Targeting drugs to mitochondria

Lightening flavin by amination for fluorescent sensing

Monitoring of reactive oxygen species (ROS), such as O2˙-, etc., in organisms is of great significance, not only for their essential role in biological processes, but their excessive production may also result in many diseases. Flavin (FL) is a fluorophore that naturally exists in flavoenzymes, and its fluorescent emission (FE) becomes negligible when reduced. This enables the application of FL derivatives as fluorescent sensors for ROS. We presented a theoretical investigation to address the impact of amino substitution on the photophysical properties of aminoflavins (AmFLs). Resulting from the interplay of electronic and positional effects, amination at C8 enhances the electronic coupling between the ground state and the first singlet excited state by enlarging the adiabatic energy change of the electronic transitions and the emission transition dipole moments, weakens the vibronic coupling by decreasing the contribution of isoalloxazine to the frontier molecular orbitals, redshifts the absorption band, and enhances the fluorescent emission drastically in 8AmFL. The theoretically estimated fluorescent emission intensity of 8AmFL is ∼40 times that of FL, suggesting its potential application as a fluorescent sensor.

Unlocking mitochondrial drug targets: The importance of mitochondrial transport proteins

A disturbed mitochondrial function contributes to the pathology of many common diseases. These organelles are therefore important therapeutic targets. On the contrary, many adverse effects of drugs can be explained by a mitochondrial off-target effect, in particular, due to an interaction with carrier proteins in the inner membrane. Yet this class of transport proteins remains underappreciated and understudied. The aim of this review is to provide a deeper understanding of the role of mitochondrial carriers in health and disease and their significance as drug targets. We present literature-based evidence that mitochondrial carrier proteins are associated with prevalent diseases and emphasize their potential as drug (off-)target sites by summarizing known mitochondrial drug-transporter interactions. Studying these carriers will enhance our knowledge of mitochondrial drug on- and off-targets and provide opportunities to further improve the efficacy and safety of drugs.

The Therapeutic Potential of Targeting Ferroptosis in the Treatment of Mitochondrial Cardiomyopathies and Heart Failure

ABSTRACT

Ferroptosis is a form of iron-regulated cell death implicated in a wide array of diseases, including heart failure, hypertension, and numerous cardiomyopathies. In addition, mitochondrial dysfunction has been associated with several of these same disease states. However, the role of the mitochondrion in ferroptotic cell death remains debated. As a major regulator of cellular iron levels, the mitochondria may very well play a crucial role in the mechanisms behind ferroptosis, but at this point, this has not been adequately defined. Emerging evidence from our laboratory and others indicates a critical role of mitochondrial Sirtuin 3, a deacetylase linked with longevity and protection against numerous conditions, in the prevention of cardiovascular diseases. Here, we provide a brief overview of the potential roles of Sirtuin 3 in mitochondrial iron homeostasis and its contribution to the mitochondrial cardiomyopathy of Friedreich's ataxia and diabetic cardiomyopathy. We also discuss the current knowledge of the involvement of ferroptosis and the mitochondria in these and other cardiovascular disease states, including doxorubicin-induced cardiomyopathy, and provide insight into areas requiring further investigation.

The small-molecule kinase inhibitor ceritinib, unlike imatinib, causes a significant disturbance of lipid membrane integrity: A combined experimental and MD study

Ceritinib and imatinib are small-molecule protein kinase inhibitors which are applied as therapeutic agents against various diseases. The fundamentals of their clinical use, i.e. their pharmacokinetics as well as the mechanisms of the inhibition of the respective kinases, are relatively well studied. However, the interaction of the drugs with membranes, which can be a possible cause of side effects, has hardly been investigated so far. Therefore, we have characterized the interaction of both drugs with lipid membranes consisting of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) in the absence and in the presence of cholesterol. For determining the membrane impact of both drugs on a molecular level, different experimental (NMR, ESR, fluorescence) and theoretical (MD simulations) approaches were applied. The data show that ceritinib, in contrast to imatinib, interacts more effectively with membranes significantly affecting various physico-chemical membrane parameters like membrane order and transmembrane permeation of polar solutes. The pronounced membrane impact of ceritinib can be explained by a strong affinity of the drug towards POPC which competes with the POPC-cholesterol interaction by that attenuating the ordering effect of cholesterol. The data are relevant for understanding putative toxic and cytotoxic side effects of these drugs such as the triggering of cell lysis or apoptosis.

Dendrimers in Alzheimer’s Disease: Recent Approaches in Multi-Targeting Strategies

Nanomaterials play an increasingly important role in current medicinal practice. As one of the most significant causes of human mortality, and one that is increasing year by year, Alzheimer’s disease (AD) has been the subject of a very great body of research and is an area in which nanomedicinal approaches show great promise. Dendrimers are a class of multivalent nanomaterials which can accommodate a wide range of modifications that enable them to be used as drug delivery systems. By means of suitable design, they can incorporate multiple functionalities to enable transport across the blood–brain barrier and subsequently target the diseased areas of the brain. In addition, a number of dendrimers by themselves often display therapeutic potential for AD. In this review, the various hypotheses relating to the development of AD and the proposed therapeutic interventions involving dendrimer–base systems are outlined. Special attention is focused on more recent results and on the importance of aspects such as oxidative stress, neuroinflammation and mitochondrial dysfunction in approaches to the design of new treatments.

Flecainide induces a sustained countercurrent dependent effect on RyR2 in permeabilized WT ventricular myocytes but not in intact cells

Background and purpose: While flecainide is now an accepted treatment for arrhythmias associated with catecholaminergic polymorphic ventricular tachycardia (CPVT), its mechanism of action remains controversial. In studies on myocytes from CPVT mice, inhibition of proarrhythmic Ca²⁺ waves was initially attributed to a novel action on the type-2 ryanodine receptor (RyR2). However, subsequent work on wild type (WT) myocytes questioned the conclusion that flecainide has a direct action on RyR2. In the present study, the effects of flecainide were compared in intact and permeabilized WT myocytes. Experimental approach: Intracellular Ca²⁺ was measured using confocal microscopy in intact or saponin permeabilized adult rat ventricular myocytes (ARVM). In some experiments on permeabilized cells, flecainide was studied following partial inhibition of the sarcoplasmic reticulum (SR) counter-current. Key results: Flecainide induced sustained changes Ca²⁺ sparks and waves in permeabilized ARVM, which were comparable to those reported in intact or permeabilized myocytes from CPVT mice. However, a relatively high level of flecainide (25 μM) was required to induce these effects. Inhibition of the SR counter-current potentiated the effects of flecainide on SR Ca²⁺ waves. In intact field stimulated ARVM, prolonged exposure to 15 μM flecainide decreased wave frequency but RyR2 dependent effects on Ca²⁺ sparks were absent; higher drug concentrations blocked field stimulation, consistent with inhibition of Nav1.5. Conclusions and implications: In intact ARVM, the absence of effects on Ca²⁺ sparks suggests that the intracellular flecainide concentration was insufficient to influence RyR2. Wave inhibition in intact ARVM may reflect secondary effects of Nav1.5 inhibition. Potentiation of flecainide's action by counter-current inhibition can be explained if transient polarization of the SR membrane during SR Ca²⁺ release facilitates its action on RyR2.

Aggregation-Induced Emission Luminogens for Enhanced Photodynamic Therapy: From Organelle Targeting to Tumor Targeting

Photodynamic therapy (PDT) has attracted much attention in the field of anticancer treatment. However, PDT has to face challenges, such as aggregation caused by quenching of reactive oxygen species (ROS), and short ¹O₂ lifetime, which lead to unsatisfactory therapeutic effect. Aggregation-induced emission luminogen (AIEgens)-based photosensitizers (PSs) showed enhanced ROS generation upon aggregation, which showed great potential for hypoxic tumor treatment with enhanced PDT effect. In this review, we summarized the design strategies and applications of AIEgen-based PSs with improved PDT efficacy since 2019. Firstly, we introduce the research background and some basic knowledge in the related field. Secondly, the recent approaches of AIEgen-based PSs for enhanced PDT are summarized in two categories: (1) organelle-targeting PSs that could cause direct damage to organelles to enhance PDT effects, and (2) PSs with tumor-targeting abilities to selectively suppress tumor growth and reduce side effects. Finally, current challenges and future opportunities are discussed. We hope this review can offer new insights and inspirations for the development of AIEgen-based PSs for better PDT effect.

Mitochondria and sensory processing in inflammatory and neuropathic pain

Rheumatic diseases, such as osteoarthritis and rheumatoid arthritis, affect over 750 million people worldwide and contribute to approximately 40% of chronic pain cases. Inflammation and tissue damage contribute to pain in rheumatic diseases, but pain often persists even when inflammation/damage is resolved. Mechanisms that cause this persistent pain are still unclear. Mitochondria are essential for a myriad of cellular processes and regulate neuronal functions. Mitochondrial dysfunction has been implicated in multiple neurological disorders, but its role in sensory processing and pain in rheumatic diseases is relatively unexplored. This review provides a comprehensive understanding of how mitochondrial dysfunction connects inflammation and damage-associated pathways to neuronal sensitization and persistent pain. To provide an overall framework on how mitochondria control pain, we explored recent evidence in inflammatory and neuropathic pain conditions. Mitochondria have intrinsic quality control mechanisms to prevent functional deficits and cellular damage. We will discuss the link between neuronal activity, mitochondrial dysfunction and chronic pain. Lastly, pharmacological strategies aimed at reestablishing mitochondrial functions or boosting mitochondrial dynamics as therapeutic interventions for chronic pain are discussed. The evidence presented in this review shows that mitochondria dysfunction may play a role in rheumatic pain. The dysfunction is not restricted to neuronal cells in the peripheral and central nervous system, but also includes blood cells and cells at the joint level that may affect pain pathways indirectly. Pre-clinical and clinical data suggest that modulation of mitochondrial functions can be used to attenuate or eliminate pain, which could be beneficial for multiple rheumatic diseases.

Silver nanoparticles induce developmental toxicity via oxidative stress and mitochondrial dysfunction in zebrafish (Danio rerio)

Sliver nanoparticles (AgNPs) are widely used in industry, agriculture, and medicine, potentially resulting in adverse effects on human health and aquatic environments. Here, we investigated the developmental toxicity of zebrafish embryos with acute exposure to AgNPs. Our results demonstrated developmental defects in 4 hpf zebrafish embryos after exposure to different concentrations of AgNPs for 72 h. In addition, RNA-seq profiling of zebrafish embryos after AgNPs treatment. Further Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses showed that the differentially expressed genes (DEGs) were enriched in DNA replication initiation, oxidoreductase activity, DNA replication, cellular senescence, and oxidative phosphorylation signaling pathways in the AgNPs-treated group. Notably, we also found that AgNPs exposure could result in the accumulation of reactive oxygen species (ROS) and malondialdehyde (MDA), the inhibition of superoxide dismutase (SOD), catalase (CAT), and mitochondrial complex I-V activities, and the downregulated expression of SOD, CAT, and mitochondrial complex I-IV chain-related genes. Moreover, the expression of mitochondrion-mediated apoptosis signaling pathway-related genes, such as bax, bcl2, caspase-3, and caspase-9, was significantly regulated after AgNPs exposure in zebrafish. Therefore, these findings demonstrated that AgNPs exposure could cause oxidative stress, induce mitochondrial dysfunction, and ultimately lead to developmental toxicity.

Synthesis, Characterization and Anticancer Efficacy Studies of Iridium (III) Polypyridyl Complexes against Colon Cancer HCT116 Cells

In this paper, two new iridium (III) complexes, [Ir(ppy)2(ipbp)](PF6) (Ir1) (ppy = 2-phenylpyridine, ipbp = 3-(1H-imidazo[4,5-f][1,10]phenanthrolin-2yl)-4H-chromen-4-one) and [Ir(bzq)2(ipbp)](PF6) (Ir2) (bzq = benzo[h]quinolone), were synthesized and characterized. The cytotoxicity of the complexes against human colon cancer HCT116 and normal LO2 cells was evaluated by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method. The complexes Ir1 and Ir2 show high cytotoxic efficacy toward HCT116 cells with a low IC50 value of 1.75 ± 0.10 and 6.12 ± 0.2 µM. Interestingly, Ir1 only kills cancer cells, not normal LO2 cells (IC50 > 200 µM). The inhibition of cell proliferation and migration were investigated by multiple tumor spheroid (3D) and wound healing experiments. The cellular uptake was explored under a fluorescence microscope. The intracellular reactive oxygen species (ROS), change of mitochondrial membrane potential, glutathione (GSH) and adenine nucleoside triphosphate (ATP) were studied. Apoptosis and cell cycle arrest were performed by flow cytometry. The results show that the complexes induce early apoptosis and inhibit the cell proliferation at the G0/G1 phase. Additionally, the apoptotic mechanism was researched by Western blot analysis. The results obtained demonstrate that the complexes cause apoptosis in HCT116 cells through ROS-mediated mitochondrial dysfunction and the inhibition of PI3K/AKT signaling pathways.

An Epigenetic Role of Mitochondria in Cancer

Mitochondria are not only the main energy supplier but are also the cell metabolic center regulating multiple key metaborates that play pivotal roles in epigenetics regulation. These metabolites include acetyl-CoA, α-ketoglutarate (α-KG), S-adenosyl methionine (SAM), NAD⁺, and O-linked beta-N-acetylglucosamine (O-GlcNAc), which are the main substrates for DNA methylation and histone post-translation modifications, essential for gene transcriptional regulation and cell fate determination. Tumorigenesis is attributed to many factors, including gene mutations and tumor microenvironment. Mitochondria and epigenetics play essential roles in tumor initiation, evolution, metastasis, and recurrence. Targeting mitochondrial metabolism and epigenetics are promising therapeutic strategies for tumor treatment. In this review, we summarize the roles of mitochondria in key metabolites required for epigenetics modification and in cell fate regulation and discuss the current strategy in cancer therapies via targeting epigenetic modifiers and related enzymes in metabolic regulation. This review is an important contribution to the understanding of the current metabolic-epigenetic-tumorigenesis concept.

Intracellular Physical Properties with Small Organic Fluorescent Probes: Recent Advances and Future Perspectives

The intracellular physical parameters i. e., polarity, viscosity, fluidity, tension, potential, and temperature of a live cell are the hallmark of cellular health and have garnered immense interest over the past decade. In this context, small molecule organic fluorophores exhibit prominent useful properties including easy functionalizability, environmental sensitivity, biocompatibility, and fast yet efficient cellular uptakability which has made them a popular tool to understand intra-cellular micro-environmental properties. Throughout this discussion, we have outlined the basic design strategies of small molecules for specific organelle targeting and quantification of physical properties. The values of these parameters are indicative of cellular homeostasis and subtle alteration may be considered as the onset of disease. We believe this comprehensive review will facilitate the development of potential future probes for superior insight into the physical parameters that are yet to be quantified.

Dual Stimuli-Responsive Multifunctional Silicon Nanocarriers for Specifically Targeting Mitochondria in Human Cancer Cells

Specific targeting, selective stimuli-responsiveness, and controlled release of anticancer agents are requested for high therapeutic efficiency with a minimal adverse effect. Herein, we report the sophisticated synthesis and functionalization of fluorescent mesoporous silicon (FMPSi) nanoparticles decorated with graphene oxide (GO) nanosheets. GO-wrapped FMPSi (FMPSi@GO) was loaded with a cisplatin (Cis) anticancer agent, and Cis-loaded FMPSi@GO (FMPSi-Cis@GO) exhibited the dual stimuli (pH and NIR)-responsiveness of controlled drug release, i.e., the drug release rate was distinctly enhanced at acidic pH 5.5 than at neutral pH 7.0 and further enhanced under NIR irradiation at acidic pH condition. Notably, dequalinium-conjugated FMPSi-Cis@GO (FMPSi-Cis@GO@DQA) demonstrated an excellent specificity for mitochondrial targeting in cancer cells without noticeable toxicity to normal human cells. Our novel silicon nanocarriers demonstrated not only stimuli (pH and NIR)-responsive controlled drug release, but also selective accumulation in the mitochondria of cancer cells and destroying them.

Emerging trends in nano-bioactive-mediated mitochondria-targeted therapeutic stratagems using polysaccharides, proteins and lipidic carriers

The emergence of new lifestyle disorders and pharmaco-resistant variants of diseases has necessitated the search for effective therapeutic moieties and approaches that could overcome the limitations in the existing treatment modalities. In this context, bioactives such as flavonoids, polyphenols, tannins, terpenoids and alkaloids have demonstrated promise in therapy owing to their ability to scavenge free radicals and modulate the mitochondrial function as well as regulate metabolic pathways. However, their clinical applicability is low owing to their poor bioavailability and aqueous solubility. The encapsulation of bioactives in nanodimensional particles has overcome these limitations to a large extent while simultaneously conferring additional advantages of improved circulation time, enhanced cell uptake and target specific release. A wide range of nanocarriers derived from biopolymers such as polysaccharides, lipids and proteins, have been explored for encapsulation of different bioactives and have reported significant improvement of the bioavailability and therapeutic efficacy of the encapsulated cargo. However, incorporation of cell-specific and mitochondria-specific elements on the nanocarriers has been relatively less explored. This review summarizes some of the recent attempts to treat different disorders using bioactives encapsulated in biopolymer nanostructures and few instances of mitochondria-specific delivery.

Alzheimer's Disease: Pathogenesis and Therapeutic Interventions

BACKGROUND

Alzheimer's Disease (AD) is the most common cause of dementia. Genetics, excessive exposure to environmental pollutants, as well as unhealthy lifestyle practices are often linked to the development of AD. No therapeutic approach has achieved complete success in treating AD; however, early detection and management with appropriate drugs are key to improving prognosis.

INTERVENTIONS

The pathogenesis of AD was extensively discussed in order to understand the reasons for the interventions suggested. The interventions reviewed include the use of different therapeutic agents and approaches, gene therapy, adherence to healthy dietary plans (Mediterranean diet, Okinawan diet and MIND diet), as well as the use of medicinal plants. The potential of nanotechnology as a multidisciplinary and interdisciplinary approach in the design of nano-formulations of AD drugs and the use of Superparamagnetic Iron Oxide Nanoparticles (SPIONs) as theranostic tools for early detection of Alzheimer's disease were also discussed.

The role of FUNDC1 in mitophagy, mitochondrial dynamics and human diseases

Mitochondria are the principal sites of energy metabolism and provide most of the energy needed for normal cellular function. They are dynamic organelles that constantly undergo fission, fusion and mitophagy to maintain their homeostasis and function. However, dysregulated mitochondrial dynamics and mitophagy leads to reduced ATP generation and mutation of their DNA, which ultimately leads to cell death. Increasing evidence has shown that the FUN14 domain-containing protein 1 (FUNDC1), a novel mitophagy receptor, participates in the process of mitochondrial dynamics and mitophagy and plays a critical role in various human diseases. Herein, we review the role of FUNDC1 in mitophagy and mitochondrial dynamics, thus providing a better understanding of the relationship between the two processes. Moreover, we summarize the treatments targeting FUNDC1, and suggest that FUNDC1 may represent a promising therapeutic target for the treatment of several human diseases such as cardiovascular diseases, metabolic syndrome, cancer and chronic obstructive pulmonary disease (COPD).

Precise Subcellular Organelle Targeting for Boosting Endogenous-Stimuli-Mediated Tumor Therapy

Though numerous external-stimuli-triggered tumor therapies, including phototherapy, radiotherapy, and sonodynamic therapy have made great progress in cancer therapy, the low penetration depth of the laser, safety concerns of radiation, the therapeutic resistance, and the spatio-temporal constraints of the specific equipment restrict their convenient clinical applications. What is more, the inherent physiological barriers of the tumor microenvironment (TME), including hypoxia, heterogeneity, and high expression of antioxidant molecules also restrict the efficiency of tumor therapy. As a result, the development of nanoplatforms responsive to endogenous stimuli (such as glucose, acidic pH, cellular redox events, and etc.) has attracted great attention for starvation therapy, ion therapy, prodrug-mediated chemotherapy, or enzyme-catalyzed therapy. In addition, nanomedicines can be modified by some targeted units for precisely locating in subcellular organelles and boosting the destroying of tumor tissue, decreasing the dosage of nanoagents, reducing side effects, and enhancing the therapeutic efficiency. Herein, the properties of the TME, the advantages of endogenous stimuli, and the principles of subcellular-organelle-targeted strategies will be emphasized. Some necessary considerations for the exploitation of precision medicine and clinical translation of multifunctional nanomedicines in the future are also pointed out.

A bright, red-emitting water-soluble BODIPY fluorophore as an alternative to the commercial Mito Tracker Red for high-resolution mitochondrial imaging

With the emergence and rapid development of super-resolution fluorescence microscopy, monitoring of mitochondrial morphological changes has aroused great interest for exploring the role of mitochondria in the process of cell metabolism. However, in the absence of water-soluble, photostable and low-toxicity fluorescent dyes, ultra-high-resolution mitochondrial imaging is still challenging. Herein, we designed two fluorescent BODIPY dyes, namely Mito-BDP 630 and Mito-BDP 760, for mitochondrial imaging. The results proved that Mito-BDP 760 underwent aggregation-caused quenching (ACQ) in the aqueous matrix owing to its hydrophobicity and was inaccessible to the cells, which restricted its applications in mitochondrial imaging. In stark contrast, water-soluble Mito-BDP 630 readily penetrated cellular and mitochondrial membranes for mitochondrial imaging with high dye densities under wash-free conditions as driven by membrane potential. As a comparison, Mito Tracker Red presented high photobleaching (the fluorescence intensity dropped by nearly 50%) and high phototoxicity after irradiation by a laser for 30 min. However, Mito-BDP 630 possessed excellent biocompatibility, photostability and chemical stability. Furthermore, clear and bright mitochondria distribution in living HeLa cells after incubation with Mito-BDP 630 could be observed by CLSM. Convincingly, the morphology and cristae of mitochondria could be visualized using an ultra-high-resolution microscope. In short, Mito-BDP 630 provided a powerful and convenient tool for monitoring mitochondrial morphologies in living cells. Given the facile synthesis, photobleaching resistance and low phototoxicity of Mito-BDP 630, it is an alternative to the commercial Mito Tracker Red.

Green tea catechins EGCG and ECG enhance the fitness and lifespan of Caenorhabditis elegans by complex I inhibition

Green tea catechins are associated with a delay in aging. We have designed the current study to investigate the impact and to unveil the target of the most abundant green tea catechins, epigallocatechin gallate (EGCG) and epicatechin gallate (ECG).

Experiments were performed in Caenorhabditis elegans to analyze cellular metabolism, ROS homeostasis, stress resistance, physical exercise capacity, health- and lifespan, and the underlying signaling pathways. Besides, we examined the impact of EGCG and ECG in isolated murine mitochondria.

A concentration of 2.5 μM EGCG and ECG enhanced health- and lifespan as well as stress resistance in C. elegans. Catechins hampered mitochondrial respiration in C. elegans after 6–12 h and the activity of complex I in isolated rodent mitochondria. The impaired mitochondrial respiration was accompanied by a transient drop in ATP production and a temporary increase in ROS levels in C. elegans. After 24 h, mitochondrial respiration and ATP levels got restored, and ROS levels even dropped below control conditions. The lifespan increases induced by EGCG and ECG were dependent on AAK-2/AMPK and SIR-2.1/SIRT1, as well as on PMK-1/p38 MAPK, SKN-1/NRF2, and DAF-16/FOXO. Long-term effects included significantly diminished fat content and enhanced SOD and CAT activities, required for the positive impact of catechins on lifespan.

In summary, complex I inhibition by EGCG and ECG induced a transient drop in cellular ATP levels and a temporary ROS burst, resulting in SKN-1 and DAF-16 activation. Through adaptative responses, catechins reduced fat content, enhanced ROS defense, and improved healthspan in the long term.

Gasping for Sulfide: A Critical Appraisal of Hydrogen Sulfide in Lung Disease and Accelerated Aging

Hydrogen sulfide (H₂S) is a gaseous signaling molecule involved in a plethora of physiological and pathological processes. It is primarily synthesized by cystathionine-β-synthase, cystathionine-γ-lyase, and 3-mercaptopyruvate sulfurtransferase as a metabolite of the transsulfuration pathway. H₂S has been shown to exert beneficial roles in lung disease acting as an anti-inflammatory and antiviral and to ameliorate cell metabolism and protect from oxidative stress. H₂S interacts with transcription factors, ion channels, and a multitude of proteins via post-translational modifications through S-persulfidation ("sulfhydration"). Perturbation of endogenous H₂S synthesis and/or levels have been implicated in the development of accelerated lung aging and diseases, including asthma, chronic obstructive pulmonary disease, and fibrosis. Furthermore, evidence indicates that persulfidation is decreased with aging. Here, we review the use of H₂S as a biomarker of lung pathologies and discuss the potential of using H₂S-generating molecules and synthesis inhibitors to treat respiratory diseases. Furthermore, we provide a critical appraisal of methods of detection used to quantify H₂S concentration in biological samples and discuss the challenges of characterizing physiological and pathological levels. Considerations and caveats of using H₂S delivery molecules, the choice of generating molecules, and concentrations are also reviewed. Antioxid. Redox Signal. 35, 551-579.

Routes for Potassium Ions across Mitochondrial Membranes: A Biophysical Point of View with Special Focus on the ATP-Sensitive K+ Channel

Potassium ions can cross both the outer and inner mitochondrial membranes by means of multiple routes. A few potassium-permeable ion channels exist in the outer membrane, while in the inner membrane, a multitude of different potassium-selective and potassium-permeable channels mediate K+ uptake into energized mitochondria. In contrast, potassium is exported from the matrix thanks to an H+/K+ exchanger whose molecular identity is still debated. Among the K+ channels of the inner mitochondrial membrane, the most widely studied is the ATP-dependent potassium channel, whose pharmacological activation protects cells against ischemic damage and neuronal injury. In this review, we briefly summarize and compare the different hypotheses regarding the molecular identity of this patho-physiologically relevant channel, taking into account the electrophysiological characteristics of the proposed components. In addition, we discuss the characteristics of the other channels sharing localization to both the plasma membrane and mitochondria.

Mitochondrial nanomedicine: Subcellular organelle-specific delivery of molecular medicines

As mitochondria network together to act as the master sensors and effectors of apoptosis, ATP production, reactive oxygen species management, mitophagy/autophagy, and homeostasis; this organelle is an ideal target for pharmaceutical manipulation. Mitochondrial dysfunction contributes to many diseases, for example, β-amyloid has been shown to interfere with mitochondrial protein import and induce apoptosis in Alzheimer's Disease while some forms of Parkinson's Disease are associated with dysfunctional mitochondrial PINK1 and Parkin proteins. Mitochondrial medicine has applications in the treatment of an array of pathologies from cancer to cardiovascular disease. A challenge of mitochondrial medicine is directing therapies to a subcellular target. Nanotechnology based approaches combined with mitochondrial targeting strategies can greatly improve the clinical translation and effectiveness of mitochondrial medicine. This review discusses mitochondrial drug delivery approaches and applications of mitochondrial nanomedicines. Nanomedicine approaches have the potential to drive the success of mitochondrial therapies into the clinic.

Triphenylphosphonium functionalized Ficus religiosa L. extract loaded nanoparticles improve the mitochondrial function in oxidative stress induced diabetes

The present study was aimed to enhance the mitochondrial function in oxidative stress-induced diabetes. To achieve this, Ficus religiosa L. extract loaded solid lipid nanoparticles (ETNPs) were prepared and functionalized by using triphenylphosphonium. Developed nanoparticles demonstrated desired quality attributes with sustained release for up to 24 h and excellent storage stability for up to 180 days at 40 ± 2°C and 75 ± 5% relative humidity. In vitro cytotoxicity assessment showed no toxicity of ETNPs. Interestingly, oral administration of ETNPs to diabetic rats demonstrated improved mitochondrial function by normalizing the mitochondrial morphology, intracellular calcium ion concentration, complexes I, II, IV, and V activity, mitochondrial membrane potential, and antioxidant levels. Further, reduction in apoptotic markers viz. cytochrome-C, caspase-3, and caspase-9 was observed following the ETNP treatment. Moreover, significant reduction in blood glucose and glycosylated hemoglobin while significant improvement in plasma insulin was observed as compared to the diabetic group following the treatment with developed formulation. Furthermore, histopathology studies confirmed the safety of the developed formulation and thus, data in hand collectively suggest that proposed strategy can be effectively used to improve the mitochondrial function in oxidative stress-induced diabetes along with better control over blood glucose and glycosylated hemoglobin.

Atherosclerosis as Mitochondriopathy: Repositioning the Disease to Help Finding New Therapies

Atherosclerosis is a complex pathology that involves both metabolic dysfunction and chronic inflammatory process. During the last decade, a considerable progress was achieved in describing the pathophysiological features of atherosclerosis and developing approaches that target the abnormal lipid metabolism and chronic inflammation. However, early events in the arterial wall that initiate the disease development still remain obscure. Finding effective therapeutic targets in these early processes would allow developing methods for disease prevention and, possibly, atherosclerotic plaque regression. Currently, these early events are being actively studied by several research groups. One of the processes that are being investigated is the development of mitochondrial dysfunction, which was demonstrated to be present in the affected areas of the arterial wall. Detection and characterization of mitochondrial dysfunction associated with several chronic human disorders was made possible by the improved methods of studying mitochondrial biology and detecting mitochondrial DNA (mtDNA) mutations. It was found to be involved in several key atherogenic processes, such as oxidative stress, chronic inflammation, and intracellular lipid accumulation. Mitochondrial dysfunction can occur in all types of cells involved in the pathogenesis of atherosclerosis: monocytes and macrophages, smooth muscle cells, lymphocytes, and the endothelial cells. However, therapies that would specifically target the mitochondria to correct mitochondrial dysfunction and neutralize the defective organelles are still remain to be developed and characterized. The aim of this review is to outline the prospects for mitochondrial therapy for atherosclerosis. We discuss mechanisms of mitochondria-mediated atherogenic processes, known mitochondria-targeting therapy strategies, and novel mitochondria-targeting drugs in the context of atherosclerosis.

Majonoside-R2 extracted from Vietnamese ginseng protects H9C2 cells against hypoxia/reoxygenation injury via modulating mitochondrial function and biogenesis

Vietnamese ginseng has a therapeutic effect on various diseases; however its bioactivity against cardiac hypoxia/reoxygenation (HR) injury remains unclear. In this study, we evaluated the protective roles of total saponin extract (TSE) and majonoside-R2 (MR2) targeting mitochondria in HR-induced rat cardiomyocyte H9C2 cells. The results showed that both TSE and MR2 effectively protected the cells from HR damage. Particularly, 9 µM of MR2 significantly increased the viability of HR-induced cells (p < 0.05). Interestingly, MR2 treatment markedly prevented the loss of mitochondrial membrane potential and cardiolipin content, and an increase in reactive oxygen species production in HR-treated H9C2 cells. Moreover, MR2 treatment altered the mRNA expression of genes involved in mitochondrial biogenesis under HR conditions. The present study documented for the first time the cardioprotective effects of MR2 against HR injury by maintaining mitochondrial function and modulating mitochondrial biogenesis.

Mitochondria-targeted antioxidant, mito-TEMPO mitigates initiation phase of N-Nitrosodiethylamine-induced hepatocarcinogenesis

Targeting mitochondrial oxidative stress during initial stages of hepatocarcinogenesis can be an effective and promising strategy to prevent hepatocellular carcinoma (HCC). In the present study, mitochondria targeted antioxidant, mito-TEMPO was administered to male BALB/c mice at a dosage 0.1 mg/kg b.w. (intraperitoneal) twice a week, followed by single N-Nitrosodiethylamine (NDEA) intraperitoneal injection (10 mg/kg b.w.). After 24 h of NDEA administration, animals were sacrificed, blood and liver tissue were collected. Liver injury markers, histoarchitecture, antioxidant defence status, mitochondrial reactive oxygen species (ROS), lipid peroxidation (LPO), mitochondrial dysfunction analysis, and mitochondrial membrane potential were investigated. Mito-TEMPO pre-treatment protected animals from the damaging effects of NDEA as observed by normalization of liver injury markers. NDEA metabolism resulted in a significantly increased intracellular and mitochondrial ROS generation with concomitant increase in LPO formation. The activity of mitochondrial complex I, complex II, malate dehydrogenase were significantly reduced and mitochondrial membrane potential was increased. Mito-TEMPO effectively scavenged NDEA-induced ROS generation and reduced LPO formation. A significant improvement was also observed in the activity of mitochondrial complex I, complex II, malate dehydrogenase and normalisation of mitochondrial membrane potential. Results suggested that mito-TEMPO had significant impact on the initiation phase of hepatocarcinogensis which could be one of the reason for its reported chemopreventive effect.

Anti-metastasis and anti-proliferation effect of mitochondria-accumulating ruthenium(II) complexes via redox homeostasis disturbance and energy depletion

The antiproliferative activity of three cyclometalated Ru(II) complexes with the formula [Ru(bpy)₂L]PF₆, where bpy = 2,2'-bipyridine, Ru1: L1 = phenanthro[4,5-fgh]quinoxaline; Ru2: L2 = benzo[f]naphtho[2,1-h]quinoxaline; and Ru3: L3 = phenanthro[9,10-b]pyrazine, have been synthesized and characterized. The lipophilicity of the three Ru(II) complexes was modulated by the alteration of the planarity in the ligands of the complexes. With appropriate lipophilicity, Ru1-Ru3 exhibited mitochondrial accumulating property and cytotoxic activity against a spectrum of cancer cell lines. The underlying mechanism study indicated that these Ru(II) complexes can selectively accumulate in mitochondria and disrupt physiological processes, including the redox balance and energy generation in cancer cells. Elevation of iron content in triple-negative breast cancer (MDA-MB-231 cells) was observed after treatment with Ru(II) complexes, which may contribute to the production of reactive oxygen species (ROS) via Fenton reaction chemistry. Besides, the Ru(II) complexes decreased the intracellular glutathione (GSH) in cancer cells, leading to the failure in the cells to combat oxidative damage. Both of the mentioned processes contribute to the high oxidative stress and eventually lead to cancer cell death. On the other hand, Ru1-Ru3 significantly induced the depletion of adenosine triphosphate (ATP), causing disturbance of energy generation. Moreover, the results of wound-healing assay and transwell invasion assay, as well as the tube formation assay indicated the anti-migration and anti-angiogenesis properties of Ru1-Ru3. Our study demonstrated that these Ru(II) complexes are promising chemotherapeutic agents with oxidative stress induction and energy generation disturbance.

Triphenylphosphonium derivatives disrupt metabolism and inhibit melanoma growth in vivo when delivered via a thermosensitive hydrogel

Despite dramatic improvements in outcomes arising from the introduction of targeted therapies and immunotherapies, metastatic melanoma is a highly resistant form of cancer with 5 year survival rates of <35%. Drug resistance is frequently reported to be associated with changes in oxidative metabolism that lead to malignancy that is non-responsive to current treatments. The current report demonstrates that triphenylphosphonium(TPP)-based lipophilic cations can be utilized to induce cytotoxicity in pre-clinical models of malignant melanoma by disrupting mitochondrial metabolism. In vitro experiments demonstrated that TPP-derivatives modified with aliphatic side chains accumulated in melanoma cell mitochondria; disrupted mitochondrial metabolism; led to increases in steady-state levels of reactive oxygen species; decreased total glutathione; increased the fraction of glutathione disulfide; and caused cell killing by a thiol-dependent process that could be rescued by N-acetylcysteine. Furthermore, TPP-derivative-induced melanoma toxicity was enhanced by glutathione depletion (using buthionine sulfoximine) as well as inhibition of thioredoxin reductase (using auranofin). In addition, there was a structure-activity relationship between the aliphatic side-chain length of TPP-derivatives (5–16 carbons), where longer carbon chains increased melanoma cell metabolic disruption and cell killing. In vivo bio-distribution experiments showed that intratumoral administration of a C¹⁴-TPP-derivative (12-carbon aliphatic chain), using a slow-release thermosensitive hydrogel as a delivery vehicle, localized the drug at the melanoma tumor site. There, it was observed to persist and decrease the growth rate of melanoma tumors. These results demonstrate that TPP-derivatives selectively induce thiol-dependent metabolic oxidative stress and cell killing in malignant melanoma and support the hypothesis that a hydrogel-based TPP-derivative delivery system could represent a therapeutic drug-delivery strategy for melanoma.

High expression of the TEFM gene predicts poor prognosis in hepatocellular carcinoma

BACKGROUND

Mitochondrial transcription elongation factor (TEFM) is an essential molecule that regulates the replication-transcription switch of mitochondrial DNA. TEFM modulates both transcription elongation and RNA processing in mitochondria. The purpose of the present study was to determine the association of TEFM with tumor progression and prognosis in hepatocellular carcinoma (HCC) patients.

METHODS

The different protein expression level of TEFM among HCC cell lines was detected by Western blotting. The gene expression profiling interactive analysis (GEPIA) was used to dynamically analyze the mRNA expression of TEFM gene in different stages of HCC. The protein and mRNA expression levels of TEFM were detected by immunohistochemistry, Western blotting and qRT-PCR. The mRNA-SeqV2 expression of TEFM and clinical information of HCC patients were downloaded from the TCGA database by using R3.6.3 software. Next, the relationships between the expression level of TEFM and clinicopathological characteristics and the prognostic value of TEFM were analyzed. A Cox regression model was used for multivariate analysis of the factors that affected the prognosis of HCC. Finally, the association between the expression levels of TEFM and other mitochondrial regulatory genes and HCC biomarker genes was analyzed by GEPIA.

RESULTS

TEFM is upregulated in HCC cell lines compared to noncancerous liver cell line. TEFM protein and mRNA expression levels in HCC tissues were significantly upregulated compared with those in noncancerous liver tissues. In addition, the mRNA expression level of TEFM was significantly correlated with sex, serum AFP level, and vascular invasion (P<0.05). Further analysis showed that high expression level of TEFM was unfavorable in terms of the prognosis of patients with HCC. Cox multivariate regression analysis showed that patient age, vascular invasion, and TEFM expression were independent factors affecting the prognosis of HCC patients (P<0.05). The expression level of the TEFM gene was significantly positively correlated with the expression of multiple mitochondrial regulatory genes and biomarker genes of HCC (P<0.01, R>0).

CONCLUSIONS

Our findings reveal that TEFM may play an important role in the progression of HCC. More importantly, the elevated expression of TEFM may potentially predict poor overall survival (OS) and disease-free survival (DFS) in patients with HCC.

Mitocans Revisited: Mitochondrial Targeting as Efficient Anti-Cancer Therapy

Mitochondria are essential cellular organelles, controlling multiple signalling pathways critical for cell survival and cell death. Increasing evidence suggests that mitochondrial metabolism and functions are indispensable in tumorigenesis and cancer progression, rendering mitochondria and mitochondrial functions as plausible targets for anti-cancer therapeutics. In this review, we summarised the major strategies of selective targeting of mitochondria and their functions to combat cancer, including targeting mitochondrial metabolism, the electron transport chain and tricarboxylic acid cycle, mitochondrial redox signalling pathways, and ROS homeostasis. We highlight that delivering anti-cancer drugs into mitochondria exhibits enormous potential for future cancer therapeutic strategies, with a great advantage of potentially overcoming drug resistance. Mitocans, exemplified by mitochondrially targeted vitamin E succinate and tamoxifen (MitoTam), selectively target cancer cell mitochondria and efficiently kill multiple types of cancer cells by disrupting mitochondrial function, with MitoTam currently undergoing a clinical trial.

Chromon-3-aldehyde derivatives restore mitochondrial function in rat cerebral ischemia

Objectives

This work aimed to assess the effect of 10 new chromon-3-aldehyde derivatives on changes of mitochondrial function under the conditions of brain ischemia in rats.

Materials and Methods

The work was executed on BALB/c male-mice (acute toxicity was evaluated) and male Wistar rats, which were used to model cerebral ischemia by permanent middle cerebral artery occlusion. The test-substances, 10 derivatives of chromon-3-aldehyde and the reference drug, N-acetylcysteine, were injected after modeling of ischemia for 3 days. After that, neurological symptoms, the area of cerebral infarction, and change in mitochondrial function were evaluated.

Results

It was established that use of all chromon-3-aldehyde derivatives contributed to the recovery of mitochondrial function, which was reflected in enhanced ATP-generating activity, maximum respiration level, respiratory capacity, as well as reduction in the intensity of anaerobic reactions, apoptosis, and normalization of the mitochondrial membrane potential. The most pronounced changes were noted with the use of 6-acetyl substituted chromon-3-aldehyde derivative, the administration of which decreased neurological symptoms and size of brain necrosis area.

Conclusion

The obtained data may indicate the most pronounced neurotropic effect in a number of test-objects has the 6-acetyl substituted derivative of chromon-3 aldehyde, realized by restoration of mitochondrial function, which may be the basis for further study of chromon-3-aldehyde derivatives.

Smart Design of Nanomaterials for Mitochondria-Targeted Nanotherapeutics

Mitochondria are the powerhouse of cells. They are vital organelles that maintain cellular function and metabolism. Dysfunction of mitochondria results in various diseases with a great diversity of clinical appearances. In the past, strategies have been developed for fabricating subcellular-targeting drug-delivery nanocarriers, enabling cellular internalization and subsequent organelle localization. Of late, innovative strategies have emerged for the smart design of multifunctional nanocarriers. Hierarchical targeting enables nanocarriers to evade and overcome various barriers encountered upon in vivo administration to reach the organelle with good bioavailability. Stimuli-responsive nanocarriers allow controlled release of therapeutics to occur at the desired target site. Synergistic therapy can be achieved using a combination of approaches such as chemotherapy, gene and phototherapy. In this Review, we survey the field for recent developments and strategies used in the smart design of nanocarriers for mitochondria-targeted therapeutics. Existing challenges and unexplored therapeutic opportunities are also highlighted and discussed to inspire the next generation of mitochondrial-targeting nanotherapeutics.

Targeting Mitochondria in Tumor-Associated Macrophages using a Dendrimer-Conjugated TSPO Ligand that Stimulates Antitumor Signaling in Glioblastoma

Mitochondria mediate critical cellular processes, including proliferation, apoptosis, and immune responses; as such, their dysfunction is pathogenic in many neurodegenerative disorders and cancers. In glioblastoma, targeted delivery of mitochondria-focused anticancer therapies has failed to translate into clinical success due to the nonspecific cellular localization, heterogeneity of receptor expression across patients, poor transport across biological barriers to reach the brain, tumor, and mitochondria, and systemic side effects. Strategies that can overcome brain and solid tumor barriers and selectively target mitochondria within specific cell types may lead to improvements in glioblastoma treatment. Developments in dendrimer-mediated nanomedicines have shown promise targeting tumor-associated macrophages (TAMs) in glioblastoma, following systemic administration. Here, we present a novel dendrimer conjugated to the translocator protein (18 kDa) (TSPO) ligand 5,7-dimethylpyrazolo[1,5-α]pyrimidin-3-ylacetamide (DPA). We developed a clickable DPA for conjugation on the dendrimer surface and demonstrated in vitro that the dendrimer-DPA conjugate (D-DPA) significantly increases dendrimer colocalization with mitochondria. Compared to free TSPO ligand PK11195, D-DPA stimulates greater antitumor immune signaling. In vivo, we show that D-DPA targets mitochondria specifically within TAMs following systemic administration. Our results demonstrate that dendrimers can achieve TAM-specific targeting in glioblastoma and can be further modified to target specific intracellular compartments for organelle-specific drug delivery.

Mitochondrial Potassium Channels as Druggable Targets

Mitochondrial potassium channels have been described as important factors in cell pro-life and death phenomena. The activation of mitochondrial potassium channels, such as ATP-regulated or calcium-activated large conductance potassium channels, may have cytoprotective effects in cardiac or neuronal tissue. It has also been shown that inhibition of the mitochondrial Kv1.3 channel may lead to cancer cell death. Hence, in this paper, we examine the concept of the druggability of mitochondrial potassium channels. To what extent are mitochondrial potassium channels an important, novel, and promising drug target in various organs and tissues? The druggability of mitochondrial potassium channels will be discussed within the context of channel molecular identity, the specificity of potassium channel openers and inhibitors, and the unique regulatory properties of mitochondrial potassium channels. Future prospects of the druggability concept of mitochondrial potassium channels will be evaluated in this paper.

Metformin rescues rapamycin-induced mitochondrial dysfunction and attenuates rheumatoid arthritis with metabolic syndrome

Background

Rapamycin, an inhibitor of the serine/threonine protein kinase mTOR, is an immunosuppressant used to treat renal transplant recipients, but it can cause endothelial and mitochondrial dysfunction. Metformin is used for the treatment of type 2 diabetes and was reported to exert therapeutic effects against rheumatoid arthritis and obesity by improving mitochondrial dysfunction via the activation of fibroblast growth factor 21. We investigated the therapeutic effects of rapamycin–metformin combination therapy in obese mice with collagen-induced arthritis (CIA).

Methods

Mouse embryonic fibroblasts were treated with rapamycin, metformin, or rapamycin–metformin, and their respiratory level and mitochondrial gene expression were assayed. Mice were fed a high-fat diet, immunized with type II collagen, and subsequently treated with rapamycin–metformin daily for 10 weeks.

Results

Rapamycin-treated cells exhibited dysfunction of mitochondrial respiration and decreased mitochondrial gene expression compared with rapamycin–metformin-treated cells. Moreover, rapamycin–metformin reduced the clinical arthritis score and the extent of histological inflammation and improved the metabolic profile in obese mice with CIA. Rapamycin–metformin enhanced the balance between T helper 17 and regulatory T cells in vitro and in vivo.

Conclusions

These results suggest that rapamycin–metformin is a potential therapeutic option for autoimmune arthritis.

Combinatory antitumor therapy by cascade targeting of a single drug

Combination therapy has shown its promise in the clinic for enhancing the efficacy of tumor treatment. However, the dose control of multiple drugs and their non-overlapping toxicity from different drugs are still great challenge. In this work, a single model drug, paclitaxel (PTX), is used to realize combination therapy and solve the problems mentioned above. Either PTX or its triphenylphosphine derivative (TPTX) is encapsulated in galactose-modified liposomes (GLips) to obtain GLips-P or GLips-TP, which are simply mixed in different ratios to finely control the proportion of PTX and TPTX. These mixed liposomes, GLips-P/TP, feature a cascade target delivery of PTX, from tissue to cell, and then to organelle. PTX plays a primary role to cause the cytotoxicity by microtubule bindings in cytoplasm, while TPTX is proved to increase the intracellular levels of caspase-3 and caspase-9 that cause apoptosis via a mitochondria-mediated pathway. Notably, GLips-P/TP 3:1 exhibited the significant drug synergy in both cytotoxicity assay of HepG2 cells and the treatment efficacy in Heps xenograft ICR mouse models. This work not only demonstrates the great promise of a cascade targeting delivery for precise tumor treatment, but also offers a novel platform to design combinatory therapy systems using a single drug.

Cyanine dye mediated mitochondrial targeting enhances the anti-cancer activity of small-molecule cargoes

Organelle-specific delivery systems are of significant clinical interest. We demonstrate the use of common cyanine dyes Cy3 and Cy5 as vectors for targeting and delivering cargoes to mitochondria in cancer cells. Specifically, conjugation to the dyes can increase cytotoxicity by up to 1000-fold.

Cu(ii) phenanthroline–phenazine complexes dysregulate mitochondrial function and stimulate apoptosis

Herein we report the central role of the mitochondria in the cytotoxicity of four developmental cytotoxic copper(ii) complexes [Cu(phen)₂]²⁺, [Cu(DPQ)(Phen)]²⁺, [Cu(DPPZ)(Phen)]²⁺and [Cu(DPPN)(Phen)]²⁺superior to cisplatin and independent of resistance in a range of cells.