Functionalized nanosystems for targeted mitochondrial delivery

Targeted Treatment Strategies for Mitochondria Dysfunction: Correlation with Neurological Disorders

Mitochondria are an essential intracellular organelle for medication targeting and delivery since they seem to create energy and conduct many other cellular tasks, and mitochondrial dysfunctions and malfunctions lead to many illnesses. Many initiatives have been taken to detect, diagnose, and image mitochondrial abnormalities, and to transport and accumulate medicines precisely to mitochondria, all because of special mitochondrial aspects of the pathophysiology of cancer. In addition to the negative membrane potential and paradoxical mitochondrial dynamics, they include high temperatures, high levels of reactive oxygen species, high levels of glutathione, and high temperatures. Neurodegenerative diseases represent a broad spectrum of debilitating illnesses. They are linked to the loss of certain groups of neurons based on an individual's physiology or anatomy. The mitochondria in a cell are generally accepted as the authority with respect to ATP production. Disruption of this system is linked to several cellular physiological issues. The development of neurodegenerative disorders has been linked to mitochondrial malfunction, according to pathophysiological studies. There seems to be substantial evidence connecting mitochondrial dysfunction and oxidative stress to the development of neurodegenerative disorders. It has been extensively observed that mitochondrial malfunction triggers autophagy, which plays a role in neurodegenerative disorders. In addition, excitotoxicity and mitochondrial dysfunction have been linked to the development of neurodegenerative disorders. The pathophysiology of neurodegenerative illnesses has been linked to increased apoptosis and necrosis, as well as mitochondrial malfunction. A variety of synthetic and natural treatments have shown efficacy in treating neurodegenerative illnesses caused by mitochondrial failure. Neurodegenerative illnesses can be effectively treated with existing drugs that target mitochondria, although their precise formulations are poorly understood. Therefore, there is an immediate need to focus on creating drug delivery methods specifically targeted at mitochondria in the treatment and diagnosis of neurodegenerative disorders.

Management of Brain Cancer and Neurodegenerative Disorders with Polymer-Based Nanoparticles as a Biocompatible Platform

The blood-brain barrier (BBB) serves as a protective barrier for the central nervous system (CNS) against drugs that enter the bloodstream. The BBB is a key clinical barrier in the treatment of CNS illnesses because it restricts drug entry into the brain. To bypass this barrier and release relevant drugs into the brain matrix, nanotechnology-based delivery systems have been developed. Given the unstable nature of NPs, an appropriate amount of a biocompatible polymer coating on NPs is thought to have a key role in reducing cellular cytotoxicity while also boosting stability. Human serum albumin (HSA), poly (lactic-co-glycolic acid) (PLGA), Polylactide (PLA), poly (alkyl cyanoacrylate) (PACA), gelatin, and chitosan are only a few of the significant polymers mentioned. In this review article, we categorized polymer-coated nanoparticles from basic to complex drug delivery systems and discussed their application as novel drug carriers to the brain.

Therapeutic Potential of Targeting Mitochondria for Alzheimer's Disease Treatment

Alzheimer's disease (AD), a chronic and progressive neurodegenerative disease, is characterized by memory and cognitive impairment and by the accumulation in the brain of abnormal proteins, more precisely beta-amyloid (β-amyloid or Aβ) and Tau proteins. Studies aimed at researching pharmacological treatments against AD have focused precisely on molecules capable, in one way or another, of preventing/eliminating the accumulations of the aforementioned proteins. Unfortunately, more than 100 years after the discovery of the disease, there is still no effective therapy in modifying the biology behind AD and nipping the disease in the bud. This state of affairs has made neuroscientists suspicious, so much so that for several years the idea has gained ground that AD is not a direct neuropathological consequence taking place downstream of the deposition of the two toxic proteins, but rather a multifactorial disease, including mitochondrial dysfunction as an early event in the pathogenesis of AD, occurring even before clinical symptoms. This is the reason why the search for pharmacological agents capable of normalizing the functioning of these subcellular organelles of vital importance for nerve cells is certainly to be considered a promising approach to the design of effective neuroprotective drugs aimed at preserving this organelle to arrest or delay the progression of the disease. Here, our intent is to provide an updated overview of the mitochondrial alterations related to this disorder and of the therapeutic strategies (both natural and synthetic) targeting mitochondrial dysfunction.

Ultrasensitive Reagent for Ratiometric Detection and Detoxification of III in Water and Mitochondria

Toxicity induced by inorganic arsenic as AsO₃^3- (iAs^III) is of global concern. Reliable detection of the maximum allowed contaminant level for arsenic in drinking water and in the cellular system remains a challenge for the water quality management and assessment of toxicity in the cellular milieu, respectively. A new Ir(III)-based phosphorescent molecule (AS-1; λ_Ext = 415 nm and λ_Ems = 600 nm, Φ = 0.3) is synthesized for the selective detection of iAs^III in an aqueous solution with a ratiometric luminescence response even in the presence of iAs^V and all other common inorganic cations and anions. The relatively higher affinity of the thioimidazole ligand (HPBT) toward iAs^III led to the formation of a fluorescent molecule iAs^V-HPBT (λ_Ext = 415 nm and λ_Ems = 466 nm, Φ = 0.28) for the reaction of iAs^III and AS-1. An improved limit of quantitation (LOQ) down to 0.2 ppb is achieved when AS-1 is used in the CTAB micellar system. Presumably, the cationic surfactants favor the localization of AS-1@CTAB^Micelle in mitochondria of MCF7 cells, and this is confirmed from the images of the confocal laser fluorescence scanning microscopic studies. Importantly, cell viability assay studies confirm that AS-1@CTAB^Micelle induces dose-dependent detoxification of iAs^III in live cells. Further, luminescence responses at 466 nm could be utilized for developing a hand-held device for the in-field application. Such a reagent that allows for ratiometric detection of iAs^III with LOQ of 2.6 nM (0.5 ppb) in water, as well as helps in visualizing its distribution in mitochondria with a detoxifying effect, is rather unique in contemporary literature.

Negatively charged gold nanoclusters protect against diabetic cardiomyopathy by inhibiting mitophagy

Negatively charged AuNCs were found to stabilize the membrane potential and inhibit mitophagy, thereby preventing diabetic cardiomyopathy.

Multifunctional Mitochondria-Targeting Nanosystems for Enhanced Anticancer Efficacy

Mitochondria, a kind of subcellular organelle, play crucial roles in cancer cells as an energy source and as a generator of reactive substrates, which concern the generation, proliferation, drug resistance, and other functions of cancer. Therefore, precise delivery of anticancer agents to mitochondria can be a novel strategy for enhanced cancer treatment. Mitochondria have a four-layer structure with a high negative potential, which thereby prevents many molecules from reaching the mitochondria. Luckily, the advances in nanosystems have provided enormous hope to overcome this challenge. These nanosystems include liposomes, nanoparticles, and nanomicelles. Here, we summarize the very latest developments in mitochondria-targeting nanomedicines in cancer treatment as well as focus on designing multifunctional mitochondria-targeting nanosystems based on the latest nanotechnology.

Mitochondria-targeted nanoparticles in treatment of neurodegenerative diseases

Neurodegenerative diseases (NDs) are a class of heterogeneous diseases that includes Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis. Mitochondria play an important role in oxidative balance and metabolic activity of neurons; therefore, mitochondrial dysfunction is associated with NDs and mitochondria are considered a potential treatment target for NDs. Several obstacles, including the blood-brain barrier (BBB) and cell/mitochondrial membranes, reduce the efficiency of drug entry into the target lesions. Therefore, a variety of neuron mitochondrial targeting strategies has been developed. Among them, nanotechnology-based treatments show especially promising results. Owing to their adjustable size, appropriate charge, and lipophilic surface, nanoparticles (NPs) are the ideal theranostic system for crossing the BBB and targeting the neuronal mitochondria. In this review, we discussed the role of dysfunctional mitochondria in ND pathogenesis as well as the physiological barriers to various treatment strategies. We also reviewed the use and advantages of various NPs (including organic, inorganic, and biological membrane-coated NPs) for the treatment and diagnosis of NDs. Finally, we summarized the evidence and possible use for the promising role of NP-based theranostic systems in the treatment of mitochondrial dysfunction-related NDs.

Silver Nanoparticles Stabilized with Phosphorus-Containing Heterocyclic Surfactants: Synthesis, Physico-Chemical Properties, and Biological Activity Determination

Phosphorus-containing heterocyclic cationic surfactants alkyldimethylphenylphospholium bromides with the alkyl chain length 14 to 18 carbon atoms were used for the stabilization of silver nanodispersions. Zeta potential of silver nanodispersions ranges from +35 to +70 mV, which indicates the formation of stable silver nanoparticles (AgNPs). Long-chain heptadecyl and octadecyl homologs of the surfactants series provided the most intensive stabilizing effect to AgNPs, resulting in high positive zeta potential values and smaller diameter of AgNPs in the range 50–60 nm. A comparison with non-heterocyclic alkyltrimethylphosphonium surfactants of the same alkyl chain length showed better stability and more positive zeta potential values for silver nanodispersions stabilized with heterocyclic phospholium surfactants. Investigations of biological activity of phospholium-capped AgNPs are represented by the studies of antimicrobial activity and cytotoxicity. While cytotoxicity results revealed an increased level of HepG2 cell growth inhibition as compared with the cytotoxicity level of silver-free surfactant solutions, no enhanced antimicrobial action of phospholium-capped AgNPs against microbial pathogens was observed. The comparison of cytotoxicity of AgNPs stabilized with various non-heterocyclic ammonium and phosphonium surfactants shows that AgNPs capped with heterocyclic alkyldimethylphenylphospholium and non-heterocyclic triphenyl-substituted phosphonium surfactants have the highest cytotoxicity among silver nanodispersions stabilized by the series of ammonium and phosphonium surfactants.

Mitochondrial-induced Epigenetic Modifications: From Biology to Clinical Translation

Mitochondria are maternally inherited semi-autonomous organelles that play a central role in redox balance, energy metabolism, control of integrated stress responses, and cellular homeostasis. The molecular communication between mitochondria and the nucleus is intricate and bidirectional in nature. Though mitochondrial genome encodes for several key proteins involved in oxidative phosphorylation, several regulatory factors encoded by nuclear DNA are prominent contributors to mitochondrial biogenesis and function. The loss of synergy between this reciprocal control of anterograde (nuclear to mitochondrial) and retrograde (mitochondrial to nuclear) signaling, triggers epigenomic imbalance and affects mitochondrial function and global gene expressions. Recent expansions of our knowledge on mitochondrial epigenomics have offered novel perspectives for the study of several non-communicable diseases including cancer. As mitochondria are considered beacons for pharmacological interventions, new frontiers in targeted delivery approaches could provide opportunities for effective disease management and cure through reversible epigenetic reprogramming. This review focuses on recent progress in the area of mitochondrial-nuclear cross-talk and epigenetic regulation of mitochondrial DNA methylation, mitochondrial micro RNAs, and post-translational modification of mitochondrial nucleoid-associated proteins that hold major opportunities for targeted drug delivery and clinical translation.

Mussel-Inspired Surface Immobilization of Heparin on Magnetic Nanoparticles for Enhanced Wound Repair via Sustained Release of a Growth Factor and M2 Macrophage Polarization

Efficient reconstruction of a fully functional skin after wounds requires multiple functionalities of wound dressing due to the complexity of healing. In these regards, topical administration of functionalized nanoparticles capable of sustainably releasing bioactive agents to the wound site may significantly accelerate wound repair. Among the various nanoparticles, superparamagnetic iron oxide (Fe₃O₄) nanoparticles gain increasing attractiveness due to their intrinsic response to an external magnetic field (eMF). Herein, based on the Fe₃O₄ nanoparticle, we developed a fibroblast growth factor (bFGF)-loaded Fe₃O₄ nanoparticle using a simple mussel-inspired surface immobilization method. This nanoparticle, named as bFGF-HDC@Fe₃O₄, could stabilize bFGF in various conditions and exhibited sustained release of bFGF. In addition, an in vitro study discovered that bFGF-HDC@Fe₃O₄ could promote macrophage polarization toward an anti-inflammatory (pro-healing) M2 phenotype especially under eMF. Further, in vivo full-thickness wound animal models demonstrated that bFGF-HDC@Fe₃O₄ could significantly accelerate wound healing through M2 macrophage polarization and increased cell proliferation. Therefore, this approach of realizing sustained the release of the growth factor with magnetically macrophage regulating behavior through modification of Fe₃O₄ nanoparticles offers promising potential to tissue-regenerative applications.

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.

Ultrasmall copper-based nanoparticles for reactive oxygen species scavenging and alleviation of inflammation related diseases

Oxidative stress is associated with many acute and chronic inflammatory diseases, yet limited treatment is currently available clinically. The development of enzyme-mimicking nanomaterials (nanozymes) with good reactive oxygen species (ROS) scavenging ability and biocompatibility is a promising way for the treatment of ROS-related inflammation. Herein we report a simple and efficient one-step development of ultrasmall Cu5.4O nanoparticles (Cu5.4O USNPs) with multiple enzyme-mimicking and broad-spectrum ROS scavenging ability for the treatment of ROS-related diseases. Cu5.4O USNPs simultaneously possessing catalase-, superoxide dismutase-, and glutathione peroxidase-mimicking enzyme properties exhibit cytoprotective effects against ROS-mediated damage at extremely low dosage and significantly improve treatment outcomes in acute kidney injury, acute liver injury and wound healing. Meanwhile, the ultrasmall size of Cu5.4O USNPs enables rapid renal clearance of the nanomaterial, guaranteeing the biocompatibility. The protective effect and good biocompatibility of Cu5.4O USNPs will facilitate clinical treatment of ROS-related diseases and enable the development of next-generation nanozymes.

Nanoparticles containing β-cyclodextrin potentially useful for the treatment of Niemann-Pick C

β-Cyclodextrin (β-CD) is being considered a promising therapy for Niemann-Pick C (NPC) disease because of its ability to mobilise the entrapped cholesterol from lysosomes, however, a major limitation is its inability to cross the blood-brain barrier (BBB) and address the central nervous system (CNS) manifestations of the disease. Considering this, we aimed to design nanoparticles able to cross the BBB and deliver β-CD into the CNS lysosomes. The physicochemical characteristics of β-CD-loaded nanoparticles were evaluated by dynamic light scattering, small-angle X-ray scattering, and cryogenic transmission electron microscopy. The in vitro analyses were performed with NPC dermal fibroblasts and the β-CD-loaded nanoparticles were tracked in vivo. The nanoparticles showed a mean diameter around 120 nm with a disordered bicontinuous inner structure. The nanoparticles did not cause decrease in cell viability, impairment in the antioxidant enzymes activity, damage to biomolecules or release of reactive species in NPC dermal fibroblasts; also, they did not induce genotoxicity or alter the mitochondrial function in healthy fibroblasts. The β-CD-loaded nanoparticles were taken up by lysosomes reducing the cholesterol accumulated in NPC fibroblasts and reached the CNS of mice more intensely than other organs, demonstrating advantages compared to the free β-CD. The results demonstrated the potential of the β-CD-loaded nanoparticles in reducing the brain impairment of NPC.

Role of Nanomedicine in Redox Mediated Healing at Molecular Level

Nanomedicine, the offspring born from the marriage of nanotechnology and medicine, has already brought momentous advances in the fight against a plethora of unmet diseases from cardiovascular and neurodegenerative to diabetes and cancer. Here, we review a conceptual framework that will provide a basic understanding about the molecular mechanism of action of a therapeutic nanomaterial inside biological milieu. In this review, we highlight how the catalytic nature of a transition metal oxide nanomaterial influences the cellular redox homeostasis, supports the cellular antioxidant defence system and reactivates the reactive oxygen species (ROS) mediated signalling to perform normal cell functions like cell cycle, differentiation, apoptosis, inflammation, toxicity, and protein interactions. With numerous examples, we describe the redox modulatory nature of d-block metal oxide nanomaterials and their biomimetic nanozyme activities to protect the mitochondria, the cellular redox mediator which prevents an organism from various diseases. This knowledge will be useful to design new nanomaterials capable of intracellular redox modulation, which in turn can be effective therapeutic agents for treatment of various unmet diseases that are beyond the ability of modern synthetic medicine.

Nutraceuticals and physical activity: Their role on oxysterols-mediated neurodegeneration

Over the past few years, the contribution of oxysterols to the onset and development of some of the major neurodegenerative diseases (such as Alzheimer's and Parkinson's diseases) has been scientifically asserted, being mainly related to altered brain cholesterol homeostasis. To counteract oxysterol induced inflammation at neuronal level, one possible intervention approach is the administration of some nutrients and/or plant secondary metabolites. On the other hand, the pleiotropic beneficial effects of physical activity seem to play an important role on prevention and counteraction of neurodegenerative diseases, through the modulation of oxysterol homeostasis and the prevention of demyelination. The present review provides a picture of the promising role of nutraceuticals and physical activity on oxysterol-mediated neurodegeneration, pointing out also the different in vitro and in vivo aspects that need to be further investigated for a better understanding of the association of these three counterparts and their overall effect on people at increased risk for neurodegenerative diseases.

Acidity-triggered zwitterionic prodrug nano-carriers with AIE properties and amplification of oxidative stress for mitochondria-targeted cancer theranostics

A TPE-based polyurethane prodrug has been established for mitochondria-targeting drug delivery and real-time monitoring.

Nanoparticles in Daily Life: Applications, Toxicity and Regulations

At nanoscale, man-made materials may show unique properties that differ from bulk and dissolved counterparts. The unique properties of engineered nanomaterials not only impart critical advantages but also confer toxicity because of their unwanted interactions with different biological compartments and cellular processes. In this review, we discuss various entry routes of nanomaterials in the human body, their applications in daily life, and the mechanisms underlying their toxicity. We further explore the passage of nanomaterials into air, water, and soil ecosystems, resulting in diverse environmental impacts. Briefly, we probe the available strategies for risk assessment and risk management to assist in reducing the occupational risks of potentially hazardous engineered nanomaterials including the control banding (CB) approach. Moreover, we substantiate the need for uniform guidelines for systematic analysis of nanomaterial toxicity, in silico toxicological investigations, and obligation to ensure the safe disposal of nanowaste to reduce or eliminate untoward environmental and health impacts. At the end, we scrutinize global regulatory trends, hurdles, and efforts to develop better regulatory sciences in the field of nanomedicines.

Mitochondrial Targeted Doxorubicin-Triphenylphosphonium Delivered by Hyaluronic Acid Modified and pH Responsive Nanocarriers to Breast Tumor: in Vitro and in Vivo Studies

Multidrug resistance (MDR) is the major obstacle for chemotherapy. In a previous study, we have successfully synthesized a novel doxorubicin (DOX) derivative modified by triphenylphosphonium (TPP) to realize mitochondrial delivery of DOX and showed the potential of this compound to overcome DOX resistance in MDA-MB-435/DOX cells. (1) To introduce specificity for DOX-TPP to cancer cells, here we report on the conjugation of DOX-TPP to hyaluronic acid (HA) by hydrazone bond with adipic acid dihydrazide (ADH) as the acid-responsive linker, producing HA- hydra-DOX-TPP nanoparticles. Hyaluronic acid (HA) is a natural water-soluble linear glycosaminoglycan, which was hypothesized to increase the accumulation of nanoparticles containing DOX-TPP in the mitochondria of tumor cells upon systemic administration, overcoming DOX resistance, in vivo. Our results showed HA- hydra-DOX-TPP to self-assemble to core/shell nanoparticles of good dispersibility and effective release of DOX-TPP from the HA- hydra-DOX-TPP conjugate in cancer cells, which was followed by enhanced DOX mitochondria accumulation. The HA- hydra-DOX-TPP nanoparticles also showed improved anticancer effects, better tumor cell apoptosis, and better safety profile compared to free DOX in MCF-7/ADR bearing mice.

Mitochondrial dynamics, mitophagy and biogenesis in neonatal hypoxic-ischaemic brain injury

Hypoxic-ischaemic encephalopathy, resulting from asphyxia during birth, affects 2-3 in every 1000 term infants and depending on severity, brings about life-changing neurological consequences or death. This hypoxic-ischaemia (HI) results in a delayed neural energy failure during which the majority of brain injury occurs. Currently, there are limited treatment options and additional therapies are urgently required. Mitochondrial dysfunction acts as a focal point in injury development in the immature brain. Not only do mitochondria become permeabilised, but recent findings implicate perturbations in mitochondrial dynamics (fission, fusion), mitophagy and biogenesis. Mitoprotective therapies may therefore offer a new avenue of intervention for babies who suffer lifelong disabilities due to birth asphyxia.

Strategies in the design of gold nanoparticles for intracellular targeting: opportunities and challenges

With unique physicochemical properties, gold nanoparticles (Au NPs) have demonstrated their potential as drug carriers or therapeutic agents. Effective guidance of Au NPs into specific intracellular destinations becomes increasingly important as we strive to further improve the efficiency of drug delivery and modulate controllable cellular responses. In this review, we summarized recent advances in designing Au NPs with the capabilities of cellular penetration and internalization, endosomal escape, intracellular trafficking and subcellular localization via various approaches including physical injection, tuning the physiochemical parameters of Au NPs, and surface modification with targeting ligands. Strategies for delivering Au NPs to specific subcellular destinations including the nucleus, mitochondria, endoplasmic reticulum, lysosomes are also discussed. Moreover, current challenges associated with intracellular targeting of Au NPs are discussed with future perspectives proposed.

Multifunctional decoration of alpha-tocopheryl succinate-based NP for cancer treatment: effect of TPP and LTVSPWY peptide

Active targeting not only of a specific cell but also a specific organelle maximizes the therapeutic activity minimizing adverse side effects in healthy tissues. The present work describes the synthesis, characterization, and in vitro biological activity of active targeting nanoparticles (NP) for cancer therapy based on α-tocopheryl succinate (α-TOS), a well-known mitocan, that selectively induces apoptosis of cancer cells and proliferalting endothelial cells. Human epidermal growth factor receptor 2 (HER2) targeting peptide LTVSPWY (PEP) and triphenylphosphonium lipophilic cation (TPP) were conjugated to a previously optimized RAFT block copolymer that formed self-assembled NP of appropriate size for this application and low polydispersity by self-organized precipitation method. PEP and TPP were included in order to target not only HER2 positive cancer cells, but also the mitochondria of these cancer cells, respectively. The in vitro experiments demonstrated the faster incorporation of the active-targeting NP and the higher accumulation of TPP-bearing NP in the mitochondria of MDA-MB-453 HER2 positive cancer cells compared to non-decorated NP. Moreover, the encapsulation of additional α-TOS in the hydrophobic core of the NP was achieved with high efficiencies. The loaded NP presented higher cytotoxicity than unloaded NP but preserved their selectivity against cancer cells in a range of tested concentrations.

Mitochondria-Targeted Triphenylphosphonium-Based Compounds: Syntheses, Mechanisms of Action, and Therapeutic and Diagnostic Applications

Mitochondria are recognized as one of the most important targets for new drug design in cancer, cardiovascular, and neurological diseases. Currently, the most effective way to deliver drugs specifically to mitochondria is by covalent linking a lipophilic cation such as an alkyltriphenylphosphonium moiety to a pharmacophore of interest. Other delocalized lipophilic cations, such as rhodamine, natural and synthetic mitochondria-targeting peptides, and nanoparticle vehicles, have also been used for mitochondrial delivery of small molecules. Depending on the approach used, and the cell and mitochondrial membrane potentials, more than 1000-fold higher mitochondrial concentration can be achieved. Mitochondrial targeting has been developed to study mitochondrial physiology and dysfunction and the interaction between mitochondria and other subcellular organelles and for treatment of a variety of diseases such as neurodegeneration and cancer. In this Review, we discuss efforts to target small-molecule compounds to mitochondria for probing mitochondria function, as diagnostic tools and potential therapeutics. We describe the physicochemical basis for mitochondrial accumulation of lipophilic cations, synthetic chemistry strategies to target compounds to mitochondria, mitochondrial probes, and sensors, and examples of mitochondrial targeting of bioactive compounds. Finally, we review published attempts to apply mitochondria-targeted agents for the treatment of cancer and neurodegenerative diseases.

Nanoparticles as potential clinical therapeutic agents in Alzheimer's disease: focus on selenium nanoparticles

INTRODUCTION

In etiology of Alzheimer's disease (AD), involvement of amyloid β (Aβ) plaque accumulation and oxidative stress in the brain have important roles. Several nanoparticles such as titanium dioxide, silica dioxide, silver and zinc oxide have been experimentally using for treatment of neurological disease. In the last decade, there has been a great interest on combination of antioxidant bioactive compounds such as selenium (Se) and flavonoids with the oxidant nanoparticles in AD. We evaluated the most current data available on the physiological effects of oxidant and antioxidant nanoparticles. Areas covered: Oxidative nanoparticles decreased the activities of reactive oxygen species (ROS) scavenging enzymes such as glutathione peroxidase (GSH-Px), superoxide dismutase (SOD) and catalase in the brain of rats and mice. However, Se-rich nanoparticles in small size (5-15 nm) depleted Aβ formation through decreasing ROS production. Reports on low levels of Se in blood and tissue samples and the low activities of GSH-Px, catalase and SOD enzymes in AD patients and animal models support the proposed crucial role of oxidative stress in the pathogenesis of AD. Expert commentary: In conclusion, present literature suggests that Se-rich nanoparticles appeared to be a potential therapeutic compound for the treatment of AD.

Targeted delivery of geranylgeranylacetone to mitochondria by triphenylphosphonium modified nanoparticles: a promising strategy to prevent aminoglycoside-induced hearing loss

TPP induced and GGA loaded mitochondria-targeting nanoparticles could efficiently protect hair cells from damage.

Peptide-Mediated Delivery of Chemical Probes and Therapeutics to Mitochondria

Mitochondria are organelles with critical roles in key processes within eukaryotic cells, and their dysfunction is linked with numerous diseases including neurodegenerative disorders and cancer. Pharmacological manipulation of mitochondrial function is therefore important both for basic science research and eventually, clinical medicine. However, in comparison to other organelles, mitochondria are difficult to access due to their hydrophobic and dense double membrane system as well as their negative membrane potential. To tackle the challenge of targeting these important subcellular compartments, significant effort has been put forward to develop mitochondria-targeted systems capable of transporting bioactive cargo into the mitochondrial interior. Systems now exist that utilize small molecule, peptide, liposome, and nanoparticle-based transport. The vectors available vary in size and structure and can facilitate transport of a variety of compounds for mitochondrial delivery. Notably, peptide-based delivery scaffolds offer attractive features such as ease of synthesis, tunability, biocompatibility, and high uptake both in cellulo and in vivo. Owing to their simple and modular synthesis, these peptides are highly adaptable for delivering chemically diverse cargo. Key design features of mitochondria-targeted peptides include cationic charge, which allows them to harness the negative membrane potential of mitochondria, and lipophilicity, which permits favorable interaction with hydrophobic membranes of mitochondria. These peptides have been covalently tethered to target therapeutic agents, including anticancer drugs, to enhance their drug properties, and to provide probes for mitochondrial biology. Interestingly, mitochondria-targeted DNA damaging agents demonstrate high potency and the ability to evade resistance mechanisms and off-target effects. Moreover, a combination of mitochondria-targeted DNA damaging agents was applied to an siRNA screen for the elucidation of poorly understood mitochondrial DNA repair and replication pathways. In this work, a variety of novel proteins were identified that are essential for the maintenance of mitochondrial nucleic acids. Mitochondria-targeted peptides have also been used to increase the therapeutic window of antibacterial drugs with significant mammalian toxicity. Given the evolutionary similarity of mitochondria and bacteria, peptides are effective transporters that can target both of these entities. These antimicrobial peptides are highly effective even in difficult to target intracellular bacteria which reside within host cells. This peptide-based approach to targeting mitochondria has provided a variety of insights into the "druggability" of mitochondria and new biological processes that could be future drug targets. Nevertheless, the mitochondrial-targeting field is quite nascent and many exciting applications of organelle-specific conjugates remain to be explored. In this Account, we highlight the development and optimization of the mitochondria-penetrating peptides that our laboratory has developed, the unique applications of mitochondria-targeted bioactive cargo, and offer a perspective on important directions for the field.

Triphenylphosphonium Decorated Liposomes and Dendritic Polymers: Prospective Second Generation Drug Delivery Systems for Targeting Mitochondria

Targeting specific intracellular organelles has been a biological process of significant interest. Specifically, for mitochondrial targeting, conventional liposomal and dendritic polymer nanoparticles were selected to be presented in this miniperspective. Both types of nanoparticles were decorated on their external surface with triphenylphosphonium cation (TPP), a well-known and effective mitochondrial targeting moiety. Due to their advantageous specificity toward mitochondria, these nanoparticles may be considered as prospective second generation drug delivery systems (DDSs). Functionalized liposomal and dendritic nanoparticles are conveniently prepared, and although they encounter several hurdles on their route from the extracellular environment to the interior of mitochondria, they manage to be accumulated inside them in experiments in vitro. Therefore, the TPP-functionalized nanoparticles presented in this miniperspective can prove effective DDSs and efforts should be continued to obtain results that will trigger further studies including clinical studies, hopefully leading to effective drugs for mitochondrial diseases. In fact, since these DDSs enter and act at the site where the dysfunction exists, a new medicine subspecialty is emerging, the so-called mitochondrial medicine.

Nanoparticle-Mediated Targeting of Cyclosporine A Enhances Cardioprotection Against Ischemia-Reperfusion Injury Through Inhibition of Mitochondrial Permeability Transition Pore Opening

Myocardial ischemia-reperfusion (IR) injury limits the therapeutic effects of early reperfusion therapy for acute myocardial infarction (MI), in which mitochondrial permeability transition pore (mPTP) opening plays a critical role. Our aim was to determine whether poly-lactic/glycolic acid (PLGA) nanoparticle-mediated mitochondrial targeting of a molecule that inhibits mPTP opening, cyclosporine A (CsA), enhances CsA-induced cardioprotection. In an in vivo murine IR model, intravenously injected PLGA nanoparticles were located at the IR myocardium mitochondria. Treatment with nanoparticles incorporated with CsA (CsA-NP) at the onset of reperfusion enhanced cardioprotection against IR injury by CsA alone (as indicated by the reduced MI size at a lower CsA concentration) through the inhibition of mPTP opening. Left ventricular remodeling was ameliorated 28 days after IR, but the treatment did not affect inflammatory monocyte recruitment to the IR heart. In cultured rat cardiomyocytes in vitro, mitochondrial PLGA nanoparticle-targeting was observed after the addition of hydrogen peroxide, which represents oxidative stress during IR, and was prevented by CsA. CsA-NP can be developed as an effective mPTP opening inhibitor and may protect organs from IR injury.

The mitochondria-targeted and IR780-regulated theranosomes for imaging and enhanced photodynamic/photothermal therapy

(a) A schematic of the system TPP-IR780/Ce6-TNS. (b) Illustration of the system TPP-IR780/Ce6-TNS to the tumor microenvironment.

Small molecule therapeutic-loaded liposomes as therapeutic carriers: from development to clinical applications

In this review, various methods and mechanisms for encapsulation of small therapeutic molecules in liposomes for targeted delivery and triggered release, as well as their potential in the clinical uses, are discussed.

Import of Fluorescent RNA into Mitochondria of Living Cells

Methods of in vivo visualization and manipulation of mitochondrial genetic machinery are limited due to the need to surpass not only the cytoplasmic membrane but also two mitochondrial membranes. Here, we employ the matrix-addressing sequence of mitochondrial ribosomal 5S-rRNA (termed MAM), which is naturally imported into mammalian mitochondria, to construct an import system for in vivo targeting of mitochondrial (mt) DNA or mtRNA, in order to provide fluorescence hybridization of the desired sequences.

Effect of the Conjugation Density of Triphenylphosphonium Cation on the Mitochondrial Targeting of Poly(amidoamine) Dendrimers

Many clinically relevant diseases with known poor therapeutic outcomes, including cancer and neurodegenerative disorders, have been directly linked to mitochondrial dysfunction. The ability to efficiently target therapeutics to intracellular organelles such as mitochondria may represent new opportunities for the effective treatment of such ailments. The present study reports the synthesis, cellular uptake, cytotoxicity, and mitochondrial colocalization of conjugates of triphenylphosphonium cation (TPP) to amine-terminated, generation 4, poly(amidoamine) (PAMAM) dendrimer (G4NH2) nanocarriers. The mitochondrial-targeting moiety TPP was either directly conjugated to G4NH2 (G4NH2-TPP) or to the dendrimer through a flexible polyethylene glycol (PEG) linker (G4NH2-PEGTPP). Conjugation was done at various TPP densities to assess their biological activity and potential for mitochondrial-targeted drug delivery. Tests in an in vitro model of the human alveolar carcinoma (A549 cells) showed that even at a low TPP density (∼5 TPP) both the cellular internalization and mitochondrial targeting increase significantly, as determined by fluorescence activated cell sorting (FACS) and confocal microscopy (CM), respectively. At a density of ∼10 TPP per G4NH2, further increase in cellular internalization and mitochondrial targeting was achieved. However, at this higher density, the nanocarriers also showed pronounced cytotoxicity. It was observed that the toxicity of the conjugates is decreased upon the addition of a PEG linker between the dendrimer and TPP (G4NH2-PEGTPP), while the mitochondrial targeting ability of the nanocarriers is not affected as the PEG density increases. The proposed strategies indicate that TPP-conjugated G4NH2 dendrimers represent a potentially viable strategy for the targeting of therapeutic molecules to mitochondria, which may help improve therapeutic outcomes of diseases related to mitochondrial dysfunction.

Mitochondria-targeting nanoplatform with fluorescent carbon dots for long time imaging and magnetic field-enhanced cellular uptake

In this study, a biocompatible nanoplatform has been constructed on the basis of magnetic mesoporous silica nanoparticles (Fe3O4@mSiO2) via surface modification of triphenylphospine (TPP) and then conjugation with fluorescent carbon dots (CDs). The as-prepared Fe3O4@mSiO2-TPP/CDs nanoplatform shows a very low cytotoxicity and apoptosis rate in various cell lines such as A549, CHO, HeLa, SH-SY5Y, HFF, and HMEC-1. More importantly, this nanoplatform integrates long time cell imaging, mitochondria-targeting, and magnetic field-enhanced cellular uptake functionalities into an all-in-one system. Time-dependent mitochondrial colocalization in all of the cell lines has been proved by using confocal laser scanning microscopy and flow cytometry, while the multicolored fluorescence of the Fe3O4@mSiO2-TPP/CDs could remain bright and stable after coincubation for 24 h. In addition, the cellular uptake efficiency could be enhanced in a short time as a static magnetic field of 0.30 T was applied to the coincubation system of A549 and HFF cell lines. This bionanoplatform may have potential applications in targeted drug delivery for mitochondria diseases as well as early cancer diagnosis and treatment.

Inorganic nanovectors for nucleic acid delivery

Nucleic acids show immense potential to treat cancer, acquired immune deficiency syndrome, neurological diseases and other incurable human diseases. Upon systemic administration, they encounter a series of barriers and hence barely reach the site of action, the cell. Intracellular delivery of nucleic acids is facilitated by nanovectors, both viral and non-viral. A major advantage of non-viral vectors over viral vectors is safety. Nanovectors evaluated specifically for nucleic acid delivery include polyplexes, lipoplexes and other cationic carrier-based vectors. However, more recently there is an increased interest in inorganic nanovectors for nucleic acid delivery. Nevertheless, there is no comprehensive review on the subject. The present review would cover in detail specific properties and types of inorganic nanovectors, their preparation techniques and various biomedical applications as therapeutics, diagnostics and theranostics. Future prospects are also suggested.

Nanoparticles and their applications in cell and molecular biology

Nanoparticles can be engineered with distinctive composition, size, shape, and surface chemistry to enable novel techniques in a wide range of biological applications. The unique properties of nanoparticles and their behavior in biological milieu also enable exciting and integrative approaches to studying fundamental biological questions. This review will provide an overview of various types of nanoparticles and concepts of targeting nanoparticles. We will also discuss the advantages and recent applications of using nanoparticles as tools for drug delivery, imaging, sensing, and for the understanding of basic biological processes.

Import of desired nucleic acid sequences using addressing motif of mitochondrial ribosomal 5S-rRNA for fluorescent in vivo hybridization of mitochondrial DNA and RNA

Based on the matrix-addressing sequence of mitochondrial ribosomal 5S-rRNA (termed MAM), which is naturally imported into mitochondria, we have constructed an import system for in vivo targeting of mitochondrial DNA (mtDNA) or mt-mRNA, in order to provide fluorescence hybridization of the desired sequences. Thus DNA oligonucleotides were constructed, containing the 5'-flanked T7 RNA polymerase promoter. After in vitro transcription and fluorescent labeling with Alexa Fluor(®) 488 or 647 dye, we obtained the fluorescent "L-ND5 probe" containing MAM and exemplar cargo, i.e., annealing sequence to a short portion of ND5 mRNA and to the light-strand mtDNA complementary to the heavy strand nd5 mt gene (5'-end 21 base pair sequence). For mitochondrial in vivo fluorescent hybridization, HepG2 cells were treated with dequalinium micelles, containing the fluorescent probes, bringing the probes proximally to the mitochondrial outer membrane and to the natural import system. A verification of import into the mitochondrial matrix of cultured HepG2 cells was provided by confocal microscopy colocalizations. Transfections using lipofectamine or probes without 5S-rRNA addressing MAM sequence or with MAM only were ineffective. Alternatively, the same DNA oligonucleotides with 5'-CACC overhang (substituting T7 promoter) were transcribed from the tetracycline-inducible pENTRH1/TO vector in human embryonic kidney T-REx®-293 cells, while mitochondrial matrix localization after import of the resulting unlabeled RNA was detected by PCR. The MAM-containing probe was then enriched by three-order of magnitude over the natural ND5 mRNA in the mitochondrial matrix. In conclusion, we present a proof-of-principle for mitochondrial in vivo hybridization and mitochondrial nucleic acid import.

Intracellular trafficking and cellular uptake mechanism of mPEG-PLGA-PLL and mPEG-PLGA-PLL-Gal nanoparticles for targeted delivery to hepatomas

The lysosomal escape of nanoparticles is crucial to enhancing their delivery and therapeutic efficiency. Here, we report the cellular uptake mechanism, lysosomal escape, and organelle morphology effect of monomethoxy (polyethylene glycol)-poly (D,L-lactide-co-glycolide)-poly (L-lysine) (mPEG-PLGA-PLL, PEAL) and 4-O-beta-D-Galactopyranosyl-D-gluconic acid (Gal)-modified PEAL (PEAL-Gal) for intracellular delivery to HepG2, Huh7, and PLC hepatoma cells. These results indicate that PEAL is taken up by clathrin-mediated endocytosis of HepG2, Huh7 and PLC cells. For PEAL-Gal, sialic acid receptor-mediated endocytosis and clathrin-mediated endocytosis are the primary uptake pathways in HepG2 cells, respectively, whereas PEAL-Gal is internalized by sag vesicle- and clathrin-mediated endocytosis in Huh7 cells. In the case of PLC cells, clathrin-mediated endocytosis and sialic acid receptor play a primary role in the uptake of PEAL-Gal. TEM results verify that PEAL and PEAL-Gal lead to a different influence on organelle morphology of HepG2, Huh7 and PLC cells. In addition, the results of intracellular distribution reveal that PEAL and PEAL-Gal are less entrapped in the lysosomes of HepG2 and Huh7 cells, demonstrating that they effectively escape from lysosomes and contribute to enhance the efficiency of intracellular delivery and tumor therapy. In vivo tumor targeting image results demonstrate that PEAL-Gal specifically delivers Rhodamine B (Rb) to the tumor tissue of mice with HepG2, Huh7, and PLC hepatomas and remains at a high concentration in tumor tissue until 48 h, properties that will greatly contribute to enhanced antitumor efficiency.

A matter of life, death and diseases: mitochondria from a proteomic perspective

Mitochondria are highly ordered, integrated organelles that energize cellular activities and contribute to programmed death by initiating disciplined apoptotic cascades. This review seeks to clarify our understanding of mitochondrial structural-functional integrity beyond the resolved nuclear genome by unraveling the dynamic mitochondrial proteome and elucidating proteome/genome interplay. The roles of mechanochemical coupling between mitoskeleton and cytoskeleton and crosstalk with other organelles in orchestrating cellular outcomes are explained. The authors also review the modulation of mitochondrial-related oxidative stress on apoptosis and cancer development and the context is applied to interpret pathogenetic events in neurodegenerative disorders and cardiovascular diseases. The accumulated proteomics evidence is used to describe the integral role that mitochondria play and how they influence other intracellular organelles. Possible mitochondrial-targeted therapeutic interventions are also discussed.

Why size matters - balancing mitochondrial dynamics in Alzheimer's disease

Once perceived as solitary structures, mitochondria are now recognized as highly dynamic, interconnected organelles. The tight control of their fusion and fission, a process termed 'mitochondrial dynamics', is crucial for neurons, given their unique architecture and special energy and calcium-buffering requirements at the synapse. Interestingly, in Alzheimer's disease (AD), a condition initiated at the synapse, mitochondrial dynamics are severely impaired. Of the two proteins implicated in AD pathogenesis, amyloid-β (Aβ) and TAU, only the impact of Aβ on mitochondrial dynamics has been studied in detail. We highlight recent findings that TAU exerts a determinative effect in the regulation of mitochondrial dynamics, and therefore neuronal function. In this process, the GTPase DRP1 has emerged as a key target of both Aβ and TAU.

The effect of nanoparticle uptake on cellular behavior: disrupting or enabling functions?

Nanoparticles (NPs) are materials with overall dimensions in the nanoscale range. They have unique physicochemical properties, and have emerged as important players in current research in modern medicine. In the last few decades, several types of NPs and microparticles have been synthesized and proposed for use as contrast agents for diagnostics and imaging and for drug delivery; for example, in cancer therapy. Yet specific targeting that will improve their delivery still represents an unsolved challenge. The mechanism by which NPs enter the cell has important implications not only for their fate but also for their impact on biological systems. Several papers in the literature discuss the potential risks related to NP exposure, and more recently the concept that even sublethal doses of NPs may elicit a cell response has been proposed. In this review, we intend to present an overall view of cell mechanisms that may be perturbed by cell-NP interaction. Published data, in fact, emphasize that NPs should no longer be viewed only as simple carriers for biomedical applications, but that they can also play an active role in mediating biological effects.

Mitochondrial function and dysfunction: an update

With the current explosion of knowledge on the role of mitochondrial dysfunction in the genesis of various human disease states, there is an increased interest in targeting mitochondrial processes, pathways, and proteins for drug discovery efforts in cancer and cardiovascular, metabolic, and central nervous system diseases, the latter including autism and neurodegenerative diseases. We provide an update on understanding the central role of the mitochondrion in ATP and reactive oxygen species production and in controlling cell death pathways.