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2.
NMR Biomed ; 34(7): e4533, 2021 07.
Artigo em Inglês | MEDLINE | ID: mdl-33900680

RESUMO

After administration of 13 C-labeled glucose, the activity of the pentose phosphate pathway (PPP) is often assessed by the distribution of 13 C in lactate. However, in some tissues, such as the well-oxygenated heart, the concentration of lactate may be too low for convenient analysis by NMR. Here, we examined 13 C-labeled glutamate as an alternative biomarker of the PPP in the heart. Isolated rat hearts were perfused with media containing [2,3-13 C2 ]glucose and the tissue extracts were analyzed. Metabolism of [2,3-13 C2 ]glucose yields [1,2-13 C2 ]pyruvate via glycolysis and [2,3-13 C2 ]pyruvate via the PPP. Pyruvate is in exchange with lactate or is further metabolized to glutamate through pyruvate dehydrogenase and the TCA cycle. A doublet from [4,5-13 C2 ]glutamate, indicating flux through the PPP, was readily detected in 13 C NMR of heart extracts even when the corresponding doublet from [2,3-13 C2 ]lactate was minimal. Benfotiamine, known to induce the PPP, caused an increase in production of [4,5-13 C2 ]glutamate. In rats receiving [2,3-13 C2 ]glucose, brain extracts showed well-resolved signals from both [2,3-13 C2 ]lactate and [4,5-13 C2 ]glutamate in 13 C NMR spectra. Assessment of the PPP in the brain based on glutamate had a strong linear correlation with lactate-based assessment. In summary, 13 C NMR analysis of glutamate enabled detection of the low PPP activity in isolated hearts. This analyte is an alternative to lactate for monitoring the PPP with the use of [2,3-13 C2 ]glucose.

3.
Mol Metab ; 45: 101154, 2021 03.
Artigo em Inglês | MEDLINE | ID: mdl-33359401

RESUMO

OBJECTIVE: Insulin resistance and altered hepatic mitochondrial function are central features of type 2 diabetes (T2D) and non-alcoholic fatty liver disease (NAFLD), but the etiological role of these processes in disease progression remains unclear. Here we investigated the molecular links between insulin resistance, mitochondrial remodeling, and hepatic lipid accumulation. METHODS: Hepatic insulin sensitivity, endogenous glucose production, and mitochondrial metabolic fluxes were determined in wild-type, obese (ob/ob) and pioglitazone-treatment obese mice using a combination of radiolabeled tracer and stable isotope NMR approaches. Mechanistic studies of pioglitazone action were performed in isolated primary hepatocytes, whilst molecular hepatic lipid species were profiled using shotgun lipidomics. RESULTS: Livers from obese, insulin-resistant mice displayed augmented mitochondrial content and increased tricarboxylic acid cycle (TCA) cycle and pyruvate dehydrogenase (PDH) activities. Insulin sensitization with pioglitazone mitigated pyruvate-driven TCA cycle activity and PDH activation via both allosteric (intracellular pyruvate availability) and covalent (PDK4 and PDP2) mechanisms that were dependent on PPARγ activity in isolated primary hepatocytes. Improved mitochondrial function following pioglitazone treatment was entirely dissociated from changes in hepatic triglycerides, diacylglycerides, or fatty acids. Instead, we highlight a role for the mitochondrial phospholipid cardiolipin, which underwent pathological remodeling in livers from obese mice that was reversed by insulin sensitization. CONCLUSION: Our findings identify targetable mitochondrial features of T2D and NAFLD and highlight the benefit of insulin sensitization in managing the clinical burden of obesity-associated disease.

4.
Physiol Rep ; 8(16): e14554, 2020 08.
Artigo em Inglês | MEDLINE | ID: mdl-32812387

RESUMO

The liver regenerates NADPH via multiple pathways to maintain redox balance and reductive biosynthesis. The pentose phosphate pathway (PPP) contributes to hepatic lipogenesis by supplying NADPH, and it is thought to play a major role in response to oxidative stress. This study determined the significance of the PPP and related NADPH-regenerating enzymes in the liver under oxidative stress. Fasted hamsters received acetaminophen (400 mg/kg) to deplete glutathione in the liver and [U-13 C3 ]glycerol to measure the PPP activity by analysis of 13 C distribution in plasma glucose. Blood and liver were harvested to assess NADPH-producing enzymes, antioxidant defense, PPP, and other relevant biochemical processes. Acetaminophen caused glutathione depletion and decreased activities of glutathione peroxidase and catalase in the liver, but it did not change triglyceride synthesis. Although the PPP is potentially an abundant source of NADPH, its activity was decreased and the expression of glucose 6-phosphate dehydrogenase remained unchanged after acetaminophen treatment. The effects of acetaminophen on other NADPH-producing enzymes were complex. Isocitrate dehydrogenase 1 was overexpressed, both isocitrate dehydrogenase 2 and malic enzyme 1 were underexpressed, and methylenetetrahydrofolate dehydrogenase 1 remained unchanged. In summary, isocitrate dehydrogenase 1 was most sensitive to glutathione depletion caused by acetaminophen, but glucose 6-phosphate dehydrogenase, the regulatory enzyme of PPP, was not.


Assuntos
Glutationa/metabolismo , Isocitrato Desidrogenase/metabolismo , Fígado/metabolismo , Via de Pentose Fosfato , Animais , Cricetinae , Isocitrato Desidrogenase/genética , Masculino , Mesocricetus , Mitocôndrias Hepáticas/metabolismo
5.
Obesity (Silver Spring) ; 28(7): 1254-1262, 2020 07.
Artigo em Inglês | MEDLINE | ID: mdl-32568464

RESUMO

OBJECTIVE: The aim of this study was to determine the effects of empagliflozin on glycerol-derived hepatic gluconeogenesis in adults with obesity without type 2 diabetes mellitus (T2DM) using oral carbon 13 (13 C)-labeled glycerol. METHODS: A randomized, double-blind, placebo-controlled trial was performed in participants with magnetic resonance imaging assessment of body fat and measurement of glycerol-derived 13 C enrichment in plasma glucose by nuclear magnetic resonance spectroscopy following ingestion of [U-13 C3 ]glycerol. Participants were randomized to oral empagliflozin 10 mg once daily or placebo for 3 months. Glycerol-derived 13 C enrichment studies were repeated, and treatment differences in the mean percentage of 13 C glycerol enrichment in glucose were compared using mixed linear models. RESULTS: Thirty-five participants completed the study. Empagliflozin increased glycerol-derived 13 C enrichment between baseline and follow-up by 6.5% (P = 0.005), consistent with less glycerol from visceral adipose tissue (VAT). No difference was found with placebo. Glycerol-derived 13 C enrichment was lower in participants with high VAT compared with low VAT by 12.6% (P = 0.04), but there was no heterogeneity of the treatment effect by baseline VAT. Glycerol-derived 13 C enrichment was inversely correlated with VAT but was not correlated with weight loss. CONCLUSIONS: VAT is associated with endogenous glycerol-derived hepatic gluconeogenesis, and empagliflozin reduces endogenous glycerol gluconeogenesis in adults with obesity without T2DM. These findings suggest a mechanism by which sodium-glucose cotransporter 2 inhibitors may prevent T2DM in obesity.


Assuntos
Compostos Benzidrílicos/uso terapêutico , Diabetes Mellitus Tipo 2/tratamento farmacológico , Gluconeogênese/efeitos dos fármacos , Glucosídeos/uso terapêutico , Glicerol/metabolismo , Fígado/efeitos dos fármacos , Obesidade/tratamento farmacológico , Tecido Adiposo/efeitos dos fármacos , Tecido Adiposo/metabolismo , Adulto , Glicemia/metabolismo , Diabetes Mellitus Tipo 2/complicações , Diabetes Mellitus Tipo 2/metabolismo , Método Duplo-Cego , Feminino , Humanos , Gordura Intra-Abdominal , Fígado/metabolismo , Masculino , Pessoa de Meia-Idade , Obesidade/complicações , Obesidade/metabolismo , Placebos , Perda de Peso/efeitos dos fármacos
6.
J Investig Med ; 68(1): 3-10, 2020 01.
Artigo em Inglês | MEDLINE | ID: mdl-31554675

RESUMO

Stable isotope tracers have been used to gain an understanding of integrative animal and human physiology. More commonly studied organ systems include hepatic glucose metabolism, lipolysis from adipose tissue, and whole body protein metabolism. Recent improvements in isotope methodology have included the use of novel physiologic methods/models and mathematical modeling of data during different physiologic states. Here we review some of the latest advancements in this field and highlight future research needs. First we discuss the use of an oral [U-13C3]-glycerol tracer to determine the relative contribution of glycerol carbons to hepatic glucose production after first cycling through the tricarboxylic acid cycle, entry of glycerol into the pentose phosphate pathway or direct conversion of glycerol into the glucose. Second, we describe an adaptation of the established oral minimal model used to define postprandial glucose dynamics to include glycerol dynamics in an oral glucose tolerance test with a [2H5]-glycerol tracer to determine dynamic changes in lipolysis. Simulation results were optimized when parameters describing glycerol flux were determined with a hybrid approach using both tracer-based calculations and constrained parameter optimization. Both of these methodologies can be used to expand our knowledge of not only human physiology, but also the effects of various nutritional strategies and medications on metabolism.


Assuntos
Glucose/biossíntese , Isótopos , Lipólise/fisiologia , Fígado/metabolismo , Adolescente , Criança , Feminino , Glucose/metabolismo , Teste de Tolerância a Glucose , Glicerol/metabolismo , Humanos , Modelos Biológicos , Obesidade/metabolismo , Adulto Jovem
7.
Metabolism ; 101: 153993, 2019 12.
Artigo em Inglês | MEDLINE | ID: mdl-31672442

RESUMO

BACKGROUND: Therapies targeting altered activity of pyruvate dehydrogenase (PDH) and pyruvate carboxylase (PC) have been proposed for hepatomas. However, the activities of these pathways in hepatomas in vivo have not been distinguished. Here we examined pyruvate entry into the tricarboxylic acid (TCA) cycle through PDH versus PC in vivo using hepatoma-bearing rats. METHODS: Hepatoma-bearing rats were generated by intrahepatic injection of H4IIE cells. Metabolism of 13C-labeled glycerol, a physiological substrate for both gluconeogenesis and energy production, was measured with 13C NMR analysis. The concentration of key metabolites and the expression of relevant enzymes were measured in hepatoma, surrounding liver, and normal liver. RESULTS: In orthotopic hepatomas, pyruvate entry into the TCA cycle occurred exclusively through PDH and the excess PDH activity compared to normal liver was attributed to downregulated pyruvate dehydrogenase kinase (PDK) 2/4. However, pyruvate carboxylation via PC and gluconeogenesis were minimal, which was linked to downregulated forkhead box O1 (FoxO1) by Akt activity. In contrast to many studies of cancer metabolism, lactate production in hepatomas was not increased which corresponded to reduced expression of lactate dehydrogenase. The production of serine and glycine in hepatomas was enhanced, but glycine decarboxylase was downregulated. CONCLUSIONS: The combination of [U-13C3]glycerol and NMR analysis enabled investigation of multiple biochemical processes in hepatomas and surrounding liver. We demonstrated active PDH and other related metabolic alterations in orthotopic hepatomas that differed substantially not only from the host organ but also from many earlier studies with cancer cells.


Assuntos
Carcinoma Hepatocelular/metabolismo , Gluconeogênese , Neoplasias Hepáticas/metabolismo , Complexo Piruvato Desidrogenase/metabolismo , Animais , Espectroscopia de Ressonância Magnética Nuclear de Carbono-13/métodos , Carcinoma Hepatocelular/enzimologia , Ciclo do Ácido Cítrico , Glicerol/metabolismo , Fígado/enzimologia , Neoplasias Hepáticas/enzimologia , Ratos
8.
Am J Physiol Regul Integr Comp Physiol ; 317(1): R134-R142, 2019 07 01.
Artigo em Inglês | MEDLINE | ID: mdl-31042400

RESUMO

Hepatic energy metabolism is a key element in many metabolic diseases. Hepatic anaplerosis provides carbons for gluconeogenesis (GNG) and triglyceride (TG) synthesis. We aimed to optimize a protocol that measures hepatic anaplerotic contribution for GNG, TG synthesis, and hepatic pentose phosphate pathway (PPP) activity using a single dose of oral [U-13C3]glycerol paired with an oral sugar tolerance test (OSTT) in a population with significant insulin resistance. The OSTT (75 g glucose + 25 g fructose) was administered to eight obese adolescents with polycystic ovarian syndrome (PCOS) followed by ingestion of [U-13C3]glycerol at t = 180 or t = 210 min. 13C-labeling patterns of serum glucose and TG-glycerol were determined by nuclear magnetic resonance. 13C enrichment in plasma TG-glycerol was detectable and stable from 240 to 390 min with the [U-13C3]glycerol drink at t = 180 min(3.65 ± 2.3 to 4.47 ± 1.4%; P > 0.4), but the enrichment was undetectable at 240 min with the glycerol drink at t = 210 min. The relative contribution from anaplerosis was determined at the end of the OSTT [18.5 ±3.4% (t = 180 min) vs. 16.0 ± 3.5% (t = 210 min); P = 0.27]. [U-13C3]glycerol was incorporated into GNG 390 min after the OSTT with an enrichment of 7.5-12.5%. Glucose derived from TCA cycle activity was 0.3-1%, and the PPP activity was 2.8-4.7%. In conclusion, it is possible to obtain relative measurements of hepatic anaplerotic contribution to both GNG and TG esterification following an OSTT in a highly insulin-resistant population using a minimally invasive technique. Tracer administration should be timed to allow enough de novo TG esterification and endogenous glucose release after the sugar drink.


Assuntos
Gluconeogênese/fisiologia , Fígado/metabolismo , Obesidade Pediátrica , Síndrome do Ovário Policístico , Triglicerídeos/biossíntese , Adolescente , Glicemia , Isótopos de Carbono , Feminino , Glucose/metabolismo , Glicerol/metabolismo , Humanos , Resistência à Insulina , Lipogênese , Adulto Jovem
9.
NMR Biomed ; 32(6): e4096, 2019 06.
Artigo em Inglês | MEDLINE | ID: mdl-30924572

RESUMO

The pentose phosphate pathway (PPP) is essential for reductive biosynthesis, antioxidant processes and nucleotide production. Common tracers such as [1,2-13 C2 ]glucose rely on detection of 13 C in lactate and require assumptions to correct natural 13 C abundance. Here, we introduce a novel and specific tracer of the PPP, [2,3-13 C2 ]glucose. 13 C NMR analysis of the resulting isotopomers is informative because [1,2-13 C2 ]lactate arises from glycolysis and [2,3-13 C2 ]lactate arises exclusively through the PPP. A correction for natural abundance is unnecessary. In rats receiving [2,3-13 C2 ]glucose, the PPP was more active in the fed versus fasted state in the liver and the heart, consistent with increased expression of key enzymes in the PPP. Both the PPP and glycolysis were substantially increased in hepatoma compared with liver. In summary, [2,3-13 C2 ]glucose and 13 C NMR simplify assessment of the PPP.


Assuntos
Isótopos de Carbono/metabolismo , Glucose/metabolismo , Via de Pentose Fosfato , Animais , Encéfalo/enzimologia , Espectroscopia de Ressonância Magnética Nuclear de Carbono-13 , Carcinoma Hepatocelular/metabolismo , Glicólise , Fígado/metabolismo , Masculino , Miocárdio/metabolismo , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Ratos Sprague-Dawley , Processamento de Sinais Assistido por Computador
10.
J Lipid Res ; 59(9): 1685-1694, 2018 09.
Artigo em Inglês | MEDLINE | ID: mdl-30054343

RESUMO

It is a challenge to assess metabolic dysregulation in fatty liver of human patients prior to clinical manifestations. Here, we recruited obese, but otherwise healthy, subjects to examine biochemical processes in the liver with simple triglyceride accumulation using stable isotopes and NMR analysis of metabolic products in blood. Intrahepatic triglycerides were measured using 1H magnetic resonance spectroscopy, and volunteers received 2H2O and [U-13C3]glycerol orally, followed by a series of blood draws. NMR analysis of plasma triglycerides and glucose provided detailed information about metabolic pathways in patients with simple hepatic steatosis. Compared with subjects with low hepatic fat, patients with hepatic steatosis were characterized by the following: lower 13C enrichments in the glycerol backbones of triglycerides (i.e., TG-[13C]glycerol), higher [U-13C3]glycerol metabolism through the tricarboxylic acid (TCA) cycle, delayed gluconeogenesis from [U-13C3]glycerol, and less flexibility in adjusting supporting fluxes of glucose production upon an oral load of glycerol. In summary, simple hepatic steatosis was associated with enhanced [U-13C3]glycerol metabolism through pathways that intersect the TCA cycle and delayed gluconeogenesis from glycerol.


Assuntos
Fígado Gorduroso/metabolismo , Gluconeogênese , Glicerol/metabolismo , Lipogênese , Adulto , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Adulto Jovem
11.
Am J Physiol Endocrinol Metab ; 314(6): E543-E551, 2018 06 01.
Artigo em Inglês | MEDLINE | ID: mdl-29351478

RESUMO

The pentose phosphate pathway (PPP) is widely assumed to play a key role in both reductive biosynthesis and protection from oxidative stress because it is the major source of NADPH. However, little is known about the activity of the PPP in fatty liver, which is characterized by both oxidative stress and lipogenesis. This study was designed to test whether the PPP is active in parallel with lipogenesis and antioxidant processes in the fatty liver of whole animals. Eight- and 16-wk-old obese Zucker diabetic fatty rats and their lean littermates received [U-13C3]glycerol, and 13C labeling patterns of glucose and triglycerides were analyzed for the assessment of hepatic PPP activity and the potentially related processes simultaneously. Oxidative stress, antioxidant activity, and NADPH-producing enzymes in the liver were further examined. Both PPP activity and lipogenesis increased in the fatty liver of young obese Zucker rats but decreased together in older obese Zucker rats. As expected, lipid peroxidation measured by malondialdehyde increased in the fatty liver of obese Zucker rats at both ages. However, evidence for antioxidant processes such as [glutathione] or activities of glutathione reductase, glutathione peroxidase, and catalase was not altered. Hepatic PPP activity paralleled lipogenesis but was dissociated from biomarkers of oxidative stress or antioxidant processes. In summary, NADPH from the PPP was presumably consumed for reductive biosynthesis rather than antioxidant defense in the fatty liver.


Assuntos
Antioxidantes/metabolismo , Lipogênese/fisiologia , Fígado/metabolismo , Via de Pentose Fosfato/fisiologia , Animais , Catalase/metabolismo , Fígado Gorduroso/complicações , Fígado Gorduroso/metabolismo , Fígado Gorduroso/patologia , Glutationa/metabolismo , Masculino , Malondialdeído/metabolismo , Obesidade/complicações , Obesidade/metabolismo , Obesidade/patologia , Estresse Oxidativo/fisiologia , Ratos , Ratos Zucker , Triglicerídeos/metabolismo
12.
Metabolism ; 67: 80-89, 2017 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-28081781

RESUMO

OBJECTIVE: To determine the feasibility of using oral 13C labeled glycerol to assess effects of visceral adiposity on gluconeogenic pathways in obese humans. RESEARCH DESIGN AND METHODS: Obese (BMI ≥30kg/m2) participants without type 2 diabetes underwent visceral adipose tissue (VAT) assessment and stratification by median VAT into high VAT-fasting (n=3), low VAT-fasting (n=4), and high VAT-refed (n=2) groups. Participants ingested [U-13C3] glycerol and blood samples were subsequently analyzed at multiple time points over 3h by NMR spectroscopy. The fractions of plasma glucose (enrichment) derived from [U-13C3] glycerol via hepatic gluconeogenesis, pentose phosphate pathway (PPP), and tricarboxylic acid (TCA) cycle were assessed using 13C NMR analysis of glucose. Mixed linear models were used to compare 13C enrichment in glucose between groups. RESULTS: Mean age, BMI, and baseline glucose were 49years, 40.1kg/m2, and 98mg/dl, respectively. Up to 20% of glycerol was metabolized in the TCA cycle prior to gluconeogenesis and PPP activity was minor (<1% of total glucose) in all participants. There was a 21% decrease in 13C enrichment in plasma glucose in the high VAT-fasting compared with low VAT-fasting group (p=0.03), suggesting dilution by endogenous glycerol. High VAT-refed participants had 37% less 13C enrichment in glucose compared with high VAT-fasting (p=0.02). There was a trend toward lower [1,2-13C2] (via PPP) and [5,6-13C2]/[4,5,6-13C3] (via TCA cycle) glucose in high VAT versus low VAT groups. CONCLUSIONS: We applied a simple method to detect gluconeogenesis from glycerol in obese humans. Our findings provide preliminary evidence that excess visceral fat disrupts multiple pathways in hepatic gluconeogenesis from glycerol.


Assuntos
Tecido Adiposo/metabolismo , Tecido Adiposo/fisiopatologia , Gluconeogênese , Glicerol/metabolismo , Gordura Intra-Abdominal/fisiopatologia , Obesidade/metabolismo , Adiposidade , Adulto , Idoso , Glicemia/análise , Índice de Massa Corporal , Ciclo do Ácido Cítrico , Diabetes Mellitus Tipo 2/metabolismo , Ingestão de Alimentos , Jejum/metabolismo , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Via de Pentose Fosfato
13.
J Biol Chem ; 291(36): 19031-41, 2016 09 02.
Artigo em Inglês | MEDLINE | ID: mdl-27432878

RESUMO

Drugs and other interventions for high impact hepatic diseases often target biochemical pathways such as gluconeogenesis, lipogenesis, or the metabolic response to oxidative stress. However, traditional liver function tests do not provide quantitative data about these pathways. In this study, we developed a simple method to evaluate these processes by NMR analysis of plasma metabolites. Healthy subjects ingested [U-(13)C3]glycerol, and blood was drawn at multiple times. Each subject completed three visits under differing nutritional states. High resolution (13)C NMR spectra of plasma triacylglycerols and glucose provided new insights into a number of hepatic processes including fatty acid esterification, the pentose phosphate pathway, and gluconeogenesis through the tricarboxylic acid cycle. Fasting stimulated pentose phosphate pathway activity and metabolism of [U-(13)C3]glycerol in the tricarboxylic acid cycle prior to gluconeogenesis or glyceroneogenesis. Fatty acid esterification was transient in the fasted state but continuous under fed conditions. We conclude that a simple NMR analysis of blood metabolites provides an important biomarker of pentose phosphate pathway activity, triacylglycerol synthesis, and flux through anaplerotic pathways in mitochondria of human liver.


Assuntos
Ciclo do Ácido Cítrico/efeitos dos fármacos , Ácidos Graxos/sangue , Glicerol/administração & dosagem , Fígado/metabolismo , Espectroscopia de Ressonância Magnética/métodos , Via de Pentose Fosfato/efeitos dos fármacos , Administração Oral , Adulto , Biomarcadores/sangue , Isótopos de Carbono/administração & dosagem , Isótopos de Carbono/farmacocinética , Esterificação/efeitos dos fármacos , Esterificação/fisiologia , Feminino , Humanos , Masculino , Pessoa de Meia-Idade
14.
NMR Biomed ; 29(4): 466-74, 2016 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-26836042

RESUMO

The source of hyperpolarized (HP) [(13)C]bicarbonate in the liver during metabolism of HP [1-(13)C]pyruvate is uncertain and likely changes with physiology. Multiple processes including decarboxylation through pyruvate dehydrogenase or pyruvate carboxylase followed by subsequent decarboxylation via phosphoenolpyruvate carboxykinase (gluconeogenesis) could play a role. Here we tested which metabolic fate of pyruvate contributed to the appearance of HP [(13)C]bicarbonate during metabolism of HP [1-(13)C]pyruvate by the liver in rats after 21 h of fasting compared to rats with free access to food. The (13)C NMR of HP [(13)C]bicarbonate was observed in the liver of fed rats, but not in fasted rats where pyruvate carboxylation and gluconeogenesis was active. To further explore the relative fluxes through pyruvate carboxylase versus pyruvate dehydrogenase in the liver under typical conditions of hyperpolarization studies, separate parallel experiments were performed with rats given non-hyperpolarized [2,3-(13)C]pyruvate. (13)C NMR analysis of glutamate isolated from the liver of rats revealed that flux from injected pyruvate through pyruvate dehydrogenase was dominant under fed conditions whereas flux through pyruvate carboxylase dominated under fasted conditions. The NMR signal of HP [(13)C]bicarbonate does not parallel pyruvate carboxylase activity followed by subsequent decarboxylation reaction leading to glucose production. In the liver of healthy well-fed rats, the appearance of HP [(13)C]bicarbonate exclusively reflects decarboxylation of HP [1-(13)C]pyruvate via pyruvate dehydrogenase.


Assuntos
Fígado/metabolismo , Espectroscopia de Ressonância Magnética/métodos , Ácido Pirúvico/metabolismo , Alanina/metabolismo , Animais , Bicarbonatos/metabolismo , Isótopos de Carbono , Espectroscopia de Ressonância Magnética Nuclear de Carbono-13 , Ciclo do Ácido Cítrico , Gluconeogênese , Ácido Láctico/metabolismo , Fosfoenolpiruvato Carboxiquinase (ATP) , Espectroscopia de Prótons por Ressonância Magnética , Piruvato Carboxilase/metabolismo , Complexo Piruvato Desidrogenase/metabolismo , Ratos Sprague-Dawley
15.
Cell ; 164(4): 681-94, 2016 Feb 11.
Artigo em Inglês | MEDLINE | ID: mdl-26853473

RESUMO

Non-small cell lung cancer (NSCLC) is heterogeneous in the genetic and environmental parameters that influence cell metabolism in culture. Here, we assessed the impact of these factors on human NSCLC metabolism in vivo using intraoperative (13)C-glucose infusions in nine NSCLC patients to compare metabolism between tumors and benign lung. While enhanced glycolysis and glucose oxidation were common among these tumors, we observed evidence for oxidation of multiple nutrients in each of them, including lactate as a potential carbon source. Moreover, metabolically heterogeneous regions were identified within and between tumors, and surprisingly, our data suggested potential contributions of non-glucose nutrients in well-perfused tumor areas. Our findings not only demonstrate the heterogeneity in tumor metabolism in vivo but also highlight the strong influence of the microenvironment on this feature.


Assuntos
Carcinoma Pulmonar de Células não Pequenas/metabolismo , Carcinoma Pulmonar de Células não Pequenas/patologia , Neoplasias Pulmonares/metabolismo , Neoplasias Pulmonares/patologia , Microambiente Tumoral , Adulto , Idoso , Idoso de 80 Anos ou mais , Carcinoma Pulmonar de Células não Pequenas/irrigação sanguínea , Ciclo do Ácido Cítrico , Feminino , Glicólise , Humanos , Neoplasias Pulmonares/irrigação sanguínea , Imageamento por Ressonância Magnética , Masculino , Pessoa de Meia-Idade , Tomografia por Emissão de Pósitrons
16.
J Biol Chem ; 290(51): 30486-97, 2015 Dec 18.
Artigo em Inglês | MEDLINE | ID: mdl-26491014

RESUMO

Phosphoenolpyruvate (PEP) generated from pyruvate is required for de novo synthesis of glycerol and glycogen in skeletal muscle. One possible pathway involves synthesis of PEP from the citric acid cycle intermediates via PEP carboxykinase, whereas another could involve reversal of pyruvate kinase (PK). Earlier studies have reported that reverse flux through PK can contribute carbon precursors for glycogen synthesis in muscle, but the physiological importance of this pathway remains uncertain especially in the setting of high plasma glucose. In addition, although PEP is a common intermediate for both glyconeogenesis and glyceroneogenesis, the importance of reverse PK in de novo glycerol synthesis has not been examined. Here we studied the contribution of reverse PK to synthesis of glycogen and the glycerol moiety of acylglycerols in skeletal muscle of animals with high plasma glucose. Rats received a single intraperitoneal bolus of glucose, glycerol, and lactate under a fed or fasted state. Only one of the three substrates was (13)C-labeled in each experiment. After 3 h of normal awake activity, the animals were sacrificed, and the contribution from each substrate to glycogen and the glycerol moiety of acylglycerols was evaluated. The fraction of (13)C labeling in glycogen and the glycerol moiety exceeded the possible contribution from either plasma glucose or muscle oxaloacetate. The reverse PK served as a common route for both glyconeogenesis and glyceroneogenesis in the skeletal muscle of rats with high plasma glucose. The activity of pyruvate carboxylase was low in muscle, and no PEP carboxykinase activity was detected.


Assuntos
Glicemia/metabolismo , Gluconeogênese/efeitos dos fármacos , Glicerol/metabolismo , Ácido Láctico/farmacologia , Músculo Esquelético/metabolismo , Piruvato Quinase/metabolismo , Animais , Masculino , Fosfoenolpiruvato/metabolismo , Ratos , Ratos Sprague-Dawley
17.
J Clin Endocrinol Metab ; 100(1): 235-43, 2015 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-25250633

RESUMO

CONTEXT: The ability of insulin to suppress hepatic glucose production is impaired among subjects with increased intrahepatic triglycerides (IHTG). However, little is known about the roles of insulin on the supporting fluxes of glucose production among patients with fatty liver. OBJECTIVE: To evaluate the effects of insulin on fluxes through the three potential sources of plasma glucose (glycerol, the citric acid cycle, and glycogen) among patients with fatty liver. Design, Settings, Participants, and Intervention: Nineteen men with a range of IHTG (∼0.5% to 23%) were studied after an overnight fast and during hyperinsulinemia using magnetic resonance spectroscopy and stable isotope tracers. MAIN OUTCOME MEASURES: IHTG, gluconeogenesis from glycerol, gluconeogenesis from the citric acid cycle, glycogenolysis, and (13)C-labeled glucose produced from the citric acid cycle during hyperinsulinemia were measured. RESULTS: Men with high IHTG had higher fluxes through all pathways contributing to glucose production during hyperinsulinemia, compared to men with low IHTG, but they had similar fluxes after the fast. Consequently, men with fatty liver had impaired insulin efficiency in suppressing total glucose production as well as fluxes through all three biochemical pathways contributing to glucose. The detection of glucose isotopomers with (13)C arising from [U-(13)C3]propionate ingested during hyperinsulinemia demonstrated continuous gluconeogenesis from the citric acid cycle in all subjects. CONCLUSIONS: These findings challenge the concept that individual glucose production pathways are selectively dysregulated during hepatic insulin resistance. Overproduction of glucose during hyperinsulinemia in men with fatty liver results from inadequate suppression of all the supporting fluxes of glucose production in response to insulin.


Assuntos
Gluconeogênese/fisiologia , Glucose/biossíntese , Insulina/farmacologia , Fígado/metabolismo , Triglicerídeos/metabolismo , Adulto , Fígado Gorduroso/metabolismo , Gluconeogênese/efeitos dos fármacos , Humanos , Fígado/efeitos dos fármacos , Espectroscopia de Ressonância Magnética , Masculino , Pessoa de Meia-Idade , Obesidade/metabolismo
18.
J Biol Chem ; 289(47): 32593-603, 2014 Nov 21.
Artigo em Inglês | MEDLINE | ID: mdl-25288790

RESUMO

After exposure to [U-(13)C3]glycerol, the liver produces primarily [1,2,3-(13)C3]- and [4,5,6-(13)C3]glucose in equal proportions through gluconeogenesis from the level of trioses. Other (13)C-labeling patterns occur as a consequence of alternative pathways for glucose production. The pentose phosphate pathway (PPP), metabolism in the citric acid cycle, incomplete equilibration by triose phosphate isomerase, or the transaldolase reaction all interact to produce complex (13)C-labeling patterns in exported glucose. Here, we investigated (13)C labeling in plasma glucose in rats given [U-(13)C3]glycerol under various nutritional conditions. Blood was drawn at multiple time points to extract glucose for NMR analysis. Because the transaldolase reaction and incomplete equilibrium by triose phosphate isomerase cannot break a (13)C-(13)C bond within the trioses contributing to glucose, the appearance of [1,2-(13)C2]-, [2,3-(13)C2]-, [5,6-(13)C2]-, and [4,5-(13)C2]glucose provides direct evidence for metabolism of glycerol in the citric acid cycle or the PPP but not an influence of either triose phosphate isomerase or the transaldolase reaction. In all animals, [1,2-(13)C2]glucose/[2,3-(13)C2]glucose was significantly greater than [5,6-(13)C2]glucose/[4,5-(13)C2]glucose, a relationship that can only arise from gluconeogenesis followed by passage of substrates through the PPP. In summary, the hepatic PPP in vivo can be detected by (13)C distribution in blood glucose after [U-(13)C3]glycerol administration.


Assuntos
Gluconeogênese , Glicerol/metabolismo , Fígado/metabolismo , Via de Pentose Fosfato , Animais , Glicemia/metabolismo , Isótopos de Carbono , Lactatos/metabolismo , Espectroscopia de Ressonância Magnética , Masculino , Ratos Sprague-Dawley , Fatores de Tempo , Transaldolase/metabolismo , Triose-Fosfato Isomerase/metabolismo
19.
J Biol Chem ; 289(9): 6212-24, 2014 Feb 28.
Artigo em Inglês | MEDLINE | ID: mdl-24415759

RESUMO

Metabolic reprogramming facilitates cancer cell growth, so quantitative metabolic flux measurements could produce useful biomarkers. However, current methods to analyze flux in vivo provide either a steady-state overview of relative activities (infusion of (13)C and analysis of extracted metabolites) or a dynamic view of a few reactions (hyperpolarized (13)C spectroscopy). Moreover, although hyperpolarization has successfully quantified pyruvate-lactate exchanges, its ability to assess mitochondrial pyruvate metabolism is unproven in cancer. Here, we combined (13)C hyperpolarization and isotopomer analysis to quantify multiple fates of pyruvate simultaneously. Two cancer cell lines with divergent pyruvate metabolism were incubated with thermally polarized [3-(13)C]pyruvate for several hours, then briefly exposed to hyperpolarized [1-(13)C]pyruvate during acquisition of NMR spectra using selective excitation to maximize detection of H[(13)C]O3(-) and [1-(13)C]lactate. Metabolites were then extracted and subjected to isotopomer analysis to determine relative rates of pathways involving [3-(13)C]pyruvate. Quantitation of hyperpolarized H[(13)C]O3(-) provided a single definitive metabolic rate, which was then used to convert relative rates derived from isotopomer analysis into quantitative fluxes. This revealed that H[(13)C]O3(-) appearance reflects activity of pyruvate dehydrogenase rather than pyruvate carboxylation followed by subsequent decarboxylation reactions. Glucose substantially altered [1-(13)C]pyruvate metabolism, enhancing exchanges with [1-(13)C]lactate and suppressing H[(13)C]O3(-) formation. Furthermore, inhibiting Akt, an oncogenic kinase that stimulates glycolysis, reversed these effects, indicating that metabolism of pyruvate by both LDH and pyruvate dehydrogenase is subject to the acute effects of oncogenic signaling on glycolysis. The data suggest that combining (13)C isotopomer analyses and dynamic hyperpolarized (13)C spectroscopy may enable quantitative flux measurements in living tumors.


Assuntos
Glucose/metabolismo , Glicólise , Espectroscopia de Ressonância Magnética , Neoplasias/diagnóstico por imagem , Neoplasias/metabolismo , Ácido Pirúvico/metabolismo , Isótopos de Carbono/farmacocinética , Isótopos de Carbono/farmacologia , Linhagem Celular Tumoral , Humanos , Proteínas Proto-Oncogênicas c-akt/antagonistas & inibidores , Proteínas Proto-Oncogênicas c-akt/metabolismo , Radiografia
20.
J Biol Chem ; 288(20): 14488-14496, 2013 May 17.
Artigo em Inglês | MEDLINE | ID: mdl-23572519

RESUMO

During hepatic lipogenesis, the glycerol backbone of acylglycerols originates from one of three sources: glucose, glycerol, or substrates passing through the citric acid cycle via glyceroneogenesis. The relative contribution of each substrate source to glycerol in rat liver acylglycerols was determined using (13)C-enriched substrates and NMR. Animals received a fixed mixture of glucose, glycerol, and lactate; one group received [U-(13)C6]glucose, another received [U-(13)C3]glycerol, and the third received [U-(13)C3]lactate. After 3 h, the livers were harvested to extract fats, and the glycerol moiety from hydrolyzed acylglycerols was analyzed by (13)C NMR. In either fed or fasted animals, glucose and glycerol provided the majority of the glycerol backbone carbons, whereas the contribution of lactate was small. In fed animals, glucose contributed >50% of the total newly synthesized glycerol backbone, and 35% of this contribution occurred after glucose had passed through the citric acid cycle. By comparison, the glycerol contribution was ~40%, and of this, 17% of the exogenous glycerol passed first through the cycle. In fasted animals, exogenous glycerol became the major contributor to acylglycerols. The contribution from exogenous lactate did increase in fasted animals, but its overall contribution remained small. The contributions of glucose and glycerol that had passed through the citric acid cycle first increased in fasted animals from 35 to 71% for glucose and from 17 to 24% for glycerol. Thus, a substantial fraction from both substrate sources passed through the cycle prior to incorporation into the glycerol moiety of acylglycerols in the liver.


Assuntos
Ciclo do Ácido Cítrico , Glucose/metabolismo , Glicerídeos/metabolismo , Glicerol/metabolismo , Ácido Láctico/metabolismo , Fígado/metabolismo , Animais , Jejum , Espectroscopia de Ressonância Magnética , Masculino , Músculo Esquelético/metabolismo , Ácido Pirúvico/metabolismo , Ratos , Ratos Sprague-Dawley
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