Superoxide and respiratory coupling in mitochondria of insulin-deficient diabetic rats

Oxidative Stress: A Culprit in the Progression of Diabetic Kidney Disease

Diabetic kidney disease (DKD) is the principal culprit behind chronic kidney disease (CKD), ultimately developing end-stage renal disease (ESRD) and necessitating costly dialysis or kidney transplantation. The limited therapeutic efficiency among individuals with DKD is a result of our finite understanding of its pathogenesis. DKD is the result of complex interactions between various factors. Oxidative stress is a fundamental factor that can establish a link between hyperglycemia and the vascular complications frequently encountered in diabetes, particularly DKD. It is crucial to recognize the essential and integral role of oxidative stress in the development of diabetic vascular complications, particularly DKD. Hyperglycemia is the primary culprit that can trigger an upsurge in the production of reactive oxygen species (ROS), ultimately sparking oxidative stress. The main endogenous sources of ROS include mitochondrial ROS production, NADPH oxidases (Nox), uncoupled endothelial nitric oxide synthase (eNOS), xanthine oxidase (XO), cytochrome P450 (CYP450), and lipoxygenase. Under persistent high glucose levels, immune cells, the complement system, advanced glycation end products (AGEs), protein kinase C (PKC), polyol pathway, and the hexosamine pathway are activated. Consequently, the oxidant-antioxidant balance within the body is disrupted, which triggers a series of reactions in various downstream pathways, including phosphoinositide 3-kinase/protein kinase B (PI3K/Akt), transforming growth factor beta/p38-mitogen-activated protein kinase (TGF-β/p38-MAPK), nuclear factor kappa B (NF-κB), adenosine monophosphate-activated protein kinase (AMPK), and the Janus kinase/signal transducer and activator of transcription (JAK/STAT) signaling. The disease might persist even if strict glucose control is achieved, which can be attributed to epigenetic modifications. The treatment of DKD remains an unresolved issue. Therefore, reducing ROS is an intriguing therapeutic target. The clinical trials have shown that bardoxolone methyl, a nuclear factor erythroid 2-related factor 2 (Nrf2) activator, blood glucose-lowering drugs, such as sodium-glucose cotransporter 2 inhibitors, and glucagon-like peptide-1 receptor agonists can effectively slow down the progression of DKD by reducing oxidative stress. Other antioxidants, including vitamins, lipoic acid, Nox inhibitors, epigenetic regulators, and complement inhibitors, present a promising therapeutic option for the treatment of DKD. In this review, we conduct a thorough assessment of both preclinical studies and current findings from clinical studies that focus on targeted interventions aimed at manipulating these pathways. We aim to provide a comprehensive overview of the current state of research in this area and identify key areas for future exploration.

Role of AMP deaminase in diabetic cardiomyopathy

Diabetes mellitus is one of the major causes of ischemic and nonischemic heart failure. While hypertension and coronary artery disease are frequent comorbidities in patients with diabetes, cardiac contractile dysfunction and remodeling occur in diabetic patients even without comorbidities, which is referred to as diabetic cardiomyopathy. Investigations in recent decades have demonstrated that the production of reactive oxygen species (ROS), impaired handling of intracellular Ca2+, and alterations in energy metabolism are involved in the development of diabetic cardiomyopathy. AMP deaminase (AMPD) directly regulates adenine nucleotide metabolism and energy transfer by adenylate kinase and indirectly modulates xanthine oxidoreductase-mediated pathways and AMP-activated protein kinase-mediated signaling. Upregulation of AMPD in diabetic hearts was first reported more than 30 years ago, and subsequent studies showed similar upregulation in the liver and skeletal muscle. Evidence for the roles of AMPD in diabetes-induced fatty liver, sarcopenia, and heart failure has been accumulating. A series of our recent studies showed that AMPD localizes in the mitochondria-associated endoplasmic reticulum membrane as well as the sarcoplasmic reticulum and cytosol and participates in the regulation of mitochondrial Ca2+ and suggested that upregulated AMPD contributes to contractile dysfunction in diabetic cardiomyopathy via increased generation of ROS, adenine nucleotide depletion, and impaired mitochondrial respiration. The detrimental effects of AMPD were manifested at times of increased cardiac workload by pressure loading. In this review, we briefly summarize the expression and functions of AMPD in the heart and discuss the roles of AMPD in diabetic cardiomyopathy, mainly focusing on contractile dysfunction caused by this disorder.

Interference of altered plasma trace elements profile with hyperhomocysteinemia and oxidative stress damage to insulin secretion dysfunction in Psammomys obesus: focus on the selenium

The objective of this study is to investigate the relationship between altered plasma trace elements, particularly selenium (Se), with Hyper-homocysteinemia (HhCys) as a predictive factor of insulin secretion dysfunction. The study is carried out on adult Psammomys obesus, divided in 4 experimental groups: (I) Normoglycemic/Normoinsulinemic; (II) Normoglycemic/Hyperinsulinemic; (III) Hyperglycaemic/Hyperinsulinemic and (IV) Hyperglycaemic/Insulin deficiency with ketoacidosis. The data showed that a drastic depletion of Se plasma levels is positively correlated with HhCys (>15 µmol/L; p < .001), concomitantly with decreased GPx activity, GSH levels, and GSH/GSSG ratio in group IV both in plasma and liver. In contrast, SOD activity is increased (p ≤ .001) in group IV both in plasma and liver. However, plasma Cu and Mn levels increased, while plasma Zn levels decreased in group IV (p < .001). Our study confirms the increase of plasma hCys levels seemed to be a major contributing factor to antioxidant capacities and alters the availability of selenium metabolism by interference with homocysteine synthesis in the insulin secretion deficiency stage.

Effects of altered cellular ultrastructure on energy metabolism in diabetic cardiomyopathy: an in silico study

Diabetic cardiomyopathy is a leading cause of heart failure in diabetes. At the cellular level, diabetic cardiomyopathy leads to altered mitochondrial energy metabolism and cardiomyocyte ultrastructure. We combined electron microscopy (EM) and computational modelling to understand the impact of diabetes-induced ultrastructural changes on cardiac bioenergetics. We collected transverse micrographs of multiple control and type I diabetic rat cardiomyocytes using EM. Micrographs were converted to finite-element meshes, and bioenergetics was simulated over them using a biophysical model. The simulations also incorporated depressed mitochondrial capacity for oxidative phosphorylation (OXPHOS) and creatine kinase (CK) reactions to simulate diabetes-induced mitochondrial dysfunction. Analysis of micrographs revealed a 14% decline in mitochondrial area fraction in diabetic cardiomyocytes, and an irregular arrangement of mitochondria and myofibrils. Simulations predicted that this irregular arrangement, coupled with the depressed activity of mitochondrial CK enzymes, leads to large spatial variation in adenosine diphosphate (ADP)/adenosine triphosphate (ATP) ratio profile of diabetic cardiomyocytes. However, when spatially averaged, myofibrillar ADP/ATP ratios of a cardiomyocyte do not change with diabetes. Instead, average concentration of inorganic phosphate rises by 40% owing to lower mitochondrial area fraction and dysfunction in OXPHOS. These simulations indicate that a disorganized cellular ultrastructure negatively impacts metabolite transport in diabetic cardiomyopathy.

This article is part of the theme issue ‘The cardiomyocyte: new revelations on the interplay between architecture and function in growth, health, and disease’.

Endogenous Fructose Metabolism Could Explain the Warburg Effect and the Protection of SGLT2 Inhibitors in Chronic Kidney Disease

Chronic low-grade inflammation underlies the pathogenesis of non-communicable diseases, including chronic kidney diseases (CKD). Inflammation is a biologically active process accompanied with biochemical changes involving energy, amino acid, lipid and nucleotides. Recently, glycolysis has been observed to be increased in several inflammatory disorders, including several types of kidney disease. However, the factors initiating glycolysis remains unclear. Added sugars containing fructose are present in nearly 70 percent of processed foods and have been implicated in the etiology of many non-communicable diseases. In the kidney, fructose is transported into the proximal tubules via several transporters to mediate pathophysiological processes. Fructose can be generated in the kidney during glucose reabsorption (such as in diabetes) as well as from intra-renal hypoxia that occurs in CKD. Fructose metabolism also provides biosynthetic precursors for inflammation by switching the intracellular metabolic profile from mitochondrial oxidative phosphorylation to glycolysis despite the availability of oxygen, which is similar to the Warburg effect in cancer. Importantly, uric acid, a byproduct of fructose metabolism, likely plays a key role in favoring glycolysis by stimulating inflammation and suppressing aconitase in the tricarboxylic acid cycle. A consequent accumulation of glycolytic intermediates connects to the production of biosynthetic precursors, proteins, lipids, and nucleic acids, to meet the increased energy demand for the local inflammation. Here, we discuss the possibility of fructose and uric acid may mediate a metabolic switch toward glycolysis in CKD. We also suggest that sodium-glucose cotransporter 2 (SGLT2) inhibitors may slow the progression of CKD by reducing intrarenal glucose, and subsequently fructose levels.

Therapeutic potential of targeting oxidative stress in diabetic cardiomyopathy

Even in the absence of coronary artery disease and hypertension, diabetes mellitus (DM) may increase the risk for heart failure development. This risk evolves from functional and structural alterations induced by diabetes in the heart, a cardiac entity termed diabetic cardiomyopathy (DbCM). Oxidative stress, defined as the imbalance of reactive oxygen species (ROS) has been increasingly proposed to contribute to the development of DbCM. There are several sources of ROS production including the mitochondria, NAD(P)H oxidase, xanthine oxidase, and uncoupled nitric oxide synthase. Overproduction of ROS in DbCM is thought to be counterbalanced by elevated antioxidant defense enzymes such as catalase and superoxide dismutase. Excess ROS in the cardiomyocyte results in further ROS production, mitochondrial DNA damage, lipid peroxidation, post-translational modifications of proteins and ultimately cell death and cardiac dysfunction. Furthermore, ROS modulates transcription factors responsible for expression of antioxidant enzymes. Lastly, evidence exists that several pharmacological agents may convey cardiovascular benefit by antioxidant mechanisms. As such, increasing our understanding of the pathways that lead to increased ROS production and impaired antioxidant defense may enable the development of therapeutic strategies against the progression of DbCM. Herein, we review the current knowledge about causes and consequences of ROS in DbCM, as well as the therapeutic potential and strategies of targeting oxidative stress in the diabetic heart.

NOD Mice Recapitulate the Cardiac Disturbances Observed in Type 1 Diabetes

This work aimed at testing the hypothesis that NOD/ShiLtJ mice (NOD) recapitulate the cardiac disturbances observed on type 1 diabetes (T1D). NOD mice were studied 4 weeks after the onset of hyperglycemia, and NOR/Lt mice matched as control. Cardiac function was evaluated by echocardiography and electrocardiography (ECG). Action potentials (AP) and Ca2+ transients were evaluated at whole heart level. Heart mitochondrial function was evaluated by high-resolution respirometry and H2O2 release. NOD mice presented a reduction in hearth weight. Mitochondrial oxygen fluxes and H2O2 release were similar between NOD and NOR mice. ECG revealed a QJ interval prolongation in NOD mice. Furthermore, AP duration at 30% of repolarization was increased, and it depicted slower Ca2+ transient kinetics. NOD mice presented greater number/severity of ventricular arrhythmias both in vivo and in vitro. In conclusion, NOD mice evoked cardiac electrical and calcium handling disturbances similar to the observed in T1D. Graphical Abstract .

Mitochondrial NAD+/NADH Redox State and Diabetic Cardiomyopathy

Significance: Diabetic cardiomyopathy (DCM) is a frequent complication occurring even in well-controlled asymptomatic diabetic patients, and it may advance to heart failure (HF). Recent Advances: The diabetic heart is characterized by a state of "metabolic rigidity" involving enhanced rates of fatty acid uptake and mitochondrial oxidation as the predominant energy source, and it exhibits mitochondrial electron transport chain defects. These alterations promote redox state changes evidenced by a decreased NAD⁺/NADH ratio associated with an increase in acetyl-CoA/CoA ratio. NAD⁺ is a co-substrate for deacetylases, sirtuins, and a critical molecule in metabolism and redox signaling; whereas acetyl-CoA promotes protein lysine acetylation, affecting mitochondrial integrity and causing epigenetic changes. Critical Issues: DCM lacks specific therapies with treatment only in later disease stages using standard, palliative HF interventions. Traditional therapy targeting neurohormonal signaling and hemodynamics failed to improve mortality rates. Though mitochondrial redox state changes occur in the heart with obesity and diabetes, how the mitochondrial NAD⁺/NADH redox couple connects the remodeled energy metabolism with mitochondrial and cytosolic antioxidant defense and nuclear epigenetic changes remains to be determined. Mitochondrial therapies targeting the mitochondrial NAD⁺/NADH redox ratio may alleviate cardiac dysfunction. Future Directions: Specific therapies must be supported by an optimal understanding of changes in mitochondrial redox state and how it influences other cellular compartments; this field has begun to surface as a therapeutic target for the diabetic heart. We propose an approach based on an alternate mitochondrial electron transport that normalizes the mitochondrial redox state and improves cardiac function in diabetes.

Oxaloacetic acid mediates ADP-dependent inhibition of mitochondrial complex II-driven respiration

We recently reported a previously unrecognized mitochondrial respiratory phenomenon. When [ADP] was held constant ("clamped") at sequentially increasing concentrations in succinate-energized muscle mitochondria in the absence of rotenone (commonly used to block complex I), we observed a biphasic, increasing then decreasing, respiratory response. Here we investigated the mechanism. We confirmed decades-old reports that oxaloacetate (OAA) inhibits succinate dehydrogenase (SDH). We then used an NMR method to assess OAA concentrations (known as difficult to measure by MS) as well as those of malate, fumarate, and citrate in isolated succinate-respiring mitochondria. When these mitochondria were incubated at varying clamped ADP concentrations, respiration increased at low [ADP] as expected given the concurrent reduction in membrane potential. With further increments in [ADP], respiration decreased associated with accumulation of OAA. Moreover, a low pyruvate concentration, that alone was not enough to drive respiration, was sufficient to metabolize OAA to citrate and completely reverse the loss of succinate-supported respiration at high [ADP]. Further, chemical or genetic inhibition of pyruvate uptake prevented OAA clearance and preserved respiration. In addition, we measured the effects of incremental [ADP] on NADH, superoxide, and H₂O₂ (a marker of reverse electron transport from complex II to I). In summary, our findings, taken together, support a mechanism (detailed within) wherein succinate-energized respiration as a function of increasing [ADP] is initially increased by [ADP]-dependent effects on membrane potential but subsequently decreased at higher [ADP] by inhibition of succinate dehydrogenase by OAA. The physiologic relevance is discussed.

Uncoupling proteins as a therapeutic target to protect the diabetic heart

Myocardial remodeling and dysfunction caused by accelerated oxidative damage is a widely reported phenomenon within a diabetic state. Altered myocardial substrate preference appears to be the major cause of enhanced oxidative stress-mediated cell injury within a diabetic heart. During this process, exacerbated free fatty acid flux causes an abnormal increase in mitochondrial membrane potential leading to the overproduction of free radical species and subsequent cell damage. Uncoupling proteins (UCPs) are expressed within the myocardium and can protect against free radical damage by modulating mitochondrial respiration, leading to reduced production of reactive oxygen species. Moreover, transgenic animals lacking UCPs have been shown to be more susceptible to oxidative damage and display reduced cardiac function when compared to wild type animals. This suggests that tight regulation of UCPs is necessary for normal cardiac function and in the prevention of diabetes-induced oxidative damage. This review aims to enhance our understanding of the pathophysiological mechanisms relating to the role of UCPs in a diabetic heart, and further discuss known pharmacological compounds and hormones that can protect a diabetic heart through the modulation of UCPs.

Benfotiamine, a Lipid-Soluble Analog of Vitamin B1, Improves the Mitochondrial Biogenesis and Function in Blunt Snout Bream (Megalobrama amblycephala) Fed High-Carbohydrate Diets by Promoting the AMPK/PGC-1β/NRF-1 Axis

This study evaluated the effects of benfotiamine on the growth performance and mitochondrial biogenesis and function in Megalobrama amblycephala fed high-carbohydrate (HC) diets. The fish (45.25 ± 0.34 g) were randomly fed six diets: the control diet (30% carbohydrate, C), the HC diet (43% carbohydrate), and the HC diet supplemented with different benfotiamine levels (0.7125 (HCB1), 1.425 (HCB2), 2.85 (HCB3), and 5.7 (HCB4) mg/kg) for 12 weeks. High-carbohydrate levels remarkably decreased the weight gain rate (WGR), specific growth rate (SGR), relative feed intake (RFI), feed conversion ratio (FCR), p-adenosine monophosphate (AMP)-activated protein kinase (AMPK)α/t-AMPKα ratio, peroxisome proliferator-activated receptor-γ coactivator-1β (PGC-1β) and nuclear respiratory factor-1 (NRF-1) protein expression, complexes I, III, and IV activities, and hepatic transcriptions of cytochrome b (CYT-b) and cytochrome c oxidase-2 (COX-2), whereas the opposite was true for plasma glucose, glycated serum protein, advanced glycation end product and insulin levels, tissue glycogen and lipid contents, hepatic adenosine triphosphate (ATP) and AMP contents and ATP/AMP ratio, complexes V activities, and the expressions of AMPKα-2, PGC-1β, NRF-1, mitochondrial transcription factor A (TFAM), mitofusin-1 (Mfn-1), optic atrophy-1 (Opa-1), dynamin-related protein-1 (Drp-1), fission-1 (Fis-1), mitochondrial fission factor (Mff), and ATP synthase-6 (ATP-6). As with benfotiamine supplementation, the HCB2 diet remarkably increased WGR, SGR, tissue glycogen and lipid contents, AMP content, p-AMPKα/t-AMPKα ratio, PGC-1β and NRF-1 levels, complexes I, III, IV, and V activities, and hepatic transcriptions of AMPKα-2, PGC-1β, NRF-1, TFAM, Mfn-1, Opa-1, CYT-b, COX-2, and ATP-6, while the opposite was true for the remaining indicators. Overall, 1.425 mg/kg benfotiamine improved the growth performance and mitochondrial biogenesis and function in fish fed HC diets by the activation of the AMPK/PGC-1β/NRF-1 axis and the upregulation of the activities and transcriptions of mitochondrial complexes as well as the enhancement of mitochondrial fusion coupled with the depression of mitochondrial fission.

Streptozotocin-Induced Adaptive Modification of Mitochondrial Supercomplexes in Liver of Wistar Rats and the Protective Effect of Moringa oleifera Lam

The increasing prevalence of diabetes continues to be a major health issue worldwide. Alteration of mitochondrial electron transport chain is a recognized hallmark of the diabetic-associated decline in liver bioenergetics; however, the molecular events involved are only poorly understood. Moringa oleifera is used for the treatment of diabetes. However, its role on mitochondrial functionality is not yet established. This study was aimed to evaluate the effect of M. oleifera extract on supercomplex formation, ATPase activity, ROS production, GSH levels, lipid peroxidation, and protein carbonylation. The levels of lipid peroxidation and protein carbonylation were increased in diabetic group. However, the levels were decreased in Moringa-treated diabetic rats. Analysis of in-gel activity showed an increase in all complex activities in the diabetic group, but spectrophotometric determinations of complex II and IV activities were unaffected in this treatment. However, we found an oxygen consumption abolition through complex I-III-IV pathway in the diabetic group treated with Moringa. While respiration with succinate feeding into complex II-III-IV was increased in the diabetic group. These findings suggest that hyperglycemia modifies oxygen consumption, supercomplexes formation, and increases ROS levels in mitochondria from the liver of STZ-diabetic rats, whereas M. oleifera may have a protective role against some alterations.

Mitochondrial Calpain-1 Disrupts ATP Synthase and Induces Superoxide Generation in Type 1 Diabetic Hearts: A Novel Mechanism Contributing to Diabetic Cardiomyopathy

Calpain plays a critical role in cardiomyopathic changes in type 1 diabetes (T1D). This study investigated how calpain regulates mitochondrial reactive oxygen species (ROS) generation in the development of diabetic cardiomyopathy. T1D was induced in transgenic mice overexpressing calpastatin, in mice with cardiomyocyte-specific capn4 deletion, or in their wild-type littermates by injection of streptozotocin. Calpain-1 protein and activity in mitochondria were elevated in diabetic mouse hearts. The increased mitochondrial calpain-1 was associated with an increase in mitochondrial ROS generation and oxidative damage and a reduction in ATP synthase-α (ATP5A1) protein and ATP synthase activity. Genetic inhibition of calpain or upregulation of ATP5A1 increased ATP5A1 and ATP synthase activity, prevented mitochondrial ROS generation and oxidative damage, and reduced cardiomyopathic changes in diabetic mice. High glucose concentration induced ATP synthase disruption, mitochondrial superoxide generation, and cell death in cardiomyocytes, all of which were prevented by overexpression of mitochondria-targeted calpastatin or ATP5A1. Moreover, upregulation of calpain-1 specifically in mitochondria induced the cleavage of ATP5A1, superoxide generation, and apoptosis in cardiomyocytes. In summary, calpain-1 accumulation in mitochondria disrupts ATP synthase and induces ROS generation, which promotes diabetic cardiomyopathy. These findings suggest a novel mechanism for and may have significant implications in diabetic cardiac complications.

Mitochondrial complex I defect and increased fatty acid oxidation enhance protein lysine acetylation in the diabetic heart

AIMS

Cardiomyopathy is a major complication of diabetes. Our study was aimed to identify the sites of mitochondrial dysfunction and delineate its consequences on mitochondrial metabolism in a model of type 1 diabetes.

METHODS AND RESULTS

Diabetes was induced by streptozotocin injection to male Lewis rats. We found a decrease in mitochondrial biogenesis pathway and electron transport chain complex assembly that targets Complex I. Oxidation of Complex II and long-chain fatty acid substrates support the electron leak and superoxide production. Mitochondrial defects do not limit fatty acid oxidation as the heart's preferred energy source indicating that the diabetic heart has a significant reserve in Complex I- and II-supported ATP production. Both mitochondrial fatty acid oxidation and Complex I defect are responsible for increased protein lysine acetylation despite an unchanged amount of the NAD(+)-dependent mitochondrial deacetylase sirt3. We quantitatively analysed mitochondrial lysine acetylation post-translational modifications and identified that the extent of lysine acetylation on 54 sites in 22 mitochondrial proteins is higher in diabetes compared with the same sites in the control. The increased lysine acetylation of the mitochondrial trifunctional protein subunit α may be responsible for the increased fatty acid oxidation in the diabetic heart.

CONCLUSION

We identified the specific defective sites in the electron transport chain responsible for the decreased mitochondrial oxidative phosphorylation in the diabetic heart. Mitochondrial protein lysine acetylation is the common consequence of both increased fatty acid oxidation and mitochondrial Complex I defect, and may be responsible for the metabolic inflexibility of the diabetic heart.

Protective mechanisms of mitochondria and heart function in diabetes

SIGNIFICANCE

The heart depends on continuous mitochondrial ATP supply and maintained redox balance to properly develop force, particularly under increased workload. During diabetes, however, myocardial energetic-redox balance is perturbed, contributing to the systolic and diastolic dysfunction known as diabetic cardiomyopathy (DC).

CRITICAL ISSUES

How these energetic and redox alterations intertwine to influence the DC progression is still poorly understood. Excessive bioavailability of both glucose and fatty acids (FAs) play a central role, leading, among other effects, to mitochondrial dysfunction. However, where and how this nutrient excess affects mitochondrial and cytoplasmic energetic/redox crossroads remains to be defined in greater detail.

RECENT ADVANCES

We review how high glucose alters cellular redox balance and affects mitochondrial DNA. Next, we address how lipid excess, either stored in lipid droplets or utilized by mitochondria, affects performance in diabetic hearts by influencing cardiac energetic and redox assets. Finally, we examine how the reciprocal energetic/redox influence between mitochondrial and cytoplasmic compartments shapes myocardial mechanical activity during the course of DC, focusing especially on the glutathione and thioredoxin systems.

FUTURE DIRECTIONS

Protecting mitochondria from losing their ability to generate energy, and to control their own reactive oxygen species emission is essential to prevent the onset and/or to slow down DC progression. We highlight mechanisms enforced by the diabetic heart to counteract glucose/FAs surplus-induced damage, such as lipid storage, enhanced mitochondria-lipid droplet interaction, and upregulation of key antioxidant enzymes. Learning more on the nature and location of mechanisms sheltering mitochondrial functions would certainly help in further optimizing therapies for human DC.

Protocatechuic acid protects brain mitochondrial function in streptozotocin-induced diabetic rats

Brain mitochondrial dysfunction has been demonstrated in diabetic animals with neurodegeneration. Protocatechuic acid (PCA), a major metabolite of anthocyanin, has been shown to exert glycemic control and oxidative stress reduction in the heart. However, its effects on oxidative stress and mitochondrial function in the brain under diabetic condition have never been investigated. We found that PCA exerted glycemic control, attenuates brain mitochondrial dysfunction, and contributes to the prevention of brain oxidative stress in diabetic rats.

Attenuation of Ca2+ homeostasis, oxidative stress, and mitochondrial dysfunctions in diabetic rat heart: insulin therapy or aerobic exercise?

We tested the effects of swimming training and insulin therapy, either alone or in combination, on the intracellular calcium ([Ca(2+)]i) homeostasis, oxidative stress, and mitochondrial functions in diabetic rat hearts. Male Wistar rats were separated into control, diabetic, or diabetic plus insulin groups. Type 1 diabetes mellitus was induced by streptozotocin (STZ). Insulin-treated groups received 1 to 4 UI of insulin daily for 8 wk. Each group was divided into sedentary or exercised rats. Trained groups were submitted to swimming (90 min/day, 5 days/wk, 8 wk). [Ca(2+)]i transient in left ventricular myocytes (LVM), oxidative stress in LV tissue, and mitochondrial functions in the heart were assessed. Diabetes reduced the amplitude and prolonged the times to peak and to half decay of the [Ca(2+)]i transient in LVM, increased NADPH oxidase-4 (Nox-4) expression, decreased superoxide dismutase (SOD), and increased carbonyl protein contents in LV tissue. In isolated mitochondria, diabetes increased Ca(2+) uptake, susceptibility to permeability transition pore (MPTP) opening, uncoupling protein-2 (UCP-2) expression, and oxygen consumption but reduced H2O2 release. Swimming training corrected the time course of the [Ca(2+)]i transient, UCP-2 expression, and mitochondrial Ca(2+) uptake. Insulin replacement further normalized [Ca(2+)]i transient amplitude, Nox-4 expression, and carbonyl content. Alongside these benefits, the combination of both therapies restored the LV tissue SOD and mitochondrial O2 consumption, H2O2 release, and MPTP opening. In conclusion, the combination of swimming training with insulin replacement was more effective in attenuating intracellular Ca(2+) disruptions, oxidative stress, and mitochondrial dysfunctions in STZ-induced diabetic rat hearts.

Mitochondrial hormesis and diabetic complications

The concept that excess superoxide production from mitochondria is the driving, initial cellular response underlying diabetes complications has been held for the past decade. However, results of antioxidant-based trials have been largely negative. In the present review, the data supporting mitochondrial superoxide as a driving force for diabetic kidney, nerve, heart, and retinal complications are reexamined, and a new concept for diabetes complications--mitochondrial hormesis--is presented. In this view, production of mitochondrial superoxide can be an indicator of healthy mitochondria and physiologic oxidative phosphorylation. Recent data suggest that in response to excess glucose exposure or nutrient stress, there is a reduction of mitochondrial superoxide, oxidative phosphorylation, and mitochondrial ATP generation in several target tissues of diabetes complications. Persistent reduction of mitochondrial oxidative phosphorylation complex activity is associated with the release of oxidants from nonmitochondrial sources and release of proinflammatory and profibrotic cytokines, and a manifestation of organ dysfunction. Restoration of mitochondrial function and superoxide production via activation of AMPK has now been associated with improvement in markers of renal, cardiovascular, and neuronal dysfunction with diabetes. With this Perspective, approaches that stimulate AMPK and PGC1α via exercise, caloric restriction, and medications result in stimulation of mitochondrial oxidative phosphorylation activity, restore physiologic mitochondrial superoxide production, and promote organ healing.

Deficiency of a lipid droplet protein, perilipin 5, suppresses myocardial lipid accumulation, thereby preventing type 1 diabetes-induced heart malfunction

Lipid droplet (LD) is a ubiquitous organelle that stores triacylglycerol and other neutral lipids. Perilipin 5 (Plin5), a member of the perilipin protein family that is abundantly expressed in the heart, is essential to protect LDs from attack by lipases, including adipose triglyceride lipase. Plin5 controls heart metabolism and performance by maintaining LDs under physiological conditions. Aberrant lipid accumulation in the heart leads to organ malfunction, or cardiomyopathy. To elucidate the role of Plin5 in a metabolically disordered state and the mechanism of lipid-induced cardiomyopathy, we studied the effects of streptozotocin-induced type 1 diabetes in Plin5-knockout (KO) mice. In contrast to diabetic wild-type mice, diabetic Plin5-KO mice lacked detectable LDs in the heart and did not exhibit aberrant lipid accumulation, excessive reactive oxygen species (ROS) generation, or heart malfunction. Moreover, diabetic Plin5-KO mice exhibited lower heart levels of lipotoxic molecules, such as diacylglycerol and ceramide, than wild-type mice. Membrane translocation of protein kinase C and the assembly of NADPH oxidase 2 complex on the membrane were also suppressed. The results suggest that diabetic Plin5-KO mice are resistant to type 1 diabetes-induced heart malfunction due to the suppression of the diacylglycerol/ceramide-protein kinase C pathway and of excessive ROS generation by NADPH oxidase.

Dietary fat, fatty acid saturation and mitochondrial bioenergetics

Fat intake alters mitochondrial lipid composition which can affect function. We used novel methodology to assess bioenergetics, including simultaneous ATP and reactive oxygen species (ROS) production, in liver and heart mitochondria of C57BL/6 mice fed diets of variant fatty acid content and saturation. Our methodology allowed us to clamp ADP concentration and membrane potential (ΔΨ) at fixed levels. Mice received a control diet for 17–19 weeks, a high-fat (HF) diet (60% lard) for 17–19 weeks, or HF for 12 weeks followed by 6–7 weeks of HF with 50% of fat as menhaden oil (MO) which is rich in n-3 fatty acids. ATP production was determined as conversion of 2-deoxyglucose to 2-deoxyglucose phosphate by NMR spectroscopy. Respiration and ATP production were significantly reduced at all levels of ADP and resultant clamped ΔΨ in liver mitochondria from mice fed HF compared to controls. At given ΔΨ, ROS production per mg mitochondrial protein, per unit respiration, or per ATP generated were greater for liver mitochondria of HF-fed mice compared to control or MO-fed mice. Moreover, these ROS metrics began to increase at a lower ΔΨ threshold. Similar, but less marked, changes were observed in heart mitochondria of HF-fed mice compared to controls. No changes in mitochondrial bioenergetics were observed in studies of separate mice fed HF versus control for only 12 weeks. In summary, HF feeding of sufficient duration impairs mitochondrial bioenergetics and is associated with a greater ROS “cost” of ATP production compared to controls. These effects are, in part, mitigated by MO.

Mitochondrial inefficiencies and anoxic ATP hydrolysis capacities in diabetic rat heart

As ~80% of diabetic patients die from heart failure, an understanding of diabetic cardiomyopathy is crucial. Mitochondria occupy 35-40% of the mammalian cardiomyocyte volume and supply 95% of the heart's ATP, and diabetic heart mitochondria show impaired structure, arrangement, and function. We predict that bioenergetic inefficiencies are present in diabetic heart mitochondria; therefore, we explored mitochondrial proton and electron handling by linking oxygen flux to steady-state ATP synthesis, reactive oxygen species (ROS) production, and mitochondrial membrane potential (ΔΨ) within rat heart tissues. Sprague-Dawley rats were injected with streptozotocin (STZ, 55 mg/kg) to induce type 1 diabetes or an equivalent volume of saline (control, n = 12) and fed standard rat chow for 8 wk. By coupling high-resolution respirometers with purpose-built fluorometers, we followed Magnesium Green (ATP synthesis), Amplex UltraRed (ROS production), and safranin-O (ΔΨ). Relative to control rats, the mass-specific respiration of STZ-diabetic hearts was depressed in oxidative phosphorylation (OXPHOS) states. Steady-state ATP synthesis capacity was almost one-third lower in STZ-diabetic heart, which, relative to oxygen flux, equates to an estimated 12% depression in OXPHOS efficiency. However, with anoxic transition, STZ-diabetic and control heart tissues showed similar ATP hydrolysis capacities through reversal of the F1F0-ATP synthase. STZ-diabetic cardiac mitochondria also produced more net ROS relative to oxygen flux (ROS/O) in OXPHOS. While ΔΨ did not differ between groups, the time to develop ΔΨ with the onset of OXPHOS was protracted in STZ-diabetic mitochondria. ROS/O is higher in lifelike OXPHOS states, and potential delays in the time to develop ΔΨ may delay ATP synthesis with interbeat fluctuations in ADP concentrations. Whereas diabetic cardiac mitochondria produce less ATP in normoxia, they consume as much ATP in anoxic infarct-like states.

Liver adapts mitochondrial function to insulin resistant and diabetic states in mice

BACKGROUND & AIMS

To determine if diabetic and insulin-resistant states cause mitochondrial dysfunction in liver or if there is long term adaptation of mitochondrial function to these states, mice were (i) fed with a high-fat diet to induce obesity and T2D (HFD), (ii) had a genetic defect in insulin signaling causing whole body insulin resistance, but not full blown T2D (IR/IRS-1(+/-) mice), or (iii) were analyzed after treatment with streptozocin (STZ) to induce a T1D-like state.

METHODS

Hepatic lipid levels were measured by thin layer chromatography. Mitochondrial respiratory chain (RC) levels and function were determined by Western blot, spectrophotometric, oxygen consumption and proton motive force analysis. Gene expression was analyzed by real-time PCR and microarray.

RESULTS

HFD caused insulin resistance and hepatic lipid accumulation, but RC was largely unchanged. Livers from insulin resistant IR/IRS-1(+/-) mice had normal lipid contents and a normal RC, but mitochondria were less well coupled. Livers from severely hyperglycemic and hypoinsulinemic STZ mice had massively depleted lipid levels, but RC abundance was unchanged. However, liver mitochondria isolated from these animals showed increased abundance and activity of the RC, which was better coupled.

CONCLUSIONS

Insulin resistance, induced either by obesity or genetic manipulation and steatosis do not cause mitochondrial dysfunction in mouse liver. Also, mitochondrial dysfunction is not a prerequisite for liver steatosis. However, severe insulin deficiency and high blood glucose levels lead to an enhanced performance and better coupling of the RC. This may represent an adaptation to fuel overload and the high energy-requirement of an unsuppressed gluconeogenesis.

Molecular mechanisms of diabetic cardiomyopathy

In recent years, diabetes mellitus has become an epidemic and now represents one of the most prevalent disorders. Cardiovascular complications are the major cause of mortality and morbidity in diabetic patients. While ischaemic events dominate the cardiac complications of diabetes, it is widely recognised that the risk for developing heart failure is also increased in the absence of overt myocardial ischaemia and hypertension or is accelerated in the presence of these comorbidities. These diabetes-associated changes in myocardial structure and function have been called diabetic cardiomyopathy. Numerous molecular mechanisms have been proposed to contribute to the development of diabetic cardiomyopathy following analysis of various animal models of type 1 or type 2 diabetes and in genetically modified mouse models. The steady increase in reports presenting novel mechanistic data on this subject expands the list of potential underlying mechanisms. The current review provides an update on molecular alterations that may contribute to the structural and functional alterations in the diabetic heart.

Estrogen reduces endoplasmic reticulum stress to protect against glucotoxicity induced-pancreatic β-cell death

Estrogen can improve glucose homeostasis not only in diabetic rodents but also in humans. However, the molecular mechanism by which estrogen prevents pancreatic β-cell death remains unclear. To investigate this issue, INS-1 cells, a rat insulinoma cell line, were cultured in medium with either 11.1mM or 40mM glucose in the presence or the absence of estrogen. Estrogen significantly reduced apoptotic β-cell death by decreasing nitrogen-induced oxidative stress and the expression of the ER stress markers GRP 78, ATF6, P-PERK, PERK, uXBP1, sXBP1, and CHOP in INS-1 cells after prolonged culture in medium with 40mM glucose. In contrast, estrogen increased the expression of survival proteins, including sarco/endoplasmic reticulum Ca(2+) ATPase (SERCA-2), Bcl-2, and P-p38, in INS-1 cells after prolonged culture in medium with 40mM glucose. The cytoprotective effect of estrogen was attenuated by addition of the estrogen receptor (ERα and ERβ) antagonist ICI 182,780 and the estrogen membrane receptor inhibitor G15. We showed that estrogen decreases not only oxidative stress but also ER stress to protect against 40mM glucose-induced pancreatic β-cell death.

Oxidative stress in diabetes: implications for vascular and other complications

In recent decades, oxidative stress has become a focus of interest in most biomedical disciplines and many types of clinical research. Increasing evidence shows that oxidative stress is associated with the pathogenesis of diabetes, obesity, cancer, ageing, inflammation, neurodegenerative disorders, hypertension, apoptosis, cardiovascular diseases, and heart failure. Based on these studies, an emerging concept is that oxidative stress is the “final common pathway” through which the risk factors for several diseases exert their deleterious effects. Oxidative stress causes a complex dysregulation of cell metabolism and cell–cell homeostasis; in particular, oxidative stress plays a key role in the pathogenesis of insulin resistance and β-cell dysfunction. These are the two most relevant mechanisms in the pathophysiology of type 2 diabetes and its vascular complications, the leading cause of death in diabetic patients.

Mitochondrial function in diabetes: novel methodology and new insight

Interpreting mitochondrial function as affected by comparative physiologic conditions is confounding because individual functional parameters are interdependent. Here, we studied muscle mitochondrial function in insulin-deficient diabetes using a novel, highly sensitive, and specific method to quantify ATP production simultaneously with reactive oxygen species (ROS) at clamped levels of inner mitochondrial membrane potential (ΔΨ), enabling more detailed study. We used a 2-deoxyglucose (2DOG) energy clamp to set ΔΨ at fixed levels and to quantify ATP production as 2DOG conversion to 2DOG-phosphate measured by one-dimensional (1)H and two-dimensional (1)H/(13)C heteronuclear single quantum coherence nuclear magnetic resonance spectroscopy. These techniques proved far more sensitive than conventional (31)P nuclear magnetic resonance and allowed high-throughput study of small mitochondrial isolates. Over conditions ranging from state 4 to state 3 respiration, ATP production was lower and ROS per unit of ATP generated was greater in mitochondria isolated from diabetic muscle. Moreover, ROS began to increase at a lower threshold for inner membrane potential in diabetic mitochondria. Further, ATP production in diabetic mitochondria is limited not only by respiration but also by limited capacity to use ΔΨ for ATP synthesis. In summary, we describe novel methodology for measuring ATP and provide new mechanistic insight into the dysregulation of ATP production and ROS in mitochondria of insulin-deficient rodents.

UCP2 and ANT differently modulate proton-leak in brain mitochondria of long-term hyperglycemic and recurrent hypoglycemic rats

A growing body of evidence suggests that mitochondrial proton-leak functions as a regulator of reactive oxygen species production and its modulation may limit oxidative injury to tissues. The main purpose of this work was to characterize the proton-leak of brain cortical mitochondria from long-term hyperglycemic and insulin-induced recurrent hypoglycemic rats through the modulation of the uncoupling protein 2 (UCP2) and adenine nucleotide translocator (ANT). Streptozotocin-induced diabetic rats were treated subcutaneously with twice-daily insulin injections during 2 weeks to induce the hypoglycemic episodes. No differences in the basal proton-leak, UCP2 and ANT protein levels were observed between the experimental groups. Mitochondria from recurrent hypoglycemic rats presented a decrease in proton-leak in the presence of GDP, a specific UCP2 inhibitor, while an increase in proton-leak was observed in the presence of linoleic acid, a proton-leak activator, this effect being reverted by the simultaneous addition of GDP. Mitochondria from long-term hyperglycemic rats showed an enhanced susceptibility to ANT modulation as demonstrated by the complete inhibition of basal and linoleic acid-induced proton-leak caused by the ANT specific inhibitor carboxyatractyloside. Our results show that recurrent-hypoglycemia renders mitochondria more susceptible to UCPs modulation while the proton-leak of long-term hyperglycemic rats is mainly modulated by ANT, which suggest that brain cortical mitochondria have distinct adaptation mechanisms in face of different metabolic insults.

Upregulated NLRP3 inflammasome activation in patients with type 2 diabetes

Despite the recent attention focused on the roles of the nucleotide binding and oligomerization domain-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome in the pathogenesis of type 2 diabetes, little is known about the ex vivo profile of inflammasome activation in type 2 diabetic patients. In this study, we investigated patterns of NLRP3 inflammasome activation in monocyte-derived macrophages (MDMs) from drug-naïve patients with newly diagnosed type 2 diabetes. Type 2 diabetic subjects had significantly increased mRNA and protein expression of NLRP3, apoptosis-associated speck-like protein containing a CARD (ASC), and proinflammatory cytokines in MDMs cultured with autologous sera compared with healthy controls. Upregulated interleukin (IL)-1β maturation, IL-18 secretion, and caspase-1 cleavage were observed in MDMs from type 2 diabetic patients after stimulation with various danger molecules (ATP, high-mobility group protein B1, free fatty acids, islet amyloid polypeptide, and monosodium uric acid crystals). Mitochondrial reactive oxygen species and NLRP3 were required for IL-1β synthesis in MDMs. Finally, 2 months of therapy with the antidiabetic drug metformin significantly inhibited the maturation of IL-1β in MDMs from patients with type 2 diabetes through AMP-activated protein kinase (AMPK) activation. Taken together, these data suggest that NLRP3 inflammasome activation is elevated in myeloid cells from type 2 diabetic patients and that antidiabetic treatment with metformin contributes to modulation of inflammasome activation in type 2 diabetes.

CaMKII determines mitochondrial stress responses in heart

Myocardial cell death is initiated by excessive mitochondrial Ca²⁺ entry, causing Ca²⁺ overload, mitochondrial permeability transition pore (mPTP) opening and dissipation of the mitochondrial inner membrane potential (ΔΨm)^1,2. However, the signaling pathways that control mitochondrial Ca²⁺ entry through the inner membrane mitochondrial Ca²⁺ uniporter (MCU)^3–5 are not known. The multifunctional Ca²⁺ and calmodulin-dependent protein kinase II (CaMKII) is activated in ischemia reperfusion (I/R), myocardial infarction (MI) and neurohumoral injury, common causes of myocardial death and heart failure, suggesting CaMKII could couple disease stress to mitochondrial injury. Here we show that CaMKII promotes mPTP opening and myocardial death by increasing MCU current (I_MCU). Mitochondrial-targeted CaMKII inhibitory protein or cyclosporin A (CsA), an mPTP antagonist with clinical efficacy in I/R injury⁶, equivalently prevent mPTP opening, ΔΨm deterioration and diminish mitochondrial disruption and programmed cell death in response to I/R injury. Mice with myocardial and mitochondrial-targeted CaMKII inhibition are resistant to I/R injury, MI and neurohumoral injury, suggesting pathological actions of CaMKII are substantially mediated by increasing I_MCU. Our findings identify CaMKII activity as a central mechanism for mitochondrial Ca²⁺ entry and suggest mitochondrial-targeted CaMKII inhibition could prevent or reduce myocardial death and heart failure dysfunction in response to common experimental forms of pathophysiological stress.

C-Peptide reduces mitochondrial superoxide generation by restoring complex I activity in high glucose-exposed renal microvascular endothelial cells

Hyperglycemia-mediated microvascular damage has been proposed to originate from excessive generation of mitochondrial superoxide in endothelial cells and is the suggested mechanism by which the pathogenesis of diabetes-induced renal damage occurs. C-peptide has been shown to ameliorate diabetes-induced renal impairment. Yet, the mechanisms underlying this protective benefit remain unclear. The objective of this study was to determine whether C-peptide affords protection to renal microvascular endothelial cell mitochondria during hyperglycemia. Conditionally immortalized murine renal microvascular endothelial cells (MECs) were exposed to low (5.5 mM) or high glucose (25 mM) media with either C-peptide (6.6 nM) or its scrambled sequence control peptide for 24 or 48 hours. Respiratory control ratio, a measure of mitochondrial electrochemical coupling, was significantly higher in high glucose renal MECs treated with C-peptide than those of high glucose alone. C-peptide also restored high glucose-induced renal MEC mitochondrial membrane potential changes back to their basal low glucose state. Moreover, C-peptide prevented the excessive mitochondrial superoxide generation and concomitant reductions in mitochondrial complex I activity which are mediated by the exposure of the renal MECs to high glucose. Together, these data demonstrate that C-peptide protects against high glucose-induced generation of mitochondrial superoxide in renal MECs via restoration of basal mitochondrial function.

Hepatic mitochondrial alterations and increased oxidative stress in nutritional diabetes-prone Psammomys obesus model

Mitochondrial dysfunction is considered to be a pivotal component of insulin resistance and associated metabolic diseases. Psammomys obesus is a relevant model of nutritional diabetes since these adult animals exhibit a state of insulin resistance when fed a standard laboratory chow, hypercaloric for them as compared to their natural food. In this context, alterations in bioenergetics were studied. Using liver mitochondria isolated from these rats fed such a diet for 18 weeks, oxygen consumption rates, activities of respiratory complexes, and content in cytochromes were examined. Levels of malondialdehyde (MDA) and gluthatione (GSH) were measured in tissue homogenates. Diabetic Psammomys showed a serious liver deterioration (hepatic mass accretion, lipids accumulation), accompanied by an enhanced oxidative stress (MDA increased, GSH depleted). On the other hand, both ADP-dependent and uncoupled respirations greatly diminished below control values, and the respiratory flux to cytochrome oxydase was mildly lowered. Furthermore, an inhibition of complexes I and III together with an activation of complex II were found. With emergence of oxidative stress, possibly related to a defect in oxidative phosphorylation, some molecular adjustments could contribute to alleviate, at least in part, the deleterious outcomes of insulin resistance in this gerbil species.

Genetic loss of insulin receptors worsens cardiac efficiency in diabetes

AIMS

To determine the contribution of insulin signaling versus systemic metabolism to metabolic and mitochondrial alterations in type 1 diabetic hearts and test the hypothesis that antecedent mitochondrial dysfunction contributes to impaired cardiac efficiency (CE) in diabetes.

METHODS AND RESULTS

Control mice (WT) and mice with cardiomyocyte-restricted deletion of insulin receptors (CIRKO) were rendered diabetic with streptozotocin (WT-STZ and CIRKO-STZ, respectively), non-diabetic controls received vehicle (citrate buffer). Cardiac function was determined by echocardiography; myocardial metabolism, oxygen consumption (MVO(2)) and CE were determined in isolated perfused hearts; mitochondrial function was determined in permeabilized cardiac fibers and mitochondrial proteomics by liquid chromatography mass spectrometry. Pyruvate supported respiration and ATP synthesis were equivalently reduced by diabetes and genotype, with synergistic impairment in ATP synthesis in CIRKO-STZ. In contrast, fatty acid delivery and utilization was increased by diabetes irrespective of genotype, but not in non-diabetic CIRKO. Diabetes and genotype synergistically increased MVO(2) in CIRKO-STZ, leading to reduced CE. Irrespective of diabetes, genotype impaired ATP/O ratios in mitochondria exposed to palmitoyl carnitine, consistent with mitochondrial uncoupling. Proteomics revealed reduced content of fatty acid oxidation proteins in CIRKO mitochondria, which were induced by diabetes, whereas tricarboxylic acid cycle and oxidative phosphorylation proteins were reduced both in CIRKO mitochondria and by diabetes.

CONCLUSIONS

Deficient insulin signaling and diabetes mediate distinct effects on cardiac mitochondria. Antecedent loss of insulin signaling markedly impairs CE when diabetes is induced, via mechanisms that may be secondary to mitochondrial uncoupling and increased FA utilization.

The antioxidant paradox in diabetes mellitus

There is ample empiric evidence to indicate that oxidative stress contributes to the pathogenesis of coronary artery disease and has a key role in the onset and progression of diabetes and its complications. Diabetes leads to depletion of the cellular antioxidant defense system and is associated with an increase in the production of free radicals. Oxidative stress can be the result of multiple pathways. Some of these are related to substrate-driven overproduction of mitochondrial reactive oxygen species, advanced glycation end product formation, glucose autoxidation, and depletion of micronutrients and cellular elements with antioxidative properties. There are numerous observational studies in the literature showing a beneficial outcome of the consumption of antioxidant vitamins. However, the interventional trials portray a different picture. The divide between the robust experimental evidence of the pathogenetic role of increased oxidative load in diabetes and the overwhelming failure of antioxidants to show any health benefits in clinical trials may well be characterized as the "antioxidant paradox."

High-sucrose diet increases ROS generation, FFA accumulation, UCP2 level, and proton leak in liver mitochondria

Obesity, a risk factor for insulin resistance, contributes to the development of type 2 diabetes and cardiovascular diseases. The relationship between increased levels of free fatty acids in the liver mitochondria, mitochondrial function, and ROS generation in rat model of obesity induced by a high-sucrose diet was not sufficiently established. We determined how the bioenergetic functions and ROS generation of the mitochondria respond to a hyperlipidemic environment. Mitochondria from sucrose-fed rats generated H(2)O(2) at a higher rate than the control mitochondria. Adding fatty acid-free bovine serum albumin to mitochondria from sucrose-fed rats significantly reduced the rate of H(2)O(2) generation. In contrast, adding exogenous oleic or linoleic acid exacerbated the rate of H(2)O(2) generation in both sucrose-fed and control mitochondria, and the mitochondria from sucrose-fed rats were more sensitive than the control mitochondria. The increased rate of H(2)O(2) generation in sucrose-fed mitochondria corresponded to decreased levels of reduced GSH and vitamin E and increased levels of Cu/Zn-SOD in the intermembrane space. There was no difference between the levels of lipid peroxidation and protein carbonylation in the two types of mitochondria. In addition to the normal activity of Mn-SOD, GPX and catalase detected an increased activity of complex II, and upregulation of UCP2 was observed in mitochondria from sucrose-fed rats, all of which may accelerate respiration rates and reduce generation of ROS. In turn, these effects may protect the mitochondria of sucrose-fed rats from oxidative stress and preserve their function and integrity. However, in whole liver these adaptive mechanisms of the mitochondria were inefficient at counteracting redox imbalances and inhibiting oxidative stress outside of the mitochondria.

Mitochondrial superoxide and coenzyme Q in insulin-deficient rats: increased electron leak

Mitochondrial superoxide is important in the pathogeneses of diabetes and its complications. However, there is uncertainty regarding the intrinsic propensity of mitochondria to generate this radical. Studies to date suggest that superoxide production by mitochondria of insulin-sensitive target tissues of insulin-deficient rodents is reduced or unchanged. Moreover, little is known of the role of the Coenzyme Q (CoQ), whose semiquinone form reacts with molecular oxygen to generate superoxide. We measured reactive oxygen species (ROS) production, respiratory parameters, and CoQ content in mitochondria from gastrocnemius muscle of control and streptozotocin (STZ)-diabetic rats. CoQ content did not differ between mitochondria isolated from vehicle- or STZ-treated animals. CoQ also was unaffected by weight loss in the absence of diabetes (induced by caloric restriction). Under state 4 or state 3 conditions, both respiration and ROS release were reduced in diabetic mitochondria fueled with succinate, glutamate plus malate, or with all three substrates (continuous TCA cycle). However, H(2)O(2) and directly measured superoxide production were substantially increased in gastrocnemius mitochondria of diabetic rats when expressed per unit oxygen consumed. On the basis of substrate and inhibitor effects, the mechanism involved multiple electron transport sites. More limited results using heart mitochondria were similar. ROS per unit respiration was greater in muscle mitochondria from diabetic compared with control rats during state 3, as well as state 4, while the reduction in ROS per unit respiration on transition to state 3 was less for diabetic mitochondria. In summary, ROS production is, in fact, increased in mitochondria from insulin-deficient muscle when considered relative to electron transport. This is evident on multiple energy substrates and in different respiratory states. CoQ is not reduced in diabetic mitochondria or with weight loss due to food restriction. The implications of these findings are discussed.

Nutrient excess and altered mitochondrial proteome and function contribute to neurodegeneration in diabetes

Diabetic neuropathy is a major complication of diabetes that results in the progressive deterioration of the sensory nervous system. Mitochondrial dysfunction has been proposed to play an important role in the pathogenesis of the neurodegeneration observed in diabetic neuropathy. Our recent work has shown that mitochondrial dysfunction occurs in dorsal root ganglia (DRG) sensory neurons in streptozotocin (STZ) induced diabetic rodents. In neurons, the nutrient excess associated with prolonged diabetes may trigger a switching off of AMP kinase (AMPK) and/or silent information regulator T1 (SIRT1) signaling leading to impaired peroxisome proliferator-activated receptor γ coactivator-1 (PGC-1α) expression/activity and diminished mitochondrial activity. This review briefly summarizes the alterations of mitochondrial function and proteome in sensory neurons of STZ-diabetic rodents. We also discuss the possible involvement of AMPK/SIRT/PGC-1α pathway in other diabetic models and different tissues affected by diabetes.

Glucose-induced endoplasmic reticulum stress is independent of oxidative stress: A mechanistic explanation for the failure of antioxidant therapy in diabetes

Oxidative stress contributes to the pathogenesis of diabetes and its complications. However, a large number of interventional studies have failed to show any health benefits of antioxidants. The overwhelming failure of antioxidant therapy to prevent disease can be explained by inadequacy of the doses of antioxidants used, short duration of therapy, or poor timing of initiation of the supplementation. A more likely reason for failure of antioxidants to reduce diabetes-related complications is the multiplicity of mechanisms of glucotoxicity that are independent of oxidative stress. Recently, endoplasmic reticulum (ER) stress has emerged as an important contributor to diabetes-related complications. Multiple lines of experimental evidence indicate that ER stress in endothelial cells can be uncoupled from oxidative stress induced by hyperglycemia, and antioxidants can ameliorate the latter without altering the ER stress. These observations provide a novel mechanistic explanation for the failure of antioxidant therapy in interventional clinical trials.

Signaling of reactive oxygen and nitrogen species in Diabetes mellitus

Disorder of physiological signaling functions of reactive oxygen species (ROS) superoxide and hydrogen peroxide and reactive nitrogen species (RNS) nitric oxide and peroxynitrite is an important feature of diabetes mellitus type 1 and type 2. It is now known that hyperglycemic conditions of cells are associated with the enhanced levels of ROS mainly generated by mitochondria and NADPH oxidase. It has been established that ROS stimulate many enzymatic cascades under normal physiological conditions, but hyperglycemia causes ROS overproduction and the deregulation of ROS signaling pathways initiating the development of diabetes mellitus. On the other hand the deregulation of RNS signaling leads basically to a decrease in NO formation with subsequent damaging disorders. In the present work we will consider the pathological changes of ROS and RNS signaling in enzyme/gene regulated processes catalyzed by protein kinases C and B (Akt/B), phosphatidylinositol 3'-kinase (PI3-kinase), extracellular signal-regulated kinase 1/2 (ERK1/2), and some others. Furthermore we will discuss a particularly important role of several ROS-regulated genes and adapter proteins such as the p66shc, FOXO3a, and Sirt2. The effects of low and high ROS levels in diabetes will be also considered. Thus the regulation of damaging ROS levels in diabetes by antioxidants and free radical scavengers must be one of promising treatment of this disease, however, because of the inability of traditional antioxidative vitamin E and C to interact with superoxide and hydrogen peroxide, new free radical scavengers such as flavonoids, quinones and synthetic mimetics of superoxide dismutase (SOD) should be intensively studied.

Mitochondria in the diabetic heart

Diabetes mellitus increases the risk of developing cardiovascular diseases such as coronary artery disease and heart failure. Studies have shown that the heart failure risk is increased in diabetic patients even after adjusting for coronary artery disease and hypertension. Although the cause of this increased heart failure risk is multifactorial, increasing evidence suggests that derangements in cardiac energy metabolism play an important role. In particular, abnormalities in cardiomyocyte mitochondrial energetics appear to contribute substantially to the development of cardiac dysfunction in diabetes. This review will summarize these abnormalities in mitochondrial function and discuss potential underlying mechanisms.

Mitochondrial dysfunction in diabetes: from molecular mechanisms to functional significance and therapeutic opportunities

Given their essential function in aerobic metabolism, mitochondria are intuitively of interest in regard to the pathophysiology of diabetes. Qualitative, quantitative, and functional perturbations in mitochondria have been identified and affect the cause and complications of diabetes. Moreover, as a consequence of fuel oxidation, mitochondria generate considerable reactive oxygen species (ROS). Evidence is accumulating that these radicals per se are important in the pathophysiology of diabetes and its complications. In this review, we first present basic concepts underlying mitochondrial physiology. We then address mitochondrial function and ROS as related to diabetes. We consider different forms of diabetes and address both insulin secretion and insulin sensitivity. We also address the role of mitochondrial uncoupling and coenzyme Q. Finally, we address the potential for targeting mitochondria in the therapy of diabetes.

Diabetic cardiomyopathy, causes and effects

Diabetes is associated with increased incidence of heart failure even after controlling for coronary artery disease and hypertension. Thus, as diabetic cardiomyopathy has become an increasingly recognized entity among clinicians, a better understanding of its pathophysiology is necessary for early diagnosis and the development of treatment strategies for diabetes-associated cardiovascular dysfunction. We will review recent basic and clinical research into the manifestations and the pathophysiological mechanisms of diabetic cardiomyopathy. The discussion will be focused on the structural, functional and metabolic changes that occur in the myocardium in diabetes and how these changes may contribute to the development of diabetic cardiomyopathy in affected humans and relevant animal models.

Platelets of type 2 diabetic patients are characterized by high ATP content and low mitochondrial membrane potential

Platelet dysfunction plays a critical role in vascular complications of type 2 diabetes mellitus (T2DM). But the relationship between platelet hyperactivity and its energy metabolic process remains unclear. This study was designed to explore alterations of platelet mitochondrial ATP production and the possible mechanism. A total of 39 T2DM patients without macrovascular and microvascular complications and 32 normal controls were fasting sampled. Platelet ATP content was measured by a high performance liquid chromatograph (HPLC). The flow cytometry technique was adopted to evaluate mitochondrial membrane potential (DeltaPsim), the stored force for platelet ATP production. Consequently, T2DM patients exhibited obvious hyperglycemia, hyperlipidemia and hypertension, but normal platelet morphology. Platelet ATP content was significantly higher in T2DM (0.032 +/- 0.010 micromol/10(9) platelets versus 0.017 +/- 0.006 micromol/10(9) platelets, p < 0.001) than in the control group. Interestingly, DeltaPsim was markedly decreased in T2DM patients (0.79 +/- 0.18 versus 2.70 +/- 1.03, p < 0.001) compared with normal controls. For whole subjects, a stepwise regression showed that plasma glycated hemoglobin A1c (HbA1c) level positively correlated to platelet ATP content (beta = 0.552, 95% CI = 0.072-1.451), and fasting plasma glucose (FPG) level was negatively correlated to DeltaPsim (beta = -0.372, 95% CI = -0.471 to -0.089). These data support that hyperglycemia of T2DM promotes platelet mitochondria to generate more ATP, but decreases platelet mitochondrial potential. The discordance between them requires further researches to elucidate.