doi: 10.1161/01.ATV.0000195782.07637.44
© 2006 American Heart Association, Inc.
Letters to the Editor |
Aldosterone Promotes Thrombosis Formation After Arterial Injury in Mice
University of Michigan Medical Center Ann Arbor, Mich
To the Editor:
The renin/angiotensin/aldosterone system (RAAS) has been broadly implicated in the pathogenesis of cardiovascular disease.1 Angiotensin converting enzyme (ACE) inhibitors have been shown to be beneficial in reducing cardiovascular events.2 The specific role of aldosterone in promoting ischemic cardiovascular disease is unclear. Recent evidence suggests that subjects with primary aldosteronism are at increased risk of cardiovascular events compared with subjects with essential hypertension,3 suggesting a potential direct role of aldosterone in mediating ischemic events. Human studies have demonstrated that pharmacological blockade of aldosterone with spironolactone in congestive heart failure patients leads to reduced cardiovascular mortality, even in the presence of ACE inhibition.4 Because many cardiovascular events are attributable to thrombosis in the setting of atherosclerosis, we used an animal model to directly determine the effect of elevated aldosterone on atherosclerosis as well as arterial thrombus formation after carotid artery injury.
Previous studies in apolipoprotein E–deficient mice examining the role of exogenous aldosterone in atherosclerosis have produced conflicting results with either increased5 or neutral effects.6 To further examine this issue, we used the LDL receptor–deficient mouse model of atherosclerosis on a Western chow diet. Mice were divided into two groups to receive either placebo or 90-day slow-release aldosterone pellet (0.55 µg/d; Innovative Research of America). Seven days after pellet implantation, urinary aldosterone levels were elevated &2.7-fold (Aldo: 8.3±0.8 ng/mg creatinine; Placebo: 3.0±0.28 ng/mg creatinine; P=0.003). At the end of the protocol, mice were perfusion fixed and the aorta and major branches were dissected and removed as previously described.7 Atherosclerosis was quantitated after staining with oil red O. No difference in the total lesion area between aldosterone-treated and placebo pellet mice was observed (Aldo: 4.8±0.88 mm2 [n=5]; Placebo: 3.5±0.49 mm2 [n=4]; P=0.26). Similarly, cross-sectional analyses did not reveal differences in the aortic intima to media (IM) ratio (Aldo: 0.26±0.10 [n=4]; Placebo: 0.21±0.03 [n=5]; P=0.60). We also examined whether effects of aldosterone on atherosclerosis might be revealed in the presence of a high sodium diet (&3% NaCl) rather than Western chow. However, 3 weeks of treatment with aldosterone had no effect on atherosclerosis in the 20-week-old LDL receptor–deficient mice as determined by the aortic IM ratio (Aldo: 0.10±0.027 [n=4]; Placebo: 0.06±0.016 [n=4]; P=0.22). Although our results are limited by modest statistical power, we did not observe a major increase in atherosclerotic lesions at this dose of aldosterone.
To investigate a possible effect of aldosterone on thrombosis, atherosclerotic mice on the Western chow diet were subjected to carotid photochemical injury before euthanization as previously described.7 Ninety days of aldosterone treatment resulted in a marked shortening of the time to occlusive thrombus formation in these hyperlipidemic atherosclerotic mice (aldosterone: 13±2.0 minutes, n=5; Placebo: 23±2.3 minutes, n=4; P=0.01). This is the first experimental evidence of aldosterone treatment resulting in enhanced thrombus formation following arterial injury.
To further examine the effect of aldosterone toward enhanced thrombosis, we determined whether aldosterone treatment in the absence of hyperlipidemia and atherosclerosis produced a similar prothrombotic effect. For these studies we measured the time to occlusive thrombus formation in wild-type mice (C57BL6/J) provided a placebo or aldosterone pellet using the same dosing regimen, but for only 20 days. As shown in the Figure, we observed that this aldosterone treatment also resulted in enhanced thrombus formation after photochemical injury. Furthermore, this effect was prevented by coinfusion of the aldosterone antagonist, spironolactone (&1 mg/d per mouse; Figure). These data provide strong evidence of a direct aldosterone effect on thrombosis and demonstrate that this effect can be blocked with spironolactone.
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These findings indicate that aldosterone blockade may be beneficial in subjects at risk for arterial thrombotic events. Additional studies are necessary to delineate the mechanism of this aldosterone-mediated prothrombotic effect.
References
1. Jacoby DS, Rader DJ. Renin-angiotensin system and atherothrombotic disease: from genes to treatment. Arch Intern Med. 2003; 163: 1155–1164.
2. Yusuf S, Sleight P, Pogue J, Bosch J, Davies R, Dagenais G. Effects of an angiotensin-converting-enzyme inhibitor, ramipril, on cardiovascular events in high-risk patients. The Heart Outcomes Prevention Evaluation Study Investigators. N Engl J Med. 2000; 342: 145–153.
3. Milliez P, Girerd X, Plouin PF, Blacher J, Safar ME, Mourad JJ. Evidence for an increased rate of cardiovascular events in patients with primary aldosteronism. J Am Coll Cardiol. 2005; 45: 1243–1248.
4. Pitt B, Zannad F, Remme WJ, Cody R, Castaigne A, Perez A, Palensky J, Wittes J. The effect of spironolactone on morbidity and mortality in patients with severe heart failure. Randomized Aldactone Evaluation Study Investigators. N Engl J Med. 1999; 341: 709–717.
5. Keidar S, Kaplan M, Pavlotzky E, Coleman R, Hayek T, Hamoud S, Aviram M. Aldosterone administration to mice stimulates macrophage NADPH oxidase and increases atherosclerosis development: a possible role for angiotensin-converting enzyme and the receptors for angiotensin II and aldosterone. Circulation. 2004; 109: 2213–2220.
6. Cassis LA, Helton MJ, Howatt DA, King VL, Daugherty A. Aldosterone does not mediate angiotensin II-induced atherosclerosis and abdominal aortic aneurysms. Br J Pharmacol. 2005; 144: 443–448.[CrossRef][Medline] [Order article via Infotrieve]
7. Westrick RJ, Bodary PF, Xu Z, Shen YC, Broze GJ, Eitzman DT. Deficiency of tissue factor pathway inhibitor promotes atherosclerosis and thrombosis in mice. Circulation. 2001; 103: 3044–3046.
8. Day SM, Reeve JL, Pedersen B, Farris DM, Myers DD, Im M, Wakefield TW, Mackman N, Fay WP. Macrovascular thrombosis is driven by tissue factor derived primarily from the blood vessel wall. Blood. 2005; 105: 192–198.
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