Abstract 2187: Mechanisms of Oxidative Stress in Human Aortic Abdominal Aneurysms. Role of iNOS, NADPH Oxidase and Relationship to Clinical Features.
Increased superoxide (O2-) production appears to play an important role in the pathogenesis of aortic abdominal aneurysms (AAA). However, the mechanisms regulating oxidative stress (OS) in AAA are unclear. We have investigated sources of O2- in human AAA and the relationship between O2- production and aneurysm diameter and clinical score in AAA patients.
Methods O2- production was measured in AAA segments from 40 patients undergoing AAA repair, using lucigenin enhanced chemiluminescence (5uM), and was visualized in cryosections by confocal microscopy (SOD-inhibitable dihydroethidium fluorescence). Malonylodialdehyde (MDA) levels were measured as a marker of oxidative stress by MS-HPLC. AAA diameter was determined intra-operatively and Vanzetto scale was used as a risk stratification measure in AAA.
Results Plasma MDA was higher in subjects with AAA (4.9±1μM vs 3.0±0.9μM p<0.02); Basal O2- was observed in all AAA segments and was significantly higher than in non-AAA segments (23.2±2.9 vs. 12.9±2.0 RLU/s/mg p<.001). O2- production was suppressed by pre-incubation with Tiron or the superoxide dismutase (PEG-SOD; 450U/ml). O2-production was significantly blunted by iNOS inhibitor 1400W (100μM) to 18% (4.2±2.4 RLU/s/mg p<0.01). O2- production was also significantly inhibited NADPH oxidase inhibitors: diphenyliodonium (DPI; 10uM) to 16% of control levels or by apocynin (500uM) to 51% of control levels (11.8±1 RLU/s/mg p<0.01). Modest inhibition (ca 40%) was observed in response to cyclooxygenase inhibitor indomethacin (10uM). Inhibitors of other oxidase systems (xanthine oxidase, mitochondrial) did not show effects. SOD inhibitable O2-production in AAA was localised in media and adventitia, as shown by DHE staining. Importantly we observed that AAA O2- production correlated with aneurysm diameter (R=+0.4; p=0.03). Increased risk assessed by Vanzetto score was also associated with higher O2- production (18.1±2 vs 53.7±8 RLU/s/mg; p<0.01)
Conclusions iNOS and NADPH oxidases, are the major sources of O2- in AAA. Vascular O2- production is correlated with aneurysm diameter and clinical score, as measures of disease progression. Novel antioxidant approaches directed on inhibiting iNOS and NAD(P)H oxidases may be useful in the treatment of AAA.