Role of UCP2 in the Energy Metabolism of the Cancer Cell Line A549.

The uncoupling protein UCP2 is a mitochondrial carrier for which transport activity remains controversial. The physiological contexts in which UCP2 is expressed have led to the assumption that, like UCP1, it uncouples oxidative phosphorylation and thereby reduces the generation of reactive oxygen species. Other reports have involved UCP2 in the Warburg effect, and results showing that UCP2 catalyzes the export of matrix C4 metabolites to facilitate glutamine utilization suggest that the carrier could be involved in the metabolic adaptations required for cell proliferation. We have examined the role of UCP2 in the energy metabolism of the lung adenocarcinoma cell line A549 and show that UCP2 silencing decreased the basal rate of respiration, although this inhibition was not compensated by an increase in glycolysis. Silencing did not lead to either changes in proton leakage, as determined by the rate of respiration in the absence of ATP synthesis, or changes in the rate of formation of reactive oxygen species. The decrease in energy metabolism did not alter the cellular energy charge. The decreased cell proliferation observed in UCP2-silenced cells would explain the reduced cellular ATP demand. We conclude that UCP2 does not operate as an uncoupling protein, whereas our results are consistent with its activity as a C4-metabolite carrier involved in the metabolic adaptations of proliferating cells.

Deletion of Lactate Dehydrogenase-A Impairs Oncogene-Induced Mouse Hepatocellular Carcinoma Development.

BACKGROUND AND AIMS: Hepatocellular carcinoma (HCC) is a multistep process whereby abnormally proliferating cancer cells undergo extensive metabolic reprogramming. Metabolic alterations in hepatocarcinogenesis depend on the activation of specific oncogenes, thus partially explaining HCC heterogeneity. c-Myc oncogene overexpression, frequently observed in human HCCs, leads to a metabolic rewiring toward a Warburg phenotype and production of lactate, resulting in the acidification of the extracellular space, favoring the emergence of an immune-permissive tumor microenvironment. Here, we investigated whether Ldha genetic ablation interferes with metabolic reprogramming and HCC development in the mouse. METHODS: We characterized the metabolic reprogramming in tumors induced in C57BL/6J mice hydrodynamically cotransfected with c-Myc and h-Ras. Using the same experimental model, we investigated the effect of Ldha inhibition-gained through the inducible and hepatocyte-specific Ldha knockout-on cancer cell metabolic reprogramming, number and size of HCC lesions, and tumor microenvironment alterations. RESULTS: c-Myc/h-Ras-driven tumors display a striking glycolytic metabolism, suggesting a switch to a Warburg phenotype. The tumors also exhibited enhanced pentose phosphate pathway activity, the switch of glutamine to sustain glutathione synthesis instead of the tricarboxylic acid cycle, and the impairment of oxidative phosphorylation. In addition, Ldha abrogation significantly hampered tumor number and size together with an evident inhibition of the Warburg-like metabolic feature and a remarkable increase of CD4+ lymphocytes compared with Ldha wild-type livers. CONCLUSIONS: These results demonstrate that Ldha deletion significantly impairs mouse HCC development and suggest lactate dehydrogenase as a potential target to enhance the efficacy of the current therapeutic options.

Tumor growth of neurofibromin-deficient cells is driven by decreased respiration and hampered by NAD+ and SIRT3.

Neurofibromin loss drives neoplastic growth and a rewiring of mitochondrial metabolism. Here we report that neurofibromin ablation dampens expression and activity of NADH dehydrogenase, the respiratory chain complex I, in an ERK-dependent fashion, decreasing both respiration and intracellular NAD+. Expression of the alternative NADH dehydrogenase NDI1 raises NAD+/NADH ratio, enhances the activity of the NAD+-dependent deacetylase SIRT3 and interferes with tumorigenicity in neurofibromin-deficient cells. The antineoplastic effect of NDI1 is mimicked by administration of NAD+ precursors or by rising expression of the NAD+ deacetylase SIRT3 and is synergistic with ablation of the mitochondrial chaperone TRAP1, which augments succinate dehydrogenase activity further contributing to block pro-neoplastic metabolic changes. These findings shed light on bioenergetic adaptations of tumors lacking neurofibromin, linking complex I inhibition to mitochondrial NAD+/NADH unbalance and SIRT3 inhibition, as well as to down-regulation of succinate dehydrogenase. This metabolic rewiring could unveil attractive therapeutic targets for neoplasms related to neurofibromin loss.

Protein Allostery and Ligand Design: Computational Design Meets Experiments to Discover Novel Chemical Probes.

Herein we examine the determinants of the allosteric inhibition of the mitochondrial chaperone TRAP1 by a small molecule ligand. The knowledge generated is harnessed into the design of novel derivatives with interesting biological properties. TRAP1 is a member of the Hsp90 family of proteins, which work through sequential steps of ATP processing coupled to client-protein remodeling. Isoform selective inhibition of TRAP1 can provide novel information on the biomolecular mechanisms of molecular chaperones, as well as new insights into the development of small molecules with therapeutic potential. Our analysis of the interactions between an active first-generation allosteric ligand and TRAP1 shows how the small molecule induces long-range perturbations that influence the attainment of reactive poses in the active site. At the same time, the dynamic adaptation of the allosteric binding pocket to the presence of the first-generation compound sets the stage for the design of a set of second-generation ligands: the characterization of the formation/disappearance of pockets around the allosteric site that is used to guide optimize the ligands' fit for the allosteric site and improve inhibitory activities. The effects of the newly designed molecules are validated experimentally in vitro and in vivo. We discuss the implications of our approach as a promising strategy towards understanding the molecular determinants of allosteric regulation in chemical and molecular biology, and towards speeding up the design of allosteric small molecule modulators.

HIF1α-dependent induction of the mitochondrial chaperone TRAP1 regulates bioenergetic adaptations to hypoxia.

The mitochondrial paralog of the Hsp90 chaperone family TRAP1 is often induced in tumors, but the mechanisms controlling its expression, as well as its physiological functions remain poorly understood. Here, we find that TRAP1 is highly expressed in the early stages of Zebrafish development, and its ablation delays embryogenesis while increasing mitochondrial respiration of fish larvae. TRAP1 expression is enhanced by hypoxic conditions both in developing embryos and in cancer models of Zebrafish and mammals. The TRAP1 promoter contains evolutionary conserved hypoxic responsive elements, and HIF1α stabilization increases TRAP1 levels. TRAP1 inhibition by selective compounds or by genetic knock-out maintains a high level of respiration in Zebrafish embryos after exposure to hypoxia. Our data identify TRAP1 as a primary regulator of mitochondrial bioenergetics in highly proliferating cells following reduction in oxygen tension and HIF1α stabilization.

Targeting the mitochondrial chaperone TRAP1: strategies and therapeutic perspectives.

TRAP1, the mitochondrial isoform of heat shock protein (Hsp)90 chaperones, is a key regulator of metabolism and organelle homeostasis in diverse pathological states. While selective TRAP1 targeting is an attractive goal, classical active-site-directed strategies have proved difficult, due to high active site conservation among Hsp90 paralogs. Here, we discuss advances in developing TRAP1-directed strategies, from lead modification with mitochondria delivery groups to the computational discovery of allosteric sites and ligands. Specifically, we address the unique opportunities that targeting TRAP1 opens up in tackling fundamental questions on its biology and in unveiling new therapeutic approaches. Finally, we show how crucial to this endeavor is our ability to predict the activities of TRAP1-selective allosteric ligands and to optimize target engagement to avoid side effects.

Honokiol Bis-Dichloroacetate Is a Selective Allosteric Inhibitor of the Mitochondrial Chaperone TRAP1.

Aims: TNF receptor-associated protein 1 (TRAP1), the mitochondrial paralog of the heat shock protein 90 (Hsp90) family of molecular chaperones, is required for neoplastic growth in several tumor cell models, where it inhibits succinate dehydrogenase (SDH) activity, thus favoring bioenergetic rewiring, maintenance of redox homeostasis, and orchestration of a hypoxia-inducible factor 1-alpha (HIF1α)-mediated pseudohypoxic program. Development of selective TRAP1 inhibitors is instrumental for targeted development of antineoplastic drugs, but it has been hampered up to now by the high degree of homology among catalytic pockets of Hsp90 family members. The vegetal derivative honokiol and its lipophilic bis-dichloroacetate ester, honokiol DCA (HDCA), are small-molecule compounds with antineoplastic activity. HDCA leads to oxidative stress and apoptosis in in vivo tumor models and displays an action that is functionally opposed to that of TRAP1, as it induces both SDH and the mitochondrial deacetylase sirtuin-3 (SIRT3), which further enhances SDH activity. We investigated whether HDCA could interact with TRAP1, inhibiting its chaperone function, and the effects of HDCA on tumor cells harboring TRAP1. Results: An allosteric binding site in TRAP1 is able to host HDCA, which inhibits TRAP1 but not Hsp90 ATPase activity. In neoplastic cells, HDCA reverts TRAP1-dependent downregulation of SDH, decreases proliferation rate, increases mitochondrial superoxide levels, and abolishes tumorigenic growth. Innovation: HDCA is a potential lead compound for the generation of antineoplastic approaches based on the allosteric inhibition of TRAP1 chaperone activity. Conclusions: We have identified a selective TRAP1 inhibitor that can be used to better dissect TRAP1 biochemical functions and to tailor novel tumor-targeting strategies.

Machine Learning of Allosteric Effects: The Analysis of Ligand-Induced Dynamics to Predict Functional Effects in TRAP1.

Allosteric molecules provide a powerful means to modulate protein function. However, the effect of such ligands on distal orthosteric sites cannot be easily described by classical docking methods. Here, we applied machine learning (ML) approaches to expose the links between local dynamic patterns and different degrees of allosteric inhibition of the ATPase function in the molecular chaperone TRAP1. We focused on 11 novel allosteric modulators with similar affinities to the target but with inhibitory efficacy between the 26.3 and 76%. Using a set of experimentally related local descriptors, ML enabled us to connect the molecular dynamics (MD) accessible to ligand-bound (perturbed) and unbound (unperturbed) systems to the degree of ATPase allosteric inhibition. The ML analysis of the comparative perturbed ensembles revealed a redistribution of dynamic states in the inhibitor-bound versus inhibitor-free systems following allosteric binding. Linear regression models were built to quantify the percentage of experimental variance explained by the predicted inhibitor-bound TRAP1 states. Our strategy provides a comparative MD-ML framework to infer allosteric ligand functionality. Alleviating the time scale issues which prevent the routine use of MD, a combination of MD and ML represents a promising strategy to support in silico mechanistic studies and drug design.

Dynamically Shaping Chaperones. Allosteric Modulators of HSP90 Family as Regulatory Tools of Cell Metabolism in Neoplastic Progression.

Molecular chaperones have recently emerged as fundamental regulators of salient biological routines, including metabolic adaptations to environmental changes. Yet, many of the molecular mechanisms at the basis of their functions are still unknown or at least uncertain. This is in part due to the lack of chemical tools that can interact with the chaperones to induce measurable functional perturbations. In this context, the use of small molecules as modulators of protein functions has proven relevant for the investigation of a number of biomolecular systems. Herein, we focus on the functions, interactions and signaling pathways of the HSP90 family of molecular chaperones as possible targets for the discovery of new molecular entities aimed at tuning their activity and interactions. HSP90 and its mitochondrial paralog, TRAP1, regulate the activity of crucial metabolic circuitries, making cells capable of efficiently using available energy sources, with relevant implications both in healthy conditions and in a variety of disease states and especially cancer. The design of small-molecules targeting the chaperone cycle of HSP90 and able to inhibit or stimulate the activity of the protein can provide opportunities to finely dissect their biochemical activities and to obtain lead compounds to develop novel, mechanism-based drugs.

Rational Design of Allosteric and Selective Inhibitors of the Molecular Chaperone TRAP1.

TRAP1 is the mitochondrial paralog of the heat shock protein 90 (HSP90) chaperone family. Its activity as an energy metabolism regulator has important implications in cancer, neurodegeneration, and ischemia. Selective inhibitors of TRAP1 could inform on its mechanisms of action and set the stage for targeted drug development, but their identification was hampered by the similarity among active sites in HSP90 homologs. We use a dynamics-based approach to identify a TRAP1 allosteric pocket distal to its active site that can host drug-like molecules, and we select small molecules with optimal stereochemical features to target the pocket. These leads inhibit TRAP1, but not HSP90, ATPase activity and revert TRAP1-dependent downregulation of succinate dehydrogenase activity in cancer cells and in zebrafish larvae. TRAP1 inhibitors are not toxic per se, but they abolish tumorigenic growth of neoplastic cells. Our results indicate that exploiting conformational dynamics can expand the chemical space of chaperone antagonists to TRAP1-specific inhibitors with wide therapeutic opportunities.

Thyroid hormone inhibits hepatocellular carcinoma progression via induction of differentiation and metabolic reprogramming.

BACKGROUND & AIMS: Only limited therapeutic options are currently available for hepatocellular carcinoma (HCC), making the development of effective alternatives essential. Based on the recent finding that systemic or local hypothyroidism is associated with HCC development in humans and rodents, we investigated whether the thyroid hormone triiodothyronine (T3) could inhibit the progression of HCCs. METHODS: Different rat and mouse models of hepatocarcinogenesis were investigated. The effect of T3 on tumorigenesis and metabolism/differentiation was evaluated by transcriptomic analysis, quantitative reverse transcription PCR, immunohistochemistry, and enzymatic assay. RESULTS: A short treatment with T3 caused a shift in the global expression profile of the most aggressive preneoplastic nodules towards that of normal liver. This genomic reprogramming preceded the disappearance of nodules and involved reprogramming of metabolic genes, as well as pro-differentiating transcription factors, including Kruppel-like factor 9, a target of the thyroid hormone receptor ß (TRß). Treatment of HCC-bearing rats with T3 strongly reduced the number and burden of HCCs. Reactivation of a local T3/TRß axis, a switch from Warburg to oxidative metabolism and loss of markers of poorly differentiated hepatocytes accompanied the reduced burden of HCC. This effect persisted 1 month after T3 withdrawal, suggesting a long-lasting effect of the hormone. The antitumorigenic effect of T3 was further supported by its inhibitory activity on cell growth and the tumorigenic ability of human HCC cell lines. CONCLUSIONS: Collectively, these findings suggest that reactivation of the T3/TRß axis induces differentiation of neoplastic cells towards a more benign phenotype and that T3 or its analogs, particularly agonists of TRß, could be useful tools in HCC therapy. LAY SUMMARY: Hepatocellular carcinoma (HCC) represents an important challenge for global health. Recent findings showed that systemic or local hypothyroidism is associated with HCC development. In rat models, we showed that administration of the thyroid hormone T3 impaired HCC progression, even when given at late stages. This is relevant from a translational point of view as HCC is often diagnosed at an advanced stage when it is no longer amenable to curative treatments. Thyroid hormones and/or thyromimetics could be useful for the treatment of patients with HCC.

Indomethacin for intracranial hypertension secondary to severe traumatic brain injury in adults.

BACKGROUND: Among people who have suffered a traumatic brain injury, increased intracranial pressure continues to be a major cause of early death; it is estimated that about 11 people per 100 with traumatic brain injury die. Indomethacin (also known as indometacin) is a powerful cerebral vasoconstrictor that can reduce intracranial pressure and, ultimately, restore cerebral perfusion and oxygenation. Thus, indomethacin may improve the recovery of a person with traumatic brain injury. OBJECTIVES: To assess the effects of indomethacin for adults with severe traumatic brain injury. SEARCH METHODS: We ran the searches from inception to 23 August 2019. We searched the Cochrane Central Register of Controlled Trials (CENTRAL; 2019, Issue 8) in the Cochrane Library, Ovid MEDLINE, Ovid Embase, CINAHL Plus (EBSCO), four other databases, and clinical trials registries. We also screened reference lists and conference abstracts, and contacted experts in the field. SELECTION CRITERIA: Our search criteria included randomised controlled trials (RCTs) that compared indomethacin with any control in adults presenting with severe traumatic brain injury associated with elevated intracranial pressure, with no previous decompressive surgery. DATA COLLECTION AND ANALYSIS: Two review authors independently decided on the selection of the studies. We followed standard Cochrane methods. MAIN RESULTS: We identified no eligible studies for this review, either completed or ongoing. AUTHORS' CONCLUSIONS: We found no studies, either completed or ongoing, that assessed the effects of indomethacin in controlling intracranial hypertension secondary to severe traumatic brain injury. Thus, we cannot draw any conclusions about the effects of indomethacin on intracranial pressure, mortality rates, quality of life, disability or adverse effects. This absence of evidence should not be interpreted as evidence of no effect for indomethacin in controlling intracranial hypertension secondary to severe traumatic brain injury. It means that we have not identified eligible research for this review.

Metabolic Plasticity of Tumor Cell Mitochondria.

Mitochondria are dynamic organelles that exchange a multiplicity of signals with other cell compartments, in order to finely adjust key biological routines to the fluctuating metabolic needs of the cell. During neoplastic transformation, cells must provide an adequate supply of the anabolic building blocks required to meet a relentless proliferation pressure. This can occur in conditions of inconstant blood perfusion leading to variations in oxygen and nutrient levels. Mitochondria afford the bioenergetic plasticity that allows tumor cells to adapt and thrive in this ever changing and often unfavorable environment. Here we analyse how mitochondria orchestrate the profound metabolic rewiring required for neoplastic growth.

The Chaperone TRAP1 As a Modulator of the Mitochondrial Adaptations in Cancer Cells.

Mitochondria can receive, integrate, and transmit a variety of signals to shape many biochemical activities of the cell. In the process of tumor onset and growth, mitochondria contribute to the capability of cells of escaping death insults, handling changes in ROS levels, rewiring metabolism, and reprograming gene expression. Therefore, mitochondria can tune the bioenergetic and anabolic needs of neoplastic cells in a rapid and flexible way, and these adaptations are required for cell survival and proliferation in the fluctuating environment of a rapidly growing tumor mass. The molecular bases of pro-neoplastic mitochondrial adaptations are complex and only partially understood. Recently, the mitochondrial molecular chaperone TRAP1 (tumor necrosis factor receptor associated protein 1) was identified as a key regulator of mitochondrial bioenergetics in tumor cells, with a profound impact on neoplastic growth. In this review, we analyze these findings and discuss the possibility that targeting TRAP1 constitutes a new antitumor approach.

Design of Allosteric Stimulators of the Hsp90 ATPase as New Anticancer Leads.

Allosteric compounds that stimulate Hsp90 adenosine triphosphatase (ATPase) activity were rationally designed, showing anticancer potencies in the low micromolar to nanomolar range. In parallel, the mode of action of these compounds was clarified and a quantitative model that links the dynamic ligand-protein cross-talk to observed cellular and in vitro activities was developed. The results support the potential of using dynamics-based approaches to develop original mechanism-based cancer therapeutics.

Regulation of death induction and chemosensitizing action of 3-bromopyruvate in myeloid leukemia cells: energy depletion, oxidative stress, and protein kinase activity modulation.

3-Bromopyruvate (3-BrP) is an alkylating, energy-depleting drug that is of interest in antitumor therapies, although the mechanisms underlying its cytotoxicity are ill-defined. We show here that 3-BrP causes concentration-dependent cell death of HL60 and other human myeloid leukemia cells, inducing both apoptosis and necrosis at 20-30 µM and a pure necrotic response at 60 µM. Low concentrations of 3-BrP (10-20 µM) brought about a rapid inhibition of glycolysis, which at higher concentrations was followed by the inhibition of mitochondrial respiration. The combination of these effects causes concentration-dependent ATP depletion, although this cannot explain the lethality at intermediate 3-BrP concentrations (20-30 µM). The oxidative stress caused by exposure to 3-BrP was evident as a moderate overproduction of reactive oxygen species and a concentration-dependent depletion of glutathione, which was an important determinant of 3-BrP toxicity. In addition, 3-BrP caused glutathione-dependent stimulation of p38 mitogen-activated protein kinase (MAPK), mitogen-induced extracellular kinase (MEK)/extracellular signal-regulated kinase (ERK), and protein kinase B (Akt)/mammalian target of rapamycin/p70S6K phosphorylation or activation, as well as rapid LKB-1/AMP kinase (AMPK) activation, which was later followed by Akt-mediated inactivation. Experiments with pharmacological inhibitors revealed that p38 MAPK activation enhances 3-BrP toxicity, which is conversely restrained by ERK and Akt activity. Finally, 3-BrP was seen to cooperate with antitumor agents like arsenic trioxide and curcumin in causing cell death, a response apparently mediated by both the generation of oxidative stress induced by 3-BrP and the attenuation of Akt and ERK activation by curcumin. In summary, 3-BrP cytotoxicity is the result of several combined regulatory mechanisms that might represent important targets to improve therapeutic efficacy.

Beneficial effects of silibinin against the progression of metabolic syndrome, increased oxidative stress, and liver steatosis in Psammomys obesus, a relevant animal model of human obesity and diabetes.

BACKGROUND: Insulin resistance and oxidative stress are major pathogenic mechanisms leading to chronic liver diseases in diabetic subjects. The gerbil Psammomys obesus is a unique model of nutritional diabetes resembling the disease in humans. This study investigated whether the natural ingredient silibinin, known as hepatoprotective, could decrease oxidative stress and reduce liver damage in obese gerbils. METHODS: Control animals were fed their vegetable-based low caloric diet while two other rat groups ingested a high calorie diet for 14 weeks. Silibinin, or its vehicle, was administrated by gastric intubation (100 mg/kg per day) from the 7th week of treatment, which corresponds to an established insulin resistance state. At the end of the experiments, the hepatic biochemical profile, markers of oxidative stress in either plasma or liver tissue, and histological alterations were examined. RESULTS: Diabetic P. obesus displayed many metabolic disturbances (hyperinsulinemia, hyperglycemia, dyslipidemia), which were aggravated for the last 8 weeks. These events were coupled with greater oxidative stress (decline in glutathione, rise in lipoperoxidation). In addition, glutathione peroxidase activity was reduced while the level of superoxide dismutase was elevated. Interestingly, treatment with silibinin alleviated most of the metabolic defects, especially high triglyceride levels, reduced insulin resistance and largely restored antioxidant status. Also, Masson's trichrome staining revealed distinct steatosis, yet silibinin partially reversed this manifestation. CONCLUSION: Silibinin affords substantial protection against the progression of insulin resistance in Type 2 diabetes mellitus for P. obesus by hampering the oxidative process and improving hepatic metabolism.

UCP2 deficiency helps to restrict the pathogenesis of experimental cutaneous and visceral leishmaniosis in mice.

BACKGROUND: Uncoupling protein 2 (UCP2) is a mitochondrial transporter that has been shown to lower the production of reactive oxygen species (ROS). Intracellular pathogens such as Leishmania upregulate UCP2 and thereby suppress ROS production in infected host tissues, allowing the multiplication of parasites within murine phagocytes. This makes host UCP2 and ROS production potential targets in the development of antileishmanial therapies. Here we explore how UCP2 affects the outcome of cutaneous leishmaniosis (CL) and visceral leishmaniosis (VL) in wild-type (WT) C57BL/6 mice and in C57BL/6 mice lacking the UCP2 gene (UCP2KO). METHODOLOGY AND FINDINGS: To investigate the effects of host UCP2 deficiency on Leishmania infection, we evaluated parasite loads and cytokine production in target organs. Parasite loads were significantly lower in infected UCP2KO mice than in infected WT mice. We also found that UCP2KO mice produced significantly more interferon-γ (IFN-γ), IL-17 and IL-13 than WT mice (P<0.05), suggesting that UCP2KO mice are resistant to Leishmania infection. CONCLUSIONS: In this way, UCP2KO mice were better able than their WT counterparts to overcome L. major and L. infantum infections. These findings suggest that upregulating host ROS levels, perhaps by inhibiting UPC2, may be an effective approach to preventing leishmaniosis.

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.

Acute mitochondrial actions of glitazones on the liver: a crucial parameter for their antidiabetic properties.

BACKGROUND/AIMS: Glitazones are synthetic insulin-sensitizing drugs which act as agonists of peroxisome proliferator-activated receptor gamma (PPARγ). However, TZDs action does not exclude independent PPARγ-activation effects. Remarkably, direct mitochondrial action of these agents has not been fully studied yet. METHODS: Oxygen consumption rates (JO(2)) were measured using a Clark-type oxygen electrode in intact hepatocytes and isolated liver mitochondria. Mitochondrial reactive oxygen species (ROS) production was quantified by fluorescence assay. Moreover, activities of mitochondrial respiratory chain complex I, II and III were spectrometrically determined. RESULTS: Pioglitazone and rosiglitazone inhibited JO(2) in liver cells and mitochondria. This inhibition affected the state 3 of respiration (in the presence of ADP) and the uncoupled state (after addition of dinitrophenol). Moreover, these agents dramatically reduced mitochondrial ROS production in all situations tested. We also demonstrated that both glitazones specifically inhibited the activities of complex I and complex III, by 50% and 35% respectively. Additionally, they do not modify neither the oxidative phosphorylation yield nor the permeability transition pore opening. CONCLUSIONS: Pioglitazone and rosiglitazone reduce both respiration intensity and ROS production, acutely and by a probable PPARγ-independent way, through inhibition of complex I and III activities. This new finding could positively contribute to their anti-diabetic properties.