Krebs Cycle Metabolites Research Articles

Prospective serum metabolomic profile of prostate cancer by size and extent of primary tumor.

Two recent investigations found serum lipid and energy metabolites related to aggressive prostate cancer up to 20 years prior to diagnosis. To elucidate whether those metabolomic profiles represent etiologic or tumor biomarker signals, we prospectively examined serum metabolites of prostate cancer cases by size and extent of primary tumors in a nested case-control analysis in the ATBC Study cohort that compared cases diagnosed with T2 (n = 71), T3 (n = 51), or T4 (n = 15) disease to controls (n = 200). Time from fasting serum collection to diagnosis averaged 10 years (range 1–20). LC/MS-GC/MS identified 625 known compounds, and logistic regression estimated odds ratios (ORs) associated with one-standard deviation differences in log-metabolites. N-acetyl-3-methylhistidine, 3-methylhistidine and 2′-deoxyuridine were elevated in men with T2 cancers compared to controls (ORs = 1.38–1.79; 0.0002 ≤ p ≤ 0.01). By contrast, four lipid metabolites were inversely associated with T3 tumors: oleoyl-linoleoyl-glycerophosphoinositol (GPI), palmitoyl-linoleoyl-GPI, cholate, and inositol 1-phosphate (ORs = 0.49–0.60; 0.000017 ≤ p ≤ 0.003). Secondary bile acid lipids, sex steroids and caffeine-related xanthine metabolites were elevated, while two Krebs cycle metabolites were decreased, in men diagnosed with T4 cancers. Men with T2, T3, and T4 prostate cancer primaries exhibit qualitatively different metabolite profiles years in advance of diagnosis that may represent etiologic factors, molecular patterns reflective of distinct primary tumors, or a combination of both.

Inhibition of homologous phosphorolytic ribonucleases by citrate may represent an evolutionarily conserved communicative link between RNA degradation and central metabolism.

Ribonucleases play essential roles in all aspects of RNA metabolism, including the coordination of post-transcriptional gene regulation that allows organisms to respond to internal changes and environmental stimuli. However, as inherently destructive enzymes, their activity must be carefully controlled. Recent research exemplifies the repertoire of regulatory strategies employed by ribonucleases. The activity of the phosphorolytic exoribonuclease, polynucleotide phosphorylase (PNPase), has previously been shown to be modulated by the Krebs cycle metabolite citrate in Escherichia coli. Here, we provide evidence for the existence of citrate-mediated inhibition of ribonucleases in all three domains of life. In silico molecular docking studies predict that citrate will bind not only to bacterial PNPases from E. coli and Streptomyces antibioticus, but also PNPase from human mitochondria and the structurally and functionally related archaeal exosome complex from Sulfolobus solfataricus. Critically, we show experimentally that citrate also inhibits the exoribonuclease activity of bacterial, eukaryotic and archaeal PNPase homologues in vitro. Furthermore, bioinformatics data, showing key citrate-binding motifs conserved across a broad range of PNPase homologues, suggests that this regulatory mechanism may be widespread. Overall, our data highlight a communicative link between ribonuclease activity and central metabolism that may have been conserved through the course of evolution.

Abstract LB-308: Effects of the IDH1 R132H mutation on redox status and metabolism are cell type dependent but independent from D-2-hydroxyglutarate accumulation

Abstract IDH1 R132H mutations are considered to play a key role in the development of low grade gliomas and therefrom derived secondary glioblastomas (GBM). Wild type IDH1 converts isocitrate to α-ketoglutarate (a-KG) while reducing NADP+. IDH1R132H has a neomorphic enzymatic function using a-KG to generate high amounts of the oncometabolite D-2-hydroxyglutarate (D-2-HG). While the effects of D-2-HG have been subject to intense research, D-2-HG independent effects of IDH1R132H on energy homeostasis and redox status are not well studied. Here we demonstrate that IDH1R132H transduction but not D-2-HG alone leads to significantly decreased Krebs cycle metabolite concentrations and proliferation in U87 and the primary GBM cell line HT7606 as well as in immortalized astrocytes SVGp12. Furthermore, IDH1R132H mutation, but not D-2-HG treatment, resulted in a significant drop in NADPH levels in tumor cells (U87 and HT7606), whereas immortalized astrocytes retained normal NADPH levels. Since NAPDH levels can be restored via the reaction of the NAD-kinase, we analyzed NAD levels and enzymes involved in NAD-synthesis in our cell lines. Indeed we found a significant drop of NAD levels and in the activity of the NAD-dependent enzyme sirtuin in IDH1R132H mutant U87 and HT7606 but not in NADPH stable SVGp12-IDH1R132H. Interestingly, there were marked differences in expression of NAD-synthesis enzymes between the different cell-lines. In particular, NAMPT-levels were much higher in U87 and HT7606 then in astrocytes (SVGp12) and significantly decreased in U87-IDH1R132H and HT7606-IDH1R132H. Importantly, we also found decreased levels of NAMPT in primary tumor tissues and patient derived glioma cell lines with IDH1 R132H compared to wild type gliomas. Altogether our results for the first time show that the IDH1 mutation directly affects energy homeostasis and redox status in a cell-type dependent manner. We hypothesize that this leads to a drop in NADPH and NAD-levels during malignant progression, resulting in a disadvantage for proliferating tumor cells. This is in line with the favorable prognosis and good response to chemo- and radiation therapy clinically observed in IDH-mutated gliomas. Our findings suggest that the impaired metabolism in IDH1-mutant tumors might be a promising target for future therapies. Citation Format: Evelin Schrock, Julia Biedermann, Khalil Abou-El-Ardat, Matthias Lehmann, Marina Conde, Mirko Peitzsch, Susan Richter, Ralf Wiedemuth, Matthias Meinhardt, William P. J. Leenders, Christel Herold-Mende, Graeme Eisenhofer, Simone P. Niclou, Leoni Kunz-Schughart, Achim Temme, Barbara Klink. Effects of the IDH1 R132H mutation on redox status and metabolism are cell type dependent but independent from D-2-hydroxyglutarate accumulation. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr LB-308.

Metabolic Modulation of Clear-cell Renal Cell Carcinoma with Dichloroacetate, an Inhibitor of Pyruvate Dehydrogenase Kinase

BackgroundClear-cell renal cell carcinoma (ccRCC) exhibits suppressed mitochondrial function and preferential use of glycolysis even in normoxia, promoting proliferation and suppressing apoptosis. ccRCC resistance to therapy is driven by constitutive hypoxia-inducible factor (HIF) expression due to genetic loss of von Hippel-Lindau factor. In addition to promoting angiogenesis, HIF suppresses mitochondrial function by inducing pyruvate dehydrogenase kinase (PDK), a gatekeeping enzyme for mitochondrial glucose oxidation. ObjectiveTo reverse mitochondrial suppression of ccRCC using the PDK inhibitor dichloroacetate (DCA). Design, setting, and participantsRadical nephrectomy specimens from patients with ccRCC were assessed for PDK expression. The 786-O ccRCC line and two animal models (chicken in ovo and murine xenografts) were used for mechanistic studies. Outcome measurements and statistical analysisMitochondrial function, proliferation, apoptosis, HIF transcriptional activity, angiogenesis, and tumor size were measured in vitro and in vivo. Independent-sample t-tests and analysis of variance were used for statistical analyses. ResultsPDK was elevated in 786-O cells and in ccRCC compared to normal kidney tissue from the same patient. DCA reactivated mitochondrial function (increased respiration, Krebs cycle metabolites such as α-ketoglutarate [cofactor of factor inhibiting HIF], and mitochondrial reactive oxygen species), increased p53 activity and apoptosis, and decreased proliferation in 786-O cells. DCA reduced HIF transcriptional activity in an FIH-dependent manner, inhibiting angiogenesis in vitro. DCA reduced tumor size and angiogenesis in vivo in both animal models. ConclusionsDCA can reverse the mitochondrial suppression of ccRCC and decrease HIF transcriptional activity, bypassing its constitutive expression. Its previous clinical use in humans makes it an attractive candidate for translation to ccRCC patients. Patient summaryWe show that an energy-boosting drug decreases tumor growth and tumor blood vessels in animals carrying human kidney cancer cells. This generic drug has been used in patients for other conditions and thus could be tested in kidney cancer that remains incurable.

Therapeutic potential of alpha-ketoglutarate against acetaminophen-induced hepatotoxicity in rats.

Objective:Alpha-ketoglutarate (α-KG) is a cellular intermediary metabolite of Krebs cycle, involved in energy metabolism, amino acid synthesis, and nitrogen transport. It is available over-the-counter and marketed as a nutritional supplement. There is a growing body of evidence to suggest that dietary α-KG has the potential to maintain cellular redox status and thus can protect various oxidative stress induced disease states. The aim of the present study was to investigate the hepatoprotective role of α-KG in acetaminophen (APAP) induced toxicity in rats.Materials and Methods:Animals were divided into three groups of six animals each. Group I (Vehicle control): Normal Saline, Group II (APAP): A single intraperitoneal injection of 0.6 g/kg, Group III (APAP + α-KG): APAP as in Group II with α-KG treatment at a dose of 2 g/kg, orally for 5 days. Then the levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), and alkaline phosphatase (ALP) with oxidative stress markers including malondialdehyde (MDA), reduced glutathione (GSH), superoxide dismutase (SOD), catalase (CAT), and histopathology were analyzed.Results:The results indicate that APAP caused significant elevations in ALT, AST, ALP, and MDA levels, while GSH, SOD, and CAT were significantly depleted while co-administration of α-KG showed a significant (P < 0.05) reduction in the severity of these damages. Histologically, the liver showed inflammation and necrosis after APAP treatment, which were significantly restored with co-administration of α-KG.Conclusion:These results indicate the possible therapeutic potential of α-KG in protecting liver damage by APAP in rats.

Trauma/hemorrhagic shock instigates aberrant metabolic flux through glycolytic pathways, as revealed by preliminary (13)C-glucose labeling metabolomics.

BackgroundMetabolic derangement is a key hallmark of major traumatic injury. The recent introduction of mass spectrometry-based metabolomics technologies in the field of trauma shed new light on metabolic aberrations in plasma that are triggered by trauma and hemorrhagic shock. Alteration in metabolites associated with catabolism, acidosis and hyperglycemia have been identified. However, the mechanisms underlying fluxes driving such metabolic adaptations remain elusive.MethodsA bolus of U-13C-glucose was injected in Sprague–Dawley rats at different time points. Plasma extracts were analyzed via ultra-high performance liquid chromatography-mass spectrometry to detect quantitative fluctuations in metabolite levels as well as to trace the distribution of heavy labeled carbon isotopologues.ResultsRats experiencing trauma did not show major plasma metabolic aberrations. However, trauma/hemorrhagic shock triggered severe metabolic derangement, resulting in increased glucose levels, lactate and carboxylic acid accumulation. Isotopologue distributions in late Krebs cycle metabolites (especially succinate) suggested a blockade at complex I and II of the electron transport chain, likely due to mitochondrial uncoupling. Urate increased after trauma and hemorrhage. Increased levels of unlabeled mannitol and citramalate, metabolites of potential bacterial origin, were also observed in trauma/hemorrhagic shock rats, but not trauma alone or controls.ConclusionsThese preliminary results are consistent with observations we have recently obtained in humans, and expand upon our early results on rodent models of trauma and hemorrhagic shock by providing the kinetics of glucose fluxes after trauma and hemorrhage. Despite the preliminary nature of this study, owing to the limited number of biological replicates, results highlight a role for shock, rather than trauma alone, in eliciting systemic metabolic aberrations. This study provides the foundation for tracing experiments in rat models of trauma. The goal is to improve our understanding of substrate specific metabolic derangements in trauma/hemorrhagic shock, so as to design resuscitative strategies tailored toward metabolic alterations and the severity of trauma.Electronic supplementary materialThe online version of this article (doi:10.1186/s12967-015-0612-z) contains supplementary material, which is available to authorized users.

BI-27 * ANALYSIS OF THE BIOCHEMICAL PROFILE OF LOW GRADE GLIOMA WITH DIFFERENT IDH1 MUTATION STATUS USING VIBRATIONAL SPECTROSCOPY

Mutations in human cytosolic isocitrate dehydrogenases 1 (IDH1) are a common feature of low grade gliomas (LGG) and cause profound changes of the metabolites of the Krebs cycle. Vibrational spectroscopy comprises label-free techniques that probe a sample's molecular composition. Therefore, we investigated the ability of fourier-transform infrared (FT-IR) spectroscopy to analyze the IDH1-mutation status in cell culture systems and human brain tumor samples. Cell lines (U87-MG, SVG p12 and the primary glioblastoma cell lines HT7606, HT12346 and HT12347) were transduced with either IDH1 wild-type or mutated IDH1. Clusteranalysis and principal-component-analysis were able to detect differences in the respective FT-IR spectral datasets in regions assigned to saccharides (1050 and 1120 cm−1) and proteins (1236, 1545 and 1651 cm−1). Brain tumor samples of human LGG were obtained during routine surgery and the IDH1 mutation status was determined by DNA sequencing (n = 17). Difference spectra (IDH1-mut vs. IDH1-wt) showed changes in the region around 1100 cm−1 which is attributed to saccharides. Additionally, amide I and amide II spectral bands (around 1550 and 1650 cm−1, respectively) were reduced in the IDH1-mut dataset whereas the band at 1740 cm−1 assigned to C = O stretching vibrations was more pronounced. Principal-component-analysis confirmed differences between the two groups based on spectral regions assigned to saccharides, proteins and to C = O stretching vibrations, as identified previously in the difference spectra. Supervised classification recognized relevant spectral regions at 974, 1005, 1038-1044, 1078-1082, 1267-1275, 1342, 1417-1421, 1479 cm−1 and was able to assign 16 of the 17 tumor samples to the correct group. On the basis of FT-IR spectroscopy samples of LGG carrying IDH1 mutations can be discerned from IDH1 wildtype tumors. Relevant spectral regions assigned to saccharides and C = O stretching vibrations can be explained by changes in the Krebs cycle and in particular by the accumulation of 2-hydroxyglutarate (rich in C = O bonds).

Abstract 1424: Enhanced pyruvate carboxylation is crucial to non-small cell lung cancer proliferation and anabolism

Abstract Proliferating cancer cells require an active Krebs cycle for generating anabolic precursors, in addition to energy production. Diversion of the Krebs cycle intermediates to meet anabolic demands cannot be sustained without anaplerosis. The two major anaplerotic pathways are the deamidation of glutamine to form glutamate catalyzed by glutaminase (GLS) or glutaminolysis, and the carboxylation of pyruvate to oxaloacetate by pyruvate carboxylase (PC). We determined the expression of PC and GLS proteins in fresh tumor tissue and paired adjacent benign tissue from 86 human NSCLC patients. PC was elevated (median 8-10 fold) in 94% of the tumor tissues, whereas GLS expression did not differ significantly between tumor and paired non tumorous lung tissue. Using 13C6 glucose as tracer and stable isotope-resolved metabolomics (SIRM), we also observed elevated PC activity in vivo in human patients with early stage NSCLC. To examine the importance of PC in the growth and survival of NSCLC, 5 NSCLC cell lines were transduced with a lentiviral vector containing an shRNA against PC. PC knockdown slowed proliferation, induced multinucleation, and reduced colony formation in soft agar. To validate attenuated PC activity and to profile the metabolic effect of PC knockdown, A549 cells were grown in 13C6 glucose or 13C5 glutamine and the incorporation of 13C into various metabolic pathways was measured by NMR and MS by SIRM. We found reduced entry of both glucose and glutamine carbon into the Krebs cycle metabolites, fatty acyl chains of lipids, and nucleotides, suggesting that both energy production and anabolic pathways were hindered and blocking the PC pathway was not compensated by GLS activity. In addition, glutathione biosynthesis and homeostasis were perturbed by PC suppression, leading to compromised anti-oxidation capacity. We further found that PC knockdown in A549 cells reduced their growth rate in mouse xenografts, and recapitulate the metabolic perturbations seen both in cell culture and in human patients. Together, these results suggest that PC is indispensible for the growth and anabolism of NSCLC. This work was funded by 5P20RR018733, 1R01CA118434-01A2, 1P01CA163223-01A1, 1R01ES022191-01, and 3R01CA118434-02S1; and the KLCRP, CTSPGP, and the KY Challenge for Excellence. Citation Format: Katherine E. Sellers, Matthew P. Fox, Michael Bousamra, Jun Yan, Mariia Yuneva, Richard M. Higashi, Andrew N. Lane, Teresa WM Fan. Enhanced pyruvate carboxylation is crucial to non-small cell lung cancer proliferation and anabolism. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1424. doi:10.1158/1538-7445.AM2014-1424

P01.03 * FUNCTIONAL CHARACTERISATION OF THE ISOCITRATE DEHYDROGENASE 1 (IDH 1) R132H MUTATION IN GLIOMAS

INTRODUCTION: Diffuse gliomas are the most prevalent brain tumors in adults and cannot be cured. Amino-acid substitution at position 132 of cytoplasmic enzyme isocitrate dehydrogenase 1 (IDH1) are characteristic for lower grade gliomas and therefrom derived secondary glioblastomas (GBM). The most frequent mutation observed in low grade gliomas is IDH1 c.395G>A (p.R132H). The wild type IDH1 converts isocitrate to α-ketoglutarate while reducing nicotinamide adenine dinucleotide phosphate (NADP). In contrast, IDH1 R132H produces high amounts of 2-hydroxyglutarate (2HG), which leads to a hypermethylation phenotype and is therefore considered to be an oncometabolite. Nevertheless, the accumulation of 2HG cannot explain all the observed phenomena in gliomas. We aimed to investigate other mechanisms by which IDH1 R132H mutation contributes to gliomagenesis. MATERIALS AND METHODS: We have stably transduced three cell lines (a established GBM cell line, a primary patient-derived GBM cell line, and an immortalized astrocyte cell line) with IDH1 c.395G>A cDNA using viral vectors. Transduction success was validated on DNA, RNA and protein levels using Sanger sequencing, allele-specific PCR and Western blots. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) was performed to measure Krebs cycle metabolite concentrations. In order to find effects independent of 2HG, we added the oncometabolite to empty vector controls. NADP+/NADPH quantification kits were used to determine the concentrations of this coenzyme. RESULTS: We confirmed the presence of IDH1 c.395G>A;p.R132H mutation in the cells transduced with the mutant variant of IDH1. There was an up to 1700-fold increase of the oncometabolite 2HG in the cells with the mutation compared to an empty vector control. The levels of glutamate significantly decreased in cells with the IDH1 mutation as well as in empty vector controls after 2HG treatment. We found a ∼50% decrease in NADPH concentration in GBM cells with the IDH1 mutation but not in astrocytes. Interestingly, there was a decrease in proliferation of GBM cells with IDH1 R132H. This effect was confirmed in 3D spheroid cell cultures. CONCLUSION: The mechanisms of how IDH1 R132H mutations contribute to gliomagenesis are still far from clear. We found that mutations in IDH1 lead to changes in Krebs cycle metabolite concentrations and energy homeostasis while decreasing proliferation in vitro. We are currently analyzing the effect of IDH1 R132H on the transcriptome level in comparison with IDH1 wt cells treated with 2HG. Based on these profiles we aim to investigate possible genetic mechanisms which are independet of the oncometabolite 2HG. These results will also be presented.

Krebs cycle metabolite profiling for identification and stratification of pheochromocytomas/paragangliomas due to succinate dehydrogenase deficiency.

Mutations of succinate dehydrogenase A/B/C/D genes (SDHx) increase susceptibility to development of pheochromocytomas and paragangliomas (PPGLs), with particularly high rates of malignancy associated with SDHB mutations. We assessed whether altered succinate dehydrogenase product-precursor relationships, manifested by differences in tumor ratios of succinate to fumarate or other metabolites, might aid in identifying and stratifying patients with SDHx mutations. PPGL tumor specimens from 233 patients, including 45 with SDHx mutations, were provided from eight tertiary referral centers for mass spectrometric analyses of Krebs cycle metabolites. Diagnostic performance of the succinate:fumarate ratio for identification of pathogenic SDHx mutations. SDH-deficient PPGLs were characterized by 25-fold higher succinate and 80% lower fumarate, cis-aconitate, and isocitrate tissue levels than PPGLs without SDHx mutations. Receiver-operating characteristic curves for use of ratios of succinate to fumarate or to cis-aconitate and isocitrate to identify SDHx mutations indicated areas under curves of 0.94 to 0.96; an optimal cut-off of 97.7 for the succinate:fumarate ratio provided a diagnostic sensitivity of 93% at a specificity of 97% to identify SDHX-mutated PPGLs. Succinate:fumarate ratios were higher in both SDHB-mutated and metastatic tumors than in those due to SDHD/C mutations or without metastases. Mass spectrometric-based measurements of ratios of succinate:fumarate and other metabolites in PPGLs offer a useful method to identify patients for testing of SDHx mutations, with additional utility to quantitatively assess functionality of mutations and metabolic factors responsible for malignant risk.

Novel mutation in the mitochondrial transfer RNACys gene in a child with vomiting and migraine

We report an 11-year-old female with vomiting episodes and migraine. The patient, a full-term infant, presented with epilepsy in the neonatal period that resolved with valproate treatment (EEG was normal); at 18 months of life she developed paroxysmal torticollis episodes and at the age of 4 years she begun with vomiting episodes (mainly during sleep) and migraine. Her psychomotor developmental milestones were within the normal range. Metabolic investigations were normal except for the presence of Krebs cycle metabolites in urinary organic acid profile. The mother is clinically normal. The maternal relatives show clinical alterations, one of her sisters is deaf-mute, the other presents with hypotonia and developmental delay, and the brother (deceased at the age of three months) presented with severe developmental delay

Role of the Krebs Cycle Metabolites in Retinal Angiogenesis

PurposeRetinopathy of prematurity (ROP), a major cause of blindness in developed countries, occurs in two phases : the cessation of normal eye development after birth and a subsequent abnormal and exaggerated vessel growth. Peripheral hypoxia occur after the first phase in premature eye and induce production of many growth factors implicated in this second destructive neovascularization phase. Our laboratory has previously demonstrated the role of succinate/GPR91 in the modulation of retinal vessel growth. Here, we investigated the role of α‐ketoglutarate (α‐KG) and its cognate receptor GPR99 in retinal angiogenesis.MethodsEffects of α‐KG on developmental retinal vascularization were assessed following intravitreal injection of Sprague‐Dawley rat pups in development. Moreover, the effects of a siGPR99 knockdown following intravitreal injection were investigated in the neovascular phase of ROP. Endogenous expression of retinal GPR99 was examined in Sprague‐Dawley rat retinas by immunohistochemistry. In vitro, we investigated the expression of GPR99 and pro‐angiogenic factors by Western blot and PCR analysis. The ability of α‐KG to promote vessel sprouting was determined by aortic rings cultured.Resultsα‐KG significantly enhanced developmental vascular densities at different time points. Neovascularization was blocked by a siGPR99 and allowed normal vessel growth in ROP. Moreover, GPR99 was robustly expressed in RGCs as confirmed by co‐labeling with neuron markers and, in vitro, mainly in neuronal cells. Conditioned media from α‐KG stimulated‐neurons induced aortic rings sprouting, in correlation with an up‐regulation of pro‐angiogenic factors expression.ConclusionsOur results disclose a pro‐angiogenic role for α‐KG and its receptor GPR99, providing additional supports for the involvement of metabolite signalling in ischemic conditions.

Proteomic and metabolomic profiling reveals time-dependent changes in hippocampal metabolism upon paroxetine treatment and biomarker candidates

Most of the commonly used antidepressants block monoamine reuptake transporters to enhance serotonergic or noradrenergic neurotransmission. Effects besides or downstream of monoamine reuptake inhibition are poorly understood and yet presumably important for the drugs' mode of action. In the present study we aimed at identifying hippocampal cellular pathway alterations in DBA/2 mice using paroxetine as a representative Selective Serotonin Reuptake Inhibitor (SSRI). Furthermore we identified biomarker candidates for the assessment of antidepressant treatment effects in plasma. Hippocampal protein levels were compared between chronic paroxetine- and vehicle-treated animals using in vivo15N metabolic labeling combined with mass spectrometry. We also studied the time course of metabolite level changes in hippocampus and plasma using a targeted polar metabolomics profiling platform. In silico pathway analyses revealed profound alterations related to hippocampal energy metabolism. Glycolytic metabolite levels acutely increased while Krebs cycle metabolite levels decreased upon chronic treatment. Changes in energy metabolism were influenced by altered glycogen metabolism rather than by altered glycolytic or Krebs cycle enzyme levels. Increased energy levels were reflected by an increased ATP/ADP ratio and by increased ratios of high-to-low energy purines and pyrimidines. In the course of our analyses we also identified myo-inositol as a biomarker candidate for the assessment of antidepressant treatment effects in the periphery. This study defines the cellular response to paroxetine treatment at the proteome and metabolome levels in the hippocampus of DBA/2 mice and suggests novel SSRI modes of action that warrant consideration in antidepressant development efforts.

Abstract 18852: Adenylate Kinase Phosphotransfer and AMP Signaling Regulate Cardiomyocyte Cell Cycle and Heart Regenerative Capacity

The mammalian heart loses its regenerative potential within a week after birth. Although under certain circumstances adult cardiomyocytes can re-enter the cell cycle, initiate DNA synthesis and progress towards mitosis, however, they do not complete a conventional mitosis cycle and proceed towards endomitosis resulting in polyploidy. This suggests that high-energy dependent steps in cell cycle and myofibrillar disassembly are malfunctioning in adult cardiomyocytes. It is known that nucleotide-based energetic signaling and metabolic environment are critical for initiation of tissue regeneration after injury. The regulatory mechanisms and energetic-metabolic signaling circuits that govern cardiomyocyte cell cycle withdrawal and binucleation are poorly understood. Using mouse neonatal (2 and 10 days) hearts, with high and low regenerative capacity, respectively, we have determined metabolomic profiles and dynamics of phosphotransfer circuits and AMP-signaling using 18O-phosphoryl labeling mass-spectrometric and 18O-assisted 31P NMR techniques. The results demonstrate that loss of heart regenerative capacity 10 days after birth is associated with marked changes in heart metabolome and adenylate kinase (AK)-catalyzed phosphotransfer flux. Among most altered metabolites were putrescine and myo-inositol, involved in tissue regeneration, Krebs cycle and amino acid metabolites, creatinine, glucose-6-phosphate and lactate indicating rearrangements in energy and substrate metabolic systems. AK flux was the only phosphotransfer flux significantly upregulated in hearts at 10 days of age along with increased in mitochondrial and glycolytic capacities and mitochondrial AK2 expression. Increased AK2 expression was associated with augmented AMP phosphorylation, measured by generation of β-ATP[18O], and reduction of AMPK activity. Thus, increased channeling of AMP into mitochondria and reduction of AK-AMP-AMPK signaling axis could contribute to the withdrawal from completion of cell cycle in terminally differentiated adult cardiomyocytes. The uncovered metabolic signaling mechanism opens new avenues for targeted regulation of heart regenerative potential critical for repair of injured hearts.

Everolimus and Sirolimus in Combination with Cyclosporine Have Different Effects on Renal Metabolism in the Rat

Enhancement of calcineurin inhibitor nephrotoxicity by sirolimus (SRL) is limiting the clinical use of this drug combination. We compared the dose-dependent effects of the structurally related everolimus (EVL) and sirolimus (SRL) alone, and in combination with cyclosporine (CsA), on the rat kidney. Lewis rats were treated by oral gavage for 28 days using a checkerboard dosing format (0, 3.0, 6.0 and 10.0 CsA and 0, 0.5, 1.5 and 3.0 mg/kg/day SRL or EVL, n = 4/dose combination). After 28 days, oxidative stress, energy charge, kidney histologies, glomerular filtration rates, and concentrations of the immunosuppressants were measured along with 1H-magnetic resonance spectroscopy (MRS) and gas chromatography- mass spectrometry profiles of cellular metabolites in urine. The combination of CsA with SRL led to higher urinary glucose concentrations and decreased levels of urinary Krebs cycle metabolites when compared to controls, suggesting that CsA+SRL negatively impacted proximal tubule metabolism. Unsupervised principal component analysis of MRS spectra distinguished unique urine metabolite patterns of rats treated with CsA+SRL from those treated with CsA+EVL and the controls. SRL, but not EVL blood concentrations were inversely correlated with urine Krebs cycle metabolite concentrations. Interestingly, the higher the EVL concentration, the closer urine metabolite patterns resembled those of controls, while in contrast, the combination of the highest doses of CsA+SRL showed the most significant differences in metabolite patterns. Surprisingly in this rat model, EVL and SRL in combination with CsA had different effects on kidney biochemistry, suggesting that further exploration of EVL in combination with low dose calcineurin inhibitors may be of potential benefit.

Abstract 244: Regenerative Metabolome and Energetic Signaling Mechanisms Governing Heart Renewal Capacity

The mammalian heart loses its regenerative potential within a week after birth. Although under certain circumstances adult cardiomyocytes can re-enter the cell cycle, initiate DNA synthesis and progress towards mitosis, however, they do not complete a conventional mitosis cycle and proceed towards endomitosis resulting in polyploidy. This suggests that high-energy dependent steps in cell cycle and myofibrillar disassembly are malfunctioning in adult cardiomyocytes. It is known that nucleotide-based energetic signaling and metabolic environment are critical for initiation of tissue regeneration after injury. The regulatory mechanisms and energetic-metabolic signaling circuits that govern cardiomyocyte cell cycle withdrawal and binucleation are poorly understood. Using mouse neonatal (2 and 10 days) hearts, with high and low regenerative capacity, respectively, we have determined metabolomic profiles and dynamics of phosphotransfer circuits and AMP-signaling using 18O-phosphoryl labeling mass-spectrometric and 18O-assisted 31P NMR techniques. The results demonstrate that loss of heart regenerative capacity 10 days after birth is associated with marked changes in heart metabolome and adenylate kinase (AK)-catalyzed phosphotransfer flux. Among most altered metabolites were putrescine and myo-inositol, involved in tissue regeneration, Krebs cycle and amino acid metabolites, creatinine, glucose-6-phosphate and lactate indicating rearrangements in energy and substrate metabolic systems. AK flux was the only phosphotransfer flux significantly upregulated in hearts at 10 days of age along with increased in mitochondrial and glycolytic capacities and mitochondrial AK2 expression. Increased AK2 expression was associated with augmented AMP phosphorylation, measured by generation of β-ATP[18O], and reduction of AMPK activity. Thus, increased channeling of AMP into mitochondria and reduction of AK-AMP-AMPK signaling axis could contribute to the withdrawal from completion of cell cycle in terminally differentiated adult cardiomyocytes. The uncovered metabolic signaling mechanism opens new avenues for targeted regulation of heart regenerative potential critical for repair of injured hearts.

Polynucleotide Phosphorylase Activity May Be Modulated by Metabolites in Escherichia coli

RNA turnover is an essential element of cellular homeostasis and response to environmental change. Whether the ribonucleases that mediate RNA turnover can respond to cellular metabolic status is an unresolved question. Here we present evidence that the Krebs cycle metabolite citrate affects the activity of Escherichia coli polynucleotide phosphorylase (PNPase) and, conversely, that cellular metabolism is affected widely by PNPase activity. An E. coli strain that requires PNPase for viability has suppressed growth in the presence of increased citrate concentration. Transcriptome analysis reveals a PNPase-mediated response to citrate, and PNPase deletion broadly impacts on the metabolome. In vitro, citrate directly binds and modulates PNPase activity, as predicted by crystallographic data. Binding of metal-chelated citrate in the active site at physiological concentrations appears to inhibit enzyme activity. However, metal-free citrate is bound at a vestigial active site, where it stimulates PNPase activity. Mutagenesis data confirmed a potential role of this vestigial site as an allosteric binding pocket that recognizes metal-free citrate. Collectively, these findings suggest that RNA degradative pathways communicate with central metabolism. This communication appears to be part of a feedback network that may contribute to global regulation of metabolism and cellular energy efficiency.

Succinyl-CoA Ligase Deficiency: A Mitochondrial Hepatoencephalomyopathy

This patient presented on the first day of life with pronounced lactic acidosis with an elevated lactate/pyruvate ratio. Urine organic acids showed Krebs cycle metabolites and mildly elevated methylmalonate and methylcitrate. The acylcarnitine profile showed elevated propionylcarnitine and succinylcarnitine. Amino acids showed elevated glutamic acid, glutamine, proline, and alanine. From the age 2 of mo on, she had elevated transaminases and intermittent episodes of liver failure. Liver biopsy showed steatosis and a decrease of mitochondrial DNA to 50% of control. She had bilateral sensorineural hearing loss. Over the course of the first 2 y of life, she developed a progressively severe myopathy with pronounced muscle weakness eventually leading to respiratory failure, Leigh disease, and recurrent hepatic failure. The hepatic symptoms and the metabolic parameters temporarily improved on treatment with aspartate, but neither muscle symptoms nor brain lesions improved. Laboratory testing revealed a deficiency of succinyl-CoA ligase enzyme activity and protein in fibroblasts because of a novel homozygous mutation in the SUCLG1 gene: c.40A>T (p.M14L). Functional analysis suggests that this methionine is more likely to function as the translation initiator methionine, explaining the pathogenic nature of the mutation. Succinyl-CoA ligase deficiency due to an SUCLG1 mutation is a new cause for mitochondrial hepatoencephalomyopathy.

Extended Ischemia Prevents HIF1α Degradation at Reoxygenation by Impairing Prolyl-hydroxylation: ROLE OF KREBS CYCLE METABOLITES

Hypoxia-inducible factor (HIF) is a heterodimeric transcription factor that activates the cellular response to hypoxia. The HIF1alpha subunit is constantly synthesized and degraded under normoxia, but degradation is rapidly inhibited when oxygen levels drop. Oxygen-dependent hydroxylation by prolyl-4-hydroxylases (PHD) mediates HIF1alpha proteasome degradation. Brain ischemia limits the availability not only of oxygen but also of glucose. We hypothesized that this circumstance could have a modulating effect on HIF. We assessed the separate involvement of oxygen and glucose in HIF1alpha regulation in differentiated neuroblastoma cells subjected to ischemia. We report higher transcriptional activity and HIF1alpha expression under oxygen deprivation in the presence of glucose (OD), than in its absence (oxygen and glucose deprivation, OGD). Unexpectedly, HIF1alpha was not degraded at reoxygenation after an episode of OGD. This was not due to impairment of proteasome function, but was associated with lower HIF1alpha hydroxylation. Krebs cycle metabolites fumarate and succinate are known inhibitors of PHD, while alpha-ketoglutarate is a co-substrate of the reaction. Lack of HIF1alpha degradation in the presence of oxygen was accompanied by a very low alpha-ketoglutarate/fumarate ratio. Furthermore, treatment with a fumarate analogue prevented HIF1alpha degradation under normoxia. In all, our data suggest that postischemic metabolic alterations in Krebs cycle metabolites impair HIF1alpha degradation in the presence of oxygen by decreasing its hydroxylation, and highlight the involvement of metabolic pathways in HIF1alpha regulation besides the well known effects of oxygen.

Time-Resolved and Tissue-Specific Systems Analysis of the Pathogenesis of Insulin Resistance

BackgroundThe sequence of events leading to the development of insulin resistance (IR) as well as the underlying pathophysiological mechanisms are incompletely understood. As reductionist approaches have been largely unsuccessful in providing an understanding of the pathogenesis of IR, there is a need for an integrative, time-resolved approach to elucidate the development of the disease.Methodology/Principal FindingsMale ApoE3Leiden transgenic mice exhibiting a humanized lipid metabolism were fed a high-fat diet (HFD) for 0, 1, 6, 9, or 12 weeks. Development of IR was monitored in individual mice over time by performing glucose tolerance tests and measuring specific biomarkers in plasma, and hyperinsulinemic-euglycemic clamp analysis to assess IR in a tissue-specific manner. To elucidate the dynamics and tissue-specificity of metabolic and inflammatory processes key to IR development, a time-resolved systems analysis of gene expression and metabolite levels in liver, white adipose tissue (WAT), and muscle was performed. During HFD feeding, the mice became increasingly obese and showed a gradual increase in glucose intolerance. IR became first manifest in liver (week 6) and then in WAT (week 12), while skeletal muscle remained insulin-sensitive. Microarray analysis showed rapid upregulation of carbohydrate (only liver) and lipid metabolism genes (liver, WAT). Metabolomics revealed significant changes in the ratio of saturated to polyunsaturated fatty acids (liver, WAT, plasma) and in the concentrations of glucose, gluconeogenesis and Krebs cycle metabolites, and branched amino acids (liver). HFD evoked an early hepatic inflammatory response which then gradually declined to near baseline. By contrast, inflammation in WAT increased over time, reaching highest values in week 12. In skeletal muscle, carbohydrate metabolism, lipid metabolism, and inflammation was gradually suppressed with HFD.Conclusions/SignificanceHFD-induced IR is a time- and tissue-dependent process that starts in liver and proceeds in WAT. IR development is paralleled by tissue-specific gene expression changes, metabolic adjustments, changes in lipid composition, and inflammatory responses in liver and WAT involving p65-NFkB and SOCS3. The alterations in skeletal muscle are largely opposite to those in liver and WAT.