The metabolism of styrene in the rat and the stimulatory effect of phenobarbital

Identification and hazard prediction of tattoo pigments by means of pyrolysis-gas chromatography/mass spectrometry

The implementation of regulation for tattoo ink ingredients across Europe has generated the need for analytical methods suitable to identify prohibited compounds. Common challenges of this subject are the poor solubility and the lack of volatility for most pigments and polymers applied in tattoo inks. Here, we present pyrolysis coupled to online gas chromatography and electron impact ionization mass spectrometry (py-GC/MS) as quick and reliable tool for pigment identification using both purified pigments and tattoo ink formulations. Some 36 organic pigments frequently used in tattoo inks were subjected to py-GC/MS with the aim to establish a pyrogram library. To cross-validate pigment identification, 28 commercially available tattoo inks as well as 18 self-made pigment mixtures were analyzed. Pyrograms of inks and mixtures were evaluated by two different means to work out the most reliable and fastest strategy for an otherwise rather time-consuming data review. Using this approach, the declaration of tattoo pigments currently used on the market could be verified. The pyrolysis library presented here is also assumed suitable to predict decomposition patterns of pigments when affected by other degradation scenarios, such as sunlight exposure or laser irradiation. Thus, the consumers’ risk associated with the exposure to toxicologically relevant substances that originate from pigment decomposition in the dermal layers of the skin can be assessed. Differentiation between more or less harmful pigments for this field of application now will become feasible.

Effects of Styrene-metabolizing Enzyme Polymorphisms and Lifestyle Behaviors on Blood Styrene and Urinary Metabolite Levels in Workers Chronically Exposed to Styrene

The aim of this study was to investigate whether genetic polymorphisms of CYP2E1, GSTM1, and GSTT1 and lifestyle habits (smoking, drinking, and exercise) modulate the levels of urinary styrene metabolites such as mandelic acid (MA) and phenylglyoxylic acid (PGA) after occupational exposure to styrene. We recruited 79 male workers who had received chronic exposure in styrene fiberglass-reinforced plastic manufacturing factories. We found that serum albumin was significantly correlated with blood styrene/ambient styrene (BS/AS), urinary styrene (US)/AS, and US/BS ratios as well as urinary metabolites, that total protein correlated with US/MA and US/PGA ratios, and that low density lipoprotein (LDL)-cholesterol significantly correlated with US/BS, US/MA, and US/PGA ratios. Multiple logistic regression analyses using styrene-metabolizing enzyme genotypes and lifestyle habits as dependent variables and blood and urine styrene concentrations and urine styrene metabolite levels as independent variables revealed that CYP2E1*5 was associated with the MA/US ratio and GSTM1 with US/BS, that a smoking habit was associated with US/AS and MA/US ratios and MA and PGA levels, and that regular exercise was correlated with PGA/US. In conclusion, the results suggested that genetic polymorphisms of styrene-metabolizing enzymes, lifestyle behaviors, and albumin and LDL-cholesterol serving as homeostasis factors together are involved in styrene metabolism.

Male reproductive impacts of styrene in rat

To determine the effect of styrene on the male reproductive function of rats, male Wistar rats received a daily intraperitoneal (ip) injection of the xenobiotic at a dose of 600 mg/kg body weight. Serum testosterone (T) level was measured in duplicate by radioimmunoassay (RIA). Blood luteinizing hormone (LH) and follicle stimulating hormone (FSH) concentrations were determined using enzyme-linked immunosorbent assay (ELISA). After 10 days of treatment, an increase of the relative weight of the testis occurred, but that of the seminal vesicles and prostate remained unchanged compared to controls injected with an equivalent volume of the vehicle (corn oil). Serum T concentration dropped, while serum hypophyse hormone levels increased. Testicular histological observations revealed a pronounced morphological alteration, with enlarged intracellular spaces, loosening of tissue, and dramatic loss of gametes in the lumen of the seminiferous tubules. Spermatogenesis damage was also confirmed by the decrease in motility and the number of epididymal spermatozoa of treated rats. According to these results, with regard to the lack of a dose response relationship in this study, we may conclude that the testis, precisely the germinal and Sertoli cells, are the major targets for styrene toxicity.

Chiral separations of mandelic acid by HPLC using molecularly imprinted polymers

Styrene is used in a variety of chemical industries. Environmental and occupational exposures to styrene occur predominantly through inhalation. The major metabolite of styrene is present in two enantiomeric forms, chiral R- and S- hydroxy-1-phenyl-acetic acid (R-and S-mandelic acid, MA). Thus, the concentration of MA, particularly of its enantiomers, has been used in urine tests to determine whether workers have been exposed to styrene. This study describes a method of analyzing mandelic acid using molecular imprinting techniques and HPLC detection to perform the separation of diastereoisomers of mandelic acid. The molecularly imprinted polymer (MIP) was prepared by non-covalent molecular imprinting using (+) MA, (-) MA or (+) phenylalanine, (-) phenylalanine as templates. Methacrylic acid (MAA) and ethylene glycol dimethacrylate (EGDMA) were copolymerized in the presence of the template molecules. The bulk polymerization was carried out at 4ºC under UV radiation. The resulting MIP was grounded into 25~44¼m particles, which were slurry packed into analytical columns. After the template molecules were removed, the MIP-packed columns were found to be effective for the chromatographic resolution of (±)-mandelic acid. This method is simpler and more convenient than other chromatographic methods.

Stereochemistry of styrene biotransformation

Metabolism of styrene, an important industrial monomer, is reviewed. Attention is focused on the stereoselectivity of its oxidation to 7,8-styrene oxide as well as on further stereoselective biotransformation by hydrolytic and mercapturic acid pathway. Toxic effects such as mutagenicity, genotoxicity, hepatotoxicity, and pneumotoxicity may be related to the ratio of styrene oxide enantiomers at the target site. In rats formation of the less mutagenic (S)-styrene oxide and a faster detoxication of the (R)-enantiomer is favored. In mice metabolic activation of styrene favors the formation of (R)-styrene oxide but this more toxic enantiomer is detoxified faster, so that a nearly racemic styrene oxide results. Stereochemistry of biotransformation can contribute to the species differences in toxicity but can hardly be interpreted as a crucial factor. Due to lack of relevant data the stereochemistry of human metabolism cannot be interpreted in relation to the toxic effects.

Styrene toxicity: an ecotoxicological assessment

Although other aromatic compounds (e.g., benzene, toluene, polycyclic aromatic hydrocarbons (PAH), etc.) have been thoroughly studied over the years, styrene has been given little attention probably due to its lower rate of industrial use. In addition, it is less toxic than benzene and PAH, proven carcinogens. However, it is classified as a mutagen and thus potentially carcinogenic. Its main use is in the production of the polymer polystyrene and in the production of plastics, rubber, resins, and insulators. Entry into the environment is mainly through industrial and municipal discharges. In this review, the toxicological effects of styrene on humans, animals, and plants are discussed. Its mode of entry and methods of monitoring its presence are examined. Although its effects on humans and aquatic life have been studied, the data on short- or long-term exposures to plants, birds, and land animals are insufficient to be conclusive. Since exposure to workers can result in memory loss, difficulties in concentration and learning, brain and liver damage, and cancer, development of accurate methods to monitor its exposure is essential. In addition, the review outlines the present state of styrene in the environment and suggests ways to deal with its presence. It might appear that the quantities are not sufficient to harm humans, but more data are necessary to evaluate its effect, especially on workers who are regularly exposed to it.

Effects of various pretreatments on the hepatotoxicity of inhaled styrene in the B6C3F1 mouse

1. The roles of cytochrome P450 monooxygenases (P450) and glutathione (GSH) in styrene hepatotoxicity were investigated in mice by pretreating with either phenobarbital (PB; P450 inducer), SKF 525A (P450 inhibitor), N-acetylcysteine (NAC; GSH precursor), or saline (vehicle control) prior to a 6-h exposure to either 500 ppm styrene on air. 2. Styrene caused hepatocellular degeneration or necrosis in all groups; these changes were more extensive and severe in mice pretreated with PB. Styrene significantly increased relative liver weights and serum ALT and SDH levels only in mice pretreated with PB. NAC did not prevent GSH depletion or hepatotoxicity. 3. In the fat of SKF 525A-pretreated mice a slight but statistically significant increase in styrene levels was observed, suggesting that metabolism was decreased; the SO/styrene ratio in the fat of PB-pretreated mice showed a slight, but statistically significant, increase indicating a slight increase in styrene metabolism. Neither SKF 525A nor PB caused changes in microsomal enzyme activity in vitro. 4. These results suggest that styrene may be activated by a pathway not totally dependent upon P450 enzyme activity, or more likely that PB and SKF 525A are not specific for the P450 enzymes involved in activation and detoxification of styrene.

The evidence for conjugated mandelic and phenylglyoxylic acids in the urine of rats dosed with styrene

Male Wistar rats were dosed intraperitoneally with styrene (400 mg/kg). Urine samples were collected over phosphate buffer, pH 6.5 for 24 h. Excretion of mandelic (MA) and phenylglyoxylic acid (PGA) amounted to 1.66 +/- 0.62 and 5.21 +/- 2.44% of dose, respectively, as determined by ion-pair HPLC. After acidic hydrolysis, the amount of MA and PGA found in urine increased to 2.10 +/- 0.84 and 6.81 +/- 3.20% (mean +/- S.D.; n = 7), respectively. A similar increase was observed after alkaline hydrolysis of urine samples. Differences between hydrolysed and non-hydrolysed samples were significant in the paired t-test (P < 0.05). Further, urine samples were fractionated by HPLC. Fractions were subjected to acidic hydrolysis and analysed by HPLC and GC/MS. Both MA and PGA were detected in the fraction which did not contain any of these metabolites before hydrolytic treatment. Thus, MA and PGA, which are used as biomarkers of exposure to styrene, form hydrolysable conjugates in the rat. At least a minor part of the total urinary MA and PGA is bound in these conjugates.

Styrene metabolism in Exophiala jeanselmei and involvement of a cytochrome P-450-dependent styrene monooxygenase

The yeast-like fungus Exophiala jeanselmei degrades styrene via initial oxidation of the vinyl side chain to phenylacetic acid, which is subsequently hydroxylated to homogentisic acid. The initial reactions are catalyzed by a NADPH- and flavin adenine dinucleotide-dependent styrene monooxygenase, a styrene oxide isomerase, and a NAD(+)-dependent phenylacetaldehyde dehydrogenase. The reduced CO-difference spectrum of microsomal preparations of styrene-grown cells shows a characteristic absorption maximum at 450 nm, which strongly suggests the involvement of a cytochrome P-450-dependent styrene monooxygenase. Inhibition of styrene monooxygenase activity in cell extracts by cytochrome P-450 inhibitors SKF-525-A, metyrapone, and CO confirms this assumption.

Species-specific pharmacokinetics of styrene in rat and mouse

The pharmacokinetics of styrene were investigated in male Sprague-Dawley rats and male B6C3F1 mice using the closed chamber technique. Animals were exposed to styrene vapors of initial concentrations ranging from 550 to 5000 ppm, or received intraperitoneal (i.p.) doses of styrene from 20 to 340 mg/kg or oral (p.o.) doses of styrene in olive oil from 100 to 350 mg/kg. Concentration-time courses of styrene in the chamber atmosphere were monitored and analyzed by a pharmacokinetic two-compartment model. In both species, the rate of metabolism of inhaled styrene was concentration dependent. At steady state it increased linearly with exposure concentration up to about 300 ppm; more than 95% of inhaled styrene was metabolized and only small amounts were exhaled unchanged. At these low concentrations transport to the metabolizing enzymes and not their metabolic capacity was the rate limiting step for metabolism. Pharmacokinetic behaviour of styrene was strongly influenced by physiological parameters such as blood flow and especially the alveolar ventilation rate. At exposure concentrations of styrene above 300 ppm the rate of metabolism at steady state was progressively limited by biochemical parameters of the metabolizing enzymes. Saturation of metabolism (Vmax) was reached at atmospheric concentrations of about 700 ppm in rats and 800 ppm in mice, Vmax being 224 mumol/(h.kg) and 625 mumol/(h.kg), respectively. The atmospheric concentrations at Vmax/2 were 190 ppm in rats and 270 ppm in mice. Styrene accumulates preferentially in the fatty tissue as can be deduced from its partition coefficients in olive oil:air and water:air which have been determined in vitro at 37 degrees C to be 5600 and 15. In rats and mice exposed to styrene vapors below 300 ppm, there was little accumulation since the uptake was rate limiting. The bioaccumulation factor body:air at steady state (K'st*) was rather low in comparison to the thermodynamic partition coefficient body:air (Keq) which was determined to be 420. K'st* increased from 2.7 at 10 ppm to 13 at 310 ppm in the rat and from 5.9 at 20 ppm to 13 at 310 ppm in the mouse. Above 300 ppm, K'st* increased considerably with increasing concentration since metabolism became saturated in both species. At levels above 2000 ppm K'st* reached its maximum of 420 being equivalent to Keq. Pretreatment with diethyldithiocarbamate, administered intraperitoneally (200 mg/kg in rats, 400 mg/kg in mice) 15 min prior to exposure of styrene vapours, resulted in effective inhibition of styrene metabolism, indicating that most of the styrene is metabolized by cytochrome P450-dependent monooxygenases.(ABSTRACT TRUNCATED AT 400 WORDS)

Biotransformation of diethenylbenzenes. III: Identification of metabolites of 1,3-diethenylbenzene in rat

1. Biotransformation of 1,3-diethenylbenzene (1) in rat gave four major metabolites, namely, 3-ethenylphenylglyoxylic acid (2), 3-ethenylmandelic acid (3), N-acetyl-S-[2-(3-ethenylphenyl)-2-hydroxyethyl]-L-cysteine (4) and N-acetyl-S-[1-(3-ethenylphenyl)-2-hydroxyethyl]-L-cysteine (5) were isolated from urine and identified by n.m.r. and mass spectrometry. 2. Four minor metabolites, 3-ethenylbenzoic acid (6), 3-ethenylphenylacetic acid (7), 3-ethenylbenzoylglycine (8) and 2-(3-ethenylphenyl)ethanol (9) were identified by g.l.c.-mass spectrometric analysis of urine extract derivatized in two different ways. 3. All identified metabolites are derived from 3-ethenylphenyloxirane (10), a reactive metabolic intermediate. No product of any metabolic transformation of second ethenyl group has been identified. However, several minor unidentified metabolites were detected by g.l.c.-mass spectrometry. 4. Total thioether excretion in 24 h urine after a single i.p. dose of 1 amounted to 28.3 +/- 3.5 dose (mean +/- SD). No significant differences in the thioether fraction were observed in the dose range 100-300 mg/kg. 5. Thioether metabolites consisted mainly of mercapturic acids 4 and 5. The ratio of metabolites 5 to 4 was 62:38. Each mercapturic acid consisted of two diastereomers. Their ratio, as determined by quantitative 13C-n.m.r. measurement was 95:5 and 79:21 for mercapturic acids 4 and 5, respectively.

The hearing loss associated with exposure to toluene is not caused by a metabolite

Exposure to toluene causes a marked hearing loss in rats, and this effect has been observed in some human solvent abusers. The issue of whether toluene or one of its metabolites is responsible for this effect has not been examined. To attempt to resolve this issue, we manipulated the metabolism, and thus the circulating levels, of toluene as follows. Two groups of rats were exposed to phenobarbital (PB) in their drinking water (0.1%) for seven days to induce detoxifying liver enzymes; two other groups had access to PB-free water. Then half of the rats exposed to PB or water were exposed to filtered air or a concentration of toluene expected to cause hearing loss. Levels of toluene in blood were markedly reduced by the PB and the excretion of hippuric acid was increased. All rats were tested for auditory sensitivity by brainstem auditory-evoked response (BAER) audiometry using a 16-kHz tone pip. The rats exposed to toluene alone showed a marked reduction in the integrated BAER waveform, indicative of the expected hearing deficit. None of the other treated rats showed any deviation from controls (i.e., water and air). These results provide strong evidence that toluene itself is responsible for the auditory dysfunction. Toluene also caused the rats to increase their fluid consumption and urine output; these effects were not altered by PB. Identification of toluene as the proximal ototoxicant should facilitate the search for the mechanism of this effect.

Metabolism of inhaled styrene in acetone-, phenobarbital- and 3-methylcholanthrene-pretreated rats: stimulation and stereochemical effects by induction of cytochromes P450IIE1, P450IIB and P450IA

1. The effect of various cytochrome P-450 inducers, namely acetone, phenobarbital (PB) and 3-methylcholanthrene (MC), on the pharmacokinetics of styrene metabolism was studied. 2. Styrene metabolism in vivo was studied measuring phenylglyoxylic acid (PGA), the enantiomers of mandelic acid (MA), and total thioethers excreted in the urine during a 24 h period of airborne exposure to styrene at 500 cm3/m3 (2100 mg/m3). In acetone-pretreated rats, PGA and MA and thioether formation were elevated 30-50%. The R/S ratio of MA enantiomers was about two in all styrene-exposed groups except PB-pretreated rats, which showed a ratio of four. 3. Styrene metabolism in liver microsomes measured in vitro was increased by styrene 140%, acetone plus styrene by 190%, methylcholanthrene plus styrene by 180% and phenobarbital plus styrene by 250%. 4. N-Nitrosodimethylamine demethylation (NDMAD) and 7-pentoxyresorufin dealkylation (PROD) in liver microsomes were enhanced 100-150% by styrene inhalation. The metabolism of 7-ethoxyresorufin was not significantly enhanced. 5. Monoclonal antibodies to P-450 IA1, IA2, IIB1 and IIE1 were utilized to identify cytochrome P-450s by Western blot analysis. These studies showed clearly that styrene inhalation induced principally cytochrome P450IE1, whereas styrene given by gavage at a high narcotic dosage induced both P450IIE1 (NDMAD, 60%) and P450IIB (PROD, 3000%). 6. Our conclusions are that styrene metabolism in vivo in both autoinduced and induced by other foreign compounds, that cytochrome P450IIE1 induction has a major impact on styrene metabolism and that P450IIB1 induction yields an altered MA metabolite enantiomer ratio.

Biotransformation of diethenylbenzenes. I. Identification of the main urinary metabolites of 1,4-diethenylbenzene in the rat

1. Biotransformation of 1,4-diethenylbenzene (1) in rat was studied. Six urinary metabolites, namely, N-acetyl-S-[2-(4-ethenylphenyl)-2-hydroxyethyl]-L-cysteine (3), N-acetyl-S-[1-(4-ethenylphenyl)-2-hydroxyethyl]-L-cysteine (4), N-acetyl-S-[1-(4-formylphenyl)-2-hydroxyethyl]-L-cysteine (5), 1-(4-ethenylphenyl)ethane-1,2-diol (6), 4-ethenylbenzoic acid (9) and 4-ethenylbenzoyl-glycine (12) were isolated and identified by n.m.r. and mass spectrometry. 2. G.l.c.-mass spectral analysis of the methylated urine extract allowed the identification of four other metabolites, as 4-ethenylphenylacetic acid (11), 4-ethenylphenylacetylglycine (13), 4-ethenylmandelic acid (7), and 4-ethenylphenylglyoxylic acid (8). 3. The structures of the identified metabolites indicate that the main reactive intermediate in the metabolism of 1 is 4-ethenylphenyloxirane (2). The first step in the biotransformation of 1, formation of an oxirane, is very similar to the metabolic activation of styrene. However, subsequent steps lead not only to analogues of styrene metabolites but also to oxidation of the second ethenyl group leading to compound(s) which may contribute to the toxicity of 1, e.g. to the aldehyde 5. 4. Rats dosed with a single i.p. dose of 1 excreted nearly 5.6% of the dose as the glycine conjugate 12, irrespective of the dose. 5. In contrast, the total thioether fraction decreased significantly with increasing dose, being 23 +/- 3, 17 +/- 5 and 12 +/- 1% of dose at 100, 200 and 300 mg/kg, respectively (mean +/- SD).

Review of the toxicology of styrene

Styrene is used in the production of plastics and resins, which include polystyrene resins, acrylonitrile-butadiene-styrene resins, styrene-acrylonitrile resins, styrene-butadiene copolymer resins, styrene-butadiene rubber, and unsaturated polyester resins. In 1985, styrene ranked in the top ten of synthetic organic chemicals produced in the U.S. This review focuses on various aspects of styrene toxicology including acute and chronic toxicity, carcinogenicity, genotoxicity, pharmacokinetics, effects on hepatic and extrahepatic xenobiotic-metabolizing enzymes, pharmacokinetic modeling, and covalent interactions with macromolecules. There appear to be many similarities between the toxicity and metabolism of styrene in rodents and humans. Needed areas of future research on styrene include studies on the molecular dosimetry of styrene in terms of both hemoglobin and DNA adducts. The results of such research should improve our ability to assess the relationship between exposure to styrene and surrogate measures of "effective dose", thereby improving our ability to estimate the effects of low-level human exposures.

Effects of various pretreatments on the acute nephrotoxic potential of styrene in Fischer-344 rats

The effects of various inducers and inhibitors of hepatic microsomal mixed-function oxidase (MFO) system and diethylmaleate treatment on styrene-induced acute nephrotoxicity in male Fischer-344 rats were studied. Groups of rats were pretreated with either 3-methylcholanthrene (15 mg/kg, i.p., 3 days), or phenobarbital (80 mg/kg, i.p., 3 days), or SKF525-A (50 mg/kg, i.p., 1 h), or piperonyl butoxide (300 mg/kg, i.p., 2 h), or diethylmaleate (400 mg/kg, i.p., 90 min) prior to an i.p. administration of styrene (0, 0.6 and 0.9 g/kg) in corn oil. The uptake of p-aminohippurate (PAH) by renal cortical slices, the morphology of renal cortices, as well as urinary excretion of N-acetyl-beta-D-glucosaminidase (NAG) and gamma-glutamyl transpeptidase (gamma-GT) of control and pretreated rats were examined 24 h after styrene. The inducers and inhibitors of MFO system failed to modify further the acute nephrotoxicity of styrene. On the other hand, diethylmaleate pretreatment not only reduced further the uptake of PAH, but also produced further significant increase in the urinary excretion of NAG and gamma-GT observed at the higher dose of styrene. Similarly, ultrastructural studies showed a moderate increase in the severity of kidney damage induced at the higher dose of styrene due to pretreatment with diethylmaleate. These data suggest that tissue glutathione concentrations and hence, corresponding conjugating activity might be important determinants of styrene nephrotoxicity. The results further indicate that a metabolic activation system not involving certain cytochrome P-450 might be responsible in styrene-induced nephrotoxicity.

Evaluation of the nephrotoxic potential of styrene in man and in rat

The urinary excretion of beta 2-microglobulin, retinol-binding protein and albumin was measured in 65 workers exposed to styrene at levels averaging 50 percent of the current threshold limit value (215 mg/m2) for 1-13 years (mean: 6 years). By comparison with a control group matched for age and socioeconomic status, no significant difference was observed in the urinary excretion of proteins. In rats, styrene was weakly nephrotoxic. No functional or morphological renal change could be disclosed in rats exposed to 565 mg of styrene/m3, 5 days/week for 13 weeks. The repeated i.p. injection of 1 g styrene/kg (1/5 of oral LD50) for 10 days induced only a slight tubular dysfunction as evidenced by a 5-fold increase in beta 2-microglobulinuria. Altogether, these epidemiological and experimental data suggest that the current threshold limit value for styrene (215 mg/m3) proposed by the American Conference of Governmental and Industrial Hygienists does not entail any risk of renal toxicity.

Determination of metabolites (including thioethers) of mutagens and/or carcinogens as exposure indicators

Biological assessment of exposure to environmental hazards offers the potential for: (1) evaluation of exposure to prevent health impairment and (2) early detection of health effects. Two main methods of assessment can be used: (1) evaluation of the biological specimen for the exposed chemical or its metabolites and (2) measurement of the biological or clinical effects. There has been rapid improvement in the sensitivity of analytical techniques in the last decade and biological specimens of trace quantity can now be used for routine determinations. In this paper the current practice for monitoring populations exposed to benzene, styrene trichloroethylene, tetrachloroethylene and to some mutagens/ carcinogens are described. The practical concerns associated with routine urinary analyses, such as sample collection, sample preparation and interpretation of results are also discussed.

Effect of in vitro exposure to styrene, styrene oxide, and other structurally related compounds on murine cell-mediated immunity

Spleen cells from C57BL/6 mice were exposed to nontoxic doses of styrene, styrene oxide, styrene glycol, allylbenzene, ethylbenzene and toluene. None of these compounds except allylbenzene showed any great suppression or stimulation of the cytotoxic-T lymphocyte response. Allylbenzene was a strong suppressor of the cytotoxic-T lymphocyte response but, like the other compounds, had no effect on natural cytotoxicity. Styrene glycol, ethylbenzene and toluene also did not suppress natural killer cell activity. In contrast, styrene, styrene oxide and allylbenzene were strong suppressors of natural killer cell activity. The natural killer cell inhibition caused by styrene oxide did not occur if treatment was performed at 0 degree C instead of 37 degrees C, and was reversed by the addition of 5 mM glutathione or a 30 min recovery period at 37 degrees C. The natural killer cell suppression caused by allylbenzene was not reversed by these methods. These compounds may be causing natural killer cell suppression by different mechanisms, depending on the compound under study, and on whether these compounds contain a double bond or an epoxide moiety.

Covalent binding of styrene and styrene-7,8-oxide to plasma proteins, hemoglobin and DNA in the mouse

The extent of covalent binding to plasma proteins, hemoglobin and guanine-N-7 in DNA was determined after intraperitoneal administration of radiolabelled styrene and styrene-7,8-oxide to mice. The degree of alkylation increased non-linearly with the dose. It was proportionally higher after the highest doses of styrene-7,8-oxide while the reverse was observed with respect to the ability of styrene to alkylate plasma proteins and DNA. Thus, a dose dependence was indicated in the elimination of both styrene and styrene-7,8-oxide. A comparison of the degree of alkylation of plasma proteins, hemoglobin and guanine-N-7 in DNA suggests that the two compounds are about equally effective as alkylating agents in vivo at moderate dose levels. At high doses styrene-7,8-oxide is the more effective alkylator. The alkylation of DNA in liver, brain and lung after administration of styrene-7,8-oxide exceeded that in spleen and testis.

Effect of blood on styrene oxidation in perfused rat liver

The oxidation of styrene to styrene oxide was studied in the isolated perfused rat liver in the presence and absence of blood at styrene concentrations of 2.5 and 50 mM. Erythrocytes contained in whole blood increased the levels of styrene glycol about 5 times after a short perfusion time with both concentrations. This increase was observed up to 1 h with 2.5 mM styrene. At both styrene concentrations styrene oxide was not detectable, either in the presence or absence of blood indicating that the liver was able completely to detoxify the styrene oxide produced by the mixed-function oxidases (MFO) and the oxyhemoglobin in the erythrocytes.

Uptake, distribution, metabolism, and elimination of styrene in man. A comparison between single exposure and co-exposure with acetone

Six male subjects were exposed for two hours during light physical exercise to 2.81 mmol/m3 (293 mg/m3) of styrene on one occasion and to a mixture of 2.89 mmol/m3 (301 mg/m3) of styrene and 21.3 mmol/m3 (1240 mg/m3) of acetone on another (combination study). About 68% of the dose (somewhat more than 4 mmol) of styrene was taken up. The arterial blood concentration of styrene reached a relatively stable level after about 75 minutes of exposure of about 18 and 20 mumol/l after the single and combined exposure, respectively. Calculated values of mean blood clearance were 1.9 l/min in the styrene study and 1.6 l/min in the combination study; the half life of styrene in blood was about 40 minutes in both studies. The concentration of non-conjugated styrene glycol increased linearly during exposure and reached about 3 mumol/l at the end of exposure and was eliminated with a half life of about 70 minutes. Styrene-7,8-oxide was detected and quantified in the blood in a complementary study. The half lives for the excretion of mandelic and phenylglyoxylic acid in the urine were about four and nine hours, respectively, in both studies.

A physiologically based description of the inhalation pharmacokinetics of styrene in rats and humans

A physiologically based pharmacokinetic model which describes the behavior of inhaled styrene in rats accurately predicts the behavior of inhaled styrene in humans. The model consists of a series of mass-balance differential equations which quantify the time course of styrene concentration within four tissue groups representing (1) highly perfused organs, (2) moderately perfused tissues such as muscle, (3) slowly perfused fat tissue, and (4) organs with high capacity to metabolize styrene (principally liver). The pulmonary compartment of the model incorporates uptake of styrene controlled by ventilation and perfusion rates and the blood:air partition coefficient. The metabolizing tissue group incorporates saturable Michaelis-Menten metabolism controlled by the biochemical constants Vmax and Km. With a single set of physiological and biochemical constants, the model adequately simulates styrene concentrations in blood and fat of rats exposed to 80, 200, 600, or 1200 ppm styrene (data from previously published studies). The simulated behavior of styrene is particularly sensitive to changes in the constants describing the fat tissue group, and to the maximum metabolic rate described by Vmax. The constants used to simulate the fate of styrene in rats were scaled up to represent humans. Simulated styrene concentrations in blood and exhaled air of humans are in good agreement with previously published data. Model simulations show that styrene metabolism is saturated at inhaled concentrations above approximately 200 ppm in mice, rats, and humans. At inhaled concentrations below 200 ppm, the ratio of styrene concentration in blood to inhaled air is controlled by perfusion limited metabolism. At inhaled concentrations above 200 ppm, this ratio is controlled by the blood:air partition coefficient and is not linearly related to the ratio attained at lower (nonsaturating) exposure concentrations. These results show that physiologically based pharmacokinetic models provide a rational basis with which (1) to explain the relationship between blood concentration and air concentration of an inhaled chemical, and (2) to extrapolate this relationship from experimental animals to humans.

Inhalation pharmacokinetics: evaluating systemic extraction, total in vivo metabolism, and the time course of enzyme induction for inhaled styrene in rats based on arterial blood:inhaled air concentration ratios

A method is described for evaluating systemic extraction of soluble vapors during inhalation exposures. The physiological basis of the method is the inability to achieve complete equilibrium of vapor between arterial blood and inhaled air whenever there is substantial extraction of the soluble vapor during a single pass through the systemic circulation. The technique was applied to estimate styrene extraction ratios at the end of 6-hr exposures in male rats exposed to various concentrations of inhaled styrene. From extraction ratios and several physiological constants, metabolic constants were evaluated for styrene metabolism in vivo. In naive rats, the maximum velocity of metabolism was 10.0 mg/kg/hr, and Km was of the order of 0.2 mg/liter. Pretreatment with pyrazole (320 mg/kg, 1/2 hr before exposure) essentially abolished in vivo styrene metabolism, while pretreatment with phenobarbital (80 mg/kg/day for the 4 days before styrene exposure) increased Vmax about sixfold. Prior exposure to styrene (1000 ppm for 6 hr/day on each of 4 days before experimentation) increased Vmax by a factor of 2. Significant induction of styrene metabolism in vivo was observed in 24-hr continuous exposure to 400, 600, or 1200 ppm. A curve fitting routine was employed with a physiological model of styrene inhalation kinetics to estimate the dynamics of the induction process in the 24-hr exposures. At 400 ppm, induction began after a lag of 15.5 hr, had a half-life of 3.5 hr, and reached 2.7 times the Vmax in naive rats. At 600 ppm, it began after 10.6 hr, proceeded with a half-life of 2.2 hr, and increased Vmax by 3.4 times. At 1200 ppm, induction began earlier, 4.6 hr, and reached a greater value, 4.4 times Vmax, but had a half-life similar to that at 600 ppm. No induction occurred in 48-hr exposure to 200 ppm. Induction complicates kinetic modeling of continuous inhalation with soluble, well-metabolized vapors because it is time and concentration dependent. These methods should prove useful for studying the in vivo metabolism of other soluble, well-metabolized vapors and for examining the time course of induction of the metabolizing enzymes for these chemicals.

The metabolism of 4-(4-hydroxyphenyl)butan-2-one (raspberry ketone) in rats, guinea-pigs and rabbits

1. The metabolism of 4-(4-hydroxyphenyl)butan-2-one(raspberry ketone) was studied in rats, guinea-pigs and rabbits. 2. Following intragastric dosage (1 mmol/kg) urinary metabolite excretion was nearly complete within 24 h, amounting to roughly 90% of the dose in all species. 3. The most prominent urinary metabolites were raspberry ketone and its corresponding carbinol, both largely conjugated with glucuronic acid and/or sulphate. The extent of ketone reduction was greatest in rabbits. 4. Oxidative metabolism included ring hydroxylation and side-chain oxidation. The latter pathway led to 1,2- and 2,3-diol derivatives. It is proposed that the latter undergo cleavage to furnish the C6-C3 and C6-C2 derivatives detected.

Styrene exposure and biologic monitoring in FRP boat production plants

A survey on styrene exposure was conducted in five small to medium-sized fiber-reinforced plastic (FRP) boat plants utilizing carbon felt dosimeters as personal and stationary samplers to measure 4h (TWA) exposure during workday afternoons. The heaviest exposure, up to 256 ppm by personal sampling and 174 ppm by stationary sampling, took place during the lamination on a mold to produce a boat shell, and the work inside narrow holds also resulted in exposures of a comparable degree. Styrene levels were much lower in other auxiliary works. The TWA of exposure in an entire boat production was estimated to be 40-50 ppm. Installation of several flexible hoses as an exhaust system was proved to be effective in decreasing the vapor concentration. Gas masks were also useful in reducing the exposure. Urine samples were collected from 96 male workers at the end of 8h work (4h in the morning and 4h in the afternoon) and also from 22 nonexposed male subjects, and analyzed for mandelic acid (MA), phenylglyoxylic acid (PhGA), and hippuric acid (HA). When the results of urinalyses were compared with 4-h styrene TWA as monitored by personal sampling, the best correlation was obtained with MA + PhGA/creatinine (the correlation coefficient, 0.88), followed by MA (0.84). For these two cases, regression lines and 95% confidence limits for the group means and for the individual values were calculated. The urinary level of MA, PhGA, and HA in the 22 nonexposed male subjects were also tabulated.

Mutagenicity of (R) and (S) styrene 7,8-oxide and the intermediary mercapturic acid metabolites formed from styrene 7,8-oxide

We have tested the two enantiomers of styrene 7,8-oxide and various thioether metabolites of racemic styrene 7,8-oxide for their direct mutagenicity in Salmonella typhimurium TA100. The mutagenicity data suggests that the (R) enantiomer is more mutagenic than the (S) enantiomer, with the racemic mixture intermediate between the two. The thioether metabolites were not mutagenic. The difference in the mutagenicities of enantiomers probably resulted from a stereoselective process in the Salmonella tester strain. At the present time it is not clear whether the rate-limiting reaction is the interaction of the enantiomers with DNA or some other cellular component.

Stereoselective oxidation of styrene to styrene oxide in rats as measured by mercapturic acid excretion

1. Administration of styrene (I) and styrene oxide (II) to rats resulted in the excretion of 2-hydroxymercapturic acids, N-acetyl-S-(1-phenyl-2-hydroxyethyl)cysteine (III) and N-acetyl-S-(2-phenyl-2-hydrosyethyl)cysteine (IV). Each appeared to be a mixture of diastereoisomers. 2. Administration of optically pure styrene oxide resulted in formation of one set of diastereoisomers. Racemic styrene oxide gave equal amounts of diastereoisomers. Thus the opening of the epoxide ring by glutathione S-transferases was stereospecific and the transferases showed no preference for one of the isomers of styrene oxide. 3. After administration of styrene the observed ratio of the diastereoisomers for both hydroxymercapturic acids was about 1:4. This leads to the conclusion that there is a stereoselective oxidation of styrene to styrene oxide, with a preference for the R-isomer.

Metabolism and acute hepatotoxicity of styrene oxide in rats

The metabolism and acute hepatotoxicity of styrene oxide were studied after ip administration of a high dose of 375 mg/kg to adult male rats. Liver glutathione was significantly depleted at 2 h, but became normal at 6 h. The activity of serum glutamic-oxaloacetic transaminase was increased during the entire period (24 h) of study, while the activities of alkaline phosphatase and serum glutamic-pyruvic transaminase were elevated at 2 and 24 h, respectively, after administration of the dose. Decreased body weights and increased liver weights were observed at 24 h. Both prothrombin time and urinary urobilinogen concentration were temporarily increased. While urinary mandelic and phenylglyoxylic acids were increased during the entire time period, urinary (but no fecal) nonprotein sulfhydryl contents were increased at 2 and 6 h. The results of biochemical tests of liver function suggest a mild liver pattern in rats treated acutely with styrene oxide.

Chromosomal aberrations and sister-chromatid exchanges in lymphocytes of men occupationally exposed to styrene in a plastic-boat factory

Workers in a Swedish factory making boats from plastics reinforced with glass fibre are exposed to a variety of chemicals, including styrene which is mutagenic after metabolic activation. The concentration of styrene in the air was measured in the breathing zones of workers occupied with various processes in boat making. Samples of air were taken 6 times during the years 1973-1978. The total exposure to styrene for the workers during this period was calculated and expressed as the average concentration in mg per m3 air during an 8-h workshift multiplied by the number of years of employment. A low-dose group (mean = 137 mg x m-3) and a high-dose group)mean - 1204 mg x m-3) were identified. Blood samples were taken in 1978 from workers belonging to the exposed groups and from a matched control group of employees in the same factory not exposed to styrene. Lymphocytes were cultured and examined for chromosomal aberrations and sister-chromatid exchanges. Exposed workers had a significantly (p less than 0.001) higher number of chromosomal aberrations (36 persons, mean = 7.9 aberrations/100 cells) compared with employees in the control group (37 persons, mean = 3.2 aberrations/100 cells). There was no significant difference between the mean values of the number of chromosomal aberrations between the highly exposed and the less exposed groups. But in the less exposed group there was an increase in the frequency of chromosomal aberrations with increasing exposure to styrene (r = 0.576). In the highly exposed group this dose response was not observed (r = 0.231). For the frequency of sister-chromatid exchanges (SCE) a slight (p less than 0.05) increase was found in the styrene-exposed group (20 persons, mean = 8.4 SCE/cell). The control group (21 persons) had a mean value of 7.5 SCE/cell. Again there was no difference between the highly exposed and the less exposed groups. Other environmental factors that may have clastogenic effects were studied, but multiple regression analysis failed to show a candidate responsible for the increase in chromosomal abnormalities in the exposed group.

Potential carcinogenic and mutagenic industrial chemicals. I. Alkylating agents

A variety of alkylating agents, acylating agents, peroxides, halogenated derivatives, and nitrogen derivatives have been reviewed, principally in terms of their synthesis, areas of utility, stability, distribution, reactivity, levels of exposure, population at risk, metabolism, carcinogenicity, and mutagenicity.

Non-linear kinetics of microsomal styrene monooxygenase after phenobarbital pre-treatment

Pretreatment of rats with phenobarbital, but not with 3-methylcholanthrene, induces liver microsomal styrene monooxygenase. Under these conditions the kinetic profile is not linear and can be divided into 2 distinct curves. Evidence is presented indicating that the combined treatment with phenobarbital and CoCl2 destroy the affinity enzyme, suggesting that the native cytochrome is less sensitive to the action of CoCl2.

Phenaceturic acid, a new urinary metabolite of styrene in the rat

1. After administration of styrene to rat, phenaceturic acid, a new metabolite, was isolated. After administration of d8-styrene to rat, deuterium-labelled phenaceturic acid was excreted in the urine. 2. Two metabolic pathways are proposed, based on mass spectra of the deuterium-labelled phenaceturic acid. 3. After a single dose of styrene (250 mg/kg), the excreted phenaceturic acid originating from styrene in the urine amounted to 1.4% dose.

Different role of biotransformation in the elimination of some important pharmaceuticals and industrial xenobiotics

Unlike lipophilic pharmaceuticals, many lipophilic industrial xenobiotics may be excreted unchanged due to their volatility. Consequently, enzyme induction of inhibition may thus affect only the rate of metabolism of the lipophilic drugs, whereas in case of volatile xenobiotics it is both the rate and the extent (metabolized portion) of their biotransformation which are influenced by these processes. The influence of these metabolic changes on the rate of elimination is more pronounced in lipophilic pharmaceuticals than in volatile xenobiotics whose alternative elimination via lungs compensates for the metabolic rate differences.

Isolation and structure determination of enzymatically formed styrene oxide glutathione conjugates

When styrene oxide was incubated with glutathione in the presence of rat liver cytosolic fraction, two conjugates were formed. Structural investigation by mass spectrometry (MS), proton magnetic resonance (PMR) analysis and chemical fragmentation showed the presence of two positional isomers, namely S-(1-phenyl-2-hydroxyethyl)glutathione and S-(2-phenyl-2-hydroxyethyl)glutathione in a ratio of approx. 60 : 40.

Effect of styrene and fiber glass on small airways of mice

Three groups of 20 mice each were exposed to respirable glass fibers, to 300 ppm styrene vapor, and to glass fibers plus 300 ppm styrene. The glass fiber concentration was congruent to 1070/cm3; fiber diameters were under 3 micron and fiber lenths under 10 microns. The 5 h/d, 5 d/wk inhalation experiment lasted 6 wk. Glass fibers did not cause any lung damage when inhaled separately but combined styrene and glass fibers induced a change in the cellularity of the bronchiolar lining, where aprocrine-type cells became predominant. The same type of bronchiolar epithelial change was found in 10% of the styrene-exposed mice, while most of the styrene-exposed animals (90%) presented thickened bronchiolar walls becasue of stratification of the bronchiolar epithelium.

Identification of three sulphur-containing urinary metabolites of styrene in the rat

1. After administration of styrene (1) to rat, three sulphur-containing urinary metabolites were isolated in the molar ratio of III : IV : V equal to 65 : 34 : 1. 2. These metabolites were identified as N-acetyl-S-(1-phenyl-2-hydroxyethyl)cysteine (III), N-acetyl-S-(2-phenyl-2-hydroxyethyl)cysteine (IV) and N-acetyl-S-(phenacyl)cysteine (V). 3. After a single dose (250 mg/kg, 2.4 mmol/kg) styrene, the totally excreted mercapturic acids in the urine amounted to 10.7 +/- 1.0% (n = 5) of the dose.

Vinyl chloride and vinyl benzene (styrene)--metabolism, mutagenicity and carcinogenicity

Vinyl chloride and vinyl benzene (styrene) are mutagenic in microbial tests, in Drosophila, in yeast, and in mammalian cells. Reports from various countries have shown an excess of chromosomal aberrations in the lymphocytes of workers exposed to vinyl chloride monomer when the workers were compared with controls. Workers occupationally exposed to styrene also revealed a clear increase in the rate of chromosome aberrations in their lymphocytes. Both chloroethylene oxide and styrene oxide, the primary biotransformation products of vinyl chloirde and styrene respectively, bind covalently to cellular macromolecules. Vinyl chloride is a carcinogen in both animals and man. Styrene is currently being tested in animals. These findings, the demonstration of mutagenic response via microbial and other test systems and with observations of significant excesses of chromosomal aberrations among workers exposed to these agents, raise scientific and health oriented concern about the possible genetic risks of vinyl chloride and styrene to man.