Stiffness of aortic arch and carotid arteries increases in ApoE-knockout mice with high-fat diet: evidence from echocardiography

Abstract

Arterial stiffness is an effective predictor of atherosclerosis. Measurement of pulse-wave velocity (PWV) is a gold-standard approach to study arterial stiffness. This study aims to examine arterial stiffness and heart functions via echocardiography at an early stage of atherosclerosis. A model of atherosclerosis in ApoE-knockout (ApoE^-/- ) mice fed on high-fat diet (HFD) was used, with normal chow diet (ND) as a control. Stiffness of aortic arch and carotid arteries and left ventricular (LV) systolic/diastolic functions were measured by echocardiography. The plasma cholesterol levels and atherosclerotic plaque areas in the aortas were measured. The PWV values of aortic arch and carotid arteries were compared at 2, 4, 6 and 8 weeks with different diets. Compared with ND mice, PWV values in aortic arch and carotid arteries were significantly increased in HFD mice after 8 weeks (Aortic arch: 516.65 ± 216.89 cm/s vs. 192.53 ± 71.71 cm/s; Carotid arteries: 514.26 ± 211.01 cm/s vs. 188.03 ± 75.14 cm/s, respectively; both P < 0.01) accompanied by the decrease in LV systolic/diastolic functions. These were well correlated with the increase in plasma cholesterol levels. Echo-based PWV measurement in the aortic arch was found more sensitive to predict atherosclerosis than in the carotid arteries in ApoE^-/- mice. Measuring aortic arch PWV via echocardiography could represent a new diagnostic strategy for early detection of atherosclerosis.

Keywords: Arterial stiffness; atherosclerosis; echocardiography; pulse wave velocity.

Figure 1

Measurement of aortic arch PWV, peak velocity and aortic root dimension in mice. Representative B-mode view of aortic arch distance (A) and aortic root dimension (B) from the different groups are shown (scale bar = 1 mm). (C) Pulse wave Doppler tracing of the ascending (lower panel) and descending aorta (upper panel). T1 was measured from the onset of the QRS complex to the onset of the ascending aortic Doppler waveform and T2 was measured from the onset of the QRS complex to the onset of the descending aortic Doppler waveform. D1 was measured between the 2 sample volume positions along the central axis of the aortic arch. Aortic arch PWV was determined as PWV = D1/[T2 - T1 (cm/s)]. (D) Aortic arch PWV was significantly increased in the high-fat diet (HFD) group compared with the normal chow diet (ND) group. Ascending aortic peak velocity (E) and descending aortic peak velocity (F) of ApoE^-/- mice from two diet groups are shown. Diameters of the (G) aortic annulus [L1], (H) sinus of Valsalva [L2] and (I) sinotubular junction [L3] were significantly increased in HFD group versus ND group. n = 15 per group. *P < 0.05, **P < 0.01.

Figure 2

Measurement of carotid artery PWV. A. Pulse wave Doppler tracing of the carotid artery. T3 was measured from the onset of the QRS complex to the onset of the proximal internal carotid arterial Doppler waveform and T4 was measured from the onset of the QRS complex to the onset of the distal internal carotid arterial Doppler waveform. D2 was measured between the 2 sample volume positions along the central axis of the carotid artery. The carotid artery PWV was calculated as PWV = D2/[T4 - T3 (cm/s)]. B. B-mode view of carotid arteries from the different groups. C. Carotid arterial PWV was significantly increased in HFD group versus ND group. D. Correlations between carotid artery PWV and aortic arch PWV of HFD and ND mice, respectively. Carotid artery PWV in HFD mice was directly proportional to aortic arch PWV (R-squared = 0.5804, P = 0.0010), but not in ND mice (R-squared = 0.02606, P = 0.5654). n = 15 per group. *P < 0.05, **P < 0.01.

Figure 3

Left ventricular diastolic function of ND and HFD mice. Representative images of mitral inflow velocity (A) and mitral annulus velocity (B) are shown. (C) MV E velocity, (D) MV A velocity, (E) E/A ratio, (F) TD e, (G) TD a, (H) e/a ratio, (I) E/e ratio, and (J) IVRT were measured from ND and HFD mice, respectively. MV, mitral valve; TD, tissue Doppler; IVRT, isovolumic relaxation time. n = 10 per group. *P < 0.05, **P < 0.01.

Figure 4

Left ventricular systolic function of ND and HFD mice. (A) Representative images for measuring left ventricular systolic function at the left ventricular parasternal short-axis view from the different groups are shown. (B) Ejection fraction, (C) normalized CO, (D) normalized SV and (E) fractional shortening were measured from ND and HFD mice, respectively. (F) The ratio of left ventricular weight to body weight was examined. CO, cardiac output; SV, stroke volume; LV, left ventricular; BW, body weight. n = 10 per group. *P < 0.05, **P < 0.01.

Figure 6

Early detection of PWV and LV systolic/diastolic functions by echocardiography. (A) The flow chat shows the high fat diet feeding starting at 8 weeks of age in mice. (B and C) Aortic arch PWV was significantly increased in HFD mice versus ND mice at week 2 and continued to increase in HFD mice during the 8 weeks, while carotid artery PWV was increased at week 6. E/A ratio (D) and e/a ratio (E) were significantly decreased in HFD mice versus ND mice at week 6, indicating the left ventricular diastolic dysfunction occurred after being fed on high-fat diet for 6 weeks. EF (F) and CO (G) were significantly decreased in HFD mice versus ND mice at week 8, suggesting the left ventricular systolic dysfunction occurred after being fed on high-fat diet for 8 weeks. n = 5 per group. *P < 0.05, **P < 0.01.

Figure 5

Histological analysis of ND and HFD mice. (A) Representative views of aortic arch from the two groups of mice. Atherosclerotic plaque was found in the aortic arch from HFD mice, while plaque was not found in the aortic arch from ND mice. (B) Atherosclerotic lesions in Oil red O stained whole aorta from ND and HFD mice. (C) Representative histological images stained with Van Gieson’s staining from the different groups are shown. Quantification of (D) lesion areas based on Oil-red O staining and (E) elastin fragmentations based on Van Gieson staining in aortas from ND and HFD mice are shown. n = 5 per group. Plasma levels of (F) total cholesterol, (G) LDL-C and (H) HDL-C from ND and HFD mice were determined. Aortic arch PWV was directly proportional to total cholesterol in ND (R-squared = 0.6820, P = 0.0032) and HFD mice (R-squared = 0.6546, P = 0.0046), LDL-C in HFD mice (R-squared = 0.6323, P = 0.0059), and HDL-C in ND mice (R-squared = 0.4372, P = 0.0373), while was not proportional to LDL-C in ND mice (R-squared = 0.1548, P = 0.2606) and HDL-C in HFD mice (R-squared = 0.2131, P = 0.1793). LDL-C, low-density lipoprotein cholesterol; HDL-C, high-density lipoprotein cholesterol. n = 10 per group. *P < 0.05, **P < 0.01.