Organohalogen concentrations and a gross and histologic ...

Chapter 3
Bone mineral density and periodontitis in
East Greenland polar bear skulls collected
from 1892 to 2002
Of the 283 skulls analysed for FA, all were analysed for periodontitis and 149
were X-ray scanned for bone mineral density (BMD) to detect signs of osteoporosis.
Information on age and gender was unfortunately missing in 10 individuals
and therefore only 139 skulls could be used in the further statistical
analysis. The purpose was to investigate period differences (1892-1960 vs.
1961-202), a continuous time trend over the entire period (1892-2002) and the
relation between individual levels of organohalogens (∑-PCBs, ∑-DDTs, dieldrin,
∑-HCHs, ∑-CHLs, HCB and ∑-PBDEs) in subcutaneous adipose tissue
and BMD (BMD was also analysed in 52 bacula in the present investigation).
These results are described in details in paper III-a,b.
Background
Calcium-phosphate (hydroxyapatite) and the double-helix collagen (type 1)
are the two major components of bone tissue and determines the hardness
and the elasticity, respectively (e.g. Ganong 1991, Doige and Weisbrode 1995,
Geneser 1996). Bone density expresses the bone mineral content determined
by the activity of osteoblastic bone formation and osteoclastic bone resorption
which is primarily regulated by parathyroid hormone, androgens and estrogens
through cytokines and growth factors (e.g. Ganong 1991, Doige and
Weisbrode 1995, Manalagas and Jilka 1995, Manalagas et al. 1995, Geneser
1996). Exogenous organohalogens have the potential of disrupting this homeostasis
through their agonism and antagonism to naturally endogenous
hormones (sex steroids, parat hormone, calcitonin, thyroid hormones, cortisol
a.o.) leading to dysosteogenesis (osteoporosis, periodontitis a.o.) (e.g. Bergman
and Olsson 1985, Bergman et al. 1992a, Colborn et al. 1993, Feldman 1995,
de March et al. 1998, Sandau et al. 2000, Damstra et al. 2002, Letcher et al. 2002,
Hakk and Letcher 2003, AMAP 2004).
Specific in polar bears, recent studies of endocrine disruption on Svalbard of
121 male polar bears have shown that Σ-PCB concentrations (sum of 16 congeners)
made significantly contributions to the variation in plasma testosterone
levels (Oskam et al. 2003). In female polar bears (n=86) progesterone was
found to be positively correlated with Σ-PCBs (Haave et al. 2003) and in both
sexes Σ-PCBs and chlorinated pesticides was altering the cortisol levels
(Oskam et al. 2004). Regarding plasma retinol concentrations and the ratio of
total T 4 to free T 4 , these decreased linearly with increasing concentrations of Σ-
PCBs in Svalbard bears of varying sex and age investigated in 1991-1994
(Skaare et al. 2001). These studies all indicate that organohalogens in Svalbard
polar bears (and likely also East Greenland bears, as the OHC levels are comparable)
potentially affect the endocrine homeostasis, which again may lead to
bone mineral disturbances (osteoporosis, periodontitis a.o.) (Ibid.). Another
polar bear study from Svalbard have associated high levels of OCs with low
levels of IgG suggesting possible immunotoxic effects (Bernhoft et al. 2000, Lie
et al. 2004, Lie et al. Submitted). This potential effect may decrease the immune
response and enhance stress-induced bone mineral changes through an activation
of the hypophyseal-adrenal/thyroid axis, leading to enhanced parathy-
35