Identification of novel biomarkers in postmenopausal osteoporosis

Osteoporosis is a degenerative disorder characterised by a reduction in bone strength manifesting itself in fragility fractures. Current diagnosis relies on the measurement o f bone mineral density (BMD) generated by dual X-ray absorptiometry (DXA) scanners. Serological markers of disease or biomarkers, present themselves as a useful and potentially inexpensive methodology o f assessing disease status. Proteomic technologies utilised on biofluids have proven themselves as capable o f identifying candidate biomarkers of disease. The aim of the work in this thesis was to utilise proteomic platforms 2D DIGE and antibody array technology to identify candidate markers of osteopenia and osteoporosis.

2D DIGE was utilised to analyse serum from 36 postmenopausal women with a decline in BMD. Prior to analysis, a serum depletion strategy was developed utilising the Seppro® IgY14 Spin Column with an altered protocol resulting serum being produced depleted o f 14 abundant proteins. 16 unique protein identifications resulted from the 2D DIGE study. Levels o f both glial fibrillary acidic protein (GFAP) and vitronectin, were elevated in postmenopausal women with osteopenia and osteoporosis compared with normal by ELISA (p<0.05). Analysis of the area under the curve (AUC) generated b y receiver operating characteristic (ROC) curves, ascertained that the combination o f measurement o f GFAP and vitronectin produced the optimum specific ity and sensitivity levels (0.825).

Antibody array analys is of whole serum taken from 101 postmenopausal women identified 156 significantly differentially expressed proteins (p<0.0001). Levels of Dickkop f-1 (Dkkl) were sign ificantly inversely correlated with BM D parameters (p<0.05) and Wnt inhibitory factor 1 (WIFI) was elevated in the osteoporosis group compared with both normal and osteopenia (p<0.05). Dkk1 and WIF1 combined produced the best AUC values for identifying individua ls with osteopenia from those with osteoporosis (0.736).

Measuring circulating levels o f Dkk1, WIF1, GFAP and vitronectin both alone and in combination, is a promising methodology for assessing BMD .