Aneurysm or occlusive disease - Factors determining the clinical course of atherosclerosis of the infrarenal aorta

Atherosclerosis of the infrarenal aorta results in distinct clinical entities-aortoiliac occlusive disease (AOD) and abdominal aortic aneurysm (AAA). Although loss of collagen has been implicated in AAA, collagen accumulation plays a role in AOD. In vivo collagen-gene expression can be assessed using complementary DNA for collagen types I and III α-chains. The purpose of this study is to compare total collagen (type I + III) and collagen types I and III messenger RNA in AAA, AOD and normal aorta. Specimens were collected from the infrarenal aorta during operation for AOD (n = 7), AAA (n = 7), autopsy, or organ procurement (normal; n = 7). Northern transfer analysis of total RNA was used to compare mRNA levels for type I and III collagen. After preliminary extraction, specimens were hydrolyzed for hydroxyproline analysis used to calculate total collagen (type I + III). Relative levels of type I (pro-a1 [1]) mRNA were greater in both AOD (0.77 ± 0.35) and AAA tissue (0.94 ± 0.24; p = 0.6) than in normal aorta (0.02 ± 0.03). Type III (pro-a1 [III]) mRNA levels were also greater in AOD (2.52 ± 0.19; p = 0.09) and AAA tissue (3.15 ± 1.3) than in normals (0.97 ± 0.47). Total collagen concentration was increased in AOD (45.6% ± 3.1% dry weight; p < 0.05) but not AAA tissue (27.8% ± 4%) when compared to normal aorta (34.7% ± 2.3%). Collagen type I and III gene expression is greater in older, diseased aorta, yet collagen accumulated only in AOD. This implies a similar synthetic response in both AOD and AAA. Thus, proteolytic degradation in AAA appears to determine collagen content and possibly the clinical course of the atherosclerotic process.