Characterization of Fatty Acid Composition in Bone Marrow Fluid From Postmenopausal Women: Modification After Hip Fracture

Abstract

Bone marrow adipose tissue (BMAT) is associated with low bone mass, although the functional consequences for skeletal maintenance of increased BMAT are currently unclear. BMAT might have a role in systemic energy metabolism, and could be an energy source as well as an endocrine organ for neighboring bone cells, releasing cytokines, adipokines and free fatty acids into the bone marrow microenvironment. The aim of the present report was to compare the fatty acid composition in the bone marrow supernatant fluid (BMSF) and blood plasma of postmenopausal women women (65 to 80 years old). BMSF was obtained after spinning the aspirated bone marrow samples; donors were classified as control, osteopenic or osteoporotic after dual-energy X-ray absorptiometry. Total lipids from human bone marrow fluid and plasma were extracted, converted to the corresponding methyl esters, and finally analyzed by a gas chromatographer coupled with a mass spectrometer. Results showed that fatty acid composition in BMSF was dynamic and distinct from blood plasma, implying significance in the locally produced lipids. The fatty acid composition in the BMSF was enriched in saturated fatty acid and decreased in unsaturated fatty acids as compared to blood plasma, but this relationship switched in women who suffered a hip fracture. On the other hand, there was no relationship between BMSF and bone mineral density. In conclusion, lipid composition of BMSF is distinct from the circulatory compartment, most likely reflecting the energy needs of the marrow compartment.

Unsaturation level decreased in bone marrow fat of postmenopausal women with low bone density using high resolution magic angle spinning (HRMAS) 1H NMR spectroscopy

“…Our result showing the association between NMR measured unsaturation level with BMD was in contrast to two previous studies that found no significant difference in marrow fat composition in subjects with different BMD using gas chromatographers (16, 17). This difference in experimental findings may result from differences in the quantification methods, different sensitivity and reproducibility of the techniques, differences in specimen location and preparation, and differences in study cohort.…”

“…The unsaturation level quantified using HRMAS 1 H-NMR showed a large range from 15.3% to 51.8%. This unsaturation level was in the range, but with lower average values as compared to previous studies that quantified marrow fat composition using gas chromatography (GC) (16, 17). This under estimate of unsaturation level of NMR methods as compared to GC was consistent with the report from Yeung et al (24).…”

“…Specifically with specimen collection, marrow supernatant fluids were examined in this study, which is the same as the study by Miranda et al (17), but different from the marrow samples that contain adipocytes as used in the study by Griffth et al (16). The lipid composition in the marrow fluid gives account of lipids in the interstitial compartment surrounding cells in the bone marrow.…”

“…The lipid composition in the marrow fluid gives account of lipids in the interstitial compartment surrounding cells in the bone marrow. It does not denote directly adipocytes, nor plasma circulating lipids composition (17). The relative levels of unsaturated and saturated fatty acids compares well to those observed in the human marrow fat tissue, implying a distinct lipid content in marrow supernatant fluids which replicate relevant fatty acids derived from the activity of adipocytes and other marrow cells, rather than those provided by blood plasma composition (17).…”

“…Using in vivo 1 H-MRS, Yeung et al observed increased marrow fat contents and decreased unsaturation level in osteopenic and osteoporotic women compared to controls (9); Bredella et al reported that high saturation level or lower unsaturation level of marrow fat were correlated with low BMD in women with anorexia nervosa (15). Two studies using ex vivo specimens and gas chromatography methods for lipid analysis, however, reported no correlation between marrow composition and BMD (16, 17). Previous studies also suggested that less unsaturated and more saturated fatty acids in MAT, as measured by in vivo MRS, were associated with type-2 diabetes (18), and associated with fractures in postmenopausal women (19).…”