Lipids in biocalcification: contrasts and similarities between intimal and medial vascular calcification and bone by NMR (original) (raw)

2012, Journal of Lipid Research

Supplementary key words cholesterol • fatty acid • matrix vesicle • hydroxyapatite • osteogenesis • biomineralization • atherosclerosis • diabetes mellitus • renal insuffi ciency • nuclear magnetic resonance Calcifi cations, which often occur in atherosclerosis, are almost exclusively in the intimal layer of the arterial wall. Small mineral deposits in the fi brous cap are associated with plaque rupture, whereas large calcium phosphate crystals may stabilize it (1). On the other hand, renal insuffi ciency and diabetes mellitus (2), in particular, provoke calcifi cation in the medial layer of the arterial wall, which is also associated with increased cardiovascular morbidity and mortality (3). Lipids are widely believed to be important participants in some apatitic biomineralization processes (4), in both normal hard tissue and tissue of pathological origin (5), although the source of lipids is far from clear in either case. In atherosclerotic calcifi cation, thinking focuses on the role of matrix vesicles (MV), small (20-200 nm) spherical bodies bounded by a lipid layer that often contains particles of calcium phosphate. MVs are released by vascular smooth muscle cells (VSMC) after prolonged exposure in vitro to calcium and phosphate levels, mimicking the mineral imbalance in chronic kidney disease (6). In vivo, ultrastructural studies have identifi ed hydroxyapatitecontaining MVs in human atherosclerotic aortas with calcifi ed lesions, suggesting that these structures may serve as a fi rst nidus for vascular calcifi cation (7). Moreover, MVs are Abstract Pathomechanisms underlying vascular calcifi cation biogenesis are still incompletely understood. Biomineral from human atherosclerotic intimal plaques; human, equine, and bovine medial vascular calcifi cations; and human and equine bone was released from collagenous organic matrix by sodium hydroxide/sodium hypochlorite digestion. Solid-state 13 C NMR of intimal plaque mineral shows signals from cholesterol/cholesteryl esters and fatty acids. In contrast, in mineral from pure medial calcifi cations and bone mineral, fatty acid signals predominate. Refl uxing (chloroform/methanol) intimal plaque calcifi cations removes the cholesterylic but not the fatty acyl signals. The lipid composition of this refluxed mineral now closely resembles that of the medial and bone mineral, which is unchanged by refl ux. Thus, intimal and medial vascular calcifi cations and bone mineral have in common a pool of occluded mineral-entrained fatty acyl-rich lipids. This population of fatty acid may contain methyl-branched fatty acids, possibly representing lipoprotein particle remnants. Cell signaling and mechanistic parallels between physiological (orthotopic) and pathological (ectopic) calcifi cation are also refl ected thus in the NMR spectroscopic fi ngerprints of mineral-associated and mineral-entrained lipids. Additionally the atherosclerotic plaque mineral alone shows a significant independent pool of cholesterylic lipids. Colocalization of mineral and lipid may be coincidental, but it could also refl ect an essential mechanistic component of biomineralization.