NEAR INFRARED SPECTROSCOPIC ASSESSMENT OF BONE WATER BINDING TO COLLAGEN AND MINERAL

Abstract

Cortical bone fragility increases with age, therapeutic drug use and disease states. Clinically, bone fragility is evaluated by assessment of bone mineral density (BMD); however, studies have shown that other factors such as bone architecture, cell turnover and tissue composition influence bone quality. There is growing evidence that age related changes in bone water associated with collagen and/or mineral have a direct impact on bone mechanical competence and structural integrity. Understanding these compositional changes will aid in improved diagnose and prediction of fractures. Magnetic resonance imaging (MRI) is used to evaluate bone water, but this modality is limited in spatial resolution and is still being developed. Although still in the experimental stage, vibrational spectroscopy in the near infrared region (NIR) also known as near infrared spectroscopy (NIRS) is a nondestructive modality that can spatially evaluate alterations of bone composition. NIRS is a unique nondestructive technique that produces a signature spectrum by penetrating high frequency (4000-12,000 cm-1) non-ionizing radiation into material. NIRS permits a depth of penetration from millimeters to centimeters, dependent on frequency (wavelength). NIRS is very sensitive to water and can be used to provide molecular information of water related to collagen and mineral in bone samples. To date, definitive information on which NIR absorbances are linked to collagen or mineral bound water have not been identified. The overarching hypothesis is that water associated with collagen and/or mineral can be identified using NIRS and will serve as a biomarker for bone fragility in future preclinical studies. This will be achieved with the following three aims: First, to develop a method to image human cortical bone tissue using NIRS; second, to identify NIRS absorbances of water bound with mineral and collagen in bone; and finally, the third aim, to correlate the NIRS-derived water content in human cortical bone to structural properties determined by micro-computed tomography (micro-CT). Together these studies will establish the NIRS technique as a powerful tool to screen and monitor aging and diseased tissues in preclinical studies.