Background Little is known about hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase expression in human coronary atherosclerotic plaques.

Objective To investigate the expression of HMG-CoA reductase in coronary atherectomy tissues obtained from patients with unstable and stable angina and examine the relationship of HMG-CoA with plaque instability.

Methods Atherectomy specimens were obtained from 43 patients with unstable (n=22) or stable (n=21) angina who underwent directional coronary atherectomy for de novo coronary artery lesions. The specimens were stained with haematoxylin–eosin and incubated with antibodies specific to HMG-CoA reductase, macrophages, smooth muscle cells and endothelial cells. Histology and immunohistochemistry data were morphometrically evaluated using an image-analysing system.

Results Baseline characteristics were similar between the two groups. Immunopositive areas of HMG-CoA reductase, macrophages, endothelial cells and thrombi were significantly greater in patients with unstable angina than those in patients with stable angina. However, the immunopositive area of smooth muscle cells was not different between the two groups. Macrophage-positive areas correlated well with areas of HMG-CoA reductase in patients with unstable angina (r=0.72, p<0.001), but not in patients with stable angina (r=0.02, p=0.937).

Conclusion HMG-CoA reductase was present in coronary atherosclerotic plaques and was more commonly expressed in unstable plaques than in stable plaques. Local HMG-CoA reductase in coronary artery lesions may contribute to plaque instability.