* National Public Health Institute, Department of Environmental Health, FIN-70701 Kuopio, Finland; Department of Medical Technology, University of Oulu, 90014 University of Oulu, Finland;
Department of Anatomy and Cell Biology, University of Oulu, FIN-90014 University of Oulu, Finland;
Department of Public Health and General Practice, University of Kuopio, FIN-70211 Kuopio, Finland
1 To whom correspondence should be addressed at National Public Health Institute, Department of Environmental Health, Laboratory of Toxicology, P.O. Box 95, FIN-70701 Kuopio, Finland. Fax: +358-17201265. E-mail: hanna.miettinen{at}ktl.fi.
Received December 8, 2004; accepted February 19, 2005
![]() |
ABSTRACT |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Key Words: dioxin; development; bone; peripheral quantitative computed tomography; biomechanics.
![]() |
INTRODUCTION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
We have recently reported that long-term exposure to TCDD dose-dependently interferes with bone growth, modeling, and mechanical strength in adult Long-Evans (Turku/AB; L-E) and Han/Wistar (Kuopio; H/W) rats (Jämsä et al., 2001). Decreased tibial growth was associated with altered bone geometry, as indicated by decreased cross-sectional and medullary areas at the diaphysis. Cortical bone mineral density (BMD) was not affected, but the three-point bending test indicated decreased bending breaking force and stiffness of the tibial diaphysis. These changes were observed at exposure levels that are not much higher than current average human dioxin exposures. Interestingly, the dioxin-resistant H/W rats with mutated AHR (Pohjanvirta et al., 1998
) were more resistant to these effects than L-E rats with normal AHR structure and high dioxin sensitivity. H/W rats have a point mutation in Ahr, which results in loss of amino acids from the transactivation domain of the receptor protein and a high resistance to some but not all end points of dioxin toxicity (Pohjanvirta et al., 1998
; Simanainen et al., 2002
; Tuomisto et al., 1999
). In addition, H/W rats have another, still unknown allele Bhw that has a smaller influence on dioxin resistance. By selective crossing of H/W and L-E rat strains, three new rat lines were created, which differ in their sensitivity to short-term toxic effects of TCDD (Simanainen et al., 2003
; Tuomisto et al., 1998
, 1999
). Line A rats have the altered H/W type AHR (Ahrhw), line B rats have the other resistance allele Bhw, and line C rats have no resistance alleles. These lines exhibit highly different LD50 values for TCDD: >2000, 410, and 19 µg/kg in line A, B, and C females, respectively.
Because of the general sensitivity of developing animals to dioxins and the high potential dioxin exposure via mother's milk, we studied the effects of low-dose prenatal and postnatal TCDD exposure on rat bone development. The studies were designed (1) to establish the doseresponse relationships of possible bone effects, (2) to define the critical window of sensitivity during development, (3) to examine the reversibility of the effects, and (4) to study the influence of the dioxin-resistance alleles Ahrhwand Bhw on sensitivity to these effects by using differentially sensitive line A, B, and C rats.
![]() |
MATERIALS AND METHODS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Animals.
Line A, B, and C rats were received from the SPF barrier unit of the National Public Health Institute (Kuopio, Finland). After mating, pregnant rats were kept in plastic Macrolon cages containing aspen-chip bedding (Tapvei Co, Kaavi, Finland) and covered with wire-mesh lids until the pups were weaned on postnatal day (PND) 28. The pups were kept in Macrolon cages similarly with their dams. The rats were kept under a photoperiodic cycle of 12 h light/12 h dark in an air-conditioned room. The mean temperature was 21° ± 0.5°C and the relative humidity 40 ± 7%. Pelleted rat feed (R36, Lactamin) and tap water were available ad libitum.
Experimental design.
Three different studies were carried out; a doseresponse study in lines A, B, and C (Kattainen et al., 2001; Miettinen et al., 2002
) was followed by a study with different timing of exposure in the most sensitive line C (Kattainen et al., 2001
; Miettinen et al., 2002
) and a one-year follow-up study in all three rat lines. Observations on tooth development in the first two studies have been previously published by Kattainen et al. (2001)
and Miettinen et al. (2002)
, respectively, and observations on the male reproductive system development are presented in the first study by Simanainen et al. (2004)
. Rats were mated overnight 12 females with one male, and the day sperm was confirmed in a vaginal smear was assigned gestational day (GD) 0. Pregnant dams were given a single oral dose of 0.03, 0.1, 0.3, or 1 µg/kg TCDD in the doseresponse study, and 1 µg/kg in the one-year follow-up study on GD15 at a volume of 4 ml/kg. The highest dose had to be limited to 1 µg/kg in TCDD-resistant lines A and B also, because a pilot study had revealed that a maternal dose of 3 µg/kg on GD15 resulted in 100% postnatal death of line A offspring. In the timing of exposure study, pregnant line C rats received a single dose of 1 µg/kg during gestation on GD11, GD13, or GD19, or after delivery on PND 0, PND2, or PND4 at volume of 4 ml/kg. Control rats received corn oil on GD15. For cross-fostering groups, two groups of dams from the timing of exposure study were dosed on GD15 with either TCDD or corn oil. Pups from dosed dams were transferred to control dams and vice versa on PND0, before the dams started to lactate. In all studies, the offspring number was recorded and litter size was adjusted to six animals (three males + three females) on PND1, if possible, and there were 36 litters in each group (2 in the TCDD group exposed on PND13). In the exposure timing study, both male and female offspring were examined, but the other studies were carried out in female offspring. The offspring were weaned on PND28, after which they were housed with same-sex littermates. Body weight was measured weekly. The offspring were killed by CO2 asphyxiation and cervical dislocation on PND35 (doseresponse study; only females studied), PND40 (exposure timing study; both males and females studied), or at the age of 52 weeks (one-year follow-up study; only females studied). Femurs and tibias were stored at 20°C until analysis. The bones were thawed at room temperature immediately before analysis, and the soft tissue was removed. Bone length was measured with a digital Vernier caliper.
Bone densitometry.
The bones were scanned with a Stratec XCT 960 A pQCT system with software version 5.21 (Norland Stratec Medizintechnik GmbH). The bones were inserted into a plastic tube filled with 0.9% NaCl to position the samples for the measurements. A voxel size of 0.148 x 0.148 x 1.25 mm3 was used for the measurement. An attenuation threshold value of 0.7 cm1 was used to define cortical bone. The precision and accuracy of the pQCT system used had been verified previously (Jämsä et al., 2001). One cross-sectional slice from each bone was scanned at midshaft, which was determined from the scout view of the pQCT system. Cross-sectional area of cortex (CSA) and cortical bone mineral density (BMD), polar cross-sectional moment of inertia (PMI), and periosteal and endosteal circumferences (PERI and ENDO, respectively) were measured at the midshaft of the bone.
Mechanical testing.
After the pQCT measurements, the bones were subjected to mechanical testing, as described elsewhere (Jämsä et al., 1998; Peng et al., 1994
). Briefly, the materials testing machine (Jämsä et al. 1998
) with amplifier (Jämsä and Jalovaara, 1996
) and force sensor (Gefran TU K5D, 050 kg, Gefran Sensori) was used to measure the failure load of the three-point bending strength of tibia, femur, and femoral neck. In the three-point bending test, the bone was placed on a supporter with two loading points, 13 mm apart. The pressing force was directed vertically to the midshaft of the bone. To measure the failure load of the femoral neck, the proximal half of the femur was placed axially into a suitable hole on the supporter and pressed in a direction parallel to the femoral shaft. The constant compression speed of 0.155 mm/s was used in both configurations. A laboratory plotter (Yokogawa LR 102, Yokogawa Europe) recorded the compression load in dependence on the time. The loaddeformation relationship was obtained by conversion of the loadtime curve. The maximal load (N) was used for evaluation of bone strength and the stiffness (N/mm) was calculated according to the slope of the linear part of the curve.
Analysis of TCDD tissue concentrations.
Pregnant line C females were exposed to 0.5 µg/kg TCDD on GOD, GD11 or GD15 (35 rats per group), at volume of 4 ml/kg. On GD22, females were monitored every half-hour and born offspring were moved from the cage to prevent suckling. Dams were killed with CO2 asphyxiation and cervical dislocation and offspring with an overdose of pentobarbital (Mebunat, Orion Pharma). One group of rats exposed on GD15 was allowed to rear offspring until PND5, when the animals were killed and studied. Offspring were frozen as a whole at 20°C until homogenization with Bamix M133 mixer (ESGE AG). Each litter was homogenized to gain a litter sample. The same amount of homogenized offspring tissue from each litter was then pooled to gain a group sample. The same amount of perirenal adipose tissue from each dam was pooled for a group fat sample. Tissue samples were freeze-dried and extracted in a Soxhlet apparatus with toluene for 18 h. The solvent was changed to hexane and the fat% was determined gravimetrically.
The extract or an aliquot was spiked with an internal standard solution containing 13C-labeled TCDD and was purified using silica gel, carbon, and aluminum oxide columns (Vartiainen et al., 1995). Prior to analyses of TCDD by gas chromatography/mass spectrometry (GC/MS), the purified extract was spiked with a recovery standard solution containing 13C-1,2,3,4-TCDD and was concentrated with nitrogen flow to final volume of 30 µl nonane.
GC/MS analyses were carried out with a VG 70250SE high-resolution mass spectrometer (VG Analytical) interfaced to a HP 6890 high-resolution gas chromatograph (Hewlett-Packard). The mass spectrometer was operated in the selected ion monitoring (SIM) mode at a resolution of 10,000 in electron impact ionization (EI) mode (35 eV). Two ions of the molecular ion cluster (M+ and (M+2)+) were recorded for each followed compound.
Identification of 2,3,7,8-TCDD was verified by a comparison of the GC retention time and ion ratios with those of the reference compound. Detection limits were as follows: liver 0.1 pg/g fresh weight, lipid tissue 0.55 pg/g lipid weight.
Statistics.
A femur and a tibia of one female and one male per litter were examined; otherwise, additional samples were studied from randomly selected litters to gain a minimum of six studied offspring. Because of the small number of offspring in groups exposed on GD11 and GD13, all of them were studied. The results were analyzed on a litter basis, maintaining litter independence. The parameters were tested with the analysis of variance (ANOVA) followed by the least significant difference (LSD) test in the cases where the data displayed normal distribution (Levene's test); otherwise, the nonparametric Kruskal-Wallis ANOVA was used, followed by the Mann-Whitney U-test. The limit of statistical significance was set at p < 0.05.
![]() |
RESULTS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Bone Length and Geometry
Changes in bone length and geometry were observed only in line C rats and only at the highest maternal dose of 1 µg/kg TCDD (Table 2; data for lines A and B not shown). The length of tibias and femurs of line C offspring exposed to 1 µg/kg TCDD was slightly but nonsignificantly shorter than that of control offspring in the doseresponse study. In the exposure timing study, tibias were significantly shorter in both genders exposed on GD11 and GD13, as well as in females exposed on GD19 and in males in the cross-fostered group exposed only via lactation. Femur length was significantly shorter only in males exposed on GD11, GD19, PND2 and in both cross-fostered groups as compared to controls. Cross-sectional area of femoral cortex (CSA) was decreased in line C at 1 µg/kg TCDD in the doseresponse study (Table 2, Fig. 1). In the exposure timing study, tibial and femoral CSA was decreased in males and tibial CSA was decreased in females exposed on GD11, GD 13, and GD19. Dose-dependent decrease in medullary area, as indicated by smaller endosteal circumference (ENDO), was seen in both long bones, and the decrease was significant at 1 µg/kg in femur. In the exposure timing study, ENDO and periosteal circumference (PERI) in femur were decreased in both genders, though not significantly in all groups. In tibia, PERI was significantly decreased only in females in all groups except PND4. Polar cross-sectional moment of inertia (PMI) was decreased in femurs of line C rats at 1 µg/kg in both genders, although statistical significances was not found in all groups, and results were similar in tibia of females in the time-exposure study.
|
|
|
Mechanical Parameters
TCDD-treatment resulted in consistent changes in the bone mechanical parameters only in line C rats (Table 3, Fig. 3; data for line A and B rats not shown).
|
|
Males
In male offspring, the breaking force of tibia and femur was significantly reduced in groups exposed on GD11 and GD13. The breaking force of femoral neck was also slightly but nonsignificantly decreased. The only significant change in bending stiffness was found in femur in groups GD11, GD13, and PND2.
Gender Differences
No significant differences between males and females were observed in bone geometry, densitometry, or mechanical parameters in the exposure timing study groups where both genders were examined.
Reversibility of the Effects
The one-year follow-up study showed that most of the bone effects induced by in utero and lactational exposure to TCDD in line C rats were reversed at the age of 1 year. Tibial and femoral length as well as BMD had returned to normal during the 1-year observation period. Of the geometric changes, tibial ENDO and PERI circumferences as well as PMI were still decreased, but without statistical significance (Table 2). Similarly, mechanical strength of exposed 1-year-old line C rat bones was slightly but nonsignificantly reduced compared to controls (Table 3).
TCDD Concentration in Newborn and Dam
Fresh weight-based and lipid-adjusted average TCDD tissue concentrations of offspring and maternal adipose tissue TCDD concentrations analyzed on PND0 are shown in Figure 2. The average body weight of newborns on PND0 was 5.2, 5.3, 5.7, and 5.5 g in GD8, GD11, GD15, and control groups, respectively, and the average fat percentages were 1.1%, 1.3%, 1.4%, and 1.1%, respectively. Body weight and fat percentage of offspring studied on PND5 were 9.3 g and 7.7%, respectively. TCDD concentrations were the lower the earlier the dams were exposed, reflecting elimination. Lactation resulted in considerably increased accumulation of TCDD as the average tissue concentration of the offspring (on fresh weight basis) was an order of magnitude higher on PND5 than on PND0 (Fig. 2).
|
![]() |
DISCUSSION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Exposure times were selected so that all phases of bone development were covered, as the earliest time of exposure (GD11) was 2 days before the first signs of skeletal system development are detectable and the last time of exposure was 4 days after birth. A single maternal dose of TCDD is sufficient to cover the whole prenatal and neonatal period, as the elimination half-life of TCDD is about 26 days in female rats (Li et al., 1995) The development of rat skeleton begins on GD13 as a condensation of mesenchymal tissue (Hebel and Stromberg, 1986
). Two days later, cartilaginous structures appear in skeleton and by GD17 ossification of the limb bones is observable. The ossification proceeds rapidly, and 2 days after birth all the skeletal elements are ossified (Fritz and Hess, 1970
). Ossification continues after birth as bones grow, and in rats epiphyseal cartilages remain open until senescence. Our results showed that the early TCDD exposure on GD11 resulted in the most severe bone effects. Therefore, the sensitive period for bone effects starts from the initial phase of bone development and the sensitivity decreases during later stages of development. Although the contribution of gestational exposure via placenta to the TCDD body burden of a weanling rat is negligible compared to lactational exposure (Hurst et al., 2000a
; Li et al., 1995
), combined exposure during pregnancy and via lactation was clearly more effective than only lactational exposure starting after birth. This may be so because ossification of rat skeleton is already nearly complete at term (Fritz and Hess, 1970
). Bone growth is based on further ossification after birth, but it seems to be more resistant to TCDD than the earlier phases of bone formation (cf. Jämsä et al., 2001
). The most sensitive period of bone development has therefore passed before the higher exposure via lactation starts. However, gestational exposure alone did not cause severe bone defects. In the cross-fostered groups, the effects were limited to bone geometry, as no remarkable alterations were found in mechanical properties of the bones. It is interesting to note that, in spite of different timing, the lower TCDD exposure during gestation resulted in very similar bone effects to higher lactational exposure during the neonatal period. Therefore both gestational and postnatal exposures are required for the complete spectrum of TCDD-induced adverse effects in bone development.
We have previously shown that in adult rats bone effects are observed after repeated and prolonged TCDD treatment and they require higher dose than developing rats (Jämsä et al., 2001). Treatment of 10-week-old rats with weekly doses of TCDD for 20 weeks resulted in quite similar changes with those found in the present study, i.e., altered bone geometry and decreased mechanical strength, but no BMD changes. In TCDD-sensitive adult L-E rats, bone effects were observed at the total dose level of 1.7 µg/kg TCDD and above, whereas in this study the effects were limited to the offspring of TCDD-sensitive line C rats after a single maternal dose of 1 µg/kg. Analysis of TCDD tissue concentration indicated that TCDD body burden (average tissue concentration) of the offspring was only about 5% of the initial maternal dosage (0.5 µg/kg) on PND0 and about 54% on PND5. However, TCDD concentrations in lipid - that are in equilibrium with toxicologically effective concentrations - were quite similar in dams and offspring during gestation. Despite fundamentally different dosing schemes in adult study and in the present study.
Although rat bones proved to be more sensitive to TCDD during perinatal development than in adulthood, the changes observed were qualitatively rather similar in spite of different stages of development at exposure. The only remarkable difference between in utero/lactational and adult (Jämsä et al., 2001) TCDD exposure was in BMD. Interestingly, decreased volumetric BMD was observed only in rats whose TCDD exposure started prenatally, and the decrease in BMD was the greater the earlier the rat was exposed. In addition, the decreased BMD returned to normal levels during the first year of life. In previous studies, exposure of adult rats to dioxin-like coplanar polychlorinated biphenyl (PCB)126 did not affect BMD at all (Lind et al., 1999
, 2000b
) or resulted in increased BMD (Lind et al., 2000a
).
Decreased length of long bones had been observed in rats exposed to TCDD (Jämsä et al., 2001) or PCB126 (Lind et al., 1999
, 2000b
) during adulthood. The present data indicate that impaired bone growth is reversible after elimination of TCDD from the body. Of the bone geometric parameters CSA, ENDO, and PMI were decreased in juvenile line C rats at 1 µg/kg. We observed similar decreases in CSA and ENDO also in the tibial diaphysis of L-E rats exposed to TCDD in adulthood (Jämsä et al., 2001
).
Mechanical testing of juvenile line C rats revealed significant decreases in mechanical strength of tibial and femoral diaphysis as well as femoral neck, and this effect was most consistent in rats with prenatal exposure. This is also in line with our previous report from adult rats, whose tibial breaking force and bending stiffness were decreased in response to TCDD (Jämsä et al., 2001; Lind et al., 2000b
). The one-year follow-up study revealed that there was still a slight, although statistically nonsignificant decrease in mechanical properties 1 year after birth. Diaphyseal bending strength and stiffness are absolute measures of bone mechanical strength, and they are strongly associated with the combination of geometrical and qualitative properties of bone (Jämsä et al., 1998
) that were also diminished in line with bone mineral density. Therefore, bone mechanical strength reflects the TCDD-induced changes observed in bone geometry and BMD.
Studies in mice lacking the functional AHR have confirmed its essential role in mediating toxic effects of dioxins (Bunger et al., 2003; Fernandez-Salguero et al., 1996
; Mimura et al., 1997
; Peters et al., 1999
). The characteristic TCDD-induced developmental defects cleft palate and hydronephrosis are not induced in these mice. AHR seems also to play a physiological role in bone development, because at fetal examination AHR knockout mice had a lower incidence of large interfrontal bones than wild-type mice (Peters et al., 1999
). Our recent studies indicated that AHR is strongly expressed in osteoblasts and osteoclasts of 12-day-old rats, immunostaining being especially prominent in osteoclasts with clear perinuclear staining (Ilvesaro et al., 2005
; Sahlberg et al., 2002
). The presence of the AHR signaling pathway in developing bone suggests that the observed bone effects of TCDD may be directly mediated via AHR. Inhibited differentiation of cultured fetal rat calvarial osteoblasts exposed to 10 nM TCDD in vitro (Gierthy et al., 1994
) speak for a direct effect on bone cells. In the present study the maternal dose of 0.5 µg/kg resulted in fresh weight based TCDD concentrations of 27 and 276 pg/g (=0.86 nM) in groups exposed on GD15 and analyzed on PND0 and PND15, respectively. As the bone effects were observed at the maternal dose of 1 µg/kg, the corresponding tissue concentrations are about 0.17 and 1.71 nM. Therefore the tissue concentration in our study (on GD5) was 5.8-fold lower than the concentration used by Gierthy et al. (1994)
, and as the TCDD body burden is likely to continue to increase during lactation, it will become more similar toward the end of the lactation period. This shows that the TCDD concentrations causing bone effects in vivo and in vitro are of similar magnitude.
A possible mechanism or contributing factor for dioxin-induced developmental bone effects is modulated cross talk between AHR and estrogen receptor (ER) and ß signaling pathways. Estrogen signaling is important for normal bone development and homeostasis, and TCDD has a variety of antiestrogenic effects from a complex modulation of cross talk between AHR and ERs (Kietz et al., 2004
; Nilsson et al., 2001
; Ohtake et al., 2003
). It remains to be clarified whether this type of modulation also takes place under the conditions of the present study, i.e., in fetal and neonatal rats in vivo at very low dose in utero and lactational TCDD exposure.
In addition to direct effects on bone cells mediated by AHR or AHR/ER modulation, dioxin-induced alterations in hormonal and nutritional status may be a secondary mechanism of developmental bone toxicity. Estradiol levels were unaffected by TCDD in both developing and adult rats (Gray et al., 1997b; Pohjanvirta and Tuomisto, 1994
). In agreement with these findings, our present and earlier results (Jämsä et al., 2001
) indicate that the effects of TCDD on bone are fundamentally different from those of estrogen deficiency. Moreover, dioxin-like PCB126 with antiestrogenic effects did not cause trabecular bone loss and the increasing bone dimensions that are typical effects of estrogen deficiency (Lind et al., 1999
). Although exposure of adult animals to higher doses of TCDD results in decreased circulating testosterone and dihydrotestosterone levels, no changes in hormone levels were found in male Holzman rats exposed to a single dose of up to 0.8 µg/kg TCDD on GD15 (Ohsako et al., 2001
). These findings, and the fact that bone effects were observed at low dose levels that are not generally associated with hormonal alterations, suggest that they are not the primary cause of dioxin-induced bone toxicity. However, hormonal and nutritional factors potentially affecting bone modeling and remodeling have not yet been systematically monitored in developing TCDD-treated animals.
Previous studies in dioxin-resistant H/W, line A, and line B rats have shown that the resistance to several end points of dioxin toxicity is linked to the altered AHR C-terminal transactivation domain (Jämsä et al., 2001; Kattainen et al., 2001
; Pohjanvirta et al., 1997; Simanainen et al., 2002
, 2003
; Tuomisto et al., 1998
; Viluksela et al., 2000
). Interestingly, dioxin resistance associated with resistance alleles Ahrhwand Bhw is end-pointdependent and, based on short-term dioxin toxicity, they can be classified into two categories (Simanainen et al., 2002
, 2003
; Tuomisto et al., 1999
). Type I end points (e.g., increased CYP1A activity, thymic involution) show similar sensitivity in dioxin-sensitive ("normal") rats and in dioxin-resistant (H/W and line A) rats, and are independent of genotype variation. On the other hand, for type II end points (e.g., weight loss, liver toxicity, increased serum bilirubin), the efficacy (magnitude of effect) of TCDD is suppressed by the resistance alleles. The lack of effects in line A and B rats in the present study classifies the developmental bone toxicity to the type II category. This is in accordance with the previous findings on TCDD bone effects in adult H/W and L-E rats (Jämsä et al., 2001
). Of other developmental end points of dioxin toxicity prevention of the third molar development (Kattainen et al., 2001
), and reduced sperm counts (Simanainen et al., 2004
) are also influenced by the resistance alleles.
In conclusion, the present study demonstrated that low perinatal TCDD exposure results in adverse changes in three aspects of bone quality: bone geometry, bone mineral density, and bone mechanical properties. Bone toxicity belongs to the group of sensitive developmental end points of dioxin toxicity, together with impaired development of the reproductive system and teeth. TCDD exposure covering the early phases of bone development results in more severe effects than later exposure. There is a marked, but not complete recovery during 1 year. In addition, the dioxin-resistance alleles Ahrhwand Bhw increase the resistance of rats to the bone effects, which indicate that they belong to dioxin type II effects. However, almost complete lack of bone effects in line A and B rats did not allow quantification of the influence of resistance alleles. Future studies should examine dioxin effects on bone cells and on their differentiation, as well as the role of hormonal and nutritional status in these effects.
![]() |
ACKNOWLEDGMENTS |
---|
![]() |
REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Alaluusua, S., Lukinmaa, P.-L., Torppa, J., Tuomisto, J., and Vartiainen, T. (1999). Developing teeth as biomarker of dioxin exposure. Lancet 353, 206.
Birnbaum, L. S. (1995). Developmental effects of dioxins and related endocrine disrupting chemicals. Toxicol. Lett. 8283, 734750.
Bunger, M. K., Moran, S. M., Glover, E., Thomae, T. L., Lahvis, G. P., Lin, B. C., and Bradfield, C. A. (2003). Resistance to 2,3,7,8-tetrachlorodibenzo-p-dioxin toxicity and abnormal liver development in mice carrying a mutation in the nuclear localization sequence of the aryl hydrocarbon receptor. J. Biol. Chem. 278, 1776717774.
Fernandez-Salguero, P. M., Hilbert, D. M., Rudikoff, S., Ward, J. M., and Gonzalez, F. J. (1996). Aryl-hydrocarbon receptordeficient mice are resistant to 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced toxicity. Toxicol. Appl. Pharmacol. 140, 173179.[CrossRef][ISI][Medline]
Fritz, H., and Hess, R. (1970). Ossification of the rat and mouse skeleton in the perinatal period. Teratology 3, 331338.[ISI][Medline]
Gierthy, J. F., Silkworth, J. B., Tassinari, M., Stein, G. S., and Lian, J. B. (1994). 2,3,7,8-Tetrachlorodibenzo-p-dioxin inhibits differentiation of normal diploid rat osteoblasts in vitro. J. Cell Biochem. 54, 231238.[ISI][Medline]
Gray,L. E., Jr., Ostby, J. S., and Kelce, W. R. (1997a). A dose-response analysis of the reproductive effects of a single gestational dose of 2,3,7,8-tetrachlorodibenzo-p-dioxin in male Long Evans hooded rat offspring. Toxicol. Appl. Pharmacol. 146, 1120.[CrossRef][ISI][Medline]
Gray, L. E., Jr., Wolf, C., Mann, P., and Ostby, J. S. (1997b). In utero exposure to low doses of 2,3,7,8-tetrachlorodibenzo-p-dioxin alters reproductive development of female Long Evans hooded rat offspring. Toxicol. Appl. Pharmacol. 146, 237244.[CrossRef][ISI][Medline]
Hebel, R., and Stromberg, M. W. (1986). Anatomy and Embryology of the Laboratory Rat. BioMed Verlag, Günzburg, Germany.
Hurst, C. H., DeVito, M. J., and Birnbaum, L. S. (2000a). Tissue disposition of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in maternal and developing Long-Evans rats following subchronic exposure. Toxicol. Sci. 57, 275283.
Hurst, C. H., DeVito, M. J., Setzer, W., and Birnbaum, L. S. (2000b). Acute administration of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in pregnant Long-Evans rats: Association of measured tissue concentrations with developmental effects. Toxicol. Sci. 53, 411420.
Ilvesaro, J., Pohjanvirta, R., Tuomisto, J., Viluksela, M., and Tuukkanen, J. (2005). Aryl hydrocarbon receptor is strongly expressed in osteoclasts and osteoblasts. Life Sci., in press.
Jämsä, T., and Jalovaara, P. (1996). A cost effective, accurate machine for testing the torsional strength of sheep long bones. Med. Eng. Phys. 18, 433435.[CrossRef][ISI][Medline]
Jämsä, T., Jalovaara, P., Peng, Z., Väänänen, H. K., and Tuukkanen, J. (1998). Comparison of three-point bending test and peripheral quantitative computed tomography analysis in the evaluation of the strength of mouse femur and tibia. Bone 23, 155161.[CrossRef][ISI][Medline]
Jämsä, T., Viluksela, M., Tuomisto, J. T., Tuomisto, J., and Tuukkanen, J. (2001). Effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin on bone in two rat strains with different aryl hydrocarbon receptor structures. J. Bone Miner. Res. 16, 18121820.[ISI][Medline]
Kattainen, H., Tuukkanen, J., Simanainen, U., Tuomisto, J. T., Kovero, O., Lukinmaa, P.-L., Alaluusua, S., Tuomisto, J., and Viluksela, M. (2001). In utero/lactational TCDD exposure impairs molar tooth development in rats. Toxicol. Appl. Pharmacol. 174, 216224.[CrossRef][ISI][Medline]
Kietz, S., Thomsen, J. S., Matthews, J., Pettersson, K., Strom, A., and Gustafsson, J. A. (2004). The Ah receptor inhibits estrogen-induced estrogen receptor beta in breast cancer cells. Biochem. Biophys. Res. Commun. 320, 7682.[CrossRef][ISI][Medline]
Li, X., Weber, L., and Rozman, K. (1995). Toxicokinetics of 2,3,7,8-tetrachlorodibenzo-p-dioxin in female Sprague-Dawley rats including placental and lactational transfer to fetuses and neonates. Fundam. Appl. Toxicol. 27, 7076.[CrossRef][ISI][Medline]
Lind, P. M., Eriksen, E. F., Sahlin, L., Edlund, M., and Orberg, J. (1999). Effects of the antiestrogenic environmental pollutant 3,3',4,4', 5-pentachlorobiphenyl (PCB #126) in rat bone and uterus: Diverging effects in ovariectomized and intact animals. Toxicol. Appl. Pharmacol. 154, 236244.[CrossRef][ISI][Medline]
Lind, P. M., Larsson, S., Johansson, S., Melhus, H., Wikstrom, M., Lindhe, O., and Orberg, J. (2000a). Bone tissue composition, dimensions and strength in female rats given an increased dietary level of vitamin A or exposed to 3,3',4, 4',5-pentachlorobiphenyl (PCB126) alone or in combination with vitamin C. Toxicology 151, 1123.[CrossRef][ISI][Medline]
Lind, P. M., Larsson, S., Oxlund, H., Håkanson, H., Nyberg, K., Eklund, T., and Örberg, J. (2000b). Change of bone tissue composition and impaired bone strength in rats exposed to 3,3',4,4',5-pentachlorobiphenyl (PCB126). Toxicology 150, 4151.[CrossRef][ISI][Medline]
Mably, T. A., Bjerke, D. L., Moore, R. W., Gendron-Fitzpatrick, A., and Peterson, R. E. (1992a). In utero and lactational exposure of male rats to 2,3,7,8-tetrachlorodibenzo-p-dioxin. 3. Effects on spermatogenesis and reproductive capability. Toxicol. Appl. Pharmacol. 114, 118126.[CrossRef][ISI][Medline]
Mably, T. A., Moore, R. W., Goy, R. W., and Peterson, R. E. (1992b). In utero and lactational exposure of male rats to 2,3,7,8-tetrachlorodibenzo-p-dioxin. 2. Effects on sexual behavior and the regulation of luteinizing hormone secretion in adulthood. Toxicol. Appl. Pharmacol. 114, 108117.[CrossRef][ISI][Medline]
Miettinen, H. M., Alaluusua, S., Tuomisto, J., and Viluksela, M. (2002). Effect of in utero and lactational TCDD exposure on rat molar development: The role of exposure time. Toxicol. Appl. Pharmacol. 184, 5766.[CrossRef][ISI][Medline]
Mimura, J., Yamashita, K., Nakamura, K., Morita, M., Takagi, T. N., Nakao, K., Ema, M., Sogawa, K., Yasuda, M., Katsuki, M., et al. (1997). Loss of teratogenic response to by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in mice lacking the Ah (dioxin) receptor. Genes Cells 2, 645654.
Nilsson, S., Mäkelä, S., Treuter, E., Tujague, M., Thomsen, J., Andersson, G., Enmark, E., Pettersson, K., Warner, M., and Gustafsson, J. A. (2001). Mechanisms of estrogen action. Physiol. Rev. 81, 15351565.
Ohsako, S., Miyabara, Y., Nishimura, N., Kurosawa, S., Sakaue, M., Ishimura, R., Sato, M., Takeda, K., Aoki, Y., Sone, H., et al. (2001). Maternal exposure to a low dose of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) suppressed the development of reproductive organs of rats: Dose-dependent increase of mRNA levels of 5 alpha-reductase type 2 in contrast to decrease of androgen receptor in the pubertal ventral prostate. Toxicol. Sci. 60, 132143.
Ohtake, F., Takeyama, K., Matsumoto, T., Kitagawa, H., Yamamoto, Y., Nohara, K., Tohyama, C., Krust, A., Mimura, J., Chambon, P., et al. (2003). Modulation of oestrogen receptor signalling by association with the activated dioxin receptor. Nature 423, 545550.[CrossRef][ISI][Medline]
Peng, Z., Tuukkanen, J., Zhang, H., Jämsä, T., and Väänänen, H. K. (1994). The mechanical strength of bone in different rat models of experimental osteoporosis. Bone 15, 523532.[CrossRef][ISI][Medline]
Peters, J. M., Narotsky, M. G., Elizondo, G., Fernandez-Salguero, P. M., Gonzalez, F. J., and Abbot, B. D. (1999). Amelioration of TCDD-induced teratogenesis in aryl hydrocarbon receptor (AhR)-null mice. Toxicol. Sci. 47, 8692.[Abstract]
Peterson, R. E., Theobald, H. M., and Kimmel, G. L. (1993). Developmental and reproductive toxicity of dioxins and related compounds: Cross-species comparisons. Crit. Rev. Toxicol. 23, 283335.[ISI][Medline]
Pohjanvirta, R., and Tuomisto, J. (1994). Short-term toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin in laboratory animals: Effects, mechanisms and animal models. Pharmacol. Rev. 46, 483549.[ISI][Medline]
Pohjanvirta, R., Wong, J. M. Y., Li, W., Harper, P. A., Tuomisto, J., and Okey, A. B. (1998). Point mutation in intron sequence causes altered C-terminal structure in the AH receptor of the most TCDD-resistant rat strain. Mol. Pharmacol. 54, 8693.
Päpke, O. (1998). PCDD/PCDF: Human background data for Germany, a 10-year experience. Environ. Health Perspect. 106 Suppl. 2, 723731.[ISI][Medline]
Sahlberg, C., Pohjanvirta, R., Gao, Y., Alaluusua, S., Tuomisto, J., and Lukinmaa, P.-L. (2002). Expression of the mediator of dioxin toxicity, aryl hydrocarbon receptor (AHR) and the AHR nuclear translocator (ARNT), is developmentally regulated in mouse teeth. Int. J. Dev. Biol. 46, 295300.[CrossRef][ISI][Medline]
Schmidt, J. V., and Bradfield, C. A. (1996). Ah receptor signaling pathways. Annu. Rev. Cell Dev. Biol. 12, 5589.[CrossRef][ISI][Medline]
Simanainen, U., Haavisto, T., Tuomisto, J. T., Paranko, J., Toppari, J., Tuomisto, J., Peterson, R. E., and Viluksela, M. (2004). Pattern of male reproductive system effects after in utero and lactational 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure in three differentially TCDD sensitive rat lines. Toxicol. Sci. 80, 101108.
Simanainen, U., Tuomisto, J. T., Tuomisto, J., and Viluksela, M. (2002). Structureactivity relationships and doseresponses of polychlorinated dibenzo-p-dioxins (PCDDs) for short-term effects in TCDD-resistant and TCDD-sensitive rat strains. Toxicol. Appl. Pharmacol. 181, 3847.[CrossRef][ISI][Medline]
Simanainen, U., Tuomisto, J. T., Tuomisto, J., and Viluksela, M. (2003). Doseresponse analysis of short-term effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin in three differentially susceptible rat lines. Toxicol. Appl. Pharmacol. 187, 128136.[CrossRef][ISI][Medline]
Tuomisto, J. T., Viluksela, M., Pohjanvirta, R., and Tuomisto, J. (1999). The Ah receptor and a novel gene determine acute toxic responses to TCDD: Segregation of the resistant alleles to different rat lines. Toxicol. Appl. Pharmacol. 155, 7181.[CrossRef][ISI][Medline]
Tuomisto, J. T., Viluksela, M., and Tuomisto, J. (1998). Separation of AH receptor and another dioxin resistance gene in new rat lines. Toxicologist 42, 326.
Vartiainen, T., Lampi, K., Tolonen, K., and Tuomisto, J. (1995). Polychlorodibenzo-p-dioxin and polychlorodibenzofuran concentrations in lake sediments and fish after a ground water pollution with chlorophenols. Chemosphere 30, 14391451.[CrossRef][ISI]
WHO (World Health Organization). (2000). Consultation on assessment of the health risk of dioxins; re-evaluation of the tolerable daily intake (TDI): Executive summary. Food Addit. Contam. 17, 223240.[CrossRef][ISI]
Viluksela, M., Bager, Y., Tuomisto, J. T., Scheu, G., Unkila, M., Pohjanvirta, R., Flodström, S., Kosma, V.-M., Mäki-Paakkanen, J., Vartiainen, T., et al. (2000). Liver tumor-promoting activity of 2,3,7,8.tetrachlodibenzo-p-dioxin (TCDD) in TCDD-sensitive and TCDD-resistant rat strains. Cancer Res. 60, 69116920.
|