg BW (calculated up to 100mg ST/kg BW in humans). Taking into account the results of cytogenetic studies in ST-exposed rats, it was deduced that no genotoxic effects of SO are to be expected in ST-exposed humans, at least up to a daily amount of 100mg ST/kg BW, which is equivalent to 100 times the amount originating from the Overall Migration Limit in the EU for ST migrating from food contact plastics. Therefore, no potential genotoxic concern is predicted for ST uptake from food packaging, based on the reported combined measured and modelled data.

Styrene-maleic acid copolymer-encapsulated CORM2, a water-soluble carbon monoxide (CO) donor with a constant CO-releasing property, exhibits therapeutic potential for inflammatory bowel disease.

Carbon monoxide (CO), the physiological product of heme oxygenase during catabolic breakdown of heme, has versatile functions and fulfills major anti-oxidative and anti-apoptotic roles in cell systems. Administration of CO is thus thought to be a reasonable therapeutic approach in diseases-such as inflammatory bowel disease-that are induced by reactive oxygen species (ROS). Tricarbonyldichlororuthenium(II) dimer (CORM2) is a commonly used CO donor, but it has poor aqueous solubility and a very short CO-releasing half-life (t1/2). In the present study, we prepared micelles consisting of water-soluble styrene-maleic acid copolymer (SMA) encapsulating CORM2 (SMA/CORM2) that had a hydrodynamic size of 165.3nm. Compared with free CORM2, SMA/CORM2 demonstrated better water solubility (>50mg/ml in a physiological water solution). Moreover, because of micelle formation in an aqueous environment, the CO release rate was slow and sustained. These properties resulted in much longer in vivo bioactivity of SMA/CORM2 compared with that of free CORM2, i.e. the t1/2 in blood of SMA/CORM2 in mice after intravenous (i.v.) injection was about 35 times longer than that of free CORM2. We then evaluated the therapeutic potential of SMA/CORM2 in a murine model of inflammatory colitis induced by dextran sulfate sodium (DSS). Administration (either i.v. or oral) of SMA/CORM2 once at the beginning of colitis, 3days after DSS treatment, significantly improved colitis symptoms-loss of body weight, diarrhea, and hematochezia-as well as histopathological colonic changes-shortening of the colon and necrosis or ulcers in the colonic mucosa. Up-regulation of inflammatory cytokines including monocyte chemotactic protein-1, tumor necrosis factor-α, and interleukin-6 in this DSS-induced colitis was significantly suppressed in SMA/CORM2-treated mice. SMA/CORM2 may thus be a superior CO donor and may be a candidate drug, which involves cytokine suppression, for ROS-related diseases including inflammatory bowel disease.

[Influence of genetic polymorphisms of epoxide hydrolase 1 on metabolism of styrene in body].

OBJECTIVE: To investigate the role of genetic polymorphisms of epoxide hydrolase 1 (EPHX1) in the metabolism of styrene in vivo. METHODS: Fifty-six styrene-exposed workers, who worked in the painting workshop of an enterprise for manufacturing glass fiber-reinforced plastic yachts in Shandong Province, China for over one year and were protected in approximately the same way, were selected as study subjects. The 8-hour time-weighted average concentration (8 h-TWA) of styrene and the concentrations of mandelic acid (MA) and phenyl glyoxylic acid (PGA) as urinary metabolites were measured. The genetic polymorphisms of EPHX1 were detected by polymerase chain reaction-restriction fragment length polymorphism analysis. RESULTS: The urinary concentrations of MA and PGA were 177.25±82.36 mg/g Cr and 145.91±69.73 mg/g Cr, respectively, and the 8 h-TWA of styrene was 133.28±95.81 mg/m3. Urinary concentrations of MA and PGA were positively correlated with 8 h-TWA of styrene (R=0.861, P < 0.05; R=0.868, P < 0.05). The subjects were divided into high-exposure group (8 h-TWA >50 mg/m(3)) and low-exposure group (8 h-TWA ≤ 50 mg/m(3), and in the two groups, the urinary concentrations of MA and PGA were significantly higher in the individuals carrying high-activity genotypes of EPHX1 than in those carrying low-activity genotypes of EPHX1 (P < 0.05). CONCLUSION: Genetic polymorphisms of EPHX1 play an important role in the metabolic process of styrene in vivo.

Physiologically based pharmacokinetic/toxicokinetic modeling.

Physiologically based pharmacokinetic (PBPK) models differ from conventional compartmental pharmacokinetic models in that they are based to a large extent on the actual physiology of the organism. The application of pharmacokinetics to toxicology or risk assessment requires that the toxic effects in a particular tissue are related in some way to the concentration time course of an active form of the substance in that tissue. The motivation for applying pharmacokinetics is the expectation that the observed effects of a chemical will be more simply and directly related to a measure of target tissue exposure than to a measure of administered dose. The goal of this work is to provide the reader with an understanding of PBPK modeling and its utility as well as the procedures used in the development and implementation of a model to chemical safety assessment using the styrene PBPK model as an example.

A drug-in-adhesive matrix based on thermoplastic elastomer: evaluation of percutaneous absorption, adhesion, and skin irritation.

A novel drug-in-adhesive matrix was designed and prepared. A thermoplastic elastomer, styrene-isoprene-styrene (SIS) block copolymer, in combination with tackifying resin and plasticizer, was employed to compose the matrix. Capsaicin was selected as the model drug. The drug percutaneous absorption, adhesion properties, and skin irritation were investigated. The results suggested that the diffusion through SIS matrix was the rate-limiting step of capsaicin percutaneous absorption. [SI] content in SIS and SIS proportions put important effects on drug penetration and adhesion properties. The chemical enhancers had strong interactions with the matrix and gave small effect on enhancement of drug skin permeation. The in vivo absorption of samples showed low drug plasma peaks and a steady and constant plasma level for a long period. These results suggested that the possible side effects of drug were attenuated, and the pharmacological effects were enhanced with an extended therapeutic period after application of SIS matrix. The significant differences in pharmacokinetic parameters produced by different formulations demonstrated the influences of SIS copolymer on drug penetrability. Furthermore, the result of skin toxicity test showed that no skin irritation occurred in guinea pig skin after transdermal administration of formulations.

Using population physiologically based pharmacokinetic modeling to determine optimal sampling times and to interpret biological exposure markers: The example of occupational exposure to styrene.

BACKGROUND: Biomonitoring of chemicals in the workplace provides an integrated characterization of exposure that accounts for uptake through multiple pathways and physiological parameters influencing the toxicokinetics. OBJECTIVES: We used the case of styrene to (i) determine the best times to sample venous blood and end-exhaled air, (ii) characterize the inter-individual variability in biological levels following occupational exposure and (iii) propose biological limit values using a population physiologically based pharmacokinetic (PBPK) model. METHODS: We performed Monte Carlo simulations with various physiological, exposure and workload scenarios. Optimal sampling times were identified through regression analyses between levels in biological samples and 24-h area under the arterial blood concentration vs. time curve. We characterized the variability in levels of styrene in biological samples for exposures to a time weighted average (TWA) of 20ppm. RESULTS: Simulations suggest that the best times to sample venous blood are at the end of shift in poorly ventilated workplaces and 15min after the shift in highly ventilated workplaces. Exhaled air samples are most informative 15min after the shift. For a light workload, simulated styrene levels have a median (5th-95th percentiles) of 0.4mg/l (0.2-0.6) in venous blood at the end of shift and 0.5ppm (0.3-0.8) in exhaled air 15min after the end of shift. CONCLUSION: This study supports the current BEI(®) of the ACGIH of 0.2mg/l of styrene in venous blood at the end of shift and indicates a biological limit value of 0.3ppm in end-exhaled air 15min after the end of shift.

Simultaneous determination of aromatic acid metabolites of styrene and styrene-oxide in rat urine by gas chromatography-flame ionization detection.

A convenient and reliable gas chromatographic method was developed for the simultaneous determination of six aromatic acid metabolites of styrene and styrene-oxide in rat urine; i.e., benzoic (BA), phenylacetic (PAA), mandelic (MA), phenylglyoxylic (PGA), hippuric (HA) and phenylaceturic (PAUA) acids. The method involves a one-pot esterification-extraction procedure, performed directly on urine without prior treatment. Analyses were performed on a RTX-1701 capillary column and the recovered isopropyl esters derivatives were detected by flame ionization detection. The analytical method was validated for selectivity, linearity, detection and quantification limits, recovery and intra-day and inter-day precisions. Calibration curves showed linearity in the range of 8-800 mg/L, except for HA and PAUA (40-800 mg/L). Limits of detection were between 0.2 (PPA) and 7.0 (PAUA) mg/L. The intra-day precisions determined at three concentrations levels were less than 5% for BA, PAA, MA and PGA and 9% for HA and PAUA, respectively. The corresponding mean inter-day precisions for these two groups were 8 and 16%, respectively. The method was successfully applied to quantitatively analyze styrene, styrene-oxide, ethylbenzene and toluene metabolites in urine samples from rats exposed by inhalation to these compounds at levels close to the occupational threshold limit values. Provided that this method can be transposed to human urine, it could have applications as part of biological monitoring for workers exposed to styrene or related compounds.

Assessing the impact of the duration and intensity of inhalation exposure on the magnitude of the variability of internal dose metrics in children and adults.

The objective of this study was to assess the impact of the exposure duration and intensity on the human kinetic adjustment factor (HKAF). A physiologically based pharmacokinetic model was used to compute target dose metrics (i.e. maximum blood concentration (C(max)) and amount metabolized/L liver/24 h (Amet)) in adults, neonates (0-30 days), toddlers (1-3 years), and pregnant women following inhalation exposure to benzene, styrene, 1,1,1-trichloroethane and 1,4-dioxane. Exposure scenarios simulated involved various concentrations based on the chemical's reference concentration (low) and six of U.S. EPA's Acute Exposure Guideline Levels (AEGLs) (high), for durations of 10 min, 60 min, 8 h, and 24 h, as well as at steady-state. Distributions for body weight (BW), height (H), and hepatic CYP2E1 content were obtained from the literature or from P3M software, whereas blood flows and tissue volumes were calculated from BW and H. The HKAF was computed based on distributions of dose metrics obtained by Monte Carlo simulations [95th percentile in each subpopulation/median in adults]. At low levels of exposure, ranges of C(max)-based HKAF were 1-6.8 depending on the chemical, with 1,4-dioxane exhibiting the greatest values. At high levels of exposure, this range was 1.1-5.2, with styrene exhibiting the greatest value. Neonates were always the most sensitive subpopulation based on C(max), and pregnant women were most sensitive based on Amet in the majority of the cases (1.3-2.1). These results have shown that the chemical-specific HKAF varies as a function of exposure duration and intensity of inhalation exposures, and sometimes exceeds the default value used in risk assessments.

Detection of phenolic metabolites of styrene in mouse liver and lung microsomal incubations.

Metabolic activation is considered to be a critical step for styrene-induced pulmonary toxicity. Styrene-7,8-oxide is a primary oxidative metabolite generated by vinyl epoxidation of styrene. In addition, urinary 4-vinylphenol (4-VP), a phenolic metabolite formed by aromatic hydroxylation, has been detected in workers and experimental animals after exposure to styrene. In the present study, new oxidative metabolites of styrene, including 2-vinylphenol (2-VP), 3-vinylphenol (3-VP), vinyl-1,4-hydroquinone, and 2-hydroxystyrene glycol were detected in mouse liver microsomal incubations. The production rates of 2-VP, 3-VP, 4-VP, and styrene glycol were 0.0527 ± 0.0045, 0.0019 ± 0.0006, 0.0053 ± 0.0002, and 4.42 ± 0.33 nmol/(min · mg protein) in mouse liver microsomes, respectively. Both disulfiram (100 µM) and 5-phenyl-1-pentyne (5 µM) significantly inhibited the formation of the VPs and styrene glycol. 2-VP, 3-VP, and 4-VP were metabolized in mouse liver microsomes at rates of 2.50 ± 0.30, 2.63 ± 0.13, and 3.45 ± 0.11 nmol/(min · mg protein), respectively. The three VPs were further metabolized to vinylcatechols and/or vinyl-1,4-hydroquinone and the corresponding glycols. Pulmonary toxicity of 2-VP, 3-VP, and 4-VP was evaluated in CD-1 mice, and 4-VP was found to be more toxic than 2-VP and 3-VP.

Role of metabolic activation and the TRPA1 receptor in the sensory irritation response to styrene and naphthalene.

The current study was aimed at examining the role of cytochrome P450 (CYP450) activation and the electrophile-sensitive transient receptor potential ankyrin 1 receptor (TRPA1) in mediating the sensory irritation response to styrene and naphthalene. Toward this end, the sensory irritation to these vapors was measured in female C57Bl/6J mice during 15-min exposure via plethysmographic measurement of the duration of braking at the onset of each expiration. The sensory irritation response to 75 ppm styrene and 7 ppm naphthalene was diminished threefold or more in animals pretreated with the CYP450 inhibitor metyrapone, providing evidence of the role of metabolic activation in the response to these vapors. The sensory irritation response to styrene (75 ppm) and naphthalene (7.6 ppm) was virtually absent in TRPA1-/- knockout mice, indicating the critical role of this receptor in mediating the response. Thus, these results support the hypothesis that styrene and naphthalene vapors initiate the sensory irritation response through TRPA1 detection of their CYP450 metabolites.

Use of the CYP2E1 genotype and phenotype for the biological monitoring of occupational exposure to styrene.

The CYP2E1 has been identified as the main cytochrome P450 isoform involved in human styrene metabolism. CYP2E1 presents polymorphism in humans and the different genotypes may, at least partly, be related to the different levels of individual expression of enzyme activity. We studied whether the genetic polymorphisms and phenotype of CYP2E1 modulate the level of urinary styrene metabolites and if they can be used for assessing risks of occupational exposure to styrene. A population of 49 male workers exposed to styrene (average level 362.7mg/m(3)) and a control group were selected. Samples of urine, blood and buccal swab were taken to determine the urinary biological indicators (phenylglyoxylic acid and mandelic acid), to quantify mRNA of CYP2E1 in blood using RT-PCR and to analyse different polymorphisms of enzyme CYP2E1 from buccal swab. We found decreased expression of mRNA of the enzyme, as well as decreased excretion of the styrene metabolites in individuals carrying the CYP2E1*5B heterozygote allele (cl/c2) with respect to the wild-type homozygote (c1/c1), which indicates a reduction in the inducibility of the enzyme in the presence of this polymorphism. The results show that the combined effect of both the CYP2E1 phenotype, measured by the expression of the specific mRNA in blood samples, and the CYP2E1*5B allele genotype, may explain the variability of urinary excretion of the styrene metabolites.

Assessing variability and comparing short-term biomarkers of styrene exposure using a repeated measurements approach.

The aim of this work is to compare several short-term biomarkers of styrene exposure, namely urinary styrene (StyU), mercapturic acids (M1+M2), mandelic acid (MA), phenylglyoxylic acid (PGA), phenylglycine (PHG), and 4-vinylphenol conjugates (VP), for use as biomarkers of exposure in epidemiologic studies. A repeated measurements protocol (typically 4 measurements per worker over 6 weeks) was applied to measure airborne styrene (StyA) and urinary biomarkers in 10 varnish and 8 fiberglass reinforced plastic workers. Estimated geometric mean personal exposures to StyA were 2.96mg/m(3) in varnish workers and 15.7mg/m(3) in plastic workers. The corresponding levels of StyU, M1+M2, MA, PGA, MA+PGA, PHG and VP were 5.13microg/L, 0.111, 38.2, 22.7, 62.6, 0.978, and 3.97mg/g creatinine in varnish workers and 8.38microg/L, 0.303, 146, 83.4, 232, 2.85 and 3.97mg/g creatinine in plastic workers. Within-worker (sigma(wY)(2)) and between-worker (sigma(bY)(2)) variance components were estimated from the log-transformed data as were the corresponding fold ranges containing 95% of the respective lognormal distributions of daily levels ((w)R(0.95)) and subject-specific mean levels ((b)R(0.95)). Estimates of (w)R(0.95) (range: 4-26) were generally smaller than those of (b)R(0.95) (range: 5-790) for both environmental and biological markers; this indicates that exposures varied much more between workers than within workers in these groups. Since attenuation bias in an estimated exposure-response relationship increases with the variance ratio lambda=sigma(wY)(2)/sigma(bY)(2), we estimated values of lambda for all exposure measures in our study. Values of lambda were typically much less than one (median=0.220) and ranged from 0.089 for M1+M2 in plastic workers to 1.38 for PHG in varnish workers. Since values of lambda were 0.147 and 0.271 for StyA in varnish workers and plastic workers, respectively, compared to 0.178 and 0.210 for MA in the same groups, our results suggest that either air measurements or conventional biomarker measurements (urinary MA) would be comparable surrogates for individual exposures in epidemiologic studies.

[Association between CYP2B6, CYP2D6, GSTP1 genetic polymorphisms and urinary styrene metabolites in professional workers].

OBJECTIVE: To evaluate the influence of individual genetic polymorphisms of metabolic enzymes on urinary styrene metabolites. METHODS: 58 workers occupationally exposed to styrene were divided into the high exposure group (≥ 100 mg/m³) and the low exposure group (< 100 mg/m³). The microfluidic chip technology was used to determine the SNPs of CYP2B6, CYP2D6 and GSTP1 and the influence of gene polymorphisms on the metabolism of styrene was statistically analyzed. RESULTS: The level of urine styrene metabolites level was influenced by genotypes of CYP2B6, CYP2D6 and GSTP1 [(280.28 +/- 100.60) mg/g Cr vs (183.48 +/- 127.52) mg/g Cr, (233.04 +/- 77.56) mg/g Cr vs (152.46 +/- 95.47) mg/g Cr, (32.88 +/- 7.14) mg/g Cr vs (24.47 +/- 5.59) mg/g Cr, P < 0.05)]. The metabolism of CYP2B6 G/G homozygotic genotype to styrene was more active than G/T heterozygotic genotype and T/T mutation genotype. The level of PHEMA in GSTP1 homozygotic genotype subjects was significantly higher than that in the group of homozygotic genotype [(32.07 +/- 7.32) mg/g Cr vs (25.59 +/- 6.95) mg/g Cr, P < 0.05)]. The influence of CYP2D6 genotypes on urinary metabolites was also observed in the same study [(56.36 +/- 109.72) mg/g Cr vs (177.13 +/- 116.21) mg/g Cr, (118.73 +/- 84.55) mg/g Cr vs (148.48 +/- 99.83) mg/g Cr, (18.29 +/- 13.50) mg/g Cr vs (19.95 +/- 13.30) mg/g Cr, P < 0.05)]. CONCLUSION: Genotypes of CYP2B6, GSTP1 and CYP2D6 are related to susceptibility to the metabolism of styrene in human.

Critical appraisal of the expression of cytochrome P450 enzymes in human lung and evaluation of the possibility that such expression provides evidence of potential styrene tumorigenicity in humans.

Styrene is widely used with significant human exposure, particularly in the reinforced plastics industry. In mice it is both hepatotoxic and pneumotoxic, and this toxicity is generally thought to be associated with its metabolism to styrene oxide. Styrene causes lung tumors in mice but not in rats. The question is how the tumorigenic effect in mouse lung may relate to the human. This review examines the comparison of the metabolic activation rates (1) between the liver and lung and (2) for the lung, between the rodent and human. Emphasis is placed on the specific cytochromes P450 present in the lungs of humans and what role they might play in the bioactivation of styrene and other compounds. In general, pulmonary metabolism is very slow compared to hepatic metabolism. Furthermore, metabolic rates in humans are slow compared to those in rats and mice. There is a wide difference in what specific cytochromes P450 investigators have reported as being present in human lung which makes comparisons, both inter-species and inter-organ, difficult. The general low activity for cytochrome P450 activity in the lung, especially for CYP2F1, the human homolog for CYP2F2 which has been identified in mice as being primarily responsible for styrene metabolism, argues against the hypothesis that human lung would produce enough styrene oxide to damage pulmonary epithelial cells leading to cell death, increased cell replication and ultimately tumorigenicity, the presumed mode of action for styrene in the production of the mouse lung tumors.

Biomonitoring as a tool in the human health risk characterization of dermal exposure.

Dermal exposure is an important factor in risk characterization. In occupational settings it becomes relatively more important because of the continuous reduction in inhalation exposure. In the public health arena, dermal exposure may also form a significant contribution to the total exposure. Dermal exposure, however, is difficult to assess directly because it is determined by a host of factors, which are difficult to quantify. As a consequence, dermal exposure is often estimated by application of models for external exposure. In combination with modeled or measured data for percutaneous penetration, these provide an estimate for the internal exposure that is directly related to the systemic effects. The advantages and drawbacks of EASE (Estimation and Assessment of Substance Exposure) and RISKOFDERM (Risk Assessment of Occupational Dermal Exposure), two models for external exposure that are mentioned in the Technical Guidance Document for the European Union risk assessments performed under the Existing Substances Regulation (EEC/793/93), are discussed. Although new chemicals regulation (REACh, 1907/2006/EC) is now in place in the European Union, the principles applied under the previous legislation do not change and the same models will continue to be used. The results obtained with these models for styrene, 2-butoxyethanol, and 1-methoxy-2-propanol in specific exposure scenarios are compared with an alternative method that uses biomonitoring data to assess dermal exposure. Actual external exposure measurements combined with measured or modeled percutaneous penetration data give acceptable results in risk assessment of dermal exposure, but modeled data of external dermal exposure should only be used if no other data are available. However, if available, biomonitoring should be considered the method of choice to assess (dermal) exposure.