Effects of 3,3',4,4',5-pentachlorobiphenyl (PCB126) on vertebral bone mineralization and on thyroxin and vitamin D levels in Sprague-Dawley rats.

The aim of the present study is to use Fourier transform infrared spectrometry (FTIR), and transmission electron microscopy (TEM) techniques, to make a more detailed description of toxic effects of 3,3',4,4',5-pentachlorobiphenyl (PCB126) on bone tissue at the microstructural and at the molecular level as a result of an altered bone metabolism. We have analysed potential changes on vitamin D and thyroxin serum levels since these hormones represent endocrine endpoints that are critical for bone growth and development. For this purpose Sprague-Dawley rats were exposed (n=10) to PCB126 (i.p.) for 3 months (total dose, 384microg/kg bodyweight), while control rats (n=10) were injected with corn oil (vehicle). Results from FTIR showed that vertebrae from the exposed rats had an overall lower degree of mineralization (-8.5%; p<0.05) compared with the controls. In addition, results from peripheral quantitative computed tomography (pQCT) analyses showed significant increases in the trabecular bone mineral density (+12%; p<0.05) in the exposed group compared with the controls. The TEM analyses also showed an alteration in the crystallinity properties of vertebral bone mineral with a significant decrease in the size and crystallinity of apatite crystal forming the bone tissue in the exposed vs. non-exposed rats. Serum analysis revealed lower levels of thyroid hormones, FT4 (-42%; p<0.005), TT4 (-26%; p<0.005), and vitamin D (-21%; p<0.005) in exposed group compared to control animals. The complementary techniques (TEM and FTIR) used in this study have revealed insights into possible bone mineralization alteration due to PCB126 exposure. The lowering of both the thyroxin and vitamin D serum levels might be an underlying explanation for the observed effects on bone mineralization.

In utero and lactational exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) affects bone tissue in rhesus monkeys.

Bone tissue is one of the target tissues for dioxins and dioxin-like compounds. Therefore, the aim of this study was to investigate effects of in utero and lactational exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), on bone tissue in rhesus monkey, the most human-like experimental model available. Pregnant rhesus monkeys (Macaca mulatta; age 4-10 years) were exposed to TCDD with a total dose of 40.5-42.0 or 405-420ng/kg bodyweight by repeated subcutaneous injections starting at gestational day 20 and followed by injections every 30 days until 90 days after delivery. At a mean age of 7 years the offspring were sacrificed and the femur bone dissected. Results from peripheral Quantitative Computed Tomography (pQCT) analyses of the metaphyseal part of the femur bones in female offspring showed significant increases in trabecular bone mineral content (BMC; +84.6%, p<0.05, F-value (F)=5.9) in the low-dose treatment group compared with the controls. In the same animals, analysis of the mid-diaphyseal part revealed increases in total BMC (+21.3%, p<0.05, F=5.2) and cortical cross-sectional area (CSA; +16.4%, p<0.01, F=7.4) compared with the controls. In males, changes in biomechanical properties indicating more fragile bone were observed. Displacement at failure were significantly increased in the male low-dose group compared to the controls (+38.0%, p<0.05, F=11). The high dose of TCDD did not induce any significant changes in bone morphology. In conclusion, in utero and lactational low-dose, but not high-dose exposure to 2,3,7,8-TCDD induced disruption of bone tissue development in rhesus monkey, a result suggesting that similar effects might occur in humans also.

Subchronic toxicity of baltic herring oil and its fractions in the rat (III) bone tissue composition and dimension, and ratio of n-6/n-3 fatty acids in serum phospholipids.

Changes in total bone mineral density determined by the bone-ash method were recently demonstrated in rats, exposed to Herring oil from the contaminated southern part of the Baltic Sea. In the present study more detailed analysis of bone structure and biomechanics was performed and obtained results were evaluated in the context of dietary factors, such as polyunsaturated fatty acids, vitamin D and vitamin A. Baltic Sea herring oil was fractionated into one relatively pollutant-free fraction (F1), and two fractions with pronounced enrichment of pollutants (F2 and F3). Female Sprague-Dawley rats were fed diets supplemented with Baltic Herring oil, its fractions, Nordic Sea capelin oil or soy oil. Femur was scanned with peripheral quantitative computed tomography (pQCT) and also tested by a mechanical compression analysis. Polyunsaturated fatty acids, vitamin A and D were analysed in serum. Rats fed the high dose of herring oil exhibited shorter femur length with decreased diaphyseal cortical bone mineral density, as well as lowered metaphyseal cross-sectional area compared to the soy oil group. Rats fed the high dose of F1 diet had increased cortical and decreased trabecular area, and higher total and trabecular bone mineral density. Rats fed the low dose of F2 diet showed similar changes associated with increased maximum load and energy absorption in compression test of the femoral metaphysis. In summary, our findings in changes of bone geometry and density could not be linked to any isolated exposure parameter, suggesting synergistic or antagonistic effects of several components of the test diets.

Estrogen supplementation modulates effects of the endocrine disrupting pollutant PCB126 in rat bone and uterus: diverging effects in ovariectomized and intact animals.

The aims of the present study are to compare effects of estrogen depletion (OVX) and estradiol (E2) supplementation on the tissue effects of exposure to the endocrine disrupting organochlorine 3,3',4,4',5-pentachlorobiphenyl (PCB126). For this purpose two highly estrogen-dependent tissues, bone and uterus, were studied. Forty rats exposed to PCB126 (ip) for 3 months (total dose 384 microg/kg body weight (bw)) were randomized in to OVX/sham operation or E2 supplementation (ip, 23 microg/kg, 3 days weekly) per vehicle (corn oil) groups in a 2 x 2 factorial design. Sham operated rats were treated with vehicle, PCB or PCB plus E2 (sham, sham + PCB and sham + PCB + E2, n=10 per group) whereas ovariectomized were treated with vehicle, PCB or PCB plus E2(OVX, OVX + PCB and OVX + PCB + E2, n=10 per group). As control groups served OVX or sham, and OVX + E2 (n=10 in each group). In OVX rats PCB126 + E2 treatment increased trabecular bone volume (TBV) (P<0.01), whilst the opposite was found in sham-operated rats (P<0.01). In OVX animals exposed to PCB126, E2 supplementation decreased the uterine weight and increased the uterine ERbeta mRNA level, whilst no difference was found between the PCB126 and PCB126 + E2 exposed groups in the sham-operated animals. In conclusion, estrogen modulates PCB126 induced effects on trabecular bone, as well as several uterine parameters. These results further support an important role of estrogen on the toxic effects of PCB126 on bone and uterus.