Multidrug Resistance In Epilepsy Research Articles

Expressional Study of Permeability Glycoprotein and Multidrug Resistance Protein 1 in Drug-resistant Mesial Temporal Lobe Epilepsy.

About 30% of patients with epilepsy do not respond to anti-epileptic drugs, leading to refractory seizures. The pathogenesis of drug-resistance in mesial temporal lobe epilepsy (MTLE) is not completely understood. Increased activity of drug-efflux transporters might be involved, resulting in subclinical concentrations of the drug at the target site. The major drug-efflux transporters are permeability glycoprotein (P-gp) and multidrug-resistance associated protein-1 (MRP-1). The major drawback so far is the expressional analysis of transporters in equal numbers of drug-resistant epileptic tissue and age-matched non-epileptic tissue. We have studied P-gp and MRP-1 drug-efflux transporters in the sclerotic hippocampal tissues resected from the epilepsy surgery patients (n=15) and compared their expression profile with the tissues resected from non-epileptic autopsy cases (n=15). Statistically significant over expression of both P-gp (P<0.0001) and MRP-1 (P=0.01) at gene and protein levels were found in the MTLE cases. The fold change of P-gp was more pronounced than MRP-1. Immunohistochemistry of the patient group showed increased immunoreactivity of P-gp at blood-brain barrier and increased reactivity of MRP-1 in the parenchyma. The results were confirmed by confocal immunofluorescence microscopy. Our results suggested that P-gp in association with MRP-1 might be responsible for the multi-drug resistance in epilepsy. P-gp and MRP-1 could be important determinants of bio availability and tissue distribution of anti-epileptic drugs in the brain which can pharmacologically inhibited to achieve optimal drug penetration to target site.

Low-dose digoxin enhances the anticonvulsive potential of carbamazepine and lamotrigine in chemo-induced seizures with different neurochemical mechanisms

"Non-antiepileptic" drugs have a strong potential as adjuvants in multidrug-resistant epilepsy treatment. In previous study the influence of low doses of digoxin, which do not affect the myocardium, on the anticonvulsant potential of classical commonly used anti-epileptic drugs under conditions of seizures, induced by pentylenetetrazole and maximal electroshock, has been investigated.&#x0D; The aim of the study was to investigate the influence of digoxin at a sub-cardiotonic dose on the anticonvulsant potential of carbamazepine and lamotrigine in experimental seizures with different neurochemical mechanisms.&#x0D; Material and methods: A total of 192 random-bred male albino mice weighting 22–25 g were used. Carbamazepine and lamotrigine were administered intragastrically in conditionally effective (ED50) and sub-effective (½ ED50) doses: carbamazepine at doses of 100 and 50 mg/kg; lamotrigine at doses of 25 and 12.5 mg/kg. Digoxin was administered subcutaneously at a sub-cardiotonic dose of 0.8 mg/kg as an adjuvant to carbamazepine and lamotrigine in ½ ED50. Picrotoxin (2.5 mg/kg subcutaneously); thiosemicarbazide (25 mg/kg intraperitoneally); strychnine (1.2 mg/kg subcutaneously); camphor (1000 mg/kg intraperitoneally) were used as convulsant agents.&#x0D; Results: It was found that digoxin not only has its own permanent anticonvulsant effect on different models of paroxysms with different neurochemical mechanisms of development, but also significantly enhances the anticonvulsant potential of carbamazepine (to a lesser extent – lamotrigine) regardless of the pathogenesis of experimental paroxysms.&#x0D; Conclusion: Based on the results, it can be concluded that digoxin has a high potential as an adjuvant medicine in complex epilepsy treatment because it enhances the efficiency of low-dose traditional anticonvulsants carbamazepine and lamotrigine

The association between MDR1 C3435T genetic polymorphism and the risk of multidrug-resistant epilepsy in Egyptian children

BackgroundEpilepsy is a chronic disease affecting about 2% of the population and is considered a serious neurological disease. Despite its good prognosis, 20–30% of epileptic patients were not cured of their seizures even with the many trials of antiepileptic drug (AED) therapy. The resistance mechanism is still unclear, maybe due to the effect of the genetic factors on the bioavailability of the drugs. Consequently, the association between therapy resistance and the presence of a gene called “multidrug resistance 1 (MDR1)” had been proposed. Thus, the present study aimed to understand the relationship between the genetic polymorphism of MDR1C3435T and the resistance to AEDs.ResultA non-significant association was found between MDR1 C3435T single-nucleotide polymorphism (SNP) and drug-resistant epilepsy. However, there was statistical significance in the association between the drug type and the genotype distribution, in cases that were maintained on sodium valproate and MDR1C3435T genotype.ConclusionPossible involvement of the MDR1 gene C 3435T polymorphism with sodium valproate resistance clarifies the importance of genetic variability in response to the drug and may help to find novel genetic therapy for epilepsy, by targeting the biological mechanisms responsible for epilepsy in each specific individual. Future studies with bigger sample sizes and in other racial populations will be necessary.

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.

Therapeutic difficulties in recurrent, multidrug-resistant epilepsy and vagal nerve stimulation, with recent traumatic brain complications needing iterative neurosurgical interventions

Introduction: Focal epilepsy (possible with secondary generalization) may be a secondary complication to any brain damage (traumatic, vascular, infectious), and is characterized by abnormal excessive neuronal activity with motor, cognitive and psychosocial manifestations. About one third of the patients who suffer from epilepsy have a refractory, multidrug clinical form. Falls are one of the most common medical complications in neurologic patients, occurring during paroxysmal epileptic attacks, or due to sequelary gait limitations. Physical injuries are common, and about 47% patients with epilepsy report at least one injury in the past 12 months. Case presentation: We present a 36-years-old male patient with a medical history of right frontal congenital arteriovenous malformation, ruptured and operated at the age of eight, complicated with left spastic hemiplegia and refractory epilepsy, needing three antiepileptic drugs (AED) and vagus nerve-stimulation (VNS).This presentation was approved by THEBA Bioethics Committee (No.17464/14.06.2019). During a recent epileptic seizure he suffered a severe traumatic brain injury with coma (GCS 5), needing iterative neurosurgical interventions, intensive care supervision, and orotracheal intubation. CT cerebral scan revealed right hemispheric subdural hematoma, operated (on the 2nd May 2019). Rebleeding occurred seven days later, due to an extradural hematoma, and neurosurgical intervention was performed again. The patient was transferred in our neurorehabilitation clinic with left spastic hemiplegia (global motor score was 65/100, and functional independence measure (FIM) 24/91. Neuropsychological assessment revealed an obtunded level of consciousness, depression and dysmnesia for recent events, MMSE 9/30. During hospitalization the patient has continued his previous daily AED treatment with: levetiracetamum 2000 mg + clonazepamum 1mg + carbamazepinum retard 600 mg, associated with VNS. During hospitalization emerged three new short jacksonian seizures, who gave up spontaneously. The overall evolution was favorable with rehabilitation program and psychological support, with improvement of the global motor score, FIM (44/91), and partial restoration of walking ability, but still needing human help. Discussion: The pathophysiological mechanism of relapsed seizures has complex, multiple causes: imbalance of the local brain metabolism and /or a dysfunctional VNS procedure (a possible technical issue due to an impaired electronic device or a bioelectrical one, due to local fibrosis and increased impedance at the contact level between the electrode and the vagal nerve). Specialized technical control disclosed normal electric parameters provided by the electronic device. Other neuromodulatory devices and related technologies, such as deep brain stimulation (DBS) immediately demonstrate their effect control (motor correction) of Parkinson's or dystonic movements. Unfortunately VNS has not the possibility of immediate clinical feed-back control. The AED schedule was modified, by increasing clonazepamum to 2 mg daily. Video-EEG monitoring was recommended. The quod ad vitam prognosis might be unfavorable, because seizures can relapse anytime and evolution is uncontrolled. Furthermore, new brain injures may exacerbate the severity of the epilepsy, any new seizure may worsen the neurologic evolution. The quod ad functionem rehabilitation outcome might be precarious. The family support is essential in the therapeutic efforts. This clinical case underlines the necessity to implement a fall prevention program in patients with epilepsy, the importance of therapeutically tailoring AED for different pathophysiological stages of the disease, and emphasizes the limits of the modern techniques for seizures control. A multi-/ interdisciplinary team management of a such complex clinical case is mandatory. Key words: cerebral arteriovenous malformation, multidrug-resistant (refractory) epilepsy, vagal nerve electrostimulation (VNS), falls, traumatic brain injury,

Autologous bone marrow derived mononuclear cells for the treatment of drug resistant epilepsy

Epilepsy is a neurological disorder characterized by two or more unprovoked seizures with abnormal brain activity, Cognitive and behavioral changes usually accompanies epilepsy, like hallucinations delusions and apathy. Of all cases of epilepsy 30% are resistant to conventional treatment. Drug resistant epilepsy is defined as recurrent seizures refractory to a regimen of two or more antiepileptic drugs. Stem cell therapy is a possible alternative with minimal side effects; it is currently used for treatment of variety of diseases including neurological disorders like multiple sclerosis and stroke. In this clinical study, 20 Iraqi patients included, aged 2-39 year. 8 females and 12 male with multidrug resistant epilepsy, at least after 3 months of diagnosis and treatment. The 20 patients were kept on drugs, more than 2 drugs 80%, 2 drugs 20%, all the patients underwent autologous bone marrow mononuclear cells infusion intravenously. Mononuclear cell counts ranges from 2-4 x10 8 per product with 97 % viability. Two sessions done in 8 weeks' time. Out of 20 patients 13 patients showed improvement (65%) in seizure activity in form of 50-100% reduction in 6 months after stem cell therapy, in addition there was improvement in appetite and sleep rhythm. Autologous bone marrow derived mononuclear cells systemic infusion is a safe clinical procedure with promising results in drug resistant epilepsy.

Correlation between ABCB1 gene polymorphisms, antiepileptic drug concentrations and treatment response

Abstract Aim: A possible molecular mechanism of clinically defined multidrug-resistant epilepsy involves drug efflux transporters such as P glycoprotein (P-gp), a member of the ATP-binding cassette subfamily B1 (ABCB1). We have investigated the prevalence of the C3435T, G 2677T/A, and T129C single-nucleotide polymorphisms in the promoter region of MDR1 gene, in Romanian epileptic patients. Methods: 70 epileptic patients evaluated in the Neurology Department of Cluj County Hospital were included in the study. The response to treatment was assessed by reviewing the seizure diaries and the patients were classified as responders or non-responders. Antiepileptic drug (AED) plasmatic concentrations were measured and the patients were divided into 2 groups: first group with AED concentrations in therapeutic range and the second one with sub-optimal AED concentrations. Genotyping the DNA samples, we investigated MDR1 gene polymorphism by polymerase chain reaction (PCR). Results were expressed as genotype and allele frequencies per response group and compared between subgroups. Results: 33 patients (47.14%) were classified as responders, while the remaining 37 patients (52.86%) were classified as non-responders. A comparison of responders and non-responders revealed no significant difference in genotype frequency for any of the three mutations studied. The CT heterozygote for ABCB1 T129C had significantly lower AED concentrations (p=0.041), with no significant difference for the other polymorphisms studied. Conclusions: In our study we found an association of CT variant in ABCB1 C129T with lower AED plasmatic concentrations and no association between ABCB1 variants and the drug responsiveness.

Genetic association analysis of ATP binding cassette protein family reveals a novel association of ABCB1 genetic variants with epilepsy risk, but not with drug-resistance.

Epilepsy constitutes a heterogeneous group of disorders that is characterized by recurrent unprovoked seizures due to widely different etiologies. Multidrug resistance remains a major issue in clinical epileptology, where one third of patients with epilepsy continue to have seizures. Role of efflux transporters in multidrug resistant epilepsy has been attributed to drug-resistant epilepsy although, with discrepant observation in genetic studies. These discrepancies could be attributed to variety of factors such as variable definition of the anti-epileptic drug (AED)-resistance, variable epilepsy phenotypes and ethnicities among the studies. In the present study we inquired the role of multidrug transporters ABCB1 and ABCG2 variants in determining AED-resistance and susceptibility to epilepsy in three well-characterized cohorts comprising of mesial temporal lobe epilepsy with hippocampal sclerosis (MTLE-HS) (prototype for AED-resistant epilepsy); juvenile myoclonic epilepsy (JME) (prototype for AED-responsive epilepsy); and healthy non-epileptic controls, in 738 subjects of Malayalam speaking south Indian ancestry. ABCB1 and ABCG2 variants were not found to be associated with drug resistance when AED-resistant and AED-responsive cohorts were compared. However, a significant association was observed between ABCB1 (C3435T) rs1045642 and risk of having epilepsy (MTLE-HS and JME pooled cohort; genotypic p-value = 0.0002; allelic p-value = 0.004). This association was seen persistent with MTLE-HS (genotypic p-value = 0.0008; allelic p-value = 0.004) and also with JME (genotypic p-value = 0.01; allelic p-value = 0.05) cohort individually. In-silico functional prediction indicated that ABCB1 rs1045642 has a deleterious impact on protein coding function and in splicing regulation. We conclude that the ABCB1 and ABCG2 variants do not confer to AED-resistance in the study population. However, ABCB1 rs1045642 increases vulnerability to epilepsy with greater tendency for MTLE-HS in south Indian ancestry from Kerala.

The drug-transporter gene MDR1 C3435T and G2677T/A polymorphisms and the risk of multidrug-resistant epilepsy in Turkish children

One-third of all individuals with epilepsy are resistant to antiepileptic drug (AED) treatment. Antiepileptic treatment response has been suggested to be modulated by genetic polymorphisms of drug efflux transporters. Several polymorphic variants within the multidrug resistance 1 (MDR1) gene, which encodes the major transmembrane efflux transporter P-glycoprotein, have been proposed to be associated with AED resistance in epilepsy patients. The aim of this study was to evaluate the effect of C3435T and G2677T/A polymorphisms of MDR1 on AED resistance in Turkish children with epilepsy. MDR1 C3435T and G2677T/A were genotyped in 152 patients with epilepsy, classified as drug-resistant in 69 and drug-responsive in 83. Genotypes of the C3435T and G2677T/A polymorphisms were determined by polymerase chain reaction followed by restriction fragment length polymorphism. Genotype and allele frequencies of C3435T and G2677T/A polymorphisms of the MDR1 gene did not differ between drug-resistant and drug-responsive epilepsy patients. Our results suggest that MDR1 C3435T and G2677T/A polymorphisms are not associated with AED resistance in Turkish epileptic patients. To clarify the exact clinical implication of the MDR1 polymorphisms on the multidrug resistance in epilepsy, further investigations in various ethnic populations would be necessary.

Gene-Wide Tagging Study of the Association Between ABCC2 , ABCC5 and ABCG2 Genetic Polymorphisms and Multidrug Resistance in Epilepsy

To determine the association between polymorphisms of the multidrug transporter genes ABCC2, ABCC5 and ABCG2, and drug resistance in epilepsy by genotyping comprehensive sets of tagging SNPs. A total of 25 tagging SNPs from ABCC2, ABCC5 and ABCG2 genes were genotyped in a total of 590 Han Chinese epilepsy patients (262 drug resistant and 328 drug responsive). Genotype and allele distributions in drug-responsive and drug-resistant patients were compared. Genotype distributions of all the selected SNPs were consistent with Hardy-Weinberg equilibrium. None of the polymorphisms, either genotype or allele distributions, were significantly associated with drug resistance. For each gene, no haplotypes of over 1% frequency, and that included all SNPs of the gene, were associated with drug resistance. This gene-wide tagging study revealed no association between ABCC2, ABCC5 and ABCG2 genetic polymorphisms and multidrug resistance in epilepsy.

Drug resistance in epilepsy and the ABCB1 gene: The clinical perspective

Multidrug resistance is one of the most serious problems in the treatment of epilepsy that is likely to have a complex genetic and acquired basis. Various experimental data support the hypothesis that over-expression of antiepileptic drug (AED) transporters may play a pivotal role in drug resistance. Hyyt 6however, key questions concerning their functionality remain unanswered. The idea that P-glycoprotein, encoded by the ABCB1 gene, might mediate at least part of the drug resistance was met with both enthusiasm and skepticism. As in oncology, initial optimism has been clouded subsequently by conflicting results. The first study reporting a positive association between genetic variation in the P-glycoprotein and multidrug-resistant epilepsy was published in 2003. Since then, several other genetic association studies have attempted to verify this result. However, taken overall, the role of P-glycoprotein in drug resistance in epilepsy still remains uncertain. We intend to critically review the inherent problems associated with epilepsy pharmacogenetic studies in general and with ABCB1 polymorphisms studies in particular. The lessons learnt from the ABCB1 studies can help us to guide future association genetics studies to investigate AED resistance, and thereby taking us closer to the cherished dream of personalized AED therapy.

Gene-Wide Tagging Study Of Association Between ABCB1 Polymorphisms and Multidrug Resistance in Epilepsy in Han Chinese

It remains controversial whether polymorphisms of the multidrug resistance gene ABCB1 are associated with pharmacoresistance in epilepsy. To further study the potential association, we genotyped a broad set of tagging SNPs, and explored whether any associations were affected by other host factors. We correlated any association with cerebral mRNA expression of ABCB1. A total of 12 tagging and candidate SNPs of ABCB1 were genotyped in 464 Chinese epilepsy patients (270 drug responsive, 194 drug resistant). Genotype and allele distributions in drug-responsive and drug-resistant patients were compared. ABCB1 mRNA was quantified by real-time PCR in brain samples resected from 20 patients with drug-resistant epilepsy. Its level was compared between patients with different genotypes of ABCB1 SNPs found to be associated with drug resistance. The intronic polymorphism rs3789243 (p = 0.009 for allele analysis) and the coding polymorphism 2677G/T/A (p = 0.02), and haplotypes containing them, were associated with drug resistance. The 2677G/T/A genotypes remained significantly associated with drug resistance after multiple logistic regression and correction for multiple comparisons. The associations with drug resistance were found in males (p = 0.004 for rs3789243 and p = 0.0007 for 2677T/A>G) but not females, and in patients with localization-related (p = 0.006 for rs3789243 and p = 0.01 for 2677T/A>G) but not idiopathic-generalized epilepsy. ABCB1 mRNA levels did not correlate with genotypes. In Chinese epilepsy patients, the ABCB1 intronic polymorphism rs3789243 and the coding polymorphism 2677, and haplotypes containing them, may be associated with drug resistance, without an effect on mRNA expression. There was preliminary evidence of interactions between these polymorphisms and gender and epilepsy syndrome.

MDR1/ABCB1 Polymorphisms and Multidrug Resistance In Epilepsy: in and out of Fashion

been satisfied for the transporter hypothesis, however, only in rodent models of epilepsy as yet [7]. Accordingly, P-gp expression is: increased in epileptogenic brain tissue of rodents; associated with lower brain levels of AEDs; higher in AED-resistant rats than in responsive animals; and most importantly, co-administration of the highly selective P-gp inhibitor, tariquidar, reverses AED resistance. Thus, it is reasonable to conclude that P-gp plays a significant role in mediating resistance to AEDs in rodent models of temporal lobe epilepsy and that inhibition of P-gp can circumvent this mechanism – however, whether this phenomenon extends to at least some human refractory epilepsy remains unclear [7]. Increased brain expression of efflux transporters, such as P-gp, could be a result either of prolonged or frequent seizures, as demonstrated in rodent models of epilepsy, or of genetic factors, such as polymorphisms in the ABCB1 gene or, theoretically, of both [2]. Siddiqui et al. were the first to report that a SNP in the ABCB1 gene is associated with resistance to multiple AEDs, leading to the suggestion that drug resistance in epilepsy might be genetically determined [8]. In this study, patients with AED-resistant epilepsy were more likely to have the CC genotype at the ABCB1 C3435T polymorphism, which is associated with increased expression of the protein, than the TT genotype [8]. Since then, different studies of various designs have tried to confirm the association between the 3435C>T polymorphism and AED resistance in epilepsy, but most of these subsequent studies were negative [9]. A recent meta-ana lysis of 11 case–control studies involving 3371 patients (1646 patients with drug-resistant epilepsy and 1725 controls) did not identify a significant association between AED resistance and ABCB1 polymorphisms, including the 3435 SNP [10]. However, in most of these pharmacogenetic studies, patients were treated with various AEDs, ignoring the fact that not all AEDs are substrates Resistance to multiple anti-epileptic drugs (AEDs) is a significant problem in epilepsy affecting at least 30% of patients with this common and often devastating disease [1]. One prominent hypothesis to explain this multidrug resistance suggests an inadequate penetration or excess efflux of AEDs across the blood–brain barrier (BBB) as a result of overexpressed efflux transporters, such as P-glycoprotein (P-gp), the encoded product of the multidrug resistance-1 (MDR1, ABCB1) gene [2]. Drug efflux transporters such as P-gp have a major impact on the pharmacological behavior of most clinically used drugs, critically affecting drug absorption, disposition and elimination in the body [3]. The idea that enhanced BBB expression of P-gp could be involved in AED resistance was first proposed by Tishler et al. in 1995, who reported that P-gp and ABCB1 are markedly increased in brain tissue of pa tients with medically intractable partial epilepsy [4]. This finding was subsequently confirmed by several other groups and formed the basis of the transporter hypothesis of intractable epilepsy [5].

Multidrug resistance in epilepsy and polymorphisms in the voltage-gated sodium channel genes SCN1A, SCN2A, and SCN3A: correlation among phenotype, genotype, and mRNA expression

Many antiepileptic drugs (AEDs) prevent seizures by blocking voltage-gated brain sodium channels. However, treatment is ineffective in 30% of epilepsy patients, which might, at least in part, result from polymorphisms of the sodium channel genes. We investigated the association of AED responsiveness with genetic polymorphisms and correlated any association with mRNA expression of the neuronal sodium channels. We performed genotyping of tagging and candidate single nucleotide polymorphisms (SNPs) of SCN1A, 2A, and 3A in 471 Chinese epilepsy patients (272 drug responsive and 199 drug resistant). A total of 27 SNPs were selected based on the HapMap database. Genotype distributions in drug-responsive and drug-resistant patients were compared. SCN2A mRNA was quantified by real-time PCR in 24 brain and 57 blood samples. Its level was compared between patients with different genotypes of an SCN2A SNP found to be associated with drug responsiveness. SCN2A IVS7-32A>G (rs2304016) A alleles were associated with drug resistance (odds ratio = 2.1, 95% confidence interval: 1.2-3.7, P=0.007). Haplotypes containing the IVS7-32A>G allele A were also associated with drug resistance. IVS7-32A>G is located within the putative splicing branch site for splicing exons 7 and 9. PCR of reverse-transcribed RNA from blood or brain of patients with different IVS7-32A>G genotypes using primers in exons 7 and 9 showed no skipping of exon 8, and real-time PCR showed no difference in SCN2A mRNA levels among genotypes. Results of this study suggest an association between SCN2A IVS7-32A>G and AED responsiveness, without evidence of an effect on splicing or mRNA expression.

Longstanding epileptic encephalopathy and linear localized scleroderma: two distinct pathologic processes in an adolescent

We report a 7-year-old boy who unexpectedly developed a multi-drug resistant epilepsy with negative neuroimaging results, followed by the insidious appearance of linear localized scleroderma involving the right leg. When the boy was 16 and severely affected by epileptic encephalopathy, we have evaluated this case for the first time: his localized scleroderma had reached the right buttock and positive anti-nuclear antibody was the only positive laboratory test. Methotrexate administered for 12 months was ineffective in improving both the organization of his electroencephalographic pattern and seizure control, though seemed to stabilize the progression of linear scleroderma. This report suggests that neurological abnormality and extracranial scleroderma might represent two own distinct processes in a same patient.

Multidrug resistance in epilepsy: a pharmacogenomic update

Multidrug resistance is one of the most serious problems in the treatment of epilepsy and is likely to have a complex genetic and environmental basis. Various experimental data support the hypothesis that overexpression of antiepileptic drug transporters may be important. However, key questions concerning their functionality remain unanswered. The first study reporting a positive association – between genetic variation in a putative antiepileptic drug transporter (P-glycoprotein, encoded by ABCB1) and multidrug resistant epilepsy was published in 2003. Since then, several other association genetics studies have sought to confirm this result, but, taken overall, do not support a major role for this polymorphism. Lessons learnt from the ABCB1 studies can help guide future association genetics studies, both for multidrug resistance in epilepsy, and for other epilepsy phenotypes.

Expression and cellular distribution of multidrug resistance-related proteins in patients with focal cortical dysplasia

Recent arouse of interest indicated that drug resistant proteins are markedly over-expressed in the epileptogenic tissue and they may be responsible for the one-third of the epileptic patients who were refractory to anti-epileptic drugs (AEDs). Since several AEDs may act as substrates for these drug resistant proteins, the enhanced function of such proteins may increase drug extrusion, resulting in inadequate response to drug therapy in patients with epilepsy. We studied expression of the multidrug resistance protein 1 (MDR1) and multidrug resistance-associated protein 1 (MRP1) in the epileptic tissues resected surgically in 28 patients with focal cortical dysplasia (FCD) by immunohistochemistry. The results were compared with 10 normal necropsy brain tissues. Normal brain showed no MDR1 expression in neurons and astrocytes, while MRP1 expression was very weak, which were encountered in a few samples. MDR1 expression was mainly localized on the vascular endothelial cells. In contrast to normal brain, we found intense MDR1 and MRP1 expression in both neurons and reactive astrocytes in the vast majority of dysplastic tissues. The majority of the dysplastic neurons demonstrated moderate to strong MRP1 immunoreactivity. Endothelial cells showed both MDR1 and MRP1 expression in the majority of the specimens studied. Multidrug transporters are over-expressed in the epileptogenic zone in patients with FCD. These results are concordant with previous studies, in which over-expression of multidrug proteins were shown in epileptogenic brain tissue in patients with FCD, that the over-expression of drug transport proteins in tissue from patients with refractory epilepsy may explain one possible mechanism for drug resistant in these pathologies.

Common ABCB1 polymorphisms are not associated with multidrug resistance in epilepsy using a gene-wide tagging approach

P-glycoprotein, the product of the ABCB1 gene, is a proposed mechanism of pharmacoresistance in epilepsy. Previous attempts to correlate the ABCB1 C3435T SNP, or a three-SNP haplotype containing C3435T with epilepsy pharmacoresistance have produced discordant findings. We analysed these single nucleotide polymorphisms (SNPs), plus a more comprehensive set of tagging SNPs describing common variation in ABCB1 in a case-control study. No significant association of C3435T (P=0.55), the three-SNP haplotype (lowest P=0.14) or any gene-wide tagging SNP (lowest P=0.17) with multidrug resistance in epilepsy was identified. Meta-analysis of studies using the same definition of multidrug resistance (n=1064) also demonstrated no significant association of C3435T with multidrug resistance (P=0.31). These findings suggest that C3435T is unlikely to be a marker for epilepsy multidrug resistance. In addition, no evidence for a role of other common ABCB1 polymorphisms was found using a potentially more powerful gene-wide tagging approach.

The multidrug transporter hypothesis of drug resistance in epilepsy: Proof-of-principle in a rat model of temporal lobe epilepsy

Resistance to drug treatment is an important hurdle in the therapy of many diseases, including cancer, infectious diseases and brain disorders such as epilepsy. A phenotype that is referred to as multidrug resistance was first described for chemotherapy-resistant cancer cells that overexpressed the drug efflux transporter P-glycoprotein (P-gp). More recently, overexpression of P-gp has been found in capillary endothelial cells of epileptogenic brain tissue from patients with medically intractable epilepsy. Such regionally restricted P-gp overexpression in the blood-brain barrier is likely to reduce the concentration of antiepileptic drugs at epileptic neurons, which would be a plausible explanation for multidrug resistance in epilepsy. However, a definite proof-of-principle for this hypothesis is lacking. In the present study, we used a rat model of temporal lobe epilepsy that allows selecting drug-resistant and drug-responsive subgroups of epileptic rats by prolonged treatment with the antiepileptic drug phenobarbital at maximum tolerated doses. We have shown recently that drug-resistant rats selected from this model exhibit a marked overexpression of P-gp in the hippocampus and other limbic brain regions. This model is thus ideally suited to prove the multidrug transporter hypothesis of drug resistance. For this purpose, we selected a group of phenobarbital-resistant rats, which was subsequently treated by combinations of phenobarbital with the selective P-gp inhibitor tariquidar. Coadministration of tariquidar (15-20 mg/kg) fully restored the anticonvulsant activity of phenobarbital without altering plasma pharmacokinetics or neurotoxicity of the antiepileptic drug. These data demonstrate that inhibiting P-gp in epileptic rats with proven drug resistance counteracts resistance, providing the first proof-of-principle of the multidrug transporter hypothesis of medically refractory epilepsy.

Clinical factors and ABCB1 polymorphisms in prediction of antiepileptic drug response: a prospective cohort study

The ABCB1 3435C-->T single-nucleotide polymorphism (SNP) or a three-SNP haplotype containing 3435C-->T has been implicated in multidrug resistance in epilepsy in three retrospective case-control studies, but a further three have failed to replicate the association. We aimed to determine the effect of the ABCB1 gene on epilepsy drug response, using a unique large cohort of epilepsy patients with prospectively measured seizure and drug response outcomes. The ABCB1 3435C-->T polymorphism and three-SNP haplotype, plus a comprehensive set of tag SNPs across ABCB1 and adjacent ABCB4, were genotyped in a cohort of 503 epilepsy patients with prospectively measured seizure and drug response outcomes. Clinical, demographic, and genetic data were analysed. Treatment outcome was measured in terms of time to 12-month remission, time to first seizure, and time to drug withdrawal due to inadequate seizure control or side-effects. Randomly selected genome-wide HapMap SNPs (n=129) were genotyped in all patients for genomic control. Number of seizures before treatment was the dominant feature predicting seizure outcome after starting antiepileptic drug therapy, measured by both time to first seizure (hazard ratio 1.34, 95% CI 1.21-1.49, p<0.0001) and time to 12-month remission (0.83, 0.73-0.94, p=0.003). There was no association of the ABCB1 3435C-->T polymorphism, the three-SNP haplotype, or any gene-wide tag SNP with time to first seizure after starting drug therapy, time to 12-month remission, or time to drug withdrawal due to unacceptable side-effects or to lack of seizure control. We found no evidence that ABCB1 common variation influences either seizure or drug withdrawal outcomes after initiation of antiepileptic drug therapy.