The effect of lead on bone mineral properties from female adult C57/BL6 mice

Abstract

Lead toxicity is a significant problem in the U.S. with elevated blood lead levels being highest among very young children and older adults >50 years old. Bone is the major reservoir of body lead, accounting for 75% in children and 90% in adults. Very little is known about the effect of lead on bone mineral properties in adults. We investigated the effect of lead on the femora from adult, 6 month old female C57/BL6 mice who were administered lead in the drinking water (250 ppm, blood lead 33 μg/dL) for 4 months. Bone mineral properties were examined using Fourier Transform Infrared Microscopy (FTIRM), quantitative microcomputed tomography (microCT) and whole bone mechanical testing. Lead significantly decreased the bone mineral density in the cortical and proximal cancellous bone and increased the marrow area in the cortical bone with microCT. Whole bone three-point bending showed a trend of decreased maximum and failure moments in the lead treated bones compared to controls. Lead significantly decreased the mineral/matrix ratio, collagen maturity and crystallinity in the trabecular bone as measured by FTIRM. In the cortical bone lead significantly decreased collagen maturity and bone crystal size by FTIRM. In contrast to cell culture studies, lead significantly increased serum osteocalcin levels. Lead also significantly increased the bone formation and resorption markers suggesting increased bone turnover. These data show that lead increases bone turnover resulting in weaker cortical bone in adult female mice and suggest that lead may exacerbate bone loss and osteoporosis in the elderly.

Figure 1

Representative three dimensional μCT images of control and lead treated cortical diaphysis (A) and control and lead treated proximal trabecular bone (B). Lead exposed cortical and trabecular bone showed a reduced bone mineral density (A,B). Lead was also shown to increase the bone marrow area in cortical bone (A).

Figure 2

Typical FTIRIs of various spectral parameters in control and leaded treated cortices. Representative images of (A) mineral to matrix ratio, (B) collagen maturity (peak height ratio 1660/1690) and (C) crystallinity (peak height ratio 1030/1020).

Figure 3

Regional graphs of (A) Mineral to matrix ratio, (N = 8 control and 8 lead treated). (B) Carbonate to mineral ratio, (N = 8 control and 8 lead treated). (C) Collagen maturity (1660/1690 intensity ratio) (N = 9 control and 8 lead treated) and (D) Crystallinity (1030/1020 intensity ratio) for the periosteum, central cortex and endosteal regions of cortical bone (N = 8 control and 8 lead treated) in control and lead exposed cortical bone samples. Significance is indicated by letter ((a) p < 0.02, (b) p < 0.001, (e) p < 0.01, (f) p < 0.05) as compared to the respective controls. Values are reported as mean ± SD.

Figure 4

Plots of (A) Mineral to matrix ratio (N = 8 control and 8 lead treated), (B) Carbonate to mineral ratio (N = 8 control and 7 lead treated), (C) Collagen maturity (1660/1690 intensity ratio) (N = 8 control and 7 lead treated) and (D) Crystallinity (1030/1020 intensity ratio) (N = 8 control and 7 lead treated) for control and lead exposed cancellous bone FTIRI images. Significance is indicated by letter ((b) p < 0.001, (e) p < 0.01, (f) p < 0.05) as compared to the respective controls. Values are reported as mean ± SD.

Figure 5

Plots of osteocalcin (N = 10 control and 10 lead exposed), P1NP (N = 10 control and 10 lead exposed) and CTX (N = 9 control and 7 lead exposed) concentrations in serum from control and lead exposed samples.