BACKGROUNDNitric oxide (NO) is an important mediator in the pathophysiology of many vascular diseases. However, the definite role of NO in human abdominal aortic aneurysm (AAA) formation is unclear. The aim of this study was to investigate production of NO and expression of inducible nitric oxide synthase (iNOS), and their possible role in AAA.

METHODSA total of 28 patients with AAA, 10 healthy controls, and 8 patients with arterial occlusive disease were enrolled into this study. Standard colorimetric assay was used to examine NO concentration in plasma from patients with AAA and normal controls, and in cultured smooth muscle cells (SMCs). Expression of iNOS in aortas and cultured SMCs were detected by immunochemistry. The correlation of iNOS expression with age of the patient, size of aneurysm, and degree of inflammation was also investigated by Cochran-Mantel-Haenszel chi2 test and Kendall' Tau correlation.

RESULTSExpression of iNOS increased significantly in the wall of aneurism in the patients with AAA compared to the healthy controls (P < 0.05) and the patients with occlusive arteries (P < 0.05). iNOS protein and media NOx (nitrite + nitrate) also increased in cultured SMCs from human AAA (n = 4, P < 0.05), while plasma NOx decreased in patients with AAA (n = 25) compared to the healthy controls (n = 20). There was a positive correlation between iNOS protein and degree of inflammation in aneurismal wall (Kendall coefficient = 0.5032, P = 0.0029).

CONCLUSIONSSMCs and inflammatory cells were main cellular sources of increased iNOS in AAA, and NO may play a part in pathogenesis in AAA through inflammation.