The metabolism of proline, a stress substrate, modulates carcinogenic pathways

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.

A fragment-like approach to PYCR1 inhibition

Pyrroline-5-carboxylate reductase 1 (PYCR1) is the final enzyme involved in the biosynthesis of proline and has been found to be upregulated in various forms of cancer. Due to the role of proline in maintaining the redox balance of cells and preventing apoptosis, PYCR1 is emerging as an attractive oncology target. Previous PYCR1 knockout studies led to a reduction in tumor growth. Accordingly, a small molecule inhibitor of PYCR1 could lead to new treatments for cancer, and a focused screening effort identified pargyline as a fragment-like hit. We report the design and synthesis of the first tool compounds as PYCR1 inhibitors, derived from pargyline, which were assayed to assess their ability to attenuate the production of proline. Structural activity studies have revealed the key determinants of activity, with the most potent compound (4) showing improved activity in vitro in enzyme (IC50 = 8.8 µM) and pathway relevant effects in cell-based assays.

Various proline food sources and blood pressure: substitution analysis

The aim of this study was to investigate the association of total proline intake, proline of various food sources, and substitution analysis for proline of food sources with blood pressure (BP) and 3.1-year incidence of hypertension in the framework of the Tehran Lipid and Glucose Study. The cohort consisted of 4287 participants (41.9% male), aged ≥ 20-70 years. In fully-adjusted model, individuals in the highest tertile for proline intake had an increased risk of incident hypertension than those in the lowest one (OR: 1.45; 95%CI: 1.06-1.97; p for trend: .017). Replacing proline of cheese and legumes source with that of yogurt, poultry, milk, and red meat source was associated with significant negative β coefficient for BP. The present study indicated that high dietary intakes of proline may increase the risk of incident hypertension. Also, substituting proline intake of cheese and legumes by those of proline intake of meats and milk is associated with a lower risk of high BP.

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.

Proline mediates metabolic communication between retinal pigment epithelial cells and the retina

The retinal pigment epithelium (RPE) is a monolayer of pigmented cells between the choroid and the retina. RPE dysfunction underlies many retinal degenerative diseases, including age-related macular degeneration, the leading cause of age-related blindness. To perform its various functions in nutrient transport, phagocytosis of the outer segment, and cytokine secretion, the RPE relies on an active energy metabolism. We previously reported that human RPE cells prefer proline as a nutrient and transport proline-derived metabolites to the apical, or retinal, side. In this study, we investigated how RPE utilizes proline in vivo and why proline is a preferred substrate. By using [13C]proline labeling both ex vivo and in vivo, we found that the retina rarely uses proline directly, whereas the RPE utilizes it at a high rate, exporting proline-derived mitochondrial intermediates for use by the retina. We observed that in primary human RPE cell culture, proline is the only amino acid whose uptake increases with cellular maturity. In human RPE, proline was sufficient to stimulate de novo serine synthesis, increase reductive carboxylation, and protect against oxidative damage. Blocking proline catabolism in RPE impaired glucose metabolism and GSH production. Notably, in an acute model of RPE-induced retinal degeneration, dietary proline improved visual function. In conclusion, proline is an important nutrient that supports RPE metabolism and the metabolic demand of the retina.

Modelling of Neuronal Ceroid Lipofuscinosis Type 2 in Dictyostelium discoideum Suggests That Cytopathological Outcomes Result from Altered TOR Signalling

The neuronal ceroid lipofuscinoses comprise a group of neurodegenerative disorders with similar clinical manifestations whose precise mechanisms of disease are presently unknown. We created multiple cell lines each with different levels of reduction of expression of the gene coding for the type 2 variant of the disease, Tripeptidyl peptidase (Tpp1), in the cellular slime mould Dictyostelium discoideum. Knocking down Tpp1 in Dictyostelium resulted in the accumulation of autofluorescent material, a characteristic trait of Batten disease. Phenotypic characterisation of the mutants revealed phenotypic deficiencies in growth and development, whilst endocytic uptake of nutrients was enhanced. Furthermore, the severity of the phenotypes correlated with the expression levels of Tpp1. We propose that the phenotypic defects are due to altered Target of Rapamycin (TOR) signalling. We show that treatment of wild type Dictyostelium cells with rapamycin (a specific TOR complex inhibitor) or antisense inhibition of expression of Rheb (Ras homologue enriched in the brain) (an upstream TOR complex activator) phenocopied the Tpp1 mutants. We also show that overexpression of Rheb rescued the defects caused by antisense inhibition of Tpp1. These results suggest that the TOR signalling pathway is responsible for the cytopathological outcomes in the Dictyostelium Tpp1 model of Batten disease.

Investigation of graded-level soybean meal diets in red drum (Sciaenops ocellatus) using NMR-based metabolomics analysis

We investigated changes in the metabolome in juvenile red drum (Sciaenops ocellatus) induced by increasing amounts of soybean meal (0% to 60%) in extruded, fishmeal-free diets using a nuclear magnetic resonance spectroscopy (NMR)-based metabolomics approach in a 12-week feeding trial. All of the diets were composed of ≈40% total crude protein, ≈11% total crude lipid and were energetically balanced. A fishmeal-containing, commercial extruded diet was used as a control diet throughout the trial. Each week, liver, muscle, intestine and plasma samples were collected and analyzed by NMR to provide a "snapshot" of the metabolome at different time points. Results indicate significant time-dependence of the metabolic profiles in various tissues with stable metabolomic profiles forming after about 9-weeks on the experimental diets. We identify a previously unexploited biomarker of potential dietary stress (N‑formimino‑l‑glutamate (FIGLU)) in the fish that may prove to be useful for optimization of alternative diet formulations.

Integrative analysis of transcriptomics and metabolomics profiling on flesh quality of large yellow croaker Larimichthys crocea fed a diet with hydroxyproline supplementation

A previous study showed that flesh quality of large yellow croaker (LYC) was improved by feeding dietary hydroxyproline (Hyp, 0·69 %). The aim of the present study was to explore the underlying mechanisms using transcriptomics and metabolomics analysis. The metabolomics analysis showed that muscle metabolite profiles could be clearly separated between the basal diet and Hyp supplementation diet. Metabolites including betaine, Hyp, lactate, glucose-6-phosphate, trimethylamine N-oxide, taurine, creatine, inosine monophosphate, histamine and serine made significant contribution to the separation. Compared with the control diet, the transcriptomics analysis identified a total of 334 different expressed genes, of which 298 genes were up-regulated and thirty-six genes were down-regulated in the Hyp supplementation group. The altered genes of the Hyp supplementation group were involved in collagen metabolism, lipid metabolism and energy metabolism. The integrated results revealed that the increased muscle collagen content in the Hyp supplementation diet was partly because of its enhancement of biosynthesis and the reduction of degradation. The improvement of muscle quality by dietary Hyp supplementation could also be related to a good utilisation of glucose through enhancement of glycolysis. It was concluded that dietary Hyp supplementation could improve flesh quality because of comprehensive metabolism changes including elevated collagen content, glycolysis, lipid metabolism and flesh flavour of LYC. The present study provided a novel strategy to understand the underlying molecular mechanism of flesh quality of LYC fed diet with Hyp supplementation.

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.

Proline Metabolism in Cell Regulation and Cancer Biology: Recent Advances and Hypotheses

SIGNIFICANCE

It is increasingly clear that proline metabolism plays an important role in metabolic reprogramming, not only in cancer but also in related fields such as aging, senescence, and development. Although first focused on proline catabolism, recent studies from a number of laboratories have emphasized the regulatory effects of proline synthesis and proline cycling. Recent Advances: Although proline dehydrogenase/proline oxidase (PRODH/POX) has been known as a tumor protein 53 (P53)-activated source of redox signaling for initiating apoptosis and autophagy, senescence has been added to the responses. On the biosynthetic side, two well-recognized oncogenes, c-MYC and phosphoinositide 3-kinase (PI3K), markedly upregulate enzymes of proline synthesis; mechanisms affected include augmented redox cycling and maintenance of pyridine nucleotides. The reprogramming has been shown to shift in clonogenesis and/or metastasis.

CRITICAL ISSUES

Although PRODH/POX generates reactive oxygen species (ROS) for signaling, the cellular endpoint is variable and dependent on metabolic context; the switches for these responses remain unknown. On the synthetic side, the enzymes require more complete characterization in various cancers, and demonstration of coupling of proline metabolites to other pathways may require studies of protein-protein interactions, membrane transporters, and shuttles.

FUTURE DIRECTIONS

The proline metabolic axis can serve as a scaffold on which a variety of regulatory mechanisms are integrated. Once understood as a central mechanism in cancer metabolism, proline metabolism may be a good target for adjunctive cancer therapy.

Amino Acid Biosignature in Plasma among Ischemic Stroke Subtypes

Ischemic stroke is a neurovascular disorder caused by reduced or blockage of blood flow to the brain, which may permanently affect motor and cognitive abilities. The diagnostic of stroke is performed using imaging technologies, clinical evaluation, and neuropsychological protocols, but no blood test is available yet. In this work, we analyzed amino acid concentrations in blood plasma from poststroke patients in order to identify differences that could characterize the stroke etiology. Plasma concentrations of sixteen amino acids from patients with chronic ischemic stroke (n = 73) and the control group (n = 16) were determined using gas chromatography coupled to mass spectrometry (GC-MS). The concentration data was processed by Partial Least Squares-Discriminant Analysis (PLS-DA) to classify patients with stroke and control. The amino acid analysis generated a first model able to discriminate ischemic stroke patients from control group. Proline was the most important amino acid for classification of the stroke samples in PLS-DA, followed by lysine, phenylalanine, leucine, and glycine, and while higher levels of methionine and alanine were mostly related to the control samples. The second model was able to discriminate the stroke subtypes like atherothrombotic etiology from cardioembolic and lacunar etiologies, with lysine, leucine, and cysteine plasmatic concentrations being the most important metabolites. Our results suggest an amino acid biosignature for patients with chronic stroke in plasma samples, which can be helpful in diagnosis, prognosis, and therapeutics of these patients.

d-amino acid oxidase promotes cellular senescence via the production of reactive oxygen species

This study reveals a novel role of d-amino acid oxidase in promoting cellular senescence induced by genotoxic stresses via enzymatic generation of reactive oxygen species.

d-amino acid oxidase (DAO) is a flavin adenine dinucleotide (FAD)–dependent oxidase metabolizing neutral and polar d-amino acids. Unlike l-amino acids, the amounts of d-amino acids in mammalian tissues are extremely low, and therefore, little has been investigated regarding the physiological role of DAO. We have recently identified DAO to be up-regulated in cellular senescence, a permanent cell cycle arrest induced by various stresses, such as persistent DNA damage and oxidative stress. Because DAO produces reactive oxygen species (ROS) as byproducts of substrate oxidation and the accumulation of ROS mediates the senescence induction, we explored the relationship between DAO and senescence. We found that inhibition of DAO impaired senescence induced by DNA damage, and ectopic expression of wild-type DAO, but not enzymatically inactive mutant, enhanced it in an ROS-dependent manner. Furthermore, addition of d-amino acids and riboflavin, a metabolic precursor of FAD, to the medium potentiated the senescence-promoting effect of DAO. These results indicate that DAO promotes senescence through the enzymatic ROS generation, and its activity is regulated by the availability of its substrate and coenzyme.

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.

Is the Response of Tumours Dependent on the Dietary Input of Some Amino Acids or Ratios among Essential and Non-Essential Amino Acids? All That Glitters Is Not Gold

Energy production is the main task of the cancer cell metabolism because the costs of duplicating are enormous. Although energy is derived in cells by dismantling the carbon-to-carbon bonds of any macronutrient, cancer nutritional needs for energetic purposes have been studied primarily as being dependent on glycolysis. Since the end of the last century, the awareness of the dependence of cancer metabolism on amino acids not only for protein synthesis but also to match energy needs has grown. The roles of specific amino acids such as glutamine, glycine and serine have been explored in different experimental conditions and reviewed. Moreover, epidemiological evidence has revealed that some amino acids used as a supplement for therapeutic reasons, particularly the branched-chain ones, may reduce the incidence of liver cancer and a specific molecular mechanism has been proposed as functional to their protective action. By contrast and puzzling clinicians, the metabolomic signature of some pathologies connected to an increased risk of cancer, such as prolonged hyperinsulinemia in insulin-resistant patients, is identified by elevated plasma levels of the same branched-chain amino acids. Most recently, certain formulations of amino acids, deeply different from the amino acid compositions normally present in foods, have shown the power to master cancer cells epigenetically, slowing growth or driving cancer cells to apoptotic death, while being both beneficial for normal cell function and the animal’s health and lifespan. In this review, we will analyze and try to disentangle some of the many knots dealing with the complexities of amino acid biology and links to cancer metabolism.

Mitochondrial aconitase is a key regulator of energy production for growth and protein expression in Chinese hamster ovary cells

INTRODUCTION

Mammalian cells like Chinese hamster ovary (CHO) cells are routinely used for production of recombinant therapeutic proteins. Cells require a continuous supply of energy and nutrients to sustain high cell densities whilst expressing high titres of recombinant proteins. Cultured mammalian cells are primarily dependent on glucose and glutamine metabolism for energy production.

OBJECTIVES

The TCA cycle is the main source of energy production and its continuous flow is essential for cell survival. Modulated regulation of TCA cycle can affect ATP production and influence CHO cell productivity.

METHODS

To determine the key metabolic reactions of the cycle associated with cell growth in CHO cells, we transiently silenced each gene of the TCA cycle using RNAi.

RESULTS

Silencing of at least four TCA cycle genes was detrimental to CHO cell growth. With an exception of mitochondrial aconitase (or Aco2), all other genes were associated with ATP production reactions of the TCA cycle and their resulting substrates can be supplied by other anaplerotic and cataplerotic reactions. This study is the first of its kind to have established key role of aconitase gene in CHO cells. We further investigated the temporal effects of aconitase silencing on energy production, CHO cell metabolism, oxidative stress and recombinant protein production.

CONCLUSION

Transient silencing of mitochondrial aconitase inhibited cell growth, reduced ATP production, increased production of reactive oxygen species and reduced cell specific productivity of a recombinant CHO cell line by at least twofold.

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.

Meta-analysis on the association between genetic polymorphisms and prepulse inhibition of the acoustic startle response

Sensorimotor gating measured by prepulse inhibition (PPI) of the acoustic startle response (ASR) has been proposed as one of the most promising electrophysiological endophenotypes of schizophrenia. During the past decade, a number of publications have reported significant associations between genetic polymorphisms and PPI in samples of schizophrenia patients and healthy volunteers. However, an overall evaluation of the robustness of these results has not been published so far. Therefore, we performed the first meta-analysis of published and unpublished associations between gene polymorphisms and PPI of ASR. Unpublished associations between genetic polymorphisms and PPI were derived from three independent samples. In total, 120 single observations from 16 independent samples with 2660 study participants and 43 polymorphisms were included. After correction for multiple testing based on false discovery rate and considering the number of analyzed polymorphisms, significant associations were shown for four variants, even though none of these associations survived a genome-wide correction (P<5∗10-8). These results imply that PPI might be modulated by four genotypes - COMT rs4680 (primarily in males), GRIK3 rs1027599, TCF4 rs9960767, and PRODH rs385440 - indicating a role of these gene variations in the development of early information processing deficits in schizophrenia. However, the overall impact of single genes on PPI is still rather small suggesting that PPI is - like the disease phenotype - highly polygenic. Future genome-wide analyses studies with large sample sizes will enhance our understanding on the genetic architecture of PPI.

Effects of dietary L-arginine levels on small intestine protein turnover and the expression of genes related to protein synthesis and proteolysis of layers

The aim of this study was to test the effects of dietary L-arginine (Arg) levels on protein turnover in the small intestine and the expression of genes related to protein synthesis and proteolysis of laying hens. Xinyang Black commercial laying hens (n = 864, aged 217 d) were randomly distributed to 6 treatments with 4 replicates of 36 birds. The dietary treatments were corn-corn gluten meal based diets containing 0.64, 0.86, 1.03, 1.27, 1.42 and 1.66% L-Arg, respectively. Fractional protein synthesis rate (FSR) and fractional protein gain rate (FGR) in the jejunum were the highest in the 1.27% L-Arg group. The mRNA expression of target of rapamycin (TOR), ribosomal protein S6 kinase 1 (S6K1), and eukaryotic initiation factor 4E-binding protein 1 (4E-BP1) in the duodenum reached the highest in the 1.27% L-Arg group, while the mRNA expression of 20S proteasome (20S) was the lowest in the 1.27% L-Arg group. The mRNA abundances of TOR and S6K1 in the jejunum were the highest in the 1.27% L-Arg group, while the mRNA expression of 20S was the lowest in the 1.27% L-Arg group, and the protein expression and phosphorylation levels of TOR in the 1.27% L-Arg group were higher than those in the 0.64% L-Arg group. These results indicate that the action of an appropriate level of dietary L-Arg to improve the protein synthesis of the small intestine involves up-regulating the protein expression and phosphorylation level of TOR in the jejunum accompanied by inhibiting the mRNA expression of 20S of laying hens.

p53 and metabolism: from mechanism to therapeutics

The tumor cell changes itself and its microenvironment to adapt to different situations, including action of drugs and other agents targeting tumor control. Therefore, metabolism plays an important role in the activation of survival mechanisms to keep the cell proliferative potential. The Warburg effect directs the cellular metabolism towards an aerobic glycolytic pathway, despite the fact that it generates less adenosine triphosphate than oxidative phosphorylation; because it creates the building blocks necessary for cell proliferation. The transcription factor p53 is the master tumor suppressor; it binds to more than 4,000 sites in the genome and regulates the expression of more than 500 genes. Among these genes are important regulators of metabolism, affecting glucose, lipids and amino acids metabolism, oxidative phosphorylation, reactive oxygen species (ROS) generation and growth factors signaling. Wild-type and mutant p53 may have opposing effects in the expression of these metabolic genes. Therefore, depending on the p53 status of the cell, drugs that target metabolism may have different outcomes and metabolism may modulate drug resistance. Conversely, induction of p53 expression may regulate differently the tumor cell metabolism, inducing senescence, autophagy and apoptosis, which are dependent on the regulation of the PI3K/AKT/mTOR pathway and/or ROS induction. The interplay between p53 and metabolism is essential in the decision of cell fate and for cancer therapeutics.

Proline oxidase controls proline, glutamate, and glutamine cellular concentrations in a U87 glioblastoma cell line

L-Proline is a multifunctional amino acid that plays an essential role in primary metabolism and physiological functions. Proline is oxidized to glutamate in the mitochondria and the FAD-containing enzyme proline oxidase (PO) catalyzes the first step in L-proline degradation pathway. Alterations in proline metabolism have been described in various human diseases, such as hyperprolinemia type I, velo-cardio-facial syndrome/Di George syndrome, schizophrenia and cancer. In particular, the mutation giving rise to the substitution Leu441Pro was identified in patients suffering of schizophrenia and hyperprolinemia type I. Here, we report on the expression of wild-type and L441P variants of human PO in a U87 glioblastoma human cell line in an attempt to assess their effect on glutamate metabolism. The subcellular localization of the flavoenzyme is not altered in the L441P variant, for which specific activity is halved compared to the wild-type PO. While this decrease in activity is significantly less than that previously proposed, an effect of the substitution on the enzyme stability is also apparent in our studies. At 24 hours of growth from transient transfection, the intracellular level of proline, glutamate, and glutamine is decreased in cells expressing the PO variants as compared to control U87 cells, reaching a similar figure at 72 h. On the other hand, the extracellular levels of the three selected amino acids show a similar time course for all clones. Furthermore, PO overexpression does not modify to a significant extent the expression of GLAST and GLT-1 glutamate transporters. Altogether, these results demonstrate that the proline pathway links cellular proline levels with those of glutamate and glutamine. On this side, PO might play a regulatory role in glutamatergic neurotransmission by affecting the cellular concentration of glutamate.

Measurement of Mitochondrial Oxygen Consumption in Permeabilized Fibers of Drosophila Using Minimal Amounts of Tissue

The fruit fly, Drosophila melanogaster, represents an emerging model for the study of metabolism. Indeed, drosophila have structures homologous to human organs, possess highly conserved metabolic pathways and have a relatively short lifespan that allows the study of different fundamental mechanisms in a short period of time. It is, however, surprising that one of the mechanisms essential for cellular metabolism, the mitochondrial respiration, has not been thoroughly investigated in this model. It is likely because the measure of the mitochondrial respiration in Drosophila usually requires a very large number of individuals and the results obtained are not highly reproducible. Here, a method allowing the precise measurement of mitochondrial oxygen consumption using minimal amounts of tissue from Drosophila is described. In this method, the thoraxes are dissected and permeabilized both mechanically with sharp forceps and chemically with saponin, allowing different compounds to cross the cell membrane and modulate the mitochondrial respiration. After permeabilization, a protocol is performed to evaluate the capacity of the different complexes of the electron transport system (ETS) to oxidize different substrates, as well as their response to an uncoupler and to several inhibitors. This method presents many advantages compared to methods using mitochondrial isolations, as it is more physiologically relevant because the mitochondria are still interacting with the other cellular components and the mitochondrial morphology is conserved. Moreover, sample preparations are faster, and the results obtained are highly reproducible. By combining the advantages of Drosophila as a model for the study of metabolism with the evaluation of mitochondrial respiration, important new insights can be unveiled, especially when the flies are experiencing different environmental or pathophysiological conditions.

Constituents of Propolis: Chrysin, Caffeic Acid, p-Coumaric Acid, and Ferulic Acid Induce PRODH/POX-Dependent Apoptosis in Human Tongue Squamous Cell Carcinoma Cell (CAL-27)

Propolis evokes several therapeutic properties, including anticancer activity. These activities are attributed to the action of polyphenols. Previously it has been demonstrated, that one of the most abundant polyphenolic compounds in ethanolic extracts of propolis are chrysin, caffeic acid, p-coumaric acid, and ferulic acid. Although their pro-apoptotic activity on human tongue squamous cell carcinoma cells (CAL-27) was established previously, the detailed mechanism of this process remains unclear. Considering the crucial role of proline metabolism and proline dehydrogenase/proline oxidase (PRODH/POX) in the regulation of cancer cell survival/apoptosis, we studied these processes in polyphenol-treated CAL-27 cells. All studied polyphenols evoked anti-proliferative activity, accompanied by increased PRODH/POX, P53, active caspases-3 and -9 expressions and decreased collagen biosynthesis, prolidase activity and proline concentration in CAL-27 cells. These data suggest that polyphenols of propolis induce PRODH/POX-dependent apoptosis through up-regulation of mitochondrial proline degradation and down-regulation of proline utilization for collagen biosynthesis.

Proline oxidase silencing induces proline-dependent pro-survival pathways in MCF-7 cells

Proline degradation by proline dehydrogenase/proline oxidase (PRODH/POX) contributes to apoptosis or autophagy. The identification of specific pathway of apoptosis/survival regulation is the aim of this study. We generated knocked-down PRODH/POX MCF-7 breast cancer cells (MCF-7^shPRODH/POX). PRODH/POX silencing did not affect cell viability. However, it contributed to decrease in DNA and collagen biosynthesis, increase in prolidase activity and intracellular proline concentration as well as increase in the expression of iNOS, NF-κB, mTOR, HIF-1α, COX-2, AMPK, Atg7 and Beclin-1 in MCF-7^shPRODH/POX cells. In these cells, glycyl-proline (GlyPro, substrate for prolidase) further inhibited DNA and collagen biosynthesis, maintained high prolidase activity, intracellular concentration of proline and up-regulated HIF-1α, AMPK, Atg7 and Beclin-1, compared to GlyPro-treated MCF-7 cells. In MCF-7 cells, GlyPro increased collagen biosynthesis, concentration of proline and expression of caspase-3, cleaved caspases -3 and -9, iNOS, NF-κB, COX-2 and AMPKβ. PRODH/POX knock-down contributed to pro-survival autophagy pathways in MCF-7 cells and GlyPro-derived proline augmented this process. However, GlyPro induced apoptosis in PRODH/POX-expressing MCF-7 cells as detected by up-regulation of active caspases -3 and -9. The data suggest that PRODH/POX silencing induces autophagy in MCF-7 cells and GlyPro-derived proline supports this process.

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.

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.

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.

Acetylenic derivative of betulin induces apoptosis in endometrial adenocarcinoma cell line

Since betulin (Bet) and its acetylenic derivative, 28-O-propynoylbetulin (proBet) were shown to induce apoptosis in several cancer cell lines, we studied the mechanism of this process in human endometrial adenocarcinoma cells (EA). Previous studies suggested that this group of compounds affect prolidase activity (proline releasing enzyme from imidodipeptides) and collagen biosynthesis (proline utilizing process) providing substrate (proline) for proline oxidase (POX) dependent apoptosis. Here we provide evidence that Bet and proBet exhibit prolidase-inducing activity in EA cell line. However, in contrast to Bet, proBet inhibited collagen biosynthesis, increased intracellular proline concentration and induced apoptosis in EA cells, as detected by caspase-3, and -9 expressions and annexin V staining. Although POX expression was not affected by both compounds, the process of apoptosis was accompanied by increase in cytoplasmic level of proline. The mechanism for proBet-induced prolidase activity was found at the level of β1 integrin signaling. The inhibition of collagen biosynthesis was due to up-regulation of NF-κB p65, an inhibitor of collagen type I gene transcription. Although Bet and proBet induced expression of pro-apoptotic p53 in EA cells, the effect of proBet on the processes was much stronger. In contrast to proBet, Bet strongly induced expression of pro-survival factors, HIF-1α and VEGF. The data suggest that massive production of proline by proBet-dependent activation of prolidase and inhibition of proline utilization for collagen biosynthesis may represent mechanism for POX-dependent apoptosis in EA cells.

Differential expression of novel metabolic and immunological biomarkers in oysters challenged with a virulent strain of OsHV-1

Early lifestages of the Pacific oyster (Crassostrea gigas) are highly susceptible to infection by OsHV-1 μVar, but little information exists regarding metabolic or pathophysiological responses of larval hosts. Using a metabolomics approach, we identified a range of metabolic and immunological responses in oyster larvae exposed to OsHV-1 μVar; some of which have not previously been reported in molluscs. Multivariate analyses of entire metabolite profiles were able to separate infected from non-infected larvae. Correlation analysis revealed the presence of major perturbations in the underlying biochemical networks and secondary pathway analysis of functionally-related metabolites identified a number of prospective pathways differentially regulated in virus-exposed larvae. These results provide new insights into the pathogenic mechanisms of OsHV-1 infection in oyster larvae, which may be applied to develop disease mitigation strategies and/or as new phenotypic information for selective breeding programmes aiming to enhance viral resistance.

Extracellular matrix endocytosis in controlling matrix turnover and beyond: emerging roles in cancer

The extracellular matrix (ECM) is a network of secreted proteins that, beyond providing support for tissues and organs, is involved in the regulation of a variety of cell functions, including cell proliferation, polarity, migration and oncogenic transformation. ECM homeostasis is maintained through a tightly controlled balance between synthesis, deposition and degradation. While the role of metalloproteases in ECM degradation is widely recognised, the contribution of ECM internalisation and intracellular degradation to ECM maintenance has been mostly overlooked. In this review, I will summarise what is known about the molecular mechanisms mediating ECM endocytosis and how this process impacts on diseases, such as fibrosis and cancer.

Pre-diagnostic metabolite concentrations and prostate cancer risk in 1077 cases and 1077 matched controls in the European Prospective Investigation into Cancer and Nutrition

BACKGROUND

Little is known about how pre-diagnostic metabolites in blood relate to risk of prostate cancer. We aimed to investigate the prospective association between plasma metabolite concentrations and risk of prostate cancer overall, and by time to diagnosis and tumour characteristics, and risk of death from prostate cancer.

METHODS

In a case-control study nested in the European Prospective Investigation into Cancer and Nutrition, pre-diagnostic plasma concentrations of 122 metabolites (including acylcarnitines, amino acids, biogenic amines, glycerophospholipids, hexose and sphingolipids) were measured using targeted mass spectrometry (AbsoluteIDQ p180 Kit) and compared between 1077 prostate cancer cases and 1077 matched controls. Risk of prostate cancer associated with metabolite concentrations was estimated by multi-variable conditional logistic regression, and multiple testing was accounted for by using a false discovery rate controlling procedure.

RESULTS

Seven metabolite concentrations, i.e. acylcarnitine C18:1, amino acids citrulline and trans-4-hydroxyproline, glycerophospholipids PC aa C28:1, PC ae C30:0 and PC ae C30:2, and sphingolipid SM (OH) C14:1, were associated with prostate cancer (p < 0.05), but none of the associations were statistically significant after controlling for multiple testing. Citrulline was associated with a decreased risk of prostate cancer (odds ratio (OR1SD) = 0.73; 95% confidence interval (CI) 0.62-0.86; p trend = 0.0002) in the first 5 years of follow-up after taking multiple testing into account, but not after longer follow-up; results for other metabolites did not vary by time to diagnosis. After controlling for multiple testing, 12 glycerophospholipids were inversely associated with advanced stage disease, with risk reduction up to 46% per standard deviation increase in concentration (OR1SD = 0.54; 95% CI 0.40-0.72; p trend = 0.00004 for PC aa C40:3). Death from prostate cancer was associated with higher concentrations of acylcarnitine C3, amino acids methionine and trans-4-hydroxyproline, biogenic amine ADMA, hexose and sphingolipid SM (OH) C14:1 and lower concentration of glycerophospholipid PC aa C42:4.

CONCLUSIONS

Several metabolites, i.e. C18:1, citrulline, trans-4-hydroxyproline, three glycerophospholipids and SM (OH) C14:1, might be related to prostate cancer. Analyses by time to diagnosis indicated that citrulline may be a marker of subclinical prostate cancer, while other metabolites might be related to aetiology. Several glycerophospholipids were inversely related to advanced stage disease. More prospective data are needed to confirm these associations.

Gastric cancer: Metabolic and metabolomics perspectives (Review)

Gastric cancer is one of the most malignant tumors worldwide and remains a major health threat in Asia-Pacific regions, while its pathological mechanism is generally unknown. Recent research has advanced the understanding of the relationship between metabolic reprogramming and carcinogenesis. In particular, metabolic regulation and cancer research are being further brought into sharp focus with the emergence of metabolomics. Not only can metabolomics provide global information on metabolic profiles of specific tumors, but it can also act as a promising tool to discover biomarkers regarding diagnosis, metastatic surveillance and chemotherapeutic sensitivity prediction. Meanwhile, metabolism-based anticancer therapies will be further discovered. Up to now, accumulative studies have highlighted the application of metabolomics in gastric cancer research regarding different aspects; therefore we summarized the current available results of how metabolic changes are linked to gastric carcinogenesis, and how metabolomics holds promise for the diagnosis, metastatic surveillance, treatment and prognosis prediction of gastric cancer.

Metabolic analysis of radioresistant medulloblastoma stem-like clones and potential therapeutic targets

Medulloblastoma is a fatal brain tumor in children, primarily due to the presence of treatment-resistant medulloblastoma stem cells. The energy metabolic pathway is a potential target of cancer therapy because it is often different between cancer cells and normal cells. However, the metabolic properties of medulloblastoma stem cells, and whether specific metabolic pathways are essential for sustaining their stem cell-like phenotype and radioresistance, remain unclear. We have established radioresistant medulloblastoma stem-like clones (rMSLCs) by irradiation of the human medulloblastoma cell line ONS-76. Here, we assessed reactive oxygen species (ROS) production, mitochondria function, oxygen consumption rate (OCR), energy state, and metabolites of glycolysis and tricarboxylic acid cycle in rMSLCs and parental cells. rMSLCs showed higher lactate production and lower oxygen consumption rate than parental cells. Additionally, rMSLCs had low mitochondria mass, low endogenous ROS production, and existed in a low-energy state. Treatment with the metabolic modifier dichloroacetate (DCA) resulted in mitochondria dysfunction, glycolysis inhibition, elongated mitochondria morphology, and increased ROS production. DCA also increased radiosensitivity by suppression of the DNA repair capacity through nuclear oxidization and accelerated the generation of acetyl CoA to compensate for the lack of ATP. Moreover, treatment with DCA decreased cancer stem cell-like characters (e.g., CD133 positivity and sphere-forming ability) in rMSLCs. Together, our findings provide insights into the specific metabolism of rMSLCs and illuminate potential metabolic targets that might be exploited for therapeutic benefit in medulloblastoma.

Proline dehydrogenase promotes senescence through the generation of reactive oxygen species

Cellular senescence is a complex stress response characterized by permanent loss of proliferative capacity and is implicated in age-related disorders. Although the transcriptional activity of p53 (encoded by TP53) is known to be vital for senescence induction, the downstream effector genes critical for senescence remain unsolved. Recently, we have identified the proline dehydrogenase gene (PRODH) to be upregulated specifically in senescent cells in a p53-dependent manner, and the functional relevance of this to senescence is yet to be defined. Here, we conducted functional analyses to explore the relationship between PRODH and the senescence program. We found that genetic and pharmacological inhibition of PRODH suppressed senescent phenotypes induced by DNA damage. Furthermore, ectopic expression of wild-type PRODH, but not enzymatically inactive forms, induced senescence associated with the increase in reactive oxygen species (ROS) and the accumulation of DNA damage. Treatment with N-acetyl-L-cysteine, a ROS scavenger, prevented senescence induced by PRODH overexpression. These results indicate that PRODH plays a causative role in DNA damage-induced senescence through the enzymatic generation of ROS.

Gingival crevicular fluid levels of prolidase and alkaline phosphatase in periodontitis

Background/Aim: The purpose of this study was to investigate gingival crevicular fluid (GCF) alkaline phosphatase (ALP) and prolidase levels in subjects with different periodontal status. Material and Methods: Fifteen periodontitis, fifteen gingivitis and fifteen healthy subject were included. GCF samples were collected from participants. Probing depth, clinical attachment level, gingival index was recorded. ALP and prolidase levels were determined in GCF by spectrophotometrically. Results: Higher values of ALP were found in periodontitis compared with gingivitis and healthy control (p<0.001). The values of prolidase were lower in periodontitis than healthy control (p<0.05). A statistically significant positive correlation was found between clinical parameters and ALP levels (p<0.001). There is no significant correlation between clinical parameters and prolidase levels (p>0.05). Additionally, no significant correlation was detected between ALP and prolidase (r= -0.309, p>0.05). Conclusion: Our preliminary data suggest that low prolidase level in periodontitis was not associated with ALP and clinical parameters, which represent periodontal destruction and inflammation.

Evidence that COMT genotype and proline interact on negative-symptom outcomes in schizophrenia and bipolar disorder

Elevated peripheral proline is associated with psychiatric disorders, and there is evidence that proline is a neuromodulator. The proline dehydrogenase (PRODH) gene, which encodes the enzyme that catalyzes proline catabolism, maps to human chromosome 22q11.2, a region conferring risk of schizophrenia. In the Prodh-null mouse, an interaction between elevated peripheral proline and another 22q11.2 gene, catechol-O-methyltransferase (COMT), on neurotransmission and behavior has been reported. We explored the relationship between fasting plasma proline levels and COMT Val(158)Met genotype on symptoms (positive, negative and total) in schizophrenia patients. In an exploratory study we also examined symptom change in patients with bipolar disorder. There was a significant interaction between peripheral proline and COMT on negative symptoms in schizophrenia (P<0.0001, n=95). In COMT Val/Val patients, high proline was associated with low Scale for the Assessment of Negative Symptom (SANS) scores. In contrast, high proline was associated with high SANS scores in patients carrying a Met allele. The relationship between proline and COMT also appears to modify negative symptoms across psychiatric illness. In bipolar disorder, a significant interaction was also observed on negative-symptom change (P=0.007, n=43). Negative symptoms are intractable and largely unaddressed by current medications. These data indicate a significant interaction between peripheral proline and COMT genotype, influencing negative symptoms in schizophrenia and bipolar disorder. That high proline has converse effects on symptoms by COMT genotype, may have implications for therapeutic decisions.

Prolidase-proline dehydrogenase/proline oxidase-collagen biosynthesis axis as a potential interface of apoptosis/autophagy

Prolidase is a cytosolic imidodipeptidase that specifically splits imidodipeptides with C-terminal proline or hydroxyproline. The enzyme plays an important role in the recycling of proline from imidodipeptides for resynthesis of collagen and other proline-containing proteins. The mechanism of prolidase-dependent regulation of collagen biosynthesis was found at both transcriptional and post-transcriptional level. The increase in the enzyme activity is due to its phosphorylation on serine/threonine residues. Prolidase-dependent transcriptional regulation of collagen biosynthesis was found at the level of NF-κB, known inhibitor of type I collagen gene expression. Proline dehydrogenase/proline oxidase (PRODH/POX) is flavin-dependent enzyme associated with the inner mitochondrial membrane. The enzyme catalyzes conversion of proline into Δ(1) -pyrroline-5-carboxylate (P5C), during which reactive oxygen species (ROS) are produced, inducing intrinsic and extrinsic apoptotic pathways. Alternatively, under low glucose stress, PRODH/POX activation produces ATP for energy supply and survival. Of special interest is that PRODH/POX gene is induced by P53 and peroxisome proliferator-activated gamma receptor (PPARγ). Among down-regulators of PRODH/POX is an oncogenic transcription factor c-MYC and miR-23b*. On the other hand, PRODH/POX suppresses HIF-1α transcriptional activity, the MAPK pathway, cyclooxygenase-2, epidermal growth factor receptor and Wnt/b-catenin signaling. PRODH/POX expression is often down-regulated in various tumors, limiting mitochondrial proline utilization to P5C. It is accompanied by increased cytoplasmic level of proline. Proline availability for PRODH/POX-dependent ATP or ROS generation depends on activity of prolidase and utilization of proline in process of collagen biosynthesis. Therefore, Prolidase-PRODH/POX-Collagen Biosynthesis axis may represent potential interface that regulate apoptosis and survival. © 2016 BioFactors, 42(4):341-348, 2016.

Metabolomics identifies the intersection of phosphoethanolamine with menaquinone-triggered apoptosis in an in vitro model of leukemia

Altered metabolism is increasingly acknowledged as an important aspect of cancer, and thus serves as a potentially fertile area for the identification of therapeutic targets or leads. Our recent work using transcriptional data to predict metabolite levels in cancer cells led to preliminary evidence of the antiproliferative role of menaquinone (vitamin K2) in the Jurkat cell line model of acute lymphoblastic leukemia. However, nothing is known about the direct metabolic impacts of menaquinone in cancer, which could provide insights into its mechanism of action. Here, we used metabolomics to investigate the process by which menaquinone exerts antiproliferative activity on Jurkat cells. We first validated the dose-dependent, semi-selective, pro-apoptotic activity of menaquinone treatment on Jurkat cells relative to non-cancerous lymphoblasts. We then used mass spectrometry-based metabolomics to identify systems-scale changes in metabolic dynamics that are distinct from changes induced in non-cancerous cells or by other chemotherapeutics. One of the most significantly affected metabolites was phosphoethanolamine, which exhibited a two-fold increase in menaquinone-treated Jurkat cells compared to vehicle-treated cells at 24 h, growing to a five-fold increase at 72 h. Phosphoethanolamine elevation was observed prior to the induction of apoptosis, and was not observed in menaquinone-treated lymphoblasts or chemotherapeutic-treated Jurkat cells. We also validated the link between menaquinone and phosphoethanolamine in an ovarian cancer cell line, suggesting potentially broad applicability of their relationship. This metabolomics-based work is the first detailed characterization of the metabolic impacts of menaquinone treatment and the first identified link between phosphoethanolamine and menaquinone-induced apoptosis.

Inhibition of pulmonary metastasis by Emilia sonchifolia (L.) DC: An in vivo experimental study

BACKGROUND

Emilia sonchifolia (L.) DC is a widely distributed medicinal herb used mainly in the indigenous Ayurvedic system of medicine in India. This plant is one among the ten sacred plants of Kerala state in India, collectively known as Dasapushpam.

PURPOSE

To assess the therapeutic efficacy of this well-known medicinal plant in a catastrophic complication like metastatic cancer progression. This study further aimed to scientifically validate the traditional medicinal use of this sacred plant.

STUDY DESIGN

Highly metastatic B16F10 melanoma will spontaneously metastasize in C57BL/6 mice and is accepted as a useful murine model for the study on metastasis. Three different experimental modalities of prophylactic, simultaneous and after tumour development were used for data accumulation and analysis.

METHODS

Whole plant genuine extract of E. sonchifolia (25 mg/kg bodyweight) was administered intraperitoneally to C57BL/6 mice. Animals were sacrificed on 21st day after tumour induction and the lung tumour nodules were counted. Various lung and serum biochemical parameters along with major cytokine levels were recorded. Survival rate was monitored. Histopathology of the lung tissue and expression studies of the major genes involved in metastasis was also carried out.

RESULTS

E. sonchifolia significantly inhibited pulmonary tumour formation and increased the life span of animals. Lung collagen hydroxyproline, uronic acid, hexosamine, serum sialic acid, γ-glutamyl transpeptidase, vascular endothelial growth factor (VEGF), granulocyte monocyte colony-stimulating factor and other cytokine levels were significantly lowered in the treated group of animals. Histopathological analysis was also correlated with these findings. E. sonchifolia down regulated the expression of matrix metalloproteinases; extracellular signal-regulated kinases and VEGF at the same time up regulated the expression of tissue inhibitor of matrix metalloproteinases.

CONCLUSION

Previous studies on E. sonchifolia proved its significant biological properties including anti-tumour, anti-inflammatory and antioxidant activities. Present report is so far the first study to demonstrate the anti-metastatic potential of this medicinal herb justifying its conventional use in the traditional medicine.

The Emerging Hallmarks of Cancer Metabolism

Tumorigenesis is dependent on the reprogramming of cellular metabolism as both direct and indirect consequence of oncogenic mutations. A common feature of cancer cell metabolism is the ability to acquire necessary nutrients from a frequently nutrient-poor environment and utilize these nutrients to both maintain viability and build new biomass. The alterations in intracellular and extracellular metabolites that can accompany cancer-associated metabolic reprogramming have profound effects on gene expression, cellular differentiation, and the tumor microenvironment. In this Perspective, we have organized known cancer-associated metabolic changes into six hallmarks: (1) deregulated uptake of glucose and amino acids, (2) use of opportunistic modes of nutrient acquisition, (3) use of glycolysis/TCA cycle intermediates for biosynthesis and NADPH production, (4) increased demand for nitrogen, (5) alterations in metabolite-driven gene regulation, and (6) metabolic interactions with the microenvironment. While few tumors display all six hallmarks, most display several. The specific hallmarks exhibited by an individual tumor may ultimately contribute to better tumor classification and aid in directing treatment.

Downregulation of pyrroline-5-carboxylate reductase-2 induces the autophagy of melanoma cells via AMPK/mTOR pathway

Melanoma is the most aggressive form of skin cancer and causes 50,000 deaths annually worldwide. The roles of proline-dependent process and autophagy have both been reported in studies on melanoma. In the present study, we focused on the effect of pyrroline-5-carboxylate reductase-2 (PYCR2) on inducing autophagy process in melanoma. The expression of PYCR2 was regulated by an RNAi technique, and the cell proliferation of A375 cell line was determined by methyl thiazolyl tetrazolium test; the effect of PYCR2 on the apoptosis process and AMPK/mTOR pathway was evaluated by flow cytometry assay and Western blot. It was found that silence of PYCR2 resulted in the decrease of proliferative ability and activation of AMPK/mTOR-induced autophagy of A375 cells. PYCR2 silencing also activated AMPK/mTOR pathway in another melanoma cell line, CHL-1. However, the overexpression of PYCR2 seemed to make no difference to the cell viability and targeted pathway. Our results offered a preliminary illustration on the mechanism of the PYCR2-dependent autophagy and showed that PYCR2 was a potential therapeutic target of melanoma.

Graphene Functionalized with Arginine Decreases the Development of Glioblastoma Multiforme Tumor in a Gene-Dependent Manner

Our previous studies revealed that graphene had anticancer properties in experiments in vitro with glioblastoma multiforme (GBM) cells and in tumors cultured in vivo. We hypothesized that the addition of arginine or proline to graphene solutions might counteract graphene agglomeration and increase the activity of graphene. Experiments were performed in vitro with GBM U87 cells and in vivo with GBM tumors cultured on chicken embryo chorioallantoic membranes. The measurements included cell morphology, mortality, viability, tumor morphology, histology, and gene expression. The cells and tumors were treated with reduced graphene oxide (rGO) and rGO functionalized with arginine (rGO + Arg) or proline (rGO + Pro). The results confirmed the anticancer effect of graphene on GBM cells and tumor tissue. After functionalization with amino acids, nanoparticles were distributed more specifically, and the flakes of graphene were less agglomerated. The molecule of rGO + Arg did not increase the expression of TP53 in comparison to rGO, but did not increase the expression of MDM2 or the MDM2/TP53 ratio in the tumor, suggesting that arginine may block MDM2 expression. The expression of NQO1, known to be a strong protector of p53 protein in tumor tissue, was greatly increased. The results indicate that the complex of rGO + Arg has potential in GBM therapy.