ATP-dependent potassium channels and mitochondrial permeability transition pores play roles in the cardioprotection of theaflavin in young rat

Current understanding and future perspectives on the extraction, structures, and regulation of muscle function of tea pigments

With the aggravating aging of modern society, the sarcopenia-based aging syndrome poses a serious potential threat to the health of the elderly. Natural dietary supplements show great potential to reduce muscle wasting and enhance muscle performance. Tea has been widely recognized for its health-promoting effects. which contains active ingredients such as tea polyphenols, tea pigments, tea polysaccharides, theanine, caffeine, and vitamins. In different tea production processes, the oxidative condensation and microbial transformation of catechins and other natural substances from tea promotes the production of various tea pigments, including theaflavins (TFs), thearubigins (TRs), and theabrownins (TBs). Tea pigments have shown a positive effect on maintaining muscle health. Nevertheless, the relationship between tea pigments and skeletal muscle function has not been comprehensively elucidated. In addition, the numerous research on the extraction and purification of tea pigments is disordered with the limited recent progress due to the complexity of species and molecular structure. In this review, we sort out the strategies for the separation of tea pigments, and discuss the structures of tea pigments. On this basis, the regulation mechanisms of tea pigments on muscle functional were emphasized. This review highlights the current understanding on the extraction methods, molecular structures and regulation mechanisms of muscle function of tea pigments. Furthermore, main limitations and future perspectives are proposed to provide new insights into broadening theoretical research and industrial applications of tea pigments in the future.

Flavonoids as Modulators of Potassium Channels

Potassium channels are widely distributed integral proteins responsible for the effective and selective transport of K+ ions through the biological membranes. According to the existing structural and mechanistic differences, they are divided into several groups. All of them are considered important molecular drug targets due to their physiological roles, including the regulation of membrane potential or cell signaling. One of the recent trends in molecular pharmacology is the evaluation of the therapeutic potential of natural compounds and their derivatives, which can exhibit high specificity and effectiveness. Among the pharmaceuticals of plant origin, which are potassium channel modulators, flavonoids appear as a powerful group of biologically active substances. It is caused by their well-documented anti-oxidative, anti-inflammatory, anti-mutagenic, anti-carcinogenic, and antidiabetic effects on human health. Here, we focus on presenting the current state of knowledge about the possibilities of modulation of particular types of potassium channels by different flavonoids. Additionally, the biological meaning of the flavonoid-mediated changes in the activity of K+ channels will be outlined. Finally, novel promising directions for further research in this area will be proposed.

Flavonoids as new regulators of mitochondrial potassium channels: contribution to cardioprotection

Objectives

Acute myocardial ischemia is one of the major causes of illness in western society. Reduced coronary blood supply leads to cell death and loss of cardiomyocyte population, resulting in serious and often irreversible consequences on myocardial function. Mitochondrial potassium (mitoK) channels have been identified as fine regulators of mitochondrial function and, consequently, in the metabolism of the whole cell, and in the mechanisms underlying the cardioprotection. Interestingly, mitoK channels represent a novel putative target for treating cardiovascular diseases, particularly myocardial infarction, and their modulators represent an interesting tool for pharmacological intervention. In this review, we took up the challenge of selecting flavonoids that show cardioprotective properties through the activation of mitoK channels.

Key findings

A brief overview of the main information on mitoK channels and their participation in the induction of cytoprotective processes was provided. Then, naringenin, quercetin, morin, theaflavin, baicalein, epigallocatechin gallate, genistein, puerarin, luteolin and proanthocyanidins demonstrated to be effective modulators of mitoK channels activity, mediating many beneficial effects.

Summary

The pathophysiological role of mitoK channels has been investigated as well as the impact of flavonoids on this target with particular attention to their potential role in the prevention of cardiovascular disorders.

Mitochondrial Damage in Myocardial Ischemia/Reperfusion Injury and Application of Natural Plant Products

Ischemic heart disease (IHD) is currently one of the leading causes of death among cardiovascular diseases worldwide. In addition, blood reflow and reperfusion paradoxically also lead to further death of cardiomyocytes and increase the infarct size. Multiple evidences indicated that mitochondrial function and structural disorders were the basic driving force of IHD. We summed up the latest evidence of the basic associations and underlying mechanisms of mitochondrial damage in the event of ischemia/reperfusion (I/R) injury. This review then reviewed natural plant products (NPPs) which have been demonstrated to mitochondria-targeted therapeutic effects during I/R injury and the potential pathways involved. We realized that NPPs mainly maintained the integrality of mitochondria membrane and ameliorated dysfunction, such as improving abnormal mitochondrial calcium handling and inhibiting oxidative stress, so as to protect cardiomyocytes during I/R injury. This information will improve our knowledge of mitochondrial biology and I/R-induced injury's pathogenesis and exhibit that NPPs hold promise for translation into potential therapies that target mitochondria.

Protective effects of natural products against myocardial ischemia/reperfusion: Mitochondria-targeted therapeutics

Patients with ischemic heart disease receiving reperfusion therapy still need to face left ventricular remodeling and heart failure after myocardial infarction. Reperfusion itself paradoxically leads to further cardiomyocyte death and systolic dysfunction. Ischemia/reperfusion (I/R) injury can eliminate the benefits of reperfusion therapy in patients and causes secondary myocardial injury. Mitochondrial dysfunction and structural disorder are the basic driving force of I/R injury. We summarized the basic relationship and potential mechanisms of mitochondrial injury in the development of I/R injury. Subsequently, this review summarized the natural products (NPs) that have been proven to targeting mitochondrial therapeutic effects during I/R injury in recent years and related cellular signal transduction pathways. We found that these NPs mainly protected the structural integrity of mitochondria and improve dysfunction, such as reducing mitochondrial division and fusion abnormalities, improving mitochondrial Ca²⁺ overload and inhibiting reactive oxygen species overproduction, thereby playing a role in protecting cardiomyocytes during I/R injury. This data would deepen the understanding of I/R-induced mitochondrial pathological process and suggested that NPs are expected to be transformed into potential therapies targeting mitochondria.

Pharmacology of Catechins in Ischemia-Reperfusion Injury of the Heart

Catechins represent a group of polyphenols that possesses various beneficial effects in the cardiovascular system, including protective effects in cardiac ischemia-reperfusion (I/R) injury, a major pathophysiology associated with ischemic heart disease, myocardial infarction, as well as with cardioplegic arrest during heart surgery. In particular, catechin, (−)-epicatechin, and epigallocatechin gallate (EGCG) have been reported to prevent cardiac myocytes from I/R-induced cell damage and I/R-associated molecular changes, finally, resulting in improved cell viability, reduced infarct size, and improved recovery of cardiac function after ischemic insult, which has been widely documented in experimental animal studies and cardiac-derived cell lines. Cardioprotective effects of catechins in I/R injury were mediated via multiple molecular mechanisms, including inhibition of apoptosis; activation of cardioprotective pathways, such as PI3K/Akt (RISK) pathway; and inhibition of stress-associated pathways, including JNK/p38-MAPK; preserving mitochondrial function; and/or modulating autophagy. Moreover, regulatory roles of several microRNAs, including miR-145, miR-384-5p, miR-30a, miR-92a, as well as lncRNA MIAT, were documented in effects of catechins in cardiac I/R. On the other hand, the majority of results come from cell-based experiments and healthy small animals, while studies in large animals and studies including comorbidities or co-medications are rare. Human studies are lacking completely. The dosages of compounds also vary in a broad scale, thus, pharmacological aspects of catechins usage in cardiac I/R are inconclusive so far. Therefore, the aim of this focused review is to summarize the most recent knowledge on the effects of catechins in cardiac I/R injury and bring deep insight into the molecular mechanisms involved and dosage-dependency of these effects, as well as to outline potential gaps for translation of catechin-based treatments into clinical practice.

Evaluating the possible role of mitochondrial ATP-sensitive potassium channels in the cardioprotective effects of morin in the isolated rat heart

AIMS

During heart ischemia, the lack of oxygen in the myocardial cells causes pH and ion disturbances and cell death through opening mitochondrial permeability transition pores (mPTP). Considering the inhibitory effects of mitochondrial ATP-dependent potassium channels (mt-KATP) on these pores and anti-ischemic effects of morin, we hypothesized that it may exert its positive effects via activating mt-KATP as well as its anti-oxidative effects.

MAIN METHODS

Isolated rat hearts were perfused by Krebs-Henseleit solution enriched with the morin (0.25, 0.5 and 1 mg/L) or 5-hydroxydecanoate (5-HD, a mt-KATP blocker;100 μM) or both as needed 5 min before starting regional ischemia till the first 10 min of the reperfusion period. The reperfusion was developed with Krebs-Henseleit solution 60 or 120 min respectively for biochemical evaluations (lactate dehydrogenase and malondialdehyde level) or the assessment of myocardial infarct size. During the experiments, hemodynamic functions were recorded and cardiac arrhythmias were determined.

KEY FINDINGS

Our findings demonstrated that morin reduced the infarct size. Also, morin perfusion could remarkably prevent the malondialdehyde over-production during ischemia. Total ventricular ectopic beats had the same significant changes as the malondialdehyde level, in both ischemia and reperfusion phases. Morin could also relatively improve the ischemia-induced hemodynamic dysfunction. All mentioned protective effects of morin were reversed by concomitant perfusion of 5-HD.

SIGNIFICANCE

Morin has protective effects against ischemic hearts through anti-oxidative effects. It also suggests a link between the cardioprotective effects of morin and mt-KATP. However, additional studies are required to prove this preliminary hypothesis.

Cardioprotection and natural polyphenols: an update of clinical and experimental studies

Mechanisms involved in ischemia–reperfusion injury.

Oxidative Stress and Acute Kidney Injury in Critical Illness: Pathophysiologic Mechanisms-Biomarkers-Interventions, and Future Perspectives

Acute kidney injury (AKI) is a multifactorial entity that occurs in a variety of clinical settings. Although AKI is not a usual reason for intensive care unit (ICU) admission, it often complicates critically ill patients' clinical course requiring renal replacement therapy progressing sometimes to end-stage renal disease and increasing mortality. The causes of AKI in the group of ICU patients are further complicated from damaged metabolic state, systemic inflammation, sepsis, and hemodynamic dysregulations, leading to an imbalance that generates oxidative stress response. Abundant experimental and to a less extent clinical data support the important role of oxidative stress-related mechanisms in the injury phase of AKI. The purpose of this article is to present the main pathophysiologic mechanisms of AKI in ICU patients focusing on the different aspects of oxidative stress generation, the available evidence of interventional measures for AKI prevention, biomarkers used in a clinical setting, and future perspectives in oxidative stress regulation.

Remote ischaemic pre-conditioning for the prevention of acute kidney injury

Acute kidney injury (AKI) is a common complication associated with high morbidity and mortality in hospitalized patients. One potential mechanism underlying renal injury is ischaemia/reperfusion injury (IRI), which attributed the organ damage to the inflammatory and oxidative stress responses induced by a period of renal ischaemia and subsequent reperfusion. Therapeutic strategies that aim at minimizing the effect of IRI on the kidneys may prevent AKI and improve clinical outcomes significantly. In this review, we examine the technique of remote ischaemic preconditioning (rIPC), which has been shown by several trials to confer organ protection by applying transient, brief episodes of ischaemia at a distant site before a larger ischaemic insult. We provide an overview of the current clinical evidence regarding the renoprotective effect of rIPC in the key clinical settings of cardiac or vascular surgery, contrast-induced AKI, pre-existing chronic kidney disease (CKD) and renal transplantation, and discuss key areas for future research.

Remote Ischemic Preconditioning and Protection of the Kidney--A Novel Therapeutic Option

OBJECTIVE

Acute kidney injury is a common complication in critically ill patients and is associated with increased morbidity and mortality. Sepsis, major surgery, and nephrotoxic drugs are the most common causes of acute kidney injury. There is currently no effective strategy available to prevent or treat acute kidney injury. Therefore, novel treatment regimens are required to decrease acute kidney injury prevalence and to improve clinical outcomes. Remote ischemic preconditioning, triggered by brief episodes of ischemia and reperfusion applied in distant tissues or organs before the injury of the target organ, attempts to invoke adaptive responses that protect against acute kidney injury. We sought to evaluate the clinical evidence for remote ischemic preconditioning as a potential strategy to protect the kidney and to review the underlying mechanisms in light of recent studies.

DATA SOURCES

We searched PubMed for studies reporting the effect of remote ischemic preconditioning on kidney function in surgical patients (search terms: "remote ischemic preconditioning," "kidney function," and "surgery"). We also reviewed bibliographies of relevant articles to identify additional citations.

STUDY SELECTION

Published studies, consisting of randomized controlled trials, are reviewed.

DATA EXTRACTION

The authors used consensus to summarize the evidence behind the use of remote ischemic preconditioning.

DATA SYNTHESIS

In addition, the authors suggest patient populations and clinical scenarios in which remote ischemic preconditioning might be best applied.

CONCLUSIONS

Several experimental and clinical studies have shown tissue-protective effects of remote ischemic preconditioning in various target organs, including the kidneys. Remote ischemic preconditioning may offer a novel, noninvasive, and inexpensive treatment strategy for decreasing acute kidney injury prevalence in high-risk patients. Although many new studies have further advanced our knowledge in this area, the appropriate intensity of remote ischemic preconditioning, its mechanisms of action, and the role of biomarkers for patient selection and monitoring are still unknown.

Condensed catechins and their potential health-benefits

Condensed catechins are commonly present in fermented tea, and are produced by the oxidation of monomeric catechins. Due to their auto-oxidation, catechins have diverse structural features, including different binding modes and degrees of polymerization. Because of their structural complexity, their physiological functions and possible health-benefits have not yet been fully investigated. This review focuses on the physiological potentials of dimeric and trimeric catechins in the intestine (regulation of absorption across the intestinal membrane), blood vessels (vasorelaxation in vessel regulation), and muscle organs (promotion of glucose uptake resulting in an anti-diabetic effect). Furthermore, the roles of non-absorbable theaflavins (dimeric catechins), absorbable theasinensins (dimeric catechins), and absorbable procyanidins (dimeric and trimeric catechins) on target organs are discussed.

K(ATP) channels and MPTP are involved in the cardioprotection bestowed by chronic intermittent hypobaric hypoxia in the developing rat

The aim of this study was to explore the mechanism underlying the cardioprotection bestowed by chronic intermittent hypobaric hypoxia (CIHH) against ischemia/reperfusion (I/R) injury in developing rats. Neonatal male rats were subjected to CIHH treatments that simulated an altitude of 3000 m a.s.l. for 28 days (CIHH28) and 42 days (CIHH42), respectively, or no treatment (control). The left ventricular function of isolated hearts was evaluated. The ultra-microstructure, superoxide dismutase (SOD) activity and total anti-oxidation capacity (TAC) of the myocardium were determined. The basic left ventricular function remained unchanged in CIHH rats, except for an increased coronary flow. The recovery of cardiac function from I/R, however, was much better in CIHH rats than in control rats. Compared to control rats, CIHH rats had much higher SOD levels and TAC, and the ultra-microstructure damage to mitochondria was considerably less. The cardiac protection of CIHH was canceled out by glibenclamide, an inhibitor of the ATP-sensitive potassium (K(ATP)) channel, 5-hydroxydecanoate, an inhibitor of mitochondrial K(ATP) (mitoKATP), and atractyloside, an opener of the mitochondrial permeability transition pore (MPTP). To the contrary, diazoxide, an opener of mitoKATP, and cyclosporin A, a blocker of MPTP opening, induced cardioprotection in control rats. These results suggest that CIHH protects the heart against I/R injury in developing rats through opening of the K(ATP) channel and inhibiting of opening of the MPTP.

Flavonoids and mitochondrial pharmacology: A new paradigm for cardioprotection

Acute myocardial ischemia is one of the major causes of illness and of deaths in Western society; therefore the definition of the signaling pathways involved in the cardioprotection represents a challenging goal in order to discover novel pharmacological approaches. In this regard, a number of epidemiologic studies demonstrate a relationship between intake of flavonoid-rich foods and reduction of cardiovascular risk factors and mortality. Moreover, numerous experimental studies have examined flavonoid-induced cardioprotective effects on several animal models of myocardial ischemia/reperfusion. As concerns the mechanisms of action, although the antioxidant effect of flavonoids has been long thought to be a crucial factor accounting for cardioprotection, mitochondrial pathways (ion channels, protein kinases, etc.) are presently emerging as specific pharmacological targets more relevantly involved in the anti-ischemic effects of some flavonoids. Since these pharmacodynamic features seem to be poorly considered, this review examines the mitochondrial role in the cardioprotective mechanisms of some members of this phytochemical class, by describing the biological pathways and reporting an overview of the most important experimental evidence in this field.

Contribution of apoptosis in myocardial reperfusion injury and loss of cardioprotection in diabetes mellitus

Ischemic heart disease is one of the major causes of death worldwide. Ischemia is a condition in which blood flow of the myocardium declines, leading to cardiomyocyte death. However, reperfusion of ischemic regions decreases the rate of mortality, but it can also cause later complications. In a clinical setting, ischemic heart disease is always coincident with other co-morbidities such as diabetes. The risk of heart disease increases 2-3 times in diabetic patients. Apoptosis is considered to be one of the main pathophysiological mechanisms of myocardial ischemia-reperfusion injury. Diabetes can disrupt the anti-apoptotic intracellular signaling cascades involved in myocardial protection. Therefore, targeting these changes may be an effective cardioprotective approach in the diabetic myocardium against ischemia-reperfusion injury. In this article, we review the interaction of diabetes with the pathophysiology of myocardial ischemia-reperfusion injury, focusing on the contribution of apoptosis in this context, and then discuss the alterations of pro-apoptotic or anti-apoptotic pathways probably responsible for the loss of cardioprotection in diabetes.

Anti-arrhythmic effect of diosgenin in reperfusion-induced myocardial injury in a rat model: activation of nitric oxide system and mitochondrial KATP channel

This study was designed to investigate the anti-arrhythmic effect of diosgenin preconditioning in myocardial reperfusion injury in rat, focusing on the involvement of the nitric oxide (NO) system and mitochondrial ATP-dependent potassium (mitoKATP) channels in this scenario. After isolation of the hearts of male Wister rats, the study was conducted in an isolated buffer-perfused heart model. Global ischemia (for 30 min) was induced by interruption of the aortic supply, which was followed by 90-min reperfusion. Throughout the experiment, the electrocardiograms of hearts were monitored using three golden surface electrodes connected to a data acquisition system. Arrhythmias were assessed based on the Lambeth convention and were categorized as number, duration and incidence of ventricular tachycardia (VT), ventricular fibrillation (VF), and premature ventricular complexes (PVC), and arrhythmic score. Additionally, lactate dehydrogenase (LDH) levels in coronary effluent were estimated colorimetrically. Diosgenin pre-administration for 20 min before ischemia reduced the LDH release into the coronary effluent, as compared with control hearts (P < 0.05). In addition, the diosgenin-receiving group showed a lower number of PVC, VT and VF, a reduced duration and incidence of VT and VF, and less severe arrhythmia at reperfusion phase, in comparison with controls. Blocking the mitoKATP channels using 5-hydroxydecanoate as well as inhibiting the NO system through prior administration of L-NAME significantly reduced the positive effects of diosgenin. Our finding showed that pre-administration of diosgenin could provide cardioprotection through anti-arrhythmic effects against ischemia-reperfusion (I/R) injury in isolated rat hearts. In addition, mitoKATP channels and NO system may be the key players in diosgenin-induced cardioprotective mechanisms.

Polyphenols and mitochondria: an update on their increasingly emerging ROS-scavenging independent actions

Polyphenols, ubiquitously present in fruits and vegetables, have been traditionally viewed as antioxidant molecules. Such contention emerged, mainly from their well established in vitro ability to scavenge free radicals and other reactive oxygen species (ROS). During the last decade, however, increasing evidence has emerged supporting the ability of certain polyphenols to also exert numerous ROS-scavenging independent actions. Although the latter can comprise the whole cell, particular attention has been placed on the ability of polyphenols to act, whether favorably or not, on a myriad of mitochondrial processes. Thus, some particular polyphenols are now recognized as molecules capable of modulating pathways that define mitochondrial biogenesis (i.e., inducing sirtuins), mitochondrial membrane potential (i.e., mitochondrial permeability transition pore opening and uncoupling effects), mitochondrial electron transport chain and ATP synthesis (i.e., modulating complexes I to V activity), intra-mitochondrial oxidative status (i.e., inhibiting/inducing ROS formation/removal enzymes), and ultimately mitochondrially-triggered cell death (i.e., modulating intrinsic-apoptosis). The present review describes recent evidence on the ability of some polyphenols to modulate each of the formerly mentioned pathways, and discusses on how, by acting on such mitochondrial processes, polyphenols may afford protection against those mitochondrial damaging events that appear to be key in the cellular toxicity induced by various xenobiotics as well as that seen during the development of several ROS-related diseases.

The effects of bioactive compounds from plant foods on mitochondrial function: a focus on apoptotic mechanisms

Mitochondria are essential organelles for cellular integrity and functionality maintenance and their imparement is implicated in the development of a wide range of diseases, including metabolic, cardiovascular, degenerative and hyperproliferative pathologies. The identification of different compounds able to interact with mitochondria for therapeutic purposes is currently becoming of primary importance. Indeed, it is well known that foods, particularly those of vegetable origin, present several constituents with beneficial effects on health. This review summarizes and updates the most recent findings concerning the mechanisms through which different dietary compounds from plant foods affect mitochondria functionality in healthy and pathological in vitro and in vivo models, paying particular attention to the pathways involved in mitochondrial biogenesis and apoptosis.

Mitochondrial permeability transition pore plays a role in the cardioprotection of CB2 receptor against ischemia–reperfusion injury

The aim of this study was to investigate whether the mitochondrial permeability transition pore (MPTP) opening was involved in the protective effects of CB2 receptor against ischemia–reperfusion (I-R) injury. For this, isolated perfused rat hearts were subjected to 30 min global ischemia followed by 120 min reperfusion, and left ventricle function was recorded. At the end of reperfusion, the infarct size in the hearts was measured by staining with triphenyltetrazolium chloride. MPTP opening and the mitochondrial membrane potential (ΔΨm) were measured by flow cytometry. Western blot analysis of cytochrome c in the mitochondrion and cytosol, as well as ERK1/2 and p-ERK1/2 were performed. Administration of CB2 receptor agonist JWH133 before ischemia significantly improved the recovery of cardiac ventricular function during reperfusion, increased coronary flow, reduced infarct size, prevented the loss of ΔΨm and MPTP opening, reduced the release of cytochrome c from mitochondria, and increased levels of p-ERK1/2. These effects of JWH133 were abolished by pretreatment with CB2 receptor antagonist AM630, or ERK1/2 inhibitor PD98059. Furthermore, JWH133 reversed the MPTP opening induced by atractyloside. The protective effect of JWH133 on the heart against I-R injury may be through increased ERK1/2 phosphorylation, inhibiting MPTP opening.

Chronic exposure to valproic acid promotes insulin release, reduces KATP channel current and does not affect Ca (2+) signaling in mouse islets

Hyperinsulinemia is one of the reported side effects of valproic acid (VPA), a medicine used to treat epilepsy. However, its underlying mechanism remains unknown. The present study was designed to investigate a direct effect of VPA on insulin secretion by using mouse pancreactic islets and β-cells. VPA had no acute effect on insulin secretion from islets, or on cytosolic Ca(2+) ([Ca(2+)]i) in single β-cells. However, following long-term exposure to VPA (48 h), both basal and glucose-stimulated insulin secretion were markedly elevated (5-fold), while the insulin gene expression level was unaltered. Following long-term exposure to VPA, β-cells showed a decrease in whole cell KATP channel current. However, the increase in [Ca(2+)]i in response to the sulfonylurea drug, tolbutamide was attenuated. The present study shows that VPA has no acute effects, but long-term treatment results in enhancement of both basal and glucose-stimulated insulin secretion. This long-term effect may mediate the KATP channel, while VPA can also attenuate the effect of the KATP channel blocker tolbutamide.

Remote ischemic preconditioning and renoprotection: from myth to a novel therapeutic option?

There is currently no effective prophylactic regimen available to prevent contrast-induced AKI (CI-AKI), a frequent and life-threatening complication after cardiac catheterization. Therefore, novel treatment strategies are required to decrease CI-AKI incidence and to improve clinical outcomes in these patients. Remote ischemic preconditioning (rIPC), defined as transient brief episodes of ischemia at a remote site before a subsequent prolonged ischemia/reperfusion injury of the target organ, is an adaptational response that protects against ischemic and reperfusion insult. Indeed, several studies demonstrated the tissue-protective effects of rIPC in various target organs, including the kidneys. In this regard, rIPC may offer a novel noninvasive and virtually cost-free treatment strategy for decreasing CI-AKI incidence. This review evaluates the current experimental and clinical evidence for rIPC as a potential renoprotective strategy, and discusses the underlying mechanisms and key areas for future research.