Liquid scintillation based quantitative measurement of dual radioisotopes ( ³H and ⁴⁵Ca) in biological samples for bone remodeling studies

Acute and prolonged bone complications associated with radiation and chemotherapy in cancer survivors underscore the importance of establishing a laboratory-based complementary dual-isotope tool to evaluate short- as well as long-term bone remodeling in an in vivo model. To address this need, a liquid scintillation dual-label method was investigated using different scintillation cocktails for quantitative measurement of ³H-tetracycline ( ³H-TC) and ⁴⁵Ca as markers of bone turnover in mice. Individual samples were prepared over a wide range of known ⁴⁵Ca/ ³H activity ratios. Results showed that ⁴⁵Ca/ ³H activity ratios determined experimentally by the dual-label method were comparable to the known activity ratios (percentage difference ~2%), but large variations were found in samples with ⁴⁵Ca/ ³H activity ratios in range of 2-10 (percentage difference ~20-30%). Urine and fecal samples from mice administered with both ³H-TC and ⁴⁵Ca were analyzed with the dual-label method. Positive correlations between ³H and ⁴⁵Ca in urine (R=0.93) and feces (R=0.83) indicate that ³H-TC and ⁴⁵Ca can be interchangeably used to monitor longitudinal in vivo skeletal remodeling.