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Metabolic multianalyte microphysiometry reveals extracellular acidosis is an essential mediator of neuronal preconditioning.

ABSTRACT: Metabolic adaptation to stress is a crucial yet poorly understood phenomenon, particularly in the central nervous system (CNS). The ability to identify essential metabolic events which predict neuronal fate in response to injury is critical to developing predictive markers of outcome, for interpreting CNS spectroscopic imaging, and for providing a richer understanding of the relevance of clinical indices of stress which are routinely collected. In this work, real-time multianalyte microphysiometry was used to dynamically assess multiple markers of aerobic and anaerobic respiration through simultaneous electrochemical measurement of extracellular glucose, lactate, oxygen, and acid. Pure neuronal cultures and mixed cultures of neurons and glia were compared following a 90 min exposure to aglycemia. This stress was cytotoxic to neurons yet resulted in no appreciable increase in cell death in age-matched mixed cultures. The metabolic profile of the cultures was similar in that aglycemia resulted in decreases in extracellular acidification and lactate release in both pure neurons and mixed cultures. However, oxygen consumption was only diminished in the neuron enriched cultures. The differences became more pronounced when cells were returned to glucose-containing media upon which extracellular acidification and oxygen consumption never returned to baseline in cells fated to die. Taken together, these data suggest that lactate release is not predictive of neuronal survival. Moreover, they reveal a previously unappreciated relationship of astrocytes in maintaining oxygen uptake and a correlation between metabolic recovery of neurons and extracellular acidification.

SUBMITTER: McKenzie JR

PROVIDER: S-EPMC3399578 | biostudies-other | 2012 Jul

REPOSITORIES: biostudies-other

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Extracellular spermine exacerbates ischemic neuronal injury through sensitization of ASIC1a channels to extracellular acidosis.

Project description:Ischemic brain injury is a major problem associated with stroke. It has been increasingly recognized that acid-sensing ion channels (ASICs) contribute significantly to ischemic neuronal damage, but the underlying mechanism has remained elusive. Here, we show that extracellular spermine, one of the endogenous polyamines, exacerbates ischemic neuronal injury through sensitization of ASIC1a channels to extracellular acidosis. Pharmacological blockade of ASIC1a or deletion of the ASIC1 gene greatly reduces the enhancing effect of spermine in ischemic neuronal damage both in cultures of dissociated neurons and in a mouse model of focal ischemia. Mechanistically, spermine profoundly reduces desensitization of ASIC1a by slowing down desensitization in the open state, shifting steady-state desensitization to more acidic pH, and accelerating recovery between repeated periods of acid stimulation. Spermine-mediated potentiation of ASIC1a activity is occluded by PcTX1 (psalmotoxin 1), a specific ASIC1a inhibitor binding to its extracellular domain. Functionally, the enhanced channel activity is accompanied by increased acid-induced neuronal membrane depolarization and cytoplasmic Ca(2+) overload, which may partially explain the exacerbated neuronal damage caused by spermine. More importantly, blocking endogenous spermine synthesis significantly attenuates ischemic brain injury mediated by ASIC1a but not that by NMDA receptors. Thus, extracellular spermine contributes significantly to ischemic neuronal injury through enhancing ASIC1a activity. Our data suggest new neuroprotective strategies for stroke patients via inhibition of polyamine synthesis and subsequent spermine-ASIC interaction.

| S-EPMC3101878 | biostudies-literature

Metabolic Acidosis and Subclinical Metabolic Acidosis in CKD.

Project description:Metabolic acidosis is not uncommon in CKD and is linked with bone demineralization, muscle catabolism, and higher risks of CKD progression and mortality. Clinical practice guidelines recommend maintaining serum total CO2 at ?22 mEq/L to help prevent these complications. Although a definitive trial testing whether correcting metabolic acidosis improves clinical outcomes has not been conducted, results from small, single-center studies support this notion. Furthermore, biologic plausibility supports the notion that a subset of patients with CKD have acid-mediated organ injury despite having a normal serum total CO2 and might benefit from oral alkali before overt acidosis develops. Identifying these individuals with subclinical metabolic acidosis is challenging, but recent results suggest that urinary acid excretion measurements may be helpful. The dose of alkali to provide in this setting is unknown as well. The review discusses these topics and the prevalence and risk factors of metabolic acidosis, mechanisms of acid-mediated organ injury, results from interventional studies, and potential harms of alkali therapy in CKD.

| S-EPMC5791070 | biostudies-other

Plasma volume expansion reveals hidden metabolic acidosis in patients with diabetic ketoacidosis.

Project description:BackgroundHyperchloremic metabolic acidosis that develops during the treatment of diabetic ketoacidosis is usually attributed to the chloride content of resuscitation fluids. We explored an alternative explanation, namely that fluid-induced plasma volume expansion alters the absolute differences in the concentrations of sodium and chloride (the Na-Cl gap) enough to affect the acid-base balance. We analyzed data from a prospective single-center cohort study of 14 patients treated for diabetic ketoacidosis. All patients received 1 L of 0.9% saline over 30 min on two consecutive days. Blood gases were sampled before and after the infusions.ResultsThe initial plasma volume was estimated to be 25 ± 13% (mean ± SD) below normal on admission to the intensive care unit. At that time, most patients had an increased actual Na-Cl gap, which counteracts acidosis. However, the correction of the plasma volume deficit revealed that these patients would have had a decreased Na-Cl gap upon admission if they had been normovolemic at that time; the estimated "virtual Na-Cl gap" of 29 ± 5 mmol/L was significantly lower than the uncorrected value, which was 39 ± 5 mmol/L (P < 0.001). On Day 2, most patients had a decreased actual Na-Cl gap (33 ± 5 mmol/L), approaching the corrected value on Day 1.ConclusionsThe hyperchloremic acidosis commonly seen in diabetic ketoacidosis may not be primarily caused by the chloride content of resuscitation fluids but, rather, by the restoration of plasma volume, which reveals the hidden metabolic acidosis caused by a decreased Na-Cl gap. Trial registration Clinical Trials Identifier NCT02172092, registered June 24, 2014, https://www.Clinicaltrialsgov/NCT02172092.

| S-EPMC9424448 | biostudies-literature

Neuronal expression of sodium/bicarbonate cotransporter NBCn1 (SLC4A7) and its response to chronic metabolic acidosis.

Project description:The sodium-bicarbonate cotransporter NBCn1 (SLC4A7) is an acid-base transporter that normally moves Na(+) and HCO(3)(-) into the cell. This membrane protein is sensitive to cellular and systemic pH changes. We examined NBCn1 expression and localization in the brain and its response to chronic metabolic acidosis. Two new NBCn1 antibodies were generated by immunizing a rabbit and a guinea pig. The antibodies stained neurons in a variety of rat brain regions, including hippocampal pyramidal neurons, dentate gyrus granular neurons, posterior cortical neurons, and cerebellar Purkinje neurons. Choroid plexus epithelia were also stained. Double immunofluorescence labeling showed that NBCn1 and the postsynaptic density protein PSD-95 were found in the same hippocampal CA3 neurons and partially colocalized in dendrites. PSD-95 was pulled down from rat brain lysates with the GST/NBCn1 fusion protein and was also coimmunoprecipitated with NBCn1. Chronic metabolic acidosis was induced by feeding rats with normal chow or 0.4 M HCl-containing chow for 7 days. Real-time PCR and immunoblot showed upregulation of NBCn1 mRNA and protein in the hippocampus of acidotic rats. NBCn1 immunostaining was enhanced in CA3 neurons, posterior cortical neurons, and cerebellar granular cells. Intraperitoneal administration of N-methyl-d-aspartate caused neuronal death determined by caspase-3 activity, and this effect was more severe in acidotic rats. Administering N-methyl-d-aspartate also inhibited NBCn1 upregulation in acidotic rats. We conclude that NBCn1 in neurons is upregulated by chronic acid loads, and this upregulation is associated with glutamate excitotoxicity.

| S-EPMC2867381 | biostudies-literature

Metabolic phenotyping reveals a lipid mediator response to ionizing radiation.

Project description:Exposure to ionizing radiation has dramatically increased in modern society, raising serious health concerns. The molecular response to ionizing radiation, however, is still not completely understood. Here, we screened mouse serum for metabolic alterations following an acute exposure to ? radiation using a multiplatform mass-spectrometry-based strategy. A global, molecular profiling revealed that mouse serum undergoes a series of significant molecular alterations following radiation exposure. We identified and quantified bioactive metabolites belonging to key biochemical pathways and low-abundance, oxygenated, polyunsaturated fatty acids (PUFAs) in the two groups of animals. Exposure to ? radiation induced a significant increase in the serum levels of ether phosphatidylcholines (PCs) while decreasing the levels of diacyl PCs carrying PUFAs. In exposed mice, levels of pro-inflammatory, oxygenated metabolites of arachidonic acid increased, whereas levels of anti-inflammatory metabolites of omega-3 PUFAs decreased. Our results indicate a specific serum lipidomic biosignature that could be utilized as an indicator of radiation exposure and as novel target for therapeutic intervention. Monitoring such a molecular response to radiation exposure might have implications not only for radiation pathology but also for countermeasures and personalized medicine.

| S-EPMC4156265 | biostudies-literature

Metabolic acidosis post kidney transplantation.

Project description:Metabolic acidosis, a common complication in patients with chronic kidney disease (CKD), results in a multitude of deleterious effects. Though the restoration of kidney function following transplantation is generally accompanied by a correction of metabolic acidosis, a subset of transplant recipients remains afflicted by this ailment and its subsequent morbidities. The vulnerability of kidney allografts to metabolic acidosis can be attributed to reasons similar to pathogenesis of acidosis in non-transplant CKD, and to transplant specific causes, including donor related, recipient related, immune mediated factors, and immunosuppressive medications. Correction of metabolic acidosis in kidney transplantation either with alkali therapy or through dietary manipulations may have potential benefits and the results of such clinical trials are eagerly awaited. This review summarizes the published evidence on the pathogenesis and clinical consequences of chronic metabolic acidosis in kidney transplant recipients.

| S-EPMC9445136 | biostudies-literature

Extracellular Adenosine Formation by Ecto-5'-Nucleotidase (CD73) Is No Essential Trigger for Early Phase Ischemic Preconditioning.

Project description:BackgroundAdenosine is a powerful trigger for ischemic preconditioning (IPC). Myocardial ischemia induces intracellular and extracellular ATP degradation to adenosine, which then activates adenosine receptors and elicits cardioprotection. Conventionally extracellular adenosine formation by ecto-5'-nucleotidase (CD73) during ischemia was thought to be negligible compared to the massive intracellular production, but controversial reports in the past demand further evaluation. In this study we evaluated the relevance of ecto-5'-nucleotidase (CD73) for infarct size reduction by ischemic preconditioning in in vitro and in vivo mouse models of myocardial infarction, comparing CD73-/- and wild type (WT) mice.Methods and results3x5 minutes of IPC induced equal cardioprotection in isolated saline perfused hearts of wild type (WT) and CD73-/- mice, reducing control infarct sizes after 20 minutes of ischemia and 90 minutes of reperfusion from 46 ± 6.3% (WT) and 56.1 ± 7.6% (CD73-/-) to 26.8 ± 4.7% (WT) and 25.6 ± 4.7% (CD73-/-). Coronary venous adenosine levels measured after IPC stimuli by high-pressure liquid chromatography showed no differences between WT and CD73-/- hearts. Pharmacological preconditioning of WT hearts with adenosine, given at the measured venous concentration, was evenly cardioprotective as conventional IPC. In vivo, 4x5 minutes of IPC reduced control infarct sizes of 45.3 ± 8.9% (WT) and 40.5 ± 8% (CD73-/-) to 26.3 ± 8% (WT) and 22.6 ± 6.6% (CD73-/-) respectively, eliciting again equal cardioprotection. The extent of IPC-induced cardioprotection in male and female mice was identical.ConclusionThe infarct size limiting effects of IPC in the mouse heart in vitro and in vivo are not significantly affected by genetic inactivation of CD73. The ecto-5'-nucleotidase derived extracellular formation of adenosine does not contribute substantially to adenosine's well known cardioprotective effect in early phase ischemic preconditioning.

| S-EPMC4532361 | biostudies-literature

Mechanism of Hyperkalemia-Induced Metabolic Acidosis.

Project description:Background Hyperkalemia in association with metabolic acidosis that are out of proportion to changes in glomerular filtration rate defines type 4 renal tubular acidosis (RTA), the most common RTA observed, but the molecular mechanisms underlying the associated metabolic acidosis are incompletely understood. We sought to determine whether hyperkalemia directly causes metabolic acidosis and, if so, the mechanisms through which this occurs.Methods We studied a genetic model of hyperkalemia that results from early distal convoluted tubule (DCT)-specific overexpression of constitutively active Ste20/SPS1-related proline-alanine-rich kinase (DCT-CA-SPAK).Results DCT-CA-SPAK mice developed hyperkalemia in association with metabolic acidosis and suppressed ammonia excretion; however, titratable acid excretion and urine pH were unchanged compared with those in wild-type mice. Abnormal ammonia excretion in DCT-CA-SPAK mice associated with decreased proximal tubule expression of the ammonia-generating enzymes phosphate-dependent glutaminase and phosphoenolpyruvate carboxykinase and overexpression of the ammonia-recycling enzyme glutamine synthetase. These mice also had decreased expression of the ammonia transporter family member Rhcg and decreased apical polarization of H+-ATPase in the inner stripe of the outer medullary collecting duct. Correcting the hyperkalemia by treatment with hydrochlorothiazide corrected the metabolic acidosis, increased ammonia excretion, and normalized ammoniagenic enzyme and Rhcg expression in DCT-CA-SPAK mice. In wild-type mice, induction of hyperkalemia by administration of the epithelial sodium channel blocker benzamil caused hyperkalemia and suppressed ammonia excretion.Conclusions Hyperkalemia decreases proximal tubule ammonia generation and collecting duct ammonia transport, leading to impaired ammonia excretion that causes metabolic acidosis.

| S-EPMC5967781 | biostudies-literature

Apolipoprotein a-I is a potential mediator of remote ischemic preconditioning.

Project description:BackgroundRemote ischemic preconditioning (RIPC) has emerged as an attractive strategy in clinical settings. Despite convincing evidence of the critical role played by circulating humoral mediators, their actual identities remain unknown. In this study, we aimed to identify RIPC-induced humoral mediators using a proteomic approach.Methodsand Results Rats were exposed to 10-min limb ischemia followed by 5- (RIPC 5') or 10-min (RIPC 10') reperfusion prior to blood sampling. The control group only underwent blood sampling. Plasma samples were analyzed using surface-enhanced laser desorption and ionization - time of flight - mass spectrometry (SELDI-TOF-MS). Three protein peaks were selected for their significant increase in RIPC 10'. They were identified and confirmed as apolipoprotein A-I (ApoA-I). Additional rats were exposed to myocardial ischemia-reperfusion (I/R) and assigned to one of the following groups RIPC+myocardial infarction (MI) (10-min limb ischemia followed by 10-min reperfusion initiated 20 minutes prior to myocardial I/R), ApoA-I+MI (10 mg/kg ApoA-I injection 10 minutes before myocardial I/R), and MI (no further intervention). In comparison with untreated MI rats, RIPC reduced infarct size (52.2±3.7% in RIPC+MI vs. 64.9±2.6% in MI; p<0.05). Similarly, ApoA-I injection decreased infarct size (50.9±3.8%; p<0.05 vs. MI).ConclusionsRIPC was associated with a plasmatic increase in ApoA-I. Furthermore, ApoA-I injection before myocardial I/R recapitulated the cardioprotection offered by RIPC in rats. This data suggests that ApoA-I may be a protective blood-borne factor involved in the RIPC mechanism.

| S-EPMC3796499 | biostudies-literature

Lactic acidosis triggers starvation response with distinct metabolic profiles

Project description:[1] Lactic acidosis time course: MCF7 cells were exposed to lactic acidosis for different length of time. We used microarrays to examine the genomic programs of cells incubated under lactic acidosis for different length of time [2] Metabolic profiling: MCF7 cells were exposed to control condition, 25mM lactic acidosis, glucose deprivation (zero glucose) and hypoxia (1% oxygen level). [3] Mouse study: Lactic acidosis triggers starvation response with paradoxical induction of TXNIP through MondoA. Wild-type mouse embryo fibroblasts (MEFs) and TXNIP-null MEFs were exposed to Ctrl versus lactic acidosis conditions for 24hrs and the RNAs from cells were extracted with MiRVana kit (Ambion) and applied to Affymetrix 430A mouse chips We used microarrays to examine the genomic programs of cells incubated under different microenvironmental stresses. [1] Lactic acidosis time course: MCF7 cells were exposed to lactic acidosis for 1, 4, 12 and 24 hours. [2] Metabolic profiling: MCF7 cells were exposed to lactic acidosis, glucose deprivation and hypoxia for 4hours. [3] wild-type mouse embryo fibroblasts (MEFs) and TXNIP-null MEFs were exposed to Ctrl versus lactic acidosis conditions for 24hrs.

2010-09-27 | E-GEOD-19123 | biostudies-arrayexpress

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