Proline metabolism and cancer: emerging links to glutamine and collagen

Arginine metabolism and deprivation in cancer therapy

Certain cancer cells with nutrient auxotrophy and have a much higher nutrient demand compared with normal human cells. Arginine as a versatile amino acid, has multiple biological functions in metabolic and signaling pathways. Depletion of this amino acid by arginine depletor is generally well tolerated and has become a targeted therapy for arginine auxotrophic cancers. However, the modulatory eff ;ect of arginine on cancer cells is very complicated and still controversial. Therefore, this article focuses on arginine metabolism and depletion therapy in cancer treatment to provide systemical review on this issue.

Preparation and in vivo evaluation of a topical hydrogel system incorporating highly skin-permeable growth factors, quercetin, and oxygen carriers for enhanced diabetic wound-healing therapy

PURPOSE

We created and evaluated an enhanced topical delivery system featuring a combination of highly skin-permeable growth factors (GFs), quercetin (QCN), and oxygen; these synergistically accelerated re-epithelialization and granulation tissue formation of/in diabetic wounds by increasing the levels of GFs and antioxidants, and the oxygen partial pressure, at the wound site.

METHODS

To enhance the therapeutic effects of exogenous administration of GFs for the treatment of diabetic wounds, we prepared highly skin-permeable GF complexes comprised of epidermal growth factor (EGF), insulin-like growth factor-I (IGF-I), platelet-derived growth factor-A (PDGF-A), and basic fibroblast growth factor (bFGF), genetically attached, via the N-termini, to a low-molecular-weight protamine (LMWP) to form LMWP-EGF, LMWP-IGF-I, LMWP-PDGF-A, and LMWP-bFGF, respectively. Furthermore, quercetin (QCN)- and oxygen-carrying 1-bromoperfluorooctane (PFOB)-loaded nanoemulsions (QCN-NE and OXY-PFOB-NE) were developed to improve the topical delivery of QCN and oxygen, respectively. After confirming the enhanced penetration of LMWP-GFs, QCN-NE, and oxygen delivered from OXY-PFOB-NE across human epidermis, we evaluated the effects of combining LMWP-GFs, QCN-NE, and OXY-PFOB-NE on proliferation of keratinocytes and fibroblasts, and the chronic wound closure rate of a diabetic mouse model.

RESULTS

The optimal ratios of LMWP-EGF, LMWP-IGF-I, LMWP-PDGF-A, LMWP-bFGF, QCN-NE, and OXY-PFOB-NE were 1, 1, 0.02, 0.02, 0.2, and 60, respectively. Moreover, a Carbopol hydrogel containing LMWP-GFs, QCN-NE, and OXY-PFOB-NE (LMWP-GFs/QCN-NE/OXY-PFOB-NE-GEL) significantly improved scratch-wound recovery of keratinocytes and fibroblasts in vitro compared to that afforded by hydrogels containing each component alone. LMWP-GFs/QCN-NE/OXY-PFOB-NE-GEL significantly accelerated wound-healing in a diabetic mouse model, decreasing wound size by 54 and 35% compared to the vehicle and LMWP-GFs, respectively.

CONCLUSION

LMWP-GFs/QCN-NE/OXY-PFOB-NE-GEL synergistically accelerated the healing of chronic wounds, exerting both rapid and prolonged effects.

Integrative analysis reveals disrupted pathways regulated by microRNAs in cancer

MicroRNAs (miRNAs) are small endogenous regulatory molecules that modulate gene expression post-transcriptionally. Although differential expression of miRNAs have been implicated in many diseases (including cancers), the underlying mechanisms of action remain unclear. Because each miRNA can target multiple genes, miRNAs may potentially have functional implications for the overall behavior of entire pathways. Here, we investigate the functional consequences of miRNA dysregulation through an integrative analysis of miRNA and mRNA expression data using a novel approach that incorporates pathway information a priori. By searching for miRNA-pathway associations that differ between healthy and tumor tissue, we identify specific relationships at the systems level which are disrupted in cancer. Our approach is motivated by the hypothesis that if an miRNA and pathway are associated, then the expression of the miRNA and the collective behavior of the genes in a pathway will be correlated. As such, we first obtain an expression-based summary of pathway activity using Isomap, a dimension reduction method which can articulate non-linear structure in high-dimensional data. We then search for miRNAs that exhibit differential correlations with the pathway summary between phenotypes as a means of finding aberrant miRNA-pathway coregulation in tumors. We apply our method to cancer data using gene and miRNA expression datasets from The Cancer Genome Atlas and compare ∼10⁵ miRNA-pathway relationships between healthy and tumor samples from four tissues (breast, prostate, lung and liver). Many of the flagged pairs we identify have a biological basis for disruption in cancer.

The clinical significance of PYCR1 expression in renal cell carcinoma

Pyrroline-5-carboxylate reductase 1 (PYCR1) is an enzyme involved in cell metabolism and is upregulated in cancer. However, the correlations of PYCR1 expression with the clinicopathological features and prognosis of renal cell carcinoma (RCC) remain unclear. The purpose of this study was to identify the expression of PYCR1 and its clinical relevance in RCC patients.PYCR1 mRNA expression differences between RCC and the adjacent normal renal tissues were assessed using the Cancer Genome Atlas database (TCGA). Subsequently, the expression of PYCR1 mRNA and protein were evaluated by quantitative real-time polymerase chain reaction, Western blot, and immunochemistry using 30 paired frozen samples of RCC and the adjacent normal renal tissues. The protein expression of PYCR1 was evaluated by immunostaining formalin-fixed, paraffin-embedded sections of RCC samples from 96 patients who underwent radical nephrectomy, and its relationship with clinical features were analyzed. Nonpaired t tests were used to statistically analyze the differences between the 2 groups. Cox univariable and multivariable analyses of overall survival (OS) among RCC patients were performed.The expression of PYCR1 mRNA was significantly upregulated in RCC tissues compared to adjacent normal renal tissues in the TCGA database (P < .01). The area under the receiver operating characteristic curve value was 0.748. The expression of PYCR1 mRNA and protein was significantly upregulated in RCC compared with that in paired normal renal tissues (P < .01). Higher PYCR1 levels were associated with metastasis (P < .01). Kaplan-Meier survival curves indicated that higher PYCR1 expression was correlated with poorer OS. Therefore, PYCR1 may act as a novel prognostic marker and therapeutic target in the diagnosis and treatment of RCC.

Metabolomic Study on Nude Mice Models of Gastric Cancer Treated with Modified Si Jun Zi Tang via HILIC UHPLC-Q-TOF/MS Analysis

Recently, metabolomic methods have been used to explore the complex pathogenesis of cancer and the mechanism of action of traditional Chinese medicine (TCM) formulae. In this study, first, modified Si Jun Zi Tang (MSJZT) was prepared with strict quality control using the instrument method of ultra performance liquid chromatography and photodiode array detector (UPLC-PDA). Subsequently, in vivo experiments with tumour-bearing nude mice demonstrated that MSJZT exerted good antitumour effects. MSJZT not only significantly increased mouse body weight but also shrank the tumour volume. Then, the HILIC UHPLC-Q-TOF/MS-based metabolomics approach was used for exploring the pathogenesis of gastric cancer and the molecular mechanism of MSJZT. A total of 59 potential biomarkers in plasma were identified, and 6 pathways were found to be disturbed in gastric cancer. In contrast, after 3 weeks of MSJZT intervention, 32 potential biomarkers were identified, and 4 altered pathways were detected. The changes in glycolytic, amino acid, and lipid metabolisms could be partially regulated by MSJZT through decreasing the content of lactic dehydrogenase (LDH), glutamine synthetase (GS), phosphocholine cytidylyltransferase (PCYT2) mRNA, and protein level. In conclusion, we established a HILIC UHPLC-Q-TOF/MS metabolomic analysis method to demonstrate a complex metabolic profile of gastric cancer. The disordered metabolism could be partially regulated by MSJZT. These findings not only establish a solid foundation for TCM to treat gastric cancer but also provide a basis for further exploration of the precise mechanism of MSJZT activity.

Glutamine to proline conversion is associated with response to glutaminase inhibition in breast cancer

INTRODUCTION

Glutaminase inhibitors target cancer cells by blocking the conversion of glutamine to glutamate, thereby potentially interfering with anaplerosis and synthesis of amino acids and glutathione. The drug CB-839 has shown promising effects in preclinical experiments and is currently undergoing clinical trials in several human malignancies, including triple-negative breast cancer (TNBC). However, response to glutaminase inhibitors is variable and there is a need for identification of predictive response biomarkers. The aim of this study was to determine how glutamine is utilized in two patient-derived xenograft (PDX) models of breast cancer representing luminal-like/ER+ (MAS98.06) and basal-like/triple-negative (MAS98.12) breast cancer and to explore the metabolic effects of CB-839 treatment.

EXPERIMENTAL

MAS98.06 and MAS98.12 PDX mice received CB-839 (200 mg/kg) or drug vehicle two times daily p.o. for up to 28 days (n = 5 per group), and the effect on tumor growth was evaluated. Expression of 60 genes and seven glutaminolysis key enzymes were determined using gene expression microarray analysis and immunohistochemistry (IHC), respectively, in untreated tumors. Uptake and conversion of glutamine were determined in the PDX models using HR MAS MRS after i.v. infusion of [5-¹³C] glutamine when the models had received CB-839 (200 mg/kg) or vehicle for 2 days (n = 5 per group).

RESULTS

Tumor growth measurements showed that CB-839 significantly inhibited tumor growth in MAS98.06 tumors, but not in MAS98.12 tumors. Gene expression and IHC analysis indicated a higher proline synthesis from glutamine in untreated MAS98.06 tumors. This was confirmed by HR MAS MRS of untreated tumors demonstrating that MAS98.06 used glutamine to produce proline, glutamate, and alanine, and MAS98.12 to produce glutamate and lactate. In both models, treatment with CB-839 resulted in accumulation of glutamine. In addition, CB-839 caused depletion of alanine, proline, and glutamate ([1-13C] glutamate) in the MAS98.06 model.

CONCLUSION

Our findings indicate that TNBCs may not be universally sensitive to glutaminase inhibitors. The major difference in the metabolic fate of glutamine between responding MAS98.06 xenografts and non-responding MAS98.12 xenografts is the utilization of glutamine for production of proline. We therefore suggest that addiction to proline synthesis from glutamine is associated with response to CB-839 in breast cancer. The effect of glutaminase inhibition in two breast cancer patient-derived xenograft (PDX) models. ¹³C HR MAS MRS analysis of tumor tissue from CB-839-treated and untreated models receiving ¹³C-labeled glutamine ([5-¹³C] Gln) shows that the glutaminase inhibitor CB-839 is causing an accumulation of glutamine (arrow up) in two PDX models representing luminal-like breast cancer (MAS98.06) and basal-like breast cancer (MAS98.12). In MAS98.06 tumors, CB-839 is in addition causing depletion of proline ([5-¹³C] Pro), alanine ([1-¹³C] Ala), and glutamate ([1-¹³C] Glu), which could explain why CB-839 causes tumor growth inhibition in MAS98.06 tumors, but not in MAS98.12 tumors.

In Situ Surface-Enhanced Raman Spectroscopy of Cellular Components: Theory and Experimental Results

In the last decade, surface-enhanced Raman spectroscopy (SERS) met increasing interest in the detection of chemical and biological agents due to its rapid performance and ultra-sensitive features. Being SERS a combination of Raman spectroscopy and nanotechnology, it includes the advantages of Raman spectroscopy, providing rapid spectra collection, small sample sizes, characteristic spectral fingerprints for specific analytes. In addition, SERS overcomes low sensitivity or fluorescence interference that represents two major drawbacks of traditional Raman spectroscopy. Nanoscale roughened metal surfaces tremendously enhance the weak Raman signal due to electromagnetic field enhancement generated by localized surface plasmon resonances. In this paper, we detected label-free SERS signals for arbitrarily configurations of dimers, trimers, etc., composed of gold nanoshells (AuNSs) and applied to the mapping of osteosarcoma intracellular components. The experimental results combined to a theoretical model computation of SERS signal of specific AuNSs configurations, based on open cavity plasmonics, give the possibility to quantify SERS enhancement for overcoming spectral fluctuations. The results show that the Raman signal is locally enhanced inside the cell by AuNSs uptake and correspondent geometrical configuration generating dimers are able to enhance locally electromagnetic fields. The SERS signals inside such regions permit the unequivocal identification of cancer-specific biochemical components such as hydroxyapatite, phenylalanine, and protein denaturation due to disulfide bonds breaking between cysteine links or proline.

Molecular determinants as therapeutic targets in cancer chemotherapy: An update

It is well known that cancer cells are heterogeneous in nature and very distinct from their normal counterparts. Commonly these cancer cells possess different and complementary metabolic profile, microenvironment and adopting behaviors to generate more ATPs to fulfill the requirement of high energy that is further utilized in the production of proteins and other essentials required for cell survival, growth, and proliferation. These differences create many challenges in cancer treatments. On the contrary, such situations of metabolic differences between cancer and normal cells may be expected a promising strategy for treatment purpose. In this article, we focus on the molecular determinants of oncogene-specific sub-organelles such as potential metabolites of mitochondria (reactive oxygen species, apoptotic proteins, cytochrome c, caspase 9, caspase 3, etc.), endoplasmic reticulum (unfolded protein response, PKR-like ER kinase, C/EBP homologous protein, etc.), nucleus (nucleolar phosphoprotein, nuclear pore complex, nuclear localization signal), lysosome (microenvironment, etc.) and plasma membrane phospholipids, etc. that might be exploited for the targeted delivery of anti-cancer drugs for therapeutic benefits. This review will help to understand the various targets of subcellular organelles at molecular levels. In the future, this molecular level understanding may be combined with the genomic profile of cancer for the development of the molecularly guided or personalized therapeutics for complete eradication of cancer.

Mechano-regulation of proline metabolism and cancer progression by kindlin-2

Alterations of cell mechano-environment and metabolism are common features of malignant neoplasm. We recently showed that increased stiffness of extracellular matrix is intrinsically linked to up-regulation of proline synthesis through a mechano-responsive fermitin family homolog 2 (FERMT2, best known as kindlin-2) and pyrroline-5-carboxylate reductase 1(PYCR1) complex, which in turn promotes collagen matrix synthesis, cell proliferation, survival, and cancer progression.

Wide spectrum targeted metabolomics identifies potential ovarian cancer biomarkers

AIMS

Despite of almost a hundred years of research on cancer metabolism, the biological background of cancerogenesis and cancer-related reprogramming of metabolism remains not fully understood. In order to comprehensively and effectively diagnose and treat the deadliest diseases, the mechanisms underlying these diseases have to be discovered urgently. Among the gynecological malignancies, ovarian cancer is the most common cause of death. The aim of the study was to search for potential cancer-related differences in concentrations of metabolites and interactions between them in serum of women with ovarian cancer and benign ovarian tumor in comparison with healthy controls using targeted metabolomics. These metabolites might serve as biomarkers in the future.

MAIN METHODS

We used wide spectrum targeted metabolomics to evaluate serum concentrations of metabolites related to ovarian cancer and compared them against benign ovarian tumors and healthy controls. The measurements were performed using high performance liquid chromatography coupled with triple quadrupole tandem mass spectrometry technique in highly-selective multiple reaction monitoring mode.

KEY FINDINGS

In this study we confirmed our previous findings about the role of histidine and citrulline in ovarian cancer as well as we indicated new lipid compounds (lysoPC a C16:1, PC aa C32:2, PC aa C34:4 and PC aa C 36:6) potentially involved in cancer metabolism.

SIGNIFICANCES

We indicated interesting interactions between metabolites for further in-depth research which could potentially serve as clinically useful biomarkers in future. Moreover, the presented work attempts to visualize a possible 3D-network of relationships between the molecules found to be related to ovarian malignancy.

PYCR1 promotes the progression of non-small-cell lung cancer under the negative regulation of miR-488

PYCR1 is over-expressed in non-small-cell lung cancer (NSCLC) and its high expression accelerates the progression of NSCLC. However, the underlying mechanisms of PYCR1 in NSCLC progression remain poorly understood. Our study determined the mechanisms of PYCR1 in promotion of the occurrence and development of NSCLC in vitro and in vivo. Firstly, the expression patterns of PYCR1 in NSCLC tissues and cells were determined by RT-PCR, western blot and immunohistochemistry. Then, the effects of PYCR1 on cell proliferation and apoptosis were evaluated by CCK-8 and flow cytomery assays. Finally, we explored the up-regulatory microRNAs (miRs) of PYCR1 and determined if MAPK pathway involved in this process. PYCR1 expression was elevated in NSCLC tissue samples and cells, and the high expression of PYCR1 closely associated with patients' advanced clinical process and poor outcome. Up-regulation of PYCR1 significantly increased the expression of p38 and promoted its nuclear accumulation. Besides, PYCR1 expression was negatively regulated by miR-488, and up-regulation of miR-488 significantly inhibited cell proliferation and tumorigenesis and increased cell apoptosis, and decreased p38 expression and its nuclear accumulation, whereas up-regulation of PYCR1 rescued these results induced by miR-488 over-expression. Collectively, these data suggest the mechanism of PYCR1 in promotion of NSCLC progression. PYCR1 is negatively regulated by miR-488 and then promotes the occurrence and development of NSCLC and activates p38 MAPK pathway.

Kindlin-2 links mechano-environment to proline synthesis and tumor growth

Cell metabolism is strongly influenced by mechano-environment. We show here that a fraction of kindlin-2 localizes to mitochondria and interacts with pyrroline-5-carboxylate reductase 1 (PYCR1), a key enzyme for proline synthesis. Extracellular matrix (ECM) stiffening promotes kindlin-2 translocation into mitochondria and its interaction with PYCR1, resulting in elevation of PYCR1 level and consequent increase of proline synthesis and cell proliferation. Depletion of kindlin-2 reduces PYCR1 level, increases reactive oxygen species (ROS) production and apoptosis, and abolishes ECM stiffening-induced increase of proline synthesis and cell proliferation. In vivo, both kindlin-2 and PYCR1 levels are markedly increased in lung adenocarcinoma. Ablation of kindlin-2 in lung adenocarcinoma substantially reduces PYCR1 and proline levels, and diminishes fibrosis in vivo, resulting in marked inhibition of tumor growth and reduction of mortality rate. Our findings reveal a mechanoresponsive kindlin-2-PYCR1 complex that links mechano-environment to proline metabolism and signaling, and suggest a strategy to inhibit tumor growth.

Structural Biology of Proline Catabolic Enzymes

SIGNIFICANCE

Proline catabolism refers to the 4-electron oxidation of proline to glutamate catalyzed by the enzymes proline dehydrogenase (PRODH) and l-glutamate γ-semialdehyde dehydrogenase (GSALDH, or ALDH4A1). These enzymes and the intermediate metabolites of the pathway have been implicated in tumor growth and suppression, metastasis, hyperprolinemia metabolic disorders, schizophrenia susceptibility, life span extension, and pathogen virulence and survival. In some bacteria, PRODH and GSALDH are combined into a bifunctional enzyme known as proline utilization A (PutA). PutAs are not only virulence factors in some pathogenic bacteria but also fascinating systems for studying the coordination of metabolic enzymes via substrate channeling. Recent Advances: The past decade has seen an explosion of structural data for proline catabolic enzymes. This review surveys these structures, emphasizing protein folds, substrate recognition, oligomerization, kinetic mechanisms, and substrate channeling in PutA.

CRITICAL ISSUES

Major unsolved structural targets include eukaryotic PRODH, the complex between monofunctional PRODH and monofunctional GSALDH, and the largest of all PutAs, trifunctional PutA. The structural basis of PutA-membrane association is poorly understood. Fundamental aspects of substrate channeling in PutA remain unknown, such as the identity of the channeled intermediate, how the tunnel system is activated, and the roles of ancillary tunnels.

FUTURE DIRECTIONS

New approaches are needed to study the molecular and in vivo mechanisms of substrate channeling. With the discovery of the proline cycle driving tumor growth and metastasis, the development of inhibitors of proline metabolic enzymes has emerged as an exciting new direction. Structural biology will be important in these endeavors.

Metabolism, Nutrition, and Redox Signaling of Hydroxyproline

SIGNIFICANCE

Hydroxyproline is a structurally and physiologically important imino acid in animals. It is provided from diets and endogenous synthesis, and its conversion into glycine enhances the production of glutathione, DNA, heme, and protein. Furthermore, oxidation of hydroxyproline by hydroxyproline oxidase (OH-POX) plays an important role in cell antioxidative reactions, survival, and homeostasis. Understanding the mechanisms whereby hydroxyproline participates in metabolism and cell signaling can improve the nutrition and health of animals and humans. Recent Advances: Hydroxyproline is highly abundant in milk and is utilized for renal synthesis of glycine to support neonatal growth, development, and survival. The oxidation of hydroxyproline by mitochondrial OH-POX generates reactive oxygen species (ROS). Enhanced ROS production contributes to the regulation of oxidative defense, apoptosis, angiogenesis, tumorigenesis, hypoxic responses, and cell survival in animals.

CRITICAL ISSUES

Although dietary hydroxyproline enters the portal circulation, its utilization by the portal-drained viscera is unknown. Pathways for hydroxyproline metabolism and their regulation at the molecular, cellular, and whole-body levels remain to be defined. Furthermore, the mechanisms responsible for hydroxyproline-derived ROS and related metabolites to induce cell survival or apoptosis are unknown.

FUTURE DIRECTIONS

Interorgan metabolism of hydroxyproline (including synthesis, catabolism, and flux) in animals must be quantified using isotope technologies. Efforts should also be directed toward studying dietary, hormonal, and epigenetic regulation of OH-POX expression at transcriptional and translational levels. Another emerging research need is to understand the roles of cellular redox and signaling networks involving both ROS and Δ¹-pyrroline-3-hydroxy-5-carboxylate in nutrition, health, and disease.

Enzymes in Metabolic Anticancer Therapy

Cancer treatment has greatly improved over the last 50 years, but it remains challenging in several cases. Useful therapeutic targets are normally unique peculiarities of cancer cells that distinguish them from normal cells and that can be tackled with appropriate drugs. It is now known that cell metabolism is rewired during tumorigenesis and metastasis as a consequence of oncogene activation and oncosuppressors inactivation, leading to a new cellular homeostasis typically directed towards anabolism. Because of these modifications, cells can become strongly or absolutely dependent on specific substrates, like sugars, lipids or amino acids. Cancer addictions are a relevant target for therapy, as removal of an essential substrate can lead to their selective cell-cycle arrest or even to cell death, leaving normal cells untouched. Enzymes can act as powerful agents in this respect, as demonstrated by asparaginase, which has been included in the treatment of Acute Lymphoblastic Leukemia for half a century. In this review, a short outline of cancer addictions will be provided, focusing on the main cancer amino acid dependencies described so far. Therapeutic enzymes which have been already experimented at the clinical level will be discussed, along with novel potential candidates that we propose as new promising molecules. The intrinsic limitations of their present molecular forms, along with molecular engineering solutions to explore, will also be presented.

Spatially resolved metabolomics to discover tumor-associated metabolic alterations

Tumor cells reprogram their metabolism to support cell growth, proliferation, and differentiation, thus driving cancer progression. Profiling of the metabolic signatures in heterogeneous tumors facilitates the understanding of tumor metabolism and introduces potential metabolic vulnerabilities that might be targeted therapeutically. We proposed a spatially resolved metabolomics method for high-throughput discovery of tumor-associated metabolite and enzyme alterations using ambient mass spectrometry imaging. Metabolic pathway-related metabolites and metabolic enzymes that are associated with tumor metabolism were efficiently discovered and visualized in heterogeneous esophageal cancer tissues. Spatially resolved metabolic alterations hold the key to defining the dependencies of metabolism that are most limiting for cancer growth and exploring metabolic targeted strategies for better cancer treatment.

Characterization of tumor metabolism with spatial information contributes to our understanding of complex cancer metabolic reprogramming, facilitating the discovery of potential metabolic vulnerabilities that might be targeted for tumor therapy. However, given the metabolic variability and flexibility of tumors, it is still challenging to characterize global metabolic alterations in heterogeneous cancer. Here, we propose a spatially resolved metabolomics approach to discover tumor-associated metabolites and metabolic enzymes directly in their native state. A variety of metabolites localized in different metabolic pathways were mapped by airflow-assisted desorption electrospray ionization mass spectrometry imaging (AFADESI-MSI) in tissues from 256 esophageal cancer patients. In combination with in situ metabolomics analysis, this method provided clues into tumor-associated metabolic pathways, including proline biosynthesis, glutamine metabolism, uridine metabolism, histidine metabolism, fatty acid biosynthesis, and polyamine biosynthesis. Six abnormally expressed metabolic enzymes that are closely associated with the altered metabolic pathways were further discovered in esophageal squamous cell carcinoma (ESCC). Notably, pyrroline-5-carboxylate reductase 2 (PYCR2) and uridine phosphorylase 1 (UPase1) were found to be altered in ESCC. The spatially resolved metabolomics reveal what occurs in cancer at the molecular level, from metabolites to enzymes, and thus provide insights into the understanding of cancer metabolic reprogramming.

Pyrroline-5-carboxylate reductase 1 promotes cell proliferation via inhibiting apoptosis in human malignant melanoma

Introduction

Human malignant melanoma (MM) is a highly malignant tumor of cutaneous melanocytes with a fast progression. We investigated the cellular effects of pyrroline-5- carboxylate reductase 1 (PYCR1) in the MM cell lines, A375 and M14.

Methods

Cell Counting Kit-8 assay, transwell assay, and flow cytometry analysis were performed to evaluate the proliferation, migration and apoptosis of MM cell lines, respectively. To gain more insight into the role of PYCR1 in tumor growth, we analyzed the AKT phosphorylation level in PYCR1-specific siRNA (siPYCR1) and negative control (NC) cells.

Results

Biochemical analysis revealed a clear increase in PYCR1 expression in human MM samples, and its high expression predicted a poor prognosis. Silencing of PYCR1 suppressed the proliferation and migration of A375 and M14 cells. The percentage of apoptosis in cells transfected with siPYCR1 significantly increased in comparison to that of cells transfected with negative control siRNA (NC). The enhanced apoptosis in PYCR1 knockdown cells was consistent with an increased level of markers of apoptosis. siPYCR1 inhibited AKT phosphorylation, as well as the expression of its downstream protein, P70, suggesting that PYCR1 promoted cell growth of the MM cell lines A375 and M14 through stimulation of the AKT pathway. Moreover, forkhead box K2 and regulatory associated protein of MTOR complex 1 shared a similar expression pattern to that of PYCR1 and were significantly downregulated in PYCR1 knockdown cells.

Conclusion

PYCR1 promoted tumor progression through the AKT pathway in human MM in vitro. Our results expand the knowledge of PYCR1 functions in solid tumors and provide a potential target for the clinical treatment of human MM.

Inhibition of Amino Acid Metabolism Selectively Targets Human Leukemia Stem Cells

In this study we interrogated the metabolome of human acute myeloid leukemia (AML) stem cells to elucidate properties relevant to therapeutic intervention. We demonstrate that amino acid uptake, steady-state levels, and catabolism are all elevated in the leukemia stem cell (LSC) population. Furthermore, LSCs isolated from de novo AML patients are uniquely reliant on amino acid metabolism for oxidative phosphorylation and survival. Pharmacological inhibition of amino acid metabolism reduces oxidative phosphorylation and induces cell death. In contrast, LSCs obtained from relapsed AML patients are not reliant on amino acid metabolism due to their ability to compensate through increased fatty acid metabolism. These findings indicate that clinically relevant eradication of LSCs can be achieved with drugs that target LSC metabolic vulnerabilities.

In-vitro metabolomics to evaluate toxicity of particulate matter under environmentally realistic conditions

In this pilot study three fractions of particulate matter (PM_0.25, PM_2.5-0.25, and PM_10-2.5) were collected in three environments (classroom, home, and outdoors) in a village located nearby an industrial complex. Time-activity pattern of 20 students attending the classroom was obtained, and the dose of particles reaching the children's lungs under actual environmental conditions (i.e. real dose) was calculated via dosimetry model. The highest PM concentrations were reached in the classroom. Simulations showed that heavy intensity outdoor activities played a major role in PM deposition, especially in the upper part of the respiratory tract. The mass of PM_10-2.5 reaching the alveoli was minor, while PM_2.5-0.25 and PM_0.25 apportion for most of the PM mass retained in the lungs. Consequently, PM_2.5-0.25 and PM_0.25 were the only fractions used in two subsequent toxicity assays onto alveolar cells (A549). First, a cytotoxicity dose-response assay was performed, and doses corresponding to 5% mortality (LC₅) were estimated. Afterwards, two LC-MS metabolomic assays were conducted: one applying LC₅, and another applying real dose. A lower estimated LC₅ value was obtained for PM_0.25 than PM_2.5-0.25 (8.08 and 73.7 ng/mL respectively). The number of altered features after LC₅ exposure was similar for both fractions (39 and 38 for PM_0.25 and PM_2.5-0.25 respectively), while after real dose exposure these numbers differed (10 and 5 for PM_0.25 and PM_2.5-0.25 respectively). The most metabolic changes were related to membrane and lung surfactant lipids. This study highlights the capacity of PM to alter metabolic profile of lung cells at conventional environmental levels.

Urinary and plasma metabolite differences detected by HPLC-ESI-QTOF-MS in systemic sclerosis patients

Systemic Sclerosis (SSc) is a chronic autoimmune disease whose origin and pathogenesis are not yet well known. Recent studies are allowing a better definition of the disease. However, few studies have been performed based on metabolomics. In this way, this study aims to find altered metabolites in SSc patients in order to improve their diagnosis, prognosis and treatment. For that, 59 SSc patients and 28 healthy volunteers participated in this study. Urine and plasma samples were analysed by a fingerprinting metabolomic approach based on HPLC-ESI-QTOF-MS. We observed larger differences in urine than plasma metabolites. The main deregulated metabolic families in urine were acylcarnitines, acylglycines and metabolites derived from amino acids, specifically from proline, histidine and glutamine. These results indicate perturbations in fatty acid beta oxidation and amino acid pathways in scleroderma patients. On the other hand, the main plasma biomarker candidate was 2-arachidonoylglycerol, which is involved in the endocannabinoid system with potential implications in the induction and propagation of systemic sclerosis and autoimmunity.

Diastolic left ventricular function in relation to circulating metabolic biomarkers in a population study

Aims

We studied the association of circulating metabolic biomarkers with asymptomatic left ventricular diastolic dysfunction, a risk-carrying condition that affects 25% of the population.

Methods and results

In 570 randomly recruited people, we assessed in 2005–2010 and in 2009–2013 the multivariable-adjusted correlations of e’ (early left ventricular relaxation) and E/e’ (left ventricular filling pressure) measured by Doppler echocardiography with 43 serum metabolites, quantified by magnetic resonance spectroscopy. In 2009–2013, e’ cross-sectionally increased (Bonferroni corrected p ≤ 0.016) with the branched-chain amino acid valine (per one standard deviation increment, +0.274 cm/s (95% confidence interval, 0.057–0.491)) and glucose+the amino acid (AA) taurine (+0.258 cm/s (0.067–0.481)), while E/e’ decreased ( p ≤ 0.017) with valine (–0.264 (–0.496– –0.031)). The risk of developing left ventricular diastolic dysfunction over follow-up (9.4%) was inversely associated ( p ≤ 0.0059) with baseline glucose+amino acid taurine (odds ratio, 0.64 (0.44–0.94). In partial least squares analyses of all the baseline and follow-up data, markers consistently associated with better diastolic left ventricular function included the amino acids 2-aminobutyrate and 4-hydroxybutyrate and the branched-chain amino acids leucine and valine, and those consistently associated with worse diastolic left ventricular function glucose+amino acid glutamine and fatty acid pentanoate. Branched-chain amino acid metabolism (–log10 p = 12.6) and aminoacyl-tRNA biosynthesis (9.9) were among the top metabolic pathways associated with left ventricular diastolic dysfunction.

Conclusion

The associations of left ventricular diastolic dysfunction with circulating amino acids and branched-chain amino acids were consistent over a five-year interval and suggested a key role of branched-chain amino acid metabolism and aminoacyl-tRNA biosynthesis in maintaining diastolic left ventricular function.

HIV-1 Envelope Protein gp120 Promotes Proliferation and the Activation of Glycolysis in Glioma Cell

Patients infected with human immunodeficiency virus (HIV) are more prone to developing cancers, including glioblastomas (GBMs). The median survival for HIV positive GBM patients is significantly shorter than for those who are uninfected, despite the fact that they receive the same treatments. The nature of the GBM–HIV association remains poorly understood. In this study, we analyzed the effect of the HIV envelope glycoprotein gp120 on GBM cell proliferation. Specifically, we performed cell cycle, western blot, protein synthesis and metabolomics analysis as well as ATP production and oxygen consumption assays to evaluate proliferation and metabolic pathways in primary human glioma cell line, U87, A172 cells and in the HIVgp120tg/GL261 mouse model. Glioma cells treated with gp120 (100 ng/mL for 7–10 days) showed higher proliferation rates and upregulation in the expression of enolase 2, hexokinase and glyceraldehyde-3-phosphate dehydrogenase when compared to untreated cells. Furthermore, we detected an increase in the activity of pyruvate kinase and a higher glycolytic index in gp120 treated cells. Gp120 treated GBM cells also showed heightened lipid and protein synthesis. Overall, we demonstrate that in glioma cells, the HIV envelope glycoprotein promotes proliferation and activation of glycolysis resulting in increased protein and lipid synthesis.

N-terminal phosphorylation of glutaminase C decreases its enzymatic activity and cancer cell migration

The mitochondrial phosphate-activated glutaminase C (GAC) is produced by the alternative splicing of the GLS gene. Compared to the other GLS isoform, the kidney-type glutaminase (KGA), GAC is more enzymatically efficient and of particular importance for cancer cell growth. Although its catalytic mechanism is well understood, little is known about how post-translational modifications can impact GAC function. Here, we identified by mass spectrometry a phosphorylated serine at the GLS N-terminal domain (at position 95) and investigated its role on regulating GAC activity. The ectopic expression of the phosphomimetic mutant (GAC.S95D) in breast cancer cells, compared to wild-type GAC (GAC.WT), led to decreased glutaminase activity, glutamine uptake, glutamate release and intracellular glutamate levels, without changing GAC sub-cellular localization. Interestingly, cells expressing the GAC.S95D mutant, compared to GAC.WT, presented decreased migration and vimentin level, an epithelial-to-mesenchymal transition marker. These results reveal that GAC is post-translationally regulated by phosphorylation, which affects cellular glutamine metabolism and glutaminase-related cell phenotype.

Metabolomic identification of diagnostic serum-based biomarkers for advanced stage melanoma

INTRODUCTION

Melanoma is a highly aggressive malignancy and is currently one of the fastest growing cancers worldwide. While early stage (I and II) disease is highly curable with excellent prognosis, mortality rates rise dramatically after distant spread. We sought to identify differences in the metabolome of melanoma patients to further elucidate the pathophysiology of melanoma and identify potential biomarkers to aid in earlier detection of recurrence.

METHODS

Using ¹H NMR and DI-LC-MS/MS, we profiled serum samples from 26 patients with stage III (nodal metastasis) or stage IV (distant metastasis) melanoma and compared their biochemical profiles with 46 age- and gender-matched controls.

RESULTS

We accurately quantified 181 metabolites in serum using a combination of ¹H NMR and DI-LC-MS/MS. We observed significant separation between cases and controls in the PLS-DA scores plot (permutation test p-value = 0.002). Using the concentrations of PC-aa-C40:3, DL-carnitine, octanoyl-L-carnitine, ethanol, and methylmalonyl-L-carnitine we developed a diagnostic algorithm with an AUC (95% CI) = 0.822 (0.665-0.979) with sensitivity and specificity of 100 and 56%, respectively. Furthermore, we identified arginine, proline, tryptophan, glutamine, glutamate, glutathione and ornithine metabolism to be significantly perturbed due to disease (p < 0.05).

CONCLUSION

Targeted metabolomic analysis demonstrated significant differences in metabolic profiles of advanced stage (III and IV) melanoma patients as compared to controls. These differences may represent a potential avenue for the development of multi-marker serum-based assays for earlier detection of recurrences, allow for newer, more effective targeted therapy when tumor burden is less, and further elucidate the pathophysiologic changes that occur in melanoma.

Metabolic Regulation in Mitochondria and Drug Resistance

Mitochondria are generally considered as a powerhouse in a cell where the majority of the cellular ATP and metabolite productions occur. Metabolic rewiring and reprogramming may be initiated and regulated by mitochondrial enzymes. The hypothesis that cellular metabolic rewiring and reprogramming processes may occur as cellular microenvironment is disturbed, resulting in alteration of cell phenotype, such as cancer cells resistant to therapeutics seems to be now acceptable. Cancer metabolic reprogramming regulated by mitochondrial enzymes is now one of the hallmarks of cancer. This chapter provides an overview of cancer metabolism and summarizes progress made in mitochondria-mediated metabolic regulation in cancer drug resistance.

Metabolomics reveals perturbations in endometrium and serum of minimal and mild endometriosis

Endometriosis is a common benign gynecological disease, characterized by growth and proliferation of endometrial glands and stroma outside the uterus. With studies showing metabolic changes in various biofluids of endometriosis women, we have set upon to investigate whether endometrial tissue show differences in their metabolic profiles. ¹H NMR analysis was performed on eutopic endometrial tissue of women with endometriosis and controls. Analysis was performed on spectral data and on relative concentrations of metabolites obtained from spectra using multivariate and univariate data analysis. Analysis shows that various energy, ketogenic and glucogenic metabolites have significant altered concentrations in various stages of endometriosis. In addition, altered tissue metabolites in minimal and mild stages of endometriosis were explored in serum of these patients to assess their role in disease diagnosis. For Stage I diagnosis alanine was found to have 90% sensitivity (true positives) and 58% specificity (true negatives). For Stage II diagnosis alanine, leucine, lysine, proline and phenylalanine showed significant altered levels in serum. While sensitivity of these serum metabolites varied between 69.2–100% the specificity values ranged between 58.3–91.7%. Further, a regression model generated with this panel of serum markers showed an improved sensitivity and specificity of 100% and 83%, respectively for Stage II diagnosis.

Amino Acid Signature in Human Melanoma Cell Lines from Different Disease Stages

Cancer cells rewire metabolism to sustain high proliferation rates. Beside glycolysis and glutaminolysis, amino acids substitute as energy source, feed fatty acid biosynthesis and represent part of the secretome of transformed cells, including melanoma. We have therefore investigated acetate, pyruvate and the amino acid composition of the secretome of human melanoma cells representing the early slow (WM35, WM278, WM793b and VM21) and metastatic fast (A375, 518a2, 6F and WM8) growth phase in order to identify possible signalling components within these profiles. Proliferation assays and a principle component analysis revealed a stringent difference between the fast and slow growing melanoma cells. Moreover, upon inhibition of the mevalonate pathway, glutamic acid and alanine were identified as the central difference in the conditional media. A supplementation of the media with glutamic acid and the combination with alanine significantly accelerated the proliferation, migration and invasion of early stage melanoma cells, but not metastatic cells. Finally, the inhibition of the mevalonate pathway abolished the growth advantage of the melanoma cells in a time dependent manner. Taken together, these data corroborate a stage specific response in growth and aggressiveness to extracellular glutamic acid and alanine, indicative for microenvironmental signalling of individual amino acids.

Extracellular matrix internalization links nutrient signalling to invasive migration

Integrins are the key mediators of cell-extracellular matrix (ECM) interaction, linking the ECM to the actin cytoskeleton. Besides localizing at the cell surface, they can be internalized and transported back to the plasma membrane (recycled) or delivered to the late endosomes/lysosomes for degradation. We and others have shown that integrin can be endocytosed together with their ECM ligands. In this short review, I will highlight how extracellular protein (including ECM) endocytosis impinges on the activation of the mechanistic target of rapamycin (mTOR) pathway, a master regulator of cell metabolism and growth. This supports the intriguing hypothesis that ECM components may be considered as nutrient sources, primarily under soluble nutrient-depleted conditions.

The amino acid transporter SLC7A5 confers a poor prognosis in the highly proliferative breast cancer subtypes and is a key therapeutic target in luminal B tumours

BACKGROUND

Breast cancer (BC) is a heterogeneous disease characterised by variant biology and patient outcome. The amino acid transporter, SLC7A5, plays a role in BC although its impact on patient outcome in different BC subtypes remains to be validated. This study aimed to determine whether the clinicopathological and prognostic value of SLC7A5 is different within the molecular classes of BC.

METHODS

SLC7A5 was assessed at the genomic level, using Molecular Taxonomy of Breast Cancer International Consortium (METABRIC) data (n = 1980), and proteomic level, using immunohistochemical analysis and tissue microarray (TMA) (n = 2664; 1110 training and 1554 validation sets) in well-characterised primary BC cohorts. SLC7A5 expression correlated with clinicopathological and biological parameters, molecular subtypes and patient outcome.

RESULTS

SLC7A5 mRNA and protein expression were strongly correlated with larger tumour size and higher grade. High expression was observed in triple negative (TN), human epidermal growth factor receptor 2 (HER2)+, and luminal B subtypes. SLC7A5 mRNA and protein expression was significantly associated with the expression of the key regulator of tumour cell metabolism, c-MYC, specifically in luminal B tumours only (p = 0.001). High expression of SLC7A5 mRNA and protein was associated with poor patient outcome (p < 0.001) but only in the highly proliferative oestrogen receptor (ER)+/ luminal B (p = 0.007) and HER2+ classes of BC (p = 0.03). In multivariate analysis, SLC7A5 protein was an independent risk factor for shorter breast-cancer-specific survival only in ER+ high-proliferation tumours (p = 0.02).

CONCLUSIONS

SLC7A5 appears to play a role in the aggressive highly proliferative ER+ subtype driven by MYC and could act as a potential therapeutic target. Functional assessment is necessary to reveal the specific role played by this transporter in the ER+ highly proliferative subclass and HER2+ subclass of BC.

Resistance to the Antiproliferative In Vitro Effect of PI3K-Akt-mTOR Inhibition in Primary Human Acute Myeloid Leukemia Cells Is Associated with Altered Cell Metabolism

Constitutive signaling through the phosphatidylinositol-3-kinase-Akt-mechanistic target of rapamycin (PI3K-Akt-mTOR) pathway is present in acute myeloid leukemia (AML) cells. However, AML is a heterogeneous disease, and we therefore investigated possible associations between cellular metabolism and sensitivity to PI3K-Akt-mTOR pathway inhibitors. We performed non-targeted metabolite profiling to compare the metabolome differences of primary human AML cells derived from patients susceptible or resistant to the in vitro antiproliferative effects of mTOR and PI3K inhibitors. In addition, the phosphorylation status of 18 proteins involved in PI3K-Akt-mTOR signaling and the effect of the cyclooxygenase inhibitor indomethacin on their phosphorylation status was investigated by flow cytometry. Strong antiproliferative effects by inhibitors were observed only for a subset of patients. We compared the metabolite profiles for responders and non-responders towards PI3K-mTOR inhibitors, and 627 metabolites could be detected. Of these metabolites, 128 were annotated and 15 of the annotated metabolites differed significantly between responders and non-responders, including metabolites involved in energy, amino acid, and lipid metabolism. To conclude, leukemia cells that are susceptible or resistant to PI3K-Akt-mTOR inhibitors differ in energy, amino acid, and arachidonic acid metabolism, and modulation of arachidonic acid metabolism alters the activation of mTOR and its downstream mediators.

Global Metabolic Profiling Identifies a Pivotal Role of Proline and Hydroxyproline Metabolism in Supporting Hypoxic Response in Hepatocellular Carcinoma

Purpose: Metabolic reprogramming is frequently identified in hepatocellular carcinoma (HCC), which is the most common type of liver malignancy. The reprogrammed cellular metabolisms promote tumor cell survival, proliferation, angiogenesis, and metastasis. However, the mechanisms of this process remain unclear in HCC.Experimental Design: The global nontargeted metabolic study in 69 paired hepatic carcinomas and adjacent tissue specimens was performed using capillary electrophoresis-time of flight mass spectrometry-based approach. Key findings were validated by targeted metabolomic approach. Biological studies were also performed to investigate the role of proline biosynthesis in HCC pathogenesis.Results: Proline metabolism was markedly changed in HCC tumor tissue, characterized with accelerated consumption of proline and accumulation of hydroxyproline, which significantly correlated with α-fetoprotein levels and poor prognosis in HCC. In addition, we found that hydroxyproline promoted hypoxia- and HIF-dependent phenotype in HCC. Moreover, we demonstrated that hypoxia activated proline biosynthesis via upregulation of ALDH18A1, subsequently leading to accumulation of hydroxyproline via attenuated PRODH2 activity. More importantly, we showed that glutamine, proline, and hydroxyproline metabolic axis supported HCC cell survival through modulating HIF1α stability in response to hypoxia. Finally, inhibition of proline biosynthesis significantly enhanced cytotoxicity of sorafenib in vitro and in vivoConclusions: Our results demonstrate that hypoxic microenvironment activates proline metabolism, resulting in accumulation of hydroxyproline that promotes HCC tumor progression and sorafenib resistance through modulating HIF1α. These findings provide the proof of concept for targeting proline metabolism as a potential therapeutic strategy for HCC. Clin Cancer Res; 24(2); 474-85. ©2017 AACR.

MYC regulation of glutamine-proline regulatory axis is key in luminal B breast cancer

BACKGROUND

Altered cellular metabolism is a hallmark of cancer and some are reliant on glutamine for sustained proliferation and survival. We hypothesise that the glutamine-proline regulatory axis has a key role in breast cancer (BC) in the highly proliferative classes.

METHODS

Glutaminase (GLS), pyrroline-5-carboxylate synthetase (ALDH18A1), and pyrroline-5-carboxylate reductase 1 (PYCR1) were assessed at DNA/mRNA/protein levels in large, well-characterised cohorts.

RESULTS

Gain of PYCR1 copy number and high PYCR1 mRNA was associated with Luminal B tumours. High ALDH18A1 and high GLS protein expression was observed in the oestrogen receptor (ER)+/human epidermal growth factor receptor (HER2)- high proliferation class (Luminal B) compared with ER+/HER2- low proliferation class (Luminal A) (P=0.030 and P=0.022 respectively), however this was not observed with mRNA. Cluster analysis of the glutamine-proline regulatory axis genes revealed significant associations with molecular subtypes of BC and patient outcome independent of standard clinicopathological parameters (P=0.012). High protein expression of the glutamine-proline enzymes were all associated with high MYC protein in Luminal B tumours only (P<0.001).

CONCLUSIONS

We provide comprehensive clinical data indicating that the glutamine-proline regulatory axis plays an important role in the aggressive subclass of luminal BC and is therefore a potential therapeutic target.

Discovery of the Membrane Binding Domain in Trifunctional Proline Utilization A

Escherichia coli proline utilization A (EcPutA) is the archetype of trifunctional PutA flavoproteins, which function both as regulators of the proline utilization operon and bifunctional enzymes that catalyze the four-electron oxidation of proline to glutamate. EcPutA shifts from a self-regulating transcriptional repressor to a bifunctional enzyme in a process known as functional switching. The flavin redox state dictates the function of EcPutA. Upon proline oxidation, the flavin becomes reduced, triggering a conformational change that causes EcPutA to dissociate from the put regulon and bind to the cellular membrane. Major structure/function domains of EcPutA have been characterized, including the DNA-binding domain, proline dehydrogenase (PRODH) and l-glutamate-γ-semialdehyde dehydrogenase catalytic domains, and an aldehyde dehydrogenase superfamily fold domain. Still lacking is an understanding of the membrane-binding domain, which is essential for EcPutA catalytic turnover and functional switching. Here, we provide evidence for a conserved C-terminal motif (CCM) in EcPutA having a critical role in membrane binding. Deletion of the CCM or replacement of hydrophobic residues with negatively charged residues within the CCM impairs EcPutA functional and physical membrane association. Furthermore, cell-based transcription assays and limited proteolysis indicate that the CCM is essential for functional switching. Using fluorescence resonance energy transfer involving dansyl-labeled liposomes, residues in the α-domain are also implicated in membrane binding. Taken together, these experiments suggest that the CCM and α-domain converge to form a membrane-binding interface near the PRODH domain. The discovery of the membrane-binding region will assist efforts to define flavin redox signaling pathways responsible for EcPutA functional switching.

Metabolic recycling of ammonia via glutamate dehydrogenase supports breast cancer biomass

Ammonia is a ubiquitous by-product of cellular metabolism; however, the biological consequences of ammonia production are not fully understood, especially in cancer. We found that ammonia is not merely a toxic waste product but is recycled into central amino acid metabolism to maximize nitrogen utilization. In our experiments, human breast cancer cells primarily assimilated ammonia through reductive amination catalyzed by glutamate dehydrogenase (GDH); secondary reactions enabled other amino acids, such as proline and aspartate, to directly acquire this nitrogen. Metabolic recycling of ammonia accelerated proliferation of breast cancer. In mice, ammonia accumulated in the tumor microenvironment and was used directly to generate amino acids through GDH activity. These data show that ammonia is not only a secreted waste product but also a fundamental nitrogen source that can support tumor biomass.

Pyrroline-5-carboxylate reductase 1 promotes proliferation and inhibits apoptosis in non-small cell lung cancer

Disordered tumor cell metabolism is involved in the process of tumorigenesis. Proline metabolism is of critical importance for tumor cells, and pyrroline-5-carboxylate reductase 1 (PYCR1), a key proline biosynthesis enzyme, has been reported to be overexpressed in prostate cancer and to promote tumor cell growth in breast cancer. The present study investigated the relationship between PYCR1 and non-small cell lung cancer (NSCLC). The results revealed that PYCR1 was overexpressed in NSCLC tumor tissues compared with adjacent normal tissues. High PYCR1 expression was associated with poor prognosis in patients with NSCLC. Following knockdown of PYCR1 by small interfering RNA, cell proliferation was revealed to be significantly inhibited and the cell cycle was arrested, while apoptosis was increased in SPC-A1 and H1703 NSCLC cells. Furthermore, the silencing of PYCR1 resulted in the downregulation of expression of the cell cycle regulator cyclin D1, the regulator of the mitochondrial apoptotic pathway B-cell lymphoma-2, and B-cell lymphoma-extra large. The results of the present study indicated the involvement of PYCR1 in the proliferation and apoptosis of NSCLC. Therefore, PYCR1 may be a novel therapeutic target for inhibiting cell proliferation in lung cancer.

Systematic analyses of glutamine and glutamate metabolisms across different cancer types

BACKGROUND

Glutamine and glutamate are known to play important roles in cancer biology. However, no detailed information is available in terms of their levels of involvement in various biological processes across different cancer types, whereas such knowledge could be critical for understanding the distinct characteristics of different cancer types. Our computational study aimed to examine the functional roles of glutamine and glutamate across different cancer types.

METHODS

We conducted a comparative analysis of gene expression data of cancer tissues versus normal control tissues of 11 cancer types to understand glutamine and glutamate metabolisms in cancer. Specifically, we developed a linear regression model to assess differential contributions by glutamine and/or glutamate to each of seven biological processes in cancer versus control tissues.

RESULTS

While our computational predictions were consistent with some of the previous observations, multiple novel predictions were made: (1) glutamine is generally not involved in purine synthesis in cancer except for breast cancer, and is similarly not involved in pyridine synthesis except for kidney cancer; (2) glutamine is generally not involved in ATP production in cancer; (3) glutamine's contribution to nucleotide synthesis is minimal if any in cancer; (4) glutamine is not involved in asparagine synthesis in cancer except for bladder and lung cancers; and (5) glutamate does not contribute to serine synthesis except for bladder cancer.

CONCLUSIONS

We comprehensively predicted the roles of glutamine and glutamate metabolisms in selected metabolic pathways in cancer tissues versus control tissues, which may lead to novel approaches to therapeutic development targeted at glutamine and/or glutamate metabolism. However, our predictions need further functional validation.

Structure, function, and mechanism of proline utilization A (PutA)

Proline has important roles in multiple biological processes such as cellular bioenergetics, cell growth, oxidative and osmotic stress response, protein folding and stability, and redox signaling. The proline catabolic pathway, which forms glutamate, enables organisms to utilize proline as a carbon, nitrogen, and energy source. FAD-dependent proline dehydrogenase (PRODH) and NAD⁺-dependent glutamate semialdehyde dehydrogenase (GSALDH) convert proline to glutamate in two sequential oxidative steps. Depletion of PRODH and GSALDH in humans leads to hyperprolinemia, which is associated with mental disorders such as schizophrenia. Also, some pathogens require proline catabolism for virulence. A unique aspect of proline catabolism is the multifunctional proline utilization A (PutA) enzyme found in Gram-negative bacteria. PutA is a large (>1000 residues) bifunctional enzyme that combines PRODH and GSALDH activities into one polypeptide chain. In addition, some PutAs function as a DNA-binding transcriptional repressor of proline utilization genes. This review describes several attributes of PutA that make it a remarkable flavoenzyme: (1) diversity of oligomeric state and quaternary structure; (2) substrate channeling and enzyme hysteresis; (3) DNA-binding activity and transcriptional repressor function; and (4) flavin redox dependent changes in subcellular location and function in response to proline (functional switching).

The construction of a panel of serum amino acids for the identification of early chronic kidney disease patients

BACKGROUND

Serum creatinine, urea, and cystatin-c are standardly used for the evaluation of renal function in the clinic. However, some patients have chronic kidney disease but still retain kidney function; a conventional serum index in these patients can be completely normal. Serum amino acid levels can reflect subtle changes in metabolism and are closely related to renal function. Here, we investigated how amino acids change as renal impairment increases.

METHODS

Subjects were divided into three groups by renal function glomerular filtration rate: healthy controls, patients with chronic kidney disease with normal kidney function, and patients with chronic kidney disease with decreased kidney function group. We identified 11 amino acids of interest using LC-MS/MS on MRM (+) mode.

RESULTS

Statistical analysis indicated that alanine (ALA), valine (VAL), and tyrosine (TYR) decrease with renal function impairment, whereas phenylalanine (PHE) and citrulline (CIT) increase. We tried to construct a diagnostic model utilizing a combination of amino acids capable of identifying early chronic kidney disease patients. The accuracy, specificity, and sensitivity of the combining predictors were 86.9%, 84.6%, and 90.9%, respectively, which is superior to the reported values for serum creatinine, urea, and cystatin-c.

CONCLUSION

Our data suggest that serum amino acid levels may supply important information for the early detection of chronic kidney disease. We are the first to establish a diagnostic model utilizing serum levels of multiple amino acids for the diagnosis of patients with early-stage chronic kidney disease.

Rapid discrimination of human oesophageal squamous cell carcinoma by mass spectrometry based on differences in amino acid metabolism

Oesophageal cancer (OC) is associated with high morbidity and mortality, and surgery is the most effective approach to treat it. In order to reduce surgical risks and duration of surgery, we explored a new strategy to determine tumour margins in surgery. In this study, we included 128 cancerous and 128 noncancerous database entries obtained from 32 human patients. Using internal extractive electrospray ionization-MS, in positive ion detection mode, the relative abundances of m/z 104.13, m/z 116.10, m/z 132.13, and m/z 175.13 were higher in cancer tissue while the relative abundances of m/z 82.99, m/z 133.11, m/z 147.08, m/z 154.06, and m/z 188.05 were higher in normal tissue. Using partial least squares analysis, the mass spectra of cancer samples was discriminated from those of normal tissues, and the discriminatory ions were obtained from loading plots. Dimethylglycine(m/z 104), proline(m/z 116), isoleucine(m/z 132), asparagine(m/z 133), glutamine(m/z 147), and arginine(m/z 175) were identified by collision-induced dissociation experiments. Using the ROC curve analysis, we verified the validity of six amino acids for the identification of tumour tissue. Further investigations of tissue amino acids may allow us to better understand the underlying mechanisms involved in OC and develop novel means to identify tumour tissue during operation.

Roles of amino acids in preventing and treating intestinal diseases: recent studies with pig models

Animal models are needed to study and understand a human complex disease. Because of their similarities in anatomy, structure, physiology, and pathophysiology, the pig has proven its usefulness in studying human gastrointestinal diseases, such as inflammatory bowel disease, ischemia/reperfusion injury, diarrhea, and cancer. To understand the pathogenesis of these diseases, a number of experimental models generated in pigs are available, for example, through surgical manipulation, chemical induction, microbial infection, and genetic engineering. Our interests have been using amino acids as therapeutics in pig and human disease models. Amino acids not only play an important role in protein biosynthesis, but also exert significant physiological effects in regulating immunity, anti-oxidation, redox regulation, energy metabolism, signal transduction, and animal behavior. Recent studies in pigs have shown that specific dietary amino acids can improve intestinal integrity and function under normal and pathological conditions that protect the host from different diseases. In this review, we summarize several pig models in intestinal diseases and how amino acids can be used as therapeutics in treating pig and human diseases.

Amino acid homeostasis and signalling in mammalian cells and organisms

Cells have a constant turnover of proteins that recycle most amino acids over time. Net loss is mainly due to amino acid oxidation. Homeostasis is achieved through exchange of essential amino acids with non-essential amino acids and the transfer of amino groups from oxidised amino acids to amino acid biosynthesis. This homeostatic condition is maintained through an active mTORC1 complex. Under amino acid depletion, mTORC1 is inactivated. This increases the breakdown of cellular proteins through autophagy and reduces protein biosynthesis. The general control non-derepressable 2/ATF4 pathway may be activated in addition, resulting in transcription of genes involved in amino acid transport and biosynthesis of non-essential amino acids. Metabolism is autoregulated to minimise oxidation of amino acids. Systemic amino acid levels are also tightly regulated. Food intake briefly increases plasma amino acid levels, which stimulates insulin release and mTOR-dependent protein synthesis in muscle. Excess amino acids are oxidised, resulting in increased urea production. Short-term fasting does not result in depletion of plasma amino acids due to reduced protein synthesis and the onset of autophagy. Owing to the fact that half of all amino acids are essential, reduction in protein synthesis and amino acid oxidation are the only two measures to reduce amino acid demand. Long-term malnutrition causes depletion of plasma amino acids. The CNS appears to generate a protein-specific response upon amino acid depletion, resulting in avoidance of an inadequate diet. High protein levels, in contrast, contribute together with other nutrients to a reduction in food intake.

Metabolic PET Imaging in Oncology

OBJECTIVE

In this article, we provide a general overview of how cancer cells subvert critical metabolic pathways to support their growth and unchecked division. Furthermore, we outline how molecular imaging can diagnostically exploit the resulting differences between cancer and normal cells.

CONCLUSION

Molecular PET can provide valuable information about the metabolic dysregulation in cancer.

Cartilaginous Metabolomic Study Reveals Potential Mechanisms of Osteophyte Formation in Osteoarthritis

Osteophyte is one of the inevitable consequences of progressive osteoarthritis with the main characteristics of cartilage degeneration and endochondral ossification. The pathogenesis of osteophyte formation is not fully understood to date. In this work, metabolomic approaches were employed to explore potential mechanisms of osteophyte formation by detecting metabolic variations between extracts of osteophyte cartilage tissues (n = 32) and uninvolved control cartilage tissues (n = 34), based on the platform of ultraperformance liquid chromatography tandem quadrupole time-of-flight mass spectrometry, as well as the use of multivariate statistic analysis and univariate statistic analysis. The osteophyte group was significantly separated from the control group by the orthogonal partial least-squares discriminant analysis models, indicating that metabolic state of osteophyte cartilage had been changed. In total, 28 metabolic variations further validated by mass spectrum (MS) match, tandom mass spectrum (MS/MS) match, and standards match mainly included amino acids, sulfonic acids, glycerophospholipids, and fatty acyls. These metabolites were related to some specific physiological or pathological processes (collagen dissolution, boundary layers destroyed, self-restoration triggered, etc.) which might be associated with the procedure of osteophyte formation. Pathway analysis showed phenylalanine metabolism (PI = 0.168, p = 0.004) was highly correlative to this degenerative process. Our findings provided a direction for targeted metabolomic study and an insight into further reveal the molecular mechanisms of ostophyte formation.

The fluctuation of free amino acids in serum during acute ischemic stroke

Currently, little data exists regarding the involvement of free amino acids (AA) in the pathogenesis of ischemic stroke (IS). Thus, our objective was to study the degree of the degree of fluctuation of free amino acids level in serum during the acute phase of IS. The study consisted of eighteen patients (female/male: 10/8; age: 73.1 ± 4.1) with acute IS that was confirmed by way of computed tomography, while twelve sex and age matched individuals were assigned as control group. During the study period, the patients did not receive any supplemental amino acids therapy that could affect the obtained results. The venous blood was obtained after >3 hours fasting at two time-points; time-point 1 – at admission to the hospital; time-point 2 – on day 5 from stroke onset. The blood for control purposes was collected only once, and the blood collection at time-point 1 was done before thrombolytic treatment (nine patients). The amino acids were identified using the Amino Acids Analyser (AAA 400) by INGOS Corp., Praha, Czech Republic. Our results revealed a statistically significant increase of glutamate, cystine and methionine on day 1 of stroke, in comparison to control, whereas, proline level was decreased on day 1 of stroke – in comparison to control serum. On comparing day 5 to the initial day of IS, elevation was observed of levels of asparagine, glycine, tyrosine, arginine, threonine, valine, leucine and phenylalanine. It can be said, then, that ischemic stroke induces both essential and nonessential amino acid fluctuations. Moreover, the decrease in proline and glutamine serum level with the simultaneous increase in the concentration of branch chain amino acids, Glu and Thr suggests a violent mobilization of the body’s proteins. Thus, a decrease of Pro and a simultaneous increase of Glu serum level could be considered as a marker of acute IS.