Mice lacking L-12/15-lipoxygenase show increased mortality during kindling despite demonstrating resistance to epileptogenesis

Ironing out the Links: Ferroptosis in epilepsy and SUDEP

Iron is a crucial element for almost all organisms because it plays a vital role in oxygen transport, enzymatic processes, and energy generation due to its electron transfer capabilities. However, its dysregulation can lead to a form of programmed cell death known as ferroptosis, which is characterized by cellular iron accumulation, reactive oxygen species (ROS) production, and unrestricted lipid peroxidation. Both iron and ferroptosis have been identified as key players in the pathogenesis of various neurodegenerative diseases. While in epilepsy this phenomenon remains relatively understudied, seizures can be considered hypoxic-ischemic episodes resulting in increased ROS production, lipid peroxidation, membrane disorganization, and cell death. All of this is accompanied by elevated intracellular free Fe2+ concentration and hemosiderin precipitation, as existing reports suggest a significant accumulation of iron in the brain and heart associated with epilepsy. Generalized tonic-clonic seizures (GTCS), a primary risk factor for Sudden Unexpected Death in Epilepsy (SUDEP), not only have an impact on the brain but also lead to cardiogenic dysfunctions associated with "Iron Overload and Cardiomyopathy" (IOC) and "Epileptic heart" characterized by electrical and mechanical dysfunction and a high risk of malignant bradycardia. In line with this phenomenon, studies conducted by our research group have demonstrated that recurrent seizures induce hypoxia in cardiomyocytes, resulting in P-glycoprotein (P-gp) overexpression, prolonged Q-T interval, severe bradycardia, and hemosiderin precipitation, correlating with an elevated spontaneous death ratio. In this article, we explore the intricate connections among ferroptosis, epilepsy, and SUDEP. By synthesizing current knowledge and drawing insights from recent publications, this study provides a comprehensive understanding of the molecular underpinnings. Furthermore, this review offers insights into potential therapeutic avenues and outlines future research directions.

Disruption of adenosine metabolism increases risk of seizure-induced death despite decreased seizure severity

OBJECTIVE

Respiratory arrest plays an important role in sudden unexpected death in epilepsy (SUDEP). Adenosine is of interest in SUDEP pathophysiology due to its influence on seizures and breathing. The objective of this investigation was to examine the role of adenosine in seizure severity, seizure-induced respiratory disruption, and seizure-induced death using mouse models. Understanding adenosinergic contributions to seizure cessation and seizure-induced death may provide insights into how SUDEP can be prevented while avoiding increased seizure severity.

METHODS

Our approach was to examine: (1) seizure severity and seizure-induced death after 15 mA electroshock seizures and during repeated pentylenetetrazol (PTZ) administration in wild-type mice (Adk+/+) and transgenic mice with reduced adenosine metabolism (Adk+/-); (2) the postictal hypercapnic ventilatory response (HCVR) in wild-type mice (the postictal HCVR could not be examined in Adk+/- mice due to their high mortality rate); and (3) the effects of adenosinergic drugs on seizure severity and seizure-induced death following maximal electroshock (MES).

RESULTS

Adk+/- mice were more vulnerable to seizure-induced death in the 15 mA electroshock and repeated PTZ models. Despite increased mortality, Adk+/- mice had comparable seizure severity in the PTZ model and reduced seizure severity in the 15 mA electroshock model. Breathing and HCVR were suppressed by 15 mA electroshock seizures in wild-type mice. Pharmacological inhibition of adenosine metabolism decreased MES seizure severity but did not increase mortality. A1 selective and nonselective adenosine receptor antagonists increased seizure-induced death following MES.

SIGNIFICANCE

Adenosine has opposing effects on seizure severity and seizure-induced death. On the one hand, our seizure severity data highlight the importance of adenosine in seizure suppression. On the other hand, our mortality data indicate that excessive extracellular adenosine signaling can increase the risk of seizure-induced respiratory arrest.

Sex- and age-dependent contribution of System xc- to cognitive, sensory, and social behaviors revealed by comprehensive behavioral analyses of System xc- null mice

Background

System xc- (Sxc-) is an important heteromeric amino acid cystine/glutamate exchanger that plays a pivotal role in the CNS by importing cystine into cells while exporting glutamate. Although certain behaviors have been identified as altered in Sxc- null mutant mice, our understanding of the comprehensive impact of Sxc- on behavior remains incomplete.

Methods

To address this gap, we compared motor, sensory and social behaviors of male and female mice in mice null for Sxc- (SLC7A11sut/sut) with wildtype littermates (SLC7A11+/+) in a comprehensive and systematic manner to determine effects of genotype, sex, age, and their potential interactions.

Results

Motor performance was not affected by loss of Sxc- in both males and females, although it was impacted negatively by age. Motor learning was specifically disrupted in female mice lacking Sxc- at both 2 and 6 months of age. Further, female SLC7A11sut/sut mice at both ages exhibited impaired sociability, but normal spatial and recognition memory, as well as sensorimotor gating. Finally, pronounced open-space anxiety was displayed by female SLC7A11sut/sut when they were young. In contrast, young SLC7A11sut/sut male mice demonstrated normal sociability, delayed spatial learning, increased open-space anxiety and heightened sensitivity to noise. As they aged, anxiety and noise sensitivity abated but hyperactivity emerged.

Discussion

We find that the behavioral phenotypes of female SLC7A11sut/sut are similar to those observed in mouse models of autism spectrum disorder, while behaviors of male SLC7A11sut/sut resemble those seen in mouse models of attention deficit hyperactivity disorder. These results underscore the need for further investigation of SLC7A11 in neurodevelopment. By expanding our understanding of the potential involvement of Sxc-, we may gain additional insights into the mechanisms underlying complex neurodevelopmental conditions.

Clinical response to EPA supplementation in patients with major depressive disorder is associated with higher plasma concentrations of pro-resolving lipid mediators

Chronic inflammation has been implicated in the pathophysiology of major depressive disorder (MDD). Activating the resolution of inflammation through ω-3 fatty acid supplementation may prove to be a successful therapeutic strategy for the treatment of MDD. Patients with MDD, body mass index >25 kg/m², and plasma high-sensitivity C-reactive protein ≥3 μg/mL (n = 61) were enrolled in a 12-week randomized trial consisting of 4 parallel arms: EPA 1, 2, and 4 g/d, and placebo. The supplement contained EPA and DHA in a 3.9:1 ratio. Depression symptoms were assessed using the IDS-C30 scale. Plasma fatty acids and pro-resolving lipid mediators (SPMs) were measured in 42 study completers at baseline and at the end of treatment by liquid chromatography/mass spectrometry. The response rate (≥50% reduction in IDS-30 score) was higher in the 4 g/d EPA arm than placebo (Cohen d = 0.53). In the 4 g/d EPA arm, responders had significantly greater increases in 18-hydroxyeicosapentaenoic acid (18-HEPE) and 13-hydroxydocosahexaenoic acid (13-HDHA) than non-responders (p < 0.05). Within the 4 g/d EPA arm, the increase in 18-HEPE was significantly associated with reductions in plasma hs-CRP concentrations (p < 0.05) and IDS-C30 scores (p < 0.01). In summary, response rates were greater among patients with MDD randomized to EPA 4 g/d supplementation and in those who showed a greater ability to activate the synthesis of 18-HEPE. The inverse association of 18-HEPE with both systemic inflammation and symptoms of depression highlights the activation of the resolution of inflammation as a likely mechanism in the treatment of MDD with ω-3 fatty acid supplementation.

The functions of repressor element 1-silencing transcription factor in models of epileptogenesis and post-ischemia

Epilepsy is a debilitating neurological disorder characterised by recurrent seizures for which 30% of patients are refractory to current treatments. The genetic and molecular aetiologies behind epilepsy are under investigation with the goal of developing new epilepsy medications. The transcriptional repressor REST (Repressor Element 1-Silencing Transcription factor) is a focus of interest as it is consistently upregulated in epilepsy patients and following brain insult in animal models of epilepsy and ischemia. This review analyses data from different epilepsy models and discusses the contribution of REST to epileptogenesis. We propose that in healthy brains REST acts in a protective manner to homeostatically downregulate increases in excitability, to protect against seizure through downregulation of BDNF (Brain-Derived Neurotrophic Factor) and its receptor, TrkB (Tropomyosin receptor kinase B). However, in epilepsy patients and post-seizure, REST may increase to a larger degree, which allows downregulation of the glutamate receptor subunit GluR2. This leads to AMPA glutamate receptors lacking GluR2 subunits, which have increased permeability to Ca²⁺, causing excitotoxicity, cell death and seizure. This concept highlights therapeutic potential of REST modulation through gene therapy in epilepsy patients.

Cepharanthine attenuates cerebral ischemia/reperfusion injury by reducing NLRP3 inflammasome-induced inflammation and oxidative stress via inhibiting 12/15-LOX signaling

Cepharanthine (CEP) is a potential candidate for treatment of cerebral ischemia/reperfusion (I/R) injury, due to its anti-inflammatory and anti-oxidative properties. To investigate the effect of CEP on cerebral I/R injury, we established a mouse model of transient middle cerebral artery occlusion (tMCAO) and a microglia cell model of oxygen and glucose deprivation/reoxygenation (OGD/R). Administration of CEP attenuated neurological deficits, reduced infarct volume and edema, and decreased microglia activation in MCAO mice. Immunofluorescence staining showed an up-regulation in NLR Family Pyrin Domain Containing 3 (NLRP3) immunoreactivity in Iba1-labled microglia together with total Iba1 and NLRP3 expression in the brain following tMCAO, while down-regulated by CEP treatment. In both tMCAO-induced mice and OGD/R-treated BV-2 cells, CEP exhibited dose-dependent inhibition on the expression of NLRP3, ASC and cleaved caspase-1. Importantly, CEP attenuated tMCAO or OGD/R-induced overproduction of M1 microglia-regulated pro-inflammation cytokines IL-1β and IL-18, suggesting that CEP might involve in suppressing microglia polarization to M1 phenotype in vivo and in vitro. Moreover, CEP dose-dependently inhibited tMCAO-induced arachidonate 15 lipoxygenase (ALOX15) together with Iba1-labled microglia. The subsequent ALOX15-mediated oxidative stress was decreased by CEP treatment in vivo and in vitro, as evidenced by reduced ROS generation and MDA level, and increased SOD activity. Taken together, we demonstrate that CEP attenuates cerebral I/R injury probably by inhibiting microglia activation and NLRP3 inflammasome-induced inflammation and reducing oxidative stress via suppressing 12/15-LOX signaling.

Baicalein Exerts Neuroprotective Effects in FeCl3-Induced Posttraumatic Epileptic Seizures via Suppressing Ferroptosis

Posttraumatic epilepsy (PTE) is a prevalent type of acquired epilepsy secondary to traumatic brain injury, and is characterized by repeated seizures. Traditional antiepileptic drugs have minimal response in preventing posttraumatic epileptic seizures. It is essential for the development of new therapeutic strategy. Our previous work disclosed a potent neuroprotective role of baicalein, a flavonoid extracted from Scutellaria baicalensis Georgi, against inherited epilepsy in rats. Whether baicalein has protective potential in posttraumatic epileptic seizures and the possible molecular mechanism remain elusive. Additionally, the brain is vulnerable to lipid peroxidation-induced damage due to high consumption of oxygen and abundant polyunsaturated fatty acids in neuronal membranes. Our present investigation aimed to elucidate whether baicalein exerts neuroprotective effects on posttraumatic epileptic seizures by inhibiting ferroptosis, a newly discovered lipid peroxidation-dependent cell death modality. We found that baicalein significantly reduced seizure score, number of seizures, and average seizure duration in an iron chloride (FeCl₃)-induced PTE mouse model. The neuroprotective effect of baicalein was also validated in a ferric ammonium citrate (FAC)-induced HT22 hippocampal neuron damage model. Moreover, in vitro, baicalein could remarkably decrease ferroptotic indices (lipid reactive oxygen species, 4-hydroxynonenal, and prostaglandin endoperoxide synthase 2) and inhibit the expression of 12/15-lipoxygenase (12/15-LOX) in an iron-induced HT22 cell damage model. These findings were also validated in a mouse PTE model. It was concluded that baicalein exerted neuroprotective effects against posttraumatic epileptic seizures via suppressing ferroptosis and 12/15-LOX was likely to be involved in baicalein’s neuroprotection.