REDUCED CONCENTRATION OF COLLAGEN REDUCIBLE CROSS-LINKS IN HUMAN TRABECULAR BONE WITH RESPECT TO AGE AND OSTEOPOROSIS

The decrease of bone strength in relation to age and osteoporosis is m ore pronounced than would be expected from the relative deficit in the amount of bone, Besides bone mass, the mechanical properties of cance llous bone also depend on the microarchitecture and possibly on the mo lecular structure of inorganic and organic components, The present stu dy examines the bone collagen, especially the collagen cross links, in relation to age and osteoporosis, Samples of vertebral trabecular bon e were taken at autopsy from 43 normal individuals, aged 15-90 years, Eleven of these served as sex- and age-matched controls for similar sa mples from 11 osteoporotic individuals, 70-90 years, The volume of eac h trabecular bone sample was estimated. After removal of the marrow, t he trabeculae were ground to powder and decalcified, The extractabilit y of the bone collagen was studied by repeated extractions with acetic acid and pepsin, The divalent reducible collagen cross-links, dehydro -dihydroxylysinonorleucine (DHLNL) and dehydro-hydroxylysinonorleucine (HLNL), were determined by reducing the bone collagen with tritiated potassium borohydride followed by ion-exchange chromatography, The mat ure trivalent pyridinium cross links were determined by reverse-phase HPLC with fluorescence detection, The extractability of collagen prepa red from the vertebral trabecular bone of control individuals was incr eased with age, Bone collagen of osteoporotic individuals showed incre ased extractability and a substantial decrease in the concentration of the divalent reducible collagen cross links (DHLNL reduced by 30% and HLNL by 24%) compared with the sex- and age-matched controls, No alte rations were observed in the concentration of the pyridinolines. The d ivalent reducible cross-links are the most frequent known cross links in bone (2-4 times the concentration of the pyridinium cross links), T hese changes would therefore be expected to reduce the strength of the bone trabeculae and could explain why the osteoporotic individuals ha d bone fractures even though the collagen density (mg/cm(3)) did not d iffer from that of the sex- and age-matched controls, The microarchite cture of the cancellous bone was not assessed, The osteoporotic and co ntrol individuals seemed to have the same amount of trabecular bone, b ut the quality of the osteoporotic bone collagen was reduced. (C) 1996 by Elsevier Science Inc.