Dabrafenib, an inhibitor of RIP3 kinase-dependent necroptosis, reduces ischemic brain injury

Dabrafenib alleviates hepatotoxicity caused by lenvatinib via inhibiting the death receptor signaling pathway

Lenvatinib is a multi-target inhibitor that exerts anti-tumor effects by inhibiting angiogenesis and is now commonly used as a first-line treatment for hepatocellular carcinoma. However, with the widespread use of lenvatinib, the problem of serious and fatal hepatotoxicity has become increasingly prominent. Currently, the mechanism behind this toxicity is not yet understood, and as a result, there is a lack of safe and effective intervention strategies with minimal side effects. Here, we established the model of lenvatinib-induced liver injury in vivo and in vitro and found that lenvatinib caused hepatotoxicity by inducing apoptosis. Further mechanistic studies in cellular models revealed that lenvatinib upregulated death receptor signaling pathway, which activated the downstream effector Caspase-8, and ultimately led to apoptosis. Meanwhile, lenvatinib-induced apoptosis was associated with ROS generation and DNA damage. In addition, after screening marketed drugs and natural products in combination with cellular modeling, we identified a potential co-administered drug, dabrafenib, which could alleviate lenvatinib-induced hepatotoxicity. Further mechanistic studies revealed that dabrafenib attenuated lenvatinib-induced hepatotoxicity by inhibiting the activation of the death receptor signaling pathway. Subsequently, cancer cell proliferation assays confirmed that dabrafenib did not antagonize the antitumor effects of lenvatinib. In conclusion, our results validate that apoptosis caused by the death receptor signaling pathway is the key cause of lenvatinib-induced hepatotoxicity, and dabrafenib alleviates lenvatinib-induced hepatotoxicity by inhibiting this pathway.

RIP3 in Necroptosis: Underlying Contributions to Traumatic Brain Injury

Traumatic brain injury (TBI) is a global public safety issue that poses a threat to death, characterized by high fatality rates, severe injuries and low recovery rates. There is growing evidence that necroptosis regulates the pathophysiological processes of a variety of diseases, particularly those affecting the central nervous system. Thus, moderate necroptosis inhibition may be helpful in the management of TBI. Receptor-interacting protein kinase (RIP) 3 is a key mediator in the necroptosis, and its absence helps restore the microenvironment at the injured site and improve cognitive impairment after TBI. In this report, we review different domains of RIP3, multiple analyses of necroptosis, and associations between necroptosis and TBI, RIP3, RIP1, and mixed lineage kinase domain-like. Next, we elucidate the potential involvement of RIP3 in TBI and highlight how RIP3 deficiency enhances neuronal function.

The Role of Necroptosis in Cerebral Ischemic Stroke

Cerebral ischemia, also known as ischemic stroke, accounts for nearly 85% of all strokes and is the leading cause of disability worldwide. Due to disrupted blood supply to the brain, cerebral ischemic injury is trigged by a series of complex pathophysiological events including excitotoxicity, oxidative stress, inflammation, and cell death. Currently, there are few treatments for cerebral ischemia owing to an incomplete understanding of the molecular and cellular mechanisms. Accumulated evidence indicates that various types of programmed cell death contribute to cerebral ischemic injury, including apoptosis, ferroptosis, pyroptosis and necroptosis. Among these, necroptosis is morphologically similar to necrosis and is mediated by receptor-interacting serine/threonine protein kinase-1 and -3 and mixed lineage kinase domain-like protein. Necroptosis inhibitors have been shown to exert inhibitory effects on cerebral ischemic injury and neuroinflammation. In this review, we will discuss the current research progress regarding necroptosis in cerebral ischemia as well as the application of necroptosis inhibitors for potential therapeutic intervention in ischemic stroke.

Identification of Pyrido[3,4-d]pyrimidine derivatives as RIPK3-Mediated necroptosis inhibitors

Necroptosis executed by RIPK3-mediated phosphorylation of MLKL is a programmed necrotic cell death and implicated with various diseases such as sterile inflammation. We designed and synthesized pyrido[3,4-d]pyrimidine derivatives as novel necroptosis inhibitors capable of suppressing the phosphorylation of MLKL. Our SAR studies reveal that 20 possesses comparable inhibitory activity against RIPK3-mediated pMLKL in HT-29 cells relative to GSK872 (2), a representative selective RIPK3 inhibitor. Based on biochemical kinase assay results, 20 is comparable to GSK872 (2) with regard to activity against RIPK3 and less potent against RIPK1 than GSK872, indicating selectivity of 20 towards RIPK3 over RIPK1 is higher than that of GSK872. In HT-29 cells, 20 inhibits necroptosis via MLKL oligomerization impediment. Moreover, 20 suppresses migration and invasion of AsPC-1 cells by necroptosis induced- CXCL5 secretion downregulation. Significantly, 20 could relieve the TNFα-induced systemic inflammatory response syndrome in vivo. Taken together, this study would provide a useful insight into the design of novel necroptosis inhibitors possessing RIPK3-mediated pMLKL inhibitory activity.

Role of Necroptosis in Intervertebral Disc Degeneration

Apoptosis has historically been considered the primary form of programmed cell death (PCD) and is responsible for regulating cellular processes during development, homeostasis, and disease. Conversely, necrosis was considered uncontrolled and unregulated. However, recent evidence has unveiled the significance of necroptosis, a regulated form of necrosis, as an important mechanism of PCD alongside apoptosis. The activation of necroptosis leads to cellular membrane disruption, inflammation, and vascularization. This process is crucial in various pathological conditions, including intervertebral disc degeneration (IVDD), neurodegeneration, inflammatory diseases, multiple cancers, and kidney injury. In recent years, extensive research efforts have shed light on the molecular regulation of the necroptotic pathway. Various stimuli trigger necroptosis, and its regulation involves the activation of specific proteins such as receptor-interacting protein kinase 1 (RIPK1), RIPK3, and the mixed lineage kinase domain-like (MLKL) pseudokinase. Understanding the intricate mechanisms governing necroptosis holds great promise for developing novel therapeutic interventions targeting necroptosis-associated IVDD. The objective of this review is to contribute to the growing body of scientific knowledge in this area by providing a comprehensive overview of necroptosis and its association with IVDD. Ultimately, these understandings will allow the development of innovative drugs that can modulate the necroptotic pathway, offering new therapeutic avenues for individuals suffering from necroptosis.

Novel, non-conventional pathways of necroptosis in the heart and other organs: Molecular mechanisms, regulation and inter-organelle interplay

Necroptosis, a cell death modality that is defined as a necrosis-like cell death depending on the receptor-interacting protein kinase 3 (RIPK3) and mixed lineage kinase domain-like pseudokinase (MLKL), has been found to underlie the injury of various organs. Nevertheless, the molecular background of this cell loss seems to also involve, at least under certain circumstances, some novel axes, such as RIPK3-PGAM5-Drp1 (mitochondrial protein phosphatase 5-dynamin-related protein 1), RIPK3-CaMKII (Ca2+/calmodulin-dependent protein kinase II) and RIPK3-JNK-BNIP3 (c-Jun N-terminal kinase-BCL2 Interacting Protein 3). In addition, endoplasmic reticulum stress and oxidative stress via the higher production of reactive oxygen species produced by the mitochondrial enzymes and the enzymes of the plasma membrane have been implicated in necroptosis, thereby depicting an inter-organelle interplay in the mechanisms of this cell death. However, the role and relationship between these novel non-conventional signalling and the well-accepted canonical pathway in terms of tissue- and/or disease-specific prioritisation is completely unknown. In this review, we provide current knowledge on some necroptotic pathways being not directly associated with RIPK3-MLKL execution and report studies showing the role of respective microRNAs in the regulation of necroptotic injury in the heart and in some other tissues having a high expression of the pro-necroptotic proteins.

Muscle fiber necroptosis in pathophysiology of idiopathic inflammatory myopathies and its potential as target of novel treatment strategy

Idiopathic inflammatory myopathies (IIMs), which are a group of chronic and diverse inflammatory diseases, are primarily characterized by weakness in the proximal muscles that progressively leads to persistent disability. Current treatments of IIMs depend on nonspecific immunosuppressive agents (including glucocorticoids and immunosuppressants). However, these therapies sometimes fail to regulate muscle inflammation, and some patients suffer from infectious diseases and other adverse effects related to the treatment. Furthermore, even after inflammation has subsided, muscle weakness persists in a significant proportion of the patients. Therefore, the elucidation of pathophysiology of IIMs and development of a better therapeutic strategy that not only alleviates muscle inflammation but also improves muscle weakness without increment of opportunistic infection is awaited. Muscle fiber death, which has been formerly postulated as "necrosis", is a key histological feature of all subtypes of IIMs, however, its detailed mechanisms and contribution to the pathophysiology remained to be elucidated. Recent studies have revealed that muscle fibers of IIMs undergo necroptosis, a newly recognized form of regulated cell death, and promote muscle inflammation and dysfunction through releasing inflammatory mediators such as damage-associated molecular patterns (DAMPs). The research on murine model of polymyositis, a subtype of IIM, revealed that the inhibition of necroptosis or HMGB1, one of major DAMPs released from muscle fibers undergoing necroptosis, ameliorated muscle inflammation and recovered muscle weakness. Furthermore, not only the necroptosis-associated molecules but also PGAM5, a mitochondrial protein, and reactive oxygen species have been shown to be involved in muscle fiber necroptosis, indicating the multiple target candidates for the treatment of IIMs acting through necroptosis regulation. This article overviews the research on muscle injury mechanisms in IIMs focusing on the contribution of necroptosis in their pathophysiology and discusses the potential treatment strategy targeting muscle fiber necroptosis.

Understanding necroptosis and its therapeutic target for intervertebral disc degeneration

Intervertebral disc degeneration (IVDD) is a complex pathological condition associated with the development of low back pain. Despite numerous studies, the specific molecular mechanisms underlying IVDD remain unclear. At the cellular level, IVDD involves a series of changes, including cell proliferation, cell death, and inflammation. Of these, cell death plays a critical role in the progression of the condition. In recent years, necroptosis has been identified as a new form of programmed cell death (PCD). Necroptosis can be activated by ligands of death receptors, which then interact with RIPK1, RIPK3 and MLKL and lead to necrosome formation.. According to various previous studies, the necroptosis related pathway is activated in IVDD, and plays a significant role in the pathogenesis of IVDD. Furthermore, necroptosis may serve as a target for the IVDD treatment. Recently, several studies have reported the role of necroptosis in IVDD, but few studies have summarized the association between IVDD and necroptosis. The review gives a brief summary of the research progress of necroptosis, and discusses strategies and mechanisms that target necroptosis in IVDD. Lastly, matters needing attention in the necroptosis targeted therapy of IVDD are put forward at last. To the best of our knowledge, the review paper is the first one that integrates current research about the impact of necroptosis on IVDD, and contributes to the future therapy of IVDD from new perspectives.

Unwinding the modalities of necrosome activation and necroptosis machinery in neurological diseases

Necroptosis, a regulated form of cell death, is involved in the genesis and development of various life-threatening diseases, including cancer, neurological disorders, cardiac myopathy, and diabetes. Necroptosis initiates with the formation and activation of a necrosome complex, which consists of RIPK1, RIPK2, RIPK3, and MLKL. Emerging studies has demonstrated the regulation of the necroptosis cell death pathway through the implication of numerous post-translational modifications, namely ubiquitination, acetylation, methylation, SUMOylation, hydroxylation, and others. In addition, the negative regulation of the necroptosis pathway has been shown to interfere with brain homeostasis through the regulation of axonal degeneration, mitochondrial dynamics, lysosomal defects, and inflammatory response. Necroptosis is controlled by the activity and expression of signaling molecules, namely VEGF/VEGFR, PI3K/Akt/GSK-3β, c-Jun N-terminal kinases (JNK), ERK/MAPK, and Wnt/β-catenin. Herein, we briefly discussed the implication and potential of necrosome activation in the pathogenesis and progression of neurological manifestations, such as Alzheimer's disease, Parkinson's disease, multiple sclerosis, traumatic brain injury, and others. Further, we present a detailed picture of natural compounds, micro-RNAs, and chemical compounds as therapeutic agents for treating neurological manifestations.

Kinases control of regulated cell death revealing druggable targets for Parkinson's disease

Parkinson's disease (PD) is the second most prevalent neurodegenerative disorder in the world. Motor impairment seen in PD is associated with dopaminergic neurotoxicity in the striatum, and dopaminergic neuronal death in the substantia nigra pars compacta. Cell death has a significant effect on the development and progression of PD. Extensive research over the last few decades has unveiled new regulated cell death (RCD) mechanisms that are not dependent on apoptosis such as necroptosis, ferroptosis, and others. In this review, we will overview the mechanistic pathways of different types of RCD. Unlike accidental cell death, RCD subroutines can be regulated and the RCD-associated kinases are potential druggable targets. Hence, we will address an overview and analysis of different kinases regulating apoptosis such as receptor-interacting protein kinase 1 (RIPK-1), RIPK3, mixed lineage kinase (MLK), Ataxia telangiectasia muted (ATM), cyclin-dependent kinase (CDK), death-associated protein kinase 1 (DAPK1), Apoptosis-signaling kinase-1 (ASK-1), and Leucine-rich repeat kinase-2 (LRRK2). In addition to the role of RIPK1, RIPK3, and Mixed Lineage Kinase Domain like Pseudokinase (MLKL) in necroptosis. We also overview functions of AMP-kinase (AMPK), protein kinase C (PKC), RIPK3, and ATM in ferroptosis. We will recap the anti-apoptotic, anti-necroptotic, and anti-ferroptotic effects of different kinase inhibitors in different models of PD. Finally, we will discuss future challenges in the repositioning of kinase inhibitors in PD. In conclusion, this review kicks-start targeting RCD from a kinases perspective, opening novel therapeutic disease-modifying therapeutic avenues for PD.

Necroptosis in CNS diseases: Focus on astrocytes

In the last few years, necroptosis, a recently described type of cell death, has been reported to play an important role in the development of various brain pathologies. Necroptosis is a cell death mechanism that has morphological characteristics similar to necrosis but is mediated by fundamentally different molecular pathways. Necroptosis is initiated by signaling through the interaction of RIP1/RIP3/MLKL proteins (receptor-interacting protein kinase 1/receptor-interacting protein kinase 3/mixed lineage kinase domain-like protein). RIPK1 kinase is usually inactive under physiological conditions. It is activated by stimulation of death receptors (TNFR1, TNFR2, TLR3, and 4, Fas-ligand) by external signals. Phosphorylation of RIPK1 results in the formation of its complex with death receptors. Further, complexes with the second member of the RIP3 and MLKL cascade appear, and the necroptosome is formed. There is enough evidence that necroptosis plays an important role in the pathogenesis of brain ischemia and neurodegenerative diseases. In recent years, a point of view that both neurons and glial cells can play a key role in the development of the central nervous system (CNS) pathologies finds more and more confirmation. Astrocytes play complex roles during neurodegeneration and ischemic brain damage initiating both impair and protective processes. However, the cellular and molecular mechanisms that induce pathogenic activity of astrocytes remain veiled. In this review, we consider these processes in terms of the initiation of necroptosis. On the other hand, it is important to remember that like other types of programmed cell death, necroptosis plays an important role for the organism, as it induces a strong immune response and is involved in the control of cancerogenesis. In this review, we provide an overview of the complex role of necroptosis as an important pathogenetic component of neuronal and astrocyte death in neurodegenerative diseases, epileptogenesis, and ischemic brain damage.

Cell death regulation: A new way for natural products to treat osteoporosis

Osteoporosis is a common metabolic bone disease that results from the imbalance of homeostasis within the bone. Intra-bone homeostasis is dependent on a precise dynamic balance between bone resorption by osteoclasts and bone formation by mesenchymal lineage osteoblasts, which comprises a series of complex and highly standardized steps. Programmed cell death (PCD) (e.g., apoptosis, autophagy, ferroptosis, pyroptosis, and necroptosis) is a cell death process that involves a cascade of gene expression events with tight structures. These events play a certain role in regulating bone metabolism by determining the fate of bone cells. Moreover, existing research has suggested that natural products derived from a wide variety of dietary components and medicinal plants modulate the PCDs based on different mechanisms, which show great potential for the prevention and treatment of osteoporosis, thus revealing the emergence of more acceptable complementary and alternative drugs with lower costs, fewer side effects and more long-term application. Accordingly, this review summarizes the common types of PCDs in the field of osteoporosis. Moreover, from the perspective of targeting PCDs, this review also discussed the roles of currently reported natural products in the treatment of osteoporosis and the involved mechanisms. Based on this, this review provides more insights into new molecular mechanisms of osteoporosis and provides a reference for developing more natural anti-osteoporosis drugs in the future.

FDA-Approved Kinase Inhibitors in Preclinical and Clinical Trials for Neurological Disorders

Cancers and neurological disorders are two major types of diseases. We previously developed a new concept termed "Aberrant Cell Cycle Diseases" (ACCD), revealing that these two diseases share a common mechanism of aberrant cell cycle re-entry. The aberrant cell cycle re-entry is manifested as kinase/oncogene activation and tumor suppressor inactivation, which are hallmarks of both tumor growth in cancers and neuronal death in neurological disorders. Therefore, some cancer therapies (e.g., kinase inhibition, tumor suppressor elevation) can be leveraged for neurological treatments. The United States Food and Drug Administration (US FDA) has so far approved 74 kinase inhibitors, with numerous other kinase inhibitors in clinical trials, mostly for the treatment of cancers. In contrast, there are dire unmet needs of FDA-approved drugs for neurological treatments, such as Alzheimer's disease (AD), intracerebral hemorrhage (ICH), ischemic stroke (IS), traumatic brain injury (TBI), and others. In this review, we list these 74 FDA-approved kinase-targeted drugs and identify those that have been reported in preclinical and/or clinical trials for neurological disorders, with a purpose of discussing the feasibility and applicability of leveraging these cancer drugs (FDA-approved kinase inhibitors) for neurological treatments.

Cpd-42 protects against calcium oxalate nephrocalcinosis-induced renal injury and inflammation by targeting RIPK3-mediated necroptosis

Calcium oxalate (CaOx) crystals, as the predominant component of human kidney stones, can trigger excessive cell death and inflammation of renal tubular epithelial cells, involved in the pathogenesis of nephrocalcinosis. Necroptosis mediated by receptor-interacting protein kinase 3 (RIPK3) serves a critical role in the cytotoxicity of CaOx crystals. Here, we assessed the therapeutic potential of a novel RIPK3 inhibitor, compound 42 (Cpd-42), for CaOx nephrocalcinosis by comparison with dabrafenib, a classic RIPK3 inhibitor. Our results demonstrated that Cpd-42 pretreatment attenuated CaOx crystals-induced renal tubular epithelial cell (TEC) injury by inhibiting necroptosis and inflammation in vitro and in vivo. Furthermore, in an established mouse model of CaOx nephrocalcinosis, Cpd-42 also reduced renal injury while improving the impaired kidney function and intrarenal crystal deposition. Consistent with this finding, Cpd-42 was confirmed to exhibit superior inhibition of necroptosis and protection against renal TEC injury compared to the classic RIPK3 inhibitor dabrafenib in vitro and in vivo. Mechanistically, RIPK3 knockout (KO) tubular epithelial cells pretreated with Cpd-42 did not show further enhancement of the protective effect on crystals-induced cell injury and inflammation. We confirmed that Cpd-42 exerted protective effects by specifically targeting and inhibiting RIPK3-mediated necroptosis to block the formation of the RIPK1-RIPK3 necrosome. Taken together, targeted inhibition of RIPK3-mediated necroptosis with Cpd-42 may provide a potential therapeutic approach for CaOx nephrocalcinosis.

Necroptosis: A Pathogenic Negotiator in Human Diseases

Over the past few decades, mechanisms of programmed cell death have attracted the scientific community because they are involved in diverse human diseases. Initially, apoptosis was considered as a crucial mechanistic pathway for programmed cell death; recently, an alternative regulated mode of cell death was identified, mimicking the features of both apoptosis and necrosis. Several lines of evidence have revealed that dysregulation of necroptosis leads to pathological diseases such as cancer, cardiovascular, lung, renal, hepatic, neurodegenerative, and inflammatory diseases. Regulated forms of necrosis are executed by death receptor ligands through the activation of receptor-interacting protein kinase (RIPK)-1/3 and mixed-lineage kinase domain-like (MLKL), resulting in the formation of a necrosome complex. Many papers based on genetic and pharmacological studies have shown that RIPKs and MLKL are the key regulatory effectors during the progression of multiple pathological diseases. This review focused on illuminating the mechanisms underlying necroptosis, the functions of necroptosis-associated proteins, and their influences on disease progression. We also discuss numerous natural and chemical compounds and novel targeted therapies that elicit beneficial roles of necroptotic cell death in malignant cells to bypass apoptosis and drug resistance and to provide suggestions for further research in this field.

No Time to Die: How Kidney Cancer Evades Cell Death

The understanding of the pathogenesis of renal cell carcinoma led to the development of targeted therapies, which dramatically changed the overall survival rate. Nonetheless, despite innovative lines of therapy accessible to patients, the prognosis remains severe in most cases. Kidney cancer rarely shows mutations in the genes coding for proteins involved in programmed cell death, including p53. In this paper, we show that the molecular machinery responsible for different forms of cell death, such as apoptosis, ferroptosis, pyroptosis, and necroptosis, which are somehow impaired in kidney cancer to allow cancer cell growth and development, was reactivated by targeted pharmacological intervention. The aim of the present review was to summarize the modality of programmed cell death in the pathogenesis of renal cell carcinoma, showing in vitro and in vivo evidence of their potential role in controlling kidney cancer growth, and highlighting their possible therapeutic value.

Role of Induced Programmed Cell Death in the Chemopreventive Potential of Apigenin

The flavonoid apigenin (4′,5,7-trihydroxyflavone), which is one of the most widely distributed phytochemicals in the plant kingdom, is one of the most thoroughly investigated phenolic components. Previous studies have attributed the physiological effects of apigenin to its anti-allergic, antibacterial, antidiabetic, anti-inflammatory, antioxidant, antiviral, and blood-pressure-lowering properties, and its documented anticancer properties have been attributed to the induction of apoptosis and autophagy, the inhibition of inflammation, angiogenesis, and cell proliferation, and the regulation of cellular responses to oxidative stress and DNA damage. The most well-known mechanism for the compound’s anticancer effects in human cancer cell lines is apoptosis, followed by autophagy, and studies have also reported that apigenin induces novel cell death mechanisms, such as necroptosis and ferroptosis. Therefore, the aim of this paper is to review the therapeutic potential of apigenin as a chemopreventive agent, as well as the roles of programmed cell death mechanisms in the compound’s chemopreventive properties.

Synthesis and characterization of potent RIPK3 inhibitors based on a tricyclic scaffold

Background: Necroptosis is an important form of regulated cell death involved in inflammatory diseases, degenerative diseases and cancer. RIPK3 is an interesting target for intervention of necroptosis-associated diseases. Methodology: Herein the authors report the synthesis of a series RIPK3 inhibitors under the guidance of structure-based drug design which leads to the identification of compound 37. Results: Compound 37 potently rescued human and mouse cells from necroptotic stimuli TNFα, Smac mimetic, z-VAD and LPS + z-VAD, displayed high affinity to RIPK3 (Kd = 14 nM) but no observable affinity to RIPK1 and inhibited RIPK3 kinase function. Importantly, compound 37 significantly alleviated TNF-induced systemic inflammatory response syndrome in the mouse model. Conclusion: These results support compound 37 as a prototype RIPK3 inhibitor for lead optimization.

Interplay of Oxidative Stress and Necrosis-like Cell Death in Cardiac Ischemia/Reperfusion Injury: A Focus on Necroptosis

Extensive research work has been carried out to define the exact significance and contribution of regulated necrosis-like cell death program, such as necroptosis to cardiac ischemic injury. This cell damaging process plays a critical role in the pathomechanisms of myocardial infarction (MI) and post-infarction heart failure (HF). Accordingly, it has been documented that the modulation of key molecules of the canonical signaling pathway of necroptosis, involving receptor-interacting protein kinases (RIP1 and RIP3) as well as mixed lineage kinase domain-like pseudokinase (MLKL), elicit cardioprotective effects. This is evidenced by the reduction of the MI-induced infarct size, alleviation of myocardial dysfunction, and adverse cardiac remodeling. In addition to this molecular signaling of necroptosis, the non-canonical pathway, involving Ca2+/calmodulin-dependent protein kinase II (CaMKII)-mediated regulation of mitochondrial permeability transition pore (mPTP) opening, and phosphoglycerate mutase 5 (PGAM5)–dynamin-related protein 1 (Drp-1)-induced mitochondrial fission, has recently been linked to ischemic heart injury. Since MI and HF are characterized by an imbalance between reactive oxygen species production and degradation as well as the occurrence of necroptosis in the heart, it is likely that oxidative stress (OS) may be involved in the mechanisms of this cell death program for inducing cardiac damage. In this review, therefore, several observations from different studies are presented to support this paradigm linking cardiac OS, the canonical and non-canonical pathways of necroptosis, and ischemia-induced injury. It is concluded that a multiple therapeutic approach targeting some specific changes in OS and necroptosis may be beneficial in improving the treatment of ischemic heart disease.

Necroptosis: A new target for prevention of osteoporosis

Multiple causes may contribute to osteoporosis, characterized by a loss in bone mass and density as a consequence of the degradation of bone microstructure and a resultant rise in bone fragility. Recently, increasing attention has been paid to the role of necroptosis in the development of osteoporosis. Necroptosis is orchestrated by a set of proteins known as receptor-interacting protein kinase (RIPK)1, RIPK3, and mixed lineage kinase domain-like protein (MLKL). A necrosome is formed by MLKL, RIPK1, RIPK3, and RIPK3-RIPK3. A dissociated MLKL forms pores in the plasma membrane and eventually leads to necroptosis after translocating from the necrosome. In this review, we discuss a detailed understanding of necroptosis and its associated processes, a better understanding of its interactions with osteoclasts, osteoblasts, and osteocytes, and the associations between necroptosis and diabetic osteoporosis, steroid-induced osteoporosis, and postmenopausal osteoporosis. In addition, a variety of experimental medicines capable of modulating crucial necroptosis processes are highlighted. It's important to note that this is the first review paper to consolidate current data on the role of necroptosis in osteoporosis, and it offers fresh hope for the future treatment of this disease.

Genetic inhibition of RIPK3 ameliorates functional outcome in controlled cortical impact independent of necroptosis

Traumatic brain injury (TBI) is a leading cause of death and disability with no specific effective therapy, in part because disease driving mechanisms remain to be elucidated. Receptor interacting protein kinases (RIPKs) are serine/threonine kinases that assemble multi-molecular complexes that induce apoptosis, necroptosis, inflammasome and nuclear factor kappa B activation. Prior studies using pharmacological inhibitors implicated necroptosis in the pathogenesis of TBI and stroke, but these studies cannot be used to conclusively demonstrate a role for necroptosis because of the possibility of off target effects. Using a model of cerebral contusion and RIPK3 and mixed lineage kinase like knockout (MLKL^-/-) mice, we found evidence for activation of RIPK3 and MLKL and assembly of a RIPK1-RIPK3-MLKL necrosome complex in pericontusional brain tissue. Phosphorylated forms of RIPK3 and MLKL were detected in endothelium, CD11b + immune cells, and neurons, and RIPK3 was upregulated and activated in three-dimensional human endothelial cell cultures subjected to CCI. RIPK3^-/- and MLKL^-/- mice had reduced blood-brain barrier damage at 24 h (p < 0.05), but no differences in neuronal death (6 h, p = ns in CA1, CA3 and DG), brain edema (24 h, p = ns), or lesion size (4 weeks, p = ns) after CCI. RIPK3^-/-, but not MLKL^-/- mice, were protected against postinjury motor and cognitive deficits at 1-4 weeks (RIPK3^-/- vs WT: p < 0.05 for group in wire grip, Morris water maze hidden platform trials, p < 0.05 for novel object recognition test, p < 0.01 for rotarod test). RIPK3^-/- mice had reduced infiltrating leukocytes (p < 0.05 vs WT in CD11b + cells, microglia and macrophages), HMGB1 release and interleukin-1 beta activation at 24-48 h (p < 0.01) after CCI. Our data indicate that RIPK3 contributes to functional outcome after cerebral contusion by mechanisms involving inflammation but independent of necroptosis.

The Role of Epithelial Damage in the Pulmonary Immune Response

Pulmonary epithelial cells are widely considered to be the first line of defence in the lung and are responsible for coordinating the innate immune response to injury and subsequent repair. Consequently, epithelial cells communicate with multiple cell types including immune cells and fibroblasts to promote acute inflammation and normal wound healing in response to damage. However, aberrant epithelial cell death and damage are hallmarks of pulmonary disease, with necrotic cell death and cellular senescence contributing to disease pathogenesis in numerous respiratory diseases such as idiopathic pulmonary fibrosis (IPF), chronic obstructive pulmonary disease (COPD) and coronavirus disease (COVID)-19. In this review, we summarise the literature that demonstrates that epithelial damage plays a pivotal role in the dysregulation of the immune response leading to tissue destruction and abnormal remodelling in several chronic diseases. Specifically, we highlight the role of epithelial-derived damage-associated molecular patterns (DAMPs) and senescence in shaping the immune response and assess their contribution to inflammatory and fibrotic signalling pathways in the lung.

Emerging immune and cell death mechanisms in stroke: Saponins as therapeutic candidates

The complexity of the ischemic cascade is based on the integrated crosstalk of every cell type in the neurovascular unit. Depending on the features of the ischemic insult, several cell death mechanisms are triggered, such as apoptosis, necroptosis, ferroptosis/oxytosis, ETosis or pyroptosis, leading to reactive astrogliosis. However, emerging evidence demonstrates a dual role for the immune system in stroke pathophysiology, where it exerts both detrimental and also beneficial functions. In this review, we discuss the relevance of several cell death modalities and the dual role of the immune system in stroke pathophysiology. We also provide an overview of some emerging immunomodulatory therapeutic strategies, amongst which saponins, which are promising candidates that exert multiple pharmacological effects.

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Several cell death mechanisms coexist in stroke pathophysiology.

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Neurons are more vulnerable to necroptosis than glial cells.

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Inhibitors of receptor-interacting protein kinases and of ferroptosis induce neuroprotection.

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Saponins exert modulatory effects on inflammation and neuronal cell death in stroke.

Programmed cell death in aortic aneurysm and dissection: A potential therapeutic target

Rupture of aortic aneurysm and dissection (AAD) remains a leading cause of death. Progressive smooth muscle cell (SMC) loss is a crucial feature of AAD that contributes to aortic dysfunction and degeneration, leading to aortic aneurysm, dissection, and, ultimately, rupture. Understanding the molecular mechanisms of SMC loss and identifying pathways that promote SMC death in AAD are critical for developing an effective pharmacologic therapy to prevent aortic destruction and disease progression. Cell death is controlled by programmed cell death pathways, including apoptosis, necroptosis, pyroptosis, and ferroptosis. Although these pathways share common stimuli and triggers, each type of programmed cell death has unique features and activation pathways. A growing body of evidence supports a critical role for programmed cell death in the pathogenesis of AAD, and inhibitors of various types of programmed cell death represent a promising therapeutic strategy. This review discusses the different types of programmed cell death pathways and their features, induction, contributions to AAD development, and therapeutic potential. We also highlight the clinical significance of programmed cell death for further studies.

Antioxidant and food additive BHA prevents TNF cytotoxicity by acting as a direct RIPK1 inhibitor

Butylate hydroxyanisole (BHA) is a synthetic phenol that is widely utilized as a preservative by the food and cosmetic industries. The antioxidant properties of BHA are also frequently used by scientists to claim the implication of reactive oxygen species (ROS) in various cellular processes, including cell death. We report on the surprising finding that BHA functions as a direct inhibitor of RIPK1, a major signaling hub downstream of several immune receptors. Our in silico analysis predicts binding of 3-BHA, but not 2-BHA, to RIPK1 in an inactive DLG-out/Glu-out conformation, similar to the binding of the type III inhibitor Nec-1s to RIPK1. This predicted superior inhibitory capacity of 3-BHA over 2-BHA was confirmed in cells and using in vitro kinase assays. We demonstrate that the reported protective effect of BHA against tumor necrosis factor (TNF)-induced necroptotic death does not originate from ROS scavenging but instead from direct RIPK1 enzymatic inhibition, a finding that most probably extends to other reported effects of BHA. Accordingly, we show that BHA not only protects cells against RIPK1-mediated necroptosis but also against RIPK1 kinase-dependent apoptosis. We found that BHA treatment completely inhibits basal and induced RIPK1 enzymatic activity in cells, monitored at the level of TNFR1 complex I under apoptotic conditions or in the cytosol under necroptosis. Finally, we show that oral administration of BHA protects mice from RIPK1 kinase-dependent lethality caused by TNF injection, a model of systemic inflammatory response syndrome. In conclusion, our results demonstrate that BHA can no longer be used as a strict antioxidant and that new functions of RIPK1 may emerge from previously reported effects of BHA.

Necroptosis: A Novel Pathway in Neuroinflammation

Neuroinflammation is a complex inflammatory process in the nervous system that is expected to play a significant role in neurological diseases. Necroptosis is a kind of necrosis that triggers innate immune responses by rupturing dead cells and releasing intracellular components; it can be caused by Toll-like receptor (TLR)-3 and TLR-4 agonists, tumor necrosis factor (TNF), certain microbial infections, and T cell receptors. Necroptosis signaling is modulated by receptor-interacting protein kinase (RIPK) 1 when the activity of caspase-8 becomes compromised. Activated death receptors (DRs) cause the activation of RIPK1 and the RIPK1 kinase activity-dependent formation of an RIPK1-RIPK3-mixed lineage kinase domain-like protein (MLKL), which is complex II. RIPK3 phosphorylates MLKL, ultimately leading to necrosis through plasma membrane disruption and cell lysis. Current studies suggest that necroptosis is associated with the pathogenesis of neuroinflammatory diseases, such as Alzheimer’s disease, Parkinson’s disease, and traumatic brain injury. Inhibitors of necroptosis, such as necrostatin-1 (Nec-1) and stable variant of Nec (Nec-1s), have been proven to be effective in many neurological diseases. The purpose of this article is to illuminate the mechanism underlying necroptosis and the important role that necroptosis plays in neuroinflammatory diseases. Overall, this article shows a potential therapeutic strategy in which targeting necroptotic factors may improve the pathological changes and clinical symptoms of neuroinflammatory disorders.

Insight into Crosstalk between Ferroptosis and Necroptosis: Novel Therapeutics in Ischemic Stroke

Ferroptosis is a nonapoptotic form of cell death characterized by iron-dependent accumulation of lipid hydroperoxides to lethal levels. Necroptosis, an alternative form of programmed necrosis, is regulated by receptor-interacting protein (RIP) 1 activation and by RIP3 and mixed-lineage kinase domain-like (MLKL) phosphorylation. Ferroptosis and necroptosis both play important roles in the pathological progress in ischemic stroke, which is a complex brain disease regulated by several cell death pathways. In the past few years, increasing evidence has suggested that the crosstalk occurs between necroptosis and ferroptosis in ischemic stroke. However, the potential links between ferroptosis and necroptosis in ischemic stroke have not been elucidated yet. Hence, in this review, we overview and analyze the mechanism underlying the crosstalk between necroptosis and ferroptosis in ischemic stroke. And we find that iron overload, one mechanism of ferroptosis, leads to mitochondrial permeability transition pore (MPTP) opening, which aggravates RIP1 phosphorylation and contributes to necroptosis. In addition, heat shock protein 90 (HSP90) induces necroptosis and ferroptosis by promoting RIP1 phosphorylation and suppressing glutathione peroxidase 4 (GPX4) activation. In this work, we try to deliver a new perspective in the exploration of novel therapeutic targets for the treatment of ischemic stroke.

Ring closure strategy leads to potent RIPK3 inhibitors

Necroptosis is a form of regulated necrotic cell death that is independent of caspases. Receptor-interacting protein kinase 3 (RIPK3) has been identified as a key regulator for necroptosis, and has been proposed as a potential therapeutic target for the treatment of diseases associated with necroptosis. In this report, we describe the design, synthesis, and evaluation of a series of novel RIPK3 inhibitors. The lead compound 38 exhibited potent activity (EC₅₀ = 0.42 μM) in blocking TNFα, Smac mimetic and z-VAD (TSZ) induced cell death in HT-29 cells. Mechanistic studies showed that compound 38 bound to RIPK3 with high affinity (K_d = 7.1 nM), and inhibited RIPK3 kinase activity in a ADP-Glo functional assay. In addition, compound 38 displayed good selectivity over another necroptosis regulator RIPK1 (K_d = 6000 nM). Furthermore, compound 38 demonstrated excellent in vitro safety profiles with minimal inhibition of CYP isozymes and hERG potassium channel. Lastly, compound 38 efficiently blocked hypothermia and death in mice in the TNFα-induced systemic inflammatory response syndrome model.

Cell death in head and neck cancer pathogenesis and treatment

Many cancer therapies aim to trigger apoptosis in cancer cells. Nevertheless, the presence of oncogenic alterations in these cells and distorted composition of tumour microenvironment largely limit the clinical efficacy of this type of therapy. Luckily, scientific consensus describes about 10 different cell death subroutines with different regulatory pathways and cancer cells are probably not able to avoid all of cell death types at once. Therefore, a focused and individualised therapy is needed to address the specific advantages and disadvantages of individual tumours. Although much is known about apoptosis, therapeutic opportunities of other cell death pathways are often neglected. Molecular heterogeneity of head and neck squamous cell carcinomas (HNSCC) causing unpredictability of the clinical response represents a grave challenge for oncologists and seems to be a critical component of treatment response. The large proportion of this clinical heterogeneity probably lies in alterations of cell death pathways. How exactly cells die is very important because the predominant type of cell death can have multiple impacts on the therapeutic response as cell death itself acts as a second messenger. In this review, we discuss the different types of programmed cell death (PCD), their connection with HNSCC pathogenesis and possible therapeutic windows that result from specific sensitivity to some form of PCD in some clinically relevant subgroups of HNSCC.

Neuronal protein-tyrosine phosphatase 1B hinders sensory-motor functional recovery and causes affective disorders in two different focal ischemic stroke models

Ischemic brain injury causes neuronal death and inflammation. Inflammation activates protein-tyrosine phosphatase 1B (PTP1B). Here, we tested the significance of PTP1B activation in glutamatergic projection neurons on functional recovery in two models of stroke: by photothrombosis, focal ischemic lesions were induced in the sensorimotor cortex (SM stroke) or in the peri-prefrontal cortex (peri-PFC stroke). Elevated PTP1B expression was detected at 4 days and up to 6 weeks after stroke. While ablation of PTP1B in neurons of neuronal knockout (NKO) mice had no effect on the volume or resorption of ischemic lesions, markedly different effects on functional recovery were observed. SM stroke caused severe sensory and motor deficits (adhesive removal test) in wild type and NKO mice at 4 days, but NKO mice showed drastically improved sensory and motor functional recovery at 8 days. In addition, peri-PFC stroke caused anxiety-like behaviors (elevated plus maze and open field tests), and depression-like behaviors (forced swimming and tail suspension tests) in wild type mice 9 and 28 days after stroke, respectively, with minimal effect on sensory and motor function. Peri-PFC stroke-induced affective disorders were associated with fewer active (FosB⁺) neurons in the PFC and nucleus accumbens but more FosB⁺ neurons in the basolateral amygdala, compared to sham-operated mice. In contrast, mice with neuronal ablation of PTP1B were protected from anxiety-like and depression-like behaviors and showed no change in FosB⁺ neurons after peri-PFC stroke. Taken together, our study identifies neuronal PTP1B as a key component that hinders sensory and motor functional recovery and also contributes to the development of anxiety-like and depression-like behaviors after stroke. Thus, PTP1B may represent a novel therapeutic target to improve stroke recovery. All procedures for animal use were approved by the Animal Care and Use Committee of the University of Ottawa Animal Care and Veterinary Service (protocol 1806) on July 27, 2018.

The Role of RIPK1 and RIPK3 in Cardiovascular Disease

Cardiovascular diseases, including peripheral arterial and venous disease, myocardial infarction, and stroke, are the number one cause of death worldwide annually. In the last 20 years, the role of necroptosis, a newly identified form of regulated necrotic cell death, in cardiovascular disease has come to light. Specifically, the damaging role of two kinase proteins pivotal in the necroptosis pathway, Receptor Interacting Protein Kinase 1 (RIPK1) and Receptor Interacting Protein Kinase 3 (RIPK3), in cardiovascular disease has become a subject of great interest and importance. In this review, we provide an overview of the current evidence supporting a pathologic role of RIPK1 and RIPK3 in cardiovascular disease. Moreover, we highlight the evidence behind the efficacy of targeted RIPK1 and RIPK3 inhibitors in the prevention and treatment of cardiovascular disease.

Targeting necroptosis in anticancer therapy: mechanisms and modulators

Necroptosis, a genetically programmed form of necrotic cell death, serves as an important pathway in human diseases. As a critical cell-killing mechanism, necroptosis is associated with cancer progression, metastasis, and immunosurveillance. Targeting necroptosis pathway by small molecule modulators is emerging as an effective approach in cancer therapy, which has the advantage to bypass the apoptosis-resistance and maintain antitumor immunity. Therefore, a better understanding of the mechanism of necroptosis and necroptosis modulators is necessary to develop novel strategies for cancer therapy. This review will summarize recent progress of the mechanisms and detecting methods of necroptosis. In particular, the relationship between necroptosis and cancer therapy and medicinal chemistry of necroptosis modulators will be focused on.

Lytic Cell Death Mechanisms in Human Respiratory Syncytial Virus-Infected Macrophages: Roles of Pyroptosis and Necroptosis

Human respiratory syncytial virus (RSV) is the most common cause of viral bronchiolitis and pneumonia in infants and children worldwide. Inflammation induced by RSV infection is responsible for its hallmark manifestation of bronchiolitis and pneumonia. The cellular debris created through lytic cell death of infected cells is a potent initiator of this inflammation. Macrophages are known to play a pivotal role in the early innate immune and inflammatory response to viral pathogens. However, the lytic cell death mechanisms associated with RSV infection in macrophages remains unknown. Two distinct mechanisms involved in lytic cell death are pyroptosis and necroptosis. Our studies revealed that RSV induces lytic cell death in macrophages via both of these mechanisms, specifically through the ASC (Apoptosis-associated speck like protein containing a caspase recruitment domain)-NLRP3 (nucleotide-binding domain, leucine-rich-containing family, pyrin domain-containing-3) inflammasome activation of both caspase-1 dependent pyroptosis and receptor-interacting serine/threonine-protein kinase 3 (RIPK3), as well as a mixed lineage kinase domain like pseudokinase (MLKL)-dependent necroptosis. In addition, we demonstrated an important role of reactive oxygen species (ROS) during lytic cell death of RSV-infected macrophages.

RSK3 mediates necroptosis by regulating phosphorylation of RIP3 in rat retinal ganglion cells

Receptor-interacting protein 3 (RIP3) plays an important role in the necroptosis signaling pathway. Our previous studies have shown that the RIP3/mixed lineage kinase domain-like protein (MLKL)-mediated necroptosis occurs in retinal ganglion cell line 5 (RGC-5) following oxygen-glucose deprivation (OGD). However, upstream regulatory pathways of RIP3 are yet to be uncovered. The purpose of the present study was to investigate the role of p90 ribosomal protein S6 kinase 3 (RSK3) in the phosphorylation of RIP3 in RGC-5 cell necroptosis following OGD. Our results showed that expression of RSK3, RIP3, and MLKL was upregulated in necroptosis of RGC-5 after OGD. A computer simulation based on our preliminary results indicated that RSK3 might interact with RIP3, which was subsequently confirmed by co-immunoprecipitation. Further, we found that the application of a specific RSK inhibitor, LJH685, or rsk3 small interfering RNA (siRNA), downregulated the phosphorylation of RIP3. However, the overexpression of rip3 did not affect the expression of RSK3, thereby indicating that RSK3 could be a possible upstream regulator of RIP3 phosphorylation in OGD-induced necroptosis of RGC-5 cells. Moreover, our in vivo results showed that pretreatment with LJH685 before acute high intraocular pressure episodes could reduce the necroptosis of retinal neurons and improve recovery of impaired visual function. Taken together, our findings suggested that RSK3 might work as an upstream regulator of RIP3 phosphorylation during RGC-5 necroptosis.

RIPK3 blockade attenuates tubulointerstitial fibrosis in a mouse model of diabetic nephropathy

Receptor-interacting protein kinase-3 (RIPK3) is a multifunctional regulator of cell death and inflammation. RIPK3 controls cellular signalling through the formation of the domain-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome, which is recognised to mediate renal fibrogenesis. The role of RIPK3 in diabetic kidney disease (DKD) induced renal fibrosis has not been previously determined. To define the action of RIPK3 in the development of diabetic kidney disease, wild-type (WT), RIPK3 -/- and endothelium-derived nitric oxide synthase (eNOS)-/- mice were induced to develop diabetes mellitus using multiple low doses of streptozotocin and maintained for 24 weeks. RIPK3 activity and NLRP3 expression were upregulated and fibrotic responses were increased in the kidney cortex of WT mice with established diabetic nephropathy compared to control mice. Consistently, mRNA expression of inflammasome components, as well as transforming growth factor beta 1 (TGFβ1), α smooth muscle actin (α-SMA) and collagen deposition were increased in diabetic kidneys of WT mice compared to control mice. However, these markers were normalised or significantly reversed in kidneys of diabetic RIPK3 -/- mice. Renoprotection was also observed using the RIPK3 inhibitor dabrafenib in eNOS-/- diabetic mice as demonstrated by reduced collagen deposition and myofibroblast activation. These results suggest that RIPK3 is associated with the development of renal fibrosis in DKD due to the activation of the NLRP3 inflammasome. Inhibition of RIPK3 results in renoprotection. Thus, RIPK3 may be a potential target for therapeutic intervention in patients with diabetic kidney disease.

RIPK3: A New Player in Renal Fibrosis

Chronic kidney disease (CKD) is the end result of a plethora of renal insults, including repeated episodes of acute or toxic kidney injury, glomerular, or diabetic kidney disease. It affects a large number of the population worldwide, resulting in significant personal morbidity and mortality and economic cost to the community. Hence it is appropriate to focus on treatment strategies that interrupt the development of kidney fibrosis, the end result of all forms of CKD, in addition to upstream factors that may be specific to certain diseases. However, the current clinical approach to prevent or manage renal fibrosis remains unsatisfactory. The rising importance of receptor-interacting serine/threonine-protein kinase (RIPK) 3 in the inflammatory response and TGF-β1 signaling is increasingly recognized. We discuss here the biological functions of RIPK3 and its role in the development of renal fibrosis.

RIPK3 blockade attenuates kidney fibrosis in a folic acid model of renal injury

Renal fibrosis is common to all forms of progressive kidney disease. However, current therapies to limit renal fibrosis are largely ineffective. Phosphorylation of receptor-interacting serine/threonine-protein kinase (RIPK) 3 has been recently suggested to be a key regulator of the pyrin domain containing 3 (NLRP3) inflammasome, which provides new insights into mechanisms of chronic kidney disease (CKD). However, the specific effect of RIPK3 on renal cortical fibrosis has not been fully understood. To study the function of RIPK3, both genetic ablation and pharmacological inhibition of RIPK3 (dabrafenib) were used in the study. Our studies identify that RIPK3 promotes renal fibrosis via the activation of the NLRP3 inflammasome in a mouse model of folic acid-induced nephropathy. Both interventional strategies decreased the renal fibrotic response, and beneficial effects converged on the NLRP3 inflammasome. This study demonstrates a role for RIPK3 as the mediator of renal fibrosis via the upregulation of inflammasome activation. Dabrafenib, as an inhibitor of RIPK3, may be an effective treatment to limit the progression of the tubulointerstitial fibrosis.

Non-Apoptotic Cell Death Signaling Pathways in Melanoma

Resisting cell death is a hallmark of cancer. Disturbances in the execution of cell death programs promote carcinogenesis and survival of cancer cells under unfavorable conditions, including exposition to anti-cancer therapies. Specific modalities of regulated cell death (RCD) have been classified based on different criteria, including morphological features, biochemical alterations and immunological consequences. Although melanoma cells are broadly equipped with the anti-apoptotic machinery and recurrent genetic alterations in the components of the RAS/RAF/MEK/ERK signaling markedly contribute to the pro-survival phenotype of melanoma, the roles of autophagy-dependent cell death, necroptosis, ferroptosis, pyroptosis, and parthanatos have recently gained great interest. These signaling cascades are involved in melanoma cell response and resistance to the therapeutics used in the clinic, including inhibitors of BRAFmut and MEK1/2, and immunotherapy. In addition, the relationships between sensitivity to non-apoptotic cell death routes and specific cell phenotypes have been demonstrated, suggesting that plasticity of melanoma cells can be exploited to modulate response of these cells to different cell death stimuli. In this review, the current knowledge on the non-apoptotic cell death signaling pathways in melanoma cell biology and response to anti-cancer drugs has been discussed.

Inhibitors Targeting RIPK1/RIPK3: Old and New Drugs

The scaffolding function of receptor-interacting protein kinase 1 (RIPK1) regulates prosurvival signaling and inflammatory gene expression, while its kinase activity mediates both apoptosis and necroptosis; the latter involving RIPK3 kinase activity. The mutual transition between the scaffold and kinase functions of RIPK1 is regulated by (de)ubiquitylation and (de)phosphorylation. RIPK1-mediated cell death leads to disruption of epithelial barriers and/or release of damage-associated molecular patterns (DAMPs), cytokines, and chemokines, propagating inflammatory and degenerative diseases. Many drug development programs have pursued targeting RIPK1, and to a lesser extent RIPK3 kinase activity. In this review, we classify existing and novel small-molecule drugs based on their pharmacodynamic (PD) type I, II, and III binding mode. Finally, we discuss their applicability and therapeutic potential in inflammatory and degenerative experimental disease models.

RIP3/MLKL-mediated neuronal necroptosis induced by methamphetamine at 39°C

Methamphetamine is one of the most prevalent drugs abused in the world. Methamphetamine abusers usually present with hyperpyrexia (39°C), hallucination and other psychiatric symptoms. However, the detailed mechanism underlying its neurotoxic action remains elusive. This study investigated the effects of methamphetamine + 39°C on primary cortical neurons from the cortex of embryonic Sprague-Dawley rats. Primary cortex neurons were exposed to 1 mM methamphetamine + 39°C. Propidium iodide staining and lactate dehydrogenase release detection showed that methamphetamine + 39°C triggered obvious necrosis-like death in cultured primary cortical neurons, which could be partially inhibited by receptor-interacting protein-1 (RIP1) inhibitor Necrostatin-1 partially. Western blot assay results showed that there were increases in the expressions of receptor-interacting protein-3 (RIP3) and mixed lineage kinase domain-like protein (MLKL) in the primary cortical neurons treated with 1 mM methamphetamine + 39°C for 3 hours. After pre-treatment with RIP3 inhibitor GSK’872, propidium iodide staining and lactate dehydrogenase release detection showed that neuronal necrosis rate was significantly decreased; RIP3 and MLKL protein expression significantly decreased. Immunohistochemistry staining results also showed that the expressions of RIP3 and MLKL were up-regulated in brain specimens from humans who had died of methamphetamine abuse. Taken together, the above results suggest that methamphetamine + 39°C can induce RIP3/MLKL regulated necroptosis, thereby resulting in neurotoxicity. The study protocol was approved by the Medical Ethics Committee of the Third Xiangya Hospital of Central South University, China (approval numbers: 2017-S026 and 2017-S033) on March 7, 2017.

B-RAFV600E Inhibitor Dabrafenib Attenuates RIPK3-Mediated Necroptosis and Promotes Functional Recovery after Spinal Cord Injury

The receptor-interacting protein kinase 3 (RIPK3) is a key regulator of necroptosis and is involved in various pathologies of human diseases. We previously reported that RIPK3 expression is upregulated in various neural cells at the lesions and necroptosis contributed to secondary neural tissue damage after spinal cord injury (SCI). Interestingly, recent studies have shown that the B-RAF^V600E inhibitor dabrafenib has a function to selectively inhibit RIPK3 and prevents necroptosis in various disease models. In the present study, using a mouse model of thoracic spinal cord contusion injury, we demonstrate that dabrafenib administration in the acute phase significantly inhibites RIPK3-mediated necroptosis in the injured spinal cord. The administration of dabrafenib attenuated secondary neural tissue damage, such as demyelination, neuronal loss, and axonal damage, following SCI. Importantly, the neuroprotective effect of dabrafenib dramatically improved the recovery of locomotor and sensory functions after SCI. Furthermore, the electrophysiological assessment of the injured spinal cord objectively confirmed that the functional recovery was enhanced by dabrafenib. These findings suggest that the B-RAF^V600E inhibitor dabrafenib attenuates RIPK3-mediated necroptosis to provide a neuroprotective effect and promotes functional recovery after SCI. The administration of dabrafenib may be a novel therapeutic strategy for treating patients with SCI in the future.

Protective effect of dabrafenib on renal ischemia-reperfusion injury in vivo and in vitro

AIMS

Ischemia-reperfusion injury (IRI) is a major cause of acute kidney injury (AKI), which can lead to poor outcome and increased risk of mortality. Dabrafenib (DAB) is an approved cancer treatment. Little is known about the effect of DAB in prevention or treatment of renal IRI.

METHODS

For in vivo experiments, C57BL/6 mice were divided into four groups: sham (no IRI, no DAB), IRI, DAB, and DAB + IRI. IRI was induced by clamping of bilateral renal pedicles for 30 min. For in vitro experiments, HK-2 cells were used to establish the hypoxia/reoxygenation (H/R) injury model, with four groups: control (no H/R, no DAB), H/R, DAB, and DAB + H/R. Renal function and renal histological changes were recorded. Expression of NGAL and KIM-1 proteins and mRNAs were determined by western blotting and qRT-PCR; secretion of inflammatory cytokines (IL-6 and TNF- α) was determined by qRT-PCR; Cell death was determined using the TUNEL assay, measurement of cleaved caspase-3, and flow cytometry. Necroptosis-related proteins were determined by western blotting.

RESULTS

In mice, DAB pretreatment improved renal function and also reduced histological injury, inflammation, cell death, and expression of necroptosis-associated proteins. In HK-2 cells, DAB significantly decreased the levels of NGAL and KIM-1, inflammatory cytokines, cell death, and necroptosis-related proteins.

CONCLUSION

Our in vitro and in vivo experiments indicated that DAB appears to alleviate renal IRI by suppressing cell death and inhibiting inflammatory responses. DAB has potential use for the clinical prevention and treatment of AKI-induced IRI.

Current translational potential and underlying molecular mechanisms of necroptosis

Cell death has a fundamental impact on the evolution of degenerative disorders, autoimmune processes, inflammatory diseases, tumor formation and immune surveillance. Over the past couple of decades extensive studies have uncovered novel cell death pathways, which are independent of apoptosis. Among these is necroptosis, a tightly regulated, inflammatory form of cell death. Necroptosis contribute to the pathogenesis of many diseases and in this review, we will focus exclusively on necroptosis in humans. Necroptosis is considered a backup mechanism of apoptosis, but the in vivo appearance of necroptosis indicates that both caspase-mediated and caspase-independent mechanisms control necroptosis. Necroptosis is regulated on multiple levels, from the transcription, to the stability and posttranslational modifications of the necrosome components, to the availability of molecular interaction partners and the localization of receptor-interacting serine/threonine-protein kinase 1 (RIPK1), receptor-interacting serine/threonine-protein kinase 3 (RIPK3) and mixed lineage kinase domain-like protein (MLKL). Accordingly, we classified the role of more than seventy molecules in necroptotic signaling based on consistent in vitro or in vivo evidence to understand the molecular background of necroptosis and to find opportunities where regulating the intensity and the modality of cell death could be exploited in clinical interventions. Necroptosis specific inhibitors are under development, but >20 drugs, already used in the treatment of various diseases, have the potential to regulate necroptosis. By listing necroptosis-modulated human diseases and cataloging the currently available drug-repertoire to modify necroptosis intensity, we hope to kick-start approaches with immediate translational potential. We also indicate where necroptosis regulating capacity should be considered in the current applications of these drugs.

Guidelines for evaluating myocardial cell death

Cell death is a fundamental process in cardiac pathologies. Recent studies have revealed multiple forms of cell death, and several of them have been demonstrated to underlie adverse cardiac remodeling and heart failure. With the expansion in the area of myocardial cell death and increasing concerns over rigor and reproducibility, it is important and timely to set a guideline for the best practices of evaluating myocardial cell death. There are six major forms of regulated cell death observed in cardiac pathologies, namely apoptosis, necroptosis, mitochondrial-mediated necrosis, pyroptosis, ferroptosis, and autophagic cell death. In this article, we describe the best methods to identify, measure, and evaluate these modes of myocardial cell death. In addition, we discuss the limitations of currently practiced myocardial cell death mechanisms.

Necroptosis: a crucial pathogenic mediator of human disease

Necroptosis is a genetically regulated form of necrotic cell death that has emerged as an important pathway in human disease. The necroptosis pathway is induced by a variety of signals, including death receptor ligands, and regulated by receptor-interacting protein kinases 1 and 3 (RIPK1 and RIPK3) and mixed-lineage kinase domain-like pseudokinase (MLKL), which form a regulatory necrosome complex. RIPK3-mediated phosphorylation of MLKL executes necroptosis. Recent studies, using animal models of tissue injury, have revealed that RIPK3 and MLKL are key effectors of injury propagation. This Review explores the functional roles of RIPK3 and MLKL as crucial pathogenic determinants and markers of disease progression and severity in experimental models of human disease, including acute and chronic pulmonary diseases; renal, hepatic, cardiovascular, and neurodegenerative diseases; cancer; and critical illness.

Necroptosis is one of the modalities of cell death accompanying ischemic brain stroke: from pathogenesis to therapeutic possibilities

Due to very limited therapeutic options, ischemic brain injury is one of the leading causes of death and lifelong disability worldwide, which imposes enormous public health burden. One of the main events occurring with ischemic brain stroke is cell death. Necroptosis is a type of cell death described as a regulated necrosis characterized by cell membrane disruption mediated by phosphorylated mixed lineage kinase like protein (MLKL). It can be triggered by activation of death receptors (eg, FAS, TNFR1), which lead to receptor-interacting serine/threonine-protein kinase 3 (RIPK3) activation by RIPK1 in the absence of active caspase-8. Here, we review articles that have reported that necroptosis significantly contributes to negative events occurring with the ischemic brain stroke, and that its inhibition is protective both in vitro and in vivo. We also review articles describing positive effects obtained by reducing necroptosis, including the reduction of infarct volume and improved functional recovery in animal models. Since necroptosis is characterized by cell content leakage and subsequent inflammation, in addition to reducing cell death, inhibition of necroptosis in ischemic brain stroke also reduces some inflammatory cytokines. By comparing various approaches in inhibition of necroptosis, we analyze the achieved effects from the perspective of controlling necroptosis as a part of future therapeutic interventions in brain ischemia.

RIP1/RIP3-regulated necroptosis as a target for multifaceted disease therapy (Review)

Necroptosis is a type of programmed cell death with necrotic morphology, occurring in a variety of biological processes, including inflammation, immune response, embryonic development and metabolic abnormalities. The current nomenclature defines necroptosis as cell death mediated by signal transduction from receptor‑interacting serine/threonine kinase (RIP) 1 to RIP3 (hereafter called RIP1/RIP3). However, RIP3‑dependent cell death would be a more precise definition of necroptosis. RIP3 is indispensable for necroptosis, while RIP1 is not consistently involved in the signal transduction. Notably, deletion of RIP1 even promotes RIP3‑mediated necroptosis under certain conditions. Necroptosis was previously thought as an alternate process of cell death in case of apoptosis inhibition. Currently, necroptosis is recognized to serve a pivotal role in regulating various physiological processes. Of note, it mediates a variety of human diseases, such as ischemic brain injury, immune system disorders and cancer. Targeting and inhibiting necroptosis, therefore, has the potential to be used for therapeutic purposes. To date, research has elucidated the suppression of RIP1/RIP3 via effective inhibitors and highlighted their potential application in disease therapy. The present review focused on the molecular mechanisms of RIP1/RIP3‑mediated necroptosis, explored the functions of RIP1/RIP3 in necroptosis, discussed their potential as a novel therapeutic target for disease therapy, and provided valuable suggestions for further study in this field.

Ligustroflavone reduces necroptosis in rat brain after ischemic stroke through targeting RIPK1/RIPK3/MLKL pathway

Receptor-interacting protein kinase 1/3 (RIPK1/3) and mixed lineage kinase domain-like (MLKL)-mediated necroptosis contributes to brain injury after ischemic stroke. Ligustroflavone is an ingredient of common privet with activities of anti-inflammation and complement inhibition. This study aims to explore the effect of ligustroflavone on ischemic brain injury in stroke rat and the underlying mechanisms. A rat model of ischemic stroke was established by middle cerebral artery occlusion (MCAO), which showed ischemic injury (increase in neurological deficit score and infarct volume) and upregulation of necroptosis-associated proteins (RIPK1, RIPK3 and MLKL/p-MLKL). Administration of ligustroflavone (30 mg/kg, i.g.) 15 min before ischemia evidently improved neurological function, reduced infarct volume, and decreased the levels of necroptosis-associated proteins except the RIPK1. Consistently, hypoxia-cultured PC12 cells (O₂/N2/CO₂, 1:94:5, 8 h) caused cellular injury (LDH release and necroposis) concomitant with up-regulation of necroptosis-associated proteins, and these phenomena were blocked in the presence of ligustroflavone (25 μM) except the elevated RIPK1 levels. Using the Molecular Operating Environment (MOE) program, we identified RIPK1, RIPK3, and MLKL as potential targets of ligustroflavone. Further studies showed that the interaction between RIPK3 and RIPK1 or MLKL was significantly enhanced, which was blocked in the presence of ligustroflavone. Based on these observations, we conclude that ligustroflavone protects rat brain from ischemic injury, and its beneficial effect is related to the prevention of necroptosis through a mechanism involving targeting RIPK1, RIPK3, and/or MLKL.