Inhibition Of Pyruvate Dehydrogenase Research Articles

Dichloroacetate should be considered with platinum-based chemotherapy in hypoxic tumors rather than as a single agent in advanced non-small cell lung cancer

Dichloroacetate (DCA) is a highly bioavailable small molecule that inhibits pyruvate dehydrogenase kinase, promoting glucose oxidation and reversing the glycolytic phenotype in preclinical cancer studies. We designed this open-label phase II trial to determine the response rate, safety, and tolerability of oral DCA in patients with metastatic breast cancer and advanced stage non-small cell lung cancer (NSCLC). This trial was conducted with DCA 6.25 mg/kg orally twice daily in previously treated stage IIIB/IV NSCLC or stage IV breast cancer. Growth inhibition by DCA was also evaluated in a panel of 54 NSCLC cell lines with and without cytotoxic chemotherapeutics (cisplatin and docetaxel) in normoxic and hypoxic conditions. Under normoxic conditions in vitro, single-agent IC50 was >2 mM for all evaluated cell lines. Synergy with cisplatin was seen in some cell lines under hypoxic conditions. In the clinical trial, after seven patients were enrolled, the study was closed based on safety concerns. The only breast cancer patient had stable disease after 8 weeks, quickly followed by progression in the brain. Two patients withdrew consent within a week of enrollment. Two patients had disease progression prior to the first scheduled scans. Within 1 week of initiating DCA, one patient died suddenly of unknown cause and one experienced a fatal pulmonary embolism. We conclude that patients with previously treated advanced NSCLC did not benefit from oral DCA. In the absence of a larger controlled trial, firm conclusions regarding the association between these adverse events and DCA are unclear. Further development of DCA should be in patients with longer life expectancy, in whom sustained therapeutic levels can be achieved, and potentially in combination with cisplatin.

Abstract 90: Pyruvate Dehydrogenase is Inhibited in Post Cardiac Arrest Patients

Introduction: Pyruvate Dehydrogenase (PDH) activity has been shown to be inhibited in animal models of post-cardiac arrest. This depressed activity has been postulated to be directly related to neurologic injury secondary to aerobic metabolic dysfunction and accumulation of toxic metabolites. The objective of this study was to determine if PDH inhibition occurs after cardiac arrest (CA) in humans. Methods: Patients were enrolled as part of a prospective observational trial of CA at a single urban academic medical center from 1/13 to 4/13. A blood sample was collected as early after ROSC as informed consent could be obtained (<24 hours). Our control group consisted of volunteers with no significant medical history. We used a novel method to measure PDH activity from peripheral blood mononuclear cells isolated from fresh blood. We quantified total PDH in 15mg / ml of isolated protein and determined overall PDH activity (PDH activity / total protein) and specific PDH activity (PDH activity / PDH protein). Wilcoxon rank sum test was used to compare median quantity and activity between the two groups. A p-value < 0.05 was considered statistically significant. All tests of the data were performed in SAS v. 9.3 (SAS Institute Inc., Cary, NC, USA). Results: We enrolled 10 post-arrest patients; average age was 48 and 50% were female. Mortality was 50%. Overall PDH activity was significantly lower in the CA group (2.20 IQR 1.70 - 3.49) compared to controls (8.40 IQR 5.51 - 8.67) (p = .007). PDH quantity was also significantly lower in the CA group (1.26 IQR 0.90 - 2.02) compared to controls (4.88 IQR 3.08 - 6.09) (p = .009). There was no difference in specific PDH activity between the groups (p = 0.84). Conclusions: PDH activity is inhibited in the post-arrest period compared to healthy controls. The main driver of inhibition may be loss of PDH protein as opposed to changes in intrinsic activity. These findings are pertinent as animal models suggest PDH inhibition may drive neurologic injury after CA.

Synergistic Antileukemic Effect Of Sequential Administration Of Dichloroacetate (DCA) Combined With Arsenic Trioxide (ATO) In Primary Blasts From Patients With Acute Myeloid Leukemia (AML) and FLT3-ITD AML Cell Lines

BackgroundOutcomes of treatment for AML are suboptimal with ara-C and anthracyclines particularly in AML with internal tandem duplication (ITD) mutation of the fms-like tyrosine kinase 3 (FLT3-ITD), which is known for hyperproliferative state with activation of glycolytic metabolism and increased intracellular reactive oxygen species (ROS). ATO is highly effective in treatment of acute promyelocytic leukemia (APL). In addition to degradation of PML-RARα in APL, ATO has multiple targets within the cell including reduction of phosphorylation of STAT proteins (downstream of FLT3) and decreasing mitochondrial membrane potential leading to apoptosis. By inhibiting pyruvate dehydrogenase kinase, DCA is known to shunt pyruvate away from lactate production and into mitochondrial respiration, resulting in enhanced oxidative phosphorylation. DCA has been used clinically for treatment of lactic acidosis in children and adults. We hypothesized that treating leukemic cells, particularly with FLT3-ITD mutations, for short periods of time with sublethal dose of DCA (priming) might thus activate mitochondria to produce more ROS on exposure to ATO, resulting in enhanced anti-leukemic activity. MethodsIC50s for ATO and DCA were generated in AML cell lines with FLT3-ITD (MOLM14, and MV4-11), with FLT3 point mutation (MonoMac6), and with FLT3-WT (THP-1), and normal karyotype FLT3-WT primary AML cells (AML13, AML15, AML16). To generate potentiation factors, cells were primed with IC30 of DCA or vehicle for 48 h and then treated with a range of ATO concentrations in the presence or absence of DCA (IC30) for an additional 48 h. Primary cells were treated with DCA or vehicle for 24 h and then the combination for 24 h. Each experiment was terminated with WST1 (Roche). Cell viability assays were carried out similarly except the endpoint was trypan blue exclusion. Combination Index (CI) was calculated by the fixed ratio method of Chou and Talalay. Apoptosis was monitored using the FITC Annexin V Kit (BD Pharmingen) while mitochondrial potential was assessed by MitoRed Kit (Millipore); cells were analyzed by FACScan (BD Biosciences) and Flow Jo Software (Tree Flo). Numbers are mean ± SD (triplicates). ResultsIC50s of ATO and DCA alone, and when ATO is combined sequentially with IC30 of DCA are shown in Table 1. Presence of DCA increased the cytotoxicity of ATO by 1.3- to 2.2-fold (potentiation factor), and decreased cell viability by approximately 45-95% only in cell lines with FLT3 mutations (MOLM-14, MV4-11, MonoMac6). Cytotoxicity of ATO in FLT3-WT cells, THP-1, was not potentiated with DCA because cells were highly sensitive to DCA alone. A clear synergistic, but not additive, anti-leukemic effect (CI< 1.0) was observed with DCA and ATO in FLT3 mutated cell lines. When MOLM-14 cells were primed with DCA for 24 h and treated with ATO at IC50 for 48 h, an 83% increase in apoptosis (p=0.002), and a 55% increase in loss of mitochondrial membrane potential (p=0.003) were observed compared to no priming. With no DCA priming and combination of ATO+DCA for 48 h, apoptosis and loss of mitochondrial membrane potential were increased by 50% (p= 0.003), and 120% (p=0.008), respectively, compared to ATO alone. To a lower extent, the same effect was observed in primary AML cells. ConclusionIn AML cells with FLT3 mutations, priming with sublethal dose of DCA, as a mitochondrial enhancer, significantly potentiated the cytotoxicity of ATO. Mechanistic studies on FLT3 signaling in primary AML cells with FLT3-ITD are ongoing. These data suggest that targeting cellular metabolism in leukemia may provide a chemotherapy-free therapeutic option for AML patients who are medically unfit or patients with unfavorable risk such as relapsed/refractory FLT3-ITD and warrants further clinical investigation. Disclosures:Off Label Use: Arsenic trioxide in AML.

Muscle insulin sensitivity and glucose metabolism are controlled by the intrinsic muscle clock

Circadian rhythms control metabolism and energy homeostasis, but the role of the skeletal muscle clock has never been explored. We generated conditional and inducible mouse lines with muscle-specific ablation of the core clock gene Bmal1. Skeletal muscles from these mice showed impaired insulin-stimulated glucose uptake with reduced protein levels of GLUT4, the insulin-dependent glucose transporter, and TBC1D1, a Rab-GTPase involved in GLUT4 translocation. Pyruvate dehydrogenase (PDH) activity was also reduced due to altered expression of circadian genes Pdk4 and Pdp1, coding for PDH kinase and phosphatase, respectively. PDH inhibition leads to reduced glucose oxidation and diversion of glycolytic intermediates to alternative metabolic pathways, as revealed by metabolome analysis. The impaired glucose metabolism induced by muscle-specific Bmal1 knockout suggests that a major physiological role of the muscle clock is to prepare for the transition from the rest/fasting phase to the active/feeding phase, when glucose becomes the predominant fuel for skeletal muscle.

Rapid Inhibition of Pyruvate Dehydrogenase: An Initiating Event in High Dietary Fat-Induced Loss of Metabolic Flexibility in the Heart

Cardiac function depends on the ability to switch between fatty acid and glucose oxidation for energy production in response to changes in substrate availability and energetic stress. In obese and diabetic individuals, increased reliance on fatty acids and reduced metabolic flexibility are thought to contribute to the development of cardiovascular disease. Mechanisms by which cardiac mitochondria contribute to diet-induced metabolic inflexibility were investigated. Mice were fed a high fat or low fat diet for 1 d, 1 wk, and 20 wk. Cardiac mitochondria isolated from mice fed a high fat diet displayed a diminished ability to utilize the glycolytically derived substrate pyruvate. This response was rapid, occurring within the first day on the diet, and persisted for up to 20 wk. A selective increase in the expression of pyruvate dehydrogenase kinase 4 and inhibition of pyruvate dehydrogenase are responsible for the rapid suppression of pyruvate utilization. An important consequence is that pyruvate dehydrogenase is sensitized to inhibition when mitochondria respire in the presence of fatty acids. Additionally, increased expression of pyruvate dehydrogenase kinase 4 preceded any observed diet-induced reductions in the levels of glucose transporter type 4 and glycolytic enzymes and, as judged by Akt phosphorylation, insulin signaling. Importantly, diminished insulin signaling evident at 1 wk on the high fat diet did not occur in pyruvate dehydrogenase kinase 4 knockout mice. Dietary intervention leads to a rapid decline in pyruvate dehydrogenase kinase 4 levels and recovery of pyruvate dehydrogenase activity indicating an additional form of regulation. Finally, an overnight fast elicits a metabolic response similar to that induced by high dietary fat obscuring diet-induced metabolic changes. Thus, our data indicate that diet-induced inhibition of pyruvate dehydrogenase may be an initiating event in decreased oxidation of glucose and increased reliance of the heart on fatty acids for energy production.

Revisiting the biosynthesis of dehydrophos reveals a tRNA-dependent pathway

Bioactive natural products containing a C-P bond act as mimics of phosphate esters and carboxylic acids, thereby competing with these compounds for active sites of enzymes. Dehydrophos (DHP), a broad-spectrum antibiotic, is a phosphonotripeptide produced by Streptomyces luridus, in which glycine and leucine are linked to an aminophosphonate analog of dehydroalanine, ΔAla(P). This unique feature, in combination with the monomethylation of the phosphonic acid, renders DHP a Trojan horse type antibiotic because peptidase-mediated hydrolysis will release methyl acetylphosphonate, a potent inhibitor of pyruvate dehydrogenase. Bioinformatic analysis of the biosynthetic gene cluster suggested that ΔAla(P) would be generated from Ser(P), the phosphonate analog of Ser, by phosphorylation and subsequent elimination, and that ΔAla(P) would be condensed with Leu-tRNA(Leu). DhpH was anticipated to carry out this elimination/ligation cascade. DhpH is a multidomain protein, in which a pyridoxal phosphate binding domain is fused to an N-acetyltransferase domain related to the general control nonderepressible-5 (GCN5) family. In this work, the activity of DhpH was reconstituted in vitro. The enzyme was able to catalyze the β-elimination reaction of pSer(P) to generate ΔAla(P), but it was unable to condense ΔAla(P) with Leu. Instead, ΔAla(P) is hydrolyzed to acetyl phosphonate, which is converted to Ala(P) by a second pyridoxal phosphate-dependent enzyme, DhpD. Ala(P) is the substrate for the condensation with Leu-tRNA(Leu) catalyzed by the C-terminal domain of DhpH. DhpJ, a 2-oxoglutarate/Fe(II)-dependent enzyme, introduces the vinyl functionality into Leu-Ala(P) acting as a desaturase, and addition of Gly by DhpK in a Gly-tRNA(Gly)-dependent manner completes the in vitro biosynthesis of dehydrophos.

Extracorporeal membrane oxygenation promotes long chain fatty acid oxidation in the immature swine heart in vivo

Extracorporeal membrane oxygenation (ECMO) supports infants and children with severe cardiopulmonary compromise. Nutritional support for these children includes provision of medium- and long-chain fatty acids (FAs). However, ECMO induces a stress response, which could limit the capacity for FA oxidation. Metabolic impairment could induce new or exacerbate existing myocardial dysfunction. Using a clinically relevant piglet model, we tested the hypothesis that ECMO maintains the myocardial capacity for FA oxidation and preserves myocardial energy state. Provision of 13-Carbon labeled medium-chain FA (octanoate), long-chain free FAs (LCFAs), and lactate into systemic circulation showed that ECMO promoted relative increases in myocardial LCFA oxidation while inhibiting lactate oxidation. Loading of these labeled substrates at high dose into the left coronary artery demonstrated metabolic flexibility as the heart preferentially oxidized octanoate. ECMO preserved this octanoate metabolic response, but also promoted LCFA oxidation and inhibited lactate utilization. Rapid upregulation of pyruvate dehydrogenase kinase-4 (PDK4) protein appeared to participate in this metabolic shift during ECMO. ECMO also increased relative flux from lactate to alanine further supporting the role for pyruvate dehydrogenase inhibition by PDK4. High dose substrate loading during ECMO also elevated the myocardial energy state indexed by phosphocreatine to ATP ratio. ECMO promotes LCFA oxidation in immature hearts, while maintaining myocardial energy state. These data support the appropriateness of FA provision during ECMO support for the immature heart.

Determination of leelamine in mouse plasma by LC–MS/MS and its pharmacokinetics

Leelamine may be applicable to treat diabetes and is known to inhibit pyruvate dehydrogenase kinase 4. In this study, we developed and validated a quantification method using liquid chromatography (LC) coupled with tandem mass spectrometry analysis, which was applied to a pharmacokinetic investigation in mouse plasma. Leelamine transition ions in multiple reaction-monitoring modes using positive ionization were observed at m/z 286.4 to m/z 173.2. LC was performed using an ACE 5 C18 column, and a mixture of acetonitrile and water containing 0.1% formic acid was used as the mobile phase at a flow rate of 0.22mL/min. Leelamine and the internal standard (reserpine) had retention times of 4.1 and 3.9min, respectively. Acceptable linearity (r(2)=0.995) was observed over the concentration range of 10-3000ng/mL, with a lower limit of quantification of 10ng/mL in mouse plasma. The intra-day and inter-day accuracy and precision were less than 15%, which was sufficient for quality-control purposes. This method was used to determine leelamine concentrations in mouse plasma and showed that the oral bioavailability of leelamine was 7.6%.

A first-in-human phase I trial of AR-12, a PDK-1 inhibitor, in patients with advanced solid tumors.

2608 Background: AR-12 (OSU-03012) is an oral celecoxib analogue lacking COX-2 inhibitory activity that inhibits pyruvate dehydrogenase kinase isoenzyme 1 (PDK-1), AKT and impacts the endoplastic reticulum stress pathway. Preclinical studies indicate antitumor activity of AR-12 in various models and enhanced activity in combination. We completed a first in human clinical trial to determine its safety and tolerability, maximum tolerated dose (MTD) and recommended phase II dose (RD). Secondary objectives included assessment of tumor response, pharmacokinetics (PK) and pharmacodynamics (PD) including food effect. Methods: Patients (pts) with advanced solid tumors, ECOG PS 0-1, and adequate organ function were recruited in a modified 3+3 dose-escalation study. Pts received a run-in dose of AR-12 to analyze PK-PD and food effect, followed by continuous daily (QD) dosing in 28-day cycles. A twice daily (BID) cohort was initiated based on safety data. PD analysis was performed in platelet-rich plasma (PRP) and paired tumor biopsies when feasible. Results: 35 pts received at least one dose of study drug; 30 were evaluable for dose limiting toxicities (DLT) at dose ranges 100-3200mg QD and 800-1600mg BID. No DLT were observed in the QD cohort; DLT in the BID cohort are listed in table 1. Drug-related events (NCI-CTCAE v3) included rash (G2-2pts; G3-1pt), fatigue (G2-2pts; G3-4pts), nausea (G2-7pts; G3-1pt) and bloating (G2-1pt). Cmax after single dose was dose-proportional but high PK variability was observed, likely due to inadequate disintegration and dissolution of the formulation in the stomach. At RD, partial GSK3ß inhibition in PRP after 4 hours suggests AKT-pathway modulation. Best response (RECIST v1.0) was stable disease &gt;6 cycles for 2 pts. Conclusions: The RD based on safety data is 800mg BID. Signs of pathway modulation were observed in concordance with the expected mechanism of action but were short-lasting. Considering limited drug absorption and PK variability, a new formulation of the drug will be developed to overcome these limitations. Clinical trial information: NCT00978523. [Table: see text]

La tumeur cancéreuse : un parasite métabolique ?

Cancer cells activate glycolysis, glutaminolysis and β-oxidation to promote their biosynthesis. The low activity of pyruvate kinase, reexpressed in its embryonic isoform PKM2, generates a bottleneck at the end of glycolysis, which reorients glucose catabolism towards formation of molecules implied in numerous synthesis: ribose for nucleic acids, glycerol for lipid synthesis, etc. However, a part of glucose is transformed in pyruvate, which also comes from aminoacids catabolism. Due to the inhibition of pyruvate dehydrogenase, pyruvate is preferentially transformed into lactate, either in the presence of oxygen (Warburg effect). Lactate dehydrogenase reaction furnishes lactic acid, which acidifies the tumoral microenvironment, a process which favors the cellular growth and regenerates NAD+, a crucial cofactor for the functioning of various metabolic pathways (glycolysis, DNA synthesis and repair…). Cancer cells consume a lot of glutamine, which replenish Krebs cycle (coupled with ATP production), and/or furnishes aspartate for nucleotides synthesis. This particular metabolism is sustained by activation of oncogenes (Myc, AKT, etc.) and suppressors inactivation (P53, PTEN…). Like a parasite, cells draw on reserves of the host to supply their own biosynthesis, while they secrete waste products (NO, polyamines, ammonia, lactate…) that promote cellular growth. A “symbiotic” cooperation could be established between tumor cells themselves, and/or with environmental cells, to maximize ATP production in relation with resources and oxygen concentration.

Abstract 1852: Pyruvate dehydrogenase kinase expression and metabolic changes following dichloroacetate exposure in anoxia in human colorectal cancer cells.

Abstract Introduction: While glycolysis is a suboptimal metabolic strategy used by cells under hypoxic conditions, many cancer cells preferentially utilize glycolysis for energy production in the presence of abundant oxygen, a phenomenon known as the “Warburg Effect”. Dichloroacetate (DCA) is a small molecule metabolic modulator that shifts cellular metabolism to glucose oxidation by inhibition of pyruvate dehydrogenase kinase (PDK), an enzymatic inhibitor of pyruvate dehydrogenase (PDH). Furthermore, DCA has been shown to induce apoptosis in cancer but not normal cells. Our previous work showed that some human colorectal cancer (CRC) cells are protected from anoxia-induced apoptosis upon exposure to DCA, through as yet unclear mechanisms. Hypothesis: It is hypothesized that differential expression of PDK isoforms will correlate with the ability of different cancer cells to withstand the apoptotic effects of DCA in anoxia. Methods: SW480, LS174T (CRC) and IEC-18 (normal intestinal epithelial) cell lines were exposed to 10 mM DCA in either normoxic (20% O2) or anoxic (&amp;lt; 0.1% O2) conditions for 24 hours. Following treatment, expression of different PDK isoforms was determined through qRT-PCR and western blotting. Phosphorylation of PDH at Ser293 and Ser300 was assessed through western blotting. Glucose consumption and lactate production was determined using a colorimetric-based assay. Changes in mitochondrial function were quantified through Mitotracker staining and subsequent flow cytometry. Cell viability was assessed using the neutral red assay. Results: In all three cell lines: A) PDK isoforms 1 and 3 are highly expressed relative to isoforms 2 and 4, B) DCA and/or anoxic treatment induced a greater effect on PDH phosphorylation at Ser300 than Ser293, and C) DCA had minimal effect on glucose consumption in either normoxia or anoxia. Conclusions: Altered PDK expression and PDH activation may not fully explain the differences in resistance to DCA-induced apoptosis observed in human CRC cells. Investigating the mechanisms by which certain cancer cells are protected from DCA-induced apoptosis will lead to a better understanding of cancer metabolism and thus provide better therapeutic opportunities. Citation Format: Nelson Ho, Brenda L. Coomber. Pyruvate dehydrogenase kinase expression and metabolic changes following dichloroacetate exposure in anoxia in human colorectal cancer cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1852. doi:10.1158/1538-7445.AM2013-1852

Abstract 1857: Dichloroacetate (DCA), pyruvate dehydrogenase kinase (PDK) inhibitor, enhances the cytotoxic effect induced by metformin .

Abstract It has been recently reported that metformin, widely used as an antidiabetic drug, reduces risk of cancer development in human and animals based on its inhibitory effects observed in the several cancer cells and mouse tumor models. Metformin shows anti-tumor activity indirectly by enhancing insulin sensitivity and decreasing the level of insulin and IGF in serum. And it was also reported that metformin has direct anti-tumor activity through AMPK activation and mTOR inhibition. We also observed that metformin induces cytotoxicity in several different types of cancer cell lines. However when metformin was treated in high glucose condition, cytotoxic effect of metformin was significantly reduced and AMPK activation and mTOR inhibition were not observed. Metformin increased glycolysis by inhibiting mitochondrial respiratory complex I activity weakly and also inhibiting pyruvate dehydrogenase activity more significantly. So cytotoxic effect induced by metformin was dependent on glucose availability. Significant mitochondrial ROS production was observed in metformin treated cancer cells. NADPHs are produced by enhanced glycolysis through the pentose phosphate pathway. Since reducing power of NADPH is important for protection from ROS induced damage, we hypothesized that enhanced glycolysis by inhibition of PDH activity observed in metformin treated cancer cells is a protective role from metformin induced ROS injury. So when PDH activity was enhance by dichloroacetate (DCA), pyruvate dehydrogenase kinase (PDK) inhibitor, ROS production was more increased and resulted in significant cell death. Citation Format: Yong Won Choi, In Kyoung Lim. Dichloroacetate (DCA), pyruvate dehydrogenase kinase (PDK) inhibitor, enhances the cytotoxic effect induced by metformin . [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1857. doi:10.1158/1538-7445.AM2013-1857

Adaptation of the Heart to High‐Dietary Fat: Rapid Inhibition Of Pyruvate Dehydrogenase

Cardiac function depends on the ability to switch between fatty acid and glucose oxidation for energy production in response to changes in substrate availability and energetic stress. In obese and diabetic individuals, increased reliance on fatty acids and reduced metabolic flexibility are thought to contribute to the development of cardiovascular disease. Mechanisms by which cardiac mitochondria contribute to diet‐induced metabolic inflexibility were investigated. Mice were fed a high fat or control diet for varying durations. Cardiac mitochondria isolated from mice fed a high fat diet displayed a diminished ability to utilize the glycolytically derived substrate pyruvate. This was the consequence of pyruvate dehydrogenase (PDH) inhibition through a selective increase in PDH kinase 4 expression. This response was rapid, occurring within 1 d on the high fat diet and persisted for at least 20 wks. Strikingly, PDK4 content was rapidly diminished and PDH inhibition relieved upon removal of the mice from the high fat diet. While PDH was activated by in vivo epinephrine stimulation following high fat feeding, the enzyme did not reach the same level of activation as the control. The rapid nature of this response suggests that mechanisms are in place to coordinately regulate cardiac glucose and fatty acid utilization, but may affect the ability of the heart to respond to physiological stress.

Metabolic flexibility and carnitine flux: The role of carnitine acyltransferase in glucose homeostasis

Metabolic flexibility and carnitine flux: The role of carnitine acyltransferase in glucose homeostasis

Pyruvate dehydrogenase kinase as a potential therapeutic target for malignant gliomas.

Metabolic aberrations in the form of altered flux through key metabolic pathways are the major hallmarks of several life-threatening malignancies including malignant gliomas. These adaptations play an important role in the enhancement of the survival and proliferation of gliomas at the expense of the surrounding normal/healthy tissues. Recent studies in the field of neurooncology have directly targeted the altered metabolic pathways of malignant tumor cells for the development of anti-cancer drugs. Aerobic glycolysis due to elevated production of lactate from pyruvate regardless of oxygen availability is a common metabolic alteration in most malignancies. Aerobic glycolysis offers survival advantages in addition to generating substrates such as fatty acids, amino acids and nucleotides required for the rapid proliferation of cells. This review outlines the role of pyruvate dehydrogenase kinase (PDK) in gliomas as an inhibitor of pyruvate dehydrogenase that catalyzes the oxidative decarboxylation of pyruvate. An in-depth investigation on the key metabolic enzyme PDK may provide a novel therapeutic approach for the treatment of malignant gliomas.

Metabolism and Bioenergetics in the Right Ventricle and Pulmonary Vasculature in Pulmonary Hypertension

Pulmonary arterial hypertension (PAH) is a syndrome in which pulmonary vascular cross sectional area and compliance are reduced by vasoconstriction, vascular remodeling, and inflammation. Vascular remodeling results in part from increased proliferation and impaired apoptosis of vascular cells. The resulting increase in afterload promotes right ventricular hypertrophy (RVH) and RV failure. Recently identified mitochondrial-metabolic abnormalities in PAH, notably pyruvate dehydrogenase kinase-mediated inhibition of pyruvate dehydrogenase (PDH), result in aerobic glycolysis in both the lung vasculature and RV. This glycolytic shift has diagnostic importance since it is detectable early in experimental PAH by increased lung and RV uptake of 18F-fluorodeoxyglucose on positron emission tomography. The metabolic shift also has pathophysiologic and therapeutic relevance. In RV myocytes, the glycolytic switch reduces contractility while in the vasculature it renders cells hyperproliferative and apoptosis-resistant. Reactivation of PDH can be achieved directly by PDK inhibition (using dichloroacetate), or indirectly via activating the Randle cycle, using inhibitors of fatty acid oxidation (FAO), trimetazidine and ranolazine. In experimental PAH and RVH, PDK inhibition increases glucose oxidation, enhances RV function, regresses pulmonary vascular disease by reducing proliferation and enhancing apoptosis, and restores cardiac repolarization. FAO inhibition increases RV glucose oxidation and RV function in experimental RVH. The trigger for metabolic remodeling in the RV and lung differ. In the RV, metabolic remodeling is likely triggered by ischemia (due to microvascular rarefaction and/or reduced coronary perfusion pressure). In the vasculature, metabolic changes result from redox-mediated activation of transcription factors, including hypoxia-inducible factor 1α, as a consequence of epigenetic silencing of SOD2 and/or changes in mitochondrial fission/fusion. Randomized controlled trials are required to assess whether the benefits of enhancing glucose oxidation are realized in patients with PAH.

Pyruvate dehydrogenase kinase as a novel therapeutic target in oncology

Current drug development in oncology is non-selective as it typically focuses on pathways essential for the survival of all dividing cells. The unique metabolic profile of cancer, which is characterized by increased glycolysis and suppressed mitochondrial glucose oxidation (GO) provides cancer cells with a proliferative advantage, conducive with apoptosis resistance and even increased angiogenesis. Recent evidence suggests that targeting the cancer-specific metabolic and mitochondrial remodeling may offer selectivity in cancer treatment. Pyruvate dehydrogenase kinase (PDK) is a mitochondrial enzyme that is activated in a variety of cancers and results in the selective inhibition of pyruvate dehydrogenase, a complex of enzymes that converts cytosolic pyruvate to mitochondrial acetyl-CoA, the substrate for the Krebs’ cycle. Inhibition of PDK with either small interfering RNAs or the orphan drug dichloroacetate (DCA) shifts the metabolism of cancer cells from glycolysis to GO and reverses the suppression of mitochondria-dependent apoptosis. In addition, this therapeutic strategy increases the production of diffusible Krebs’ cycle intermediates and mitochondria-derived reactive oxygen species, activating p53 or inhibiting pro-proliferative and pro-angiogenic transcription factors like nuclear factor of activated T cells and hypoxia-inducible factor 1α. These effects result in decreased tumor growth and angiogenesis in a variety of cancers with high selectivity. In a small but mechanistic clinical trial in patients with glioblastoma, a highly aggressive and vascular form of brain cancer, DCA decreased tumor angiogenesis and tumor growth, suggesting that metabolic-targeting therapies can be translated directly to patients. More recently, the M2 isoform of pyruvate kinase (PKM2), which is highly expressed in cancer, is associated with suppressed mitochondrial function. Similar to DCA, activation of PKM2 in many cancers results in increased mitochondrial function and decreased tumor growth. Therefore, reversing the mitochondrial suppression with metabolic-modulating drugs, like PDK inhibitors or PKM2 activators holds promise in the rapidly expanding field of metabolic oncology.

Ginsenoside Rh1 Eliminates the Cytoprotective Phenotype of Human Immunodeficiency Virus Type 1-Transduced Human Macrophages by Inhibiting the Phosphorylation of Pyruvate Dehydrogenase Lipoamide Kinase Isozyme 1

Red ginseng (the steamed root of Panax ginseng C.A. MEYER, Araliaceae), which contains ginsenosides as its main constituents, is frequently used to treat tumor, inflammation, diabetes, stress and acquired immunodeficiency syndrome in Asian countries. Of these ginsenosides, only protopanaxadiol compound K has been reported to abolish the cytoprotective phenotype of human immunodeficiency virus type 1 (HIV-1)-transfected human macrophages. Here, we investigated the anti-cytoprotective effect of protopanaxatriol ginsenoside Rh1 on Tat-expressing cytoprotective CHME5 cells and D3-infected human primary macrophages. Treatment with ginsenoside Rh1 in the presence of lipopolysaccharide/cycloheximide (LPS/CHX) potently abolished the cytoprotective phenotype of Tat-transduced CHME5 cells as well as D3-infected human primary macrophages. Ginsenoside Rh1 significantly inhibited LPS/CHX-induced Akt phosphorylation, as well as mammalian target of rapamycin and Bcl-2-associated death promoter activation in both cell types. Furthermore, ginsenoside Rh1 inhibited pyruvate dehydrogenase lipoamide kinase isozyme 1 (PDK-1) phosphorylation. However, ginsenoside Rh1 did not inhibit phosphoinositide 3-kinase phosphorylation. Ginsenosides Rh1 in the presence of miltefosine (5 µM) additively increased the anti-cytoprotective activity against HIV-1 Tat-expressing macrophages. On the basis of these findings, we propose that ginsenoside Rh1 could possibly eliminate HIV-1 infected macrophages by inhibiting the PDK1/Akt pathway.

S-Allyl cysteine improves nonalcoholic fatty liver disease in type 2 diabetes Otsuka Long-Evans Tokushima Fatty rats via regulation of hepatic lipogenesis and glucose metabolism

It is important to prevent and improve diabetes mellitus and its complications in a safe and low-cost manner. S-Allyl cysteine, an aged garlic extract with antioxidant activity, was investigated to determine whether S-allyl cysteine can improve type 2 diabetes in Otsuka Long-Evans Tokushima Fatty rats with nonalcoholic fatty liver disease. Male Otsuka Long-Evans Tokushima Fatty rats and age-matched Long-Evans Tokushima Otsuka rats were used and were divided into two groups at 29 weeks of age. S-Allyl cysteine (0.45% diet) was administered to rats for 13 weeks. Rats were killed at 43 weeks of age, and detailed analyses were performed. S-Allyl cysteine improved hemoglobinA1c, blood glucose, triglyceride, and low-density lipoprotein cholesterol levels. Furthermore, S-allyl cysteine normalized plasma insulin levels. S-Allyl cysteine activated the mRNA and protein expression of both peroxisome proliferator-activated receptor α and γ, as well as inhibiting pyruvate dehydrogenase kinase 4 in Otsuka Long-Evans Tokushima Fatty rat liver. Sterol regulatory element-binding protein 1c and forkhead box O1 proteins were normalized by S-allyl cysteine in Otsuka Long-Evans Tokushima Fatty rat liver. In conclusions, these findings support the hypothesis that S-allyl cysteine has diabetic and nonalcoholic fatty liver disease therapeutic potential as a potent regulating agent against lipogenesis and glucose metabolism.

Weed control efficacy and winter wheat safety of a novel herbicide HW02

HW02, a pyruvate dehydrogenase inhibitor, is a newly developed herbicide for broadleaf weed control in wheat, maize and turf in China. Greenhouse and field experiments were conducted to evaluate its efficacy against weeds and safety to winter wheat. In the greenhouse experiment, this herbicide had higher activities than 2,4-D against Descurainia sophia (L.) Schur., Amaranthus retroflexus L., Capsella bursa-pastoris (L.) Medic., and Malachium aquaticum (L.) Fries.. When it was applied at late tillering stage of winter wheat in spring, the herbicide provided weed biomass reduction of 98%–100% at the rates 225–525 g a.i. ha−1 and was safe to the crop at the rate of up to 900 g a.i. ha−1. These results showed HW02 could be an alternative herbicide for resistant weed management because its mode of action is different from herbicides presently used.