Smooth muscle cell migration and proliferation is enhanced in abdominal aortic aneurysms

The aetiology of abdominal aortic aneurysms (AAA) is as yet undetermined. Smooth muscle cells (SMC) have been implicated in the pathogenesis of AAA as a result of their ability to produce elastin degrading proteases. The present study was undertaken to examine AAA SMC and aortic occlusive disease (AOD) SMC in terms of their respective migration and proliferation in vitro, in order to identify intrinsic differences between these cells.

Five AAA specimens, four AOD and five inferior mesenteric artery (IMA) specimens were established in culture. The cultures were examined for the extent and the rate of SMC outgrowth and proliferation. Cells were counted following trypsinization using a haemocytometer.

For the AAA explants, the cellular outgrowths were first seen at 6.7 days, after culture initiation, while the corresponding outgrowth in the AOD group required 8.8 days (P < 0.05) and the IMA group 11.4 days (P < 0.05). AAA cells reached confluency at a mean of 22.4 days while AOD SMC required 28.6 days (P < 0.05) and IMA 31 days (P < 0.05). In the first passage, the time for AAA SMC doubling was 5.3 days compared to 6.2 days for AOD (P < 0.05) and 8.1 days for the IMA group (P < 0.05). Greater than 98% of the cells, in both groups, stained positive to SMC alpha-actin.

From these data it is clear that there are intrinsic differences in cellular kinetics between SMC from the two disease states, supporting the hypothesis that AAA are not the result of atherosclerosis.