MDR1/ABCB1 polymorphisms and multidrug resistance in epilepsy: in and out of fashion

Polymorphism in drug transporter gene ABCB1 is associated with drug resistance in Pakistani epilepsy patients

Despite the best possible medication and treatment protocols, one-third of epilepsy patients have drug resistance which is associated with an elevated risk of mortality and debilitating psychological consequences. P-glycogen encoded by ABCB1 is major drug transporter for a wide variety of AED. To evaluate the complex haplotypic association, genetic and allelic frequency distribution of rs1128503, rs1045642, and rs2032582 polymorphisms of ABCB1 gene with drug resistance in Pakistani pediatric epilepsy patients, we performed this study. A total of 337 individuals including 100 healthy control, 110 drug-resistant patients, and 127 drug-responsive patients were enrolled and genotyped for three polymorphisms. PCR and direct sequencing of DNA were done for genotyping. All the studied SNPs showed a statistically significant association with drug-resistant epilepsy at p < 0.01. In addition, we identified a novel variant at c 0.2678C > A (SCV001712095) position. The haplotype analysis indicated strong linkage disequilibrium between three SNPs. The in-silico analysis indicated that rs2032582 polymorphism at c 0.2677T > A is benign while c 0.2677T > G and c 0.2678C > A are possibly damaging. Our findings showed that pharmacogenetic variants play a key role in disease. Our findings shed light on the pharmacogenomic association of ABCB1 with epilepsy which might facilitate study on pharmacokinetics concerning ethnology.

Association between ABCB1 polymorphisms and response to antiepileptic drugs among Jordanian epileptic patients

BACKGROUND

Genetic polymorphisms of drug efflux transporters as ATP-binding cassette subfamily B, member 1 (ABCB1) have been suggested to modulate antiepileptic drugs (AEDs) response. We aimed to explore the association of ABCB1 polymorphisms and AEDs resistance among epileptic patients.

METHODS

A total of 86 Jordanian epileptic patients treated with AEDs was included in the study. DNA was extracted from blood samples and genotyping and haplotypes analyses were conducted for Nine single nucleotide polymorphisms (SNPs) on the ABCB1 gene.

RESULTS

Data revealed that none of the examined SNPs were associated with resistance to AEDs neither on the level of alleles nor genotypes. However, strong association was found between rs2235048 (OR = 10.6; 95%CI = [1.89-59.8], p= 0.01), rs1045642 (OR = 14; 95%CI = [1.3-156.7], p= 0.02), rs2032582 (OR = 9.1; 95%CI = [1.4-57.3], p= 0.04) and rs1128503 (OR = 18.7; 95%CI = [1.6-222.9], p= 0.02), ABCB1 polymorphisms and resistance to AEDs among females but not males. Haplotype analysis revealed statistically significant associations. The strongest significant associations were for haplotypes containing 2677G_1236 T in two-SNPshaplotypes (OR = 4.2; 95%CI = [1.2-14.9], p = 0.024); three-SNPs-haplotypes (OR = 4.2; 95% CI = [1.2-14.9], p = 0.02); four-SNPs-haplotypes (OR = 4.1; 95%CI = [1.2-14.3], p = 0.026).

CONCLUSION

Data suggests that there is a gender dependent association between ABCB1 genetic polymorphisms and response to AEDs. Additionally, ABCB1 haplotypes influence the response to AEDs. Further investigation is needed to confirm the results of this study.

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

Background

Epilepsy 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.

Result

A 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.

Conclusion

Possible 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.

Association of ABCB1 gene polymorphism (C1236T and C3435T) with refractory epilepsy in Iraqi patients

The mechanisms of refractory epilepsy (RE) are most likely multifactorial, involving environmental, genetic, as well as disease- and drug-related factors. We aimed to study is to investigate the possible association of two ABCB1 gene polymorphism (C3435T and C1236T) with the development of RE in Iraqi patients. One hundred patients with either generalized tonic-clonic seizures, myoclonic epilepsy, or absence epilepsy comprised of 60 patients responsive to AEDs and 40 patients who were refractory to treatment who used multi AEDs for at least one month were studied. Fifty family-unrelated age- and sex-matched healthy subjects represent the control group. ABCB1 gene fragments corresponding to two targeted polymorphisms were amplified with conventional polymerase chain reaction using specific sets of primers. Genotyping was performed by restriction fragment length polymorphism (RFLP) technique. Epileptic patients refractory to AEDs showed a significantly higher frequency of CC genotypes of C3435T polymorphism than controls. Allele C was significantly higher in patients than controls and far more frequent among patients with RE. C1235T polymorphism had no significant role neither in the incidence of epilepsy nor in the AEDs resistance. The CT haplotype was more frequent among patients refractory to AEDs. In contrast, the haplotype block TT was more frequent among responsive (41.3%) than refractory patients (28.7%) (p = 0.068). The CC genotype and C allele of the C3435T polymorphism can increase the risk of RE. The haplotype block CT of C3435T and C1236T can predispose for epilepsy as well as the drug resistance.

ABCB1 Polymorphisms and Drug-Resistant Epilepsy in a Tunisian Population

Background

Epilepsy is one of the most common neurological disorders with about 30% treatment failure rate. An interindividual variations in efficacy of antiepileptic drugs (AEDs) make the treatment of epilepsy challenging, which can be attributed to genetic factors such as ATP-Binding Cassette sub-family B, member1 (ABCB1) gene polymorphisms.

Objective

The main objective of the present study is to evaluate the association of ABCB1 C1236T, G2677T, and C3435T polymorphisms with treatment response among Tunisian epileptic patients.

Materials and Methods

One hundred epileptic patients, originated from north of Tunisia, were recruited and categorized into 50 drug-resistant and 50 drug-responsive patients treated with antiepileptic drugs (AEDs) as per the International League Against Epilepsy. DNA of patients was extracted and ABCB1 gene polymorphisms studied using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method.

Results

The C1236T, G2677T, and C3435T polymorphisms were involved into AED resistance. Significant genotypic (C1236T TT (p ≤ 0.001); G2677T TT (p = 0.001); C3435T TT (p ≤ 0.001)) and allelic associations (C1236T T (3.650, p ≤ 0.001); G2677TT (1.801, p = 0.044); C3435T T (4.730, p ≤ 0.001)) with drug resistance epilepsy (DRE) were observed. A significant level of linkage disequilibrium (LD) was also noted between ABCB1 polymorphisms. Patients with the haplotypes CT and TT (C1236T-G2677T); GT, TC, and TT (G2677T-C3435T); CT and TT (C1236T-C3435T); CTT, TTC, TGT, and TTT (C1236T-G2677T-C3435T) were also significantly associated to AED resistance.

Conclusions

The response to antiepileptics seems to be modulated by TT genotypes, T alleles, and the predicted haplotypes for the tested SNPs in our population. Genetic analysis is a valuable tool for predicting treatment response and thus will contribute to personalized medicine for Tunisian epileptic patients.

The potential implication of SCN1A and CYP3A5 genetic variants on antiepileptic drug resistance among Egyptian epileptic children

PURPOSE

Despite the advances in the pharmacological treatment of epilepsy, pharmacoresistance still remains challenging. Understanding of the pharmacogenetic causes is critical to predict drug response hence providing a basis for personalized medications. Genetic alteration in activity of drug target and drug metabolizing proteins could explain the development of pharmacoresistant epilepsy. So the aim of this study was to explore whether SCN1A c.3184 A/G (rs2298771) and CYP3A5*3 (rs776746) polymorphisms could serve as genetic based biomarkers to predict pharmacoresistance among Egyptian epileptic children.

METHODS

Genotyping of SCN1A c.3184 A/G and CYP3A5*3 polymorphisms using the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method was performed in 65 healthy control subjects and 130 patients with epilepsy, of whom 50 were drug resistant and 80 were drug responsive.

RESULTS

There was a significant higher frequency of the AG genotype (p=0.001) and G allele (p=0.006) of SCN1A polymorphism in epileptic patients than in controls. Also their frequency was significantly higher in drug resistant patients in comparison with drug responders (p=0.005 and 0.054 respectively). No significant association between CYP3A5*3 polymorphism and drug-resistance was found.

CONCLUSIONS

Overall, results confirmed the claimed role of SCN1A c.3184 A/G polymorphism in epilepsy and moreover in development of pharmacoresistance among Egyptian epileptic children. CYP3A5*3 variants have no contributing effect on pharmacoresistance among Egyptian epileptic children.

Polymorphism of ABCB1/MDR1 C3435T in children and adolescents with partial epilepsy is due to different criteria for drug resistance - preliminary results

Background

The diagnosis of “drug resistance” in epilepsy can be defined and interpreted in various ways. This may be due to discrepant definitions of drug resistance to pharmacotherapy.

The aim of our study was to investigate the relationship between C3435T polymorphism of the MDR1 gene and drug resistance in epilepsy with the consideration of 4 different criteria for qualification to groups sensitive and resistant to applied pharmacotherapy.

Material/Methods

Evaluation of C3435T polymorphism of MDR1/ABCB1 gene was conducted on a group of 82 white children and young adolescents up to 18 years old. While qualifying the patients to the group of sensitive or drug resistant, the following 4 definitions of drug resistance were applied: the ILAE’s, Appleton’s, Siddiqui’s, and Berg’s.

Results

A detailed analysis of genotypes of the MDR1 gene did not show any significant discrepancies between the groups of patients resistant and sensitive to antiepileptic drugs (AEDs) in 4 consecutive comparisons taking into consideration various criteria of sensitivity and resistance to pharmacotherapy.

Conclusions

The obtained results clearly confirm the lack of a connection between the occurrence of drug-resistant epilepsy and C435T polymorphism of the MDR1 gene irrespective of the definition of drug resistance applied to the patient.

The search for circulating epilepsy biomarkers

Few would experience greater benefit from the development of biomarkers than those who suffer from epilepsy. Both the timing of individual seizures and the overall course of the disease are highly unpredictable, and the associated morbidity is considerable. Thus, there is an urgent need to develop biomarkers that can predict the progression of epilepsy and treatment response. Doing so may also shed light on the mechanisms of epileptogenesis and pharmacoresistance, which remain elusive despite decades of study. However, recent advances suggest the possible identification of circulating epilepsy biomarkers – accessible in blood, cerebrospinal fluid or urine. In this review, we focus on advances in several areas: neuroimmunology and inflammation; neurological viral infection; exemplary pediatric syndromes; and the genetics of pharmacoresistance, as relevant to epilepsy. These are fertile areas of study with great potential to yield accessible epilepsy biomarkers.

Significance of MDR1 gene polymorphism C3435T in predicting drug response in epilepsy

Antiepileptic drug (AED) treatment in epilepsy is often compromised by the unpredictability of efficacy and inter-individual variability among patients, which at least in part is the result of genetic variation. The idea to determine an individual's response to a prescribed medicine came into inception around 29 years ago. Pharmacogenetics is used to predict the drug response and efficacy, as well as potential adverse effects. We investigated the functional significance of the C3435T polymorphism of the MDR1 gene in a South Indian population. The patients were divided into responders and non-responders based on their clinical outcome and AED response. The risk of drug resistance was significantly higher in patients bearing TT genotype in comparison to carriers of the homozygous CC genotype [TT vs. CC, χ(2)=12.52; p=0.001, Odds ratio=2.34 (95% CI: 1.942-11.32)]. We suggest that the influence of the C3435T polymorphism in predicting the drug-resistance in epilepsy, might be significant and further investigations focusing on carbamazepine and phenytoin, in various ethnic populations are necessary to clarify the effect of C3435T polymorphism on the multidrug resistance in epilepsy patients.

CYP3A5*3 and C3435T MDR1 polymorphisms in prognostication of drug-resistant epilepsy in children and adolescents

Drug-resistant epilepsies still remain one of the most profound problems of contemporary epileptology. Several mechanisms of drug resistance are possible; among them, genetic factors have a prominent place. Much importance is attached to genes, which encode enzymes that metabolize antiepileptic drugs CYP 3A, which belong to the family of cytochromes P450 and the genome of multidrug resistance, such as multidrug resistance 1 (MDR1) that expresses P-glycoprotein (P-gp), a drug transporter protein. The aim of the study was to assess the relation between polymorphism of gene CYP3A5 and polymorphism C3435T of MDR1 gene with the occurrence of focal, drug-resistant epilepsy in children and youths up to 18 years of age. The study comprised 85 patients, and their age range was from 33 months to 18 years of age, suffering from epilepsy, partly responding well to treatment, partly drug resistant. The polymorphism of both genes has been analysed using the PCR-RFLP method. The study failed to corroborate association between polymorphism CYP3A5∗3 and C3435T polymorphism in MDR1 gene and pharmacoresistant epilepsy. The results of our research do not confirm the prognostic value of the polymorphisms examined in the prognostication of drug resistance in epilepsies.

Several new diverse anticonvulsant agents discovered in a virtual screening campaign aimed at novel antiepileptic drugs to treat refractory epilepsy

A virtual screening campaign was conducted in order to discover new anticonvulsant drug candidates for the treatment of refractory epilepsy. To this purpose, a topological discriminant function to identify antiMES drugs and a sequential filtering methodology to discriminate P-glycoprotein substrates and nonsubstrates were jointly applied to ZINC 5 and DrugBank databases. The virtual filters combine an ensemble of 2D classifiers and docking simulations. In the light of the results, 10 structurally diverse compounds were acquired and tested in animal models of seizure and the rotorod test. All 10 candidates showed some level of protection against MES test.

The pharmacogenomics of mood stabilizer response in bipolar disorder

Bipolar Disorder (BD) is a common psychiatric illness that has a recurring course and 17% - 24% lifetime prevalence of suicide attempts. Difficulty in diagnosis and individual variation in response point to a great need for personalized medicine. Studies to date have focused largely on lithium and suggest the idea that different medication responses may reflect different disease mechanisms. An overview of current pharmacogenomic studies will be presented and needs and future directions discussed.