Induction of Heme Oxygenase-1 Is Linked to the Severity of Disease in Human Abdominal Aortic Aneurysm

Background Rupture of abdominal aortic aneurysm (rAAA) is associated with high case fatality rates, and risk of rupture increases with the AAA diameter. Heme oxygenase-1 (gene HMOX1, protein HO-1) is a stress-induced protein and induction has protective effects in the vessel wall. HMOX1^-/- mice are more susceptible to angiotensin II-induced AAA formation, but the regulation in human nonruptured and ruptured AAA is only poorly understood. Our hypothesis proposed that HO-1 is reduced in AAA and lowering is inversely associated with the AAA diameter. Methods and Results AAA walls from patients undergoing elective open repair (eAAA) or surgery because of rupture (rAAA) were analyzed for aortic HMOX1/HO-1 expression by quantitative real-time polymerase chain reaction and Western blot. Aortas from patients with aortic occlusive disease served as controls. HMOX1/HO-1 expression was 1.1- to 7.6-fold upregulated in eAAA and rAAA. HO-1 expression was 3-fold higher in eAAA specimen with a diameter >84.4 mm, whereas HO-1 was not different in rAAA. Other variables that are known for associations with AAA and HO-1 induction were tested. In eAAA, HO-1 expression was negatively correlated with aortic collagen content and oxidative stress parameters H₂O₂ release, oxidized proteins, and thiobarbituric acid reactive substances. Serum HO-1 concentrations were analyzed in patients with eAAA, and maximum values were found in an aortic diameter of 55 to 70 mm with no further increase >70 mm, compared with <55 mm. Conclusions Aortic HO-1 expression was increased in eAAA and rAAA. HO-1 increased with the severity of disease but was additionally connected to less oxidative stress and vasoprotective mechanisms.