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.