Non-essential Amino Acid Metabolism Research Articles

Metabolomics-guided global pathway analysis reveals better insights into the metabolic alterations of breast cancer

Accurate metabolome measurements are critical for improved insights into breast cancer metabolic disturbances and enhanced exploration of novel therapeutic targets. Nevertheless, conventional functional interpretation is limited by metabolite identification capacity, which diminishes the scientific value of untargeted metabolomics analyses. In this study, we conducted a metabolomics-guided global pathway meta-analysis to investigate the metabolic alterations of breast cancer. Metabolic features were directly investigated in the pathway meta-analysis to identify breast cancer-associated metabolic processes. Conventional pathway analysis was also conducted involving identified metabolites alone. Comparison of the two strategies revealed that the global pathway meta-analysis approach could avoid the loss of functionally relevant information, relative to the conventional analysis findings. Furthermore, the pathway meta-analysis accurately captured alterations in the following components of the breast cancer metabolome: central carbon metabolism, oxidative glutamine metabolism, purine metabolism, nonessential amino acid metabolism, and glutathione metabolism. There were also substantial alterations of fatty acyl carnitine species and fatty acid β-oxidation processes. These pathways contribute to breast cancer initiation, progression, metastasis, and drug resistance. In conclusion, we suggest that global pathway analysis and the conventional approach with identified metabolites should be employed together to maximize the exploration of breast cancer's metabolic landscape.

Proline Metabolism in Tumor Growth and Metastatic Progression.

Cancer cells show a formidable capacity to survive under stringent conditions, to elude mechanisms of control, such as apoptosis, and to resist therapy. Cancer cells reprogram their metabolism to support uncontrolled proliferation and metastatic progression. Phenotypic and functional heterogeneity are hallmarks of cancer cells, which endow them with aggressiveness, metastatic capacity, and resistance to therapy. This heterogeneity is regulated by a variety of intrinsic and extrinsic stimuli including those from the tumor microenvironment. Increasing evidence points to a key role for the metabolism of non-essential amino acids in this complex scenario. Here we discuss the impact of proline metabolism in cancer development and progression, with particular emphasis on the enzymes involved in proline synthesis and catabolism, which are linked to pathways of energy, redox, and anaplerosis. In particular, we emphasize how proline availability influences collagen synthesis and maturation and the acquisition of cancer cell plasticity and heterogeneity. Specifically, we propose a model whereby proline availability generates a cycle based on collagen synthesis and degradation, which, in turn, influences the epigenetic landscape and tumor heterogeneity. Therapeutic strategies targeting this metabolic-epigenetic axis hold great promise for the treatment of metastatic cancers.

The Diverse Functions of Non-Essential Amino Acids in Cancer.

Far beyond simply being 11 of the 20 amino acids needed for protein synthesis, non-essential amino acids play numerous important roles in tumor metabolism. These diverse functions include providing precursors for the biosynthesis of macromolecules, controlling redox status and antioxidant systems, and serving as substrates for post-translational and epigenetic modifications. This functional diversity has sparked great interest in targeting non-essential amino acid metabolism for cancer therapy and has motivated the development of several therapies that are either already used in the clinic or are currently in clinical trials. In this review, we will discuss the important roles that each of the 11 non-essential amino acids play in cancer, how their metabolic pathways are linked, and how researchers are working to overcome the unique challenges of targeting non-essential amino acid metabolism for cancer therapy.

Abstract ES6-2: PI3K in breast cancer, glutamine changes and methionine addiction

Abstract Mutations in the PI 3-kinase and AKT signaling pathway are highly prevalent in breast cancer. In luminal, estrogen receptor-positive breast cancer patients, oncogenic mutations in PIK3CA, the gene that encodes the catalytic subunit of class 1a PI3K occur with a frequency of approximately 40%. By contrast, inactivating mutations and loss of heterozygosity in the tumor suppressors PTEN and INPP4B that normally terminate PI3K signaling, are found more frequently in basal-like, triple negative breast tumors. Regardless, in all cases the net result is hyperactivation of PI3K/AKT signaling leading to induction of phenotypes associated with malignancy. In spite of the frequency of genetic lesions in the PI3K pathway and the development of potent and specific small molecule inhibitors targeting the PI3K pathway, results from clinical trials with these inhibitors have been disappointing most often due to dose-limiting on-target toxicities. Consequently, numerous combination trials with PI3K inhibitors and other targeted therapies are underway. Separate pre-clinical and clinical efforts have also been initiated targeting PI3K oncogene addition with therapies that impact cellular states and programs, including metabolic pathways and enzymes. The concept that metabolic reprogramming is a feature of all cancer cells, and not merely a byproduct of accelerated growth, goes back to the days of Otto Warburg who in the 1920s proposed that increased levels of aerobic glycolysis followed by lactate fermentation occurs in tumor cells undergoing rapid growth. This so-called 'Warburg effect' spurred the recent development of numerous drugs that target glycolysis in human tumors, many of which are in clinical trials. Equally promising are strategies that target non-essential amino acid metabolism. The concept of metabolic starvation, whereby one or more metabolite is limiting or removed has gained traction in the field, with the finding that certain non-essential amino acids, particularly glutamine, can be synthesized by normal cells, whereas tumor cells rely on an extracellular supply to the extent that glutamine deprivation sensitizes tumor cells to death. Glutamine is the most widely studied nutrient, other than glucose, in the field of tumor metabolism. The presentation will focus on the intersection of PI3K, AKT and glutamine metabolism in breast cancer, as well as how these pathways modulate methionine dependency in breast cancers that display PI3K pathway hyperactivation. A greater understanding of the mechanisms by which glutamine and methionine sustain cancer cells may lead to the development or repurposing of other successful targeted metabolic therapies and use of the pathway enzymes and metabolites as biomarkers. Citation Format: Toker A. PI3K in breast cancer, glutamine changes and methionine addiction [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr ES6-2.

Lactic acidosis: an update.

Lactate is one of the most crucial intermediates in carbohydrate and nonessential amino acid metabolism. The complexity of cellular interactions and metabolism means that lactate can be considered a waste product for one cell but a useful substrate for another. The presence of elevated lactate levels in critically ill patients has important implications for morbidity and mortality. In this review, we provide a brief outline of the metabolism of lactate, the pathophysiology of lactic acidosis, the clinical significance of D-lactate, the role of lactate measurement in acutely ill patients, the methods used to measure lactate in blood or plasma and some of the methodological issues related to interferences in these assays, especially in the case of ethylene glycol poisoning.

Phenotyping hepatocellular metabolism using uniformly labeled carbon-13 molecular probes and LC-HRMS stable isotope tracing

Metabolite stable isotope tracing is a powerful bioanalytical strategy that has the potential to unravel phenotypic markers of early pharmaceutical efficacy by monitoring enzymatic incorporation of carbon-13 atoms into targeted pathways over time. The practice of probing biological systems with carbon-13 labeled molecules using broad MS-based screens has been utilized for many years in academic laboratories but has had limited application in the pharmaceutical R&D environment. The goal of this work was to establish a LCMS analytical workflow that was capable of monitoring carbon-13 isotope changes in glycolysis, the TCA and urea cycles, and non-essential amino acid metabolism. This work applies a standardized protein precipitation with 80% cold methanol and two distinct reverse-phase ion-pair liquid chromatography methods coupled to either a positive- or negative-ion mode high-resolution accurate mass spectrometry screening method. The data herein combines thousands of single-point peak integrations into a novel metabolite network map as a visualization aid to probe and monitor stable isotope incorporation in murine hepatocytes using uniformly labeled 13C6 glucose, 13C3 lactate, and 13C5 glutamine. This work also demonstrates that nitrogen metabolism may have a large influence on the TCA cycle and gluconeogenic carbon fluxes in hepatocyte cell culture.

Nonessential amino acid metabolism in breast cancer.

Interest in studying cancer metabolism has risen in recent years, as it has become evident that the relationship between cancer and metabolic pathways could reveal novel biomarkers and therapeutic targets. Metabolic starvation therapy is particularly promising due to its low toxicity. Nonessential amino acids are promising metabolites for such therapy because they become essential in many tumor cells, including breast cancer cells. This review will focus on four nonessential amino acid metabolism pathways: glutamine-glutamate, serine-glycine, cysteine, and arginine-proline metabolism. Recent studies of these amino acids have revealed metabolic enzymes that have the potential to be effective as cancer therapy targets or biomarkers for response to metabolic starvation therapy. The review will also discuss features of nonessential amino acid metabolism that merit further investigation to determine their relevancy to breast cancer treatment.

Loss of succinate dehydrogenase activity results in dependency on pyruvate carboxylation for cellular anabolism.

The tricarboxylic acid (TCA) cycle is a central metabolic pathway responsible for supplying reducing potential for oxidative phosphorylation and anabolic substrates for cell growth, repair and proliferation. As such it thought to be essential for cell proliferation and tissue homeostasis. However, since the initial report of an inactivating mutation in the TCA cycle enzyme complex, succinate dehydrogenase (SDH) in paraganglioma (PGL), it has become clear that some cells and tissues are not only able to survive with a truncated TCA cycle, but that they are also able of supporting proliferative phenotype observed in tumours. Here, we show that loss of SDH activity leads to changes in the metabolism of non-essential amino acids. In particular, we demonstrate that pyruvate carboxylase is essential to re-supply the depleted pool of aspartate in SDH-deficient cells. Our results demonstrate that the loss of SDH reduces the metabolic plasticity of cells, suggesting vulnerabilities that can be targeted therapeutically.

The proline regulatory axis and cancer.

Studies in metabolism and cancer have characterized changes in core pathways involving glucose and glutamine, emphasizing the provision of substrates for building cell mass. But recent findings suggest that pathways previously considered peripheral may play a critical role providing mechanisms for cell regulation. Several of these mechanisms involve the metabolism of non-essential amino acids, for example, the channeling of glycolytic intermediates into the serine pathway for one-carbon transfers. Historically, we proposed that the proline biosynthetic pathway participated in a metabolic interlock with glucose metabolism. The discovery that proline degradation is activated by p53 directed our attention to the initiation of apoptosis by proline oxidase/dehydrogenase. Now, however, we find that the biosynthetic mechanisms and the metabolic interlock may depend on the pathway from glutamine to proline, and it is markedly activated by the oncogene MYC. These findings add a new dimension to the proline regulatory axis in cancer and present attractive potential targets for cancer treatment.

Patterns of Amino Acid Metabolism by Proliferating Human Mesenchymal Stem Cells

The nutritional requirements of stem cells have not been determined; in particular, the amino acid metabolism of stem cells is largely unknown. In this study, we investigated the amino acid metabolism of human mesenchymal stem cells (hMSCs), with focus on two questions: Which amino acids are consumed and/or secreted by hMSCs and at what rates? To answer these questions, hMSCs were cultured on tissue culture plastic and in a bioreactor, and their amino acid profile was analyzed. The results showed that the kinetics of hMSCs growth and amino acid metabolism were significantly higher for hMSCs in tissue culture plastic than in the bioreactor. Despite differences in culture conditions, 8 essential and 6 nonessential amino acids were consumed by hMSCs in both tissue culture plastic and bioreactor cultures. Glutamine was the most consumed amino acid with significantly higher rates than for any other amino acid. The metabolism of nonessential amino acids by hMSCs deviated significantly from that of other cell lines. The secretion of alanine, glycine, glutamate, and ornithine by hMSCs showed that there is a strong overflow metabolism that can be due to the high concentrations of amino acids provided in the medium. In addition, the data showed that there is a metabolic pattern for proliferating hMSCs, which can contribute to the design of medium without animal serum for stem cells. Further, this study shows how to implement amino acid rates and metabolic principles in three-dimensional stem cell biology.

Effects of postoperative hyperlactatemia on patients' intensive therapy unit length of stay

Lactate is one of the most crucial intermediates of carbohydrate and nonessential amino acid metabolism. Moderate hyperlactatemia in the immediate postoperative cardiac surgical period is associated with a high risk of major complications [1,2].

Activity and expression of aspartate aminotransferase during the reproductive cycle of a fresh water fish, Clarias batrachus

Aspartate amino transferase (AspT; EC: 2.6.1.1) is one of the key enzyme of aspartate malate shuttle and non-essential amino acid metabolism. In order to clarify the change of the activities of both cytosolic (c-) and mitochondrial (m-) AspT isoenzymes during the different reproductive stages of Clarias batrachus, an air-breathing carnivorous freshwater fish, the c- and m- AspT activities were measured spectrophotometrically in liver, heart, kidney, brain and ovary during the pre-spawning, spawning and post-spawning phases of the annual reproductive cycle of this fish. Maximum activities were observed during the spawning phase, followed by pre- and post-spawning phases. The native agarose gel electrophoretic pattern revealed two AspT forms, c-AspT and m-AspT, throughout the pre- to post-spawning phases. However, the spawning phase was marked by the expression of an additional anionic form of c-AspT in all tissues studied. These results indicate a distinct utilization of aspartate particularly in the spawning phase in fish in the central metabolic path via transamination reactions, and suggest a control of the enzyme activity by the expression of the additional c-AspT gene, especially at the spawning phase.