Effect of essential trace metal on bone metabolism in the femoral-metaphyseal tissues of rats with skeletal unloading: Comparison with zinc-chelating dipeptide

The effect of essential trace metals on bone metabolism was investigated in the femoral-metaphyseal tissues obtained from skeletal-unloaded rats. Skeletal unloading was designed by using the model of hindlimb suspension in rats; the animals were fed for 4 days with the unloading. Femoral-metaphyseal tissues were cultured for 24 hours in a medium containing either vehicle (control), nickel, manganese, cobalt, copper, zinc, or zinc-chelating dipeptide (ß-alanyl-L-histidinato zinc; AHZ) in the concentration range of 10^-6 to 1(T^-4 M. Bone biochemical components (alkaline phosphatase activity, glucose consumption, and DNA content) were significantly decreased by skeletal unloading. The presence of zinc sulfate or AHZ (10~5 and 10^-4 M) caused a significant increase of alkaline phosphatase activity in the bone tissues from unloaded rats. This effect was not seen by nickel, manganese, cobalt and copper (10^-6 to 10⁴ M). The culture medium glucose was clearly consumed by the bone tissues. This consumption was inhibited by nickel, manganese, or copper (10^-5 and 10^-4 M), while cobalt, zinc, and AHZ had no effect. DNA content in the bone tissues from unloaded rats was significantly increased by all metal compounds (10^-5 M). The effect of AHZ on bone components was greater than zinc sulfate. The AHZ (10^-5 M)-increased alkaline phosphatase activity in the bone tissues from unloaded rats was clearly blocked by the presence of cycloheximide (10^-6 M), staurosporine (10^-T7 M), dibucaine (10^-4 M), or okadaic acid (10⁷ M). The present study demonstrates that, of various essential trace metals, zinc compounds have an unique anabolic effect on bone metabolism in the femoral-metaphyseal tissues of rats with skeletal unloading. Zinc-chelating dipeptide may stimulate bone protein synthesis through the mechanism that is involved in protein kinases.