Weakness in the mechanical properties of the femur of growing female rats exposed to cadmium

Recommendations for the reference concentration of cadmium exposure based on a physiologically based toxicokinetic model integrated with a human respiratory tract model

Cadmium (Cd) poses a significant threat to human health. However, chronic toxicity parameters for inhalation exposure are lacking, especially for noncritical systemic toxic effects. A physiologically based toxicokinetic (PBTK) model can be used to extrapolate toxicity parameters across various exposure routes. We combined a PBTK model with a human respiratory tract (HRT) model, which is applicable to the general population and capable of simulating the deposition and clearance processes of various airborne Cd compounds in the respiratory tract. Monte Carlo analysis was used to simulate the distribution of sensitive parameters to reflect individual variability. Validation based on datasets from general and occupational populations showed that the improved model had acceptable or better predictive performance, outperforming the original model with a 14.45 % decrease in the root mean square error (RMSE). Using this PBTK-HRT model, we extrapolated toxicity parameters from oral exposure to inhalation exposure for four systemic toxic effects with doseresponse relationships but no known inhalation toxicity parameters, and ultimately recommended reference concentrations (RfCs) for four diseases (chronic kidney disease: 0.01 μg/m3, osteoporosis: 0.01 μg/m3, stroke: 0.04 μg/m3, diabetes mellitus: 0.13 μg/m3), contributing to a comprehensive assessment of the health risks of Cd inhalation exposure. ENVIRONMENTAL IMPLICATION: Cadmium (Cd), a heavy metal, can cause lung cancer, chronic kidney disease, and osteoporosis and pose a significant threat to human health. We combined a physiologically based toxicokinetic (PBTK) model with a human respiratory tract (HRT) model to achieve better predictive performance and wider applicability; this model was subsequently employed for route-to-route extrapolation of toxicity parameters. Additionally, for the first time, we focused on multiple subchronic and chronic systemic toxic effects in addition to critical effects and derived their reference concentrations (RfCs), which can be used to assess the health risk of Cd inhalation exposure more comprehensively and accurately.

Minimal Risk Level Derivation for Cadmium: Acute and Intermediate Duration Exposures

The Agency for Toxic Substances and Disease Registry (ATSDR) lists cadmium as one of its priority hazardous substances. The agency conducted a comprehensive literature review of cadmium and used the information to develop a toxicological profile that identified the full range of health effects associated with exposure to cadmium. It included an assessment that identified screening levels, termed health guidance values or minimal risk levels (MRLs), below which adverse health effects are not expected. In this paper, we describe how MRLs for cadmium are derived. For the acute inhalation MRL, the traditional no observed adverse effect level or lowest observed adverse effect level (NOAEL/LOAEL) approach is used; for the oral intermediate MRL, the benchmark dose (BMD) approach is used. MRLs were developed for the most sensitive route-specific end points, other than mortality and cancer that were sufficiently supported and justified by the data. These included an acute duration (1-14 day exposure) inhalation MRL of 0.03 µg Cd/m³ for alveolar histiocytic infiltration and focal inflammation in alveolar septa and an intermediate duration (15-365 day exposure) oral MRL of 0.5 µg Cd/kg/day for decreased bone mineral density.

Protective Effect of Chokeberry (Aronia melanocarpa L.) Extract against Cadmium Impact on the Biomechanical Properties of the Femur: A Study in a Rat Model of Low and Moderate Lifetime Women Exposure to This Heavy Metal

The hypothesis that the consumption of Aronia melanocarpa berries (chokeberries) extract, recently reported by us to improve bone metabolism in female rats at low-level and moderate chronic exposure to cadmium (1 and 5 mg Cd/kg diet for up to 24 months), may increase the bone resistance to fracture was investigated. Biomechanical properties of the neck (bending test with vertical head loading) and diaphysis (three-point bending test) of the femur of rats administered 0.1% aqueous chokeberry extract (65.74% of polyphenols) or/and Cd in the diet (1 and 5 mg Cd/kg) for 3, 10, 17, and 24 months were evaluated. Moreover, procollagen I was assayed in the bone tissue. The low-level and moderate exposure to Cd decreased the procollagen I concentration in the bone tissue and weakened the biomechanical properties of the femoral neck and diaphysis. Chokeberry extract administration under the exposure to Cd improved the bone collagen biosynthesis and femur biomechanical properties. The results allow for the conclusion that the consumption of chokeberry products under exposure to Cd may improve the bone biomechanical properties and protect from fracture. This study provides support for Aronia melanocarpa berries being a promising natural agent for skeletal protection under low-level and moderate chronic exposure to Cd.

Effects of remifemin treatment on bone integrity and remodeling in rats with ovariectomy-induced osteoporosis

This study aims to evaluate the effects of Remifemin (isopropanolic extract of Cimicifuga Racemosa) on postmenopausal osteoporosis. 120 female Sprague-Dawley rats were randomly assigned to four groups: sham surgery with vehicle, ovariectomy with vehicle, ovariectomy with estradiol valerate, or ovariectomy with Remifemin. Daily oral administrations of the vehicle, estradiol valerate, or Remifemin began 2 weeks after surgery and lasted to 4, 8, or 12 weeks. Ten rats in each group were sacrificed at each timestep with assessment of bone mineral density, trabecular bone structure, and biomechanical parameters of the femur and lumbar vertebra. Bone turnover markers were evaluated 12 weeks after surgery. Both drugs prevented bone density loss in the distal end of the femur and preserved the trabecular bone structure in both the lumbar vertebra and distal end of the femur following ovariectomy. Both drugs protected bone stiffness at the tested regions and reduced bone reabsorption in ovariectomized rats. The preventive effects of Remifemin against bone-loss can rival those of estradiol valerate if treatment duration is adequately extended. In conclusion, Remifemin may demonstrate equivalent effects to estradiol valerate in terms of preventing postmenopausal osteoporosis.

Cadmium impact and osteoporosis: mechanism of action

CONTEXT

Cadmium (Cd) is a widespread environmental pollutant that is associated with increased risk of osteoporosis. It has been proposed that Cd's toxic effect on bone is exerted via impaired activation of vitamin D, secondary to the kidney effects.

OBJECTIVE

The present study was designed to investigate the damaging impact of Cd in drinking water on bone from biochemical and histopathological point of view.

MATERIALS AND METHODS

This study was conducted on 30, 3-months-old female Sprague Dawley rats exposed to cadmium chloride in a dose of 50 mg Cd/L in drinking water for 3 months. Serum was taken for determination of calcium, phosphorous levels, parathyroid hormone, 1,25 dihydroxy vitamin D(3), osteocalcin (OC) and bone specific alkaline phosphatase (BALP) activity.

RESULTS

The result revealed that Cd administration induces significant increase in serum calcium (Ca), phosphorous (P) and parathyroid hormone (PTH) levels in concomitant with significant reduction in serum vitamin D(3), osteocalcin (OC) levels and bone specific alkaline phosphatase (BALP) activity.

CONCLUSION

The present study provided clear evidence that long-term exposure to cadmium chloride produced marked abnormalities in bone biomarkers and increasing risk of fracture.

Effect of Epimedium pubescen flavonoid on bone mineral density and biomechanical properties of femoral distal end and femoral diaphysis of passively smoking male rats

BACKGROUND

Based on a rat model of human relatively high exposure to cigarette smoke, this study aimed to estimate whether Epimedium pubescen flavonoid (EPF) may prevent a smoke-induced decrease in bone mineral density (BMD) and weakening of the biomechanical properties of bone.

METHODS

Fifty male Wistar rats were randomized into five groups: controls, passively smoking groups and passively smoking rats administered EPF at three dosage levels (75, 150 or 300 mg/kg/day) in drinking water for 4 months. A rat model of passive cigarette smoking was prepared by breeding male rats in a cigarette-smoking box for 4 months. Bone metabolic makers, BMD and biomechanical properties of the femoral distal end and femoral diaphysis were examined.

RESULTS

Exposure to cigarette smoke decreased the BMD, affected bone turnover (inhibited bone formation and stimulated its resorption) and weakened the biomechanical properties of the femur at its distal end and diaphysis. EPF supplementation during cigarette smoke exposure prevented the decrease in BMD, accelerated bone turnover and weakened the biomechanical properties of bone.

CONCLUSION

Our data suggest that EPF supplementation can prevent the adverse effects of smoke exposure on BMD and biomechanical properties by inhibiting bone turnover and preventing bone resorption, and in this way it can decrease the risk of bone fractures.

Effects of cadmium on bone microstructure and serum tartrate-resistant acid phosphatase 5b in male rats

This study investigated the effects of cadmium on bone microstructure and serum tartrate-resistant acid phosphatase 5b (Tracp 5b) in male rats. Sprague-Dawley male rats were divided into three groups that were given CdCl2 by subcutaneous injection at doses of 0, 0.1 and 0.5 mg/kg body weight (bw) for 12 weeks, respectively. Before killing at the 12th week, microcomputed tomography scanning was performed on the proximal tibia, and urine samples were collected from all of the rats. All rats were then killed, and their blood was collected for biomarkers assay. Bone tissues were dissected for mineral density determinations and histology. The concentration of cadmium in the blood, urine and bone of rats treated with cadmium were significantly higher than in the control group. The bone mineral density, bone mineral concentrations and bone microstructure index of rats treated with cadmium at 0.5 mg/kg bw were clearly lower than in the control rats. Histological investigation also revealed damage to the bone microstructure caused by cadmium. Tracp 5b concentrations in rats treated with cadmium were dose dependently higher than the control. The concentration of cadmium in blood, urine and bone was significantly correlated with Tracp 5b and bone microstructure parameters. Cadmium was shown to induce bone microstructure damage, especially to trabecular bone. The elevated concentrations of serum Tracp 5b suggest that bone resorption mediated via osteoclasts is an important mechanism for the toxic effects of cadmium on bone.

Bone turnover in passive smoking female rat: relationships to change in bone mineral density

Background

Many studies have identified smoking as a risk factor for osteoporosis, but it is unclear whether passive smoking has an effect on bone mineral density and bone turnover and if such an effect could cause osteoporosis.The purpose of the study was to investigate the effect of passive smoking on bone mineral density (BMD) and bone turnover and the relationship between BMD and bone turnover in female rat.

Methods

Forty-eight female Wistar rats were randomized into six groups: 2-month, 3-month,4-month smoke-exposed rats and their controls. A rat model of passive cigarette smoking was prepared by breeding female rats in a cigarette-smoking box for 2, 3 or 4 months. Serums were analyzed for levels of osteocalcin, bone-specific alkaline phosphatase (b-ALP) and Tartrate-resistant acid phosphatase 5b (TRACP 5b). BMD was assessed at lumbar vertebrae and femur by dual energy X-ray absorptiometry in passive smoking rats and in control rats.

Results

BMD of lumbar spine and femur was lower in 4-month smoke-exposed female rats than that in controls. However, there was no significant difference in serum osteocalcin levels between smoke-exposed rats and controls. Significantly lower b-ALP and higher TRACP 5b were found in the 3-month or 4-month smoke-exposed rats compared to controls. Subsequent analysis showed that b-ALP positively correlated with BMD of the lumbar vertebrae(r = 0.764, P = 0.027) and femur(r = 0.899, P = 0.002) in 4-month smoke-exposed female rats. Furthermore, TRACP 5b levels negatively correlated with BMD of lumbar vertebrae (r = -0.871, P = 0.005) and femur (r = -0.715, P = 0.046) in 4-month smoke-exposed female rats.

Conclusion

Our data suggest that smoke exposure can inhibit bone formation and increase bone resorption. The hazardous effects of passive smoking on bone status are associated with increased bone turnover in female rat.

Effects of low, moderate and relatively high chronic exposure to cadmium on long bones susceptibility to fractures in male rats

The study investigated the risk of the femur and tibia fractures on a male rat model of low, moderate and relatively high human exposure to cadmium (1, 5 and 50mg Cd/l in drinking water for 12 months). Bone mineral density (BMD) and biomechanical properties at the proximal and distal femur, and femoral and tibial diaphysis as well as the bone content of mineral and organic components, were evaluated. The exposure to 1mg Cd/l caused only very subtle changes in biomechanical properties at the femoral neck and distal femur. In the rats treated with 5mg Cd/l, a decrease in the distal femur BMD (by 5.5%) and enhanced vulnerability to fracture at the femoral neck, distal femur, and tibia diaphysis were observed. At the highest Cd treatment, the BMD decreased (by 6.5-11%) and the biomechanical properties weakened at all regions of the femur and tibia. Moreover, a decrease in the femur and tibia content of mineral components (by 11.5% and 10%, respectively) and the tibia content of organic components (by 7%) was noted. The results seem to indicate that low chronic exposure to Cd can have no influence on the bone resistance to fracture, whereas moderate (and particularly relatively high) exposure seriously increases the risk of fracture of long bones in males. The observations, together with our findings on an analogous female rat model, provide evidence that males are less vulnerable to Cd-induced demineralization and weakening of biomechanical properties of the femur and tibia than females.

Cadmium osteotoxicity in experimental animals: mechanisms and relationship to human exposures

Extensive epidemiological studies have recently demonstrated increased cadmium exposure correlating significantly with decreased bone mineral density and increased fracture incidence in humans at lower exposure levels than ever before evaluated. Studies in experimental animals have addressed whether very low concentrations of dietary cadmium can negatively impact the skeleton. This overview evaluates results in experimental animals regarding mechanisms of action on bone and the application of these results to humans. Results demonstrate that long-term dietary exposures in rats, at levels corresponding to environmental exposures in humans, result in increased skeletal fragility and decreased mineral density. Cadmium-induced demineralization begins soon after exposure, within 24 h of an oral dose to mice. In bone culture systems, cadmium at low concentrations acts directly on bone cells to cause both decreases in bone formation and increases in bone resorption, independent of its effects on kidney, intestine, or circulating hormone concentrations. Results from gene expression microarray and gene knock-out mouse models provide insight into mechanisms by which cadmium may affect bone. Application of the results to humans is considered with respect to cigarette smoke exposure pathways and direct vs. indirect effects of cadmium. Clearly, understanding the mechanism(s) by which cadmium causes bone loss in experimental animals will provide insight into its diverse effects in humans. Preventing bone loss is critical to maintaining an active, independent lifestyle, particularly among elderly persons. Identifying environmental factors such as cadmium that contribute to increased fractures in humans is an important undertaking and a first step to prevention.

Low-exposure cadmium is more toxic on osteoporotic rat femoral bone: mechanical, biochemical, and histopathological evaluation

This study aimed to investigate the effects of low-exposure Cd on normal and osteoporotic bone. For this purpose, 12-week-old Sprague-Dawley female rats were assigned randomly to a control group, a Cd group, and an ovariectomy (OVX)+Cd group. OVX+Cd rats underwent bilateral ovariectomy via ventral incision. Twelve weeks after ovariectomy, cadmium chloride (CdCl(2)) was given to rats (Cd and OVX+Cd groups) as intraperitoneal (ip) injection of 0.5mg/kg three times a week for 18 weeks and distilled water was given to control group via ip route for 18 weeks. Bone mineral density (BMD) was measured at mid-diaphysis femoral region by dual-energy X-ray absorbsiometry. Cross-sectional area of the femoral shaft was evaluated by computerized tomography. Biomechanical measurements were performed at the mid-diaphysis of the left femur. Collagen fibers were evaluated at light microscopic level. BMD, cortical thickness, cortical area, and femur length were not changed in Cd and OVX+Cd groups in comparision to controls. In the OVX+Cd group, strength, displacement, energy, stress, strain, and toughness were significantly lower than those of the control group. The Cd concentration of bone was significantly increased in the OVX+Cd group compared to that in the control group. Collagen fiber intensity was decreased in all groups except control group. The results of the present study indicate that the administration of low-dose Cd does not affect normal bone biomechanical parameters, but it has a significant effect on osteoporotic bone.

Effect of low-level lifetime exposure to cadmium on calciotropic hormones in aged female rats

The effect of low-level lifetime exposure to cadmium (Cd) on calciotropic hormones and the possible association between the Cd-induced disorders in bone metabolism and these hormones were investigated on a female rat model of human environmental exposure in areas unpolluted by this metal. For this purpose, the concentrations of 25-hydroxyvitamin D (25OHD), 1,25-dihydroxyvitamin D (1,25(OH)(2)D), calcitonin (CT) and parathormone (PTH) were measured in the serum of control and Cd-exposed (1 mg Cd/l in drinking water for 24 months) female rats. Calcium (Ca) and inorganic phosphorus (P(i)) serum concentrations, renal tubular reabsorption of Ca (TRCa) and phosphate (TRP) and the glomerular filtration rate (GFR) were estimated as well. Moreover, 1,25(OH)(2)D, metallothionein (MT) and Cd were determined in the kidney. The exposure to Cd led to a decrease in the serum concentrations of 25OHD and 1,25(OH)(2)D (by 50 and 31%, respectively) and the concentration of 1,25(OH)(2)D in the kidney mitochondrial fraction (by 55%). The serum concentrations of CT and PTH increased (5.2-fold and by 29%, respectively) and those of Ca and P(i) were unchanged, whereas the TRCa, TRP and GFR decreased due to the exposure to Cd. The results give evidence that the low lifetime exposure to Cd disturbs the metabolism of calciotropic hormones and damages the reabsorptive and filtrative function of the kidney in aged female rats. Numerous correlations noted between calciotropic hormones and the indices of kidney function, and indices of bone turnover and bone mineral status (bone mineral content and density) of these females indicate a relationship between these hormones and the kidney functional status and bone metabolism. The results of the present study together with our previous findings on the bone status in the experimental model allow for the conclusion that the low lifetime exposure to Cd by affecting the metabolism and proper function of calciotropic hormones may contribute to the advancement of bone damage at the elderly.