Lack of association between ABCB1 gene polymorphisms and pharmacoresistant epilepsy: an analysis in a western Chinese pediatric population

Molecular Insights of Drug Resistance in Epilepsy: Multi-omics Unveil

Epilepsy is a devastating neurological disorder mainly associated with impaired synchronic discharge that leads to sensory, motor, and psychomotor impairments. Till now, about 30 anti-seizure medications (ASMs) have been approved for the management of epilepsy, yet one-third of individuals still have uncontrollable epilepsy and develop resistance. Drug resistance epilepsy (DRE) is defined as the condition where two ASMs fail to control the seizure in epileptic patients. The leading cause of the resistance was the extended use of ASMs. According to various studies, alterations in some genes and their expressions, along with specific metabolic impairments, are suggested to be associated with ASMs resistance and DRE pathophysiology. Several factors aid in the pathophysiology of DRE, such as alterations in protein-encoding genes such as neurotransmitter receptors, drug transporters, ion channels, and drug targets. Furthermore, the altered metabolite levels of metabolites implicated in neurotransmitter signaling, energetic pathways, oxidative stress, and neuroinflammatory signaling differentiate the epileptic patient from the DRE patient. Various DRE biomarkers can be identified using the "integrated omics approach," which includes the study of genomics, transcriptomics, and metabolomics. The current review has been compiled to understand the pathophysiological mechanisms of DRE by focusing on genomics, transcriptomics, and metabolomics. An effort has also been made to identify the therapeutic targets based on identifying significant markers by a multi-omics approach. This has the potential to develop novel therapeutic interventions in the future.

Association of ABCB1 Polymorphisms with Efficacy and Adverse Drug Reactions of Valproic Acid in Children with Epilepsy

Genetic polymorphisms in ATP-binding cassette subfamily B member 1 (ABCB1, also known as MDR1) have been reported to be possibly associated with the regulation of response to antiseizure medications. The aim of this study was to investigate the association of ABCB1 polymorphisms with the efficacy of and adverse drug reactions to valproic acid among Chinese children with epilepsy. A total of 170 children from southern China with epilepsy treated with valproic acid for more than one year were recruited, including 61 patients with persistent seizures and 109 patients who were seizure-free. Two single nucleotide polymorphisms of ABCB1, rs1128503 and rs3789243, were genotyped using the Sequenom MassArray system. The two single nucleotide polymorphisms of ABCB1 were found to be significantly associated with treatment outcomes of valproic acid in children with epilepsy. Carriers with the TT genotype of ABCB1 rs1128503 were more inclined to exhibit persistent seizures after treatment with valproic acid (p = 0.013). The CC genotype of rs3789243 was observed to be a potential protective factor for valproic acid-induced gastrointestinal adverse drug reactions (p = 0.018), but possibly increased the risk of valproic acid-induced cutaneous adverse drug reactions (p = 0.011). In contrast, the CT genotype of rs3789243 was associated with a lower risk of valproic acid-induced cutaneous adverse drug reactions (p = 0.011). Haplotype analysis showed that CC haplotype carriers tended to respond better to valproic acid treatment (p = 0.009). Additionally, no significant association was found between ABCB1 polymorphisms and serum concentrations of valproic acid. This study revealed that the polymorphisms and haplotypes of the ABCB1 gene might be associated with the treatment outcomes of valproic acid in Chinese children with epilepsy.

Polymorphisms in the Drug Transporter Gene ABCB1 Are Associated with Drug Response in Saudi Epileptic Pediatric Patients

Epilepsy is one of the most common chronic neurodisorders in the pediatric age group. Despite the availability of over 20 anti-seizure medications (ASMs) on the market, drug-resistant epilepsy still affects one-third of individuals. Consequently, this research aimed to investigate the association between single-nucleotide polymorphisms (SNPs) of the ATP-binding cassette subfamily B member 1 (ABCB1) gene in epileptic pediatric patients and their response to ASMs. This multicentric, cross-sectional study was conducted among Saudi children with epilepsy in Jeddah, Saudi Arabia. The polymorphism variants of ABCB1 rs1128503 at exon 12, rs2032582 at exon 21, and rs1045642 at exon 26 were genotyped using the Sanger sequencing technique. The study included 85 children with epilepsy: 43 patients demonstrated a good response to ASMs, while 42 patients exhibited a poor response. The results revealed that good responders were significantly more likely to have the TT genotypes at rs1045642 and rs2032582 SNPs compared to poor responders. Additionally, haplotype analysis showed that the T-G-C haplotype at rs1128503, rs2032582, and rs1045642 was only present in poor responders. In conclusion, this study represents the first pharmacogenetic investigation of the ABCB1 gene in Saudi epileptic pediatric patients and demonstrates a significant association between rs1045642 and rs2032582 variants and patient responsiveness. Despite the small sample size, the results underscore the importance of personalized treatment for epileptic patients.

Association between G2677T/A polymorphism in ABCB1 gene and the risk of drug resistance epilepsy: An updated systematic review and meta-analysis

PURPOSE

Epilepsy is a common serious brain condition characterized by the abnormal electrical activity of neurons. In most cases, epileptic patients respond to antiepileptic drugs. Approximately, one-third of patients prove medically intractable. The ABCB1 gene is a superfamily of ATP-binding cassette (ABC) transporters that encode a drug-transport protein, lead to cells and organs protects and eliminates toxic agents. We performed this meta-analysis to assess the association between G2677T/A in the ABCB1 gene and the risk of drug resistance in epileptic patients.

METHODS

Two online libraries (PubMed and Scopus) were used to identify studies that report the relationship between G2677T/A polymorphism in the MDR1 gene and the risk of antiepileptic drug resistance. The meta-analysis was performed using Review Manager 5.3 software. The pooled odds ratios and 95 % confidence intervals (CIs) were calculated using a random or fixed effects model according to the heterogeneity between studies.

RESULTS

A total of 33 eligible studies were included in this meta-analysis which 4192 patients were drug-resistant and 5079 patients were drug-responsive. As a result, a significant association was observed in overall population for the genetic model GG+GA vs AA (OR with 95 % CI = 0,56 [0.34,0.93]; P = 0.02). The subgroup ethnicity analysis showed a significant decrease in the risk of AEDs resistance in the Caucasian population.

CONCLUSION

In conclusion, our analysis demonstrates that G2677T/A polymorphism in the ABCB1 gene decreases the risk of drug resistance. More studies are needed in the different ethnic groups to clarify the role of polymorphism in AEDs resistance.

Impact of ABCB1 Polymorphisms on Lacosamide Serum Concentrations in Uygur Pediatric Patients With Epilepsy in China

BACKGROUND

P-glycoprotein, encoded by ABCB1 (or MDR1), may contribute to drug resistance in epilepsy by limiting gastrointestinal absorption and brain access to antiseizure medications. The study aimed to evaluate the impact of ABCB1 polymorphisms on lacosamide (LCM) serum concentrations in Uygur pediatric patients with epilepsy.

METHODS

The serum concentrations of LCM were determined by ultrahigh performance liquid chromatography, and the ABCB1 polymorphism was analyzed through polymerase chain reaction-fluorescence staining in situ hybridization. The χ2 test and the Fisher exact test were used to analyze the allelic and genotypic distributions of ABCB1 polymorphisms between the drug-resistant and drug-responsive patient groups. Differences in steady-state and dose-corrected LCM serum concentrations between different genotypes were analyzed using the one-way analysis of variance and the Mann-Whitney test.

RESULTS

A total of 131 Uygur children with epilepsy were analyzed, and of them, 41 demonstrated drug resistance. The frequency of the GT genotype of ABCB1 G2677T/A was significantly higher in the drug-resistant group than that in the drug-responsive group (P < 0.05, OR = 1.966, 95% CI, 1.060-3.647). Patients with the G2677T/A-AT genotype had a statistically significantly lower concentration-to-dose (CD) value than patients with the G2677T/A-GG genotype (mean: 0.6 ± 0.2 versus 0.8 ± 0.5 mcg/mL per mg/kg, P < 0.001). Significantly lower LCM serum concentrations were observed in ABCB1 C3435T CT and TT genotype carriers than those in the CC carriers (P = 0.008 and P = 0.002), and a significantly lower LCM CD value was observed in ABCB1 C3435T CT genotype carriers than that in the CC carriers (P = 0.042).

CONCLUSIONS

ABCB1 G2677T/A and C3435T polymorphisms may affect LCM serum concentrations and treatment efficacy in Uygur pediatric patients with epilepsy, leading to drug resistance in pediatric patients.

The ABCB1, ABCC2 and RALBP1 polymorphisms are associated with carbamazepine response in epileptic patient: a systematic review

Despite a dramatic increase in treatment options over the past 30 years, Carbamazepine (CBZ) is still considered the standard of care and the most prescribed initial treatment for focal epilepsy. Hence, the identification of genetic biomarkers that influence the response, resistance and toxicity to CBZ remains a challenge. Several research studies have looked into this to highlight the polymorphisms responsible for the variability in the response to CBZ in patients with epilepsy. The aim of this review is to compare the different results published in the literature The systematic review included thirty-nine studies (2005-2021), Meta-analyses were performed on more than twelve polymorphisms in three genes (ABCB1, ABCC2, RALBP1) involved in CBZ cell transport. The current challenges are to identify other new biomarkers of antiepileptic drugs that can only materialize with large-scale collaborative research efforts.

Effects of genetic polymorphism of drug-metabolizing enzymes on the plasma concentrations of antiepileptic drugs in Chinese population

As a chronic brain disease, epilepsy affects ~50 million people worldwide. The traditional antiepileptic drugs (AEDs) are widely applied but showing various problems. Although the new AEDs have partially solved the problems of traditional AEDs, the current clinical application of traditional AEDs are not completely replaced by new drugs, particularly due to the large individual differences in drug plasma concentrations and narrow therapeutic windows among patients. Therefore, it is still clinically important to continue to treat patients using traditional AEDs with individualized therapeutic plans. To date, our understanding of the molecular and genetic mechanisms regulating plasma concentrations of AEDs has advanced rapidly, expanding the knowledge on the effects of genetic polymorphisms of genes encoding drug-metabolizing enzymes on the plasma concentrations of AEDs. It is increasingly imperative to summarize and conceptualize the clinical significance of recent studies on individualized therapeutic regimens. In this review, we extensively summarize the critical effects of genetic polymorphisms of genes encoding drug-metabolizing enzymes on the plasma concentrations of several commonly used AEDs as well as the clinical significance of testing genotypes related to drug metabolism on individualized drug dosage. Our review provides solid experimental evidence and clinical guidance for the therapeutic applications of these AEDs.

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.

Impact of ABCB1 Polymorphism on Levetiracetam Serum Concentrations in Epileptic Uygur Children in China

BACKGROUND

Interindividual variations in the efficacy of antiseizure medications make epilepsy treatment challenging. This is due to genetic factors such as gene polymorphisms in Adenosine-triphosphate (ATP)-binding cassette sub-family B member 1 (ABCB1). In this article, the impact of polymorphisms in the P-glycoprotein-encoding gene, ABCB1 (C1236T, G2677T/A, and C3435T), on levetiracetam disposition was evaluated in Uygur Chinese children with epilepsy.

METHODS

MDR1 C3435T polymorphism was analyzed by polymerase chain reaction-fluorescence staining in situ hybridization. The χ test and Fisher exact test were used to analyze the allelic and genotypic distribution of ABCB1, C1236T, G2677T, and C3435T between the drug-resistant and drug-responsive groups. Differences in steady-state and dose-corrected levetiracetam serum concentrations between the different genotypes were analyzed using 1-way analysis of variance and Mann-Whitney test.

RESULTS

Total 245 Uygur children with epilepsy were analyzed [drug-resistant, n = 117 (males:females = 53:64) and drug-responsive, n = 128 (males:females = 76:52)]. The frequency of ABCB1 C1236T, G2677T/A, and ABCB1 C3435T genotypes, alleles, haplotypes, or diplotypes did not differ significantly between the 2 groups (P > 0.05). Significantly higher levetiracetam concentrations and serum concentration/body mass dose were seen in ABCB1 2677-GT, TT, GA, and AT genotypes and 3435-TT carriers compared with GG and CC carriers (P = 0.021 and P = 0.002 versus P = 0.001 and P = 0.000, respectively).

CONCLUSIONS

ABCB1 G2677T/A and C3435T may affect levetiracetam disposition and therapeutic efficacy in Uygur children with epilepsy. Genetic analysis could be a valuable tool for predicting the response to antiseizure medications before the start of treatment and could contribute to personalized medicine for Uygur children with epilepsy.

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.

Association of a genetic variant in ATP-binding cassette sub-family B member 1 gene with poor prognosis in patients with squamous cell carcinoma of the esophagus

Esophageal cancer is a common cause of death from cancer in men and the eighth most prevalent cancer globally. The morbidity and mortality rates are four times higher in men than in women. Genetic factors are among the susceptibility factors for squamous cell carcinoma of the esophagus. The rs2032582 polymorphism is a triallelic missense variant of the ABCB1 gene, that has been reported to be associated with several cancers. Here we have explored the association of the ABCB1 rs2032582 polymorphism with esophageal squamous cell carcinoma (ESCC) for the first time in a total of 251 subjects, with and without ESCC. Data from patient's record were obtained from the Mashhad University of Medical Sciences, and were used to recruit ESCC patients into the study. A total of 89 ESCC patients and 162 healthy controls were included. DNAs were extracted and genotyped using a TaqMan real-time PCR-based method. Caplan Meier method was applied to analyze patients overall survival, and progression-free survival and log-rank were used in order to compare the results. Logistic regression was used to calculate the association between risk of ESCC and different genotypes. Our data showed that patients with ESCC had a higher frequency of a T/A (TT/TA/AA) genotype for rs2032592 than individuals with GG-genotype. There were no associations between BMI and genotypic frequencies. Furthermore patients with TT/TA/AA genotypes had a poorer disease-free survival (P = 0.016) in comparison with GG genotype. We found a significant association of the ABCB1 rs2032582 polymorphism with prognosis, although further studies in a larger and multicenter setting are needed to value these findings. © 2019 IUBMB Life, 71(9):1252-1258, 2019.

Association between MDR1 gene polymorphism and clinical course of pediatric pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a progressive disease with a complex pathogenesis. The polymorphism of the gene of multidrug resistance-1 (MDR1) has been associated with many diseases including PAH.

Objective. In this study we aimed to investigate the relevance of the MDR1 polymorphism to pediatric PAH clinical course.

Methods. A total of 40 pediatric patients with PAH (secondary to congenital heart defects or idiopathic) and 40 control subjects were enrolled. Patients with PAH were divided into 2 groups, according to their evolution: 28 patients who remained clinically stable at 12-months (non-worsening group) and 12 patients who presented clinical worsening at 12-months (worsening group). Genomic DNA was genotyped for MDR1 gene polymorphisms as follows: C1236T, G2677T and C3435T.

Results. There were no significant differences between PAH children groups (clinical worsening and non-worsening) nor between PAH children and controls in terms of frequency distribution of the three studied genotypes or alleles.

Conclusions. The MDR1 polymorphism could not be correlated with the clinical evolution of pediatric PAH patients in our study.

Clinical reappraisal of the influence of drug-transporter polymorphisms in epilepsy

INTRODUCTION

Although novel antiepileptic drugs (AEDs) have been recently released, the issue of drug resistance in epileptic patients remains unsolved and largely unpredictable. Areas covered: We aim to assess the clinical impact of genetic variations that may influence the efficacy of medical treatment in epilepsy patients. Indeed, many genes, including genes encoding drug transporters (ABCB1), drug targets (SCN1A), drug-metabolizing enzymes (CYP2C9, CYP2C19), and human leucocyte antigen (HLA) proteins, may regulate the mechanisms of drug resistance in epilepsy. This review specifically focuses on the ABC genes, which encode multidrug resistance-associated proteins (MRPs) and may reduce the blood-brain barrier penetration of anticonvulsant AEDs. Expert opinion: Drug resistance remains a crucial problem in epilepsy patients. Pharmacogenomic studies may improve our understanding of drug responses and drug resistance by exploring the impact of gene variants and predicting drug responses and tolerability.

Pharmacogenetics of antiepileptic drug efficacy in childhood absence epilepsy

OBJECTIVE

To determine whether common polymorphisms in CACNA1G, CACNA1H, CACNA1I, and ABCB1 are associated with differential short-term seizure outcome in childhood absence epilepsy (CAE).

METHODS

Four hundred forty-six CAE children in a randomized double-blind trial of ethosuximide, lamotrigine, and valproate had short-term seizure outcome determined. Associations between polymorphisms (minor allele frequency ≥ 15%) in 4 genes and seizure outcomes were assessed. In vitro electrophysiology on transfected CACNA1H channels determined impact of 1 variant on T-type calcium channel responsiveness to ethosuximide.

RESULTS

Eighty percent (357 of 446) of subjects had informative short-term seizure status (242 seizure free, 115 not seizure free). In ethosuximide subjects, 2 polymorphisms (CACNA1H rs61734410/P640L, CACNA1I rs3747178) appeared more commonly among not-seizure-free participants (p = 0.011, odds ratio [OR] = 2.63, 95% confidence limits [CL] = 1.25-5.56; p = 0.026, OR = 2.38, 95% CL = 1.11-5.00). In lamotrigine subjects, 1 ABCB1 missense polymorphism (rs2032582/S893A; p = 0.015, OR = 2.22, 95% CL = 1.16-4.17) was more common in not-seizure-free participants, and 2 CACNA1H polymorphisms (rs2753326, rs2753325) were more common in seizure-free participants (p = 0.038, OR = 0.52, 95% CL = 0.28-0.96). In valproate subjects, no common polymorphisms were associated with seizure status. In vitro electrophysiological studies showed no effect of the P640L polymorphism on channel physiology in the absence of ethosuximide. Ethosuximide's effect on rate of decay of CaV 3.2 was significantly less for P640L channel compared to wild-type channel.

INTERPRETATION

Four T-type calcium channel variants and 1 ABCB1 transporter variant were associated with differential drug response in CAE. The in vivo P640L variant's ethosuximide effect was confirmed by in vitro electrophysiological studies. This suggests that genetic variation plays a role in differential CAE drug response. Ann Neurol 2017;81:444-453.

Significance of MDR1 gene C3435T polymorphism in predicting childhood refractory epilepsy

The association between the MDR1 gene C3435T polymorphism and childhood intractable epilepsy remains controversial. In this study, we performed a meta-analysis to clarify this issue. We searched the PubMed, Medline, Embase and CNKI databases for studies published through October 2016 that evaluated the association between the MDR1 C3435T polymorphism and childhood refractory epilepsy. Eleven studies involving 863 cases in the group with drug-resistant epilepsy and 915 cases in the group with drug-responsive epilepsy were included in this systematic review and meta-analysis. The analysis showed that there was not a significant association of the MDR1 C3435T polymorphism overall with risk of drug-resistance. But the allelic association of MDR1 C3435T and the association of the MDR1 3435 CC genotype with risk of drug-resistance were significant among European population and a '>2010' group based on publication year subgroup analysis. The relationship between the MDR1 C3435T polymorphism and childhood refractory epilepsy needs further validation.

Impact of Genetic Polymorphisms of ABCB1 (MDR1, P-Glycoprotein) on Drug Disposition and Potential Clinical Implications: Update of the Literature

ATP-binding cassette transporter B1 (ABCB1; P-glycoprotein; multidrug resistance protein 1) is an adenosine triphosphate (ATP)-dependent efflux transporter located in the plasma membrane of many different cell types. Numerous structurally unrelated compounds, including drugs and environmental toxins, have been identified as substrates. ABCB1 limits the absorption of xenobiotics from the gut lumen, protects sensitive tissues (e.g. the brain, fetus and testes) from xenobiotics and is involved in biliary and renal secretion of its substrates. In recent years, a large number of polymorphisms of the ABCB1 [ATP-binding cassette, sub-family B (MDR/TAP), member 1] gene have been described. The variants 1236C>T (rs1128503, p.G412G), 2677G>T/A (rs2032582, p.A893S/T) and 3435C>T (rs1045642, p.I1145I) occur at high allele frequencies and create a common haplotype; therefore, they have been most widely studied. This review provides an overview of clinical studies published between 2002 and March 2015. In summary, the effect of ABCB1 variation on P-glycoprotein expression (messenger RNA and protein expression) and/or activity in various tissues (e.g. the liver, gut and heart) appears to be small. Although polymorphisms and haplotypes of ABCB1 have been associated with alterations in drug disposition and drug response, including adverse events with various ABCB1 substrates in different ethnic populations, the results have been majorly conflicting, with limited clinical relevance. Future research activities are warranted, considering a deep-sequencing approach, as well as well-designed clinical studies with appropriate sample sizes to elucidate the impact of rare ABCB1 variants and their potential consequences for effect sizes.

The roles of variants in human multidrug resistance (MDR1) gene and their haplotypes on antiepileptic drugs response: a meta-analysis of 57 studies

Objective

Previous studies reported the associations between the ATP-binding cassette sub-family B member 1 (ABCB1, also known as MDR1) polymorphisms and their haplotypes with risk of response to antiepileptic drugs in epilepsy, however, the results were inconclusive.

Methods

The Pubmed, Embase, Web of Science, CNKI and Chinese Biomedicine databases were searched up to July 15, 2014. Pooled odds ratios (ORs) and 95% confidence intervals (CIs) were calculated using a fixed-effects or random-effects model based on heterogeneity tests. Meta-regression and Galbraith plot analysis were carried out to explore the possible heterogeneity.

Results

A total of 57 studies involving 12407 patients (6083 drug-resistant and 6324 drug-responsive patients with epilepsy) were included in the pooled-analysis. For all three polymorphisms (C3435T, G2677T/A, and C1236T), we observed a wide spectrum of minor allele frequencies across different ethnicities. A significantly decreased risk of AEDs resistance was observed in Caucasian patients with T allele of C3435T variant, which was still significant after adjusted by multiple testing corrections (T vs C: OR=0.83, 95%CI=0.71-0.96, p=0.01). However, no significant association was observed between the other two variants and AEDs resistance. Of their haplotypes in ABCB1 gene (all studies were in Indians and Asians), no significant association was observed with AEDs resistance. Moreover, sensitivity and Cumulative analysis showed that the results of this meta-analysis were stable.

Conclusion

In summary, this meta-analysis demonstrated that effect of C3435T variant on risk of AEDs resistance was ethnicity-dependent, which was significant in Caucasians. Additionally, further studies in different ethnic groups are warranted to clarify possible roles of haplotypes in ABCB1 gene in AEDs resistance, especially in Caucasians.

ABCB1 gene C3435T polymorphism and drug resistance in epilepsy: evidence based on 8,604 subjects

BACKGROUND

The present study aimed to assess the role of C3435T polymorphism in drug-resistance in epilepsy by a meta-analysis.

MATERIAL AND METHODS

Databases were obtained from the Cochrane Library, MEDLINE, EMBASE, PubMed, Science Direct database, CNKI, and Wanfang up to October 2014. All the case-control association studies evaluating the role of ABCB1 C3435T in pharmacoresistance to anti-epileptic drug (AED) were identified. RevMan 5.0 software was utilized to perform quantitative analyses in an allele model (C vs. T) and a genotype model (CC vs. CT+TT).

RESULTS

From the 189 potential studies, we included 28 articles for the meta-analysis, including 30 independent case-control studies involving 4124 drug-resistant epileptic patients and 4480 epileptic patients for whom drug treatment was effective. We excluded 164 studies because of duplication, lack of genotype data, and non-clinical research. We found that C3435T polymorphism was not significantly associated with drug resistance in epilepsy, either in allele model (C vs. T: OR=1.07; 95%CI: 0.95-1.19) or in genotype model (CC vs. CT+TT: OR=1.05; 95%CI: 0.89-1.24, P=0.55). Subgroup analyses suggested that in Caucasian populations there are significant differences between resistance group (NR) and control group (R) in both allele model (C vs. T: OR=1.09; 95%CI: 1.00-1.18, P=0.05) and genotype model (CC vs. CT+TT: OR=1.20; 95%CI: 1.04-1.40, P=0.01). However, we did not find this association in Asian populations.

CONCLUSIONS

We conclude that the ABCB1 C3435T polymorphism may be a genetic marker for drug resistance in epilepsy in Caucasian populations.

MDR-1 and MRP2 Gene Polymorphisms in Mexican Epileptic Pediatric Patients with Complex Partial Seizures

Although the Pgp efflux transport protein is overexpressed in resected tissue of patients with epilepsy, the presence of polymorphisms in MDR1/ABCB1 and MRP2/ABCC2 in patients with antiepileptic-drugs resistant epilepsy (ADR) is controversial. The aim of this study was to perform an exploratory study to identify nucleotide changes and search new and reported mutations in patients with ADR and patients with good response (CTR) to antiepileptic drugs (AEDs) in a rigorously selected population. We analyzed 22 samples In Material and Methods, from drug-resistant patients with epilepsy and 7 samples from patients with good response to AEDs. Genomic DNA was obtained from leukocytes. Eleven exons in both genes were genotyped. The concentration of drugs in saliva and plasma was determined. The concentration of valproic acid in saliva was lower in ADR than in CRT. In ABCB1, five reported SNPs and five unreported nucleotide changes were identified; rs2229109 (GA) and rs2032582 (AT and AG) were found only in the ADR. Of six SNPs associated with the ABCC2 that were found in the study population, rs3740066 (TT) and 66744T > A (TG) were found only in the ADR. The strongest risk factor in the ABCB1 gene was identified as the TA genotype of rs2032582, whereas for the ABCC2 gene the strongest risk factor was the T allele of rs3740066. The screening of SNPs in ACBC1 and ABCC2 indicates that the Mexican patients with epilepsy in this study display frequently reported ABCC1 polymorphisms; however, in the study subjects with a higher risk factor for drug resistance, new nucleotide changes were found in the ABCC2 gene. Thus, the population of Mexican patients with AED-resistant epilepsy (ADR) used in this study exhibits genetic variability with respect to those reported in other study populations; however, it is necessary to explore this polymorphism in a larger population of patients with ADR.

Maternal medication use, fetal 3435 C>T polymorphism of the ABCB1 gene, and risk of isolated septal defects in a Han Chinese population

The fundamental etiology of the majority of nonsyndromic congenital heart defects is commonly believed to involve the interaction of multiple environmental and genetic factors. This study aimed to explore the joint effects of fetal 3435 C>T polymorphism in the ABCB1 gene and maternal medication use on the risk of septal defects in a Han Chinese population. An age- and gender-matched case-control study involving 265 pairs was conducted from March 2012 to September 2013. Information on maternal periconceptional medication use was obtained through questionnaires. The genotyping of 3435 C>T polymorphism was performed by sequencing. Logistic regression analysis was performed to assess the joint effects of ABCB1 gene 3435 C>T polymorphism and maternal medication use on the risk of septal defects. Use of maternal medication periconceptionally was significantly associated with an increased risk of septal defects [adjusted odds ratio (OR) 2.133; 95 % confidence interval (CI) 1.361-3.444; P = 0.001)]. The genotype distributions of 3435 C>T polymorphism differed significantly between cases and control subjects (P < 0.001). Meanwhile, more patients were carriers of the ABCB1 CC/CT genotypes, which were significantly associated with an increased risk of septal defects (OR 2.414; 95 % CI 1.418-4.110; P = 0.001). Children who carry the CC/CT genotype and have been exposed periconceptionally to medication have an almost fourfold increased risk of having septal defects than nonexposed children with the TT genotype (adjusted OR 3.932; 95 % CI 1.708-9.051), particularly perimembranous ventricular septal defects (VSD) (adjusted OR 4.070; 95 % CI 1.570-10.552). In conclusion, fetal 3435 C>T polymorphism in the ABCB1 gene increases the risk for isolated septal defects in the presence of maternal medication use periconceptionally, particularly for perimembranous VSD.

Association between MDR1 C3435T polymorphism and refractory epilepsy in the Chinese population: a systematic review and meta-analysis

The association between the C3435T polymorphism in the MDR1 gene and refractory epilepsy remains controversial. The association appears to be influenced by ethnicity and region. We have performed a systematic review and meta-analysis to assess the link between the MDR1 C3435T polymorphism and refractory epilepsy in the Chinese population. We searched the Cochrane Library, MIDLINE, EMBASE, CBM disc, CNKI, VIP, and WANFANG databases for literature published through August 2013 for case-control studies that evaluated the association between the MDR1 C3435T polymorphism and refractory epilepsy. Twenty-one case-control studies involving 4269 patients (1863 cases in the group with drug-resistant epilepsy and 2406 in the group with drug-responsive epilepsy) were included in the systematic review and meta-analysis. The analysis showed that there were significantly more cases with the MDR1 3435 CC genotype in the group with drug-resistant epilepsy than in the group with drug-responsive epilepsy [odds ratio (OR)=1.50, 95% confidence interval (CI)=1.09-2.06, P=0.01]. In a subanalysis of patients from the southern regions of China, the correlation was not significant [odds ratio (OR)=1.2, 95% confidence interval (CI)=0.89-1.64, P=0.24]. The relationship established in a subset of the Chinese population between the MDR1 C3435T polymorphism and refractory epilepsy will guide epilepsy treatment and development of new AEDs.

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.

Association of MDR1 gene C3435T polymorphism with childhood intractable epilepsy: a meta-analysis

Drug-resistant epilepsy is also referred to as intractable, medically refractory, or pharmacoresistant epilepsy. Approximately, one-third of patients with epilepsy have recurrent seizures despite therapy. Multidrug resistance 1 (MDR1) gene may play a role in drug-resistance in epilepsy. To assess the association between MDR1 C3435T polymorphism and the response to anticonvulsants in childhood intractable epilepsy, we conducted a systematic review and meta-analysis. Studies were obtained from the electronic database of PubMed, Medline, Embase and CNKI up to September 2013. All the case-control association researches evaluating the role of MDR1 C3435T polymorphism in childhood epilepsy to antiepileptic drugs were identified. The odds ratios (ORs) with 95% confidence intervals (CIs) were calculated for comparisons of the alleles and genotypes with co-dominant (C/C vs. T/T, C/T vs. T/T), dominant (C/C + C/T vs. T/T), and recessive (C/C vs. C/T + T/T) models in overall and in ethnicity subgroups to measure the strength of genetic association. A total of 8 related studies, including 634 drug-resistant patients, 615 drug-responsive patients and 1,052 healthy controls were pooled in this meta-analysis. The allelic association of MDR1 C3435T with risk of drug-resistance was not significant (OR 1.03, 95% CI 0.87-1.22, P = 0.73; OR 1.00, 95% CI 0.86-1.16, P = 0.98) in overall and in the subgroup analysis by ethnicity (Asian: OR 0.95, 95% CI 0.77-1.18, P = 0.67; Caucasian: OR 1.18, 95% CI 0.89-1.57, P = 0.25). Neither association was found in other genetic models. Our results did not show a significant association between MDR1 C3435T polymorphism and response to anticonvulsant drugs, suggesting that this polymorphism may not be a risk factor to childhood intractable epilepsy.

The nervous system and metabolic dysregulation: emerging evidence converges on ketogenic diet therapy

A link between metabolism and brain function is clear. Since ancient times, epileptic seizures were noted as treatable with fasting, and historical observations of the therapeutic benefits of fasting on epilepsy were confirmed nearly 100 years ago. Shortly thereafter a high fat, low-carbohydrate ketogenic diet (KD) debuted as a therapy to reduce seizures. This strict regimen could mimic the metabolic effects of fasting while allowing adequate caloric intake for ongoing energy demands. Today, KD therapy, which forces predominantly ketone-based rather than glucose-based metabolism, is now well-established as highly successful in reducing seizures. Cellular metabolic dysfunction in the nervous system has been recognized as existing side-by-side with nervous system disorders - although often with much less obvious cause-and-effect as the relationship between fasting and seizures. Rekindled interest in metabolic and dietary therapies for brain disorders complements new insight into their mechanisms and broader implications. Here we describe the emerging relationship between a KD and adenosine as a way to reset brain metabolism and neuronal activity and disrupt a cycle of dysfunction. We also provide an overview of the effects of a KD on cognition and recent data on the effects of a KD on pain, and explore the relative time course quantified among hallmark metabolic changes, altered neuron function and altered animal behavior assessed after diet administration. We predict continued applications of metabolic therapies in treating dysfunction including and beyond the nervous system.

The effect of ABCB1 genetic variants on chemotherapy response in HIV and cancer treatment

Despite their clearly distinct pathophysiologies, HIV and cancer are diseases whose response to chemotherapy treatment varies substantially amongst patients, in particular for those with prior drug exposure. This has been attributed, in part, to elevated expression of the ABCB1 drug transporter in some patients, which results in reduced drug accumulation in target tissues. Many mechanisms have been identified for this elevated expression of ABCB1, including variations in the sequence of the gene coding for the transporter (ABCB1). Over 50 SNPs within ABCB1 have been identified. Associations have been made between the presence of specific ABCB1 SNPs/haplotypes and both ABCB1 expression and the efficacy or toxicity of certain chemotherapy regimens. If these associations are strong and reproducibly demonstrated, then this would greatly aid in the development of individualized therapy regimes for specific cancer or HIV patients, based on their ABCB1 genotypes. This article highlights the significant recent progress made in this direction, but cautions that the utility of ABCB1 gene variants as biomarkers of chemotherapy drug response remains unclear to date.

Functional significance of genetic polymorphisms in P-glycoprotein (MDR1, ABCB1) and breast cancer resistance protein (BCRP, ABCG2)

Recent pharmacogenomic/pharmacogenetic (PGx) studies have disclosed important roles for drug transporters in the human body. Changes in the functions of drug transporters due to drug/food interactions or genetic polymorphisms, for example, are associated with large changes in pharmacokinetic (PK) profiles of substrate drugs, leading to changes in drug response and side effects. This information is extremely useful not only for drug development but also for individualized treatment. Among drug transporters, the ATP-binding cassette (ABC) transporters are expressed in most tissues in humans, and play protective roles; reducing drug absorption from the gastrointestinal tract, enhancing drug elimination into bile and urine, and impeding the entry of drugs into the central nervous system and placenta. In addition to PK/pharmacodynamic (PD) issues, ABC transporters are reported as etiologic and prognostic factors (or biomarkers) for genetic disorders. Although a consensus has not yet been reached, clinical studies have demonstrated that the PGx of ABC transporters influences the overall outcome of pharmacotherapy and contributes to the pathogenesis and progression of certain disorders. This review explains the impact of PGx in ABC transporters in terms of PK/PD, focusing on P-glycoprotein and breast cancer resistance protein (BCRP).