Changes in peripheral energy metabolism during audiogenic seizures in rats

A Genetic Model of Epilepsy with a Partial Alzheimer's Disease-Like Phenotype and Central Insulin Resistance

Studies have suggested an important connection between epilepsy and Alzheimer's disease (AD), mostly due to the high number of patients diagnosed with AD who develop epileptic seizures later on. However, this link is not well understood. Previous studies from our group have identified memory impairment and metabolic abnormalities in the Wistar audiogenic rat (WAR) strain, a genetic model of epilepsy. Our goal was to investigate AD behavioral and molecular alterations, including brain insulin resistance, in naïve (seizure-free) animals of the WAR strain. We used the Morris water maze (MWM) test to evaluate spatial learning and memory performance and hippocampal tissue to verify possible molecular and immunohistochemical alterations. WARs presented worse performance in the MWM test (p < 0.0001), higher levels of hyperphosphorylated tau (S396) (p < 0.0001) and phosphorylated glycogen synthase kinase 3 (S21/9) (p < 0.05), and lower insulin receptor levels (p < 0.05). Conversely, WARs and Wistar controls present progressive increase in amyloid fibrils (p < 0.0001) and low levels of soluble amyloid-β. Interestingly, the detected alterations were age-dependent, reaching larger differences in aged than in young adult animals. In summary, the present study provides evidence of a partial AD-like phenotype, including altered regulation of insulin signaling, in a genetic model of epilepsy. Together, these data contribute to the understanding of the connection between epilepsy and AD as comorbidities. Moreover, since both tau hyperphosphorylation and altered insulin signaling have already been reported in epilepsy and AD, these two events should be considered as important components in the interconnection between epilepsy and AD pathogenesis and, therefore, potential therapeutic targets in this field.

Changes in lipid profiles of epileptic mouse model

INTRODUCTION

Approximately 1% of the world's population is impacted by epilepsy, a chronic neurological disorder characterized by seizures. One-third of epileptic patients are resistant to AEDs, or have medically refractory epilepsy (MRE). One non-invasive treatment that exists for MRE includes the ketogenic diet, a high-fat, low-carbohydrate diet. Despite the KD's success in seizure attenuation, it has a few risks and its mechanisms remain poorly understood. The KD has been shown to improve metabolism and mitochondrial function in epileptic phenotypes. Potassium channels have implications in epileptic conditions as they have dual roles as metabolic sensors and control neuronal excitation.

OBJECTIVES

The goal of this study was to explore changes in the lipidome in hippocampal and cortical tissue from Kv1.1-KO model of epilepsy.

METHODS

FT-ICR/MS analysis was utilized to examine nonpolar metabolome of cortical and hippocampal tissue isolated from a Kv1.1 channel knockout mouse model of epilepsy (n = 5) and wild-type mice (n = 5).

RESULTS

Distinct metabolic profiles were observed, significant (p < 0.05) features in hippocampus often being upregulated (FC ≥ 2) and the cortex being downregulated (FC ≤ 0.5). Pathway enrichment analysis shows lipid biosynthesis was affected. Partition ratio analysis revealed that the ratio of most metabolites tended to be increased in Kv1.1-/-. Metabolites in hippocampal tissue were commonly upregulated, suggesting seizure initiation in the hippocampus. Aberrant mitochondrial function is implicated by the upregulation of cardiolipin, a common component in the mitochondrial membrane.

CONCLUSION

Generally, our study finds that the lipidome is changed in the hippocampus and cortex in response to Kv1.1-KO indicating changes in membrane structural integrity and synaptic transmission.

Evaluation of Maternal Reproductive Outcomes and Biochemical Analysis from Wistar Audiogenic Rats (WAR) and Repercussions in Their Offspring

The objective of the present study was to evaluate maternal reproductive performance, body weight, and frequency of external and internal anomalies of newborns of Wistar Audiogenic Rat (WAR) females as compared with Wistar rats. The adult WAR and Wistar rats were mated within their respective strains. After confirming the pregnancy, the body weights were weekly evaluated. On day 21 of pregnancy, the female rats were anesthetized and sacrificed to evaluate the maternal reproductive outcomes and biochemical profile, newborn weight, and external and internal anomalies. The WAR strain gained less weight during the pregnancy and presented hyperproteinemia, hypertriglyceridemia, and embryonic losses concerning Wistar rats, suggesting an inadequate intrauterine condition for embryonic development and fetal viability. WAR also presented a higher percentage of newborns classified as small for gestational age related to intrauterine growth restriction, which was confirmed by the lower number of ossification centers. There was a higher percentage of skeletal anomalies compared with fetuses of the Wistar dams, confirming their greater susceptibility during the formation and development of their skeletal system. Thus, the WAR presents physiological alterations compromising the viability of their embryos and fetuses, leading to impaired development of the newborns.

Modeling of Focal Seizures with Automatisms in Rats with Pendulum Movements

Phenotypical study was carried out in rats with pendulum movements. The animals exhibited a high level of abortive seizures in response to audiogenic stimuli and longer postictal catalepsy in comparison with those in Wistar population. Seizure severity positively correlated with the duration of poststimulus catalepsy (r=0.90). High aggressiveness towards humans, the absence of BP elevation in stress, lower body weights, and lower weights of the kidneys and spleen in PM rats are considered concomitant traits. Correlations were detected between startle-1 and BP in rats with pendulum movements (r=0.70) and between startle-10 and BP in narcotized Wistar rats (r=-0.0.71). The newly described signs in rats with pendulum movements did not contradict the signs of the focal seizure model with typical automatisms in humans.

Energy Metabolism and Redox State in Brains of Wistar Audiogenic Rats, a Genetic Model of Epilepsy

The Wistar Audiogenic Rat (WAR) strain is a genetic model of epilepsy, specifically brainstem-dependent tonic-clonic seizures, triggered by acute auditory stimulation. Chronic audiogenic seizures (audiogenic kindling) mimic temporal lobe epilepsy, with significant participation of the hippocampus, amygdala, and cortex. The objective of the present study was to characterize the mitochondrial energy metabolism in hippocampus and cortex of WAR and verify its relationship with seizure severity. Hippocampus of WAR naïve (no seizures) presented higher oxygen consumption in respiratory states related to the maximum capacities of phosphorylation and electron transfer system, elevated mitochondrial density, lower GSH/GSSG and catalase activity, and higher protein carbonyl and lactate contents, compared with their Wistar counterparts. Audiogenic kindling had no adding functional effect in WAR, but in Wistar, it induced the same alterations observed in the audiogenic strain. In the cortex, WAR naïve presented elevated mitochondrial density, lower GSH/GSSG and catalase activity, and higher protein carbonyl levels. Chronic acoustic stimulation in Wistar induced the same alterations in cortex and hippocampus. Mainly in the hippocampus, WAR naïve presented elevated mRNA expression of glucose, lactate and excitatory amino acids transporters, several glycolytic enzymes, lactate dehydrogenase, and Na⁺/K⁺ ATPase in neurons and in astrocytes. In vivo treatment with mitochondrial uncoupler 2,4-dinitrophenol (DNP) or N-acetylcysteine (NAC) in WAR had no effect on mitochondrial metabolism, but lowered oxidative stress. Unlike DNP, NAC downregulated all enzyme genes involved in glucose and lactate uptake, and metabolism in neurons and astrocytes. Additionally, it was able to reduce brainstem seizure severity in WAR. In conclusion, in WAR naïve animals, both cerebral cortex and hippocampus display elevated mitochondrial density and/or activity associated with oxidative damage, glucose and lactate metabolism pathways upregulation, and increased Na⁺/K⁺ ATPase mRNA expression. Only in vivo treatment with NAC was able to reduce seizure severity of kindled WARs, possibly via down regulation of glucose/lactate metabolism. Taken together, our results are a clear contribution to the field of mitochondrial metabolism associated to epileptic seizures.

The highly efficient powerhouse in the Wistar audiogenic rat, an epileptic rat strain

The Wistar audiogenic rat (WAR) is an animal model of tonic-clonic epileptic seizures, developed after genetic selection by sister × brother inbreeding of Wistar rats susceptible to sound stimuli. Although metabolic changes have been described in this strain, nothing is known about its mitochondrial metabolism. Here, we addressed mitochondrial aspects of oxidative phosphorylation, oxidative stress, biogenesis, and dynamics in liver, skeletal muscle, and heart of male WARs and correlating them with physiological aspects of body metabolism. The results showed higher mitochondrial content, respiration rates in phosphorylation and noncoupled states, and H₂O₂ production in WARs. Liver presented higher content of peroxisome proliferator-activated receptor-γ coactivator 1α (PGC1α) and mammalian target of rapamycin, proteins related to mitochondrial biogenesis. In agreement, isolated liver mitochondria from WARs showed higher respiration rates in phosphorylation state and ADP-to-O ratio, as well as higher content of proteins related to electron transport chain ATP synthase, TCA cycle, and mitochondrial fusion and fission compared with their Wistar counterparts. Mitochondria with higher area and perimeter and more variable shapes were found in liver and soleus from WARs in addition to lower reduced-to-oxidized glutathione ratio. In vivo, WARs demonstrated lower body mass and energy expenditure but higher food and water intake and amino acid oxidation. When exposed to a running test, WARs reached higher speed and resisted for a longer time and distance than their Wistar controls. In conclusion, the WAR strain has mitochondrial changes in liver, skeletal muscle, and heart that improve its mitochondrial capacity of ATP production, making it an excellent rat model to study PGC1α overexpression and mitochondrial function in different physiological conditions or facing pathological challenges.

The Wistar Audiogenic Rat (WAR) strain and its contributions to epileptology and related comorbidities: History and perspectives

In the context of modeling epilepsy and neuropsychiatric comorbidities, we review the Wistar Audiogenic Rat (WAR), first introduced to the neuroscience international community more than 25years ago. The WAR strain is a genetically selected reflex model susceptible to audiogenic seizures (AS), acutely mimicking brainstem-dependent tonic-clonic seizures and chronically (by audiogenic kindling), temporal lobe epilepsy (TLE). Seminal neuroethological, electrophysiological, cellular, and molecular protocols support the WAR strain as a suitable and reliable animal model to study the complexity and emergent functions typical of epileptogenic networks. Furthermore, since epilepsy comorbidities have emerged as a hot topic in epilepsy research, we discuss the use of WARs in fields such as neuropsychiatry, memory and learning, neuroplasticity, neuroendocrinology, and cardio-respiratory autonomic regulation. Last, but not least, we propose that this strain be used in "omics" studies, as well as with the most advanced molecular and computational modeling techniques. Collectively, pioneering and recent findings reinforce the complexity associated with WAR alterations, consequent to the combination of their genetically-dependent background and seizure profile. To add to previous studies, we are currently developing more powerful behavioral, EEG, and molecular methods, combined with computational neuroscience/network modeling tools, to further increase the WAR strain's contributions to contemporary neuroscience in addition to increasing knowledge in a wide array of neuropsychiatric and other comorbidities, given shared neural networks. During the many years that the WAR strain has been studied, a constantly expanding network of multidisciplinary collaborators has generated a growing research and knowledge network. Our current and major wish is to make the WARs available internationally to share our knowledge and to facilitate the planning and execution of multi-institutional projects, eagerly needed to contribute to paradigm shifts in epileptology. This article is part of a Special Issue entitled "Genetic and Reflex Epilepsies, Audiogenic Seizures and Strains: From Experimental Models to the Clinic".

Peripheral glucose metabolism is altered by epileptic seizures

The aim of the present study was to investigate the status of jejunal absorption and peripheral metabolism of glucose in Wistar Audiogenic Rats (WAR), a genetic model of epilepsy, after seizures induced by intensive sound exposure. The jejunal loop of rats was isolated and infused (0.5 mL min(-1)) with Tyrode solution containing twice the normal concentrations of glucose, sodium, and potassium. Samples were taken at 5 or 10-min intervals over a 40-min period. At the end of the experiment, samples of liver and gastrocnemius muscle were taken to measure the levels of glycogen, glucose-6-phosphate, fructose-6-phosphate and glucose transporter-4 (GLUT4). Hepatic glucose-6-phosphate increased in WAR submitted to audiogenic seizure (21.90 +/- 3.08) as compared to non-susceptible Wistar rats (8.12 +/- 0.87) and to WAR not submitted to audiogenic stimulation (5.17 +/- 0.97). In addition, an increase in hepatic fructose-6-phosphate, an intermediate metabolite of the glycolytic pathway, was observed in WAR submitted to audiogenic seizure (5.98 +/- 0.99) compared to non-susceptible Wistar rats (2.38 +/- 0.53). According to the present results, jejunal absorption of glucose was not changed by seizures. However, generalized tonic-clonic seizures produced by sound stimulation resulted in a decrease in muscle glycogen content. In addition, our results demonstrated that the concentration of GLUT4 in the gastrocnemius muscle of WAR was 1.6-fold higher than that observed in resistant rats and that the audiogenic stimulus led to decreased concentration of this receptor in the muscle of WAR animals.