Background and Aims: Vascular calcification (VC), a hallmark of atherosclerosis, appears in both inflammatory associated microcalcification and plaque stabilising macrocalcification morphologies, resulting from the differentiation of vascular smooth muscle cells (VSMC) into bone-like cells. Although atherogenic lipoproteins are well characterised in atherosclerosis and implicated in VC, their effects on VC remain unknown and this prevalent disease remains untreatable. This study therefore examines the roles of lipoproteins on VC.

Methods and Results: VSMCs were pre-treated with native and oxidised VLDL, LDL, HDL then CaPO4 (Ca 2.7mM, PO4 2.0 mM) for 15 days.  Pre-treating VSMCs with reconstituted HDL (rHDL: 20 mg/kg) inhibited calcification (-17.87%, p<0.01) as detected by Alizarin Red staining (ARS), whereas ox-rHDL negated these effects. Additionally, oxidised atherogenic lipoproteins upregulated calcium deposition (oxLDL: +15.3%, p<0.05; oxVLDL: +23.3% p<0.0001) while their native counterparts had no effect. In vivo studies found Osteoprotegerin-/- (OPG-/-) x ApoE-/- double knockout mice (8 w old, n=3-10), fed a western diet for 40 weeks had increased plaque volume (67.71%, p<0.01) and VC (304.14%, p<0.01) compared to ApoE-/- mice. rHDL infusions (3 times weekly in weeks 36-40) in ApoE-/- mice caused a significant reduction in plaque calcification (-92.43%, p<0.05) and collagen content (25.26%, p<0.05), whereas in OPG-/-ApoE-/-mice, rHDL infusions showed a trend towards an increase in plaque calcification (n=3, 29.82%).

Conclusion: This is the first demonstration that lipoproteins regulate the initiation of VC. In vitro, rHDL prevents calcification, whereas atherogenic lipoproteins initiate the calcification of VSMCs. In vivo, infusions of rHDL suppress microcalcifications in ApoE-/- mice and increase macrocalcifications in OPG-/-ApoE-/- mice. Our findings highlight the complexity of VC and the potential for targeted therapeutics.

01 - LIPOPROTEINS AND THEIR MODIFIED FORMS REGULATE EARLY STAGE VASCULAR SMOOTH MUSCLE CELL CALCIFICATION