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Occurrence of styrene-7,8-oxide and styrene glycol in mouse after the administration of styrene.

Styrene-7,8-oxide and its hydrated product styrene glycol were determined in mouse tissues at different times (0.5-5 h) after the intraperitoneal administration of 7-[14C]-styrene (3.8 mmol/kg). In a study of the influence of dose on the metabolite pattern of styrene, mice were killed 2 h after a dose of 1.1, 2.3, 3.4, and 5.1 mmol/kg, respectively. The mouse tissues studied (blood, liver, kidney, lung, brain, subcutaneous adipose tissue) were isolated and extracted first with hexane to remove styrene and styrene-7,8-oxide and then with ethyl acetate to remove styrene glycol. beta-Glucuronidase was used to liberate conjugated styrene glycol. A gas-liquid chromatographic method based on the use of an electron capture detector (GLC-EC) was used to quantify styrene glycol, as well as styrene-7,8-oxide, after hydrolysis. In addition all homogenates and extracts were assayed by radioactivity counting. Styrene-7,8-oxide and styrene glycol reached maximum concentrations within 2 h. The highest levels of styrene-7,8-oxide were detected in the kidneys and subcutaneous adipose tissue, while the lungs showed the lowest levels. Styrene glycol was found in the highest concentrations in the kidneys, liver, blood, and lungs. The concentration of unmetabolized styrene increased exponentially at higher doses. There seemed to be a linear increase with the dose of styrene-7,8-oxide and styrene glycol in all the tissues studied. The more polar metabolites occurred at relatively lower levels in the liver and kidneys at higher doses. In a complementary study the epoxide hydratase inhibitor trichloropropene oxide was added to the removed tissues, and the hexane extracts were analyzed for styrene-7,8-oxide both by GLC-EC and mass spectrometry (GLC-MS).

Animals

Dosimetry of styrene 7,8-oxide in styrene- and styrene oxide-exposed mice and rats by quantification of haemoglobin adducts.

Rats (Sprague Dawley) and mice (NMRI) were administered nonlabelled or labelled styrene and styrene oxide by i.p. injection. Blood samples were collected 6 and 24 h after treatment for studies of dose-response and 6 h to 32 days after treatment for studies of adduct stability. Haemoglobin (Hb) and plasma protein adduct levels were determined by radioactivity measurements or, in the case of adducts to N-terminal valine in Hb, by the so-called N-alkyl Edman procedure. Adducts to N-terminal valine were found to be chemically stable during the life-span of the erythrocytes, whereas adducts to carboxylic acid residues showed a reduced stability. The Hb-adduct levels found after styrene oxide treatment were compatible with a linear dose-response at low doses (< or = 0.4 mmol/kg body weight). At higher doses the detoxification of styrene oxide was overloaded resulting in a higher than proportional increase in adduct levels. Saturation of detoxification of styrene oxide could also explain the non-linear dose-response relationship observed in the mouse following treatment with styrene. Styrene oxide gave 4-7 times higher adduct levels than styrene when administered to the animals at equimolar low concentration. For both compounds, the levels of adducts to N-terminal valine were 2-3 times higher in the mouse than in the rat. A comparison of Hb-adduct levels in the styrene-exposed animals with adduct levels in styrene-exposed reinforced plastics workers (Christakopoulos et al., Scand. J. Work Environ. Health, 19(4) (1993) 255-263) suggests that styrene is less effective in humans than in mice and rats.

Animals

Tissue distribution of styrene, styrene glycol and more polar styrene metabolites in the mouse.

A primary objective of the present investigation was to determine the tissue distribution of styrene, styrene glycol, and more polar metabolites in mice at different times (0.5-5 h) after the intraperitoneal administration of styrene (3.3 mmol/kg). Another aim was to determine the dose dependence of the metabolite pattern of styrene in the different tissues. The dose range chosen was 1.1-4.9 mmol of styrene/kg administered intraperitoneally, and the time delay 2 h after dosing. The highest initial concentrations of unchanged styrene were found in adipose tissue, pancreas, liver, and brain. Styrene glycol reached its maximum concentration within 1 h in most tissues. The levels in the kidneys, lungs, pancreas, and liver far exceeded those in subcutaneous adipose tissue. Only in the liver and kidneys was a notable amount of styrene glycol conjugated. Polar metabolites occurred to a considerable extent in the liver, kidneys, lungs, and plasma. The concentration of unmetabolized styrene seemed to increase exponentially with the dose in subcutaneous adipose tissue, liver, kidneys, lungs, and brain. No tendency towards a decreased relative occurrence of styrene glycol was observed at higher doses. However, when the dose was increased, the more polar metabolites occurred at relatively lower levels in all tissues except brain.

Animals

Toxicity of the components of styrene polymers: polystyrene, acrylonitrile-butadiene-styrene (ABS) and styrene-butadiene-rubber (SBR). Reactants and additives.

The toxicity of the components of styrene polymers, e.g., polystyrene, ABS and SBR, were reviewed with primary focus on the reactive monomers (except styrene) (e.g., acrylonitrile, butadiene) as well as on impurities and solvents such as benzene, hexane and methylethyl ketone, and additives such as phenyl-2-naphthylamine, di-n-butyl phthalate, and a number of peroxide initiators and flame retardants (e.g., 2,3-dibromopropanol, decadibromodiphenyl oxide and antimony trioxide). It is stressed that toxicity data are generally lacking for the majority of additives employed in the production of styrene polymers. Information is also lacking as to the numbers of individuals at potential risk and the extent of their exposure to the large number of additives employed.

1-Naphthylamine

Investigation of styrene in the liver perfusion/cell culture system. No indication of styrene-7,8-oxide as the principal mutagenic metabolite produced by the intact rat liver.

Mutagenic effect of styrene and styrene-7,8-oxide was studied with the isolated perfused rat liver as metabolizing system and Chinese hamster V79 cells as genetic target cells. Styrene-7,8-oxide which is mutagenic per se was rapidly metabolized by the perfused rat liver. Thus no mutagenic effect was detected neither in the perfusion medium nor in the bile. However when styrene was added to the perfusion system, an increase in V79 mutants was observed regardless of where in the circulating perfusion medium the V79 cells were placed: the same effect was obtained with V79 cells close to the liver as well as at a distance from the liver. No mutagenic effect was observed in the bile. Simultaneous analysis of the styrene-7,8-oxide concentration in the perfusion medium, suggest that this metabolite is not the cause of the mutagenic effect observed during perfusion with styrene. The effect of the two test compounds on some liver functions was also studied. Both styrene and styrene-7,8-oxide changed the bile flow without affecting bile acid secretion: styrene caused a reduction in bile flow as compared to control perfusions and styrene-7,8-oxide increased the bile flow. Styrene, but not styrene-7,8-oxide, reduced gluconeogenesis from lactate. Styrene had no effect on the liver's capacity to incorporate amino acids into plasma proteins, whereas styrene-7,8-oxide reduced the amino acid incorporation. The microsomal cytochrome P-450 content was not affected by the two test compounds. No alteration in microsomal N- and C-oxygenation of N,N-dimethylaniline (DMA) was observed with styrene-7,8-oxide or the lower styrene dose used (240 mumol), whereas the higher styrene concentration (480 mumol) reduced N-oxygenation and thus also the total DNA metabolism. It is suggested that the results on styrene and styrene-7,8-oxide found here using the liver perfusion/cell culture system mimic the metabolism expected to be found in the intact animal, thus indicating that styrene-7,8-oxide is not the principal mutagenic metabolite of styrene in vivo.

Animals

Effects of indomethacin and arachidonic acid on sister chromatid exchange induction by styrene and styrene-7,8-oxide.

Styrene is converted into styrene-7,8-oxide in human lymphocyte cultures, in a reaction probably mediated by oxyhemoglobin. As a consequence, styrene induces sister-chromatid exchanges (SCEs) in whole-blood lymphocyte cultures without exogenous metabolic activation systems. Another metabolic pathway that could be involved in the metabolism of styrene is cooxidation by prostaglandin-endoperoxide synthase (PES). To study the role of PES in the metabolism of styrene, human whole-blood lymphocyte cultures were treated for the entire culture time of 72-h with styrene (0.5 and 1 mM) or styrene-7,8-oxide (50 and 100 microM), in the presence and absence of 75 or 150 microM indomethacin (an inhibitor of PES) and arachidonic acid (substrate of PES). Indomethacin potentiated SCE induction by both styrene and styrene-7,8-oxide; a slight but statistically significant enhancement (16-32%; p < 0.05-p < 0.001) was observed in all treatments with styrene and at 150 microM indomethacin in the case of styrene-7,8-oxide. At 150 microM, arachidonic acid induced a 15-20% suppression (p < 0.01) in SCE induction by both styrene (1 mM only) and styrene-7,8-oxide (100 microM only). Indomethacin or arachidonic acid did not alone influence the frequency of SCEs. The results suggest that PES acts as an inactivation route for styrene and styrene-7,8-oxide in human whole-blood lymphocyte cultures, possibly through PES-mediated binding to glutathione.

Adult

[Inhibition of delta-aminolevulinic acid dehydratase by styrene and styrene oxide].

Effects of styrene and styrene oxide on delta-aminolevulinic acid dehydratase in rats were investigated, in vivo and in vitro. In the in vivo study, rats were exposed to styrene or styrene oxide intraperitoneally for seven days. delta-Aminolevulinic acid dehydratase in the erythrocyte was inhibited by both styrene and styrene oxide. The inhibition by styrene oxide had a clear dose-response relationship, but that by styrene did not. In the liver, however, these substances did not inhibit delta-aminolevulinic acid dehydratase. In the in vitro study, styrene oxide inhibited delta-aminolevulinic acid dehydratase both in the erythrocyte and in the liver, but styrene failed to inhibit it. These results suggest that styrene is metabolized to styrene oxide, and this metabolite inhibits delta-aminolevulinic acid dehydratase. It is also thought that the discrepancy of inhibition between the erythrocyte and the liver is due to a difference of distribution and metabolism of the substances.

Animals

In vitro transformation and tumor promotion studies of styrene and styrene oxide.

The carcinogenic properties of styrene and styrene oxide were investigated using C3H/10T1/2C18 cells as a test system. In vitro transformation was not observed for either of the two chemicals; however, styrene oxide at three different concentrations enhanced the morphological transformation in the two-stage transformation assay. 0.1, 1 and 10 microM styrene oxide added twice weekly resulted in 32.4, 26.8 and 31.4 per cent of the dishes with one or more type III foci. Styrene and styrene oxide were only slightly toxic to the cells at the concentrations used. Styrene oxide did not affect the growth rate of the C3H/10T1/2 cells at 10 microM. However, 100 microM styrene oxide added to logarithmically growing cells caused a significant decrease in growth rate within 24 to 48 h. The tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate inhibited DNA synthesis approximately 60% 8 h after initiation of treatment. When styrene oxide at concentrations up to 100 microM was tested in a similar experiment, however, no significant effect was observed. Total RNA synthesis increased by 70% 1.5 h after initiation of treatment at 1 microM styrene oxide; this effect was not seen after 24 h. Styrene oxide at concentrations of 1 and 0.1 microM stimulated the incorporation of [3H]choline into cells by approximately 20% during a 2 h incubation, the major site of incorporation being the nuclear-associated endoplasmic reticulum.

Animals

Sub-chronic effects of styrene and styrene oxide on lipid peroxidation and the metabolism of glutathione in rat liver and brain.

Sub-chronic effects of styrene and styrene oxide on lipid peroxidation, glutathione contents and glutathione reductase activities in the liver and brain were examined after intraperitoneal administration to rats 3 times a week for 7 weeks. Styrene (300, 400 and 500 mg/kg) and styrene oxide (200 and 300 mg/kg) increased lipid peroxidation in the liver after 7 weeks of treatment. Hepatic lipid peroxidation in the rats treated with a higher dose of styrene oxide (400 mg/kg) was significantly enhanced even after 2 weeks of treatment. On the other hand, no change in lipid peroxidation was observed in the brain under the above conditions. Neither glutathione contents nor glutathione reductase activities in the liver and brain were altered at 40 h after the last of these sub-chronic treatments. To elucidate the cause of lipid peroxidation, the time courses of glutathione content after treatment with either styrene or styrene oxide (300 mg/kg) were studied in more detail. Significant decreases in both the GSH and GSSG contents were detected shortly after these treatments and the levels recovered to the control values at 40 h in these organs, although the changes were less significant in the brain of rats treated with styrene. These results suggest that enhancement of lipid peroxidation in the liver after treatment with styrene or styrene oxide was a consequence of repeated depletions of glutathione to certain critical levels and delayed recovery of lipid peroxides.

Animals

Biological indicators of exposure in styrene polymerization workers. Styrene in blood and adipose tissue and mandelic and phenylglyoxylic acids in urine.

The concentrations of mandelic and phenylglyoxylic acids, urinary metabolites of styrene, and styrene in blood were determined for 491 styrene polymerization workers. Styrene in subcutaneous fat was determined for 25 workers. The levels of styrene exposure were estimated to be less than 10 ppm, and urinary metabolite and blood styrene concentrations indicated that significant recent exposure (within 4 h) had occurred among workers in areas of styrene polymerization and styrene monomer production. Styrene analysis of subcutaneous fat suggested that the monomer may have been present for as long as 3 d after exposure, a time when urinary metabolites and blood styrene were almost invariably undetectable. All three biological parameters were correlated with recency of exposure and estimated intensity of exposure within job categories.

Adipose Tissue

Influence of simultaneous exposure to acrylonitrile and styrene on the toxicity and metabolism of styrene in rats.

Nine groups of adult male rats were given different combinations of styrene and acrylonitrile and each chemical was administered at three doses (styrene 0, 5.8, and 11.6 mmol/kg, ip; acrylonitrile 0, 0.3, and 0.6 mmol/kg, po). The animals were killed 24 hr later and blood and urine samples were collected. The results of biochemical analyses due to the toxicity of both chemicals and of the determination of urinary metabolites of styrene were then subjected to a factorial (3 X 3) analysis of variance. There was: (1) a significant elevation of blood urea nitrogen (BUN) and serum glutamic-pyruvic transaminase (SGPT), and a diminution of urinary creatinine due to styrene; (2) an increase in serum creatinine and serum glutamicoxaloacetic transaminase (SGOT) due to styrene that was further increased by acrylonitrile; and (3) an increase in the concentrations of urinary metabolites (thioethers, mandelic, phenylglyoxylic, and hippuric acids) due to styrene that was considerably reduced by acrylonitrile. These results suggest that styrene causes renal toxicity which may be potentiated by acrylonitrile; furthermore, the significant diminution of the urinary metabolites of styrene due to acrylonitrile obscures interpretation of the results of the biological monitoring of exposure to styrene.

Acrylonitrile

Bacterial degradation of styrene involving a novel flavin adenine dinucleotide-dependent styrene monooxygenase.

By using styrene as the sole source of carbon and energy in concentrations of 10 to 500 microM, 14 strains of aerobic bacteria and two strains of fungi were isolated from various soil and water samples. In cell extracts of 11 of the bacterial isolates, a novel flavin adenine dinucleotide-requiring styrene monooxygenase activity that oxidized styrene to styrene oxide (phenyl oxirane) was detected. In one bacterial strain (S5), styrene metabolism was studied in more detail. In addition to styrene monooxygenase, cell extracts from strain S5 contained styrene oxide isomerase and phenylacetaldehyde dehydrogenase activities. A pathway for styrene degradation via styrene oxide and phenylacetaldehyde to phenylacetic acid is proposed.

Bacteria

A very sensitive gas chromatographic method for the evaluation of styrene oxidase and styrene oxide hydratase activities.

Styrene is a compound widely used in the manufacture of polystyrenic plastics and it has recently been shown to exert mutagenic effects after metabolic activation into styrene oxide by the microsomal mixed function oxidases; this oxide is further converted into inactive styrene glycol. In order to investigate the relative importance of activation and desactivation processes of styrene, we developed a gas chromatographic method which enables us to simultaneously measure styrene oxide and styrene glycol formed after incubation of styrene with microsomal preparations from different tissues. After selective extraction of the two compounds from the incubation mixture, they are derivatized with pentafluorobenzoyl chloride and measured by gas chromatography using an electron capture detector. The high sensitivity of the method, which allows 0.01 ng of both compounds to be measured, as well as its selectiveity, has permitted us to adequately evaluate the kinetic parameters of styrene oxidase and styrene oxide hydratase activities, as well as their modifications under the influence of various pretreatments of the animals.

Animals

Cytogenetic effects of styrene and styrene oxide.

Styrene and styrene oxide induce various cytogenetic effects, similar in both human lymphocytes in vitro and onion root-tip cells in vivo. Styrene appears to cause chromosome breakage in both systems, and in Allium it shows a strong c-mitotic effect. Styrene oxide, on the other hand, seems to destroy the tertiary folding of the chromatin. Cytotoxicity of styrene oxide is very high (complete mitotic inhibition occurs on 0.03% v/v) in human lymphocytes, whereas, in Allium, styrene is slightly more toxic than styrene oxide. Styrene glycol, a further metabolite of styrene oxide, does not cause mitotic inhibition.

Cells, Cultured

[Studies on the industrial styrene poisoning (Part X). Determination of styrene in biological materials by gas chromatography (author's transl)].

For monitoring solvents exposure, it is useful to determine not only metabolites of the solvents in urine but also the solvents themselves in blood and tissues. In a series of studies on the industrial styrene poisoning, we have been determining styrene in blood and other tissues as occasion calls. Our examination of the method is presented in this report. The outline on the method is as follows: Aliquots of 0.5g of tissues being added 5 ml of n-hexane are homogenized by a high-speed homogenizer (Polytoron) for 10 to 30 seconds and the filtrates containing extracts are analyzed for styrene by gas chromatography. The linearity was ascertained from the calibration curve obtained by adding the known quantities of styrene (4, 10, 20, 40, 100 ppm) to the blood, liver and adipose tissues of rats. Rates of recoveries of styrene from the above tissues were 92 to 101 per cent. Reproducibility of this method was examined by repeating determinations of styrene in the blood, liver and adipose tissues of rats exposed to 500 ppm styrene for 4 hours, the coefficients of variation being 2.8 to 14.0 per cent. There was an approximately linear relationship between the styrene concentration (0 to 1,000 ppm) of the exposed air and those in the blood of exposed rats. We conclude that our simple and rapid method is applicable to determination of solvents other than styrene in organs and tissues by combining suitable solvents for extraction and packings of gas chromatography.

Animals