Bone marrow cell chromosomal aberrations and styrene biotransformation in mice given styrene on a repeated oral schedule

Investigations on the genotoxic potential of styrene in Fischer 344 rats using multiple endpoints

Genotoxicity of styrene monomer was evaluated in male Fischer 344 rats using the alkaline comet assay for DNA damage, micronucleus assay for cytogenetic damage and the Pig-a assay for gene mutations. In a dose range finding (DRF) study, styrene was administered by oral gavage in corn oil for 28 consecutive days at 0, 100, 500, and 1000 mg/kg/day. The bioavailability of styrene was confirmed in the DRF by measuring its plasma levels at approximately 7- or 15-min following dosing. The 1000 mg/kg/day group exceeded the maximum tolerated dose based on body weight and organ weight changes and signs of central nervous system depression. Based on these findings, doses of 0, 100, 250, and 500 mg/kg/day (for 28 or 29 days) were selected for the genotoxicity assays. Animals were sacrificed 3-4 h after treatment on Day 28 or 29 for assessing various genotoxicity endpoints. Pig-a mutant frequencies and micronucleus frequencies were determined in peripheral blood erythrocytes. The comet assay was conducted in the glandular stomach, duodenum, liver, lung, and kidney. These studies were conducted in accordance with the relevant OECD test guidelines. Oral administration of styrene did not lead to genotoxicity in any of the investigated endpoints. The adequacy of the experimental conditions was assured by including animals treated by oral gavage with the positive control chemicals ethyl nitrosourea and ethyl methane sulfonate. Results from these studies supplement to the growing body of evidence suggesting the lack of in vivo genotoxic potential for styrene.

Genotoxicity evaluation of orally administered styrene monomer in mice using comet, micronucleus, and Pig-a endpoints

Male B6C3F1 mice were administered styrene monomer by oral gavage for 29 consecutive days at dose levels of 0, 75, 150, or 300 mg/kg/day. The highest dose level represented the maximum tolerated dose based on findings in a 28-day dose range-finding study, in which the bioavailability of orally administered styrene was also confirmed. The positive control group received ethyl nitrosourea (ENU; 51.7 mg/kg/day) on Study Days 1-3 and ethyl methanesulfonate (EMS; 150 mg/kg/day) on Study Days 27-29 by oral gavage. Approximately 3 h following the final dose, blood was collected to assess erythrocyte Pig-a mutant and micronucleus frequencies. DNA strand breakage was assessed in glandular stomach, duodenum, kidney, liver, and lung tissues using the alkaline comet assay. The %tail DNA for stomach, liver, lung, and kidney in the comet assay among the styrene-treated groups was neither significantly different from the respective vehicle controls nor was there any dose-related increasing trend in any of the tissues; results for duodenum were interpreted to be inconclusive because of technical issues. The Pig-a and micronucleus frequencies among styrene-treated groups also did not show significant increases relative to the vehicle controls and there was also no evidence for a dose-related increasing trend. Thus, orally administered styrene did not induce DNA damage, mutagenesis, or clastogenesis/aneugenesis in these Organization of Economic Co-operation and Development test guideline-compliant genotoxicity studies. Data from these studies can contribute to the overall assessment of genotoxic hazard and risk posed to humans potentially exposed to styrene.

In vivo mutagenicity assessment of styrene in MutaMouse liver and lung

BACKGROUND

Styrene (CAS 100-42-5) is widely used as polystyrene and acrylonitrile-butadiene-styrene resin such as plastic, rubber, and paint. One of the primary uses of styrene is food utensils and containers, but a small amount of styrene transferred into food can be ingested by eating. Styrene is metabolized into styrene 7,8-oxide (SO). SO is mutagenic in bacteria and mouse lymphoma assays. It is clastogenic in cultured mammalian cells. However, styrene and SO are not clastogenic/aneugenic in rodents, and no rodent in vivo gene mutation studies were identified.

METHODS

To investigate the mutagenicity of orally administered styrene, we used the transgenic rodent gene mutation assay to perform an in vivo mutagenicity test (OECD TG488). The transgenic MutaMouse was given styrene orally at doses of 0 (corn oil; negative control), 75, 150, and 300 mg/kg/day for 28 days, and mutant frequencies (MFs) were determined using the lacZ assay in the liver and lung (five male mice/group).

RESULTS

There were no significant differences in the MFs of the liver and lung up to 300 mg/kg/day (close to maximum tolerable dose (MTD)), when one animal with extremely high MFs that were attributed to an incidental clonal mutation was omitted. Positive and negative controls produced the expected results.

CONCLUSIONS

These findings show that styrene is not mutagenic in the liver and lung of MutaMouse under this experimental condition.

Safety and efficacy of feed additives consisting of essential oils from the bark and the leaves of Cinnamomum verum J. Presl (cinnamon bark oil and cinnamon leaf oil) for use in all animal species (FEFANA asbl)

Following a request from the European Commission, the EFSA Panel on Additives and Products or Substances used in Animal Feed (FEEDAP) was asked to deliver a scientific opinion on the safety and efficacy of essential oils from the bark and the leaves of Cinnamomum verum J. Presl (cinnamon bark oil and cinnamon leaf oil), when used as sensory additives (flavourings) in feed and water for drinking for all animal species. Owing to the presence of styrene in the essential oils under assessment, the FEEDAP Panel is not in the position to conclude on the safety for long‐living animals and animals for reproduction. For ‘short‐living’ animals, the FEEDAP Panel concluded that cinnamon bark oil and cinnamon leaf oil are considered as safe up to the maximum proposed use levels in complete feed. For ‘short‐living’ animals, the Panel considered the use of cinnamon bark oil in water for drinking as safe provided that the total daily intake of the additive does not exceed the daily amount that is considered safe when consumed via feed. For cinnamon leaf oil, the proposed use level in water for drinking of 3 mg/L is considered as safe for ‘short‐living’ animals. No concerns for consumers were identified following the use of the additives at the use level considered safe in feed for the target species. Based on the presence of safrole ≥0.1%, cinnamon leaf oil and bark oil are classified as carcinogen (category 1B) and handled accordingly. The use of the additives under the proposed conditions in animal feed was not expected to pose a risk for the environment. Since C. verum and its preparations are recognised to flavour food and its function in feed would be essentially the same, no further demonstration of efficacy is considered necessary for cinnamon essential oils.

Safety and efficacy of a feed additive consisting of an essential oil from Cinnamomum cassia (L.) J. Presl (cassia leaf oil) for use in all animal species (FEFANA asbl)

Following a request from the European Commission, the EFSA Panel on Additives and Products or Substances used in Animal Feed (FEEDAP) was asked to deliver a scientific opinion on the safety and efficacy of an essential oil from leaves, stalks and twigs of Cinnamomum cassia (L.) J. Presl (cassia leaf oil) when used as a sensory additive (flavouring) in feed and water for drinking for all animal species. Owing to the presence of styrene in cassia leaf oil, the FEEDAP Panel is not in the position to conclude for long-living animals and animals for reproduction. For 'short-living' animals, the FEEDAP Panel concluded that cassia leaf oil is considered as safe up to the maximum proposed use levels in complete feed of 28.5 mg/kg for chickens for fattening and other minor poultry, 38 mg/kg for turkeys for fattening, 51 mg/kg for piglets and other minor Suidae, 61 mg/kg for pigs for fattening, 100 mg/kg for veal calves (milk replacer), 60 mg/kg for cattle for fattening and other ruminants for fattening, 30 mg/kg for horses, 25 mg/kg for rabbits, 125 mg/kg for salmonids and other fin fish. For the other minor species, the additive is considered as safe at 28.5 mg/kg complete feed. For 'short-living' animals, the FEEDAP Panel considered the use in water for drinking as safe provided that the total daily intake of the additive does not exceed the daily amount that is considered safe when consumed via feed. No concerns for consumers were identified following the use of the additive at the use levels considered safe in feed for the target species. When handling the essential oil, exposure of unprotected users to styrene cannot be excluded. Therefore, to reduce the risk, the exposure of the users should be minimised. The use of the additive under the proposed conditions in animal feed was not expected to pose a risk for the environment. Cassia leaf oil was recognised to flavour food. Since its function in feed would be essentially the same as that in food, no further demonstration of efficacy was considered necessary.

Assessment of the impact of the IARC Monograph Vol. 121 on the safety of the substance styrene (FCM No 193) for its use in plastic food contact materials

The EFSA Panel on Food Contact Materials, Enzymes and Processing Aids (CEP) was requested by the European Commission to re-evaluate the safety of styrene (FCM No 193) for use in plastic food contact materials (FCM) following the classification by the International Agency for Research on Cancer (IARC) as 'probably carcinogenic to humans'. The IARC Monograph pertains to hazard identification, based on studies on high-dose occupational exposures by inhalation and animal studies, also mainly by inhalation. The Panel considered that the IARC conclusions cannot be directly applied to the evaluation of risks for consumers from the oral exposure to styrene, but also concluded that, based on the data provided in the IARC Monograph and by the industry, a concern for genotoxicity associated with oral exposure to styrene cannot be excluded. The migration of styrene into foods packed in styrenic plastics is below 10 μg/kg for the majority of the foods, but up to 230 μg/kg was reported. Migration tends to be high for contact with fatty foods, and/or with high surface to volume ratios of the FCM. Dietary exposure of the consumers to styrene migrating from styrenic plastics was estimated in the order of 0.1 μg/kg body weight (bw) per day. It is in the same range as exposure from styrene present in foods as such. The dietary exposure (food component plus migration from styrenic plastics) is similar or lower than that by inhalation in the general population. Taking the human exposure data into account, the Panel concluded that a systematic review of genotoxicity and mechanistic data, comparative toxicokinetics and analysis of species differences is required for assessing the safety of styrene for its use in FCM.

Critical review of styrene genotoxicity focused on the mutagenicity/clastogenicity literature and using current organization of economic cooperation and development guidance

Styrene is an important high production volume chemical used to manufacture polymeric products. In 2018, International Agency for Research on Cancer classified styrene as probably carcinogenic to humans; National Toxicology Program lists styrene as reasonably anticipated to be a human carcinogen. The genotoxicity literature for styrene and its primary metabolite, styrene 7,8-oxide (SO), begins in the 1970s. Organization of Economic Cooperation and Development (OECD) recently updated most genotoxicity test guidelines, making substantial new recommendations for assay conduct and data evaluation for the standard mutagenicity/clastogenicity assays. Thus, a critical review of the in vitro and in vivo rodent mutagenicity/clastogenicity studies for styrene and SO, based on the latest OECD recommendations, is timely. This critical review considered whether a study was optimally designed, conducted, and interpreted and provides a critical assessment of the evidence for the mutagenicity/clastogenicity of styrene/SO. Information on the ability of styrene/SO to induce other types of genotoxicity endpoints is summarized but not critically reviewed. We conclude that when styrene is metabolized to SO, it can form DNA adducts, and positive in vitro mutagenicity/clastogenicity results can be obtained. SO is mutagenic in bacteria and the in vitro mouse lymphoma gene mutation assay. No rodent in vivo mutation studies were identified. SO is clastogenic in cultured mammalian cells. Although the in vitro assays gave positive responses, styrene/SO is not clastogenic/aneugenic in vivo in rodents. In addition to providing updated information for styrene, this review demonstrates the application of the new OECD guidelines for chemicals with large genetic toxicology databases where published results may or may not be reliable. Environ. Mol. Mutagen. 2019. © 2019 Wiley Periodicals, Inc.

Simultaneous determination of phenylglyoxylic acid, mandelic acid, styrene glycol and hippuric acid in primary culture of rat hepatocytes incubate by high-performance liquid chromatography

A simple HPLC method for the simultaneous determination of phenylglyoxylic acid (PGA), mandelic acid (MA), styrene glycol (SG) and hippuric acid (HA) in cell culture medium was developed. Analysis was performed on a C(18) column with a mobile phase composed of methanol-potassium dihydrogen phosphate (pH 2.5; 10 mM; 10:90, v/v) at 220 nm. The flow-rate of mobile phase was set at 0.5 mL/min. The mean absolute recoveries of PGA, MA, SG and HA were 95.9, 98.4, 98.0 and 97.1%, respectively. The inter-day and intra-day precisions, determined at three concentration levels, were less than 10% of RSD. The limits of quantification for PGA, MA, SG and HA were 13.2, 13.1, 14.5 and 11.2 microM with RSD less than 20%. The limits of detection for PGA, MA, SG and HA were 4.6, 4.6, 5.1 and 3.9 microM, respectively. The method was successfully applied to study the stereoselective metabolism of SG and MA in primary culture of rat hepatocytes. The results show that there is stereoselective metabolism for both of MA and SG in primary culture of rat hepatocytes. The extent of biotransformation from S-MA to PGA is significantly greater than that from the R enantiomer and the main metabolites are PGA and HA for S-SG and R-SG, respectively.

Review of the in vivo genotoxicity tests performed with styrene

Results from new genotoxicity tests in laboratory animals have necessitated a comprehensive re-evaluation of the mutagenic potential of styrene in vivo. Available data suggest that styrene, after being metabolized to styrene oxide, is weakly positive in indicator tests detecting DNA adducts, DNA strand breaks and sister chromatid exchanges (SCEs). There is no convincing evidence of styrene clastogenicity in experimental animals when the quality of the studies and the plausibility of the test results are considered. Equivocal results were obtained after exposure to high doses causing lethality. A recently published in vivo micronucleus test (MNT) in bone marrow cells of mice conforming to the current OECD guideline was clearly negative. Consequently, our evaluation of the published genotoxicity data comes to the conclusion that styrene at high doses can induce genotoxic effects in indicator tests. These DNA effects depend upon the exposure levels of the target cells, the metabolic activation to styrene oxide and the efficiency of detoxification. Mutagenic effects of styrene can only be expected under extreme exposure conditions if styrene oxide is not efficiently detoxified and primary DNA lesions are not completely repaired. However, there is no clear evidence that styrene induces mutagenic/clastogenic effects in vivo when tested under appropriate test conditions.

Modeling the acute neurotoxicity of styrene

Styrene is a widely used industrial solvent associated with acute neurotoxicity. To investigate the relationships between exposure, blood concentrations, and the appearance of neurotoxic effects, four healthy males were exposed to styrene concentrations of 5-200 ppm in four different exposure-time profiles. A digit recognition test and P300 event-related evoked potential were used to measure neurologic function. A physiologically based kinetic (PBK) model generated close predictions of measured styrene blood concentrations, in the range of 0.01-12 mg/L, from this and 21 previous studies. Simulated peak brain concentration, durationXaverage exposure, and peak exposure level were predictive of toxicity. Central nervous system effects were expected at a blood concentration near 2.4 mg/L. A standard of 20 ppm was expected to protect styrene-exposed workers from acute central nervous system toxicity under light work conditions.

A re-evaluation of the cytogenetic effects of styrene

Results from new chromosome studies in laboratory animals, comparative investigations of styrene metabolism and pharmacokinetics in humans and animals, and several recent cytogenetic surveys of styrene-exposed workers have necessitated a comprehensive re-evaluation of the chromosome-damaging effects of this chemical. Both styrene and its genotoxic metabolite, styrene oxide, can induce chromosome aberrations (CA) and sister chromatid exchanges (SCE) in vitro, but the chromosome-damaging ability of styrene is only manifested if test conditions favour its metabolic activation over inactivation. There is no convincing evidence of styrene clastogenicity in experimental animals. Styrene oxide is clastogenic only at lethal concentrations via i.p. injection in Chinese hamsters (but not via inhalation) or after oral treatment of mice, a route considered inappropriate for investigating the chromosome-damaging potential of inhaled styrene in man. Styrene and styrene oxide can induce SCE in animals at very high concentrations. Eighteen of 52 cytogenetic studies (CA, micronuclei, SCE) on peripheral blood lymphocytes of styrene workers have reported increases in chromosome damage. The positive findings are not compatible with the conclusion that styrene is responsible for the cytogenetic effects for the following reasons. (a) The positive or negative outcome of the various investigations bears no relationship to the degree of exposure of the workers. (b) There is no convincing evidence of a positive dose response relationship. (c) The relative induction of CA and SCE in worker studies are the opposite of observations of styrene effects in cultured lymphocytes and in laboratory animals. (d) The reports of chromosome-type exchanges in some studies of styrene workers is inconsistent with observations of styrene clastogenicity in cultured lymphocytes. (e) Reports of SCE induction in workers exposed to low concentrations of styrene are not compatible with results of animal inhalation studies, particularly in view of the differences in styrene metabolism and pharmacokinetics between humans and rodents. The increases in cytogenetic effects reported in some studies on styrene workers are probably attributable to the presence of other chromosome-damaging agents in the workplace and/or to inadequate investigations.

Sister chromatid exchange and chromosome aberration analyses in mice after in vivo exposure to acrylonitrile, styrene, or butadiene monoxide

The use of polymers in plastic and rubber products has generated concern that monomers potentially active in biological systems may be eluted from these substances. We have evaluated two such monomers, acrylonitrile and styrene, for the induction of chromosome damage in mice. Butadiene monoxide, a presumed metabolite of a third important monomer, 1,3-butadiene, was also tested. These chemicals were administered as a single intraperitoneal injection; sister chromatid exchanges and chromosome aberrations were analyzed in bone marrow cells. Acrylonitrile and styrene were largely negative for these endpoints when tested at doses ranging to 60 mg/kg and 1,000 mg/kg, respectively. Butadiene monoxide, which previously has not been tested in a mammalian system, was determined to be a very effective inducer of sister chromatid exchanges and chromosome aberrations. Both endpoints showed a clear dose response and a greater than ten-fold increase over control levels at high doses. These studies represent an initial step in our efforts to evaluate genetic risk associated with exposure to common polymeric chemicals.

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.