Arterial stiffening precedes systolic hypertension in diet-induced obesity

Abstract

Stiffening of conduit arteries is a risk factor for cardiovascular morbidity. Aortic wall stiffening increases pulsatile hemodynamic forces that are detrimental to the microcirculation in highly perfused organs, such as the heart, brain, and kidney. Arterial stiffness is associated with hypertension but presumed to be due to an adaptive response to increased hemodynamic load. In contrast, a recent clinical study found that stiffness precedes and may contribute to the development of hypertension although the mechanisms underlying hypertension are unknown. Here, we report that in a diet-induced model of obesity, arterial stiffness, measured in vivo, develops within 1 month of the initiation of the diet and precedes the development of hypertension by 5 months. Diet-induced obese mice recapitulate the metabolic syndrome and are characterized by inflammation in visceral fat and aorta. Normalization of the metabolic state by weight loss resulted in return of arterial stiffness and blood pressure to normal. Our findings support the hypothesis that arterial stiffness is a cause rather than a consequence of hypertension.

Keywords: hypertension; inflammation; obesity; pulse wave velocity; vascular stiffness.

Figure 1. Arterial stiffness precedes hypertension in diet-induced obese mice

Pulse wave velocity (PWV, mm/ms), an index of arterial stiffness measured by Doppler echocardiography, mean ± SD, n=4-10 each group (A) and invasively with high-fidelity pressure catheters, mean ± SEM, n=8 each group (B) is increased in HFHS-fed mice within 2 months. Mean arterial pressure was modulated by intravenous infusion of phenylephrine (0.1 μg/g BW). *, p<0.05 vs ND or ND-baseline; ^#, p<0.05 vs HFHS-baseline; ^$, p<0.05 vs ND-phenylephrine. Mice develop systolic hypertension after 6 months of HFHS (C) compared to ND (D). SBP, systolic blood pressure. *, p<0.05 vs baseline (time 0) or ND.

Figure 2. Impaired NO bioavailability and aortic inflammation in diet-induced obese mice

(A) Vasorelaxation to acetylcholine (1×10⁻⁹-1×10⁻⁵ mol/L) in aortas from mice fed ND or HFHS diet. n=5 each group; *, p<0.05. (B) Transglutaminase-2 (TG-2) activity, an index of NO bioavailability, measured on aortic lysates from ND- and HFHS-fed mice. Dot blot intensity quantitation expressed graphically as % normal diet. n=4 each group. *, p<0.05. (C) Inflammatory cytokines TNFα, MCP-1 and MIP1α mRNA were significantly upregulated in aortic extracts from HFHS-fed mice (n=8) compared to ND (n=8). Data are expressed as fold change over ND. *, p<0.05.

Figure 3. Reversal to normal diet reduces arterial stiffness and hypertension in HFHS-fed mice

(A) Body weights (BW, g) and PWV (mm/ms) in HFHS-fed mice decreased to control values after reversal to ND. n=8 each group; *, p<0.05 vs ND-baseline; ^#, p<0.05 vs HFHS-baseline. (B) Reversal to ND rapidly reduced fat mass (g, left y axis) and plasma insulin levels (μg/L, right y axis) in obese mice. n=4-14 in each group. (C) Systolic (SBP) and mean arterial (MAP) pressures of obese mice were significantly decreased after reversal to ND while diastolic pressure (DBP) did not change (n=6). *, p< 0.05 vs baseline. Baseline indicates 5 months on diet (ND or HFHS) and Reversal indicates 4 months of ND after 5 months of HFHS or ND.

Figure 4. In vitro aortic stiffness and medial area are increased in diet-induced obesity

(A) Stiffness modulus (kPa) on aortic rings subjected to 0.1 μm indentation was increased in HFHS-fed mice and reduced to normal values after reversal to ND (HFHS/ND). n=7-10 each group; ***, p<0.0005 vs ND. (B) Medial area of thoracic aortas from HFHS-fed mice was significantly increased compared to ND and was not affected by reversal to ND; n=4-8; *, p<0.05 vs ND. (C) HFHS-induced inflammatory cytokines TNFα, MCP-1 and MIP1α mRNA in aortic extracts were reduced to normal levels after reversal to ND (n=8 each group). Data are expressed as fold change over ND. *, p<0.05 vs ND; ^#, p<0.05 vs HFHS.

Figure 5. Aortic extracellular matrix crosslinks and oxidant stress are induced by HFHS and reduced after diet reversal

Representative pictures of (A) extracellular matrix N-ε-(γ-glutamyl)-lysine crosslinks (10X magnification), indicative of TG-2 activity, and (B) SERCA sulphonylated at cysteine 674 (OxSERCA) (40X magnification), used as index of oxidants, in aortas from ND-, HFHS-fed mice and after reversal to ND (HFHS/ND). n=8-16; *, p<0.05 vs ND; ^#, p<0.05 vs HFHS. Graphs indicate immunostaining intensities (expressed in millions of pixels). For a color version, see Figure S6 in supplemental material.