Exogenous fructose 1,6-bisphosphate reduces K+ permeability in isolated rat hepatocytes

A fully integrated new paradigm for lithium's mode of action - lithium utilizes latent cellular fail-safe mechanisms

It is proposed that lithium's therapeutic effects occur indirectly by augmenting a cascade of protective "fail-safe" pathways pre-configured to activate in response to a dangerous low cell [Mg⁺⁺] situation, eg, posttraumatic brain injury, alongside relative cell adenosine triphosphate depletion. Lithium activates cell protection, as it neatly mimics a lowered intracellular [Mg⁺⁺] level.

Altered expression profile of glycolytic enzymes during testicular ischemia reperfusion injury is associated with the p53/TIGAR pathway: effect of fructose 1,6-diphosphate

Background. Testicular ischemia reperfusion injury (tIRI) is considered the mechanism underlying the pathology of testicular torsion and detorsion. Left untreated, tIRI can induce testis dysfunction, damage to spermatogenesis and possible infertility. In this study, we aimed to assess the activities and expression of glycolytic enzymes (GEs) in the testis and their possible modulation during tIRI. The effect of fructose 1,6-diphosphate (FDP), a glycolytic intermediate, on tIRI was also investigated. Methods. Male Sprague-Dawley rats were divided into three groups: sham, unilateral tIRI, and tIRI + FDP (2 mg/kg). tIRI was induced by occlusion of the testicular artery for 1 h followed by 4 h of reperfusion. FDP was injected peritoneally 30 min prior to reperfusion. Histological and biochemical analyses were used to assess damage to spermatogenesis, activities of major GEs, and energy and oxidative stress markers. The relative mRNA expression of GEs was evaluated by real-time PCR. ELISA and immunohistochemistry were used to evaluate the expression of p53 and TP53-induced glycolysis and apoptosis regulator (TIGAR). Results. Histological analysis revealed tIRI-induced spermatogenic damage as represented by a significant decrease in the Johnsen biopsy score. In addition, tIRI reduced the activities of hexokinase 1, phosphofructokinase-1, glyceraldehyde 3-phosphate dehydrogenase, and lactate dehydrogenase C. However, mRNA expression downregulation was detected only for hexokinase 1, phosphoglycerate kinase 2, and lactate dehydrogenase C. ATP and NADPH depletion was also induced by tIRI and was accompanied by an increased Malondialdehyde concentration, reduced glutathione level, and reduced superoxide dismutase and catalase enzyme activities. The immunoexpression of p53 and TIGAR was markedly increased after tIRI. The above tIRI-induced alterations were attenuated by FDP treatment. Discussion. Our findings indicate that tIRI-induced spermatogenic damage is associated with dysregulation of GE activity and gene expression, which were associated with activation of the TIGAR/p53 pathway. FDP treatment had a beneficial effect on alleviating the damaging effects of tIRI. This study further emphasizes the importance of metabolic regulation for proper spermatogenesis.

Mechanisms of astrocytic K(+) clearance and swelling under high extracellular K(+) concentrations

In response to the elevation of extracellular K(+) concentration ([K(+)]out), astrocytes clear excessive K(+) to maintain conditions necessary for neural activity. K(+) clearance in astrocytes occurs via two processes: K(+) uptake and K(+) spatial buffering. High [K(+)]out also induces swelling in astrocytes, leading to edema and cell death in the brain. Despite the importance of astrocytic K(+) clearance and swelling, the underlying mechanisms remain unclear. Here, we report results from a simulation analysis of astrocytic K(+) clearance and swelling. Astrocyte models were constructed by incorporating various mechanisms such as intra/extracellular ion concentrations of Na(+), K(+), and Cl(-), cell volume, and models of Na,K-ATPase, Na-K-Cl cotransporter (NKCC), K-Cl cotransporter, inwardly-rectifying K(+) (KIR) channel, passive Cl(-) current, and aquaporin channel. The simulated response of astrocyte models under the uniform distribution of high [K(+)]out revealed significant contributions of NKCC and Na,K-ATPase to increases of intracellular K(+) and Cl(-) concentrations, and swelling. Moreover, we found that, under the non-uniform distribution of high [K(+)]out, KIR channels localized at synaptic clefts absorbed excess K(+) by depolarizing the equivalent potential of K(+) (E K) above membrane potential, while K(+) released through perivascular KIR channels was enhanced by hyperpolarizing E K and depolarizing membrane potential. Further analysis of simulated drug effects revealed that astrocyte swelling was modulated by blocking each of the ion channels and transporters. Our simulation analysis revealed controversial mechanisms of astrocytic K(+) clearance and swelling resulting from complex interactions among ion channels and transporters.

Efficiency of primary saliva secretion: an analysis of parameter dependence in dynamic single-cell and acinus models, with application to aquaporin knockout studies

Secretion from the salivary glands is driven by osmosis following the establishment of osmotic gradients between the lumen, the cell and the interstitium by active ion transport. We consider a dynamic model of osmotically driven primary saliva secretion and use singular perturbation approaches and scaling assumptions to reduce the model. Our analysis shows that isosmotic secretion is the most efficient secretion regime and that this holds for single isolated cells and for multiple cells assembled into an acinus. For typical parameter variations, we rule out any significant synergistic effect on total water secretion of an acinar arrangement of cells about a single shared lumen. Conditions for the attainment of isosmotic secretion are considered, and we derive an expression for how the concentration gradient between the interstitium and the lumen scales with water- and chloride-transport parameters. Aquaporin knockout studies are interpreted in the context of our analysis and further investigated using simulations of transport efficiency with different membrane water permeabilities. We conclude that recent claims that aquaporin knockout studies can be interpreted as evidence against a simple osmotic mechanism are not supported by our work. Many of the results that we obtain are independent of specific transporter details, and our analysis can be easily extended to apply to models that use other proposed ionic mechanisms of saliva secretion.

Fructose 1,6 biphosphate administration to rats prevents metabolic acidosis and oxidative stress induced by deep hypothermia and rewarming

Fructose 1,6 biphosphate (F1,6BP) exerts a protective effect in several in vitro models of induced injury and in isolated organs; however, few studies have been performed using in vivo hypothermia. Here we studied the effects of deep hypothermia (21ºC) and rewarming in anaesthetised rats after F1,6BP administration (2 g/kg body weight). Acid-base and oxidative stress parameters (plasma malondialdehyde and glutathione, and erythrocyte antioxidant enzymes) were evaluated. Erythrocyte and leukocyte numbers in blood and plasma nitric oxide were also measured 3 h after F1,6BP administration in normothermia animals. In the absence of F1,6BP metabolic acidosis developed after rewarming. Oxidative stress was also evident after rewarming, as shown by a decrease in thiol groups and in erythrocyte superoxide dismutase, catalase and GSH-peroxidase, which corresponded to an increase in AST in rewarmed animals. These effects were reverted in rats treated with F1,6BP. Blood samples of F1,6BP-treated animals showed a significant increase in plasma nitric oxide 3 h after administration, coinciding with a significant rise in leukocyte number. F1,6BP protection may be due to the decrease in oxidative stress and to the preservation of the antioxidant pool. In addition, we propose that the reduction in extracellular acidosis may be due to improved tissue perfusion during rewarming and that nitric oxide may play a central role.

Fructose 1,6-bisphosphate reduced TNF-alpha-induced apoptosis in galactosamine sensitized rat hepatocytes through activation of nitric oxide and cGMP production

Fructose 1,6-P2 (F1,6BP) protects rat liver against experimental hepatitis induced by galactosamine (GalN) by means of two parallel effects: prevention of inflammation, and reduction of hepatocyte sensitization to tumour necrosis factor-alpha (TNF-alpha). In a previous paper we reported the underlying mechanism involved in the prevention of inflammation. In the present study, we examined the intracellular mechanisms involved in the F1,6BP inhibition of the apoptosis induced by TNF-alpha in parenchyma cells of GalN-sensitized rat liver. We hypothesized that the increased nitric oxide (NO) production in livers of F1,6BP-treated rats mediates the antiapoptotic effect. This hypothesis was evaluated in cultured primary rat hepatocytes challenged by GalN plus tumour necrosis factor-alpha (GalN+TNF-alpha), to reproduce in vitro the injury associated with experimental hepatitis. Our results show a reduction in apoptosis concomitant with an increase in NO production and with a reduction in oxidative stress. In such conditions, guanylyl cyclase is activated and the increase in cGMP reduces the TNF-alpha-induced apoptosis in hepatocytes. These results provide new insights in the protective mechanism activated by F1,6BP and confirm its interest as a hepatoprotective agent.

Ionic mechanisms of cardiac cell swelling induced by blocking Na+/K+ pump as revealed by experiments and simulation

Although the Na⁺/K⁺ pump is one of the key mechanisms responsible for maintaining cell volume, we have observed experimentally that cell volume remained almost constant during 90 min exposure of guinea pig ventricular myocytes to ouabain. Simulation of this finding using a comprehensive cardiac cell model (Kyoto model incorporating Cl⁻ and water fluxes) predicted roles for the plasma membrane Ca²⁺-ATPase (PMCA) and Na⁺/Ca²⁺ exchanger, in addition to low membrane permeabilities for Na⁺ and Cl⁻, in maintaining cell volume. PMCA might help maintain the [Ca²⁺] gradient across the membrane though compromised, and thereby promote reverse Na⁺/Ca²⁺ exchange stimulated by the increased [Na⁺]_i as well as the membrane depolarization. Na⁺ extrusion via Na⁺/Ca²⁺ exchange delayed cell swelling during Na⁺/K⁺ pump block. Supporting these model predictions, we observed ventricular cell swelling after blocking Na⁺/Ca²⁺ exchange with KB-R7943 or SEA0400 in the presence of ouabain. When Cl⁻ conductance via the cystic fibrosis transmembrane conductance regulator (CFTR) was activated with isoproterenol during the ouabain treatment, cells showed an initial shrinkage to 94.2 ± 0.5%, followed by a marked swelling 52.0 ± 4.9 min after drug application. Concomitantly with the onset of swelling, a rapid jump of membrane potential was observed. These experimental observations could be reproduced well by the model simulations. Namely, the Cl⁻ efflux via CFTR accompanied by a concomitant cation efflux caused the initial volume decrease. Then, the gradual membrane depolarization induced by the Na⁺/K⁺ pump block activated the window current of the L-type Ca²⁺ current, which increased [Ca²⁺]_i. Finally, the activation of Ca²⁺-dependent cation conductance induced the jump of membrane potential, and the rapid accumulation of intracellular Na⁺ accompanied by the Cl⁻ influx via CFTR, resulting in the cell swelling. The pivotal role of L-type Ca²⁺ channels predicted in the simulation was demonstrated in experiments, where blocking Ca²⁺ channels resulted in a much delayed cell swelling.

Fructose 1,6-bisphosphate prevented endotoxemia, macrophage activation, and liver injury induced by D-galactosamine in rats

OBJECTIVE

Fructose 1,6-bisphosphate (F1,6BP) protects organs against a wide range of challenges involving inflammation. We hypothesized that the primary action of F1,6BP is to prevent macrophage activation and cytokine release. Our aim was to determine the tissue and cellular targets for this bisphosphorylated sugar and to provide new insights into its mechanisms of action.

DESIGN

Prospective, controlled laboratory study.

SETTING

Animal resource facilities and research laboratory.

SUBJECTS

Male Sprague-Dawley rats (200-250 g body weight).

INTERVENTIONS

The protective action of F1,6BP was analyzed in galactosamine (GalN)-induced hepatitis in rats. The in vivo effects of F1,6BP were evaluated by changes in transaminase activities, blood endotoxins, and tumor necrosis factor (TNF)-alpha production in GalN-challenged rats. The targets of F1,6BP to reduce macrophage response to lipopolysaccharide (LPS) were determined by correlation between changes in TNF-alpha production and K+ fluxes through cell membrane in primary cultures of Kupffer cells.

MEASUREMENTS AND MAIN RESULTS

The in vivo results indicate that F1,6BP treatment prevented GalN-induced injury in liver parenchymal cells. This protection was mainly associated with a reduction of the inflammatory response. F1,6BP prevention of GalN-induced endotoxemia correlated with preclusion of mast cell degranulation and histamine release that preceded the increased plasma endotoxins and liver production of TNF-alpha. In addition, F1,6BP treatment decreased sensitivity to LPS, which reduced the GalN-induced increase in TNF-alpha. The in vitro results show that F1,6BP inhibited Kupffer cell response and reduced TNF-alpha production by preventing LPS-induced K+ channel activation.

CONCLUSIONS

The role of exogenous F1,6BP as a K+ channel modulator underlies its antihistaminic and anti-inflammatory action and increases its interest as a protective compound.

Fructose-1,6 diphosphate as a protective agent for experimental ischemic acute renal failure

Cold ischemia time is a risk factor for the development of acute renal failure in the immediate post-transplant period. In this study, we aimed to determine if intravenous fructose-1,6-diphosphate (FDP), given before nephrectomy, attenuates renal cell injury in a cold ischemia model. Male adult Wistar rats were subjected to infusion of either FDP 350 mg/kg (group F, n=6), an equal volume of 0.9% NaCl (group S, n=6), an equal volume/osmolality of mannitol (group M, n=6) or no infusion (group C, n=7). Kidneys were then perfused in situ with Collins solution and nephrectomy was performed. Other kidney slices were stored in Collins solution at 4 degrees C. Adenosine triphosphate (ATP) levels and lactate dehydrogenase (LDH) release were examined at 0, 24, 48 and 72 h. Other slices, obtained after 50 min immersion in Collins solution at 37 degrees C, were frozen for characterization of cytoskeletal preservation using phalloidin-FITC staining. Apical fluorescence intensity of proximal tubule cells, indicative of the F-actin concentration, was measured in a fluorescence microscope interfaced with computer image analysis system. Adenosine triphosphate levels, after up to 72 h of tissue incubation, were higher (P<0.05) in the FDP group when compared to other groups. In addition, LDH release was smaller (P<0.0001) in the FDP group. The F-actin concentration of proximal tubule cells cells was greater in the FDP group (P<0.0001). Results indicate that FDP is a useful tool to increase tissue viability in a rat kidney subjected to cold ischemia, by maintaining ATP cell content, decreasing LDH release and preventing microfilament disruption of proximal tubule cells.

Molecular mechanisms of cation transport by the renal Na+-K+-Cl- cotransporter: structural insight into the operating characteristics of the ion transport sites

Two variants of the renal Na(+)-K(+)-Cl(-) cotransporter (NKCC2), called NKCC2A and NKCC2F, display marked differences in Na(+), Rb(+), and Cl(-) affinities, yet are identical to one another except for a 23-residue membrane-associated domain that is derived from alternatively spliced exons. The proximal portion of these exons is predicted to encode the second transmembrane domain (tm2) in the form of an alpha-helix, and the distal portion, part of the following connecting segment (cs1a). In recent studies, we have taken advantage of the A-F differences in kinetic behavior to determine which regions in tm2-cs1a are involved in ion transport. Functional characterizations of chimeras in which tm2 or cs1a were interchanged between the variants showed that both regions are important in specifying ion affinities, but did not allow delineating the contribution of individual residues. Here, we have extended these structure-function analyses by studying additional mutants in which variant residues between A and F were interchanged individually in the tm2-cs1a region (amino acid number 216, 220, 223, 229, or 233 in NKCC2). None of the substitutions were found to affect K(m (C1-)), suggesting that the affinity difference for anion transport is conveyed by a combination of variant residues in this domain. However, 2 substitutions in the tm2 of F were found to affect cation constants specifically; interestingly, one of these mutations (residue 216) only affected K(m (Rb+)) while the other (residue 220) only affected K(m (Na+)). We have thus identified two novel residues in NKCC2 that play a key role in cation transport. Because such residues should be adjacent to one another on the vertical axis of the tm2 alpha-helix, our results imply, furthermore, that the ion transport sites in NKCC2 could be physically linked.

Frutose em humanos: efeitos metabólicos, utilização clínica e erros inatos associados

Revisa-se o metabolismo da frutose e do sorbitol, suas principais indicações e conseqüências decorrentes do uso inadequado. A frutose é um importante carboidrato da dieta, sendo encontrada principalmente nas frutas e vegetais, e é produzida no organismo a partir da glicose pela via do sorbitol. A frutose é conhecida pelos erros inatos do seu metabolismo, cujas manifestações clínicas são potencialmente graves, e por seu uso como substituta da glicose na dieta de diabéticos, visto não depender da insulina para o seu metabolismo. Nos últimos anos, especialmente em países desenvolvidos, seu consumo tem aumentado acentuadamente em virtude do emprego como adoçante em produtos industrializados. Porém, o uso excessivo de frutose não é isento de efeitos adversos, representados pelo aumento de triglicerídios e de colesterol no sangue. O conhecimento dos níveis sangüíneos normais é importante tanto para estabelecer a quantidade segura a ser administrada, como para permitir avaliar doenças metabólicas associadas à frutose.

Apoptosis inhibition during preservation by fructose-1,6-diphosphate and theophylline in rat intestinal transplantation

OBJECTIVE

This study evaluated the effect of fructose-1,6-diphosphate (FDP), theophylline, or the addition of both together to the preservation solution (University of Wisconsin [UW]) on apoptosis during preservation and the effect of apoptosis minimization on the early reperfusion period after transplantation.

DESIGN

Prospective, randomized, and controlled animal study.

SETTING

Laboratory of a research institute.

SUBJECT

Male Wistar rats.

INTERVENTIONS

The jejunum was isolated and preserved for 6 hrs in UW solution. FDP and theophylline were added to the UW solution to evaluate their effects on apoptosis both alone and together. The role of adenosine with respect to FDP was examined by increasing endogenous adenosine. In addition, rats were subjected to intestinal transplantation for the evaluation of the effect of apoptosis on bacterial translocation, histology, and neutrophil infiltration after reperfusion.

MEASUREMENTS AND MAIN RESULTS

Caspase-3 activity, assayed both in vitro or by cleaved caspase-3 levels in Western blots or immunohistochemically, and the number of terminal deoxynucleotidyl transferase-mediated biotin-dUTP nick-end labeling (TUNEL)-positive cells decreased with FDP and with theophylline addition to UW solution. Increase of endogenous adenosine reversed the antiapoptotic effect of FDP. FDP and theophylline together demonstrated a more pronounced antiapoptotic effect and prevented bacterial translocation after transplantation.

CONCLUSION

Supplementary FDP to UW solution decreased apoptosis through an adenosine-independent mechanism. Addition of theophylline to UW solution decreased both apoptosis and bacterial translocation. Concomitant theophylline and FDP addition to preservation solution is recommended to maintain low levels of apoptosis during intestinal hypothermic preservation and to decrease bacterial translocation.

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.

Molecular Mechanisms of Cl- Transport by the Renal Na+-K+-Cl- Cotransporter

The 2nd transmembrane domain (tm) of the secretory Na(+)-K(+)-Cl(-) cotransporter (NKCC1) and of the kidney-specific isoform (NKCC2) has been shown to play an important role in cation transport. For NKCC2, by way of illustration, alternative splicing of exon 4, a 96-bp sequence from which tm2 is derived, leads to the formation of the NKCC2A and F variants that both exhibit unique affinities for cations. Of interest, the NKCC2 variants also exhibit substantial differences in Cl- affinity as well as in the residue composition of the first intracellular connecting segment (cs1a), which immediately follows tm2 and which too is derived from exon 4. In this study, we have prepared chimeras of the shark NKCC2A and F (saA and saF) to determine whether cs1a could play a role in Cl- transport; here, tm2 or cs1a in saF was replaced by the corresponding domain from saA (generating saA/F or saF/A, respectively). Functional analyses of these chimeras have shown that cs1a-specific residues account for most of the A-F difference in Cl- affinity. For example, Km(Cl-)s were approximately 8 mm for saF/A and saA, and approximately 70 mm for saA/F and saF. Intriguingly, variant residues in cs1a also affected cation transport; here, Km(Na+)s for the chimeras and for saA were all approximately 20 mM, and Km(Rb+) all approximately 2 mM. Regarding tm2, our studies have confirmed its importance in cation transport and have also identified novel properties for this domain. Taken together, our results demonstrate for the first time that an intracellular loop in NKCC contributes to the transport process perhaps by forming a flexible structure that positions itself between membrane spanning domains.

Using fructose-1,6-diphosphate during hypothermic rabbit-heart preservation: a high-energy phosphate study

BACKGROUND

In this study, we evaluated the effects of fructose-1,6-diphosphate (FDP) on high-energy phosphate metabolism during 18-hour hypothermic rabbit-heart preservation.

METHODS

Under general anesthesia and artificial ventilation, hearts from 42 adult New Zealand white rabbits were harvested, flushed, and preserved in St. Thomas solution at 4(o)C for 18 hours. In the study group (n = 15), FDP (5 mmol/liter) was added to the St. Thomas solution, whereas in the control group (n = 17), fructose (5 mmol/liter) was added. Another 10 hearts did not undergo hypothermic storage, but were used as the normal group for high-energy phosphate concentration comparison.

RESULTS

After 18 hours of hypothermic preservation, myocardial high-energy phosphate content decreased in both preservation groups. In the study group, left ventricular adenosine triphosphate (ATP) content was 33% of that in the normal hearts, but in the control group, ATP decreased to 14% of normal. Adenosine diphosphate (ADP) content, energy charge, and ATP-to-ADP ratio showed similar decreases. The high-energy phosphate profile (content in the atria and ventricles and the ratio of ATP to ADP to AMP) was maintained in the study group but not in the control group. High-energy phosphate metabolites such as inosine monophosphate (IMP), inosine, and hypoxanthine increased in both preservation groups, but the increase was more prominent in the control group.

CONCLUSION

Adding FDP to St. Thomas solution attenuated the depletion of high-energy phosphate concentration in the preserved hearts. This difference was especially prominent in the left and right ventricles. The protective effect of FDP during hypothermic heart preservation deserves further study.

Immunomodulatory effect of fructose-1,6-bisphosphate on T-lymphocytes

Sepsis remains an important and life-threatening problem, and is the most common cause of death in the intensive care unit. One promising therapeutic candidate for protection against injury in sepsis is fructose-1,6-bisphosphate (FBP), a high-energy glycolytic pathway intermediate. The objective of the study was to establish a role for FBP on the immune system, especially in lymphocyte proliferation. Peripheral blood mononuclear cells (PBMCs) were isolated from the blood of healthy humans by gradient centrifugation. T-lymphocytes were stimulated for 96 h with phytohemagglutinin (PHA) and varying concentration of FBP. Fructose-1,6-bisphosphate at concentrations between 1.2 and 10 mM decreased proliferation of T-lymphocytes and reduced the viability only at concentrations 5.0 and 10 mM. The levels of soluble IL-2 receptor were reduced at FBP concentrations between 1.2 and 10 mM. In conclusion, this study demonstrates that FBP has important effect on immunomodulatory and this result can be correlated with the protection against injury in sepsis.

An assessment of fructose-1,6-bisphosphate as an antimicrobial and anti-inflammatory agent in sepsis

Tissue lesion mechanisms provoked by sepsis include the infectious process, inflammation, and cellular energy deficit. We chose to test fructose-1,6-bisphosphate (FBP) because of its possible anti-inflammatory and antimicrobial actions. Wistar rats were used and divided into three experimental groups: a control group (n=10), in which a capsule was introduced into the peritoneum of the animals; a septic group (n=10), in which a capsule containing non-sterile fecal matter was introduced together with Escherichia coli (1.5 x 10(9)CFU); and a septic group treated with FBP 500 mg/kg (n=10). The blood cell tests revealed that levels of leukocytes increased significantly in the septic group when compared to both the septic group treated with FBP and the control group. The blood cultures were 100% positive in both the septic group and the septic group treated with bisphosphorylated sugar. The antibiogram only revealed an inhibitory halo in the case of the antibiotic ampicillin, there was no such indication for FBP. The anti-inflammatory power of FBP remained at 60% for 5 h in the rats that received the carrageenan injection. What is more, the sugar reduced the levels of ionic calcium in relation to the control group. This data proves the validity of using FBP in the treatment of sepsis, possibly due to its anti-inflammatory rather than antimicrobial action.

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.

Physiopathological studies in septic rats and the use of fructose 1,6-bisphosphate as cellular protection

OBJECTIVE

The aim of this research project was to test the ability of fructose 1,6-bisphosphate (FBP), which has anti-inflammatory effects and maintains cellular energy levels, to inhibit the septic process in an experimental model in rats.

DESIGN

Prospective, controlled animal trial.

SETTING

Research laboratory.

SUBJECTS

Fed male Wistar rats.

INTERVENTIONS

Three experimental groups were formed for the test: control group, untreated septic group, and septic group treated with FBP (500 mg/kg).

MEASUREMENTS AND MAIN RESULTS

In the control group, there were no deaths; in the untreated septic group, the mortality rate was 100% within 15 hrs; in the septic group treated with FBP, the mortality rate reached 20% within 15 hrs. The blood cell tests revealed that concentrations of hematocrit, leukocytes, monocytes, and immature cells increased significantly in the untreated septic group compared with both the FBP-treated septic group and the control group. The histologic lesions verified in the heart, lungs, liver, and kidneys of septic animals were smaller and even absent in those treated with FBP.

CONCLUSION

FBP reduced the mortality rate provoked by experimental sepsis and ameliorated hematologic and histologic alterations.

Fructose-1,6-diphosphate attenuates acute lung injury induced by ischemia-reperfusion in rats

OBJECTIVE

To determine whether fructose-1,6-diphosphate (FDP) pretreatment can attenuate acute lung injury induced by ischemia-reperfusion in our isolated lung model in rats.

DESIGN

Randomized, controlled study.

SETTING

Animal care facility procedure room.

SUBJECTS

Twenty-four adult male Sprague-Dawley rats each weighing 250-350 g.

INTERVENTIONS

Typical acute lung injury in rats was induced successfully by 10 mins of hypoxia followed by 75 mins of ischemia and 50 mins of reperfusion. Ischemia-reperfusion significantly increased microvascular permeability as measured by the capillary filtration coefficient, lung weight gain, lung weight to body weight ratio, pulmonary arterial pressure, and protein concentration of bronchoalveolar lav-age fluid.

MEASUREMENTS AND MAIN RESULTS

Pretreatment with FDP significantly attenuated the acute lung injury induced by ischemia-reperfusion as shown by a significant decrease in all of the assessed variables (p <.05 p <.001). The protective effect of FDP was nearly undetectable when promazine (an ecto-adenosine 5-triphosphatase inhibitor) was added before FDP pretreatment.

CONCLUSIONS

Pretreatment with FDP significantly ameliorates acute lung injury induced by ischemia-reperfusion in rats.

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.

Cells overexpressing fructose-2,6-bisphosphatase showed enhanced pentose phosphate pathway flux and resistance to oxidative stress

Changes in the content of fructose-2,6-bisphosphate, a modulator of glycolytic flux, also affect other metabolic fluxes such as the non-oxidative pentose phosphate pathway. Since this is the main source of precursors for biosynthesis in proliferating cells, PFK-2/FBPase-2 has been proposed as a potential target for neoplastic treatments. Here we provide evidence that cells with a low content of fructose-2,6-bisphosphate have a lower energy status than controls, but they are also less sensitive to oxidative stress. This feature is related to the activation of the oxidative branch of the pentose phosphate pathway and the increased production of NADPH.

Hepatic preconditioning preserves energy metabolism during sustained ischemia

We evaluated the possibility that ischemic preconditioning could modify hepatic energy metabolism during ischemia. Accordingly, high-energy nucleotides and their degradation products, glycogen and glycolytic intermediates and regulatory metabolites, were compared between preconditioned and nonpreconditioned livers. Preconditioning preserved to a greater extent ATP, adenine nucleotide pool, and adenylate energy charge; the accumulation of adenine nucleosides and bases was much lower in preconditioned livers, thus reflecting slower adenine nucleotide degradation. These effects were associated with a decrease in glycogen depletion and reduced accumulation of hexose 6-phosphates and lactate. 6-Phosphofructo-2-kinase decreased in both groups, reducing the availability of fructose-2, 6-bisphosphate. Preconditioning sustained metabolite concentration at higher levels although this was not correlated with an increased glycolytic rate, suggesting that adenine nucleotides and cAMP may play the main role in the modulation of glycolytic pathway. Preconditioning attenuated the rise in cAMP and limited the accumulation of hexose 6-phosphates and lactate, probably by reducing glycogen depletion. Our results suggest the induction of metabolic arrest and/or associated metabolic downregulation as energetic cost-saving mechanisms that could be induced by preconditioning.

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.

Na(+)-K(+) pump and metabolic activities of trout erythrocytes during anoxia

Metabolic activity in the red blood cells of brown trout was monitored under conditions of oxygen depletion and chemically induced anoxia. Although metabolic activity was reduced during anoxia to one-third of the normoxic value, these cells maintained their ATP contents stable and were viable for hours in the absence of oxygen. In addition, Na(+)-K(+) pump activity was not down-regulated when metabolic activity was reduced during anoxia. The compatibility of this finding with energy equilibrium and ion homeostasis was investigated.