Neuroprotective effects of an adenoviral vector expressing the glucose transporter: a detailed description of the mediating cellular events

Ketogenic diet, neuroprotection, and antiepileptogenesis

High fat, low carbohydrate ketogenic diets (KD) have been in use for the treatment of epilepsy for almost a hundred years. Remarkably, seizures that are resistant to conventional anti-seizure drugs can in many cases be controlled by the KD therapy, and it has been shown that many patients with epilepsy become seizure free even after discontinuation of the diet. These findings suggest that KD combine anti-seizure effects with disease modifying effects. In addition to the treatment of epilepsy, KDs are now widely used for the treatment of a wide range of conditions including weight reduction, diabetes, and cancer. The reason for the success of metabolic therapies is based on the synergism of at least a dozen different mechanisms through which KDs provide beneficial activities. Among the newest findings are epigenetic mechanisms (DNA methylation and histone acetylation) through which KD exerts long-lasting disease modifying effects. Here we review mechanisms through which KD can affect neuroprotection in the brain, and how a combination of those mechanisms with epigenetic alterations can attenuate and possibly reverse the development of epilepsy.

Homeostatic control of brain function - new approaches to understand epileptogenesis

Neuronal excitability of the brain and ongoing homeostasis depend not only on intrinsic neuronal properties, but also on external environmental factors; together these determine the functionality of neuronal networks. Homeostatic factors become critically important during epileptogenesis, a process that involves complex disruption of self-regulatory mechanisms. Here we focus on the bioenergetic homeostatic network regulator adenosine, a purine nucleoside whose availability is largely regulated by astrocytes. Endogenous adenosine modulates complex network function through multiple mechanisms including adenosine receptor-mediated pathways, mitochondrial bioenergetics, and adenosine receptor-independent changes to the epigenome. Accumulating evidence from our laboratories shows that disruption of adenosine homeostasis plays a major role in epileptogenesis. Conversely, we have found that reconstruction of adenosine's homeostatic functions provides new hope for the prevention of epileptogenesis. We will discuss how adenosine-based therapeutic approaches may interfere with epileptogenesis on an epigenetic level, and how dietary interventions can be used to restore network homeostasis in the brain. We conclude that reconstruction of homeostatic functions in the brain offers a new conceptual advance for the treatment of neurological conditions which goes far beyond current target-centric treatment approaches.

Neighbor effects of neurons bearing protective transgenes

Viral vectors bearing protective transgenes can decrease neurotoxicity after varied necrotic insults. A neuron that dies necrotically releases glutamate, calcium and reactive oxygen species, thereby potentially damaging neighboring neurons. This raises the possibility that preventing such neuron death via gene therapy can secondarily protect neighboring neurons that, themselves, do not express a protective transgene. We determined whether such "good neighbor" effects occur, by characterizing neurons that, while uninfected themselves, are in close proximity to a transgene-bearing neuron. We tested two genes whose overexpression protects against excitotoxicity: anti-apoptotic Bcl-2, and a calcium-activated K(+) channel, SK2. Using herpes simplex virus type 2-mediated transgene delivery to hippocampal cultures, we observed "good neighbor" effects on neuronal survival following an excitotoxic insult. However, in the absence of insult, "bad neighbor" effects could also occur (i.e., where being in proximity to a neuron constitutively expressing one of those transgenes is deleterious). We also characterized the necessity for cell-cell contact for these effects. These phenomena may have broad implications for the efficacy of gene overexpression strategies in the CNS.

Gene expression profiling of MPP+-treated MN9D cells: A mechanism of toxicity study

Parkinson's disease (PD) is a common neurodegenerative disease characterized by progressive loss of midbrain dopaminergic neurons with unknown etiology. MPP+ (1-methyl-4-phenylpyridinium) is the active metabolite of the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), which induces Parkinson's-like syndromes in humans and animals. MPTP/MPP+ treatment produces selective dopaminergic neuronal degeneration, therefore, these agents are commonly used to study the pathogenesis of PD. However, the mechanisms of their toxicity have not been elucidated. In order to gain insights into MPP+-induced neurotoxicity, a gene expression microarray study was performed using a midbrain-derived dopaminergic neuronal cell line, MN9D. Utilizing a two-color reference design, Agilent mouse oligonucleotide microarrays were used to examine relative gene expression changes in MN9D cells treated with 40microM MPP+ compared with controls. Bioinformatics tools were used for data evaluation. Briefly, raw data were imported into the NCTR ArrayTrack database, normalized using a Lowess method and data quality was assessed. The Student's t-test was used to determine significant changes in gene expression (set as p<0.05, fold change >1.5). Gene Ontology for Function Analysis (GOFFA) and Ingenuity Pathway Analysis were employed to analyze the functions and roles of significant genes in biological processes. Of the 51 significant genes identified, 44 were present in the GOFFA or Ingenuity database. These data indicate that multiple pathways are involved in the underlying mechanisms of MPP+-induced neurotoxicity, including apoptosis, oxidative stress, iron binding, cellular metabolism, and signal transduction. These data also indicate that MPP+-induced toxicity shares common molecular mechanisms with the pathogenesis of PD and further pathway analyses will be conducted to explore these mechanisms.

The potential application of gene therapy in the treatment of traumatic brain injury

Advances in molecular biology have allowed the possibility of using gene therapy in the treatment of traumatic brain injury. The major tactics involve picking out the appropriate gene target and, by controlling its specific regional expression, inhibiting neuronal cell deaths and/or promoting neuronal regeneration. This review addresses the preliminary usage of gene therapy in in vitro experiments and in animal models to treat traumatic brain injury. The gene targets with therapeutic potentials, the vectors that can be employed to deliver the candidate genes, as well as different approaches for gene therapy are discussed in detail in this review. Despite the existence of several major obstacles to making it practical and effective, gene therapy could provide a new strategy for treatment of the traumatically injured brain.

Hypoxic preconditioning protects against ischemic brain injury

Animals exposed to brief periods of moderate hypoxia (8% to 10% oxygen for 3 hours) are protected against cerebral and cardiac ischemia between 1 and 2 days later. This hypoxia preconditioning requires new RNA and protein synthesis. The mechanism of this hypoxia-induced tolerance correlates with the induction of the hypoxia-inducible factor (HIF), a transcription factor heterodimeric complex composed of inducible HIF-1alpha and constitutive HIF-1beta proteins that bind to the hypoxia response elements in a number of HIF target genes. Our recent studies show that HIF-1alpha correlates with hypoxia induced tolerance in neonatal rat brain. HIF target genes, also induced following hypoxia-induced tolerance, include vascular endothelial growth factor, erythropoietin, glucose transporters, glycolytic enzymes, and many other genes. Some or all of these genes may contribute to hypoxia-induced protection against ischemia. HIF induction of the glycolytic enzymes accounts in part for the Pasteur effect in brain and other tissues. Hypoxia-induced tolerance is not likely to be equivalent to treatment with a single HIF target gene protein since other transcription factors including Egr-1 (NGFI-A) have been implicated in hypoxia regulation of gene expression. Understanding the mechanisms and genes involved in hypoxic tolerance may provide new therapeutic targets to treat ischemic injury and enhance recovery.

Dual-gene, dual-cell type therapy against an excitotoxic insult by bolstering neuroenergetics

Increasing evidence suggests that glutamate activates the generation of lactate from glucose in astrocytes; this lactate is shuttled to neurons that use it as a preferential energy source. We explore this multicellular "lactate shuttle" with a novel dual-cell, dual-gene therapy approach and determine the neuroprotective potential of enhancing this shuttle. Viral vector-driven overexpression of a glucose transporter in glia enhanced glucose uptake, lactate efflux, and the glial capacity to protect neurons from excitotoxicity. In parallel, overexpression of a lactate transporter in neurons enhanced lactate uptake and neuronal resistance to excitotoxicity. Finally, overexpression of both transgenes in the respective cell types provided more protection than either therapy alone, demonstrating that a dual-cell, dual-gene therapy approach gives greater neuroprotection than the conventional single-cell, single-gene strategy.

Genetic and Cellular Therapies for Cerebral Infarction

Neurosurgeons, working as surgical scientists, can have a prominent role in developing and implementing genetic and cellular therapies for cerebral ischemia. The rapid emergence of both genetic and cellular therapies for neural regeneration warrants a careful analysis before implementation of human studies to understand the pitfalls and promises of this strategy. In this article, we review the topic of genetic and cellular therapy for stroke to provide a foundation for practicing neurosurgeons and clinical scientists who may become involved in this type of work. In Part 1, we review preclinical approaches with gene transfer, such as 1) improved energy delivery, 2) reduction of intracellular calcium availability, 3) abrogation of effects of reactive oxygen species, 4) reduction of proinflammatory cytokine signaling, 5) inhibition of apoptosis mediators, and 6) restorative gene therapy, that are paving the way to develop new strategies to treat cerebral infarction. In Part 2, we discuss the results of studies that address the possibility of using cellular therapies for stroke in animal models and in human trials by reviewing 1) the basics of stem cell biology, 2) exogenous and 3) and endogenous cell sources for therapy, and 4) clinical considerations in cell therapy applications. These emerging technologies based on the advancements made in recent years in the fields of genetics, therapeutic cloning, neuroscience, stem cell biology, and gene therapy provide significant potential for new therapies for stroke.

A ketogenic diet increases brain insulin-like growth factor receptor and glucose transporter gene expression

A ketogenic diet suppresses seizure activity in children and in juvenile rats. To investigate whether alteration in brain IGF activity could be involved in the beneficial effects of the ketogenic diet, we examined the effects of this diet on IGF system gene expression in the rat brain. Juvenile rats were fed one of three different diets for 7 d: ad libitum standard rat chow (AL-Std), calorie-restricted standard chow (CR-Std), or a calorie-restricted ketogenic diet (CR-Ket). The calorie-restricted diets contained 90% of the rats' calculated energy requirements. The AL-Std diet group increased in weight, whereas the two CR groups merely maintained their weight during the 7-d diet. Glucose levels were significantly reduced in both CR groups compared with the AL-Std group, but only the CR-Ket group developed ketonemia. IGF1 mRNA levels were reduced by 30-50% in most brain regions in both CR groups. IGF1 receptor (IGF1R) mRNA levels were decreased in the CR-Std group but were increased in the CR-Ket diet group. Brain IGF binding protein (IGFBP)-2 and -5 mRNA levels were not altered by diet, but IGFBP-3 mRNA levels were markedly increased by the ketogenic diet while not altered by calorie restriction alone. Brain glucose transporter expression was also investigated in this study. Glucose transporter (GLUT) 4 mRNA levels were quite low and not appreciably altered by the different diets. Parenchymal GLUT1 mRNA levels were increased by the CR-Ket diet, but endothelial GLUT1 mRNA levels were not affected. Neuronal GLUT3 expression was decreased with the CR-Std diet and increased with the CR-Ket diet, in parallel with the IGF1R pattern. These observations reveal divergent effects of dietary caloric content and macronutrient composition on brain IGF system and GLUT expression. In addition, the data may be consistent with a role for enhanced IGF1R and GLUT expression in ketogenic diet-induced seizure suppression.

Cytotoxicity of conventional and atypical antipsychotic drugs in relation to glucose metabolism

The goal of these studies was to analyze the cytotoxicity of both the conventional and atypical antipsychotic drugs in relation to their effects on glucose metabolism. The drugs were evaluated for their effects on the viability of PC12 cells, which are an established model of neuronal cells in culture. In general, the conventional drugs, such as chlorpromazine, fluphenazine and pimozide, were more toxic than the atypical drugs, including clozapine, quetiapine and risperidone. Olanzapine was unique in that it stimulated cell proliferation in this system. There was a good correlation between the cytotoxicity of a drug and its ability to block glucose transport, although there were some exceptions to this trend. Conventional antipsychotics also affected the expression of glucose transporter proteins in whole cell extracts and at the cell surface. Overall, the data support the notion that many of the antipsychotic drugs associated with the development of movement disorders in patients are cytotoxic for cultured cells.

Gene therapy for acute diseases

The use of gene transfer systems to study cell function makes it apparent that overexpression of a transgene can restore or improve the function of a protein and positively influence cell function in a predetermined manner for purposes of counterbalancing cellular pathophysiology. The ability of some gene transfer vehicles to produce transgene product within hours of delivery positions gene transfer as a unique pharmaceutical administration system that can quickly affect production of biologic response modifiers in a highly compartmentalized fashion. This approach can be expected to overcome many of the adverse effects and high costs of systemic delivery of recombinant pharmaceuticals. This review highlights recent advances toward development of gene therapies for acute illnesses with particular emphasis on preclinical models of disease. In this context, a growing body of data suggests that gene therapies for polygenic and non-genetic diseases such as asthma, cardiogenic and non-cardiogenic pulmonary edema, stroke, subarachnoid hemorrhage, seizures, acute myocardial infarction, endovascular thrombosis, and infections may someday be options for the treatment of patients.