Cancer-Specific Production of N-Acetylaspartate via NAT8L Overexpression in Non-Small Cell Lung Cancer and Its Potential as a Circulating Biomarker

Reprogrammed mitochondria: a central hub of cancer cell metabolism

Mitochondria represent the metabolic hub of normal cells and play this role also in cancer but with different functional purposes. While cells in differentiated tissues have the prerogative of maintaining basal metabolism and support the biosynthesis of specialized products, cancer cells have to rewire the metabolic constraints imposed by the differentiation process. They need to balance the bioenergetic supply with the anabolic requirements that entail the intense proliferation rate, including nucleotide and membrane lipid biosynthesis. For this aim, mitochondrial metabolism is reprogrammed following the activation of specific oncogenic pathways or due to specific mutations of mitochondrial proteins. The main process leading to mitochondrial metabolic rewiring is the alteration of the tricarboxylic acid cycle favoring the appropriate orchestration of anaplerotic and cataplerotic reactions. According to the tumor type or the microenvironmental conditions, mitochondria may decouple glucose catabolism from mitochondrial oxidation in favor of glutaminolysis or disable oxidative phosphorylation for avoiding harmful production of free radicals. These and other metabolic settings can be also determined by the neo-production of oncometabolites that are not specific for the tissue of origin or the accumulation of metabolic intermediates able to boost pro-proliferative metabolism also impacting epigenetic/transcriptional programs. The full characterization of tumor-specific mitochondrial signatures may provide the identification of new biomarkers and therapeutic opportunities based on metabolic approaches.

Baicalein induces apoptosis by inhibiting the glutamine-mTOR metabolic pathway in lung cancer

INTRODUCTION

Baicalein, a bioactive component of Scutellaria baicalensis Georgi, has been shown to promote apoptosis in non-small cell lung cancer cells. However, previous studies have not determined if baicalein exerts proapoptotic effects by modulating the metabolic pathways.

OBJECTIVE

To investigate if baicalein induces apoptosis in lung cancer cells by modulating the glutamine-mTOR metabolic pathway.

METHODS

The in vivo anti-lung cancer activity of baicalein (50, 100, and 200 mg/kg) was evaluated using a xenograft model. In vitro experiments were used to assess the efficacy of baicalein (for H1299: 12.5, 25, and 50 μM; for A549: 10, 20, and 40 μM) on lung cancer cell proliferation, colony formation, and apoptosis. Metabolomics analysis was performed using liquid chromatography-mass spectrometry. The binding of baicalein to glutamine transporters and glutaminase was examined using molecular docking. The overexpression of glutamine transporters was validated using qRT-PCR and western blot analyses. The levels of ASCT2, LAT1, GLS1, p-mTOR, mTOR, and apoptosis-related proteins were evaluated using western blot analysis.

RESULTS

Baicalein inhibited lung cancer xenograft tumor growth in vivo and suppressed proliferation and promoted apoptosis in lung cancer cells in vitro. Additionally, baicalein altered amino acid metabolites, especially glutamine metabolites, in H1299 and A549 cells. Mechanistically, baicalein interacted with glutamine transporters as well as glutaminase and inhibited their activation. The expression of mTOR, an apoptosis-related protein and downstream target of glutamine metabolism, was also inhibited by baicalein treatment. Importantly, we next demonstrated the suppression of mTOR signaling and the induction of apoptosis by baicalein were achieved by regulating glutamine metabolism.

CONCLUSION

Baicalein inhibited the mTOR signaling pathway and induced apoptosis by downregulating glutamine metabolism. The potential of baicalein to induce apoptosis in lung cancer cells by selectively targeting the glutamine-mTOR pathway suggests an encouraging approach for treating lung cancer.

N-acetyl-aspartate metabolism at the interface of cancer, immunity, and neurodegeneration

N-acetyl-L-aspartic acid (NAA) is a prominent amino acid derivative primarily associated with vertebrate brain metabolism. This review delineates the critical role of NAA across various cell types and its significance in pathophysiological contexts, including Canavan disease and cancer metabolism. Although traditionally linked with myelination and aspartoacylase-driven carbon donation, its significance as a carbon source for myelination remains debated. Evidence suggests that intact NAA might substantially impact cellular signaling, particularly processes such as histone acetylation. Beyond the brain, NAA metabolism's relevance is evident in diverse tissues, such as adipocytes, immune cells, and notably, cancer cells. In several cancer types, there is an observed upregulation of NAA synthesis accompanied by a simultaneous downregulation of its degradation. This pattern highlights the potential signaling role of intact NAA in disease.

Metabolomics Study Revealing Purines as Potential Diagnostic Biomarkers of Acute Respiratory Distress Syndrome in Patients with Community─Acquired Pneumonia

Community-acquired pneumonia (CAP) is a significant threat to human health and the leading cause of acute respiratory distress syndrome (ARDS). We aimed to reveal the metabolic profiling whether can be used for assessing CAP with or without ARDS (nARDS) and therapeutic effects on CAP patients after treatment. Urine samples were collected at the onset and recovery periods, and metabolomics was employed to identify robust biomarkers. 19 metabolites were significantly changed in the ARDS relative to nARDS, mainly involving purines and fatty acids. After treatment, 7 metabolites in the nARDS and 14 in the ARDS were found to be significantly dysregulated, including fatty acids and amino acids. In the validation cohort, we observed that the biomarker panel consisted of N2,N2-dimethylguanosine, 1-methyladenosine, 3-methylguanine, 1-methyladenosine, and uric acid exhibited better AUCs of 0.900 than pneumonia severity index and acute physiology and chronic health evaluation II (APACHE II) scores between the ARDS and nARDS. Combining L-phenylalanine, phytosphingosine, and N-acetylaspartylglutamate as biomarkers for discriminating the nARDS and ARDS patients after treatment exhibited good AUCs of 0.811 and 0.821, respectively. The metabolic pathway and defined biomarkers may serve as crucial indicators for predicting the development of ARDS in CAP patients and for assessing therapeutic effects.

The BinDiscover database: a biology-focused meta-analysis tool for 156,000 GC-TOF MS metabolome samples

Metabolomics by gas chromatography/mass spectrometry (GC/MS) provides a standardized and reliable platform for understanding small molecule biology. Since 2005, the West Coast Metabolomics Center at the University of California at Davis has collated GC/MS metabolomics data from over 156,000 samples and 2000 studies into the standardized BinBase database. We believe that the observations from these samples will provide meaningful insight to biologists and that our data treatment and webtool will provide insight to others who seek to standardize disparate metabolomics studies. We here developed an easy-to-use query interface, BinDiscover, to enable intuitive, rapid hypothesis generation for biologists based on these metabolomic samples. BinDiscover creates observation summaries and graphics across a broad range of species, organs, diseases, and compounds. Throughout the components of BinDiscover, we emphasize the use of ontologies to aggregate large groups of samples based on the proximity of their metadata within these ontologies. This adjacency allows for the simultaneous exploration of entire categories such as "rodents", "digestive tract", or "amino acids". The ontologies are particularly relevant for BinDiscover's ontologically grouped differential analysis, which, like other components of BinDiscover, creates clear graphs and summary statistics across compounds and biological metadata. We exemplify BinDiscover's extensive applicability in three showcases across biological domains.

Acetyl-CoA regulates lipid metabolism and histone acetylation modification in cancer

Acetyl-CoA, as an important molecule, not only participates in multiple intracellular metabolic reactions, but also affects the post-translational modification of proteins, playing a key role in the metabolic activity and epigenetic inheritance of cells. Cancer cells require extensive lipid metabolism to fuel for their growth, while also require histone acetylation modifications to increase the expression of cancer-promoting genes. As a raw material for de novo lipid synthesis and histone acetylation, acetyl-CoA has a major impact on lipid metabolism and histone acetylation in cancer. More importantly, in cancer, acetyl-CoA connects lipid metabolism with histone acetylation, forming a more complex regulatory mechanism that influences cancer growth, proliferation, metastasis.

Hindering NAT8L expression in hepatocellular carcinoma increases cytosolic aspartate delivery that fosters pentose phosphate pathway and purine biosynthesis promoting cell proliferation

N-acetylaspartate (NAA) is synthesized by the mitochondrial enzyme NAT8L, which uses acetyl-CoA and aspartate as substrates. These metabolites are fundamental for bioenergetics and anabolic requirements of highly proliferating cells, thus, NAT8L modulation may impinge on the metabolic reprogramming of cancer cells. Specifically, aspartate represents a limiting amino acid for nucleotide synthesis in cancer. Here, the expression of the NAT8L enzyme was modulated to verify how it impacts the metabolic adaptations and proliferative capacity of hepatocellular carcinoma. We demonstrated that NAT8L downregulation is associated with increased proliferation of hepatocellular carcinoma cells and immortalized hepatocytes. The overexpression of NAT8L instead decreased cell growth. The pro-tumoral effect of NAT8L silencing depended on glutamine oxidation and the rewiring of glucose metabolism. Mechanistically, NAT8L downregulation triggers aspartate outflow from mitochondria via the exporter SLC25A13 to promote glucose flux into the pentose phosphate pathway, boosting purine biosynthesis. These results were corroborated by the analyses of human and mouse hepatocellular carcinoma samples revealing a decrease in NAT8L expression compared to adjacent non-tumoral tissues. Overall, this work demonstrates that NAT8L expression in liver cells limits the cytosolic availability of aspartate necessary for enhancing the pentose phosphate pathway and purine biosynthesis, counteracting cell proliferation.

Comprehensive metabolomics expands precision medicine for triple-negative breast cancer

Metabolic reprogramming is a hallmark of cancer. However, systematic characterizations of metabolites in triple-negative breast cancer (TNBC) are still lacking. Our study profiled the polar metabolome and lipidome in 330 TNBC samples and 149 paired normal breast tissues to construct a large metabolomic atlas of TNBC. Combining with previously established transcriptomic and genomic data of the same cohort, we conducted a comprehensive analysis linking TNBC metabolome to genomics. Our study classified TNBCs into three distinct metabolomic subgroups: C1, characterized by the enrichment of ceramides and fatty acids; C2, featured with the upregulation of metabolites related to oxidation reaction and glycosyl transfer; and C3, having the lowest level of metabolic dysregulation. Based on this newly developed metabolomic dataset, we refined previous TNBC transcriptomic subtypes and identified some crucial subtype-specific metabolites as potential therapeutic targets. The transcriptomic luminal androgen receptor (LAR) subtype overlapped with metabolomic C1 subtype. Experiments on patient-derived organoid and xenograft models indicate that targeting sphingosine-1-phosphate (S1P), an intermediate of the ceramide pathway, is a promising therapy for LAR tumors. Moreover, the transcriptomic basal-like immune-suppressed (BLIS) subtype contained two prognostic metabolomic subgroups (C2 and C3), which could be distinguished through machine-learning methods. We show that N-acetyl-aspartyl-glutamate is a crucial tumor-promoting metabolite and potential therapeutic target for high-risk BLIS tumors. Together, our study reveals the clinical significance of TNBC metabolomics, which can not only optimize the transcriptomic subtyping system, but also suggest novel therapeutic targets. This metabolomic dataset can serve as a useful public resource to promote precision treatment of TNBC.

Current Adenosinergic Therapies: What Do Cancer Cells Stand to Gain and Lose?

A key objective in immuno-oncology is to reactivate the dormant immune system and increase tumour immunogenicity. Adenosine is an omnipresent purine that is formed in response to stress stimuli in order to restore physiological balance, mainly via anti-inflammatory, tissue-protective, and anti-nociceptive mechanisms. Adenosine overproduction occurs in all stages of tumorigenesis, from the initial inflammation/local tissue damage to the precancerous niche and the developed tumour, making the adenosinergic pathway an attractive but challenging therapeutic target. Many current efforts in immuno-oncology are focused on restoring immunosurveillance, largely by blocking adenosine-producing enzymes in the tumour microenvironment (TME) and adenosine receptors on immune cells either alone or combined with chemotherapy and/or immunotherapy. However, the effects of adenosinergic immunotherapy are not restricted to immune cells; other cells in the TME including cancer and stromal cells are also affected. Here we summarise recent advancements in the understanding of the tumour adenosinergic system and highlight the impact of current and prospective immunomodulatory therapies on other cell types within the TME, focusing on adenosine receptors in tumour cells. In addition, we evaluate the structure- and context-related limitations of targeting this pathway and highlight avenues that could possibly be exploited in future adenosinergic therapies.

Lipidomic and metabolomic analysis reveals changes in biochemical pathways for non-small cell lung cancer tissues

Lung cancer represents one of the leading worldwide causes of cancer death, but the pathobiochemistry of this disease is still not fully understood. Here we characterize the lipidomic and metabolomic profiles of the tumor and surrounding normal tissues for 23 patients with non-small cell lung cancer. In total, 500 molecular species were identified and quantified by a combination of the lipidomic shotgun tandem mass spectrometry (MS/MS) analysis and the targeted metabolomic approach using liquid chromatography (LC) - MS/MS. The statistical evaluation includes multivariate and univariate methods with the emphasis on paired statistical approaches. Our research revealed significant changes in several biochemical pathways related to the central carbon metabolism, acylcarnitines, dipeptides as well as the disruption in the lipid metabolism observed mainly for glycerophospholipids, sphingolipids, and cholesteryl esters.

N-acetylaspartate release by glutaminolytic ovarian cancer cells sustains protumoral macrophages

Glutaminolysis is known to correlate with ovarian cancer aggressiveness and invasion. However, how this affects the tumor microenvironment is elusive. Here, we show that ovarian cancer cells become addicted to extracellular glutamine when silenced for glutamine synthetase (GS), similar to naturally occurring GS-low, glutaminolysis-high ovarian cancer cells. Glutamine addiction elicits a crosstalk mechanism whereby cancer cells release N-acetylaspartate (NAA) which, through the inhibition of the NMDA receptor, and synergistically with IL-10, enforces GS expression in macrophages. In turn, GS-high macrophages acquire M2-like, tumorigenic features. Supporting this in␣vitro model, in silico data and the analysis of ascitic fluid isolated from ovarian cancer patients prove that an M2-like macrophage phenotype, IL-10 release, and NAA levels positively correlate with disease stage. Our study uncovers the unprecedented role of glutamine metabolism in modulating macrophage polarization in highly invasive ovarian cancer and highlights the anti-inflammatory, protumoral function of NAA.

The Ability of Metabolomics to Discriminate Non-Small-Cell Lung Cancer Subtypes Depends on the Stage of the Disease and the Type of Material Studied

Identification of the NSCLC subtype at an early stage is still quite sophisticated. Metabolomics analysis of tissue and plasma of NSCLC patients may indicate new, and yet unknown, metabolic pathways active in the NSCLC. Our research characterized the metabolomics profile of tissue and plasma of patients with early and advanced NSCLC stage. Samples were subjected to thorough metabolomics analyses using liquid chromatography-mass spectrometry (LC-MS) technique. Tissue and/or plasma samples from 137 NSCLC patients were analyzed. Based on the early stage tissue analysis, more than 200 metabolites differentiating adenocarcinoma (ADC) and squamous cell lung carcinoma (SCC) subtypes as well as normal tissue, were identified. Most of the identified metabolites were amino acids, fatty acids, carnitines, lysoglycerophospholipids, sphingomyelins, plasmalogens and glycerophospholipids. Moreover, metabolites related to N-acyl ethanolamine (NAE) biosynthesis, namely glycerophospho (N-acyl) ethanolamines (GP-NAE), which discriminated early-stage SCC from ADC, have also been identified. On the other hand, the analysis of plasma of chronic obstructive pulmonary disease (COPD) and NSCLC patients allowed exclusion of the metabolites related to the inflammatory state in lungs and the identification of compounds (lysoglycerophospholipids, glycerophospholipids and sphingomyelins) truly characteristic to cancer. Our results, among already known, showed novel, thus far not described, metabolites discriminating NSCLC subtypes, especially in the early stage of cancer. Moreover, the presented results also indicated the activity of new metabolic pathways in NSCLC. Further investigations on the role of NAE biosynthesis pathways in the early stage of NSCLC may reveal new prognostic and diagnostic targets.

An Integrative Transcriptomic and Metabolomic Study Revealed That Melatonin Plays a Protective Role in Chronic Lung Inflammation by Reducing Necroptosis

It has been reported that melatonin can relieve the symptoms of chronic obstructive pulmonary disease (COPD) by improving sleep quality, that is to say, the pineal secreted hormone melatonin has a protective effect in the pathogenesis of COPD, but its underlying mechanism remains unclear. In this study, we recruited 73 people into control (n = 22), stable COPD (n = 20), and acute exacerbation of COPD (n = 31) groups to detect the serum melatonin levels. Then, through the mouse model, we employed a systematic study based on the metabolomic and transcriptomic analyses to investigate the molecular mechanisms involved in the progression of the disease. Circulating melatonin in acute exacerbation of COPD patients was decreased compared with that in healthy donors and stable COPD patients. The serum melatonin level was positively correlated with lung function parameters, such as FEV1, FEV1/FVC, and FEV1% predicted in acute exacerbation of COPD patients. Animal experiments showed that melatonin can not only alleviate chronic lipopolysaccharide (LPS)-induced mouse lung destruction and chronic lung inflammation but also reduce necroptosis (RIP1/RIP3/MLKL), a programmed cell death process in bronchial epithelial cells. The protective effect of melatonin on chronic lung inflammation was further suggested to be dependent on targeting its membrane receptor MT1/MT2. In addition, transcriptomic and metabolomic profiling in the lungs of mice indicated that LPS can induce perturbations of the mainstream metabolites associated with amino acid and energy metabolism. Melatonin may reduce the necroptosis by modifying the disordered pathways of alanine, aspartate, and glutamate metabolism caused by LPS. This study suggests that melatonin may act as a potential therapeutic agent for alleviating the chronic inflammation associated with COPD.

Screening of Methylation Gene Sites as Prognostic Signature in Lung Adenocarcinoma

PURPOSE

Most lung adenocarcinoma (LUAD) patients are diagnosed at the advanced stage and have poor prognosis. DNA methylation plays an important role in the prognosis prediction of cancers. The objective of this study was to identify new DNA methylation sites as biomarkers for LUAD prognosis.

MATERIALS AND METHODS

We downloaded DNA methylation data from The Cancer Genome Atlas data portal. Cox proportional hazard regression model and random survival forest algorithm were applied to identify the DNA-methylation sites. Methylation of sites were validated in the Gene Expression Omnibus cohorts. Function annotation were done to explore the biological function of DNA methylated sites signature.

RESULTS

Six DNA methylation sites were identified as prognosis signature. The signature yielded acceptable discrimination between the high-risk group and low-risk group. The discrimination effect of this DNA methylation signature for the OS was obvious, with a median OS of 21.89 months vs. 17.74 months for high-risk vs. low-risk groups. This prognostic prediction model was validated by the test group and GEO dataset. The predictive survival value was higher for the prognostic prediction model than that for the tumor node metastasis stage. Adjuvant hemotherapy could not affect the prediction of the signature. Functional analysis indicated that these signature genes were involved in protein binding and cytoplasm.

CONCLUSION

We identified the prognostic signature for LUAD by combining six DNA methylation sites. This could service as potential robust and specificity signature in the prognosis prediction of LUAD.

Acetate Revisited: A Key Biomolecule at the Nexus of Metabolism, Epigenetics, and Oncogenesis - Part 2: Acetate and ACSS2 in Health and Disease

Acetate, the shortest chain fatty acid, has been implicated in providing health benefits whether it is derived from the diet or is generated from microbial fermentation of fiber in the gut. These health benefits range widely from improved cardiac function to enhanced red blood cell generation and memory formation. Understanding how acetate could influence so many disparate biological functions is now an area of intensive research. Protein acetylation is one of the most common post-translational modifications and increased systemic acetate strongly drives protein acetylation. By virtue of acetylation impacting the activity of virtually every class of protein, acetate driven alterations in signaling and gene transcription have been associated with several common human diseases, including cancer. In part 2 of this review, we will focus on some of the roles that acetate plays in health and human disease. The acetate-activating enzyme acyl-CoA short-chain synthetase family member 2 (ACSS2) will be a major part of that focus due to its role in targeted protein acetylation reactions that can regulate central metabolism and stress responses. ACSS2 is the only known enzyme that can recycle acetate derived from deacetylation reactions in the cytoplasm and nucleus of cells, including both protein and metabolite deacetylation reactions. As such, ACSS2 can recycle acetate derived from histone deacetylase reactions as well as protein deacetylation reactions mediated by sirtuins, among many others. Notably, ACSS2 can activate acetate released from acetylated metabolites including N-acetylaspartate (NAA), the most concentrated acetylated metabolite in the human brain. NAA has been associated with the metabolic reprograming of cancer cells, where ACSS2 also plays a role. Here, we discuss the context-specific roles that acetate can play in health and disease.

Simultaneous Detection of Zinc and Its Pathway Metabolites Using MALDI MS Imaging of Prostate Tissue

Levels of zinc, along with its mechanistically related metabolites citrate and aspartate, are widely reported as reduced in prostate cancer compared to healthy tissue and are therefore pointed out as potential cancer biomarkers. Previously, it has only been possible to analyze zinc and metabolites by separate detection methods. Through matrix-assisted laser desorption/ionization mass spectrometry imaging (MSI), we were for the first time able to demonstrate, in two different sample sets (n = 45 and n = 4), the simultaneous spatial detection of zinc, in the form of ZnCl₃^–, together with citrate, aspartate, and N-acetylaspartate on human prostate cancer tissues. The reliability of the ZnCl₃^– detection was validated by total zinc determination using laser ablation inductively coupled plasma MSI on adjacent serial tissue sections. Zinc, citrate, and aspartate were correlated with each other (range r = 0.46 to 0.74) and showed a significant reduction in cancer compared to non-cancer epithelium (p < 0.05, log₂ fold change range: −0.423 to −0.987), while no significant difference between cancer and stroma tissue was found. Simultaneous spatial detection of zinc and its metabolites is not only a valuable tool for analyzing the role of zinc in prostate metabolism but might also provide a fast and simple method to detect zinc, citrate, and aspartate levels as a biomarker signature for prostate cancer diagnostics and prognostics.

UPLC‑MS/MS‑based metabolomic characterization and comparison of pancreatic adenocarcinoma tissues using formalin‑fixed, paraffin‑embedded and optimal cutting temperature‑embedded materials

The purpose of the present study was to compare metabolites from formalin-fixed and paraffin-embedded (FFPE) pancreatic tissue blocks with those identified in optimal cutting temperature (OCT)-embedded pancreatic tissue blocks. Thus, ultra-performance liquid chromatograph-mass spectrometry/mass spectrometry-based metabolic profiling was performed in paired frozen (n=13) and FFPE (n=13) human pancreatic adenocarcinoma tissue samples, in addition to their benign counterparts. A total of 206 metabolites were identified in both OCT-embedded and FFPE tissue samples. The method feasibility was confirmed through reproducibility and a consistency assessment. Partial least-squares discriminant analysis and heatmap analysis reliably distinguished tumor and normal tissue phenotypes. The expression of 10 compounds, including N-acetylaspartate and creatinine, was significantly different in both OCT-embedded and FFPE tumor samples. These ten compounds may be viable candidate biomarkers of malignant pancreatic tissues. The super-categories to which they belonged exhibited no significant differences between FFPE and OCT-embedded samples. Furthermore, purine, arginine and proline, and pyrimidine metabolism used a shared pathway found in both OCT-embedded and FFPE tissue samples. These results supported the notion that metabolomic data acquired from FFPE pancreatic cancer specimens are reliable for use in retrospective and clinical studies.

Expression of LDH and CEA in serum in the process of targeted therapy of lung adenocarcinoma and the association between them and prognosis

Expression of lactate dehydrogenase (LDH) and carcinoembryonic antigen (CEA) in serum was investigated in the process of epidermal growth factor receptor-tyrosine kinase inhibitor (EGFR-TKI) targeting for treating lung adenocarcinoma and the association between LDH, CEA and prognosis of patients was evaluated. A retrospective analysis of 89 patients with lung adenocarcinoma admitted to The First People's Hospital of Chuzhou from January 2014 to February 2015 was performed. Fifty-one patients who received resection were considered the operation group, while the other 38 patients received EGFR-TKI targeted therapy and were considered the targeted group. Electrochemiluminescence and automatic biochemical analyzer were respectively used to detect the expression of CEA and LDH in serum. The therapeutic effective rates and the expression levels of LDH and CEA of the patients were compared. The patients in the targeted group were divided into LDH high-expression group, LDH low-expression group, CEA high-expression group and CEA low-expression group according to the median of the expression levels of LDH and CEA. The therapeutic effective rate in LDH high-expression group (65.00%) was significantly lower than that in LDH low-expression group (100.00%) (P=0.004). The therapeutic effective rate in CEA high-expression group (64.71%) was significantly lower than that in CEA low-expression group (95.24%) (P=0.016). The 3-year overall mortality rate in LDH high-expression group (47.37%) was significantly higher than that in LDH low-expression group (11.11%) (P=0.034). The 3-year overall mortality rate in CEA high-expression group (56.25%) was significantly higher than that in CEA low-expression group (4.76%) (P=0.020). The levels of CEA and LDH in serum were abnormally expressed in the process of the treatment of lung adenocarcinoma targeted by EGFR-TKI, which had great significance for monitoring the efficacy and prognosis of the treatment of lung adenocarcinoma targeted by EGFR-TKI.

N-acetylaspartate pathway is nutrient responsive and coordinates lipid and energy metabolism in brown adipocytes

The discovery of significant amounts of metabolically active brown adipose tissue (BAT) in adult humans renders it a promising target for anti-obesity therapies by inducing weight loss through increased energy expenditure. The components of the N-acetylaspartate (NAA) pathway are highly abundant in BAT. Aspartate N-acetyltransferase (Asp-NAT, encoded by Nat8l) synthesizes NAA from acetyl-CoA and aspartate and increases energy expenditure in brown adipocytes. However, the exact mechanism how the NAA pathway contributes to accelerated mobilization and oxidation of lipids and the physiological regulation of the NAA pathway remained elusive. Here, we demonstrate that the expression of NAA pathway genes corresponds to nutrient availability and specifically responds to changes in exogenous glucose. NAA is preferentially produced from glucose-derived acetyl-CoA and aspartate and its concentration increases during adipogenesis. Overexpression of Nat8l drains glucose-derived acetyl-CoA into the NAA pool at the expense of cellular lipids and certain amino acids. Mechanistically, we elucidated that a combined activation of neutral and lysosomal (acid) lipolysis is responsible for the increased lipid degradation. Specifically, translocation of the transcription factor EB to the nucleus activates the biosynthesis of autophagosomes and lysosomes. Lipid degradation within lysosomes accompanied by adipose triglyceride lipase-mediated lipolysis delivers fatty acids for the support of elevated mitochondrial respiration. Together, our data suggest a crucial role of the NAA pathway in energy metabolism and metabolic adaptation in BAT.

Cytosolic Aspartate Availability Determines Cell Survival When Glutamine Is Limiting

Mitochondrial function is important for aspartate biosynthesis in proliferating cells. Here, we show that mitochondrial aspartate export via the aspartate-glutamate carrier 1 (AGC1) supports cell proliferation and cellular redox homeostasis. Insufficient cytosolic aspartate delivery leads to cell death when TCA cycle carbon is reduced following glutamine withdrawal and/or glutaminase inhibition. Moreover, loss of AGC1 reduces allograft tumor growth that is further compromised by treatment with the glutaminase inhibitor CB-839. Together, these findings argue that mitochondrial aspartate export sustains cell survival in low-glutamine environments and AGC1 inhibition can synergize with glutaminase inhibition to limit tumor growth.

N-acetylaspartate (NAA) induces neuronal differentiation of SH-SY5Y neuroblastoma cell line and sensitizes it to chemotherapeutic agents

Neuroblastoma is the most commonly extra-cranial solid tumor of childhood frequently diagnosed. The nervous system-specific metabolite N-acetylaspartate (NAA) is synthesized from aspartate and acetyl-CoA in neurons, it is among the most abundant metabolites present in the central nervous system (CNS) and appears to be involved in many CNS disorders. The functional significance of the high NAA concentration in the brain remains uncertain, but it confers to NAA a unique clinical significance exploited in magnetic resonance spectroscopy. In the current study, we show that treatment of SH-SY5Y neuroblastoma-derived cell line with sub-cytotoxic physiological concentrations of NAA inhibits cell growth. This effect is partly due to enhanced apoptosis, shown by decrease of the anti-apoptotic factors survivin and Bcl-xL, and partly to arrest of the cell-cycle progression, linked to enhanced expression of the cyclin-inhibitors p53, p21^Cip1/Waf1 and p27^Kip1. Moreover, NAA-treated SH-SY5Y cells exhibited morphological changes accompanied with increase of the neurogenic markers TH and MAP2 and down-regulation of the pluripotency markers OCT4 and CXCR4/CD184. Finally, NAA-pre-treated SH-SY5Y cells resulted more sensitive to the cytotoxic effect of the chemotherapeutic drugs Cisplatin and 5-fluorouracil.

To our knowledge, this is the first study demonstrating the neuronal differentiating effects of NAA in neuroblastoma cells. NAA may be a potential preconditioning or adjuvant compound in chemotherapeutic treatment.

Metabolic effects of Hedyotis diffusa on rats bearing Walker 256 tumor revealed by NMR-based metabolomics

Hedyotis diffusa, a traditional Chinese herbal medicine, is widely used for oncotherapy and shows a positive effect in the clinical treatment. But its mechanism of anticancer activities is complicated and unclear. This study was undertaken to assess the therapeutic effects and reveal detailed mechanisms of H. diffusa for oncotherapy. A Walker 256 tumor-bearing rat model was established, and metabolomic profiles of plasma and urine were obtained from ¹ H NMR technique. Multivariate statistical analysis methods were used to characterize the discriminating metabolites between control (C), Walker 256 tumor-bearing rats model (M), and H. diffusa treatment (H) groups. Finally, 13 and 10 metabolomic biomarkers in urine and plasma samples were further identified as characteristic metabolites in M group, whereas H group showed a partial metabolic balance recovered, such as ornithine, N-acetyl-l-aspartate, l-aspartate, and creatinine in urine samples, and acetate, lactate, choline, l-glutamine, and 3-hydroxybutyrate in plasma samples. On the basis of the methods above, we hypothesized H. diffusa treatment reduced the injury caused by Walker 256 tumor and maintained a metabolic balance. Our study demonstrated that this method provided new insights into metabolic alterations in tumor-bearing biosystems and researching on the effects of H. diffusa on the endogenous metabolism in tumor-bearing rats.

Cancer Metabolism and Tumor Heterogeneity: Imaging Perspectives Using MR Imaging and Spectroscopy

Cancer cells reprogram their metabolism to maintain viability via genetic mutations and epigenetic alterations, expressing overall dynamic heterogeneity. The complex relaxation mechanisms of nuclear spins provide unique and convertible tissue contrasts, making magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) pertinent imaging tools in both clinics and research. In this review, we summarized MR methods that visualize tumor characteristics and its metabolic phenotypes on an anatomical, microvascular, microstructural, microenvironmental, and metabolomics scale. The review will progress from the utilities of basic spin-relaxation contrasts in cancer imaging to more advanced imaging methods that measure tumor-distinctive parameters such as perfusion, water diffusion, magnetic susceptibility, oxygenation, acidosis, redox state, and cell death. Analytical methods to assess tumor heterogeneity are also reviewed in brief. Although the clinical utility of tumor heterogeneity from imaging is debatable, the quantification of tumor heterogeneity using functional and metabolic MR images with development of robust analytical methods and improved MR methods may offer more critical roles of tumor heterogeneity data in clinics. MRI/MRS can also provide insightful information on pharmacometabolomics, biomarker discovery, disease diagnosis and prognosis, and treatment response. With these future directions in mind, we anticipate the widespread utilization of these MR-based techniques in studying in vivo cancer biology to better address significant clinical needs.

N-Acetylaspartate Metabolism Outside the Brain: Lipogenesis, Histone Acetylation, and Cancer

N-acetylaspartate (NAA) is a highly abundant brain metabolite. Aberrant NAA concentrations have been detected in many pathological conditions and although the function of NAA has been extensively investigated in the brain it is still controversial. Only recently, a role of NAA has been reported outside the brain. In brown adipocytes, which show high expression of the NAA-producing and the NAA-cleaving enzyme, the metabolism of NAA has been implicated in lipid synthesis and histone acetylation. Increased expression of N-acetyltransferase 8-like (Nat8l, the gene encoding the NAA synthesizing enzyme) induces de novo lipogenesis and the brown adipocyte phenotype. Accordingly silencing of aspartoacylase, the NAA-cleaving enzyme, reduced brown adipocyte differentiation mechanistically by decreasing histone acetylation and gene transcription. Notably, the expression of Nat8l and the amount of NAA were also shown to be increased in several tumors and inversely correlate with patients' survival. Additionally, Nat8l silencing reduced cell proliferation in tumor and non-tumor cells, while NAA supplementation could rescue it. However, the mechanism behind has not yet been clarified. It remains to be addressed whether NAA per se and/or its catabolism to acetate and aspartate, metabolites that have both been implicated in tumor growth, are valuable targets for future therapies.

Increasing N-acetylaspartate in the Brain during Postnatal Myelination Does Not Cause the CNS Pathologies of Canavan Disease

Canavan disease is caused by mutations in the gene encoding aspartoacylase (ASPA), a deacetylase that catabolizes N-acetylaspartate (NAA). The precise involvement of elevated NAA in the pathogenesis of Canavan disease is an ongoing debate. In the present study, we tested the effects of elevated NAA in the brain during postnatal development. Mice were administered high doses of the hydrophobic methyl ester of NAA (M-NAA) twice daily starting on day 7 after birth. This treatment increased NAA levels in the brain to those observed in the brains of Nur7 mice, an established model of Canavan disease. We evaluated various serological parameters, oxidative stress, inflammatory and neurodegeneration markers and the results showed that there were no pathological alterations in any measure with increased brain NAA levels. We examined oxidative stress markers, malondialdehyde content (indicator of lipid peroxidation), expression of NADPH oxidase and nuclear translocation of the stress-responsive transcription factor nuclear factor (erythroid-derived 2)-like 2 (NRF-2) in brain. We also examined additional pathological markers by immunohistochemistry and the expression of activated caspase-3 and interleukin-6 by Western blot. None of the markers were increased in the brains of M-NAA treated mice, and no vacuoles were observed in any brain region. These results show that ASPA expression prevents the pathologies associated with excessive NAA concentrations in the brain during postnatal myelination. We hypothesize that the pathogenesis of Canavan disease involves not only disrupted NAA metabolism, but also excessive NAA related signaling processes in oligodendrocytes that have not been fully determined and we discuss some of the potential mechanisms.

Screening and Early Detection of Lung Cancer

OBJECTIVE

To review current risk factors for lung cancer, identify screening and early detection guidelines while describing new approaches that use genomic technologies.

DATA SOURCES

Published scientific literature, clinical literature, and published lung cancer screening guidelines from the United States and Canada.

CONCLUSION

Nurses are caring for lung cancer patients who, historically, do not live for long periods after diagnosis. Research is revealing promising screening methodologies that can detect lung cancer 1 to 4 years earlier than the current approaches.

IMPLICATIONS FOR NURSING PRACTICE

Current knowledge about screening for lung cancer is a vital tool for nurses working with persons at high risk for this potentially aggressive and life-threatening malignancy. While old methods remain the standard of care, new detection methods use a variety of genomic-based technologies. These developing approaches emphasize the need for nurses at all levels of practice to have a working knowledge of genetics to educate patients and conference with colleagues.

Quantitative metabolic flux analysis reveals an unconventional pathway of fatty acid synthesis in cancer cells deficient for the mitochondrial citrate transport protein

The mitochondrial citrate transport protein (CTP), encoded by SLC25A1, accommodates bidirectional trafficking of citrate between the mitochondria and cytosol, supporting lipid biosynthesis and redox homeostasis. Genetic CTP deficiency causes a fatal neurodevelopmental syndrome associated with the accumulation of L- and D-2-hydroxyglutaric acid, and elevated CTP expression is associated with poor prognosis in several types of cancer, emphasizing the importance of this transporter in multiple human pathologies. Here we describe the metabolic consequences of CTP deficiency in cancer cells. As expected from the phenotype of CTP-deficient humans, somatic CTP loss in cancer cells induces broad dysregulation of mitochondrial metabolism, resulting in accumulation of lactate and of the L- and D- enantiomers of 2-hydroxyglutarate (2HG) and depletion of TCA cycle intermediates. It also eliminates mitochondrial import of citrate from the cytosol. To quantify the impact of CTP deficiency on metabolic flux, cells were cultured with a set of ¹³C-glucose and ¹³C-glutamine tracers with resulting data integrated by metabolic flux analysis (MFA). CTP-deficient cells displayed a major restructuring of central carbon metabolism, including suppression of pyruvate dehydrogenase (PDH) and induction of glucose-dependent anaplerosis through pyruvate carboxylase (PC). We also observed an unusual lipogenic pathway in which carbon from glucose supplies mitochondrial production of alpha-ketoglutarate (AKG), which is then trafficked to the cytosol and used to supply reductive carboxylation by isocitrate dehydrogenase 1 (IDH1). The resulting citrate is cleaved to produce lipogenic acetyl-CoA, thereby completing a novel pathway of glucose-dependent reductive carboxylation. In CTP deficient cells, IDH1 inhibition suppresses lipogenesis from either glucose or glutamine, implicating IDH1 as a required component of fatty acid synthesis in states of CTP deficiency.

RhoC GTPase Is a Potent Regulator of Glutamine Metabolism and N-Acetylaspartate Production in Inflammatory Breast Cancer Cells

Inflammatory breast cancer (IBC) is an extremely lethal cancer that rapidly metastasizes. Although the molecular attributes of IBC have been described, little is known about the underlying metabolic features of the disease. Using a variety of metabolic assays, including (13)C tracer experiments, we found that SUM149 cells, the primary in vitro model of IBC, exhibit metabolic abnormalities that distinguish them from other breast cancer cells, including elevated levels of N-acetylaspartate, a metabolite primarily associated with neuronal disorders and gliomas. Here we provide the first evidence of N-acetylaspartate in breast cancer. We also report that the oncogene RhoC, a driver of metastatic potential, modulates glutamine and N-acetylaspartate metabolism in IBC cells in vitro, revealing a novel role for RhoC as a regulator of tumor cell metabolism that extends beyond its well known role in cytoskeletal rearrangement.

Bridging the gap between non-targeted stable isotope labeling and metabolic flux analysis

BACKGROUND

Metabolism gained increasing interest for the understanding of diseases and to pinpoint therapeutic intervention points. However, classical metabolomics techniques only provide a very static view on metabolism. Metabolic flux analysis methods, on the other hand, are highly targeted and require detailed knowledge on metabolism beforehand.

RESULTS

We present a novel workflow to analyze non-targeted metabolome-wide stable isotope labeling data to detect metabolic flux changes in a non-targeted manner. Furthermore, we show how similarity-analysis of isotopic enrichment patterns can be used for pathway contextualization of unidentified compounds. We illustrate our approach with the analysis of changes in cellular metabolism of human adenocarcinoma cells in response to decreased oxygen availability. Starting without a priori knowledge, we detect metabolic flux changes, leading to an increased glutamine contribution to acetyl-CoA production, reveal biosynthesis of N-acetylaspartate by N-acetyltransferase 8-like (NAT8L) in lung cancer cells and show that NAT8L silencing inhibits proliferation of A549, JHH-4, PH5CH8, and BEAS-2B cells.

CONCLUSIONS

Differential stable isotope labeling analysis provides qualitative metabolic flux information in a non-targeted manner. Furthermore, similarity analysis of enrichment patterns provides information on metabolically closely related compounds. N-acetylaspartate and NAT8L are important players in cancer cell metabolism, a context in which they have not received much attention yet.