Bone Quality PART 3 Collagen/Mineral Matrix Conclusions Supplemental Slides

Bone Quality Adapted from NIH Consensus Development Panel on Osteoporosis. JAMA 285:785-95; 2001 Architecture Turnover Rate Damage Accumulation Degree of Mineralization Properties of the Collagen/Mineral Matrix

Bone Cells and Matrix Properties of collagen and mineral matrix Suppressed turnover and accumulation of microdamage Altered mechanosensation State of mineralization

Properties of the Collagen/Mineral Matrix -Antiresorptive Drugs Fourier Transform Infrared Microscopic Imaging (FTIRI) of Iliac Crest Bone Sections TR2 COLL X X Axis Title Y Axis Title IR-spectrometer Bone section

FTIR Imaging – Mineral Crystallinity E. Paschalis et al (in press). Baseline Pixel Population Distribution Mineral Crystallinity Pixel Population Distribution 2 Year Estrogen Therapy Mineral Crystallinity

FTIR Imaging – Mineral:Matrix Ratio E. Paschalis et al (in press). Baseline Mineral Matrix Pixel Population Distribution 2 Year Estrogen Therapy Pixel Population Distribution Mineral Matrix

FTIR Imaging – Collagen Cross-Link Ratio E. Paschalis et al (in press) Y Axis Title X Axis Title collxtr TR2 COLL X X Axis Title Y Axis Title Pixel Population Distribution Pyr/DHLNL 2 Year Estrogen Therapy

Conclusion Slides

Bone quality is an integral component of bone strength Maintaining or restoring bone architecture is required for optimal bone quality An imbalance in bone turnover rate affects the degree of mineralization of bone Optimal collagen/mineral matrix properties contribute to bone quality Bone Quality

Possible Contributing Factors to the Fracture Efficacy of Antiresorptives Increased bone mineral density Decreased bone turnover Improved bone quality Decrease remodeling sites Maintain trabecular thickness and connectivity Decrease number of trabecular perforations Decrease microfractures Improve matrix properties

Biochemical markers and bone turnover significantly reduced to premenopausal range Normal bone turnover allows adequate repair of microdamage No adverse effect on bone architecture (iliac crest histomorphometry) Bone Quality -Raloxifene

Weinstein RS, et al. J Bone Miner Res. 14:S279; 1999 Prestwood KM, et al. J Clin Endocrinol Metab. 85: ; 2000 Ott SM, et al. J Bone Miner Res. 17: ; 2002 Bone Quality -Raloxifene Histomorphometry No woven bone No marrow fibrosis No mineralization defect No cellular toxicity (light microscopy) Normal histologic appearance

Bone Quality -Raloxifene No adverse effects on bone histology Changes in BMD explain only a small proportion of vertebral fracture risk reduction Reduces bone turnover to the normal premenopausal range allowing Adequate repair of microdamage A moderate increase in mineralization and preservation of heterogeneous mineral distribution Long-term efficacy with sustained fracture reduction in the fourth year of treatment

Architecture Increase trabecular thickness and connectivity Increases cortical thickness and improves cortical geometry Turnover Increases formation on quiescent (neutral) surface Increase in formation is greater than resorption (positive bone balance) Damage Accumulation Forms new bone Increased bone turnover reduces damage accumulation Bone Quality Conclusions Teriparatide

Relationship Between Excessive Suppression Of Bone Turnover and Damage Accumulation Excessive suppression of bone turnover Long-term fracture efficacy and safety? Prolonged mineralization Insufficient repair of microdamage Damage accumulation Increase in bone fragility

The Optimal Effect of an Antiresorptive Agent on Bone Quality Adequate suppression of bone turnover Sufficient mineralization Physiological repair of microdamage Preservation of architecture Long-term fracture efficacy and safety

Osteoporosis Severe Osteoporosis Normal Courtesy Dr. A. Boyde

What Is the Optimal Reduction in Bone Turnover for an Antiresorptive Drug? Adapted from Weinstein RS, J Bone Miner Res 2000; Physiological Range Bone Strength Bone Turnover Excessive turnover Increase in stress risers (weak zones) Increase in perforations Loss of connectivity Insufficient turnover Accumulation of microdamage Increased brittleness due to excessive mineralization

Supplemental Slides

Effect of Size on Areal BMD BMC 111 AREABMD “TRUE” VALUE = 1 g/cm 3 Adapted from Carter DR, et al. J Bone Miner Res 1992

The Effect of Antiresorptive Therapy on Fracture Healing Study Protocol Cao Y et al. J Bone Miner Res 17: ; 2002 Female OVX rats (n=140) Five study groups Sham control OVX placebo control OVX + estrogen OVX + raloxifene OVX + alendronate Objective: To evaluate the effect of antiresorptives on fracture healing.

The Effect of Antiresorptive Therapy on Fracture Healing External Callus Formation Reproduced with permission from Cao Y et al. J Bone Miner Res 17: , Weeks Callus formation Fracture visible 16 Weeks OVX Fracture line dissapeared ALN fracture line still visible Callus width largest in ALN group Fracture repair was delayed with ALN treatment

The Effect of Antiresorptive Therapy on Fracture Healing Cross-sectional Microradiographs at the Fracture Plane Reproduced with permission from Cao Y et al. J Bone Miner Res 17: ; weeks 16 weeks ShamOVXEE2RLXALN

The Effect of Antiresorptive Therapy on Fracture Healing Photomicrographs of the Callus Reproduced with permission from Cao Y et al. J Bone Miner Res 17: , 2002 ShamOVXEE2RLXALN