Low-intensity pulsed ultrasound enhances angiogenesis and ameliorates contractile dysfunction of pressure-overloaded heart in mice

<div><p>Introduction</p><p>Chronic left ventricular (LV) pressure overload causes relative ischemia with resultant LV dysfunction. We have recently demonstrated that low-intensity pulsed ultrasound (LIPUS) improves myocardial ischemia in a pig model of chronic myocardial ischemia through enhanced myocardial angiogenesis. In the present study, we thus examined whether LIPUS also ameliorates contractile dysfunction in LV pressure-overloaded hearts.</p><p>Methods and results</p><p>Chronic LV pressure overload was induced with transverse aortic constriction (TAC) in mice. LIPUS was applied to the whole heart three times in the first week after TAC and was repeated once a week for 7 weeks thereafter (n = 22). Animals in the control groups received the sham treatment without LIPUS (n = 23). At 8 weeks after TAC, LV fractional shortening was depressed in the TAC-Control group, which was significantly ameliorated in the TAC-LIPUS group (30.4±0.5 vs. 36.2±3.8%, P<0.05). Capillary density was higher and perivascular fibrosis was less in the LV in the TAC-LIPUS group than in the TAC-Control group. Myocardial relative ischemia evaluated with hypoxyprobe was noted in the TAC-Control group, which was significantly attenuated in the TAC-LIPUS group. In the TAC-LIPUS group, as compared with the control group, mRNA expressions of BNP and collagen III were significantly lower (both P<0.05) and protein expressions of VEGF and eNOS were significantly up-regulated associated with Akt activation (all P<0.05). No adverse effect related to the LIPUS therapy was noted.</p><p>Conclusions</p><p>These results indicate that the LIPUS therapy ameliorates contractile dysfunction in chronically pressure-overloaded hearts through enhanced myocardial angiogenesis and attenuated perivascular fibrosis. Thus, the LIPUS therapy may be a promising, non-invasive treatment for cardiac dysfunction due to chronic pressure overload.</p></div

Intracellular signaling pathways for the beneficial effects of the LIPUS.

<p>The LIPUS therapy ameliorates cardiac contractile dysfunction by enhancing angiogenesis through up-regulation of VEGF, eNOS and p-Akt and attenuating perivascular fibrosis through down-regulation of collagen III in the LV, suppressing the transition from compensated LVH to decompensated HF.</p

Study protocol.

<p>(A) Study protocol. LIPUS was applied to the whole heart three times in the first week after TAC and was thereafter repeated once a week for 7 weeks in the LIPUS group, while the control group underwent the same procedures but without the LIPUS therapy. (B) Study setup. (C) Peak flow velocity at TAC. (D) Heart weight/body weight (HW/BW). (E) Lung weight /body weight (LW/BW). Results are expressed as mean±SD.</p

The LIPUS therapy ameliorates cardiac contractile dysfunction.

<p>(A) Representative echocardiographic images at 8 weeks after TAC. (B~G) Graphs showing the time course of anterior wall thickness (AWT) and posterior wall thickness (PWT) of the LV, LV dimension at end-diastole (LVDd), LVD at end-systole (LVDs), LV fractional shortening (LVFS), and LV ejection fraction (LVEF). Results are expressed as mean±SD. n.s., not statistically significant. Statistical analysis was performed at 8 weeks after TAC.</p

The LIPUS therapy activates the angiogenic signaling pathways.

<p>Protein levels of VEGF and eNOS, phosphorylation state of eNOS (Ser1177), Akt and ERK1/2, and protein levels of CD31 (n = 3, 3, 6, 6 for each group). Results are expressed as mean±SD.</p