Laura L. Dugan

Ketamine-Induced Loss of Phenotype of Fast-Spiking Interneurons Is Mediated by NADPH-Oxidase

Abuse of the dissociative anesthetic ketamine can lead to a syndrome indistinguishable from schizophrenia. In animals, repetitive exposure to this N-methyl-d-aspartate–receptor antagonist induces the dysfunction of a subset of cortical fast-spiking inhibitory interneurons, with loss of expression of parvalbumin and the γ-aminobutyric acid–producing enzyme GAD67. We show here that exposure of mice to ketamine induced a persistent increase in brain superoxide due to activation in neurons of reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. Decreasing superoxide production prevented the effects of ketamine on inhibitory interneurons in the prefrontal cortex. These results suggest that NADPH oxidase may represent a novel target for the treatment of ketamine-induced psychosis.

Early elevation of cochlear reactive oxygen species following noise exposure.

Reactive oxygen species (ROS) have been implicated in a growing number of neurological disease states, from acute traumatic injury to neurodegenerative conditions such as Alzheimer’s disease. Considerable evidence suggests that ROS also mediate ototoxicant- and noise-induced cochlear injury, although most of this evidence is indirect. To obtain real-time assessment of noise-induced cochlear ROS production in vivo, we adapted a technique which uses the oxidation of salicylate to 2,3-dihydroxybenzoic acid as a probe for the generation of hydroxyl radical. In a companion paper we described the development and characterization of this method in cochlear ischemia-reperfusion. In the present paper we use this method to demonstrate early elevations in ROS production following acute noise exposure. C57BL/6J mice were exposed for 1 h to intense broad-band noise sufficient to cause permanent threshold shift (PTS), as verified by auditory brainstem responses. Comparison of noise-exposed animals with unexposed controls indicated that ROS levels increase nearly 4-fold in the period 1–2 h following exposure and do not decline over that time. Our ROS measures extend previous results indicating that noise-induced PTS is associated with elevated cochlear ROS production and ROS-mediated injury. Persistent cochlear ROS elevation following noise exposure suggests a sustained process of oxidative stress which might be amenable to intervention with chronic antioxidant therapy.

Buckminsterfullerenol Free Radical Scavengers Reduce Excitotoxic and Apoptotic Death of Cultured Cortical Neurons

Novel anti-oxidants based on the buckminsterfullerene molecule were explored as neuroprotective agents in cortical cell cultures exposed to excitotoxic and apoptotic injuries. Two polyhydroxylated C60 derivatives, C60(OH)n, n = 12, and C60(OH)nOm, n = 18-20, m = 3-7 hemiketal groups, demonstrated excellent anti-oxidant capabilities when tested by electron paramagnetic spectroscopy with a spin-trapping agent and a hydroxyl radical-generating system. These water-soluble agents decreased excitotoxic neuronal death following brief exposure to NMDA (by 80%), alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA; by 65%), or kainate (by 50%). Electrophysiology and tracer 45Ca(2+)-uptake studies verified that buckminsterfullerenois are not NMDA or AMPA/kainate receptor antagonists. Buckminsterfullerenols also reduced neuronal apoptosis induced by serum deprivation. These results support the idea that oxidative stress contributes to both excitotoxic and apoptotic neuronal death, and furthermore suggest that fullerenols represent a novel type of biological anti-oxidant compound.

Fullerene-based antioxidants and neurodegenerative disorders

Water-soluble derivatives of buckminsterfullerene (C(60)) derivatives are a unique class of compounds with potent antioxidant properties. Studies on one class of these compounds, the malonic acid C(60) derivatives (carboxyfullerenes), indicated that they are capable of eliminating both superoxide anion and H(2)O(2), and were effective inhibitors of lipid peroxidation, as well. Carboxyfullerenes demonstrated robust neuroprotection against excitotoxic, apoptotic and metabolic insults in cortical cell cultures. They were also capable of rescuing mesencephalic dopaminergic neurons from both MPP(+) and 6-hydroxydopamine-induced degeneration. Although there is limited in vivo data on these compounds to date, we have previously reported that systemic administration of the C(3) carboxyfullerene isomer delayed motor deterioration and death in a mouse model of familial amyotrophic lateral sclerosis (FALS). Ongoing studies in other animal models of CNS disease states suggest that these novel antioxidants are potential neuroprotective agents for other neurodegenerative disorders, including Parkinsons disease.

Differential Effects of cAMP in Neurons and Astrocytes ROLE OF B-RAF

Mitogen-activated protein kinase (MAPK) activation provides cell type-specific signals important for cellular differentiation, proliferation, and survival. Cyclic AMP (cAMP) has divergent effects on MAPK activity depending on whether signaling is through Ras/Raf-1 or Rap1/B-raf. We found that central nervous system-derived neurons, but not astrocytes, express B-raf. In neurons, cAMP activated MAPK in a Rap1/B-raf-dependent manner, while in astrocytes, cAMP decreased MAPK activity. Inhibition of MAPK in neurons decreased neuronal growth factor-mediated survival, and activation of MAPK by cAMP analogues rescued neurons from death. Furthermore, constitutive expression of B-raf in astrocytoma cells increased MAPK activation, as seen in neurons, and enhanced proliferation. These data provide the first experimental evidence that B-raf is the molecular switch which dominantly permits differential cAMP-dependent regulation of MAPK in neuronsversus astrocytes, with important implications for both survival and proliferation.

AMPK dysregulation promotes diabetes-related reduction of superoxide and mitochondrial function

Diabetic microvascular complications have been considered to be mediated by a glucose-driven increase in mitochondrial superoxide anion production. Here, we report that superoxide production was reduced in the kidneys of a steptozotocin-induced mouse model of type 1 diabetes, as assessed by in vivo real-time transcutaneous fluorescence, confocal microscopy, and electron paramagnetic resonance analysis. Reduction of mitochondrial biogenesis and phosphorylation of pyruvate dehydrogenase (PDH) were observed in kidneys from diabetic mice. These observations were consistent with an overall reduction of mitochondrial glucose oxidation. Activity of AMPK, the major energy-sensing enzyme, was reduced in kidneys from both diabetic mice and humans. Mitochondrial biogenesis, PDH activity, and mitochondrial complex activity were rescued by treatment with the AMPK activator 5-aminoimidazole-4-carboxamide-1-β-D-ribofuranoside (AICAR). AICAR treatment induced superoxide production and was linked with glomerular matrix and albuminuria reduction in the diabetic kidney. Furthermore, diabetic heterozygous superoxide dismutase 2 (Sod2(+/-)) mice had no evidence of increased renal disease, and Ampka2(-/-) mice had increased albuminuria that was not reduced with AICAR treatment. Reduction of mitochondrial superoxide production with rotenone was sufficient to reduce AMPK phosphorylation in mouse kidneys. Taken together, these results demonstrate that diabetic kidneys have reduced superoxide and mitochondrial biogenesis and activation of AMPK enhances superoxide production and mitochondrial function while reducing disease activity.

Clusterin contributes to caspase-3-independent brain injury following neonatal hypoxia-ischemia.

Clusterin, also known as apolipoprotein J, is a ubiquitously expressed molecule thought to influence a variety of processes including cell death. In the brain, it accumulates in dying neurons following seizures and hypoxic-ischemic (H-I) injury. Despite this, in vivo evidence that clusterin directly influences cell death is lacking. Following neonatal H-I brain injury in mice (a model of cerebral palsy), there was evidence of apoptotic changes (neuronal caspase-3 activation), as well as accumulation of clusterin in dying neurons. Clusterin-deficient mice had 50% less brain injury following neonatal H-I. Surprisingly, the absence of clusterin had no effect on caspase-3 activation, and clusterin accumulation and caspase-3 activation did not colocalize to the same cells. Studies with cultured cortical neurons demonstrated that exogenous purified astrocyte-secreted clusterin exacerbated oxygen/glucose-deprivation–induced necrotic death. These results indicate that clusterin may be a new therapeutic target to modulate non-caspase-dependent neuronal death following acute brain injury.

Interleukin-6 Mediates the Increase in NADPH-Oxidase in the Ketamine Model of Schizophrenia

Adult exposure to NMDA receptor antagonists, such as ketamine, produces psychosis in humans, and exacerbates symptoms in schizophrenic patients. We recently showed that ketamine activates the innate immune enzyme NADPH-oxidase in brain, and that the superoxide produced leads to dysfunction of a subset of fast-spiking inhibitory interneurons expressing the calcium-binding protein parvalbumin (PV). Here we show that neuronal production of interleukin-6 (IL-6) is necessary and sufficient for ketamine-mediated activation of NADPH-oxidase in brain. Removal of IL-6 in neuronal cultures by anti-IL-6 blocking antibodies, or in vivo by use of IL-6-deficient mice, prevented the increase in superoxide by ketamine and rescued the interneurons. Accumulating evidence suggests that schizophrenia patients suffer from diminished antioxidant defenses, and a recent clinical trial showed that enhancing these defenses may ameliorate symptoms of the disease. Our results showing that ketamine-induced IL-6 is responsible for the activation of NADPH-oxidase in brain suggest that reducing brain levels of this cytokine may protect the GABAergic phenotype of fast-spiking PV-interneurons and thus attenuate the propsychotic effects of ketamine.

Ceruloplasmin gene expression in the murine central nervous system.

Aceruloplasminemia is an autosomal recessive disorder resulting in neurodegeneration of the retina and basal ganglia in association with iron accumulation in these tissues. To begin to define the mechanisms of central nervous system iron accumulation and neuronal loss in this disease, cDNA clones encoding murine ceruloplasmin were isolated and characterized. RNA blot analysis using these clones detected a 3.7-kb ceruloplasmin-specific transcript in multiple murine tissues including the eye and several regions of the brain. In situ hybridization of systemic tissues revealed cell-specific ceruloplasmin gene expression in hepatocytes, the splenic reticuloendothelial system and the bronchiolar epithelium of the lung. In the central nervous system, abundant ceruloplasmin gene expression was detected in specific populations of astrocytes within the retina and the brain as well as the epithelium of the choroid plexus. Analysis of primary cell cultures confirmed that astrocytes expressed ceruloplasmin mRNA and biosynthetic studies revealed synthesis and secretion of ceruloplasmin by these cells. Taken together these results demonstrate abundant cell-specific ceruloplasmin expression within the central nervous system which may account for the unique clinical and pathologic findings observed in patients with aceruloplasminemia.

Effects of Methylprednisolone and the Combination of α-Tocopherol and Selenium on Arachidonic Acid Metabolism and Lipid Peroxidation in Traumatized Spinal Cord Tissue

Abstract: Traumatic injury of the spinal cord leads to a series of pathological events that result in tissue necrosis and paralysis. Among the earliest biochemical reactions are hydrolysis of fatty acids from membrane phospholipids, production of biologically active eicosanoids, and peroxidation of lipids. This study examines the effect of agents purported to improve recovery following spinal cord trauma, methyl‐prednisolone sodium succinate (MPSS) and the combination of α‐tocopherol and selenium (Se), on the posttraumatic alterations of membrane lipid metabolism. Pretreatment with either MPSS or a‐tocopherol and Se reduced the trauma‐induced release of total FFA including arachidonate in the injured spinal cord tissue. In addition, these agents decreased the postinjury levels of prostanoids. Pre‐treatment with either MPSS or a‐tocopherol and Se also completely prevented the trauma‐induced loss of cholesterol while inhibiting the increase of a cholesterol peroxidation product, 25‐hydroxycholesterol. These data suggest that: (a) perturbation of membrane lipid metabolism may contribute to the tissue necrosis and functional deficit of spinal cord injury and (b) MPSS or the combination of a‐tocopherol and Se may protect injured spinal cord tissue, at least in part, by limiting these posttraumatic membrane lipid changes.