Uncoupling between bone formation and resorption in ovariectomized rats with chronic cadmium exposure

Low-level cadmium exposure is associated with decreased cortical thickness, cortical area and trabecular bone volume fraction in elderly men: The MrOS Sweden study

It is well known that high-level exposure to cadmium can cause bone disease such as osteoporosis, osteomalacia and fractures. However, the effect of low-level exposure, as found in the general population (mainly derived from diet and smoking), has only been assessed recently. The aim of this study was to examine if cadmium exposure in the general Swedish population causes other bone changes than decreased areal bone mineral density as measured by traditional DXA technology, e.g. changes in microstructure and geometry, such as cortical thickness or area, cortical porosity and trabecular bone volume. The study population consisted of 444 men, aged 70-81 years at inclusion year 2002-2004, from the Swedish cohort of the Osteoporotic Fractures in Men Study (MrOS). Cadmium was analyzed in baseline urine samples (U-Cd). Different parameters of bone geometry and microstructure were measured at the distal tibia at follow-up in 2009, including examination with high-resolution peripheral quantitative computed tomography (HR-pQCT). Associations between bone parameters and U-Cd in tertiles were estimated in multivariable analyses, including potential confounding factors (age, smoking, BMI, and physical activity). We found significant associations between U-Cd and several bone geometry or microstructure parameters, with 9% lower cortical thickness (p = 0.03), 7% lower cortical area (p = 0.04), and 5% lower trabecular bone volume fraction (p = 0.02) in the third tertile of U-Cd, using the first tertile as the reference. Furthermore, significant negative associations were found between log-transformed U-Cd and cortical thickness, cortical area, trabecular number and trabecular bone volume fraction, and a significant positive association with trabecular separation. The results indicate that low-level Cd exposure in the general population has negative effects on both cortical and trabecular bone.

Impact of occupational cadmium exposure on bone in sewage workers

Cadmium (Cd) is one of the environmental risk factors for bone loss. The present study included 40 sewage workers occupationally exposed to Cd. Forty nonexposed men were included as a control group. Current smokers represented 65% and 47.5% of the exposed and control groups, respectively. The study aimed to investigate the hazard of occupational Cd exposure on bone health. This was achieved through measuring serum and urinary Cd, and calcium (Ca), in addition to serum osteoprotegerin (OPG) and estrogen receptor-α gene. Results showed significant elevation in serum Cd, OPG, and urinary Ca levels in the exposed compared to the controls. Bony aches and joint pain were more prevalent among the exposed workers. Serum and urinary Cd increased in exposed smokers relative to control smokers. Also, serum OPG levels showed significant rise among exposed smoker and nonsmoker compared to control smoker and nonsmoker groups. Serum Cd level increased significantly in PP and pp genotypes in exposed workers compared to controls, while elevated levels of serum OPG was observed in PP and Pp genotypes in exposed workers relative to controls. Urinary Cd exhibited significant rise in both PP and pp genotypes in exposed workers, while Ca excretion was elevated in pp genotype only. The study reflected an association of genetic predisposition and Cd exposure in progression of osteoporosis. Further research is needed to explain the mechanisms of Cd impact on bone. The role of smoking is important and hence smoking cessation programs are essential for sewage workers.

CT Imaging Biomarkers of Bone Damage Induced by Environmental Level of Cadmium Exposure in Male Rats

Cadmium (Cd) can induce bone loss and osteoporosis. Histologic methods have shown that Cd can induce microarchitecture change of the trabecular bone. The aim of this study is to evaluate the imaging biomarkers of osteoporosis induced by Cd using micro-computed tomography (micro-CT). Twenty-four male Sprague-Dawley rats were randomly divided into four groups that were exposed to Cd via drinking water at concentrations of 0, 2, 10, and 50 mg/L for 3 months. Before sacrifice, micro-CT scanning was performed on the proximal tibia. Three-dimensional images were analyzed by using commercial software to measure apparent bone mineral density (ABMD), tissue bone mineral density (TBMD), bone volume/total volume fraction (BV/TV), trabecular number (Tb.N), trabecular thickness (Tb.Th), trabecular separation (Tb.Sp), and structural model index (SMI) as imaging biomarkers. Histologic analyses were performed using hematoxylin and eosin (HE) and Goldner's trichrome stain. Exposure to Cd resulted in a marked decrease of ABMD, BV/TV, and Tb.N and an increase of Tb.Sp and SMI compared with control, especially for those treated with 50 mg Cd/L (p < 0.05). Decreased Tb.N and increased Tb.Sp compared to that of control were also observed in histologic findings. The micro-CT imaging is a promising tool for assessing the bone damage induced by Cd, and Tb.N, Tb.Sp, and SMI may be the potential sensitive imaging biomarkers.

Association between blood cadmium level and bone mineral density reduction modified by renal function in young and middle-aged men

The association between cadmium exposure and bone mineral density (BMD) has not been well studied in young and middle-aged men. This study examined the relationship between the level of blood Cd (BCd) and BMD in a young to middle-aged representative male population while considering renal function. Using data from the 4th Korea National Health and Nutrition Examination Survey, 2008-2009, 1275 adult men aged 20-64 years were analyzed. BCd was measured by atomic absorption spectrophotometry and renal function was assessed by the estimated glomerular filtration rate (eGFR) with CKD-EPI formula. The risk of lower bone density was increased according to the increase in BCd levels after adjusting for eGFR and covariates, in which a significant interaction between BCd and eGFR existed. Significant negative associations between BCd and BMD were found: beta (p-value) were -0.03 (0.02), -0.04 (0.004) and -0.03 (0.04) in total femur, lumbar spine and femoral neck, respectively, which were limited to the people with eGFR≤lower 25%. Although, a causal relationship could not be determined because of a cross-sectional design in the present study, the results suggest low level Cd toxicity to bone via low eGFR and that measures to reduce environmental Cd exposure may be helpful to prevent bone loss in men.

Dietary phosphorus exacerbates bone loss induced by cadmium in ovariectomized rats

OBJECTIVE

Postmenopausal bone loss can be exacerbated by environmental contaminants, including the heavy metal cadmium (Cd). We hypothesized that incorporating phosphorus (P) into the diet would lead to the chelation of Cd into P, preventing its absorption and subsequent bone loss.

METHODS

To test this hypothesis, we used ovariectomized rats as a model of postmenopausal osteoporosis to examine the deleterious effects of Cd on bone with and without added P. Fifty 3-month-old ovariectomized Sprague-Dawley rats were assigned to five treatment groups (n = 10 per group) for 3 months as follows: (1) control; (2) 50 ppm Cd; (3) 50 ppm Cd plus 1.2% P; (4) 200 ppm Cd; and (5) 200 ppm Cd plus 1.2% P.

RESULTS

Cd plus P caused a significant loss of whole body (P = 0.0001 and P < 0.001) and femoral (P = 0.0005 and P < 0.001) bone mineral density (BMD) and bone mineral content, respectively, and a loss of fourth lumbar vertebra BMD and bone mineral content (P < 0.0001 and P < 0.001, respectively). Nonetheless, 200 ppm Cd plus 1.2% P had the most deleterious effects on whole body and femoral BMD. For femoral neck microstructural properties, 50 ppm Cd plus 1.2% P caused an increase in trabecular separation, whereas 200 ppm Cd plus 1.2% P caused a decrease in bone volume-to-total volume ratio, a decrease in trabecular number, and an increase in trabecular separation and structural model index.

CONCLUSIONS

Our findings indicate that Cd exposure, along with high intake of P, may be a public health hazard with respect to bone health.

Molecular mechanisms of cadmium-induced fibroblast growth factor 23 upregulation in osteoblast-like cells

Itai-itai disease is thought to be the result of chronic cadmium (Cd) intoxication. Renal proximal tubules are a major target of Cd toxicity. The whole mechanism of the adverse effects of Cd remains unresolved, especially how renal damage is related to the development of bone lesions. Fibroblast growth factor 23 (FGF23) is a bone-derived phosphaturic factor that regulates vitamin D and inorganic phosphate metabolism in the kidney. To clarify the role of FGF23 on Cd toxicity, we investigated the mechanisms of Cd-induced FGF23 production in the bone. Cd injection into mice significantly increased plasma FGF23 concentrations, but did not change FGF23 mRNA expression in bone. GalNAc-T3 is involved in secreting intact FGF23. To determine potential roles of GalNAc-T3 in Cd-induced FGF23 production, we examined the effect of Cd on GalNAc-T3 mRNA expression in vivo and in vitro. GalNAc-T3 gene expression was significantly increased in the bones of Cd-injected mice. Cd also enhanced the expression of GalNAc-T3 in cultured osteosarcoma UMR106 cells and primary osteocytes. Cd activated aryl hydrocarbon receptors (AhR) and AhR were required for GalNAc-T3 gene expression induced by Cd. In addition, Cd-dependent FGF23 production was completely inhibited by an AhR antagonist. AhR siRNA markedly suppressed the stimulation of transcriptional activity by Cd. Furthermore, Cd induced AhR activation via phosphorylation of Ser-68 by p38 kinase in the nuclear export signal of AhR. Thus, Cd stimulated GalNAc-T3 gene transcription via enhanced AhR binding to the GalNAc-T3 promoter. These findings suggest that the Cd-induced increase in GalNAc-T3 suppresses proteolytic processing of FGF23 and increases serum FGF23 concentrations.

The potential protective role of lysophospholipid mediators in nephrotoxicity induced by chronically exposed cadmium

Cadmium is a hazardous metal whose chronic exposure induces renal failure due to fibrosis, but the mechanisms are not well known. In this study we analyzed the molecular species of lysophosphatidic acid (LPA) and related phospholipids, together with their metabolic enzyme activity, in plasma from Wistar rats exposed up to 300ppm Cd(2+) in drinking water for 114days. Exposure of 300ppm Cd(2+) for 114days enhanced autotoxin (ATX)/lysophospholipase D activity, but significantly lowered the total levels of LPA and lysophosphatidylethanolamine. Interestingly, the total level of sphingosine-1-phosphate (S1P) was elevated dose-dependently by Cd(2+). Cultured rat kidney-derived interstitial fibroblast cells, NRK49F cells and proximal epithelial cells, NRK52E cells, were both responsive to the protective action of LPA or S1P against Cd(2+) toxicity. The former cell expresses ATX RNA. In conclusion, the elevation of LPA-producing enzyme activity and S1P concentrations in plasma after exposure of rats to Cd(2+) would protect from the renal toxicity of Cd(2+).

Environmental level of cadmium exposure stimulates osteoclasts formation in male rats

Low level of cadmium (Cd) exposure may enhance osteoclasts formation in vitro. The aim of the study was to observe the effects of Cd on osteoclasts formation in vivo. Sprague-Dawley male rats were divided into 4 groups which were given Cd via drinking water at concentrations of 0, 2, 10 and 50 mg/L for 12 weeks. At the 12th week, urine samples were collected from all of the rats. All rats were then sacrificed and the blood was collected for biomarkers assay. Bone tissues were dissected for mineral density determinations, histological investigation, tartrate resistant acid phosphatase staining and immunohistochemical staining. The bone mineral density and bone microstructure index of rats treated with 50mg Cd/L were obviously lower than in control rats. Histochemical investigation showed that Cd could induce osteoclasts formation in a dose-dependent manner. Tartrate resistant acid phosphatase 5b levels in rats treated with Cd were higher than the control. Immunohistochemical investigation showed that Cd could enhance receptor-activated nuclear factor kappa B ligand expression (RANKL) and inhibit osteoprotegerin (OPG) expression. Our study evidences in vivo that excessive bone resorption mediated via osteoclasts is an important way for Cd toxic effects on bone and OPG/RANKL may play an important role.

Cadmium exposure affects the expression of genes involved in skeletogenesis and stress response in gilthead sea bream larvae

Gilthead sea bream larvae (Sparus aurata) aged 47 days post hatching (dph) (11.6-12.8 mg in wet weight) were exposed to several sublethal concentrations of Cd(2+) (0.1, 5 and 10 mg/L) during 6 days in order to investigate the effects of this heavy metal on the expression of selected genes involved in detoxification (metallothionein-mt, glutathione peroxidase 1-gpx1), stress response (heat shock protein 70-hsp70, tumour necrosis factor α-tnfα) and ossification (osteocalcin-oc) processes. For this purpose, specimens of 47 dph were exposed first for 72 h from 0.1 to 20 mg/L of Cd(2+) in order to evaluate the median lethal concentration (LC(50)) for this metal, which was determined at 15.32 mg/L. Considering the results regarding the relative transcript levels of gpx1 and hsp70, Cd(2+) at any of the tested levels (0.1, 5 and 10 mg/L) did not induce oxidative stress in gilthead sea bream larvae, whereas relative transcript levels of mt were increased at 5 and 10 mg/L of Cd(2+) probably to detoxify this metal excess. Relative transcript levels of tnfα were not level dependent and were down-regulated in larvae exposed to 5 and 10 mg/L of Cd(2+). At those concentrations, transcript levels of oc were down-regulated suggesting a disruption in bone mineralization. Results from this study provided insights in some molecular mechanisms underlying Cd(2+)-induced toxicity in fish at early stages of development. This is the first study to show that cadmium contamination can depress oc expression in teleosts.

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.

Combined effects of γ-irradiation and cadmium exposures on osteoblasts in vitro

The combined effects of γ-irradiation and cadmium (Cd) exposures on osteoblasts were observed in the present study. Osteoblasts were exposed to γ-irradiation (0.5 Gy) and Cd (0-0.5 μmol/L). Cell viability, alkaline phosphatase (ALP) activity, mineralization ability, cell apoptosis and genes expression of ALP, osteocalcin (OC) and caspase 3 were observed. Low concentrations of Cd exposure had no obvious influence on cell viability, ALP activity and apoptosis. However, low levels of Cd exposure combined with γ-irradiation induced more toxic effects on osteoblasts than those treated with Cd or irradiation alone. High concentrations of Cd combined with irradiation exposure induced more significant inhibition in cell viability, ALP activity and mineralization ability than those exposed to Cd or irradiation alone. Meanwhile, OC and ALP mRNA expression of cells treated with Cd combined with irradiation were down-regulated more significantly than those treated with Cd or irradiation alone. Cd combined with γ-irradiation could obviously enhance osteoblast apoptosis and up-regulated caspase 3 mRNA expression compared with those treated with Cd or irradiation alone. This study indicated that ionizing irradiation can enhance Cd toxic effects on osteoblast viability and differentiation and apoptosis may play an important role in this progress.

Bone-prognostic status after cessation of cadmium exposure for one month in male rats

This study investigated bone status after decreased cadmium (Cd) exposure in male rats. Sprague-Dawley male rats were randomly divided into three groups. One group was injected subcutaneously with sodium chloride as control. The others were given CdCl2 by subcutaneous injection at doses of 0.5 mg Cd/kg body weight (bw) for 2 months (Cd+2m) and for 3 months (Cd+3m). For the Cd+2m group, the rats were shifted to cessation of Cd injection for 1 month after 2 months' exposure. At month 3, micro-computed tomography (micro-CT) analyses were performed on the proximal tibia and lumbar spine, and urine was collected from all rats. Rats were then killed and blood collected for metabolic-marker measurement and Cd assay. Bone tissues were also collected for bone-mass assay, biomechanical test, and bone-histology analysis. Cd burdens of rats in the Cd+2m and Cd+3m groups were both significantly greater than those in the control group. Cd burdens of rats were lower in the Cd+2m group compared with the Cd+3m group. Bone damage occurred in the Cd+2m and Cd+3m groups compared with the control group (p<0.05), but no significant improvement was found in the Cd+2m group compared with the Cd+3m group. Cd damage to bone could not be reversed over the short term. More attention should be paid to Cd's toxic effects on bone after decreased exposure.

Cadmium is more toxic on volume bone mineral density than tissue bone mineral density

It has been showed that Cd induces low areal bone mineral density, but we do not know the effect of Cd on cubic bone density. This study was aimed to investigate the effects of Cd on volumetric bone mineral density (VBMD) and tissue bone mineral density (TBMD) in male rats. Twenty-four Sprague-Dawley male rats were randomly divided into four groups that were given cadmium chloride by subcutaneous injection at doses of 0, 0.1, 0.5, and 1.5 mg/kg body weight for 8 weeks, respectively. Then, microcomputed tomography scanning was performed on the proximal tibia, and region of interest was reconstructed using microview software. The VBMD, bone volume fraction of rats treated with 1.5 mg Cd/kg, were significantly decreased compared to control (p < 0.01). The trabecular numbers of rats exposed to Cd were all significantly decreased relative to control (p < 0.05). The trabecular separation of rats treated with 1.5 mg Cd/kg was obviously increased compared to control (p < 0.01). However, Cd had no obvious influence on TBMD. Cd induced low VBMD but not TBMD; Cd effect on bone may be related with trabecular bone loss but not with trabecular bone demineralization.

Retinol may counteract the negative effect of cadmium on bone

Cadmium and high vitamin A intake are both proposed risk factors for low bone mineral density (BMD), but potential interactions have not been studied. Within the Women's Health in the Lund Area, a population-based study in southern Sweden, we measured retinol in serum among 606 women aged 54-64 y. Data on BMD were measured by DXA at the distal forearm. Parathyroid hormone (PTH), bone alkaline phosphatase (bALP), and osteocalcin in serum and deoxypyridinoline (DPD) and cadmium in urine were available. Associations were evaluated using multivariable-adjusted linear regression analysis. Serum retinol concentrations (median, 1.9; range, 0.97-4.3 μmol/L) were inversely associated with the bone formation markers bALP and osteocalcin (P ≤ 0.04) and with PTH (P = 0.07) and tended to be positively associated with BMD (P = 0.08) but not with the bone resorption marker DPD, indicating different effects on bone compared to urinary cadmium (median, 0.66; range, 0.12-3.6 nmol/mmol creatinine). Women with serum retinol less than the median and cadmium greater than the median had lower BMD than those with retinol greater than the median and cadmium less than the median (P = 0.016 among all women and P = 0.010 among never-smokers). Our findings suggest that adequate vitamin A status may counteract the adverse association between cadmium and BMD.

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 mineral density is related with previous renal dysfunction caused by cadmium exposure

Relationship between bone mineral density (BMD) and previous renal dysfunction caused by cadmium exposure was investigated. A total of 457 persons, living in polluted and control areas, were followed up in this study. The inhabitants living in exposure areas ceased ingesting cadmium-contaminated rice in 1996. Blood and urinary cadmium levels and BMD in 1998 and 2006 were measured. Urinary N-acetyl-β-d-glucosaminidase and albumin determined in 1998 and 2006 were used to evaluate kidney status. BMD of subjects with tubular damage was significant lower than those without damage in female (p < 0.05). The prevalence of osteoporosis was significantly different between those with and without kidney damage (p = 0.003, in total population; p = 0.039, in female) and those with and without tubular damage (p = 0.0005, in total population; p = 0.007, in female). The results suggested that BMD was correlated with previous kidney impairment caused by cadmium exposure, especially to tubular damage and especially for female.

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.

The effects of low environmental cadmium exposure on bone density

Recent epidemiological data indicate that low environmental exposure to cadmium, as shown by cadmium body burden (Cd-U), is associated with renal dysfunction as well as an increased risk of cadmium-induced bone disorders. The present study was designed to assess the effects of low environmental cadmium exposure, at the level sufficient to induce kidney damage, on bone metabolism and mineral density (BMD). The project was conducted in the area contaminated with cadmium, nearby a zinc smelter located in the region of Poland where heavy industry prevails. The study population comprised 170 women (mean age=39.7; 18-70 years) and 100 men (mean age=31.9; 18-76 years). Urinary and blood cadmium and the markers of renal tubular dysfunction (beta(2)M-U RBP, NAG), glomerular dysfunction (Alb-U and beta(2)M-S) and bone metabolism markers (BAP-S, CTX-S) as well as forearm BMD, were measured. The results of this study based on simple dose-effect analysis showed the relationship between increasing cadmium concentrations and an increased excretion of renal dysfunction markers and decreasing bone density. However, the results of the multivariate analysis did not indicate the association between exposure to cadmium and decrease in bone density. They showed that the most important factors that have impact on bone density are body weight and age in the female subjects and body weight and calcium excretion in males. Our investigation revealed that the excretion of low molecular weight proteins occurred at a lower level of cadmium exposure than the possible loss of bone mass. It seems that renal tubular markers are the most sensitive and significant indicators of early health effects of cadmium intoxication in the general population. The correlation of urinary cadmium concentration with markers of kidney dysfunction was observed in the absence of significant correlations with bone effects. Our findings did not indicate any effects of environmental cadmium exposure on bone density.

Changes in bone mineral density 10 years after marked reduction of cadmium exposure in a Chinese population

The main focus of this study was to evaluate the long-term effects of Cd on forearm bone mineral density after the cessation of the ingestion of Cd-polluted rice. A total of 458 persons (294 women, 164 men) from three Cd exposure areas (low, moderately, and heavy) participated in this study. Those living in the moderate and heavy exposure areas ceased ingesting Cd-polluted rice (0.51 and 3.7mg/kg, respectively) in 1996 (10 years prior to present analysis). The participants completed a questionnaire and bone mineral density (BMD) was measured by dual energy X-ray absorptiometry (DXA) at the proximal radius and ulna. The changes and change percentage in forearm bone density and the prevalence of osteoporosis between 1998 and 2006 were used as markers of bone recovery. The Cd concentrations in urine (UCd) and blood (BCd) in 1998 were used as Cd exposure markers. The values of the BMD change and change percentage of groups in which UCd was above 5microg/g creatinine (microg/g crea) and BCd was above 10microg/L were significantly higher than those of the low-exposure groups (in women, p<0.001; in men, p>0.05). The BMD change and change percentage correlated positively with the UCd and BCd (in women, p<0.01; in men, p>0.05). Analysis of the Z-score revealed that the prevalence of osteoporosis in 2006 was higher than that in 1998 and increased along with the level of UCd and BCd in both women and men, especially for those subjects with the higher BCd [BCd>5microg/L, OR=3.45 (0.95-13.6); BCd>10microg/L, OR=4.51(1.57-13.54)] and UCd [UCd>10microg/g crea, OR=4.74 (1.82-12.81)] in women. It is concluded that decreasing dietary cadmium exposure at the population level is not associated with bone recovery at the individual level, and the adverse bone effects of Cd exposure persisted after the main source of Cd exposure had been blocked, especially in women.

High bone matrix turnover predicts blood levels of lead among perimenopausal women

Skeletal bone is the primary endogenous source of lead in circulating blood, particularly under conditions of accelerated bone turnover and mineral loss, such as pregnancy and postmenopausal osteoporosis. We studied the influence of bone turnover rate on the release of lead from bone in 1225 female farmers from 5 districts in Japan. We collected peripheral blood and urine samples and medical nutritional information, and measured forearm bone mineral density (BMD). We found that blood lead levels in perimenopausal women were highest among all groups studied. Analysis of data for subjects grouped by level of markers of bone metabolism suggested that, in perimenopausal women, blood lead levels were higher in groups with high levels of N-telopeptide cross-linked collagen type I (NTx) and high levels of bone-specific alkaline phosphates (BALP) or osteocalcin (OC) compared with groups with low NTx and low BALP or OC levels. Linear multivariate models showed that markers of bone turnover were significantly positively related to blood lead levels. These results provide evidence that high bone turnover rates increase the release of lead stored in bone into the circulation. It is likely that markers of bone metabolism can be used to predict blood lead levels.

Effects of cadmium on osteoblasts and osteoclasts in vitro

Cadmium (Cd) may have direct effects on bone metabolism and the mechanism is not fully understood. To investigate the effects of Cd on bone metabolism, effects of Cd on osteoblasts and osteoclasts in vitro were observed at cellular and molecular levels. Osteoblasts were cultured by sequential enzyme digestion from Sprague-Dawley rats calvarial bone and osteoclasts were isolated from long bones of new-born male and female Sprague-Dawley rats, and then cells were exposed to different concentrations of Cd (0-2.0 μ mol/L for osteoblasts; 0.03 μmol/L for osteoclasts). As for osteoblasts, cell viability, alkaline phosphatase (ALP) activity, and mineralization were determined. Osteoprotegerin (OPG) and receptor activator of NF-kB ligand (RANKL) were studied via reverse transcription-polymerase chain reaction (RT-PCR). For osteoclasts, after exposure to Cd (0.03 μmol/L) for 72 h and 120 h, number of osteoclasts and pits formation was observed. Cd inhibited the viability, ALP activity, mineralization and up-regulated RANKL mRNA expression in osteoblasts. But Cd had no obvious effect on OPG mRNA expression. For osteoclasts, cadmium (0.03 μmol/L) could increase the numbers of osteoclasts (p<0.05) and enhance pits formation (p<0.05). These results suggested that Cd could inhibit bone formation at high concentrations and enhance bone resorption at low level. OPG/RANKL may constitute an important pathway of Cd effects on bone.

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.

Cadmium-induced bone effect is not mediated via low serum 1,25-dihydroxy vitamin D

Cadmium is a widespread environmental pollutant, which is associated with increased risk of osteoporosis. It has been proposed that cadmium's toxic effect on bone is exerted via impaired activation of vitamin D, secondary to the kidney effects. To test this, we assessed the association of cadmium-induced bone and kidney effects with serum 1,25-dihydroxyvitamin D (1,25(OH)(2)D); measured by enzyme immunoassay. For the assessment, we selected 85 postmenopausal women, based on low (0.14-0.39 microg/L) or high (0.66-2.1 microg/L) urinary cadmium, within a cross-sectional population-based women's health survey in Southern Sweden. We also measured 25-hydroxy vitamin D, cadmium in blood, bone mineral density and several markers of bone remodeling and kidney effects. Although there were clear differences in both kidney and bone effect markers between women with low and high cadmium exposure, the 1,25(OH)(2)D concentrations were not significantly different (median, 111 pmol/L (5-95th percentile, 67-170 pmol/L) in low- and 125 pmol/L (66-200 pmol/L) in high-cadmium groups; p=0.08). Also, there was no association between 1,25(OH)(2)D and markers of bone or kidney effects. It is concluded that the low levels of cadmium exposure present in the studied women, although high enough to be associated with lower bone mineral density and increased bone resorption, were not associated with lower serum concentrations of 1,25(OH)(2)D. Hence, decreased circulating levels of 1,25(OH)(2)D are unlikely to be the proposed link between cadmium-induced effects on kidney and bone.

Gender differences in the disposition and toxicity of metals

There is increasing evidence that health effects of toxic metals differ in prevalence or are manifested differently in men and women. However, the database is small. The present work aims at evaluating gender differences in the health effects of cadmium, nickel, lead, mercury and arsenic. There is a markedly higher prevalence of nickel-induced allergy and hand eczema in women compared to men, mainly due to differences in exposure. Cadmium retention is generally higher in women than in men, and the severe cadmium-induced Itai-itai disease was mainly a woman's disease. Gender differences in susceptibility at lower exposure are uncertain, but recent data indicate that cadmium has estrogenic effects and affect female offspring. Men generally have higher blood lead levels than women. Lead accumulates in bone and increased endogenous lead exposure has been demonstrated during periods of increased bone turnover, particularly in women in pregnancy and menopause. Lead and mercury, in the form of mercury vapor and methylmercury, are easily transferred from the pregnant women to the fetus. Recent data indicate that boys are more susceptible to neurotoxic effects of lead and methylmercury following exposure early in life, while experimental data suggest that females are more susceptible to immunotoxic effects of lead. Certain gender differences in the biotransformation of arsenic by methylation have been reported, and men seem to be more affected by arsenic-related skin effect than women. Experimental studies indicate major gender differences in arsenic-induced cancer. Obviously, research on gender-related differences in health effects caused by metals needs considerable more focus in the future.

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.

Cadmium-induced effects on bone in a population-based study of women

High cadmium exposure is known to cause bone damage, but the association between low-level cadmium exposure and osteoporosis remains to be clarified. Using a population-based women's health survey in southern Sweden [Women's Health in the Lund Area (WHILA) ] with no known historical cadmium contamination, we investigated cadmium-related effects on bone in 820 women (53-64 years of age) . We measured cadmium in blood and urine and lead in blood, an array of markers of bone metabolism, and forearm bone mineral density (BMD) . Associations were evaluated in multiple linear regression analysis including information on the possible confounders or effect modifiers: weight, menopausal status, use of hormone replacement therapy, age at menarche, alcohol consumption, smoking history, and physical activity. Median urinary cadmium was 0.52 microg/L adjusted to density (0.67 microg/g creatinine) . After multivariate adjustment, BMD, parathyroid hormone, and urinary deoxypyridinoline (U-DPD) were adversely associated with concentrations of urinary cadmium (p < 0.05) in all subjects. These associations persisted in the group of never-smokers, which had the lowest cadmium exposure (mainly dietary) . For U-DPD, there was a significant interaction between cadmium and menopause (p = 0.022) . Our results suggest negative effects of low-level cadmium exposure on bone, possibly exerted via increased bone resorption, which seemed to be intensified after menopause. Based on the prevalence of osteoporosis and the low level of exposure, the observed effects, although slight, should be considered as early signals of potentially more adverse health effects. Key words: biochemical bone markers, bone mineral density, cadmium, lead, osteoporosis, women.

Bone mineral density, chemical composition and biomechanical properties of the tibia of female rats exposed to cadmium since weaning up to skeletal maturity

The influence of exposure to cadmium (Cd) during skeletal development on the risk of bone fractures at the stage of skeletal maturity was investigated on a female rat model of human exposure. The tibias of rats treated with 1, 5 or 50 mg Cd/l in drinking water for 3, 6, 9 and 12 months (since weaning) were used. The exposure to Cd dose- and time-dependently influenced the tibia bone mineral density (BMD) and chemical composition. In skeletally matured animals, at each level of the exposure to Cd, the BMD at the whole tibia and its diaphysis as well as the percentage of minerals content in the bone, including the content of zinc, copper and iron, were decreased compared to control. Moreover, in the 50 mg Cd/l group, the percentage of organic components content increased. The Cd-induced changes, at all levels of exposure, resulted in weakening in the yield strength and fracture strength of the tibia (a three-point bending test of the diaphysis and compression test with vertical loading) of the skeletally matured females. A very important and clinically useful finding of this study is that a decrease (even by several percent) in the tibia BMD results in weakness in the bone biomechanical properties and that the BMD may predict the risk of its fracture at the exposure to Cd. Moreover, the results together with our previous findings seem to suggest that tibia, due to higher vulnerability of its diaphysis, compared to the femoral diaphysis, to damage by Cd may be more useful than femur to investigate the effect of Cd on the cortical bone. The present study revealed that a low exposure to Cd (1 mg Cd/l), corresponding to low human environmental exposure, during the skeletal development affects the tibia mineral status leading to weakening in its mechanical properties at the skeletal maturity. The findings allow for the conclusion that environmental exposure to Cd during childhood and adolescence may enhance the risk of low BMD and fractures at adulthood.

Bone metabolism of male rats chronically exposed to cadmium

Recently, based on a female rat model of human exposure, we have reported that low-level chronic exposure to cadmium (Cd) has an injurious effect on the skeleton. The purpose of the current study was to investigate whether the exposure may also affect bone metabolism in a male rat model and to estimate the gender-related differences in the bone effect of Cd. Young male Wistar rats received drinking water containing 0, 1, 5, or 50 mg Cd/l for 12 months. The bone effect of Cd was evaluated using bone densitometry and biochemical markers of bone turnover. Renal handling of calcium (Ca) and phosphate, and serum concentrations of vitamin D metabolites, calcitonin, and parathormone were estimated as well. At treatment with 1 mg Cd/l, corresponding to the low environmental exposure in non-Cd-polluted areas, the bone mineral content (BMC) and density (BMD) at the femur and lumbar spine (L1-L5) and the total skeleton BMD did not differ compared to control. However, from the 6th month of the exposure, the Z score BMD indicated osteopenia in some animals and after 12 months the bone resorption very clearly tended to an increase. The rats' exposure corresponding to human moderate (5 mg Cd/l) and especially relatively high (50 mg Cd/l) exposure dose- and duration-dependently disturbed the processes of bone turnover and bone mass accumulation leading to formation of less dense than normal bone tissue. The effects were accompanied by changes in the serum concentration of calciotropic hormones and disorders in Ca and phosphate metabolism. It can be concluded that low environmental exposure to Cd may be only a subtle risk factor for skeletal demineralization in men. The results together with our previous findings based on an analogous model using female rats give clear evidence that males are less vulnerable to the bone effects of Cd compared to females.

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

The study assessed the effect of cadmium (Cd) intoxication on the risk of deformities and fractures of the growing bones of female rats, in order to model human exposure to this metal. For this purpose, bone mineral density and mechanical properties of the proximal and distal ends and diaphysis of the femur were investigated in female Wistar rats exposed to 1, 5 and 50 mg Cd/l in drinking water for 3, 6, 9 and 12 months after the onset of weaning. Daily Cd doses received from drinking water during the treatment period were in the following ranges: 0.059-0.219, 0.236-1.005 and 2.247-9.649 mg/kg body weight at 1, 5 and 50 mg Cd/l, respectively. Biomechanical properties of the femoral proximal and distal ends were evaluated in a compression test, and those of the femoral diaphysis in a cutting test, with loading perpendicular to the longitudinal axis of the bone in all tests. The mineralization and mechanical properties of the bone tissue at various locations on the femur were affected by exposure to Cd in a dose- and duration-dependent manner. Exposure to 1 mg Cd/l (corresponding to low human exposure) during skeletal development weakened the fracture strength of the femoral neck and the trabecular bone at the level of the distal end of the femur and affected the elastic properties of the cortical bone at the femoral diaphysis. At higher levels of Cd exposure, adverse effects were generally observed after a shorter exposure period than for 1 mg Cd/l, and were more advanced. The cadmium-induced weakening of the biomechanical properties of bone at particular sites on the femur correlated with the decreased bone mineralization. The results indicate that even a low exposure to Cd may affect the mineralization and biomechanical properties of growing bone, thus enhancing the risk of fracture.

Effect of chronic exposure to cadmium on the mineral status and mechanical properties of lumbar spine of male rats

The effect of cadmium (Cd) on the risk of vertebral damage was investigated on a male rat model of human exposure. Young Wistar rats were treated with Cd in drinking water at the concentration of 1, 5 or 50 mgCd/l for 12 months. Bone mineral density (BMD) of the lumbar spine (L1-L5), the rate of deformities and fractures, biomechanical properties (compression test) and the chemical composition of the fourth lumbar vertebral body (L4) were estimated. The exposure to 1 mgCd/l (corresponding to low environmental exposure in non-Cd-polluted areas) had no effect on the L4 composition, density and mechanical strength; in one animal only (10%) it was deformed. In the 5 mgCd/l group, the content of minerals (including calcium, zinc and phosphate) in the L4 and the displacement at ultimate decreased, whereas its ultimate strength and the L1-L5 BMD tended to decline. In most of the rats, the L4 was intact and there were no vertebral fractures. At 50 mgCd/l, the BMD of the L1-L5 and the content of minerals in the L4 (including calcium, magnesium, zinc, copper, iron and phosphate) were lower compared to control, and these changes were accompanied by a weakness in the L4 mechanical strength. The L4 was intact only in 30% of these rats; in other animals it was deformed (40%) or fractured (30%). The results allow for the conclusion that moderate environmental exposure to Cd (5 mgCd/l in the model applied) may enhance the risk of vertebral damage in men. These, together with our previous findings on an analogous female rat model, seem to indicate that males may be less vulnerable to the vertebral fractures due to exposure to Cd compared to females.

Mechanical properties of femoral diaphysis and femoral neck of female rats chronically exposed to various levels of cadmium

The effect of chronic exposure to cadmium (Cd) on the mechanical properties of femoral diaphysis and femoral neck was investigated on a rat model of human exposure. Three-week-old female Wistar rats were exposed to Cd in drinking water at concentrations of 1, 5, 50, or 100 mg/L for 12 months. Biomechanical properties of the femoral diaphysis were evaluated in a three-point bending test and those of the femoral neck in a bending test with vertical loading of the head. Bone mineral content (BMC) and bone mineral density (BMD) at the whole femur, and BMD at the diaphysis and proximal femur (head and neck region) of the Cd-treated rats decreased in a dose-dependent manner, except for the diaphyseal BMD at a Cd concentration of 1 mg/L. Exposure to Cd concentrations of 1 and 5 mg/L had only little effect on the diaphyseal mechanical properties (decreased yield load with unchanged bending strength, stiffness, yield stress, ultimate stress, and Young modulus), whereas the bending strength and stiffness of the neck decreased and the yield load clearly tended to decline or declined. The effect of Cd at the two locations was more marked in the 50 and 100 mg/L groups, and changes in the bone geometry were observed in these animals. The results clearly revealed that chronic, even low-level, exposure to Cd results in demineralization and weakening of the femur. The femoral neck seems to be more vulnerable than the diaphysis to failure from Cd. We conclude that environmental exposure to Cd may be an important risk factor for femoral neck fracture.

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

This study was aimed at assessing the effect of cadmium (Cd) intoxication on the risk of deformities and fractures of the growing bone on a female rat model of human exposure to this metal. For this purpose, bone mineral density (BMD) and mechanical properties of the proximal and distal ends and diaphysis of the femur were investigated in female Wistar rats exposed to 1, 5, and 50 mg Cd L(-1) in drinking water for 3, 6, 9, and 12 months since weaning. Daily Cd doses received from the drinking water during the treatment period were in the ranges 0.059-0.219, 0.236-1.005, and 2.247-9.649 mg kg(-1) body weight at 1, 5, and 50 mg Cd L(-1), respectively. Biomechanical properties of the femoral proximal and distal ends were evaluated in a compression test and those of the femoral diaphysis in a cutting test with loading perpendicular to the bone longitudinal axis in all tests. Cd dose- and exposure duration-dependently affected the mineralization and mechanical properties of the bone tissue at various locations of the femur. Exposure to 1 mg Cd L(-1) (corresponding to low human exposure) during skeletal development weakened the fracture strength of the femoral neck and of the trabecular bone at the level of the distal end of the femur and affected the elastic properties of the cortical bone at the femoral diaphysis. At the higher levels of Cd treatment, the adverse action generally occurred after shorter exposure than at 1 mg Cd L(-1) and was more seriously advanced. The Cd-induced weakening in the bone biomechanical properties at particular sites of the femur correlated with the decreased bone mineralization. The results indicate that even low exposure to Cd may affect the mineralization and biomechanical properties of growing bone, thus increasing the risk of fractures.

Infrared imaging of calcified tissue in bone biopsies from adults with osteomalacia

Osteomalacia is a pathological bone condition in which there is deficient primary mineralization of the matrix, leading to an accumulation of osteoid tissue and reduced bone mechanical strength. The hypothesis that there are no qualitative or quantitative differences in osteomalacic bone mineral or matrix compared to disease-free bones was tested by examining unstained sections of polymethyl methacrylate (PMMA) embedded iliac crest biopsies using Fourier transform infrared imaging (FTIRI) at approximately 6-microm spatial resolution. Controls were seven female subjects, aged 36-57, without apparent bone disease. The experimental group consisted of 11 patients aged 22-72, diagnosed with osteomalacia. The spectroscopic parameters analyzed in each data set were previously established as sensitive to bone quality: phosphate/amide I band area ratio (mineral content), 1660/1690 cm(-1) peak ratio (collagen cross-links), and the 1030/1020 cm(-1) peak ratio (mineral crystallinity). The correspondence between spectroscopic mineral content (phosphate/amide I ratio) and ash weight was validated for apatite crystals of different composition and crystallite size. The FTIRI results from the biopsies expressed as color-coded images and pixel population means were compared with the nonparametric Mann-Whitney U test. There were no significant differences in the cortical parameters. Significant difference was found in the mineral content of the trabecular regions with a lower mean value in osteomalacia (P = 0.01) than in controls. Mineral crystallinity tended to be decreased in the trabecular bone (P = 0.09). This study supports the hypothesis that, in osteomalacia, the quality of the organic matrix and of mineral in the center of bone does not change, while less-than-optimal mineralization occurs at the bone surface. This study provides the first spectroscopic evaluation of whole bone mineral and matrix properties in osteomalacia, demonstrating that there are few differences in collagen cross-links between biopsies from patients with osteomalacia and from individuals without histological evidence of bone disease.

Disorders in bone metabolism of female rats chronically exposed to cadmium

The effect of cadmium (Cd) on bone metabolism during skeletal development and maturity was investigated on a rat model of human exposure. Young female Wistar rats were exposed to 1, 5, or 50 mg Cd/l in drinking water for 3, 6, 9, and 12 months. Total bone mineral density (T-BMD), bone mineral content (BMC), density (BMD), and bone area at the femur and lumbar spine (L1-L5) were measured densitometrically. Alkaline phosphatase (ALP) and osteocalcin (OC) as bone formation markers, and carboxy-terminal cross-linking telopeptides of type I collagen (CTX) in bone (trabecular and cortical) or serum as bone resorption markers were measured. Renal calcium (Ca) handling and Cd body burden were evaluated as well. At the stage of intensive skeletal development (the first 6 months of the experiment), at all exposure levels, Cd inhibited the processes of bone formation and as a result disturbed the accumulation of bone mass leading to osteopenia (- 1 > Z score/T score BMD > -2.5) and at 5 and 50 mg Cd/l even to more advanced disorders in the BMD. Continuation of the exposure up to skeletal maturity led to high bone turnover with increased resorption enhancing the prevalence of osteopenia or the BMD values having the Z score/T score < -2.5. The results allow for the conclusion that chronic, even low-level exposure to Cd disturbs bone metabolism during skeletal development and maturity by affecting bone turnover most probably through a direct influence on bone formation and resorption, and indirectly via disorders in Ca metabolism. Our findings confirm the hypothesis that environmental exposure to Cd may be a risk factor for low BMD.

Low-level lifetime exposure to cadmium decreases skeletal mineralization and enhances bone loss in aged rats

The effects of low-level lifetime exposure to cadmium (Cd) on the skeleton mineral status and the risk of bone loss in the elderly were studied in an experimental model of human environmental exposure in non-Cd-polluted areas. Young female Wistar rats were exposed to 1 mg Cd/l in drinking water for 24 months. Bone mineral content (BMC), density (BMD) and area of the lumbar spine (L1-L5) and femur, and total skeleton BMD (T-BMD) were measured densitometrically at the baseline and after 6, 12, 18, and 24 months. Prevalence of osteopenia and osteoporosis was evaluated based on the BMD T score and Z score. Osteocalcin (OC) in the serum and total alkaline phosphatase (total ALP) in the serum, cortical and trabecular bone samples as bone formation markers, and C-terminal cross-linking telopeptide of type I collagen (CTX) in the serum and urine as bone resorption markers were measured. Calcium (Ca) and Cd concentrations in the serum/blood and urine were determined as well. In the Cd-exposed females, the L1-L5 and femur BMC and BMD at all the studied time points were lower compared to control. The exposure to Cd resulted in lower accumulation of peak bone mass, accelerated osteopenia, and enhanced the prevalence of osteoporosis in aged rats. The effect of Cd was more pronounced at the L1-L5 than at the femur. CTX concentration in the urine was decreased after 6 months and next increased compared to control, whereas the urinary loss of Ca was enhanced during the exposure to Cd. After 24 months of the treatment, the serum total ALP activity and the activity of this enzyme in cortical and trabecular bone decreased and serum CTX concentration increased, whereas the concentrations of OC and Ca were unchanged. The study clearly revealed that low-level lifetime exposure to Cd diminishes the accumulation of bone mass during skeletal growth and influences bone metabolism at maturity causing osteopenia, and enhances the age-related bone loss due to high turnover rate leading in consequence to osteoporosis in aged rats. The results together with our previous findings confirm the hypothesis that environmental exposure to Cd may be a risk factor for skeletal diseases.

Low-Level Exposure to Cadmium during the Lifetime Increases the Risk of Osteoporosis and Fractures of the Lumbar Spine in the Elderly: Studies on a Rat Model of Human Environmental Exposure

In this study, based on a rat model of human environmental exposure to cadmium (Cd), it has been examined whether low-level lifetime Cd exposure increases the risk of vertebral osteoporosis and vertebrae fractures in the elderly. For this purpose, the lumbar vertebral bodies (L4 or L3) of control and Cd-exposed (1 mg Cd/l in drinking water for 24 months) female Wistar rats were assigned to densitometric, radiographic, biomechanical (compression test), and biochemical studies, as well as to assess their dimensions and chemical composition. The exposure to Cd affected the mineral status of the L4. The decreased mineral content, density (BMD) and bone mineral area of the vertebral body together with the unchanged ratio of non-organic and organic components indicate osteoporotic nature of the Cd-induced changes. The activity of alkaline phosphatase in the L3 decreased. Cd also influenced the mechanical properties of the L4. The yield load and ultimate load decreased indicating a weakness in the vertebral body compression strength. Stiffness of the L4 decreased and the displacement at ultimate increased suggesting its enhanced susceptibility to deformities. Indeed, in the Cd group vertebral deformities (in 30% of females) or even fractures (in 40% of females), including those with disruption of bone continuity were evident. Z-score values for the L4 BMD revealed vertebral osteopenia in 30% and osteoporosis in 70% of the Cd-exposed females. The results allow for the conclusion that low lifetime exposure to Cd may become an important factor increasing the risk of lumbar spine osteoporosis with vertebral deformities and fractures in the elderly.

Cadmium exposure and distal forearm fractures

The aim of this study was to analyze the relationship between low-level cadmium exposure and distal forearm fractures. Altogether, 1021 men and women exposed to cadmium in Sweden were included. The study indicates that cadmium exposure is associated with increased risk of forearm fractures in people over the age of 50.

INTRODUCTION

Very few studies have been performed on environmental risk factors for fractures. Cadmium is known to cause damage to the kidneys and in high doses to the bone. The aim of this study was to analyze the relationship between low-level cadmium exposure and distal forearm fractures.

MATERIALS AND METHODS

A total of 479 men and 542 women, 16-81 years of age, that were environmentally or occupationally exposed to cadmium were examined in 1997. Cadmium in urine was used to estimate dose, and information about previous fractures and risk factors for fractures was obtained from questionnaires. Fractures were validated using medical records. The association between cadmium dose and risk of forearm fracture was evaluated using Cox proportional hazard regression analysis.

RESULTS AND CONCLUSION

The mean urinary cadmium in the study population was 0.74 nmol cadmium/mmol creatinine (10% and 90% percentiles are 0.19 and 1.42, respectively). For fractures occurring after the age of 50 years (n = 558, 32 forearm fractures), the fracture hazard ratio, adjusted for gender and other relevant co-variates, increased by 18% (95% CI, 1.0-38%) per unit urinary cadmium (nmol cadmium/mmol creatinine). When subjects were grouped in exposure categories, the hazard ratio reached 3.5 (90% CI, 1.1, 11) in the group of subjects with urinary cadmium between 2 and 4 nmol/mmol creatinine and 8.8 (90% CI, 2.6, 30) in the group of subjects with > or = 4 nmol/mmol creatinine. Associations between cadmium and fracture risk were absent before the age of 50. Cadmium exposure is associated with increased risk of forearm fractures in people over 50 years of age.

Metals and women's health

There is a lack of information concerning whether environmental-related health effects are more or less prevalent or manifested differently in women compared to men. Previously, most research in the area of toxicology and environmental and occupational health involved male subjects. The present work aims at reviewing exposure and health effects of cadmium, nickel, lead, mercury, and arsenic manifested differently in women than in men. The gender difference in exposure to nickel results in a much higher prevalence of nickel allergy and hand eczema in women than in men. The internal cadmium dose is generally higher in women than in men, due to a higher gastro-intestinal absorption at low iron stores. This was probably one major reason why Itai-itai disease was mainly a woman's disease. Yet, data are sparse regarding the risk for women relative to men to develop cadmium-induced kidney damage in populations exposed to low levels of cadmium. Lead is accumulated mainly in bone and increased endogenous lead exposure has been demonstrated in women during periods of increased bone turnover, e.g., menopause. Both lead and mercury exposure in pregnant women has to be kept low in order to prevent neurodevelopment effects in the developing fetus and child. Limited data indicate that women are more affected than men following exposure to methylmercury at adult age, while males seem to be more sensitive to exposure during early development. Regarding arsenic, some data indicate gender differences in the biotransformation by methylation, possibly also in susceptibility to certain arsenic-related cancers. Obviously, gender-related differences in exposure and health effects caused by metals are highly neglected research areas, which need considerable focus in the future.