Metabolic effects of a mitochondrial-targeted coenzyme Q analog in high fat fed obese mice

Therapeutic effects of mitoquinol during an acute heat stress challenge in growing barrows

Study objectives were to determine the effects of mitoquinol (MitoQ, a mitochondrial-targeted antioxidant) on biomarkers of metabolism and inflammation during acute heat stress (HS). Crossbred barrows [n = 32; 59.0 ± 5.6 kg body weight (BW)] were blocked by BW and randomly assigned to 1 of 4 environmental-therapeutic treatments: 1) thermoneutral (TN) control (n = 8; TNCon), 2) TN and MitoQ (n = 8; TNMitoQ), 3) HS control (n = 8; HSCon), or 4) HS and MitoQ (n = 8; HSMitoQ). Pigs were acclimated for 6 d to individual pens before study initiation. The trial consisted of two experimental periods (P). During P1 (2 d), pigs were fed ad libitum and housed in TN conditions (20.6 ± 0.8 °C). During P2 (24 h), HSCon and HSMitoQ pigs were exposed to continuous HS (35.2 ± 0.2 °C), while TNCon and TNMitoQ remained in TN conditions. MitoQ (40 mg/d) was orally administered twice daily (0700 and 1800 hours) during P1 and P2. Pigs exposed to HS had increased rectal temperature, skin temperature, and respiration rate (+1.5 °C, +6.8 °C, and +101 breaths per minute, respectively; P < 0.01) compared to their TN counterparts. Acute HS markedly decreased feed intake (FI; 67%; P < 0.01); however, FI tended to be increased in HSMitoQ relative to HSCon pigs (1.5 kg vs. 0.9 kg, respectively; P = 0.08). Heat-stressed pigs lost BW compared to their TN counterparts (-4.7 kg vs. +1.6 kg, respectively; P < 0.01); however, the reduction in BW was attenuated in HSMitoQ compared to HSCon pigs (-3.9 kg vs. -5.5 kg, respectively; P < 0.01). Total gastrointestinal tract weight (empty tissue and luminal contents) was decreased in HS pigs relative to their TN counterparts (6.2 kg vs. 8.6 kg, respectively; P < 0.01). Blood glucose increased in HSMitoQ relative to HSCon pigs (15%; P = 0.04). Circulating non-esterified fatty acids (NEFA) increased in HS compared to TN pigs (P < 0.01), although this difference was disproportionately influenced by elevated NEFA in HSCon relative to HSMitoQ pigs (251 μEq/L vs. 142 μEq/L; P < 0.01). Heat-stressed pigs had decreased circulating insulin relative to their TN counterparts (47%; P = 0.04); however, the insulin:FI ratio tended to increase in HS relative to TN pigs (P = 0.09). Overall, circulating leukocytes were similar across treatments (P > 0.10). Plasma C-reactive protein remained similar among treatments; however, haptoglobin increased in HS relative to TN pigs (48%; P = 0.03). In conclusion, acute HS exposure negatively altered animal performance, inflammation, and metabolism, which were partially ameliorated by MitoQ.

Therapeutic effects of the combination of moderate-intensity endurance training and MitoQ supplementation in rats with isoproterenol-induced myocardial injury: The role of mitochondrial fusion, fission, and mitophagy

INTRODUCTION

Mitochondrial dysfunction causes myocardial disease. This study investigated the effects of MitoQ alone and in combination with moderate-intensity endurance training (EX) on cardiac function and content and mRNA expression of several proteins involved in mitochondrial quality control in isoproterenol (ISO)-induced heart injuries METHODS: Seven groups of CTL, ISO, ISO-EX, ISO-MitoQ-125, ISO-MitoQ-250, ISO-EX+MitoQ-125, and ISO-EX+MitoQ-250 were assigned. Rats were trained on a treadmill, and the MitoQ groups received MitoQ in drinking water for 8 weeks, starting one week after the induction of heart injury. Arterial pressure and cardiac function indices, mRNA expression, protein content, oxidant and antioxidant markers, fibrosis, and histopathological changes were assessed by physiograph, Real-Time PCR, immunofluorescence, calorimetry, Masson's trichrome, and H&E staining, respectively.

RESULTS

The impacts of MitoQ-125, EX+MitoQ-125, and EX+MitoQ-250 on arterial pressure and left ventricular systolic pressure were higher than MitoQ-250 or EX alone. ± dp/dt max were higher in ISO-EX+MitoQ-125 and ISO-EX+MitoQ-250 than ISO-MitoQ-125 and ISO-MitoQ-250 groups, respectively. Histopathological scores and fibrosis decreased in ISO-EX, ISO-MitoQ-125, ISO-EX+MitoQ-125, and ISO-EX+MitoQ-250 groups. The restoration of MFN2, PINK-1, and FIS-1 changes was higher in ISO-EX+MitoQ-125 and ISO-EX+MitoQ-250 than ISO-EX, ISO-MitoQ-125 and ISO-MitoQ-250 groups. The expression of MFN2 and PINK-1 was lower in ISO-MitoQ-125 and ISO-EX+MitoQ-125 than ISO and CTL groups. The expression of FIS-1 in ISO-EX and ISO-EX+MitoQ-250 increased compared to CTL and ISO groups. MDA decreased in ISO-MitoQ-125 and ISO-EX+MitoQ-125 groups.

CONCLUSION

Exercise and MitoQ combination have additive effects on cardiac function by modulating cardiac mitochondria quality. This study provided a possible therapy to treat heart injuries.

Cysteine 253 of UCP1 regulates energy expenditure and sex-dependent adipose tissue inflammation

Uncoupling protein 1 (UCP1) is a major regulator of brown and beige adipocyte energy expenditure and metabolic homeostasis. However, the widely employed UCP1 loss-of-function model has recently been shown to have a severe deficiency in the entire electron transport chain of thermogenic fat. As such, the role of UCP1 in metabolic regulation in vivo remains unclear. We recently identified cysteine-253 as a regulatory site on UCP1 that elevates protein activity upon covalent modification. Here, we examine the physiological importance of this site through the generation of a UCP1 cysteine-253-null (UCP1 C253A) mouse, a precise genetic model for selective disruption of UCP1 in vivo. UCP1 C253A mice exhibit significantly compromised thermogenic responses in both males and females but display no measurable effect on fat accumulation in an obesogenic environment. Unexpectedly, we find that a lack of C253 results in adipose tissue redox stress, which drives substantial immune cell infiltration and systemic inflammatory pathology in adipose tissues and liver of male, but not female, mice. Elevation of systemic estrogen reverses this male-specific pathology, providing a basis for protection from inflammation due to loss of UCP1 C253 in females. Together, our results establish the UCP1 C253 activation site as a regulator of acute thermogenesis and sex-dependent tissue inflammation.

A Novel Triphenylphosphonium Carrier to Target Mitochondria without Uncoupling Oxidative Phosphorylation

Mitochondrial dysfunction is an underlying pathology in numerous diseases. Delivery of diagnostic and therapeutic cargo directly into mitochondria is a powerful approach to study and treat these diseases. The triphenylphosphonium (TPP⁺) moiety is the most widely used mitochondriotropic carrier. However, studies have shown that TPP⁺ is not inert; TPP⁺ conjugates uncouple mitochondrial oxidative phosphorylation. To date, all efforts toward addressing this problem have focused on modifying lipophilicity of TPP⁺-linker-cargo conjugates to alter mitochondrial uptake, albeit with limited success. We show that structural modifications to the TPP⁺ phenyl rings that decrease electron density on the phosphorus atom can abrogate uncoupling activity as compared to the parent TPP⁺ moiety and prevent dissipation of mitochondrial membrane potential. These alterations of the TPP⁺ structure do not negatively affect the delivery of cargo to mitochondria. Results here identify the 4-CF₃-phenyl TPP⁺ moiety as an inert mitochondria-targeting carrier to safely target pharmacophores and probes to mitochondria.

Riding the tiger - physiological and pathological effects of superoxide and hydrogen peroxide generated in the mitochondrial matrix

Elevated mitochondrial matrix superoxide and/or hydrogen peroxide concentrations drive a wide range of physiological responses and pathologies. Concentrations of superoxide and hydrogen peroxide in the mitochondrial matrix are set mainly by rates of production, the activities of superoxide dismutase-2 (SOD2) and peroxiredoxin-3 (PRDX3), and by diffusion of hydrogen peroxide to the cytosol. These considerations can be used to generate criteria for assessing whether changes in matrix superoxide or hydrogen peroxide are both necessary and sufficient to drive redox signaling and pathology: is a phenotype affected by suppressing superoxide and hydrogen peroxide production; by manipulating the levels of SOD2, PRDX3 or mitochondria-targeted catalase; and by adding mitochondria-targeted SOD/catalase mimetics or mitochondria-targeted antioxidants? Is the pathology associated with variants in SOD2 and PRDX3 genes? Filtering the large literature on mitochondrial redox signaling using these criteria highlights considerable evidence that mitochondrial superoxide and hydrogen peroxide drive physiological responses involved in cellular stress management, including apoptosis, autophagy, propagation of endoplasmic reticulum stress, cellular senescence, HIF1α signaling, and immune responses. They also affect cell proliferation, migration, differentiation, and the cell cycle. Filtering the huge literature on pathologies highlights strong experimental evidence that 30-40 pathologies may be driven by mitochondrial matrix superoxide or hydrogen peroxide. These can be grouped into overlapping and interacting categories: metabolic, cardiovascular, inflammatory, and neurological diseases; cancer; ischemia/reperfusion injury; aging and its diseases; external insults, and genetic diseases. Understanding the involvement of mitochondrial matrix superoxide and hydrogen peroxide concentrations in these diseases can facilitate the rational development of appropriate therapies.

Diabetes Mellitus, Mitochondrial Dysfunction and Ca2+-Dependent Permeability Transition Pore

Diabetes mellitus is one of the most common metabolic diseases in the developed world, and is associated either with the impaired secretion of insulin or with the resistance of cells to the actions of this hormone (type I and type II diabetes, respectively). In both cases, a common pathological change is an increase in blood glucose—hyperglycemia, which eventually can lead to serious damage to the organs and tissues of the organism. Mitochondria are one of the main targets of diabetes at the intracellular level. This review is dedicated to the analysis of recent data regarding the role of mitochondrial dysfunction in the development of diabetes mellitus. Specific areas of focus include the involvement of mitochondrial calcium transport systems and a pathophysiological phenomenon called the permeability transition pore in the pathogenesis of diabetes mellitus. The important contribution of these systems and their potential relevance as therapeutic targets in the pathology are discussed.

The Bacterial Toxin CNF1 Protects Human Neuroblastoma SH-SY5Y Cells against 6-Hydroxydopamine-Induced Cell Damage: The Hypothesis of CNF1-Promoted Autophagy as an Antioxidant Strategy

Several chronic neuroinflammatory diseases, including Parkinson’s disease (PD), have the so-called ‘redox imbalance’ in common, a dynamic system modulated by various factors. Among them, alteration of the mitochondrial functionality can cause overproduction of reactive oxygen species (ROS) with the consequent induction of oxidative DNA damage and apoptosis. Considering the failure of clinical trials with drugs that eliminate ROS directly, research currently focuses on approaches that counteract redox imbalance, thus restoring normal physiology in a neuroinflammatory condition. Herein, we used SH-SY5Y cells treated with 6-hydroxydopamine (6-OHDA), a neurotoxin broadly employed to generate experimental models of PD. Cells were pre-treated with the Rho-modulating Escherichia coli cytotoxic necrotizing factor 1 (CNF1), before the addition of 6-OHDA. Then, cell viability, mitochondrial morphology and dynamics, redox profile as well as autophagic markers expression were assessed. We found that CNF1 preserves cell viability and counteracts oxidative stress induced by 6-OHDA. These effects are accompanied by modulation of the mitochondrial network and an increase in macroautophagic markers. Our results confirm the Rho GTPases as suitable pharmacological targets to counteract neuroinflammatory diseases and evidence the potentiality of CNF1, whose beneficial effects on pathological animal models have been already proven to act against oxidative stress through an autophagic strategy.

Mitochondrially-targeted treatment strategies

Disruption of mitochondrial function is a common feature of inherited mitochondrial diseases (mitochondriopathies) and many other infectious and non-infectious diseases including viral, bacterial and protozoan infections, inflammatory and chronic pain, neurodegeneration, diabetes, obesity and cardiovascular diseases. Mitochondria therefore become an attractive target for developing new therapies. In this review we describe critical mechanisms involved in the maintenance of mitochondrial functionality and discuss strategies used to identify and validate mitochondrial targets in different diseases. We also highlight the most recent preclinical and clinical findings using molecules targeting mitochondrial bioenergetics, morphology, number, content and detoxification systems in common pathologies.

Nanomaterials for the theranostics of obesity

As a chronic and lifelong disease, obesity not only significant impairs health but also dramatically shortens life span (at least 10 years). Obesity requires a life-long effort for the successful treatment because a number of abnormalities would appear in the development of obesity. Nanomaterials possess large specific surface area, strong absorptivity, and high bioavailability, especially the good targeting properties and adjustable release rate, which would benefit the diagnosis and treatment of obesity and obesity-related metabolic diseases. Herein, we discussed the therapy and diagnosis of obesity and obesity-related metabolic diseases by using nanomaterials. Therapies of obesity with nanomaterials include improving intestinal health and reducing energy intake, targeting and treating functional cell abnormalities, regulating redox homeostasis, and removing free lipoprotein in blood. Diagnosis of obesity-related metabolic diseases would benefit the therapy of these diseases. The development of nanomaterials will promote the diagnosis and therapy of obesity and obesity-related metabolic diseases.

Strategies to target bioactive molecules to subcellular compartments. Focus on natural compounds

Many potential pharmacological targets are present in multiple subcellular compartments and have different pathophysiological roles depending on location. In these cases, selective targeting of a drug to the relevant subcellular domain(s) may help to sharpen its impact by providing topological specificity, thus limiting side effects, and to concentrate the compound where needed, thus increasing its effectiveness. We review here the state of the art in precision subcellular delivery. The major approaches confer "homing" properties to the active principle via permanent or reversible (in pro-drug fashion) modifications, or through the use of special-design nanoparticles or liposomes to ferry a drug(s) cargo to its desired destination. An assortment of peptides, substituents with delocalized positive charges, custom-blended lipid mixtures, pH- or enzyme-sensitive groups provide the main tools of the trade. Mitochondria, lysosomes and the cell membrane may be mentioned as the fronts on which the most significant advances have been made. Most of the examples presented here have to do with targeting natural compounds - in particular polyphenols, known as pleiotropic agents - to one or the other subcellular compartment.

The Antioxidant Moiety of MitoQ Imparts Minimal Metabolic Effects in Adipose Tissue of High Fat Fed Mice

Mitochondrial dysfunction is associated with a diverse array of diseases ranging from dystrophy and heart failure to obesity and hepatosteatosis. One of the major biochemical consequences of impaired mitochondrial function is an accumulation of mitochondrial superoxide, or reactive oxygen species (ROS). Excessive ROS can be detrimental to cellular health and is proposed to underpin many mitochondrial diseases. Accordingly, much research has been committed to understanding ways to therapeutically prevent and reduce ROS accumulation. In white adipose tissue (WAT), ROS is associated with obesity and its subsequent complications, and thus reducing mitochondrial ROS may represent a novel strategy for treating obesity related disorders. One therapeutic approach employed to reduce ROS abundance is the mitochondrial-targeted coenzyme Q (MitoQ), which enables mitochondrial specific delivery of a CoQ10 antioxidant via its triphenylphosphonium bromide (TPP+) cation. Indeed, MitoQ has been successfully shown to accumulate at the outer mitochondrial membrane and prevent ROS accumulation in several tissues in vivo; however, the specific effects of MitoQ on adipose tissue metabolism in vivo have not been studied. Here we demonstrate that mice fed high-fat diet with concomitant administration of MitoQ, exhibit minimal metabolic benefit in adipose tissue. We also demonstrate that both MitoQ and its control agent dTPP+ had significant and equivalent effects on whole-body metabolism, suggesting that the dTPP+ cation rather than the antioxidant moiety, was responsible for these changes. These findings have important implications for future studies using MitoQ and other TPP+ compounds.

The impact of age and sex on body composition and glucose sensitivity in C57BL/6J mice

A paucity of data exists regarding sex differences in age-related obesity and insulin resistance, particularly in the preclinical murine model. The purpose of this study was to determine the effects of age and sex on insulin action and body composition in C57BL/6J mice. Aged (AG, 18 months old) male C57BL/6J mice, glucose tolerance was diminished compared to young (YG, 6 months old) male mice (Area Under Curve: 95,103 ± 6818 vs. 64,005 ± 2031, P = 0.002). However, there was no age-related decline in glucose or insulin tolerance in females. Body composition analysis revealed that AG males had significantly greater body mass (42.2 ± 1.9 vs. 30.0 ± 0.4 g, P < 0.0001), fat mass (18.7 ± 2.0 vs. 3.3 ± 0.4 g, P < 0.0001), body fat (43.0 ± 3.0 vs. 11.0 ± 1.5%, P < 0.0001) than YG males. In AG females, body mass (32.8 ± 1.6 vs. 26.3 ± 0.9 g, P = 0.02) was higher, but fat mass (13.3 ± 2.0 vs. 9.5 ± 1.3 g, P = 0.24) and body fat (37.8 ± 4.8 vs. 35.5 ± 3.8%, P = 0.67) were similar when compared to YG females. AG males had significantly higher body mass (42.2 ± 1.9 vs. 32.8 ± 1.6 g, P = 0.001) and fat mass (18.7 ± 2.0 vs. 13.3 ± 2.0 g, P = 0.04) compared to AG females; however, body fat (43.0 ± 3.0 vs. 37.8 ± 4.8%, P = 0.28) was similar. Six weeks of treatment with MitoQ, a mitochondrial-targeted antioxidant, did not reverse age-related obesity in male mice. Surprisingly, obesity and insulin resistance appear to be reversed in the oldest of the old male mice (28 vs. 20 months). Our findings indicate that female mice, unlike males, are protected from age-related obesity and insulin resistance.

Effect of a mitochondrial-targeted coenzyme Q analog on pancreatic β-cell function and energetics in high fat fed obese mice

We recently reported that mitoquinone (mitoQ, 500 μmol/L) added to drinking water of C57BL/6J mice attenuated weight gain and reduced oxidative stress when administered to high-fat (HF) fed mice. Here, we examined the effects of mitoQ administered to HF fed mice on pancreatic islet morphology, dynamics of insulin secretion, and islet mitochondrial metabolism. C57BL/6J mice were fed HF for 130 days while we administered vehicle (cyclodextrin [CD]) or mitoQ added to the drinking water at up to 500 μmol/L. MitoQ-treated mice vs vehicle gained significantly less weight, expended significantly more energy as determined by indirect calorimetry, and trended to consume less (nonsignificant) food. As we and others reported before, mitoQ-treated mice drank less water but showed no difference in percent body fluid by nuclear magnetic resonance. Circulating insulin and glucose-stimulated insulin secretion by isolated islets were decreased in mitoQ-treated mice while insulin sensitivity (plasma insulin x glucose) was greater. Islet respiration as basal oxygen consumption (OCR), OCR directed at ATP synthesis, and maximal uncoupled OCR were also reduced in mitoQ-treated mice. Quantitative morphologic studies revealed that islet size was reduced in the mitoQ-treated mice while visual inspection of histochemically stained sections suggested that mitoQ reduced islet lipid peroxides. MitoQ markedly improved liver function as determined by plasma alanine aminotransferase. In summary, mitoQ treatment reduced the demand for insulin and reduced islet size, likely consequent to the action of mitoQ to mitigate weight gain and improve liver function.

Regulation of ATP production: dependence on calcium concentration and respiratory state

Nanomolar free calcium enhances oxidative phosphorylation. However, the effects over a broad concentration range, at different respiratory states, or on specific energy substrates are less clear. We examined the action of varying [Ca²⁺] over respiratory states ranging 4 to 3 on skeletal muscle mitochondrial respiration, potential, ATP production, and H₂O₂ production using ADP recycling to clamp external [ADP]. Calcium at 450 nM enhanced respiration in mitochondria energized by the complex I substrates, glutamate/malate (but not succinate), at [ADP] of 4-256 µM, but more substantially at intermediate respiratory states and not at all at state 4. Using varied [Ca²⁺], we found that the stimulatory effects on respiration and ATP production were most prominent at nanomolar concentrations, but inhibitory at 10 µM or higher. ATP production decreased more than respiration at 10 µM calcium. However, potential continued to increase up to 10 µM; suggesting a calcium-induced inability to utilize potential for phosphorylation independent of opening of the mitochondrial permeability transition pore (MTP). This effect of 10 µM calcium was confirmed by direct determination of ATP production over a range of potential created by differing substrate concentrations. Consistent with past reports, nanomolar [Ca²⁺] had a stimulatory effect on utilization of potential for phosphorylation. Increasing [Ca²⁺] was positively and continuously associated with H₂O₂ production. In summary, the stimulatory effect of calcium on mitochondrial function is substrate dependent and most prominent over intermediate respiratory states. Calcium stimulates or inhibits utilization of potential for phosphorylation dependent on concentration with inhibition at higher concentration independent of MTP opening.

Metabolic effects of a mitochondrial-targeted coenzyme Q analog in high fat fed obese mice

We recently reported that mitoquinone (mitoQ, 500 μmol/L) added to drinking water of C57BL/6J mice attenuated weight gain, decreased food intake, increased hypothalamic orexigenic gene expression, and mitigated oxidative stress when administered from the onset of high‐fat (HF) feeding. Here, we examined the effects of mitoQ on pre‐existing obesity in C57BL/6J mice first made obese by 107 days of HF feeding. In contrast to our preventative study, we found that already obese mice did not tolerate mitoQ at 500 μmol/L. Within 4 days of administration, obese mice markedly decreased food and water intake and lost substantial weight necessitating a dose reduction to 250 μmol/L. Food and water intake then improved. Over the next 4 weeks, body mass of the mitoQ‐treated mice increased faster than vehicle‐treated controls but did not catch up. Over the subsequent 10 weeks, weights of the mitoQ‐treated group remained significantly less than vehicle control, but percent fat and food intake did not differ. Although the mitoQ‐treated groups continued to drink less, there was no difference in percent body fluid and no laboratory evidence of dehydration at study end. At the time of killing, hypothalamic NPY gene expression was reduced in the mitoQ‐treated mice . Liver fat was markedly increased by HF feeding but did not differ between mitoQ and vehicle groups and, in contrast to our previous preventative study, there was no improvement in plasma alanine amino transferase or liver hydroperoxides. In summary, administration of mitoQ to already obese mice attenuated weight gain, but showed limited overall benefit.