Smooth Muscle Cell Elastase, Atherosclerosis, and Abdominal Aortic Aneurysms

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Abstract
Smooth muscle cells (SMC) were obtained by outgrowth of human aortic explants from abdominal aortic aneurysm (AAA) patients, aortic occlusive disease (AOD) patients, and transplant donors (controls). Specimens were incubated with medium alone or medium with either elastin-derived peptides (EDP, 5 micrograms/mL) or low-density lipoproteins (LDL, 5 micrograms/mL). Elastase activity (ng/mg total protein) was assayed from 4-week-old cultures. Control aortas obtained from patients significantly younger secrete an increased amount of elastase at baseline compared with AOD and AAA patients (p less than 0.05). Elastin-derived peptides caused a significant increase in elastase secretion in all groups. The increase in elastase secretion in response to EDP in AAA patients was significantly higher compared with AOD or control. Low-density lipoprotein had no effect on SMC elastase secretion. These data suggest that (1) aortic SMCs secrete elastase in response to EDP, (2) SMC elastase is age dependent, and (3) AAA SMC secrete an abnormally high amount of elastase compared with AOD and control aortas in response to EDP. Like the neutrophil, the SMC is highly responsive to the degradation products of elastin and in AAA patients secrete significantly increased amounts of elastase in response to the breakdown products of atherosclerosis.