In East Greenland polar bears (Ursus maritimus), anthropogenic organohalogen compounds (OHCs) (e.g., polychlorinated biphenyls, dichlorodiphenyltrichloroethane, and polybrominated diphenyl ethers) contributed to renal lesions and are believed to reduce bone mineral density. Because OHCs are also hepatotoxic, we investigated liver histology of 32 subadult, 24 adult female, and 23 adult male East Greenland polar bears sampled during 1999-2002. Light microscopic changes consisted of nuclear displacement from the normal central cytoplasmic location in parenchymal cells, mononuclear cell infiltrations (mainly portally and as lipid granulomas), mild bile duct proliferation accompanied by fibrosis, and fat accumulation in hepatocytes and pluripotent Ito cells. Lipid accumulation in Ito ceils and bile duct hyperplasia accompanied by portal fibrosis were correlated to age, whereas no changes were associated with either sex or season (summer vs. winter). For adult females, hepatocytic intracellular fat increased significantly with concentrations of the sum of hexachlorocyclohexanes, as was the case for lipid granulomas and hexachlorobenzene in adult males. Based on these relationships and the nature of the chronic inflammation, we suggest that these findings were caused by aging and long-term exposure to OHCs. Therefore, these changes may be used as biomarkers for OHC exposure in wildlife and humans. To our knowledge, this is the first time liver histology has been evaluated in relation to OHC concentrations in a mammalian wildlife species, and the information is important to future polar bear conservation strategies and health assessments of humans relying on OHC-contaminated food resources. Key words: bile duct proliferation, chlordanes, dichlorodiphenyltrichloroethane, dieldrin, East Greenland, HCB, hexacydohexanes, Ito cells, lipid granulomas, liver, mononuclear cell infiltrations, polar bear, polybrominated diphenyl ethers, polychlorinated biphenyls, portal fibrosis, [SIGMA]DDT, [SIGMA]HCH, [SIGMA]PBD, [SIGMA]PCB, Ursus maritimus. Environ Health Perspect 113:1569-1574 (2005). doi: 10.1289/ehp.8038 available via http://dx.doi.org/[Online 5 July 2005]
In rats and mink, several acute studies of polychlorinated biphenyls (PCBs) have associated these compounds with hepatotoxicity (Bergman et al. 1992; Bruckner et al. 1974; Chu et al. 1994; Jonsson et al. 1981; Kelly 1993; Kimbrough et al. 1971; MacLachlan and Cullen 1995; Parkinson 1996). Specifically in the liver, acute organohalogen compound (OHC) toxicity is mediated through subcellular toxicity, leading to impaired ATP, protein synthesis, and other changes (Kelly 1993; Parkinson 1996), and chronic exposure also may affect endocrine homeostasis via upregulation of cytochrome P450 isozymes (e.g., CYP1A and CYP1B) (Boon et al. 1992; Lin et al. 2003; van Duursen et al. 2003; Wong et al. 1992).
In marine wildlife, chronic exposure to organohalogen compounds [OHCs; e.g., PCBs, dichlorodiphenyltrichloroethane (DDT), and polybrominated diphenyl ethers (PBDEs)] has been associated with toxic effects on several organ systems (Bergman 1999; Bergman and Olsson 1985; Bergman et al. 2001; Schumacher et al. 1993). However, histologic liver changes associated with high environmental levels of OHCs in wildlife have been investigated only in birds, such as cormorants (Phalacrocorax carbo) (Fabczak et al. 2000), and fish, such as common bream (Abramis brama) (Koponen et al. 2001), but never in marine or terrestrial mammals.
Polar bears are the most OHC-contaminated species in the Arctic, and those from East Greenland and Svalbard (Norway) carry the most contaminants because of their reliance on OHC-polluted blubber, mainly from ringed seal (Phoca hispida) and bearded seal (Erignathus barbatus), contaminated by OHCs originating from lower-latitude airborne pollution [Arctic Monitoring and Assessment Programme (AMAP) 2004; de March et al. 1998; Ramsay and Stifling 1988]. At Svalbard, recent studies of PCBs and organochlorine (OC) pesticides in polar bears have indicated negative associations with plasma testosterone (males), progesterone (females), cortisol (both sexes), retinol (both sexes), and thyroxine hormone (both sexes) (Braathen et al. 2004; Haave et al. 2003; Oskam et al. 2003, 2004; Skaare et al. 2001). Additionally, high levels of PCBs/OC pesticides were associated with low levels of IgG in the Svalbard bears, suggesting possible immunotoxic effects (Bernhoft et al. 2000; Lie et al. 2004, 2005). In East Greenland polar bears, OHCs are believed to reduce bone mineral density (BMD) and to be a cofactor in the development of renal lesions and splenic changes (Kirkegaard et al. 2005; Sonne et al. 2004, in press). To determine if OHCs are also a cofactor in hepatotoxicity, liver tissue histology was examined in 79 East Greenland polar bears sampled during the subsistence hunt from 1999 to 2002, and liver histology was compared with individual OHC adipose tissue levels in 65 of the bears. These new results are intended to fill part of the existing knowledge gap in understanding the significance, nature, and effects of chronic environmental OHC exposure.
Materials and Methods
Sampling. All polar bear samples were collected from January through September by local subsistence hunters in the Scoresby Sound area in central East Greenland (69[degrees]00'N to 74[degrees]00'N) during 1999-2002. A tissue subsample from the periphery of a randomly chosen liver lobe was collected from 79 individuals and fixed in a phosphate-buffered formaldehyde/alcohol solution (3.5% formaldehyde, 86% ethanol, and 10.5% [H.sub.2]O), which prevented freeze damage. In addition, sternal subcutaneous adipose tissue was sampled from 65 of the individuals for OHC analyses and stored in separate polyethylene plastic bags until arrival at the laboratory in Roskilde, where they were transferred into rinsed [acetone (Supra solv. 1.00012), n-hexane (Uni-solv 1.04369) both from Merck, KGAA, Darmstadt, Germany] glass containers, and covered with aluminum foil in between the sample and the plastic lid. All samples were taken < 12 hr postmortem and preserved frozen during the hunt and later kept at -20[degrees]C before preparation and examination at the veterinary pathology laboratory in Copenhagen, Denmark (histology); GLIER, Windsor, Ontario, Canada (organochlorines); and NWRI, Burlington, Ontario, Canada (PBDEs).
Age estimation. The age determination was carried out by counting the cementum growth layer groups of the lower left incisor ([I.sub.3]) after decalcification, thin sectioning (14 [micro]m), and staining (toluidine blue) using the method described by Dietz et al. (1991) and Hensel and Sorensen (1980). When necessary, the individuals were categorized as adult males [greater than or equal to] 6 years of age), adult females ([greater than or equal to] 5 years of age), and subadults (those remaining) (Rosing-Asvid et al. 2002). In the evaluation of sex difference in the prevalence of histologic liver changes, bears were categorized as old at [greater than or equal to] 15 years of age based on Derocher and Stirling (1994).
Histology. The liver tissue was trimmed, processed conventionally, embedded in paraffin, sectioned at about 4 [micro]m, and stained with hematoxylin (aluminum-hematein) and eosin (H&E) and periodic acid-Schiff for routine diagnostics; Van Gieson and Masson Trichrome to detect fibrous tissue (collagen); Best's carmine to demonstrate glycogen storage; Sudan III to detect lipid (frozen tissue); and Perls' Prussian blue reaction and Schmorl technique for detecting hemosiderin and lipofuscin pigments, respectively (Bancroft and Stevens 1996; Lyon et al. 1991).
We evaluated six histologic changes and grouped them semiquantitatively as follows:
* Portal mononuclear cell infiltrations: absent, unifocally, multifocally, or diffuse
* Random mononuclear cell infiltrations: absent, unifocally, multifocally, or diffuse
* Lipid granulomas: average number in five fields at 10X magnification
* Hepatocytic intracellular fat: absent, foamy, multifocal macrovesiculary, or diffuse macrovesiculary
* Visible Ito cells: average number in five fields at 20x magnification
* Mild multifocal bile duct hyperplasia accompanied by portal fibrosis: absent or present.
For each histologic change, the degree of change was measured as follows:
* Portal mononuclear cell infiltrations: mild (unifocally), moderate (multifocally), severe (diffuse)
* Random cell infiltrations: mild (< 1), moderate (1-3), severe (> 3)
* Lipid granulomas: mild (< 1), moderate (1 to < 2), severe (2-5)
* Hepatocytic intracellular fat: mild (foamy), moderate (multifocal macrovesiculary), severe (diffuse macrovesiculary)
* Ito cells: mild (< 10), moderate (10 to < 50), severe (50-200).
Analyses of OHCs. Polar bear subcutaneous adipose tissue samples (n = 65) were analyzed for PCBs, DDTs, chlordanes (CHLs), dieldrin, hexacyclohexanes (HCHs), and hexachlorobenzene (HCB) according to Dietz et al. (2004) and Sandala et al. (2004) at the Great Lakes Institute for Environmental Research (University of Windsor, Windsor, Ontario, Canada). An external standard quantification approach used for PCBs and OC pesticides in the subcutaneous adipose tissues was based on peak area of the gas chromatography-electron capture detection response, which is described in detail by Luross et al. (2002).
Briefly, [SIGMA]PCB is the sum of the concentrations of the 51 individual or coeluting PCB congeners (if detected), given by International Union of Pure and Applied Chemistry (IUPAC) number: 31/28, 52, 49, 44, 42, 64/71, 74, 70, 66/95, 60, 101/84, 99, 97, 87, 110, 151,149, 118, 146, 153, 105, 141, 179, 138, 158, 129/178, 182/187, 183, 128, 174, 177, 171/202/156, 200, 172, 180, 170/190, 201,203/ 196, 195, 194, and 206. [SIGMA]DDT is the sum of 4,4'-DDT, 4,4'-dichlorodiphenyldichloroethane (DDD), and 4,4'-dichlorodiphenyldichloroethylene (DDE). [SIGMA]HCH is the sum of the [alpha], [beta]-, and [gamma]-hexachlorocyclohexane. [SIGMA]CHL is the sum of oxychlordane, trans-chlordane, cis-chlordane, trans-nonachlor, cis-nonachlor, and heptachlor epoxide. OHC fractions were subsequently sent to the National Water Research Institute for determination of brominated diphenyl ether (PBDE) flame retardants. PBDEs (n = 65) were determined by electron capture negative ion (low resolution) mass spectroscopy using an external standard. Briefly, [SIGMA]PBDE is the sum of the concentrations of the 35 individual or coeluting congeners (if detected), given by IUPAC number: 10, 7, 11, 8, 12/13, 15, 30, 32, 28/33, 35, 37, 75, 71, 66, 47, 49, 77, 100, 119, 99, 116, 85, 155/126, 105, 154, 153, 140, 138, 166, 183, 181, and 190. Gas chromatographic conditions for the PBDEs were as described by Luross et al. (2002).
Statistics. The statistical analyses were performed with SAS statistical software (version 8, and Enterprise Guide, version 1; SAS Institute, Cary, NC, USA); the level of significance was set at p[less than or equal to] 0.05, and levels of significance at 0.05 < p [less than or equal to] 0.10 were considered a trend. The OHC data were log-transformed (base e) before the analyses in order to meet the assumption of normality and homogeneity of the variance.
For each specific histologic liver change, we performed a one-way analysis of variance (ANOVA) to test for differences in mean age between individuals with and without that specific histologic liver change (Table 1). In the case of hepatocytic lipid, we compared foamy cytoplasm with macrovesicular lipid. Furthermore, we tested whether there was a relationship between sex or season (summer, 1 June through 30 September; winter, 1 October through 31 May), and histologic liver changes using a chi-square test. In the case of Ito cells and bile duct hyperplasia accompanied by portal fibrosis, we performed the chisquare test within subadult, adult, and old bears to determine age dependency. The chi-square test was also used to test the relationship between Ito cells and fatty granulomas.
We then performed a one-way ANOVA to test for differences in mean concentrations of each group of OHCs (PCBs, DDTs, CHLs, dieldrin, HCHs, HCB, and PBDEs) between subadults, adult females, and adult males (Table 2). The results were then evaluated from Tukey's post hoc test. In order to test the relationship between concentrations of OHCs and age, we used a linear regression model for subadults, adult females, and adult males.
Finally, we tested the relationship between the concentrations of each group of OHCs (PCBs, DDTs, CHLs, dieldrin, HCHs, HCB, and PBDEs, respectively) and each histologic liver change (absent vs. present) by an analysis of covariance (Table 3). This was conducted for each of the three age/sex groups using OHC concentration as the dependent variable, age as the covariable, and histologic liver change as the class variable, including their first-order interaction links (age x histologic liver change). The statistical analyses were performed separately on subaduhs, adult females, and adult males in cases of CHLs, dieldrin, HCHs, and HCB, because the age relationships and/or concentrations differed among these three age/sex groups. In the case of lipid granulomas, the relationship to OHCs was analyzed based on the presence or absence of Ito cells. After a successive reduction of non-significant interactions, judged from the type III sum of squares (p [less than or equal to] 0.05), the significance of each of the remaining factors was evaluated from the final model least-square mean.
We studied a total of 79 free-ranging East Greenland polar bears (24 subadults, 24 adult females, 22 adult males, 4 old females, and 5 old males), collected from 1999 through 2002 (Table 1). No background data describing the general liver histology of free-ranging polar bears were available in the scientific literature. The morphology of the liver tissue was similar to other carnivorous species; however, intedobular fibrous septa were lacking as in other ursid species (Frappier 1998; Heier et al. 2003, in press; Kelly 1993; Leighton et al. 1988; MacLachlan and Cullen 1995; Prunescu et al. 2003). Kupffer cells, located in the space of Disse, tested positive for hemosiderin (iron pigments) (Lyon et al. 1991), and hepatocytes tested positive for deposits compatible with glycogen (Bancroft and Stevens 1996). In all individuals, parenchymal cells exhibited nuclear displacement toward the cell membrane (Figure 1) (Sato et al. 2001).
[FIGURE 1 OMITTED]
Mononuclear cell infiltrations and lipid granulomas. We found portal mononuclear cell infiltrations (lymphocytes, macrophages, and neutrophils), as described by Kelly (1993) and MacLachlan and Cullen (1995), in 18% of the animals and multifocally mononuclear cell infiltrations in 12% of the bears examined (Table 1, Figure 1). Additionally, we detected lipid granulomas, also described by these authors, in 76% of the animals. None of these three cell infiltration types was related to age, sex, or season (all, p > 0.05) (Table 1). Finally, we found a trend of livers with visible Ito cells showing a larger frequency of fatty granulomas, compared with livers without visible Ito cells (p < 0.06).
In addition, we found one case of unifocal necrosis and a single case of fibrin exudation, described by Kelly (1993) and MacLachlan and Cullen (1995), but we did not investigate the significance further.
Lipids. All animals showed hepatocytic microvesicular lipid accumulation (foamy cytoplasm), and 84% showed sharply demarcated macrovesicular lipid vacuoles in mainly periacinar (zones 2-3) hepatocytes (Table 1, Figure 2). In addition, we found non-parenchymal lipid vacuoles of diverging size and numbers in centroacinary Ito cells--located in the narrow space of Disse, between hepatocytes--mainly periacinary (zones 2-3) (Table 1, Figure 2) (Kelly 1993; Leighton et al. 1988; MacLachlan and Cullen 1995; Senoo et al. 1999, 2001). Intrahepatocytic lipid accumulation was not related to age (p > 0.05), whereas Ito cell lipid accumulation was highly related to age (p < 0.01) (Table 1). None of the lipid changes was related to sex or season (summer vs. winter) (Table 1).
[FIGURE 2 OMITTED]
Bile duct proliferation and portal fibrosis. Mild bile duct proliferation accompanied by portal fibrosis was found in 8% of the animals (Table 1, Figure 3). These changes were associated with age (both, p < 0.01); no relationships were found to sex or season (Table 1).
[FIGURE 3 OMITTED]
OHCs and histologic changes. Levels of [SIGMA]PCB, [SIGMA]CHL, [SIGMA]DDT, dieldrin, [SIGMA]HCH, HCB, and [SIGMA]PBDE in 65 of the examined polar bears are presented in Table 2. [SIGMA]CHL, [SIGMA]PCB, [SIGMA]DDT, dieldrin, [SIGMA]HCH, and [SIGMA]PBDE did not differ significantly among age/sex groups, but HCB was higher in subadults when compared with adult males (p [less than or equal to] 0.05) (Table 2). We found a significant negative relationship between age and HCHs, HCB, and dieldrin (all, p < 0.05) for adult females, and between age and [SIGMA]CHL and dieldrin in adult males (both, p < 0.01) (Table 2). Further information about age and sex variation of OHCs in the present East Greenland polar bears has been published by Dietz et al. (2004) and Sandala et al. (2004).
The statistical analyses were performed separately on subadults, adult females, and adult males in cases of [SIGMA]CHL, dieldrin, [SIGMA]HCH, and HCB because concentrations and/or age relationships differed between the three groups of individuals (Table 2). We tested whether the concentrations of each OHC group differed between the degree of histologic liver changes (absent vs. present); for adult females we found a significant relationship between [SIGMA]HCH and hepatocytic macrovesicular lipids (vacuoles), and for adult males we found a significant relationship between HCB and lipid granulomas (both, p < 0.05) (Table 3).
We found nuclear displacement toward the cell membrane in all individuals. In studies of polar bears from Svalbard, Sato et al. (2001) revealed the same findings. It has been proposed that this displacement is related to the high vitamin A accumulation (natural storage) in Ito cell cytoplasmic lipid droplets and hepatocytes, accumulated through the extensive feeding on blubber from ringed seal and bearded seal (Kakela et al. 1997; Ramsay and Stifling 1988). In general, such a displacement is associated with hepatitis, carcinomas, hyperplasia (adenomatous), or regeneration (Sato et al. 2001). However, such changes were not found in the Svalbard study (Sato et al. 2001), and in only two cases were unifocal hepatitis and regeneration found in the present study. We could not evaluate whether there was a relation between nuclear displacement and OHCs or hepatocytic lipid accumulation because we found the displacement in nearly all individuals. Therefore, we hypothesize that displacement may be a natural phenomenon in free-ranging polar bears, probably related to vitamin A intake and/or a result of lipid/OHCs accumulation (cytoskeletal displacement).
Mononuclear cell infiltrations and lipid granulomas. Mononuclear cell infiltrates--accompanied by fibrosis--is a reaction to local depositioning of microorganisms and/or injury of local blood vessels from, for example, toxic compounds (Kelly 1993; MacLachlan and Cullen 1995). These cell infiltrates are therefore a nonspecific inflammatory reaction that can be linked to even minor tissue damage (Kelly 1993; MacLachlan and Cullen 1995). The fact that liver tissue, rich in visible Ito cells, had a higher number of lipid granulomas indicates that microorganisms (originating from the blood supply) play a role in the random multifocal necrosis (rupture of Ito cells) observed (Kelly 1993; MacLachlan and Cullen 1995). However, if the lipophilic toxic OHCs accumulate in the lipid rich Ito cells, we hypothesize that OHCs may play a role in the burst of Ito cells, as well.
Lipids. In the present study, we found macrovesicular lipid in periacinar hepatocytes. Because polar bears are hyperphagic from April to July, they build up their fat deposits during this period (Messier et al. 1992; Ramsay and Stirling 1988), and a seasonal pattern in Ito cell numbers may be expected as was the case for the fatty tissue lipid percentage (Dietz et al. 2004). Intrahepatocytic accumulated lipid vacuoles showed a zonary pattern similar to that found in individuals exposed to toxic substances, which produce a characteristic periacinar injury due to the low oxygen gradient (hypoxia and high concentrations of, for example, cytochrome P450).
This could sensitize the liver parenchyma in this zone to metabolic disorders, resulting in lipid accumulation (Kelly 1993; MacLachlan and Cullen 1995; Parkinson 1996). We also found lipid accumulation in periacinary Ito cells. In polar bears, the Ito cells are one of the major accumulation and storage sites for lipophilic vitamin A (Leighton et al. 1988; Senoo et al. 1999, 2001) and probably also lipophilic OHCs, as mentioned above. As for hepatocytic lipid accumulation, we did not find a seasonal pattern in the number of Ito cells, but we did find that the number of Ito cells is related to age. If the Ito cell number reflects the vitamin A exposure through marine prey species, mainly ringed seal and bearded seal (Ramsay and Stirling 1988), young bears would have lower numbers of Ito cells because they do not start eating prey rich in vitamin A until they are weaned at approximately 2 years of age (Derocher and Stirling 1994). This may then explain the age difference in the number of Ito cells in the liver.
Bile duct proliferation and portal fibrosis. Bile duct proliferation has been associated with toxic injury, parasitism, or periductular fibrosis in terrestrial animals (Kelly 1993; MacLachlan and Cullen 1995) and is therefore a nonspecific reaction to chronic extrinsic and/or environmental factors. Specifically in arctic mammals, bile duct proliferations have been reported in arctic beluga whale (Delphinapterus leucas), but the pathogenesis of this could not be determined (Woshner et al. 2002).
Age-related portal fibrosis, due to chronic infections (cholangitis and biliary obstruction), is a common nonspecific histologic diagnosis in mammals (Kelly 1993; MacLachlan and Cullen 1995), and it has been reported in the Romanian brown bear (Ursus arctos) (Prunescu et al. 2003) and arctic beluga whale (Woshner et al. 2002). Prunescu et al. (2003) showed seasonal liver fibrosis (highest in spring) of the hepatic venous system, possibly due to prehibernation physiologic adaptations. Our findings were not in agreement with such a seasonal fibrosis pattern, however, because portal fibrosis was present with bile duct proliferations in all individuals.
Liver changes and OHCs. To our knowledge, liver histology in relation to environmental levels of OHCs has been studied only in birds, such as cormorants (Fabczak et al. 2000), and fish, such as common bream (Koponen et al. 2001), but never in marine or terrestrial mammals. Therefore, it is difficult to evaluate the relationship between liver histology and chronic exposure to environmental levels of OHCs in the East Greenland polar bear because basic knowledge in this field is extremely sparse.
Mononuclear cell infiltrates (lymphocytes and neutrophils) randomly distributed (lipid granulomas) or portally (around triads) have been associated with subacute PCB exposure in mink (Mustela vison) (Bergman et al. 1992). We found the same pattern in polar bears, which supports the hypothesis that OHCs could be a cofactor in the liver changes of the East Greenland polar bears in the present study. However, this could also be a result of microorganisms. Although the results from the laboratory studies are nonspecific reactions, parallels to our results are obvious.
Hepatotoxic substances (e.g., copper, pyrrolizidine alkaloids, carbon tetrachloride, and phytotoxins) usually produce a periacinar zone 2-3 injury due to the low oxygen gradient (hypoxia) and high concentrations of, for example, cytochrome P450 isozymes (activation of reactive metabolites) of this zone (Kelly 1993; MacLachlan and Cullen 1995; Parkinson 1996). We found such a zonary appearance in hepatocytic accumulation in the polar bears in the present study. Abnormal amounts of fat are known to be accumulated in the liver during high lipid ingestion, starvation, abnormal hepatocytic function, excessive dietary intake of carbohydrates, and decreased synthesis of--apoproteins (lipoproteins) (Kelly 1993; MacLachlan and Cullen 1995; Parkinson 1996). Hence, the large content of lipids in polar bear livers could be a function of hyperphagia and starvation due to seasonal changes in food resources, as discussed above, although we did not find a seasonal pattern. However, acute toxic investigations of PCBs, DDTs, and dieldrin in laboratory rats have shown to induce high lipid accumulation--probably due to decreased production of lipoproteins through impaired ATP synthesis and protein synthesis--in periacinary hepatocytes (accumulated as foamy cytoplasm or large vacuoles) (Bergman et al. 1992; Bruckner et al. 1974; Kelly 1993; Kimbrough et al. 1971, 1972; MacLachlan and Cullen 1995; Parkinson 1996). Therefore, OHCs may be a cofactor in the development of lipid accumulation in the present study, although significant differences in OHC concentrations were not found.
The signs of chronic inflammation, also in relation to Glisson's triads (bile duct proliferation accompanied by portal fibrosis), as well as the hepatocytic lipid accumulation, could possibly indicate long-term exposure to liver toxic substances (OHCs) in the East Greenland polar bear, as well. However, other than the OHC considerations and age, liver histology in flee-ranging Atlantic bottlenose dolphin (Tursiops truncatus) (Rawson et al. 1993) and arctic beluga whale (Woshner et al. 2002), in relation to mercury exposure, have shown changes similar to those in the present study. The East Greenland polar bears in the present study have also accumulated considerable amounts of mercury in the liver tissue (2.13-13.4 [micro]g/g wet weight) (Dietz et al. 1990, 2000), which are in the range of adverse toxic effect levels for terrestrial mammals (Thompson 1996).
In the present study, we found the following histologic changes in liver tissue from 79 East Greenland polar bears: nuclear displacement, mononuclear cell infiltrations, mild bile duct proliferation accompanied by portal fibrosis, and fat accumulation. Two of the changes (Ito cells and bile duct hyperplasia accompanied by portal fibrosis) were related to age, whereas none were related to sex or season. The signs and type of chronic inflammation, and the zonary lipid accumulation in hepatocytes, may indicate chronic exposure to environmental levels of OHCs. In addition, we found significant relationships for [SIGMA]HCH and hepatocytic lipid accumulation in adult females and between HCB and lipid granulomas in adult males. We therefore suggest that the histologic changes were a result of aging and long-term exposure to OHCs, but other environmental factors, such as microorganisms and mercury, cannot be excluded.
The range of mercury in liver tissue of East Greenland polar bears was incorrect in the original manuscript published online but has been corrected here. The authors also found additional information that was not included in their original manuscript: Hori et al. [Hori S, Obana H, Kashimoto T, Otake T, Nishimura H, Ikegami N, et al. 1982. Effect of polychlorinated biphenyls and polychlorinated quaterphenyls in cynomolgus monkey (Macaca fascicularis). Toxicology 24(2):123-139] found an association between bile duct proliferation and PCB exposure, and also reported that mononuclear cell infiltrates were associated with subacute PCB exposure in cynomolgus monkeys (Macaca fascicularis). Also, the authors would like to state that it is impossible to evaluate whether liver changes and possible demineralization of the skeletal system (Sonne et al. 2004) and renal lesions (Sonne et al., in press) have an impact on the health status of each individual polar bear.
Received 24 February 2005; accepted 5 July 2005.
AMAP. 2004. AMAP Assessment 2002: Persistent Organic Pollutants in the Arctic. Oslo:Arctic Monitoring and Assessment Programme.
Bancroft JD, Stevens A. 1996. Theory and Practice of Histological Techniques. New York:Churchill Livingstone.
Bergman A. 1999. Health condition of the Baltic grey seal (Halichoerus grypus) during two decades. Gynaecological health improvement but increased prevalence of colonic ulcers. Apmis 107(3):270-282.
Bergman A, Backlin BM, Jarpild B, Grimelius L, Wilander E. 1992. Influence of commercial polychlorinated biphenyls and fractions there of on liver histology in female mink (Mustela vison). Ambio 21(8):591-595.
Bergman A, Bergstrand A, Bignert A. 2001. Renal lesions in Baltic grey seals (Halichoerus grypus) and ringed seals (Phoca hispida bomica). Ambio 30(7):397-409.
Bergman A, Olsson M. 1985. Pathology of baltic grey seal and ringed seal females with special reference to adrenocortical hyperplasia: is environmental pollution the cause of a widely distributed disease syndrome? Finnish Game Res 44:47-62.
Bernhoft A, Skaare JU, Wiig O, Derocher AE, Larsen HJS. 2000. Possible immunotoxic effects of organochlorines in polar bears (Ursus maritimus) at Svalbard. J Toxicol Environ Health A 57(7):561-574.
Boon JP, Everaarts JM, Hillebrand MTJ, Eggens ML, Pijnenburg J, Goksoyr A. 1992. Changes in levels of hepatic biotransformation enzymes and hemoglobin levels in female plaice (Pleuronectes platessa) after oral-administration of technical polychlorinated biphenyl mixture (Clophen A40). Sci Total Environ 114:113-133.
Braathen M, Derocher AE, Wiig O, Sormo EG, Lie E, Skaare JU, et al. 2004. Relationships between PCBs and thyroid hormones and retinol in female and male polar bears. Environ Health Perspect 112:826-833.
Bruckner JV, Khanna KL, Cornish HH. 1974. Effect of prolonged ingestion of polychlorinated biphenyls on the rat. Food Cosmet Toxicol 12:323-330.
Chu I, Villeneuve DC, Yagminas A, LeCavalier P, Poon R, Feeley M, et al. 1994. Subchronic toxicity of 3,3',4,4',5-pentachlorobiphenyl in the rat. Clinical, biochemical, hematological and histopathological changes. Fundam Appl Toxicol 22:457-468.
de March BGE, de Wit CA, Muir DCG, Braune B, Gregor DJ, Norstrom RJ, et al. 1998. Persistent organic pollutants. In: AMAP Assessment Report: Arctic Pollution Issues. Oslo:Arctic Monitoring and Assessment Programme, 183-372.
Derocher AE, Stirling I. 1994. Age-specific reproductive-performance of female polar bears (Ursus maritimus). Can J Zool 234(4):527-536.
Dietz R, Heide-Jorgensen MP, Harkonen T, Teilmann J, Valentin N. 1991. Age determination of european harbour seal (Phoca vitulina L.). Sarsia 76:17-21.
Dietz R, Overgaard Nielsen C, Munk Hansen M, Hansen CT. 1990. Organic mercury in Greenland birds and mammals. Sci Total Environ 95:41-51.
Dietz R, Riget F, Born EW. 2000. Geographical differences of zinc, cadmium, mercury and selenium in polar bears (Ursus maritimus) from Greenland. Sci Total Environ 245:25-48.
Dietz R, Riget FF, Sonne-Hansen C, Letcher RJ, Born EW, Muir DCG. 2004. Seasonal and temporal trends in polychlorinated biphenyls and organochlorine pesticides in East Greenland polar bears (Ursus maritimus), 1990-2001. Sci Total Environ 331:107-124.
Fabczak J, Szarek J, Andrzejewska A, Smoczynski SS. 2000. The PCB level and ultrastructural pattern of the liver of cormorants. Med Weter 56(12):788-792.
Frappier BL. 1998. Digestive system. In: Textbook of Veterinary Histology (Dellmann HD, Eurell JA, eds). Baltimore, MD:Lippincott Williams & Wilkins, 164-202.
Haave M, Ropstad E, Derocher AE, Lie E, Dahl E, Wiig O, et al. 2003. Polychlorinated biphenyls and reproductive hormones in female polar bears at Svalbard. Environ Health Perspect 111:431-436.
Heier A, Grone A, Vollm J, Kubber-Heiss A, Bacciarini LN. 2003. Immunohistochemical study of retinol-binding protein in livers of polar bears (Thalarctos maritimus). Vet Pathol 40(2):196-202.
Heier A, Sonne C, Grone A, Leifsson PS, Dietz R, Born EW, et al. In press. Liver RBP immunohistechemistry in free-ranging polar bears. An immunohistochemical study of retinol-binding protein (RBP) in livers of polar bears (Ursus maritimus) from East Greenland. Zoo Wild Med.
Hensel RJ, Sorensen FE. 1980. Age determination of live polar bears. Int Conf Bear Res Manage 4:93-100.
Jonsson HT, Walker EM, Greene WB, Hughson MD, Hennigar GR. 1981. Effects of prolonged exposure to dietary DOT and PCB on rat liver morphology. Arch Environ Contain Toxiaol 10:171-183.
Kakela R, Hyvarinen H, Kakela A. 1997. Vitamins A1 (retinol), A2 (3,4-didehydroretinol) and E ([gamma]-tocopherol) in the liver and blubber of lacustrine and marine ringed seals (Phoca hispida sp.). Comp Biochem Physiol 116B(1):27-33.
Kelly WR. 1993. The liver and biliary system. In: Pathology of Domestic Animals (Jubb KVF, Kennedy PC, Palmer N, eds). San Diego:Academic Press, 319-406.
Kimbrough RD, Gaines TB, Linder RE. 1971. The ultrastructure of livers of rats fed DOT and dieldrin. Arch Environ Health 22:460-467.
Kimbrough RD, Linder RE, Gaines TB. 1972. Morphological changes in livers of rats fed poly-chlorinated biphenyls. Light microscopy and ultrastructure. Arch Environ Health 25:354-364.
Kirkegaard M, Sonne C, Leifsson PS, Dietz R, Born EW, Letcher RJ, Muir DCG. 2005. Histology of selected immunological organs in polar bear (Ursus maritimus) from East Greenland in relation to levels of organohalogens. Sci Total Environ 341(14):119-132.
Koponen K, Myers MS, Ritola O, Huuskonen SE, Seppa-Lindstrom P. 2061. Histopathology of feral fish from a PCB-contaminated freshwater lake. Amble 30(3):122-126.
Leighton FA, Cattet M, Norstrom R, Trudeau S. 1988. A cellular basis for high-levels of vitamin-A in livers of polar bears (Ursus maritimus)--the Ito cell. Can J Zool 66(2):480-482.
Lie E, Larsen HJS, Larsen S, Johansen GM, Derocher AE, Lunn NJ, et al. 2004. Does high organochlerine (OC) exposure impair the resistance to infection in polar bears (Ursus maritimus)? Part I: Effect of OCs on the humeral immunity. J Toxicol Environ Health A 67:555-582.
Lie E, Larsen HJS, Larsen S, Johansen GM, Derocher AE, Lunn NJ, et al. 2005. Does high organochlorine (OC) exposure impair the resistance to infection in polar bears (Ursus maritimus)? Part II: Possible effects of OCs on mitogen- and antigen-induced lymphocyte proliferation. J Toxicol Environ Health A 68:457-484.
Lin PP, Hu SW, Chang TH. 2003. Correlation between gene expression of aryl hydrocarbon receptor (AhR), hydrocarbon receptor nuclear translocator (Arnt), cytochromes P4501A1 (CYP1A1) and 1B1 (CYP1B1), and inducibility of CYP1A1 and CYP1B1 in human lymphocytes. Toxicol Sci 71(1):20-26.
Luross JM, Alaee M, Sergeant DB, Cannon CM, Whittle DM, Solomon SR, et al. 2002. Spatial distribution of polybrominated diphenyl ethers and polybrominated biphenyls in lake trout from the Laurentian Great Lakes. Chemosphere 46:665-672.
Lyon H, Andersen AP, Hasselager E, Hayer PE, Moller M, Prento, et al. 1991. Theory and Strategy in Histochemistry. Berlin:Springer Verlag.
MacLachlan NJ, Cullen JM. 1995. Liver, biliary system and exocrine pancreas. In: Thomsons Special Veterinary Pathology (Carlton WW, Donald McGavin M, eds). St. Louis, MO:Mosby Year Book, 81-115.
Messier F, Taylor MK, Ramsay MA. 1992. Seasonal activity patterns of female polar bears (Ursus maritimus) in the Canadian Arctic as revealed by satellite telemetry. J Zool (Lend) 992(226):219-229.
Oskam IC, Ropstad E, Dahl E, Lie E, Derocher AE, Wiig O, et al. 2003. Organochlorines affect the major androgenic hormone, testosterone, in male polar bears (Ursus maritimus) at Svalbard. J Toxicol Environ Health A 66(22):2119-2139.
Oskam IC, Ropstad E, Dahl E, Lie E, Derocher AE, Wiig O, et al. 2004. Organochlorines affect the steroid hormone cortisol in polar bears (Ursus maritimus) at Svalbard, Norway. J Toxicol Environ Health A 67:959-977.
Parkinson A. 1996. Biotransformation of xenobiotics. In: Casarett and Doull's Toxicology--the Basic Science of Poisons (Klaassen CD, ed). New York:McGraw-Hill, 113-186.
Prunescu CC, Serban-Parau N, Brock JH, Vaughan DM, Prunescu P. 2003. Liver and kidney structure and iron content in romanian brown bears (Ursus arctos) before and after hibernation. Comp Biochem Phys A 134:21-26.
Ramsay MA, Stirling I. 1988. Reproductive biology and ecology of female polar bears (Ursus maritimus). J Zool (Lond) 214:601-634.
Rawson AJ, Patton GW, Hofmann S, Pietra GG, Johns L. 1993. Liver abnormalities associated with chronic mercury accumulation in stranded Atlantic bottlenose dolphins. Ecotoxicel Environ Saf 25:41-47.
Rosing-Asvid A, Born EW, Kingsley MCS. 2062. Age at sexual maturity of males and timing of the mating season of polar bears (Ursus maritimus) in Greenland. Polar Biol 25:878-883.
Sandala GM, Sonne-Hansen C, Dietz R, Muir DCG, Valters K, Bennett ER, et al. 2004. Methyl sulfone and hydroxylated PCB metabolites in adipose and whole blood of polar bear (Ursus maritimus) from Scoresby Sound, Greenland. Sci Total Environ 331:125-141.
Sato M, Miura M, Kojima N, Higashi N, Imai K, Sato T, et al. 2001. Nuclear deviation in hepatic parenchymal cells on sinusoidal surfaces in arctic animals. Cell Struct Funct 26:71-77.
Schumacher U, Zahler S, Horny HP, Heidemann G, Skirnisson K, Welsch U. 1993. Histological investigations on the thyroid glands of marine mammals (Phoca vitulina, Phocoena phocoena) and the possible implications of marine pollution. J Wildlife Dis 29(1):103-108.
Senoo H, Imai K, Higashi N, Wake K, Kojima N, Miura M, et al. 2001. Transport and hepatic storage of vitamin A in arctic animals. In: Cells of the Hepatic Sinusoid, Vol 8 (Wiss E, Knook DL, de Zanger R, Fraaser R, eds). Leiden, the Netherlands:Kupffer Cell Foundation, 207-209.
Senoo H, Imai K, Wake K, Wold H, Moskaug J, Kojima N, et al. 1999. Vitamin A-storing system in mammals and birds in an arctic area--a study in the Svalbard Archipelago. In: Cells of the Hepatic Sinusoid, Vol 7 (Wiss E, Knook DL, de Zanger R, Fraaser R, eds). Leiden, the Netherlands: Kupffer Cell Foundation, 34-35.
Skaare JU, Bernhoft A, Wiig O, Norum KR, Haug E, Eide DM, et al. 2001. Relationship between plasma levels of organochlorines, retinol and thyroid hormones from polar bears (Ursus maritimus) at Svalbard. J Toxicol Environ Health A 62:227-241.
Sonne C, Dietz R, Born EW, Riget FF, Kirkegaard M, Hyldstrup L, et al. 2004. Is bone mineral composition disrupted by organochlorines in East Greenland polar bears (Ursus maritimus)? Environ Health Perspect 112:1711-1716.
Sonne C, Dietz R, Leifsson PS, Born EW, Kirkegaard M, Letcher RJ, et al. In press. Are organohalogen contaminants a cofactor in the development of renal lesions in East Greenland Polar Bears (Ursus maritimus)? Environ Toxicol Chem.
Thompson DR. 1996. Mercury in birds and terrestrial mammals. In: Environmental Contaminants in Wildlife. Interpreting Tissue Concentrations (Beyer WM, Heinz GH, Redmon-Norwood AW, eds). New York:CRC Press, 341-356.
van Duursen MBM, Sanderson JT, van der Bruggen M, van der Linden J, van den Berg M. 2003. Effects of several dioxin-like compounds on estrogen metabolism in the malignant MCF-7 and nontumorigenic MCF-10A human mammary epithelial cell lines. Texicol Appl Pharmacol 190(3):241-250.
Wong S, Fournier M, Coderre D, Banska W, Krzystyniak K. 1992. Environmental Immunotoxicology. In: Animal Biomarkers as Pollution Indicators (Peakall DB, eds). London:Chapman and Hall, 8-189.
Woshner VM, O'Hara TM, Eurell JA, Wallig MA, Bratton GR, Suydam RS, et al. 2002. Distribution of inorganic mercury in liver and kidney of beluga and bowhead whales through autometallographic development of light microscopic tissue sections. Toxicol Pathol 30(2):209-215.
Christian Sonne,(1,2) Rune Dietz,(1) Pall S. Leifsson, (3) Erik W. Born,(4) Robert J. Letcher, (5) Maja Kirkegaard, (1) Derek C. G. Muir, (8) Frank F. Riget, (1) and Lars Hyldstrup (7)
(1) Department of Arctic Environment, National Environmental Research Institute, Roskilde, Denmark; (2)Department of Veterinary Basic Sciences, and (3)Department of Veterinary Pathobiology, Royal Veterinary and Agricultural University, Frederiksberg, Denmark; (4) Greenland Institute of Natural Resources, Nuuk, Greenland; (5) National Wildlife Research Centre, Canadian Wildlife Service, Environment Canada, Carleton University, Ottawa, Ontario, Canada; (6) National Water Research Institute, Environment Canada, Burlington, Ontario, Canada; (7) University Hospital of Hvidovre, Hvidovre, Denmark
Address correspondence to C. Sonne, Arctic Wildlife Research Veterinarian, National Environmental Research Institute, Department of Arctic Environment, Frederiksborgvej 399, P.O. Box 358, DK-4000 Roskilde, Denmark. Telephone: 45-46-30-19-54. Fax: 45-46-30-19-14. E-mail: email@example.com
We thank H. Tuborg, B. Sandell, J. Bronlund, and local hunters for organizing sampling in East Greenland, and E. Heier for sharing digital images.
Financial support was provided by the Danish Cooperation for Environment in the Arctic, the Commission for Scientific Research in Greenland, and the Canada Research Chairs Program.
The authors declare they have no competing financial interests.
COPYRIGHT 2005 National Institute of Environmental Health Sciences
COPYRIGHT 2005 Gale Group