Dose-Dependent Influence of Dietary Cu-Glycine Complex on Bone and Hyaline Cartilage Development in Adolescent Rats

Administration of the amino acid copper (Cu) complex ensures higher Cu bioavailability through enhanced absorption from intestine and decreases the dietary Cu level, compared to the recommended Cu dose. The objective of this study was to investigate the effect of Cu-low diet on the bone development in adolescent rats. Male rats at the age of 6 weeks were used in the 12-week experiment. The control diet provided the required Cu level from sulfate (S-Cu) and other diets were supplemented with Cu as a glycine complex (Cu-Gly) at 25%, 50%, 75%, and 100% of daily requirement. After the 12-week treatment, rats from the Cu-Gly100 group were heavier, compared to the other groups. The copper and calcium plasma and bone concentrations of the rats in the groups treated with the organic form of Cu (irrespective of its dose) was similar to the control values noted in the rats administered with S-Cu. A decrease in the femur weight and length was observed in the Cu-Gly75 and Cu-Gly50 groups. Cu-Gly increased the cross section area, mean relative wall thickness, and cortical index only in the Cu-Gly75 group. A decrease in the ultimate strength, elastic stress, and ultimate stress was noted in the Cu-Gly100 and Cu-Gly75 groups. In the Cu-Gly50 group, a decrease in the ultimate stress and an increase in the maximal elastic strength and bending moment were noted. Adolescent rats treated with Cu-Gly at a Cu-deficient level exhibited a dose-dependent strongly osteoporotic cancellous bone. Lower proteoglycan content was found in groups fed the Cu-low diet. In the control rats supplemented with S-Cu, there was no evident gradient in safranin O staining. It is difficult to indicate which dose of the Cu-Gly complex among the investigated Cu-poor diet exerted a positive effect on bone metabolism. It appears that the use of this Cu-Gly complex at a significantly reduced dose than S-Cu at the recommended dose did not inhibit the development of bone and hyaline cartilage in adolescent rats.