Carbohydrate metabolism in HT29 colon cancer cells cultured in a glucose free medium supplemented with inosine

Metabolomic Detection Between Pancreatic Cancer and Liver Metastasis Nude Mouse Models Constructed by Using the PANC1-KAI1/CD82 Cell Line

Background: Pancreatic cancer (PC) has a poor prognosis and is prone to liver metastasis. The KAI1/CD₈₂ gene inhibits PC metastasis. This study aimed to explore differential metabolites and enrich the pathways in serum samples between PC and liver metastasis nude mouse models stably expressing KAI1/CD₈₂. Methods: KAI1/CD₈₂-PLV-EF1α-MCS-IRES-Puro vector and PANC1 cell line stably expressing KAI1/CD₈₂ were constructed for the first time. This cell line was used to construct 3 PC nude mouse models and 3 liver metastasis nude mouse models. The different metabolites and Kyoto encyclopedia of genes and genomes (KEGG) and human metabolome database (HMDB) enrichment pathways were analyzed using the serum samples of the 2 groups of nude mouse models on the basis of untargeted ultra-performance liquid chromatography-tandem mass spectrometry platform. Results: KAI1/CD₈₂-PLV-EF1α-MCS-IRES-Puro vector and PANC1 cell line stably expressing KAI1/CD₈₂ were constructed successfully, and all nude mouse models survived and developed cancers. Among the 1233 metabolites detected, 18 metabolites (9 upregulated and 9 downregulated) showed differences. In agreement with the literature data, the most significant differences between both groups were found in the levels of bile acids (taurocholic acid, chenodeoxycholic acid), glycine, prostaglandin E2, vitamin D, guanosine monophosphate, and inosine. Bile recreation, primary bile acid biosynthesis, and purine metabolism KEGG pathways and a series of HMDB pathways (P < .05) contained differential metabolites that may be associated with liver metastasis from PC. However, the importance of these metabolites on PC liver metastases remains to be elucidated. Conclusions: Our findings suggested that the metabolomic approach may be a useful method to detect potential biomarkers in PC.

PCK2 activation mediates an adaptive response to glucose depletion in lung cancer

Cancer cells are reprogrammed to utilize glycolysis at high rates, which provides metabolic precursors for cell growth. Consequently, glucose levels may decrease substantially in underperfused tumor areas. Gluconeogenesis results in the generation of glucose from smaller carbon substrates such as lactate and amino acids. The key gluconeogenic enzyme, phosphoenolpyruvate carboxykinase (PEPCK), has been shown to provide metabolites for cell growth. Still, the role of gluconeogenesis in cancer is unknown. Here we show that the mitochondrial isoform of PEPCK (PCK2) is expressed and active in three lung cancer cell lines and in non-small cell lung cancer samples. PCK2 expression and activity were enhanced under low-glucose conditions. PEPCK activity was elevated threefold in lung cancer samples over normal lungs. To track the conversion of metabolites along the gluconeogenesis pathway, lung cancer cell lines were incubated with (13)C₃-lactate and label enrichment in the phosphoenolpyruvate (PEP) pool was measured. Under low glucose, all three carbons from (13)C₃-lactate appeared in the PEP pool, further supporting a conversion of lactate to pyruvate, via pyruvate carboxylase to oxaloacetate, and via PCK2 to phosphoenolpyruvate. PCK2 small interfering RNA and the pharmacological PEPCK inhibitor 3-mercaptopicolinate significantly enhanced glucose depletion-induced apoptosis in A549 and H23 cells, but not in H1299 cells. The growth of H23 multicellular spheroids was significantly reduced by 3-mercaptopicolinate. The results of this study suggest that lung cancer cells may utilize at least some steps of gluconeogenesis to overcome the detrimental metabolic situation during glucose deprivation and that in human lung cancers this pathway is activated in vivo.

CRNDE, a long non-coding RNA responsive to insulin/IGF signaling, regulates genes involved in central metabolism

Colorectal neoplasia differentially expressed (CRNDE) is a novel gene that is activated early in colorectal cancer but whose regulation and functions are unknown. CRNDE transcripts are recognized as long non-coding RNAs (lncRNAs), which potentially interact with chromatin-modifying complexes to regulate gene expression via epigenetic changes. Complex alternative splicing results in numerous transcripts from this gene, and we have identified novel transcripts containing a highly-conserved sequence within intron 4 ("gVC-In4"). In colorectal cancer cells, we demonstrate that treatment with insulin and insulin-like growth factors (IGF) repressed CRNDE nuclear transcripts, including those encompassing gVC-In4. These repressive effects were negated by use of inhibitors against either the PI3K/Akt/mTOR pathway or Raf/MAPK pathway, suggesting CRNDE is a downstream target of both signaling cascades. Expression array analyses revealed that siRNA-mediated knockdown of gVC-In4 transcripts affected the expression of many genes, which showed correlation with insulin/IGF signaling pathway components and responses, including glucose and lipid metabolism. Some of the genes are identical to those affected by insulin treatment in the same cell line. The results suggest that CRNDE expression promotes the metabolic changes by which cancer cells switch to aerobic glycolysis (Warburg effect). This is the first report of a lncRNA regulated by insulin/IGFs, and our findings indicate a role for CRNDE nuclear transcripts in regulating cellular metabolism which may correlate with their upregulation in colorectal cancer.

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.

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.

Effect of purine supplementation on the growth of salmonid cell lines in different mammalian sera

The Chinook salmon embryo cell line, CHSE-214, grew well in fetal bovine serum (FBS) but poorly in dialyzed (d) FBS. Purines restored most but not all growth-promoting activity to dFBS, which suggests that purines account for a large portion of the dialyzable fraction's growth-promoting activity. CHSE-214 died in newborn calf serum (NCS) but grew slightly in dNCS, which suggests that the dialyzable fraction of NCS contains a toxic component(s). Little or no proliferation occurred in calf serum (CS); some took place in horse serum (HS). Porcine serum (PS) was very toxic. In all these sera except PS and HS, the purine nucleoside, inosine, significantly enhanced growth, whereas the pyrimidine nucleoside, uridine, was without effect. The other purines, hypoxanthine, adenine, adenosine and guanosine also stimulated proliferation but not as well as inosine. Inosine also enhanced the growth of the rainbow trout gonadal cell line, RTG-2. Although their morphology underwent minor alterations in medium with inosine, CHSE-214 cells could be grown indefinitely in CS and inosine as effectively as in the more expensive FBS.

Antioxidant protection systems of rat lung after chronic ethanol inhalation

The effect of chronic ethanol administration on pulmonary antioxidant protection systems was investigated in male Sprague-Dawley rats exposed to room air or room air containing ethanol vapors for 5 weeks. Blood ethanol concentrations in ethanol-exposed rats were usually between 200 and 300 mg/dl. Glutathione, vitamin E, and malondialdehyde concentrations were measured in lung homogenates, and antioxidant enzyme activities (catalase, glutathione peroxidase, Cu/Zn-superoxide dismutase, glutathione reductase) were determined in the supernatant fractions. For comparison, the measurements were also made using liver fractions. Ethanol treatment increased the activities of catalase (117%) and Cu/Zn-superoxide dismutase (25%) in lung but not in liver. Although chronic ethanol inhalation lowered hepatic glutathione (19%) and hepatic vitamin E (33%), there was no increase in malondialdehyde content in either liver or lung of ethanol-exposed rats. The elevation of pulmonary antioxidant enzyme activities could be interpreted to mean that lung is a target for ethanol-induced oxidative stress. However, as there was no loss of pulmonary GSH or vitamin E and no increase in malondialdehyde formation, it appears that long-term ethanol exposure did not produce a significant degree of oxidative stress in rat lung.

Effect of VIP on the glycogen metabolism of human colon adenocarcinoma cells studied by 13C nuclear magnetic resonance spectroscopy

Metabolic pathways of glucose utilization have been investigated in a human colon adenocarcinoma cell line (HT29) using carbon-13 Nuclear Magnetic Resonance spectroscopy. HT29 cells were adapted to grow on a polystyrene beaded microcarrier and were perfused when attached to the beads in a specially designed NMR cell. Abnormalities in carbohydrate metabolism already observed in several cancer cells were studied in HT29 cells fed with (1-13C)-enriched glucose. The cells were first perfused with a glucose-free medium for 2 h in order to deplete the intracellular store of glycogen, and they were subsequently perfused with a medium containing enriched glucose at an initial concentration of 5.5 mM. Sequential 13C-NMR spectra, recorded at 100.5 MHz (5 min accumulation), show that HT29 cells were able to utilize glucose through the glycolytic pathway while storing glucose as glycogen (glucose was utilized at a rate of 3.9 mumol/mg protein/hr). The glycolytic activity determined by the amount of lactic acid produced was 4.6 microns/mg protein/hr, corresponding to the formation of 1.2 lactic acid per glucose molecule. Glycogen accumulation corresponded to 16 micrograms/mg of protein. Treatment of HT29 with 10 nM vasoactive intestinal peptide (VIP) induced a transient decrease in the level of labelled glycogen to 50% of the initial value. Control level was recovered 12 min after VIP loading.

Respiration of mitochondria isolated from differentiated and undifferentiated HT29 colon cancer cells in the presence of various substrates and ADP generating systems

1. Oxygen consumption was investigated in two cultured subpopulations of either undifferentiated (Glc+ cells) or differentiated (Glc- cells) HT29 colon cancer cells and in the corresponding isolated mitochondria. In Glc+ cells, a decrease of the respiration is induced by the presence of glucose (Crabtree effect), whereas it is not the case in Glc- cells. 2. The oxidative phosphorylation rate of Glc- mitochondria is found to be much higher than that of Glc+ mitochondria, due to a higher efficiency to oxidize glutamine, glutamate, 2-oxoglutarate, succinate or malate. 3. In both types of mitochondria, respiration can be supported by the ADP formed by adenylate kinase or nucleotide diphosphate kinase, and, although to a lesser extent in Glc- mitochondria, by hexokinase. 4. Glc+ cells are characterized by a low respiration capacity and a high glycolytic flux leading to the Crabtree effect. Glc- cells are characterized by a better correlation between a moderate glycolytic flux and a high respiratory capacity.