Identification of Osteoporosis-Associated Protein Biomarkers from Ovariectomized Rat Urine

Objective: Osteoporotic fracture is one of the most common health risks and aggravates the quality of life among postmenopausal women worldwide. In this study, osteoporosis-associated protein biomarkers were identified from urine of osteoporotic female Sprague-Dawley rats developed by ovariectomy. Method: Four months after the operation, the bone mineral density of the femur of ovariectomized rats was significantly lowered in comparison with that of the sham operated rats. The protein profiles of the urine samples collected from the sham, ovariectomized (OVX) and 2 month-old non-operated (Young) rats were compared by 2-D gel and MS spectrometry. Results: Proteins consistently expressed between Young and sham but differentially expressed in OVX rats were selected and identified. One down-regulated 21 kDa protein, superoxide dismutase (SOD), and 1 up-regulated 53-54 kDa protein, alph-1-antitrypsin (A1AT), were selected from urine of the ovariectomized rats by 2-D gel analysis. Further, a total of 30 with 19 up-regulated and 11- down-regulated proteins were selected by LC-MS analysis with more than 2-fold differences in spectral counts. The fact that SOD and A1AT are also listed in the 30 differential proteins suggests that our biomarker isolation procedure suitably represents osteoporosis-associated proteins in urine. Conclusion: Supporting the facts, the differential expressions of SOD and A1AT in urine could be validated by Western blotting. These urinary osteoporosis-associated proteins have high potentials to become candidates for non-invasive diagnosis of osteoporosis from urine. Keywords: 2-D gel, biomarker, mass spectrometry, osteoporosis, ovariectomized rat urine, proteomics.