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PubMed1990

Effects of vanadate on 6-phosphofructo 2-kinase activity and fructose 2,6-bisphosphate levels in cultured rat hepatocytes.

The presence of vanadate in primary cultures of rat hepatocytes produced a significant increase in the concentration of fructose 2,6-bisphosphate and in the activity of 6-phosphofructo 2-kinase. Compared with insulin, vanadate had a more potent action on the metabolite increase, but a similar effect on the 6-phosphofructo 2-kinase activity. Both the insulin- and the vanadate-dependent enhancements of 6-phosphofructo 2-kinase were inhibited by cycloheximide which specifically blocks protein synthesis on the translational level, suggesting that the increase of the enzyme activity was due to induction rather than to a change in the catalytic activity.

Animals↗
PubMed1994

Fructose 1,6-bisphosphate prevents oxidative stress in the isolated and perfused rat heart.

Rat hearts were perfused with the Langendorff technique at constant flux in the presence of the oxidizing agents hydrogen peroxide and diamide. Fructose 1,6-bisphosphate strongly prevented the decline of heart contractility due to the infusion of these oxidizing agents. On the other hand, fructose 1,6-bisphosphate had no effect on the release of total glutathione into the perfusate but prevented the loss of lactate dehydrogenase indicating a protective effect on cell membranes. Comparing the cytosolic and mitochondrial loss of glutathione, fructose 1,6-bisphosphate exerted a beneficial action only on the mitochondrial fraction. Several mechanisms of action have been considered to explain the protective action of fructose 1,6-bisphosphate. In our experimental conditions fructose 1,6-bisphosphate might stimulate its own production giving rise to dihydroxyacetone phosphate, that, after reduction to glycerol 3-phosphate, can permeate the mitochondrial membrane with the final production of energy.

Animals↗
PubMed1992

Effect of galactosamine on hepatic carbohydrate metabolism: protective role of fructose 1,6-bisphosphate.

Intraperitoneal administration of galactosamine (400 mg/kg body wt) to rats results in reversible liver cell injury that is related to a dose-dependent depletion of uridine phosphates by formation of UDP-sugar derivatives. This damage was monitored through changes in serum enzymatic activities that increased after the first 6 hr of drug administration. Glycemia and serum albumin remained stable during liver injury, whereas cholesterol and triglycerides decreased. To maintain plasma glucose concentration, the hepatic carbohydrate metabolism was greatly altered. Glycogen dropped during the first hours, remaining low for up to 48 hr. Fructose 2,6-bisphosphate and ATP levels decreased even faster than glycogen, with lactate following a similar diminution and being restored in parallel with both metabolites. The reduction in fructose 2,6-bisphosphate can be explained by changes in the substrates or modulators of the 6-phosphofructo-2-kinase/fructose 2,6-bisphosphatase, because neither the cyclic AMP levels nor the activity ratio of the enzyme were modified. Simultaneous administration of galactosamine and fructose 1,6-bisphosphate (2 gm/kg) prevented liver cell death, as monitored by serum enzyme activities. Furthermore, the bisphosphorylated metabolite had protective effects on the changes in liver calcium content and ATP and fructose 2,6-bisphosphate concentrations. In contrast, fructose, fructose-1-phosphate and fructose-6-phosphate had no significant protection. Fructose 1,6-bisphosphate might decrease galactosamine toxicity by increasing fructose 2,6-bisphosphate and ATP levels, the changes in both metabolites probably being related. The significance of these findings with respect to the mechanism of galactosamine-induced liver injury is also discussed.

Adenosine Triphosphate↗
PubMed1992

Isoenzymes of carbohydrate metabolism in primary cultures of hepatocytes from thioacetamide-induced rat liver necrosis: responses to growth factors.

Hepatocytes isolated from the liver of rats after a necrotizing dose of thioacetamide (6.6 mmol/kg) were used to study the postnecrotic process of liver regeneration. Flow cytometry analysis revealed populations of dedifferentiated hepatocytes exhibiting physical properties (size and fluorescence emission at 530 nm) similar to those found in fetal (22 days old) liver cells. The percentage of these cells increased progressively from 24 to 48 and 72 hr after thioacetamide administration. In primary cultures of hepatocytes the effects of phorbol 12-myristate 13-acetate, bombesin and insulin were investigated on the 6-phosphofructo 2-kinase/fructose 2,6 bisphosphate system. Bombesin and insulin stimulated 6-phosphofructo 2-kinase activity and fructose 2,6-bisphosphate content both in control and in thioacetamide-treated hepatocytes. However, phorbol 12-myristate 13-acetate stimulated 6-phosphofructo 2-kinase activity and increased fructose 2,6-bisphosphate concentration in thioacetamide-treated liver cells, whereas no similar response was found in hepatocytes from control rats. The response of postnecrotic thioacetamide-treated hepatocytes to phorbol 12-myristate 13-acetate was similar to that obtained from 22-day-old fetal liver cells, which reveals that different methods might control fructose 2,6-bisphosphate content and therefore the mechanisms of glycolysis and gluconeogenesis at this regulatory step. The lack of response to glucagon of glycogen phosphorylase a and 6-phosphofructo 2-kinase from thioacetamide-treated hepatocytes may indicate that the expression of specific enzymes of carbohydrate metabolism undergoes transitions to less-differentiated isoenzymatic forms. Moreover, the isoenzyme pattern of hexokinases elicits a complete disturbance in glucokinase and hexokinases activities.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Lack of control of liver gluconeogenesis in cholestatic rats with reduced portal blood flow.

Previous studies indicated a role for ischemia in the metabolic changes induced by cholestasis. Liver pyruvate kinase is a key enzyme for the concurrent control of glycolysis and gluconeogenesis. In this experiment the control of pyruvate kinase activity was investigated in cholestatic rats. Pyruvate kinase kinetics changed from a sigmoidal type in sham-operated rats to a hyperbolic type in obstructed rats. The change in the enzymatic kinetics paralleled the reduction in the portal blood flow, which reached 50% of the control value 7 days after obstruction. Dibutyryl cyclic AMP (5 mumol/kg body wt) plus theophylline 0.1 mmol/L failed to inactivate the enzyme when injected into the portal veins of rats whose livers were obstructed 7 days before. Both the kinetics changes and the lack of phosphorylation control are compatible with ischemia.

Animals↗
PubMed1992

The cooperative binding of fructose-1,6-bisphosphate to yeast pyruvate kinase.

The cooperative binding of the allosteric activator fructose-1,6-bisphosphate [Fru(1,6)P2] to yeast pyruvate kinase was investigated by equilibrium dialysis and fluorescence quench titration. The results show that yeast pyruvate kinase binds four molecules of Fru(1,6)P2 per tetramer and the observed fluorescence quench follows the binding of the ligand and not the cooperative T to R state transition. Additionally it is shown that the binding of Fru(1,6)P2 to yeast pyruvate kinase is compatible with the model of cooperativity that has been proposed and incorporates an intermediate state, R', with properties between those of the T and R states.

Allosteric Regulation↗
PubMed1988

Improved exercise tolerance by i.v. fructose-1,6-diphosphate in chronic, stable angina pectoris.

The effect of IV fructose-1,6-diphosphate (FDP) on transient, reproducible myocardial ischemia was evaluated in ten patients, aged 50 to 66 years, with chronic, stable exertional angina. FDP or placebo (glucose) were administered between basal and posttreatment ergometric stress testing; an identical procedure was repeated in each patient with the second treatment on the following day according to a single-blind, cross-over design. FDP improved exercise tolerance and total work capacity, significantly delaying the onset of ST-segment depression and angina. Nevertheless, the critical level of the rate x pressure (R X P) product, causing appearance of myocardial ischemia, was not remarkably changed. However, the R X P product at same workload was significantly lower after FDP. These results suggest that improved exercise tolerance might have resulted from peripheral (increased oxygen delivery to skeletal muscle) rather than from central (cardiac) effects of FDP.

Aged↗
PubMed2001

Caveolae and the organization of carbohydrate metabolism in vascular smooth muscle.

We have previously found that glycolysis and gluconeogenesis occur in separate "compartments" of the VSM cell. These compartments may result from spatial separation of glycolytic and gluconeogenic enzymes (Lloyd and Hardin [1999] Am J Physiol Cell Physiol. 277:C1250-C1262). We have also found that an intact plasma membrane is essential for compartmentation to exist (Lloyd and Hardin [2000] Am J Physiol Cell Physiol. 278:C803-C811), suggesting that glycolysis and gluconeogenesis may be associated with distinct plasma membrane microdomains. Caveolae are one such microdomain, in which proteins of related function colocalize. Thus, we hypothesized that membrane-associated glycolysis occurs in association with caveolae, while gluconeogenesis is localized to non-caveolae domains. To test this hypothesis, we disrupted caveolae in vascular smooth muscle (VSM) of pig cerebral microvessels (PCMV) with beta methyl-cyclodextrin (CD) and examined the metabolism of [2-(13)C]glucose (a glycolytic substrate) and [1-(13)C]fructose 1,6-bisphosphate (FBP, a gluconeogenic substrate in PCMV) using (13)C nuclear magnetic resonance spectroscopy. Caveolar disruption reduced flux of [2-(13)C]glucose to [2-(13)C]lactate, suggesting that caveolar disruption partially disrupted the glycolytic pathway. Caveolae disruption may also have resulted in a breakdown of compartmentation, since conversion of [1-(13)C]FBP to [3-(13)C]lactate was increased by CD treatment. Alternatively, the increased [3-(13)C]lactate production may reflect changes in FBP uptake, since conversion of [1-(13)C]FBP to [3-(13)C]glucose was also elevated in CD-treated cells. Thus, a link between caveolar organization and metabolic organization may exist.

Animals↗
PubMed1994

Alteration of aldolase isozymes in serum and tissues of patients with cancer and other diseases.

We studied the alteration of aldolase isozymes in the serum and tissues of patients with cancer and other diseases using radioimmunoassays specific for aldolase A, B, and C subunits. Aldolase B was predominantly found in adult liver, where aldolase A and C were distinctly low. Aldolase A and B showed almost the same concentration in fetal liver, while in neonatal liver aldolase B protein concentrations were much higher than aldolase A. In contrast, aldolase A was the predominant isozyme found in hepatoma and gastric cancer tissues, whereas aldolase B was distinctly low in hepatoma tissues, and extremely low in gastric cancer tissues. These results suggest that the aldolase A is a more fetal type of liver isozyme than the aldolase B and C, and aldolase B is a more differentiated type of liver isozyme than aldolase A and C. Serum FDP aldolase activities were elevated in half of patients with liver diseases, all patients with muscle diseases and a few patients with cancer. Serum aldolase A levels were elevated in patients with muscle diseases and cancer, but not elevated in patients with liver diseases. In contrast, serum aldolase B levels were elevated in patients with liver disease, but not elevated in patients with muscle diseases and other diseases without liver injury. Serum aldolase B levels showed a trend to decrease in cancer patients with normal GPT levels. Serum aldolase A/B ratios were significantly increased in cancer patients with normal GPT levels, whereas they showed the decreased levels in patients with liver diseases.(ABSTRACT TRUNCATED AT 250 WORDS)

Fructose-Bisphosphate Aldolase↗
PubMed1980

Catalytic and regulatory properties of muscle pyruvate kinase from Cancer magister.

Despite the marked changes that crustacean muscle undergoes during the molt cycle, pyruvate kinase is present as the same form throughout the molt cycle. This pyruvate kinase was subject to feed-forward activation by fructose-1, 6 bisphosphate (FBP) as well as feed-back inhibition by MgATP. The enzyme showed a high affinity for phosphoenolpyruvate (Km = 0.1 mM) but showed no cooperativity in substrate binding. The addition of 0.05 mM FBP reduced the PEP Km to 0.05 mM. MgATP inhibition showed a Ki of 1.8 mM versus PEP. The inhibition due to MgATP could be reversed by FBP. Various other compounds inhibited the enzyme, including citrate, alpha-ketoglutarate, tryptophan, and malate, although at rather high levels. Measurements of the reversal of this pyruvate kinase, taken together with the low levels of phosphoenolpyruvate carboxykinase and pyruvate carboxylase, predict only minimal levels of gluconeogenic flux in crustacean muscle.

Adenosine Triphosphate↗
PubMed1984

Serum lysozyme increased by fructose-1, 6-diphosphate in men, rabbits, and mice.

Fructose-1, 6-diphosphate hydrated sodium salt (FDP), intravenously injected, remarkably stimulates the production of serum lysozyme in man, rabbit, and mouse with a different kinetics in each of them: Man and rabbit show, in the first hour, a concentration peak followed by a slow decrease, whereas in mouse the concentration is less variable with time.

Animals↗
PubMed1996

Anti-CD69 antibodies enhance phorbol-dependent glucose metabolism and Ca2+ levels in human thymocytes. Antagonist effect of cyclosporin A.

The human activation antigen CD69 is an early inducible surface glycoprotein acquired by T cells in the thymus at the stage of positive selection and during activation of mature lymphoid cells both in vivo and in vitro. We have studied the regulatory influence of CD69 activation pathway on the glycolytic process and transduction signals of thymocytes. Treatment of human thymocytes with different anti-CD69 monoclonal antibodies (mAbs), in the presence of submitogenic doses of phorbol ester, produced an enhanced release of lactate without significant alterations in Fru 2,6-P2 levels or phosphofructokinase-2 (PFK-2) and pyruvate kinase activities. A small increase in phosphofructokinase-1 (PFK-1) activity was also detected. Furthermore, anti-CD69 mAb increased the glucose detritiation from [2-3H] and [3-3H]glucose, thus indicating an enhanced flux through hexokinase and PFK-1 steps. In addition, de novo synthesis of diacylglycerol and intracellular Ca2+ levels increased after anti-CD69 mAb treatment. The stimulatory effects of anti-CD69 mAb on both glycolysis and Ca2+ levels were inhibited by cyclosporin A. Because CD69 molecules are present in certain subset populations of immature thymocytes, the ability of anti-CD69 mAb to stimulate the glycolysis, the synthesis of diacylglycerol and the intracellular Ca2+ levels suggest that the activation signals delivered through CD69 molecules could play a role in the thymus cells maturation.

Antibodies, Monoclonal↗
PubMed1993

Fructose-2,6-bisphosphate level and beta-lactam formation in Penicillium chrysogenum.

The rate of penicillin formation in the medium containing lactose as sole carbon source markedly decreased after addition of glucose but at the same time the growth rate of fungal mycelium increased. Significant correlation was found between the formation of penicillin and the intracellular concentration of fructose-2,6-bisphosphate. It appears that penicillin production is influenced by the level of fructose-2,6-bisphosphate.

Cyclic AMP↗
PubMed1998

Induction of apoptosis in two mammalian cell lines results in increased levels of fructose-1,6-bisphosphate and CDP-choline as determined by 31P MRS.

Programmed cell death or apoptosis was induced in human promyelocytic leukemia (HL-60) and Chinese hamster ovary (CHO-K1) cells using several cytotoxic drugs that have different modes of action, including camptothecin, ceramide, chelerythrine, etoposide, farnesol, geranyl geraniol, and hexadecylphosphocholine. The consequent changes in cellular metabolism were monitored using 31P MRS measurements on intact cells and cell extracts. Cells undergoing programmed cell death exhibited characteristic changes in the levels of glycolytic and phospholipid metabolites. The most significant changes were increases in the concentration of the glycolytic intermediate, fructose-1,6-bisphosphate and in the concentration of CDP-choline, which is an intermediate in phosphatidylcholine biosynthesis. In HL-60 cells, the increase in fructose-1,6-bisphosphate levels could be explained by depletion of cellular NAD(H) levels. All of the agents used to induce apoptosis caused the accumulation of CDP-choline. Since the resonances of this compound occur in a relatively well resolved region of tissue spectra, it could provide a marker for apoptosis that would allow the noninvasive detection of the process in vivo using 31P MRS measurements.

Animals↗