Hypercholesterolemia affects cardiac function, infarct size and inflammation in APOE*3-Leiden mice following myocardial ischemia-reperfusion injury

Abstract

Background: Hypercholesterolemia is a major risk factor for ischemic heart disease including acute myocardial infarction. However, long-term effects of hypercholesterolemia in a rodent myocardial ischemia-reperfusion injury model are unknown. Therefore, the effects of diet-induced hypercholesterolemia on cardiac function and remodeling were investigated up to eight weeks after myocardial ischemia-reperfusion (MI-R) injury which was induced in either normocholesterolemic (NC-MI) or hypercholesterolemic (HC-MI) APOE*3-Leiden mice.

Methods: Left ventricular (LV) dimensions were serially assessed using parasternal long-axis echocardiography followed by LV pressure-volume measurements. Subsequently, infarct size and the inflammatory response were analyzed by histology and fluorescence-activated cell sorting (FACS) analysis.

Results: Intrinsic LV function eight weeks after MI-R was significantly impaired in HC-MI compared to NC-MI mice as assessed by end-systolic pressure, dP/dtMAX, and -dP/dtMIN. Paradoxically, infarct size was significantly decreased in HC-MI compared to NC-MI mice, accompanied by an increased wall thickness. Hypercholesterolemia caused a pre-ischemic peripheral monocytosis, in particular of Ly-6Chi monocytes whereas accumulation of macrophages in the ischemic-reperfused myocardium of HC-MI mice was decreased.

Conclusion: Diet-induced hypercholesterolemia caused impaired LV function eight weeks after MI-R injury despite a reduced post-ischemic infarct size. This was preceded by a pre-ischemic peripheral monocytosis, while there was a suppressed accumulation of inflammatory cells in the ischemic-reperfused myocardium after eight weeks. This experimental model using hypercholesterolemic APOE*3-Leiden mice exposed to MI-R seems suitable to study novel cardioprotective therapies in a more clinically relevant animal model.

Fig 1. Lipid profiles.

Plasma (A) total cholesterol and (B) triglycerides levels in the NC-MI (open bars) and HC-MI (closed bars) group. Data are means ± SEM. ***P<0.001 vs. NC-MI group.

Fig 2. Serial echocardiography.

(A) End-diastolic volume, (B) end-systolic volume, (C) ejection fraction, and (D) cardiac output in NC-MI (open bars) and HC-MI (closed bars) groups at baseline, 1, 3, and 8 weeks after MI-R (n = 16–18). Data are means ± SEM. *P<0.05, **P<0.01, ***P<0.001 all vs. week 0.

Fig 3. Pressure-volume loops.

PV loops 8 weeks after MI-R of the NC-MI and HC-MI groups. The oblique lines represent the end-systolic (E_ES) and end-diastolic (E_ED) pressure-volume relations.

Fig 4. Infarct size, LV wall thickness, and vascular profile 8 weeks after MI-R.

Infarct size (n = 8) was significantly smaller in the HC-MI group compared with the NC-MI group (A). Wall thickness of the infarct area was significantly larger in the HC-MI group (B). Sirius red staining in the HC-MI group showed a more pronounced subendocardial and epicardial border of surviving cardiomyocytes in the HC-MI group (D) compared to the NC-MI group (C). Vascular analysis showed no differences in number of small capillaries (<20μm) or large vessels (>20μm) in the border zone (BZ) or infarct area (MI) between both groups (E). Data are means ± SEM. *P<0.05, **P<0.01.

Fig 5. Inflammatory response as a result of the cholesterol-enriched diet and MI-R.

Quantification of monocytes as a percentage of total leukocytes (A) and activated (Ly-6C^hi) monocytes as a percentage of total monocytes (B) in whole blood 1 week before induction of MI-R (n = 11–15) and 3 weeks after MI-R (n = 6–7). **P<0.01 vs. time-corresponding NC-MI group. Quantification of leukocytes (C) and macrophages (D) 8 weeks after MI-R in the infarct area, border zone and septum, expressed as the number per area. Data are means ± SEM. *P<0.05.