The Effects of Low Molecular Weight and Standard Heparin on Calcium

Osteoporosis is a well-recognized complication of long-term heparin use. However, the mechanisms by which heparin can influence bone metabolism are unclear. We report here that unfractionated heparin stimulates the process of bone resorption and that the low molecular weight heparins (LMWHs), enoxaparin, fragmin, logiparin, and ardeparin produce significantly less calcium loss than unfractionated heparin. To assess calcium loss from bone, we quantified the release of “Ca into the culture medium of fetal rat c lvaria. ‘%a release was increased in a dose-dependent manner by the addition of either unfractionated heparin or the LMWHs; but more than 50-fold higher LMWH concentrations were required to obtain an equivalent effect to unfractionated heparin. Thus, at concentrations 2 2 pg/mL (0.35 anti-Xa unitslml), unfractionated heparin stimulated =Ca release 1.53 2 0.06 fold. ‘%a release was increased to a similar extent by the addition of either I O ” mol/L parathyroid hormone (PTH) or lo-’ mol/L 1.25 dihydroxyvitamin D, (1,25 Vit