Structural and metabolic studies on normal and pathological bone

Abstract

Bone is refractory to most conventional biochemical Procedures. However because it is now possible to cut sections (e. g. lopm) of fresh, undemineralized adult bone, this tissue can be analyzed by suitably modified methods of quantitative cytochemistry. A new substrate for assaying hydroxyacyl dehydrogenase activity demonstrated that bone cells may use fatty acids as a major source of energy: detailed analysis of the activities of key enzymes indicated that the paradox of ‘aerobic glycolysis’ of bone could be explained by fatty acid oxidation satisfying the requirements of the Krebs' cycle and directing the conversion of pyruvate to lactate The influence of glucose 6-phosphate dehydrogenase (G6PD) activity in aerobic glycolysis has been considered. The inverse relationships between this activity and that of Na-K-ATPase led to the development of a new method for the latter, based on a new concept in cytochemistry ('hidden-capture' procedure). A major feature of fracture-healing is increased periosteal G6PD activity. The association with the vitamin K cycle has been investigated by feeding rats with dicoumarol which not only inhibited bone-formation but also G6PD activity. The stimulation of this activity in fracture-healing has been linked with ornithine decarboxylase (ODC) activity, for which a new method has been developed. Rats deficient in pyridoxal phosphate (cofactor for ODC) had decreased G6PD responses and also appeared to become osteoporotic. Studies on osteoporotic fractures in the human showed the presence of relatively large apatite crystals close to the fracture-site, and disorganized glycosaminoglycans (demonstrated by the new method of ‘induced birefringence’).