MITOCHONDRIA – TARGETED ANTIOXIDANT: AGING

MITOCHONDRIA - TARGETED ANTIOXIDANT: AGING

Binu Varghese^*, N. L. Gowrishankar, K. Drisya and Mohammed T. Ramees

Department of Pharmaceutical Analysis, Prime College of Pharmacy, Erattayal, Palakkad - 678551, Kerala, India.

ABSTRACT: The mitochondrion, the “power house of cell”, plays a central role in energy-generating processes so called as ‘‘master of life and death’’. A decline in mitochondrial function plays a key role in the aging process and increases the incidence of age-related disorders. With advanced age, mitochondrial DNA volume, integrity and functionality decrease due to accumulation of mutations and oxidative damage induced by reactive oxygen species (ROS). In aged subjects, mitochondria are characterized by impaired function such as lowered oxidative capacity, reduced oxidative phosphorylation, decreased ATP production, significant increase in ROS generation, and diminished antioxidant defense. Antioxidant defense system, which is responsible for eliminating a wide range of oxidants, especially reactive oxygen species (ROS). As mitochondria are the major site for production of large amount of ROS, mitochondria-targeted antioxidant therapies have shown great effectiveness against the damage caused by enhanced ROS generation, is discussed in this review article.

Mitochondria, Aging, Mitochondrial dysfunction, Reactive oxygen species, Mitochondria targeted antioxidants

INTRODUCTION: Mitochondria are double-membrane organelles that are found in most eukaryotic cells and that execute many metabolic functions including ATP synthesis through oxidative phosphorylation (OXPHOS) ¹. The electron transport chain (ETC) consists of about 80 different polypeptides, which are organized into five transmembrane protein complexes (I-V). The proton gradient generated by complexes I, III and IV is released through ATP synthase or complex V, which results in phosphorylation of adenosine di phosphate (ADP) to ATP ². In addition to the OXPHOS machinery, mitochondria are also known as metabolic signalling center of the cells,

Performing many important biological functions such as regulation of apoptosis maintenance of cytosolic calcium homeostasis, lipid biosynthesis and iron sulphur cluster biogenesis ^{1, 3, 4}. Mitochondria undergo constant morphological changes by the process of continuous cycles of fusion and fission that determines their morphology and most mitochondrial functions.

Mitochondria are structurally complex and highly dynamic motile organelles ⁵. Its unique structure is consisted of four distinct sub-structures with different specific functions: the mitochondrial matrix, the inner mitochondrial membrane (IMM), the outer mitochondrial membrane (OMM) and the inter membrane space (IMS).

The structure of the inner mitochondrial membrane (IMM) is extensively folded and compartmen-talized. The numerous invaginations of the membrane are called cristae, which house the 4 complexes of the mitochondrial respiratory chain and ATP synthase, controlling the vital levels of cellular bioenergetics Fig. 1. This primary function of the mitochondrion is responsible for supplying cellular energy, the reason why we call it power plant of the cell. However, it is not the only important function of mitochondria in the cell ⁶.

FIG. 1: MITOCHONDRIA

Mitochondria are double membrane encoded organelles with their own genome that consume oxygen and substrates to generate the vast majority of ATP while producing reactive oxygen species in the process. They also participate in a wide range of other cellular processes, including signal transduction, cell cycle regulation, oxidative stress, thermogenesis, and apoptosis. In doing so, they are highly dynamic organelles that are continuously remodeling through biogenesis, fission, fusion, and autophagy, thus responding to and modulating cellular dynamics. They undergo biogenesis to meet increased energy demands in response to exercise, and they ensure cellular quality by initiating an apoptotic program to remove defective cells.

Energetics of Mitochondria: Mitochondria transduce energy from substrates through the tricarboxylic acid (TCA) cycle and the electron transport system (ETS) Fig. 2 to generate ATP. The ETS consists of multi polypeptide complexes (I–V) embedded in the inner mitochondrial membrane (IMM) that receive electrons from reducing equivalents NADH and FADH2, generated by dehydrogenase activity in the TCA cycle. The electrons are transferred along the complexes with O₂ serving as the final acceptor at complex IV ⁷. The reduction potential (propensity to accept an electron) increases along the chain of complexes, and the energy generate is sufficient to drive the translocation of hydrogen ions across the IMM. This creates a proton gradient and membrane potential (collectively termed the proton motive force) that drives the synthesis of ATP as protons flow back to the matrix via complex V (ATP synthase). This process is also called oxidative phosphorylation (OXPHOS). However, the ETS is not a perfectly efficient system and significant (and highly variable) proton “leak” occurs by the movement of hydrogen ions back into the matrix space that is not mediated through complex V. In this manner, proton transfer can be uncoupled from ATP phosphorylation, and this inefficiency contributes to the demand for reducing equivalents. Mitochondria are therefore thought to have a much greater capacity to generate ATP than what is usually required ⁸.

FIG. 2: ELECTRON TRANSPORT SYSTEM

Because of this metabolic latitude, many assume that mild impairment in mitochondrial function per se does not cause cellular disturbances associated with aging and with chronic diseases ⁸. Indeed, whether mitochondrial dysfunction is a cause or a consequence of cellular impairment and the aging process is a subject of intense debate. Moreover, the definition of mitochondrial dysfunction itself has been the subject of controversy. For example, alterations in mitochondrial mRNA transcripts may not result in changes in protein levels, so it is not wholly clear whether this state - whether compensatory or not - can be counted as a disruption in normal function ⁹. Given their central role in cellular homeostasis, mitochondrial dysfunction has been linked to many age-related disorders including mitochondrial diseases, cancers, metabolic diseases and diabetes, inflammatory conditions, neuropathy, and neurodegenerative diseases such as Alzheimer’s, Parkinson’s, and Huntington’s disease ^{10, 11}. Mitochondrial dysfunction, including decreased oxidative capacity and increased oxidative damage, is thought to substantially contribute to biological aging ^{12, 13}.

Mitochondria in Aging: Aging is thought to be a time dependent degenerative process caused by accumulated damage that leads to cellular dysfunction, tissue failure, and death. The aging process results in a gradual and progressive structural and functional deterioration of biomolecules that is associated with many pathological conditions, including cancer, neurodegenerative diseases, sarcopenia (loss of muscle mass) and liver dysfunction ¹⁴. The exact causes of ageing are unknown; current theories are assigned to the damage concept, whereby the accumulation of damage (such as DNA breaks, oxidized DNA and / or mitochondrial malfunctions) may cause biological systems to fail, or to the programmed ageing concept, whereby internal processes (such as DNA telomere shortening) may cause ageing ¹⁵.

Although several theories have been proposed to explain the fundamental mechanisms mediating these age-related diseases and conditions, the free-radical theory of aging is by far the most popular. This theory proposes that cumulative damage to biological macromolecules by oxygen radicals (reactive oxygen species; ROS) leads to irreversible cell damage and an overall functional decline ¹⁶. The free-radical theory has also been extended to include mitochondria, as the accumulation of aging-associated mutations and deletions in mitochondrial DNA (mtDNA) can impair the function of the respiratory chain and enhance ROS production ^{13, 17}. The increased ROS production can subsequently lead to a vicious cycle of exponentially increasing levels of mtDNA damage and oxidative stress in the cell Fig. 3 ^{18 - 20}. Although various genetic problems in mitochondria cause phenotypes that resemble premature aging, additional support for this theory was provided by studies showing a direct link between mtDNA mutations and mammalian aging ²¹.

FIG. 3: MITOCHONDRIAL DYSFUNCTION IN AGING

In particular, mice with a proofreading-deficient version of PolgA, the catalytic subunit of mitochondrial DNA polymerase (POLG), accumulate mtDNA mutations that are associated with impaired respiratory-chain function and increased levels of apoptosis. These mtDNA-mutator mice, with accelerated levels of mutations, had a shorter life span and displayed age-related phenotypes [such as hair loss, kyphosis (curvature of the spine), osteoporosis and sarcopenia] at an early age ^{4, 22}. Interestingly, these changes were not accompanied by increased levels of oxidative stress, a finding that has also been confirmed in humans ²³. This has resulted in much controversy regarding the idea that mtDNA mutations contribute to aging through increased ROS production and enhanced levels of oxidative stress in mitochondria. However, it is possible that the accumulation of mtDNA mutations that occur with age leads to alterations in cell-signaling pathways that can induce cell dysfunction and initiate apoptosis, irrespective of increased ROS production and oxidative stress in mitochondria. Whether mtDNA mutations play a causal role in the aging process is still an ongoing debate; however, the fact that a functional decline in mitochondria occurs with age and that properly functioning mitochondria are crucial for longevity and minimizing age-related diseases cannot be refuted ²⁴.

Reactive Oxygen Species: Reactive oxygen species (ROS) are highly reactive molecules that consist of a number of diverse chemical species including superoxide anion (O₂⁻), hydroxyl radical (•OH), and hydrogen peroxide (H₂O₂). Because of their potential to cause oxidative deterioration of DNA, protein, and lipid, ROS have been implicated as one of the causative factors of aging. As ROS are generated mainly as by products of mitochondrial respiration, mitochondria are thought to be the primary target of oxidative damage and play an important role in aging ^{16, 25}.

There are several sources of ROS within a cell. ROS are generated as by-products of aerobic respiration and various other catabolic and anabolic processes ²⁶. Once they are produced, ROS react with lipids, proteins, and nucleic acids causing oxidative damage to the macromolecules ^{27 - 30}. ROS readily attack DNA and generate a variety of DNA lesions, such as oxidized DNA bases, a basic sites, and DNA strand breaks, which ultimately lead to genomic instability ³¹. 7, 8-dihydro-8-oxodeoxyguanosine (8-oxo-dG) is one of the most abundant and well-characterized DNA lesions caused by ROS. Consistently, many studies have shown that 8-oxo-dG, one of the common oxidative lesions, is detected at higher level in mtDNA than nuclear DNA, suggesting that mtDNA is more susceptible to oxidative damage ³². It is a highly mutagenic lesion that results in G:C to T:A transversion ³³. Mitochondrial complexes I and III are the main sites of superoxide generation and contribute the most to ROS production ³⁴. The reactive oxygen species, including O₂^•− and H₂O₂, can cause oxidative damage to surrounding structures and the particularly vulnerable mtDNA, which is in close proximity to the primary site of ROS production. Oxidation by ROS results in the synthesis of faulty proteins, oxidized lipids, and mtDNA mutations, which may lead to cellular and mitochondrial dysfunction. These processes are implicated in the mitochondrial theory of aging, which holds that the accumulation of ROS damage over time leads to age-associated mitochondrial impairment ^{16, 35, 36}. This increase in ROS production is associated with oxidation of ETS complex V, leading to decreased ATP production, increased levels of 8 oxo deoxy guanosine (8-oxoG) from DNA oxidation, increased levels of protein carbonyls, and increased nitration ^{36 - 40}.

In particular, proteomic studies have found increased nitration of complex II and altered carbonylation of complex I, complex V, and isocitrate dehydrogenase ⁴¹. To limit the cellular damage caused by ROS, mammalian cells have evolved a number of sophisticated defense mechanisms. ROS-generated DNA lesions are repaired mainly by base excision repair as well as other DNA repair pathways including nucleotide excision repair, double-strand break repair, and mismatch repair ^{42, 43}.

In addition, the damaging effects of ROS can be neutralized via elevated antioxidant defense, which includes superoxide dismutase, catalase, and glutathione peroxidase to scavenge ROS to nontoxic forms ⁴⁴. Cumulative oxidative damage may in part be attributed to a reduction in ETS activity that would extend the length of time that electrons remain at complexes I and III, increasing the potential for donation of electrons to oxygen ⁴⁵. In theory, it could also be attributed to reduced activity of antioxidant defenses, including manganese superoxide dismutase (MnSOD), catalase (CAT), and glutathione peroxidase (GPx). These enzymes work together to convert O₂^•− to H₂O₂, which is then further reduce to H₂O ^{46 - 48}.

Mitochondria are the major producer of ROS in mammalian cells, the close proximity to ROS places mitochondrial DNA (mtDNA) prone to oxidative damage ⁷. The bulk of mitochondrial ROS is generated at the electron transport chain ^{49, 50}. Electrons leak from the electron transport chain directly to oxygen, producing short-lived free radicals such as superoxide anion(O₂⁻) ^{51, 52} O₂⁻ can be converted to non radical derivatives such as hydrogen peroxide (H₂O₂) either spontaneously or catalyzed by superoxide dismutase (SOD) ^{53 - 55}. H₂O₂ is relatively stable and membrane permeable. It can be diffused within the cell and be removed by cytosolic antioxidant systems such as catalase, glutathione peroxidase, and thioredoxin peroxidise ^{56, 57}.

In addition to being generated during cellular metabolism in mitochondria, ROS can be produced in response to different environmental stimuli such as growth factors, inflammatory cytokines, ionizing radiation, UV, chemical oxidants, chemo-therapeutics, hyperoxia, toxins, and transition metals ^{58 - 61}. Other than mitochondrial respiration, a number of cytosolic enzymes are able to generate ROS ⁶². The nicotinamide adenine dinucleotide phosphate (NADPH) oxidases are a group of plasma membrane-associated enzymes found in a variety of cell types ⁶³. The function of NADPH oxidases is to produce superoxide from oxygen using electrons from NADPH ⁶⁴. Although it remains unclear whether increased ROS levels area consequence of mitochondrial dysfunction or the cause of disruption to this organelle, it is clear that increased ROS levels are critical in many pathologic disorders.

The mitochondrial theory of aging, extended from the free radical theory, proposes that oxidative damage generated during oxidative phosphory-lation of mitochondrial macromolecules such as mtDNA, proteins, or lipids is responsible for aging ⁶⁵. As mtDNA encodes essential components of oxidative phosphorylation and protein synthesis machinery, oxidative damage induced mtDNA mutations that impair either the assembly or the function of the respiratory chain will in turn trigger further accumulation of ROS, which results in a vicious cycle leading to energy depletion in the cell and ultimately cell death ^{13, 20, 65 - 67}. Therefore, over the past decade, this organelle has become an attractive target for the delivery of therapeutic treatment, including antioxidants.

Targeting Antioxidants to Mitochondria: An antioxidant is a molecule stable enough to donate an electron to a rampaging free radical and neutralize it, thus reducing its capacity to damage. These antioxidants delay or inhibit cellular damage mainly through their free radical scavenging property ⁶⁸. These low molecular weight antioxidants can safely interact with free radicals and terminate the chain reaction before vital molecules are damaged. Antioxidants act as radical scavenger, hydrogen donor, electron donor, peroxide decomposer, singlet oxygen quencher, enzyme inhibitor, synergist, and metal - chelating agents ⁶⁹. Antioxidants are molecules that inhibit oxidants from reacting with other molecules by the transfer of electrons, thereby removing the potential for damage and maintaining cellular redox homeostasis ^{70, 71}.

There are several different types of antioxidants, and they can be broadly grouped into 2 major categories: endogenous (adaptive) and exogenous ^{72 - 74}. Both these enzymatic and non enzymatic antioxidants exist in the intracellular and extracellular environment to detoxify ROS. The adaptive or endogenous antioxidant defense system consists of both enzymatic antioxidants, such as the SODs, GPx, catalase, TPx and the non enzymatic antioxidants, which are represented by a-tocopherol (Vitamin E), glutathione, and bilirubin ^{71, 73 - 75}.

These antioxidants are synthesized in the body, and a large proportion of these cytoprotective proteins are encoded by the Nrf2 (nuclear factor erythroid 2-related factor 2)-Keap1 (kelch-like ECH-associated protein1) pathway ^{76, 77}. Exogenous antioxidants (either naturally obtained from the diet or derived synthetically) include tiron (4, 5-dihydroxy-1,3-benzenedisulfonic), carotenoids (clycopene and lutein), flavonoids (anthocyanidins), and Vitamins (A and C) ^{78, 79}. Both endogenous and exogenous antioxidants are widely distributed in the body; however, they are differentially distributed within the cells, with the most localized within the cytosol and a small number localized within the mitochondria ^{80 - 82}.

Mechanism of Action of Antioxidants: Two principle mechanisms of action have been proposed for antioxidants ⁸³. The first is a chain- breaking mechanism by which the primary antioxidant donates an electron to the free radical present in the systems. The second mechanism involves removal of ROS / reactive nitrogen species initiators (secondary antioxidants) by quenching chain-initiating catalyst. Antioxidants may exert their effect on biological systems by different mechanisms including electron donation, metal ion chelation, co- antioxidants, or by gene expression regulation ⁸⁴.

Levels of Antioxidant Action: The antioxidants acting in the defense systems act at different levels such as preventive, radical scavenging, repair and de novo, and the fourth line of defense, i.e., the adaptation. The first line of defense is the preventive antioxidants, which suppress the formation of free radicals. Although the precise mechanism and site of radical formation in vivo are not well elucidated yet, the metal- induced decompositions of hydroperoxides and hydrogen peroxide must be one of the important sources. To suppress such reactions, some antioxidants reduce hydroperoxides and hydrogen peroxide before hand to alcohols and water, respectively, without generation of free radicals and some proteins sequester metal ions. Glutathione peroxidase, glutathione-s-transferase, phospholipid hydro-peroxide glutathione peroxidise (PHGPX), and peroxidase are known to decompose lipid hydroperoxides to corresponding alcohols.

PHGPX is unique in that it can reduce hydroperoxides of phospholipids integrated into biomembranes. Glutathione peroxidase and catalase reduce hydrogen peroxide to water. The second line of defense is the antioxidants that scavenge the active radicals to suppress chain initiation and / or break the chain propagation reactions. Various endogenous radical-scavenging antioxidants are known: some are hydrophilic and others are lipophilic. Vitamin C, uric acid, bilirubin, albumin, and thiols are hydrophilic, radical-scavenging antioxidants, while Vitamin E and ubiquinol are lipophilic radical-scavenging antioxidants. Vitamin E is accepted as the most potent radical- scavenging lipophilic antioxidant. The third line of defense is the repair and de novo antioxidants. The proteolytic enzymes, proteinases, proteases, and peptidases, present in the cytosol and in the mitochondria of mammalian cells, recognize, degrade, and remove oxidatively modified proteins and prevent the accumulation of oxidized proteins. The DNA repair systems also play an important role in the total defense system against oxidative damage. Various kinds of enzymes such as glycosylases and nucleases, which repair the damaged DNA, are known. There is another important function called adaptation where the signal for the production and reactions of free radicals induces formation and transport of the appropriate antioxidant to the right site ⁸⁵.

Life span is determined by the rate of free radical damage at the cellular and tissue levels. Cells protect themselves from oxidative damage by expressing a variety of non-enzymatic and enzymatic antioxidant defenses that convert ROS into less harmful byproducts. Thus, equilibrium between oxidants and antioxidants is essential to prevent cellular functional impairment. From this perspective, lowering ROS levels by increasing cellular antioxidant defenses should slow the progression of age-related alterations and eventually result in the life span prolongation. In contrast to expectations, genetic manipulations of antioxidant defense genes in animal models show no clear correlation between oxidative damage and life span regulation ^{86 - 88}. For instance, over expression of mitochondrial antioxidant enzymes did not extend life spans in different species and even resulted in the shortening of life spans in some cases ⁸⁹.

While there are reports that dietary supplementation with antioxidants may improve cellular functions, decrease oxidative stress, and reverse age-related decline in antioxidant defenses in rodents, numerous human intervention studies suggest that dietary antioxidant supplementation with Vitamin E, beta carotene, or Vitamin A has no beneficial effect in prevention of age-related diseases and may even lead to an overall increase of mortality ^{90 - 92}. Thus, in contrast to the popular notion that increased intake of antioxidants like Vitamin C and Vitamin E will have beneficial effects on health and life span, these studies suggest that antioxidants should be used with care as therapeutic tools. The efficacy of a given antioxidant might also depend on the presence of the other antioxidants or on certain physiological conditions.

Although it is unclear whether mitochondria play a causative role in the pathology of neuro-degenerative diseases, aging, and carcinogenesis, mitochondria-targeted antioxidants have been shown to be potent at sequestering reactive oxygen intermediates ^{80, 81, 93}. The use of mitochondrial-targeted antioxidants is a step toward understanding whether antioxidants can be efficient preventive or therapeutic tools against age-related diseases. Similar to what has been reported concerning antioxidant defense status, the rate of ROS production also does not clearly correlate with species-specific life span. The ability of mitochondria-targeted antioxidants to confer greater protection against oxidative damage in the mitochondria than untargeted cellular antioxidants provide has been attributed to their ability to cross the mitochondrial phospholipids bilayer and eliminate ROS at the heart of the source ^{80, 82, 94}.

During the past decade, considerable progress in developing mitochondria targeted antioxidants had been made. A well established approach is conjugation to lipophilic cation, such as triphenyl phosphonium (TPP) ⁹⁴. phosphonium derivatives have been used traditionally to determine the mitochondrial inner membrane potential. Triphenyl phosphonium cations consist of a positively charged phosphorus atom surrounded by a large hydrophobic surface, thereby giving it the ability to directly and rapidly permeate the lipid bilayers while retaining the positive charge. This positive charge is used to facilitate TPP cation accumulation within the mitochondrial matrix driven by the large mitochondrial memebrne potential (ΔѰm) of 150 -180 mV (negative inside), which was generated by the proton gradient during the transfer of an electron to oxygen.

The plasma membrane potential (30 - 60 mV negative inside) enables upto a 10-fold accumulation of TPP in the cytoplasm Fig. 4. The large negative potential gradient across the mitochondrial inner membrane potentiates the redistribution of TPP from the intracellular space in the mitochondria, leading to a 100-500 fold higher concentration of TPP inside mitochondria ⁹⁵.

FIG. 4: MITOCHONDRIAL ACCUMULATION OF TARGETED CATIONIC ANTIOXIDANTS (TPP)

A series of orally bioavailable mitochondria targeted antioxidants (MTAs) were discovered, including MitoQ, MitoVit E, MitoTEMPOL. These compounds are known to pass through all the biological membranes and accumulate within mitochondria more easily than their non-targeted antioxidants, rendering them far more effective in protecting against mitochondrial oxidative damage. Work by several investigators has provided strong evidence for the argument that mitochondria targeted antioxidants, such as MitoQ could be effective antioxidant therapies against the damage caused by enhanced ROS generation ^{94, 95}.

Triphenyl Phosphonium Based Mitochondria Targeted Antioxidant:

MitoQ: {10- (6’-ubiqunolyl)- decyl triphenyl phosphonium bromide and 10-(6,-uniquinonyl)-decyl triphenyl phosphonium bromide}.

MitoQ (mitoquinone) is the most studied and widely used antioxidant targeted to mitochondria. It consist of TPP covalently attached to the ubiquinone moiety of the endogenous antioxidant CoQ₁₀ through a ten carbon aliphatic carbon chain Fig. 5A. MitoQ predominantly accumulates in mitochondria, where it is primarily absorbed to the matrix facing surface of the inner mitochondrial membrane with the ubiquinone component penetrating deeply into the hydrophobic interior of the membrane ⁹⁵. Like the parent antioxidant CoQ₁₀, MitoQ continuously scavenges peroxyl, peroxynitrite and superoxide, thus can protect mitochondria against lipid peroxidation. After detoxifying oxidants, MitoQ is recycled back to the active ubiquinol antioxidant form by the respiratory chain complex II. Under certain conditions, it may become pro-oxidant and proapoptotic due to the redox cycling of the quione and generation of superoxide ⁹⁶.

MitoVitE: {[2- (3, 4-dihydro-6-hydroxy-2, 5, 7, 8-tetramethyl-2H-1-benzopyran-2-yl)ethyl]triphenyl phosphonium bromide}.

MitoVitE (mitotocopherol) was the first mitochondria targeted antioxidant to be discovered, and consist of TPP conjugated to the α-tocopherol moiety of vitamin E through a two carbon chain Fig. 5B. Internalized MitoVitE is immobilized by insertion in the bilipid layer of the mitochondrial inner membrane. Like MitoQ, MitoVit E appers to protect mitochondria and cwlls from oxidative damage by inhibiting lipid peroxidation ⁹⁷.

MitoTEMPOL: {(4- hydroxy- 2, 2, 6, 6, -tetra methyl piperidine-1-oxyl) triphenyl phosphonium bromide}.

MitoTEMPOL is another TPP⁺ derivative, but one with the stable piperidine nitroxide radical TEMPOL (4- hydroxy- 2, 2, 6, 6,-tetra methyl piperidine-1-oxyl) Fig. 5C, which accepts an electron from the potent radical scavenger hydroxylamine. MitoTEMPOL may act as a cytosolic SOD mimetic, which converts superoxide molecules into water, and is able to detoxify ferrous ion by oxidizing it to ferric ion. The conjugated compound accumulated inside energized, isolated mitochondria ⁹⁸.

MitoPBN: {[4- [4- [[(1, 1- dimethylethyl) oxido-imino]methyl]phenoxy]butyl]triphenylphosphonium bromide}.

Nitrones and phenyl tert-butyl nitrone (PBN) in particular have been investigated as neuro-protective agents and antioxidants Fig. 5E. Although reacts readily with carbon-centered radicals, it apparently does not function as a chain breaking antioxidants and does not react with superoxide. Because of the selectivity of PBN in reacting with carbon centered radicals, a mitochondrial targeted analogue, MitoPBN was prepared to dissect the roles of ROS in the activation of uncoupling proteins (UCPs); studies shows that MitoVitE and MitoQ block super oxide induced activation of UCPs ⁹⁹.

MitoPeroxidase: {2-[4-(4-triphenylphosphoniobu-toxy)- phenyl]- 1, 2- benzisoselenazol- 3(2H)-one iodide}.

MitoPeroxidase is a mitochondria targeted analogue of ebselen, which is a organ selenium compound that shows antioxidant effects through its glutathione peroxidase like action Fig. 5F. MitoPeroxidase and ebselen inhibit mitochondrial respiration and decrease the mitochondrial memebrane potential. The binding of MitoPeroxidase to isolated mitochondria was studied with a TPP⁺ sensitive electrode. Binding of MitoPeroxidase to mitochondria is rapid, and the addition of deenergized mitochondria decreases the concentration of free MitoPeroxidase. Mito Peroxidase and ebselen degrade phospholipid hydroperoxides and prevent Fe²⁺ / H₂O₂ induced lipid peroxidation in intact mitochondria, but these antioxidant effects requires glutathione or thioredoxin to generate the selenol form of MitoPeroxidase and ebselen ¹⁰⁰.

“Sk” Compounds: An alternative series of mitochondria targeted antioxidants, termed as “SkQs”, developed by using plastoquinone to replace the ubiquinone antioxidant moiety of MitoQ. The compound SkQ1 Fig. 5D, which is a TPP+ derivative conjugated with plastoquinone itself, is the most studied Sk compound.SkQ1 performed as a potent antioxidant in isolated mitochondria. Cell culture studies have confirmed that very low concentrations of SkQ1 and its analogues inhibited cell death induced by hydrogen peroxide. Extensive animal studies have demonstrated beneficial roles of SkQ1 and related compounds in a number of diseases associated with elevated oxidative stress ¹⁰¹.

   A                                                                             B

C                                                                             D

E                                                                             F

FIG. 5: A) MitoQ; B) MitoVitE; C) MitoTEMPOL; D) SkQ1; E) MitoPBN; F) MitoPeroxidase

Amino Acid and Peptide - Based, Mitochondria Targeted Antioxidants:                                  

SS tetrapeptides: SS tetrapeptids are aromatic-cationic peptides that bear the structural modification of alternating aromatic and basic amino acid residues along with a 2’, 6’-dimethyltyrosine (Dmt) residue. The SS tetra-peptides were originally prepared in an attempt to develop centrally acting opioid analgesics ¹⁰².

The compounds studied include Dmt-D-Arg-Phe-Lys-NH₂(SS-02), Phe- D-Arg-Phe-Lys-NH₂(SS-20) (a tetrapeptide that lacks the antioxidant Dmt), D- Arg- Dmt- Lys- Phe- NH₂ (SS-31), Dmt-D-Arg-Phe-atnDap-NH₂(SS-19), a fluorescent analog in which β- anthraniloyl- L- α- β- diaminiopropionic acid replaces Lys was prepared to study mitochondrial and cellular uptake Fig. 6A, 6B, 6C. SS-02 scavenges H₂O₂ and inhibits the oxidation of linoleic acid and low density lipoproteins (LDL), thereby demonstrating the antioxidant properties of these tetrapeptides. SS-31, which contains the same amino acid residues as SS-02 but in a different sequence, shows antioxidant properties similar to SS-02, but analogs SS-20, which lack the Dmt residue, did not demonstrate antioxidant activity. These may have the advantage in excerting effective antioxidant action in depolarized mitochondria ^{102, 103}.

Choline Esters of Glutathione and N-acetyl-L-cysteine: Glutathione (L-γ-glutamyl-L-cysteinyl-glycine) is the most abundant nonprotein thiol in cells. Glutathione plays an critical role in antioxidant defence mechanisms and in the detoxification of endobiotic and xenobiotic electrophiles. Mitochondria are not component to synthesize glutathione, and glutathione is transported from the cytoplasm to the mitochondria.

Dicarboxylate and 2-oxoglutarate carriers serve to transport glutathione into mitochondria. The mitochondrial glutathione pool is approximately 15 % of total cellular glutathione, but the mitochondrial glutathione pool plays a critical role in cytoprotection. To increase the mitochondrial content of glutathione and other thiol-based antioxidants may serve to protect mitochondria, along with cells and organs, against oxidative damage. Glutathione choline esters and N-acetyl-L-cysteine choline ester Fig. 7A, 7B, which are hydrophilic antioxidants designed to exploit the high negative internal potential of mitochondria, which should lead to their concentration in mitochondria ¹⁰⁴.

A                                                                                       B

C

FIG. 6: A) SS-02; B) SS-20; C) SS-31

A                                                                    B

FIG. 7: A) MitoGSH; B) MitoNAC

CONCLUSION: Mitochondria are attractive targets for drug delivery because of their roles in cellular energy metabolism, programmed cell death, Ca⁺⁺ homeostasis, cell signalling. A decline in mitochondrial function plays a key role in the aging process and increases the incidence of age-related disorders. Direct mechanisms of mitochondrial damage include the inhibition of electron transport chain complexes, transcriptions of these complexes and enzymes required for glycolysis and b-oxidation. Indirect mechanisms include damage via ROS overproduction or decrease in endogenous antioxidants. The field of antioxidants turned out to be much more challenging; much effort has been directed to the study of the efficacy of different antioxidants in human diseases. Redox homeostasis is maintained by the antioxidant defense system, which is responsible for eliminating a wide range of oxidants, including reactive oxygen species (ROS), lipid peroxides, and metals. Mitochondria-targeted antioxidants are widely studied because the mitochondria, the major producers of intracellular ROS, have been linked to the cause of aging and other chronic diseases.

Mitochondria-targeted antioxidants have shown great potential because they cross the mitochondrial phospholipid bilayer and eliminate ROS at the heart of the source. Mitochondria targeted antioxidants have shown great promise, with compounds such as MitoQ currently in clinical trials; however, further investigative work is needed, to improve the potency of current antioxidants and therapeutic treatments. There is also a need to develop novel experimental strategies to interfere with ROS production in a selective way, to reduce oxidative damage without affecting cell signalling.

An increased basic understanding of the role for ROS in different cellular processes should make it possible to substantially improve the design of human intervention studies aimed at reducing the oxidative damage associated with disease and aging. The search for effective therapies should include treatments that target mitochondria or pathways affected by mitochondrial function. In the future, well-designed and well-executed clinical trials will provide more definitive information on the therapeutic efficacy of agents aimed at improving mitochondrial health.

ACKNOWLEDGEMENT: Nil

CONFLICTS OF INTEREST: Nil

REFERENCES:

1. Giezen VM and Tovar J: Degenerate mitochondria. European Molecular Biology Organaization 2005; 6: 525-30.
2. Okuno D, Iino R and Noji H: Rotation and structure of F0F1-ATP synthase. Journal of Biochemistry 2011; 149: 655-64.
3. Nunnari J and Suomalainen A: Mitochondria: in sickness and in health. Cell 2012; 148(6): 1145-59.
4. Kujoth GC, Hiona A, Pugh TD, Someya S, Panzer K and Wohlgemuth SE: Mitochondrial DNA mutations, oxidative stress, and apoptosis in mammalian aging. Science 2005; 309: 481-4.
5. Chen H and Chan DC: Mitochondrial dynamics-fusion, fission, movement, and mitophagy-in neurodegenerative diseases. Human Molecular Genetics 2009; 18(2): 169-76.
6. Kirkwood TB: Evolution of ageing. Nature 1977; 270(5635): 301-304.
7. Courtney M, Darcy L and Ravussin E: Skeletal Muscle Mitochondria and Aging: A Review. Journal of Aging Research 2012; 1-20.
8. Holloszy JO: Skeletal muscle, mitochondrial deficiency does not mediate insulin resistance. The American Journal of Clinical Nutrition 2009; 89(1): 463-6.
9. Miller BF, Robinson MM, Bruss MD, Hellerstein M and Hamilton KL: A comprehensive assessment of mitochon-drial protein synthesis and cellular proliferation with age and caloric restriction. Aging Cell 2012; 11(1): 150-61.
10. Greaves LC, Reeve AK, Taylor RW and Turnbull DM: Mitochondrial DNA and disease. Journal of Pathology 2012; 226(2): 274-86.
11. Bhat AH, Dar KB, Anees S, Zargar MA, Masood A, Sofi MA and Ganie SA: Oxidative stress, mitochondrial dysfunction and neurodegenerative diseases; a mechanistic insight. Biomedicine and Pharmacotherapy 2015; 74: 101-10.
12. Chistiakov DA, Sobenin IA, Revin VV, Orekhov AN and Bobryshev YV: Mitochondrial Aging and Age-Related Dysfunction of Mitochondria. BioMed Research International 2014; 1-7.
13. Harman D: The biologic clock: the mitochondria. Journal of the American Geriatrics Society 1972; 20(4): 145-7.
14. Chung HY, Cesari M, Anton S, Marzetti E, Giovannini S, Seo AY, Carter C, Yu BP and Leeuwenburgh C: Molecular inflammation: underpinnings of aging and age-related diseases. Ageing Research and Reviews 2009; 8(2): 18-30.
15. Park CB and Larsson NG: Mitochondrial DNA mutations in disease and aging. Journal Cell Biology 2011; 193(5): 809-818.
16. Harman D: Aging: a theory based on free radical and radiation chemistry. Journal of Gerontology 1959; 11(3): 298-300.
17. Chomyn A and Attardi G: MtDNA mutations in aging and apoptosis. Biochemical and Biophysical Research Communications 2003; 304: 519-29.
18. Seo AY, Xu J, Servais S, Hofer T, Marzetti E, Wohlgemuth SE, Knutson MD, Chung HY and Leeuwenburgh C: Mitochondrial iron accumulation with age and functional consequences. Aging Cell 2008; 7: 706-16.
19. Bandy B and Davison AJ: Mitochondrial mutations may increase oxidative stress: implications for carcinogenesis and aging. Free Radical Biology and Medicine 1996; 8: 523-39.
20. Hiona A and Leeuwenburgh C: The role of mitochondrial DNA mutations in aging and sarcopenia: implications for the mitochondrial vicious cycle theory of aging. Experimental Gerontology 2008; 43: 24-33.
21. Wallace DC and Fan W: The pathophysiology of mitochondrial disease as modeled in the mouse. Genes and Development 2009; 23: 1714-36.
22. Trifunovic A, Wredenberg A, Falkenberg M, Spelbrink JN, Rovio AT, Bruder CE, Bohlooly YM, Gidlof S, Oldfors A and Wibom R: Premature ageing in mice expressing defective mitochondrial DNA polymerase. Nature 2004; 429: 417-23.
23. Hutter E, Skovbro M, Lener B, Prats C, Rabol R, Dela F and Jansen-Durr P: Oxidative stress and mitochondrial impairment can be separated from lipofuscin accumulation in aged human skeletal muscle. Aging Cell 2007; 6: 245-56.
24. Arnold Y, Joseph AM, Dutta D, Judy CY, Hwang JP and Leeuwenburgh C: New insights into the role of mitochondria in aging: mitochondrial dynamics and more. Journal of Cell Science 2010; 123(15): 2533-42.
25. Cui H, Kong Y and Zhang H: Oxidative Stress, Mitochondrial Dysfunction, and Aging. Journal of Signal Transduction 2011; 1-13.
26. Halliwell B: Reactive oxygen species in living systems: source, biochemistry, and role in human disease. American Journal of Medicine 1991; 91(3): 14-22.
27. Chakravarti B and Chakravarti DN: Oxidative modification of proteins: age-related changes. Gerontology 2007; 53(3): 128-39.
28. Cooke MS, Evans MD, Dizdaroglu M and Lunec J: Oxidative DNA damage: mechanisms, mutation, and disease. Fedaration of Ameriacn Societies for Experimental Biology Journal 2003; 17(10): 1195-214.
29. Filipcik P, Cente M, Ferencik M, Hulin I and Novak M: The role of oxidative stress in the pathogenesis of Alzheimer’s disease. Bratislavsk´e Lekarske Listy 2006; 107(9): 384-94.
30. Karihtala P and Soini Y: Reactive oxygen species and antioxidant mechanisms in human tissues and their relation to malignancies. Acta Pharmacologica Microbiologica et Immunologica Scandinavica 2007; 115(2): 81-103.
31. Krokan HE, Standal R and Slupphaug G: DNA glycosylases in the base excision repair of DNA. Biochemical Journal 1997; 325(1): 1-16.
32. Dizdaroglu M, Jaruga P, Birincioglu M and Rodriguez H: Free radical-induced damage to DNA: mechanisms and measurement. Free Radical Biology and Medicine 2002; 32(11): 1102-15.
33. Grollman P and Moriya M: Mutagenesis by 8- oxoguanine: an enemy within. Trends in Genetics 1993; 9(7): 246-9.
34. Nakamura S, Takamura T and Matsuzawa-Nagata N: Palmitate induces insulin resistance in H4IIEC3 hepatocytes through reactive oxygen species produced by mitochondria. The Journal of Biological Chemistry 2009; 284(22): 14809-18.
35. Harman D: Free radical theory of aging: an update: increasing the functional life span. Annals of the New York Academy of Sciences 2006; 1067: 10-21.
36. Chabi B, Ljubicic V, Menzies KJ, Huang JH, Saleem A and Hood DA: Mitochondrial function and apoptotic susceptibility in aging skeletal muscle. Aging Cell 2008; 7(1): 2-12.
37. Mansouri FL and Muller Y: Alterations in mitochondrial function, hydrogen peroxide release and oxidative damage in mouse hind-limb skeletal muscle during aging. Mechanisms of Ageing and Development 2006; 127(3): 298-306.
38. Yarian S, Rebrin I and Sohal RS: Aconitase and ATP synthase are targets of malondialdehyde modification and undergo an age-related decrease in activity in mouse heart mitochondria. Biochemical and Biophysical Research Communications 2005; 330(1): 151-6.
39. Pesce V, Cormio A and Fracasso A: Age-related mitochondrial genotypic and phenotypic alterations in human skeletal muscle. Free Radical Biology and Medicine 2001; 30(11): 1223-33.
40. Beal MF: Oxidatively modified proteins in aging and disease. Free Radical Biology and Medicine 2002; 32(9): 797-803.
41. Staunton L, O’Connell K and Ohlendieck K: Proteomic profiling of mitochondrial enzymes during skeletal muscle aging. Journal of Aging Research 2011; 9.
42. Wilson DM, Sofinowski TM and McNeill DR: Repair mechanisms for oxidative DNA damage. Frontiers in Bioscience 2003; 8: 963-981.
43. Maynard S, Schurman SH, Harboe C, De SouzaPinto NC and Bohr VA: Base excision repair of oxidative DNA damage and association with cancer and aging. Carcinogenesis 2009; 30(1): 2-10.
44. Alexeyev MF: Is there more to aging than mitochondrial DNA and reactive oxygen species. Fedaration of Ameriacn Societies for Experimental Biology Journal 2009; 276(20): 5768-87.
45. Kushnareva Y, Murphy AN and Andreyev A: Complex Imediated reactive oxygen species generation: modulation by cytochrome c and NAD(P)⁺ oxidation-reduction state. The Biochemical Journal 2002; 368(2): 545-53.
46. Barreiro E, Coronell C, Lavina B, Ramırez-Sarmiento R, Orozco-Levi M and Gea J: Aging, sex differences, and oxidative stress in human respiratory and limbmuscles. Free Radical Biology and Medicine 2006; 41(5): 797-809.
47. Ji LL, Dillon and Dand Wu E: Alteration of antioxidant enzymes with aging in rat skeletal muscle and liver. The American Journal of Physiology 1990; 258(4): 918-23.
48. Luhtala TA, Roecker EB, Pugh T, R. Feuers RJ and Weindruch R: Dietary restriction attenuates age-related increases in rat skeletal muscle antioxidant enzyme activities. Journals of Gerontology 1994; 49(5): 231-38.
49. Chance B, Sies H and Boveris A: Hydroperoxide metabolism in mammalian organs. Physiological Reviews 1979; 59(3): 527-605.
50. Hansford RG, Hogue BA and Mildaziene A: Dependence of H₂O₂ formation by rat heart mitochondria on substrate availability and donor age. Journal of Bioenergetics and Biomembranes 1997; 29(1): 89-95.
51. Droge W: Free radicals in the physiological control of cell function. Physiological Reviews 2002; 82(1): 47-95.
52. Fridovich: Superoxide radical and superoxide dismutases. Annual Review of Biochemistry 1995; 64:97-112.
53. Weisiger RA and Fridovich I: Mitochondrial superoxide dismutase. Site of synthesis and intra mitochondrial localization. Journal of Biological Chemistry 1973; 248(13): 4793-6.
54. Sturtz LA, Diekert K, Jensen LT, Lill R and Culotta VC: A fraction of yeast Cu, Zn-superoxide dismutase and its metallo chaperone, CCS, localize to the intermembrane space of mitochondria. A physiological role for SOD1 in guarding against mitochondrial oxidative damage. Journal of Biological Chemistry 2001; 276(41): 38084-9.
55. Turrens JF: Mitochondrial formation of reactive oxygen species. Journal of Physiology 2003; 552(2): 335-44.
56. Nordberg J and Arner SJ: Reactive oxygen species, antioxidants, and the mammalian thioredoxin system. Free Radical Biology and Medicine 2001; 31(11): 1287-312.
57. McMillan TJ, Leatherman E, Ridley A, Shorrocks J, Tobi SE and Whiteside JR: Cellular effects of long wavelength UV light (UVA) in mammalian cells. Journal of Pharmacy and Pharmacology 2008; 60(8): 969-76.
58. Norbury CJ and Hickson ID: Cellular responses to DNA damage. Annual Review of Pharmacology and Toxicology 2001; 41: 367-401.
59. Ercal N, Gurer-Orhan H and Aykin-Burns N: Toxic metals and oxidative stress part I: mechanisms involved in metal-induced oxidative damage. Current Topics in Medicinal Chemistry 2001; 1(6): 529-39.
60. Wink DA, Hanbauer I and Grisham MB: Chemical biology of nitric oxide: regulation and protective and toxic mechanisms. Current Topics in Cellular Regulation 1996; 34: 159-87.
61. Finkel T and Holbrook NJ: Oxidants, oxidative stress and the biology of ageing. Nature 2000; 408(6809): 239-47.
62. Lambeth JD: NOX enzymes and the biology of reactive oxygen. Nature Reviews Immunology 2004; 4(3): 181-9.
63. Quinn MT, Ammons MCB and DeLeo FR: The expanding role of NADPH oxidases in health and disease: no longer just agents of death and destruction. Clinical Science 2006; 111(1): 1-20.
64. Miquel J, Economos AC, Fleming J and Johnson JE: Mitochondrial role in cell aging. Experimental Gerontology 1980; 15(6): 575-91.
65. Falkenberg M, Larsson NG and Gustafsson CM: DNA replication and transcription in mammalian mitochondria. Annual Review of Biochemistry 2007; 76: 679-99.
66. Chomyn and Attardi G: MtDNA mutations in aging and apoptosis. Biochemical and Biophysical Research Communications 2003; 304(3): 519-29.
67. Halliwell B: How to characterize an antioxidant-An update. Biochemical Society Symposia 1955; 61: 73-10.
68. Shi HL, Noguchi N and Niki N: Comparative study on dynamics of antioxidative action of α- tocopheryl hydroquinone, 578 ubiquinol and α- tocopherol, against lipid peroxidation. Free Radical Biology and Medicine 1999; 27: 334-46.
69. Chen L, Hu JY and Wang SQ: The role of antioxidants in photoprotection: A critical review. Journal of the American Acadamy of Dermatology 2012; 67: 1013-24.
70. Wu Y, Chen HD, Li YH, Gao XH, Preedy VR and Preedy VR: Antioxidants and skin: an overview. In Handbook of Diet, Nutrition and the Skin 2012; 2: 68-90.
71. Roche MD, Seagrove S, Mehta A, Divekar P, Campbell S and Curnow A: Using natural dietary sources of antioxidants to protect against ultraviolet and visible radiation induced DNA damage: an investigation of human green tea ingestion. Journal of Photochemistry and Photobiology 2010; 101: 169-73.
72. Meewes C, Brenneisen P, Wenk J, Kuhr L, Ma W, Alikoski J, Poswig, Krieg T, Scharffetter-Kochanek K: Adaptive antioxidant response protects dermal fibroblasts fromUVA-induced phototoxicity. Free Radical Biology and Medicine 2001; 30: 238-47.
73. Shindo Y, Witt E, Han D, Epstein W and Packer L: Enzymic and non-enzymic antioxidants in epidermis and dermis of human skin. Journal of Investigative Dermatology 1994; 102: 122-4.
74. Schafer M, Farwanah H, Willrodt AH, Huebner AJ, Sandhoff K, Roop D, Hohl D, Bloch W and Werner S: Nrf2 links epidermal barrier function with antioxidant defense. European Molecular Biology Organisation and Molecular Medicine 2012; 4: 364-79.
75. Magesh S, Chen Y and Hu L: Small molecule modulators of Keap1-Nrf2-ARE pathway as potential preventive and therapeutic agents. Medicinal Research and Reviews 2012; 32: 687-726.
76. Ungvari Z, Bagi Z, Feher A, Recchia FA, Sonntag WE, Pearson K, De Cabo R and Csiszar A: Resveratrol confers endothelial protection via activation of the antioxidant transcription factor Nrf2. American Journal of Physiology Heart Circulatory Physiology 2012; 299: 18-24.
77. Agati G, Azzarello E, Pollastri S and Tattini M: Flavonoids as antioxidants in plants: location and functional significance. Plant Science 2012; 196: 67-76.
78. Bendich A, Machlin LJ, Scandurra O, Burton GW and Wayner DM: The antioxidant role of Vitamin C. Adv. Free Radical Biology and Medicine 1986; 2: 419-44.
79. Genrikhs EE, Stelmashook EV, Popova OV, Kapay NA, Korshunova GA, Sumbatyan NV, Skrebitsky VG, Skulachev VP and Isaev NK: Mitochondria-targeted antioxidant SkQT1 decreases trauma-induced neurological deficit in rat and prevents amyloid-b-induced impairment of long-term potentiation in rat hippocampal slices. Journal of Drug Targeting 2015; 23: 347-52.
80. Jauslin ML, Meier T, Smith RA and Murphy MP: Mitochondria-targeted antioxidants protect Friedreich Ataxia fibroblasts from endogenous oxidative stress more effectively than untargeted antioxidants. Fedaration of Ameriacn Societies for Experimental Biology Journal 2003; 17: 1972-4.
81. Gioscia-Ryan RA, LaRocca TJ, Sindler AL, Zigler MC, Murphy MP and Seals DR: Mitochondria-targeted antioxidant (MitoQ) ameliorates age-related arterial endothelial dysfunction in mice. Journal of Physiology 2014; 592: 2549-61.
82. Evans CA, Diplock AT: Current status of antioxidant therapy. Free Radical Biology and Medicine 1933; 15: 77-96.
83. Krinsky NI: Mechanism of action of biological antioxidants. Proceedings of the society for Experimental Biology and Medicine 1992; 200: 248-54.
84. Niki E: Antioxidant defenses in eukaryotic cells. Free radicals: From basic science to medicine. Proceedings of the society for Experimental Biology and Medicine 1993; 365-73.
85. Orr WC and Sohal RS: Extension of life-span by over expression of superoxide dismutase and catalase in Drosop hila melanogaster. Science 1994; 263(5): 1128-30.
86. VanRaamsdonk JM and Hekimi S: Deletion of the mitochondrial superoxide dismutase sod-2 extends lifespan in Caenorhabditis elegans. PLoS Genetics 2009; 5(2): 100-361.
87. Sun J, Folk D, Bradley TJ and Tower J: Induced overexpression of mitochondrial Mn-superoxide dismutase extends the life span of adult Drosophila melanogaster. Genetics 2002; 161(2): 661-72.
88. Mockett RJ, Sohal BH and Sohal RS: Expression of multiple copies of mitochondrially targeted catalase or genomic Mn superoxide dismutase transgenes does not extend the life span of Drosophila melanogaster. Free Radical Biology and Medicine 2010; 49(12): 2028-31.
89. O’donnell E and Lynch M: Dietary antioxidant supplementation reverses age-related neuronal changes. Neurobiol Aging 1998; 19(5): 461-7.
90. Alvarado C: Dietary supplementation with antioxidants improves functions and decreases oxidative stress of leukocytes from prematurely aging mice. Nutrition 2006; 22(7): 767-77.
91. Bjelakovic G, Nikolova D, Gluud LL, Simonetti RG and Gluud C: Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseases. Cochrane Database System Reveiws 2012; 3: 71-6.
92. Oyewole AO, Wilmot MC, Fowler M and Birch-Machin MA: Comparing the effects of mitochondrial targeted and localized antioxidants with cellular antioxidants in human skin cells exposed to UV and hydrogen peroxide. Fedaration of Ameriacn Societies for Experimental Biology Journal 2014; 28: 485-94.
93. Supinski GS, Murphy MP and Callahan LA: MitoQ administration prevents endotoxin-induced cardiac dysfunction. American Journal of Physiology Regulatory Integrative Comparative Physiology 2009; 297: 1095-102.
94. Liberman EA, Topaly VA, Tsofina LM, Jasaitis AA and Skulachev VP: Mechanism of coupling of oxidative phophorylation and the membrane potential of mitochondria. Nature 1969; 222: 1076-78.
95. Smith RA, Murphy MP, Coulter CV and Porteous C: Selective targeting of an antioxidant to mitochondria. European journal of biochemistry 1999; 263: 709-16.
96. Smith RA and Murphy MP: Mitochondria targeted antioxidants as therapies. Discovery Medicine 2011; 11: 106-14.
97. Tranka J, Blaikie FH. Smith RA and Murphy MP: A mitochondria targeted nitroxide is reduced to its hydroxylamine by uniquinol in mitochondria. Free radical Biology and medicine 2008; 44: 1406-19.
98. Kotake Y: Pharmacologic properties of phenyl tert-butylnitrone. Antioxidant redox signal 1999; 1: 481-99.
99. Murugesh G, Dumont WW, and Sies H: Chemistry of biologically important synthetic organoselenium compounds. Chemical reviews 2001; 101: 2125-79.
100. Antonenko YN, Skulachev VP and Skulachev IV: Mitochondria targeted plastoquinone derivatives as tools to interrupt execution of the aging programme. Biochemistry 2008; 73: 1273-87.
101. Sheu SS, Nauduri D and Anders MW: Targeting antioxidants to mitochondria: a new therapeutic direction. Biochimica et biophysica acta. 2006; 1762: 256-65.
102. Jin H, Kanthasamy A, Ghosh A, Anantharam V, Kalyanaramam B and Kanthasamy AG: Mitochondria targeted antioxidants for treatment of parkinson’s disease: preclinical and clinical outcomes. Biochimica et biophysica acta. 2014; 1842: 1282-94.
103. Chen Z, Putt DA and Lash LH: Evidence for mitochondrial uptake of glutathione by dicarboxylate and 2-oxoglutarate carriers. Journal of pharmacology and Experimental Therapeutics 1998; 285: 608-18.
     

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     Varghese B, Gowrishankar NL, Drisya K and Ramees MT: Mitochondria - targeted antioxidant: Aging. Int J Pharm Sci Res 2018; 9(2): 442-55.doi: 10.13040/IJPSR.0975-8232.9(2).442-55.

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