Peripheral markers of catecholaminergic dysfunction and symptoms of neurotoxicity among styrene-exposed workers

Relationship between styrene exposure and prolactin secretion in human and animal studies: A systematic review

Styrene is widely used in industrial applications. Inhalation exposure occurs in the industry. Some studies indicated that serum prolactin concentrations increased after exposure to styrene, while other studies found no change. In this systematic review, the search was done with the keywords styrene and prolactin in the PubMed, Science Direct, Web of Science and Scopus databases, regardless of the publication period. 118 studies were obtained and only seven articles were finally selected according to exclusion and inclusion criteria. The effect of styrene on prolactin secretion was selected in both human and animal studies. The increased response was seen in inhalation exposures. Subcutaneous exposure has no significant effect on prolactin levels. The observed responses were both dose-dependent and gender-dependent. Changes in serum prolactin were more frequent in women compared to exposed men. Dopamine depletion was not observed in all studies, so more tests on laboratory animals are necessary to clarify the possible mechanism.

Styrene alters potassium endolymphatic concentration in a model of cultured utricle explants

Despite well-documented neurotoxic and ototoxic properties, styrene remains commonly used in industry. Its effects on the cochlea have been extensively studied in animals, and epidemiological and animal evidence indicates an impact on balance. However, its influence on the peripheral vestibular receptor has yet to be investigated. Here, we assessed the vestibulotoxicity of styrene using an in vitro model, consisting of three-dimensional cultured newborn rat utricles filled with a high‑potassium (K⁺) endolymph-like fluid, called "cysts". K⁺ entry in the cyst ("influx") and its exit ("efflux") are controlled by secretory cells and hair cells, respectively. The vestibular epithelium's functionality is thus linked to K⁺ concentration, measured using a microelectrode. Known inhibitors of K⁺ efflux and influx validated the model. Cysts were subsequently exposed to styrene (0.25; 0.5; 0.75 and 1 mM) for 2 h or 72 h. The decrease in K⁺ concentration measured after both exposure durations was dose-dependent, and significant from 0.75 mM styrene. Vacuoles were visible in the cytoplasm of epithelial cells from 0.5 mM after 2 h and from 0.25 mM after 72 h. The results presented here are the first evidence that styrene may deregulate K⁺ homeostasis in the endolymphatic space, thereby altering the functionality of the vestibular receptor.

Cochlear dysfunction is associated with styrene exposure in humans

AIM

Occupational exposure to styrene has been shown to be associated with an increased probability of developing hearing loss. However, the sites of lesions in the auditory system in humans remain unknown. The aim of this study was to investigate the possible adverse effects of styrene exposure on the cochlea of human subjects.

DESIGN

The hearing function of 98 styrene-exposed male workers from the glass fibre-reinforced plastics industry (mean concentration of 55 mg/m3) was evaluated bilaterally using pure-tone audiometry (1000-16000 Hz), distortion product otoacoustic emissions (DPOAEs), and auditory brainstem response (ABR). The results were compared to a group of 111 male workers exposed to noise (above 85 dBA) and 70 male white-collar workers exposed to neither noise nor solvents. Age and noise exposure levels were accounted for as confounding variables in all statistical models.

RESULTS

Styrene exposure was significantly associated with poorer pure-tone thresholds (1-8 kHz), lower DPOAE amplitudes (5-6 kHz), and shorter wave V latencies in both ears compared to control-group subjects. Similar results were found among noise-exposed subjects. A further analysis with wave V latency showed that styrene-exposed subjects showed significantly shorter latencies than expected according to normative data. These results suggest that occupational exposure to styrene at moderate concentrations is associated with cochlear dysfunction, at least at high frequencies. DPOAEs may be considered a valuable diagnostic tool in hearing conservation programs in workers exposed to styrene.

Evaluation of potential health effects associated with occupational and environmental exposure to styrene - an update

The potential chronic health risks of occupational and environmental exposure to styrene were evaluated to update health hazard and exposure information developed since the Harvard Center for Risk Analysis risk assessment for styrene was performed in 2002. The updated hazard assessment of styrene's health effects indicates human cancers and ototoxicity remain potential concerns. However, mechanistic research on mouse lung tumors demonstrates these tumors are mouse-specific and of low relevance to human cancer risk. The updated toxicity database supports toxicity reference levels of 20 ppm (equates to 400 mg urinary metabolites mandelic acid + phenylglyoxylic acid/g creatinine) for worker inhalation exposure and 3.7 ppm and 2.5 mg/kg bw/day, respectively, for general population inhalation and oral exposure. No cancer risk value estimates are proposed given the established lack of relevance of mouse lung tumors and inconsistent epidemiology evidence. The updated exposure assessment supports inhalation and ingestion routes as important. The updated risk assessment found estimated risks within acceptable ranges for all age groups of the general population and workers with occupational exposures in non-fiber-reinforced polymer composites industries and fiber-reinforced polymer composites (FRP) workers using closed-mold operations or open-mold operations with respiratory protection. Only FRP workers using open-mold operations not using respiratory protection have risk exceedances for styrene and should be considered for risk management measures. In addition, given the reported interaction of styrene exposure with noise, noise reduction to sustain levels below 85 dB(A) needs be in place.

A critical review finds styrene lacks direct endocrine disruptor activity

The European Commission lists styrene (S) as an endocrine disruptor based primarily on reports of increased prolactin (PRL) levels in S-exposed workers. The US Environmental Protection Agency included S in its list of chemicals to be tested for endocrine activity. Therefore, the database of S for potential endocrine activity is assessed. In vitro and in vivo screening studies, as well as non-guideline and guideline investigations in experimental animals indicate that S is not associated with (anti)estrogenic, (anti)androgenic, or thyroid-modulating activity or with an endocrine activity that may be relevant for the environment. Studies in exposed workers have suggested elevated PRL levels that have been further examined in a series of human and animal investigations. While there is only one definitively known physiological function of PRL, namely stimulation of milk production, many normal stress situations may lead to elevations without any chemical exposure. Animal studies on various aspects of dopamine (DA), the PRL-regulating neurotransmitter, in the central nervous system did not give mechanistic explanations on how S may affect PRL levels. Overall, a neuroendocrine disruption of PRL regulation cannot be deduced from a large experimental database. The effects in workers could not consistently be reproduced in experimental animals and the findings in humans represented acute reversible effects clearly below clinical and pathological levels. Therefore, unspecific acute workplace-related stress is proposed as an alternative mode of action for elevated PRL levels in workers.

Biomonitoring for Exposure Assessment to Styrene in the Fibreglass Reinforced Plastic Industry: Determinants and Interferents

Fifty-eight workers exposed to styrene were monitored in four fibreglass reinforced plastic industries of Central Italy. The aim of the study was to explore the factors that can influence the levels of styrene exposure biomarkers of the workers and the aspects that might interfere with the exposure assessment measures, such as the co-exposure to acetone. Personal monitoring of professional exposure to airborne styrene and acetone was carried out by Radiello samplers and GC/MS analysis. Biological monitoring was performed by the determination of urinary metabolites, mandelic (MA), and phenylglyoxylic (PGA) acids with HPLC/MS/MS and unmetabolized styrene in saliva and venous blood by HS/GC/MS. The median values of the four sites ranged between 24.1 to 94.0mg m(-3) and 7.3 to 331.1mg g(-1) creatinine for airborne styrene and MA + PGA, respectively. A good linear correlation was found between styrene in air and its urinary metabolites (r = 0.854). The median value for airborne styrene was found to exceed the (Threshold Limit Value - Time Weighted Average) of 85 mg m(-3) in one site for all the workers and in two if only moulders are considered. The multiple linear regression model showed that the determinants of urinary MA + PGA excretion were the type of process, workers' tasks, level of acetone co-exposure, and the use of respiratory protection devices. Data show that the simultaneous exposure to acetone modify the styrene metabolism with a reduction in the levels of (MA + PGA) excreted. A significant linear log-correlation was found between salivary levels of styrene and blood concentration (r = 0.746) sampled at the same t x time.

Thyroid function and exposure to styrene

BACKGROUND

Many natural substances and drugs have long been known to cause goiter or thyroid dysfunction. More recently, several environmental pollutants, such as pesticides and industrial compounds, have been investigated for their thyroid-disrupting activity and related adverse effects on human health. The aim of this study was to evaluate the effects of styrene on the thyroid axis in occupationally exposed workers.

METHODS

Thirty-eight exposed (E) and 123 nonexposed (NE) male workers (controls) were assessed. Serum concentrations of thyrotropin (TSH; basal and after thyrotropin-releasing hormone [TRH] administration.), free thyroxine (FT(4)), free triiodothyronine (FT(3)), anti-thyroglobulin, thyroid peroxidase antibody, and calcitonin were measured. Thyroid ultrasound examination was also performed. In E workers, urinary creatinine, mandelic acid (MA), and phenylglyoxylic acid (PGA) were also measured.

RESULTS

No significant differences between E and NE workers were demonstrated, as far as thyroid volume, nodularity, serum thyroid antibodies, and calcitonin were analyzed. However, in the E group a positive correlation between duration of exposure and thyroid volume was detected. After exclusion of subjects with nodular or autoimmune thyroid diseases, serum concentrations of FT(4), FT(3), and TSH did not differ between the two groups. In E workers there was a positive correlation between the urinary concentrations of styrene metabolites (MA plus PGA) and FT(4) or FT(4)/FT(3) ratio (p < 0.05; r = 0.45 and p < 0.005; r = 0.61, respectively), while no correlation was observed between urinary concentrations of MA plus PGA and serum TSH (either basal and stimulated).

CONCLUSIONS

Chronic exposure to styrene is not associated with an increase in nodular or autoimmune thyroid diseases. However, styrene could interfere with peripheral metabolism of thyroid hormones by inhibiting T(4) to T(3) conversion. Whether this is a direct effect on iodothyronine deiodinases or a consequence of a general distress, such as in nonthyroidal illnesses, remains to be established. Further studies in a larger population of exposed workers are needed to confirm these preliminary observations.

Persistent cognitive functioning deficits in operating rooms: two cases

BACKGROUND

To date, chronic toxic encephalopathy (CTE) has never been described in operating room personnel.

CASE REPORT

We report two cases of anaesthetists who developed this pathology. They have both used anaesthetic gases for many years in paediatric surgery. Air conditioning was deficient during three years in operating rooms and atmospheric anaesthetics concentration was high (N(2)O mean concentration: 311 ppm, peak levels 1,600 ppm; halogenated: 16 ppm, peak levels: 1,600 ppm).

CLINICAL SYMPTOMS

Mood troubles and non-specific neuropsychic deficits gradually evolved until they had to stop working. Neuropsychological assessment showed important deficits in attention, executive functioning, short-term memory and visuo-spatial organization. Blood tests, VEPs, MRI, neuroSPECT and cardiovascular exams were normal. Troubles had slowly improved after cessation of exposure and sequels still remain.

CONCLUSION

These CTE cases seem to be the consequence of a long-term exposure to important levels of anaesthetic gases, and particularly nitrous oxide. It points out the importance of preventive measures in operating rooms, where occupational hazards are varied.

Differential gene expression by styrene in rat reproductive tissue

Styrene is an important industrial chemical that is extensively used in the production of resins, rubbers and fiberglass-reinforced plastics. Exposing male rats to high doses of styrene may produce sperm abnormalities or infertility. To determine the mechanism underlying styrene-mediated toxicity in male reproductive organs, a reverse transcription-polymerase chain reaction (RT-PCR) technology was employed using annealing control primers (ACPs) to identify the differentially expressed genes following styrene treatment in isolated testis of male rats. By using 120 ACPs, a total of 6 expressed sequence tags (ESTs) of genes were differentially expressed in styrene-treated rats, as compared to untreated, which were cloned and sequenced. Of the genes analyzed, 5 genes (testis-specific expressed gene 101, protein kinase C, H+-ATPase isoform 2, peroxiredoxin 1, and aquaporin 9) were inducible and one gene expression (clusterin) was significantly suppressed by styrene. Regulation of each gene by styrene was confirmed by RT-PCR. It was shown that styrene decreased clusterin expression in a concentration-dependent manner and these effects occurred mainly in testis. Taken together, these results indicate that repression of clusterin gene expression by styrene may play an important role in styrene-mediated toxicities.

Prolactin Levels in Workers Exposed to Chemical, Physical and Psycho‐Social Urban Stressors

The aim of this study was to evaluate whether traffic police officers exposed to chemical, physical and psycho-social stressors, are at risk for alterations in plasma levels of prolactin (PRL) compared to a control group. Plasma PRL levels were evaluated in 92 male and 51 female, non-smoker, traffic police officers exposed to urban stressors and in 92 male and 51 female controls, matched by sex, age and working life (mean, SD and distribution), after excluding workers with the principal extra-occupational confounding factors. Mean PRL levels were significantly higher than controls in non-smoker, male and female traffic police officers (respectively, p=0.000 and p=0.013). The number of non-smoker, male and female traffic police officers with PRL values outside the upper normal limit for our laboratory was higher than, but not significantly different from controls. Mean PRL levels were not significantly higher than controls in smoker, male and female traffic police officers. The number of smoker, male and female traffic police officers with PRL values outside the normal limit for our laboratory was not significantly different from controls. The results suggest that exposure to urban chemical and physical stressors, interacting with psychosocial factors, may have an influence on PRL levels in traffic police officers. The level of plasma PRL might be a useful early biological marker for workers exposed to urban stressors.

Associations between platelet monoamine oxidase-B activity and acquired colour vision loss in a fish-eating population

Platelet monoamine oxidase-B (MAO-B) has been considered a surrogate biochemical marker of neurotoxicity, as it may reflect changes in the monoaminergic system in the brain. Colour vision discrimination, in part a dopamine dependent process, has been used to identify early neurological effects of some environmental and industrial neurotoxicants. The objective of this cross-sectional study was to explore the relationship between platelet MAO-B activity and acquired colour discrimination capacity in fish-consumers from the St. Lawrence River region of Canada. Assessment of acquired dyschromatopsia was determined using the Lanthony D-15 desaturated panel test. Participants classified with dyschromatopsia (n=81) had significantly lower MAO-B activity when compared to those with normal colour vision (n=32) (26.5+/-9.6 versus 31.0+/-9.9 nmol/min/20 microg, P=0.030)). Similarly, Bowman's Colour Confusion Index (CCI) was inversely correlated with MAO-B activity when the vision test was performed with the worst eye only (r=-0.245, P=0.009), the best eye only (r=-0.188, P=0.048) and with both eyes together (r=-0.309, P=0.001). Associations remained significant after adjustment for age and gender when both eyes (P=0.003) and the worst eye (P=0.045) were tested. Adjustment for heavy smoking weakened the association between MAO-B and CCI in the worst eye (P=0.140), but did not alter this association for both eyes (P=0.006). Adjustment for blood-mercury concentrations did not change the association. This study suggests a relationship between reduced MAO-B activity and acquired colour vision loss and both are associated with tobacco smoking. Therefore, results show that platelet MAO-B may be used as a surrogate biochemical marker of acquired colour vision loss.

Effects of subchronic exposure to styrene on the extracellular and tissue levels of dopamine, serotonin and their metabolites in rat brain

At present, there is controversy over the neurotoxic potential of styrene. Several epidemiological and clinical studies have shown that styrene exposure causes alterations of central nervous system functions in humans. Neurotransmitters have been implicated in the pathogenesis of styrene neurotoxicity in rodents. Several studies carried out on postmortem brain tissue suggest that styrene may alter dopaminergic neurotransmission in rabbit or rat brain. Moreover, in vitro studies suggest that both styrene and styrene oxide inhibit the uptake of dopamine (DA) in purified synaptic vesicles prepared from rat brain striata. To date, biochemical studies on animals have explored global tissue levels of neurotransmitters with sub-acute exposures to styrene. However, extracellular levels of neurotransmitters are more closely related to behaviour than are global tissue levels. The present study determined changes in the extracellular concentrations of DA, serotonin (5-HT) and their acid metabolites, dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 5-hydroxyindolacetic acid (5-HIAA), in striatal dialysates from freely moving adult male rats after exposure to 750 and 1,000 ppm styrene, 6 h per day, 5 days per week for 4 weeks. We also determined the concentrations of DA, 5-HT and their acid metabolites in striatum, nucleus accumbens and prefrontal cortex obtained postmortem from similarly exposed rats. Exposure to 1,000 ppm of styrene caused a significant decrease in extracellular acid metabolite concentrations. Tissue levels of acid metabolites were also decreased to a lesser extent. The effects were observed 72 h after discontinuing exposure but had vanished 17 days later. There was no change in DA or 5-HT concentrations either in the dialysates or tissues. Exposure to 750 ppm styrene caused no changes in the concentrations of DA, 5-HT and their acid metabolites either in the dialysates or tissues. The possibility that the effect of styrene is mediated by monoamine oxidase (MAO) inhibition is discussed.

The Oxidative and Morphological Effects of High Concentration Chronic Toluene Exposure on Rat Sciatic Nerves

This study was designed to investigate the effects of chronic toluene inhalation in high concentration on lipid peroxidation, antioxidant enzyme activities and ultrastructural changes in the sciatic nerves of rats. Male Wistar albino rats (150-250 g) were divided in two experimental groups: the control and the toluene treated group (n = 10 for each). Toluene treatment was performed by inhalation of 3000 ppm toluene, in a 8 h/day and 6 day/week order for 16 weeks. Blood and tissue samples were obtained for biochemical and histopathological investigation. The blood and sciatic nerves were assayed for toluene by gas chromatography. Toluene significantly increased blood and tissue malondialdehyde (MDA), and decreased tissue superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px), but not tissue catalase (CAT) levels when compared with controls. Electron micrographs of sciatic nerve in the toluene group shows myelin destructions with onion-bulb and bubble form protrusion on the myelin sheath and axolemma border of myelinated axons. The area of injury on the myelin sheath were measured by Image-Pro Plus. Mean of the injury area were estimated 34% each myelin. These findings indicate that chronic toluene inhalation might be involved with free radical processes.

Evaluation of the efficiency of respiratory protective equipment based on the biological monitoring of styrene in fibreglass reinforced plastics industries

The purpose of the present study was to determine the efficiency of respiratory protective equipment in a fibreglass reinforced plastic factory by comparing results of environmental and biological monitoring of exposure to styrene. Five factories including 39 workers were investigated. Three types of respiratory protective equipment were tested: one was a half-mask air-purifying respirator equipped with a cartridge for organic solvents, another was a disposable gauze respirator impregnated with charcoal filter, and the third was a dust-proof respirator. The frequency of cartridge exchange of a half-mask respirator was twice a day only at one factory, and that was less than once a month at other factories. The site concentrations exceeded 20 ppm at 10 of the 82 sampling points (12.2%), and 22 of the 39 workers' (56.4%) personal exposure exceeded 20 ppm which is the current occupational exposure limit recommended by the Japan Society for Occupational Health. The efficiency of disposable gauze respirators and dust-proof respirators was low or rather zero. The average efficiency of half-mask respirators in which cartridges were exchanged twice a day and once a month was 83.6% and 46.6%, respectively. There was a significant disparity in the efficiency of the respirator depending on the frequency of cartridge exchange (p<0.05). Overall this study showed that even though a half-mask respirator is used and its cartridge is exchanged every half a day, workers exposed to a styrene concentration at or over 122 ppm are expected to inhale more than 20 ppm of styrene.

Temporal association between serum prolactin concentration and exposure to styrene

BACKGROUND

Previous studies have suggested that occupational exposure to styrene is associated with increased serum levels of the anterior pituitary hormone prolactin (PRL).

AIMS

To test the hypotheses that: (1) the effect of styrene exposure on PRL secretion is an acute effect, not a subchronic or chronic effect; (2) blood styrene, as a measure of absorbed dose, is a stronger predictor of serum PRL level than personal breathing zone air styrene concentration.

METHODS

Subjects were recruited from 17 workplaces in the reinforced plastics industry. Personal breathing zone air styrene, whole blood styrene, and serum PRL were measured during one to three sessions, approximately one year apart. Linear multiple regression was used to model the relations between acute (air styrene or blood styrene obtained at same time as PRL), subchronic (average air or blood styrene over two or three sessions), and chronic (years of work in industry or facility times average air styrene over all sessions) indices of styrene exposure and serum PRL.

RESULTS

Acute blood styrene concentration was the strongest predictor of serum PRL concentration, with the model predicting a 2.06-fold increase in PRL (95% CI 1.11 to 3.84) for every 10-fold increase in blood styrene. Serum PRL tended to increase with increasing styrene exposure in both men and women; however, women tended to have higher PRL levels. For women, the change in blood styrene between sessions 1 and 2 was a significant predictor of the change in serum PRL between sessions.

CONCLUSIONS

Results confirm that styrene exposure enhances serum PRL concentrations and support an acute effect of styrene on PRL secretion.

Sperm-FISH analysis and human monitoring: a study on workers occupationally exposed to styrene

Occupational exposure to styrene, a chemical extensively used worldwide, is under investigation for possible detrimental effects on human health, including male reproductive capacity. Aneuploidy in germ cells is the main cause of infertility, abortions and congenital diseases. Fluorescence in situ hybridisation (FISH), is the most efficient cytogenetic molecular technique to date to analyse numerical alterations of chromosomes in spermatozoa. We investigated the frequencies of aneuploidy and diploidy in individuals occupationally exposed to styrene and in healthy unexposed controls. We performed multicolour FISH, using DNA probes specific for the centromeric regions of sex chromosomes and chromosome 2, in decondensed sperm nuclei of samples with normal semen parameters for a total of 18 styrene-exposed subjects and 13 unexposed controls of the same age range. Exposed individuals had worked for at least 2 years during the last 5 years, and continuously for 6 months, in factories producing reinforced plastics. The incidence of aneuploidy and diploidy for the tested chromosomes did not show a statistically significant difference between workers and controls. The exposure to styrene was associated with increased frequencies of nullisomy for sex chromosomes in the group of non-smokers, although only a limited number of subjects belonged to this sub-group. Considering the whole study population, age was associated with an increased frequency of XX disomy, whereas smoking was associated with meiosis II non-disjunction of sex chromosomes. Overall, confounding factors appeared to exert a more important effect than exposure to styrene on numerical chromosome alterations in sperm nuclei of subjects selected for normal semen parameters.

Styrene 7,8-oxide induces caspase activation and regular DNA fragmentation in neuronal cells

Neurobehavioral changes have been described in workers occupationally exposed to styrene vapors. Alterations of neurotransmitters and loss of neurons have been observed in brains of styrene-exposed rats. However, the mechanisms of neuronal damage are not yet clearly understood. We have characterized the cellular alterations induced by the main reactive intermediate of styrene metabolism, styrene 7,8-oxide (SO) in the human neuroblastoma SK-N-MC cell line and primary culture of rat cerebellar granule cells (CGC). SK-N-MC cells exposed to SO (0.3-1 mM) displayed apoptotic morphology, together with chromatin condensation and DNA cleavage into high molecular weight fragments of regular size. These features were accompanied by the activation of class II caspases, as detected with the DEVD assay, by following the cleavage of the caspase-substrate poly (ADP-ribose) polymerase (PARP) and by detection of the active fragment of caspase-3. Pre-incubation of the cells with the caspase inhibitor z-VAD-fmk reduced the cellular damage induced by SO, suggesting that caspases play an important role in SO toxicity. Increased proteolysis by class II caspases was detected also in primary culture of CGC exposed to SO. In addition, the presence of the 150-kDa cleavage product of alpha-fodrin suggests a possible activation of calpains in SK-N-MC cells. Moreover, SO did not affect the level of expression of the p53 protein, even though it is known to cause DNA damage. The identified intracellular pathways affected by SO exposure provides end-points that can be used in future studies for the evaluation of the neurotoxic effect of styrene in vivo.

Evaluation of a modified German version of the Q16 questionnaire for neurotoxic symptoms in workers exposed to solvents

OBJECTIVES

To assess sensitivity and specificity of a questionnaire designed to detect neurotoxic symptoms in workers exposed to solvents and in patients with a psycho-organic syndrome.

METHODS

The Swedish Q16 is a self administered questionnaire for neurotoxic symptoms. The modified German version consists of 18 questions. The results were analysed from 1166 questionnaires which were completed by adults belonging to the following groups; 483 workers with occupational exposure to solvents and 193 non-exposed controls, 25 patients with a psycho-organic syndrome, 25 sex and age matched patients with a lung disease, and a sample of 440 people from the general population.

RESULTS

The German Q18 was easy to handle and quick to perform. Workers exposed to solvents reported significantly more complaints than controls (2.9 v 2.5). All patients with a psycho-organic syndrome had five or more complaints. This was true for only 32% of patients with lung disease. These comparisons showed that chronic exposure to solvents was associated with subjective complaints related particularly to cognitive functions. In the sample of the general population, age, education level, smoking habits, and time of performance showed no significant influence on the Q18 result. Women had significantly more complaints than men (3.2 v 2.3). People who reported drinking alcohol occasionally or moderately had significantly fewer complaints than teetotalers.

CONCLUSIONS

The German Q18 has an acceptable sensitivity and reliability, a reasonable specificity, and a good practicability. It is a useful instrument for screening workers exposed to solvents. A cut off point of 5 for men is recommended, and a cut off point of 6 for women is proposed.

Assessing effects of neurotoxic pollutants by biochemical markers

Neurotoxins cause biochemical and molecular events which indicate early stage effects in exposed persons well before or well below the induction of overt disease. Monitoring these early events may represent a valid approach to developing markers of neurotoxicity in individuals exposed to environmental chemicals. In neurotoxicology, the use of biochemical markers is more problematic compared to other fields due to the complexity of central nervous system function, the multistage nature of neurotoxic events, and the inaccessibility of target tissue. Nevertheless, new biochemical assays have been developed in recent years to assess exposure, subclinical effects, and susceptibility to neurotoxic disorders. This paper reviews novel biomarkers of neurotoxicity and discusses perspectives and limitations of their use in occupational and environmental medicine.

A review of the developmental and reproductive toxicity of styrene

The reproductive and developmental toxicity of styrene has been studied in animals and humans. The animal studies on styrene have diverse study designs and conclusions. Developmental or reproductive toxicity studies have been conducted in rats, mice, rabbits, and hamsters. In most cases, high doses are required to elicit effects, and the effects are not unique to reproduction or development. In a number of the reports, either the experimental designs are limited or the descriptions of the designs and the endpoints measured are insufficient to draw conclusions about the toxicity of styrene. The more complete and better-reported studies show that styrene does not cause developmental toxicity at dose levels that are not maternally toxic. Some neurochemical or neurobehavioral effects have been reported at high exposures. Styrene does not affect fertility or reproductive function. Considerable animal toxicity data on styrene support the conclusion that styrene is neither an endocrine-active substance nor an endocrine disrupter. Human studies often suffer from either inadequate exposure data or exposure to a wide variety of materials, so that attribution of effects to styrene exposure is impossible. Furthermore, investigators often have failed to account for other exposures in the workplace or for other potentially confounding factors in their studies. Menstrual cycle irregularities and congenital abnormalities were initially reported; however, the better and more recent reports do not show that styrene causes developmental or reproductive effects in humans. Human studies also support the conclusion that styrene is not an endocrine disrupter. Although some study authors have concluded that styrene is either a human or an animal reproductive or developmental toxicant, careful review demonstrates that such conclusions are not justified.

Occupational and environmental agents as endocrine disruptors: experimental and human evidence

In the last few years great concern has arisen from the description of adverse endocrine effects of several occupational and environmental chemical agents on human and/or wildlife health. Such agents may exert their effects directly, specifically binding to hormone receptors, and/or indirectly, by altering the structure of endocrine glands and/or synthesis, release, transport, metabolism or action of endogenous hormones. Many studies have been focused on the outcomes of the exposure to those chemicals mimicking estrogenic or androgenic actions. Nonetheless, the disruption of other hormonal pathways is not negligible. This paper reviews the experimental and human evidence of the effects of occupational and environmental chemical agents on hypothalamus-pituitary unit, pineal gland, parathyroid and calcium metabolism and adrenal glands.

Styrene inhibits monoamine oxidase A, but not monoamine oxidase B in monkey brain mitochondria

The effects of styrene on mitochondrial monoamine oxidase (MAO) activity in rat and monkey brains were compared in vitro. After preincubation at 25 degrees C for 20 min with 1 mM styrene monomer MAO-A activity in monkey brain was inhibited potently using 5-HT (for MAO-A substrate), but MAO-B activity in monkey brain and platelets were slightly inhibited using beta-PEA (for MAO-B substrate). Styrene monomer also competitively inhibited MAO-A activity in a dose-dependent manner. MAO-A in monkey brain was inhibited by styrene in ascending order of potency: styrene trimer>styrene dimer>styrene monomer. In contrast styrene monomer slightly inhibited both MAO-A and MAO-B activities in rat brain mitochondria. In the present study styrene monomer potently inhibits MAO-A activity, but not MAO-B activity, in monkey brain mitochondria in vitro. These results indicate the inhibiting action of styrene differs depending on animal species and MAO isoforms.

Altered regulation of dopaminergic activity and impairment in motor function in rats after subchronic exposure to styrene

Animal and human studies suggest a dopamine-mediated effect of styrene neurotoxicity. However, the results reported to date are incomplete and not consistent. As such, the mechanism of its neurotoxicity is still unclear. The present study has, therefore, reexamined the central dopaminergic system in relation to some neurobehavioral effects in rats following subchronic exposure to styrene. Groups of adult male Sprague-Dawley rats received 0, 0.25, or 0.5 g styrene per kg b.wt. by gavage for 13 consecutive weeks. Twenty-four hours after cessation of such treatment with the higher dose (0.5 g/kg), the contents of dopamine (DA) and its metabolites were significantly reduced in the corpus striatum, hypothalamus, and lateral olfactory tract regions. In vitro styrene showed a significant increase in DA release from rat striatal synaptosomes similar to that of tyramine. Significant loss of motor function was observed on days 56, 70, and 84 during the styrene treatment with the higher dose, and lasted over a month after such treatment. However, the treated animals recovered their motor function within 45-60 days after cessation of such treatment, along with the recovery of normal levels of dopamine and its metabolites. Furthermore, styrene-induced initial impairments in measures of dopaminergic activity cannot be attributed to altered regulation of tyrosine hydroxylase activity. Specific [3H]-spiroperidol binding was also unaltered 7 or 15 days after subchronic treatment with styrene. These data imply that despite the dopaminergic neuronal loss due to styrene, dopaminergic transmission was not reduced to a level that would result in an overall development of dopamine receptor supersensitivity in the striatum. Collectively, these studies indicate that the subchronic neurotoxic action of styrene may be primarily presynaptic in nature and may involve impaired regulation of DA content and stimulation of DA release.

Toluene and styrene intoxication route in the rat cochlea

It is well established that organic solvents such as toluene and styrene are ototoxic in the rat; however, the intoxication route used to reach the organ of Corti is still questionable. The distribution of toluene and styrene in various tissues of Long-Evans rats (n = 2 x 8) was studied after inhalation of either 1750 ppm toluene or 1750 ppm styrene for 10 h (6 consecutive h + 4 h the following day). At the end of the solvent exposures, blood, brain, auditory nerves, the organ of Corti, cerebrospinal (CSF), and inner ear fluids (IEF) were sampled or removed to measure the rates of solvent uptake in each tissue by gas chromatography. Results indicate that CSF and IEF were free from detectable solvents, whereas the organ of Corti, the nerves, and the brain were contaminated. Therefore, both toluene- and styrene-induced hearing losses are caused by tissue intoxication rather than by fluid contamination. It is proposed that the outer sulcus is used as an intoxication route to reach the organ of Corti.

Styrene and styrene oxide affect the transport of dopamine in purified rat striatal synaptic vesicles

Animal and human studies suggest a dopamine-mediated effect of styrene neurotoxicity. To date, mechanisms of cerebral membrane transport of neurotransmitter amines in the presence of styrene in relation to its neurotoxicity have not been addressed properly. So, the present study has examined to test the hypothesis that dopaminergic malfunction in vesicular transport is a critical component in styrene-induced neurotoxicity in rats. Both styrene and its intermediate reactive metabolite, styrene oxide antagonized the in vitro striatal binding of [3H] tyramine, a putative marker of the vesicular transporter for dopamine. Both styrene and styrene oxide potently inhibited the uptake of [3H] dopamine in purified synaptic vesicles prepared from rat brain striata, in a dose-related manner, with inhibitory constants (Ki) 2.5 and 2.2 microM respectively. However, neither styrene nor styrene oxide significantly increased the basal efflux of [3H] dopamine that has been preloaded into striatal vesicles in vitro. On the other hand, both styrene and styrene oxide have failed to significantly inhibit the uptake of either [3H] norepinephrine, or [3H] serotonin into striatal synaptic vesicles. It is concluded that both styrene and styrene oxide are capable of producing impairments in dopaminergic transport in purified striatal synaptic vesicles, an effect which may be a critical component in styrene-induced neurotoxicity.