Abstract 497: Ovariectomy Increases Vascular Calcification Via the Receptor Activator of Nuclear Factor-kB Ligand/Osteoprotegerin Cytokine Signaling Pathway
Introduction: Observational studies suggest a relationship between menopause and vascular calcification. Rank activator of nuclear factor-κΒ ligand (RANKL) and osteoprotegerin (OPG) are critical regulators of bone remodeling, and increased bone tissue RANKL:OPG ratio and subsequent osteoporosis are associated with ovariectomy. Both molecules modulate vascular calcification, but the role is unclear. We assessed the hypothesis that ovariectomy increases vascular calcification, possibly via the RANKL/OPG axis.
Methods: New Zealand White rabbits were randomized to ovariectomy (OVX, n=12) or sham procedure (SHAM, n=12). One month post-procedure, atherosclerosis was induced by 15-months 0.2%-cholesterol diet and two aortic endothelial balloon denudations (at months 1 and 3). Aortic atherosclerosis was assessed in vivo by magnetic resonance imaging (MRI) at month 9 and 15. At sacrifice, aortas were harvested for ex vivo micro-computed tomography (μCT) and then molecular analysis of the vascular tissue.
Results: Vascular calcification density of the abdominal aorta was significantly greater in OVX than SHAM (8.4±2.8 vs. 1.9±0.6 mg/cm3, p<0.05). Calcific particle number was similarly increased in OVX (94±26 vs. 33±7 particles/cm3 for SHAM, p<0.05). Calcification morphology, as assessed by the arc angle subtended by the largest calcific particle, showed no difference between groups (OVX 33±7° vs. SHAM 33±5°, p=0.99). By Western blot analysis, OVX decreased the vascular RANKL:OPG ratio by 40%, p<0.05, primarily through a decrease in RANKL (0.24±0.03 vs. 0.42±0.08 Arbitrary Units for SHAM, p=0.06). There was no statistically significant difference in OPG (OVX 0.52±0.10 vs. SHAM 0.42±0.06, p=0.49) or bone morphogenetic protein-2 expression (OVX 0.38±0.06 vs. SHAM 0.33±0.06, p=0.56). At month 9, MRI demonstrated no difference in atheroma volume between OVX and SHAM, and no significant change was seen by the end of the study.
Conclusions: In contrast to bone, vascular RANKL:OPG ratio decreased in response to ovariectomy with corresponding four-fold increase in arterial calcification. This diametrical organ-specific response may explain the co-morbid association of osteoporosis with calcifying atherosclerosis in post-menopausal women.