[18F]FDG PET Neuroimaging Predicts Pentylenetetrazole (PTZ) Kindling Outcome in Rats

Characterization of the anticonvulsant effect of dapsone on metabolic activity assessed by [18F]FDG -PET after kainic acid-induced status epilepticus in rats

BACKGROUND

Development of effective drugs for epilepsy are needed, as nearly 30 % of epileptic patients, are resistant to current treatments. This study is aimed to characterize the anticonvulsant effect of dapsone (DDS), in the kainic acid (KA)-induced Status Epilepticus (SE) by recording the brain metabolic activity with an [¹⁸F]FDG-PET analysis.

METHODS

Wistar rats received KA (10 mg/kg, i.p., single dose) to produce sustained seizures. [¹⁸F]FDG-PET and electroencephalographic (EEG) studies were then performed. DDS or vehicle were administered 30 min before KA. [¹⁸F]FDG uptake and EEG were evaluated at baseline, 2 and 25 h after KA injection. Likewise, caspase-8, 3 hippocampal activities and Fluoro-Jade B neuronal degeneration and Hematoxylin-eosin staining were measured 25 h after KA.

RESULTS

PET data evaluated at 2 h showed hyper-uptake of [¹⁸F]FDG in the control group, which was decreased by DDS. At 25 h, hypo-uptake was observed in the control group and higher values due to DDS effect. EEG spectral power was increased 2 h after KA administration in the control group during the generalized tonic-clonic seizures, which was reversed by DDS, correlated with [¹⁸F]FDG-PET uptake changes. The values of caspases-8 activity decreased 48 and 43 % vs control group in the groups treated with DDS (12.5 y 25 mg/kg respectively), likewise; caspase-3 activity diminished by 57 and 53 %. Fewer degenerated neurons were observed due to DDS treatments.

CONCLUSIONS

This study pinpoints the anticonvulsant therapeutic potential of DDS. Given its safety and effectiveness, DDS may be a viable alternative for patients with drug-resistant epilepsy.

Significance of Brain Glucose Hypometabolism, Altered Insulin Signal Transduction, and Insulin Resistance in Several Neurological Diseases

Several neurological diseases share pathological alterations, even though they differ in their etiology. Neuroinflammation, altered brain glucose metabolism, oxidative stress, mitochondrial dysfunction and amyloidosis are biological events found in those neurological disorders. Altered insulin-mediated signaling and brain glucose hypometabolism are characteristic signs observed in the brains of patients with certain neurological diseases, but also others such as type 2 diabetes mellitus and vascular diseases. Thus, significant reductions in insulin receptor autophosphorylation and Akt kinase activity, and increased GSK-3 activity and insulin resistance, have been reported in these neurological diseases as contributing to the decline in cognitive function. Supporting this relationship is the fact that nasal and hippocampal insulin administration has been found to improve cognitive function. Additionally, brain glucose hypometabolism precedes the unmistakable clinical manifestations of some of these diseases by years, which may become a useful early biomarker. Deficiencies in the major pathways of oxidative energy metabolism have been reported in patients with several of these neurological diseases, which supports the hypothesis of their metabolic background. This review remarks on the significance of insulin and brain glucose metabolism alterations as keystone common pathogenic substrates for certain neurological diseases, highlighting new potential targets.

Differential effects of inhibitors of PTZ-induced kindling on glutamate transporters and enzyme expression

Epilepsy is a neurological disorder resulting from abnormal neuronal firing in the brain. Glutamate transporters and the glutamate-glutamine cycle play crucial roles in the development of seizures. In the present study, the correlation of epilepsy with glutamate transporters and enzymes was investigated. Herein, male Wistar rats were randomly allocated into four groups (six animals/group); 35 mg/kg pentylenetetrazole (PTZ) was used to induce a kindling model of epilepsy. Once the kindling model was established, animals were treated for 15 days with either valproic acid (VPA, 350 mg/kg) or ceftriaxone (CEF, 200 mg/kg) in addition to the control group receiving saline. After treatment, electrocorticography (ECoG) was performed to record the electrical activity of the cerebral cortex. The glutamate reuptake time (T80 ) was also determined in situ using an in vivo voltammetry. The expression levels of glutamate transporters and enzymes in the M1 and CA3 areas of the brain were determined using a real-time polymerase chain reaction (RT-PCR). ECoG measurements showed that the mean spike number of the PTZ + VPA and PTZ + CEF groups was significantly lower (p < 0.05) than that of the PTZ group. Compared with the PTZ group, VPA or CEF treatment decreased the glutamate reuptake time (T80 ). The expression levels of EAAC1, GLT-1, GLAST, glutamine synthetase (GS), and glutaminase were increased in the PTZ group. Treatment with VPA or CEF enhanced the expression levels of GLT-1, GLAST, EAAC1, and GS, whereas the glutaminase expression level was reduced. The current results suggest that VPA or CEF decreases seizure activity by increasing glutamate reuptake by upregulating GLT-1 and GLAST expression, implying a possible mechanism for treating epilepsy. Also, we have suggested a novel mechanism for the antiepileptic activity of VPA via decreasing glutaminase expression levels. To our knowledge, this is the first study to measure the glutamate reuptake time in situ during the seizure (i.e., real-time measurement).

Choice of anesthesia and data analysis method strongly increases sensitivity of 18F-FDG PET imaging during experimental epileptogenesis

Purpose

Alterations in brain glucose metabolism detected by 2-deoxy-2-[¹⁸F]-fluoro-D-glucose (¹⁸F-FDG) positron emission tomography (PET) may serve as an early predictive biomarker and treatment target for epileptogenesis. Here, we aimed to investigate changes in cerebral glucose metabolism before induction of epileptogenesis, during epileptogenesis as well as during chronic epilepsy. As anesthesia is usually unavoidable for preclinical PET imaging and influences the distribution of the radiotracer, four different protocols were compared.

Procedures

We investigated ¹⁸F-FDG uptake phase in conscious rats followed by a static scan as well as dynamic scans under continuous isoflurane, medetomidine-midazolam-fentanyl (MMF), or propofol anesthesia. Furthermore, we applied different analysis approaches: atlas-based regional analysis, statistical parametric mapping, and kinetic analysis.

Results

At baseline and compared to uptake in conscious rats, isoflurane and propofol anesthesia resulted in decreased cortical ¹⁸F-FDG uptake while MMF anesthesia led to a globally decreased tracer uptake. During epileptogenesis, MMF anesthesia was clearly best distinctive for visualization of prominently increased glucometabolism in epilepsy-related brain areas. Kinetic modeling further increased sensitivity, particularly for continuous isoflurane anesthesia. During chronic epilepsy, hypometabolism affecting more or less the whole brain was detectable with all protocols.

Conclusion

This study reveals evaluation of anesthesia protocols for preclinical ¹⁸F-FDG PET imaging as a critical step in the study design. Together with an appropriate data analysis workflow, the chosen anesthesia protocol may uncover otherwise concealed disease-associated regional glucometabolic changes.

Envisioning the role of inwardly rectifying potassium (Kir) channel in epilepsy

Epilepsy is a devastating neurological disorder characterized by recurrent seizures attributed to the disruption of the dynamic excitatory and inhibitory balance in the brain. Epilepsy has emerged as a global health concern affecting about 70 million people worldwide. Despite recent advances in pre-clinical and clinical research, its etiopathogenesis remains obscure, and there are still no treatment strategies modifying disease progression. Although the precise molecular mechanisms underlying epileptogenesis have not been clarified yet, the role of ion channels as regulators of cellular excitability has increasingly gained attention. In this regard, emerging evidence highlights the potential implication of inwardly rectifying potassium (Kir) channels in epileptogenesis. Kir channels consist of seven different subfamilies (Kir1-Kir7), and they are highly expressed in both neuronal and glial cells in the central nervous system. These channels control the cell volume and excitability. In this review, we discuss preclinical and clinical evidence on the role of the several subfamilies of Kir channels in epileptogenesis, aiming to shed more light on the pathogenesis of this disorder and pave the way for future novel therapeutic approaches.

Characterization of metabolic activity induced by kainic acid in adult rat whole brain at the early stage: A 18FDG-PET study

OBJECTIVE

Brain metabolic processes are not fully characterized in the kainic acid (KA)-induced Status Epilepticus (KASE). Thus, we evaluated the usefulness of ¹⁸F-fluorodeoxyglucose positron emission tomography (FDG-PET) as an experimental strategy to evaluate in vivo, in a non-invasive way, the glucose consumption in several brain regions, in a semi-quantitative study to compare and to correlate with data from electroencephalography and histology studies.

METHODS

Sixteen male Wistar rats underwent FDG-PET scans at basal state and after KA injection. FDG-PET images were normalized to an MRI-based atlas and segmented to locate regions. Standardized uptake values (SUV) were obtained at several time points. EEGs and cell viability by histological analysis, were also evaluated.

RESULTS

FDG-PET data showed changes in regions such as: amygdala, hippocampus, accumbens, entorhinal cortex, motor cortex and hypothalamus. Remarkably, hippocampal hypermetabolism was found (mean SUV = 2.66 ± 0.057) 2 h after KA administration, while hypometabolism at 24 h (mean SUV = 1.83 ± 0.056) vs basal values (mean SUV = 2.19 ± 0.057). EEG showed increased spectral power values 2 h post-KA administration. Hippocampal viable-cell counting 24 h after KA was decreased, while Fluoro-Jade B-positive cells were increased, as compared to control rats, coinciding with the hypometabolism detected in the same region by semi-quantitative FDG-PET at 24 h after KASE.

CONCLUSIONS

PET is suitable to measure metabolic brain changes in the rat model of status epilepticus induced by KA (KASE) at the first 24 h, compared to that of EEG; PET data may also be sensitive to cell viability.

The antioxidant and neuroprotective effects of the Psychotria camptopus Verd. Hook. (Rubiaceae) stem bark methanol extract contributes to its antiepileptogenic activity against pentylenetetrazol kindling in male Wistar rats

A substantial number of epileptic patients are resistant to the current medication thus necessitating the search for alternative therapies for intractable forms of the disease. Previous studies demonstrated the acute anticonvulsant properties of the methanol extract of the stem bark of Psychotria camptopus (MEPC) in rats. This study investigated the effects of MEPC on pentylenetetrazole-kindled Wistar rats. Kindling was induced by intraperitoneal injection of pentylenetetrazole (37.5 mg/kg) on every alternate day, 1 h after each daily oral pretreatment of rats (8 ≤ n ≤ 10) with MEPC (40, 80 and 120 mg/kg), vehicle or diazepam (3 mg/kg) for 43 days. The kindling development was monitored based on seizure episodes and severity. Rats' brains were collected on day 43 for the determination of oxidative stress parameters. The histomorphological features and neuronal cell viability of the prefrontal cortex (PFC) and hippocampus were also assessed using H&E and Cresyl violet stains. Chronic administration of pentylenetetrazole time-dependently decreased the latency to myoclonic and generalized seizures, and increased seizure scores and the number of kindled rats. MEPC and diazepam significantly increased the latencies to myoclonic jerks and generalized tonic-clonic seizures. These substances also reduced seizure score and the number of rats with PTZ-kindling. MEPC improved glutathione status and decreased lipid peroxidation in the brains of kindled rats. MEPC also exhibited neuroprotection against pentylenetetrazole-induced hippocampal and PFC neuronal damages. These results suggest that P. camptopus has antiepileptogenic activity, which might be related to the augmentation of antioxidant and neuroprotective defense mechanisms, and further confirm its usefulness in the management of epilepsy.

Divergent metabolic substrate utilization in brain during epileptogenesis precedes chronic hypometabolism

Alterations in metabolism during epileptogenesis may be a therapy target. Recently, an increase in amino acid transport into the brain was proposed to play a role in epileptogenesis. We aimed to characterize alterations of substrate utilization during epileptogenesis and in chronic epilepsy. The lithium-pilocarpine post status epilepticus (SE) rat model was used. We performed longitudinal O-(2-[(18)F]fluoroethyl)-l-tyrosine (18F-FET) and 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography (PET) and calculated 18F-FET volume of distribution (Vt) and 18F-FDG uptake. Correlation analyses were performed with translocator protein-PET defined neuroinflammation from previously acquired data. We found reduced 18F-FET Vt at 48 h after SE (amygdala: -30.2%, p = 0.014), whereas 18F-FDG showed increased glucose uptake 4 and 24 h after SE (hippocampus: + 43.6% and +42.5%, respectively; p < 0.001) returning to baseline levels thereafter. In chronic epileptic animals, we found a reduction in 18F-FET and 18F-FDG in the hippocampus. No correlation was found for 18F-FET or 18F-FDG to microglial activation at seven days post SE. Whereas metabolic alterations do not reflect higher metabolism associated to activated microglia, they might be partially driven by chronic neuronal loss. However, both metabolisms diverge during early epileptogenesis, pointing to amino acid turnover as a possible biomarker and/or therapeutic target for epileptogenesis.

Attenuation of epileptogenesis by 2-deoxy-d-glucose is accompanied by increased cerebral glucose supply, microglial activation and reduced astrocytosis

RATIONALE

Neuronal excitability and brain energy homeostasis are strongly interconnected and evidence suggests that both become altered during epileptogenesis. Pharmacologic modulation of cerebral glucose metabolism might therefore exert anti-epileptogenic effects. Here we provide mechanistic insights into effects of the glycolytic inhibitor 2-deoxy-d-glucose (2-DG) on experimental epileptogenesis by longitudinal 2-deoxy-2[¹⁸F]fluoro-d-glucose positron emission tomography ([¹⁸F]FDG PET) and histology.

METHODS

To imitate epileptogenesis, 6 Hz-corneal kindling was performed in male NMRI mice by twice daily electrical stimulation for 21 days. Kindling groups were treated i.p. 1 min after each stimulation with either 250 mg/kg 2-DG (CoKi_2-DG) or saline (CoKi_vehicle). A separate group of unstimulated mice was treated with 2-DG (2-DG_only). Dynamic 60-min [¹⁸F]FDG PET/CT scans were acquired at baseline and interictally on days 10 and 17 of kindling. [¹⁸F]FDG uptake (%injected dose/cc) was quantified in predefined regions of interest (ROI) using a MRI-based brain atlas, and kinetic modelling was performed to evaluate glucose net influx rate K_i and glucose metabolic rate MR_Glu. Furthermore, statistical parametric mapping (SPM) analysis was applied on kinetic brain maps. For histological evaluation, brain sections were stained for glucose transporter 1 (GLUT1), astrocytes, microglia, as well as dying neurons.

RESULTS

Post-stimulation 2-DG treatment attenuated early kindling progression, indicated by a reduction of fully-kindled mice, and a lower overall percentage of type five seizures. While 2-DG treatment alone led to globally increased K_i and MR_Glu values at day 17, kindling progression per se did not influence glucose turnover. Kindling accompanied by 2-DG treatment, however, resulted in regionally elevated [¹⁸F]FDG uptake as well as increased K_i at days 10 and 17 compared both to baseline and to the 2-DG_only group. In hippocampus and thalamus, higher MR_Glu values were found in the CoKi_2-DG vs. the CoKi_vehicle group at day 17. t maps resulting from SPM analysis generally confirmed the results of the ROI analysis, and additionally revealed increased MR_Glu restricted to the ventral hippocampus when comparing the CoKi_2-DG and the 2-DG_only group both at days 10 and, more distinct, day 17. Immunohistochemical staining showed an attenuated kindling-induced regional activation of astrocytes in the CoKi_2-DG group. Interestingly, 2-DG treatment alone (and also in combination with kindling, but not kindling alone) led to increased microglial activation scores, whereas neither staining of GLUT1 nor of dying neurons revealed any differences to untreated controls.

CONCLUSIONS

Post-stimulation treatment with 2-DG exerts disease-modifying effects in the mouse 6 Hz corneal kindling model. The observed local increase in glucose supply and turnover, the alleviation of astroglial activation and the activation of microglia by 2-DG might contribute separately or in combination to its positive interference with epileptogenesis.

PET Neuroimaging Reveals Serotonergic and Metabolic Dysfunctions in the Hippocampal Electrical Kindling Model of Epileptogenesis

Glucose metabolism and serotonergic neurotransmission have been reported to play an important role in epileptogenesis. We therefore aimed to use neuroimaging to evaluate potential alterations in serotonin 5-HT_1A receptor and glucose metabolism during epileptogenesis in the rat electrical kindling model. To achieve this goal, we performed positron emission tomography (PET) imaging in a rat epileptogenesis model triggered by electrical stimulation of the hippocampus using 2-deoxy-2-[¹⁸F]fluoro-D-glucose (¹⁸F-FDG), a radiolabeled analog of glucose, and 2'-methoxyphenyl-(N-2'-pyridinyl)-p-¹⁸F-fluoro-benzamidoethylpiperazine (¹⁸F-MPPF), a radiolabeled 5-HT_1A receptor ligand, to evaluate brain metabolism and 5-HT_1A receptor functionality. Since the 5-HT_1A receptor is also highly expressed in astrocytes, glial fibrillary acidic protein (GFAP) immunofluorescence was performed to detect astrogliosis arising from the kindling procedure once the study was finalized. Lastly, in vitro¹⁸F-MPPF autoradiography was performed to evaluate changes in 5HT_1A receptor expression. ¹⁸F-FDG PET showed reduction of glucose uptake in cortical structures, whereas ¹⁸F-MPPF PET revealed an enhancement of tracer binding potential (BP_ND) in key areas rich in 5-HT_1A receptor involved in epilepsy, including septum, hippocampus and entorhinal cortex of kindled animals compared to controls. However, in vitro 5-HT_1A receptor autoradiography showed no changes in densitometric signal in any brain region, suggesting that the augmentation in BP_ND found by PET could be caused by reduction of synaptic serotonin. Importantly, astroglial activation was detected in the hippocampus of kindled rats. Overall, electrical kindling induced hypometabolism, astrogliosis and serotonergic alterations in epilepsy-related regions. Furthermore, the present findings point to 5-HT_1A receptor as a valuable epileptogenesis biomarker candidate and a potential therapeutic target.

Decreased vesicular acetylcholine transporter related to memory deficits in epilepsy: A [18 F] VAT positron emission tomography brain imaging study

OBJECTIVE

Vesicular acetylcholine transporter (VAChT) is a rate-limiting factor for synaptic acetylcholine transport. Our study focused on whether [¹⁸ F] VAT, a novel positron emission tomography (PET) tracer, could be used in detecting cognitive deficits in epilepsy.

METHODS

Morris water maze test was used to evaluate learning and memory deficits in pilocarpine-induced chronic epilepsy rats 12 weeks after status epilepticus. Interictal [¹⁸ F] VAT PET was performed 13 weeks after status epilepticus to evaluate the level of VAChT in cholinergic pathways compared with [¹⁸ F] fluorodeoxyglucose PET. The association between VAChT levels and memory measures was analyzed. Neuropathological tests were performed.

RESULTS

Epileptic rats exhibited significant memory deficits in Morris water maze test. [¹⁸ F] VAT uptake decreased in septum, hippocampus, thalamus, and basal forebrain, and correlated to memory function. Of note, the level of VAChT in basal forebrain significantly decreased, yet no glucose hypometabolism was detected. Immunofluorescence and Western blot demonstrated decreased expression of VAChT in hippocampus and basal forebrain in the epilepsy group, but no change of expression of acetyltransferase or activity of acetylcholinesterase was detected.

SIGNIFICANCE

[¹⁸ F] VAT PET is a promising method to test the level of VAChT as a valuable biomarker for memory deficits in pilocarpine-induced chronic epileptic rats.

Neurochemical evidence based suggested therapy for safe management of epileptogenesis

Most of the clinically available antiepileptic drugs have only antiseizure effects and are reported unable to prevent epileptogenesis. In the past decade, several drugs underwent clinical trials for management of epileptogenesis, but none of the drugs tested was found effective. One of the major lacunas is availability of appropriate preclinical approaches to delineate mechanisms of epileptogenesis. Thus, the present study attempts to suggest a neurochemistry based approach for safe management of epileptogenesis. The altered neurochemical milieu in amygdala, cortex and hippocampus areas of the mice brain in naïve, kindled and kindling resistant animals has been delineated. The endogenous natural antiepileptogenic neurochemical defense mechanism observed in kindling resistant animals may uncover neurochemical mechanisms of epileptogenesis and in turn suggest us novel interventions for safe management of epileptogenesis. The kindling epileptogenesis was carried out in two month old male Swiss albino mice by administering subconvulsive pentylenetetrazole (35mg/kg; i.p.) at an interval of 48±2h for 42days. 2h after the last pentylenetetrazole injection, the animals were subjected to behavioral evaluations. Four hours after behavioral evaluation, all animals were euthanized and discrete parts of brain (amygdala, cortex and hippocampus) were harvested for neurochemical analysis. Results revealed that 60% of animals responded to kindling as observed with decreased seizure threshold, while the rest were found resistant. The kindled animals were found to be associated with anxiety, depression and cognitive impairment; while in kindling resistant animals no such behavioral deficits were observed. The neurochemical analysis revealed that in kindled animals altered glutamate-GABA neurotransmission, and decreased taurine, glycine, d-serine, monoamine levels with elevated indoleamine 2,3-dioxygenase activity were observed, which may be convicted for progression of kindling epileptogenesis. However, in kindling resistant animals elevated GABA, taurine, tryptophan, serotonin, glycine, and d-serine levels with decreased indoleamine 2,3-dioxygenase activity were observed as natural endogenous antiepileptogenic mechanisms, which may be foreseen as safe pharmacological targets for management of epileptogenesis.

The vicious circle of hypometabolism in neurodegenerative diseases: Ways and mechanisms of metabolic correction

Hypometabolism, characterized by decreased brain glucose consumption, is a common feature of many neurodegenerative diseases. Initial hypometabolic brain state, created by characteristic risk factors, may predispose the brain to acquired epilepsy and sporadic Alzheimer's and Parkinson's diseases, which are the focus of this review. Analysis of available data suggests that deficient glucose metabolism is likely a primary initiating factor for these diseases, and that resulting neuronal dysfunction further promotes the metabolic imbalance, establishing an effective positive feedback loop and a downward spiral of disease progression. Therefore, metabolic correction leading to the normalization of abnormalities in glucose metabolism may be an efficient tool to treat the neurological disorders by counteracting their primary pathological mechanisms. Published and preliminary experimental results on this approach for treating Alzheimer's disease and epilepsy models support the efficacy of metabolic correction, confirming the highly promising nature of the strategy. © 2017 Wiley Periodicals, Inc.