Microcalcifications in atherosclerotic lesion of apolipoprotein E-deficient mouse

Summary Evidence is accumulating that calcium‐rich microdeposits in the vascular wall might play a crucial role in the onset and progression of atherosclerosis. Here we investigated an atherosclerotic lesion of the carotid artery in an established murine model, i.e. the apolipoprotein E‐deficient (APOE−/−) mouse to identify (i) the presence of microcalcifications, if any, (ii) the elemental composition of microcalcifications with special reference to calcium/phosphorus mass ratio and (iii) co‐localization of increased concentrations of iron and zinc with microcalcifications. Atherosclerosis was induced by a flow‐divider placed around the carotid artery resulting in low and high shear‐stress regions. Element composition was assessed with a proton microprobe. Microcalcifications, predominantly present in the thickened intima of the low shear‐stress region, were surrounded by areas with normal calcium levels, indicating that calcium‐precipitation is a local event. The diameter of intimal microcalcifications varied from 6 to 70 μm. Calcium/phosphorus ratios of microcalcifications varied from 0.3 to 4.8, mainly corresponding to the ratio of amorphous calcium‐phosphate. Increased iron and zinc concentrations commonly co‐localized with microcalcifications. Our findings indicate that the atherosclerotic process in the murine carotid artery is associated with locally accumulated calcium, iron and zinc. The calcium‐rich deposits resemble amorphous calcium phosphate rather than pure hydroxyapatite. We propose that the APOE−/− mouse, in which atherosclerosis was evoked by a flow‐divider, offers a useful model to investigate the pathophysiological significance of accumulation of elements such as calcium, iron and zinc.