2-Deoxy-D-glucose reduces epilepsy progression by NRSF-CtBP-dependent metabolic regulation of chromatin structure

Ang II and Ang IV: unraveling the mechanism of action on synaptic plasticity, memory, and epilepsy

The central angiotensin system plays a crucial role in cardiovascular regulation. More recently, angiotensin peptides have been implicated in stress, anxiety, depression, cognition, and epilepsy. Angiotensin II (Ang II) exerts its actions through AT(1) and AT(2) receptors, while most actions of its metabolite Ang IV were believed to be independent of AT(1) or AT(2) receptor activation. A specific binding site with high affinity for Ang IV was discovered and denominated "AT(4) receptor". The beneficiary effects of AT(4) ligands in animal models for cognitive impairment and epileptic seizures initiated the search for their mechanism of action. This proved to be a challenging task, and after 20 years of research, the nature of the "AT(4) receptor" remains controversial. Insulin-regulated aminopeptidase (IRAP) was first identified as the high-affinity binding site for AT(4) ligands. Recently, the hepatocyte growth factor receptor c-MET was also proposed as a receptor for AT(4) ligands. The present review focuses on the effects of Ang II and Ang IV on synaptic transmission and plasticity, learning, memory, and epileptic seizure activity. Possible interactions of Ang IV with the classical AT(1) and AT(2) receptor subtypes are evaluated, and other potential mechanisms by which AT(4) ligands may exert their effects are discussed. Identification of these mechanisms may provide a valuable target in the development in novel drugs for the treatment of cognitive disorders and epilepsy.

The ketogenic diet in a pill: is this possible?

Over the past decade, much progress has been made in understanding the mechanisms of ketogenic diet (KD) action. From the complex systemic and metabolic changes induced by the KD have emerged innovative hypotheses attempting to link biochemical adaptations to its clinical effects. Despite such developments, the fundamental question of how the KD works remains as elusive as ever. At present, it is unclear which of the many potential mechanisms proposed thus far are directly relevant to the clinical effects of the KD. It is unlikely that these numerous hypotheses can be unified into a single mechanism (or a final common pathway). Nevertheless, it may be instructive to consider each of these putative mechanisms in turn and ask the following question: if the mechanism or target in question is a critical determinant of the anticonvulsant efficacy of the KD, then would a similar intervention known to be based on that mechanism yield a comparable effect? Perhaps answering this question for each mechanistic speculation might help substantiate (or invalidate) that particular hypothesis. Can the KD be packaged into a pill? At present, the answer is likely "no." We have yet to discover a "magic bullet" that completely mirrors the anticonvulsant (and potential neuroprotective) effects of the KD. However, without a clearer understanding of the mechanistic elements comprising the complex metabolic puzzle posed by the KD, we would be left only with empiric observations, and to wonder curiously how a high-fat diet can exert such profound clinical effects.

Seizure suppression via glycolysis inhibition with 2-deoxy-D-glucose (2DG)

Metabolic regulation of neuronal excitability is increasingly recognized as a factor in seizure pathogenesis and control. Inhibiting or bypassing glycolysis may be one way through which the ketogenic diet provides an anticonvulsant effect. 2-deoxy-D-glucose (2DG), a nonmetabolizable glucose analog that partially inhibits glycolysis, was tested in several acute and chronic seizure models. Acutely, 2DG decreases the frequency of high-K(+)-, bicuculline- and 4-aminopyridine-induced interictal bursts in the CA3 region of hippocampal slices; 2DG also exerts anticonvulsant effects in vivo against perforant path kindling in rats. Chronically, 2DG has novel antiepileptic effects by retarding the progression of kindled seizures. Finally, 2DG has a favorable preliminary toxicity profile. These factors support the possibility that 2DG or other modifiers of glycolysis can be used as novel treatments for epilepsy.

Calorie restriction and glucose regulation

Ketogenic diets (KDs) are effective treatments for epilepsy. The mechanisms of action are poorly understood. In some experimental seizure models, calorie restriction and hypoglycemia may augment the antiseizure effects of KDs. In addition, inhibiting glycolysis or diverting glucose from the glycolytic pathway inhibits seizures and possibly epileptogenesis, suggesting an interaction between energy regulation and the anticonvulsant actions of these interventions. Children on KDs frequently exhibit poor weight gain and have lower blood glucose levels compared to children on standard, balanced diets. Young rodents on a KD also exhibit slow weight gain, lower blood glucose and insulin levels, and elevated leptin levels. This review considers the possibility that calorie restriction, low serum glucose, and KDs share common cell signaling pathways to alter brain excitability. AMP-activated protein kinase (AMPK) is an attractive candidate signaling protein that could link energy balance to gene expression in such a way so as to reduce brain excitability.

Ketone bodies, glycolysis, and KATP channels in the mechanism of the ketogenic diet

The ketogenic diet (KD) has shown remarkable efficacy in the treatment of drug-resistant childhood epilepsy. Our understanding of how the KD produces its anticonvulsant and antiepileptogenic effects remains incomplete, which is perhaps not surprising for a biological manipulation as sweeping as dietary change. Several hypotheses focus on ketone bodies, fuel molecules that circulate at millimolar concentrations in the blood of patients on a KD, as causative agents. Here I consider some recent evidence for one such hypothesis, involving a possible role for altered glycolysis and consequent activation of a class of potassium channels called K(ATP)channels.

Possible mechanisms for the anticonvulsant activity of fructose-1,6-diphosphate

Fructose-1,6-diphosphate (FDP), an intracellular metabolite of glucose, has anticonvulsant activity in several models of acute seizures in laboratory animals. The anticonvulsant effect of FDP is most likely due to a direct effect since intraperitoneal and oral administration results in significant increases in brain levels. A number of mechanisms have been proposed for this action of FDP. One possibility is that peripheral administration of FDP results in changes in brain metabolism that are anticonvulsant. Glucose can be metabolized through the glycolytic or pentose phosphate pathway. There is evidence that the pentose phosphate pathway is more active in the brain than in other tissues, and that, in the presence of elevated levels of FDP, the majority of glucose is metabolized by the pentose phosphate pathway. The pentose phosphate pathway generates NADPH, which is used to reduce glutathione. The reduced form of endogenous glutathione has been shown to have anticonvulsant activity. Taken together, the data suggest a hypothesis that exogenously administered FDP gets into the brain and astrocytes where it increases the flux of glucose through the pentose phosphate pathway, generating additional NADPH for the reduction of glutathione.

A Drosophila systems model of pentylenetetrazole induced locomotor plasticity responsive to antiepileptic drugs

Background

Rodent kindling induced by PTZ is a widely used model of epileptogenesis and AED testing. Overlapping pathophysiological mechanisms may underlie epileptogenesis and other neuropsychiatric conditions. Besides epilepsy, AEDs are widely used in treating various neuropsychiatric disorders. Mechanisms of AEDs' long term action in these disorders are poorly understood. We describe here a Drosophila systems model of PTZ induced locomotor plasticity that is responsive to AEDs.

Results

We empirically determined a regime in which seven days of PTZ treatment and seven days of subsequent PTZ discontinuation respectively cause a decrease and an increase in climbing speed of Drosophila adults. Concomitant treatment with NaVP and LEV, not ETH, GBP and VGB, suppressed the development of locomotor deficit at the end of chronic PTZ phase. Concomitant LEV also ameliorated locomotor alteration that develops after PTZ withdrawal. Time series of microarray expression profiles of heads of flies treated with PTZ for 12 hrs (beginning phase), two days (latent phase) and seven days (behaviorally expressive phase) showed only down-, not up-, regulation of genes; expression of 23, 2439 and 265 genes were downregulated, in that order. GO biological process enrichment analysis showed downregulation of transcription, neuron morphogenesis during differentiation, synaptic transmission, regulation of neurotransmitter levels, neurogenesis, axonogenesis, protein modification, axon guidance, actin filament organization etc. in the latent phase and of glutamate metabolism, cell communication etc. in the expressive phase. Proteomic interactome based analysis provided further directionality to these events. Pathway overrepresentation analysis showed enrichment of Wnt signaling and other associated pathways in genes downregulated by PTZ. Mining of available transcriptomic and proteomic data pertaining to established rodent models of epilepsy and human epileptic patients showed overrepresentation of epilepsy associated genes in our PTZ regulated set.

Conclusion

Systems biology ultimately aims at delineating and comprehending the functioning of complex biological systems in such details that predictive models of human diseases could be developed. Due to immense complexity of higher organisms, systems biology approaches are however currently focused on simpler organisms. Amenable to modeling, our model offers a unique opportunity to further dissect epileptogenesis-like plasticity and to unravel mechanisms of long-term action of AEDs relevant in neuropsychiatric disorders.

Astroglial metabolic networks sustain hippocampal synaptic transmission

Astrocytes provide metabolic substrates to neurons in an activity-dependent manner. However, the molecular mechanisms involved in this function, as well as its role in synaptic transmission, remain unclear. Here, we show that the gap-junction subunit proteins connexin 43 and 30 allow intercellular trafficking of glucose and its metabolites through astroglial networks. This trafficking is regulated by glutamatergic synaptic activity mediated by AMPA receptors. In the absence of extracellular glucose, the delivery of glucose or lactate to astrocytes sustains glutamatergic synaptic transmission and epileptiform activity only when they are connected by gap junctions. These results indicate that astroglial gap junctions provide an activity-dependent intercellular pathway for the delivery of energetic metabolites from blood vessels to distal neurons.

Mouse models of Wolf-Hirschhorn syndrome

Subtelomeric deletion syndromes represent a significant cause of mental retardation and craniofacial disease. However, for most of these syndromes the pathogenic genes have yet to be identified. Currently there is every indication that identification of these genes will be a slow process if we continue to rely strictly upon clinical data. An alternative approach is the use of mouse models to complement the patient studies. Wolf-Hirschhorn syndrome (WHS), caused by deletions in 4p16.3, is the first recognized subtelomeric deletion syndrome. As with other syndromes of this class, WHS has not yet been subjected to an intensive, systematic analysis using mouse models. Nonetheless, a significant number of targeted mutations have been introduced into mouse genomic region, 5B1, which is orthologous to 4p16.3. Included among these mutations are a series of deletions approximating the deletions in some patients. The mouse lines carrying these deletions display a remarkable concordance of phenotypes with the human patient's characteristics, strongly indicating that the mouse models can be used to phenocopy WHS. In this review, we will catalog the currently existing targeted mutations in mice in the regions orthologous to the WHS critical regions. For each mutation we will discuss the resulting phenotype and its potential relevance to the pathogenesis of the syndrome. Further, we will describe how the phenotypes of some of the mutations suggest new directions for the clinical studies. Finally we will outline approaches for the efficient creation of new mouse models of WHS going forward.

MED19 and MED26 are synergistic functional targets of the RE1 silencing transcription factor in epigenetic silencing of neuronal gene expression

A key hub for the orchestration of epigenetic modifications necessary to restrict neuronal gene expression to the nervous system is the RE1 silencing transcription factor (REST; also known as neuron restrictive silencer factor, NRSF). REST suppresses the nonspecific and premature expression of neuronal genes in non-neuronal and neural progenitor cells, respectively, via recruitment of enzymatically diverse corepressors, including G9a histone methyltransferase (HMTase) that catalyzes di-methylation of histone 3-lysine 9 (H3K9me2). Recently, we identified the RNA polymerase II transcriptional Mediator to be an essential link between RE1-bound REST and G9a in epigenetic suppression of neuronal genes in non-neuronal cells. However, the means by which REST recruits Mediator to facilitate G9a-dependent extra-neuronal gene silencing remains to be elucidated. Here, we identify the MED19 and MED26 subunits in Mediator as direct physical and synergistic functional targets of REST. We show that although REST independently binds to both MED19 and MED26 in isolation, combined depletion of both subunits is required to disrupt the association of REST with Mediator. Furthermore, combined, but not individual, depletion of MED19/MED26 impairs REST-directed recruitment to RE1 elements of Mediator and G9a, leading to a reversal of G9a-dependent H3K9me2 and de-repression of REST-target gene expression. Together, these findings identify MED19/MED26 as a probable composite REST interface in Mediator and further clarify the mechanistic basis by which Mediator facilitates REST-imposed epigenetic restrictions on neuronal gene expression.

Ketogenic diet is antiepileptogenic in pentylenetetrazole kindled mice and decrease levels of N-acylethanolamines in hippocampus

The ketogenic diet (KD) is used for the treatment of refractory epilepsy in children, however, the mechanism(s) remains largely unknown. Also, the antiepileptogenic potential in animal models of epilepsy has been poorly addressed. Activation of cannabinoid type-1 receptor (CB(1)-R) upon seizure activity may mediate neuroprotection as may several N-acylethanolamines. It is unknown how the KD interfere with the endocannabinoid system. We investigated the antiepileptogenic potential of the KD in the pentylenetetrazole kindling model in young mice and measured the hippocampal levels of CB(1)-R by Western blot and of endocannabinoids and N-acylethanolamines by mass spectrometry. The KD significantly decreased incidence and severity of seizures, and significantly increased the latency to clonic convulsions. There were no changes in levels of endocannabinoids or CB(1)-R expression by either seizure activity or type of diet. The level of oleoylethanolamide as well as the sum of N-acylethanolamines were significantly decreased by the KD, but were unaffected by seizure activity. The study shows that the KD had clear antiepileptogenic properties in the pentylenetetrazole kindling model and does not support a role of endocannabinoids in this model. The significance of the decreased hippocampal level of oleoylethanolamide awaits further studies.

Progress report on new antiepileptic drugs: a summary of the Ninth Eilat Conference (EILAT IX)

The Ninth Eilat Conference on New Antiepileptic Drugs (AEDs)-EILAT IX, took place in Sitges, Barcelona from the 15th to 19th of June 2008. Over 300 basic scientists, clinical pharmacologists and neurologists from 25 countries attended the conference, whose main themes included old and new AEDs in generalized epilepsies, novel formulations and routes of administration of AEDs, common targets and mechanisms of action of drugs for treating epilepsy and other central nervous system (CNS) disorders, and opportunities and perspectives in new AED discovery. Consistent with previous formats of this conference, a large part of the programme was devoted to a review of AEDs in development, as well as updates on AEDs introduced since 1989. Unlike previous EILAT manuscripts, the current (EILAT IX) manuscript focuses only on the preclinical and clinical pharmacology of AEDs that are currently in development. These include brivaracetam, carisbamate (RWJ-333369), 2-deoxy-d-glucose, eslicarbazepine acetate (BIA-2-093), ganaxolone, huperzine, JZP-4, lacosamide, NAX-5055, propylisopropylacetamide (PID), retigabine, T-2000, tonabersat, valrocemide and YKP-3089. The CNS efficacy of these compounds in anticonvulsant animal models as well as other disease model systems are presented in first and second tables and their proposed mechanisms of action are summarized in the third table.

A catabolic block does not sufficiently explain how 2-deoxy-D-glucose inhibits cell growth

The glucose analogue 2-deoxy-D-glucose (2-DG) restrains growth of normal and malignant cells, prolongs the lifespan of C. elegans, and is widely used as a glycolytic inhibitor to study metabolic activity with regard to cancer, neurodegeneration, calorie restriction, and aging. Here, we report that separating glycolysis and the pentose phosphate pathway highly increases cellular tolerance to 2-DG. This finding indicates that 2-DG does not block cell growth solely by preventing glucose catabolism. In addition, 2-DG provoked similar concentration changes of sugar-phosphate intermediates in wild-type and 2-DG-resistant yeast strains and in human primary fibroblasts. Finally, a genome-wide analysis revealed 19 2-DG-resistant yeast knockouts of genes implicated in carbohydrate metabolism and mitochondrial homeostasis, as well as ribosome biogenesis, mRNA decay, transcriptional regulation, and cell cycle. Thus, processes beyond the metabolic block are essential for the biological properties of 2-DG.

Pharmacodynamic and pharmacokinetic interactions between common antiepileptic drugs and acetone, the chief anticonvulsant ketone body elevated in the ketogenic diet in mice

PURPOSE

Acetone is the principal ketone body elevated in the ketogenic diet (KD), with demonstrated robust anticonvulsant properties across a variety of seizure tests and models of epilepsy. Because the majority of patients continue to receive antiepileptic drugs (AEDs) during KD treatment, interactions between acetone and AEDs may have important clinical implications. Therefore, we investigated whether acetone could affect the anticonvulsant activity and pharmacokinetic properties of several AEDs against maximal electroshock (MES)-induced seizures in mice.

METHODS

Effects of acetone given in subthreshold doses were tested on the anticonvulsant effects of carbamazepine (CBZ), lamotrigine (LTG), oxcarbazepine (OXC), phenobarbital (PB), phenytoin (PHT), topiramate (TPM) and valproate (VPA) against MES-induced seizures in mice. In addition, acute adverse effects of acetone-AEDs combinations were assessed in the chimney test (motor performance) and passive avoidance task (long-term memory). Pharmacokinetic interactions between acetone and AEDs were also studied in the mouse brain tissue.

RESULTS

Acetone (5 or 7.5 mmol/kg, intraperitoneally [i.p.]) enhanced the anticonvulsant activity of CBZ, LTG, PB, and VPA against MES-induced seizures; effects of OXC, PHT, and TPM were not changed. Acetone (7.5 mmol/kg) did not enhance the acute adverse-effect profiles of the studied AEDs. Acetone (5 or 7.5 mmol/kg, i.p.) did not affect total brain concentrations of the studied AEDs. In contrast, VPA, CBZ, LTG, OXC, and TPM significantly decreased the concentration of free acetone in the brain; PB and PHT had no effect.

CONCLUSIONS

Acetone enhances the anticonvulsant effects of several AEDs such as VPA, CBZ, LTG, and PB without affecting their pharmacokinetic and side-effect profiles.

The neuroprotective properties of calorie restriction, the ketogenic diet, and ketone bodies

Both calorie restriction and the ketogenic diet possess broad therapeutic potential in various clinical settings and in various animal models of neurological disease. Following calorie restriction or consumption of a ketogenic diet, there is notable improvement in mitochondrial function, a decrease in the expression of apoptotic and inflammatory mediators and an increase in the activity of neurotrophic factors. However, despite these intriguing observations, it is not yet clear which of these mechanisms account for the observed neuroprotective effects. Furthermore, limited compliance and concern for adverse effects hamper efforts at broader clinical application. Recent research aimed at identifying compounds that can reproduce, at least partially, the neuroprotective effects of the diets with less demanding changes to food intake suggests that ketone bodies might represent an appropriate candidate. Ketone bodies protect neurons against multiple types of neuronal injury and are associated with mitochondrial effects similar to those described during calorie restriction or ketogenic diet treatment. The present review summarizes the neuroprotective effects of calorie restriction, of the ketogenic diet and of ketone bodies, and compares their putative mechanisms of action.

Multiphoton microscopy and fluorescence lifetime imaging microscopy (FLIM) to monitor metastasis and the tumor microenvironment

Cancer metastasis involves complex cell behavior and interaction with the extracellular matrix by metabolically active cells. To observe invasion and metastasis with sub-cellular resolution in vivo, multiphoton microscopy (MPM) allows imaging more deeply into tissues with less toxicity, compared with other optical imaging methods. MPM can be combined with second harmonic generation (SHG), fluorescent lifetime imaging microscopy (FLIM), and spectral-lifetime imaging microscopy (SLIM). SHG facilitates imaging of stromal collagen and tumor-stroma interactions, including the architecture and remodeling of the tumor microenvironment. FLIM allows characterization of exogenous and endogenous fluorophores, such as the metabolites FAD and NADH to score for metabolic state and provide optical biomarkers. SLIM permits additional identification and separation of endogenous and exogenous fluorophores by simultaneously collecting their spectra and lifetime, producing an optical molecular "fingerprint". Both FLIM and SLIM also serve as an improved method for the assessment of Förster (or fluorescence) resonance energy transfer (FRET). Hence, the use and further development of these approaches strongly enhances the visualization and quantification of tumor progression, invasion, and metastasis. Herein, we review recent developments of multiphoton FLIM and SLIM to study 2D and 3D cell migration, invasion into the tumor microenvironment, and metastasis.

Ketogenic diets cause opposing changes in synaptic morphology in CA1 hippocampus and dentate gyrus of late-adult rats

Ketogenic diets (KDs) have beneficial effects on several diseases, such as epilepsy, mitochondriopathies, cancer, and neurodegeneration. However, little is known about their effects on aging individuals. In the present study, late-adult (19-month-old) rats were fed for 8 weeks with two medium chain triglycerides (MCT)-KDs, and the following morphologic parameters reflecting synaptic plasticity were evaluated in stratum moleculare of hippocampal CA1 region (SM CA1) and outer molecular layer of hippocampal dentate gyrus (OML DG): average area (S), numeric density (Nv(s)), and surface density (Sv) of synapses, and average volume (V), numeric density (Nv(m)), and volume density (Vv) of synaptic mitochondria. In SM CA1, MCT-KDs induced the early appearance of the morphologic patterns typical of old animals (higher S and V, and lower Nv(s) and Nv(m)). On the contrary, in OML DG, Sv and Vv of MCT-KDs-fed rats were higher (as a result of higher Nv(s) and Nv(m)) versus controls; these modifications are known to improve synaptic function and metabolic supply. The opposite effects of MCT-KDs might reflect the different susceptibility to aging processes: OML DG is less vulnerable than SM CA1, and the reactivation of ketone bodies uptake and catabolism might occur more efficiently in this region, allowing the exploitation of their peculiar metabolic properties. Present findings provide the first evidence that MCT-KDs may cause opposite morphologic modifications, being potentially harmful for SM CA1 and potentially advantageous for OML DG. This implies risks but also promising potentialities for their therapeutic use during aging.

Can reducing sugar retard kindling?

2-Deoxy-d-Glucose Reduces Epilepsy Progression by NRSF-CtBP-Dependent Metabolic Regulation of Chromatin Structure. Garriga-Canut M, Schoenike B, Qazi R, Bergendahl K, Daley TJ, Pfender RM, Morrison JF, Ockuly J, Stafstrom C, Sutula T, Roopra A. Nat Neurosci 2006;9(11):1382–1387. Temporal lobe epilepsy is a common form of drug-resistant epilepsy that sometimes responds to dietary manipulation such as the ‘ketogenic diet’. Here we have investigated the effects of the glycolytic inhibitor 2-deoxy-d-glucose (2DG) in the rat kindling model of temporal lobe epilepsy. We show that 2DG potently reduces the progression of kindling and blocks seizure-induced increases in the expression of brain-derived neurotrophic factor and its receptor, TrkB. This reduced expression is mediated by the transcription factor NRSF, which recruits the NADH-binding co-repressor CtBP to generate a repressive chromatin environment around the BDNF promoter. Our results show that 2DG has anticonvulsant and antiepileptic properties, suggesting that anti-glycolytic compounds may represent a new class of drugs for treating epilepsy. The metabolic regulation of neuronal genes by CtBP will open avenues of therapy for neurological disorders and cancer.

Are purines mediators of the anticonvulsant/neuroprotective effects of ketogenic diets?

Abnormal neuronal signaling caused by metabolic changes characterizes several neurological disorders, and in some instances metabolic interventions provide therapeutic benefits. Indeed, altering metabolism either by fasting or by maintaining a low-carbohydrate (ketogenic) diet might reduce epileptic seizures and offer neuroprotection in part because the diet increases mitochondrial biogenesis and brain energy levels. Here we focus on a novel hypothesis that a ketogenic diet-induced change in energy metabolism increases levels of ATP and adenosine, purines that are critically involved in neuron-glia interactions, neuromodulation and synaptic plasticity. Enhancing brain bioenergetics (ATP) and increasing levels of adenosine, an endogenous anticonvulsant and neuroprotective molecule, might help with understanding and treating a variety of neurological disorders.

Collagen density promotes mammary tumor initiation and progression

BACKGROUND

Mammographically dense breast tissue is one of the greatest risk factors for developing breast carcinoma. Despite the strong clinical correlation, breast density has not been causally linked to tumorigenesis, largely because no animal model has existed for studying breast tissue density. Importantly, regions of high breast density are associated with increased stromal collagen. Thus, the influence of the extracellular matrix on breast carcinoma development and the underlying molecular mechanisms are not understood.

METHODS

To study the effects of collagen density on mammary tumor formation and progression, we utilized a bi-transgenic tumor model with increased stromal collagen in mouse mammary tissue. Imaging of the tumors and tumor-stromal interface in live tumor tissue was performed with multiphoton laser-scanning microscopy to generate multiphoton excitation and spectrally resolved fluorescent lifetimes of endogenous fluorophores. Second harmonic generation was utilized to image stromal collagen.

RESULTS

Herein we demonstrate that increased stromal collagen in mouse mammary tissue significantly increases tumor formation approximately three-fold (p < 0.00001) and results in a significantly more invasive phenotype with approximately three times more lung metastasis (p < 0.05). Furthermore, the increased invasive phenotype of tumor cells that arose within collagen-dense mammary tissues remains after tumor explants are cultured within reconstituted three-dimensional collagen gels. To better understand this behavior we imaged live tumors using nonlinear optical imaging approaches to demonstrate that local invasion is facilitated by stromal collagen re-organization and that this behavior is significantly increased in collagen-dense tissues. In addition, using multiphoton fluorescence and spectral lifetime imaging we identify a metabolic signature for flavin adenine dinucleotide, with increased fluorescent intensity and lifetime, in invading metastatic cells.

CONCLUSION

This study provides the first data causally linking increased stromal collagen to mammary tumor formation and metastasis, and demonstrates that fundamental differences arise and persist in epithelial tumor cells that progressed within collagen-dense microenvironments. Furthermore, the imaging techniques and signature identified in this work may provide useful diagnostic tools to rapidly assess fresh tissue biopsies.

Normal Neurogenesis but Abnormal Gene Expression in Human Fragile X Cortical Progenitor Cells

Human stem and progenitor cells offer an innovative way to study early events in development. An exciting new opportunity for these cells is their application to study the underlying developmental consequences of genetic diseases. Because many diseases, ranging from leukemias to developmental disorders, are caused by single-gene defects, stem and progenitor cells that carry disease-causing genetic mutations are invaluable in understanding and treating disease. We have characterized human neural progenitor (hNPCs) cells that carry a single-gene defect that leads to the neurodevelopmental disorder Fragile X syndrome (FX). A loss-of-function mutation in the FMR1 gene leads to subtle changes in neural development and subsequent mental impairment characteristic of FX. hNPCs were isolated from fetal cortex carrying the FMR1 mutation to determine whether aberrations occur in their proliferation and differentiation. As expected, FX hNPCs have reduced expression of the FMR1 gene product Fragile X mental retardation protein (FMRP), and this decrease is maintained in culture and following differentiation. In contrast to a previously published report, the proliferation of FX hNPCs and their differentiation into neurons is not different from unaffected controls. Although the early development of FX hNPCs is essentially normal, microarray analysis reveals novel changes in the expression of signal transduction genes in FX hNPCs. Therefore, hNPCs have intrinsic characteristics that can be investigated to further our understanding and potential treatment of developmental disorders such as FX.

The ketogenic diet and epilepsy

PURPOSE OF REVIEW

The ketogenic diet has long been used to treat medically refractory epilepsy. The mechanisms underlying its clinical effects, however, have remained a mystery. The evidence to date suggests that a fundamental shift from glycolysis to intermediary metabolism induced by the ketogenic diet is necessary and sufficient for clinical efficacy. This notion is supported by a growing number of studies indicating that glucose restriction, ketone bodies and polyunsaturated fatty acids may all play mechanistic roles, possibly by enhancing mitochondrial respiration and ATP production, and decreasing reactive oxygen species production.

RECENT FINDINGS

Recent reports indicate that ketone bodies can reduce oxidative stress and that fatty acid-induced mitochondrial uncoupling may also yield similar protective effects. Ketone bodies may attenuate spontaneous firing of ATP-sensitive potassium channels in central neurons, and pharmacological inhibition of glycolysis has been shown to retard epileptogenesis in a rat kindling model.

SUMMARY

While the mechanisms underlying the broad clinical efficacy of the ketogenic diet remain unclear, there is growing evidence that the ketogenic diet alters the fundamental biochemistry of neurons in a manner that not only inhibits neuronal hyperexcitability but also induces a protective effect. Thus, the ketogenic diet may ultimately be useful in the treatment of a variety of neurological disorders.

Inhibition of agouti-related peptide expression by glucose in a clonal hypothalamic neuronal cell line is mediated by glycolysis, not oxidative phosphorylation

The regulation of neuroendocrine electrical activity and gene expression by glucose is mediated through several distinct metabolic pathways. Many studies have implicated AMP and ATP as key metabolites mediating neuroendocrine responses to glucose, especially through their effects on AMP-activated protein kinase (AMPK), but other studies have suggested that glycolysis, and in particular the cytoplasmic conversion of nicotinamide adenine dinucleotide (NAD+) to reduced NAD (NADH), may play a more important role than oxidative phosphorylation for some effects of glucose. To address these molecular mechanisms further, we have examined the regulation of agouti-related peptide (AgRP) in a clonal hypothalamic cell line, N-38. AgRP expression was induced monotonically as glucose concentrations decreased from 10 to 0.5 mm glucose and with increasing concentrations of glycolytic inhibitors. However, neither pyruvate nor 3-beta-hydroxybutyrate mimicked the effect of glucose to reduce AgRP mRNA, but on the contrary, produced the opposite effect of glucose and actually increased AgRP mRNA. Nevertheless, 3beta-hydroxybutyrate mimicked the effect of glucose to increase ATP and to decrease AMPK phosphorylation. Similarly, inhibition of AMPK by RNA interference increased, and activation of AMPK decreased, AgRP mRNA. Additional studies demonstrated that neither the hexosamine nor the pentose/carbohydrate response element-binding protein pathways mediate the effects of glucose on AgRP expression. These studies do not support that either ATP or AMPK mediate effects of glucose on AgRP in this hypothalamic cell line but support a role for glycolysis and, in particular, NADH. These studies support that cytoplasmic or nuclear NADH, uniquely produced by glucose metabolism, mediates effects of glucose on AgRP expression.

Dynamic rerouting of the carbohydrate flux is key to counteracting oxidative stress

BACKGROUND

Eukaryotic cells have evolved various response mechanisms to counteract the deleterious consequences of oxidative stress. Among these processes, metabolic alterations seem to play an important role.

RESULTS

We recently discovered that yeast cells with reduced activity of the key glycolytic enzyme triosephosphate isomerase exhibit an increased resistance to the thiol-oxidizing reagent diamide. Here we show that this phenotype is conserved in Caenorhabditis elegans and that the underlying mechanism is based on a redirection of the metabolic flux from glycolysis to the pentose phosphate pathway, altering the redox equilibrium of the cytoplasmic NADP(H) pool. Remarkably, another key glycolytic enzyme, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), is known to be inactivated in response to various oxidant treatments, and we show that this provokes a similar redirection of the metabolic flux.

CONCLUSION

The naturally occurring inactivation of GAPDH functions as a metabolic switch for rerouting the carbohydrate flux to counteract oxidative stress. As a consequence, altering the homoeostasis of cytoplasmic metabolites is a fundamental mechanism for balancing the redox state of eukaryotic cells under stress conditions.

Fructose-1,6-bisphosphate has anticonvulsant activity in models of acute seizures in adult rats

A variety of observations suggest that decreasing glycolysis and increasing levels of reduced glutathione, generated by metabolism of glucose through the pentose phosphate pathway, would have an anticonvulsant effect. Because fructose-1,6-bisphosphate (F1,6BP) shifts the metabolism of glucose from glycolysis to the pentose phosphate pathway, it was hypothesized to have anticonvulsant activity. The anticonvulsant activity of F1,6BP was determined in rat models of acute seizures induced by pilocarpine, kainic acid, or pentylenetetrazole. The efficacy of F1,6BP was compared with that of 2-deoxyglucose (2-DG; an inhibitor of glucose uptake and glycolysis), valproic acid (VPA), and the ketogenic diet. One hour before each convulsant, Sprague Dawley rats received either saline (as seizure controls), F1,6BP (0.25, 0.5 or 1 g/kg), 2-DG (0.25 or 0.5 g/kg), or VPA (0.3 g/kg). Additional animals received the ketogenic diet (starting at 20 or 60 d old). Time to seizure onset, seizure duration, and seizure score were measured in each group. F1,6BP had dose-dependent anticonvulsant activity in all three models, whereas VPA had partial efficacy. 2-DG was only effective in the pilocarpine model. The ketogenic diet had no effect in these models. F1,6BP was also partially effective when given at the first behavioral seizure after pilocarpine. Administration of sodium lactate, which bypasses the block in the glycolytic pathway, abolished the anticonvulsant activity of 2-DG in the pilocarpine model, but only decreased the efficacy of F1,6BP. These data demonstrate that F1,6BP has significant anticonvulsant efficacy.

Role of the PLDLS-binding cleft region of CtBP1 in recruitment of core and auxiliary components of the corepressor complex

C-terminal binding protein (CtBP) family proteins CtBP1 and CtBP2 are highly homologous transcriptional corepressors and are recruited by a large number of transcription factors to mediate sequence-specific transcriptional repression. In addition to DNA-binding repressors, the nuclear protein complex of CtBP1 consists of enzymatic constituents such as histone deacetylases (HDAC1/2), histone methyl transferases (HMTases; G9a and GLP), and the lysine-specific demethylase (LSD1). Additionally, CtBPs also recruit the components of the sumoylation machinery. The CtBPs contain two different unique structural elements, a hydrophobic cleft, with which factors that contain motifs related to the E1A PLDLS motif bind, and a surface groove that binds with factors containing motifs related to the sequence RRTGXPPXL (RRT motif). By structure-based functional dissection of CtBP1, we show that the PLDLS-binding cleft region functions as the primary recruitment center for DNA-binding factors and for the core and auxiliary enzymatic constituents of the CtBP1 corepressor complex. We identify HDAC1/2, CoREST/LSD1, and Ubc9 (E2) as the core constituents of the CtBP1 complex, and these components interact with the PLDLS cleft region through non-PLDLS interactions. Among the CtBP core constituents, HDACs contribute predominantly to the repression activity of CtBP1. The auxiliary components include an HMTase complex (G9a/Wiz/CDYL) and two SUMO E3 ligases, HPC2 and PIAS1. The interaction of auxiliary components with CtBP1 is excluded by PLDLS (E1A)-mediated interactions. Although monomeric CtBP1 is proficient in the recruiting of both core and auxiliary components, NAD(H)-dependent dimerization is required for transcriptional repression. We also provide evidence that CtBP1 functions as a platform for sumoylation of cofactors.

Chromatin crosstalk in development and disease: lessons from REST

Protein complexes that contain chromatin-modifying enzymes have an important role in regulating gene expression. Recent studies have shown that a single transcription factor, the repressor element 1-silencing transcription factor (REST), can act as a hub for the recruitment of multiple chromatin-modifying enzymes, uncovering interdependencies among individual enzymes that affect gene regulation. Research into the function of REST and its corepressors has provided novel insight into how chromatin-modifying proteins cooperate, and how alterations in this function cause disease. These mechanisms will be relevant to the combinatorial functioning of modular transcriptional regulators that work together to regulate a common promoter; they should also identify targets for potential therapies for a range of human diseases.

Etiology and management of refractory epilepsies

The epilepsies are an important, common and diverse group of symptom complexes characterized by recurrent spontaneous seizures. Although many patients with epilepsy have their seizures controlled effectively by antiepileptic drugs (AEDs), about one-third of patients continue to have seizures, despite trying a range of AEDs. Such patients bear the heaviest burden of epilepsy, with increased morbidity and risk of premature mortality. Our current understanding of the refractory epilepsies--the most common of which are focal--is limited; even their definition is problematic. Standard treatments for refractory epilepsies include optimization of existing AED regimens, trials of further AEDs, and, for some patients, therapeutic resective neurosurgery. Recent basic research has explored possible underlying causes of refractory epilepsy, and two main hypotheses have emerged to account for the failure of AED treatment. According to one hypothesis, AEDs might fail because of alterations in the properties of their usual targets. Alternatively, they might fail because multidrug transporter mechanisms limit concentrations of the drugs at their targets. The refractory epilepsies can be viewed as offering remarkable insights into biological processes in the epilepsies, and their effective treatment remains an important aim; treatment would potentially bring much-needed relief to hundreds of thousands of patients across the world.

Epilepsia refratária: a experiência do Núcleo Avançado de Tratamento das Epilepsias do Hospital Felício Rocho (NATE) no período de março de 2003 a dezembro de 2006

INTRODUÇÃO: A epilepsia é um problema de saúde pública. Afeta mais de cinqüenta milhões de pessoas em todo mundo e mais de vinte milhões deles continuam apresentando crises que não controlam satisfatoriamente com o uso de medicamentos. As epilepsias refratárias correspondem a cerca de 20% dos pacientes epilépticos e boa parte desses apresentam crises parciais complexas passíveis de tratamento cirúrgico. A indicação cirúrgica criteriosa tem se mostrado eficiente para o controle das crises. OBJETIVO: Apresentar dados epidemiológicos e cirúrgicos dos pacientes submetidos ao tratamento cirúrgico no NATE. METODOLOGIA: Estudo retrospectivo com análise de prontuários e classificação do controle de crises de 46 pacientes considerando a Escala de Engel. RESULTADOS: Predomina o sexo masculino, solteiros, sem história familiar para epilepsia. Pacientes procedentes do Estado de Minas Gerais e outros estados da união. Início das crises na infância para 58,8% dos pacientes sendo o tipo de crise mais freqüente a crise parcial complexa. O déficit de memória foi a queixa cognitiva mais comum. CONCLUSÃO: O controle de crise foi compatível com Engel Ia (sem crise) para 67% dos pacientes. O tratamento cirúrgico revelou-se eficiente para o controle das crises dos pacientes portadores de epilepsia refratária ao tratamento medicamentoso.

Ketogenic diet metabolites reduce firing in central neurons by opening K(ATP) channels

A low-carbohydrate ketogenic diet remains one of the most effective (but mysterious) treatments for severe pharmacoresistant epilepsy. We have tested for an acute effect of physiological ketone bodies on neuronal firing rates and excitability, to discover possible therapeutic mechanisms of the ketogenic diet. Physiological concentrations of ketone bodies (beta-hydroxybutyrate or acetoacetate) reduced the spontaneous firing rate of neurons in slices from rat or mouse substantia nigra pars reticulata. This region is thought to act as a "seizure gate," controlling seizure generalization. Consistent with an anticonvulsant role, the ketone body effect is larger for cells that fire more rapidly. The effect of ketone bodies was abolished by eliminating the metabolically sensitive K(ATP) channels pharmacologically or by gene knock-out. We propose that ketone bodies or glycolytic restriction treat epilepsy by augmenting a natural activity-limiting function served by K(ATP) channels in neurons.

The neuropharmacology of the ketogenic diet

The ketogenic diet is a valuable therapeutic approach for epilepsy, one in which most clinical experience has been with children. Although the mechanism by which the diet protects against seizures is unknown, there is evidence that it causes effects on intermediary metabolism that influence the dynamics of the major inhibitory and excitatory neurotransmitter systems in brain. The pattern of protection of the ketogenic diet in animal models of seizures is distinct from that of other anticonvulsants, suggesting that it has a unique mechanism of action. During consumption of the ketogenic diet, marked alterations in brain energy metabolism occur, with ketone bodies partly replacing glucose as fuel. Whether these metabolic changes contribute to acute seizure protection is unclear; however, the ketone body acetone has anticonvulsant activity and could play a role in the seizure protection afforded by the diet. In addition to acute seizure protection, the ketogenic diet provides protection against the development of spontaneous recurrent seizures in models of chronic epilepsy, and it has neuroprotective properties in diverse models of neurodegenerative disease.

Anticonvulsant mechanisms of the ketogenic diet

The ketogenic diet (KD) is a broadly effective treatment for medically refractory epilepsy. Despite nearly a century of use, the mechanisms underlying its clinical efficacy remain unknown. In this review, we present one intersecting view of how the KD may exert its anticonvulsant activity against the backdrop of several seemingly disparate mechanistic theories. We summarize key insights gleaned from experimental and clinical studies of the KD, and focus particular attention on the role that ketone bodies, fatty acids, and limited glucose may play in seizure control. Chronic ketosis is anticipated to modify the tricarboxcylic acid cycle to increase GABA synthesis in brain, limit reactive oxygen species (ROS) generation, and boost energy production in brain tissue. Among several direct neuro-inhibitory actions, polyunsaturated fatty acids increased after KD induce the expression of neuronal uncoupling proteins (UCPs), a collective up-regulation of numerous energy metabolism genes, and mitochondrial biogenesis. These effects further limit ROS generation and increase energy production. As a result of limited glucose and enhanced oxidative phosphorylation, reduced glycolytic flux is hypothesized to activate metabolic K(ATP) channels and hyperpolarize neurons and/or glia. Although it is unlikely that a single mechanism, however well substantiated, will explain all of the diet's clinical benefits, these diverse, coordinated changes seem poised to stabilize synaptic function and increase the resistance to seizures throughout the brain.

The ketogenic diet: one decade later

The ketogenic diet, a high fat, adequate protein, low carbohydrate diet, has, during the past decade, had a resurgence of interest for the treatment of difficult-to-control seizures in children. This review traces its history, reviews its uses and side effects, and discusses possible alternatives and the diet's possible mechanisms of action. Finally, this review looks toward possible future uses of the ketogenic diet for conditions other than epilepsy.

Metabolic regulation of SIRT1 transcription via a HIC1:CtBP corepressor complex

The Sir2 histone deacetylases are important for gene regulation, metabolism, and longevity. A unique feature of these enzymes is their utilization of NAD(+) as a cosubstrate, which has led to the suggestion that Sir2 activity reflects the cellular energy state. We show that SIRT1, a mammalian Sir2 homologue, is also controlled at the transcriptional level through a mechanism that is specific for this isoform. Treatment with the glycolytic blocker 2-deoxyglucose (2-DG) decreases association of the redox sensor CtBP with HIC1, an inhibitor of SIRT1 transcription. We propose that the reduction in transcriptional repression mediated by HIC1, due to the decrease of CtBP binding, increases SIRT1 expression. This mechanism allows the specific regulation of SIRT1 in response to nutrient deprivation.

Transcriptional regulation by C-terminal binding proteins

C-terminal binding protein family members function predominantly as transcriptional corepressors in association with sequence specific DNA-binding transcriptional repressors. The vertebrates have two CtBP genes while the invertebrates contain a single gene. Genetic studies indicate that the CtBP genes play pivotal roles in animal development. The vertebrate C-terminal binding proteins (CtBP1 and CtBP2) are highly related and are functionally redundant for certain developmental processes and non-redundant for others. The animal C-terminal binding proteins exhibit structural and functional similarity to d-isomer-specific 2-hydroxy acid dehydrogenases (D2-HDH). They function as dimers, recruiting transcriptional regulators through two protein-binding interfaces in each monomer. The corepressor complex of CtBP1 contains enzymatic constituents that mediate coordinated histone modification by deacetylation and methylation of histone H3-Lysine 9 and demethylation of histone H3-Lysine 4. CtBP also recruits the small ubiquitin-related modifier (SUMO) conjugating E2 enzyme UBC9 and a SUMO E3 ligase (HPC2), suggesting that CtBP-mediated transcriptional regulation may also involve SUMOylation of transcription factors. In addition to gene-specific transcriptional repression, CtBP1 appears to antagonize the activity of the global transcriptional coactivators, p300/CBP. Genetic evidence also suggests that the fly CtBP (dCtBP) and the vertebrate CtBP2 might activate transcription in a context-dependent manner. The transcriptional regulatory activity of CtBP is modulated by the nuclear NADH/NAD+ ratio and hence appears to be influenced by the metabolic status of the cell. The nuclear dinucleotide ratio may differentially influence the repression activities of factors that recruit CtBP through PLDLS-like motifs and those through non-PLDLS-motifs.