MitoQ administration prevents endotoxin-induced cardiac dysfunction

Mitochondria and heart disease

Mitochondria play a key role in the normal functioning of the heart, and in the pathogenesis and development of various types of heart disease. Physiologically, mitochondrial ATP supply needs to be matched to the often sudden changes in ATP demand of the heart, and this is mediated to a large extent by the mitochondrial Ca(2+) transport pathways allowing elevation of mitochondrial [Ca(2+)] ([Ca(2+)](m)). In turn this activates dehydrogenase enzymes to increase NADH and hence ATP supply. Pathologically, [Ca(2+)](m) is also important in generation of reactive oxygen species, and in opening of the mitochondrial permeability transition pore (MPTP); factors involved in both ischaemia-reperfusion injury and in heart failure. The MPTP has proved a promising target for protective strategies, with inhibitors widely used to show cardioprotection in experimental, and very recently human, studies. Similarly mitochondrially-targeted antioxidants have proved protective in various animal models of disease and await clinical trials. The mitochondrial Ca(2+) transport pathways, although in theory promising therapeutic targets, cannot yet be targeted in human studies due to non-specific effects of drugs used experimentally to inhibit them. Finally, specific mitochondrial cardiomyopathies due to mutations in mtDNA have been identified, usually in a gene for a tRNA, which, although rare, are almost always very severe once the mutation has exceeded its threshold.

The mitochondria-targeted antioxidant MitoQ prevents loss of spatial memory retention and early neuropathology in a transgenic mouse model of Alzheimer's disease

Considerable evidence suggests that mitochondrial dysfunction and oxidative stress contribute to the progression of Alzheimer's disease (AD). We examined the ability of the novel mitochondria-targeted antioxidant MitoQ (mitoquinone mesylate: [10-(4,5-dimethoxy-2-methyl-3,6-dioxo-1,4-cycloheexadienl-yl) decyl triphenylphosphonium methanesulfonate]) to prevent AD-like pathology in mouse cortical neurons in cell culture and in a triple transgenic mouse model of AD (3xTg-AD). MitoQ attenuated β-amyloid (Aβ)-induced neurotoxicity in cortical neurons and also prevented increased production of reactive species and loss of mitochondrial membrane potential (Δψ(m)) in them. To determine whether the mitochondrial protection conferred by MitoQ was sufficient to prevent the emergence of AD-like neuropathology in vivo, we treated young female 3xTg-AD mice with MitoQ for 5 months and analyzed the effect on the progression of AD-like pathologies. Our results show that MitoQ prevented cognitive decline in these mice as well as oxidative stress, Aβ accumulation, astrogliosis, synaptic loss, and caspase activation in their brains. The work presented herein suggests a central role for mitochondria in neurodegeneration and provides evidence supporting the use of mitochondria-targeted therapeutics in diseases involving oxidative stress and metabolic failure, namely AD.

Mitochondria-targeted small molecule therapeutics and probes

SIGNIFICANCE

Mitochondrial function is central to a wide range of biological processes in health and disease and there is considerable interest in developing small molecules that are taken up by mitochondria and act as either probes of mitochondrial function or therapeutics in vivo.

RECENT ADVANCES

Various strategies have been used to target small molecules to mitochondria, particularly conjugation to lipophilic cations and peptides, and most of the work so far has been on mitochondria-targeted antioxidants and redox probes. In vivo studies will reveal whether there are differences in the types of bioactive functionalities that can be delivered using different carriers.

CRITICAL ISSUES

The outstanding challenge in the area is to discover how to combine the established selective delivery to mitochondria with the specific delivery to particular organs.

FUTURE DIRECTIONS

These targeting methods will be used to direct many other bioactive molecules to mitochondria and many more wider applications other than just to antioxidants can be anticipated in the future.

Resolution of mitochondrial oxidative stress rescues coronary collateral growth in Zucker obese fatty rats

OBJECTIVE

We have previously found abrogated ischemia-induced coronary collateral growth in Zucker obese fatty (ZOF) rats compared with Zucker lean (ZLN) rats. Because ZOF rats have structural abnormalities in their mitochondria suggesting dysfunction and also show increased production of O(2), we hypothesized that mitochondrial dysfunction caused by oxidative stress impairs coronary collateral growth in ZOF.

METHODS AND RESULTS

Increased levels of reactive oxygen species were observed in aortic endothelium and smooth muscle cells in ZOF rats compared with ZLN rats. Reactive oxygen species levels were decreased by the mitochondria-targeted antioxidants MitoQuinone (MQ) and MitoTempol (MT) as assessed by MitoSox Red and dihydroethidine staining. Lipid peroxides (a marker of oxidized lipids) were increased in ZOF by ≈47% compared with ZLN rats. The elevation in oxidative stress was accompanied by increased antioxidant enzymes, except glutathione peroxidase-1, and by increased uncoupling protein-2 in ZOF versus ZLN rats. In addition, elevated respiration rates were also observed in the obese compared with lean rats. Administration of MQ significantly normalized the metabolic profiles and reduced lipid peroxides in ZOF rats to the same level observed in lean rats. The protective effect of MQ also suppressed the induction of uncoupling protein-2 in the obese rats. Resolution of mitochondrial oxidative stress by MQ or MT restored coronary collateral growth to the same magnitude observed in ZLN rats in response to repetitive ischemia.

CONCLUSIONS

We conclude that mitochondrial oxidative stress and dysfunction play a key role in disrupting coronary collateral growth in obesity and the metabolic syndrome, and elimination of the mitochondrial oxidative stress with MQ or MT rescues collateral growth.

Novel insights into interactions between mitochondria and xanthine oxidase in acute cardiac volume overload

Xanthine oxidoreductase (XOR) is increased in the left ventricle (LV) of humans with volume overload (VO), and mitochondrial inhibition of the respiratory chain occurs in animal models of VO. Because mitochondria are both a source and a target of reactive oxygen and nitrogen species, we hypothesized that activation of XOR and mitochondrial dysfunction are interdependent. To test this we used the aortocaval fistula (ACF) rat model of VO and a simulation of the stretch response in isolated adult cardiomyocytes with and without the inhibitor of XOR, allopurinol, or the mitochondrially targeted antioxidant MitoQ. Xanthine oxidase (XO) activity was increased in cardiomyocytes from ACF vs sham rats (24h) without an increase in XO protein. A twofold increase in LV end-diastolic pressure/wall stress and a decrease in LV systolic elastance with ACF were improved when allopurinol treatment (100mg/kg) was started at ACF induction. Subsarcolemmal State 3 mitochondrial respiration was significantly decreased in ACF and normalized by allopurinol. Cardiomyocytes subjected to 3h cyclical stretch resulted in an increase in XO activity and mitochondrial swelling, which was prevented by allopurinol or MitoQ pretreatment. These studies establish an early interplay between cardiomyocyte XO activation and bioenergetic dysfunction that may provide a new target that prevents progression to heart failure in VO.

Coenzyme Q10 deficiency in septic shock patients

Donnino and colleagues provide new insights into the field of oxidative stress and mitochondrial dysfunction during septic shock. These authors suggest a coenzyme Q₁₀ (CoQ₁₀) deficiency in patients with septic shock. Larger prospective observational trials measuring CoQ₁₀ in patients with septic shock are required to confirm the possibility of CoQ₁₀ depletion. This study is a new step toward a study testing CoQ₁₀ as a potential therapeutic agent for patients with septic shock.

Inhibition of c-Jun-N-terminal kinase increases cardiac peroxisome proliferator-activated receptor alpha expression and fatty acid oxidation and prevents lipopolysaccharide-induced heart dysfunction

Septic shock results from bacterial infection and is associated with multi-organ failure, high mortality, and cardiac dysfunction. Sepsis causes both myocardial inflammation and energy depletion. We hypothesized that reduced cardiac energy production is a primary cause of ventricular dysfunction in sepsis. The JNK pathway is activated in sepsis and has also been implicated in impaired fatty acid oxidation in several tissues. Therefore, we tested whether JNK activation inhibits cardiac fatty acid oxidation and whether blocking JNK would restore fatty acid oxidation during LPS treatment. LPS treatment of C57BL/6 mice and adenovirus-mediated activation of the JNK pathway in cardiomyocytes inhibited peroxisome proliferator-activated receptor α expression and fatty acid oxidation. Surprisingly, none of the adaptive responses that have been described in other types of heart failure, such as increased glucose utilization, reduced αMHC:βMHC ratio or induction of certain microRNAs, occurred in LPS-treated mice. Treatment of C57BL/6 mice with a general JNK inhibitor (SP600125) increased fatty acid oxidation in mice and a cardiomyocyte-derived cell line. JNK inhibition also prevented LPS-mediated reduction in fatty acid oxidation and cardiac dysfunction. Inflammation was not alleviated in LPS-treated mice that received the JNK inhibitor. We conclude that activation of JNK signaling reduces fatty acid oxidation and prevents the peroxisome proliferator-activated receptor α down-regulation that occurs with LPS.

Mitochondria-targeted ubiquinone (MitoQ) decreases ethanol-dependent micro and macro hepatosteatosis

Chronic alcohol-induced liver disease results in inflammation, steatosis, and increased oxidative and nitrosative damage to the mitochondrion. We hypothesized that targeting an antioxidant to the mitochondria would prevent oxidative damage and attenuate the steatosis associated with alcoholic liver disease. To test this we investigated the effects of mitochondria-targeted ubiquinone (MitoQ) (5 and 25 mg/kg/day for 4 weeks) in male Sprague-Dawley rats consuming ethanol using the Lieber-DeCarli diet with pair-fed controls. Hepatic steatosis, 3-nitrotyrosine (3-NT), 4-hydroxynonenal (4-HNE), hypoxia inducible factor α (HIF1α), and the activity of the mitochondrial respiratory chain complexes were assessed. As reported previously, ethanol consumption resulted in hepatocyte ballooning, increased lipid accumulation in the form of micro and macrovesicular steatosis, and induction of cytochrome P450 2E1 (CYP2E1). MitoQ had a minor effect on the ethanol-dependent decrease in mitochondrial respiratory chain proteins and their activities; however, it did decrease hepatic steatosis in ethanol-consuming animals and prevented the ethanol-induced formation of 3-NT and 4-HNE. Interestingly, MitoQ completely blocked the increase in HIF1α in all ethanol-fed groups, which has previously been demonstrated in cell culture models and shown to be essential in ethanol-dependent hepatosteatosis.

CONCLUSION

These results demonstrate the antioxidant capacity of MitoQ in alleviating alcohol-associated mitochondrial reactive oxygen species (ROS) and several downstream effects of ROS/RNS (reactive nitrogen species) production such as inhibiting protein nitration and protein aldehyde formation and specifically ROS-dependent HIF1α stabilization.

The mitochondria-targeted antioxidant mitoquinone protects against cold storage injury of renal tubular cells and rat kidneys

The majority of kidneys used for transplantation are obtained from deceased donors. These kidneys must undergo cold preservation/storage before transplantation to preserve tissue quality and allow time for recipient selection and transport. However, cold storage (CS) can result in tissue injury, kidney discardment, or long-term renal dysfunction after transplantation. We have previously determined mitochondrial superoxide and other downstream oxidants to be important signaling molecules that contribute to CS plus rewarming (RW) injury of rat renal proximal tubular cells. Thus, this study's purpose was to determine whether adding mitoquinone (MitoQ), a mitochondria-targeted antioxidant, to University of Wisconsin (UW) preservation solution could offer protection against CS injury. CS was initiated by placing renal cells or isolated rat kidneys in UW solution alone (4 h at 4°C) or UW solution containing MitoQ or its control compound, decyltriphenylphosphonium bromide (DecylTPP) (1 μM in vitro; 100 μM ex vivo). Oxidant production, mitochondrial function, cell viability, and alterations in renal morphology were assessed after CS exposure. CS induced a 2- to 3-fold increase in mitochondrial superoxide generation and tyrosine nitration, partial inactivation of mitochondrial complexes, and a significant increase in cell death and/or renal damage. MitoQ treatment decreased oxidant production ~2-fold, completely prevented mitochondrial dysfunction, and significantly improved cell viability and/or renal morphology, whereas DecylTPP treatment did not offer any protection. These findings implicate that MitoQ could potentially be of therapeutic use for reducing organ preservation damage and kidney discardment and/or possibly improving renal function after transplantation.

SOD1 and MitoTEMPO partially prevent mitochondrial permeability transition pore opening, necrosis, and mitochondrial apoptosis after ATP depletion recovery

Generation of excessive reactive oxygen species (ROS) leads to mitochondrial dysfunction, apoptosis, and necrosis in renal ischemia-reperfusion (IR) injury. Previously we showed that lentiviral vector-mediated overexpression of superoxide dismutase-1 (SOD1) in proximal tubular epithelial cells (LLC-PK(1)) reduced cytotoxicity in an in vitro model of IR injury. Here, we examined the effects of SOD1 overexpression on mitochondrial signaling after ATP depletion-recovery (ATP-DR). To examine the role of mitochondrial ROS, a subset of cells was treated with the mitochondrial antioxidant MitoTEMPO. ATP-DR-mediated increase in mitochondrial calcium, loss of mitochondrial membrane potential, and increase in mitochondrial permeability transition pore (MPTP) were attenuated by SOD1 and MitoTEMPO (P<0.01). SOD1 prevented ATP-DR-induced mitochondrial Bax translocation, although the release of proapoptotic proteins from mitochondria was not prevented by SOD1 alone and required the presence of both SOD1 and MitoTEMPO. SOD1 suppressed the increase in c-jun phosphorylation, suggesting that JNK signaling regulates Bax translocation to mitochondria via ROS. ATP-DR-mediated changes in MPTP and mitochondrial signaling increased necrosis and apoptosis, both of which were partially attenuated by SOD1 and MitoTEMPO. These studies show that SOD1 and MitoTEMPO preserve mitochondrial integrity and attenuate ATP-DR-mediated necrosis and apoptosis.

Bench-to-bedside review: Targeting antioxidants to mitochondria in sepsis

Development of organ dysfunction associated with sepsis is now accepted to be due at least in part to oxidative damage to mitochondria. Under normal circumstances, complex interacting antioxidant defense systems control oxidative stress within mitochondria. However, no studies have yet provided conclusive evidence of the beneficial effect of antioxidant supplementation in patients with sepsis. This may be because the antioxidants are not accumulating in the mitochondria, where they are most needed. Antioxidants can be targeted selectively to mitochondria by several means. This review describes the in vitro studies and animal models of several diseases involving oxidative stress, including sepsis, in which antioxidants targeted at mitochondria have shown promise, and the future implications for such approaches in patients.

Animal and human studies with the mitochondria-targeted antioxidant MitoQ

As mitochondrial oxidative damage contributes to a wide range of human diseases, antioxidants designed to be accumulated by mitochondria in vivo have been developed. The most extensively studied of these mitochondria-targeted antioxidants is MitoQ, which contains the antioxidant quinone moiety covalently attached to a lipophilic triphenylphosphonium cation. MitoQ has now been used in a range of in vivo studies in rats and mice and in two phase II human trials. Here, we review what has been learned from these animal and human studies with MitoQ.

A pore way to die: the role of mitochondria in reperfusion injury and cardioprotection

In addition to their normal physiological role in ATP production and metabolism, mitochondria exhibit a dark side mediated by the opening of a non-specific pore in the inner mitochondrial membrane. This mitochondrial permeability transition pore (MPTP) causes the mitochondria to breakdown rather than synthesize ATP and, if unrestrained, leads to necrotic cell death. The MPTP is opened in response to Ca2+ overload, especially when accompanied by oxidative stress, elevated phosphate concentration and adenine nucleotide depletion. These conditions are experienced by the heart and brain subjected to reperfusion after a period of ischaemia as may occur during treatment of a myocardial infarction or stroke and during heart surgery. In the present article, I review the properties, regulation and molecular composition of the MPTP. The evidence for the roles of CyP-D (cyclophilin D), the adenine nucleotide translocase and the phosphate carrier are summarized and other potential interactions with outer mitochondrial membrane proteins are discussed. I then review the evidence that MPTP opening mediates cardiac reperfusion injury and that MPTP inhibition is cardioprotective. Inhibition may involve direct pharmacological targeting of the MPTP, such as with cyclosporin A that binds to CyP-D, or indirect inhibition of MPTP opening such as with preconditioning protocols. These invoke complex signalling pathways to reduce oxidative stress and Ca2+ load. MPTP inhibition also protects against congestive heart failure in hypertensive animal models. Thus the MPTP is a very promising pharmacological target for clinical practice, especially once more specific drugs are developed.

Mitochondrial oxidative stress and mammalian healthspan

Aging of the American society is leading to a growing need for disease-modifying interventions to treat age-related diseases and enhance healthspan. Mitochondria and mitochondrially generated reactive oxygen species appear to play a central role in these processes and are a likely target for interventions. Conventional, untargeted antioxidants have not demonstrated a clear benefit in human studies. As a result, approaches have been developed to target antioxidants specifically to mitochondria. Studies have employed a wide array of targeted molecules including antioxidant enzymes such as catalase, peroxiredoxin, superoxide dismutases and small molecular compounds which recapitulate the antioxidant activities of these enzymes. Lifespan and healthspan effects differ between interventions suggesting varied roles for specific mitochondrial reactive oxygen species and their impact on usual aging. Consistent findings in myocardial protection across various interventions support a focus on the impact of cardiac aging on healthspan. The advancement of mitochondrially targeted small-molecule antioxidants suggests the prospect of swift translation to human use.

Mitochondrial medicine for neurodegenerative diseases

Mitochondrial dysfunction has been reported in a wide array of neurological disorders ranging from neuromuscular to neurodegenerative diseases. Recent studies on neurodegenerative diseases have revealed that mitochondrial pathology is generally found in inherited or sporadic neurodegenerative diseases and is believed to be involved in the pathophysiological process of these diseases. Commonly seen types of mitochondrial dysfunction in neurodegenerative diseases include excessive free radical generation, lowered ATP production, mitochondrial permeability transition, mitochondrial DNA lesions, perturbed mitochondrial dynamics and apoptosis. Mitochondrial medicine as an emerging therapeutic strategy targeted to mitochondrial dysfunction in neurodegenerative diseases has been proven to be of value, though this area of research is still at in its early stage. In this article, we report on recent progress in the development of several mitochondrial therapies including antioxidants, blockade of mitochondrial permeability transition, and mitochondrial gene therapy as evidence that mitochondrial medicine has promise in the treatment of neurodegenerative diseases.