SK-Channel Activation Alters Peripheral Metabolic Pathways in Mice, but Not Lipopolysaccharide-Induced Fever or Inflammation

Purpose

Previously, we have shown that CyPPA (cyclohexyl-[2-(3,5-dimethyl-pyrazol-1-yl)-6-methyl-pyrimidin-4-yl]-amine), a pharmacological small-conductance calcium-activated potassium (SK)–channel positive modulator, antagonizes lipopolysaccharide (LPS)-induced cytokine expression in microglial cells. Here, we aimed to test its therapeutic potential for brain-controlled sickness symptoms, brain inflammatory response during LPS-induced systemic inflammation, and peripheral metabolic pathways in mice.

Methods

Mice were pretreated with CyPPA (15 mg/kg IP) 24 hours before and simultaneously with LPS stimulation (2.5 mg/kg IP), and the sickness response was recorded by a telemetric system for 24 hours. A second cohort of mice were euthanized 2 hours after CyPPA or solvent treatment to assess underlying CyPPA-induced mechanisms. Brain, blood, and liver samples were analyzed for inflammatory mediators or nucleotide concentrations using immunohistochemistry, real-time PCR and Western blot, or HPLC. Moreover, we investigated CyPPA-induced changes of UCP1 expression in brown adipose tissue (BAT)–explant cultures.

Results

CyPPA treatment did not affect LPS-induced fever, anorexia, adipsia, or expression profiles of inflammatory mediators in the hypothalamus or plasma or microglial reactivity to LPS (CD11b staining and CD68 mRNA expression). However, CyPPA alone induced a rise in core body temperature linked to heat production via altered metabolic pathways like reduced levels of adenosine, increased protein content, and increased UCP1 expression in BAT-explant cultures, but no alteration in ATP/ADP concentrations in the liver. CyPPA treatment was accompanied by altered pathways, including NFκB signaling, in the hypothalamus and cortex, while circulating cytokines remained unaltered.

Conclusion

Overall, while CyPPA has promise as a treatment strategy, in particular according to results from in vitro experiments, we did not reveal anti-inflammatory effects during severe LPS-induced systemic inflammation. Interestingly, we found that CyPPA alters metabolic pathways inducing short hyperthermia, most likely due to increased energy turnover in the liver and heat production in BAT.

Eimeria bovis Macromeront Formation Induces Glycolytic Responses and Mitochondrial Changes in Primary Host Endothelial Cells

Eimeria bovis is an intracellular apicomplexan parasite that causes considerable economic losses in the cattle industry worldwide. During the first merogony, E. bovis forms large macromeronts with >140,000 merozoites I in host endothelial cells. Because this is a high-energy demanding process, E. bovis exploits the host cellular metabolism to fulfill its metabolic requirements. We here analyzed the carbohydrate-related energetic metabolism of E. bovis–infected primary bovine umbilical vein endothelial cells during first merogony and showed that during the infection, E. bovis–infected culture presented considerable changes in metabolic signatures, glycolytic, and mitochondrial responses. Thus, an increase in both oxygen consumption rates (OCR) and extracellular acidification rates (ECAR) were found in E. bovis–infected host cells indicating a shift from quiescent to energetic cell status. Enhanced levels of glucose and pyruvate consumption in addition to increased lactate production, suggesting an important role of glycolysis in E. bovis–infected culture from 12 days p.i. onward. This was also tested by glycolytic inhibitors (2-DG) treatment, which reduced the macromeront development and diminished merozoite I production. As an interesting finding, we observed that 2-DG treatment boosted sporozoite egress. Referring to mitochondrial activities, intracellular ROS production was increased toward the end of merogony, and mitochondrial potential was enhanced from 12 d p. i. onward in E. bovis–infected culture. Besides, morphological alterations of membrane potential signals also indicated mitochondrial dysfunction in macromeront-carrying host endothelial culture.

Phytocompounds Targeting Metabolic Reprogramming in Cancer: An Assessment of Role, Mechanisms, Pathways, and Therapeutic Relevance

The metabolism of cancer is remarkably different from that of normal cells and confers a variety of benefits, including the promotion of other cancer hallmarks. As the rewired metabolism is a near-universal property of cancer cells, efforts are underway to exploit metabolic vulnerabilities for therapeutic benefits. In the continued search for safer and effective ways of cancer treatment, structurally diverse plant-based compounds have gained substantial attention. Here, we present an extensive assessment of the role of phytocompounds in modulating cancer metabolism and attempt to make a case for the use of plant-based compounds in targeting metabolic vulnerabilities of cancer. We discuss the pharmacological interactions of phytocompounds with major metabolic pathways and evaluate the role of phytocompounds in the regulation of growth signaling and transcriptional programs involved in the metabolic transformation of cancer. Lastly, we examine the potential of these compounds in the clinical management of cancer along with limitations and challenges.

Metabolic Signatures of Cryptosporidium parvum-Infected HCT-8 Cells and Impact of Selected Metabolic Inhibitors on C. parvum Infection under Physioxia and Hyperoxia

Cryptosporidium parvum is an apicomplexan zoonotic parasite recognized as the second leading-cause of diarrhoea-induced mortality in children. In contrast to other apicomplexans, C. parvum has minimalistic metabolic capacities which are almost exclusively based on glycolysis. Consequently, C. parvum is highly dependent on its host cell metabolism. In vivo (within the intestine) infected epithelial host cells are typically exposed to low oxygen pressure (1-11% O₂, termed physioxia). Here, we comparatively analyzed the metabolic signatures of C. parvum-infected HCT-8 cells cultured under both, hyperoxia (21% O₂), representing the standard oxygen condition used in most experimental settings, and physioxia (5% O₂), to be closer to the in vivo situation. The most pronounced effect of C. parvum infection on host cell metabolism was, on one side, an increase in glucose and glutamine uptake, and on the other side, an increase in lactate release. When cultured in a glutamine-deficient medium, C. parvum infection led to a massive increase in glucose consumption and lactate production. Together, these results point to the important role of both glycolysis and glutaminolysis during C. parvum intracellular replication. Referring to obtained metabolic signatures, we targeted glycolysis as well as glutaminolysis in C. parvum-infected host cells by using the inhibitors lonidamine [inhibitor of hexokinase, mitochondrial carrier protein (MCP) and monocarboxylate transporters (MCT) 1, 2, 4], galloflavin (lactate dehydrogenase inhibitor), syrosingopine (MCT1- and MCT4 inhibitor) and compound 968 (glutaminase inhibitor) under hyperoxic and physioxic conditions. In line with metabolic signatures, all inhibitors significantly reduced parasite replication under both oxygen conditions, thereby proving both energy-related metabolic pathways, glycolysis and glutaminolysis, but also lactate export mechanisms via MCTs as pivotal for C. parvum under in vivo physioxic conditions of mammals.

Mesenchymal stem cells promote pancreatic β-cell regeneration through downregulation of FoxO1 pathway

Background

Mesenchymal stem cells (MSC) are non-haematopoietic, fibroblast-like multipotent stromal cells. In the injured pancreas, these cells are assumed to secrete growth factors and immunomodulatory molecules, which facilitate the regeneration of pre-existing β-cells. However, when MSC are delivered intravenously, their majority is entrapped in the lungs and does not reach the pancreas. Therefore, the aim of this investigation was to compare the regenerative support of hTERT-MSC (human telomerase reverse transcriptase mesenchymal stem cells) via intrapancreatic (IPR) and intravenous route (IVR).

Methods

hTERT-MSC were administered by IPR and IVR to 50% pancreatectomized NMRI nude mice. After eight days, blood glucose level, body weight, and residual pancreatic weight were measured. Proliferating pancreatic β-cells were labelled and identified with bromodeoxyuridine (BrdU) in vivo. The number of residual islets and the frequency of proliferating β-cells were compared in different groups with sequential pancreatic sections. The pancreatic insulin content was evaluated by enzyme-linked immunosorbent assay (ELISA) and the presence of hTERT-MSC with human Alu sequence. Murine gene expression of growth factors, β-cell specific molecules and proinflammatory cytokines were inspected by real-time polymerase chain reaction (RT-PCR) and Western blot.

Results

This study evaluated the regenerative potential of the murine pancreas post-hTERT-MSC administration through the intrapancreatic (IPR) and intravenous route (IVR). Both routes of hTERT-MSC transplantation (IVR and IPR) increased the incorporation of BrdU by pancreatic β-cells compared to control. MSC induced epidermal growth factor (EGF) expression and inhibited proinflammatory cytokines (IFN-γ and TNF-α). FOXA2 and PDX-1 characteristics for pancreatic progenitor cells were activated via AKT/ PDX-1/ FoxO1 signalling pathway.

Conclusion

The infusion of hTERT-MSC after partial pancreatectomy (Px) through the IVR and IPR facilitated the proliferation of autochthonous pancreatic β-cells and provided evidence for a regenerative influence of MSC on the endocrine pancreas. Moderate benefit of IPR over IVR was observed which could be a new treatment option for preventing diabetes mellitus after pancreas surgery.

Supplementary information

The online version contains supplementary material available at at 10.1186/s13287-020-02007-9.

Therapeutic targeting of glutaminolysis as an essential strategy to combat cancer

Metabolic reprogramming in cancer targets glutamine metabolism as a key mechanism to provide energy, biosynthetic precursors and redox requirements to allow the massive proliferation of tumor cells. Glutamine is also a signaling molecule involved in essential pathways regulated by oncogenes and tumor suppressor factors. Glutaminase isoenzymes are critical proteins to control glutaminolysis, a key metabolic pathway for cell proliferation and survival that directs neoplasms' fate. Adaptive glutamine metabolism can be altered by different metabolic therapies, including the use of specific allosteric inhibitors of glutaminase that can evoke synergistic effects for the therapy of cancer patients. We also review other clinical applications of in vivo assessment of glutaminolysis by metabolomic approaches, including diagnosis and monitoring of cancer.

Posttranslational Modifications of Pyruvate Kinase M2: Tweaks that Benefit Cancer

Cancer cells rewire metabolism to meet biosynthetic and energetic demands. The characteristic increase in glycolysis, i.e., Warburg effect, now considered as a hallmark, supports cancer in various ways. To attain such metabolic reshuffle, cancer cells preferentially re-express the M2 isoform of pyruvate kinase (PKM2, M2-PK) and alter its quaternary structure to generate less-active PKM2 dimers. The relatively inactive dimers cause the accumulation of glycolytic intermediates that are redirected into anabolic pathways. In addition, dimeric PKM2 also benefits cancer cells through various non-glycolytic moonlight functions, such as gene transcription, protein kinase activity, and redox balance. A large body of data have shown that several distinct posttranslation modifications (PTMs) regulate PKM2 in a way that benefits cancer growth, e.g., formation of PKM2 dimers. This review discusses the recent advancements in our understanding of various PTMs and the benefits they impart to the sustenance of cancer. Understanding the PTMs in PKM2 is crucial to assess their therapeutic potential and to design novel anticancer strategies.

Impact of biopersistent fibrous dusts on glycolysis, glutaminolysis and serine metabolism in A549 cells

The conversion rates of different metabolic pathways summarized as a metabolic signature mirror the physiological functions and the general physiological status of a cell. The present study compared the impact of crocidolite and chrysotile asbestos, glass fibers and multi‑walled carbon nanotubes (MWCN) of two different lengths (1‑2 µm and 5‑15 µm) on the conversion rates in glycolysis, glutaminolysis and serine metabolism of A549 cells. The concentration tested was 1 µg/cm2 for all fibers. A concentration of 5 µg/cm2 was additionally used for chrysotile and crocidolite, and 25 µg/cm2 for glass fibers and MWCN. With respect to the inhibitory effect on cell proliferation and the extent of metabolic alterations, the present study revealed the following ranking among the fibers tested: Chrysotile>crocidolite>glass fibers>MWCN 5‑15 µm>MWCN 1‑2 µm. For the asbestos and glass fibers this ranking correlated best with the number of fibers. It appeared that the results observed for MWCN did not match this correlation. However, electron microscopy revealed an agglomeration of MWCN. The agglomeration decreased the toxicologically relevant number of fibers by forming larger particle‑like shapes and explained the smaller effects of MWCN 5‑15 µm and 1‑2 µm on cell proliferation and metabolism.

Osteogenic differentiation capacity of human mesenchymal stromal cells in response to extracellular calcium with special regard to connexin 43

The effects of extracellular calcium on osteogenic differentiation capacity of human bone-derived mesenchymal stromal cells with special regard to connexin 43 (cx43) have been investigated by means of cell culture experiments. Mesenchymal stromal cells isolated from human cancellous bone were cultured on tissue culture plates at different calcium ion (Ca²⁺) concentrations (1.8mmoll^-1, 10mmoll^-1, 20mmoll^-1). Cell responses were evaluated by quantitative RT-PCR, immunofluorescence staining, and Lucifer Yellow fluorescence uptake experiments. It could be shown that increasing Ca²⁺ concentrations correlate with increasing cx43 and bone sialoprotein mRNA levels as well as with enhanced cx43 fluorescence signaling and matrix mineralization of the cultures as shown by von Kossa staining. Hemichannel gating - assessed by Lucifer Yellow uptake - increases with increasing extracellular Ca²⁺ concentrations suggesting that regulatory effects at the hemichannel level are calcium-dependent.

Pyruvate kinase M2: regulatory circuits and potential for therapeutic intervention

Cancer cells are characterized by reprogramming of energy metabolism. Over the last decade, understanding of the metabolic changes that occur in cancer has increased dramatically, with great interest in targeting metabolism for cancer therapy. Pyruvate kinase isoenzyme type M2 (abbreviations: PKM2, M2-PK) plays a key role in modulating glucose metabolism to support cell proliferation. PKM2, like other PK isoforms, catalyzes the last energy-generating step in glycolysis, but is unique in its capacity to be regulated. PKM2 is regulated at several cellular levels, including gene expression, alternative splicing and post-translational modification. In addition, PKM2 is regulated by key metabolic intermediates and interacts with more than twenty different proteins. Hence, this isoenzyme is an important regulator of glycolysis, and additionally functions in other novel roles that have recently emerged. Recent evidence indicates that intervening with the complex regulatory network of PKM2 has severe consequences on tumor cell proliferation, indicating the potential of this enzyme as a target for tumor therapy.

Pyruvate kinase M2 and cancer: an updated assessment

Cancer cells are characterized by high glycolytic rates to support energy regeneration and anabolic metabolism, along with the expression of pyruvate kinase isoenzyme M2 (PKM2). The latter catalyzes the last step of glycolysis and reprograms the glycolytic flux to feed the special metabolic demands of proliferating cells. Besides, PKM2 has moonlight functions, such as gene transcription, favoring cancer. Accumulating evidence suggests a critical role played by the low-activity-dimeric PKM2 in tumor progression, supported by the identification of mutations which result in the down-regulation of its activity and tumorigenesis in a nude mouse model. This review discusses PKM2 regulation and the benefits it confers to cancer cells. Further, conflicting views on PKM2's role in cancer, its therapeutic relevance and future directions in the field are also discussed.

Pyruvate kinase M2 is a novel diagnostic marker and predicts tumor progression in human biliary tract cancer

BACKGROUND

The early diagnosis of biliary tract cancer (BTC) remains challenging, and there are few effective therapies. This study investigated whether the M2 isotype of pyruvate kinase (M2-PK), which serves as the key regulator of cellular energy metabolism in proliferating cells, could play a role in the diagnosis and therapy of BTC.

METHODS

Plasma and bile M2-PK concentrations were measured by enzyme-linked immunosorbent assay in 88 patients with BTC, 79 with benign biliary diseases, and 17 healthy controls. M2-PK expression was assayed in a BTC tissue array by immunohistochemistry. The role of M2-PK in tumor growth, invasion, and angiogenesis was evaluated in BTC cell lines by retrovirus-mediated M2-PK transfection and short hairpin RNA silencing techniques.

RESULTS

Sensitivity (90.3%) and specificity (84.3%) of bile M2-PK for malignancy were significantly higher than those for plasma M2-PK and serum carbohydrate antigen 19-9. M2-PK expression was specific for cancer cells and correlated with microvessel density. M2-PK positivity was a significant independent prognostic factor by multivariable analysis. Transfection of M2-PK in a negatively expressed cell line (HuCCT-1 cells) increased cell invasion, whereas silencing in an M2-PK-positive cell line (TFK cells) decreased tumor nodule formation and cellular invasion. A significant increase in endothelial tube formation was noted when supernatants from M2-PK-transfected cells were added to an in vitro angiogenesis assay, whereas supernatants from silenced cells negated endothelial tube formation.

CONCLUSIONS

Bile M2-PK is a novel tumor marker for BTC and correlates with tumor aggressiveness and poor outcome. Short hairpin RNA-mediated inhibition of M2-PK indicates the potential of M2-PK as a therapeutic target.

In vivo factors influencing tumour M2-pyruvate kinase level in human pancreatic cancer cell lines

In tumour cells, the tetramer/dimer ratio of the pyruvate kinase isoenzyme type M2 (M2-PK) determines whether glucose carbons are degraded to lactate with production of energy (tetrameric form) or are channelled into synthetic processes (dimeric form). The influence of different tumour microenvironment conditions on the tetramer/dimer ratio of M2-PK and cell doublings were investigated in a non-metastatic and metastatic pancreatic cancer cell line. The metastatic Colo357 cells contained about fourfold more M2-PK protein and about 3.5-fold more dimeric M2-PK than the non-metastatic Panc-1 cells. In Colo357 cells hypoxia, glucose starvation as well as acidification induced an increase of the dimeric form of M2-PK, whereas in Panc-1 cells no effect on M2-PK was observed. Under hypoxia in Colo357 cells, the dimerization and inactivation of M2-PK results in an inhibition of cell proliferation, whereas under glucose starvation and acidification the dimerization of M2-PK allowed further cell doublings. M2-PK expression and the quaternary structure of M2-PK are influenced by the tumour metastatic potential. The quaternary structure of M2-PK may be differently affected by hypoxia, glucose starvation and acidification with severe consequences on cell doublings.

Pyruvate kinase isoenzyme M2 is a glycolytic sensor differentially regulating cell proliferation, cell size and apoptotic cell death dependent on glucose supply

The glycolytic key regulator pyruvate kinase M2 (M2-PK or PKM2) can switch between a highly active tetrameric and an inactive dimeric form. The transition between the two conformations regulates the glycolytic flux in tumor cells. We developed specific M2-PK-binding peptide aptamers which inhibit M2-PK, but not the 96% homologous M1-PK isoenzyme. In this study we demonstrate that, at normal blood glucose concentrations, peptide aptamer-mediated inhibition of M2-PK induces a significant decrease of the population doubling (PDL rate) and cell proliferation rate as well as an increase in cell size, whereas under glucose restriction an increase in PDL and cell proliferation rates but a decrease in cell size was observed. Moreover, M2-PK inhibition rescues cells from glucose starvation-induced apoptotic cell death by increasing the metabolic activity. These findings suggest that M2-PK is a metabolic sensor which regulates cell proliferation, cell growth and apoptotic cell death in a glucose supply-dependent manner.

Isotype-specific inhibitors of the glycolytic key regulator pyruvate kinase subtype M2 moderately decelerate tumor cell proliferation

Tumor cells express the glycolytic regulator pyruvate kinase subtype M2 (M2-PK), which can occur in a tetrameric form with high affinity to its substrate phosphoenolpyruvate (PEP) and a dimeric form with a low PEP affinity. The transition between both conformations contributes to the control of glycolysis and is important for tumor cell proliferation and survival. Here we targeted M2-PK by synthetic peptide aptamers, which specifically bind to M2-PK and shift the isoenzyme into its low affinity dimeric conformation. The aptamer-induced dimerization and inactivation of M2-PK led to a significant decrease in the PK mass-action ratio as well as ATP:ADP ratio in the target cells. Furthermore, the expression of M2-PK-binding peptide aptamers moderately reduced the growth of immortalized NIH3T3 cell populations by decelerating cell proliferation, but without affecting apoptotic cell death. Moreover, the M2-PK-binding peptide aptamers also reduced the proliferation rate of human U-2 OS osteosarcoma cells. In the present study, we developed the first specific inhibitors of the pyruvate kinase isoenzyme type M2 and present evidence that these inhibitors moderately decelerate tumor cell proliferation.

Regulation of pyruvate kinase type M2 by A-Raf: a possible glycolytic stop or go mechanism

Recently a link between A-Raf cellular energy homeostasis and synthetic pathways has been suggested through the identification of pyruvate kinase type M2 (M2-PK), a key glycolytic enzyme, as interaction partner of A-Raf In this study, we demonstrated that A-Raf is an important regulator of M2-PK function. In primary mouse fibroblasts, which are characterized by glutamine production and serine degradation, A-Raf induced dimerization and inactivation of M2-PK, thereby reducing conversion rates from glucose to lactate. In immortalized NIH3T3 fibroblasts, showing glutamine degradation and serine production, oncogenic A-Raf increased the highly active tetrameric form of M2-PK and favored glycolytic energy production. High serine levels thus may be responsible for the activation of M2-PK in A-Raf transformed NIH3T3 cells.

Interference with energy metabolism by 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside induces HPV suppression in cervical carcinoma cells and apoptosis in the absence of LKB1

Carcinogenesis is a dynamic and stepwise process, which is accompanied by a variety of somatic and epigenetic alterations in response to a changing microenvironment. Hypoxic conditions will select for cells that have adjusted their metabolic profile and can maintain proliferation by successfully competing for scarce nutritional and oxygen resources. In the present study we have investigated the effects of energy depletion in the context of HPV (human papillomavirus)-induced pathogenesis. We show that cervical carcinoma cell lines are susceptible to undergoing either growth arrest or cell death under conditions of metabolic stress induced by AICAR (5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside), a known activator of the AMPK (AMP-activated protein kinase). Our results reveal that AICAR treatment leads to a reduced binding affinity of the transcription factor AP-1 (activator protein-1) and in turn to a selective suppression of HPV transcription. Moreover, the outcome of AICAR on proliferation and survival was dependent on p53 activation and the presence of LKB1, the major upstream kinase of AMPK. Using non-malignant LKB1-expressing somatic cell hybrids, which lose expression after tumorigenic segregation, as well as small interfering RNA LKB1 knockdown approaches, we could further demonstrate that expression of LKB1 protects cells from cytotoxicity induced by agents which modulate the ATP/AMP ratio. Since simulation of low energy status can selectively eradicate LKB1-negative cervical carcinoma cells, AICAR may represent a novel drug in the treatment of cervical cancer.

Pyruvate kinase type M2 and its role in tumor growth and spreading

Proliferating cells and tumor cells in particular express the pyruvate kinase isoenzyme type M2 (M2-PK). Within the tumor metabolome M2-PK regulates the proportions of glucose carbons that are channelled to synthetic processes (inactive dimeric form) or used for glycolytic energy production (highly active tetrameric form, a component of the glycolytic enzyme complex). In tumor cells, the dimeric form of M2-PK (Tumor M2-PK) is always predominant. The dimerization is caused by direct interaction of M2-PK with certain oncoproteins. The switch between the tetrameric and dimeric form of M2-PK allows tumor cells to survive in environments with varying oxygen und nutrient supply.

Faecal tumour M2 pyruvate kinase: a new, sensitive screening tool for colorectal cancer

Proliferating cells, especially tumour cells, express a special isoenzyme of pyruvate kinase, termed M2-PK, which can occur in a tetrameric form with a high affinity to its substrate, phosphoenolpyruvate (PEP), and in a dimeric form with a low PEP affinity. In tumour cells, the dimeric form is usually predominant and is therefore termed Tumour M2-PK. The levels of Tumour M2-PK within tumours and in EDTA-plasma correlate with staging and the ability of the tumour cells to metastasise. Since most colorectal tumours grow intraluminally, it appeared interesting to determine whether Tumour M2-PK is detectable in the faeces of tumour patients. Stool samples were tested by ELISA from controls without colorectal cancer and colorectal cancer patients. Whereas Tumour M2-PK levels were low in the control group (mean value+/-s.e.m.: 3.3+/-0.4, n=144), they were high in the case of colorectal cancer (56.1+/-15.3, n=60). At a cutoff value of 4 U ml(-1), the sensitivity was 73%. TNM and Dukes' classification of the tumours revealed a strong correlation between faecal Tumour M2-PK levels and staging. The determination of Tumour M2-PK in faeces provides a new promising screening tool for colorectal tumours.

Phosphoglycerate Mutase-derived Polypeptide Inhibits Glycolytic Flux and Induces Cell Growth Arrest in Tumor Cell Lines

The putative tumor metastasis suppressor protein Nm23-H1 is a nucleoside diphosphate kinase that exhibits a novel protein kinase activity when bound to glyceraldehyde-3-phosphate dehydrogenase (GAPDH). In this study we show that the glycolytic enzyme phosphoglycerate mutase B (PGM) becomes phosphorylated in the presence of the Nm23-H1.GAPDH complex in vitro. Mutation of His-10 in PGM abolishes the Nm23-H1.GAPDH complex-induced phosphorylation. Nm23-H1, GAPDH, and PGM are known to co-localize as shown by free flow isoelectric focusing. In association with Nm23-H1 and GAPDH, PGM could be activated by dCTP, which is a substrate of Nm23-H1, in addition to the well known PGM activator 2,3-bisphosphoglycerate. A synthetic cell-penetrating peptide (PGMtide) encompassing the phosphorylated histidine and several residues from PGM (LIRHGE) promoted growth arrest of several tumor cell lines, whereas proliferation of tested non-tumor cells was not influenced. Analysis of metabolic activity of one of the tumor cell lines, MCF-7, indicated that PGMtide inhibited glycolytic flux, consistent with in vivo inhibition of PGM. The specificity of the observed effect was further determined experimentally by testing the effect of PGMtide on cells growing in the presence of pyruvate, which helps to compensate PGM inhibition in the glycolytic pathway. Thus, growth of MCF-7 cells was not arrested by PGMtide in the presence of pyruvate. The data presented here provide evidence that inhibition of PGM activity can be achieved by exogenous addition of a polypeptide, resulting in inhibition of glycolysis and cell growth arrest in cell culture.

Metabolic analysis of senescent human fibroblasts reveals a role for AMP in cellular senescence

Cellular senescence is considered a major tumour-suppressor mechanism in mammals, and many oncogenic insults, such as the activation of the ras proto-oncogene, trigger initiation of the senescence programme. Although it was shown that activation of the senescence programme involves the up-regulation of cell-cycle regulators such as the inhibitors of cyclin-dependent kinases p16INK4A and p21CIP-1, the mechanisms underlying the senescence response remain to be resolved. In the case of stress-induced premature senescence, reactive oxygen species are considered important intermediates contributing to the phenotype. Moreover, distinct alterations of the cellular carbohydrate metabolism are known to contribute to oncogenic transformation, as is best documented for the phenomenon of aerobic glycolysis. These findings suggest that metabolic alterations are involved in tumourigenesis and tumour suppression; however, little is known about the metabolic pathways that contribute to these processes. Using the human fibroblast model of in vitro senescence, we analysed age-dependent changes in the cellular carbohydrate metabolism. Here we show that senescent fibroblasts enter into a metabolic imbalance, associated with a strong reduction in the levels of ribonucleotide triphosphates, including ATP, which are required for nucleotide biosynthesis and hence proliferation. ATP depletion in senescent fibroblasts is due to dysregulation of glycolytic enzymes, and finally leads to a drastic increase in cellular AMP, which is shown here to induce premature senescence. These results suggest that metabolic regulation plays an important role during cellular senescence and hence tumour suppression.

Interaction between HERC1 and M2-type pyruvate kinase

HERC proteins are characterized by having one or more RCC1-like domains as well as a C-terminal HECT domain in their amino acid sequences. This has led researchers to suggest that they may act as both guanine nucleotide exchange factors and E3 ubiquitin ligases. Here we describe a physical interaction between the HECT domain of HERC1, a giant protein involved in intracellular membrane traffic, and the M2 isoform of glycolytic enzyme pyruvate kinase (M2-PK). Partial colocalization of endogenous proteins was observed by immunofluorescence studies. This interaction neither induced M2-PK ubiquitination nor affected its enzymatic activity. The putative significance of the association is discussed.

Plasma levels of HER-2/neu, tumor type M2 pyruvate kinase and its tyrosine-phosphorylated metabolite in advanced breast cancer

INTRODUCTION

Tyrosine kinase signal transduction pathways are a focus of interest for therapeutic interventions. The oncoprotein HER-2/neu shows tyrosine kinase activity leading to phosphorylation and activation of numerous second-messenger systems. One target of phosphorylation processes is assumed to be the tumor type M2 isoenzyme of pyruvate kinase (TuM2-PK) which has been shown to be elevated in metastatic breast cancer.

MATERIALS AND METHODS

We measured the plasma levels of HER-2/neu, TuM2-PK and tyrosine-phosphorylated TuM2-PK (p-TuM2-PK) in 69 patients (pts) with breast cancer and correlated these parameters to each other and to the classical tumor marker CA 27.29. The samples were measured with ELISA assays while CA 27.29 was determined with an automated chemiluminescence assay. For analysis, we formed 5 subgroups according to the plasma HER-2/neu levels (group 1: < 15 ng/ml, n = 28; group 2: 15 < or = x < 50 ng/ml, n = 21; group 3: 50 < or = x < 100 ng/ml, n = 9; group 4: 100 < or = x < 500 ng/ml, n = 7; group 5: > or = 500 ng/ml, n = 4).

RESULTS

From the HER-2/neu group 1 to group 5, there was a statistically significant increase of CA 27.29 from 35.8 U/ml to 1095.8 U/ml (p < 0.001). There was also a trend for increasing TuM2-PK levels with increasing HER-2/neu levels (p = 0.126). From the lowest extinction (0.088) to the highest extinction result (2.167) of p-TuM2-PK we found a 25-fold increase, which was reproducible in spiking and dilution experiments proving that TuM2-PK is phosphorylated at tyrosine residues to a certain extent. However, there was no correlation between plasma HER-2/neu and p-TuM2-PK levels.

CONCLUSION

TuM2-PK is phosphorylated at tyrosine residues in breast cancer patients. Using the shed antigen of HER-2/neu in plasma as a surrogate marker, we did not find any evidence that this phosphorylation is initiated by the oncoprotein HER-2/neu.

The tumor metabolome

The tumor metabolome is characterized by high glycolytic and glutaminolytic capacities, high phosphometabolite levels and a high channelling of glucose carbons to synthetic processes. This allows tumor cells to proliferate under strong variations in oxygen and glucose supply (http://www.metabolic-database.com). One key regulator of the tumor metabolome is the glycolytic isoenzyme pyruvate kinase type M2 (M2-PK) that is generally over-expressed in all tumor cells. M2-PK can occur in a highly active tetrameric form and in a nearly inactive dimeric form. In tumor cells the dimeric form of M2-PK always predominates and has therefore been termed tumor M2-PK. The dimerization of M2-PK is caused by direct interaction of M2-PK with certain oncoproteins. When M2-PK is in its dimeric state energy is produced by glutaminolysis. The metabolic Achilles' heel of the tumor metabolome is its sensitivity to a reduction of NAD levels caused by activation of poly(ADP-ribose) polymerase after DNA damage.

Pyruvate kinase type M2: a crossroad in the tumor metabolome

Cell proliferation is a process that consumes large amounts of energy. A reduction in the nutrient supply can lead to cell death by ATP depletion, if cell proliferation is not limited. A key sensor for this regulation is the glycolytic enzyme pyruvate kinase, which determines whether glucose carbons are channelled to synthetic processes or used for glycolytic energy production. In unicellular organisms pyruvate kinase is regulated by ATP, ADP and AMP, by ribose 5-P, the precursor of the nucleic acid synthesis, and by the glycolytic intermediate fructose 1,6-P2 (FBP), thereby adapting cell proliferation to nutrient supply. The mammalian pyruvate kinase isoenzyme type M2 (M2-PK) displays the same kinetic properties as the pyruvate kinase enzyme from unicellular organisms. The mammalian M2-PK isoenzyme can switch between a less active dimeric form and a highly active tetrameric form which regulates the channeling of glucose carbons either to synthetic processes (dimeric form) or to glycolytic energy production (tetrameric form). Tumor cells are usually characterized by a high amount of the dimeric form leading to a strong accumulation of all glycolytic phosphometabolites above pyruvate kinase. The tetramer-dimer ratio is regulated by ATP, FBP and serine and by direct interactions with different oncoproteins (pp60v-src, HPV-16 E7). In solid tumors with sufficient oxygen supply pyruvate is supplied by glutaminolysis. Pyruvate produced in glycolysis and glutaminolysis is used for the synthesis of lactate, glutamate and fatty acids thereby releasing the hydrogen produced in the glycolytic glyceraldehyde 3-phosphate dehydrogenase reaction.

Pyruvate kinase type M2: a crossroad in the tumor metabolome

Cell proliferation is a process that consumes large amounts of energy. A reduction in the nutrient supply can lead to cell death by ATP depletion, if cell proliferation is not limited. A key sensor for this regulation is the glycolytic enzyme pyruvate kinase, which determines whether glucose carbons are channelled to synthetic processes or used for glycolytic energy production. In unicellular organisms pyruvate kinase is regulated by ATP, ADP and AMP, by ribose 5-P, the precursor of the nucleic acid synthesis, and by the glycolytic intermediate fructose 1,6-P2 (FBP), thereby adapting cell proliferation to nutrient supply. The mammalian pyruvate kinase isoenzyme type M2 (M2-PK) displays the same kinetic properties as the pyruvate kinase enzyme from unicellular organisms. The mammalian M2-PK isoenzyme can switch between a less active dimeric form and a highly active tetrameric form which regulates the channeling of glucose carbons either to synthetic processes (dimeric form) or to glycolytic energy production (tetrameric form). Tumor cells are usually characterized by a high amount of the dimeric form leading to a strong accumulation of all glycolytic phosphometabolites above pyruvate kinase. The tetramer-dimer ratio is regulated by ATP, FBP and serine and by direct interactions with different oncoproteins (pp60v-src, HPV-16 E7). In solid tumors with sufficient oxygen supply pyruvate is supplied by glutaminolysis. Pyruvate produced in glycolysis and glutaminolysis is used for the synthesis of lactate, glutamate and fatty acids thereby releasing the hydrogen produced in the glycolytic glyceraldehyde 3-phosphate dehydrogenase reaction.

Metabolic cooperation between different oncogenes during cell transformation: interaction between activated ras and HPV-16 E7

The metabolism of tumor cells (tumor metabolome) is characterized by a high concentration of glycolytic enzymes including pyruvate kinase isoenzyme type M2 (M2-PK), a high glutaminolytic capacity, high fructose 1,6-bisphosphate (FBP) levels and a low (ATP+GTP):(CTP+UTP) ratio. The sequence of events required for the establishment of the tumor metabolome is presently unknown. In non-transformed rat kidney (NRK) cells we observed a high glutaminolytic flux rate and a low (ATP+GTP):(CTP+UTP) ratio, whereas FBP levels and M2-PK activity are still extremely low. After stable expression of oncogenic ras in NRK cells a strong upregulation of FBP levels and of M2-PK activity was observed. Elevated FBP levels induce a tetramerization of M2-PK and its migration into the glycolytic enzyme complex. AMP levels increase whereas UTP and CTP levels strongly decrease. Thus, ras expression completes the glycolytic part of tumor metabolism leading to the inhibition of nucleic acid synthesis and cell proliferation. The HPV-16 E7 oncoprotein, which cooperates with ras in cell transformation, directly binds to M2-PK, induces its dimerization and restores nucleic acid synthesis as well as cell proliferation. Apparently, the combination of the different metabolic effects of ras and E7 constructs the perfect tumor metabolome as generally found in tumor cells.

Effects of the human papilloma virus HPV-16 E7 oncoprotein on glycolysis and glutaminolysis: role of pyruvate kinase type M2 and the glycolytic-enzyme complex

Proliferating and tumour cells express the glycolytic isoenzyme, pyruvate kinase type M2 (M2-PK), which occurs in a highly active tetrameric form and in a dimeric form with low affinity for phosphoenolpyruvate. The switch between the two forms regulates glycolytic phosphometabolite pools and the interaction between glycolysis and glutaminolysis. In the present study, we show the effects of oncoprotein E7 of the human papilloma virus (HPV)-16 (E7)-transformation on two NIH 3T3 cell strains with different metabolic characteristics. E7-transformation of the high glycolytic NIH 3T3 cell strain led to a shift of M2-PK to the dimeric form and, in consequence, to a decrease in the cellular pyruvate kinase mass-action ratio, the glycolytic flux rate and the (ATP+GTP)/(UTP+CTP) ratio, as well as to an increase in fructose 1,6-bisphosphate (FBP) levels, glutamine consumption and cell proliferation. The low glycolytic NIH 3T3 cell strain is characterized by high pyruvate and glutamine consumption rates and by an intrinsically large amount of the dimeric form of M2-PK, which is correlated with high FBP levels, a low (ATP+GTP)/(CTP+UTP) ratio and a high proliferation rate. E7-transformation of this cell strain led to an alteration in the glycolytic-enzyme complex that correlates with an increase in pyruvate and glutamine consumption and a slight increase in the flow of glucose to lactate. The association of phosphoglyceromutase within the glycolytic-enzyme complex led to an increase of glucose and serine consumption and a disruption of the linkage between glucose consumption and glutaminolysis. In both NIH 3T3 cell lines, transformation increased glutaminolysis and the positive correlation between alanine and lactate production.

Tumor M2-PK and glutaminolytic enzymes in the metabolic shift of tumor cells

The pyruvate kinase isoenzyme M2-PK is known to be associated with a metabolic shift that is characteristic for tumor cells. Meanwhile, the universal expression of this isoenzyme is the basis for the detection of various tumor diseases in human clinical diagnosis. Other enzymes which are known to be essential for this tumor specific metabolic shift in rat chemical carcinogenesis are the NADP-dependent enzymes malic enzyme, isocitrate dehydrogenase and glucose 6-phosphate dehydrogenase. To evaluate the role of these enzymes in human carcinogenesis, we compared their enzymatic activities in normal colon mucosa and tissues derived from primary colon tumors. Histochemical staining showed that the enzyme activities were restricted to mucosal colon cells and colon cancer cells. The enzymes were strongly but heterogeneously expressed in the tumor tissues, whereas staining of normal mucosa was weak. Tumor M2-PK showed the most prominent differences in normal colon mucosa and colon cancer cells.

Energy metabolism in the involuting mammary gland

A strong and coordinated upregulation of the glycolytic, glutaminolytic and pentose phosphate pathway enzymes occurs during the onset of lactation in the normal mouse mammary gland. Induction of apoptosis by removing the pups led to an inactivation of the same enzymes with different time courses. While the ATP-consuming glycolytic 6-phosphofructo 1-kinase and mitochondrial bound hexokinase still remained high on days one and two of involution, the ATP-regenerating pyruvate kinase was immediately reduced. The enzymes of the pentose phosphate and glutaminolytic pathway were inactivated on the first two days of involution. In accordance with such an inactivation of the enzymes ATP, GTP, UTP, ADP, NAD NADH and lactate concentrations decreased. The synthetic product of UTP, UDP-N-acetylglucosamine, increased. AMP was found in the milk, not in the epithelial cells. The inactivation of the enzymes was caused by partial proteolysis or by a loss of the intact proteins from the cytosol without signs of proteolysis.

Alterations in the glycolytic and glutaminolytic pathways after malignant transformation of rat liver oval cells

Oval cells are liver epithelial cells that proliferate during the early stages of hepatocarcinogenesis induced by a variety of chemicals. The oval cell lines OC/CDE 6 and OC/CDE 22 have been established in our laboratory at two time points (6 and 22 weeks) of the carcinogenic process and have been malignantly transformed by different procedures. During the transformation process, the glycolytic and glutaminolytic flux rates were consistently up-regulated and this process was accompanied by an overproportional increase in the activities of cytosolic hexokinase and 6-phosphogluconate dehydrogenase. In transformed oval cells, a strong correlation between the glycolytic flux rate and glutamine consumption as well as glutamate production was observed. Furthermore, the transport of glycolytic hydrogen, produced by the glyceraldehyde 3-phosphate dehydrogenase-catalyzed reaction, from the cytosol into the mitochondria by means of the malate-aspartate shuttle was enhanced, this being due to alterations in the activities of malate dehydrogenase and glutamate oxaloacetate transaminase. The up-regulation of the glycolytic hydrogen transport and the alterations in the glycolytic enzyme complex led to an enhanced pyruvate production at high glycolytic flux rates. Taken together, our data are further proof that a special metabolic feature (increased glycolysis and glutaminolysis) is characteristic for tumor cells and that the mechanisms by which this metabolic state is induced can be totally different.

Modulation of type M2 pyruvate kinase activity by the human papillomavirus type 16 E7 oncoprotein

We report here that the E7 oncoprotein encoded by the oncogenic human papillomavirus (HPV) type 16 binds to the glycolytic enzyme type M2 pyruvate kinase (M2-PK). M2-PK occurs in a tetrameric form with a high affinity to its substrate phosphoenolpyruvate and a dimeric form with a low affinity to phosphoenolpyruvate, and the transition between both conformations regulates the glycolytic flux in tumor cells. The glycolytic intermediate fructose 1, 6-bisphosphate induces the reassociation of the dimeric to the tetrameric form of M2-PK. The expression of E7 in an experimental cell line shifts the equilibrium to the dimeric state despite a significant increase in the fructose 1,6-bisphosphate levels. Investigations of HPV-16 E7 mutants and the nononcogenic HPV-11 subtype suggest that the interaction of HPV-16 E7 with M2-PK may be linked to the transforming potential of the viral oncoprotein.

Pyruvate kinase and the interaction of amino acid and carbohydrate metabolism in solid tumors

The interaction between glycolysis, glutaminolysis and tumor growth in WAG/Fra rnu/rnu rats has been investigated. Small tumors are characterized by a low conversion of glucose to lactate whereas the conversion of glutamine to lactate is high. In medium sized tumors the flow of glucose to lactate as well as oxygen utilization are increased whereas glutamine and serine consumption are reduced. At this stage the tumor cells start with glutamate and alanine production. Large tumors are characterized by a low oxygen and glucose supply but a high glucose and oxygen utilization rate. The conversion of glucose to glycine, alanine, glutamate, glutamine, and proline reaches high values and the amino acids are released. Pyruvate kinase increases with tumor weight and is positively correlated with an increase in glucose and oxygen utilization. The shift from glutamate consumption to glutamate production is correlated with an increase in glutamate dehydrogenase and glutamate oxaloacetate transaminase activity.

Metabolic characteristics of different malignant cancer cell lines

Extracellular AMP inhibits cell proliferation of MCF-7 and MDA-MB-453 whereas cell proliferation of the highly malignant Novikoff cell line is not affected. In medium with low glucose supply MDA-MB-453 cells grow well, Novikoff cells are slightly inhibited and MCF-7 cells are totally unable to grow. Isoelectric focusing revealed that a glyclytic enzyme complex exists in all three cell lines. In addition to the glycolytic enzymes, c-Raf-kinase, adenylate kinase, and nucleoside diphosphate kinase are also found within the complex. The differences in glucose in dependence of the three cell lines can be explained by the different constitutions of shuttle enzymes. MDA-MB-453 and Novikoff cells contain cytsolic glycerol 3-phosphate dehydrogenase which is associated with glyceraldehyde 3-phosphate dehydrogenase within the glycolytic enzyme complex and which is responsible for the transport of cytoslic hydrogen in the mitochondria. MCF-7 and Novikoff cells contain the pI 7.8 form of malate dehydrogenase which couples glycolysis with glutaminolysis.

The role of phosphometabolites in cell proliferation, energy metabolism, and tumor therapy

A common characteristic of tumor cells is the constant overexpression of glycolytic and glutaminolytic enzymes. In tumor cells the hyperactive hexokinase and the partly inactive pyruvate kinase lead to an expansion of all phosphometabolites from glucose 6-phosphate to phosphoenolpyruvate. In addition to the glycolytic phosphometabolites, synthesis of their metabolic derivatives such as P-ribose-PP, NADH, NADPH, UTP, CTP, and UDP-N-acetyl glucosamine is also enhanced during cell proliferation. Another phosphometabolite derived from P-ribose-PP, AMP, inhibits cell proliferation. The accumulation of AMP inhibits both P-ribose-PP-synthetase and the increase in concentration of phosphometabolites derived from P-ribose-PP. In cells with low glycerol 3-phosphate and malate-aspartate shuttle capacities the inhibition of the lactate dehydrogenase by low NADH levels leads to an inhibition of glycolytic ATP production. Several tumor-therapeutic drugs reduce NAD and NADH levels, thereby inhibiting glycolytic energy production. The role of AMP, NADH, and NADPH levels in the success of chemotherapeutic treatment is discussed.

The role of phosphometabolites in cell proliferation, energy metabolism, and tumor therapy

A common characteristic of tumor cells is the constant overexpression of glycolytic and glutaminolytic enzymes. In tumor cells the hyperactive hexokinase and the partly inactive pyruvate kinase lead to an expansion of all phosphometabolites from glucose 6-phosphate to phosphoenolpyruvate. In addition to the glycolytic phosphometabolites, synthesis of their metabolic derivatives such as P-ribose-PP, NADH, NADPH, UTP, CTP, and UDP-N-acetyl glucosamine is also enhanced during cell proliferation. Another phosphometabolite derived from P-ribose-PP, AMP, inhibits cell proliferation. The accumulation of AMP inhibits both P-ribose-PP-synthetase and the increase in concentration of phosphometabolites derived from P-ribose-PP. In cells with low glycerol 3-phosphate and malate-aspartate shuttle capacities the inhibition of the lactate dehydrogenase by low NADH levels leads to an inhibition of glycolytic ATP production. Several tumor-therapeutic drugs reduce NAD and NADH levels, thereby inhibiting glycolytic energy production. The role of AMP, NADH, and NADPH levels in the success of chemotherapeutic treatment is discussed.

Quantification of tumor type M2 pyruvate kinase (Tu M2-PK) in human carcinomas

Proliferating and tumor cells express a certain isoenzyme of pyruvate kinase, called PK type M2. This isoenzyme can be isolated in an active tetrameric and an inactive dimeric form. We have termed this form tumor type M2-PK. This tumor type pyruvate kinase can be quantified by a specific ELISA in blood sera and tumor homogenates. In this study we have compared 26 normal colon mucosa and colon cancer specimens from the same patients. The total specific pyruvate kinase activity and the amount of the tumour type M2-PK measured by ELISA was increased in the tumor samples compared to the normal colon mucosa of the same patient. In normal colon mucosa the specific PK-activity ranged between 0.21 and 1.25 U/mg protein whereas in colon carcinoma we found activities between 0.99 and 7.08 U/mg. The amount of tumor M2-PK measured by ELISA ranged between 0.82 and 27.10 U/mg protein in normal colon mucosa and between 1.96 and 242.40 U/mg protein in colon carcinoma. The tumor M2-PK content in the serum of 666 healthy blood donors was measured by ELISA and compared to sera from 15 colon carcinoma patients and showed a highly significant difference (Mann-Whitney rank sum test, p < 0.001). The values for the 50%-percentiles (median) of blood donors were 10.8 U/ml and 55.0 U/ml for colon carcinoma.

Effect of extracellular AMP on cell proliferation and metabolism of breast cancer cell lines with high and low glycolytic rates

In differentiated tissues, such as muscle and brain, increased adenosine monophosphate (AMP) levels stimulate glycolytic flux rates. In the breast cancer cell line MCF-7, which characteristically has a constantly high glycolytic flux rate, AMP induces a strong inhibition of glycolysis. The human breast cancer cell line MDA-MB-453, on the other hand, is characterized by a more differentiated metabolic phenotype. MDA-MB-453 cells have a lower glycolytic flux rate and higher pyruvate consumption than MCF-7 cells. In addition, they have an active glycerol 3-phosphate shuttle. AMP inhibits cell proliferation as well as NAD and NADH synthesis in both MCF-7 and MDA-MB-453 cells. However, in MDA-MB-453 cells glycolysis is slightly activated by AMP. This disparate response of glycolytic flux rate to AMP treatment is presumably caused by the fact that the reduced NAD and NADH levels in AMP-treated MDA-MB-453 cells reduce lactate dehydrogenase but not cytosolic glycerol-3-phosphate dehydrogenase reaction. Due to the different enzymatic complement in MCF-7 cells, proliferation is inhibited under glucose starvation, whereas MDA-MB-453 cells grow under these conditions. The inhibition of cell proliferation correlates with a reduction in glycolytic carbon flow to synthetic processes and a decrease in phosphotyrosine content of several proteins in both cell lines.

Studies on associations of glycolytic and glutaminolytic enzymes in MCF-7 cells: role of P36

Isoelectric focusing of MCF-7 cell extracts revealed an association of the glycolytic enzymes glyceraldehyde 3-phosphate-dehydrogenase, phosphoglycerate kinase, enolase, and pyruvate kinase. This complex between the glycolytic enzymes is sensitive to RNase. p36 could not be detected within this association of glycolytic enzymes; however an association of p36 with a specific form of malate dehydrogenase was found. In MCF-7 cells three forms of malate dehydrogenase can be detected by isoelectric focusing: the mitochondrial form with an isoelectric point between 8.9 and 9.5, the cytosolic form with pl 5.0, and a p36-associated form with pl 7.8. The mitochondrial form comprises the mature mitochondrial isoenzyme (pl 9.5) and its precursor form (pl 8.9). Refocusing of the pl 7.8 form of malate dehydrogenase also gave rise to the mitochondrial isoenzyme. Thus, the pl 7.8 form of malate dehydrogenase is actually the mitochondrial isoenzyme retained in the cytosol by the association with p36. Addition of fructose 1,6-bisphosphate to the initial focusing column induced a quantitative shift of the pl 7.8 form of malate dehydrogenase to the mitochondrial forms (pl 8.9 and 9.5). In MCF-7 cells p36 is not phosphorylated in tyrosine. Kinetic measurements revealed that the pl 7.8 form of malate dehydrogenase has the lowest affinity for NADH. Compared to both mitochondrial forms the cytosolic isoenzyme has a high capacity when measured in the NAD --> NADH direction (malate --> oxaloacetate direction). The association of p36 with the mitochondrial isoenzyme may favor the flow of hydrogen from the cytosol into the mitochondria. Inhibition of cell proliferation by AMP which leads to an inhibition of glycolysis has no effect on complex formation by glycolytic and glutaminolytic enzymes in MCF-7 cells. AMP treatment leads to an activation of malate dehydrogenase, which correlates with the increase of pyruvate and the decrease of lactate levels, but has no effect on the distribution of the various malate dehydrogenase forms.

L- and M2-pyruvate kinase expression in renal cell carcinomas and their metastases

Using immunohistochemical and enzyme biochemical methods we investigated the expression of L- and M2-pyruvate kinase (PK) in normal renal tissue, renal cell carcinomas (RCCs; of clear cell, chromophilic cell and mixed cell type) and RCC metastases. L-PK was expressed in the proximal tubules of normal renal tissue and, to a variable extent, in 23/25 primary RCCs, in 1 RCC recurrence and in 10 RCC metastases. Staining intensity and percentage of stained tissue did not correlate with tumour grade. One renal oncocytoma and all extrarenal malignancies examined lacked L-PK immunoreactivity. M2-PK was mainly expressed in the distal tubules of the normal kidney and was found in all renal tumours as well as extrarenal malignancies. Quantitative biochemical investigations yielded a two- to seventeen-fold increase in PK activity in RCCs compared to the normal renal cortex taken from the same patient, whereas fructose-1,6-bisphosphatase and cytosolic glycerol-3-phosphate dehydrogenase activity was dramatically lower in RCCs. Otherwise, the activity of all other enzymes investigated (glucose-6-phosphate dehydrogenase, enolase and lactate dehydrogenase) was not significantly changed in the RCCs. The immunocytochemical results suggest that L-PK is a useful marker for RCC and its metastases, if acetone-fixed tissue is available. The quantitative changes of the concentration of PK and other enzymes in RCCs when compared with normal renal tissue probably reflect metabolic alterations related to tumour growth.

[Assessment of outcome in treatment of cardiac shock after myocardial infarction with intravenous streptokinase]

In 1986 a prospective randomized study coordinated by the Institute of Cardiology in Warsaw was started in 10 teaching cardiology hospitals in Poland for assessment of the results of treatment with intravenous streptokinase infusion in acute myocardial infarction. The studied population comprised 927 patients admitted to intensive treatment units within 6 hours after the onset of infarction pain. For the groups treated with streptokinase or heparin 752 patients were selected at random. In 175 cases the administration of streptokinase was contraindicated. These patients received conventional treatment and served as controls. The age of the patients was from 38 to 70 years, mean age 57.6 +/- 9.3 years. In 105 out of 927 cases cardiac shock was diagnosed. In the groups of early shock during hospitalization the death rate was 82%. No statistically significant difference was found in the death rates between patients with cardiac shock treated with heparin or with streptokinase.

In vitro effect of extracellular AMP on MCF-7 breast cancer cells: inhibition of glycolysis and cell proliferation

MCF-7 human breast cancer cells propagated in vitro were treated with adenosine derivatives added to the culture medium. The effects on cell proliferation, glycolysis, and glutaminolysis were investigated. Of all adenosine derivatives tested, AMP was the most efficient inhibitor of cell proliferation. In AMP-treated cells, DNA synthesis decreased, whereas RNA and protein syntheses rose normally with time. In terms of carbohydrate metabolism, lactate production from glucose was drastically reduced; therefore, most of lactate produced must have been derived from glutamine. Increases in the enzyme activities involved in glutamate degradation and in the malate-aspartate shuttle were observed. In contrast, actual glycolytic flux rates declined, whereas key glycolytic enzyme activities increased. Metabolites such as fructose 1,6-bisphosphate and pyruvate accumulated in AMP-arrested cells. Based on the lowered NAD level in the AMP-treated cells, lactate dehydrogenase, but not malate dehydrogenase, was impaired; thereby the whole of glycolysis was inhibited. In compensation, glutamine catabolism was increased. NAD concentrations fell drastically because of the known inhibition of P-ribose-PP synthesis through heightened intracellular AMP levels. A hypothetical metabolic scheme to explain these results and to show how extracellular AMP may influence carbohydrate metabolism and cell proliferation is presented.

Ventricular arrhythmias and the autonomic tone in patients with mitral valve prolapse

The aim of this study was to evaluate a possible relation between the autonomic tone determined by daily urine catecholamine excretion and the incidence of ventricular arrhythmias (VA) in patients with mitral valve prolapse (MVP). The study included 53 patients (31 women and 22 men) aged 19-52 years (mean age 32.7). The diagnosis of MVP was based on medical history, physical examination, and echocardiography. Cardiac arrhythmias were detected by Holter monitoring and classified according to Lown grades. Daily heart rate and duration of corrected QT interval using Basett's formula were also analyzed. Daily urine adrenaline and noradrenaline levels were determined fluorometrically by Von Euler and Lishajko's method. The patients with Lown's grade III-V VA were evaluated with particular consideration. Student's t-test was used for statistical analysis. On Holter monitoring 26 patients showed VA, including 6 with grade I, 11 with grade II, 2 with grade III, 4 with grade IV, and 3 with grade V according to Lown's classification. The remaining 27 patients were free of cardiac arrhythmias. Mean daily heart rate ranged from 54-93 beats/min (73 +/- 8.44, mean +/- SD) and corrected QT from 336-494 ms (411 +/- 37.17). Daily adrenaline and noradrenaline excretion for the whole group of patients were 0.01-16.2 micrograms (2.1 +/- 2.38) and 1.6-31.0 micrograms (13.1 +/- 7.27), respectively, which was within normal range. However, the patients with serious ventricular arrhythmias showed significantly higher daily adrenaline excretion. Individual analysis of two-thirds of patients with ventricular arrhythmias grade III-V showed daily urine noradrenaline levels exceeding mean values for the whole group.(ABSTRACT TRUNCATED AT 250 WORDS)

[Arrhythmia in patients with mitral valve prolapse syndrome and the status of the sympathetic nervous system]

The study aimed at evaluating a possible relationship between the adrenergic system tone determined with the excretion of catecholamines with the urine and an incidence of the ventricular arrhythmias in patients with the mitral valve prolapse. The study included 20 patients (13 women and 7 men aged between 20 and 50 years; mean = 31.6 years) with the mitral valve prolapse syndrome diagnosed with the aid of the patients' history, physical examinations and echocardiography. Echocardiograms have shown anterior mitral leaflet prolapse in 7 patients, posterior mitral leaflet prolapse in 8 patients, and both mitral leaflets prolapse in the remaining 5 patients. Daily excretion of adrenaline and noradrenaline was measured with Van Euler and Lishajko's fluorimetric technique. Cardiac arrhythmias were determined with a 24-hour ECG monitoring and classified according to Lown. Premature ventricular contractions of class I were seen in 1 patient, of class II in 5, class III in 1, class IV in 2, and class V in 3 patients. Holter monitoring technique did not show the arrhythmias in 8 patients. Daily adrenaline and noradrenaline excretion with the urine was within the normal values (3.2-30.8 ug and 0.2-16.2 ug, respectively) in all examined patients. Daily urine noradrenaline was higher in patients with serious ventricular arrhythmias (Lown's class V) than mean values in the whole examined group.