Mineral status and mechanical properties of lumbar spine of female rats chronically exposed to various levels of cadmium

The effects of chronic exposure to cadmium (Cd) on the mineral status, mechanical properties and incidence of deformities and fractures of the lumbar spine (L1–L5) were studied in a rat model of human exposure. Young female Wistar rats were exposed to 1, 5, 50 or 100 mg Cd/l for 12 months. Cd, dose and time dependently, disturbed the mineral status of the lumbar vertebrae as reflected in decreased bone mineral content (BMC) and density (BMD) at the L1–L5 (DEXA technique) and ash weight (AW) of the fourth lumbar vertebral body (L4). However, the changes were too small to be evident radiographically. Cd had no effect on the ratio of nonorganic to organic component content, except for its decrease at the 100 mg Cd/l. Weakness in the mechanical properties (compression test; Instron machine) of the L4 was noted. At the 1 mg Cd/l, a decrease was observed in the deformation at the yield point, with a simultaneous increase in the L4 stiffness, but not in strength (defined by load at yield or ultimate load). In the 5 mg Cd/l group, similar changes took place and a decrease in the ultimate load was evident as well. At the 50 and 100 mg Cd/l, Cd more seriously affected the L4 mechanical properties. At all levels of Cd exposure, the L4 deformities and/or fractures took place. Intact L4 was noted only in the 1 and 5 mg Cd/l groups. The study clearly revealed that chronic exposure to Cd disturbs the L1–L5 mineral status resulting in weakness in its mechanical properties and in turn in vertebral body (cancellous bone) deformities and fractures. The results allow us to conclude that the critical Cd concentration for these effects is very low [about 0.06–0.09 μg/g dry defatted weight (DW)] and seem to indicate an osteoporotic character of changes. A very important finding of the study is that Cd affects cancellous bone even at low-level intoxication corresponding to the general population exposure. Thus, we hypothesize that environmental exposure to Cd may be a risk factor for the lumbar spine demineralization and increased incidence of vertebral deformities and fractures.