Studies on Amino Acid Metabolism in Osteoporosis

I. Clinical Study: Osteoporosis and Amino Acid Metabolism

Abstract

In order to examine aminoacid metabolism in osteoporosis, oral amino acid loading tests were performed in 7 normal old men, 11 severely osteoporotic and 5 mildly osteoporotic patients. All subjects were free of other important diseases including liver or renal disorders. When the ratio of vertebral density to disc density in the lateral tomogram of the lumbar spine was less than 1.0, the patients were considered osteoporotic. Presence of compression fracture indicated “severe” osteoporosis, while the absence spoke for “mild” osteoporosis.
Fasted subjects were orally loaded with amino acid mixtures in an amount corresponding to the body weight. Blood samples were drawn before and 1, 2, 3 and 4 hours after the loading. One ml of serum specimen was subjected to gaschromatographic analysis of amino acids.
Although the fasting levels of serum valine were not different between the normal and osteoporotic subjects (63±7.7γ/ml and 76±8.0), the one-hour (151±9.0 and 215±21.3) and four-hour levels (139±8.7 and 178±16.3) were significantly higher in the severely osteoporotic subjects. The peak value of serum valine was also shown to be significantly higher in the severely osteoporotic group (normals 192±9.5, osteoporotics, 263±24.6). Mild osteoporotics gave intermediate values. As for leucine and phenylalanine levels, no difference was noted between the groups.
Since valine is most rapidly absorbed from the gastrointestinal tract and most slowly metabolized in the liver among various amino acids, the behavior of valine might serve as a sensitive detector of abnormal amino acid metabolism, especially in demonstrating the difference between normals and osteoporotics.