Metformin attenuates early brain injury after subarachnoid hemorrhage in rats via AMPK-dependent mitophagy

Mitochondrial quality control in human health and disease

Mitochondria, the most crucial energy-generating organelles in eukaryotic cells, play a pivotal role in regulating energy metabolism. However, their significance extends beyond this, as they are also indispensable in vital life processes such as cell proliferation, differentiation, immune responses, and redox balance. In response to various physiological signals or external stimuli, a sophisticated mitochondrial quality control (MQC) mechanism has evolved, encompassing key processes like mitochondrial biogenesis, mitochondrial dynamics, and mitophagy, which have garnered increasing attention from researchers to unveil their specific molecular mechanisms. In this review, we present a comprehensive summary of the primary mechanisms and functions of key regulators involved in major components of MQC. Furthermore, the critical physiological functions regulated by MQC and its diverse roles in the progression of various systemic diseases have been described in detail. We also discuss agonists or antagonists targeting MQC, aiming to explore potential therapeutic and research prospects by enhancing MQC to stabilize mitochondrial function.

Mitochondrial dysfunction and quality control lie at the heart of subarachnoid hemorrhage

The dramatic increase in intracranial pressure after subarachnoid hemorrhage leads to a decrease in cerebral perfusion pressure and a reduction in cerebral blood flow. Mitochondria are directly affected by direct factors such as ischemia, hypoxia, excitotoxicity, and toxicity of free hemoglobin and its degradation products, which trigger mitochondrial dysfunction. Dysfunctional mitochondria release large amounts of reactive oxygen species, inflammatory mediators, and apoptotic proteins that activate apoptotic pathways, further damaging cells. In response to this array of damage, cells have adopted multiple mitochondrial quality control mechanisms through evolution, including mitochondrial protein quality control, mitochondrial dynamics, mitophagy, mitochondrial biogenesis, and intercellular mitochondrial transfer, to maintain mitochondrial homeostasis under pathological conditions. Specific interventions targeting mitochondrial quality control mechanisms have emerged as promising therapeutic strategies for subarachnoid hemorrhage. This review provides an overview of recent research advances in mitochondrial pathophysiological processes after subarachnoid hemorrhage, particularly mitochondrial quality control mechanisms. It also presents potential therapeutic strategies to target mitochondrial quality control in subarachnoid hemorrhage.

Neuroprotection via Carbon Monoxide Depends on the Circadian Regulation of CD36-Mediated Microglial Erythrophagocytosis in Hemorrhagic Stroke

The molecular basis for circadian dependency in stroke due to subarachnoid hemorrhagic stroke (SAH) remains unclear. We reasoned that microglial erythrophagocytosis, crucial for SAH response, follows a circadian pattern involving carbon monoxide (CO) and CD36 surface expression. The microglial BV-2 cell line and primary microglia (PMG) under a clocked medium change were exposed to blood ± CO (250 ppm, 1 h) in vitro. Circadian dependency and the involvement of CD36 were analyzed in PMG isolated from control mice and CD36-/- mice and by RNA interference targeting Per-2. In vivo investigations, including phagocytosis, vasospasm, microglia activation and spatial memory, were conducted in an SAH model using control and CD36-/- mice at different zeitgeber times (ZT). In vitro, the surface expression of CD36 and its dependency on CO and phagocytosis occurred with changed circadian gene expression. CD36-/- PMG exhibited altered circadian gene expression, phagocytosis and impaired responsiveness to CO. In vivo, control mice with SAH demonstrated circadian dependency in microglia activation, erythrophagocytosis and CO-mediated protection at ZT2, in contrast to CD36-/- mice. Our study indicates that circadian rhythmicity modulates microglial activation and subsequent CD36-dependent phagocytosis. CO altered circadian-dependent neuroprotection and CD36 induction, determining the functional outcome in a hemorrhagic stroke model. This study emphasizes how circadian rhythmicity influences neuronal damage after neurovascular events.

Mechanisms and therapeutic targets of mitophagy after intracerebral hemorrhage

Mitochondria are dynamic organelles responsible for cellular energy production. In addition to regulating energy homeostasis, mitochondria are responsible for calcium homeostasis, clearance of damaged organelles, signaling, and cell survival in the context of injury and pathology. In stroke, the mechanisms underlying brain injury secondary to intracerebral hemorrhage are complex and involve cellular hypoxia, oxidative stress, inflammatory responses, and apoptosis. Recent studies have shown that mitochondrial damage and autophagy are essential for neuronal metabolism and functional recovery after intracerebral hemorrhage, and are closely related to inflammatory responses, oxidative stress, apoptosis, and other pathological processes. Because hypoxia and inflammatory responses can cause secondary damage after intracerebral hemorrhage, the restoration of mitochondrial function and timely clearance of damaged mitochondria have neuroprotective effects. Based on studies on mitochondrial autophagy (mitophagy), cellular inflammation, apoptosis, ferroptosis, the BNIP3 autophagy gene, pharmacological and other regulatory approaches, and normobaric oxygen (NBO) therapy, this article further explores the neuroprotective role of mitophagy after intracerebral hemorrhage.

Targeting mitophagy for neurological disorders treatment: advances in drugs and non-drug approaches

Mitochondria serve as a vital energy source for nerve cells. The mitochondrial network also acts as a defense mechanism against external stressors that can threaten the stability of the nervous system. However, excessive accumulation of damaged mitochondria can lead to neuronal death. Mitophagy is an essential pathway in the mitochondrial quality control system and can protect neurons by selectively removing damaged mitochondria. In most neurological disorders, dysfunctional mitochondria are a common feature, and drugs that target mitophagy can improve symptoms. Here, we reviewed the role of mitophagy in Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, Huntington's disease, stroke, and traumatic brain injuries. We also summarized drug and non-drug approaches to promote mitophagy and described their therapeutic role in neurological disorders in order to provide valuable insight into the potential therapeutic agents available for neurological disease treatment. However, most studies on mitophagy regulation are based on preclinical research using cell and animal models, which may not accurately reflect the effects in humans. This poses a challenge to the clinical application of drugs targeting mitophagy. Additionally, these drugs may carry the risk of intolerable side effects and toxicity. Future research should focus on the development of safer and more targeted drugs for mitophagy.

Melatonin alleviates early brain injury by inhibiting the NRF2-mediated ferroptosis pathway after subarachnoid hemorrhage

Ferroptosis is a novel form of cell death that plays a critical role in the pathological and physiological processes of early brain injury following subarachnoid hemorrhage. Melatonin, as the most potent endogenous antioxidant, has shown strong protective effects against pathological changes following subarachnoid hemorrhage, but its impact on ferroptosis induced by subarachnoid hemorrhage remains unexplored. In our study, we established a subarachnoid hemorrhage model in male SD rats. We found that subarachnoid hemorrhage induced changes in ferroptosis-related indicators such as lipid peroxidation and iron metabolism, while intraperitoneal injection of melatonin (40 mg/kg) effectively ameliorated these changes to a certain degree. Moreover, in a subset of rats with subarachnoid hemorrhage who received pre-treatment via intravenous injection of the melatonin receptor antagonist Luzindole (1 mg/kg) and 4P-PDOT (1 mg/kg), we found that the protective effect of melatonin against subarachnoid hemorrhage includes inhibition of lipid peroxidation and reduction of iron accumulation depended on melatonin receptor 1B (MT2). Furthermore, our study demonstrated that melatonin inhibited neuronal ferroptosis by activating the NRF2 signaling pathway, as evidenced by in vivo inhibition of NRF2. In summary, melatonin acts through MT2 and activates NRF2 and downstream genes such as HO-1/NQO1 to inhibit ferroptosis in subarachnoid hemorrhage-induced neuronal injury, thereby improving neurological function in rats. These results suggest that melatonin is a promising therapeutic target for subarachnoid hemorrhage.

Contribution and therapeutic value of mitophagy in cerebral ischemia-reperfusion injury after cardiac arrest

Cardiopulmonary resuscitation and related life support technologies have improved substantially in recent years; however, mortality and disability rates from cardiac arrest (CA) remain high and are closely associated with the high incidence of cerebral ischemia-reperfusion injury (CIRI), which is explained by a "double-hit" model (i.e., resulting from both ischemia and reperfusion). Mitochondria are important power plants in the cell and participate in various biochemical processes, such as cell differentiation and signaling in eukaryotes. Various mitochondrial processes, including energy metabolism, calcium homeostasis, free radical production, and apoptosis, are involved in several important stages of the progression and development of CIRI. Mitophagy is a key mechanism of the endogenous removal of damaged mitochondria to maintain organelle function and is a critical target for CIRI treatment after CA. Mitophagy also plays an essential role in attenuating ischemia-reperfusion in other organs, particularly during post-cardiac arrest myocardial dysfunction. Regulation of mitophagy may influence necroptosis (a programmed cell death pathway), which is the main endpoint of organ ischemia-reperfusion injury. In this review, we summarize the main signaling pathways related to mitophagy and their associated regulatory proteins. New therapeutic methods and drugs targeting mitophagy in ischemia-reperfusion animal models are also discussed. In-depth studies of the mechanisms underlying the regulation of mitophagy will enhance our understanding of the damage and repair processes in CIRI after CA, thereby contributing to the development of new therapeutic strategies.

Metformin alleviates cerebral ischemia/reperfusion injury aggravated by hyperglycemia via regulating AMPK/ULK1/PINK1/Parkin pathway-mediated mitophagy and apoptosis

Stroke remains the main leading cause of death and disabilities worldwide, with diabetes mellitus being a significant independent risk factor for it. Metformin, as an efficient hypoglycemic drug in treating type 2 diabetes, has been reported to alleviate the risk of diabetes-related stroke. However, its underlying mechanisms remain unclear. This study aimed to investigate the role of mitophagy and its regulatory pathway in the neuroprotective mechanism of metformin against cerebral ischemia/reperfusion (I/R) injury aggravated by hyperglycemia. A hyperglycemic cerebral I/R animal model and a high glucose cultured oxygen-glucose deprivation/reperfusion (OGD/R) cell model were used in the experiment. The indexes of brain injury, cell activity, mitochondrial morphology and function, mitophagy, mitochondrial pathway apoptosis and the AMPK pathway were observed. In diabetic rats, metformin treatment decreased cerebral infarction volume and neuronal apoptosis, and improved neurological symptoms following I/R injury. Additionally, metformin induced activation of the AMPK/ULK1/PINK1/Parkin mitophagy pathway to have neuroprotective effects. In vitro, high glucose culture and OGD/R treatment impaired mitochondrial morphology and function, mitochondrial membrane potential, and induced apoptosis. However, metformin activated AMPK/ULK1/PINK1/Parkin mitophagy pathway, normalized mitochondrial injury. This protection was reversed by autophagy inhibitor 3-methyladenine (3MA) and AMPK inhibitor compound C. In conclusion, our present study validates the potential mechanism of metformin in alleviating hyperglycemia aggravated cerebral I/R injury by the activation of AMPK/ULK1/PINK1/Parkin mitophagy pathway.

Effects of early adjunctive pharmacotherapy on serum levels of brain injury biomarkers in patients with traumatic brain injury: a systematic review of randomized controlled studies

Objectives: Traumatic brain injury (TBI) is one of the top causes of morbidity and mortality worldwide. The review aimed to discuss and summarize the current evidence on the effectiveness of adjuvant neuroprotective treatments in terms of their effect on brain injury biomarkers in TBI patients. Methods: To identify relevant studies, four scholarly databases, including PubMed, Cochrane, Scopus, and Google Scholar, were systematically searched using predefined search terms. English-language randomized controlled clinical trials reporting changes in brain injury biomarkers, namely, neuron-specific enolase (NSE), glial fibrillary acid protein (GFAP), ubiquitin carboxyl-terminal esterase L1 (UCHL₁) and/or S100 beta (S100 ß), were included. The methodological quality of the included studies was assessed using the Cochrane risk-of-bias tool. Results: A total of eleven studies with eight different therapeutic options were investigated; of them, tetracyclines, metformin, and memantine were discovered to be promising choices that could improve neurological outcomes in TBI patients. The most utilized serum biomarkers were NSE and S100 ß followed by GFAP, while none of the included studies quantified UCHL₁. The heterogeneity in injury severity categories and measurement timing may affect the overall evaluation of the clinical efficacy of potential therapies. Therefore, unified measurement protocols are highly warranted to inform clinical decisions. Conclusion: Few therapeutic options showed promising results as an adjuvant to standard care in patients with TBI. Several considerations for future work must be directed towards standardizing monitoring biomarkers. Investigating the pharmacotherapy effectiveness using a multimodal biomarker panel is needed. Finally, employing stratified randomization in future clinical trials concerning potential confounders, including age, trauma severity levels, and type, is crucial to inform clinical decisions. Clinical Trial Registration: [https://www.crd.york.ac.uk/prospero/dis], identifier [CRD42022316327].

Autophagy regulates inflammation in intracerebral hemorrhage: Enemy or friend?

Intracerebral hemorrhage (ICH) is the second-largest stroke subtype and has a high mortality and disability rate. Secondary brain injury (SBI) is delayed after ICH. The main contributors to SBI are inflammation, oxidative stress, and excitotoxicity. Harmful substances from blood and hemolysis, such as hemoglobin, thrombin, and iron, induce SBI. When cells suffer stress, a critical protective mechanism called "autophagy" help to maintain the homeostasis of damaged cells, remove harmful substances or damaged organelles, and recycle them. Autophagy plays a critical role in the pathology of ICH, and its function remains controversial. Several lines of evidence demonstrate a pro-survival role for autophagy in ICH by facilitating the removal of damaged proteins and organelles. However, many studies have found that heme and iron can aggravate SBI by enhancing autophagy. Autophagy and inflammation are essential culprits in the progression of brain injury. It is a fascinating hypothesis that autophagy regulates inflammation in ICH-induced SBI. Autophagy could degrade and clear pro-IL-1β and apoptosis-associated speck-like protein containing a CARD (ASC) to antagonize NLRP3-mediated inflammation. In addition, mitophagy can remove endogenous activators of inflammasomes, such as reactive oxygen species (ROS), inflammatory components, and cytokines, in damaged mitochondria. However, many studies support the idea that autophagy activates microglia and aggravates microglial inflammation via the toll-like receptor 4 (TLR4) pathway. In addition, autophagy can promote ICH-induced SBI through inflammasome-dependent NLRP6-mediated inflammation. Moreover, some resident cells in the brain are involved in autophagy in regulating inflammation after ICH. Some compounds or therapeutic targets that regulate inflammation by autophagy may represent promising candidates for the treatment of ICH-induced SBI. In conclusion, the mutual regulation of autophagy and inflammation in ICH is worth exploring. The control of inflammation by autophagy will hopefully prove to be an essential treatment target for ICH.

Autophagy and Glycometabolic Reprograming in the Malignant Progression of Lung Cancer: A Review

Lung cancer is one of the leading causes of cancer-related deaths worldwide. However, there are currently limited treatment options that are widely available to patients with advanced lung cancer, and further research is required to inhibit or reverse disease progression more effectively. In lung and other solid tumor cancers, autophagy and glycometabolic reprograming are critical regulators of malignant development, including proliferation, drug resistance, invasion, and metastasis. To provide a theoretical basis for therapeutic strategies targeting autophagy and glycometabolic reprograming to prevent lung cancer, we review how autophagy and glycometabolism are regulated in the malignant development of lung cancer based on research progress in other solid tumors.

Oxidative Stress and Intracranial Hypertension after Aneurysmal Subarachnoid Hemorrhage

Intracranial hypertension is a common phenomenon in patients with aneurysmal subarachnoid hemorrhage (aSAH). Elevated intracranial pressure (ICP) plays an important role in early brain injuries and is associated with unfavorable outcomes. Despite advances in the management of aSAH, there is no consensus about the mechanisms involved in ICP increases after aSAH. Recently, a growing body of evidence suggests that oxidative stress (OS) may play a crucial role in physio-pathological changes following aSAH, which may also contribute to increased ICP. Herein, we discuss a potential relation between increased ICP and OS, and resultantly propose antioxidant mechanisms as a potential therapeutic strategy for the treatment of ICP elevation following aSAH.

Neuropharmacological efficacy of metformin for stroke in rodents: A meta-analysis of preclinical trials

Background: Stroke, including ischemic stroke, intracerebral hemorrhage, and subarachnoid hemorrhage (SAH), remains a leading cause of mortality globally. Different stroke subtypes have similar detrimental effects in multiple fields of health. Previous research has shown that metformin plays a neuroprotective role in experimental animal models of stroke; however, a preclinical quantitative analysis on the ability of metformin to treat stroke is still lacking. This meta-analysis evaluates the efficacy of metformin in improving stroke prognosis in rodent models of stroke. Methods: Relevant preclinical trials were retrieved from PubMed, EMBASE, and the Web of Science. The neurological score (NS), brain water content (BWC), infarct size, rotarod test, TUNEL, neuron quantity, microglia quantity, and p-AMPK levels were compared between a control group and a metformin group using the standardized mean difference (SMD) and corresponding confidence interval (CI). Quality was assessed with SYRCLE's risk of bias tool. Results: Fifteen articles published from 2010 to 2022 were included in the meta-analysis. The metformin group had statistically significant differences compared to the control group in the following aspects: NS (SMD -1.45; 95% CI -2.32, -0.58; p = 0.001), BWC (SMD -3.22; 95% CI -4.69, -1.76; p < 0.0001), infarct size (SMD -2.90; 95% CI -3.95, -1.85; p < 0.00001), rotarod test (SMD 2.55; 95% CI 1.87, 3.23; p < 0.00001), TUNEL (SMD -3.63; 95% CI -5.77, -1.48; p = 0.0009), neuron quantity (SMD 3.42; 95% CI 2.51, 4.34; p < 0.00001), microglia quantity (SMD -3.06; 95% CI -4.69, -1.44; p = 0.0002), and p-AMPK levels (SMD 2.92; 95% CI 2.02, 3.82; p < 0.00001). Furthermore, sensitivity analysis and stratified analysis were conducted for heterogeneous outcome indicators. Conclusion: Overall, metformin treatment improves severe outcomes triggered by stroke. Despite the limitations intrinsic to animal studies, this systematic review may provide a vital reference for future high-quality preclinical trials and clinical use.

The effect of metformin on ameliorating neurological function deficits and tissue damage in rats following spinal cord injury: A systematic review and network meta-analysis

Spinal cord injury (SCI) is a devastating condition with few treatment options. Metformin, a classical antidiabetic and antioxidant, has extended its application to experimental SCI treatment. Here, we performed a systematic review to evaluate the neurobiological roles of metformin for treating SCI in rats, and to assess the potential for clinical translation. PubMed, Embase, China National Knowledge Infrastructure, WanFang data, SinoMed, and Vip Journal Integration Platform databases were searched from their inception dates to October 2021. Two reviewers independently selected controlled studies evaluating the neurobiological roles of metformin in rats following SCI, extracted data, and assessed the quality of methodology and evidence. Pairwise meta-analyses, subgroup analyses and network analysis were performed to assess the roles of metformin in neurological function and tissue damage in SCI rats. Twelve articles were included in this systematic review. Most of them were of moderate-to-high methodological quality, while the quality of evidence from those studies was not high. Generally, Basso, Beattie, and Bresnahan scores were increased in rats treated with metformin compared with controls, and the weighted mean differences (WMDs) between metformin and control groups exhibited a gradual upward trend from the 3rd (nine studies, n = 164, WMD = 0.42, 95% CI = −0.01 to 0.85, P = 0.06) to the 28th day after treatment (nine studies, n = 136, WMD = 3.48, 95% CI = 2.04 to 4.92, P < 0.00001). Metformin intervention was associated with improved inclined plane scores, tissue preservation ratio and number of anterior horn motor neurons. Subgroup analyses indicated an association between neuroprotection and metformin dose. Network meta-analysis showed that 50 mg/kg metformin exhibited greater protection than 10 and 100 mg/kg metformin. The action mechanisms behind metformin were associated with activating adenosine monophosphate-activated protein kinase signaling, regulating mitochondrial function and relieving endoplasmic reticulum stress. Collectively, this review indicates that metformin has a protective effect on SCI with satisfactory safety and we demonstrate a rational mechanism of action; therefore, metformin is a promising candidate for future clinical trials. However, given the limitations of animal experimental methodological and evidence quality, the findings of this pre-clinical review should be interpreted with caution.