Direct detection and quantification of transition metal ions in human atherosclerotic plaques: Evidence for the presence of elevated levels of iron and copper

Objective-The involvement of transition metals in atherosclerosis is controversial. Some epidemiological studies have reported a relationship between iron (Fe) and cardiovascular disease, whereas others have not. Experimental studies have reported elevated levels of iron and copper (Cu) in diseased human arteries but have often used methods that release metal ions from proteins. Methods and Results-In this study, we have used the minimally invasive technique of electron paramagnetic resonance (EPR) spectroscopy and inductively coupled plasma mass spectroscopy (ICPMS) to quantify iron and copper in ex vivo healthy human arteries and carotid lesions. The EPR spectra detected are characteristic of nonheme Fe(III) complexes. Statistically elevated levels of iron were detected in the intima of lesions compared with healthy controls (0.370 versus 0.022 nmol/mg tissue for EPR, 0.525 versus 0.168 nmol/mg tissue by ICPMS, P < 0.05 in each cases). Elevated levels of copper were also detected (7.51 versus 2.01 pmol/mg tissue, lesion versus healthy control, respectively, P < 0.05). Iron levels did not correlate with the gender or age of the donor, or tissue protein or calcium levels, but cholesterol levels correlated positively with iron accumulation, as measured by EPR. Conclusions-These data support the hypothesis that iron accumulates in human lesions and may contribute to disease progression.