Transporter hypothesis of drug-resistant epilepsy: challenges for pharmacogenetic approaches

Cortical expression of IL1-β, Bcl-2, Caspase-3 and 9, SEMA-3a, NT-3 and P-glycoprotein as biological markers of intrinsic severity in drug-resistant temporal lobe epilepsy

Mesial temporal lobe epilepsy (mTLE) is the most common epilepsy induced by previous cerebral injury, and one out of three mTLE patients develops drug resistance (DR).

AIM

To assess the expression of Bcl-2, Caspase-3, Caspase-9, IL1-β, SEMA-3a, NT-3 and P-glycoprotein in the temporal cortex and their relationship with the progression of mTLE-DR clinical features in patients with mTLE-DR.

METHOD

Tissue samples from 17 patients were evaluated for protein expression by Western blot and the relationships of the evaluated proteins with the clinical features of the mTLE were assessed through hierarchical cluster analysis.

RESULTS

The mTLE-DR group showed significantly higher P-glycoprotein, Bcl-2 and Caspase-9 levels ***p < 0.0001, ****p < 0.0001 and ***p < 0.0002, respectively, than the autopsy control group. Four patient clusters were identified: Clusters 1 and 3 showed relationships among the age of mTLE onset, duration of mTLE-DR, average number of epileptic seizures per week, number of previous antiepileptic drugs (AEDs) and increased expression of Caspase-3, Caspase-9, Neurotrophin-3 and Semaphorin-3a. Clusters 2 and 4 showed relationships among the mTLE onset age, current age, average number of epileptic seizures per week, number of previous AEDs and increased expression of IL1-β, Bcl-2, P-glycoprotein, Caspase-3 and NT-3.

CONCLUSION

The relationships among the clinical data the age of mTLE onset, DR duration, number of previous AEDs, and average number of seizures per week and the expression of proteins involved in neuronal death, neuroinflammation and aberrant connection formation, as which are biological markers in the cerebral temporal cortex, are important factors in the progression and severity of mTLE-DR and support the intrinsic severity hypothesis.

ABC Transporters at the Blood-Brain Interfaces, Their Study Models, and Drug Delivery Implications in Gliomas

Drug delivery into the brain is regulated by the blood-brain interfaces. The blood-brain barrier (BBB), the blood-cerebrospinal fluid barrier (BCSFB), and the blood-arachnoid barrier (BAB) regulate the exchange of substances between the blood and brain parenchyma. These selective barriers present a high impermeability to most substances, with the selective transport of nutrients and transporters preventing the entry and accumulation of possibly toxic molecules, comprising many therapeutic drugs. Transporters of the ATP-binding cassette (ABC) superfamily have an important role in drug delivery, because they extrude a broad molecular diversity of xenobiotics, including several anticancer drugs, preventing their entry into the brain. Gliomas are the most common primary tumors diagnosed in adults, which are often characterized by a poor prognosis, notably in the case of high-grade gliomas. Therapeutic treatments frequently fail due to the difficulty of delivering drugs through the brain barriers, adding to diverse mechanisms developed by the cancer, including the overexpression or expression de novo of ABC transporters in tumoral cells and/or in the endothelial cells forming the blood-brain tumor barrier (BBTB). Many models have been developed to study the phenotype, molecular characteristics, and function of the blood-brain interfaces as well as to evaluate drug permeability into the brain. These include in vitro, in vivo, and in silico models, which together can help us to better understand their implication in drug resistance and to develop new therapeutics or delivery strategies to improve the treatment of pathologies of the central nervous system (CNS). In this review, we present the principal characteristics of the blood-brain interfaces; then, we focus on the ABC transporters present on them and their implication in drug delivery; next, we present some of the most important models used for the study of drug transport; finally, we summarize the implication of ABC transporters in glioma and the BBTB in drug resistance and the strategies to improve the delivery of CNS anticancer drugs.

Long Non-coding RNA KCNQ1OT1 Contributes to Antiepileptic Drug Resistance Through the miR-138-5p/ABCB1 Axis in vitro

Compelling evidence has verified that long non-coding RNAs (lncRNAs) play a critical role on drug resistance in various diseases, especially cancer. However, the role of lncRNAs underlying multidrug resistance in epilepsy remains to be clarified. In the present study, we investigated the potential regulatory mechanism of the lncRNA KCNQ1OT1 in regulating antiepileptic drug (AED) resistance in human brain microvascular endothelial cells (HBMECs). The results revealed that expression of P-glycoprotein (P-gp) and KCNQ1OT1 was significantly elevated in phenytoin-resistant HBMECs (HBMEC/PHT). Meanwhile, the activity of nuclear factor-kappa B (NF-κB) was increased in HBMECs/PHT cells. Microarray analysis indicated that miR-138-5p was downregulated in HBMEC/PHT cells. Interestingly, bioinformatics prediction tools indicated miR-138-5p could directly target the transcripts of KCNQ1OT1 and NF-κB p65, and these results were confirmed by luciferase assays. Moreover, KCNQ1OT1 downregulation or miR-138-5p upregulation in vitro could inhibit P-gp expression and suppress NF-κB signaling pathway activation. Additionally, knockdown of KCNQ1OT1 or overexpression of miR-138-5p could increase the accumulation of rhodamine 123 (Rh123) and AEDs in HBMEC/PHT cells. Collectively, our results suggested that KCNQ1OT1 contributes to AED resistance through the miR-138-5p/NF-κB/ABCB1 axis in HBMEC/PHT cells, and these results provide a promising therapeutic target for the treatment of medically intractable epilepsy.

Nose-to-brain delivery of levetiracetam after intranasal administration to mice

Despite being one of the most commonly prescribed antiepileptic drugs, levetiracetam is marketed in oral and intravenous dosage forms, which are associated to drug-drug interactions and drug-resistant epilepsy (DRE). The purpose of the present study was to assess the potential of the intranasal route to deliver levetiracetam into the brain, due to the particular anatomical features of the nasal cavity. After development and characterization of the drug formulation, a thermoreversible gel loaded with levetiracetam was administered to CD-1 male mice by intranasal route and its pharmacokinetics compared to those observed after intravenous administration. Similar plasma pharmacokinetic profiles were obtained and the intranasal absolute bioavailability was 107.44%, underscoring that a high drug fraction was systemically absorbed. In brain tissue, maximum drug concentrations were 4.48 and 4.02 μg/g (intranasal vs intravenous) and the mean cerebral concentrations were significantly higher after intranasal administration. The percentage of drug targeting efficiency was 182.35% while direct transport percentage was 46.38%, suggesting that almost 50% of levetiracetam undergoes direct nose-to-brain delivery. Complementarily, an in vivo intranasal repeated dose toxicity study was performed and no relevant histopathological alterations were observed. The herein proposed non-invasive and safe intranasal administration route allowed a direct nose-to-brain delivery of levetiracetam and is a promising strategy for the treatment of DRE.

Pregnane X Receptor Not Nuclear Factor-kappa B Up-regulates P-glycoprotein Expression in the Brain of Chronic Epileptic Rats Induced by Kainic Acid

Drug-resistance epilepsy (DRE) is attributed to the brain P-glycoprotein (P-gp) overexpression. We previously reported that nuclear factor-kappa B (NF-κB) played a critical role in regulating P-gp expression at the brain of the acute seizure rats. This study was extended further to investigate the interaction effect of NF-κB and pregnane X receptor (PXR) on P-gp expression at the brain of chronic epileptic rats treated with carbamazepine (CBZ). The chronic epileptic models were induced by the micro-injection of kainic acid (KA) into rats' hippocampus. Subsequently, the successful models were treated with different intervention agents of CBZ; PMA(a non-specific PXR activity inhibitor) or PDTC(a specific NF-κB activity inhibitor) respectively. The expression levels of P-gp and its encoded gene mdr1a/b were significantly up-regulated on the brain of KA-induced chronic epilepsy rats or the epilepsy rats treated with CBZ for 1 week, meanwhile with a high expression of PXR. The treatment of PMA dramatically reduced both PXR and P-gp expressions at the protein and mRNA levels in the chronic epilepsy brain. By compared to the epilepsy model group, the P-gp expression was not markedly attenuated by the inhibition of NF-κB activity with PDTC treatment, nevertheless with a decrease of NF-κB expression in this intervention group. Higher levels of proinflammatory cytokines(IL-1β, IL-6, TNF-α) were found both in the brain tissue and the serum in the epilepsy rats of each group. There was a declined trend of the pro-inflammatory cytokines expression of the PDTC treatment group but with no statistical significance. This study demonstrates for the first time that P-gp up-regulation is due to increase PXR expression in the chronic phase of epilepsy, differently from that NF-κB signaling may induce the P-gp expression in the acute seizure phase. Our results offer insights into the mechanism underlying the development of DRE using or not using CBZ treatment.

Association of SCN1A, SCN2A and ABCC2 gene polymorphisms with the response to antiepileptic drugs in Chinese Han patients with epilepsy

AIM

The purpose of this study was to investigate the potential impact of SCN1A, SCN2A and ABCC2 gene polymorphisms on the response to antiepileptic drugs in Chinese Han patients with epilepsy.

PATIENTS & METHODS

Genetic polymorphisms in the candidate genes were detected in 453 Chinese epileptic patients by high-resolution melting curve and TaqMan methods.

RESULTS

The SCN1A IVS5-91G>A AA genotype and the ABCC2 c.1249G>A GA genotype were significantly associated with carbamazepine/oxcarbamazepine (CBZ/OXC)-resistant epilepsy (p =0.002 and p = 0.036, respectively). The frequencies of haplotypes AA (SCN1A gene) and AC (ABCC2 gene) in drug-resistant patients were significantly higher than those in responsive patients (p = 0.002 and p = 0.005, respectively).

CONCLUSION

This study suggested that SCN1A and ABCC2 polymorphisms may be associated with the response to CBZ/OXC in the Chinese Han population, indicating that they could serve as predictors of drug response. Original submitted 29 January 2014; Revision submitted 30 May 2014.

Direct nose-to-brain delivery of lamotrigine following intranasal administration to mice

Pharmacoresistance is considered one of the major causes underlying the failure of the anticonvulsant therapy, demanding the development of alternative and more effective therapeutic approaches. Due to the particular anatomical features of the nasal cavity, intranasal administration has been explored as a means of preferential drug delivery to the brain. The purpose of the present study was to assess the pharmacokinetics of lamotrigine administered by the intranasal route to mice, and to investigate whether a direct transport of the drug from nose to brain could be involved. The high bioavailability achieved for intranasally administered lamotrigine (116.5%) underscored the fact that a substantial fraction of the drug has been absorbed to the systemic circulation. Nonetheless, the heterogeneous biodistribution of lamotrigine in different brain regions, with higher concentration levels attained in the olfactory bulb comparatively to the frontal cortex and the remaining portion of the brain, strongly suggest that lamotrigine was directly transferred to the brain via the olfactory neuronal pathway, circumventing the blood-brain barrier. Therefore, it seems that intranasal route can be assumed as a suitable and valuable drug delivery strategy for the chronic treatment of epilepsy, also providing a promising alternative approach for a prospective management of pharmacoresistance.

Glutamate-Mediated Down-Regulation of the Multidrug-Resistance Protein BCRP/ABCG2 in Porcine and Human Brain Capillaries

Breast cancer resistance protein (BCRP) functions as a major molecular gatekeeper at the blood-brain barrier. Considering its impact on access to the brain by therapeutic drugs and harmful xenobiotics, it is of particular interest to elucidate the mechanisms of its regulation. Excessive glutamate concentrations have been reported during epileptic seizures or as a consequence of different brain insults including brain ischemia. Previously, we have demonstrated that glutamate can trigger an induction of the transporter P-glycoprotein. These findings raised the question whether other efflux transporters are affected in a comparable manner. Glutamate exposure proved to down-regulate BCRP transport function and expression in isolated porcine capillaries. The reduction was efficaciously prevented by coincubation with N-methyl-d-aspartate (NMDA) receptor antagonist MK-801. The involvement of the NMDA receptor in the down-regulation of BCRP was further confirmed by experiments showing an effect of NMDA exposure on brain capillary BCRP transport function and expression. Pharmacological targeting of cyclooxygenase-1 and -2 (COX-1 and -2) using the nonselective inhibitor indomethacin, COX-1 inhibitor SC-560, and COX-2 inhibitor celecoxib revealed a contribution of COX-2 activity to the NMDA receptor's downstream signaling events affecting BCRP. Translational studies were performed using human capillaries isolated from surgical specimens of epilepsy patients. The findings confirmed a glutamate-induced down-regulation of BCRP transport activity in human capillaries, which argued against major species differences. In conclusion, our data reveal a novel mechanism of BCRP down-regulation in porcine and human brain capillaries. Moreover, together with previous data sets for P-glycoprotein, the findings point to a contrasting impact of the signaling pathway on the regulation of BCRP and P-glycoprotein. The effect of glutamate and arachidonic acid signaling on BCRP function might have implications for brain drug delivery and for radiotracer brain access in epilepsy patients and patients with other brain insults.

Anatomy and physiology of the blood-brain barrier

Essential requisite for the preservation of normal brain activity is to maintain a narrow and stable homeostatic control in the neuronal environment of the CNS. Blood flow alterations and altered vessel permeability are considered key determinants in the pathophysiology of brain injuries. We will review the present-day literature on the anatomy, development and physiological mechanisms of the blood-brain barrier, a distinctive and tightly regulated interface between the CNS and the peripheral circulation, playing a crucial role in the maintenance of the strict environment required for normal brain function.

Overview and introduction: the blood-brain barrier in health and disease

This article introduces the special issue on "Blood-Brain Barrier and Epilepsy." We review briefly current understanding of the structure and function of the blood-brain barrier (BBB), including its development and normal physiology, and ways in which it can be affected in pathology. The BBB formed by the endothelium of cerebral blood vessels is one of three main barrier sites protecting the central nervous system (CNS). The barrier is not a rigid structure, but a dynamic interface with a range of interrelated functions, resulting from extremely effective tight junctions, transendothelial transport systems, enzymes, and regulation of leukocyte permeation, which thereby generates the physical, transport, enzymatic, and immune regulatory functions of the BBB. The brain endothelial cells are important components of a "modular" structure, the neurovascular unit (NVU), with several associated cell types and extracellular matrix components. Modern methods have helped in identifying a range of proteins involved in barrier structure and function, and recent studies have revealed important stages, cell types, and signaling pathways important in BBB development. There is a growing list of CNS pathologies showing BBB dysfunction, with strong evidence that this can play a major role in certain disease etiologies. The articles that follow in this issue summarize in more detail reports and discussions of the recent international meeting on "BBB in Neurological Dysfunctions," which took place recently at Ben-Gurion University of the Negev Desert Campus (Beer-Sheva, Israel), focusing on the link between experimental and clinical studies, and the ways in which these lead to improved drug treatments.

Loss of the initial efficacy of levetiracetam in patients with refractory epilepsy

PURPOSE

The efficacy and safety of the anti-convulsive drug levetiracetam (LEV) has been well documented but few clinical studies have investigated tolerance to LEV. The aim of this study was to evaluate the loss of the initial efficacy of LEV in adult patients with refractory partial-onset seizures.

METHODS

We enrolled patients with refractory partial epilepsy who were started on add-on LEV treatment. The efficacy of LEV was evaluated every three months and the seizure frequency was decided by the average number of monthly seizures. A responder was defined as a patient with a ≥50% reduction in seizure frequency from the baseline. Seizure freedom was defined as a seizure-free status from the beginning of LEV treatment to the evaluation period. Loss of the initial efficacy was defined as a shift from responder status during the first three months of LEV treatment to non-responder status during the follow-up period.

RESULTS

A total of 95 epilepsy patients were analyzed. During the first three months of LEV treatment, 50 (52.6%) of the 95 patients were responders with a ≥50% seizure reduction. Nine patients (18.0%) showed a loss of initial efficacy during the second three-month period. In contrast, only two (4.0%) of the non-responders during the first three months became responders during the next three months. However, this difference did not reach statistical significance (P=0.054). Based on Kaplan-Meier survival estimates, 49.2% of the patients who initially responded to LEV treatment during the first three months were predicted to lose this response at 42 months. Loss of the initial efficacy of LEV treatment occurred mostly within 18 months.

CONCLUSION

This study suggests that the occurrence of tolerance is more common than late gain of efficacy of treatment although larger prospective studies would have to be carried out to prove this observation.

Role of CNS efflux drug transporters in antiepileptic drug delivery: overcoming CNS efflux drug transport

Experimental support for the transporter hypothesis of drug resistance in epilepsies has triggered efforts developing and validating approaches to overcome enhanced blood-brain barrier efflux transport. Testing in rodent models has rendered proof-of-concept for an add-on therapy with antiepileptic drugs. However, further development of the approach would require tolerability considerations as efflux transporters serve an important protective function throughout the body limiting distribution of harmful xenobiotics. Relevant progress has been made in the elucidation of mechanisms driving up-regulation of the multidrug transporter P-glycoprotein in response to seizure activity. Based on this knowledge, novel strategies have been evaluated targeting the signaling cascade that regulates P-glycoprotein in the epileptic brain. Further concepts might include by-passing blood-brain barrier transporters by intracerebral administration or by encapsulation of antiepileptic drugs in nano-sized carrier systems. It is important to note that the future perspectives of respective approaches are still questionable based on the limited evidence for a clinical relevance of transporter expression. Thus, techniques are urgently needed for non-invasive assessment of blood-brain barrier transporter function. Respective techniques would allow testing for a clinical correlation between pharmacosensitivity and transporter function, validating therapeutic strategies targeting efflux transporters and selecting patients with transporter over-expression for respective clinical trials. Provided that further clinical data render support for the transporter hypothesis, the main question remains whether patients exist in which transporter over-expression is the predominant mechanism of drug resistance and in which overcoming drug efflux is equivalent with overcoming drug resistance. Imaging techniques might provide a tool to address these questions in clinical epileptology. However, the complex pharmacological interactions between antiepileptic drugs, radiotracers, and transporter modulators used in these approaches as well as interindividual differences in the brain pathology might hamper clear-cut conclusions and limit the diagnostic significance.

Disease progression and treatment response of idiopathic epilepsy in Australian Shepherd dogs

BACKGROUND

Idiopathic epilepsy (IE) in Australian Shepherds (ASs) occurs worldwide but there is a lack of description of the epilepsy syndrome in this breed. The ABCB1-1Δ mutation is more prevalent in ASs than in many other dog breeds.

HYPOTHESIS

Australian Shepherds suffer from a poorly controlled IE syndrome with prevailing severe courses. Seizure control and ABCB1-1Δ mutation might be related in this breed.

ANIMALS

Fifty ASs diagnosed with IE and 50 unaffected ASs.

METHODS

Predominant study design is a longitudinal cohort study. Pedigrees, medical records, seizure, and treatment data of ASs with IE were analyzed descriptively. Sex, color, and the ABCB1-1Δ genotype were compared between case and control groups and ASs with poorly or well-controlled seizures. Differences in survival times were assessed by logrank tests and Cox regression analysis.

RESULTS

Idiopathic epilepsy in ASs is dominated by moderate and severe clinical courses with the occurrence of cluster seizures and status epilepticus and a high seizure frequency. Poor seizure control and a high initial seizure frequency (≥10 seizure days/first 6 months) are associated with shorter survival times (P < .05). Poor seizure control, unrelated to the ABCB1(MDR1) genotype, is evident in 56% of epileptic ASs. Pedigree analysis suggests a genetic basis.

CONCLUSION AND CLINICAL IMPORTANCE

Frequent severe clinical courses, poor seizure control unrelated to the ABCB1(MDR1) genotype, and a young age at death compromise animal welfare and warrant further genetic studies to unravel the underlaying molecular mechanisms of IE and seizure control in the breed.