Liquid chromatography-electrospray tandem mass spectrometry of acidic monoamine metabolites

A new method based on liquid chromatography-tandem mass spectrometry has been developed for the determination of monoamine metabolites, i.e., homovanillic acid (HVA), vanilmandelic acid (VMA), 3,4-dihydroxyphenylacetic acid (DOPAC) and 5-hydroxyindoleacetic acid (5-HIAA) in human urine. Analytes were separated on a C16 amide (5 cm, 5 microm) column and ionized by negative ion electrospray. Operating in the selected-reaction monitoring mode, linearity was established over three-orders of magnitude and limits of detection were in the range 30-70 microg/l. Precision calculated as RSD was within 0.8-5.2% for all intra- and inter-day determinations. The method was applied to the quantitative analysis of monoamine metabolites in 700 urine samples from occupationally (adults) and environmentally (both children and adults) exposed people living in areas with different soil contamination from lead. The urinary excretion of monoamine metabolites was significantly higher (P<0.001) in the subgroup of children living in polluted areas as compared to the control group (HVA, 6.03 vs. 4.57 mg/g creatinine; VMA, 5.33 vs. 4.37 mg/g creatinine; 5-HIAA 3.24 vs. 2.45 mg/g creatinine). In adults belonging to both groups of subjects occupationally and environmentally exposed, no differences were detected in the urinary concentration of monoamine metabolites. However, adults showed lower values of HVA (2.57 mg/g creatinine), VMA (2.17 mg/g creatinine) and 5-HIAA (2.09 mg/g creatinine) as compared to children groups.

Serum clara cell protein: a sensitive biomarker of increased lung epithelium permeability caused by ambient ozone

Ozone in ambient air may cause various effects on human health, including decreased lung function, asthma exacerbation, and even premature mortality. These effects have been evidenced using various clinical indicators that, although sensitive, do not specifically evaluate the O(3)-increased lung epithelium permeability. In the present study, we assessed the acute effects of ambient O(3) on the pulmonary epithelium by a new approach relying on the assay in serum of the lung-specific Clara cell protein (CC16 or CC10). We applied this test to cyclists who exercised for 2 hr during episodes of photochemical smog and found that O(3) induces an early leakage of lung Clara cell protein. The protein levels increased significantly into the serum from exposure levels as low as 0.060-0.084 ppm. Our findings, confirmed in mice exposed to the current U.S. National Ambient Air Quality Standards for O(3) (0.08 ppm for 8 hr) indicate that above the present natural background levels, there is almost no safety margin for the effects of ambient O(3) on airway permeability. The assay of CC16 in the serum represents a new sensitive noninvasive test allowing the detection of early effects of ambient O(3) on the lung epithelial barrier.

Serum clara cell protein: a sensitive biomarker of increased lung epithelium permeability caused by ambient ozone

Ozone in ambient air may cause various effects on human health, including decreased lung function, asthma exacerbation, and even premature mortality. These effects have been evidenced using various clinical indicators that, although sensitive, do not specifically evaluate the O(3)-increased lung epithelium permeability. In the present study, we assessed the acute effects of ambient O(3) on the pulmonary epithelium by a new approach relying on the assay in serum of the lung-specific Clara cell protein (CC16 or CC10). We applied this test to cyclists who exercised for 2 hr during episodes of photochemical smog and found that O(3) induces an early leakage of lung Clara cell protein. The protein levels increased significantly into the serum from exposure levels as low as 0.060-0.084 ppm. Our findings, confirmed in mice exposed to the current U.S. National Ambient Air Quality Standards for O(3) (0.08 ppm for 8 hr) indicate that above the present natural background levels, there is almost no safety margin for the effects of ambient O(3) on airway permeability. The assay of CC16 in the serum represents a new sensitive noninvasive test allowing the detection of early effects of ambient O(3) on the lung epithelial barrier.

A new method for the analysis of styrene mercapturic acids by liquid chromatography/electrospray tandem mass spectrometry

A new method based on liquid chromatography/tandem mass spectrometry has been developed for the direct determination of specific urinary mercapturic acids arising from the conjugation of (R)-and (S)-enantiomers of styrene 7,8-oxide with glutathione (GSH), i.e. (R,R)- and (S,R)-N-acetyl-S-(1-phenyl-2-hydroxyethyl)cysteine (R,R-M1 and S,R-M1) and (R,R)- and (S,R)-N-acetyl-S-(2-phenyl-2-hydroxyethyl)-cysteine (R,R-M2 and S,R-M2). The four diastereoisomers were separated on a C18-DB (7.5 cm, 3 microm) column using variable proportions of 20 mM aqueous ammonium formate buffer and methanol at a flow-rate of 0.5 mL/min. The analytes were ionized by electrospray, in negative-ion mode. Operating in selected-reaction monitoring mode, linearity of the MS response versus analyte concentration was established over 4 orders of magnitude, the detection limits being 0.7-1.0 microg/L for all the mercapturates. Precision of the method determined at 50 microg/L (n = 12), expressed as relative standard deviation, was respectively 3.1, 4.8 and 6.9% within the run, intra-day and inter-day. The corresponding figures at 1.0 mg/L (n = 12) were respectively 2.0, 3.6 and 5.5%. The method was applied to the quantitative analysis of conjugated metabolites in urine samples from workers occupationally exposed to styrene. The diastereoisomers R,R-M1 and S,R-M2 accounted respectively for 50 and 40% of total mercapturates, whereas the proportion of R,R-M2 was 7% and only minor amounts of S,R-M1 were detectable. Styrene mercapturates represented a minor fraction of total styrene metabolites, less than 1% on average. The ratio mercapturates/main metabolites (mandelic + phenylglyoxylic acid) showed a bimodal distribution, the medians of the two subgroups being 0.2 and 1%, respectively. Such subgroups are probably characterized by the genetic polymorphisms of the drug-metabolizing enzymes to be identified.

Solid-phase microextraction gas chromatographic-mass spectrometric method for the determination of inhalation anesthetics in urine

Solid-phase microextraction (SPME) has been applied to the headspace sampling of inhalation anesthetics (i.e. nitrous oxide, isoflurane and halothane) in human urine. Analysis was carried out by gas chromatography-mass spectrometry using a capillary column with a divinylbenzene porous polymeric stationary phase. A SPME divinylbenzene-Carboxen-polydimethylsiloxane coated fiber, 2 cm long, was used, and its performances were compared with those of a Carboxen-PDMS in terms of sensitivity, extraction efficiency, extraction time, fiber coating-urine distribution coefficient. For both fibers, linearity was established over four orders of magnitude, limits of detection were below 100 ng/l for nitrous oxide and below 30 ng/l for halogenated. Precision calculated as %RSD was within 3-13% for all intra- and inter-day determinations. The method was applied to the quantitative analysis of anesthetics in the urine of occupationally exposed people (operating room personnel).

Biomarkers of dose and susceptibility in cyclists exposed to monoaromatic hydrocarbons

A quasi-experimental field study was carried out in 24 volunteers with the aim of: (i) assessing personal exposure to aromatic hydrocarbons polluting urban areas; and (ii) exploring the role of polymorphic enzymes relevant to the biotransformation of benzene in the inter-individual variability of biomarkers. Each subject covered by bicycle: (i) inner city routes with often jammed traffic; and (ii) open rural routes. Time-weighted average airborne concentrations of benzene, toluene, ethylbenzene and xylenes (BTEX) were determined during 2-h runs. BTEX were determined by solid-phase micro-extraction (SPME) followed by gas chromatography coupled with mass spectrometry (GC-MS) in blood and spot urine samples collected just before and immediately after the runs. Urinary t,t-muconic acid was measured by high performance liquid chromatography (HPLC)-UV. Genotypes of epoxide hydrolase (EH) and glutathione-S-transferase class mu-1 (GSTM1) were also characterised. As compared to pre-run values, benzene and toluene in blood, and toluene and xylenes in urine significantly increased after urban runs. Urinary t,t-muconic acid was significantly higher in post-run samples after both urban (P < 0.001) and rural runs (P < 0.05). Despite a narrow range of exposure levels, a significant relationship was observed between airborne benzene and post-run t,t-muconic acid (r2 = 0.349, P < 0.00). When subgroups were distinguished according to EH and GSTM, subjects bearing both the EH wild type and GSTM 'null' genotype showed significant exposure-related changes in t,t-muconic acid excretion. Even at very low exposure levels, a 2-h bike run in a polluted urban environment may give rise to measurable changes in biomarkers of internal dose of selected aromatic hydrocarbons. Genetically-based metabolic differences may account for part of the inter-individual variability of biomarkers of exposure.

Determination of free and glucuronated hexane metabolites without prior hydrolysis by liquid- and gas-chromatography coupled with mass spectrometry

Since n-hexane metabolites are excreted as glucuronide conjugates, most conventional analytical procedures require preliminary hydrolysis, yielding to the 'total' 2,5-hexanedione (2,5-HD), but also giving rise to a number of artifacts. The whole pattern of n-hexane metabolites, both conjugated and unconjugated, as well as different methods of sample pretreatment have been evaluated by hyphenated techniques (liquid chromatography-mass spectrometry (LC-MS) and gas chromatography-mass spectrometry (GC-MS)). Aliquots of urine from rats exposed to n-hexane underwent enzymatic or acid hydrolysis or both; whereas one aliquot was applied to LC-MS, dichloromethane extracts were analyzed by GC-MS. In untreated urine, four glucuronides (-G) were identified and characterized by LC-MS: 2-hexanol-G, 5-hydroxy-2-hexanone-G, 4,5-dyhydroxy-2-hexanone-G, and 2,5-hexanediol-G. 'Free' 2,5-HD was detectable in non-hydrolyzed samples by both GC- and LC-MS. Whereas enzymatic hydrolysis did not increase the amount of 2,5-HD, acid hydrolysis led to increase 2,5-HD in variable amount and produced gamma-valerolactone as a result of a complete transformation of 4,5-dihydroxy-2-hexanone-G and the partial conversion from 5-hydroxy-2-hexanone-G. Further experiments showed that both 5-hydroxy-2-hexanone-G and 4,5-dihydroxy-2-hexanone-G, isolated by solid-phase extraction and hydrolyzed, yield comparable amount of 2,5-HD and gamma-valerolactone. In samples treated by acid hydrolysis, GC-MS only does not allow to understand the true source of 'total' 2,5-HD, which may be produced not only from 4,5-dihydroxy-2-hexanone-G but also from the more abundant 5-hydroxy-2-hexanone-G, which thus represents the main source of analytical artifacts. 'Free' 2,5-HD seems to be both suitable from an analytical point of view and meaningful for biological monitoring purposes, provided that conjugate metabolites are rapidly removed from the body leading to a negligible neurotoxic risk.

Determination of naphthalene metabolites in human urine by liquid chromatography-mass spectrometry with electrospray ionization

The use of a liquid chromatography-electrospray mass spectrometry system was investigated for the quantitative analysis of naphthalene metabolites (alpha-naphthol, alpha-naphthylglucuronide and beta-naphthylsulphate) in untreated urine samples. Chromatography was carried out under ion-suppressed reversed-phase conditions, by using high-speed (3 cm, 3 microns) columns and formic acid (2 mM) as a modifier in the mobile phase. The ionization was obtained in the negative-ion mode. Linearity, sensitivity and precision of the method were explored by operating in selected-ion monitoring mode. The method was applied to the quantitative analysis of naphthalene metabolites in untreated urine samples from workers in a naphthalene producing plant. Solid-phase extraction was used for sample clean-up and trace enrichment. Liquid chromatography-tandem mass spectrometry experiments were performed for confirmation purposes.

Exposure to hydrocarbons and renal disease: an experimental animal model

The association between hydrocarbon exposure and chronic glomerulonephritis is still a controversial scientific issue. Recent epidemiological evidence suggests a role of exposure to hydrocarbons in the progression of glomerulonephritis towards chronic renal failure. The present experimental study on rats has been designed to assess the possible role of styrene in the progression of adriamycin (ADR) nephrosis, a well known model of renal fibrosis following nephrotic syndrome induced by ADR. Female Sprague-Dawley rats were exposed to styrene, 300 ppm, 6 h/day, 5 days/week for 12 weeks (group 1); treated with ADR, 2 mg/Kg, i.v., twice on day 1 and day 15 of the study (group 2); Additional groups of animals received both the styrene and ADR treatments (group 3) or served as controls (group 4). The urinary excretion of total and single proteins (albumin, Retinol-Binding Protein (RBP), Clara Cell 16 Kd protein (CC16), fibronectin) was measured monthly, whereas histopathology and determinations requiring blood sampling were carried out at the end of the experiment. A progressive increase in total proteinuria, falling in the nephrotic range already by the 6th week was observed in ADR-treated groups. Styrene exposure caused up to a 3- to 5-fold increase as compared to controls. Co-exposure to ADR and styrene also resulted in a proteinuria much greater than that caused by ADR alone. The interactive effect of styrene and ADR was statistically significant for albuminuria and urinary fibronectin. A similar response was observed for glomerular filtration rate at the end of the experiment, styrene-exposed animals showing hyperfiltration as compared to their respective control group. At the end of the experiment, histopathological scoring for interstitial infiltration and fibrosis was also significantly higher in styrene-treated animals as compared to their respective control groups. In ADR-treated rats, low molecular weight proteinuria (l.m.w.p.) was only slightly affected, suggesting minimal tubular dysfunction associated with extensive tubular atrophy. However, styrene-exposed animals showed l.m.w.p. higher than their respective controls. In summary, in this animal model we were able to confirm both styrene-induced microproteinuria, mainly albuminuria and minor increases in l.m.w.p., observed among occupationally exposed workers and the role of hydrocarbon exposure as a factor accelerating the progression of renal disease suggested by epidemiological investigations in patients suffering from chronic renal disease. Whereas in rats exposed to styrene only, microproteinuria was stable over time and minor histopathological changes were noted at the end of the experiment, evidence of a role of solvent exposure in the progression of ADR nephropathy was obtained in terms of both renal dysfunction and interstitial fibrosis. The mechanistic basis of styrene-ADR interaction is unclear. However, experimental evidence is consistent with epidemiological findings suggesting the need to avoid solvent exposure in patients suffering from renal diseases.

Hypertension as an etiopathological factor in the development of cerebral atrophy in hemodialyzed patients

Twenty-five patients on long-term regular hemodialysis treatment (RDT) at our dialysis unit who underwent diagnostic cerebral computed tomography (CCT) participated in a study aimed at clarifying the pathogenesis of cerebral atrophy occasionally found at their original scan. The upper age limit was 55 years to exclude the physiological involutive brain changes occurring with age. Cerebral atrophy (CA), as defined morphologically (enlargement of cerebral sulci or an increased Evan's Index), was detected in all cases. Seventeen patients underwent magnetic resonance imaging (MRI) to define possible white matter changes more accurately. No significant correlation was found between the degree of atrophy and the following uremia-altered hematoseric parameters: creatinine, hematocrit, cholesterol, triglyceridemia, albumin, PTH, calcium, inorganic phosphate. There was no correlation between degree of atrophy and number of months the patients had been on RDT or time that passed between the finding of a creatinine clearance <30 ml/min and the start of RDT. Very high correlations were found between the degree of CA and predialytic blood pressure values, and between CA and the duration of hypertension (n = 13, r = 0.66, p < 0.013). Thus, hypertension seems to be an early cause of cerebral parenchymal damage in RDT patients, and should be promptly corrected.

Predictive validity of the Q16 questionnaire: a comparison between reported symptoms and neurobehavioral tests

The correspondence between the answers to the Q16 questions regarding memory and attention-concentration and relevant neurobehavioral performance test scores has been evaluated. The sensitivity, specificity and diagnostic validity of Q16 have been assessed, taking the relevant neurobehavioral test score as a reference diagnostic criterion, the lower quartile of performance being considered as a poor response. The group under study consisted of 74 volunteers (24 females), aged 40 years on average (SD:7.5) and recruited among styrene-exposed workers and healthy controls. The test battery included the logical memory (short- and long-term) and the verbal learning (short- and long-term) tests of the Wechsler Adult Intelligence Scale (WAIS). The answers to the Q16 questions were poorly related to the performance: self-perceived forgetfulness showed a limited agreement with the long-term logical memory test (r=-0.23, p<0.05). The number of false negatives (no symptom but low test scores) was generally high, giving rise to a very low sensitivity of the questionnaire, despite a relatively high specificity. Accordingly, the positive diagnostic validity was low (<30%), whereas the negative diagnostic validity was high (>80%). Different methods used to investigate subtle neurological changes give rise to inconsistencies between self-perceived disturbances and objective measurements of relevant functions. Owing to its low sensitivity and positive diagnostic value, the Q16 cannot be recommended as a screening tool among workers occupationally exposed to neurotoxic chemicals.

Determination of n-hexane metabolites by liquid chromatography/mass spectrometry. 2. Glucuronide-conjugated metabolites in untreated urine samples by electrospray ionization

A liquid chromatography atmospheric pressure electrospray mass spectrometry (ESI-LC/MS) system was evaluated for the identification and characterization of n-hexane conjugated metabolites (glucuronides) in untreated urine samples. Chromatography of glucuronides was obtained under ion-suppressed reversed-phase conditions, by using high-speed (3 cm, 3 microns) columns and formic acid (2 mM) as modifier in the mobile phase. The mass spectrometer was operated in negative ion (NI) mode. For the first time, four glucuronides were identified by ESI-LC/MS in untreated urine samples of rats exposed to n-hexane: 2-hexanol-glucuronide, 5-hydroxy-2-hexanone-glucuronide, 2,5-hexanediol-glucuronide and 4,5-dihydroxy-2-hexanone-glucuronide. Confirmation of the conjugated metabolites was obtained by LC/MS/MS experiments. Gas chromatography/mass spectrometry (GC/MS) and atmospheric pressure chemical ionization (APCI) LC/MS analyses were performed on the same samples. An integrated approach GC/MS-LC/MS for the semi-quantitative analysis of n-hexane glucuronides, whose standards are not commercially available, is discussed and proposed here. In order to understand the fate of the metabolites during sample pre-treatment, a study about the effects of enzymatic and acid hydrolysis on urine samples was conducted on glucuronides isolated by solid-phase extraction. Combined analyses by GC/MS and LC/MS enabled us to distinguish 'true' n-hexane metabolites from compounds resulting from sample treatment and handling (i.e. enzymatic and acid hydrolysis, extraction and GC injection).

Determination of n-hexane metabolites by liquid chromatography/mass spectrometry. 1. 2,5-hexanedione and other phase I metabolites in untreated and hydrolyzed urine samples by atmospheric pressure chemical ionization

The capabilities of atmospheric pressure chemical ionization liquid chromatography/mass spectrometry (APCI-LC/MS) were investigated for the analysis of urinary 2,5-hexanedione (2,5-HD) and for the identification and characterization of other n-hexane Phase I metabolites in hydrolized urine samples. Chromatography was performed under reversed phase conditions at 0.75 mL min-1 flow rate. The ionization of 2,5-HD and other n-hexane metabolites was obtained in positive ion mode. After optimization of several interface parameters, the linearity, sensitivity and precision of the method were determined operating in the selected ion monitoring mode. Detection limits were 0.02 and 0.05 mg L-1 in water and urine respectively, with linear calibration curves in the 0.05-10 L-1 concentration range. Repeatability and both intra-day and inter-day precision were determined at two concentration levels (0.5 and 5.0 mg L-1), and relative standard deviations were in the 1.3%-5.3% range. The method was applied to the quantitative analysis of 2,5-HD in urine samples from an external Quality Assurance Programme for Organic Solvent Metabolites. Moreover, the metabolites 5-hydroxy-2-hexanone, 2,5-hexanediol and 4,5-dihydroxy-2-hexanone were identified and confirmed in hydrolyzed urine of rats exposed to n-hexane.

[The toxicology and prevention of the risks of occupational exposure to aromatic polycyclic hydrocarbons. I. Guide lines for the prevention of the risks of occupational exposure to aromatic polycyclic hydrocarbons. Società Italiana Valori di Riferimento and Cattedra di Medicina del Lavoro, Università di Brescia]

These guidelines mainly deal with prevention of carcinogenic effects following occupational exposure to polycyclic aromatic hydrocarbons (PAH). After some toxicological remarks, the guidelines define a possible method to demonstrate and evaluate occupational exposure to PAH. In particular, it is illustrated the strategy of environmental monitoring and indicated which PAH should be measured, with suggestion about the most appropriate analytical techniques. As regards biological monitoring, the 1-OH-pyreneseems to be currently the most useful indicator since it reflects the recent and global exposure to PAH. The guidelines also give elements to interpret monitoring data, taking into account environmental and biological reference and limit values suggested by some authors, Associations, or current regulations. The most important health effects are carcinogenic and excess risks have been described mainly for lung, bladder and skin cancer in some PAH exposed workers. The studies on cytogenetic effects showed contradictory results. On the basis of such information and current regulations, the guidelines show how to perform health surveillance in preventive and periodical examinations and how to proceed for the information and formation of exposed workers. It is not advisable, on the basis of the current scientific data, to screen asymptomatic PAH exposed workers for early diagnosis of lung or bladder cancer, nor it is opportune the use of tumor markers for health surveillance nor is genetic screening applicable for individual susceptibility evaluation outside research programs.

[The toxicology and prevention of the risks of occupational exposure to aromatic polycyclic hydrocarbons. III. The effects: epidemiological evidence, early effects. Individual hypersusceptibility. Health surveillance]

Adverse effects following occupational exposure to polycyclic aromatic hydrocarbons (PAH) are mainly carcinogenic. The available epidemiological data suggest that some substances and industrial processes, in which PAH exposure is frequent, are classified as carcinogenic to humans: primary aluminium industry, cola gasification, coke production, iron and steel foundry, coal tar, pitch, creosote, untreated mineral oils, asphalt, soot. The target organs are mainly lung, bladder, skin. Other relevant effects are skin lesions such as folliculitis. The studies on early biological effects (chromosomal aberrations, sister chromatid exchanges, micronuclei) have shown contradictory results, mainly because of differences in exposure intensity. The metabolic polymorphism may account for a higher susceptibility to lung and bladder cancer following exposure to risk factors; the role of PAH occupational exposure is however to be examined, and the use of indicators of genetic susceptibility is currently limited to research programs. Health surveillance for PAH exposed workers is funded on the Italian laws (DPR 303/56 and D.Lgs. 626/94) and it is mainly dedicated to prevention of carcinogenic effects. Preventive examinations should consider PAH target organs (skin, lung, bladder, larynx) and look for early signs and symptoms. Particular attention will be paid to life habits such as tobacco smoking or diseases which could represent condition of susceptibility. Periodical examinations (every six months) will similarly evaluate PAH target organs. Health surveillance is also programmed for formerly exposed workers and the institution of exposure and cancer registries is mandatory. On the basis of the current scientific data, it is not advisable the use of tumor markers or cytogenetic tests at the individual level as well as the screening of asymptomatic PAH exposed workers for early diagnosis of lung or bladder cancer. Information and formation activities will be part of medical examinations and will be included in specific programs in cooperation with other company functions.

The assessment of biomarkers to detect nephrotoxicity using an integrated database

Groups of industrial workers exposed to heavy metals (cadmium, mercury, and lead) or solvents were studied together with corresponding control groups. The cohorts were collected from several European centers (countries). Eighty-one measurements were carried out on urine, blood, and serum samples and the results of these analyses together with questionnaire information on each individual were entered into a central database using the relational database package Rbase. After the completion of the database construction phase, the data were exported in a format suitable for analysis by the statistical package SAS. The potential value of each test as an indicator of nephrotoxicity was then assessed. Rigorous exclusion criteria were applied which resulted in the elimination of some tests and samples from the dataset. The measurable contributions of smoking, gender, metal exposure, and site were either singly or in combination assessed by biomarkers for nephrotoxicity. The parameters measured included three urinary enzymes, six specific proteins, total protein, two extracellular matrix markers, four prostaglandins and anti-GBM antibodies, and beta 2-microglobulin in serum. The most sensitive renal tests included the urinary enzymes N-acetyl-beta-D-glucosaminidase (NAG) and intestinal alkaline phosphatase (IAP), brush border antigens, and urinary low-molecular-weight proteins. Of the newer tests investigated the prostaglandins were the most promising. Different patterns of biomarker excretion were observed following exposure to lead, cadmium, or mercury. The dataset provides a unique repository of data which could provide the basis of an enlarging source of information on normal human reference ranges and on the effects of exposure to toxins and the use of biomarkers for monitoring nephrotoxicity.

Motor function, olfactory threshold, and hematological indices in manganese-exposed ferroalloy workers

A cross-sectional study was conducted in 35 male subjects randomly selected from workers of a ferroalloy production plant and exposed to manganese (Mn) oxides; the objective was to detect early signs of neurologic impairment. The subjects' mean age was 39.4 years (SD, 8. 4); the average exposure duration was 14.5 years (range, 5-29 years). A control group of industrial workers not exposed to neurotoxic chemicals and comparable in age and confounding factors was recruited. The intensity of Mn exposure was moderate, as reflected by airborne Mn concentrations in total dust averaging 193 [corrected] micro g/m3. Mn levels in blood (MnB) and urine (MnU) were significantly higher in the Mn-exposed workers than in control workers. A relationship (not found with MnU) was found between MnB and a cumulative exposure index calculated on the basis of air concentration and exposure history for each subject (r = 0.52; r2 = 0.27; P = 0.002). Psychomotor function scores were lower among Mn-exposed subjects. The Aiming score was negatively correlated with MnB in the exposed group. The olfactory threshold did not differ between the two groups, although it was negatively associated with MnU in the exposed group. The white blood cell count results were significantly higher in Mn-exposed subjects than in controls. These findings show that an increase in Mn body burden is associated with an impairment of motor functions, whereas the increased excretion of Mn is related to an increased olfactory perception. Changes in numbers of leukocytes could indicate possible interferences of Mn with the immunological system.

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

AIM

A cross-sectional investigation was carried out to assess possible relations between styrene-induced changes in three peripheral markers of catecholaminergic dysfunction and self-reported symptoms of neurotoxicity.

SUBJECTS

Male workers (n = 46) aged 14-60 (mean 29.5) years who had been exposed to styrene for an average of 6 (0.2-29) years were recruited in glassfiber reinforced plastics plants. A control group of 30 blue-collar workers aged 22-52 (mean 35) years and with no history of exposure to chemicals was recruited from local industries. Styrene exposure ranged from 5 to 120 ppm (8 h-TWA), the median level being relatively low (25 ppm, 8 h-TWA). Styrene metabolites, mandelic and phenylglycoxylic acids (MAPGA) in the "next morning" urine spot samples ranged from 32.0 to 931.1 mg/g creatinine (median 186.5).

METHODS

Platelet monoamine oxidases B (MAO B) and dopamine beta-hydroxylase (DBH) activities were assessed using methods based on HPLC and electrochemical detection. Plasma prolactin (PRL) was measured by a commercially available immunoassay. Questionnaire 16 (Q16) was used to survey self-reported symptoms.

RESULTS

Although there was no difference in DBH activity between exposed workers and controls, the most highly exposed workers had significantly lower activity than control subjects. A tendency to lower platelet MAO B activity in exposed than in control subjects was observed. The prevalence of plasma DBH and platelet MAO B values below the lower reference limit was similar in the two groups. PRL values exceeding the upper reference limit were higher (14/46 vs 2/30) among styrene-exposed workers, who also exhibited significantly higher median levels (10.0 vs 5.7 micrograms/l) than control subjects. Although the number of reported symptoms was similar among exposed and control subjects, in the exposed group it was positively associated with urinary MAPGA (Rho = 0.30, P = 0.04). Of the three peripheral markers of catecholaminergic dysfunction, plasma DBH was the only parameter negatively related to both urinary MAPGA (F = 9.56, P = 0.003) and the number of reported symptoms (Rho = 0.23, P = 0.05).

CONCLUSIONS

Plasma PRL appears to be a sensitive marker of styrene-induced tubero-infundibular dopaminergic dysfunction in male subjects. DBH in plasma and MAO B in platelets seem to be less suitable markers for biomonitoring effect at the individual level, although DBH was related to the number of reported symptoms and to internal dose. Further studies on a larger and more exposed population are necessary to clarify the significance of these markers for health and their predictive value with regard to both subjective disturbances and concurrently administered performance tests.

Dopamine (DA) metabolism in PC12 cells exposed to manganese (Mn) at different oxidation states

The present study was aimed at assessing the role of Mn valency state in Mn-induced changes in DA metabolism by PC12 cells. Mn(ll)Cl2, Mn(lll)Acetate, and Mn(IV)O2 were used for these experiments. PC12 cells were incubated for 3, 24 and 72 hours to Mn nominal concentrations ranging from 10-8 to 10(-4) M in 24-well plates containing 2 x 10(5) cells/well. Supernatants and cellular materials were then separated and immediately processed for the analysis of dopamine (DA), and its metabolite 3,4-di-hydroxy-phenylacetic acid (DOPAC). Lactate dehydrogenase (LDH) activity and MTT cleavage were measured as indices of cell death. In parallel experiments, Mn-containing medium (10(-5) M) was removed and cells incubated for further periods with Mn-free medium to evaluate the reversibility of observed changes. At the end of the experimental periods, none of Mn-exposed cultures showed appreciable reduction in cell viability as compared to their respective controls. After exposure to Mn(II) and Mn(III), irreversible and dose-dependent decreases in the medium but not in intra-cellular DA were apparent. Indeed, 10(-4) M Mn(II) caused the disappearance of DA and DOPAC from the medium. The same effect was caused by 10(-5) M Mn(III), the dose-effect relationship being shifted towards lower dose levels. Mn(IV) induced a parallel and dose-dependent decrease of DA and DOPAC concentrations in both intra- and extra-cellular compartments. Such an effect was reversible after removal of Mn from the medium. Multiple interferences on DA metabolism are caused by Mn. Mn(II) and Mn(III) seem to block DA secretion without affecting DA turnover rate. Mn(IV) seems to cause DA depletion and aspecific (secondary) changes in secretion rates. Further studies are necessary to understand the mechanisms underlying the differential effects of various Mn compounds on DA metabolism.

Pilot study of peripheral markers of catecholaminergic systems among workers occupationally exposed to toluene

In a pilot study, serum dopamine beta-hydroxylase (DBH), platelets monoamine oxidase type B (MAO B) activities and basal plasma prolactin (PRL) were measured, among 10 workers occupationally exposed to toluene and 10 control subjects, preceding and immediately following vacation. Six exposed subjects were employed in an adhesive tape making industry and 4 in a paint making industry. Their median basal levels of urinary hippuric acid were 0.44 mmole/mmole creatinine (cr) (range 0.23-1.97) and 0.18 mmole/mmole cr (range 0.15-0.19) respectively, the second to last morning of the work week, preceding vacation. The level of basal urinary hippuric acid among the control group was 0.26 mmole/mmole cr (range 0.03-0.38). The workers from the adhesive tape plant reported a significantly higher number of symptoms experienced frequently (Kruskal, Wallis, p < 0.05). On a group basis, serum DBH was lowest among the workers from the adhesive tape plant, who had the highest levels of basal urinary hippuric acid. In addition, a negative relation was observed between hippuric acid and serum DBH, preceding and following vacation (Rho = -0.46, p = 0.05; Rho = -0.51, p = 0.03). The observed changes in serum DBH activity are consistent with its decrease in human, following long-term exposure to styrene, another aromatic hydrocarbon. The findings of this pilot study, on a limited number of individuals suggest that DBH may be a sensitive peripheral bioindicator. Further studies of larger groups should be done to confirm the decrease in serum DBH activity with toluene exposure and explore whether this alteration is related to the neurotoxic impairments associated with exposure.

Peripheral markers of neurochemical effects among styrene-exposed workers

Monoamine oxidase B (MAO-B) activity in platelets, serum dopamine-beta-hydroxylase (DBH) activity, and serum prolactin (PRL) were measured during a cross-sectional investigation in workers occupationally exposed to styrene. The study group consisted of 53 workers (33 men and 20 women) employed for 9.3 years on average (range 1-22) in reinforced plastics plants. Sixty industrial workers with no known exposure to chemicals and comparable as to age, sex and confounding variables were recruited as controls. The activities of MAO-B in platelet-rich plasma and of DBH in serum from exposed and control subjects were measured within the same run, using methods based on the liquid-chromatographic determination of the reaction products. Serum PRL was determined by both EIA and RIA. Blood samples had been collected between 8:00 and 9:00 a.m. A lower DBH activity was found in exposed as compared to control workers (GM: 7.25 U/ml serum vs. 10.11 U/ml serum; p < 0.01), whereas MAO-B activity was significantly lower in a heavily exposed subgroup (10.1 vs. 13.8 U/10(7) platelets; p = 0.05), but not in the whole sample (p = 0.07). Serum PRL was higher both in male (GM: 8.90 ng/ml vs. 6.05 ng/ml; p < 0.01) and female (GM: 12.6 ng/ml vs. 9.33 ng/ml; p < 0.05) styrene-exposed workers as compared to their respective controls. Dose-response relationships were found for abnormally low DBH and abnormally high PRL values, with a threshold occurring at metabolite levels corresponding to 8h-TWA styrene concentrations in air around 25 ppm. In summary, this study shows that long-term exposure to relatively low levels of styrene can affect DBH activity and basal serum PRL. Owing to its sensitivity, PRL is a useful biomarker to show impairments of dopaminergic control on pituitary secretion. Since DBH is expression of catecholamine secretion, its decreased activity could represent an indirect index of altered turnover rate of the physiological substrate (i.e.dopamine) at the neuronal level. However, a direct interference by styrene metabolites on enzyme activity cannot be ruled out. Platelet MAO-B activity seems to be less sensitive to styrene exposure.

Age-related changes in interstitial norepinephrine. A microdialysis study in spontaneously hypertensive rats

This study was aimed at evaluating the time course of interstitial norepinephrine (NE) concentrations in the white adipose tissue and at assessing NE release after local perfusion with tyramine hydrochloride (TYR) in rats of different ages. Two groups of eight spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats, aged 14 to 16 weeks, were studied. The same animals were reexamined at the age of 52 to 54 weeks. A soft microdialysis probe was implanted subcutaneously in the parascapular region and was perfused with Ringer solution (flow rate: 2.0 microL/min). After an equilibration period, NE levels were monitored for 120 min, following which, TYR (0.1 nmol/min) was perfused for 90 min. Dialysates from each 30 min collection period were analyzed by HPLC using electrochemical detection. At 14 to 16 weeks, SHR showed higher NE concentrations in dialysates as compared to WKY (1124.0 pg/mL v 541.4 pg/mL; P < .001) and a blunted response to TYR challenge. The net output, estimated by subtracting basal values, was 86.0 pg NE/h in SHR as compared to 212.5 pg NE/ h in WKY (P = .005). Differences in basal NE levels persisted in the same aged groups (P < .001) as well as a blunted response to TYR. The net NE output was still lower in SHR as compared to WKY (320.4 pg NE/h v 414.7 pg NE/h in WKY; P = .023). Basal levels of NE in SHR could be accounted for by either a higher amount of the neurotransmitter stored into and released from vescicles or by an increased firing rate of the sympathetic fibers. Since TYR is known to deplete axoplasmic but not vesicular NE available for neurotransmission, the response of SHR to TYR challenge is consistent with an increased turnover rate of NE. Aging was associated with an increased response to TYR in both strains, thus suggesting an age-dependent decline in turnover rates or changes in NE reuptake mechanisms.

Biochemical markers of neurotoxicity. A review of mechanistic studies and applications

Neurotoxicology presents major challenges to the development of biological markers in accordance to conventional research strategies. Because of the inaccessibility of the nervous system, one of the proposed alternatives is the study of biochemical signals in peripheral tissues which can easily and ethically be obtained in humans, and which could represent surrogate indicators of equivalent parameters in the nervous tissue. Considerable scientific support to this approach is provided by the results of recent investigations in major areas of pharmacology and psychobiology. Studies examining parameters of neurotransmission and second messenger systems in peripheral blood cells, and variations in the peripheral body fluid content of endogenous substances reflecting nervous tissue dysfunction or damage are presented in this paper as examples of efforts toward rational development and validation of novel indicators of nervous system toxicity. Cholinergic muscarinic receptors and calcium signalling in peripheral blood lymphocytes, myelin basic protein in cerebrospinal fluid, and blood polyamines are discussed as potential surrogate indicators based on the results of in vitro or in vivo animal studies of neurotoxic metals (mercury, triethyltin), pesticides (disulfoton), drugs of abuse (d-fenfluramine) and model epileptogenic compounds (kainic acid). Data from investigations examining serum prolactin, type B monoamine oxidase (MAO-B) and dopamine beta-hydroxylase (DBH) in workers occupationally exposed to manganese, lead or styrene are also presented. Although research in this field is still at its very early stage, current evidence suggests that (i) certain neurochemical markers may be valuably used in animal studies as a complement to conventional laboratory tests to augment their sensitivity or predictivity; (ii) a mechanistic research approach is required to establish which markers offer the greatest promise for application in human biomonitoring.

Development and validation of new screening tests for nephrotoxic effects

Within the framework of an European Commission-funded project, groups of industrial workers exposed to heavy metals (cadmium, mercury and lead) or solvents were studied together with corresponding control groups. Eighty-one measurements were carried out on urine and serum samples and the scientific results together with individual questionnaire information were entered into a central database. Data obtained was assessed centrally and individually in subsidiary studies. The measurable contributions were assessed either singly or in combination, of smoking, gender, metal exposure and site, to nephrotoxicity. The potential value of each test as an indicator of nephrotoxicity was then assessed on the basis of sensitivity and specificity. A number of new tests including prostaglandins and for extracellular matrix components were investigated as well as established tests for renal damage and dysfunction. The data obtained from this comprehensive study emphasises the value of noninvasive biomarkers for the early detection of nephrotoxicity due to environmental toxins. The urinary profile varied with the type of environmental/occupational toxin. By careful selection of a small panel of markers they can be used to indicate the presence of renal damage, the principal region affected, and to monitor the progress of disease and damage. Biomarkers were also used to confirm and tentatively establish safe exposure levels to nephrotoxins.