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

Skeletal Toxicity of Coplanar Polychlorinated Biphenyl Congener 126 in the Rat Is Aryl Hydrocarbon Receptor Dependent

Epidemiological evidence links polychlorinated biphenyls (PCBs) to skeletal toxicity, however mechanisms whereby PCBs affect bone are poorly studied. In this study, coplanar PCB 126 (5 μmol/kg) or corn oil vehicle was administered to N = 5 and 6 male and female, wild type (WT) or AhR -/- rats via intraperitoneal injection. Animals were sacrificed after 4 weeks. Bone length was measured; bone morphology was assessed by microcomputed tomography and dynamic histomorphometry. Reduced bone length was the only genotype-specific effect and only observed in males (p < .05). WT rats exposed to PCB 126 had reduced serum calcium, and smaller bones with reduced tibial length, cortical area, and medullary area relative to vehicle controls (p < .05). Reduced bone formation rate observed in dynamic histomorphometry was consistent with inhibition of endosteal and periosteal bone growth. The effects of PCB 126 were abolished in AhR -/- rats. Gene expression in bone marrow and shaft were assessed by RNA sequencing. Approximately 75% of the PCB-regulated genes appeared AhR dependent with 89 genes significantly (p < .05) regulated by both PCB 126 and knockout of the AhR gene. Novel targets significantly induced by PCB 126 included Indian hedgehog (Ihh) and connective tissue growth factor (Ctgf/Ccn2), which regulate chondrocyte proliferation and differentiation in the bone growth plate and cell-matrix interactions. These data suggest the toxic effects of PCB 126 on bone are mediated by AhR, which has direct effects on the growth plate and indirect actions related to endocrine disruption. These studies clarify important mechanisms underlying skeletal toxicity of dioxin-like PCBs and highlight potential therapeutic targets.

Skeletal toxicity resulting from exposure of growing male rats to coplanar PCB 126 is associated with disruption of calcium homeostasis and the GH-IGF-1 axis and direct effects on bone formation

Skeletal toxicity has been reported following exposure to polychlorinated biphenyl (PCB) mixtures. However, molecular mechanisms remain poorly understood. We exposed groups of male 4-5-week-old Sprague-Dawley rats to 3,3', 4, 4', 5-pentachlorobiphenyl (PCB 126), a dioxin-like coplanar PCB congener by a single i.p. injection of 5 µmol/kg in soy oil vehicle or vehicle alone. After 4 weeks, rats were euthanized. PCB exposure resulted in hypocalcemia (P < 0.05) and significant increases in serum PTH without changes in serum phosphorous. Hyperparathyroidism was accompanied by increased expression of mRNAs of vitamin D3 metabolizing cytochrome P450 enzymes CYP27B1 and CYP24 in the kidney (P < 0.05). PCB exposure also reduced body weight, serum IGF-1, and hepatic expression of mRNAs encoding the male-specific GH-pattern-regulated CYP2C11 and CYP3A2 relative to controls (P < 0.05). PCB exposure reduced long bone length, diameter, and surface area, but increased trabecular thickness and volume (P < 0.05). Serum osteocalcin (P < 0.05), a marker and a regulator of bone formation, was reduced, but PCB exposure had no effect on the bone resorption marker RatLaps. Exposure of human intestinal Caco-2 cells to 10-100 nM PCB 126 in the presence of vitamin D3 resulted in inhibition of mRNAs for the calcium transporters TRPV6 and PMCA1b (P < 0.05). In addition, PCB 126 suppressed osteoblastogenesis in primary bone marrow mesenchymal stem cell cultures which was blunted by the AhR antagonist CH-223191. These data provide novel evidence that skeletal toxicity after exposure to PCB 126 is a result of disruption of calcium homeostasis and the GH-IGF-1 axis, and involves direct AhR-mediated effects on bone formation.

Circulating serum level of retinoic acid and hip fractures among postmenopausal women

PURPOSE

The aim of this study was to evaluate the serum levels of retinoic acid (RA), an active form of vitamin A, in postmenopausal women with hip fractures from Zhengzhou, China.

METHODS

This was a case-control study from the Affiliated Hospital of Zhengzhou University. Serum samples were drawn from 375 postmenopausal women who were diagnosed as having hip fracture and 750 matched controls without fracture. Serum RA levels were evaluated as both a continuous variable and a categorical variable in quintiles.

RESULTS

The results showed that the serum levels of RA were significantly (P = .039) higher in patients with hip fracture compared with controls. In univariate and multivariate logistic regression analysis, for each 1 ng/mL increase of serum level of RA, the unadjusted and adjusted risk of hip fracture would be increased by 5% (odds ratio [OR] = 1.05; 95% confidence interval [CI] = 1.00-1.10; P = .035) and 2% (OR = 1.02; 95% CI = 0.95-1.11; P = .096), respectively. In multivariate models comparing the fifth with the third quintiles of RA, the RA was associated with hip fracture, and adjusted risk of hip fracture would be increased by 52% (OR = 1.52; 95% CI = 1.13-1.42; P = .011).

CONCLUSIONS

The results of our study suggest that subclinical higher levels of RA may increase the risk of hip fracture in postmenopausal women, particularly among the top quintile of serum RA. J Am Geriatr Soc 67:336-341, 2019.

Skeletal and dental effects on rats following in utero/lactational exposure to the non-dioxin-like polychlorinated biphenyl PCB 180

Polychlorinated biphenyls (PCBs) are a large class of persistent organic pollutants that are potentially harmful to human and wildlife health. Although a small number of dioxin-like (DL) PCBs are well characterized, the majority of PCBs have non-dioxin-like (NDL) modes of action and biological effects that are less understood. We conducted a dose-response study of the skeletal and dental effects of in utero/lactational exposure to 2,2',3,4,4',5,5'-heptachlorobiphenyl (PCB 180), a NDL PCB congener that is abundantly present in the environment and foods, including mother’s milk. In a sample of 35- and 84-day-old male and female offspring from pregnant rats exposed to different doses of PCB 180 (0, 10, 30, 100, 300, and 1000 mg/kg bw), we measured the three-dimensional (3D) coordinates of 27 landmarks on the craniofacial skeleton with a Microscribe G2X system, the buccolingual width of all molars with digital sliding calipers, and a variety of tibial parameters with peripheral quantitative computed tomography (pQCT) and a biomechanical testing apparatus. The landmark coordinates were analyzed for variation in size, shape, and fluctuating asymmetry (FA) using MorphoJ software, showing no effects on cranial size, on FA in females only (i.e., decreased asymmetry), and on shape in both sexes (i.e., decreased facial length and shift in the palatal suture). In the maxillary teeth, females in the highest dose group showed a significant decrease of 0.1 mm (p = 0.033) of the second molar only, whereas males in most dose groups showed average increases of 0.1 mm (p = 0.006–0.044) in all three molars. In the mandibular teeth, the only significant response to PCB 180 exposure was the average increase of 0.1 mm (p = 0.001–0.025) in the third molars of males only. Males also shower greater sensitivity in postcranial effects of increased tibial length and decreased cortical bone mass density, although only females showed significant effects on tibial bone area and thickness. These results demonstrate marked sex differences in effects of PCB 180, which can be attributed to differences in their underlying biological mechanisms of toxicity. Furthermore, although tooth and bone development are targets of both DL and NDL compounds, this study shows that there are marked differences in their mechanisms and effects.

The Effect of Vitamin A on Fracture Risk: A Meta-Analysis of Cohort Studies

This meta-analysis evaluated the influence of dietary intake and blood level of vitamin A (total vitamin A, retinol or β-carotene) on total and hip fracture risk. Cohort studies published before July 2017 were selected through English-language literature searches in several databases. Relative risk (RR) with corresponding 95% confidence interval (CI) was used to evaluate the risk. Heterogeneity was checked by Chi-square and I² test. Sensitivity analysis and publication bias were also performed. For the association between retinol intake and total fracture risk, we performed subgroup analysis by sex, region, case ascertainment, education level, age at menopause and vitamin D intake. R software was used to complete all statistical analyses. A total of 319,077 participants over the age of 20 years were included. Higher dietary intake of retinol and total vitamin A may slightly decrease total fracture risk (RR with 95% CI: 0.95 (0.91, 1.00) and 0.94 (0.88, 0.99), respectively), and increase hip fracture risk (RR with 95% CI: 1.40 (1.02, 1.91) and 1.29 (1.06, 1.57), respectively). Lower blood level of retinol may slightly increase total fracture risk (RR with 95% CI: 1.11 (0.94, 1.30)) and hip fracture risk (RR with 95% CI: 1.27 (1.05, 1.53)). In addition, higher β-carotene intake was weakly associated with the increased risk of total fracture (RR with 95% CI: 1.07 (0.97, 1.17)). Our data suggest that vitamin A intake and level may differentially influence the risks of total and hip fractures. Clinical trials are warranted to confirm these results and assess the clinical applicability.

High dietary intake of retinol leads to bone marrow hypoxia and diaphyseal endosteal mineralization in rats

Vitamin A (retinol) is the only molecule known to induce spontaneous fractures in laboratory animals and we have identified retinol as a risk factor for fracture in humans. Since subsequent observational studies in humans and old animal data both show that high retinol intake appears to only have small effects on bone mineral density (BMD) we undertook a mechanistic study of how excess retinol reduces bone diameter while leaving BMD essentially unaffected. We fed growing rats high doses of retinol for only 1 week. Bone analysis involved antibody-based methods, histology, pQCT, biomechanics and bone compartment-specific PCR together with Fourier Transform Infrared Spectroscopy of bone mineral. Excess dietary retinol induced weakening of bones with little apparent effect on BMD. Periosteal osteoclasts increased but unexpectedly endosteal osteoclasts disappeared and there was a reduction of osteoclastic serum markers. There was also a lack of capillary erythrocytes, endothelial cells and serum retinol transport protein in the endosteal/marrow compartment. A further indication of reduced endosteal/marrow blood flow was the increased expression of hypoxia-associated genes. Also, in contrast to the inhibitory effects in vitro, the marrow of retinol-treated rats showed increased expression of osteogenic genes. Finally, we show that hypervitaminotic bones have a higher degree of mineralization, which is in line with biomechanical data of preserved stiffness in spite of thinner bones. Together these novel findings suggest that a rapid primary effect of excess retinol on bone tissue is the impairment of endosteal/marrow blood flow leading to hypoxia and pathological endosteal mineralization.

Associations of fat mass and lean mass with bone mineral density differ by levels of persistent organic pollutants: National Health and Nutrition Examination Survey 1999-2004

Persistent organic pollutants (POPs), xenobiotics that accumulate in fat tissue, may impair bone metabolism. We studied (1) the association of bone mineral density (BMD) with POPs and (2) whether associations of fat mass (FM) or lean mass (LM), two components of body composition, with BMD differed depending on levels of POPs. Participants aged ≥ 20 in the National Health and Nutrition Examination Survey 1999-2004 were included (n=2769). Eight POPs with detection rate ≥ 80% and three skeletal subregions (left arm, pelvis, and right leg) were selected. All analyses were stratified by gender and age (cutpoint 50 years or more). POPs at background concentrations were mostly unassociated with BMD. However, the associations of FM and LM with BMD depended on POPs concentrations, in particular with BMD of the left arm (usually not weight-bearing) in postmenopausal women. When POPs concentrations were low, FM showed inverse associations with BMD while LM showed positive associations. However, when POPs levels were high, FM showed positive associations with BMD while the positive associations between LM and BMD weakened. POPs may biologically modify the associations of FM and LM with BMD, especially among postmenopausal women, possibly explaining inconsistent associations between FM and BMD in previous epidemiological studies.

Perinatal exposure to environmental contaminants detected in Canadian Arctic human populations changes bone geometry and biomechanical properties in rat offspring

Arctic inhabitants consume large proportions of fish and marine mammals, and are therefore continuously exposed to levels of environmental toxicants, which may produce adverse health effects. Fetuses and newborns are the most vulnerable groups. The aim of this study was to evaluate changes in bone geometry, mineral density, and biomechanical properties during development following perinatal exposure to a mixture of environmental contaminants corresponding to maternal blood levels in Canadian Arctic human populations. Sprague-Dawley rat dams were dosed with a Northern Contaminant Mixture (NCM) from gestational day 1 to postnatal day (PND) 23. NCM contains 27 contaminants comprising polychlorinated biphenyls, organochlorine pesticides, and methylmercury. Femurs were collected on PND 35, 77 and 350, and diaphysis was analyzed by peripheral quantitative computed tomography and three-point bending test, while femoral neck was assessed in an axial loading experiment. Dose-response modeling was performed to establish the benchmark dose (BMD) for the analyzed bone parameters. Exposure to the high dose of NMC resulted in short and thin femur with reduced mechanical strength in offspring at PND35. BMD of femur length, cortical area, and stiffness were 3.2, 1.6, and 0.8 mg/kg bw/d, respectively. At PND77 femur was still thin, but at PND350 no treatment-related bone differences were detected. This study provides new insights on environmental contaminants present in the maternal blood of Canadian Arctic populations, showing that perinatal exposure induces bone alterations in the young offspring. These findings could be significant from a health risk assessment point of view.

Effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin exposure on bone material properties

Dioxins are known to decrease bone strength, architecture and density. However, their detailed effects on bone material properties are unknown. Here we used nanoindentation methods to characterize the effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on nanomechanical behaviour of bone matrix. Pregnant rats were treated with a single intragastric dose of TCDD (1 microg/kg) or vehicle on gestational day 11. Tibias of female offspring were sampled on postnatal day (PND) 35 or 70, scanned at mid-diaphysis with pQCT, and evaluated by three-point bending and nanoindentation. TCDD treatment decreased bone mineralization (p<0.05), tibial length (p<0.01), cross-sectional geometry (p<0.05) and bending strength (p<0.05). Controls showed normal maturation pattern between PND 35 and 70 with decreased plasticity by 5.3% and increased dynamic hardness, storage and complex moduli by 26%, 13% and 12% respectively (p<0.05), while similar maturation was not observed in TCDD-exposed pups. In conclusion, for the first time, we demonstrate retardation of bone matrix maturation process in TCDD-exposed animals. In addition, the study confirms that developmental TCDD exposure has adverse effects on bone size, strength and mineralization. The current results in conjunction with macromechanical behaviour suggest that reduced bone strength caused by TCDD is more associated with the mineralization and altered geometry of bones than with changes at the bone matrix level.

Effects of local point source polychlorinated biphenyl (PCB) contamination on bone mineral density in deer mice (Peromyscus maniculatus)

A former local source of PCBs has contaminated soil and the terrestrial food web at Saglek, Labrador. The relationship between PCB exposure and bone mineral density as an osteoporosis biomarker in deer mice (Peromyscus maniculatus) was investigated at two sites at Saglek: a contaminated Beach and a reference area. Bone mineral density was measured on the femur of twenty-six deer mice using dual-energy X-ray absorptiometry (DXA) technology. Bone mineral density was significantly lower in deer mice from the high exposure site (average whole body summation operatorPCB=5769 ng/g wet weight, n=20) than at the reference site (average whole body summation operatorPCB=79.8 ng/g wet weight, n=7). We used T-scores from the World Health Organization to determine the degree of decreased bone mineral density in exposed mice. Assuming the same biomechanical forces apply as for humans, and using a conservative factor of 1.5 (fracture risk increases 1.5 to 3 fold for every standard deviation decrease in bone mineral density), mice from the contaminated Beach are up to five folds more susceptible to fracture risk than mice from the reference area. Therefore, the PCB concentrations found locally at contaminated military sites such as Saglek are high enough to affect local wildlife.

Exposure to pastures fertilised with sewage sludge disrupts bone tissue homeostasis in sheep

The femurs of male and female sheep (Ovis aries), aged 18 months, bred on pastures fertilized twice annually with sewage sludge (2.25 tonnes dry matter/ha; Treated; T)) or on pastures treated with inorganic fertilizer (Control; C) were studied, using peripheral Quantitative Computed Tomography (pQCT) and the three-point bending test. Males were maintained on the respective treatments from conception to weaning and then maintained on control pastures while the females were maintained on the respective treatments until slaughter. T rams exhibited increased total bone mineral density (BMD) at the metaphyseal part of femur (+10.5%, p<0.01) compared with C rams but had a reduced total cross sectional area (CSA, -11.5%, p<0.001), trabecular CSA (-17.1%, p<0.01) and periosteal circumference (-5.7%, p<0.001). In the mid-diaphyseal part, T rams had an increased total BMD (+13.8%, p<0.0001) and stiffness (+6.4%, p<0.01) but reduced total CSA (-12.1%, p<0.0001) and marrow cavity (-25.8%, p<0.0001), relative to C rams. In ewes although pQCT analysis of neither the metaphyseal nor the mid-diaphyseal part of the female femur bones showed any significant differences with treatment, the biomechanical method revealed a reduction in load at failure (-17.3%, p<0.01) and stiffness (-10.7%, p<0.05) amongst T ewes. It is concluded that exposure to pollutants present in sewage sludge can perturb bone tissue homeostasis in sheep, but particularly in males.

Bone pain, growth failure, and skin rash after an upper respiratory illness in a boy with autism: possible association with altered retinoid metabolism

Symptoms of bone pain and skin rashes are not uncommon following a variety of infectious illnesses, but the underlying mechanisms are not well understood. The case of a 9-year-old boy with autism was recently described, who was hospitalized because of pain in the right hip, refusal to walk, fatigue, irritability, skin rash, and subsequent gingival swelling after an unspecified upper respiratory illness. The boy was diagnosed with scurvy. However, the gingival symptoms occurred after treatment with indomethacin, which lowers vitamin C levels; severe bone pain and fatigue are also well-documented symptoms of hypervitaminosis A. This review of a case report of a boy with autism provides an opportunity to present a new hypothesis of the mechanism of these postinfection symptoms in the context of an increasingly common condition of childhood.

Does the nutrition profile of vitamins, fatty acids and microelements counteract the negative impact from organohalogen pollutants on bone mineral density in Greenland sledge dogs (Canis familiaris)?

There is a great need for understanding the impact from dietary OHCs (organohalogen compounds) on bone mineral composition - and thereby osteoporosis - in especially arctic wildlife such as polar bears (Ursus maritimus) as well as humans. For that purpose, we measured BMD (bone mineral density) by DXA scanning (g/cm(-2)) in 15 age and weight normalized sledge dog (Canis familiaris) bitches and their 26 pups divided into a control group (n=26) given 50-200 g/day clean pork (Suis scrofa) fat and a treated group (n=15) given 50-200 g/day OHC polluted minke whale (Balaenoptera acutorostrata) blubber as main lipid sources. The results showed that BMD increased significantly with age (linear regression: p<0.0001, r(2)=0.83, n=41) while no sex difference was found in the F-generation (two-way ANOVA: all p>0.3). No differences in BMD(femur) or BMD(vertebrae) between exposed and control individuals in the bitch generation were found (linear mixed effect model: both p>0.38). Likewise, no difference between exposed and control subadults and juveniles in the F-generation was found (two-way ANOVA: all p>0.33). Correlation analyses between BMD(femur), BMD(vertebrae) and groups of OHCs, respectively, did not show any statistically significant relationships nor a clear or decreasing trend (Pearson's: p: 0.07-0.78; r: -0.2-0.59; n: 10-18). As the groups were similar regarding genetics, age and sex are the only factors that can explain this observation. Either the pollutants did not have an impact on BMD using the present time frame and OHC concentrations (threshold levels not reached), or the difference in food composition (mainly vitamins and n3 fatty acids) conceal the potential OHC impact on BMD. Such information is important when evaluating the positive and negative health consequences from eating polluted marine species.

Effects of short-term exposure to the DDT metabolite p,p'-DDE on bone tissue in male common frog (Rana temporaria)

Experimental studies as well as studies in free-ranging animals have shown that endocrine-disrupting chemicals (EDCs) impair bone tissue composition and strength. The aim of the present study was to expand our studies on bone tissue in a new group of animals by investigating whether bone tissue in frogs is an additional potential target of EDCs. Adult male European common frogs (Rana temporaria) were divided into 5 groups (n = 20) and injected (sc, single injection) with p,p'-DDE, a total dose of 0.01, 0.1, 1, or 10 mg of p,p'-DDE/kg body weight, respectively. A control group was treated with the vehicle (corn oil). Two weeks after injection the frogs were euthanized and samples taken. The diaphysis of the excised left femur was scanned using peripheral quantitative computed tomography (pQCT) and cortical variables, such as cortical bone mineral density (BMD), cortical cross-sectional area (CSA), and periosteal circumference, were determined. In addition, biomechanical three-point bending of the bones was conducted, with the load being applied to the same point as where the pQCT measurement was performed. The results from the pQCT measurements show that bone tissue in male frogs exposed to p,p'-DDE is negatively affected. A significant decrease in cortical BMD at the diaphysis was observed in frogs exposed to 1 mg p,p'-DDE. However, the biomechanical testing of the bones showed no significant differences between exposed and control group. Although this is the only study performed to date examining the possible relationships between EDCs and negative effects on frog bones, it supports both previous experimental findings in rodents and findings in free-ranging animals.

The Intersection Between the Aryl Hydrocarbon Receptor (AhR)‐ and Retinoic Acid‐Signaling Pathways

Data from a variety of animal and cell culture model systems have demonstrated an interaction between the aryl hydrocarbon receptor (AhR)- and retinoic acid (RA)-signaling pathways. The AhR(1) was originally identified as the receptor for the polycyclic aromatic hydrocarbon family of environmental contaminants; however, recent data indicate that the AhR binds to a variety of endogenous and exogenous compounds, including some synthetic retinoids. In addition, activation of the AhR pathway alters the function of nuclear hormone-signaling pathways, including the estrogen, thyroid, and RA pathways. Activation of the AhR pathway through exposure to environmental compounds results in significant changes in RA synthesis, catabolism, transport, and excretion. Some effects on retinoid homeostasis mediated by the AhR pathway may result from the interactions of these two pathways at the level of activating or repressing the expression of specific genes. This chapter will review these two pathways, the evidence demonstrating a link between them, and the data indicating the molecular basis of the interactions between these two pathways.

Perinatal exposure to PCB 153, but not PCB 126, alters bone tissue composition in female goat offspring

The aim of this study was to investigate if environmentally relevant doses of the putative estrogenic non dioxin-like PCB 153 and the dioxin-like PCB 126 caused changes in bone tissue in female goat offspring following perinatal exposure. Goat dams were orally dosed with PCB 153 in corn oil (98 microg/kg body wt/day) or PCB 126 (49 ng/kg body wt/day) from day 60 of gestation until delivery. The offspring were exposed to PCB in utero and through mother's milk. The suckling period lasted for 6 weeks. Offspring metacarpal bones were analysed using peripheral quantitative computed tomography (pQCT) after euthanisation at 9 months of age. The diaphyseal bone was analysed at a distance of 18% and 50% of the total bone length, and the metaphyseal bone at a distance of 9%. Also, biomechanical three-point bending of the bones was conducted, with the load being applied to the mid-diaphyseal pQCT measure point (50%). PCB 153 exposure significantly decreased the total cross-sectional area (125 mm(2)+/-4) versus non-exposed (142 mm(2)+/-5), decreased the marrow cavity (38 mm(2)+/-4) versus non-exposed (50 mm(2)+/-3) and decreased the moment of resistance (318 mm(3)+/-10) versus non-exposed (371 mm(3)+/-20) at the diaphyseal 18% measure point. At the metaphyseal measure point, the trabecular bone mineral density (121 mg/cm(3)+/-5) was increased versus non-exposed (111 mg/cm(3)+/-3). PCB 126 exposure did not produce any observable changes in bone tissue. The biomechanical testing of the bones did not show any significant changes in bone strength after PCB 153 or PCB 126 exposure. In conclusion, perinatal exposure to PCB 153, but not PCB 126, resulted in altered bone composition in female goat offspring.

Subclinical hypervitaminosis A in rat: measurements of bone mineral density (BMD) do not reveal adverse skeletal changes

We have previously shown that subclinical hypervitaminosis A in rats causes fragile bones. To begin to investigate possible mechanisms for Vitamin A action we extended our previous study. Forty-five mature female Sprague-Dawley rats were divided into three groups, each with 15 animals. They were fed a standard diet containing 12IU Vitamin A per g pellet (control, C), or a standard diet supplemented with 120 IU ("10xC") or 600 IU ("50xC") Vitamin A/g pellet for 12 weeks. At the end of the study, serum retinyl esters were elevated 4- and 20-fold. Although neither average food intake nor final body weights were significantly different between groups, a dose-dependent reduction in serum levels of Vitamin D and E, but not Vitamin K, was found. In the 50xC-group the length of the humerus was the same as in controls, but the diameter was reduced (-4.1%, p<0.05). Peripheral quantitative computed tomography (pQCT) at the diaphysis showed that bone mineral density (BMD) was unchanged and that periosteal circumference had decreased significantly (-3.7%, p<0.05). Ash weight of the humerus was not affected, but since bone volume decreased, volumetric BMD, as measured by the bone ash method, even increased (+2.5%, p<0.05). In conclusion, interference with other fat-soluble Vitamins is a possible indirect mechanism of Vitamin A action. Moreover, BMD measurements do not reveal early adverse skeletal changes induced by moderate excesses of Vitamin A in rats. Since the WHO criterium for osteoporosis is based on BMD, further studies are warranted to examine whether this is also true in humans.

Serum retinoids and beta-carotene as predictors of hip and other fractures in elderly women

There is debate about the possible deleterious effect of excessive vitamin A exposure on fracture risk. In this nested case control study in older women (312 cases and 934 controls), serum retinol, retinyl palmitate, and beta-carotene were not associated with fracture risk, and there was no evidence of excess risk with multivitamin or cod liver oil supplementation.

INTRODUCTION

Recent studies have suggested that higher vitamin A intake may account for a component of fracture risk within the general population and that supplemental vitamin A may be harmful even within recommended limits. No studies have examined the relationship between biochemical retinol status and fracture in older women.

MATERIALS AND METHODS

We examined serum retinol, retinyl palmitate, and beta-carotene as predictors of incident hip and other fractures in a large prospective study of British women over the age of 75 years (n = 2606, 312 incident osteoporotic fractures, 92 incident hip fractures; mean follow-up duration, 3.7 years). Fasting blood samples (9:00-11:00 a.m.) were collected at baseline. Using a case-control design (three controls per case), serum retinol, retinyl palmitate, and beta-carotene were assessed as univariate predictors of incident osteoporotic fracture or hip fracture. Baseline BMD at the total hip, age, 25(OH)D, serum beta Crosslaps, bone-specific alkaline phosphatase, weight, height, and smoking were considered as covariates in a multivariate model.

RESULTS

Serum retinol, retinyl palmitate, and beta-carotene were not significant univariate predictors of either hip fracture or any fracture (all p > 0.05; Cox proportional hazards regression). For all osteoporotic fractures, the hazard ratio (HR) was 0.92 (95% CI, 0.81-1.05) per 1 SD increase in serum retinol. Risk of any osteoporotic fracture was slightly less in the highest quartile of serum retinol compared with the lowest quartile (HR, 0.85; 95% CI, 0.69-1.05; p = 0.132) There was a tendency for increased serum retinol to predict benefit rather than harm in terms of BMD (r = 0.09, p = 0.002). Multivitamin or cod liver oil supplementation was associated with a significantly lower risk of any fracture (HR, 0.76; 95% CI, 0.60-0.96; p = 0.021). In multivariate analysis, only age, total hip BMD, and weight were associated with fracture risk (p < 0.05).

CONCLUSIONS

We found no evidence to support any skeletal harm associated with increased serum indices of retinol exposure or modest retinol supplementation in this population.

Effects of In Utero and Lactational TCDD Exposure on Bone Development in Differentially Sensitive Rat Lines

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is a notorious model compound of highly toxic environmental pollutants, polychlorinated dibenzo-p-dioxins (PCDDs). Their toxic effects are mediated via cytosolic aryl hydrocarbon receptor (AHR). We studied the effects of several dose levels of TCDD on developing rat bone after maternal exposure at different times of gestation and lactation in three differentially sensitive rat lines. Rat lines A, B, and C differ in their sensitivity to TCDD due to mutated AHR (Ahr(hw)) in line A and another TCDD-resistance allele (B(hw)) in line B. Line C rats have no resistance alleles. Offspring were analyzed for bone mineral density and geometry by peripheral quantitative computed tomography (pQCT) and for bone biomechanics by three-point bending at mid-diaphysis of tibia and femur and by axial loading at femoral neck. TCDD treatment resulted in bone defects, mainly in offspring of the most sensitive line C at a maternal dose of 1 microg/kg. They included decreased bone length, cross-sectional area of cortex, and bone mineral density. Mechanical testing revealed significantly reduced bending breaking force and stiffness of tibia, femur, and femoral neck. The effects were exposure time-dependent, and earlier exposure caused more severe defects. Gestational exposure alone was not sufficient, but lactational exposure was required to cause the bone defects. Most of the defects were recovered at the age of 1 year. The results indicate that dioxins affect developing bone by interfering with bone growth and mechanical strength and that the effects are mainly reversible. The dioxin-resistance alleles, Ahr(hw) and B(hw) increase the resistance to these defects.

Is bone mineral composition disrupted by organochlorines in east Greenland polar bears (Ursus maritimus)?

We analyzed bone mineral density (BMD) in skulls of polar bears (Ursus maritimus) (n = 139) from East Greenland sampled during 1892-2002. Our primary goal was to detect possible changes in bone mineral content (osteopenia) due to elevated exposure to organochlorine [polychlorinated biphenyls (PCBs), dichlorodiphenyl trichloroethane (DDT) and its metabolites, chlordanes (CHLs), dieldrin, hexacyclohexanes, hexachlorobenzene] and polybrominated diphenyl ether (PBDE) compounds. To ensure that the BMD value in skull represented the mineral status of the skeletal system in general, we compared BMD values in femur and three lumbar vertebrae with skull in a subsample. We detected highly significant correlations between BMD in skull and femur (r = 0.99; p < 0.001; n = 13) and skull and vertebrae (r = 0.97; p < 0.001; n = 8). BMD in skulls sampled in the supposed pre-organochlorine/PBDE period (1892-1932) was significantly higher than that in skulls sampled in the supposed pollution period (1966-2002) for subadult females, subadult males, and adult males (all, p < 0.05) but not adult females (p = 0.94). We found a negative correlation between organochlorines and skull BMD for the sum of PCBs (SigmaPCB; p < 0.04) and SigmaCHL (p < 0.03) in subadults and for dieldrin (p < 0.002) and SigmaDDT (p < 0.02) in adult males; indications for SigmaPBDE in subadults were also found (p = 0.06). In conclusion, the strong correlative relationships suggest that disruption of the bone mineral composition in East Greenland polar bears may have been caused by organochlorine exposure.

Effect of ascorbic acid on surgical stress response in gynecologic surgery

Surgical stress may cause neural, endocrine, metabolic and humoral responses depending on the severity of the procedure. In this study, we aimed to study the effect of the preoperatively given ascorbic acid (AA), which is an antioxidant, and its role in the biosynthesis of neuropituitary hormones on the surgical stress response. Twenty-two American Society of Anaesthesiologists I and II patients ageing between 18 and 40, who have no endocrine and metabolic disease, and undergoing abdominal operation for non-malignant diseases were allocated to the study. These non-premedicated patients were divided into two groups in random: Group I, etomidate group; and Group II, AA plus etomidate group. AA was given to patients in Group II 20min before etomidate injection. After monitoring the patient, anaesthetic induction was applied by giving 0.3 mg/kg of etomidate, 2 microg/kg of fentanyl and 0.1 mg/kg of vecuronium. Anaesthesia was continued with 1-0.7% isoflurane and N2O/O2 (67 and 37%, respectively). Tramadol was given for the management of post-operative analgesia. Blood samples were obtained from all patients before the operation and at second, sixth, twelfth and twenty-forth hours after the beginning of operation for cortisol, adrenocorticotropic hormone (ACTH), osteocalcin, insulin and blood glucose level analyses. There was no statistically significant difference in cortisol, osteocalcin, insulin and glucose levels in both groups, when compared to the control levels. Whereas, patients in Group II had higher levels of cortisol than the control group at sixth hour, which were in normal limits, and there was no decrease in osteocalcin concentration. ACTH level was increased at the second and sixth hours, which was statistically significant, but at twelfth and twenty-forth hours, they were close to control group levels. As a result, we conclude that AA given before anaesthesia achieved by etomidate is not sufficient for the prevention of surgical stress response and that AA induction before anaesthesia should be preferred, particularly for the prevention of decrease in osteocalcin levels.

Abnormal bone composition in female juvenile American alligators from a pesticide-polluted lake (Lake Apopka, Florida)

Reproductive disorders have been found in pesticide-exposed alligators living in Lake Apopka, Florida (USA). These disorders have been hypothesized to be caused by exposure to endocrine- disruptive estrogen-like contaminants. The aim of this study was to expand our analysis beyond previous studies by investigating whether bone tissue, known to be affected by sex steroid hormones, is a potential target of endocrine disruptors. Long bones from 16 juvenile female alligators from Lake Apopka (pesticide-contaminated lake) and Lake Woodruff (control lake) were evaluated by peripheral quantitative computed tomography. We observed significant differences in bone composition, with female alligators from the contaminated lake having greater trabecular bone mineral density (BMD), total BMD, and trabecular mineral content compared with females from the control lake (p < 0.05). Increased trabecular and total BMD measurements suggest that juvenile female alligators from Lake Apopka were exposed to contaminants that created an internal environment more estrogenic than that normally observed. This estrogenic environment could be caused by both natural and anthropogenic compounds. Effects on BMD indicate interference with bone homeostasis. We hypothesize that contaminants present in the lake inhibit the natural and continuous resorption of bone tissue, resulting in increased bone mass. Although this is the only study performed to date examining effects of environmental estrogenic compounds on alligator bones, it supports previous laboratory-based studies in rodents. Further, this study is important in demonstrating that the alterations in morphology and physiology induced in free-ranging individuals living in environments contaminated with endocrine-active compounds are not limited to a few systems or tissues; rather, effects can be observed in many tissues affected by these hormones.

Subclinical hypervitaminosis A causes fragile bones in rats

Excessive intake of vitamin A has been associated with an increased risk of hip fracture in humans. This finding has raised the question of whether long-term intake of relatively moderate doses ("subclinical" hypervitaminosis A) contributes to fracture risk. Although it has been known for more than half a century that toxic doses of vitamin A lead to spontaneous fractures in rats, the lowest intake that induces adverse effects is not known, and the result of exposure to excessive doses that do not cause general toxicity has been rarely investigated. In this study, mature female rats were fed a standard diet with 12 IU vitamin A/g pellet (control, C), or standard diet supplemented with either 120 IU ("10 x C") or 600 IU ("50 x C") vitamin A/g pellet for 12 weeks. Fifteen animals were included in each group. The supplemented diets correspond to a vitamin A intake of approximately 1800 IU/day and 9000 IU/day, respectively. The latter dose is about one third of that previously reported to cause skeletal lesions. At the end of the study, serum retinyl esters were elevated 4- (p < 0.01) and 20-fold (p < 0.001) and the total amount of liver retinoid had increased 3- (p < 0.001) and 7-fold (p < 0.001) in the 10 x C and 50 x C group, respectively. The animals showed no clinical signs of general toxicity, and there were no significant bone changes in the 10 x C group. However, in the 50 x C group, a characteristic thinning of the cortex (cortical area -6.5% [p < 0.001]) and reduction of the diameter of the long bones were evident (bone cross-sectional area -7.2% [p < 0.01] at the midshaft and -11.0% [p < 0.01] at the metaphysis), as measured by peripheral quantitative computed tomography. In agreement with these data and a decreased polar strength strain index (-14.0%, p < 0.01), the three-point bending breaking force of the femur was reduced by 10.3% (p < 0.01) in the 50 x C group. These data indicate that the negative skeletal effects appear at a subchronic vitamin A intake of somewhere between 10 and 50 times the standard diet. This level is considerably lower than previously reported. Our results suggest that long-term ingestion of modest excesses of vitamin A may contribute to fracture risk.

Torsional testing and peripheral quantitative computed tomography in rat humerus

Peripheral quantitative computed tomography (pQCT) is a noninvasive method mainly used to evaluate the densitometric and geometric properties of bone. In the present study, we evaluate the different variables provided by pQCT examination and their ability to predict the mechanical strength properties of the rat humerus. Humeri from 68 female rats were utilized. These humeri represented bone with a wide range of mechanical and densitometric properties as well as geometric dimensions. Various characteristics, such as volumetric cortical density, total mineral content, cortical thickness, total cross-sectional area, cortical area, and polar strength strain index (SSI), were measured by pQCT. The reproducibility of these measurements was good, with a coefficient of variation (CV) ranging from 0.8% to 4.9%. Bone composition (e.g., ash weight, water content, and inorganic content) and bone dimensions (e.g., length, waist, and volume) were also determined. The mechanical properties (maximum torque, torsion at failure, and stiffness) were measured by torsional testing. Stepwise multiple linear regression was performed to identify the best explanatory variables for each mechanical parameter. Total cross-sectional area and polar SSI were equally well correlated to stiffness (r = 0.57, p < 0.001), whereas ash weight was superior to the pQCT variables to explain maximum torque (r = 0.42, p < 0.001). No other independent pQCT variable entered the two models in the stepwise regression analysis. It was found to be feasible to measure properties of the rat humerus with pQCT. Cross-sectional area and the polar SSI were shown to be the best explanatory variables for stiffness, whereas ash weight was the best predictor for maximum torque.