RESUMO
Naive CD8+ T cells differentiating into effector T cells increase glucose uptake and shift from quiescent to anabolic metabolism. Although much is known about the metabolism of cultured T cells, how T cells use nutrients during immune responses in vivo is less well defined. Here, we combined bioenergetic profiling and 13C-glucose infusion techniques to investigate the metabolism of CD8+ T cells responding to Listeria infection. In contrast to in vitro-activated T cells, which display hallmarks of Warburg metabolism, physiologically activated CD8+ T cells displayed greater rates of oxidative metabolism, higher bioenergetic capacity, differential use of pyruvate, and prominent flow of 13C-glucose carbon to anabolic pathways, including nucleotide and serine biosynthesis. Glucose-dependent serine biosynthesis mediated by the enzyme Phgdh was essential for CD8+ T cell expansion in vivo. Our data highlight fundamental differences in glucose use by pathogen-specific T cells in vivo, illustrating the impact of environment on T cell metabolic phenotypes.
Assuntos
Linfócitos T CD8-Positivos/imunologia , Linfócitos T CD8-Positivos/metabolismo , Metabolismo Energético , Glucose/metabolismo , Ativação Linfocitária/imunologia , Metaboloma , Metabolômica , Animais , Proliferação de Células , Cromatografia Gasosa-Espectrometria de Massas , Glicólise , Interações Hospedeiro-Patógeno/genética , Interações Hospedeiro-Patógeno/imunologia , Ativação Linfocitária/genética , Metabolômica/métodos , Camundongos , Estresse Oxidativo , Viroses/genética , Viroses/imunologia , Viroses/metabolismo , Viroses/virologiaRESUMO
Metabolic regulation has been recognized as a powerful principle guiding immune responses. Inflammatory macrophages undergo extensive metabolic rewiring 1 marked by the production of substantial amounts of itaconate, which has recently been described as an immunoregulatory metabolite 2 . Itaconate and its membrane-permeable derivative dimethyl itaconate (DI) selectively inhibit a subset of cytokines 2 , including IL-6 and IL-12 but not TNF. The major effects of itaconate on cellular metabolism during macrophage activation have been attributed to the inhibition of succinate dehydrogenase2,3, yet this inhibition alone is not sufficient to account for the pronounced immunoregulatory effects observed in the case of DI. Furthermore, the regulatory pathway responsible for such selective effects of itaconate and DI on the inflammatory program has not been defined. Here we show that itaconate and DI induce electrophilic stress, react with glutathione and subsequently induce both Nrf2 (also known as NFE2L2)-dependent and -independent responses. We find that electrophilic stress can selectively regulate secondary, but not primary, transcriptional responses to toll-like receptor stimulation via inhibition of IκBζ protein induction. The regulation of IκBζ is independent of Nrf2, and we identify ATF3 as its key mediator. The inhibitory effect is conserved across species and cell types, and the in vivo administration of DI can ameliorate IL-17-IκBζ-driven skin pathology in a mouse model of psoriasis, highlighting the therapeutic potential of this regulatory pathway. Our results demonstrate that targeting the DI-IκBζ regulatory axis could be an important new strategy for the treatment of IL-17-IκBζ-mediated autoimmune diseases.
Assuntos
Fator 3 Ativador da Transcrição/metabolismo , Proteínas I-kappa B/metabolismo , Succinatos/metabolismo , Animais , Células Cultivadas , Citocinas/imunologia , Citocinas/metabolismo , Feminino , Regulação da Expressão Gênica/efeitos dos fármacos , Glutationa/metabolismo , Humanos , Inflamação/tratamento farmacológico , Inflamação/metabolismo , Interleucina-6/metabolismo , Queratinócitos/efeitos dos fármacos , Queratinócitos/metabolismo , Macrófagos/efeitos dos fármacos , Macrófagos/metabolismo , Camundongos , Camundongos Endogâmicos C57BL , Fator 2 Relacionado a NF-E2/metabolismo , Psoríase/tratamento farmacológico , Psoríase/patologia , Estresse Fisiológico/efeitos dos fármacos , Succinatos/administração & dosagem , Succinatos/química , Succinatos/farmacologia , Succinatos/uso terapêutico , Receptores Toll-Like/imunologiaRESUMO
Natural product congeners serve a useful role in the understanding of natural product biosynthesis and structure-activity relationships. A minor congener with superior activity, selectivity, and modifiable functional groups could serve as a more effective lead structure and replace even the original lead molecule that was used for medicinal chemistry modifications. Currently, no effective method exists to discover targeted congeners rapidly, specifically, and selectively from producing sources. Herein, a new method based on liquid-chromatography tandem-mass spectrometry combination is evaluated for targeted discovery of congeners of platensimycin and platencin from the extracts of Streptomyces platensis. By utilizing a precursor-ion searching protocol, tandem mass spectrometry not only confirmed the presence of known congeners but also provided unambiguous detection of many previously unknown congeners of platensimycin and platencin. This high-throughput and quantitative method can be rapidly and broadly applied for dereplication and congener discovery from a variety of producing sources, even when the targeted compounds are obscured by the presence of unrelated natural products.
Assuntos
Adamantano/química , Aminobenzoatos/química , Aminofenóis/química , Anilidas/química , Ensaios de Triagem em Larga Escala/métodos , Compostos Policíclicos/química , Streptomyces/química , Adamantano/isolamento & purificação , Aminobenzoatos/isolamento & purificação , Aminofenóis/isolamento & purificação , Anilidas/isolamento & purificação , Produtos Biológicos/química , Produtos Biológicos/isolamento & purificação , Cromatografia Líquida , Estrutura Molecular , Compostos Policíclicos/isolamento & purificação , Relação Estrutura-Atividade , Espectrometria de Massas em TandemRESUMO
Small cell lung cancer (SCLC) is a particularly aggressive subset of lung cancer, and identification of new therapeutic options is of significant interest. We recently reported that SCLC cell lines display a specific vulnerability to inhibition of squalene epoxidase (SQLE), an enzyme in the cholesterol biosynthetic pathway that catalyzes the conversion of squalene to 2,3-oxidosqualene. Since it has been reported that SQLE inhibition can result in dermatitis in dogs, we conducted a series of experiments to determine if SQLE inhibitors would be tolerated at exposures predicted to drive maximal efficacy in SCLC tumors. Detailed profiling of the SQLE inhibitor NB-598 showed that dogs did not tolerate predicted efficacious exposures, with dose-limiting toxicity due to gastrointestinal clinical observations, although skin toxicities were also observed. To extend these studies, two SQLE inhibitors, NB-598 and Cmpd-4â³, and their structurally inactive analogs, NB-598.ia and Cmpd-4â³.ia, were profiled in monkeys. While both active SQLE inhibitors resulted in dose-limiting gastrointestinal toxicity, the structurally similar inactive analogs did not. Collectively, our data demonstrate that significant toxicities arise at exposures well below the predicted levels needed for anti-tumor activity. The on-target nature of the toxicities identified is likely to limit the potential therapeutic utility of SQLE inhibition for the treatment of SCLC.
Assuntos
Inibidores Enzimáticos/sangue , Inibidores Enzimáticos/toxicidade , Esqualeno Mono-Oxigenase/antagonistas & inibidores , Esqualeno Mono-Oxigenase/sangue , Animais , Cães , Relação Dose-Resposta a Droga , Avaliação Pré-Clínica de Medicamentos/métodos , Macaca fascicularis , Masculino , Pele/efeitos dos fármacos , Pele/enzimologia , Pele/patologiaRESUMO
AIMS/HYPOTHESIS: Ceramides are sphingolipids that contribute to insulin resistance in preclinical studies. We hypothesised that plasma ceramides would be associated with body fat distribution, insulin resistance and incident type 2 diabetes in a multi-ethnic cohort. METHODS: A total of 1557 participants in the Dallas Heart Study without type 2 diabetes underwent measurements of metabolic biomarkers, fat depots by MRI and plasma ceramides by liquid chromatography-mass spectrometry. Diabetes outcomes were assessed after 7 years. Associations of body fat and insulin resistance with ceramides at baseline and of ceramides with incident diabetes outcomes were analysed. RESULTS: The cohort had a mean age of 43 years, with 58% women, 45% black participants and a mean BMI of 28 kg/m2. Total cholesterol levels were associated with all ceramides, but higher triacylglycerols and lower HDL-cholesterol and adiponectin were associated only with saturated fatty acid chain ceramides (p < 0.0003). After adjusting for clinical characteristics and total body fat, visceral adipose tissue was positively associated with saturated fatty acid ceramides (per SD, ß = 0.16 to 0.18) and inversely associated with polyunsaturated fatty acid ceramides (ß = -0.14 to -0.16, p < 0.001 for all). Lower-body subcutaneous fat showed an opposite pattern to that for visceral fat. HOMA-IR was positively associated with saturated (ß = 0.08 to 0.09, p < 0.001) and inversely with polyunsaturated ceramides (ß = -0.06 to -0.07, p < 0.05). Ceramides were not associated with incident type 2 diabetes after adjustment for clinical factors. CONCLUSIONS/INTERPRETATION: Plasma ceramides demonstrate a biologically complex relationship with metabolic and imaging indicators of dysfunctional adiposity. The role of ceramides in a shared pathway of metabolic dysfunction linking visceral adiposity and insulin resistance requires further investigation.
Assuntos
Ceramidas/sangue , Diabetes Mellitus Tipo 2/sangue , Diabetes Mellitus Tipo 2/fisiopatologia , Resistência à Insulina/fisiologia , Gordura Intra-Abdominal/metabolismo , Adiposidade/fisiologia , Adulto , Índice de Massa Corporal , Cromatografia Líquida , Feminino , Humanos , Espectroscopia de Ressonância Magnética , Masculino , Espectrometria de Massas , Pessoa de Meia-IdadeRESUMO
An increased contribution of de novo lipogenesis (DNL) may play a role in cases of dyslipidemia and adipose accretion; this suggests that inhibition of fatty acid synthesis may affect clinical phenotypes. Since it is not clear whether modulation of one step in the lipogenic pathway is more important than another, the use of tracer methods can provide a deeper level of insight regarding the control of metabolic activity. Although [2H]water is generally considered a reliable tracer for quantifying DNL in vivo (it yields a homogenous and quantifiable precursor labeling), the relatively long half-life of body water is thought to limit the ability of performing repeat studies in the same subjects; this can create a bottleneck in the development and evaluation of novel therapeutics for inhibiting DNL. Herein, we demonstrate the ability to perform back-to-back studies of DNL using [2H]water. However, this work uncovered special circumstances that affect the data interpretation, i.e., it is possible to obtain seemingly negative values for DNL. Using a rodent model, we have identified a physiological mechanism that explains the data. We show that one can use [2H]water to test inhibitors of DNL by performing back-to-back studies in higher species [i.e., treat nonhuman primates with platensimycin, an inhibitor of fatty acid synthase]; studies also demonstrate the unsuitability of [13C]acetate.
Assuntos
Óxido de Deutério/farmacologia , Ácido Palmítico/sangue , Acetatos/sangue , Adipogenia , Animais , Feminino , Meia-Vida , Lipogênese/efeitos dos fármacos , Macaca mulatta , Masculino , Camundongos Endogâmicos C57BLRESUMO
OBJECTIVE: Lp(a) [lipoprotein (a)] is composed of apoB (apolipoprotein B) and apo(a) [apolipoprotein (a)] and is an independent risk factor for cardiovascular disease and aortic stenosis. In clinical trials, anacetrapib, a CETP (cholesteryl ester transfer protein) inhibitor, causes significant reductions in plasma Lp(a) levels. We conducted an exploratory study to examine the mechanism for Lp(a) lowering by anacetrapib. APPROACH AND RESULTS: We enrolled 39 participants in a fixed-sequence, double-blind study of the effects of anacetrapib on the metabolism of apoB and high-density lipoproteins. Twenty-nine patients were randomized to atorvastatin 20 mg/d, plus placebo for 4 weeks, and then atorvastatin plus anacetrapib (100 mg/d) for 8 weeks. The other 10 subjects were randomized to double placebo for 4 weeks followed by placebo plus anacetrapib for 8 weeks. We examined the mechanisms of Lp(a) lowering in a subset of 12 subjects having both Lp(a) levels >20 nmol/L and more than a 15% reduction in Lp(a) by the end of anacetrapib treatment. We performed stable isotope kinetic studies using 2H3-leucine at the end of each treatment to measure apo(a) fractional catabolic rate and production rate. Median baseline Lp(a) levels were 21.5 nmol/L (interquartile range, 9.9-108.1 nmol/L) in the complete cohort (39 subjects) and 52.9 nmol/L (interquartile range, 38.4-121.3 nmol/L) in the subset selected for kinetic studies. Anacetrapib treatment lowered Lp(a) by 34.1% (P≤0.001) and 39.6% in the complete and subset cohort, respectively. The decreases in Lp(a) levels were because of a 41% reduction in the apo(a) production rate, with no effects on apo(a) fractional catabolic rate. CONCLUSIONS: Anacetrapib reduces Lp(a) levels by decreasing its production. CLINICAL TRIAL REGISTRATION: URL: http://www.clinicaltrials.gov. Unique identifier: NCT00990808.
Assuntos
Anticolesterolemiantes/uso terapêutico , Proteínas de Transferência de Ésteres de Colesterol/antagonistas & inibidores , Hipercolesterolemia/tratamento farmacológico , Lipoproteína(a)/sangue , Oxazolidinonas/uso terapêutico , Adulto , Idoso , Anticolesterolemiantes/efeitos adversos , Biomarcadores/sangue , Proteínas de Transferência de Ésteres de Colesterol/metabolismo , Cromatografia Líquida , Método Duplo-Cego , Regulação para Baixo , Feminino , Humanos , Hipercolesterolemia/sangue , Hipercolesterolemia/diagnóstico , Masculino , Pessoa de Meia-Idade , Cidade de Nova Iorque , Oxazolidinonas/efeitos adversos , Pennsylvania , Índice de Gravidade de Doença , Espectrometria de Massas em Tandem , Fatores de Tempo , Resultado do TratamentoRESUMO
Drug discovery and development efforts are largely based around a common expectation, namely, that direct or indirect action on a cellular process (e.g., statin-mediated enzyme inhibition or insulin-stimulated receptor activation) will have a beneficial impact on physiologic homeostasis. To expand on this, one could argue that virtually all pharmacologic interventions attempt to influence the flow of "traffic" in a biochemical network, irrespective of disease or modality. Since stable isotope tracer kinetic methods provide a measure of traffic flow (i.e., metabolic flux), their inclusion in study designs can yield novel information regarding pathway biology; the application of such methods requires the integration of knowledge in physiology, analytical chemistry, and mathematical modeling. Herein, we review the fundamental concepts that surround the use of tracer kinetics, define basic terms, and outline guiding principles via theoretical and experimental problems. Specifically, one needs to 1) recognize the types of biochemical events that change isotopic enrichments, 2) appreciate the distinction between fractional turnover and flux rate, and 3) be aware of the subtle differences between tracer kinetics and pharmacokinetics. We hope investigators can use the framework presented here to develop applications that address their specific questions surrounding biochemical flux, and thereby gain insight into the pathophysiology of disease states, and examine pharmacodynamic mechanisms.
Assuntos
Descoberta de Drogas/métodos , Análise do Fluxo Metabólico/métodos , Animais , Humanos , Marcação por Isótopo , Isótopos/química , Água/química , Água/metabolismoRESUMO
Two common missense variants in APOL1 (G1 and G2) have been definitively linked to CKD in black Americans. However, not all individuals with the renal-risk genotype develop CKD, and little is known about how APOL1 variants drive disease. Given the association of APOL1 with HDL particles, which are cleared by the kidney, differences in the level or quality of mutant APOL1HDL particles could be causal for disease and might serve as a useful risk stratification marker. We measured plasma levels of G0 (low risk), G1, and G2 APOL1 in 3450 individuals in the Dallas Heart Study using a liquid chromatography-MS method that enabled quantitation of the different variants. Additionally, we characterized native APOL1HDL from donors with no or two APOL1 risk alleles by size-exclusion chromatography and analysis of immunopurified APOL1HDL particles. Finally, we identified genetic loci associated with plasma APOL1 levels and tested for APOL1-dependent association with renal function. Although we replicated the previous association between APOL1 variant status and renal function in nondiabetic individuals, levels of circulating APOL1 did not associate with microalbuminuria or GFR. Furthermore, the size or known components of APOL1HDL did not consistently differ in subjects with the renal-risk genotype. Genetic association studies implicated variants in loci harboring haptoglobin-related protein (HPR), APOL1, and ubiquitin D (UBD) in the regulation of plasma APOL1 levels, but these variants did not associate with renal function. Collectively, these data demonstrate that the risk of renal disease associated with APOL1 is probably not related to circulating levels of the mutant protein.
Assuntos
Apolipoproteínas/sangue , Lipoproteínas HDL/sangue , Insuficiência Renal Crônica/sangue , Adulto , Apolipoproteína L1 , Apolipoproteínas/genética , Estudos de Coortes , Estudos Transversais , Feminino , Variação Genética , Genótipo , Humanos , Lipoproteínas HDL/genética , Masculino , Insuficiência Renal Crônica/epidemiologia , Insuficiência Renal Crônica/genética , Fatores de RiscoRESUMO
Studies in lipoprotein kinetics almost exclusively rely on steady-state approaches to modeling. Herein, we have used a non-steady-state experimental design to examine the role of cholesteryl ester transfer protein (CETP) in mediating HDL-TG flux in vivo in rhesus macaques, and therefore, we developed an alternative strategy to model the data. Two isotopomers ([(2)H11] and [(13)C18]) of oleic acid were administered (orally and intravenously, respectively) to serve as precursors for labeling TGs in apoB-containing lipoproteins. The flux of a specific TG (52:2) from these donor lipoproteins to HDL was used as the measure of CETP activity; calculations are also presented to estimate total HDL-TG flux. Based on our data, we estimate that the peak total postprandial TG flux to HDL via CETP is â¼ 13 mg · h(-1) · kg(-1) and show that this transfer was inhibited by 97% following anacetrapib treatment. Collectively, these data demonstrate that HDL TG flux can be used as a measure of CETP activity in vivo. The fact that the donor lipoproteins can be labeled in situ using well-established stable isotope tracer techniques suggests ways to measure this activity for native lipoproteins in free-living subjects under any physiological conditions.
Assuntos
Proteínas de Transferência de Ésteres de Colesterol/antagonistas & inibidores , Proteínas de Transferência de Ésteres de Colesterol/metabolismo , Lipoproteínas HDL/metabolismo , Oxazolidinonas/farmacologia , Triglicerídeos/metabolismo , Animais , Lipoproteínas HDL/sangue , Macaca mulatta , Masculino , Modelos Biológicos , Triglicerídeos/sangueRESUMO
Aberrant regulation of glucose production makes a critical contribution to the impaired glycemic control that is observed in type 2 diabetes. Although isotopic tracer methods have proven to be informative in quantifying the magnitude of such alterations, it is presumed that one must rely on venous access to administer glucose tracers which therein presents obstacles for the routine application of tracer methods in rodent models. Since intraperitoneal injections are readily used to deliver glucose challenges and/or dose potential therapeutics, we hypothesized that this route could also be used to administer a glucose tracer. The ability to then reliably estimate glucose flux would require attention toward setting a schedule for collecting samples and choosing a distribution volume. For example, glucose production can be calculated by multiplying the fractional turnover rate by the pool size. We have taken a step-wise approach to examine the potential of using an intraperitoneal tracer administration in rat and mouse models. First, we compared the kinetics of [U-13C]glucose following either an intravenous or an intraperitoneal injection. Second, we tested whether the intraperitoneal method could detect a pharmacological manipulation of glucose production. Finally, we contrasted a potential application of the intraperitoneal method against the glucose-insulin clamp. We conclude that it is possible to 1) quantify glucose production using an intraperitoneal injection of tracer and 2) derive a "glucose production index" by coupling estimates of basal glucose production with measurements of fasting insulin concentration; this yields a proxy for clamp-derived assessments of insulin sensitivity of endogenous production.
Assuntos
Glicemia/metabolismo , Indicadores e Reagentes , Animais , Glicemia/efeitos dos fármacos , Isótopos de Carbono , Dieta Hiperlipídica , Feminino , Técnica Clamp de Glucose , Hipoglicemiantes/farmacologia , Injeções Intraperitoneais , Injeções Intravenosas , Resistência à Insulina , Cinética , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Obesos , Projetos Piloto , Ratos , Ratos Sprague-Dawley , Ratos Zucker , Rosiglitazona , Tiazolidinedionas/farmacologiaRESUMO
Liver steatosis is a common health problem associated with hepatitis C virus (HCV) and an important risk factor for the development of liver fibrosis and cancer. Steatosis is caused by triglycerides (TG) accumulating in lipid droplets (LDs), cellular organelles composed of neutral lipids surrounded by a monolayer of phospholipids. The HCV nucleocapsid core localizes to the surface of LDs and induces steatosis in cultured cells and mouse livers by decreasing intracellular TG degradation (lipolysis). Here we report that core at the surface of LDs interferes with the activity of adipose triglyceride lipase (ATGL), the key lipolytic enzyme in the first step of TG breakdown. Expressing core in livers or mouse embryonic fibroblasts of ATGL(-/-) mice no longer decreases TG degradation as observed in LDs from wild-type mice, supporting the model that core reduces lipolysis by engaging ATGL. Core must localize at LDs to inhibit lipolysis, as ex vivo TG hydrolysis is impaired in purified LDs coated with core but not when free core is added to LDs. Coimmunoprecipitation experiments revealed that core does not directly interact with the ATGL complex but, unexpectedly, increased the interaction between ATGL and its activator CGI-58 as well as the recruitment of both proteins to LDs. These data link the anti-lipolytic activity of the HCV core protein with altered ATGL binding to CGI-58 and the enhanced association of both proteins with LDs.
Assuntos
1-Acilglicerol-3-Fosfato O-Aciltransferase/metabolismo , Lipase/metabolismo , Gotículas Lipídicas/enzimologia , Proteínas do Core Viral/fisiologia , Animais , Células COS , Linhagem Celular Tumoral , Chlorocebus aethiops , Células HEK293 , Humanos , Hidrólise , Metabolismo dos Lipídeos , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Células NIH 3T3 , Triglicerídeos/metabolismoRESUMO
Our ability to understand the pathogenesis of problems surrounding lipid accretion requires attention towards quantifying lipid kinetics. In addition, studies of metabolic flux should also help unravel mechanisms that lead to imbalances in inter-organ lipid trafficking which contribute to dyslipidemia and/or peripheral lipid accumulation (e.g. hepatic fat deposits). This review aims to outline the development and use of novel methods for studying lipid kinetics in vivo. Although our focus is directed towards some of the approaches that are currently reported in the literature, we include a discussion of the older literature in order to put "new" methods in better perspective and inform readers of valuable historical research. Presumably, future advances in understanding lipid dynamics will benefit from a careful consideration of the past efforts, where possible we have tried to identify seminal papers or those that provide clear data to emphasize essential points. This article is part of a Special Issue entitled: Modulation of Adipose Tissue in Health and Disease.
Assuntos
Tecido Adiposo/metabolismo , Metabolismo dos Lipídeos , Lipídeos/biossíntese , Triglicerídeos/metabolismo , Distribuição da Gordura Corporal , Colesterol/biossíntese , Colesterol/metabolismo , Metabolismo Energético , Humanos , Cinética , Triglicerídeos/químicaRESUMO
LC/MS quantification of multiple plasma proteins that differ by several orders of magnitude in concentration from a single sample is challenging. We present a strategy that allows the simultaneous determination of the concentration and turnover kinetics of higher and lower abundant proteins from a single digestion mixture. Our attention was directed at a cluster of proteins that interact to affect the absorption and interorgan lipid trafficking. We demonstrate that apos involved in TG metabolism such as apoC2, C3, E, and A4 (micromolar concentration), and apoB48 and apoA5 (single-digit nanomolar concentration) can be quantified from a single digestion mixture. A high degree of correlation between LC/MS and immunobased measurements for apoC2, C3, E, and B48 was observed. Moreover, apoA5 fractional synthesis rate was measured in humans for the first time. Finally, the method can be directly applied to studies involving nonhuman primates because peptide sequences used in the method are conserved between humans and nonhuman primates.
Assuntos
Apolipoproteína A-V/sangue , Apolipoproteína B-48/sangue , Triglicerídeos/sangue , Biomarcadores/sangue , Cromatografia Líquida/métodos , Feminino , Humanos , Masculino , Espectrometria de Massas/métodosRESUMO
RATIONALE: Apolipoprotein(a) is a polymorphic glycoprotein covalently bound to apoB100 in Lp(a) particles and has been described to be both atherogenic and prothrombotic, although its exact mechanism of action is not well defined. Apolipoprotein(a) is routinely measured by immunoassays. Unfortunately, the accuracy of the measurement can be affected by the apolipoprotein(a) size (number of kringles) polymorphism in Lp(a) particles. Here we describe an ultra-performance liquid chromatography/mass spectrometry (UPLC/MS) assay that is capable of measuring apolipoprotein(a) concentrations while simultaneously determining the number of kringles present per protein. METHODS: Plasma samples were diluted and proteins de-lipidated with deoxycholate prior to tryptic digestion. Distinct tryptic peptides from different regions of apolipoprotein(a) were measured to determine both concentration and the number of kringles present per protein. Separation and quantitation of tryptic peptides is carried out at 700 µL/min using a 1.7 µm C18 column (2.1 × 100 mm) coupled to a Thermo Vantage triple quadrupole (QQQ) mass spectrometer with a heated electrospray ionization (HESI) source. RESULTS: This method was compared to established methods for measuring concentration (monoclonal antibody based ELISA) and size (gel-electrophoresis) using 80 plasma samples proved by NWLRL. The slope and r(2) value for the correlation of concentrations were determined to be 0.96 and 0.98, demonstrating excellent agreement of absolute values between the UPLC/MS and ELISA methods. As measured by UPLC/MS, the average kringle number or size is smaller than determined by the electrophoretic method. CONCLUSIONS: A single UPLC/MS method was developed capable of measuring apolipoprotein(a) concentration and size (by measuring the number of kringles per protein). This assay passes criteria required for 'fit for purpose' assays including sensitivity, intra and interday reproducibility and freeze/thaw stability. While the agreement between UPLC/MS and ELISA is excellent for concentration and may provide researchers with additional tools for studying apolipoprotein(a), the dissimilarities between UPLC/MS and the electrophoretic method may also be exploited for understanding apolipoprotein(a) structure and function.
Assuntos
Apoproteína(a)/análise , Apoproteína(a)/química , Cromatografia Líquida de Alta Pressão/métodos , Espectrometria de Massas/métodos , Sequência de Aminoácidos , Humanos , Dados de Sequência Molecular , Fragmentos de Peptídeos/análise , Fragmentos de Peptídeos/química , Estabilidade Proteica , Reprodutibilidade dos Testes , Sensibilidade e EspecificidadeRESUMO
RATIONALE: The ability to quantify rates of formation, regression and/or remodeling of atherosclerotic plaque should facilitate a better understanding of the pathogenesis and management of cardiovascular disease. In the current study, we coupled a stable isotope labeled tracer protocol with matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) to examine spatial and temporal lipid dynamics in atherosclerotic plaque. METHODS: To promote plaque formation in the aorta region, ApoE KO mice were fed a high cholesterol diet (0.15% cholesterol) and orally dosed with (2,2,3,4,4,6-d(6))-cholesterol over several weeks. Tissue sections of ~10 µm thickness were analyzed by MALDI-MSI using matrix deposition by either chemical sublimation or acoustic droplet ejection. RESULTS: MALDI-MSI yielded distinct spatial distribution information for a variety of lipid classes including specific lysophosphatidylcholines typically associated with atherosclerosis-related tissue damage such as phospholipase 2 (Lp-PLA(2)) that mediate chemotactic responses to inflammation (e.g. LPC 16:0, LPC 18:0 and LPC 18:1) as well as free cholesterol and cholesteryl esters that contribute to atheroma formation. MALDI mass spectra acquired from aorta tissue sections clearly distinguished non-esterified and esterified versions of (2,2,3,4,4,6-d(6))-cholesterol within aortic plaque regions and showed distinct spatial accumulation of the cholesterol tracer. CONCLUSIONS: The ability to couple stable isotope based protocols with MALDI-MSI enables a novel strategy to characterize the effects of therapeutic treatments on atherosclerotic plaque formation, regression and potential remodeling of the complex lipid components with high chemical specificity and spatiotemporal information.
RESUMO
RATIONALE: The ability to measure low levels of (2)H-labeling is important in studies of metabolic flux, e.g. one can estimate lipid synthesis by administering (2)H2O and then measuring the incorporation of (2)H into fatty acids. Unfortunately, the analyses are complicated by the presence of more abundant naturally occurring stable isotopes, e.g. (13)C. Conventional approaches rely on coupling gas chromatographic separation of lipids with either quadrupole-mass spectrometry (q-MS) and/or pyrolysis-isotope ratio mass spectrometry (IRMS). The former is limited by high background labeling (primarily from (13)C) whereas the latter is not suitable for routine high-throughput analyses. METHODS: We have contrasted the use of continuous flow-pyrolysis-IRMS against high-resolution mass spectrometry (i.e. Qq-FT-ICR MS) for measuring the (2)H-enrichment of fatty acids and peptides. RESULTS: In contrast to IRMS, which requires ~30 min per analysis, it is possible to measure the (2)H-enrichment of palmitate via direct infusion high-resolution mass spectrometry (HRMS) in ~3 min per sample. In addition, Qq-FT-ICR MS enabled measurements of the (2)H-enrichment of peptides (which is not possible using IRMS). CONCLUSIONS: High-resolution mass spectrometry can be used to measure low levels of (2)H-labeling so we expect that this approach will enhance studies of metabolic flux that rely on (2)H-labeled tracers, e.g. (2)H2O. However, since the high-resolution analyses require greater amounts of a given analyte one potential limitation centers on the overall sensitivity. Presumably, future advances can overcome this barrier.
Assuntos
Deutério/análise , Ácidos Graxos/química , Marcação por Isótopo/métodos , Espectrometria de Massas/métodos , Animais , Chlorocebus aethiops , Deutério/química , Deutério/metabolismo , Óxido de Deutério/administração & dosagem , Ácidos Graxos/metabolismo , Feminino , Modelos Lineares , Macaca mulatta , Masculino , Peptídeos/química , Peptídeos/metabolismoRESUMO
Infusion of 13C-labeled metabolites provides a gold standard for understanding the metabolic processes used by T cells during immune responses in vivo. Through infusion of 13C-labeled metabolites (glucose, glutamine, and acetate) in Listeria monocytogenes-infected mice, we demonstrate that CD8 T effector (Teff) cells use metabolites for specific pathways during specific phases of activation. Highly proliferative early Teff cells in vivo shunt glucose primarily toward nucleotide synthesis and leverage glutamine anaplerosis in the tricarboxylic acid (TCA) cycle to support adenosine triphosphate and de novo pyrimidine synthesis. In addition, early Teff cells rely on glutamic-oxaloacetic transaminase 1 (Got1)-which regulates de novo aspartate synthesis-for effector cell expansion in vivo. CD8 Teff cells change fuel preference over the course of infection, switching from glutamine- to acetate-dependent TCA cycle metabolism late in infection. This study provides insights into the dynamics of Teff metabolism, illuminating distinct pathways of fuel consumption associated with CD8 Teff cell function in vivo.
Assuntos
Acetatos , Linfócitos T CD8-Positivos , Isótopos de Carbono , Glutamina , Glutamina/metabolismo , Animais , Linfócitos T CD8-Positivos/metabolismo , Acetatos/metabolismo , Camundongos , Listeriose/metabolismo , Listeriose/imunologia , Listeriose/microbiologia , Listeria monocytogenes , Ciclo do Ácido Cítrico , Glucose/metabolismo , Camundongos Endogâmicos C57BLRESUMO
Coordination of cellular metabolism is essential for optimal T cell responses. Here, we identify cytosolic acetyl-CoA production as an essential metabolic node for CD8 T cell function in vivo. We show that CD8 T cell responses to infection depend on acetyl-CoA derived from citrate via the enzyme ATP citrate lyase (ACLY). However, ablation of ACLY triggers an alternative, acetate-dependent pathway for acetyl-CoA production mediated by acyl-CoA synthetase short-chain family member 2 (ACSS2). Mechanistically, acetate fuels both the TCA cycle and cytosolic acetyl-CoA production, impacting T cell effector responses, acetate-dependent histone acetylation, and chromatin accessibility at effector gene loci. When ACLY is functional, ACSS2 is not required, suggesting acetate is not an obligate metabolic substrate for CD8 T cell function. However, loss of ACLY renders CD8 T cells dependent on acetate (via ACSS2) to maintain acetyl-CoA production and effector function. Together, ACLY and ACSS2 coordinate cytosolic acetyl-CoA production in CD8 T cells to maintain chromatin accessibility and T cell effector function.
Assuntos
ATP Citrato (pro-S)-Liase , Acetatos , Acetilcoenzima A , Linfócitos T CD8-Positivos , Cromatina , Camundongos Endogâmicos C57BL , Linfócitos T CD8-Positivos/imunologia , Linfócitos T CD8-Positivos/metabolismo , Animais , Cromatina/metabolismo , Acetilcoenzima A/metabolismo , ATP Citrato (pro-S)-Liase/metabolismo , ATP Citrato (pro-S)-Liase/genética , Camundongos , Acetatos/metabolismo , Acetato-CoA Ligase/metabolismo , Acetato-CoA Ligase/genética , Acetilação , Camundongos Knockout , Citosol/metabolismo , Histonas/metabolismoRESUMO
Cholesteryl ester transfer protein (CETP) transfers cholesteryl ester and triglyceride between HDL and apoB-containing lipoproteins. Anacetrapib (ANA), a reversible inhibitor of CETP, raises HDL cholesterol and lowers LDL cholesterol in dyslipidemic patients. We previously demonstrated that ANA increases macrophage-to-feces reverse cholesterol transport and fecal cholesterol excretion in hamsters, and increased preß HDL-dependent cholesterol efflux via ABCA1 in vitro. However, the effects of ANA on in vivo preß HDL have not been characterized. In vitro, ANA inhibited the formation of preß, however in ANA-treated dyslipidemic hamsters, preß HDL levels (measured by two-dimensional gel electrophoresis) were increased, in contrast to in vitro findings. Because changes in plasma preß HDL have been proposed to potentially affect markers of cholesterol absorption with other CETP inhibitors, a dual stable isotope method was used to directly measure cholesterol absorption in hamsters. ANA treatment of hamsters (on either dyslipidemic or normal diet) had no effect on cholesterol absorption, while dalcetrapib-treated hamsters displayed an increase in cholesterol absorption. Taken together, these data support the notion that ANA promotes preß HDL functionality in vivo, with no effects on cholesterol absorption.