Introduction: Ageing may cause an increase in parathormone (PTH) secretion and, subsequently, increased bone resorption and osteoporosis. In recent years two subfractions of PTH have been discovered: cyclase-activating (1-84, CAP) and cyclase-inhibiting (7-84, CIP) PTH. It is not known however, whether these may play a role in the pathogenesis of bone loss in elderly subjects.
Material and methods: Sixty elderly women were examined, of whom 29 had a T-score of the ultradistal radius < -2.5 (median age 75 [70-80] years, BMI 25 [20.6-33.8] kg/m(2), creatinine clearance 59.9 [39.2-94.9] ml/min/1.73m(2), serum Ca 2.4 [2.2-2.6] mmol/l), while 31 had a T-score > -2.5 (median age 73 [70-86] years, BMI 26.2 [18.8-32.5] kg/m(2), creatinine clearance 54.8 [23-119.2] ml/min/1.73m(2), serum Ca 2.4 [2.2-2.6] mmol/l). Median bone mineral density (BMD) (DXA, Lunar) of the ultradistal radius was 0.263 (0.195-0.449) g/cm(2) and 0.326 (0.236-0.448) g/cm(2) (p < 0.0001), with a median T-score of -3.48 and -1.4, respectively. Each patient with a serum concentration of 1-84 and 7-84 PTH was assessed.
Results: Patients with low BMD did not differ from those with higher BMD with regard to serum iPTH (16 [6-51] vs. 11.5 [7-35] pg/ml, p = 0.066) and CIP (6 [1-14] vs. 4.5 [2-13] pg/ml) concentrations. However, serum CAP concentrations (10.5 [4-41] vs. 6 [4-22] pg/ml, p < 0.05) and CAP/CIP ratios (2.0 [0.71-11] vs. 1.25 [0.5-4.2], p < 0.05) were significantly higher in the low BMD group.
Conclusion: In elderly women increased serum CAP concentrations and CAP/CIP ratios are associated with low BMD of the trabecular bone.