Hypoxia enhances the therapeutic potential of superparamagnetic iron oxide-labeled adipose-derived stem cells for myocardial infarction.

Adipose-derived stem cells (ASCs) induce therapeutic angiogenesis due to pro-angiogenic cytokines secretion. Superparamagnetic iron oxide (SPIO) nanoparticles are critical for magnetic resonance (MR) tracking of implanted cells. Hypoxia is a powerful stimulus for angiogenic activity of ASCs. In this study, we investigated whether therapeutic potency could be enhanced by implantation of hypoxia-preconditioned SPIO-labeled ASCs (SPIOASCs) into the infarcted myocardium. ASCs and SPIOASCs were cultured under 2% O2 (hypoxia) or 95% air (normoxia). Cells were intramyocardially injected into the infarcted myocardium after 48-h culture. We found that hypoxia culture increased the mRNA expression of hypoxia-inducible factor-1 alpha (HIF-1α) and vascular endothelial growth factor (VEGF) in ASCs and SPIOASCs. The VEGF protein in the conditioned medium was significantly higher in hypoxic ASCs and SPIOASCs than in normoxic ASCs and SPIOASCs. The capillary density and left ventricular contractile function in the infarcted myocardium were significantly higher 4 weeks after implantation with hypoxic ASCs and SPIOASCs than with normoxic ASCs and SPIOASCs. Improvement in the capillary density and left ventricle function didn't differ between hypoxic ASCs-transplanted rats and hypoxic SPIOASCs-transplanted rats. Hypoxic culture enhanced the angiogenic efficiency of ASCs. It was concluded that implantation of hypoxic ASCs or SPIOASCs promotes therapeutic angiogenesis and cardiac function recovery in the infarcted myocardium. SPIO labeling does not impact the beneficial effect of hypoxic ASCs.

Hypoxia Enhances the Therapeutic Potential of Superparamagnetic Iron Oxide-labeled Adipose-derived Stem Cells for Myocardial Infarction / 华中科技大学学报（医学）（英德文版）

Adipose-derived stem cells (ASCs) induce therapeutic angiogenesis due to pro-angiogenic cytokines secretion.Superparamagnetic iron oxide (SPIO) nanoparticles are critical for magnetic resonance (MR) tracking of implanted cells.Hypoxia is a powerful stimulus for angiogenic activity of ASCs.In this study,we investigated whether therapeutic potency could be enhanced by implantation of hypoxia-preconditioned SPIO-labeled ASCs (SPIOASCs) into the infarcted myocardium.ASCs and SPIOASCs were cultured under 2％ O2 (hypoxia) or 95％ air (normoxia).Cells were intramyocardially injected into the infarcted myocardium after 48-h culture.We found that hypoxia culture increased the mRNA expression of hypoxia-inducible factor-1 alpha (HIF-lαt) and vascular endothelial growth factor (VEGF) in ASCs and SPIOASCs.The VEGF protein in the conditioned medium was significantly higher in hypoxic ASCs and SPIOASCs than in normoxic ASCs and SPIOASCs.The capillary density and left ventricular contractile function in the infarcted myocardium were significantly higher 4 weeks after implantation with hypoxic ASCs and SPIOASCs than with normoxic ASCs and SPIOASCs.Improvement in the capillary density and left ventricle function didn't differ between hypoxic ASCs-transplanted rats and hypoxic SPIOASCs-transplanted rats.Hypoxic culture enhanced the angiogenic efficiency of ASCs.It was concluded that implantation of hypoxic ASCs or SPIOASCs promotes therapeutic angiogenesis and cardiac function recovery in the infarcted myocardium.SPIO labeling does not impact the beneficial effect of hypoxic ASCs.

Collateral circulation formation determines the characteristic profiles of contrast-enhanced MRI in the infarcted myocardium of pigs.

AIM: To investigate the relationship between the collateral circulation and contrast-enhanced MR signal change for myocardial infarction (MI) in pigs. METHODS: Pigs underwent permanent ligation of two diagonal branches of the left anterior descending artery. First-pass perfusion (FPP) MRI (for detecting myocardial perfusion abnormalities) and delayed enhancement (DE) MRI (for estimating myocardial infarction) using Gd-DTPA were performed at 2 h, 7 d and 4 weeks after the coronary occlusion. Myocardial blood flow (MBF) was evaluated using nonradioactive red-colored microspheres. Histological examination was performed to characterize the infarcts. RESULTS: Acute MI performed at 2 h afterwards was characterized by hypoenhancement in both FPP- and DE-MRI, with small and almost unchanged FPP-signal intensity (SI) and DE-SI due to negligible MBF. Subacute MI detected 7 d afterwards showed small but significantly increaseing FPP-SI, and was visible as a sluggish hyperenhancement in DE-MRI with considerably higher DE-SI compared to the normal myocardium; the MBF approached the half-normal value. Chronic MI detected at 4 weeks afterwards showed increasing FPP-SI comparable to the normal myocardium, and a rapid hyperenhancement in DE-MRI with even higher DE-SI; the MBF was close to the normal value. The MBF was correlated with FPP-SI (r=+0.94, P<0.01) and with the peak DE-SI (r=+0.92, P<0.01) at the three MI stages. Remodeled vessels were observed at intra-infarction and peri-infarction zones during the subacute and chronic periods. CONCLUSION: Progressive collateral recovery determines the characteristic profiles of contrast-enhanced MRI in acute, subacute and chronic myocardial infarction in pigs. The FPP- and DE-MRI signal profiles not only depend on the loss of tissue viability and enlarged interstitial space, but also on establishing a collateral circulation.

[Ischemic myocardial viability assessment with interleaved T1-T2* magnetic resonance imaging].

OBJECTIVE: To investigate the value of ischemic myocardial viability assessment using interleaved T1-T2* magnetic resonance imaging. METHODS: The left anterior descending coronary arteries (LAD) were occluded for 2 hours, followed by 1-hour reperfusion in 7 pigs. The hearts were then removed and perfused with a mixture of pig blood and crystalloid solution in 1:1 ratio. T1 relaxation times of the myocardium were measured with a TurboFLASH inversion-recovery sequence. The contrast agent, Gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA) was then injected as a bolus into the aortic perfusion line (0.05 mmol/kg body wt). The first pass of the contrast agent through the heart was followed using the interleaved T1-T2* imaging sequence. Once the concentration of Gd-DTPA was in an equilibrium state, T1 relaxation times were measured again. RESULTS: The percentage recovery of T2* intensity (PRT2*) at the maximum T1 intensity measured during the first pass of the contrast agent with the interleaved T1-T2* imaging was statistically different in normal myocardium (37 +/- 11)%, infarct rim (90 +/- 15)% and infarct core (100 +/- 5)%, F = 66.585, P = 0.000. Moreover, the infarcted regions shown on PR(T2)* maps matched well with the infarcted myocardium measured by TTC staining. The median of T(1) relaxation time in normal region, infarct rim and infarct core was 531 ms, 541 ms and 1298 ms, respectively (H = 6.284, P = 0.043). However, normal region could not be differentiated from infarct rim with T1 relaxation times (q = 0.082, P = 0.775). CONCLUSION: Infarcted myocardium and ischemic myocardial viability can be correctly identified and evaluated by the interleaved T1-T2* magnetic resonance imaging in this model.

Identification of chronic myocardial infarction with extracellular or intravascular contrast agents in magnetic resonance imaging.

AIM: To determine whether extracellular or intravascular contrast agents could detect chronic scarred myocardium in magnetic resonance imaging (MRI). METHODS: Eighteen pigs underwent a 4 week ligation of 1 or 2 diagonal coronary arteries to induce chronic myocardial infarction. The hearts were then removed and perfused in a Langendorff apparatus. Eighteen hearts were divided into 2 groups. The hearts in groups I (n=9) and II (n=9) received the bolus injection of Gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA, 0.05 mmol/kg) and gadolinium- based macromolecular agent (P792, 15 micromol/kg), respectively. First pass T2* MRI was acquired using a FLASH sequence. Delayed enhancement T1 MRI was acquired with an inversion recovery prepared TurboFLASH sequence. RESULTS: Wash-in of both agents resulted in a sharp and dramatic T2* signal loss of scarred myocardium similar to that of normal myocardium. The magnitude and velocity of T2* signal recovery caused by wash-out of extracellular agents in normal myocardium was significantly less than that in scarred myocardium. Conversely, the T2* signal of scarred and normal myocardium recovered to plateau rapidly and simultaneously due to wash-out of intravascular agents. At the following equilibrium, extracellular agent-enhanced T1 signal intensity was significantly greater in scarred myocardium than in normal myocardium, whereas there was no significantly statistical difference in intravascular agent-enhanced T1 signal intensity between scarred and normal myocardium. CONCLUSION: After administration of extracellular agents, wash-out T2* first-pass and delayed enhanced T1 MRI could identify scarred myocardium as a hyperenhanced region. Conversely, scarred myocardium was indistinguishable from normal myocardium during first-pass and the steady state of intravascular agents.