656 Altered microcalcification pattern in aorta from pigs and rats exposed for 30-days to environmental tobacco smoke

Abstract

Endothelial dysfunction and arterial stiffening are associated with environmental tobacco smoke (ETS) exposure and atherogenesis in humans. Early atherogenic events have recently been proposed to resemble osteogenesis, with microcalcification deposits in the form of calcium hydroxyapatite (Ca10(PO4)6(OH)2) reported in large artery tissue. Thus, we hypothesized that increased microcalcium deposits would be detectable using the high resolution imaging afforded by synchrotron techniques in aorta from male pigs and rats exposed 1-hr/day for 30-days to ETS compared to sham controls. Furthermore, it was hypothesized that calcium deposition would be co-localized with phosphorus. Images of formalin-fixed, paraffin-embedded aortic cross-sections (5 micron) were collected using X-ray fluorescence imaging on beamline 2-3 at Stanford Synchrotron Radiation Lightsource (SSRL, Menlo Park, CA). A striking pattern was evident when aortic calcium was viewed, with high intensity levels within the medial layer smooth muscle cells and a relative absence in the elastic laminae. Paradoxically, the average calcium level was lower in aorta after 30-days of ETS compared to sham-exposure in both pigs and rats. However, the major area where calcium co-localized with phosphorus appeared to be in the elastic laminae, not the medial layer smooth muscle cells. In the same ETS-exposed animals prior to sacrifice, impaired endothelial function (lower flow-mediated dilation) was observed in pigs and increased arterial stiffness (increased arterial pulsewave dP/dt) was evident in rats compared to respective sham controls. Therefore, the key finding of this study is that microcalcification may proceed through deposition of calcium and phosphorus in the elastic laminae. In contrast, decreased bound calcium within aortic smooth muscle cells from ETS- compared to sham-exposed rats and pigs needs to be confirmed, but could have large functional implications.