Effect of hormone replacement therapy on bone quality in early postmenopausal women

HRT is an effective prophylaxis against postmenopausal bone loss. Infrared imaging of paired iliac crest biopsies obtained at baseline and after 2 years of HRT therapy demonstrate an effect on the mineral crystallinity and collagen cross-links that may affect bone quality. Several studies have demonstrated that hormonal replacement therapy (HRT) is an effective prophylaxis against postmenopausal bone loss, although the underlying mechanisms are still debated. Infrared spectroscopy has been used previously for analyzing bone mineral crystallinity and three-dimensional structures of collagen and other proteins. In the present study, the technique of Fourier transform infrared microscopic imaging (FTIRI) was used to investigate the effect of estrogen on bone quality (arbitrarily defined as mineral/matrix ratio, mineral crystallinity/maturity, and relative ratio of collagen cross-links [pyridinoline/ deH-DHLNL]) at the ultrastructural level, in mineralized, thin tissue sections from double (before and after administration of HRT regimen; cyclic estrogen and progestogen [norethisterone acetate]) iliac crest biopsy specimens from 10 healthy, early postmenopausal women who were not on any medication with known influence on calcium metabolism. FTIRI allows the analysis of undemineralized thin tissue sections (each image analyzes a 400 x 400 microm2 area with a spatial resolution of approximately 6.3 mm). For each bone quality variable considered, the after-treatment data exhibited an increase in the mean value, signifying definite changes in bone properties at the molecular level after HRT treatment. Furthermore, these findings are consistent with suppressed osteoclastic activity.