Abstract 242: Novel Therapeutic Approach to Abdominal Aortic Aneurysm through the Inhibition of Osteoclastogenesis
Arterial calcification, which mainly consists of calcium phosphate (CaPO4) crystals, has been proven to be an organized process, just like the processes seen in bone. Osteoclast-like cells (OCLCs), which are derived from the monocyte/macrophage lineage, dissolve extracellular matrices with proteases. Although OCLCs have been reported to exist in the calcified artery, their role in abdominal aortic aneurysm (AAA) hasn’t previously been explored and was investigated in this work.
First, we obtained human aortic tissues from patients who had undergone surgical repair for AAA and aortic stenotic disease (N = 5). Calcifications were abundant in both groups. However, multinucleated cells positive for osteoclast markers (enzymatic tartrate-resistant acid phosphatase staining, calcitonin receptor, vitronectin receptor, and CD68) were identified only in AAA tissues. We then checked the expression of receptor activator of nuclear factor kappa-B ligand (RANKL) and osteoprotegerin (OPG), key regulators of osteoclastogenesis, and TNFα, a pro-inflammatory cytokine. Immunohistochemical analysis showed upregulation of TNFα but not RANKL/OPG in AAA compared with stenosis. To mimic the pathogenic conditions of aneurysm and stenotic disease in vitro, we stimulated macrophages (RAW 264.7 cell line) with CaPO4 crystals with or without TNFα (100 ng/ml). Aneurysmal conditions (CaPO4 with TNFα) induced a significantly greater number of OCLCs than stenotic conditions (CaPO4 without TNFα) or control conditions (TNFα only, P < 0.01), with higher MMP-9 secretion after 5 days. Furthermore, inhibition of OCLCs with anti-TNFα (10 μg/ml, locally) or bisphosphonate (zoledronate, 100 μg/kg, i.v.) inhibited mouse CaPO4 aneurysm and osteoclastogenesis (P < 0.01, N = 5). Finally, we confirmed a spatial correlation between fluorescein-conjugated bisphosphonate and OCLCs in the CaPO4-treated artery.
In conclusion, we have demonstrated the existence of OCLCs in AAA and therapeutic effects of OCLCs inhibition on aneurysms. Our in vitro data showed that TNFα with CaPO4 induces osteoclastogenesis. These data suggest that inflammation in the calcified artery initiates osteoclastogenesis, which may be used to differentiate between stenotic and aneurysmal degeneration.
- © 2013 by American Heart Association, Inc.