Effects of Chlorinated Acetates on the Glutathione Metabolism and on Glycolysis of Cultured Astrocytes

Early TCR Signaling Induces Rapid Aerobic Glycolysis Enabling Distinct Acute T Cell Effector Functions

To fulfill bioenergetic demands of activation, T cells perform aerobic glycolysis, a process common to highly proliferative cells in which glucose is fermented into lactate rather than oxidized in mitochondria. However, the signaling events that initiate aerobic glycolysis in T cells remain unclear. We show T cell activation rapidly induces glycolysis independent of transcription, translation, CD28, and Akt and not involving increased glucose uptake or activity of glycolytic enzymes. Rather, TCR signaling promotes activation of pyruvate dehydrogenase kinase 1 (PDHK1), inhibiting mitochondrial import of pyruvate and facilitating breakdown into lactate. Inhibition of PDHK1 reveals this switch is required acutely for cytokine synthesis but dispensable for cytotoxicity. Functionally, cytokine synthesis is modulated via lactate dehydrogenase, which represses cytokine mRNA translation when aerobic glycolysis is disengaged. Our data provide mechanistic insight to metabolic contribution to effector T cell function and suggest that T cell function may be finely tuned through modulation of glycolytic activity.

Metabolism and inflammation: implications for traumatic brain injury therapeutics

INTRODUCTION

Traumatic Brain Injury (TBI) is a leading cause of death and disability in young people, affecting 69 million people annually, worldwide. The initial trauma disrupts brain homeostasis resulting in metabolic dysfunction and an inflammatory cascade, which can then promote further neurodegenerative effects for months or years, as a 'secondary' injury. Effective targeting of the cerebral inflammatory system is challenging due to its complex, pleiotropic nature. Cell metabolism plays a key role in many diseases, and increased disturbance in the TBI metabolic state is associated with poorer patient outcomes. Investigating critical metabolic pathways, and their links to inflammation, can potentially identify supplements which alter the brain's long-term response to TBI and improve recovery. Areas covered: The authors provide an overview of literature on metabolism and inflammation following TBI, and from relevant pre-clinical and clinical studies, propose therapeutic strategies. Expert opinion: There is still no specific active drug treatment for TBI. Changes in metabolic and inflammatory states have been reported after TBI and appear linked. Understanding more about abnormal cerebral metabolism following TBI, and its relationship with cerebral inflammation, will provide essential information for designing therapies, with implications for neurocritical care and for alleviating long-term disability and neurodegeneration in post-TBI patients.

Dichloroacetate is an antimetabolite that antagonizes acetate and deprives cancer cells from its benefits: A novel evidence-based medical hypothesis

Dichloroacetate (DCA) is a promising safe anticancer drug that cured a patient with chemoresistant non-Hodgkin's lymphoma and treated lactic acidosis effectively. The well-known mechanism of DCA action is through stimulating Krebs cycle (stimulating pyruvate dehydrogenase via inhibiting pyruvate dehydrogenase kinase). This prevents lactate formation (Warburg effect) depriving cancer cells of lactate-based benefits e.g. angiogenesis, chemoresistance and radioresistance. Here, we introduce novel evidence-based hypotheses to explain DCA-induced anticancer effects. On pharmacological and biochemical bases, we hypothesize that DCA is a structural antagonist of acetate competing with it for target enzymes and biological reactions. We hypothesize that DCA exerts its anticancer effects via depriving cancer of acetate benefits. We hypothesize also that acetate is an antidote of DCA capable of treating DCA toxicity. Many reports support our hypotheses. Acetate is vital for cancer cells (tumors depend on acetate) and DCA is structurally similar to acetate. DCA exerts opposite effects to acetate. Acetate caused a decrease in serum potassium, phosphorus and glucose, and an increase in serum lactate, citrate, free fatty acids and ketone bodies (serum acetoacetate and beta-hydroxybutyrate levels). Acetate decreased the proportion of active (dephosphorylated) pyruvate dehydrogenase in perfused rat heart. DCA produced quite opposite effects. Intravenous infusion of acetate produced metabolic alkalemia while DCA caused minimal effects on acid-base status. Acetate is important for cancer cells metabolism and survival as elevated acetate can drive resistance to targeted cancer treatments. Acetate is required for epidermal growth factor receptor vIII mutation in lethal brain tumors. Experimentally, DCA inhibited acetate oxidation in hearts of normal rats and reversed inhibitory effects of acetate on the oxidation of glucose. During presence of DCA with no glucose in heart perfusions with [1-14C]acetate, DCA decreased the specific radioactivity of acetyl CoA and its product citrate. This proves our hypotheses that DCA is an antimetabolite that antagonizes acetate for vital reactions in cancer cells. Acetate may be used as an antidote to combat DCA toxicity.

The antidiabetic drug metformin decreases mitochondrial respiration and tricarboxylic acid cycle activity in cultured primary rat astrocytes

Metformin is an antidiabetic drug that is used daily by millions of patients worldwide. Metformin is able to cross the blood-brain barrier and has recently been shown to increase glucose consumption and lactate release in cultured astrocytes. However, potential effects of metformin on mitochondrial tricarboxylic acid (TCA) cycle metabolism in astrocytes are unknown. We investigated this by mapping ¹³ C labeling in TCA cycle intermediates and corresponding amino acids after incubation of primary rat astrocytes with [U-¹³ C]glucose. The presence of metformin did not compromise the viability of cultured astrocytes during 4 hr of incubation, but almost doubled cellular glucose consumption and lactate release. Compared with control cells, the presence of metformin dramatically lowered the molecular ¹³ C carbon labeling (MCL) of the cellular TCA cycle intermediates citrate, α-ketoglutarate, succinate, fumarate, and malate, as well as the MCL of the TCA cycle intermediate-derived amino acids glutamate, glutamine, and aspartate. In addition to the total molecular ¹³ C labeling, analysis of the individual isotopomers of TCA cycle intermediates confirmed a severe decline in labeling and a significant lowering in TCA cycling ratio in metformin-treated astrocytes. Finally, the oxygen consumption of mitochondria isolated from metformin-treated astrocytes was drastically reduced in the presence of complex I substrates, but not of complex II substrates. These data demonstrate that exposure to metformin strongly impairs complex I-mediated mitochondrial respiration in astrocytes, which is likely to cause the observed decrease in labeling of mitochondrial TCA cycle intermediates and the stimulation of glycolytic lactate production. © 2017 Wiley Periodicals, Inc.

The Antidiabetic Drug Metformin Stimulates Glycolytic Lactate Production in Cultured Primary Rat Astrocytes

Metformin is the most frequently used drug for the treatment of type 2 diabetes in humans. However, only little is known about effects of metformin on brain metabolism. To investigate potential metabolic consequences of an exposure of brain cells to metformin, we incubated rat astrocyte-rich primary cultures with this compound. Metformin in concentrations of up to 30 mM did not acutely compromise the viability of astrocytes, but caused a time- and concentration-dependent increase in cellular glucose consumption and lactate production. For acute incubations in the hour range, the presence of 10 mM metformin doubled the glycolytic flux, while already 1 mM metformin doubled glycolytic flux during incubation for 24 h. In addition to metformin, also other guanidino compounds increased astrocytic lactate production. After 4 h of incubation, half-maximal stimulation of glycolysis was observed for metformin, guanidine and phenformin at concentrations of around 3 mM, 3 mM and 30 µM, respectively. The acute stimulation of glycolytic lactate production by metformin was persistent after removal of extracellular metformin and was also observed, if glucose was absent from the incubation medium or replaced by other hexoses. The metformin-induced stimulation of glycolytic flux was not prevented by compound C, an inhibitor of AMP-dependent protein kinase, nor was it additive to the stimulation of glycolytic flux caused by respiratory chain inhibitors. These data demonstrate that the antidiabetic drug metformin has the potential to strongly activate glycolytic lactate production in brain astrocytes.

Glutathione-Dependent Detoxification Processes in Astrocytes

Astrocytes have a pivotal role in brain as partners of neurons in homeostatic and metabolic processes. Astrocytes also protect other types of brain cells against the toxicity of reactive oxygen species and are considered as first line of defence against the toxic potential of xenobiotics. A key component in many of the astrocytic detoxification processes is the tripeptide glutathione (GSH) which serves as electron donor in the GSH peroxidase-catalyzed reduction of peroxides. In addition, GSH is substrate in the detoxification of xenobiotics and endogenous compounds by GSH-S-transferases which generate GSH conjugates that are efficiently exported from the cells by multidrug resistance proteins. Moreover, GSH reacts with the reactive endogenous carbonyls methylglyoxal and formaldehyde to intermediates which are substrates of detoxifying enzymes. In this article we will review the current knowledge on the GSH metabolism of astrocytes with a special emphasis on GSH-dependent detoxification processes.

Chloroacetic acid triggers apoptosis in neuronal cells via a reactive oxygen species-induced endoplasmic reticulum stress signaling pathway

Chloroacetic acid (CA), a chlorinated analog of acetic acid and an environmental toxin that is more toxic than acetic, dichloroacetic, or trichloroacetic acids, is widely used in chemical industries. Furthermore, CA has been found to be the major disinfection by-products (DBPs) of drinking water. CA has been reported to be highly corrosive and to induce severe tissue injuries (including nervous system) that lead to death in mammals. However, the effects and underlying mechanisms of CA-induced neurotoxicity remain unknown. In the present study, we found that CA (0.5-2.0 mM) significantly increased LDH release, decreased the number of viable cells (cytotoxicity) and induced apoptotic events (including: increases in the numbers of apoptotic cells, the membrane externalization of phosphatidylserine (PS), and caspase-3/-7 activity) in Neuro-2a cells. CA (1.5 mM; the approximate to LD50) also triggered ER stress, which was identified by monitoring several key molecules that are involved in the unfolded protein responses (including the increase in the expressions of p-PERK, p-IRE-1, p-eIF2α, ATF-4, ATF-6, CHOP, XBP-1, GRP 78, GRP 94, and caspase-12) and calpain activity. Transfection of GRP 78- and GRP 94-specific si-RNA effectively abrogated CA-induced cytotoxicity, caspase-3/-7 and caspase-12 activity, and GRP 78 and GRP 94 expression in Neuro-2a cells. Additionally, pretreatment with 2.5 mM N-acetylcysteine (NAC; a glutathione (GSH) precursor) dramatically suppressed the increase in lipid peroxidation, cytotoxicity, apoptotic events, calpain and caspase-12 activity, and ER stress-related molecules in CA-exposed cells. Taken together, these results suggest that the higher concentration of CA exerts its cytotoxic effects in neuronal cells by triggering apoptosis via a ROS-induced ER stress signaling pathway.

Aspects of astrocyte energy metabolism, amino acid neurotransmitter homoeostasis and metabolic compartmentation

Astrocytes are key players in brain function; they are intimately involved in neuronal signalling processes and their metabolism is tightly coupled to that of neurons. In the present review, we will be concerned with a discussion of aspects of astrocyte metabolism, including energy-generating pathways and amino acid homoeostasis. A discussion of the impact that uptake of neurotransmitter glutamate may have on these pathways is included along with a section on metabolic compartmentation.

Dichloroacetate inhibits neuroblastoma growth by specifically acting against malignant undifferentiated cells

The small, water soluble molecule Dichloroacetate (DCA) is recently arousing lively interests in the field of cancer therapy for it has been shown to be able to inhibit the growth of human tumors acting specifically on the mitochondria of cancer cells without perturbing the physiology of nonmalignant cells. Neuroblastoma was one of the tumor types on which DCA was considered ineffective as it is composed of cells with few recognized mitochondrial anomalies. Neuroblastoma, however, is composed of different cell types in terms of metabolism, phenotype and malignant potential. Despite the above prediction, in this work, we show that (i) DCA exhibits an unexpected anticancer effect on NB tumor cells and (ii) this effect is selectively directed to very malignant NB cells, whereas the more differentiated/less malignant NB cells are refractory to DCA treatment. This result supports the need of a detailed investigation of DCA anticancer properties against this tumor type with the final aim of its possible use as therapeutic agent.

Copper accelerates glycolytic flux in cultured astrocytes

Astrocyte-rich primary cultures were used to investigate the consequences of a copper exposure on the glucose metabolism of astrocytes. After application of CuCl(2) (30 μM) the specific cellular copper content increased from initial 1.5 ± 0.2 nmol/mg to a steady state level of 7.9 ± 0.9 nmol/mg within about 12 h. The copper accumulation was accompanied by a significant increase in the extracellular lactate concentration. The stimulating effect of copper on the lactate production remained after removal of extracellular copper. Copper treatment accelerated the rates of both glucose consumption and lactate production by about 60%. The copper induced acceleration of glycolytic flux was prevented by inhibition of protein synthesis, and additive to the stimulation of glycolysis observed for inhibitors of respiration or prolyl hydroxylases. A copper induced stimulation of glycolytic flux in astrocytes could have severe consequences for the glucose metabolism of the brain in conditions of copper overload.