Simvastatin Attenuates Abdominal Aortic Aneurysm Formation Favoured by Lack of Nrf2 Transcriptional Activity

Abstract

Surgical intervention is currently the only option for an abdominal aortic aneurysm (AAA), preventing its rupture and sudden death of a patient. Therefore, it is crucial to determine the pathogenic mechanisms of this disease for the development of effective pharmacological therapies. Oxidative stress is said to be one of the pivotal factors in the pathogenesis of AAAs. Thus, we aimed to evaluate the significance of nuclear factor erythroid 2-related factor 2 (Nrf2) transcriptional activity in the development of AAA and to verify if simvastatin, administered as pre- and cotreatment, may counteract this structural malformation. Experiments were performed on mice with inhibited transcriptional activity of Nrf2 (tKO) and wild-type (WT) counterparts. We used a model of angiotensin II- (AngII-) induced AAA, combined with a fat-enriched diet. Mice were administered with AngII or saline for up to 28 days via osmotic minipumps. Simvastatin administration was started 7 days before the osmotic pump placement and then continued until the end of the experiment. We found that Nrf2 inactivation increased the risk of development and rupture of AAA. Importantly, these effects were reversed by simvastatin in tKO mice, but not in WT. The abrupt blood pressure rise induced by AngII was mitigated in simvastatin-treated animals regardless of the genotype. Simvastatin-affected parameters that differed between the healthy structure of the aorta and aneurysmal tissue included immune cell infiltration of the aortic wall, VCAM1 mRNA and protein level, extracellular matrix degradation, TGF-β1 mRNA level, and ERK phosphorylation, but neither oxidative stress nor the level of Angiotensin II Type 1 Receptor (AT1R). Taken together, the inhibition of Nrf2 transcriptional activity facilitates AAA formation in mice, which can be prevented by simvastatin. It suggests that statin treatment of patients with hypercholesterolemia might have not only a beneficial effect in terms of controlling atherosclerosis but also potential AAA prevention.

A Dual Role of Heme Oxygenase-1 in Angiotensin II-Induced Abdominal Aortic Aneurysm in the Normolipidemic Mice

“…The infusion of a high dose of AngII led to the formation of AAA in around 80% of animals. The frequency of appearance was significantly greater than in the case of the standard dose (Fisher’s exact test, p < 0.05), which led to the formation of AAA in 30–40% of mice, as reported by several groups, including us [ 18 ] ( Figure 1 C). Detailed morphological analysis and grading revealed the development of a wide range of aneurysms in high-dose AngII, varying from type 1 dilated AAA, through most common type 3 dissected, up to type 5-ruptured ( Figure 1 D).…”

“…Thus, we decided to inspect those parameters. Basing on our previous experience [ 18 ], and bearing in mind that aneurysms are formed by day 14, we focused on day 14 after implementation of osmotic pumps. We found that enhanced inflammatory response and oxidative imbalance are distinctive features of an aneurysm itself.…”

“…Additionally, the application of angiotensin-converting enzyme inhibitors abrogates the induction of hypertension, implying that endogenous AngII generation is indispensable for the process [ 39 ]. Irrespectively of the dose (varying between 200–2500 ng/kg/min), AngII infusion leads to around 40% increase in systolic blood pressure [ 18 , 35 , 36 ]. It substantiates that AAA formation is not solely dependent on hemodynamic parameters.…”

“…Longitudinal images of the suprarenal and infrarenal aorta and transverse images at the level of the abdominal aorta between the diaphragm and the outlet of the left renal artery were acquired in the B-mode and M-mode to assess the maximum cross-sectional diameter (during diastole) and aortic area in real-time for each mouse at each time point. The detailed analysis scheme is presented in [ 18 ].…”

“…In situ gelatinolytic activity in the media of frozen abdominal aorta was performed as described previously [ 18 ]. Slides were incubated with 20 µg/mL solution of fluorescein-conjugated, dye-quenched gelatin from pig skin (DQ™-gelatin, Thermo Fisher, Waltham, MA, USA) prepared in gelatinase reaction buffer (150 mM NaCl, 5 mM CaCl 2 , 0.2 mM NaN 3 , 50 mM Tris-HCl, pH 7.6) at 37 °C in a dark wet chamber for 2 h. Next, slides were washed in MilliQ water, fixed for 1 min in ice-cold acetone, and blocked in the wet, dark chamber with 10% GS with 0.05% Tween-20 for 1 h at RT.…”