Fructose-1,6-bisphosphate as a metabolic substrate in hog ileum smooth muscle during hypoxia

Metabonomic Analysis of the Therapeutic Effects of Chinese Medicine Sanqi Oral Solution on Rats With Exhaustive Exercise

Exhaustive exercise has emerged as an important health issue nowadays. This study was designed to assess the metabolite abnormalities of rats after exhaustive exercise and the holistic efficacy of Chinese medicine Sanqi oral solution (SQ). Through exhaustive swimming, the exhaustive exercise model in rats was established. Thirty male Sprague–Dawley rats were randomly divided into control, model, and treatment groups. SQ (12 mL·kg⁻¹·d⁻¹) or 0.9% saline solution was administrated orally by gastric gavage. After 4 weeks, serum samples were collected for biochemical measurements and ultra performance liquid chromatography (UPLC)/quadrupole time-of-flight mass spectrometry (Q-TOF-MS)-based metabonomic study. It was found that rats with SQ intervention showed longer exhaustive swimming time (P < 0.05) than model rats, with an average of 1,160.36 ± 123.89 s in SQ group and 906.57 ± 172.11 s in model group. Among the biochemical indices, the levels of creatine kinase isoenzyme, lactate dehydrogenase, and glucose of exhaustive exercise rats increased, whereas levels of creatine kinase, urea, triglyceride, and total cholesterol decreased. These biochemical indices came normal after SQ administration, except for triglyceride. Twenty-seven potential biomarkers belonging to sphingolipids, phospholipids, fatty acids, amino acid, and other classes were identified in serum. This study indicated that SQ exerted protective effects on exhaustive exercise by significantly prolonging the swimming endurance time. The metabonomic-based findings of the metabolic state and analysis of potential biomarkers in serum well correlated with biochemical assessment, confirming that SQ had a definite efficacy. Moreover, the shifts in lipid-related metabolites and glycolytic pathway suggested that SQ may serve as a potential supplementation in sports nutrition for its pharmacological effect of regulating energy metabolism as well as improving signal transduction and muscle-cell physiological functions.

Characterization of the high-affinity uptake of fructose-1,6-bisphosphate by cardiac myocytes

Previously, we reported that fructose-1,6-bisphosphate (FBP) was taken up by rat cardiac myocytes by two processes: a component that was saturable at micromolar levels and a nonsaturable component that dominated at millimolar levels. Here, we continued to characterize the saturable high-affinity component, with the aim of identifying the physiological substrate and role for this activity. ATP, ADP, and AMP inhibited the uptake of FBP with apparent affinities of 0.2-0.5 mM. Fumarate and succinate were very weak inhibitors. Several phosphorylated sugars (ribulose-1,5-phosphate, fructose-1-phosphate, ribose-5-phosphate, and inositol-2-phosphate) inhibited FBP uptake with apparent affinities of 40-500 μM. As in our previous study, no tested compound appeared to bind as well as FBP. The data suggest that the best ligands have two phosphoryl groups separated by at least 8 Å. The rates of FBP uptake were measured from 3° to 37°. The calculated activation energy was 15-50 kJ/mol, similar to other membrane transport processes. Uptake of FBP was tested in several types of cells other than cardiac myocytes, and compared to the uptake of 2-deoxyglucose and L: -glucose. While FBP uptake in excess of that of L: -glucose was observed in some cells, in no case was the uptake as high as in cardiac myocytes. The physiological substrate and role for the high-affinity FBP uptake activity remain unknown.

Fructose-1,6-bisphosphate attenuates induction of nitric oxide synthase in microglia stimulated with lipopolysaccharide

AIMS

Fructose-1,6-bisphosphate (FBP) is a glycolytic intermediate with neuroprotective action in various brain injury models. However, the mechanism underlying the neuroprotection of FBP has not been fully defined. In this study, we investigated whether FBP inhibits endotoxin-induced nitric oxide (NO) production and inducible nitric oxide synthase (iNOS) expression in microglial cells and explored the possible mechanisms of the effects of FBP.

MAIN METHODS

Murine microglial cell line BV2 and primary cultured murine microglial cells were used. NO production and iNOS expression were determined by Griess reaction, RT-PCR and Western blot. Luciferase assay using iNOS promoter-luciferase (iNOS-Luc) construct was adopted for measuring transcriptional activity.

KEY FINDINGS

FBP dose-dependently suppressed lipopolysaccharide (LPS)-induced NO production, along with reducing the expression of iNOS at both the protein and mRNA level in primary cultured murine microglia and BV2 cells. FBP significantly inhibited iNOS promoter activity but stabilized iNOS mRNA. Among transcription factors known to be related to iNOS expression, activator protein (AP-1) activation was significantly blocked by FBP. FBP suppressed LPS-induced phosphorylation of three MAPK subtypes-p38 MAPK, JNK and ERK. FBP inhibited LPS-induced production of reactive oxygen species (ROS) and decreased intracellular GSSG/GSH ratio.

SIGNIFICANCE

Our findings suggest that FBP attenuates the LPS-induced iNOS expression through inhibition of JNK and p38 MAPK, which might be related to ROS downregulation.

Oxidative stress and ischemia-reperfusion injury in gastrointestinal tract and antioxidant, protective agents

Exacerbation of hypoxic injury after reoxygenation is a crucial mechanism mediating organ injury in transplantation, and in myocardial, hepatic, gastrointestinal, cerebral, renal, and other ischemic syndromes. The occlusion and reperfusion of the splanchnic artery is a useful animal model to elucidate the mechanism of gastrointestinal injury induced by ischemia-reperfusion (I/R). Although xanthine oxidase is a major source of reactive oxygen species (ROS), which plays an important role in the I/R-induced intestinal injury, there are many other sources of intracellular ROS. Various treatment modalities have been successfully applied to attenuate the I/R injury in animal models. This review focuses on the role of oxidant stress in the mechanism of I/R injury and the use of antioxidant agents for its treatment.

Fructose-1,6-bisphosphate does not preserve ATP in hypoxic-ischemic neonatal cerebrocortical slices

Fructose-1,6-bisphosphate (FBP), an endogenous intracellular metabolite in glycolysis, was found in many preclinical studies to be neuroprotective during hypoxia-ischemia (HI) when administered exogenously. We looked for HI neuroprotection from FBP in a neonatal rat brain slice model, using 14.1 T (1)H/(31)P/(13)C NMR spectroscopy of perchloric acid slice extracts to ask: 1) if FBP preserves high energy phosphates during HI; and 2) if exogenous [1-(13)C]FBP enters cells and is glycolytically metabolized to [3-(13)C]lactate. We also asked: 3) if substantial superoxide production occurs during and after HI, thinking such might be treatable by exogenous FBP's antioxidant effects. Superfused P7 rat cerebrocortical slices (350 mum) were treated with 2 mM FBP before and during 30 min of HI, and then given 4 h of recovery with an FBP-free oxygenated superfusate. Slices were removed before HI, at the end of HI, and at 1 and 4 h after HI. FBP did not improve high energy phosphate levels or change (1)H metabolite profiles. Large increases in [3-(13)C]lactate were seen with (13)C NMR, but the lactate fractional enrichment was always (1.1+/-0.5)%, implying that all of lactate's (13)C was natural abundance (13)C, that none was from metabolism of (13)C-FBP. FBP had no effect on the fluorescence of ethidium produced from superoxide oxidation of hydroethidine. Compared to control slices, ethidium fluorescence was 25% higher during HI and 50% higher at the end of recovery. Exogenous FBP did not provide protection or enter glycolysis. Its use as an antioxidant might be worth studying at higher FBP concentrations.

NKCC2 surface expression in mammalian cells: down-regulation by novel interaction with aldolase B

Apical bumetanide-sensitive Na(+)-K(+)-2Cl(-) co-transporter, termed NKCC2, is the major salt transport pathway in kidney thick ascending limb. NKCC2 surface expression is subject to regulation by intracellular protein trafficking. However, the protein partners involved in the intracellular trafficking of NKCC2 remain unknown. Moreover, studies aimed at under-standing the post-translational regulation of NKCC2 have been hampered by the difficulty to express NKCC2 protein in mammalian cells. Here we were able to express NKCC2 protein in renal epithelial cells by tagging its N-terminal domain. To gain insights into the regulation of NKCC2 trafficking, we screened for interaction partners of NKCC2 with the yeast two-hybrid system, using the C-terminal tail of NKCC2 as bait. Aldolase B was identified as a dominant and novel interacting protein. Real time PCR on renal microdissected tubules demonstrated the expression of aldolase B in the thick ascending limb. Co-immunoprecipitation and co-immunolocalization experiments confirmed NKCC2-aldolase interaction in renal cells. Biotinylation assays showed that aldolase co-expression reduces NKCC2 surface expression. In the presence of aldolase substrate, fructose 1,6-bisphosphate, aldolase binding was disrupted, and aldolase co-expression had no further effect on the cell surface level of NKCC2. Finally, functional studies demonstrated that aldolase-induced down-regulation of NKCC2 at the plasma membrane was associated with a decrease in its transport activity. In summary, we identified aldolase B as a novel NKCC2 binding partner that plays a key role in the modulation of NKCC2 surface expression, thereby revealing a new regulatory mechanism governing the co-transporter intracellular trafficking. Furthermore, NKCC2 protein expression in mammalian cells and its regulation by protein-protein interactions, described here, may open new and important avenues in studying the cell biology and post-transcriptional regulation of the co-transporter.

Permeability of fructose-1,6-bisphosphate in liposomes and cardiac myocytes

Fructose-1,6-bisphosphate (FBP) helps preserve heart and other organs under ischemic conditions. Previous studies indicated that it can be taken up by various cell types. Here we extended observations from our group that FBP could penetrate artificial lipid bilayers and be taken up by cardiac myocytes, comparing the uptake of FBP to that of L-glucose. Using liposomes prepared by the freeze-thaw method, FBP entered about 200-fold slower than L-glucose. For liposomes of either soybean or egg lipids, 50 mM FBP enhanced the permeability of FBP itself, with little effect on general permeability (measured by uptake of L-glucose). In experiments with isolated cardiac myocytes at 21 degrees C, FBP uptake exceeded the uptake of L-glucose by several fold and appeared to equilibrate by 60 min. There was both a saturable component at micromolar levels and a nonsaturable component which dominated at millimolar levels. The saturable component was inhibited by Pi and by other phosphorylated sugars, though with lower affinity than FBP. Both saturable and nonsaturable uptakes were also observed at 3 degrees C. The results indicate that FBP enters myocytes not by simple penetration through the lipid bilayer, but via at least two distinct protein-dependent processes. The uptake could lead to intracellular effects important in hypothermic heart preservation.

Protective effects of exogenous fructose-1,6-biphosphate during small bowel transplantation in rats

BACKGROUND

We assessed the effect of adding exogenous fructose-1,6-biphosphate (F16BP) to the preservation solution (University of Wisconsin storage solution) used during an experimental procedure of small bowel transplantation in rats.

METHODS

We studied levels of the nucleotides hypoxanthine/xanthine and adenosine in tissue after cold ischemia, as well as histologic changes and associated deleterious processes such as bacterial translocation produced by the reperfusion associated with the transplantation.

RESULTS

The groups of rats treated with F16BP showed the lowest levels of hypoxanthine/xanthine and uric acid, the highest levels of adenosine, and the lowest levels of histologic damage and lactate dehydrogenase release to the bloodstream. Consumption of intestinal hypoxanthine during reperfusion was lowest in the groups treated with F16BP, as was the incidence of bacterial translocation.

CONCLUSIONS

This study shows a protective effect of exogenous F16BP added to University of Wisconsin solution during experimental intestinal transplantation in rats. This protective effect, reflected by decreased intestinal damage and bacterial translocation, was related to a decrease in adenosine triphosphate depletion during cold ischemia before intestinal transplantation, and to the reduced availability of xanthine oxidase substrates for free radical generation during reperfusion.

Effects of n-3 fatty acid, fructose-1, 6-diphosphate and glutamine on mucosal cell proliferation and apoptosis of small bowel graft after transplantation in rats

AIM: To evaluate the effects of n-3 fatty acids (n-3FA), fructose-1, 6-diphosphate (FDP) and glutamine (GLN) on mucosal cell proliferation and apoptosis of small bowel graft.

METHODS: One hundred and ninety-six inbred strain Wistar rats were grouped as donors and recipients, and underwent heterotopic small bowel transplantation (SBT). n-3FA, FDP and GLN were administered via gastric tube as well as venous infusion for 10 d before and after surgery, respectively. The proliferation and apoptosis of mucosal cells were analyzed with flow cytometry and in situ cell death detection kits.

RESULTS: Apparent apoptosis and minor proliferation of mucosal cells of small bowel graft after transplantation were observed. A higher mucosal cell proliferative index and lower apoptotic index were found in all small bowel grafts after supplying with n-3FA, FDP and GLN.

CONCLUSION: Nutritional support with n-3FA, FDP and GLN promotes mucosal cell proliferation significantly, and prevents mucosal cell from undergoing apoptosis with different degrees. These regulatory effects on the apoptosis alter the structure and absorption function of transplanted small bowel favorably.

Fructose-1,6-biphosphate and nucleoside pool modifications prevent neutrophil accumulation in the reperfused intestine

Fructose-1,6-biphosphate (F16BP) attenuates ischemia/reperfusion (I/R) injury by inhibiting microvascular leukocyte adhesion or reducing neutrophil-derived oxygen free-radical production, but the causes of this action, the mechanisms in vivo, and the possible implication of nucleoside pool modifications are still controversial issues. We explored whether F16BP's inhibition of free-radical production and neutrophil recruitment is a result of its effect on adenosine (Ado) accumulation during intestinal I/R injury. The effects of F16BP administration were tested on the nucleotide/nucleoside metabolism at the end of the ischemic period and on microvascular neutrophil recruitment and free-radical production after reperfusion in vivo, in the presence or absence of Ado deaminase (ADA). Infusion of F16BP markedly increased endogenous Ado, decreased xanthine accumulation during the ischemic period, and inhibited neutrophil recruitment and subsequent neutrophil free-radical generation during reperfusion. Administration of ADA reversed these processes. The results provide strong evidence that F16BP prevents neutrophil accumulation and neutrophil free-radical generation during intestinal I/R by a key mechanism that modifies the nucleoside pool, leading to an endogenous accumulation of Ado and to a reduction of xanthine during ischemia.

Destabilizing effects of fructose-1,6-bisphosphate on membrane bilayers

Fructose-1,6-bisphosphate (FBP) is a high-energy glycolytic intermediate that decreases the effects of ischemia; it has been used successfully in organ perfusion and preservation. How the cells utilize external FBP to increase energy production and the mechanism by which the molecule crosses the membrane bilayer are unclear. This study examined the effects ofFBP on membrane bilayer permeability, membrane fluidity, phospholipid packing, and membrane potential to determine how FBP crosses the membrane bilayer. Large unilamellar vesicles composed of egg phosphatidylcholine (Egg PC) were made and incubated with 50 mM FBP spiked with 14C-FBP at 30 degrees C. Uptake of FBP was significant (P < 0.05) and dependent on the lipid concentration, suggesting that FBP affects membrane bilayer permeability. With added calcium (10 mM), FBP uptake by lipid vesicles decreased significantly (P < 0.05). Addition of either 5 or 50 mM FBP led to a significant increase (P < 0.05) in Egg PC carboxyfluorescein leakage. We hypothesized that the membrane-permeabilizing effects of FBP may be due to a destabilization of the membrane bilayer. Small unilamellar vesicles composed of dipalmitoyl pC (DPPC) were made containing either diphenyl-1,3,5-hexatriene (DPH) or trimethylammmonia-DPH (TMA-DPH) and the effects of FBP on the fluorescence anisotropy (FA) of the fluorescent labels examined. FBP caused a significant decrease in the FA of DPH in the liquid crystalline state of DPPC (P < 0.05), had no effect on FA of TMA-DPH in the liquid crystalline state of DPPC, but increased the FA of TMA-DPH in the gel state of DPPC. From phase transition measurements with DPPC/DPH or TMA-DPH, we calculated the slope of the phase transition as an indicator of the cooperativity of the DPPC molecules. FBP significantly decreased the slope, suggesting a decrease in fatty acyl chain interaction (P< 0.05). The addition of 50 mM FBP caused a significant decrease (P< 0.05) in the liquid crystalline/gel state fluorescence ratio of merocyanine 540, indicating increased head-group packing. To determine what effects these changes would have on cellular membranes, we labeled human endothelial cells with the membrane potential probe 3,3'-dipropylthiacarbocyanine iodide (DiSC3) and then added FBP. FBP caused a significant, dose-dependent decrease in DiSC3 fluorescence, indicating membrane depolarization. We suggest that FBP destabilizes membrane bilayers by decreasing fatty acyl chain interaction, leading to significant increases in membrane permeability that allow FBP to diffuse into the cell where it can be used as a glycolytic intermediate.

Fructose- 1,6-bisphosphate did not affect hippocampal neuronal damage caused by 10 min of complete umbilical cord occlusion in fetal sheep

Fructose-1, 6-bisphosphate (FBP) has a neuroprotective effect in neonatal and adult rats. The purpose of this study was to examine the effects of FBP on hippocampal neuronal damage in fetal sheep asphyxiated by 10 min of complete umbilical cord occlusion. Thirteen fetal sheep at 124 days of gestation were surgically instrumented with catheters. Cardiorespiratory parameters were monitored, and biochemical analyses were performed with the blood samples. During the insult seven fetuses were given FBP (500 mg/kg) and six were given iso-osmotic saline, and hippocampal neuronal damage was examined histologically and scored. Cardiorespiratory changes were the same in both groups, and there was no neuroprotective effect of FBP in this study. However the decrease of serum total Ca level implied the Ca- chelating effect of FBP.

The uptake and metabolism of fructose-1,6-diphosphate in rat cardiomyocytes

Fructose-1,6-diphosphate (FDP) is a glycolytic intermediate which has been theorized to increase the metabolic activity of ischemic tissues. Here we examine the effects of externally applied FDP on cardiomyocyte uptake and metabolism. Adult rat cardiomyocytes were isolated and exposed to varying concentrations (0, 5, 25 and 50 mM) of FDP for either 1, 16 or 24 h of hypoxia (95% N2/5% CO2), each time period followed by a 1 h reoxygenation (95% air/5% CO2). The uptake of FDP by rat cardiomyocytes was more concentration-dependent than time-dependent. Furthermore, the uptake of FDP by the cardiomyocytes was similar in the hypoxia and normoxia treated cells. Alamar Blue, a redox indicator that is sensitive to metabolic activity, was used to monitor the effects of the FDP on cardiomyocyte metabolism. In the 1 h hypoxia or normoxia group, the 5, 10 and 25 mM FDP showed a significant increase in metabolism compared to the control cells. When the length of hypoxia was extended to 16 h, all doses of FDP were greater than control. And at the 24 h hypoxia or normoxia time period, only the 10, 25 and 50 mM FDP groups were greater than control. The results indicate a non-linear trend between the external concentration of FDP and the changes noted in metabolism. The findings from this study indicate that a narrow concentration range between 5-10 mM augments cardiomyocyte metabolism, but higher or lower doses may have little additional affect.

Membrane permeability of fructose-1,6-diphosphate in lipid vesicles and endothelial cells

Fructose-1,6-diphosphate (FDP) is a glycolytic intermediate which has been used an intervention in various ischemic conditions for two decades. Yet whether FDP can enter the cell is under constant debate. In this study we examined membrane permeability of FDP in artificial membrane bilayers and in endothelial cells. To examine passive diffusion of FDP through the membrane bilayer, L-alpha-phosphatidylcholine from egg yolk (Egg PC) (10 mM) multi-lamellar vesicles were created containing different external concentrations of FDP (0, 0.5, 5 and 50 mM). The passive diffusion of FDP into the vesicles was followed spectrophotometrically. The results indicate that FDP diffuses through the membrane bilayer in a dose-dependent fashion. The movement of FDP through Egg PC membrane bilayers was confirmed by measuring the conversion of FDP to dihydroxyacetone-phosphate and the formation of hydrozone. FDP (0, 0.5, 5 or 50 mM) was encapsulated in Egg PC multilamellar vesicles and placed in a solution containing aldolase. In the 5 and 50 mM FDP groups there was a significant increase in dihydroxyacetone/hydrazone indicating that FDP crossed the membrane bilayer intact. We theorized that the passive diffusion of FDP might be due to disruption of the membrane bilayer. To examine this hypothesis, small unilamellar vesicles composed of Egg PC were created in the presence of 60 mM carboxyfluorescein, and the leakage of the sequestered dye was followed upon addition of various concentrations of FDP, fructose, fructose-6-phosphate, or fructose-1-phosphate (0, 5 or 50 mM). These results indicate that increasing concentrations of FDP increase the leakage rate of carboxyfluorescein. In contrast, no concentration of fructose, fructose-6-phosphate, or fructose-1-phosphate resulted in any significant increase in membrane permeability to carboxyfluorescein. To examine whether FDP could pass through cellular membranes, we examined the uptake of 14C-FDP by endothelial cells cultured under hypoxia or normoxia for 4 or 16 h. The uptake of FDP was dose-dependent in both the normoxia and hypoxia treated cells, and was accompanied by no significant loss in endothelial cell viability. Our results demonstrate that FDP can diffuse through membrane bilayers in a dose-dependent manner.

Fructose-1,6-diphosphate and a glucose-free solution enhances functional recovery in hypothermic heart preservation

BACKGROUND

Fructose-1,6-diphosphate (FDP) has been shown to protect tissue during hypoxia under various ischemic conditions, including isolated heart perfusion. We tested the hypothesis that adding FDP to St. Thomas solution can extend hypothermic heart preservation time.

METHODS

Sixteen adult Sprague-Dawley rats were used. Under general anesthesia, the hearts were removed and preserved at 4 degrees C in St. Thomas solution (30 ml/kg) for 12 hours. FDP (5 mM) was added to the St. Thomas solution in the study group (n = 8), whereas no FDP was used in the control group (n = 10). The hearts were reperfused after 12 hours of preservation using a working heart model.

RESULTS

In the study group, cardiac output ranged from 13.00 +/- 2.34 to 17.66 +/- 1.71 ml/min, maximum aortic flow was 3.40 +/- 1.99 to 9.26 +/- 1.72 ml/min, left ventricular stroke volume ranged from 0.074 +/- 0.014 to 0.092 +/- 0.009 ml, left ventricular stroke work ranged from 6.22 +/- 0.39 to 7.95 +/- 0.44 ml/mmHg, and maximum left ventricular generated power was 14.38 +/- 2.94 to 20.16 +/- 2.49 Joules/min. All of these parameters were higher than those in the control group (p < 0.001). Coronary vascular resistance and myocardial tissue wet/dry weight ratio were lower in the study group than in the control group (p < 0.05).

CONCLUSIONS

Heart function was better preserved when FDP was added to St. Thomas solution during hypothermic rat heart preservation. The mechanism is not totally clear, but enhancement of high-energy phosphate production during ischemia is possible. Key words: heart, procurement, hypothermia, fructose-1,6-diphosphate.

Transport and metabolism of exogenous fumarate and 3-phosphoglycerate in vascular smooth muscle

The keto (linear) form of exogenous fructose 1,6-bisphosphate, a highly charged glycolytic intermediate, may utilize a dicarboxylate transporter to cross the cell membrane, support glycolysis, and produce ATP anaerobically. We tested the hypothesis that fumarate, a dicarboxylate, and 3-phosphoglycerate (3-PG), an intermediate structurally similar to a dicarboxylate, can support contraction in vascular smooth muscle during hypoxia. To assess ATP production during hypoxia we measured isometric force maintenance in hog carotid arteries during hypoxia in the presence or absence of 20 mM fumarate or 3-PG. 3-PG improved maintenance of force (p < 0.05) during the 30-80 min period of hypoxia. Fumarate decreased peak isometric force development by 9.5% (p = 0.008) but modestly improved maintenance of force (p < 0.05) throughout the first 80 min of hypoxia. 13C-NMR on tissue extracts and superfusates revealed 1,2,3,4-(13)C-fumarate (5 mM) metabolism to 1,2,3,4-(13)C-malate under oxygenated and hypoxic conditions suggesting uptake and metabolism of fumarate. In conclusion, exogenous fumarate and 3-PG readily enter vascular smooth muscle cells, presumably by a dicarboxylate transporter, and support energetically important pathways.