Bone Abstracts

Introduction: For the very first time were assessed in vivo the metabolic and lipid profiles of osteocytes. During menopause period the appearance of an osteoporotic condition can be associated with an overall metabolic decline in bone cells, as well an increase of reactive oxygen species (ROS), and we hypothesized that it is mainly attributed to osteocytes metabolic and lipid changes, which could be apparently attenuated after raising blood estradiol (E2) levels. To test this we considered control and ovariectomized (OVX) 12 week-old female rats in order to compare bone embedded osteocytes metabolic/lipid profiles, in presence or absence of high levels of E2.

Methods: Animal groups (used accordingly with FELASA procedures) - i) controls, SHAM; ii) ovariectomized animals, OVX; and iii) OVX+E2 (single bolus injection 30 mg/kg, 24 h prior sacrifice). Animals were sacrificed 4 weeks after ovariectomy. Left and right femurs and tibias were surgically removed and freeze-clamped or preserved for DXA analysis. All bone marrow and blood were discarded, just to leave mineral embedded cells. Methanol/water extracted metabolites from those cells were analyzed by high resolution 600 MHz ¹H nuclear magnetic resonance (NMR) spectroscopy. Total lipids, extracted by Bligh and Dyer method, were quantified and analyzed by an HPLC system coupled to an electrospray linear ion trap mass spectrometer (HPLC–MS), and bone mineral content was assessed by flame atomic absorption spectrophotometry.

Results: Ovariectomy induced disproportionate increase in choline-plasmalogens content (comparatively with SHAM and OVX+E2 groups), mainly PC (O20:0/22:6), and diacyl phosphatidylcholines (PC(22:0/22:1), PC(22:0/22:0)). Also, in OVX were observed an increase of the relative proportion of long chain fatty acids, attenuated by 24 h-treatment with E2. In terms of metabolites profile, OVX presented a slight decrease of lactate/alanine ratio, but with E2, osteocytes were forced to produce high levels of lactate, increasing this ratio.

Conclusions: Here is expressively evident a change in the process of lipid biosynthesis as a result of ovaries removal, and E2 partially compensated the replacement of the control levels of long chain fatty acids. High levels of PC-Plasmalogens presented in OVX could be related to a signalling/protective action against the damaging effects of ROS triggered by the E2 decline. 24 h-E2 administration in OVX induced osteocytes to probably enhance glycolysis in an attempt to compensate for the metabolic deficit associated with the ovaries removal, considering the hypothesis that osteocytes mitochondria may present an impaired respiratory chain.