Protection of astrocytes by fructose 1,6-bisphosphate and citrate ameliorates neuronal injury under hypoxic conditions

Kidney Dysfunction After Traumatic Brain Injury: Pathophysiology and General Management

Traumatic brain injury (TBI) remains a major cause of mortality and morbidity, and almost half of these patients are admitted to the intensive care unit. Of those, 10% develop acute kidney injury (AKI) and 2% even need kidney replacement therapy (KRT). Although clinical trials in patients with TBI who have AKI are lacking, some general principles in this population may apply. The present review is an overview on the epidemiology and pathophysiology of AKI in patients with TBI admitted to the intensive care unit who are at risk for or who have developed AKI. A cornerstone in severe TBI management is preventing secondary brain damage, in which reducing the intracranial pressure (ICP) and optimizing the cerebral perfusion pressure (CPP) remain important therapeutic targets. To treat episodes of elevated ICP, osmolar agents such as mannitol and hypertonic saline are frequently administered. Although we are currently awaiting the results of a prospective randomized controlled trial that compares both agents, it is important to realize that both agents have been associated with an increased risk of developing AKI which is probably higher for mannitol compared with hypertonic saline. For the brain, as well as for the kidney, targeting an adequate perfusion pressure is important. Hemodynamic management based on the combined use of intravascular fluids and vasopressors is ideally guided by hemodynamic monitoring. Hypotonic albumin or crystalloid resuscitation solutions may increase the risk of brain edema, and saline-based solutions are frequently used but have a risk of hyperchloremia, which might jeopardize kidney function. In patients at risk, frequent assessment of serum chloride might be advised. Maintenance of an adequate CPP involves the optimization of circulating blood volume, often combined with vasopressor agents. Whether individualized CPP targets based on cerebrovascular autoregulation monitoring are beneficial need to be further investigated. Interestingly, such individualized perfusion targets are also under investigation in patients as a strategy to mitigate the risk for AKI in patients with chronic hypertension. In the small proportion of patients with TBI who need KRT, continuous techniques are advised based on pathophysiology and expert opinion. The need for KRT is associated with a higher risk of intracranial hypertension, especially if osmolar clearance occurs fast, which can even occur in continuous techniques. Precise ICP and CPP monitoring is mandatory, especially at the initiation of KRT.

Acute Kidney Injury at the Neurocritical Care Unit

Neurocritical care has advanced substantially in recent decades, allowing doctors to treat patients with more complicated conditions who require a multidisciplinary approach to achieve better clinical outcomes. In neurocritical patients, nonneurological complications such as acute kidney injury (AKI) are independent predictors of worse clinical outcomes. Different research groups have reported an AKI incidence of 11.6% and an incidence of stage 3 AKI, according to the Kidney Disease: Improving Global Outcomes, that requires dialysis of 3% to 12% in neurocritical patients. These patients tend to be younger, have less comorbidity, and have a different risk profile, given the diagnostic and therapeutic procedures they undergo. Trauma-induced AKI, sepsis, sympathetic overstimulation, tubular epitheliopathy, hyperchloremia, use of nephrotoxic drugs, and renal hypoperfusion are some of the causes of AKI in neurocritical patients. AKI is the result of a sum of events, although the mechanisms underlying many of them remain uncertain; however, two important causes that merit mention are direct alteration of the physiological brain-kidney connection and exposure to injury as a result of the specific medical management and well-established therapies that neurocritical patients are subjected to. This review will focus on AKI in neurocritical care patients. Specifically, it will discuss its epidemiology, causes, associated mechanisms, and relationship to the brain-kidney axis. Additionally, the use and risks of extracorporeal therapies in this group of patients will be reviewed.

Antioxidants and Neuron-Astrocyte Interplay in Brain Physiology: Melatonin, a Neighbor to Rely on

This manuscript is a review focused onto the role of astrocytes in the protection of neurons against oxidative stress and how melatonin can contribute to the maintenance of brain homeostasis. The first part of the review is dedicated to the dependence of neurons on astrocytes by terms of survival under oxidative stress conditions. Additionally, the effects of melatonin against oxidative stress in the brain and its putative role in the protection against diseases affecting the brain are highlighted. The effects of melatonin on the physiology of neurons and astrocytes also are reviewed.

Renal replacement therapy in acute kidney injury: controversy and consensus

Renal replacement therapies (RRTs) represent a cornerstone in the management of severe acute kidney injury. This area of intensive care and nephrology has undergone significant improvement and evolution in recent years. Continuous RRTs have been a major focus of new technological and treatment strategies. RRT is being used increasingly in the intensive care unit, not only for renal indications but also for other organ-supportive strategies. Several aspects related to RRT are now well established, but others remain controversial. In this review, we review the available RRT modalities, covering technical and clinical aspects. We discuss several controversial issues, provide some practical recommendations, and where possible suggest a research agenda for the future.

Metabolomics of oxidative stress in recent studies of endogenous and exogenously administered intermediate metabolites

Aerobic metabolism occurs in a background of oxygen radicals and reactive oxygen species (ROS) that originate from the incomplete reduction of molecular oxygen in electron transfer reactions. The essential role of aerobic metabolism, the generation and consumption of ATP and other high energy phosphates, sustains a balance of approximately 3000 essential human metabolites that serve not only as nutrients, but also as antioxidants, neurotransmitters, osmolytes, and participants in ligand-based and other cellular signaling. In hypoxia, ischemia, and oxidative stress, where pathological circumstances cause oxygen radicals to form at a rate greater than is possible for their consumption, changes in the composition of metabolite ensembles, or metabolomes, can be associated with physiological changes. Metabolomics and metabonomics are a scientific disciplines that focuse on quantifying dynamic metabolome responses, using multivariate analytical approaches derived from methods within genomics, a discipline that consolidated innovative analysis techniques for situations where the number of biomarkers (metabolites in our case) greatly exceeds the number of subjects. This review focuses on the behavior of cytosolic, mitochondrial, and redox metabolites in ameliorating or exacerbating oxidative stress. After reviewing work regarding a small number of metabolites—pyruvate, ethyl pyruvate, and fructose-1,6-bisphosphate—whose exogenous administration was found to ameliorate oxidative stress, a subsequent section reviews basic multivariate statistical methods common in metabolomics research, and their application in human and preclinical studies emphasizing oxidative stress. Particular attention is paid to new NMR spectroscopy methods in metabolomics and metabonomics. Because complex relationships connect oxidative stress to so many physiological processes, studies from different disciplines were reviewed. All, however, shared the common goal of ultimately developing “omics”-based, diagnostic tests to help influence therapies.

Metabolism-induced oxidative stress is a mediator of glucose toxicity in HT22 neuronal cells

Oxidative stress has been widely considered as a key player in the adverse effects of hyperglycaemia to various tissues, including neuronal cells. This study examined the participation of oxidative stress in injurious effects of high glucose on HT22 cells along with the activity of proteasome, a proteolytic system responsible for degradation of oxidized proteins. Although 10-fold glucose concentration caused non-significant viability changes, a significant reduction of cell proliferation was found. Moreover, the cell morphology was also altered. These changes were followed by an enhancement of intracellular ROS generation, however without any significant boost of the carbonyl group concentration in proteins. Correspondingly, only a slight decline in the 20S proteasome activity was found in high-glucose-treated cells. On the other hand, substances affecting glucose metabolism or antioxidants partially preserved the oxidative stress in high glucose treated cells. In summary, these results highlight the role of metabolic oxidative stress in hyperglycaemia affecting neurons.

Aconitate hydratase of mammals under oxidative stress

Data on the structure, functions, regulation of activity, and expression of cytosolic and mitochondrial aconitate hydratase isoenzymes of mammals are reviewed. The role of aconitate hydratase and structurally similar iron-regulatory protein in maintenance of homeostasis of cell iron is described. Information on modifications of the aconitate hydratase molecule and changes in expression under oxidative stress is generalized. The role of aconitate hydratase in the pathogenesis of some diseases is considered.

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.

Fructose 1,6-Diphosphate Alleviates UV-Induced Oxidative Skin Damage in Hairless Mice

Reactive oxygen species (ROS) are involved in the deleterious effects of UV light on skin. The antioxidant defense system is considered to be crucial for protecting skin from ROS. Recently, we showed that fructose 1,6-diphosphate (FDP), a glycolytic metabolite, reduced oxidative stress in UVB-irradiated keratinocytes. This study set out to determine whether topically applied FDP could exert protective effects against UV-induced skin damage in hairless mice. An in vitro skin permeation study using Franz-type diffusion cells showed that the amount of [14C]-FDP that diffused through the skin increased in a time-dependent manner, and about 3.5% of the applied FDP penetrated the skin after 24 h. Topical application of FDP (1%) preserved the endogenous antioxidant capacity of skin such as catalase and glutathione, which were significantly reduced after UVB irradiation without FDP. FDP also reversed the loss of catalase protein and prevented the accumulation of carbonylated proteins induced by UVB irradiation. These results provide evidence that topically administered FDP could penetrate into the skin and attenuate UVB-induced oxidative skin damage in hairless mice.

Fructose- 1,6-Bisphosphate Supports Cerebral Energy Metabolism in Pigs after Ischemic Brain Injury Caused by Experimental Particle Embolization

BACKGROUND

Fructose-1,6-bisphosphate (FDP) is a high-energy intermediate that enhances glycolysis, preserves cellular adenosine triphosphate stores, and prevents the increase of intracellular calcium in ischemic tissue. Since it has been shown to provide metabolic support to the brain during ischemia, we planned this study to evaluate whether FDP is neuroprotective in the setting of combining hypothermic circulatory arrest (HCA) and irreversible embolic brain ischemic injury.

METHODS

Twenty pigs were randomly assigned to receive 2 intravenous infusions of either FDP (500 mg/kg) or saline. The first infusion was given just before a 25-minute period of HCA and the second infusion immediately after HCA. Immediately before HCA, the descending aorta was clamped and 200 mg of albumin-coated polystyrene microspheres (250-750 mm in diameter) were injected into the isolated aortic arch in both study groups.

RESULTS

There were no significant differences between the study groups in terms of neurological outcome. Brain lactate/pyruvate ratio was significantly lower (P = .015) and brain pyruvate levels (P = .013) were significantly higher in the FDP group compared with controls. Brain lactate levels were significantly higher 8 hours after HCA (P = .049).

CONCLUSION

The administration of FDP before and immediately after HCA combined with embolic brain ischemic injury was associated with significantly lower brain lactate/pyruvate ratio and significantly higher levels of brain pyruvate, as well as lower lactate levels 8 hours after HCA. FDP seems to protect the brain by supporting energy metabolism. The neurological outcome was not improved, most likely resulting from the irreversible nature of the microsphere occlusion.

Lactate and glucose as energy substrates during, and after, oxygen deprivation in rat hippocampal acute and cultured slices

The effects of raised brain lactate levels on neuronal survival following hypoxia or ischemia is still a source of controversy among basic and clinical scientists. We have sought to address this controversy by studying the effects of glucose and lactate on neuronal survival in acute and cultured hippocampal slices. Following a 1-h hypoxic episode, neuronal survival in cultured hippocampal slices was significantly higher if glucose was present in the medium compared with lactate. However, when the energy substrate during the hypoxic period was glucose and then switched to lactate during the normoxic recovery period, the level of cell damage in the CA1 region of organotypic cultures was significantly improved from 64.3 +/- 2.1 to 74.6 +/- 2.1% compared with cultures receiving glucose during and after hypoxia. Extracellular field potentials recorded from the CA1 region of acute slices were abolished during oxygen deprivation for 20 min, but recovered almost fully to baseline levels with either glucose (82.6 +/- 10.0%) or lactate present in the reperfusion medium (108.1 +/- 8.3%). These results suggest that lactate alone cannot support neuronal survival during oxygen deprivation, but a combination of glucose followed by lactate provides for better neuroprotection than either substrate alone.

Effects of fructose-1,6-bisphosphate on morphological and functional neuronal integrity in rat hippocampal slices during energy deprivation

D-fructose-1,6-bisphosphate, a high energy glycolytic intermediate, attenuates ischemic damage in a variety of tissues, including brain. To determine whether D-fructose-1,6-bisphosphate serves as an alternate energy substrate in the CNS, rat hippocampal slices were treated with D-fructose-1,6-bisphosphate during glucose deprivation. Unlike pyruvate, an endproduct of glycolysis, 10 mM D-fructose-1,6-bisphosphate did not preserve synaptic transmission or morphological integrity of CA1 pyramidal neurons during glucose deprivation. Moreover, during glucose deprivation, 10-mM D-fructose-1,6-bisphosphate failed to maintain adenosine triphosphate levels in slices. D-fructose-1,6-bisphosphate, however, attenuated acute neuronal degeneration produced by 200 microM iodoacetate, an inhibitor of glycolysis downstream of D-fructose-1,6-bisphosphate. Because (5S, 10R)-(+)-5-methyl-10, 11-dihydro-5H-dibenzo [a,d]cyclohepten-5,10-imine, an antagonist of N-methyl-D-aspartate receptors, exhibited similar protection against iodoacetate damage, we examined whether (5S, 10R)-(+)-5-methyl-10, 11-dihydro-5H-dibenzo [a,d]cyclohepten-5,10-imine and D-fructose-1,6-bisphosphate share a common neuroprotective mechanism. Indeed, D-fructose-1,6-bisphosphate diminished N-methyl-D-aspartate receptor-mediated synaptic responses and partially attenuated neuronal degeneration induced by 100-microM N-methyl-D-aspartate. Taken together, these results indicate that D-fructose-1,6-bisphosphate is unlikely to serve as an energy substrate in the hippocampus, and that neuroprotective effects of D-fructose-1,6-bisphosphate are mediated by mechanisms other than anaerobic energy supply.

Fructose-1,6-bisphosphate preserves intracellular glutathione and protects cortical neurons against oxidative stress

Fructose-1,6-bisphosphate (FBP), an endogenous intermediate of glycolysis, protects the brain against ischemia-reperfusion injury. The mechanisms of FBP protection after cerebral ischemia are not well understood. The current study was undertaken to determine whether FBP protects primary neurons against hypoxia and oxidative stress by preserving reduced glutathione (GSH). Cultures of pure cortical neurons were subjected to oxygen deprivation, a donor of nitric oxide and superoxide radicals (3-morpholinosydnonimine), an inhibitor of glutathione synthesis (L-buthionine-sulfoximine) or glutathione reductase (1,3-bis(2-chloroethyl)-1-nitrosourea) in the presence or absence of FBP (3.5 mM). Neuronal viability was determined using an 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide assay. FBP protected neurons against hypoxia-reoxygenation and oxidative stress under conditions of compromised GSH metabolism. The efficacy of FBP depended on duration of hypoxia and was associated with higher intracellular GSH concentration, an effect partly mediated via increased glutathione reductase activity.

Fructose-1,6-diphosphate attenuates prostaglandin E2 production and cyclo-oxygenase-2 expression in UVB-irradiated HaCaT keratinocytes

1. Fructose-1,6-diphosphate (FDP), a glycolytic metabolite, is reported to ameliorate inflammation and inhibit the nitric oxide production in murine macrophages stimulated with endotoxin. It is also reported that FDP has cytoprotective effects against hypoxia or ischaemia/reperfusion injury in brain and heart. However, underlying mechanisms of its various biological activities are not completely understood. 2. In this study, we examined the effects of FDP on UVB-induced prostaglandin production in HaCaT keratinocytes. 3. Ultraviolet B (UVB, 280-320 nm) irradiation (30 mJ cm(-2)) increased prostaglandin E(2)(PGE(2)) production, which was significantly decreased by FDP in a concentration dependent manner. NS-398, a cyclo-oxygenase-2 (COX-2) selective inhibitor completely inhibited UVB-induced PGE(2) production showing that COX-2 activity is responsible for the increase in PGE(2) production under our experimental conditions. 4. UVB irradiation increased total COX activity and COX-2 mRNA in HaCaT keratinocytes, which were significantly blocked by FDP in a concentration dependent manner. 5. N-acetylcysteine (NAC) significantly attenuated UVB-induced PGE(2) production, COX activity and COX-2 mRNA expression indicating oxidative components might contribute to these events. 6. FDP reduced UVB-induced increase in cellular reactive oxygen species (ROS) level although it did not show direct radical scavenging effect in the experiment using 1,1-diphenyl-2picrylhydrazil (DPPH). FDP preserved the cellular antioxidant capacity including catalase activity and GSH content after irradiation. 7. Our data obtained hitherto suggest that FDP may have a protective role in UVB-injured keratinocyte by attenuating PGE(2) production and COX-2 expression, which are possibly through blocking intracellular ROS accumulation.

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.

In vivo and in vitro glycogenic effects of methionine sulfoximine are different in two inbred strains of mice

We investigated the relationship between brain glycogen anabolism and methionine sulfoximine (MSO)-induced seizures in two inbred mouse strains that presented differential susceptibility to the convulsant. CBA/J was considered a MSO-high-reactive strain and C57BL/6J a MSO-low-reactive strain. Accordingly, the dose of MSO needed to induce seizures in CBA/J mice is lower than that in C57BL/6J mice, and CBA/J mice which had seizures, died during the first convulsion. In addition, the time--course of the MSO effect is faster in CBA/J mice than that in C57BL/6J mice. Analyses were performed in C57BL/6J and CBA/J mice after administration of 75 (subconvulsive dose) and 40 mg/kg of MSO (subconvulsive dose, not lethal dose), respectively. In the preconvulsive period, MSO induced an increase in the brain glycogen content of C57BL/6J mice only. Twenty-four hours after MSO administration, the brain glycogen content increased in both strains. The activity and expression of fructose-1,6-bisphosphatase, the last key enzyme of the gluconeogenic pathway, were increased in MSO-treated C57BL/6J mice as compared to control mice, at all experimental time points, whereas they were increased in CBA/J mice only 24 h after MSO administration. These latter results correspond to CBA/J mice that did not have seizures. Interestingly, the differences observed in vivo were consistent with results in primary cultured astrocytes from the two strains. This data suggests that the metabolism impairment, which was not a consequence of seizures, could be related to the difference in seizure susceptibility between the two strains, depending on their genetic background.

Fructose-1,6-bisphosphate and MK-801 by aortic arch flush for cerebral preservation during exsanguination cardiac arrest of 20 min in dogs. An exploratory study

In our exsanguination cardiac arrest (CA) outcome model in dogs we are systematically exploring suspended animation (SA), i.e. preservation of brain and heart immediately after the onset of CA to enable transport and resuscitative surgery during CA, followed by delayed resuscitation. We have shown in dogs that inducing moderate cerebral hypothermia with an aortic arch flush of 500 ml normal saline solution at 4 degrees C, at start of CA 20 min no-flow, leads to normal functional outcome. We hypothesized that, using the same model, but with the saline flush at 24 degrees C inducing minimal cerebral hypothermia (which would be more readily available in the field), adding either fructose-1,6-bisphosphate (FBP, a more efficient energy substrate) or MK-801 (an N-methyl-D-aspartate (NMDA) receptor blocker) would also achieve normal functional outcome. Dogs (range 19-30 kg) were exsanguinated over 5 min to CA of 20 min no-flow, and resuscitated by closed-chest cardiopulmonary bypass (CPB). They received assisted circulation to 2 h, mild systemic hypothermia (34 degrees C) post-CA to 12 h, controlled ventilation to 20 h, and intensive care to 72 h. At CA 2 min, the dogs received an aortic arch flush of 500 ml saline at 24 degrees C by a balloon-tipped catheter, inserted through the femoral artery (control group, n=6). In the FBP group (n=5), FBP (total 1440 or 4090 mg/kg) was given by flush and with reperfusion. In the MK-801 group (n=5), MK-801 (2, 4, or 8 mg/kg) was given by flush and with reperfusion. Outcome was assessed in terms of overall performance categories (OPC 1, normal; 2, moderate disability; 3, severe disability; 4, coma; 5, brain death or death), neurologic deficit scores (NDS 0-10%, normal; 100%, brain death), and brain histologic damage scores (HDS, total HDS 0, no damage; >100, extensive damage; 1064, maximal damage). In the control group, one dog achieved OPC 2, one OPC 3, and four OPC 4; in the FBP group, two dogs achieved OPC 3, and three OPC 4; in the MK-801 group, two dogs achieved OPC 3, and three OPC 4 (P=1.0). Median NDS were 62% (range 8-67) in the control group; 55% (range 34-66) in the FBP group; and 50% (range 26-59) in the MK-801 group (P=0.2). Median total HDS were 130 (range 56-140) in the control group; 96 (range 64-104) in the FBP group; and 80 (range 34-122) in the MK-801 group (P=0.2). There was no difference in regional HDS between groups. We conclude that neither FBP nor MK-801 by aortic arch flush at the start of CA, plus an additional i.v. infusion of the same drug during reperfusion, can provide cerebral preservation during CA 20 min no-flow. Other drugs and drug-combinations should be tested with this model in search for a breakthrough effect.

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

The relationship between the protective effect of fructose 1,6-bisphosphate (F-1,6-P2) against cell injury and the modifications produced in the metabolic fluxes and in the membrane permeability to K+ was studied in isolated rat hepatocytes. Incubation of these cells in the presence of F-1,6-P2 reduced metabolic activity without affecting the ATP content, which suggests a downregulation of the ATP turnover. Using 86Rb+ as a tracer, we analyzed the relationship between these metabolic changes and alterations in K+ fluxes. In the presence of F-1,6-P2 the passive and the active K+ fluxes in hepatocytes decreased. However, the Na(+)-K+ pump from semipurified membranes was not directly affected by F-1,6-P2, which suggests a secondarily induced reduction of Na(+)-K+ pump activity. Moreover, galactosamine-treated cells showed a marked increase in permeability to K+ that was abolished by the presence of F-1,6-P2. This protective effect may be related to the prevention of K+ efflux. The results reported here strongly suggest the induction of channel arrest, and the associated metabolic downregulation, as the primary protective effect of F-1,6-P2, as has been shown in the prevention of galactosamine-induced hepatotoxicity.