Glucose and lactate are equally effective in energizing activity-dependent synaptic vesicle turnover in purified cortical neurons.

This study examines the role of glucose and lactate as energy substrates to sustain synaptic vesicle cycling. Synaptic vesicle turnover was assessed in a quantitative manner by fluorescence microscopy in primary cultures of mouse cortical neurons. An electrode-equipped perfusion chamber was used to stimulate cells both by electrical field and potassium depolarization during image acquisition. An image analysis procedure was elaborated to select in an unbiased manner synaptic boutons loaded with the fluorescent dye N-(3-triethylammoniumpropyl)-4-(4-(dibutylamino)styryl)pyridinium dibromide (FM1-43). Whereas a minority of the sites fully released their dye content following electrical stimulation, others needed subsequent K(+) depolarization to achieve full release. This functional heterogeneity was not significantly altered by the nature of metabolic substrates. Repetitive stimulation sequences of FM1-43 uptake and release were then performed in the absence of any metabolic substrate and showed that the number of active sites dramatically decreased after the first cycle of loading/unloading. The presence of 1 mM glucose or lactate was sufficient to sustain synaptic vesicle cycling under these conditions. Moreover, both substrates were equivalent for recovery of function after a phase of decreased metabolic substrate availability. Thus, lactate appears to be equivalent to glucose for sustaining synaptic vesicle turnover in cultured cortical neurons during activity.

Ammonium-induced impairment of axonal growth is prevented through glial creatine.

Hyperammonemia in neonates and infants affects brain development and causes mental retardation. We report that ammonium impaired cholinergic axonal growth and altered localization and phosphorylation of intermediate neurofilament protein in rat reaggregated brain cell primary cultures. This effect was restricted to the phase of early maturation but did not occur after synaptogenesis. Exposure to NH4Cl decreased intracellular creatine, phosphocreatine, and ADP. We demonstrate that creatine cotreatment protected axons from ammonium toxic effects, although this did not restore high-energy phosphates. The protection by creatine was glial cell-dependent. Our findings suggest that the means to efficiently sustain CNS creatine concentration in hyperammonemic neonates and infants should be assessed to prevent impairment of axonogenesis and irreversible brain damage.

Bicarbonate de sodium pour ralentir la progression de la maladie rénale chronique [Sodium bicarbonate to slow the progression of chronic kidney disease].

Metabolic acidosis is a prevalent complication in moderate and late stages of chronic kidney disease (CKD). It is established that the correction of metabolic acidosis may improve metabolic bone disorders and protein degradation in the skeletal muscle, two characteristic complications of patients with advanced CKD. In the last 18 months, three randomized controlled trials have drawn the attention on a novel indication to correct metabolic acidosis in these patients, i.e., halting CKD progression. These data show that sodium bicarbonate, a cheap and easily manageable treatment, may delay the progression of CKD and the need of a renal replacement therapy such as dialysis or kidney transplantation.

Effects of lactate on glucose metabolism in healthy subjects and in severely injured hyperglycemic patients.

Hepatic glucose production is autoregulated during infusion of gluconeogenic precursors. In hyperglycemic patients with multiple trauma, hepatic glucose production and gluconeogenesis are increased, suggesting that autoregulation of hepatic glucose production may be defective. To better understand the mechanisms of autoregulation and its possible alterations in metabolic stress, lactate was coinfused with glucose in healthy volunteers and in hyperglycemic patients with multiple trauma or critical illness. In healthy volunteers, infusion of glucose alone nearly abolished endogenous glucose production. Lactate increased gluconeogenesis (as indicated by a decrease in net carbohydrate oxidation with no change in total [13C]carbohydrate oxidation) but did not increase endogenous glucose production. In patients with metabolic stress, endogenous glucose production was not suppressed by exogenous glucose, but lactate did not further increase hepatic glucose production. It is concluded that 1) in healthy humans, autoregulation of hepatic glucose production during infusion of lactate is still present when glycogenolysis is suppressed by exogenous glucose and 2) autoregulation of hepatic glucose production is not abolished in hyperglycemic patients with metabolic stress.

Brain energetics (thought needs food).

PURPOSE OF REVIEW: Almost 15 years after its initial proposal, the astrocyte-neuron lactate shuttle hypothesis still occupies the center stage in research on brain energetics. Recent developments have provided further evidence for its validity and have extended its application to different areas of neuroscience. RECENT FINDINGS: Description of cell-specific metabolic characteristics have reinforced the view that a prominent conversion of glucose into lactate takes place in astrocytes, whereas neurons preferentially take up and oxidize lactate over glucose-derived pyruvate. Indeed, specific mechanisms are activated by glutamatergic activity to favor such a net lactate transfer between the two cell types. Moreover, demonstration in vivo of the existence and implication of the astrocyte-neuron lactate shuttle hypothesis for particular neurophysiological processes is beginning to appear. SUMMARY: Brain energetics has undertaken its revolution. A new concept based on metabolic compartmentalization between astrocytes and neurons is establishing itself as the leading paradigm that opens new perspectives in areas such as functional brain imaging and regulation of energy homeostasis.

Sweet sixteen for ANLS.

Since its introduction 16 years ago, the astrocyte-neuron lactate shuttle (ANLS) model has profoundly modified our understanding of neuroenergetics by bringing a cellular and molecular resolution. Praised or disputed, the concept has never ceased to attract attention, leading to critical advances and unexpected insights. Here, we summarize recent experimental evidence further supporting the main tenets of the model. Thus, evidence for distinct metabolic phenotypes between neurons (mainly oxidative) and astrocytes (mainly glycolytic) have been provided by genomics and classical metabolic approaches. Moreover, it has become clear that astrocytes act as a syncytium to distribute energy substrates such as lactate to active neurones. Glycogen, the main energy reserve located in astrocytes, is used as a lactate source to sustain glutamatergic neurotransmission and synaptic plasticity. Lactate is also emerging as a neuroprotective agent as well as a key signal to regulate blood flow. Characterization of monocarboxylate transporter regulation indicates a possible involvement in synaptic plasticity and memory. Finally, several modeling studies captured the implications of such findings for many brain functions. The ANLS model now represents a useful, experimentally based framework to better understand the coupling between neuronal activity and energetics as it relates to neuronal plasticity, neurodegeneration, and functional brain imaging.

Uptake of particulate vaccine adjuvants by dendritic cells activates the NALP3 inflammasome.

Many currently used and candidate vaccine adjuvants are particulate in nature, but their mechanism of action is not well understood. Here, we show that particulate adjuvants, including biodegradable poly(lactide-co-glycolide) (PLG) and polystyrene microparticles, dramatically enhance secretion of interleukin-1beta (IL-1beta) by dendritic cells (DCs). The ability of particulates to promote IL-1beta secretion and caspase 1 activation required particle uptake by DCs and NALP3. Uptake of microparticles induced lysosomal damage, whereas particle-mediated enhancement of IL-1beta secretion required phagosomal acidification and the lysosomal cysteine protease cathepsin B, suggesting a role for lysosomal damage in inflammasome activation. Although the presence of a Toll-like receptor (TLR) agonist was required to induce IL-1beta production in vitro, injection of the adjuvants in the absence of TLR agonists induced IL-1beta production at the injection site, indicating that endogenous factors can synergize with particulates to promote inflammasome activation. The enhancement of antigen-specific antibody production by PLG microparticles was independent of NALP3. However, the ability of PLG microparticles to promote antigen-specific IL-6 production by T cells and the recruitment and activation of a population of CD11b(+)Gr1(-) cells required NALP3. Our data demonstrate that uptake of microparticulate adjuvants by DCs activates the NALP3 inflammasome, and this contributes to their enhancing effects on innate and antigen-specific cellular immunity.

Qualitat microbiològica dels productes vegetals frescos mínimament processats i desenvolupament de tecnologies de bioconservació mitjançant bacteris de l'àcid làctic

Food safety today is conditiones by the implementation of new Tecnologies for food preservation based on mild treatments and mínimum process, Novel foods, severe restrictions in the toxicològic profile of chemical preservatives, And the drastic limitation /prohibition of antibiotics, and as a consequence, by the New emergint pathogens or by the increase of classical food-borne pathogens. Biopreservatives appear within this context with strong expectations, because thei are safe microorganisms of ten isolated from foods, chemical compounds of natural origin -antimicrobial peptides and proteins, botanical extracts, enzymes- and sintetic compounds based on natural structures, but less toxic and more eficients, like the amtimicrobial peptides. Among the microbial biopreservatives, lactic acid bacteria have shown great possibilities in the preservation of cured meat products, ready to eat fresh fruit and vegetables, as well as to decrease microbial spoilage in food by products before processing for valorization. Our laboratory has performed an extense survey of the microbiological quality of fresh fruit and vegetables, and of ready-to-eat products, and have detect low levels, but significant of Salmonella sp., E. coli and Listeria spp., including L.monocytogenes, in retail markets and Supermarkets of Catalonia. Due to this reason, we started a project consisting of Developing application of lactic acid bacteria (LAB) obtained from these products, as biopreservatives. LAB were abundant in ready-to-eat fresh fruits and vegetables, specially in germinated seeds. From these products we obtained strains of Leuconostoc, Lactobacillus and Weissella, producing bacteriocins and with a Significant activity of control of L.monocytogenes in fresh apple and cut salad. Ather strains were efective in the inhibition of fungal rot during postharvest caused by Penicillium expansum

Effect of multiple oral doses of androgenic anabolic steroids on endurance performance and serum indices of physical stress in healthy male subjects.

Anabolic androgenic steroids (AAS) are doping agents that are mostly used for improvement of strength and muscle hypertrophy. In some sports, athletes reported that the intake of AAS is associated with a better recovery, a higher training load capacity and therefore an increase in physical and mental performances. The purpose of this study was to evaluate, the effect of multiple doses of AAS on different physiological parameters that could indirectly relate the physical state of athletes during a hard endurance training program. In a double blind settings, three groups (n = 9, 8 and 8) were orally administered placebo, testosterone undecanoate or 19-norandrostenedione, 12 times during 1 month. Serum biomarkers (creatine kinase, ASAT and urea), serum hormone profiles (testosterone, cortisol and LH) and urinary catecholamines (noradrenalin, adrenalin and dopamine) were evaluated during the treatment. Running performance was assessed before and after the intervention phase by means of a standardized treadmill test. None of the measured biochemical variables showed significant impact of AAS on physical stress level. Data from exercise testing on submaximal and maximal level did not reveal any performance differences between the three groups or their response to the treatment. In the present study, no effect of multiple oral doses of AAS on endurance performance or bioserum recovery markers was found.

Effects of lactate infusion on hepatic gluconeogenesis and glycogenolysis.

Endogenous glucose production rate (EGPR) remains constant when lactate is infused in healthy humans. A decrease of glycogenolysis or of gluconeogenesis from endogenous precursors or a stimulation of glycogen synthesis, may all be involved; This autoregulation does not depend on changes in glucoregulatory hormones. It may be speculated that alterations in basal sympathetic tone may be involved. To gain insights into the mechanisms responsible for autoregulation of EGPR, glycogenolysis and gluconeogenesis were measured, with a novel method (based on the prelabelling of endogenous glycogen with 13C glucose, and determination of hepatic 13C glycogen enrichment from breath 13CO2 and respiratory gas exchanges) in healthy humans infused with lactate or saline. These measurements were performed with or without beta-adrenergic receptor blockade (propranolol). Infusion of lactate increased energy expenditure, but did not increase EGPR; the relative contributions of gluconeogenesis and glycogenolysis to EGPR were also unaltered. This indicates that autoregulation is attained, at least in part, by inhibition of gluconeogenesis from endogenous precursors. beta-adrenergic receptor blockade alone (with propranolol) did not alter EGPR, glycogenolysis or gluconeogenesis. During infusion of lactate, propranolol decreased the thermic effect of lactate but EGPR remained constant. This indicates that alterations of beta-adrenergic activity is not required for autoregulation of EGPR.

Postgraduate Symposium: Positive influence of nutritional alkalinity on bone health.

There is growing evidence that consumption of a Western diet is a risk factor for osteoporosis through excess acid supply, while fruits and vegetables balance the excess acidity, mostly by providing K-rich bicarbonate-rich foods. Western diets consumed by adults generate approximately 50-100 mEq acid/d; therefore, healthy adults consuming such a diet are at risk of chronic low-grade metabolic acidosis, which worsens with age as a result of declining kidney function. Bone buffers the excess acid by delivering cations and it is considered that with time an overstimulation of this process will lead to the dissolution of the bone mineral content and hence to reduced bone mass. Intakes of K, Mg and fruit and vegetables have been associated with a higher alkaline status and a subsequent beneficial effect on bone health. In healthy male volunteers an acid-forming diet increases urinary Ca excretion by 74% and urinary C-terminal telopeptide of type I collagen (C-telopeptide) excretion by 19% when compared with an alkali (base-forming) diet. Cross-sectional studies have shown that there is a correlation between the nutritional acid load and bone health measured by bone ultrasound or dual-energy X-ray absorptiometry. Few studies have been undertaken in very elderly women (>75 years), whose osteoporosis risk is very pertinent. The EVAluation of Nutrients Intakes and Bone Ultra Sound Study has developed and validated (n 51) an FFQ for use in a very elderly Swiss population (mean age 80.4 (sd 2.99) years), which has shown intakes of key nutrients (energy, fat, carbohydrate, Ca, Mg, vitamin C, D and E) to be low in 401 subjects. A subsequent study to assess net endogenous acid production (NEAP) and bone ultrasound results in 256 women aged > or = 75 years has shown that lower NEAP (P=0.023) and higher K intake (P=0.033) are correlated with higher bone ultrasound results. High acid load may be an important additional risk factor that may be particularly relevant in very elderly patients with an already-high fracture risk. The latter study adds to knowledge by confirming a positive link between dietary alkalinity and bone health indices in the very elderly. In a further study to complement these findings it has also been shown in a group of thirty young women that in Ca sufficiency an acid Ca-rich water has no effect on bone resorption, while an alkaline bicarbonate-rich water leads to a decrease in both serum parathyroid hormone and serum C-telopeptide. Further investigations need to be undertaken to study whether these positive effects on bone loss are maintained over long-term treatment. Mineral-water consumption could be an easy and inexpensive way of helping to prevent osteoporosis and could be of major interest for long-term prevention of bone loss.

Role of Na+-K+-ATPase in insulin-induced lactate release by skeletal muscle.

Hyperinsulinemia increases lactate release by various organs and tissues. Whereas it has been shown that aerobic glycolysis is linked to Na+-K+-ATPase activity, we hypothesized that stimulation by insulin of skeletal muscle Na+-K+-ATPase is responsible for increased muscle lactate production. To test this hypothesis, we assessed muscle lactate release in healthy volunteers from the [13C]lactate concentration in the effluent dialysates of microdialysis probes inserted into the tibialis anterior muscles on both sides and infused with solutions containing 5 mmol/l [U-13C]glucose. On one side, the microdialysis probe was intermittently infused with the same solution additioned with 2.10(-5) M ouabain. In the basal state, [13C]lactate concentration in the dialysate was not affected by ouabain. During a euglycemic-hyperinsulinemic clamp, [13C]lactate concentration increased by 135% in the dialysate without ouabain, and this stimulation was nearly entirely reversed by ouabain (56% inhibition compared with values in the dialysate collected from the contralateral probe). These data indicate that insulin stimulates muscle lactate release by activating Na+-K+-ATPase in healthy humans.

Alteration of amino acid metabolism in neuronal aggregate cultures exposed to hypoglycaemic conditions.

The neuronal effects of glucose deficiency on amino acid metabolism was studied on three-dimensional cultures of rat telencephalon neurones. Transient (6 h) exposure of differentiated cultures to low glucose (0.25 mm instead of 25 mm) caused irreversible damage, as judged by the marked decrease in the activities of two neurone-specific enzymes and lactate dehydrogenase, 1 week after the hypoglycemic insult. Quantification of amino acids and ammonia in the culture media supernatants indicated increased amino acid utilization and ammonia production during glucose-deficiency. Measurement of intracellular amino acids showed decreased levels of alanine, glutamine, glutamate and GABA, while aspartate was increased. Added lactate (11 mm) during glucose deficiency largely prevented the changes in amino acid metabolism and ammonia production, and attenuated irreversible damage. Higher media levels of glutamine (4 mm instead of 0.25 mm) during glucose deprivation prevented the decrease of intracellular glutamate and GABA, while it further increased intracellular aspartate, ammonia production and neuronal damage. Both lactate and glutamine were readily oxidized in these neuronal cultures. The present results suggest that in neurones, glucose deficiency enhances amino acid deamination at the expense of transamination reactions. This results in increased ammonia production and neuronal damage.

Running from Paris to Beijing: biomechanical and physiological consequences.

The purpose of this study was to examine the physiological and biomechanical changes occurring in a subject after running 8,500 km in 161 days (i.e. 52.8 km daily). Three weeks before, 3 weeks after (POST) and 5 months after (POST+5) running from Paris to Beijing, energy cost of running (Cr), knee flexor and extensor isokinetic strength and biomechanical parameters (using a treadmill dynamometer) at different velocities were assessed in an experienced ultra-runner. At POST, there was a tendency toward a 'smoother' running pattern, as shown by (a) a higher stride frequency and duty factor, and a reduced aerial time without a change in contact time, (b) a lower maximal vertical force and loading rate at impact and (c) a decrease in both potential and kinetic energy changes at each step. This was associated with a detrimental effect on Cr (+6.2%) and a loss of strength at all angular velocities for both knee flexors and extensors. At POST+5, the subject returned to his original running patterns at low but not at high speeds and maximal strength remained reduced at low angular velocities (i.e. at high levels of force). It is suggested that the running pattern changes observed in the present study were a strategy adopted by the subject to reduce the deleterious effects of long distance running. However, the running pattern changes could partly be linked to the decrease in maximal strength.

Calcium reabsorption in the distal tubule: regulation by sodium, pH, and flow.

We developed a mathematical model of Ca transport along the late distal convoluted tubule (DCT2) and the connecting tubule (CNT) to investigate the mechanisms that regulate Ca reabsorption in the DCT2-CNT. The model accounts for apical Ca influx across transient receptor potential vanilloid 5 (TRPV5) channels and basolateral Ca efflux via plasma membrane Ca-ATPase pumps and type 1 Na/Ca exchangers (NCX1). Model simulations reproduce experimentally observed variations in Ca uptake as a function of extracellular pH, Na, and Mg concentration. Our results indicate that amiloride enhances Ca reabsorption in the DCT2-CNT predominantly by increasing the driving force across NCX1, thereby stimulating Ca efflux. They also suggest that because aldosterone upregulates both apical and basolateral Na transport pathways, it has a lesser impact on Ca reabsorption than amiloride. Conversely, the model predicts that full NCX1 inhibition and parathyroidectomy each augment the Ca load delivered to the collecting duct severalfold. In addition, our results suggest that regulation of TRPV5 activity by luminal pH has a small impact, per se, on transepithelial Ca fluxes; the reduction in Ca reabsorption induced by metabolic acidosis likely stems from decreases in TRPV5 expression. In contrast, elevations in luminal Ca are predicted to significantly decrease TRPV5 activity via the Ca-sensing receptor. Nevertheless, following the administration of furosemide, the calcium-sensing receptor-mediated increase in Ca reabsorption in the DCT2-CNT is calculated to be insufficient to prevent hypercalciuria. Altogether, our model predicts complex interactions between calcium and sodium reabsorption in the DCT2-CNT.