Biphasic pattern of cell turnover characterizes the progression from fatty streaks to ruptured human atherosclerotic plaques

Objective: To study the amount and phenotype of DNA-synthesizing and apoptotic cells during atherogenesis. Methods: Atherosclerotic lesions (n=76), obtained at autopsy (N=6) or during vascular surgery (N=8), were classified [type I-VI; American Heart Association (AHA) classification], immunolabeled with MIB 1 or the TUNEL technique and double stained with cell-type-specific antibodies. Subsequently, the labeled fractions were quantified. Results: In type II-VI lesions, intimal DNA synthesis was increased compared to that of the non-diseased (ND) arterial wall. DNA synthesis peaked in early type II lesions (3.7+/-0.5 vs. 0.02+/-0.02% in ND; p<0.05), and declined to 0.7+/-0.2% in type V lesions (p<0.05). Interestingly, a second peal; of DNA synthesis of 1.7+/-0.1%, was observed in type VI (ruptured plaque) lesions. Double staining revealed that DNA synthesis was mostly confined to the macrophage-derived foam cell (51.9%). In type II lesions, 100.0% of all DNA-synthesizing cells were present in the intimal foam cell-rich area, while in advanced type III, IV and V lesions, DNA synthesis had shifted to the shoulder region (74.8, 78.5 and 68.1%, respectively). In type VI lesions, DNA synthesis was present in the area underlying the plaque rupture (52.7%). Apoptosis was only elevated in advanced type IV, V and VI lesions (0.8+/-0.1, 0.8+/-0.1 and 1.1+/-0.1%, respectively, vs. 0.0+/-0.0% in ND) and was predominant in the lipid core (90.5% in type IV lesions; 54.2% in type V lesions) or equally divided between the lipid core and the region underlying the plaque rupture (31.8 and 34.6% in type VI lesions). In type III-VI lesions, 50.0, 38.9, 42.6 and 42.8% of the TUNEL-positive cells were macrophages. Conclusions: In stable atherosclerotic lesions, DNA synthesis is an early event, while apoptosis is a late event. Ruptured plaques show a second peak of cell turnover. Lastly, cell turnover is mostly confined to the macrophage-derived foam cell. (C) 1999 Elsevier Science B.V. All rights reserved.