Inhibition of mTOR Pathway by Rapamycin Decreases P-glycoprotein Expression and Spontaneous Seizures in Pharmacoresistant Epilepsy

18F-Labeled dihydropyridines via Hantzsch reaction for positron emission tomography of P-glycoprotein dysfunction

Despite the availability of various 11C-labeled positron emission tomography (PET) tracers for assessing P-glycoprotein (P-gp) function, there are still limitations related to complex metabolism, high lipophilicity, and low baseline uptake. This study aimed to address these issues by exploring a series of customized dihydropyridines (DHPs) with enhanced stability and reduced lipophilicity as alternative PET tracers for P-gp dysfunction. Compared with verapamil and the rest DHPs, dimethyl 4-(4-fluorophenyl)-2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate (1) exhibited superior cellular uptake differences between the human gastric cancer cell line SGC7901 and its drug-resistant counterpart. [18F]1 is successfully synthesized using a novel "hot-Hantzsch" approach in 22.1 ± 0.1 % radiochemical yields. MicroPET/CT imaging demonstrated that the uptake of [18F]1 in the brains of P-gp blocked mice increased by > 3 times compared to the control group. Additionally, [18F]1 displayed favorable lipophilicity (log D = 2.3) and excellent clearance characteristics, making it a promising tracer candidate with low background noise and high contrast.

PI3K-AKT/mTOR Signaling in Psychiatric Disorders: A Valuable Target to Stimulate or Suppress?

Economic development and increased stress have considerably increased the prevalence of psychiatric disorders in recent years, which rank as some of the most prevalent diseases globally. Several factors, including chronic social stress, genetic inheritance, and autogenous diseases, lead to the development and progression of psychiatric disorders. Clinical treatments for psychiatric disorders include psychotherapy, chemotherapy, and electric shock therapy. Although various achievements have been made researching psychiatric disorders, the pathogenesis of these diseases has not been fully understood yet, and serious adverse effects and resistance to antipsychotics are major obstacles to treating patients with psychiatric disorders. Recent studies have shown that the mammalian target of rapamycin (mTOR) is a central signaling hub that functions in nerve growth, synapse formation, and plasticity. The PI3K-AKT/mTOR pathway is a critical target for mediating the rapid antidepressant effects of these pharmacological agents in clinical and preclinical research. Abnormal PI3K-AKT/mTOR signaling is closely associated with the pathogenesis of several neurodevelopmental disorders. In this review, we focused on the role of mTOR signaling and the related aberrant neurogenesis in psychiatric disorders. Elucidating the neurobiology of the PI3K-AKT/mTOR signaling pathway in psychiatric disorders and its actions in response to antidepressants will help us better understand brain development and quickly identify new therapeutic targets for the treatment of these mental illnesses.

The Prevention and Reversal of a Phenytoin-Resistant Model by N-acetylcysteine Therapy Involves the Nrf2/P-Glycoprotein Pathway at the Blood-Brain Barrier

The transporter hypothesis is one of the most popular hypotheses of drug-resistant epilepsy (DRE). P-glycoprotein (P-gp), a channel protein at the blood-brain barrier (BBB), plays an important role in the transport of some anti-seizure drugs from brain tissue into vessels, which reduces drug concentrations and diminishes the effects of drug treatment. We performed this study to test whether P-gp is overexpressed in DRE and identify ways to prevent and reverse DRE. In this study, we established a phenytoin (PHT)-resistant mouse model and revealed that P-gp was overexpressed at the BBB in PHT-resistant mice. The P-gp inhibitor nimodipine decreased the resistance of phenytoin. Antioxidative preventive treatment with N-acetylcysteine (NAC) prevented the mice from entering a PHT-resistant state, and NAC therapy tended to reverse PHT resistance into sensitivity. We were also able to induce PHT resistance by activating the Nrf2/P-gp pathway, which indicates that oxidative stress plays an important role in drug resistance. Taken together, these findings suggest that antioxidative therapy may be a promising strategy for overcoming DRE.

The Establishment of Quantitatively Regulating Expression Cassette with sgRNA Targeting BIRC5 to Elucidate the Synergistic Pathway of Survivin with P-Glycoprotein in Cancer Multi-Drug Resistance

Quantitative analysis and regulating gene expression in cancer cells is an innovative method to study key genes in tumors, which conduces to analyze the biological function of the specific gene. In this study, we found the expression levels of Survivin protein (BIRC5) and P-glycoprotein (MDR1) in MCF-7/doxorubicin (DOX) cells (drug-resistant cells) were significantly higher than MCF-7 cells (wild-type cells). In order to explore the specific functions of BIRC5 gene in multi-drug resistance (MDR), a CRISPR/Cas9-mediated knocking-in tetracycline (Tet)-off regulatory system cell line was established, which enabled us to regulate the expression levels of Survivin quantitatively (clone 8 named MCF-7/Survivin was selected for further studies). Subsequently, the determination results of doxycycline-induced DOX efflux in MCF-7/Survivin cells implied that Survivin expression level was opposite to DOX accumulation in the cells. For example, when Survivin expression was down-regulated, DOX accumulation inside the MCF-7/Survivin cells was up-regulated, inducing strong apoptosis of cells (reversal index 118.07) by weakening the release of intracellular drug from MCF-7/Survivin cells. Also, down-regulation of Survivin resulted in reduced phosphorylation of PI3K, Akt, and mTOR in MCF-7/Survivin cells and significantly decreased P-gp expression. Previous studies had shown that PI3K/Akt/mTOR could regulate P-gp expression. Therefore, we speculated that Survivin might affect the expression of P-gp through PI3K/Akt/mTOR pathway. In summary, this quantitative method is not only valuable for studying the gene itself, but also can better analyze the biological phenomena related to it.

An Insight into Molecular Mechanisms and Novel Therapeutic Approaches in Epileptogenesis

Epilepsy is the second most common neurological disease with abnormal neural activity involving the activation of various intracellular signalling transduction mechanisms. The molecular and system biology mechanisms responsible for epileptogenesis are not well defined or understood. Neuroinflammation, neurodegeneration and Epigenetic modification elicit epileptogenesis. The excessive neuronal activities in the brain are associated with neurochemical changes underlying the deleterious consequences of excitotoxicity. The prolonged repetitive excessive neuronal activities extended to brain tissue injury by the activation of microglia regulating abnormal neuroglia remodelling and monocyte infiltration in response to brain lesions inducing axonal sprouting contributing to neurodegeneration. The alteration of various downstream transduction pathways resulted in intracellular stress responses associating endoplasmic reticulum, mitochondrial and lysosomal dysfunction, activation of nucleases, proteases mediated neuronal death. The recently novel pharmacological agents modulate various receptors like mTOR, COX-2, TRK, JAK-STAT, epigenetic modulators and neurosteroids are used for attenuation of epileptogenesis. Whereas the various molecular changes like the mutation of the cell surface, nuclear receptor and ion channels focusing on repetitive episodic seizures have been explored by preclinical and clinical studies. Despite effective pharmacotherapy for epilepsy, the inadequate understanding of precise mechanisms, drug resistance and therapeutic failure are the current fundamental problems in epilepsy. Therefore, the novel pharmacological approaches evaluated for efficacy on experimental models of epilepsy need to be identified and validated. In addition, we need to understand the downstream signalling pathways of new targets for the treatment of epilepsy. This review emphasizes on the current state of novel molecular targets as therapeutic approaches and future directions for the management of epileptogenesis. Novel pharmacological approaches and clinical exploration are essential to make new frontiers in curing epilepsy.

Metformin ameliorates the status epilepticus- induced hippocampal pathology through possible mTOR modulation

The initial precipitating injury such as SE progresses to chronic epilepsy through multiple epileptogenic processes. Early epileptogenic events are generally characterized by neuroinflammation, neurodegeneration and abnormal neurogenesis in the hippocampus. Metformin has exhibited anti-inflammatory and neuroprotective properties in numerous studies. The current study attempts to investigate the effect of metformin on seizure-induced inflammation and neuronal degeneration, and the involvement of the mTOR pathway. Status epilepticus (SE) was induced in male Wistar rats with systemic administration of Lithium (127 mg/kg) and Pilocarpine (30 mg/kg). In test rats, Metformin 100 mg/kg or 200 mg/kg was administered orally for 7 days, followed by SE induction. Results indicate that metformin did not alter the SE profile significantly which was evident by the behavioural scoring and electroencephalogram (EEG) recordings. However, metformin 200 mg/kg attenuated the SE-induced glial activation (p < 0.01), up regulated mRNA levels of proinflammatory cytokines (p < 0.001) and chemokines (p < 0.001) and enhanced BBB permeability (p < 0.05). In addition, metformin ameliorated the insult-induced region-specific neuronal damage (p < 0.01) and restored the hippocampal neuronal density. Metformin significantly inhibited phosphorylated S6 ribosomal protein (phospho-S6rp) (p < 0.05), thus demonstrating that the beneficial effects might be partly mediated by the mTOR pathway. The study thus reiterates that mTOR signalling is one of the mechanisms involved in inflammation and neurodegeneration in early epileptogenesis following SE.

Rationally designed rapamycin-encapsulated ZIF-8 nanosystem for overcoming chemotherapy resistance

Zeolitic imidazolate framework-8 (ZIF-8) nanoparticles are widely reported as a pH-sensitive drug delivery carrier with high loading capacity for tumor therapy. However, the mechanism of intracellular corrosion of ZIF-8 and the corresponding biological effects especially for autophagy response have been rarely reported. Herein, the as-synthesized ZIF-8 was demonstrated to induce mTOR independent and pro-death autophagy. Interestingly, the autophagic process participated in the corrosion of ZIF-8. Subsequently, zinc ion release and the generation of reactive oxygen species due to its corrosion in the acidic compartments were directly responsible for tumor cell killing. In addition, ZIF-8 could sensitize tumor cells to chemotherapy by switching cytoprotective to death promoting autophagy induced by doxorubicin. The mTOR signaling pathway activation was demonstrated to restrict tumor chemotherapy efficiency. Hence, a combined platform rapamycin encapsulated zeolitic imidazolate frameworks (Rapa@ZIF-8) was constructed and demonstrated a more significant chemo-sensitized effect relative to ZIF-8 nanoparticles or rapamycin treatment alone. Lastly, the combined administration of Rapa@ZIF-8 and doxorubicin exhibited an outstanding synergistic antitumor effect without any obvious toxicity to the major organs of mice. Collectively, the optimized nanoplatform, Rapa@ZIF-8, provides a proof of concept for intentionally interfering mTOR pathway and utilizing the switch of survival-to death-promoting autophagy for adjunct chemotherapy.

Neurodegenerative pathways as targets for acquired epilepsy therapy development

There is a growing body of clinical and experimental evidence that neurodegenerative diseases and epileptogenesis after an acquired brain insult may share common etiological mechanisms. Acquired epilepsy commonly develops as a comorbid condition in patients with neurodegenerative diseases such as Alzheimer's disease, although it is likely much under diagnosed in practice. Progressive neurodegeneration has also been described after traumatic brain injury, stroke, and other forms of brain insults. Moreover, recent evidence has shown that acquired epilepsy is often a progressive disorder that is associated with the development of drug resistance, cognitive decline, and worsening of other neuropsychiatric comorbidities. Therefore, new pharmacological therapies that target neurobiological pathways that underpin neurodegenerative diseases have potential to have both an anti-epileptogenic and disease-modifying effect on the seizures in patients with acquired epilepsy, and also mitigate the progressive neurocognitive and neuropsychiatric comorbidities. Here, we review the neurodegenerative pathways that are plausible targets for the development of novel therapies that could prevent the development or modify the progression of acquired epilepsy, and the supporting published experimental and clinical evidence.

Identification of potential drug targets for treatment of refractory epilepsy using network pharmacology

Epilepsy is the fourth most common neurological disease after migraine, stroke, and Alzheimer's disease. Approximately one-third of all epilepsy cases are refractory to the existing anticonvulsants. Thus, there is an unmet need for newer antiepileptic drugs (AEDs) to manage refractory epilepsy (RE). Discovery of novel AEDs for the treatment of RE further retards for want of potential pharmacological targets, unavailable due to unclear etiology of this disease. In this regard, network pharmacology as an area of bioinformatics is gaining popularity. It combines the methods of network biology and polypharmacology, which makes it a promising approach for finding new molecular targets. This work is aimed at discovering new pharmacological targets for the treatment of RE using network pharmacology methods. In the framework of our study, the genes associated with the development of RE were selected based on analysis of available data. The methods of network pharmacology were used to select 83 potential pharmacological targets linked to the selected genes. Then, 10 most promising targets were chosen based on analysis of published data. All selected target proteins participate in biological processes, which are considered to play a key role in the development of RE. For 9 of 10 selected targets, the potential associations with different kinds of epilepsy have been recently mentioned in the literature published, which gives additional evidence that the approach applied is rather promising.

Recombinant Human Erythropoietin Protects Against Hippocampal Damage in Developing Rats with Seizures by Modulating Autophagy via the S6 Protein in a Time-Dependent Manner

Epilepsy is among the most common neurological disorders. Recurrent seizures result in neuronal death, cognitive deficits and intellectual disabilities in children. Currently, recombinant human erythropoietin (rhEPO) is considered to play a neuroprotective role in nervous system disorders. However, the precise mechanisms through which rhEPO modulates epilepsy remain unknown. Based on results from numerous studies, we hypothesized that rhEPO protects against hippocampal damage in developing rats with seizures probably by modulating autophagy via the ribosomal protein S6 (S6) in a time-dependent manner. First, we observed that rats with recurrent seizures displayed neuronal loss in the hippocampal CA1 region. Second, rhEPO injection reduced neuronal loss and decreased the number of apoptotic cells in the hippocampal CA1 region. Moreover, rhEPO increased the Bcl-2 protein expression levels and decreased the ratio of cleaved caspase-3/caspase-3 in the hippocampus. Finally, rhEPO modulated autophagy in the hippocampus in a time-dependent manner, probably via the S6 protein. In summary, rhEPO protects against hippocampal damage in developing rats with seizures by modulating autophagy in a time-dependent manner, probably via the S6 protein. Consequently, rhEPO is a likely drug candidate that is capable of attenuating brain injury.

Preconditioning with morphine protects hippocampal CA1 neurons from ischemia-reperfusion injury via activation of the mTOR pathway

The signaling pathway of chronic morphine treatment to prevent neuronal damage following transient cerebral ischemia is not clear. In this study, we examined the role of mammalian target of rapamycin (mTOR) to identify the neuroprotective effects of chronic morphine preconditioning on the hippocampus following ischemia-reperfusion (I/R) injury. Morphine was administered for 5 days, twice a day, before inducing I/R injury. The possible role of mTOR was evaluated by the injection of rapamycin (5 mg/kg body weight, by intraperitoneal injection) before I/R was induced. The passive avoidance test was used to evaluate memory performance. Neuronal density and apoptosis were measured in the CA1 region, 72 h after I/R injury. The expressions of mTOR and phosphorylated mTOR (p-mTOR), as well as superoxide dismutase (SOD) activity were determined 24 h after I/R injury. Chronic morphine treatment attenuated apoptosis and neuronal loss in the hippocampus after I/R injury, which led to improvement in memory (P < 0.05 vs. untreated I/R) and increase in the expression of p-mTOR (P < 0.05 vs. untreated I/R) and SOD activity (P < 0.05 vs. untreated I/R) in the hippocampus. Pretreatment with rapamycin abolished all the above-mentioned protective effects. These results describe novel findings whereby chronic morphine preconditioning in hippocampal CA1 neurons is mediated by the mTOR pathway, and through increased phosphorylation of mTOR can alleviate oxidative stress and apoptosis, and eventually protect the hippocampus from I/R injury.

Synergistic protection against acute flurothyl-induced seizures by adjuvant treatment of the ketogenic diet with the type 2 diabetes drug pioglitazone

OBJECTIVE

We have previously found that the transcription factor peroxisome proliferator-activated receptor γ (PPARγ) contributes to the mechanism of action of the ketogenic diet (KD), an established treatment for pediatric refractory epilepsy. We have found that the KD increases brain PPARγ and that inhibition or genetic loss of PPARγ prevents the antiseizure effects of the KD on (1) acutely induced seizures in nonepileptic mice and (2) spontaneous recurrent seizures in epileptic mice. Here, we tested the hypothesis that adjuvant treatment of KD-treated mice with a PPARγ agonist, pioglitazone, would result in an additive effect.

METHODS

Acute seizures were induced in three groups of C57Bl/6 mice by inhalation exposure to flurothyl gas. In Group 1, mice were weaned onto either a standard diet or KD comprised of a fat:carbohydrate/protein ratio of either 6:1, 3:1, or 1:1 for 2 weeks. In Group 2, vehicle or pioglitazone (0.1, 1, 10, 80 mg/kg) was administered 4 h prior to flurothyl exposure. In Group 3, vehicle or increasing doses of pioglitazone were administered to KD-treated mice 4 h prior to flurothyl exposure. Latency times to clonic seizures and generalized tonic-clonic (GTC) seizures were recorded, and isobolographic analysis was used to determine combinatorial interactions.

RESULTS

Neither KD treatment nor pioglitazone alone or in combination affected clonic seizures. However, the latency to GTC seizures was dose-dependently and significantly increased by both KD (~57%, p < 0.05) and pioglitazone (~28%, p < 0.05). Coadministration of an ineffective 1:1 KD and pioglitazone resulted in ~47-55% (p < 0.05) increase in latency to GTC. Isobolographic analysis indicated a synergistic interaction of the KD and pioglitazone.

SIGNIFICANCE

These results suggest coadministration may enable reduction of the KD ratio without loss of seizure protection. Such adjuvant treatment could improve quality of life and limit adverse effects of a classic KD or high-dose pioglitazone.