Objective       To investigate the expression of cathepsin S and NF-κB p65 in abdominal aortic aneurysm (AAA)

and determine their roles in the occurrence

progress and rupture

of AAA.       Methods       Surgical specimens of abdominal aortic aneurysm wall tissue from 78 cases undergoing surgery in our department from January 2008 to March 2013 were collected. There were 29 cases with the aneurysm size of 5 to 7 cm

34 cases with the size of 7 to 9 cm

and 15 cases with ruptured abdominal aortic aneurysm in size of 7 to 9 cm (RAAA). Immunohistochemical assay and Western blotting were applied to detect the expression of cathepsin S and NF-κB in the tissue specimens. Spearman analysis was carried out for the correlation of the expression with aneurysm size.       Results       Immunohistochemistry assay showed that NF-κB p65 was expressed in the cytoplasm and nucleus

while cathepsin S was mainly concentrated in the cytoplasm. The positive rate of NF-κB p65 and cathepsin S was significantly higher in 7-9 cm AAA group than in 5-7 cm AAA group (

P

0.05). The positive rate of NF-κB p65 and cathepsin S was significantly higher in 7-9 cm RAAA group than in 7-9 cm AAA group (

P

0.05). The expression of both cathepsin S and NF-κB p65 in abdominal aortic aneurysm tissues was correlated with hypertension and coronary artery diseases (

P

0.05)

and NF-κB p65 expression was also associated with smoking (

P

0.05). Western blotting showed that NF-κB p65 and cathepsin S in 7-9 cm AAA group was higher than that in 5-7 cm AAA group (

P

0.05). NF-κB p65 and cathepsin S in RAAA (7-9 cm) group was higher than that in 7-9 cm AAA (

P

0.05). Among 78 cases of abdominal aortic aneurysm

NF-κB p65 and cathepsin S expression was positively correlated (

P

0.05).       Conclusion       Cathepsin S and NF-κB p65 are expressed in AAA

and their expression is positively correlated with the aneurysm size and rupture

suggesting that they might play important roles in the occurrence

development and rupture of AAA.