Occupational exposure to urban pollutants and urinary 5-hydroxy-3-indoleacetic acid.

Introduction

Serotonin (5-hydroxytriptamine, or 5-HT) is a heterocyclic amine that was first isolated by Esparmer and Vialli in 1937. Important depots in mammals were enterochromaffin cells in the gastrointestinal mucosa, serotonergic neurones of the brain, the pineal gland, and platelets. 5-HT is involved in a variety o[ physiological processes, including smooth muscle contraction, blood pressure regulation, body temperature regulation, pain sensitivity, mood control, sleep onset, and both peripheral and central nervous system neuro-transmission. It plays a major role in various psychiatric disorders, including schizophrenia (Breier, 1995), obesity (Bjorntorp, 1995: Wurtman & Wurtman, 1995), bulimia and anorexia nervosa (Kaye & Weltzin, 1991), alcoholism (Badawy, Morgan, & Thomas, 1993), obsessive-compulsive disorder (Jarry & Vaccarino, 1996), depression (Leonard, 1996; Owens & Nemeroff, 1994; Strickland et al., 2002), and impulsive violence and suicidal behavior (Linnoila & Virkkunnen, 1992; Nelson & Chiavegatto. 2001; Virkkunnen, Goldman, Nielsen, & Linnoila, 1995). The effects of 5-HT are felt most prominently in the cardiovascular system, with additional effects in the respiratory system and the intestine. Circlating 5-HT is metabolized to 5-hydroxy-3-indoleacetic acid (5-HIAA), which is excreted in the urine.

Studies on animals and human subjects have proposed that urban pollutants may cause a diminished 5-HT turnover. The agents are carbon monoxide (Muraoka, Hayakawa, Kagaya, Kojima, & Yamawaki, 1998). toluene (Arito, Tsuruta, Nakagaki & Tanaka, 1985; Hsieh, Sharma, Parker, & Coulombe. 1990), lead (Lasley, Greenland, Minnema & Michaelson, 1984) and noise (Fruhstorfer et al., 1985). By contrast, benzo[a]pyrene (Jayasekara, Sharma & Drown, 1992), benzene (Paradowski, Heimburger, Cohen, & Andrzejewski, 1984), and stirene (Husain, Srivastava, Mushtaq, & Seth, 1980) may cause an increase of 5-HT turnover.

The workers examined in this study were employees of the municipal police force of a large Italian city, for whom the authors had already studied the environmental and biological levels of some urban pollutants (Crebelli et al., 2001; Galati et al., 2001; Tomei et al., 2001; Verdina et al., 2001). Exposure dosage to benzene (for a mean of seven hours) was 10.7 [micro]g/[m.sup.3] for traffic police but about three times lower (3.6 [micro]g/[m.sup.3]) in controls (Crebelli et al., 2001; Tomei et al., 2001). Although unleaded gasoline had been introduced in Italy at the time of this study, a mixed regimen existed in Italy at the time of the study (use of both leaded and unleaded gasoline). The use of unleaded gasoline caused the increase of benzene in urban air.

In the period March-April 2001, the municipality of the city in question monitored concentrations of P[M.sub.10] in fixed stations located in districts with different intensities of traffic, registering mean monthly values respectively of 60 [micro]g/[m.sup.3], 45 [micro]g/[m.sup.3], and 30 [micro]g/[m.sup.3] in a municipal park (http:// www.comune.roma.it).

The purpose of the study reported here was to evaluate whether traffic police exposed to urban pollutants could be at risk for alterations of urinary 5-HIAA in 24 hours (5-HIAA[U]) compared with a control group.

Materials and Methods

The research was carried out on a working population of 395 municipal police employees. For admission to the study, all workers completed a questionnaire in the presence of a physician to identify, the main non-occupational confounding factors, which comprised the following points: sex; age; duration of working life; duties performed; weight; height; pharmacological therapies; cigarette-smoking habit (mean number of cigarettes smoked, duration of the habit in years); and daily intake of alcohol (wine, beer, and spirits).

To prevent the influence of confounding factors, the study excluded subjects who regularly made use of oral contraceptives (Mueck, Seeger, Petersen, Shultze-Wintrop & Wallwiener, 2001; Seeger, Ludtke, Graser, Wallwiener & Mueck, 2000), antidepressant drugs (Breier, 1995; Linnoila, Miller, Bartko, & Potter, 1984), and betablocker drugs (Neftel & Gautschi, 1986); subjects who had a body mass index (BMI Kg/[m.sup.2]) above 30 (Bjorntorp, 1995); and subjects who had a cigarette-smoking habit (Benwell, Balfour & Anderson, 1990). Subjects who mentioned habitual consumption of alcoholic spirits were not present in the study. Subjects who mentioned habitual wine/beer consumption above two glasses per day were excluded from the study (Rosenwasser, 2001).

The authors divided all the remaining subjects into traffic police and control subjects. The traffic police exposed to urban pollutants worked on parking control, control of passages, and control of crossroads or roads with heavy traffic. The subjects doing indoor activities such as administrative and bureaucratic duties, at a lesser level of exposure, were used as a control group. Traffic police and controls worked for seven hours a day at least five days a week.

Traffic police were compared with controls by sex, age, working life, and drinking habit (less than two glasses of wine or beer per day) (mean, SD. distribution) (Table 1). The study included 140 subjects: 70 traffic police (41 women and 29 men), and 70 controls (41 women and 29 men).

All the workers included in the study underwent chromatography-colorimetric assay (Shihabi & Wilson, 1982) for 5-HIAA(U): The normal values of the test were the ones normally applied in the authors' laboratory, from 2.0 to 10 mg per 24 hours for both sexes. The urine samples were collected over a period of 24 hours (6 a.m. to 6 a.m.) and kept in a refrigerator at -4[degrees]C until they were moved (by means of a container at the same temperature) to the laboratory. Urine samples were collected on a 24-hour cycle to avoid circadian-rhythm influence (Garvey, Noyes, Woodman, & Cook, 1994).

All the workers were given instructions about how to collect the urine and about foods (those rich in tyramine and tryptophan, such as avocados, bananas, coffee, plums, pineapple and pineapple juice, tomatoes, walnuts) and medicines (aspirin, corticotropin, acetaninophen, phenazetin) that were not to be taken for 72 hours before collection.

The laboratory did not know which samples came from the exposed group and which from the control group, although both physicians and technicians were aware that a study was in progress.

All of the subjects consented to have details of their personal information made available for the study. All declared they had been made aware that these data are classified as "sensitive information" and gave their consent to have the data treated in an anonymous and collective way, with scientific methods and for scientific purposes, in accordance with the principles of the Declaration of Helsinki.

Statistical Analysis

The statistical analysis of the data was based on calculation of the mean, standard deviation, distribution, range, and frequency values according to the nature of the single variables.

The differences between the means were compared with Student's t-test for the unpaired data. The frequencies of the single variables were compared with the Chi-square test and Yates's correction. The differences were considered significant when the p values were <.05. The statistical analysis was done with Solo-BMDP[TM] Statistical Software.

Results and Discussion

Mean 5-HIAA(U) levels were significantly lower in traffic police than in male controls (p = .025) (Table 1). Among females, mean 5-HIAA(U) levels also were significantly lower in traffic police than in controls (p = .027) (Table 1).

No traffic police or control subjects had 5-HIAA(U) values outside the laboratory's normal range. The distributions of the 5-HIAA(U) values in the exposed workers and controls are shown for males and females, respectively, in Figure 1 (p = .000) and Figure 2 (p = .004). Since subjects with the main confounding factors were excluded from the study, and the subjects investigated were matched by sex, age, and working life, the data suggest the possibility that occupational exposure to urban pollutants in traffic police can have an influence on 5-HT turnover and therefore on 5-HIAA(U)]excretion.

[FIGURE 1-2 OMITTED]

The significant differences between the means for exposed workers and controls suggest that they may be of some clinical relevance even when the mean is "numerically" normal.

The action mechanisms of chemical and physical agents that are present as urban pollutants and are able to modify 5-HIAA(U) levels are still uncertain. Studies on animals and human subjects have led to the hypothesis that exposure to chemical and physical agents could decrease (Arito et al., 1985; Fruhstorfer et al., 1985; Lasley et al., 1984; Muraoka et al., 1998) or increase (Jayasekara et al., 1992; Paradowski et al., 1984) serotonergic activity, probably in relation to the doses, modality, and time of exposure.

Effects of carbon monoxide (CO) exposure on 5-HT and 5-HIAA concentration in animals were evaluated by Muraoka and coauthors (1998). 5-HT concentration was significantly decreased in the frontal cortex, and 5-HIAA was increased in the frontal cortex, striatum, hypothalamus, hyppocampus, midbrain, and pons (Muraoka et al.).

In rats exposed to toluene inhalation, serotonin syndrome was found to arise; that study suggests that toluene inhalation may affect serotonergic function (Yamawaki, Segawa, & Sarai, 1982) according to Ladefoged and coauthors (1991). Repeated administration of toluene in rats was associated with lowered concentrations of 5-HT in the frontal cortex, hippocampus, and midbrain and of 5-HIAA in midbrain and hypothalamus; these alterations were associated with insomnia, hyperactivity, and hyperdipsia (Arito et al., 1985). Insomnia was found also in workers exposed to toluene vapor (Antti-Poika, 1982). Other authors showed an increase in brain 5-HT and 5-HIAA in animals exposed to toluene (Honma, Sudo, Miyagawa, Sato, & Hasegawa, 1983; Rea, Nash, Zabik, Born, & Kessler, 1984; Hsieh et al., 1990).

Exposure to styrene in rats produced a significant increase in brain 5-HT and caused a significant decrease in monoamine oxidase (MAO) activity (Husain, Srivastava, Mushtaq, & Seth, 1980).

Animals exposed to low doses of lead (Pb) had a significant 5-HIAA decrease in six of nine brain regions observed (Lasley et al., 1984). Urinary excretion of 5-HIAA was not influenced in rats and workers exposed to Pb (Ichiba & Tomokuni, 1987).

Jayasekara and co-authors (19t)2) found an increase of brain 5-HIAA in laboratory animals after injection of benzo[a]pyrene. Another study in rats exposed to benzo[a]pyrene showed an increase in cortex 5-HIAA (Stephanou, Konstandi, Pappas, & Marselos, 1998). These studies demonstrate that benzo[a]pyrene induces alterations in the serotonergic system throughout the brain.

A single injection of benzene produced a significant increase of 5-HIAA content in striatum but not in the hypothalamus (Paradowski et al., 1984).

In rats exposed to hydrocarbon fuels and solvents, alteration in serum 5-HIAA concentration was found (Rossi, Nordholm, Carpenter, Ritchie, & Malcomb, 2001). One mechanism of action that could lead to a decrease in 5-HIAA (U) excretion following exposure to urban pollutants might be inhibition by some chemical agents (such as CO, toluene, and styrene) of the principal enzymes responsible for the metabolism of serotonin (i.e., tryptophan hydroxylase, MAO A and MAO B) (Egashira, Takayama, Sakai, & Yamanaka, 2000; Husain et al., 1980; Pahwa & Kalra, 1993) even in the presence of other pollutants (such as benzene, benzo[a]pyrene) that could cause activation.

After noise exposure in human subjects, a decrease of serotonergic metabolites was found (Fruhstorfer et al., 1985).

Several studies suggest that 5-HT is an important component of the central network that provides adaptation to stress (Chaouloff, 1993; Flugge, 1995; Kirby; el al., 1997) by means of increase in 5-HT syntbesis/turnover (Berton, Aguerre, Sarrieau, Mormede, & Chaouloff, 1998; Chaouloff, Berton, & Mormede, 1999; Goldstein, Rasmusson, Bunney, & Roth, 1996). By contrast, Campmany, Pol, & Armario (1996) reported that brain 5-HT metabolism was less sensitive than adrenocorticotropic hormone (ACTH) to the process of habituation to a repeated stressor. In students, examination stress did not induce a significant alteration of urinary 5-HIAA (Frankenhaeuser, Lundberg, Rauste von Wright, von Wright, & Sedvall, 1986).

The authors' previous research has ascertained, through the compilation and elaboration of a questionnaire, a greater subjective stress and an increase in plasma ACTH levels in traffic police compared with a control group. Sources of stress for the traffic police may be relations with the public, exposure to episodes of criminality; and the need to maintain high levels of services in various contexts (Pancheri et al., 2002).

Conclusion

It might be supposed that there is an effect on serotonergic turnover and therefore on 5-HIAA(U) in employees of the city police exposed to chemical physical and psychosocial stressors present in living and working environments. If this theory, is valid, many occupational and environmental stressors could play a role in psychiatric pathologies for which the biological substrate is an alteration in 5-HT (Davis et al., 1988; Vandel et al., 1985).

The data suggest that the laboratory test used in this study, which together with examination of other biological parameters, could improve methods for early detection of occupational exposure to urban pollutants.

TABLE 1

Mean Age, Mean Working Life, Mean Values of [5-HIAA(U)] in Traffic
Police and Controls of Both Sexes

                     Male Workers (n = 58)     Female Workers (n = 82)

                    Traffic                    Traffic
                    Police       Controls       Police       Controls
                   (n = 29)      (n = 29)      (n = 41)      (n = 41)

Age
  Mean (SD)       44.6 (5.4)     45.5 (6)     38.6 (4.1)    38.4 (4.3)
  Range              35-57        34-54         33-48         32-49

Working life
    (years)
  Mean (SD)        10.4 (4)     10.2 (4.5)    6.8 (5.1)     6.7 (4.4)
  Range              2-23          4-21          1-25          1-23

5-HIAA(U)
    values (mg/
    24 hours)
  Mean (SD)       3.6 (1.5) *   4.6 (1.8)    3.1 (1.1) **   3.7 (1.3)
  Range               2-7          2-8           2-6           2-7

* p = .025 with respect to control workers.

** p = .027 with respect to control workers.

SD = standard deviation.

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Corresponding author: Professor Francesco Tomei, Via Monte delle Gioie no. 13, 00199, Rome, Italy. E-mail: [e-mail].