Objectives: Presence of free cholesterol in atherosclerotic plaques is a major determinant of plaque instability. It is hypothesized that extravasated erythrocytes may contribute to free cholesterol accumulation in atherosclerotic plaques through their rich in cholesterol membrane. In this study we assessed whether cholesterol in erythrocyte membranes (CEMs), that is, free (FCEM) versus esterified (ECEM), differs in patients with chronic stable angina (CSA) compared with patients presenting with acute coronary syndromes (ACSs).
Methods: Consecutive angina patients were prospectively assessed; 154 had CSA (118 men, 63 years, 56-69 years) and 164 ACS (124 men, 63 years, 55-71 years). FCEM and ECEM were measured using an enzymatic assay, and protein content was assessed by the Bradford method.
Results: FCEM was significantly higher (P<0.001) in the ACS patients group (94.1 microg/mg, IQ 71-116.5 microg/mg) compared with patients with CSA (61.9 microg/mg, IQ 49.3-73.1 microg/mg). ECEM levels were also significantly higher (P<0.001) in ACS patients (23.3 microg/mg, IQ 14.9-47.7 microg/mg) compared with CSA patients (10.8 microg/mg, IQ 8-22.3 microg/mg). In contrast, ratio of free-to-esterified cholesterol (P=0.110) as well as ratio of free-to-total CEM (P=0.109) were not different among CSA and ACS patients.
Conclusion: Findings of this study show that although free cholesterol is the prevailing form of CEMs, both FCEM and ECEM levels are increased in patients with ACS compared with CSA patients. These findings suggest that it is the quantity of CEM rather than the type of cholesterol present in the erythrocyte membrane that determines plaque progression.