Actions of quercetin on gluconeogenesis and glycolysis in rat liver

1. The action of quercetin on glucose catabolism and production was investigated in the perfused rat liver. 2. Quercetin inhibited lactate production from glucose: 80% inhibition was found at a quercetin concentration of 100 micro M, and at higher concentrations inhibition was complete. 3. Pyruvate production from glucose presented a complex pattern, but stimulation was evident at 100 and 300 micro M quercetin. Oxygen uptake tended to be increased. 4. Glucose synthesis from lactate and pyruvate was inhibited. Inhibition was already evident at 50 micro M quercetin and almost complete at 300 micro M. Concomitantly, the increment in oxygen uptake caused by lactate plus pyruvate was stimulated by 50 micro M quercetin, but clearly inhibited by higher concentrations (100-500 micro M). 5. Glucose phosphorylation in the high-speed supernatant fractions of liver homogenates was inhibited by quercetin, but only at concentrations above 150 micro M. 6. It is concluded that quercetin can inhibit both glucose degradation and production and increase the cytosolic NAD(+)/NADH ratio. 7. These effects are likely to arise from many causes. Reduction of oxidative phosphorylation, inhibition of Na(+)-K(+)-ATPase, inhibition of glucokinase and inhibition of glucose 6-phosphatase could all contribute to the overall action of quercetin.     

Action of quercetin on glycogen catabolism in the rat liver

1. The influence of quercetin on glycogen catabolism and related parameters was investigated in the isolated perfused rat liver and subcellular systems. 2. Quercetin stimulated glycogenolysis (glucose release). This effect was already evident at a concentration of 50 µ M maximal at 300 µ M and declined at higher concentrations. Quercetin also stimulated oxygen consumption, with a similar concentration dependence. 3. Lactate production from endogenous glycogen (glycolysis) was diminished by quercetin without significant changes in pyruvate production. 4. Quercetin did not inhibit glucose transport into cells but decreased intracellular sequestration of [5- 3 H]glucose under conditions of net glucose release. 5. In isolated mitochondria, quercetin diminished the energy transduction efficiency. It also inhibited several enzymatic activities, e.g. the K + -ATPase/Na + -ATPase of plasma membrane vesicles and the glucose 6-phosphatase of isolated microsomes. 6. No significant changes of the cellular contents of AMP, ADP and ATP were found. The cellular content of glucose 6-phosphate, however, was increased (3.12-fold). 7. Some of the effects of quercetin (glycogenolysis stimulation) can be attributed to its action on mitochondrial energy metabolism, as, for example, uncoupling of oxidative phosphorylation. However, the multiplicity of the effects on several enzymatic systems certainly produces an intricate interplay that also generates complex and apparently contradictory effects.     

Antidiabetic effects of Mukia maderaspatana and its phenolics: An in vitro study on gluconeogenesis and glucose uptake in rat tissues

Context: Traditional medicine is used by over 60% of the world’s population for health care. Mukia maderaspatana (L.) M. Roem. (Cucurbitaceae) (Mukia) is extensively used in folklore medicine as an antidiabetic plant. It is rich in phenolics that contribute to its medicinal properties.

Objective: Mukia extract and phenolics such as quercetin and phloroglucinol are investigated for their in vitro antidiabetic activity.

Materials and methods: Quercetin, phloroglucinol, and methanol extract of the dried whole plant (0.25 and 0.5?mg/ml) were studied for the inhibition of gluconeogenesis in rat liver slices and glucose uptake in isolated rat hemi-diaphragm (50 and 100?µg/ml). Phenolics of Mukia were analyzed by HPLC.

Results and discussion: Glucose (1.2?mg/g/h) was synthesized from pyruvate and the synthesis was completely inhibited by insulin (1?U/ml). Quercetin at 0.25 and 0.5?mg/ml caused 65% and 89% inhibition (0.42?mg/g/h and 0.13?mg/g/h glucose). Addition of insulin did not increase inhibition. Phloroglucinol inhibited 100% glucose production with or without insulin. Mukia (0.25?mg/ml) inhibited gluconeogenesis (0.65?mg/g/h) by 45%, and with insulin, inhibition increased to 50% (0.59?mg/g/h). At 0.5?mg/ml, glucose production was stimulated by1.2-fold, but with insulin it was inhibited by 89% (0.13?mg/g/h glucose). Mukia had no effect on glucose uptake, but potentiated the action of insulin mediated glucose uptake (152.82?±?13.30?mg/dl/g/30?min) compared with insulin control (112.41?±?9.14?mg/dl/g/30?min) (p?0.05). HPLC analysis revealed the presence of phenolics.

Conclusion: Results provide scientific rationale for the use of Mukia in folk medicine as an antidiabetic nutraceutical.     

Action of quercetin on glycogen catabolism in the rat liver

1. The influence of quercetin on glycogen catabolism and related parameters was investigated in the isolated perfused rat liver and subcellular systems. 2. Quercetin stimulated glycogenolysis (glucose release). This effect was already evident at a concentration of 50 microM maximal at 300 microM and declined at higher concentrations. Quercetin also stimulated oxygen consumption, with a similar concentration dependence. 3. Lactate production from endogenous glycogen (glycolysis) was diminished by quercetin without significant changes in pyruvate production. 4. Quercetin did not inhibit glucose transport into cells but decreased intracellular sequestration of [5-(3)H]glucose under conditions of net glucose release. 5. In isolated mitochondria, quercetin diminished the energy transduction efficiency. It also inhibited several enzymatic activities, e.g. the K(+)-ATPase/Na(+)-ATPase of plasma membrane vesicles and the glucose 6-phosphatase of isolated microsomes. 6. No significant changes of the cellular contents of AMP, ADP and ATP were found. The cellular content of glucose 6-phosphate, however, was increased (3.12-fold). 7. Some of the effects of quercetin (glycogenolysis stimulation) can be attributed to its action on mitochondrial energy metabolism, as, for example, uncoupling of oxidative phosphorylation. However, the multiplicity of the effects on several enzymatic systems certainly produces an intricate interplay that also generates complex and apparently contradictory effects.     

Inhibition of gluconeogenesis in isolated perfused rat liver by clanobutin

The effect of clanobutin {4-[p-chloro-N-(p-methoxyphenyl-)benzamido]butyric acid} on gluconeogenesis from lactate + pyruvate (1.6 + 0.2 mmoles/1) as precursors in isolated perfused liver of fasted rats was investigated. Glucose production was dose dependent inhibited up to a maximum of 81 ± 3 per cent; the half-maximum concentration of clanobutin was 0.33 ± 0.04 mmoles/1. Buformin and phenformin, respectively, used as references showed no effect on gluconeogenesis under the given experimental conditions. Oxygen uptake was not inhibited by clanobutin at concentrations up to 0.14 mmoles/1. At higher concentrations, the inhibitory effect was smaller than observed for comparable buformin doses. According to our results, clanobutin appears to be a more potent and probably more specific inhibitor of gluconeogenesis than the therapeutically used biguanides—at least in the isolated perfused rat liver.     

The action of oxybutynin on haemodynamics and metabolism in the perfused rat liver

The present study was planned to investigate the possible action of oxybutynin on liver haemodynamics and its influence on metabolic variables. The isolated liver perfused either bivascularly or monovascularly in the non-recirculating system was used for the experiments and Krebs/Henseleit-bicarbonate buffer (pH 7.4) as a perfusion fluid. Oxybutynin (25-200 microM) was infused, the infusion time for each concentration being 14 min. Portally infused oxybutynin increased the perfusion pressure starting at 100 microM. Oxygen uptake was diminished, also starting at 100 microM. Arterially infused oxybutynin also increased the perfusion pressure in the hepatic artery. Lactate and pyruvate releases were considerably diminished by oxybutynin. Glucose release showed a small initial stimulation, then returned to values slightly below the basal ones. Cessation of oxybutynin infusion resulted in progressive stimulation of glucose release. When Ca2+ was omitted all effects of oxybutynin vanished. The hepatic contents of glucose, glucose 6-phosphate and lactate in the presence of 200 microM oxybutynin increased 7.8-, 4.6- and 5.1 times, respectively. The pyruvate content was not changed. The ATP content was diminished by 26.6% in the presence of 200 microM oxybutynin, but the AMP content was increased by 64.3%. The ADP content was not changed. Apparently, upon administration of oxybutynin, a considerable fraction of the liver parenchyma ceased to be irrigated or almost so, which is apparent from the concomitant inhibition of oxygen uptake, pressure increase and inhibition of glucose, lactate and pyruvate release together with the simultaneous intracellular accumulation of glucose, lactate and glucose 6-phosphate.     

Effect of loperamide on Na+/D-glucose cotransporter activity in mouse small intestine

The mu-opioid agonist loperamide is an antidiarrhoeal drug which inhibits intestinal motility and secretion. Its anti-absorptive effects are less well investigated, but may be mediated through calmodulin. We have investigated further the effect of loperamide on the intestinal Na+-dependent D-glucose transporter (SGLT1). Brush-border membrane vesicles were prepared from mouse small intestine, and uptake of [3H]glucose was measured. Na+-dependent glucose uptake displayed the typical overshoot at 34 s; the peak value was 1.6 nmol mg(-1). The overshoot disappeared in the presence of phlorizin or when Na+ was replaced by K+. Extravesicular loperamide dose-dependently inhibited SGLT1 activity with an IC50 value of 450 micromol L(-1). Loperamide displayed a mixed inhibition type: the apparent Vmax decreased from 0.9 to 0.5 nmol mg(-1)/15 s, the apparent Km increased from 0.23 to 1.13 mmol L(-1) glucose. Na+ kinetics were more complex, but loperamide inhibited net glucose uptake by 90% at 100 mmol L(-1) Na+. Glucose uptake was unchanged by agents affecting calmodulin activity. Loperamide inhibited intestinal Na+, K+-ATPase activity, whilst sucrase activity was unaffected. SGLT1 activity was inhibited by loperamide, but this effect was not mediated through calmodulin. As this action is only evident at high concentrations of loperamide a nonspecific mechanism may be involved.     

On the mechanism of sodium 2-5-4 chlorophenylpentyloxirane-2-carboxylate (POCA) inhibition of hepatic gluconeogenesis

Inhibition of hepatic long chain fatty acid oxidation by 2-5-4 chlorophenylpentyloxirane-2-carboxylate (POCA) leads to decreased gluconeogenic rates from lactate or from low concentrations of pyruvate. The inhibitory effect is fully overcome by concentrations of pyruvate above 0.8 mM or by the simultaneous administration of a medium chain fatty acid. At low pyruvate availability the energy cost of gluconeogenesis is mainly supported by fatty acid oxidation and POCA-induced inhibition of glucose production is secondary to a decreased energy availability. This is supported by the following observations: (i) POCA decreases hepatic respiration and phosphorylation potential: (ii) the rate of pyruvate-induced respiration was the same regardless of whether gluconeogenesis was inhibited or not by POCA: and (iii) concentrations of pyruvate above 0.8 mM, at which gluconeogenesis is not inhibited, prevented the POCA-induced decrease in the phosphorylation potential. It is concluded that inhibition of long chain fatty acid oxidation by POCA leads to a switch of energy fuel, and results in the oxidation of more pyruvate to meet the cellular energy demands. When pyruvate availability is low and thus, presumably, its mitochondrial transport restricted, pyruvate carboxylation most probably becomes limiting as a result of the increased flux through pyruvate dehydrogenase, in the presence of POCA.     

The effect of 5-thioglucose on the energy metabolism of Schistosoma mansoni in vitro

5-Thioglucose (5-TG) had a marked effect on the energy metabolism of Schistosoma mansoni in vitro: the conversion of external glucose into lactate by intact worms was severely inhibited. This inhibition of glycolysis was instantaneous, independent of the oxygen concentration and competitive with respect to glucose. Degradation of 0.5 mM external (14C-labelled) glucose was inhibited for 80% in the presence of 20 mM 5-TG. On the other hand the degradation of endogeneous glycogen to lactate was uninhibited. This shows that the inhibition of glucose breakdown occurred at the entrance of glucose into the cell and/or at the hexokinase reaction. It was demonstrated that 5-TG inhibited both the uptake of glucose and the activity of hexokinase. However, it was concluded that in the intact worm 5-TG blocked glycolysis by its competitive inhibition of hexokinase. In intact S. mansoni worms hexokinase is probably the rate-limiting enzyme of glycolysis. Krebs-cycle activity and lactate production do not occur at a fixed ratio: at lower rates of pyruvate formation Krebs-cycle activity was favoured.     

Methylcyclopentadienyl manganese tricarbonyl increases cell vulnerability to oxidative stress on rat thymocytes

Methylcyclopentadienyl manganese tricarbonyl (MMT) is used as a gasoline antiknock additive. However, the toxic effect of MMT is currently not well understood. In this study, we investigated the toxic effect of MMT on rat thymocytes using a flow cytometer and fluorescent probes. MMT at 100–300?µM significantly increased the population of cells exhibiting propidium fluorescence, i.e., the population of dead cells. The intensity of BES-So-AM fluorescence significantly increased when using 100?µM MMT. In addition, the intensity of oxonol fluorescence in rat thymocytes increased with the treatment with MMT in a concentration-dependent manner (10–100?µM). The toxic effect of MMT was inhibited by quercetin, antioxidant flavonoid. Moreover, co-treatment with 30–100?µM MMT and 100?µM H₂O₂ increased the cell lethality further. These results indicate that MMT increases cell vulnerability to oxidative stress on rat thymocytes. This study provides insight into the toxic effect of MMT on the immune system.     

Fucosterol activates the insulin signaling pathway in insulin resistant HepG2 cells via inhibiting PTP1B

Insulin resistance is a characteristic feature of type 2 diabetes mellitus (T2DM) and is characterized by defects in insulin signaling. This study investigated the modulatory effects of fucosterol on the insulin signaling pathway in insulin-resistant HepG2 cells by inhibiting protein tyrosine phosphatase 1B (PTP1B). In addition, molecular docking simulation studies were performed to predict binding energies, the specific binding site of fucosterol to PTP1B, and to identify interacting residues using Autodock 4.2 software. Glucose uptake was determined using a fluorescent d-glucose analogue and the glucose tracer 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl) amino]-2-deoxyglucose, and the signaling pathway was detected by Western blot analysis. We found that fucosterol enhanced insulin-provoked glucose uptake and conjointly decreased PTP1B expression level in insulin-resistant HepG2 cells. Moreover, fucosterol significantly reduced insulin-stimulated serine (Ser307) phosphorylation of insulin receptor substrate 1 (IRS1) and increased phosphorylation of Akt, phosphatidylinositol-3-kinase, and extracellular signal- regulated kinase 1 at concentrations of 12.5, 25, and 50 µM in insulin-resistant HepG2 cells. Fucosterol inhibited caspase-3 activation and nuclear factor kappa B in insulin-resistant hepatocytes. These results suggest that fucosterol stimulates glucose uptake and improves insulin resistance by downregulating expression of PTP1B and activating the insulin signaling pathway. Thus, fucosterol has potential for development as an anti-diabetic agent.     

The action of quercetin on the mitochondrial NADH to NAD(+) ratio in the isolated perfused rat liver

It has been suggested that active forms of quercetin ( o-semiquinones) are able to oxidize NADH in mammalian cells. The purpose of this study was to investigate this proposition by measuring the beta-hydroxybutyrate to acetoacetate ratio as an indicator of the mitochondrial NADH/NAD (+) redox ratio in the isolated perfused rat liver. The NADH to NAD (+) ratio was reduced by quercetin; half-maximal reduction occurred at a concentration of 32.6 microM. Additionally, quercetin (25 to 300 microM) stimulated the Krebs cycle ( (14)CO (2) production) and inhibited oxygen uptake (50 to 300 microM). Low quercetin concentrations (25 microM) stimulated oxygen uptake. The results of the present work confirm the hypothesis that quercetin is able to participate in the oxidation of NADH in mammalian cells, shifting the cellular conditions to a more oxidized state (prooxidant activity). Stimulation of the Krebs cycle was probably caused by the increased NAD (+) availability whereas the decreased NADH availability and the inhibition of mitochondrial energy transduction could be the main causes for oxygen uptake inhibition.     

Modulation of Glucose Metabolism in Isolated Rat Hepatocytes by 1,1,1,2-Tetrafluoroethane

Modulation of Glucose Metabolism in Isolated Rat Hepatocytesby 1,1,1,2-Tetrafluoroethane. OLSON, M.J., REIDY,C. A., ANDJOHNSON, J.T. (1990). Fundam Appl Toxicol. 15,270–280.The thennodynamic behavior and lack of ozone-depleting potentialof 1,1,1,2-tetrafluoro-ethane (R-134a) suggest it as a likelyreplacement for dichlorodifluoromethane (R-12), now used asthe refrigerant in many air-conditioning systems. To furtherthe presently incomplete toxicological analysis of R- 134a,the effects of R-134a on cell viability and functional competenceof glucose metabolism were evaluated in suspension culturesof hepatocytes derived from fed or fasted rats. R-134a concentrationsup to and including 75% (750,000 ppm) in the gas phase of sealedculture flasks did not produce evidence of cytolethality (LDHleakage) following 2 hr of exposure; in contrast, halothane(l,l,l-trifluoro-2-bromo-2-chloroethane) caused cell death ata gas phase concentration of only 1250 ppm. In hepatocytes isolatedfrom fed rats, R-134a at concentrations of 12.5 to 75% increasedglycolysis (production of lactate + pyruvate) in a concentration-dependentmanner, no effect was observed at 5%. At 25%, R-12 and 1,1,2,2-tetrafluoro-l,2-dichloroethane(R-l14) were of equal potency to R-134a in stimulating glycolysis;l,l,l,2,2-pentafluoro-2-chloroethane (R-115) depressed glycolysisslightly. Halothane, at concentrations as low as 300 ppm, markedlyincreased rates of glycolysis. Glucose production by hepatocytesof fed rats was decreased by R-134a, R-12, and R-114 only atconcentrations of 25% or more. On the other hand, halothane(>300 ppm) potently decreased glucose production by hepatocytes.In cells isolated from livers of fasted rats, R-134a exposureinhibited gluconeo-genesis in a concentration-dependent manneralthough this effect was not significant until R-134a concentrationsreached 12.5%. Comparative potency studies showed that R-l 34a,R-12, or R-l 14 (25% gas phase) inhibited gluconeogenesis aboutequally while as little as 300 ppm halothane was effective andR-115 (25%) was without effect. Considering that the thresholdfor alteration of the rate of glucose metabolism in this invitro paradigm is about 12.5% R-134a, we conclude that toxicologicallysignificant alteration of glucose-linked bioenergetics is unlikelyat the levels of R-l34a exposure anticipated in workplace orenvironment     

Metabolic effects of propofol in the isolated perfused rat liver

Inhibitory effects of the intravenous anaesthetic propofol on mitochondrial energy metabolism have been reported by several authors. Impairment of energy metabolism is usually coupled to reduction in ATP production, which in turn is expected to lead to several alterations in cell metabolism such as stimulation of glycolysis and inhibition of gluconeogenesis. The present work aimed at finding an answer to the question of how propofol affects energy metabolism-linked parameters in the isolated perfused rat liver. In the fed state, propofol increased glycogenolysis (glucose release), glycolysis (lactate and pyruvate production) and oxygen uptake in the range between 10 and 500 microM. In the liver of fasted rats, propofol up to 100 microM increased oxygen uptake but decreased gluconeogenesis from three different substrates: lactate, alanine and glycerol. When lactate was the substrate 50% inhibition occurred at a propofol concentration of 50 microM. Propofol (100 microM) decreased the ATP content of the liver (-33.3%), increased the AMP content (+25%) and decreased the ATP/ADP and ATP/AMP ratios (49 and 45%, respectively). Most effects of propofol are probably due to impairment of oxidative phosphorylation. Particularly, the combined differential action on oxygen uptake (stimulation) and gluconeogenesis (inhibition) is strongly suggestive of an uncoupling action also under the conditions of the intact cell. This effect, in turn, is consistent with the reported high affinity of the cellular hepatic structure, especially membranes, for propofol.     

Inhibition of human liver microsomal cytochrome P450 activities by adefovir and tenofovir

Adefovir (PMEA) and tenofovir (PMPA) and their prodrugs, adefovir dipivoxil (bisPOM-PMEA) and tenofovir disoproxil (bisPOC-PMPA), were subjected to a detailed study of their potential to inhibit the activities of human liver microsomal cytochromes P450 (CYP). The inhibition of marker enzyme activities of CYP1A2, CYP2A6, CYP2B6, CYP2C9, CYP2D6, CYP2E1 and CYP3A4 was examined with high-performance liquid chromatography (HPLC) or spectroscopic (fluorescence, luminescence) detection. Adefovir and adefovir dipivoxil did not significantly influence activities of most CYP enzymes. The activity of CYP3A4 was inhibited by adefovir dipivoxil at concentrations over 100?µM. Adefovir and its prodrug inhibited CYP2C9 at concentrations below 100?µM; inhibition by adefovir was of the uncompetitive (at the lower inhibitor concentrations) or of the competitive nature with a K_i?=?420?µM. Tenofovir and tenofovir disoproxil influenced the activity of CYP2C9, and competitive inhibition was found with K_i?=?580 and 395?µM, respectively. Tenofovir disoproxil was shown to inhibit microsomal CYP2E1 activities by a mixed-type inhibition with K_i values at about 140?µM. The results indicate the possibility of an influence of the compounds tested on the respective CYP activities when used at high doses.     

Inhibitory effect of valproate on weak organic acid uptake in rat renal proximal tubules.

The effects of an antiepileptic drug, valproic acid (VPA), on transport mechanisms involved in renal excretion of anionic xenobiotics were investigated on rat renal proximal tubules in vitro. It was found that VPA (0.1-1 mM) dose dependently inhibited the baseline uptake of a marker organic anion, fluorescein, in the tubules. The inhibition could not be exclusively accounted for by competition between VPA and fluorescein. Taking into account a proposed relationship between the weak organic anion uptake and ammoniagenesis, the influence of VPA (0.5 mM) on the effects of glutamine and glutamate (both at 5 mM) on fluorescein uptake and ammonia production were examined. Glutamine stimulated ammonia production by the tubules, with the glutamine-induced ammoniagenesis being further augmented by VPA, while glutamate failed to affect the basal ammoniagenesis. Both glutamine (5 mM) and glutamate (5 mM) slightly inhibited fluorescein uptake, with the inhibitory effects not modified by VPA. Thus, there was no coincidence in the effects of VPA on organic anion uptake and renal ammoniagenesis. At the same time, the inhibitory effect of VPA (0.5 mM) on fluorescein uptake was largely overcome by addition of pyruvate (5 mM) to the incubation medium. In addition, VPA strongly inhibited glucose production from pyruvate. A known modulator of pyruvate metabolism, dichloroacetic acid (DCA, 1 mM), also inhibited fluorescein uptake, although its inhibitory effect was less pronounced than that of VPA. Both inhibitors failed to alter the tissue content of alpha-ketoglutarate or lactate but did slightly augment the pyruvate level. The inhibitory effects of VPA and DCA on the baseline fluorescein uptake were not additive, suggesting their similar intracellular targeting. It is assumed that the inhibitory effect of VPA on baseline fluorescein uptake in rat renal proximal tubules in vitro may be associated with its action on pyruvate metabolism.     

Inhibitory effect of plant phenolics on fMLP-induced intracellular calcium rise and chemiluminescence of human polymorphonuclear leukocytes and their chemotactic activity in vitro

Abstract

Context: Polymorphonuclear leukocytes (PMNs) produce oxidants, contributing to systemic oxidative stress. Diets rich in plant polyphenols seem to decrease the risk of oxidative stress-induced disorders including cardiovascular disease.

Objective: The objective of this study was to examine the in vitro effect of each of the 14 polyphenols on PMNs chemotaxis, intracellular calcium response, oxidants production.

Materials and methods: Blood samples and PMNs suspensions were obtained from 60 healthy non-smoking donors and incubated with a selected polyphenol (0.5–10?µM) or a control solvent. We assessed resting and fMLP-dependent changes of intracellular calcium concentration ([Ca²⁺]_i) in PMNs with the Fura-2AM method and measured fMLP-induced luminol enhanced whole blood chemiluminescence (fMLP-LBCL). Polyphenol chemoattractant activity for PMNs was tested with Boyden chambers.

Results: Polyphenols had no effect on resting [Ca²⁺]_i. Unaffected by other compounds, fMLP-dependent increase of [Ca²⁺]_i was inhibited by quercetin and catechol (5?µM) by 32?±?14 and 12?±?10% (p?<?0.04), respectively. Seven of the 14 tested substances (5?µM) influenced fMLP-LBCL by decreasing it. Catechol, quercetin, and gallic acid acted most potently reducing fMLP-LBCL by 49?±?5, 42?±?15, and 28?±?18% (p?<?0.05), respectively. 3,4-Dihydroxyhydrocinnamic, 3,4-dihydroxyphenylacetic, 4-hydroxybenzoic acid, and catechin (5?µM) revealed distinct (p?<?0.02) chemoattractant activity with a chemotactic index of 1.9?±?0.8, 1.8?±?0.7, 1.6?±?0.6, 1.4?±?0.2, respectively.

Conclusion and discussion: Catechol, quercetin, and gallic acid at concentrations commensurate in human plasma strongly suppressed the oxidative response of PMNs. Regarding quercetin and catechol, this could result from an inhibition of [Ca²⁺]_i response.     

Effects of derivatives of indole carboxylic acids on carbohydrate metabolism of the rat

Several indole derivatives were characterized on their effects on carbohydrate metabolism in the rat and compared in their insulin-like effects on hepatic gluconeogenesis and glucose consumption in muscle with 5-O-methoxyindole-2-carboxylic acid (MICA) and with indole-3-butyric acid. The substances depressed blood glucose in the fasted adrenalectomized rat at an oral dose of 50–250 mg/kg. Glucose consumption in an isolated muscle preparation was altered only a small amount. In some cases glycogen content of muscle was reduced at a millimolar concentration. All compounds revealed strong inhibition of glucose production from pyruvate in isolated liver slices at a concentration of 10^?4 M. By chemical modification of the indole structure strong inhibitors of gluconeogenesis are obtained. It was not possible to find substances which show a high stimulation of glucose uptake and low activity in inhibiting gluconeogenesis.     

Effects of physiologic concentrations of lactate, pyruvate and ascorbate on glucose metabolism in unstressed and oxidatively stressed human red blood cells

Glucose metabolism was studied in human red blood cells incubated in the presence of physiologic concentrations of ascorbate (0.1 mM) and/or lactate (2 mM) plus pyruvate (0.1 mM). The total flux through glycolysis, as measured by 14C-labeling of glycolytic intermediates, was increased about 15% by ascorbate, 30% by lactate plus pyruvate, and 40% by ascorbate plus lactate plus pyruvate. We found, however, that physiologic concentrations of ascorbate and/or lactate plus pyruvate had no effect on flux of glucose or recycling of pentoses through the hexose monophosphate shunt. Increased formation of lactate accounted for most of the observed increase in glycolysis with little change in pyruvate formation, indicating that the increased flux of reducing equivalents from glucose was stored as lactate rather than being consumed by red cell metabolism. In all experiments, there was a net increase with time in the absolute amount of both lactate and pyruvate in red cell suspensions, indicating that lactate or pyruvate present at zero time did not function as a stoichiometric source or sink for reducing equivalents. There was little effect on steady-state levels of ATP or 2,3-diphosphoglycerate. Equilibration of ascorbate between red cells and the medium was complete before the addition of 14C-labeled glucose to the medium. Glucose metabolism prevented net oxidation of ascorbate in the incubation medium. Physiologic concentrations of ascorbate, lactate and pyruvate appear to increase flux through glycolysis by increasing the turnover of ATP and/or 2,3-diphosphoglycerate. Red cells were exposed to mild oxidative stress by incubation with 0.27 mM 6-hydroxydopamine, 0.27 mM 6-aminodopamine, 0.13 mM 1,4-naphthoquinone-2-sulfonic acid or 0.27 mM phenylhydrazine. The metabolic response to oxidative stress was determined by measuring the formation of methemoglobin, pyruvate, lactate and CO2 in the presence and absence of physiologic concentrations of lactate, pyruvate and ascorbate. Lactate, pyruvate and ascorbate had no effect on the net methemoglobin accumulation but rather on the distribution of the metabolic sources of reducing equivalents and on the flux of reducing equivalents to oxygen. Physiologic lactate and pyruvate allowed increased flow of reducing equivalents from glycolysis to methemoglobin and ultimately oxygen without the necessity of increased flux through glycolysis. This was accomplished by a decrease in the ratio of newly formed lactate to newly formed pyruvate with no increase in total lactate plus pyruvate.(ABSTRACT TRUNCATED AT 400 WORDS)     

The effects of phenformin on the transport and metabolism of sugars by the rat small intestine

The effects of 0.25–10 mM phenformin on sugar transport and metabolism have been studied in a preparation for the combined perfusion of the vascular bed and the lumen. At all concentrations the effects of vascular phenformin were more pronounced than those of luminal phenformin. Phenformin inhibited galactose transport across the intestine, the pattern of inhibition depending on whether the phenformin was added to the luminal or vascular compartments. The active accumulation of galactose in the mucosal epithelial cells was also abolished. There was a linear relationship between the percentage reduction in mucosal ATP levels and vascular phenformin concentration. Phenformin reduced the rate of glucose uptake from the lumen, and the proportion of this glucose which reached the vascular effluent. Most of the glucose which did not reach the vascular side could be accounted for by the formation of lactic acid. Vascular phenformin increased glucose uptake from the vascular medium by ca 88%, 97% of which could be accounted for by lactate formation. Phenformin was sequestered by the mucosa when added to the vascular, but not the luminal, perfusates. There was very little translocation of intact phenformin across the gut in either the mucosal or serosal directions. It is suggested that the effects of phenformin on the gut mainly derive from an inhibition of mitochondrial oxidative phosphorylation, with a small contribution from a direct effect on the brush border, more pronounced at high phenformin concentrations. The results are consistent with the idea that phenformin delays sugar absorption in man, and that the intestine may be a significant source of lactate production in lactic acidosis