Ischemia-reperfusion injury: Complex pathophysiology with elusive treatment

Preconditioning with selective autoretroperfusion: In vivo and in silico evidence of washout hypothesis

Introduction

Prompt reperfusion of coronary artery after acute myocardial infarction (AMI) is crucial for minimizing heart injury. The myocardium, however, may experience additional injury due to the flow restoration itself (reperfusion injury, RI). The purpose of this study was to demonstrate that short preconditioning (10 min) with selective autoretroperfusion (SARP) ameliorates RI, based on a washout hypothesis.

Methods

AMI was induced in 23 pigs (3 groups) by occluding the left anterior descending (LAD) artery. In SARP-b (SARP balloon inflated) and SARP-nb (SARP balloon deflated) groups, arterial blood was retroperfused for 10 min via the great cardiac vein before releasing the arterial occlusion. A mathematical model of coronary circulation was used to simulate the SARP process and evaluate the potential washout effect.

Results

SARP restored left ventricular function during LAD occlusion. Ejection fraction in the SARP-b group returned to baseline levels, compared to SARP-nb and control groups. Infarct area was significantly larger in the control group than in the SARP-b and SARP-nb groups. End-systolic wall thickness was preserved in the SARP-b compared to the SARP-nb and control groups. Analyte values (pH, lactate, glucose, and others), measured every 2 min during retroperfusion, suggest a "washout" effect as one important mechanism of action of SARP in reducing infarct size. With SARP, the values progressively approached baseline levels. The mathematical model also confirmed a possible washout effect of tracers.

Discussion

RI can be ameliorated by delaying restoration of arterial flow for a brief period of time while pretreating the infarction with SARP to restore homeostasis via a washout mechanism.

The mechanism by which miR-494-3p regulates PGC1-α-mediated inhibition of mitophagy in cardiomyocytes and alleviation of myocardial ischemia-reperfusion injury

OBJECTIVE

The purpose of this study was to explore whether miR-494-3p inhibits the occurrence of mitochondrial autophagy in cardiomyocytes by inhibiting the expression of PGC1-α and to supplement the theoretical basis for the role of autophagy in cardiac injury induced by hypoxia/reperfusion (H/R).

METHODS

The expression of miR-494-3p was detected by RT‒qPCR, and the expression of PGC1-α, autophagy-related proteins (LC3, Beclin 1), apoptosis-related proteins (Bax and Bcl-2), PINK1/Parkin signaling pathway-related proteins (PINK1, Parkin) and mitochondrial change-related proteins (Mfn1, Mfn2, OPA1) was detected by Western blotting. The changes in mitochondrial membrane potential were detected by JC-1 staining (ΔΨm). The formation of autophagosomes was observed by transmission electron microscopy. Cell proliferation activity was detected by CCK-8, and cell apoptosis was detected by flow cytometry. A dual-luciferase gene reporter assay identified a targeted binding site between miR-494-3p and PGC1-α.

RESULTS

The results showed that miR-494-3p and PGC1-α were differentially expressed in H/R cardiomyocytes; that is, the expression of miR-494-3p was downregulated, and the expression of PGC1-α was upregulated. In addition, mitochondrial autophagy occurred in H/R cardiomyocytes. That is, LC3-II/LC3-I, Beclin 1, PINK1, and Parkin expression was upregulated, Mfn1, Mfn2, and OPA1 expression was downregulated, and the mitochondrial membrane potential was decreased. The transfection of miR-494-3p mimic can significantly improve the cell proliferation activity of cardiomyocytes and inhibit the occurrence of cardiomyocyte apoptosis and autophagy, while the transfection of miR-494-3p inhibitor has the opposite result. After transfection of the miR-494-3p mimic, treatment with autophagy inhibitors and activators changed the effects of miR-494-3p on cardiomyocyte proliferation and apoptosis. At the same time, the overexpression of PGC1-α reversed the promoting effect of miR-494-3p on cardiomyocyte proliferation and the inhibitory effect on apoptosis and autophagy.

CONCLUSION

MiR-494-3p can target and negatively regulate the expression of PGC1-α to inhibit mitophagy in cardiomyocytes.

lncRNA DLX6-AS1 Promotes Myocardial Ischemia-Reperfusion Injury through Mediating the miR-204-5p/FBXW7 Axis

Myocardial ischemia-reperfusion (IR) injury is the restoration of blood flow post ischemia, which threatens the human life. Long noncoding RNA distal-less homeobox 6 antisense 1 (DLX6-AS1) has been found to take part in the IR-induced cerebral injury. Here, we determined the functional role of DLX6-AS1 in IR-induced myocardial injury. We ligated the left anterior descending coronary artery of rats to induce IR injury. IR injury rats exhibited severe tissue damage and increase of infraction size. The levels of lactate dehydrogenase (LDH), creatine kinase (CK), proinflammatory factors including MCP-1, IL-6, and IL-1β, and cell apoptosis were also enhanced in IR rats, indicating that IR induced significant myocardial injury in rats. DLX6-AS1 expression was elevated in the myocardial tissues of IR injury rats, while DLX6-AS1 deficiency alleviated IR-induced myocardial injury in rats by reducing inflammatory response and cell apoptosis. Moreover, rat embryonic cardiomyocyte cell line H9c2 was subjected to hypoxia reoxygenation (HR). DLX6-AS1 was upregulated in the HR-treated H9c2 cells, and DLX6-AS1 enhanced the expression of F-box and WD40 repeat domain-containing 7 (FBXW7) by sponging miR-204-5p. Inhibition of DLX6-AS1 inhibited inflammatory response and cell apoptosis in H9c2 cells via miR-204-5p/FBXW7 axis. In conclusion, this work demonstrates that DLX6-AS1 accelerates myocardial IR injury through regulating miR-204-5p/FBXW7 axis. Thus, this work provides a novel ceRNA DLX6-AS1/miR-204-5p/FBXW7 axis in myocardial IR injury, and DLX6-AS1 may be a potential target for the treatment of myocardial IR injury.

Endless Journey of Adenosine Signaling in Cardioprotective Mechanism of Conditioning Techniques: Clinical Evidence

Myocardial ischemic injury is a primary cause of death among various cardiovascular disorders. The condition occurs due to an interrupted supply of blood and vital nutrients (necessary for normal cellular activities and viability) to the myocardium, eventually leading to damage. Restoration of blood supply to ischemic tissue is noted to cause even more lethal reperfusion injury. Various strategies, including some conditioning techniques, like preconditioning and postconditioning, have been developed to check the detrimental effects of reperfusion injury. Many endogenous substances have been proposed to act as initiators, mediators, and end effectors of these conditioning techniques. Substances, like adenosine, bradykinin, acetylcholine, angiotensin, norepinephrine, opioids, etc., have been reported to mediate cardioprotective activity. Among these agents, adenosine has been widely studied and suggested to have the most pronounced cardioprotective effects. The current review article highlights the role of adenosine signaling in the cardioprotective mechanism of conditioning techniques. The article also provides an insight into various clinical studies that substantiate the applicability of adenosine as a cardioprotective agent in myocardial reperfusion injury.

Inhibited HDAC3 or Elevated MicroRNA-494-3p Plays a Protective Role in Myocardial Ischemia-Reperfusion Injury via Suppression of BRD4

Increased histone deacetylase 3 (HDAC3) has been demonstrated to contribute to the pathogenesis of myocardial ischemia-reperfusion injury (MI/RI). Therefore, the goal of this study was to investigate how HDAC3 regulated MI/RI by mediating microRNA (miR)-494-3p/dromodomain-containing protein 4 (BRD4) axis. The MI/RI model was established by ligating the right anterior descending coronary artery. Cardiomyocytes from newborn mice were treated with hypoxia/reoxygenation (H/R). Gain-of-function and loss-of-function approaches were implemented to figure out the roles of miR-494-3p and HDAC3 in MI/RI. miR-494-3p, HDAC3, and BRD4 in myocardial tissues of mice with MI/RI and H/R-treated cardiomyocytes were detected. The relationships between miR-494-3p and HDAC3 and BRD4 were identified. Reduced miR-494-3p and upregulated HDAC3 and BRD4 exhibited in myocardial tissues of mice with MI/RI and H/R-treated cardiomyocytes. Inhibited HDAC3 or elevated miR-494-3p repressed the inflammation and apoptosis, improved cardiac function, and ameliorated myocardial injury in myocardial tissues of mice with MI/RI. Suppression of HDAC3 or elevation of miR-494-3p depressed inflammation and apoptosis and promoted cell viability of primary cardiomyocytes. miR-494-3p targeted BRD4. The study concludes that suppressed HDAC3 plays a protective role in MI/RI by upregulation of miR-494-3p and inhibition of BRD4, which could be helpful for MI/RI therapy.

Puerarin protects cardiomyocytes from ischemia-reperfusion injury by upregulating LncRNA ANRIL and inhibiting autophagy

This study analyzed the roles of puerarin and LncRNA ANRIL in myocardial ischemia-reperfusion injury. Hypoxia/reperfusion (H/R) model was established with H9C2 cells. Effects of puerarin of gradient concentrations on cardiomyocytes at different time points of hypoxia and reoxygenation were detected by quantitative real-time polymerase chain reaction (qRT-PCR), cell counting kit-8 (CCK-8), and microscope observation. Effects of puerarin on cardiomyocyte viability, ANRIL expression, contents of lactate dehydrogenase (LDH) and malondialdehyde (MDA), apoptosis, and expressions of autophagy-related genes after H/R injury were determined by CCK-8, quantitative real-time polymerase chain reaction (qRT-PCR), ELISA, flow cytometry, and Western blot, respectively. After cell transfection, the effects of overexpressed and knockdown of ANRIL on cardiomyocytes and H/R-injured cardiomyocytes were examined by rescue experiments. The ischemia-reperfusion (I/R)-injured rat model was established to examine the protective effect of puerarin in vivo. Prolonged hypoxia downregulated ANRIL expression in cardiomyocytes and reduced cardiomyocyte viability. Prolonged reoxygenation increased apoptosis. Both cardiomyocyte viability and ANRIL expression showed a dose-dependent relationship with puerarin. Puerarin reversed the effects of H/R injury on cardiomyocyte viability, ANRIL expression, contents of LDH and MDA, apoptosis, and expressions of autophagy-related genes. Overexpression and knockdown of ANRIL regulated the functions of cardiomyocytes and the expressions of autophagy-related genes. Puerarin reversed the effects of knockdown of ANRIL on H/R-injured cells. The results of In vivo experiments confirmed that puerarin protected myocardial tissues by up-regulating ANRIL and inhibiting autophagy.