Flow loading induces macrophage antioxidative gene expression in experimental aneurysms

OBJECTIVE

Reactive oxygen species may act as proinflammatory mediators in abdominal aortic aneurysm (AAA) disease. Flow loading increases antioxidative enzyme expression and limits reactive oxygen species production in vascular smooth muscle cells in vitro, limits experimental AAA enlargement in rodent models, and is indirectly associated with reduced clinical AAA risk. We attempted to determine the mechanism or mechanisms by which flow loading limits AAA enlargement.

METHODS AND RESULTS

Rodent AAAs were flow loaded via femoral arteriovenous fistula creation. Aortic wall shear stress and relative wall strain were significantly higher in flow-loaded rodents. Flow loading reduced AAA diameter by 26% despite evidence of flow-mediated aortic enlargement proximal to the aneurysmal segment. Messenger RNA from AAA tissue was harvested for cDNA labeling and hybridization to a 384-clone DNA microarray. Twenty-nine genes were differentially expressed (relative intensity/relative intensity of control ratio >1.5 and <0.67) in flow-loaded compared with normal flow AAA tissue, including heme oxygenase 1 (HO-1). Increased HO-1 expression was confirmed via reverse transcriptase-polymerase chain reaction. Immunohistochemistry localized HO-1 expression to infiltrative macrophages. alpha-Tocopherol was found to be as effective as flow loading in limiting AAA enlargement. Flow loading and alpha-tocopherol therapy reduced AAA reactive oxygen species production.

CONCLUSIONS

Flow loading may attenuate AAA enlargement via wall shear or strain-related reductions in oxidative stress.

Cause and effect relationship between myocardial mast cell number and matrix metalloproteinase activity

The objectives of this study were to investigate the temporal response of left ventricular (LV) matrix metalloproteinase (MMP) activity and collagen volume fraction (CVF) induced by an aortocaval fistula and the role of cardiac mast cells in regulating MMP activity. LV tissue was analyzed for MMP activity, CVF, and mast cell number in rats euthanized at 0.5, 1, 2, 3, 5, 14, 21, 35, and 56 days. Additional rats treated with the mast cell membrane-stabilizing drug cromolyn sodium were euthanized 1, 2, and 3 days postfistula. Marked increases in MMP activity occurred rapidly and remained significantly elevated for 5 days before returning toward normal. A significant decrease in CVF occurred by day 5, but thereafter CVF rebounded to normal or above normal values. The number of myocardial mast cells also significantly increased postfistula, and there was a close association between mast cell density and MMP activity. Cromolyn treatment prevented the increase in mast cell number and MMP activity. Thus it is concluded that cardiac mast cells play a major role in the regulation of MMP activity.

Matrix metalloproteinase inhibition limits arterial enlargements in a rodent arteriovenous fistula model

BACKGROUND

We administered a specific, nonselective matrix metalloproteinase (MMP) inhibitor (RS-113,456) to examine the effect of MMP inhibition on flow-mediated arterial enlargement in a rodent arteriovenous fistula (AVF) model.

METHODS

Four groups of male Sprague-Dawley rats were created: sham (sham operated; n = 10), control (2.0 mm left common femoral AVF alone; n = 16), vehicle (AVF plus 0.5 mL vehicle orally twice a day; n = 20), and treatment (AVF plus 25 mg/kg RS-113,456 in 0.5 mL vehicle orally twice a day; n = 16). Heart rate, mean arterial pressure, and body weight were recorded on postoperative days 0, 7, 14, and 21. On day 21, AVF patency was confirmed, the infrarenal aorta and common iliac arteries were exposed, blood flow velocity and external diameter were measured, and wall shear stress (WSS) was calculated. Analysis was performed by paired, two-tailed Student t test, one-way analysis of variance, and the Bonferroni/Dunn procedure for post hoc testing.

RESULTS

Heat rate, mean arterial pressure, and weight did not vary at any time between groups. Aortic and left iliac diameter was larger in the AVF groups than in sham groups (P < .001), and control and vehicle groups were larger than treatment groups (P < .0001). Changes in aortic and left iliac flow were also significant (AVF was more than sham and control, and vehicle was more than treatment). No difference in aortic and left iliac artery velocity and WSS or right iliac diameter, velocity, flow, or WSS was observed between groups.

CONCLUSIONS

MMP inhibition diminishes flow-mediated arterial enlargement in the rat AVF model.

Role of neutral endopeptidase 24.11 in AV fistular rat model of heart failure

OBJECTIVE

The aortovenocaval fistular (AVF) rat represents a model of heart failure caused by increased cardiac volume overload and reduced renal function. Both circulating vasoconstrictors like the renin-angiotensin-aldosterone system and vasodilators like atrial and brain natriuretic peptides (ANP and BNP) are activated in this animal model of heart failure. In addition, neutral endopeptidase 24.11 (NEP) in plasma and urine is elevated in AVF rats. In the present investigation we examined the renal and hormonal effects of the NEP inhibitor, ecadotril, in acute and chronic studies in rats with an aortovenocaval fistula (AVF).

METHODS

Sprague Dawley rats (350-430 g) were prepared by introducing a shunt between abdominal aorta and the vena cava.

RESULTS

Acute administration of the neutral endopeptidase inhibitor, ecadotril (30 mg/kg p.o.), significantly improved the reduced renal excretion of sodium in AVF rats (83 +/- 10 to 145 +/- 14 mumol/kg/h, P < 0.01) but had no significant effect in sham-operated rats. However, neutral endopeptidase activity in urine was significantly decreased after ecadotril in both groups. Plasma ANP was increased after ecadotril only in AVF rats (275 +/- 83 to 748 +/- 187 pg/ml, P < 0.05), whereas the increase in plasma BNP was not statistically significant. After 4 weeks of observation the ANP and BNP plasma levels, renin activity (PRA), angiotensin I, and neutral endopeptidase activity were significantly higher in AVF rats than in sham-operated rats. Four weeks on ecadotril (30 mg/kg p.o., b.i.d.) increased plasma ANP (245 +/- 48 as opposed to 450 +/- 77 pg/ml, P < 0.05) and decreased PRA (11.3 +/- 1.5 as opposed to 6.8 +/- 1.2 ng/ml/h, P < 0.005) in AVF rats. Plasma NEP activity was inhibited in both groups. Ventricle weight was significantly higher in AVF rats than in sham-operated controls, and ecadotril treatment over 4 weeks decreased ventricular hypertrophy to a slight extent.

CONCLUSION

These results indicate that in the AVF rat model of heart failure the neutral endopeptidase inhibitor, ecadotril, improves the reduced kidney function in AVF rats by raising natriuretic peptides in plasma and probably in urine. NEP inhibition with ecadotril could therefore offer useful therapeutic possibilities in the treatment of heart failure.