Acute, but reversible, kainic acid-induced DNA damage in hippocampal CA1 pyramidal cells of p53-deficient mice

Impaired postnatal development of the hippocampus of Krushinsky-Molodkina rats genetically prone to audiogenic seizures

The hippocampus plays an important role in epilepsy progression even if it is not involved in seizure generalization. We hypothesized that abnormal development of the hippocampus may underlie epileptogenesis. Here we analyzed postnatal development of the hippocampus of Krushinsky-Molodkina (KM) rats, which are the animal model of reflex audiogenic epilepsy. KM rats are genetically prone to audiogenic seizures that are expressed in age-dependent manner. The study was performed on seizure-naïve KM rats at several days of postnatal development (P15, P30, P60, P120). Wistar rats of the corresponding ages were used as a control. We showed that at early stages (P15, P30), the hippocampus of KM rats was characterized by significantly smaller cell population, but the number of proliferated cells was increased in comparison with control Wistar rats. Only at P60 proliferation and the total number of the hippocampal cells reached a level equal to Wistar rats. These data suggest delayed postnatal development of the hippocampus of KM rats. Analysis of apoptosis demonstrated significantly increased number of TUNEL-positive cells in the dentate gyrus (DG) of KM rats at P30 that was accompanied with expression of p53, Bcl-2 and cleaved caspases 3 and 9. Additionally, at all analyzed stages in the hilus of KM rats, the number of new-born glutamatergic cells was significantly increased that suggests formation of hilar ectopic granular cells. Our data suggest that in the case of hereditary epilepsy aberrant neurogenesis may be genetically determined.

Increased DNA Damage and Apoptosis in CDKL5-Deficient Neurons

Mutations in the CDKL5 gene, which encodes a serine/threonine kinase, causes a rare encephalopathy, characterized by early-onset epilepsy and severe intellectual disability, named CDKL5 deficiency disorder (CDD). In vitro and in vivo studies in mouse models of Cdkl5 deficiency have highlighted the role of CDKL5 in brain development and, in particular, in the morphogenesis and synaptic connectivity of hippocampal and cortical neurons. Interestingly, Cdkl5 deficiency in mice increases vulnerability to excitotoxic stress in hippocampal neurons. However, the mechanism by which CDKL5 controls neuronal survival is far from being understood. To investigate further the function of CDKL5 and dissect the molecular mechanisms underlying neuronal survival, we generated a human neuronal model of CDKL5 deficiency, using CRISPR/Cas9-mediated genome editing. We demonstrated that CDKL5 deletion in human neuroblastoma SH-SY5Y cells not only impairs neuronal maturation but also reduces cell proliferation and survival, with alterations in the AKT and ERK signaling pathways and an increase in the proapoptotic BAX protein and in DNA damage-associated biomarkers (i.e., γH2AX, RAD50, and PARP1). Furthermore, CDKL5-deficient cells were hypersensitive to DNA damage-associated stress, accumulated more DNA damage foci (γH2AX positive) and were more prone to cell death than the controls. Importantly, increased kainic acid-induced cell death of hippocampal neurons of Cdkl5 KO mice correlated with an increased γH2AX immunostaining. The results suggest a previously unknown role for CDKL5 in DNA damage response that could underlie the pro-survival function of CDKL5.

Comparison of kainate-induced seizures, cognitive impairment and hippocampal damage in male and female mice

Kainate (KA) mouse model induced by intraperitoneal injection has been widely used for epilepsy and neurodegeneration studies. KA elicits sustained epileptic activity in mouse brain revealed by recurrent behavioral seizures, deteriorative neurodegeneration and various neurological deficits. However, to date, the vast majority of the studies used male mice only, and few studies on the comparison of brain injury between male and female mice in this model were reported. Epidemiological studies indicate that sex may affect the susceptibility to seizure response and neurodegeneration process. Therefore, this study focused on the effect of sex difference on KA-induced recurrent seizures and mortality, locomotor activity and cognitive impairment, and hippocampal neurodegeneration and reactive gliosis in mice. Our results showed that, compared to females, adult male mice exhibited worse performance in mortality rate, severity of epileptic seizures, and cognitive impairment indicated by novel object recognition task. Unexpectedly, post-KA male and female mice underwent similar decline and recovery of locomotor activity. KA-induced neurodegeneration in the whole hippocampus, particularly in CA1 and CA3 subregions, along with the deteriorative reactive gliosis in astrocytes and microglia, was more severe in males than that in females. These data provided the direct in vivo evidence that indicates the key role of sex difference in studies with KA mouse model, and this could be beneficial for optimizing the design of future studies.

Design and development of letrozole nanoemulsion: A comparative evaluation of brain targeted nanoemulsion with free letrozole against status epilepticus and neurodegeneration in mice

The target of the current study is to formulate letrozole loaded nanoemulsion (LET-NE) for the direct nose to brain delivery to reduce peripheral effects of letrozole (LET). LET-NE is compared against intraperitoneally administered free LET in kainic acid (KA) induced status epilepticus (SE) in mice. LET loaded nanoemulsion (LET-NE) was prepared by aqueous microtitration method using Triacetin, Tween 80 and PEG-400 as the oil phase, surfactant, and co-surfactant. Nanoemulsion was studied for droplet size, polydispersity index (PDI), zeta potential, percentage transmittance, drug content, surface morphology. TEM images of developed formulation demonstrated spherical droplets with a mean diameter of 95.59 ± 2.34 nm, PDI of 0.162 ± 0.012 and zeta potential of -7.12 ± 0.12 mV respectively. In in-vitro and ex-vivo drug release, LET-NE showed prolonged drug release profile as compared to suspension. SE was induced by KA (10 mg/kg, i.p.) in Swiss albino mice. Behavioral seizure monitoring, biochemical estimations, and histopathological examination were performed. The onset time of SE was significantly enhanced and % incidence of SE was reduced by intranasal administration of LET-NE as compared to KA and LET administered intraperitoneally. Biochemical estimations revealed that LET-NE effectively decreased levels of 17-β estradiol while the levels of 5α-Dihydrotestosterone (5α-DHT) and 3α-androstanediol (3α-Diol) were significantly increased in the hippocampus. In cresyl violet staining LET-NE showed better protection of the hippocampus from neurotoxicity induced by KA as compared to LET. Also, in gamma scintigraphy of mouse brain, intranasal administration of nanoemulsion exhibited the presence of high concentration of LET. The study demonstrates the anticonvulsant and neuroprotective effect of LET-NE probably by inhibition of aromatization of testosterone into 17-β estradiol, proconvulsant, and diverting the pathway into the synthesis of testosterone metabolites, 3α-Diol with known anticonvulsant and neuroprotective action. Brain targeting of LET-NE showed better anticonvulsant and neuroprotective action than LET.

SIRT5 Deficiency Enhances Susceptibility to Kainate-Induced Seizures and Exacerbates Hippocampal Neurodegeneration not through Mitochondrial Antioxidant Enzyme SOD2

Epilepsy is a common and serious neurological disorder characterized by occurrence of recurrent spontaneous seizures, and emerging evidences support the association of mitochondrial dysfunction with epilepsy. Sirtuin 5 (SIRT5), localized in mitochondrial matrix, has been considered as an important functional modulator of mitochondria that contributes to ageing and neurological diseases. Our data shows that SIRT5 deficiency strikingly increased mortality rate and severity of response to epileptic seizures, dramatically exacerbated hippocampal neuronal loss and degeneration in mice exposed to Kainate (KA), and triggered more severe reactive astrogliosis. We found that the expression of mitochondrial SIRT5 of injured hippocampus was relatively up-regulated, indicating its potential contribution to the comparably increased survival of these cells and its possible neuroprotective role. Unexpectedly, SIRT5 seems not to apparently alter the decline of antioxidant enzymes superoxide dismutase 2 (SOD2) and glutathione peroxidase (GPx) in hippocampus caused by KA exposure in our paradigm, which indicates the protective role of SIRT5 on seizures and cellular degeneration might through different regulatory mechanism that would be explored in the future. In the present study, we provided strong evidences for the first time to demonstrate the association between SIRT5 and epilepsy, which offers a new understanding of the roles of SIRT5 in mitochondrial functional regulation. The neuroprotection of SIRT5 in KA-induced epileptic seizure and neurodegeneration will improve our current knowledge of the nature of SIRT5 in central nervous system (CNS) and neurological diseases.

Histamine H3 receptor antagonism by ABT-239 attenuates kainic acid induced excitotoxicity in mice

The multifaceted pathogenesis of temporal lobe epilepsy (TLE) offers a number of adjunctive therapeutic prospects. One such therapeutic strategy could be targeting H3 receptor (H3R) by selective H3R antagonists which are perceived to have antiepileptic and neuroprotective potential. Kainic acid (KA) induced seizure, a reliable model of TLE, triggers epileptogenic events resulting from initial neuronal death and ensuing recurring seizures. The present study aimed to determine whether pre-treatment with ABT-239, a novel H3R antagonist, and its combinations with sodium valproate (SVP) and TDZD-8 (glycogen synthase kinase-3β (GSK3β) inhibitor) can prevent the excitotoxic events in mice exposed to KA (10 mg/kg i.p.). ABT-239 (1 and 3 mg/kg i.p.) significantly attenuated KA-mediated behavioural and excitotoxic anomalies and restored altered expression of Bax, cleaved caspase-3, phospho-Akt (Ser473) and cAMP response element binding protein (CREB). Surprisingly, restoration of Bcl2 and phospho-GSK3β (Ser9) by ABT-239 did not reach the level of statistical significance. Co-administration of ABT-239 (1 and 3 mg/kg) with a sub-effective dose of SVP (150 mg/kg i.p.) yielded improved efficacy than when given alone. Similarly, low and high dose combinations of ABT-239 (1 and 3 mg/kg) with TDZD-8 (5 and 10 mg/kg i.p.) produced greater neuroprotection than any other treatment group. Our findings suggests a neuroprotective potential of ABT-239 and its combinations with SVP and TDZD-8 against KA-induced neurotoxicity, possibly mediated through in part each by modulating Akt/GSK3β and CREB pathways. The use of H3R antagonists as adjuvant in the treatment of human TLE might find potential utility, and can be pursued further.