Remotely Triggered LAD Occlusion Using a Balloon Catheter in Spontaneously Breathing Mice.

Acute myocardial infarction (AMI) is a prevalent and high-mortality cardiovascular condition. Despite advancements in revascularization strategies for AMI, it frequently leads to myocardial ischemia-reperfusion injury (IRI), amplifying cardiac damage. Murine models serve as vital tools for investigating both acute injury and chronic myocardial remodeling in vivo. This study presents a unique closed-chest technique for remotely inducing myocardial IRI in mice, enabling the investigation of the very early phase of occlusion and reperfusion using in-vivo imaging such as MRI or PET. The protocol utilizes a remote occlusion method, allowing precise control over ischemia initiation after chest closure. It reduces surgical trauma, enables spontaneous breathing, and enhances experimental consistency. What sets this technique apart is its potential for simultaneous noninvasive imaging, including ultrasound and magnetic resonance imaging (MRI), during occlusion and reperfusion events. It offers a unique opportunity to analyze tissue responses in almost real-time, providing critical insights into processes during ischemia and reperfusion. Extensive systematic testing of this innovative approach was conducted, measuring cardiac necrosis markers for infarction, assessing the area at risk using contrast-enhanced MRI, and staining infarcts at the scar maturation stage. Through these investigations, emphasis was placed on the value of the proposed tool in advancing research approaches to myocardial ischemia-reperfusion injury and accelerating the development of targeted interventions. Preliminary findings demonstrating the feasibility of combining the proposed innovative experimental protocol with noninvasive imaging techniques are presented herein. These initial results highlight the benefit of utilizing the purpose-built animal cradle to remotely induce myocardial ischemia while simultaneously conducting MRI scans.

Acoustic Activation Imaging With Intravenous Perfluoropropane Nanodroplets Results in Selective Bioactivation of the Risk Area.

BACKGROUND: Acoustically activatable perfluoropropane droplets (PD) can be formulated from commercially available microbubble preparations. Diagnostic transthoracic ultrasound frequencies have resulted in acoustic activation (AA) predominately within myocardial infarct zones (IZ). OBJECTIVE: We hypothesized that the AA area following acute coronary ischemia/reperfusion (I/R) would selectively enhance the developing scar zone, and target bioeffects specifically to this region. METHODS: We administered intravenous PD in 36 rats and 20 pigs at various stages of myocardial scar formation (30 minutes, 1 day, and 7 days post I/R) to determine what effect infarct age had on the AA within the IZ. This was correlated with histology, myeloperoxidase activity, and tissue nitrite activity. RESULTS: The degree of AA within the IZ in rats was not associated with collagen content, neutrophil infiltration, or infarct age. AA within 24 hours of I/R was associated with increased nitric oxide utilization selectively within the IZ (P < .05 compared with remote zone). The spatial extent of AA in pigs correlated with infarct size only when performed before sacrifice at 7 days (r = .74, P < .01). CONCLUSIONS: Acoustic activation of intravenous PD enhances the developing scar zone following I/R, and results in selective tissue nitric oxide utilization.

Oxidation-reduction imaging of myoglobin reveals two-phase oxidation in the reperfused myocardium.

Myocardial infarction (MI) is a serious acute cardiovascular syndrome that causes myocardial injury due to blood flow obstruction to a specific myocardial area. Under ischemic-reperfusion settings, a burst of reactive oxygen species is generated, leading to redox imbalance that could be attributed to several molecules, including myoglobin. Myoglobin is dynamic and exhibits various oxidation-reduction states that have been an early subject of attention in the food industry, specifically for meat consumers. However, rarely if ever have the myoglobin optical properties been used to measure the severity of MI. In the current study, we develop a novel imaging pipeline that integrates tissue clearing, confocal and light sheet fluorescence microscopy, combined with imaging analysis, and processing tools to investigate and characterize the oxidation-reduction states of myoglobin in the ischemic area of the cleared myocardium post-MI. Using spectral imaging, we have characterized the endogenous fluorescence of the myocardium and demonstrated that it is partly composed by fluorescence of myoglobin. Under ischemia-reperfusion experimental settings, we report that the infarcted myocardium spectral signature is similar to that of oxidized myoglobin signal that peaks 3 h post-reperfusion and decreases with cardioprotection. The infarct size assessed by oxidation-reduction imaging at 3 h post-reperfusion was correlated to the one estimated with late gadolinium enhancement MRI at 24 h post-reperfusion. In conclusion, this original work suggests that the redox state of myoglobin can be used as a promising imaging biomarker for characterizing and estimating the size of the MI during early phases of reperfusion.

Quantitative visualization of myocardial ischemia-reperfusion-induced cardiac lesions via ferroptosis magnetic particle imaging.

Myocardial ischemia-reperfusion (MI/R) injury is a complication in vascular reperfusion therapy for MI, occurring in approximately 60% of patients. Ferroptosis is an important process in the development of MI/R cardiac lesions. Transferrin receptor 1 (TfR1), a marker of ferroptosis, corresponds to the changes in MI/R cardiac lesions and is expected to be a biomarker for detecting MI/R-induced ferroptosis. However, the noninvasive in vivo visualization of ferroptosis in MI/R is a big challenge. Thus, this study aimed to develop a novel multimodal imaging platform to identify markers of MI/R cardiac lesions in vivo through targeting TfR1. Methods: Magnetic particle imaging (MPI) modality for ferroptosis based on superparamagnetic cubic-iron oxide nanoparticles (SCIO NPs), named feMPI, has been developed. FeMPI used TfR1 as a typical biomarker. The feMPI probe (SCIO-ICG-CRT-CPPs NPs, CCI NPs) consists of SCIO NPs, TfR1-targeting peptides (CRT), cell-penetrating peptides (CPPs), and indocyanine green (ICG). The specificity and sensitivity of CCI NPs in the MI/R mouse model were evaluated by MPI, magnetic resonance imaging (MRI), and near-infrared (NIR) fluorescent imaging. Results: The intensity of the MPI signal correlates linearly with the percentage of infarct area in MI/R stained by TTC, enabling a quantitative assessment of the extent of cardiac lesions. Notably, these findings are consistent with the standard clinical biochemical indicators in MI/R within the first 24 h. FeMPI detects cardiac injury approximately 48 h prior to the current clinical imaging detection methods of MI/R. Conclusion: The feMPI strategy can be a powerful tool for studying the process of MI/R-induced ferroptosis in vivo, providing clues for molecular imaging and drug development of ferroptosis-related treatments.

Platelet membrane-derived biomimetic microbubbles with enhanced targeting ability for the early detection of myocardial ischemia-reperfusion injury.

Myocardial ischemia-reperfusion injury (MIRI) is a widely recognized cardiovascular disease that significantly impacts the prognosis of patients undergoing myocardial infarction recanalization. This condition can be fatal and involves complex pathophysiological mechanisms. Early diagnosis of MIRI is crucial to minimize myocardial damage and reducing mortality. Based on the inherent relationship between platelets and MIRI, we developed biomimetic microbubbles coated with platelet membrane (MB-pla) for early identification of MIRI. The MB-pla were prepared through a recombination process involving platelet membrane obtained from rat whole blood and phospholipids, blended in appropriate proportions. By coating the microbubbles with platelet membrane, MB-pla acquired various adhesion molecules, thereby gaining the capability to selectively adhere to damaged endothelial cells in the context of MIRI. In vitro experiments demonstrated that MB-pla exhibited remarkable targeting characteristics, particularly toward type IV collagen and human umbilical vein endothelial cells that had been injured through hypoxia/reoxygenation procedures. In a rat model of MIRI, the signal intensity produced by MB-pla was notably higher than that of control microbubbles. These findings were consistent with results obtained from fluorescence imaging of isolated hearts and immunofluorescence staining of tissue sections. In conclusion, MB-pla has great potential as a non-invasive early detection method for MIRI. Furthermore, this approach can potentially find application in other conditions involving endothelial injury in the future.

Dynamic Assessments of Coronary Flow Reserve after Myocardial Ischemia Reperfusion in Mice.

After cardiac ischemia, there is often insufficient myocardial perfusion, even if flow has been successfully and completely restored in an upstream artery. This phenomenon, known as the "no-reflow phenomenon," is attributed to coronary microvascular dysfunction and has been associated with poor clinical outcomes. In clinical practice, a reduction in coronary flow reserve (CFR) is frequently used as an indicator of coronary artery disease. CFR is defined as the ratio of the peak flow velocity induced by pharmacologic or metabolic factors to the resting flow velocity. This protocol focused on assessing the dynamic changes in CFR before and after ischemia-reperfusion (IR) using pulse wave Doppler measurements. In this study, normal mice exhibited the ability to increase the peak velocity of coronary blood flow up to two times higher than the resting values under isoflurane stimulation. However, after ischemia-reperfusion, the CFR at 1 h significantly decreased compared to the pre-operation baseline. Over time, the CFR showed gradual recovery, but it remained below the normal level. Despite the preservation of systolic function, early detection of microvascular dysfunction is crucial, and establishing a practical guide could aid doctors in this task, while also facilitating the study of cardiovascular disease progression over time.

Controlled Release of Hydrogen-Carrying Perfluorocarbons for Ischemia Myocardium-Targeting 19 F MRI-Guided Reperfusion Injury Therapy.

Hydrogen gas is recently proven to have anti-oxidative and anti-inflammation effects on ischemia-reperfusion injury. However, the efficacy of hydrogen therapy is limited by the efficiency of hydrogen storage, targeted delivery, and controlled release. In this study, H2 -PFOB nanoemulsions (NEs) is developed with high hydrogen loading capacity for targeted ischemic myocardium precision therapy. The hydrogen-carrying capacity of H2 -PFOB NEs is determined by gas chromatography and microelectrode methods. Positive uptake of H2 -PFOB NEs in ischemia-reperfusion myocardium and the influence of hydrogen on 19 F-MR signal are quantitatively visualized using a 9.4T MR imaging system. The biological therapeutic effects of H2 -PFOB NEs are examined on a myocardial ischemia-reperfusion injury mouse model. The results illustrated that the developed H2 -PFOB NEs can efficaciously achieve specific infiltration into ischemic myocardium and exhibit excellent antioxidant and anti-inflammatory properties on myocardial ischemia-reperfusion injury, which can be dynamically visualized by 19 F-MR imaging system. Moreover, hydrogen burst release induced by low-intensity focused ultrasound (LIFU) irradiation further promotes the therapeutic effect of H2 -PFOB NEs with a favorable biosafety profile. In this study, the potential therapeutic effects of H2 -PFOB NEs is fully unfolded, which may hold great potential for future hydrogen-based precision therapeutic applications tailored to ischemia-reperfusion injury.

Development of a Golgi-targeted superoxide anion fluorescent probe for elucidating protein GOLPH3 function in myocardial ischemia-reperfusion injury.

Superoxide anion (O2•-) is an important reactive oxygen species (ROS) and participates in various physiological and pathological processes in the organism. The O2•- burst induced by ischemia-reperfusion (I/R) is associated with cardiovascular disease and promotes the cell apoptosis. In this work, a turn-on type Golgi-targeting fluorescent probe Gol-Cou-O2•- was rationally designed for sensitive and selective detection of O2•-. The minimum detection limit concentration for O2•- was about 3.9 × 10-7 M in aqueous solution. Gol-Cou-O2•- showed excellent capacity of detecting exogenous and endogenous O2•- in living cells and zebrafish, and was also used to capture the up-regulated O2•- level during the duration of I/R process in cardiomyocytes. Golgi Phosphoprotein 3 (GOLPH3) is a potential Golgi stress marker protein and plays a key role in cells apoptosis during I/R. The fluorescence imaging and flow cytometry assay results indicated that silencing GOLPH3 through siRNA could give rise to the down-regulated O2•- level and alleviation of apoptosis in I/R myocardial cells. Thus, development of Gol-Cou-O2•- provides a diagnostic tool for myocardial oxidative stress injury and distinct insights on roles of GOLPH3 in myocardial I/R injury.

1,2,4,5-Tetrazine-tethered probes for fluorogenically imaging superoxide in live cells with ultrahigh specificity.

Superoxide (O2·-) is the primary reactive oxygen species in mammal cells. Detecting superoxide is crucial for understanding redox signaling but remains challenging. Herein, we introduce a class of activity-based sensing probes. The probes utilize 1,2,4,5-tetrazine as a superoxide-responsive trigger, which can be modularly tethered to various fluorophores to tune probe sensitivity and emission color. These probes afford ultra-specific and ultra-fluorogenic responses towards superoxide, and enable multiplexed imaging of various cellular superoxide levels in an organelle-resolved way. Notably, the probes reveal the aberrant superoxide generation in the pathology of myocardial ischemia/reperfusion injury, and facilitate the establishment of a high-content screening pipeline for mediators of superoxide homeostasis. One such identified mediator, coprostanone, is shown to effectively ameliorating oxidative stress-induced injury in mice with myocardial ischemia/reperfusion injury. Collectively, these results showcase the potential of 1,2,4,5-tetrazine-tethered probes as versatile tools to monitor superoxide in a range of pathophysiological settings.

Metformin confers longitudinal cardiac protection by preserving mitochondrial homeostasis following myocardial ischemia/reperfusion injury.

PURPOSE: Myocardial ischemia-reperfusion (I/R) injury is associated with systemic oxidative stress, cardiac mitochondrial homeostasis, and cardiomyocyte apoptosis. Metformin has been recognized to attenuate cardiomyocyte apoptosis. However, the longitudinal effects and pathomechanism of metformin on the regulation of myocardial mitohormesis following I/R treatment remain unclear. This study aimed to investigate the longitudinal effects and mechanism of metformin in regulating cardiac mitochondrial homeostasis by serial imaging with the 18-kDa translocator protein (TSPO)-targeted positron emission tomography (PET) tracer 18F-FDPA. METHODS: Myocardial I/R injury was established in Sprague-Dawley rats, which were treated with or without metformin (150 mg/kg per day). Serial gated 18F-FDG and 18F-FDPA PET imaging were performed at 1, 4, and 8 weeks after surgery, followed by analysis of ventricular remodelling and cardiac mitochondrial homeostasis. The correlation between Hsp60 and 18F-FDPA uptake was analyzed. After PET imaging, the activity of antioxidant enzymes, immunostaining, and western blot analysis were performed to analyze the spatio-temporal effects and pathomechanism of metformin for cardiac protection after myocardial I/R injury. RESULTS: Oxidative stress and apoptosis increased 1 week after myocardial I/R injury (before significant progression of ventricular remodelling). TSPO expression was correlated with Hsp60 expression and was co-localized with inflammatory CD68+ macrophages in the infarct area, and TSPO uptake was associated with an upregulation of AMPK-p/AMPK and a downregulation of Bcl-2/Bax. However, these effects were reversed with metformin treatment. Eight weeks after myocardial I/R injury (representing the advanced stage of heart failure), 18F-FDPA uptake in myocardial cells in the distal non-infarct area increased without CD68+ expression, whereas the activity decreased with metformin treatment. CONCLUSION: Taken together, these results show that a prolonged metformin treatment has pleiotropic protective effects against myocardial I/R injury associated with a regional and temporal dynamic balance between mitochondrial homeostasis and cardiac outcome, which were assessed by TSPO-targeted imaging during cardiac remodelling.

Recent advances in nanomedicines for imaging and therapy of myocardial ischemia-reperfusion injury.

Myocardial ischemia-reperfusion injury (IRI) is becoming a typical cardiovascular disease with increasing worldwide incidence. It is usually induced by the restoration of normal blood flow to the ischemic myocardium after a period of recanalization and directly leads to myocardial damage. Notably, the pathological mechanism of myocardial IRI is closely related to inflammation, oxidative stress, Ca2+ overload, and the opening of mitochondrial permeability transition pore channels. Therefore, monitoring of these changes and imaging lesions is a key to timely clinical diagnosis. Nanomedicines have shown great value in the diagnosis and treatment of myocardial IRI, with advantages including passive/active targeting, prolonged circulation, improved bioavailability, versatile carrier selection, and synergistic integration of different imaging and therapeutic agents in single particles with the same pharmaceutics. Because theranostic nanomedicines for myocardial IRI have advanced rapidly, we conduct an updated review on this topic. The special focus is on how to rationally design the nanomedicines to achieve optimal imaging and therapy. We hope this review would stimulate the interest of researchers with different backgrounds and expedite the development of nanomedicines for myocardial IRI.

Evaluation of myocardial viability in patients with myocardial ischemia reperfusion injury using the dual-energy CT myocardial blood pool imaging.

OBJECTIVES: To evaluate myocardial viability in patients with myocardial ischemia reperfusion injury (MIRI) via dual-energy computed tomography myocardial blood pool imaging (DECT MBPI). METHODS: Between September 2017 and January 2019, we prospectively recruited 59 patients with acute myocardial infarction (AMI) who developed MIRI after revascularization during invasive coronary angiography (ICA). Then, they received DECT MBPI, SPECT, and PET sequentially within 1 week after the onset of MIRI. A total of 1003 myocardial segments of 59 patients were recruited for this study. The iodine reduction areas and delayed enhancement areas were calculated by cardiac iodine map with SPECT rest myocardial perfusion imaging (MPI) + PET myocardial metabolism imaging (MMI) as reference criteria. The paired sample t-test was used to measure the difference of the myocardial iodine value. Cohen's Kappa analysis was used to test the consistency among different observers. ROC analysis was used to calculate the myocardial viability of DECT MBPI. RESULTS: ROC showed the AUCs of DECT MBPI iodine value to identify a normal myocardium, an ischemic myocardium, and an infarcted myocardium were 0.957, 0.900, and 0.906 (p < 0.001). The sensitivity, specificity, and accuracy of DECT MBPI in identifying an ischemic myocardium were 87.6%, 89.3%, and 97.9% (p < 0.001). The sensitivity, specificity, and accuracy of DECT MBPI in identifying an infarcted myocardium were 88.9%, 92.2%, and 98.6% (p < 0.001). The cutoff value for DECT MBPI to differentiate between an ischemic and a normal myocardium was 0.84 mg I/mL. The cutoff value for DECT MBPI to differentiate between an infarct and a normal myocardium was 2.01 mg I/mL. CONCLUSION: DECT MBPI can be used to assess myocardial viability in patients with MIRI with high sensitivity and specificity. KEY POINTS: • Dual-energy computed tomography myocardial blood pool imaging (DECT MBPI) can evaluate myocardial viability of myocardial ischemia-reperfusion injury (MIRI). • DECT MBPI is a non-invasive and timesaving method for evaluation on myocardial ischemia-reperfusion injury in patients with acute myocardial infarction after coronary intervention.

Light-Activated Gold-Selenium Core-Shell Nanocomposites with NIR-II Photoacoustic Imaging Performances for Heart-Targeted Repair.

Mitochondrial dysfunction and oxidative damage represent important pathological mechanisms of myocardial ischemia-reperfusion injury (MI/RI). Searching for potential antioxidant agents to attenuate MI/RI is of great significance in clinic. Herein, gold-selenium core-shell nanostructures (AS-I/S NCs) with good near-infrared (NIR)-II photoacoustic imaging were designed for MI/RI treatment. The AS-I/S NCs after ischemic myocardium-targeted peptide (IMTP) and mitochondrial-targeted antioxidant peptide SS31 modification achieved cardiomyocytes-targeted cellular uptake and enhanced antioxidant ability and significantly inhibited oxygen-glucose deprivation-recovery (OGD/R)-induced cardiotoxicity of H9c2 cells by inhibiting the depletion of mitochondrial membrane potential (MMP) and restoring ATP synthase activity. Furthermore, the AS-I/S NCs after SS31 modification achieved mitochondria-targeted inhibition of reactive oxygen species (ROS) and subsequently attenuated oxidative damage in OGD/R-treated H9c2 cells by inhibition of apoptosis and oxidative damage, regulation of MAPKs and PI3K/AKT pathways. The in vivo AS-I/S NCs administration dramatically improved myocardial functions and angiogenesis and inhibited myocardial fibrosis through inhibiting myocardial apoptosis and oxidative damage in MI/RI of rats. Importantly, the AS-I/S NCs showed good safety and biocompatibility in vivo. Therefore, our findings validated the rational design that mitochondria-targeted selenium-gold nanocomposites could attenuate MI/RI of rats by inhibiting ROS-mediated oxidative damage and regulating MAPKs and PI3K/AKT pathways, which could be a potential therapy for the MI/RI treatment.

Evaluating the cardioprotective effect of metformin on myocardial ischemia-reperfusion injury using dynamic 18F-FDG micro-PET/CT imaging.

BACKGROUND: The molecular mechanisms of protective effect of metformin (Met) on ischemic myocardium have not been fully understood. This study aims to evaluate the cardioprotective effect of metformin on myocardial ischemia-reperfusion injury (MIRI) in rat models at different time points using dynamic 18F-FDG micro-PET/CT imaging. METHODS: The I/R injury model in SD rats was established by ligation of left anterior descending coronary artery near the pulmonary arch root for 30 min. SD rats (n = 12) were randomly divided into 2 groups: Control group (n = 6) without any intervention and Met group (n = 6) with oral administration of metformin (50 mg/kg) twice a day. Gated 18F-FDG (40Mbq) micro-PET/CT imaging was performed for 10 min at different time points (day 1st, day 7th, day 14th and day 30th after operation). Volumes of interest were drawn to identify different myocardium regions (ischemia center, peri-ischemia area and remote area). Standardized uptake values (SUVs) (SUVmean and SUVmax) were analyzed to evaluate the FDG uptake activity, and then the center/remote ratio was calculated. In addition, the left ventricular (LV) end-diastolic volume (EDV), end-systolic volume (ESV) and LV ejection fraction (LVEF) were obtained. On the 30th day, all rats were scarified and myocardial ischemia was analyzed by HE staining and confirmed by pathology. RESULTS: In the Control group, the center/remote ratio showed no obvious change trend at each time point after reperfusion, while the LV EDV increased gradually over time, and they were significantly negatively correlated (r = - 0.507, p < 0.05). In the Met group, the center/remote ratio gradually increased with time, there was no significant correlation between center/remote ratio and LV EDV (r = - 0.078, p > 0.05). On the 30th day, the center/remote ratio of the Met group was significantly higher than that of the Control group (0.81 ± 0.06 vs. 0.65 ± 0.09, p < 0.05), while LV EDV in Met group was significantly lower than in Control group (358.21 ± 22.62 vs. 457.53 ± 29.91, p < 0.05). There was no significant difference of LVEF between Met group and Control group at different time points after reperfusion (p < 0.05). HE staining showed that the myocardial infarction and fibrosis in ischemic center area of the Control group was more serious than that of the Met group. CONCLUSIONS: Met could attenuate the severity of MIRI, delay and prevent the progress of LV remodeling. The cardioprotective progress could be dynamically assessed by 18F-FDG micro-PET/CT imaging.

Induction of Myocardial Infarction and Myocardial Ischemia-Reperfusion Injury in Mice.

Acute myocardial infarction is a common cardiovascular disease with high mortality. Myocardial reperfusion injury can counteract the beneficial effects of heart reflow and induce secondary myocardial injury. A simple and reproducible model of myocardial infarction and myocardial ischemia-reperfusion injury is a good tool for researchers. Here, a customizable method to create a myocardial infarction (MI) model and MIRI by precision ligation of the left anterior descending coronary artery (LAD) through micromanipulation is described. Accurate and reproducible ligature positioning of the LAD helps obtain consistent results for heart injury. ST-segment changes can help to identify model accuracy. The serum level of cardiac troponin T (cTnT) is used to assess the myocardial injury, cardiac ultrasound is employed to evaluate the myocardial systolic function, and Evans-Blue/triphenyl tetrazolium chloride staining is used to measure infarct size. In general, this protocol reduces procedure duration, ensures controllable infarct size, and improves mouse survival.

Intramyocardial Hemorrhage and the "Wave Front" of Reperfusion Injury Compromising Myocardial Salvage.

BACKGROUND: Reperfusion therapy for acute myocardial infarction (MI) is lifesaving. However, the benefit of reperfusion therapy can be paradoxically diminished by reperfusion injury, which can increase MI size. OBJECTIVES: Hemorrhage is known to occur in reperfused MIs, but whether hemorrhage plays a role in reperfusion-mediated MI expansion is not known. METHODS: We studied cardiac troponin kinetics (cTn) of ST-segment elevation MI patients (n = 70) classified by cardiovascular magnetic resonance to be hemorrhagic (70%) or nonhemorrhagic following primary percutaneous coronary intervention. To isolate the effects of hemorrhage from ischemic burden, we performed controlled canine studies (n = 25), and serially followed both cTn and MI size with time-lapse imaging. RESULTS: CTn was not different before reperfusion; however, an increase in cTn following primary percutaneous coronary intervention peaked earlier (12 hours vs 24 hours; P < 0.05) and was significantly higher in patients with hemorrhage (P < 0.01). In hemorrhagic animals, reperfusion led to rapid expansion of myocardial necrosis culminating in epicardial involvement, which was not present in nonhemorrhagic cases (P < 0.001). MI size and salvage were not different at 1 hour postreperfusion in animals with and without hemorrhage (P = 0.65). However, within 72 hours of reperfusion, a 4-fold greater loss in salvageable myocardium was evident in hemorrhagic MIs (P < 0.001). This paralleled observations in patients with larger MIs occurring in hemorrhagic cases (P < 0.01). CONCLUSIONS: Myocardial hemorrhage is a determinant of MI size. It drives MI expansion after reperfusion and compromises myocardial salvage. This introduces a clinical role of hemorrhage in acute care management, risk assessment, and future therapeutics.

Magnetic susceptibility and R2* of myocardial reperfusion injury at 3T and 7T.

PURPOSE: Magnetic susceptibility (Δχ) alterations have shown association with myocardial infarction (MI) iron deposition, yet there remains limited understanding of the relationship between relaxation rates and susceptibility or the effect of magnetic field strength. Hence, Δχ and R2∗ in MI were compared at 3T and 7T. METHODS: Subacute MI was induced by coronary artery ligation in male Yorkshire swine. 3D multiecho gradient echo imaging was performed at 1-week postinfarction at 3T and 7T. Quantitative susceptibility mapping images were reconstructed using a morphology-enabled dipole inversion. R2∗ maps and quantitative susceptibility mapping were generated to assess the relationship between R2∗ , Δχ, and field strength. Infarct histopathology was investigated. RESULTS: Magnetic susceptibility was not significantly different across field strengths (7T: 126.8 ± 41.7 ppb; 3T: 110.2 ± 21.0 ppb, P = NS), unlike R2∗ (7T: 247.0 ± 14.8 Hz; 3T: 106.1 ± 6.5 Hz, P < .001). Additionally, infarct Δχ and R2∗ were significantly higher than remote myocardium. Magnetic susceptibility at 7T versus 3T had a significant association (ß = 1.02, R2 = 0.82, P < .001), as did R2∗ (ß = 2.35, R2 = 0.98, P < .001). Infarct pathophysiology and iron deposition were detected through histology and compared with imaging findings. CONCLUSION: R2∗ showed dependence and Δχ showed independence of field strength. Histology validated the presence of iron and supported imaging findings.

Luteolin alleviates ischemia/reperfusion injury-induced no-reflow by regulating Wnt/ß-catenin signaling in rats.

The no-reflow phenomenon induced by ischemia-reperfusion (I/R) injury seriously limits the therapeutic value of coronary recanalization and leads to a poor prognosis. Previous studies have shown that luteolin (LUT) is a vasoprotective factor. However, whether LUT can be used to prevent the no-reflow phenomenon remains unknown. Positron emission tomography perfusion imaging, performed to detect the effects of LUT on the no-reflow phenomenon in vivo, revealed that LUT treatment was able to reduce the no-reflow area in rat I/R models. In vitro, LUT was shown to reduce the hypoxia-reoxygenation injury-induced endothelial permeability and apoptosis. The levels of malondialdehyde, reactive oxygen species and NADPH were also measured and the results indicated that LUT could inhibit the oxidative stress. Western blot analysis revealed that LUT protected endothelial cells from I/R injury by regulating the Wnt/ß-catenin pathway. Overall, we concluded that the use of LUT to minimize I/R induced microvascular damage is a feasible strategy to prevent the no-reflow phenomenon.

Restoring Cardiac Functions after Myocardial Infarction-Ischemia/Reperfusion via an Exosome Anchoring Conductive Hydrogel.

Both myocardial infarction (MI) and the follow-up reperfusion will lead to an inevitable injury to myocardial tissues, such as cardiac dysfunctions, fibrosis, and reduction of intercellular cell-to-cell interactions. Recently, exosomes (Exo) derived from stem cells have demonstrated a robust capability to promote angiogenesis and tissue repair. However, the short half-life of Exo and rapid clearance lead to insufficient therapeutic doses in the lesion area. Herein, an injectable conductive hydrogel is constructed to bind Exo derived from human umbilical cord mesenchymal stem cells to treat myocardial injuries after myocardial infarction-ischemia/reperfusion (MI-I/R). To this end, a hyperbranched epoxy macromer (EHBPE) grafted by an aniline tetramer (AT) was synthesized to cross-link thiolated hyaluronic acid (HA-SH) and thiolated Exo anchoring a CP05 peptide via an epoxy/thiol "click" reaction. The resulting Gel@Exo composite system possesses multiple features, such as controllable gelation kinetics, shear-thinning injectability, conductivity matching the native myocardium, soft and dynamic stability adapting to heartbeats, and excellent cytocompatibility. After being injected into injured hearts of rats, the hydrogel effectively prolongs the retention of Exo in the ischemic myocardium. The cardiac functions have been considerably improved by Gel@Exo administration, as indicated by the enhancing ejection fraction and fractional shortening, and reducing fibrosis area. Immunofluorescence staining and reverse transcription-polymerase chain reaction (RT-PCR) results demonstrate that the expression of cardiac-related proteins (Cx43, Ki67, CD31, and α-SMA) and genes (VEGF-A, VEGF-B, vWF, TGF-ß1, MMP-9, and Serca2a) are remarkably upregulated. The conductive Gel@Exo system can significantly improve cell-to-cell interactions, promote cell proliferation and angiogenesis, and result in a prominent therapeutic effect on MI-I/R, providing a promising therapeutic method for injured myocardial tissues.