ToxSci Advance Access originally published online on September 15, 2006
Toxicological Sciences 2006 94(2):302-309; doi:10.1093/toxsci/kfl109
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Polybrominated Diphenyl Ethers, A Group of Brominated Flame Retardants, Can Interact with Polychlorinated Biphenyls in Enhancing Developmental Neurobehavioral Defects
Department of Environmental Toxicology, Uppsala University, Norbyvägen 18A, S-752 36 Uppsala, Sweden
1 To whom correspondence should be addressed. Fax: +46-18-518843. E-mail: per.eriksson{at}ebc.uu.se.
Received June 1, 2006; accepted September 11, 2006
 |
ABSTRACT |
|---|
 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
The present study shows that polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs) can interact and enhance developmental neurobehavioral defects when the exposure occurs during a critical stage of neonatal brain development. PBDEs are used in large quantities as flame-retardant additives in polymers, especially in the manufacture of a great variety of electrical appliances, and textiles. In contrast to the well-known persistent compounds PCBs and DDT, the PBDEs have been found to increase in the environment and in human mother's milk. We have previously shown that low-dose exposure to environmental toxic agents such as PCB can cause developmental neurotoxic effects when present during a critical stage of neonatal brain development. Epidemiological studies indicate the adverse neurobehavioral impact of PCBs. Recently, we reported that neonatal exposure to PBDEs causes developmental neurotoxic effects. In the present study, 10-day-old Naval Medical Research Institute male mice were given one single oral dose of PCB 52 (1.4 µmol/kg body weight [bw]) + PBDE 99 (1.4 µmol), PCB 52 (1.4 µmol or 14 µmol), or PBDE 99 (1.4 µmol or 14 µmol). Controls received a vehicle (20% fat emulsion). Animals exposed to the combined dose of PCB 52 (1.4 µmol) + PBDE 99 (1.4 µmol) and the high dose of PCB 52 (14 µmol) or PBDE 99 (14 µmol) showed significantly impaired spontaneous motor behavior and habituation capability at the age of 4 and 6 months. The neurobehavioral defects were also seen to worsen with age in mice neonatally exposed to PCB 52 + PBDE 99.
Key Words: PBDE; PCB; brominated flame retardants; behavior; habituation; neonatal; neurotoxicity.
|
INTRODUCTION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
A new group of environmental chemicals, regarded as persistent organic pollutants (POPs), are the brominated flame retardants (de Boer et al., 1998
; Sellström et al., 1993). Of this group, the polybrominated diphenyl ethers (PBDEs) are used in large quantities as flame-retardant additives in polymers, especially in the manufacture of a wide variety of electrical appliances, including casing for television, computer and other electronic products, building materials, and textiles (WHO, 1994). One of the earliest reports of PBDE in organisms in our environment dates from 1981 (Andersson and Blomkvist, 1981), and today, PBDEs are demonstrably present in the global environment (de Boer et al., 1998; de Wit, 2002; Johnson and Olson, 2001; Manchester-Neesvig et al., 2001) and have been found in samples taken from aquatic and terrestrial compartments, for example, sediments (Allchin et al., 1999; Sellström et al., 1993), fish (Asplund et al., 1999a,b; Hale et al., 2002), reindeer (Sellström et al., 1993), and humans (Klasson-Wehler et al., 1997; Schecter et al., 2005; Sjodin et al., 1999, 2003). Furthermore, all data, so far, indicate that PBDEs appear to have an environmental dispersion similar to that of the well-known POPs such as polychlorinated biphenyls (PCBs) and DDT (Darnerud et al., 2001; de Wit, 2002; Sellström et al., 1993).
Of the PBDEs analyzed, the most commonly found congeners in the environment today are 2,2',4,4'-tetra-BDE (PBDE 47), 2,2',4,4',5-penta-BDE (PBDE 99), 2,2',4,4',6-penta-BDE (PBDE 100), and 2,2',4,4',5,5'-hexa-BDE (PBDE-153) (Darnerud et al., 2001). Several reports of PBDEs in human milk have appeared. A breast milk-monitoring program in Sweden has shown that over the course of 20–30 years (1972–1997), organochlorines decreased to half the original concentration, whereas PBDE levels have doubled every 5 years (Meironyté et al., 1999; Norén and Meironyté, 2000). A similar increase was observed in a time-trend study in Japan (1973–2000), where the sum of PBDEs in human milk was of a magnitude similar to that in the Swedish study (Akutsu et al., 2003). It was recently reported that mother's milk in the United States contains the highest levels of PBDEs worldwide, some 10- to 100-fold, compared with the Swedish and Japanese studies (Schecter et al., 2003, 2005). The body burden of PBDEs is also approaching those of the PCBs (Johnson-Restrepo et al., 2005; Morland et al., 2005).
PCBs are one of the most known POPs and a universally spread environmental contaminant. PCBs were first manufactured industrially in 1929 but not detected in environmental samples until 1966 (Jensen, 1966). They have been used in a wide variety of commercial and industrial products such as hydraulic and heat transfer fluids, dielectric fluids in capacitors and transformers, plasticizers, lubricants, and flame retardants (Hutzinger et al., 1974). Several comprehensive epidemiological studies have revealed the detrimental neurodevelopment impacts of PCBs. In humans, perinatal exposure to PCBs is suggested to have developmental neurotoxic effects and to cause hyporeflexia, psychomotor delays, delayed cognitive development, and IQ deficits (Fein et al., 1984; Jacobson and Jacobson, 1996; Jacobson et al., 1990; Patandin et al., 1999; Schantz et al., 2003; Stewart et al., 2000). Experimental studies in animals have shown that commercial mixtures of PCBs can cause behavioral aberrations and changes in brain neurotransmitter metabolism (Seegal, 1996; Seegal and Schantz, 1994; Seegal and Shain, 1992). Exposure of mice, rats, or monkeys during development to commercial mixtures of PCBs, and to single congeners, has been shown to cause long-term neurobehavioral changes (Eriksson, 1998; Tilson and Harry, 1994; Tilson et al., 1990).
In mammals, the main elimination route of highly lipophilic chemicals which have been sequestered in adipose tissue is via lactation (Gallenberg and Vodicnik, 1989). In many mammalian species, the lactation period coincides with a period of rapid growth and development of the brain, the "brain growth spurt" (BGS) (Davison and Dobbing, 1968). In the human, the BGS begins during the third trimester of gestation and continues throughout the first 2 years of ex utero life. In mouse and rat, this period is neonatal, spanning the first 3–4 weeks of life, during which the brain undergoes several fundamental developmental phases, such as axonal and dendritic outgrowth, the establishment of neural connections, acquisition of new motor and sensory faculties (Bolles and Woods, 1964; Davison and Dobbing, 1968; Kolb and Whishaw, 1989), and peak in spontaneous motor behavior (Campbell et al., 1969). Together with numerous biochemical changes, these developments transform the feto-neonatal brain into that of the mature adult (Coyle and Yamamura, 1976; Davison and Dobbing, 1968; Fiedler et al., 1987).
We have reported earlier that neonatal exposure to neurotoxic agents that affect neuronal activity, for example, DDT, nicotine, organophosphorous compounds, and pyrethroids, during a defined period of the BGS, namely, around day 10, induces persistent neurobehavioral defects in the adult mouse, manifested as deranged spontaneous behavior, loss of habituation, impaired learning and memory, as well as changes in the cholinergic system (Ahlbom et al., 1994, 1995; Ankarberg et al., 2001; Eriksson et al., 1992, 2000). This also applies to certain PCBs (Eriksson, 1998; Eriksson and Fredriksson, 1996a,b, 1998; Eriksson et al., 1991), and recently, we have observed similar developmental neurotoxic effects of certain PBDEs, such as PBDE 47, PBDE 99, PBDE 153, and PBDE 209 (Eriksson et al., 2001, 2002; Viberg et al., 2002, 2003a,b, 2004). Regarding the studies on orthosubstituted PCBs, PCB 52 was shown to cause defective spontaneous behavior and habituation, impaired learning and memory faculties, altered response of the adult cholinergic system, and reduced density of cholinergic nicotinic receptors in hippocampus. When neonatally exposed to PBDE 99 in the same amounts on a molar level as in the PCB studies, rodents have been shown to suffer from deranged spontaneous behavior, loss of habituation, impaired learning and memory faculties, altered response of the adult cholinergic system, and a decrease in cholinergic muscarinic receptors in hippocampus. Furthermore, PCB 52 and PBDE 99 can reach the neonatal brain in about equal amounts (Eriksson, 1998; Eriksson et al., 2002). In our studies, the exposure level for PCB has resulted in a brain tissue concentration (ppb levels) of about the same order of magnitude as observed in infants less than 1 year old, see (Gallenberg and Vodicnik, 1989).
In view of the increasing levels of PBDEs in our environment and mother's milk, and with regard to our earlier results where both PCBs and PBDEs caused developmental neurotoxic effects, the present study was carried out to ascertain whether PBDE and PCB can interact to enhance developmental neurotoxic effects on spontaneous behavioral variables and habituation capability.
|
MATERIALS AND METHODS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
Animals and Chemicals
In this study, we used male Naval Medical Research Institute (NMRI) mice in the neurotoxic recordings to make it comparable with our earlier studies on PCBs and PBDEs. Pregnant NMRI mice were purchased from B&K, Sollentuna, Sweden. Following parturition, each litter, adjusted within 48 h to 8–12 pups by euthanasia of the remainder, was kept together with its respective mother in a plastic cage in a room at an ambient temperature of 22°C and a 12:12 h light:dark cycle. At the age of 10 days, pups were exposed to either the vehicle or test compounds. To keep litters and conditions standardized and as near normal as possible during the neonatal period, we exposed both sexes. At the age of 4 weeks, all females were sacrificed, and the males were kept in litters (in treatment groups) with their siblings and were raised in groups of four to seven, in a room for male mice only, and under conditions detailed above. The animals were supplied with standardized pellet food (Lactamin, Stockholm, Sweden) and tap water ad libitum.
The PBDE 2,2',4,4',5-pentabromodiphenylether (PBDE 99) and the PCB 2,2',5,5'-tetrachlorobiphenyl (PCB 52) were synthesized at the Department of Environmental Chemistry, University of Stockholm, Sweden, (Marsh et al., 1999; Örn et al., 1996). The purity of the compounds exceeded 98%. The substances were dissolved in a mixture of egg lecithin (Merck, Darmstadt, Germany) and peanut oil (Oleum arachidis) (1:10) and then sonicated together with water to yield a 20% (wt:wt) fat emulsion vehicle containing various concentrations of the compounds. The substances were administered orally, at a volume of 10 ml/kg bw, via a metal gastric-tube, as one single oral dose on postnatal day 10 to both male and female mice. The amounts of the different compounds given were as follows: 2,2',5,5'-tetrachlorobiphenyl (PCB 52), 0.4 mg (1.4 µmol), 4.0 mg (14 µmol)/kg bw; 2,2',4,4',5-pentabromodiphenylether (PBDE 99), 0.8 mg (1.4 µmol), 8.0 mg (14 µmol)/kg bw; and 2,2',5,5'-tetrachlorobiphenyl + 2,2',4,4',5-pentabromodiphenylether (PCB 52 + PBDE 99), 0.4 + 0.8 mg (1.4 +1.4 µmol)/kg bw. Mice serving as controls received 10 ml/kg bw of the 20% fat emulsion vehicle in the same manner. Each treatment group comprised mice from three to four different litters. The use of a 20% fat emulsion vehicle was to give a more physiologically appropriate absorption and hence distribution of the compounds (Keller and Yeary, 1980; Palin et al., 1982).
This experimental design of neonatal exposure to xenobiotics has been used by our laboratory for several years and thereby generated historical controls as well as reproducible developmental neurotoxicological data on environmental toxicants (Eriksson, 1997, 1998; Eriksson and Viberg, 2005; Viberg et al., 2004). In this neonatal animal model, each of the different treatment groups comprise mice from three to four different litters. Randomly selecting animals from at least three different litters will have the same statistical effect and power compared to the use of litter-based studies to evaluate developmental neurotoxicity in neonatal mice (Eriksson and Viberg, 2005; Eriksson et al., 2005).
Behavioral Tests
Spontaneous behavior.
Spontaneous behavior was tested in the male mice aged of 4 and 6 months, as described previously (Eriksson, 1998; Eriksson and Fredriksson, 1996a; Eriksson and Viberg, 2005; Eriksson et al., 2002; Viberg et al., 2004). At each test occasion, a total of eight mice, randomly selected from three to four different litters, were tested once only, and the tests were performed between 8:00 and 12:00 A.M. under the same ambient light and temperature conditions. Motor activity was measured over 3 x 20 min in an automated device consisting of cages (40 x 25 x 15 cm, same size as the housing cages) placed within two series of infrared beams (low level and high level) (Rat-O-Matic, ADEA Elektronik AB, Uppsala, Sweden) (Eriksson, 1998; Fredriksson, 1994). The cages were placed in individual soundproofed boxes with separate ventilation. Locomotion: registered when the mouse moved horizontally through the low-level grid of infrared beams. Infrared beams were placed 10 mm above the bedded floor. Rearing: vertical movement was registered at a rate of 4 counts per second, whenever and as long as a single high-level beam was interrupted, that is, the number of counts obtained was proportional to time spent rearing. Infrared beams were placed 80 mm above the bedded floor. Activity: a pickup (mounted on a lever with a counterweight) with which the test cage was in contact registered all types of vibration within the test cage, that is, those caused by mouse movements, shaking (tremors), and grooming.
Statistical Analysis
Spontaneous behavior.
The data were subjected to a split-plot ANOVA. Pairwise testing between the treated groups and the vehicle group was performed using a Tukey honestly significant difference (HSD) test (Kirk, 1968).
Habituation capability.
From the spontaneous behavior test, a ratio was calculated between the performance period 40–60 min and 0–20 min for the three different variables locomotion, rearing, and total activity. The following equation was used: 100 x (counts locomotion 40–60 min/counts locomotion 0–20 min), 100 x (counts rearing 40–60 min/counts rearing 0–20 min), and 100 x (counts total activity 40–60 min/counts total activity 0–20 min). These ratios were used to analyze any change in habituation capability between 4-month-old and 6-month-old mice. These data were subjected to a two-way ANOVA.
|
RESULTS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
There were no clinical signs of dysfunction in the treated mice throughout the experimental period nor were there any significant deviations in body weight in the mice treated with PCB 52, PBDE 99, or PCB 52 + PBDE 99, compared with the vehicle-treated mice.
Spontaneous Behavior
The results from the spontaneous behavior variables locomotion, rearing, and total activity in 4- and 6-month-old NMRI male mice exposed to a single oral dose of either PCB 52 (1.4 µmol/kg bw), PCB 52 (14 µmol), PBDE 99 (1.4 µmol), PBDE 99 (14 µmol), or PCB 52 (1.4 µmol) + PBDE 99 (1.4 µmol), and controls receiving 10 ml/kg bw of the 20% fat emulsion vehicle are shown in Figures 1 and 2.
|
|
Four months after the exposure, there were significant group x period interactions (F(10,108) = 23.21, F(10,108) = 28.14, F(10,108) = 8.22) for the three variables locomotion, rearing, and total activity. Pairwise testing between PCB 52, PBDE 99, PCB 52 + PBDE 99 and control groups showed significant differences between the different treatment groups in all three test variables. In control mice, there was a distinct decrease in activity in all behavioral variables over the 60-min period. Such a decrease is a normal spontaneous behavior profile, as was reported in our earlier developmental neurobehavioral studies on PCBs and PBDEs (see Eriksson, 1998
; Eriksson and Fredriksson, 1996a, 1998; Eriksson et al., 2001; Viberg et al., 2003a,b, 2004). In the locomotion variable, mice given PCB 52 + PBDE 99 were significantly (p 
0.01) less active during the first 20-min period (0–20 min) than controls or mice given PBDE (1.4 µmol), whereas during the third period (40–60 min) they were significantly (p 0.01) more active than the controls, mice given PBDE 99 (1.4 µmol), or mice given PCB 52 (1.4 or 14 µmol). Mice given the lower dose of PCB 52 (1.4 µmol) displayed significantly less locomotion during the first 20-min period, compared with controls, whereas mice given the higher PCB 52 dose (14 µmol) showed significantly less locomotion during the first 20-min period, but during the third period (40–60 min), they were significantly (p 0.01) more active than the controls and mice given PCB 52 (1.4 µmol). Mice given PBDE 99 (14 µmol) showed significantly less locomotion during the first 20-min period, while during the third period (40–60 min) they were significantly (p 0.01) more active than the controls and mice given 1.4 µmol PBDE 99. Regarding the rearing variable, mice given PCB 52 + PBDE 99 were significantly (p 0.01) less active during the first 20-min period (0–20 min), compared with controls, mice given PCB 52, or mice given PBDE 99 (1.4 µmol), while during the third period (40–60 min) they were significantly (p 0.01) more active than the controls, mice given PCB 52, or mice given PBDE 99 (1.4 µmol). Mice given PCB 52 or PBDE 99 (14 µmol) were significantly (p 0.01) less active during the first 20-min period (0–20 min), compared with controls, mice given PCB 52, or mice given PBDE 99 (1.4 µmol), while during the third period (40–60 min) they were significantly (p 0.01) more active than the controls, mice given PCB 52, or mice given PBDE 99 (1.4 µmol). Regarding the total activity variable, mice given PCB 52 + PBDE 99 were significantly (p 0.01) more active during the third 20-min period (40–60 min) than the controls, mice given PCB 52, or mice given PBDE 99 (1.4 µmol).
Six months after the neonatal exposure to PCB 52, PBDE 99, or PCB 52 + PBDE, there were still significant group x period interactions (F(10,108) = 46.74, F(10,108) = 35.82, F(10,108) = 17.83), for the locomotion, rearing and total activity variables, respectively (Fig. 2). Pairwise testing between the groups PCB 52, PBDE 99, PCB 52 + PBDE 99, and controls showed significant differences between the different treatment groups for all three test variables locomotion, rearing, and total activity. In all three variables, mice given PCB 52 + PBDE 99 were significantly (p 0.01) less active during the first 20-min period (0–20 min)—and significantly more active in the third period—than controls, mice given PCB 52 (1.4 µmol), or mice given PBDE 99 (1.4 µmol). Regarding the variables locomotion and total activity, mice given PCB 52 + PBDE 99 were significantly (p 0.01) more active during the third period than mice given the high dose of PCB 52 (14 µmol). In the variable total activity, mice given PCB 52 + PBDE 99 were also significantly (p 0.05) more active during the third period, than mice given the high dose of PBDE 99 (14 µmol). The high dose of PCB 52 or PBDE 99 (14 µmol) elicited, for the variables locomotion and rearing, significantly (p 0.01) less activity during the first 20-min period (0–20 min), compared with controls and the corresponding treatment group PCB 52 or PBDE 99 (1.4 –mol), while during the third period (40–60 min) the mice were significantly (p 0.01) more active than the controls, or corresponding group PCB 52 and PBDE 99 (1.4 µmol). Regarding the variable total activity, mice given the higher dose of PBDE 99 (14 µmol) were significantly (p 0.01) less active during the first 20-min period (0–20 min), compared with controls and PBDE 99 (1.4 µmol), while during the third period (40–60 min) they were significantly (p 0.01) more active than the controls and PBDE 99 (1.4 µmol). Mice given PCB 52 (14 µmol) were significantly (p 0.01) less active during the first period (0–20 min) than the controls and mice given PCB 52 (1.4 µmol).
Habituation Capability
By analyzing the habituation ratio between performance period 40–60 min and 0–20 min, we obtained information about the ability to habituate to a novel environment which can be used to analyze changes in habituation with age. The results from the habituation ratio, calculated from the spontaneous behavior variables locomotion and rearing in 4- and 6-month-old mice are given in Table 1. The habituation capability in the locomotion variable was found to decrease significantly (p 0.05) with age in mice exposed to PCB 52 + PBDE 99 (1.4 µmol + 1.4 µmol) and to the high dose of PCB 52 (14 µmol). In mice exposed to the low dose of PCB 52, high and low doses of PBDE 99, or to the vehicle alone, no significant change in habituation ratio with age was observed.
|
|
DISCUSSION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
An important endpoint to study when evaluating the effects of interaction between environmental toxicants in mammals is to analyze the behavior of affected animals. Behavior is a major function whereby animals adapt to changes in the environment, and changes in behavior may reveal effects on the nervous system caused by the influence of a toxicant. Spontaneous behavior is especially meaningful as it reflects a function dependent on the integration of a sensoric input into a motoric output and thus reveals the ability of animals to habituate to an environment and integrate new information with previously attained.
The present study has demonstrated that PCB 52 and PBDE 99 can interact in neonatal mice coexposed to low doses of these agents during a critical period in neonatal brain development to enhance developmental neurobehavioral defects. The aberration of spontaneous behavior and impaired habituation capability were also seen to worsen with age.
Mice exposed on neonatal day 10 to a combined low dose of PCB 52 (1.4 µmol/kg bw) and PBDE 99 (1.4 µmol) displayed significantly disrupted spontaneous behavior and defective habituation at the age of 4 and 6 months. Habituation, defined here as a decrease in locomotion, rearing, and total activity variables in response to the diminishing novelty of the test chamber over 60 min, was evident in the control animals, whereas mice exposed to PCB 52 + PBDE 99 were obviously hypoactive early in the 60-min test period, becoming hyperactive toward the end. A change in spontaneous behavior and habituation was also seen in mice neonatally exposed to the high doses of PCB 52 (14 µmol/kg bw) and PBDE 99 (14 µmol). An important finding was that the developmental neurotoxic effects were more pronounced in mice receiving the combined dose of PCB 52 + PBDE 99 (1.4 + 1.4 µmol), than in mice given only the high dose of PCB 52 (14 µmol), even though this dose, on a molar basis, was fivefold higher. Furthermore, no significant aberration of spontaneous behavior and habituation was observed in mice exposed only to the low dose of PCB (1.4 µmol) or the low dose of PBDE (1.4 µmol), compared with the controls.
The disturbed spontaneous behavior and nonhabituating behavior are consisent with our earlier reported results in mice neonatally exposed to the orthosubstituted PCBs, PCB 28, 52, and 153 (Eriksson, 1998; Eriksson and Fredriksson, 1996a,b), coplanar PCBs, PCB 77, 126, and 169 (Eriksson, 1998; Eriksson and Fredriksson, 1998; Eriksson et al., 1991), and to the PBDEs, PBDE 47, 99, 153, and 209 (Eriksson et al., 2001; Viberg et al., 2003a,b, 2004). The developmental neurotoxic effects of PCB 52 (0.7–14 µmol/kg bw) were manifested as persistent aberrations in spontaneous behavior, defective learning and memory, and decreased amount of the cholinergic nicotinic receptors in the cerebral cortex. In mice, neonatally exposed to PBDE 99 (1.4–21.1 µmol/kg bw), we have reported persistent aberrations in spontaneous behavior and defective learning and memory in adult mice. Mice neonatally exposed to PBDE 99 also showed abnormal spontaneous behavior in response to nicotine, and in rats, the muscarinic cholinergic receptors in hippocampus were reduced (Viberg et al., 2002, 2005). All these behavioral aberrations following neonatal exposure to PBDE 99 or PCB 52 were induced during the defined critical BGS period, occurring around postnatal day 10, and are dose-response related. Furthermore, a single oral dose of 1.4 µmol/kg bw of either PCB 52 or PBDE 99 did not affect the habituation of 4-month-old mice (Eriksson and Fredriksson, 1996a; Eriksson et al., 2001; Viberg et al., 2004), observations supported by the present study.
Whether similar changes in developmental neurobehavioral and cholinergic variables between PCB and PBDE can imply similar mechanisms of action of PBDEs and PCBs is uncertain. The observed interaction between PBDE 99 and PCB 52, showing an effect significantly more pronounced than the fivefold higher dose of PCB 52 (14 µmol/kg bw) alone indicates that different mechanisms may be involved and/or that different brain regions are differently affected. Whether the interaction is additive or synergistic cannot with certainty be concluded from the present study. However, by comparing earlier dose-response studies on PCB (Eriksson, 1998; Eriksson and Fredriksson, 1996a,b) and PBDE (Eriksson et al., 2001, 2002; Eriksson and Viberg, 2005; Viberg et al., 2002, 2003a, 2004) where higher responses are seen at higher doses suggests that the observed effect of interaction is more than additive. We have earlier observed interactive effects between different PCB congeners known to influence both spontaneous behavior and the cholinergic system. An enhanced effect on spontaneous behavior was seen when mice were exposed simultaneously to PCB 52 and a coplanar PCB (PCB 126) during neonatal brain development (Eriksson, 1998). The two different congeners have been reported to affect different parts of the adult brain, whereby PCB 52 affected the nicotinic receptors in the cerebral cortex, whereas neonatal exposure to PCB 126 was shown to affect the nicotinic receptors in the hippocampus (Eriksson and Fredriksson, 1996a, 1998). PCB 52 has also been shown to interact with the cholinergic agonist nicotine, where nicotine is known to affect nicotinic receptors in the cerebral cortex, in enhancing developmental neurobehavioral defects in spontaneous behavior of adult mice (Ankarberg et al., 1998).
The results of the spontaneous behavior tests further indicate that the functional disorders worsen with advancing age, as the aberrations in spontaneous behavior appeared to be more pronounced in 6-month-old than in 4-month-old mice. The habituation capability of mice exposed to the combined dose of PCB 52 + PBDE 99, and to the high dose of PCB 52, was seen to worsen significantly from 4 to 6 months. This type of time-response behavioral defect has earlier been observed in mice neonatally exposed to high doses of orthosubstituted and coplanar PCBs (Eriksson, 1998; Eriksson and Fredriksson, 1996a, 1998) and to PBDEs (Eriksson et al., 2001; Viberg et al., 2003a,b, 2004). Both the change in spontaneous behavior and the impaired habituation capability indicate the advance of brain dysfunction, induced at time of rapid development in the neonatal mouse. With regard to the adverse neurodevelopmental impacts of PCBs given in several epidemiological studies, together with the effects of interaction between PCB and PBDE at low doses and their role as possible environmental toxicants involved in the processes of neuronal disturbance and possible consequences, not only in children but also later in life, call for further studies.
The amounts of orthosubstituted PCBs (e.g., PCB 52 and 153) and PBDEs (e.g., PBDE 99) found in the brain 24 h after a single oral administration to 10-day-old mice were about 0.3–0.5% of the total administered dose (Eriksson, 1998; Eriksson and Darnerud, 1985; Eriksson et al., 2002). Data on actual organ/tissue levels of PCBs or PBDEs in infants are few or is lacking. The amounts of different PCBs administered in our earlier studies resulted in brain tissue concentrations (ppb levels) that can be of the same order of magnitude as observed in infants less than 1 year old (see Gallenberg and Vodicnik, 1989). In two postmortem studies, from Japan and Britain, an average value of 7 ppb was found in the cerebrum. Analogous data of PBDEs in infants is lacking. However, in a recent report by McDonald on PBDE levels among U.S. women and estimates of daily intake and risk of developmental effects indicate levels that can be associated with adverse effects on neurodevelopment in animals (McDonald, 2005). We have reported that the amount of PCB or PBDE present in the brain during the critical phase and known to induce behavioral defects was about 20 ppb. In human studies, it is difficult to distinguish between exposure of offspring by transplacental or by breast milk transfer. However, both human and animal data from a variety of species suggest that accumulation of highly persistent chemicals via milk far exceeds the contribution made by maternal-fetal transfer (Gallenberg and Vodicnik, 1989). In animal studies, using the orthosubstituted PCB 153, it was found that about 60% of the body burden was eliminated via milk during the first 5 days of lactation and virtually all by day 20 (Gallenberg and Vodicnik, 1989; Vodicnik and Lech, 1980). Various epidemiological studies on the developmental neurotoxic effects after gestational and/or lactational exposure to PCBs show the difficulty of predicting when developmental disorders may be induced. By considering the critical period for induction of permanent neurotoxic derangement during the BGS in mice, the corresponding period in humans starts during the third trimester of gestation and continues for several months after birth. According to the "window" in our mouse studies, the critical phase would roughly be perinatal.
Taken together, this study shows that neonatal coexposure to PCB 52, and PBDE 99 can enhance developmental neurotoxic effects. The study also showed that when PCB 52 and PBDE 99 interact, the effect is more than just additive. Further research with the new contaminant PBDE and the older agent PCB are of vital importance, as the levels of PBDEs are increasing in mother's milk and in the environment, generally, and bearing in mind the present background level of PCBs.
|
ACKNOWLEDGMENTS |
|---|
This work was financially supported by the Swedish Research Council for Environmental, Agricultural Sciences, and Spatial Planning and the Foundation for Strategic Environment Research.
|
REFERENCES |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
Ahlbom J, Fredriksson A, Eriksson P. (1994) Neonatal exposure to a type-I pyrethroid (bioallethrin) induces dose-response changes in brain muscarinic receptors and behaviour in neonatal and adult mice. Brain Res. 645:318–324.[CrossRef][ISI][Medline]
Ahlbom J, Fredriksson A, Eriksson P. (1995) Exposure to an organophosphate (DFP) during a defined period in neonatal life induces permanent changes in brain muscarinic receptors and behaviour in adult mice. Brain Res. 677:13–19.[CrossRef][ISI][Medline]
Akutsu K, Kitagawa M, Nakazawa H, Makino T, Iwazaki K, Oda H, Hori S. (2003) Time-trend (1973–2000) of polybrominated diphenyl ethers in Japanese mother's milk. Chemosphere 53:645–654.[Medline]
Allchin CR, Law RJ, Morris S. (1999) Polybrominated diphenylethers in sediment and biota downstream of potential sources in the UK. Environ. Pollut. 105:197–207.[CrossRef]
Andersson Ö and Blomkvist G. (1981) Polybrominated aromatic pollutants found in fish in Sweden. Chemosphere. 10:1051–1060.[CrossRef]
Ankarberg E, Fredriksson A, Eriksson P. (1998) Interactive effects of PCB and nicotine administered during the neonatal brain development. Organohalogen Compd. 37:93–96.
Ankarberg E, Fredriksson A, Eriksson P. (2001) Neurobehavioural defects in adult mice neonatally exposed to nicotine: Changes in nicotine-induced behaviour and maze learning performance. Behav. Brain Res. 123:185–192.[CrossRef][ISI][Medline]
Asplund L, Athanasiadou M, Sjödin A, Bergman Å, Börjeson H. (1999a) Organohalen substances in muscle, egg and blood from healthy Baltic salmon (Salmo salar) and baltic salmon that produces offspring with the M74 syndrome. Ambio. 28:67–76.
Asplund L, Hornung M, Peterson R, Thuresson K, Bergman Å. (1999b) Levels of polybrominated diphenyl ethers (PBDEs) in fish from the Great Lakes and Baltic Sea. Organohalogen Compd. 40:351–354.
Bolles RG and Woods PJ. (1964) The ontogeny of behaviour in the albino rat. Anim. Behav. 12:427–441.[CrossRef]
Campbell BA, Lytle LD, Fibiger HC. (1969) Ontogeny of adrenergic arousal and cholinergic inhibitory mechanisms in the rat. Science 166:635–637.
Coyle JT and Yamamura HI. (1976) Neurochemical aspects of the ontogenesis of cholinergic neurons in the rat brain. Brain Res. 118:429–440.[CrossRef][ISI][Medline]
Darnerud PO, Eriksen GS, Johannesson T, Larsen PB, Viluksela M. (2001) Polybrominated diphenyl ethers: Occurrence, dietary exposure, and toxicology. Environ. Health Perspect. 109:suppl 1, 49–68.
Davison AN and Dobbing J. (1968) Applied NeurochemistryBlackwell, Oxford.
de Boer J, Wester PG, Klamer HJ, Lewis WE, Boon JP. (1998) Do flame retardants threaten ocean life? [letter]. Nature 394:28–29.[CrossRef][Medline]
de Wit CA. (2002) An overview of brominated flame retardants in the environment. Chemosphere 46:583–624.[Medline]
Eriksson P. (1997) Developmental neurotoxicity of environmental agents in the neonate. Neurotoxicology 18:719–726.[ISI][Medline]
Eriksson P. (1998) Perinatal Developmental Neurotoxicity of PCBs(Swedish Environmental Protection Agency, Stockholm, Sweden) pp. 56.
Eriksson P, Ahlbom J, Fredriksson A. (1992) Exposure to DDT during a defined period in neonatal life induces permanent changes in brain muscarinic receptors and behaviour in adult mice. Brain Res. 582:277–281.[CrossRef][ISI][Medline]
Eriksson P, Ankarberg E, Fredriksson A. (2000) Exposure to nicotine during a defined period in neonatal life induces permanent changes in brain nicotinic receptors and in behaviour of adult mice. Brain Res. 853:41–48.[CrossRef][ISI][Medline]
Eriksson P and Darnerud PO. (1985) Distribution and retention of some chlorinated hydrocarbons and a phthalate in the mouse brain during the pre-weaning period. Toxicology 37:189–203.[CrossRef][ISI][Medline]
Eriksson P and Fredriksson A. (1996a) Developmental neurotoxicity of four ortho-substituted polychlorinated biphenyls in the neonatal mouse. Environ. Toxicol. Pharmacol. 1:155–165.[CrossRef]
Eriksson P and Fredriksson A. (1996b) Neonatal exposure to 2,2',5,5'-tetrachlorobiphenyl causes increased susceptibility in the cholinergic transmitter system at adult age. Environ. Toxicol. Pharmacol. 1:217–220.[CrossRef]
Eriksson P and Fredriksson A. (1998) Neurotoxic effects in adult mice neonatally exposed to 3,3',4,4',5-pentachlorobiphenyl or 2,3,3',4,4'-pentachlorobiphenyl. Changes in brain nicotinic receptors and behaviour. Environ. Toxicol. Pharmacol. 5:17–27.
Eriksson P, Jakobsson E, Fredriksson A. (2001) Brominated flame retardants: A novel class of developmental neurotoxicants in our environment? . Environ. Health Perspect. 109:903–908.[ISI][Medline]
Eriksson P, Lundkvist U, Fredriksson A. (1991) Neonatal exposure to 3,3',4,4'-tetrachlorobiphenyl: Changes in spontaneous behaviour and cholinergic muscarinic receptors in the adult mouse. Toxicology 69:27–34.[CrossRef][ISI][Medline]
Eriksson P and Viberg H. (2005) Tiered testing in mammals—the neonatal animal model. In Hansson S and Rudén C (Eds.). Science for a Safe Chemical Environment(A MISTRA funded research programme, Stockholm, Sweden) pp. 103–133.
Eriksson P, Viberg H, Jakobsson E, Orn U, Fredriksson A. (2002) A brominated flame retardant, 2,2',4,4',5-pentabromodiphenyl ether: Uptake, retention, and induction of neurobehavioral alterations in mice during a critical phase of neonatal brain development. Toxicol. Sci. 67:98–103.
Eriksson P, von Rosen D, Viberg H, Fredriksson A. (2005) Developmental toxicology in the neonatal mouse: the use of randomly selected individuals as statistical unit compared to the litter in mice neonatally exposed to PBDE 99. Toxicologist 84:219.
Fein GG, Jacobson JL, Jacobson SW, Schwartz PM, Dowler JK. (1984) Prenatal exposure to polychlorinated biphenyls: Effects on birth size and gestational age. J. Pediatr. 105:315–320.[CrossRef][ISI][Medline]
Fiedler EP, Marks MJ, Collins AC. (1987) Postnatal development of cholinergic enzymes and receptors in mouse brain. J. Neurochem. 49:983–990.[CrossRef][ISI][Medline]
Fredriksson A. (1994) MPTP-Induced Behavioural Deficits in Mice: Validity and Utility of a Model of Parkinsonism(Uppsala University, Uppsala, Sweden).
Gallenberg LA and Vodicnik MJ. (1989) Transfer of persistent chemicals in milk. Drug Metab. Rev. 21:277–317.[ISI][Medline]
Hale RC, La Guardia MJ, Harvey E, Mainor TM. (2002) Potential role of fire retardant-treated polyurethane foam as a source of brominated diphenyl ethers to the US environment. Chemosphere 46:729–735.[Medline]
Hutzinger O, Safe S, Zitko V. (1974) The Chemistry of PCB's(CRC Press, Cleveland, OH).
Jacobson JL and Jacobson SW. (1996) Intellectual impairment in children exposed to polychlorinated biphenyls in utero [see comments]. N. Engl. J. Med. 335:783–789.
Jacobson JL, Jacobson SW, Humphrey HE. (1990) Effects of exposure to PCBs and related compounds on growth and activity in children. Neurotoxicol. Teratol. 12:319–326.[CrossRef][ISI][Medline]
Jensen S. (1966) Report of a new chemical hazard. New Sci. 32:612.
Johnson-Restrepo B, Kannan K, Rapaport DP, Rodan BD. (2005) Polybrominated diphenyl ethers and polychlorinated biphenyls in human adipose tissue from New York. Environ. Sci. Technol. 39:5177–5182.[Medline]
Johnson A and Olson N. (2001) Analysis and occurrence of polybrominated diphenyl ethers in Washington state freshwater fish. Arch. Environ. Contam. Toxicol. 41:399–404.[CrossRef]
Keller WC and Yeary RA. (1980) A comparison of the effects of mineral oil, vegetable oil and sodium sulfate on the intestinal absorption of DDT in rodents. Clin. Toxicol. 16:223–231.[ISI][Medline]
Kirk RE. (1968) Procedures for the Behavioural Science(Brooks/Cole, Belmont, CA).
Klasson-Wehler E, Hovander L, Bergman Å. (1997) New organohalogens in human plasma—Identification and quantification. In Hites R (Ed.). 17th Symposium on Halogenated Environmental Organic Pollutants, Indianapolis, IN Vol. 33: pp. 420–429.
Kolb B and Whishaw IQ. (1989) Plasticity in the neocortex: Mechanisms underlying recovery from early brain damage. Prog. Neurobiol. 32:235–276.[CrossRef][ISI][Medline]
Manchester-Neesvig JB, Valters K, Sonzogni WC. (2001) Comparison of polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs) in Lake Michigan salmonids. Environ. Sci. Technol. 35:1072–1077.[Medline]
Marsh G, Hu J, Jakobsson E, Rahm S, Bergman Å. (1999) Synthesis and characterization of thirty-two polybrominated diphenyl ethers (PBDEs). Environ. Sci. Technol. 33:3033–3037.[CrossRef]
McDonald T. (2005) Polybrominated diphenylether levels among United States residents: Daily intake and risk of harm to the developing brain and reproductive organs. Integr. Environ. Assess. Manag. 1:343–354.[CrossRef][Medline]
Meironyté D, Norén K, Bergman A. (1999) Analysis of polybrominated diphenyl ethers in Swedish human milk. A time dependent trend study, 1972–1997. J. Toxicol. Environ. Health Part A 58:329–341.[CrossRef][ISI][Medline]
Morland KB, Landrigan PJ, Sjodin A, Gobeille AK, Jones RS, McGahee EE, Needham LL, Patterson DG Jr. (2005) Body burdens of polybrominated diphenyl ethers among urban anglers. Environ. Health Perspect. 113:1689–1692.[ISI][Medline]
Norén K and Meironyté D. (2000) Certain organochlorine and organobromine contaminants in Swedish human milk in perspective of past 20–30 years. Chemosphere 40:1111–1123.[Medline]
Örn U, Eriksson L, Jakobson E, Bergman Å. (1996) Synthesis and characterization of polybrominated diphenyl ethers—unlabelled and radiolabelled tetra-, penta-, and hexa-bromodiphenyl ethers. Acta Chem. Scand. 50:802–807.
Palin KJ, Wilson CG, Davis SS, Phillips AJ. (1982) The effects of oil on the lymphatic absorption of DDT. J. Pharm. Pharmacol. 34:707–710.[ISI][Medline]
Patandin S, Lanting CI, Mulder PG, Boersma ER, Sauer PJ, Weisglas-Kuperus N. (1999) Effects of environmental exposure to polychlorinated biphenyls and dioxins on cognitive abilities in Dutch children at 42 months of age. J. Pediatr. 134:33–41.[CrossRef][ISI][Medline]
Schantz SL, Widholm JJ, Rice DC. (2003) Effects of PCB exposure on neuropsychological function in children. Environ. Health Perspect. 111:357–576.[ISI][Medline]
Schecter A, Papke O, Tung KC, Joseph J, Harris TR, Dahlgren J. (2005) Polybrominated diphenyl ether flame retardants in the U.S. population: Current levels, temporal trends, and comparison with dioxins, dibenzofurans, and polychlorinated biphenyls. J. Occup. Environ. Med 47:199–211.[CrossRef][ISI][Medline]
Schecter A, Pavuk M, Papke O, Ryan JJ, Birnbaum L, Rosen R. (2003) Polybrominated diphenyl ethers (PBDEs) in U.S. mothers' milk. Environ. Health Perspect. 111:1723–1729.[ISI][Medline]
Seegal RF. (1996) Epidemiological and laboratory evidence of PCB-induced neurotoxicity. Crit. Rev. Toxicol. 26:709–737.[ISI][Medline]
Seegal R and Schantz SL. (1994) Neurochemical and Behavioural Sequele of Exposure to Dioxins and PCBs(Plenum Press, New York).
Seegal R and Shain W. (1992) Neurotoxicity of polychlorinated biphenyls. The role of ortho-substituted congeners in altering neurochemical function. In Isaacson R. L and Jensen K. F (Eds.). The Vulnerable Brain and Environmental Risks(Plenum Press, New York) Vol. 2: pp. 165–195.
Sellström U, Jansson B, Kierkegaard A, de Wit C. (1993) Polybrominated diphenyl ethers (PBDE) in biological samples from the Swedish environment. Chemosphere 26:1703–1718.[CrossRef]
Sjodin A, Hagmar L, Klasson-Wehler E, Kronholm-Diab K, Jakobsson E, Bergman A. (1999) Flame retardant exposure: Polybrominated diphenyl ethers in blood from Swedish workers. Environ. Health Perspect. 107:643–648.[ISI][Medline]
Sjodin A, Patterson J, Donald G, Bergman A. (2003) A review on human exposure to brominated flame retardants—particularly polybrominated diphenyl ethers. Environ. Int. 29:829–839.[CrossRef][ISI][Medline]
Stewart P, Reihman J, Lonky E, Darvill T, Pagano J. (2000) Prenatal PCB exposure and neonatal behavioral assessment scale (NBAS) performance. Neurotoxicol. Teratol. 22:21–29.[CrossRef][ISI][Medline]
Tilson HA and Harry GJ. (1994) Developmental neurotoxicology of polychlorinated biphenyls and related compounds. In Isaacson R. L and Jensen K. F (Eds.). The Vulnerable Brain and Environmental Risks(Plenum Press, New York) Vol. 3: pp. 267–279.
Tilson HA, Jacobson JL, Rogan WJ. (1990) Polychlorinated biphenyls and the developing nervous system: Cross-species comparisons. Neurotoxicol. Teratol. 12:239–248.[CrossRef][ISI][Medline]
World Health Organization (WHO). (1994) Brominated Diphenyl Ethers. WHO IPCS Environmental Health Criteria Document, 162. WHO, Geneva, Switzerland.
Viberg H, Fredriksson A, Eriksson P. (2002) Neonatal exposure to the brominated flame retardant 2,2',4,4',5-pentabromodiphenyl ether causes altered susceptibility in the cholinergic transmitter system in the adult mouse. Toxicol. Sci. 67:104–107.
Viberg H, Fredriksson A, Eriksson P. (2003a) Neonatal exposure to polybrominated diphenyl ether (PBDE 153) disrupts spontaneous behaviour, impairs learning and memory, and decreases hippocampal cholinergic receptors in adult mice. Toxicol. Appl. Pharmacol. 192:95–106.[CrossRef][ISI][Medline]
Viberg H, Fredriksson A, Eriksson P. (2004) Investigations of strain and/or gender differences in developmental neurotoxic effects of polybrominated diphenyl ethers in mice. Toxicol. Sci. 81:344–353.
Viberg H, Fredriksson A, Eriksson P. (2005) Deranged spontaneous behaviour and decrease in cholinergic muscarinic receptors in hippocampus in the adult rat, after neonatal exposure to the brominated flame-retardant, 2,2',4,4',5-pentabromodiphenyl ether (PBDE 99). Environ. Toxicol. Pharmacol. 20:283.[CrossRef]
Viberg H, Fredriksson A, Jakobsson E, Orn U, Eriksson P. (2003b) Neurobehavioral derangements in adult mice receiving decabrominated diphenyl ether (PBDE 209) during a defined period of neonatal brain development. Toxicol. Sci. 76:112–120.
Vodicnik MJ and Lech JJ. (1980) The transfer of 2,4,5,2',4',5'-hexachlorobiphenyl to fetuses and nursing offspring. I. Disposition in pregnant and lactating mice and accumulation in young. Toxicol. Appl. Pharmacol. 54:293–300.[CrossRef][ISI][Medline]
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  C. Fischer, A. Fredriksson, and P. Eriksson Coexposure of Neonatal Mice to a Flame Retardant PBDE 99 (2,2',4,4',5-Pentabromodiphenyl Ether) and Methyl Mercury Enhances Developmental Neurotoxic Defects Toxicol. Sci., February 1, 2008; 101(2): 275 - 285. [Abstract] [Full Text] [PDF]
|
|
| |||||||||||||||||||||||||||||||||||