Frequency distribution of C3435T mutation in exon 26 of the MDR1 gene in a Spanish population

Prevalence of ABCB1 3435C>T polymorphism in the Cuban population

OBJECTIVES

ABCB1 gene polymorphisms can modify P-glycoprotein function with clinical consequences.

METHODS

The 3435C>T polymorphism prevalence was analyzed using oligonucleotide probes and next-generation sequencing in 421 unrelated healthy individuals living in Cuba. Data were stratified by gender, ethnic background and residence. The genotype and allelic frequencies were determined.

RESULTS

The genotype distribution met the Hardy-Weinberg equilibrium assumption. The allelic frequency was 63.5% for the 3435C variant. The genotype frequencies were 41.1% for CC, 44.9% for CT and 14.0% for TT. The allele and genotype distributions differed between individuals living in La Habana and Santiago de Cuba (p<0.05) when ethnic background was analyzed. The allelic distribution was similar among Admixed and Black subjects, and they differed from Caucasians. The CC genotype was equally distributed among Admixed and Black subjects, and they differed from Caucasians. The TT genotype frequency differed between Caucasians and Admixed. The CT genotype was distributed differently among the three groups. Similar distribution was obtained in Brazilians, whereas some similarities were observed in African, Spanish and Chinese populations, consistent with the mixed Cuban ethnic origin.

CONCLUSIONS

This is the first report on allele and genotype frequencies of the 3435C>T polymorphism in Cuba, which may support personalized medicine programs.

Genetic Polymorphisms of Cytochrome P450 Enzymes and Transport Proteins in a Russian Population and Three Ethnic Groups of Dagestan

AIM

The objective of this study was to investigate the prevalence of polymorphic markers of the CYP2C19, CYP2C9, CYP2D6, SLCO1B1, and ABCB1 genes among the three ethnic groups in Dagestan and compare it with the carrier frequency of these markers among the Russian population living in Moscow.

METHODS

The study involved 186 healthy, unrelated, and chronic medication-free volunteers (53 males and 133 females) of the three ethnic groups in the Dagestan Republic: 46 Laks, 90 Avars, and 50 Dargins. Genotyping was performed using real-time polymerase chain reaction-based methods. The allelic prevalences of the three Dagestan peoples were compared with ethnic Russians from the Moscow region.

RESULTS

Statistically significant differences for the following gene polymorphisms: CYP2C19*17, CYP2C9*3, ABCB1 (C3435T), SLCO1B1*5 were found between the Russian population and the three ethnic groups of the Dagestan republic.

CONCLUSION

The data obtained from this study will help with prioritization genotyping in the region.

Influence of genetic polymorphisms of CYP3A5 and ABCB1 on sirolimus pharmacokinetics, patient and graft survival and other clinical outcomes in renal transplant

BACKGROUND

In transplant patients receiving de novo anticalcineurin-free sirolimus (SRL)-based immunosuppression, we determined the influence of cytochrome P450 3A5 (CYP3A5) and ATP-binding cassette, sub-family B (MDR/TAP), member (ABCB1) genotypes on SRL blood levels and medium-term relevant clinical outcomes, in order to improve effectiveness of immunosuppression strategies when anti-mammalian target of rapamycin (anti-mTOR) inhibitor is indicated for clinical reasons.

METHODS

Forty-eight renal transplant recipients (suffered 48% diabetes mellitus, 91% hypertension, and 47% dyslipidemia) were genotyped for CYP3A5 (6986A>G) and ABCB1 (3435C>T) polymorphisms by polymerase chain reaction-restriction fragment length polymorphism. Sirolimus blood levels were determined using microparticle enzyme immunoassay technique. Relationships between genotypes and pharmacokinetics, graft function, and patient-graft survival were determined by univariate analysis.

RESULTS

CYP3A5*1/*3 showed lower SRL levels than CYP3A5*3/*3 (4.13±1.54 vs. 8.49±4.18 ng/mL; p=0.003) and level/dose ratio (LDR) (92.74±37.47 vs. 178.62±116.45; p=0.019) in early post-transplant period. In ABCB1 polymorphisms, CT genotypes showed higher SRL levels than CC and TT (8.93±2.22 vs. 7.28±2.47 vs. 7.35±1.15 ng/mL; p=0.038) in the late period; LDR in CC and CT were 171.29±36.24 vs. 335.66±138.71 (p=0.003), despite receiving lower doses (p=0.018). Acute rejection rate was 14% vs. 42% for *3/*3 and 14% (TT), 48% (CT), and 31% (CC). Median patient survival was 45 months, significantly lower than that of *3/*3 patients (69 months). Death-censored graft survival during 5-year follow-up was similar for both CYP3A5 genotypes and significantly lower in TT than CT and CC groups, without survival differences.

CONCLUSIONS

CYP3A5 and ABCB1 polymorphisms influenced SRL levels; preliminary data suggest this may affect patient and graft survival. Genotyping renal transplant patients could help select candidates for SRL (genotype*3/*3 for CYP3A5 and CT for ABCB1), when anti-mTOR immunosuppression is indicated.

Clinical Pharmacogenetics of the Major Adenosine Triphosphate−Binding Cassette and Solute Carrier Drug Transporters

Interindividual variability in drug response is a significant problem in clinical practice, and it is likely that genetic variation among the drug transport genes are major contributors to such variability. Numerous genetic alterations affecting the members of the adenosine triphosphate-binding cassette (ABC) and solute carrier (SLC) families of transporters have been identified. Considerable data exist regarding how mutations in the ABCB1 gene that encodes p-glycoprotein impact drug disposition and response in vivo, but many study reports are conflicting on both the direction of any effect as well as the significance of any alteration. Many possible reasons for such discrepant study results have been identified, and efforts to improve the quality of such pharmacogenetic clinical association studies are ongoing. For most other clinically important transporters relatively, little clinical data exist regarding the significance of known genetic variants despite in vitro evidence of altered function for many of these transporters. What clinical data do exist suggest that certain mutations in ABCG2 and SLCO1B1 may be of importance clinically. Until the current uncertainties regarding the importance of genetic variants in drug transporter genes are clarified, the clinical application of existing pharmacogenetic data should be done with caution.

Genotype and allele frequencies of drug-metabolizing enzymes and drug transporter genes affecting immunosuppressants in the Spanish white population

Interpatient variability in drug response can be widely explained by genetically determined differences in metabolizing enzymes, drug transporters, and drug targets, leading to different pharmacokinetic and/or pharmacodynamic behaviors of drugs. Genetic variations affect or do not affect drug responses depending on their influence on protein activity and the relevance of such proteins in the pathway of the drug. Also, the frequency of such genetic variations differs among populations, so the clinical relevance of a specific variation is not the same in all of them. In this study, a panel of 33 single nucleotide polymorphisms in 14 different genes (ABCB1, ABCC2, ABCG2, CYP2B6, CYP2C19, CYP2C9, CYP3A4, CYP3A5, MTHFR, NOD2/CARD15, SLCO1A2, SLCO1B1, TPMT, and UGT1A9), encoding for the most relevant metabolizing enzymes and drug transporters relating to immunosuppressant agents, was analyzed to determine the genotype profile and allele frequencies in comparison with HapMap data. A total of 570 Spanish white recipients and donors of solid organ transplants were included. In 24 single nucleotide polymorphisms, statistically significant differences in allele frequency were observed. The largest differences (>100%) occurred in ABCB1 rs2229109, ABCG2 rs2231137, CYP3A5 rs776746, NOD2/CARD15 rs2066844, TPMT rs1800462, and UGT1A9 rs72551330. In conclusion, differences were recorded between the Spanish and other white populations in terms of allele frequency and genotypic distribution. Such differences may have implications in relation to dose requirements and drug-induced toxicity. These data are important for further research to help explain interindividual pharmacokinetic and pharmacodynamic variability in response to drug therapy.

ABCB1 C3435T and CYP2C19*2 polymorphisms in a Palestinian and Turkish population: A pharmacogenetic perspective to clopidogrel

Clopidogrel is an antiplatelet drug used to prevent recurrent ischemic events after acute coronary syndrome and/or coronary stent implantation. Single nucleotide polymorphisms (SNPs) such as CYP2C19*2 and ABCB1 C3435T have been found to play a role in different individual responses to clopidogrel. Since the prevalence of these SNPs is generally known to differ from one population to another, the aim of this study was to examine their prevalence in both a Palestinian and Turkish population. One hundred unrelated Palestinian subjects and 100 unrelated Turkish subjects were analyzed for CYP2C19*2 and ABCB1 C3435T polymorphisms by the amplification refractory mutation system (ARMS). Results showed an ABCB1 3435 T allele frequency of 0.46 (95% CI 0.391 to 0.529) in the Palestinian sample and 0.535 (95% CI 0.4664 to 0.6036) in the Turkish sample. CYP2C19*2 allele frequency was 0.095 (95% CI 0.0558 to 0.134) in the Palestinian sample and 0.135 (95% CI 0.088 to 0.182) in the Turkish sample. Our results provide information about the prevalence of the polymorphisms related to clopidogrel response in both the Palestinian and Turkish populations, in order to improve the safety and efficacy of clopidogrel through use of genetically guided, individualized treatment. The prevalence of these clinically significant alleles shed light on the importance of testing them before prescribing clopidogrel.

Common genetic polymorphisms in the ABCB1 gene are associated with risk of major depressive disorder in male Portuguese individuals

Major depressive disorder (MDD) is a highly prevalent disorder, which has been associated with an abnormal response of the hypothalamus-pituitary-adrenal (HPA) axis. Reports have argued that an abnormal HPA axis response can be due to an altered P-Glycoprotein (P-GP) function. This argument suggests that genetic polymorphisms in ABCB1 may have an effect on the HPA axis activity; however, it is still not clear if this influences the risk of MDD. Our study aims to evaluate the effect of ABCB1 C1236T, G2677TA and C3435T genetic polymorphisms on MDD risk in a subset of Portuguese patients. DNA samples from 80 MDD patients and 160 control subjects were genotyped using TaqMan SNP Genotyping assays. A significant protection for MDD males carrying the T allele was observed (C1236T: odds ratio (OR)=0.360, 95% confidence interval [CI]: [0.140-0.950], p=0.022; C3435T: OR=0.306, 95% CI: [0.096-0.980], p=0.042; and G2677TA: OR=0.300, 95% CI: [0.100-0.870], p=0.013). Male Portuguese individuals carrying the 1236T/2677T/3435T haplotype had nearly 70% less risk of developing MDD (OR=0.313, 95% CI: [0.118-0.832], p=0.016, FDR p=0.032). No significant differences were observed regarding the overall subjects. Our results suggest that genetic variability of the ABCB1 is associated with MDD development in male Portuguese patients. To the best of our knowledge, this is the first report in Caucasian samples to analyze the effect of these ABCB1 genetic polymorphisms on MDD risk.

Effect of the C3435T polymorphism of the multidrug resistance 1 gene on the severity of inflammatory bowel disease in Iranian Azeri Turks

BACKGROUND/AIM

Multidrug resistance 1 (MDR1) gene encodes for P-glycoprotein (P-gp), a transmembrane efflux pump transferring both exogenous and endogenous substrate from the cells. In the human gastrointestinal tract, P-gp is found in high concentrations on the epithelial cells of the colon and small intestine. It is hypothesized that the expression level of MDR1 gene is related to susceptibility of both forms of inflammatory bowel disease (IBD). The aim of this study was to investigate the association of C3435T Single Nucleotide Polymorphism in IBD patients with/without clinical symptoms in Iranian Azeri Turks.

SETTINGS AND DESIGN

A total of 116 patients with IBD and 92 healthy subjects were analyzed.

MATERIALS AND METHODS

We investigated the distribution of MDR1 C3435T polymorphism via polymerase chain reaction - Restriction Fragment Length Polymorphism technique.

STATISTICAL ANALYSIS USED

All statistical analyses were calculated with the SPSS for Windows 16.0. The Fisher exact test was used to test for departure from Hardy-Weinberg equilibrium of the genotype frequencies ( P > 0.05).

RESULTS

The data showed that IBD patient with homozygous variant carrying MDR1 3435 T/T genotype has elevated risk for development of routine IBD clinical symptoms like Abdominal pain ( P = 0.005) and chronic Diarrhea ( P = 0.013) compared with MDR1 3435 C/C homozygotes who has reduced risk for development of IBD symptoms.

CONCLUSIONS

Our data showed that patients with MDR1 3435 T/T are more susceptible to the development of some routine IBD clinical symptoms ( P < 0.05). This study suggests a protective role for the MDR1 3435 C/C versus MDR1 3435 T/Tgenotype and C versus T allele for the progression of IBD in this cohort.

Association between ABCB1 (MDR1) gene 3435 C>T polymorphism and colchicine unresponsiveness of FMF patients

The multidrug resistance gene-1 (MDR1, adenosine triphosphate-binding cassette transporter: ABCB1, P-glycoprotein) encodes membrane proteins that play a crucial role in protecting cells from xenobiotics, chemicals, and drugs. The TT genotype of 3435 codon in exon 26 of MDR1 gene causes overexpression of gene activity and effluxes many chemically diverse compounds across the plasma membrane. We studied the association between C3435T polymorphisms (single nucleotide polymorphism) of MDR1 gene and colchicine-resistant familial Mediterranean fever (FMF) patients. Total genomic DNA samples from 52 FMF patients of colchicine unresponsiveness were used for FMF (MEFV) and MDR1 genes profile analyses. Target genes were genotyped by multiplex PCR-based reverse-hybridization Strip Assay method. The preliminary current results showed increased T allele frequency (0.596) in colchicine unresponsiveness of FMF patients. The distributions of the CC, CT, and TT genotypes in colchicine nonresponder FMF patients were 17%, 46%, and 37%, respectively. Our results indicate that C3435T polymorphism in exon 26 of MDR1 gene is associated with colchicine resistance in nonresponder FMF patients during the common therapy protocol.

CYP2C19 and ABCB1 gene polymorphisms are differently distributed according to ethnicity in the Brazilian general population

Background

Recent studies have reported the clinical importance of CYP2C19 and ABCB1 polymorphisms in an individualized approach to clopidogrel treatment. The aims of this study were to evaluate the frequencies of CYP2C19 and ABCB1 polymorphisms and to identify the clopidogrel-predicted metabolic phenotypes according to ethnic groups in a sample of individuals representative of a highly admixtured population.

Methods

One hundred and eighty-three Amerindians and 1,029 subjects of the general population of 4 regions of the country were included. Genotypes for the ABCB1c.C3435T (rs1045642), CYP2C19*2 (rs4244285), CYP2C19*3 (rs4986893), CYP2C19*4 (rs28399504), CYP2C19*5 (rs56337013), and CYP2C19*17 (rs12248560) polymorphisms were detected by polymerase chain reaction followed by high resolution melting analysis. The CYP2C19*3, CYP2C19*4 and CYP2C19*5 variants were genotyped in a subsample of subjects (300 samples randomly selected).

Results

The CYP2C19*3 and CYP2C19*5 variant alleles were not detected and the CYP2C19*4 variant allele presented a frequency of 0.3%. The allelic frequencies for the ABCB1c.C3435T, CYP2C19*2 and CYP2C19*17 polymorphisms were differently distributed according to ethnicity: Amerindian (51.4%, 10.4%, 15.8%); Caucasian descent (43.2%, 16.9%, 18.0%); Mulatto (35.9%, 16.5%, 21.3%); and African descent (32.8%, 20.2%, 26.3%) individuals, respectively. As a result, self-referred ethnicity was able to predict significantly different clopidogrel-predicted metabolic phenotypes prevalence even for a highly admixtured population.

Conclusion

Our findings indicate the existence of inter-ethnic differences in the ABCB1 and CYP2C19 variant allele frequencies in the Brazilian general population plus Amerindians. This information could help in stratifying individuals from this population regarding clopidogrel-predicted metabolic phenotypes and design more cost-effective programs towards individualization of clopidogrel therapy.

Influence of MDR1 polymorphism on H. pylori-related chronic gastritis

BACKGROUND

There is evidence that changes in MDR1 function and/or expression contribute to the pathogenesis of inflammatory disorders of the gastrointestinal tract.

AIMS

We aimed to investigate the effect of C3435T polymorphism of the MDR1 gene on histological chronic gastritis, and on the risk of peptic ulcer diseases.

METHODS

Restriction fragment length polymorphism analysis was performed for polymorphisms at C3435T in the MDR1 gene in 556 cancer-free subjects including 116 gastric and 60 duodenal ulcers, and 380 non-ulcer subjects. Gastritis scores in the antrum were assessed according to the updated Sydney system in 384 subjects.

RESULTS

We did not find a significant association between MDR1 genotype and gastritis scores in any of the 384 subjects. However, the 3435T carrier was significantly associated with a higher degree of neutrophil infiltration in H. pylori-positive subjects (CC vs. T carrier: p=0.0495). When the H. pylori positive subjects were divided according to generation, the 3435T carrier was significantly associated with a higher degree of neutrophil infiltration in subjects more than 65 years of age (CC vs. T carrier: p=0.03). Also, the MDR1 3435 TT genotype was significantly associated with a higher degree of atrophy and intestinal metaplasia in the same generation (atrophy, TT vs. C carrier: p=0.038, intestinal metaplasia, TT vs. C carrier: p=0.016). No association was found between MDR1 genotypes and risk of peptic ulcer diseases.

CONCLUSIONS

It appears that the C3435T polymorphism of MDR1 influences H. pylori-related inflammatory conditions in the stomach, especially in older subjects.

MDR1 3435T and 1236T alleles delay disease progression to pediatric AIDS but have no effect on HIV-1 vertical transmission

BACKGROUND

Single nucleotide polymorphisms (SNPs) in the MDR1 gene, coding for the drug transporter P-glycoprotein, may modulate the response to antiretroviral therapy and susceptibility to HIV-1 infection. We investigated whether the MDR1 SNPs C1236T (exon 12) and C3435T (exon 26) affect HIV-1 vertical transmission and progression to pediatric AIDS.

METHODS

The MDR1 genotypes were identified by PCR-restriction fragment length polymorphism (RFLP) assays in 219 HIV-infected, 128 exposed uninfected children and 231 HIV-seronegative blood donors. Genotype and haplotype frequencies were estimated in the different groups. The median follow-up time of the infected cohort was 108 months and AIDS-free time was evaluated for the different MDR1 genotypes in 171 HIV-infected children.

RESULTS

We found that both C1236T and C3435T polymorphisms were highly frequent in the studied groups (approximately 0.44) and showed strong linkage disequilibrium. There was no association between MDR1 genotypes and HIV-1 vertical transmission. However, a protective effect against progression to AIDS was associated with MDR1 3435CT, 1236CT and 1236TT genotypes (P = 0.005, P = 0.024 and P = 0.026, respectively). Moreover, haplotype pairs' analysis showed that the 3435CT/1236CT and 3435CT/1236TT exerted a significant protection against progression to pediatric AIDS (P = 0.0025 and P = 0.006, respectively).

CONCLUSION

We conclude that in Argentinean children, MDR1 genotypes are associated with progression to AIDS, but they do not affect HIV-1 susceptibility by vertical transmission. These results support the notion that P-glycoprotein plays a role in HIV-1 infection independently from its role in drug transport.

Effect of the ABCB1 3435C>T polymorphism on tacrolimus concentrations and dosage requirements in liver transplant recipients

PURPOSE

The effect of ABCB1 3435C>T on tacrolimus concentrations in liver transplant recipients was studied. Tacrolimus is a substrate for P-glycoprotein, the product of the ABCB1 gene. To determine whether the ABCB1 single-nucleotide polymorphism (SNP) 3435C>T was associated with variation in the tacrolimus concentration:dose ratio (C:D) in 42 liver transplant recipients during three months after transplantation.

METHODS

Forty-two Caucasian patients who underwent an orthotopic liver transplantation from cadaveric donors received a basic immunosuppressive regimen containing tacrolimus and corticosteroids; mycophenolate mofetil was added in 18 cases. The SNP 3435C>T in exon 26 was investigated by MboI restriction-enzyme digestion, leading to the identification of CC, TT, or CT status at nucleotide 3435. Results obtained for the three genotypes were compared for each of three values: daily weight-adjusted tacrolimus dose, blood trough tacrolimus concentration, and C:D.

RESULTS

The wild-type genotype (3435CC) was observed in 10 patients (24%); 23 patients (55%) were heterozygous (3435CT) and 9 patients (21%) were homozygous for the mutation (3435TT). One to three days after liver transplantation, the mean +/- S.D. C:D was significantly higher in subjects homozygous for the mutation compared with subjects with the wild-type allele (236 +/- 119 ng . kg/mL . mg versus 104 +/- 74 ng . kg/mL . mg, respectively; p = 0.0167). Subjects with the heterozygous allele had an intermediate mean +/- S.D. C:D (131 +/- 108 ng . kg/mL . mg). One or three months after transplantation, no significant difference in the tacrolimus C:D was evident among the three groups.

CONCLUSION

The ABCB1 3435C>T polymorphism influenced the tacrolimus C:D in the first days after liver transplantation.

ABCB1 C1236T, G2677T/A and C3435T polymorphisms in systemic lupus erythematosus patients

P-glycoprotein (Pgp), the ABCB1 gene product, acts as an efflux pump that transports a large variety of substrates and is a mechanism of cell protection against xenobiotics. An increasing number of studies have shown that some ABCB1 polymorphisms may affect Pgp expression and activity, as well as affecting the development and susceptibility to diseases and pharmacological response. High activity of Pgp has been detected in systemic lupus erythematosus (SLE) patients. The C1236T, G2677T/A, and C3435T are the most commonly studied single nucleotide polymorphisms in the ABCB1 gene. Therefore, their frequencies were determined in Brazilian individuals with European ancestry (N = 143) and in SLE patients (N = 137). Genotyping was performed by PCR-RFLP analysis using specific primers followed by incubation with the appropriate restriction enzymes. The resulting DNA fragments were visualized on agarose or polyacrylamide gels. No statistically significant differences were observed in allelic and genotypic frequencies between SLE and healthy subjects (Fisher exact test). Nevertheless, the 2677A allelic frequency was lower in SLE patients with malar rash (0.007) compared with patients without this feature (0.04; P = 0.0054), while the frequency of this variant was higher in SLE patients with pleuritis (0.07) compared with patients without this feature (0.01; P = 0.0156). We suggest that although the ABCB1 polymorphisms do not directly interfere in SLE susceptibility, their evaluation, especially the 2677A allele, in other immunological processes may be interesting since they can interfere in clinical features of this disease.

MDR1 gene polymorphisms and clinical relevance

In vivo and in vitro studies have demonstrated that P-glycoprotein (P-gp) plays a very significant role in the ADME processes (absorption, distribution, metabolism, excretion) and drug-drug interaction (DDI) of drugs in humans. P-gp is the product of multidrug resistance gene (MDR1/ABCB1). Pharmacogenomics and pharmacogenetics studies have revealed that genetic polymorphisms of MDR1 are associated with alteration in P-gp expression and function in different ethnicities and subjects. By now, 50 single nucleotide polymorphisms (SNPs) and 3 insertion/deletion polymorphisms have been found in the MDR1 gene. Some of them, such as C3435T, have been identified to be a risk factor for numerous diseases. It is believed that further understanding of the physiology and biochemistry of P-gp with respect to its genetic variations may be important for individualized pharmacotherapy. Therefore, based on the latest public information and our studies, this review focuses on the following four aspects: 1) the impact of P-gp on pharmacokinetics; 2) MDR1 genetic polymorphisms and their impacts on pharmacogenetics; 3) relationship between altered P-gp expression and function and the MDR1(C3435T) SNP, and 4) relevance of MDR1 polymorphisms to certain human diseases.

The genetic variability of MDR1 C3435T polymorphisms in four Southern Chinese populations

OBJECTIVES

To investigate the genetic variability of multiple drug resistant 1 (MDR1) gene C3435T polymorphism in four Southern Chinese populations.

METHODS

Using discrimination real-time PCR, we determined the MDR1 C3435T polymorphism in three ethnic minority groups Lahu (n=104), Wa (n=101) and Bulang (n=100) in Yunnan Province, and Han Chinese (n=199) in Hong Kong. All of them were residents in Southern China.

RESULTS

For 3435 CC genotype, the frequency in Han Chinese in Hong Kong (44.7%) is significantly higher than in Lahu (16.3%) and Wa (29.7%) minorities, P<0.05. For 3435 CT genotype, the frequency in Han Chinese in Hong Kong (44.2%) is lower than in Lahu (58.7%), P<0.05. For 3435 TT genotype, frequency in Han Chinese in Hong Kong (11.1%) is lower than in Lahu (25%) and Wa (20.8%), P<0.05. For 3435 C allele, frequency in Han Chinese in Hong Kong (66.8%) is higher than in Lahu (45.7%) and Wa (54.5%), P<0.01. For 3435T allele, frequency in Han Chinese in Hong Kong (33.2%) is lower than in Lahu (54.3%) and Wa (45.5%), P<0.01. For MDR1 3435T allele, the frequencies are significantly higher in our four Southern Chinese populations than in African population (P<0.001) and significantly lower than in South-west Asians (P<0.05); Han Chinese in Hong Kong displayed significant difference from all the other ethnic populations except Japanese (P<0.05); compared with Caucasian and other ethnic Asians, Lahu minority showed no frequency difference (P>0.05) between Caucasian and other Asians (except Japanese).

CONCLUSIONS

This is the first study to show the C3435T polymorphism of MDR1 in Southern Chinese populations. The frequency of C3435T, an important determinant for multidrug resistance, displays significant difference in ethnics. It may help for individualizing therapy for cancer, HIV and other common diseases.

ABCB1 and ABCC1 expression in peripheral mononuclear cells is influenced by gene polymorphisms and atorvastatin treatment

This study investigated the effects of atorvastatin on ABCB1 and ABCC1 mRNA expression on peripheral blood mononuclear cells (PBMC) and their relationship with gene polymorphisms and lowering-cholesterol response. One hundred and thirty-six individuals with hypercholesterolemia were selected and treated with atorvastatin (10 mg/day/4 weeks). Blood samples were collected for serum lipids and apolipoproteins measurements and DNA and RNA extraction. ABCB1 (C3435T and G2677T/A) and ABCC1 (G2012T) gene polymorphisms were identified by polymerase chain reaction-restriction (PCR)-RFLP and mRNA expression was measured in peripheral blood mononuclear cells by singleplex real-time PCR. ABCB1 polymorphisms were associated with risk for coronary artery disease (CAD) (p<0.05). After atorvastatin treatment, both ABCB1 and ABCC1 genes showed 50% reduction of the mRNA expression (p<0.05). Reduction of ABCB1 expression was associated with ABCB1 G2677T/A polymorphism (p=0.039). Basal ABCB1 mRNA in the lower quartile (<0.024) was associated with lower reduction rate of serum low-density lipoprotein (LDL) cholesterol (33.4+/-12.4%) and apolipoprotein B (apoB) (17.0+/-31.3%) when compared with the higher quartile (>0.085: LDL-c=40.3+/-14.3%; apoB=32.5+/-10.7%; p<0.05). ABCB1 substrates or inhibitors did not affect the baseline expression, while ABCB1 inhibitors reversed the effects of atorvastatin on both ABCB1 and ABCC1 transporters. In conclusion, ABCB1 and ABCC1 mRNA levels in PBMC are modulated by atorvastatin and ABCB1 G2677T/A polymorphism and ABCB1 baseline expression is related to differences in serum LDL cholesterol and apoB in response to atorvastatin.

Single nucleotide polymorphisms in the multidrug resistance gene 1 (ABCB1): effects on its expression and clinicopathological characteristics in breast cancer patients

OBJECTIVES

Resistance of tumor cells to multiple cytostatic agents is one of the major impediments of successful cancer chemotherapy. A large part of resistance of tumors to chemotherapy is caused by the ABC transporter P-glycoprotein encoded by the ABCB1 gene. The main aim of this study was to assess the prognostic value of ABCB1 genotype and phenotype in breast cancer.

METHODS

Six ABCB1 single nucleotide polymorphisms (SNPs) were determined in 90 Czech breast cancer patients by a novel method that allows simultaneous assessment of multiple polymorphisms on a single electronic microarray. Expression levels of ABCB1 were quantified in tumor and nontumor samples of breast cancer patients by real-time PCR. T-test, analysis of variance and Fisher's exact test were used to analyze the effect of ABCB1 polymorphisms on ABCB1 expression levels and for the analysis of associations between ABCB1 expression, genotype and clinical and pathological characteristics.

RESULTS

ABCB1 was expressed in 98.9% of the tumor and in 97.5% of the nontumor samples. ABCB1 was downregulated in 79.5% of tumors compared with the nontumor samples. No significant correlation was observed between ABCB1 mRNA expression levels and clinical and pathological characteristics. High frequencies of the variant alleles in ABCB1 exon 12 (1236C>T, 38.3%) and exon 26 (3435C>T, 54.0%) were observed. Individuals with variant alleles in exons 12 and 26 had significantly lower ABCB1 expression levels in their tumors. SNPs in exons 12 and 26 also correlated with estrogen receptor status of patients.

CONCLUSION

ABCB1 SNPs may affect function of P-glycoprotein by influencing the expression level and modify breast cancer prognosis.

Associations between MDR1 gene polymorphisms and schizophrenia and therapeutic response to olanzapine in female schizophrenic patients

Multidrug resistant protein (MDR1) gene, which codes for P-glycoprotein and functions as an efflux transporter in different cells, is widely localized in normal tissues including the gastrointestinal tract, blood cells, biliary tract, kidney and brain and plays a major role in absorption, distribution and elimination of various xenobiotics. Therefore, MDR1 gene variants were proposed as potential susceptibility factors for diseases and as determinants of treatment response to various drugs. We investigated the relationships between exon 21 G2677T and exon 26 C3435T genetic variants of MDR1 gene with susceptibility and treatment response in female schizophrenic patients. The study was conducted in two steps. We first compared allele, genotype and haplotype distributions between 117 female schizophrenic patients and 123 control female subjects. Afterwards, we studied treatment response to olanzapine, in 87 out of 117 previously unmedicated female patients. Overall, we found lower representation of G2677/C3435 haplotype in schizophrenic female patients compared to controls. Test result for linkage disequilibrium between loci was found to be significant. Furthermore, we found significant associations between MDR1 exon 21 G2677T genotypes and treatment response measured with positive PANSS percentage changes, with T allele and TT genotype being associated with significantly better treatment response. A borderline, non-significant statistical association was found between MDR1 exon 26 C3435T genotypes and treatment response, with TT genotype being associated with better treatment response. Our data support functional importance of the MDR1 mutations for the susceptibility and treatment response in female schizophrenic patients.

Determination of ABCB1 polymorphisms and haplotypes frequencies in a French population

The ATP-binding cassette (ABC) transporter ABCB1, or P-glycoprotein, is a transmembrane efflux pump well known for its implication in drug transport and chemoresistance. ABCB1 substrates include either drugs, such as antiretrovirals and immunomodulators, or physiological molecules like phospholipids. Pharmacogenetic analysis of ABCB1 polymorphisms, in addition to other xenobiotic metabolizing enzymes, might help to personalize and optimize drug therapy. Indeed, some polymorphisms of ABCB1 have been implicated in susceptibility to diseases, changes in drug pharmacokinetics, and in variation of the biological response to drug treatment. In addition, variant and haplotype distributions differ depending on ethnicity. Thus, some ethnies may be at higher risk for adverse events, inefficacy of treatment or prevalence of pathologies. This study aimed to determine frequencies of ABCB1 polymorphisms and haplotypes in a sample of French healthy individuals. DNA was isolated from blood-EDTA. Polymerase chain reaction-restriction fragment length polymorphism and TaqMan single nucleotide polymorphism genotyping assays were used to genotype 227 individuals for T-129C, G-1A, A61G, G1199A, C1236T, T-76A, G2677T/A and C3435T polymorphisms. The observed frequencies of the variant allele for these eight polymorphisms are 0.04, 0.08, 0.09, 0.06, 0.42, 0.46, 0.45 and 0.46 respectively. These polymorphisms are in linkage disequilibrium and haplotype frequencies were determined, the most frequent haplotype being the one with variants at position 1236, 2677 and 3435 and wild-type alleles at the other positions. Finally, the frequencies of these eight ABCB1 polymorphisms in our French individuals supposed to be healthy population are quite similar to those described in other Caucasian populations except for the C3435T polymorphism.

Genetic polymorphism of cytochrome P450s and P-glycoprotein in the Finnish population

The objective of this study was to investigate the genetic polymorphism of selected cytochrome P450 (CYP) enzymes and ABCB1 (encoding P-glycoprotein) of central importance with regard to the disposition of clinically used drugs in the Finnish population and to compare the results to pre-existing data from Caucasian populations. A random sample of 449 Finns was studied. Single nucleotide polymorphisms (SNPs) were genotyped using blood-derived genomic DNA and 5'-nuclease assays. We found that the allele frequencies of CYP1A2 SNP g.-163C>A, CYP2C8*3, CYP2C9*2, CYP2C9*3 and CYP2C19*2 were similar to those seen in other Caucasian populations. However, the allelic frequency of the variant ABCB1 SNP c.3435C>T allele was lower than previously reported. The frequency of the homozygous CYP3A5*1 expression was significantly higher than expected based on Hardy-Weinberg calculations (observed n = 8 vs. expected n = 3, P = 0.01). Other genotype frequencies corresponded to the expected values. The strong linkage between the CYP2C8*3 and the CYP2C9*2 alleles was confirmed in this study and the number of individuals with the rare haplotype CYP2C8*3*3/CYP2C9*2*2 was higher than expected. We conclude that the frequency of mutated CYP alleles in Finns were in agreement with earlier findings in Caucasian populations, but a lower frequency of the ABCB1 variant allele 3435T corresponding to that reported in Asian populations was found. The higher than expected frequency of the CYP3A5*1*1 genotype and the CYP2C8*3*3/CYP2C9*2*2 haplotype may influence the response to treatment with drugs metabolized by these enzymes.

Multi-drug resistance 1 polymorphism is associated with reduced risk of gastric cancer in the Japanese population

BACKGROUND AND AIMS

Host genetic factors play a key role in gastric carcinogenesis, but the mechanism has not been clarified. The multi-drug resistance 1 (MDR1) gene mediates the expression of P-glycoprotein, which has a role in active transport of various substrates, including xenobiotics, and thus has a protective function in various tissues and organs like gastrointestinal epithelial cells. C3435T polymorphism in exon 26 of the MDR1 gene influences P-glycoprotein expression and activity in the gastrointestinal tract. We investigated the influences of MDR1 gene polymorphism on the risk of gastric cancer.

METHOD

The study was performed on 157 patients with gastric cancer (GC) and 104 patients without GC as the control group. C3435T polymorphism of MDR1 was investigated by PCR-RFLP in all of the patients.

RESULTS

The MDR1 3435 TT genotype showed a significantly higher frequency in controls than in GC patients (OR = 0.43; 95% CI = 0.23-0.79). There were no significant differences of the CT and CC genotype frequencies between GC patients and controls. We also found that the 3435TT genotype of MDR1 was associated with a lower risk of non-cardiac cancer (OR = 0.42; 95% CI = 0.23-0.79), middle-third cancer (OR = 0.36; 95% CI = 0.17-0.77), advanced cancer (OR = 0.31; 95% CI = 0.13-0.73), venous invasion (OR = 0.30; 95% CI = 0.10-0.91), and lymph node metastasis (OR = 0.28; 95% CI = 0.13-0.65).

CONCLUSION

Our data suggest that 3435T/T polymorphism of MDR1 is associated with a reduced risk of gastric cancer in the Japanese population.

The frequency of C3435T MDR1 gene polymorphism in Iranian patients with ulcerative colitis

BACKGROUND AND AIMS

The MDR1 (multidrug resistance) gene, located on chromosome 7, is in one of the inflammatory bowel disease susceptibility loci. It produces P-glycoprotein, a transmembrane efflux pump, transferring drugs and toxins from intracellular to extracellular domains. In the human gastrointestinal (GI) tract, P-glycoprotein is found in high concentrations on the epithelial cells of the colon and small intestine. MDR1 gene polymorphisms such as C3435T are associated with lower P-glycoprotein expression, and thus it is suggested to have an association with ulcerative colitis. We tried to determine the frequency of C3435T polymorphism of the MDR1 gene in Iranian patients with ulcerative colitis and to compare it with a healthy control population.

MATERIALS AND METHODS

In this case-control-designed study, 300 unrelated ulcerative colitis patients and 300 sex-and-age-matched healthy controls were enrolled. They were visited at a tertiary center during a 2-year period (2003-2005). DNA of patients and controls was amplified by polymerase chain reaction with specific primers, and C3435T polymorphism was detected by the restriction fragment length polymorphism method.

RESULTS

The frequency of the 3435T allele was significantly higher in ulcerative colitis patients compared to the controls (p < 0.001). The frequency of homozygote T/T and heterozygote C/T genotypes were also significantly higher in Iranian patients with ulcerative colitis (p = 0.044 and 0.041, respectively).

CONCLUSION

This study suggests that C3435T polymorphism of the MDR1 gene has an association with ulcerative colitis in Iranian population as previously reported in western countries.

Polymorphism C3435T of the MDR1 gene in Central Americans and Spaniards

The human multidrug resistance gene (MDR1) encodes for P-glycoprotein (P-gp) which is a transmembrane transporter protein that acts as an efflux pump for a number of lypophilic compounds. It plays a protective role for cells against DNA damage. The wobble C3435T polymorphism at exon 26 has been associated with different expression levels and activity. Differences in allele frequency of the C3435T polymorphism have been demonstrated between distinct ethnic groups. In our study we examined these polymorphisms in 433 healthy individuals. From these, 229 were Central American mestizos from Nicaragua (n = 117) and El Salvador (n = 112) to be compared with a group of 204 North Spaniards, with the aim of detecting potential genotypic differences between these populations. The genotypes were determined by PCR-RFLP. The frequencies of the C allele were very similar among Central Americans (0.53) and Spaniards (0.52), which is consistent with the ethnic origin of Central American individuals (Amerindians and European Caucasians). In comparison to other previously studied populations, the C allele frequency in Central Americans was significantly lower than that found in African populations and higher than that observed in the Indian and Southwest Asian populations. These data may be relevant for dose recommendation of P-gp substrate drugs and also for studies of allele disease association in the Central American population.

Multidrug resistance gene-1 polymorphisms and resistance to cyclosporine A in patients with steroid resistant ulcerative colitis

BACKGROUND

Cyclosporine A (CsA) is inconstantly effective in inducing remission in acute attacks of ulcerative colitis (UC) not responding to steroids. This study aimed to establish whether multidrug resistance gene (MDR)1 polymorphisms would be associated with CsA failure.

PATIENTS AND METHODS

The distribution of the different genotypes of single nucleotide polymorphisms (SNP) G2677T/A and C3435T of MDR1 exons 21 and 26, respectively, was studied in 154 patients (mean age, 44 yr) who had received CsA to treat severe attacks of steroid resistant UC in 11 centers in France and Belgium. Patients were classified as CsA failure (n = 50) when they needed colectomy within 30 days after CsA initiation. The SNPs were detected by use of a 5' nuclease allelic discrimination assay.

RESULTS

There was a significant association between the G2677T/A polymorphism distribution (exon 21) and the risk for CsA failure (P = 0.0001). The TT genotype of exon 21 was significantly associated with the risk compared with the two other genotypes (odds ratio, 3.77; 95% confidence interval, 1.42-9.97, P = 0.007). There was no significant association between the genotype C3435T distribution (exon 26) and the risk of CsA failure (P = 0.23).

CONCLUSION

The TT genotype of exon 21 MDR1 polymorphisms is associated with a higher risk of CsA failure in patients with steroid resistant UC. Further studies should be performed to establish whether other treatments could be more efficient to avoid surgery in this subset of patients.

Genotype and allele frequency of human multidrug resistance (MDR1) gene C3435T polymorphism in Denizli province of Turkey

Human p-glycoprotein encoded by human multidrug resistance (MDR1) gene, is a transmembrane protein that serves as efflux pump for a wide variety of lipophilic compounds possessing a physiological role in protecting cells against the DNA damaging of certain xenobiotics. According to the published data, the frequency of C3435T polymorphism differs depending on the different ethnical populations such as Asian, African, and Caucasians populations. In our study, we identified the MDR1 C3435T polymorphism in 150 healthy volunteers in Denizli province of Turkey. DNA was extracted from peripheral blood samples by standard phenol/chloroform extraction method. Polymerase chain reaction-restriction fragment length polymorphism was used for the detection of C3435T single nucleotide polymorphism. We obtained CC, CT and TT genotype frequencies as 20, 53 and 27%, respectively. According to our results, the C allele in Turkish population (Denizli province, west of Turkey) is found 47% and this data shows similarity with Caucasian (UK and German) populations and significantly lower than African populations (p < 0.001). Our study is the first data on the genotype and allele frequency of the human multidrug resistance (MDR1) Gene C3435T Polymorphism in Denizli Province at regional basis in Turkey. Our results could serve as a basis for large-scale correlation studies on the relevance of C3435T genotype in cancer therapy and other diseases in Turkish population. Investigation of genotype frequencies related with p-glycoprotein substrates should be investigated in large scale at regional bases in Turkish population. The scaled-up data might help either to the use of p-glycoprotein substrates to be used for therapeutic applications and population genetics considering the genotype frequencies possibly occurring throughout the history in Anatolian basin.

Differences in CYP3A5*3 genotype distribution and combinations with other polymorphisms between Spaniards and Other Caucasian populations

The goal of this study was to detect genotypic differences between Spaniards and other related populations regarding CYP3A4*1B, CYP3A5*3, and ABCB1 (MDR1) C3435T polymorphisms. DNA from 177 Spanish patients were analyzed for the presence of these mutations using PCR-restriction fragment length polymorphism or direct sequencing. The observed frequencies for CYP3A4*1B, CYP3A5*3, and C3435T alleles were within normal values in Caucasians (0.04, 0.91, and 0.5, respectively). However, 2.8% of the patients were homozygous for the wild-type CYP3A5*1 allele, an extremely uncommon genotype in other Caucasians. In addition, analysis of CYP3A4-3A5 haplotypes revealed the existence of 2 unusual subgroups: patients who were homozygous wild-type for both polymorphisms, and patients showing a CYP3A4*1A/*1B-CYP3A5*3/*3 genotype combination. The incidence of CYP3A5*1/*1 carriers and the occurrence of subjects combining the 2 above-mentioned unusual genotype combinations were more frequent in Spanish-Caucasians compared with American- or European-Caucasians. ABCB1 C3435T genotype frequencies were equally distributed between both single and combined CYP3A4 and 3A5 genotypes. These findings suggest that dose requirements for drugs metabolized by CYP3A and certain allele-disease association studies in white populations could show discrepancies in Spaniards.

MDR1 genotype-related pharmacokinetics: fact or fiction?

Multidrug resistant transporter MDR1/P-glycoprotein, the gene product of MDR1, is a glycosylated membrane protein of 170 kDa, belonging to the ATP-binding cassette superfamily of membrane transporters. A number of various types of structurally unrelated drugs are substrates for MDR1, and MDR1 and other transporters are recognized as an important class of proteins for regulating pharmacokinetics. The first investigation of the effects of MDR1 genotypes on pharmacotherapy was reported in 2000; a silent single nucleotide polymorphism (SNP), C3435T in exon 26, was found to be associated with the duodenal expression of MDR1, and thereby the plasma concentration of digoxin after oral administration. In the last 5 years, clinical studies have been conducted around the world on the association of MDR1 genotype with MDR1 expression and function in tissues, and with the pharmacokinetics and pharmacodynamics of drugs; however, there are still discrepancies in the results on C3435T. In 1995, a novel concept to predict in vivo oral pharmacokinetic performance from data on in vivo permeability and in vitro solubility has been proposed, and this Biopharmaceutical Classification System strongly suggested that the effects of intestinal MDR1 on the intestinal absorption of substrates is minimal in the case of commercially available oral drugs, and therefore MDR1 genotypes are little associated with the pharmacokinetics after oral administration. This review summarizes the latest reports for the future individualization of pharmacotherapy based on MDR1 genotyping, and attempts to explain discrepancies.

Single nucleotide polymorphisms in the multidrug resistance 1 gene in Korean epileptics

PURPOSE

P-glycoprotein 170 encoded by the multidrug resistance 1 (MDR1) gene exports various antiepileptic drugs out of the CNS, which leads to multidrug resistance. This study was performed to elucidate the relationship between single nucleotide polymorphisms (SNPs) in the MDR1 gene and drug resistance in Koreans with epilepsy.

SUBJECTS AND METHODS

Three SNPs at nucleotide position 1236 in exon 12, 2677 in exon 21 and 3435 in exon 26 of the MDR1 gene were genotyped in 207 Korean epileptics. Subjects were classified according to whether they had drug-resistant (RS group; N=99) or drug-responsive epilepsy (RP group; N=108). The frequencies of genotype and haplotype were compared between the RS and RP groups.

RESULTS

The frequencies of genotype and haplotype in the RS group were not statistically different from those in the RP group.

CONCLUSIONS

In Korean epileptics, there was no significant relationship between three known SNPs in MDR1 and drug resistance. And there was no association of MDR1 haplotype based on above three sites with pharmacoresistance.

High baseline serum total and LDL cholesterol levels are associated with MDR1 haplotypes in Brazilian hypercholesterolemic individuals of European descent

The MDR1 gene encodes the P-glycoprotein, an efflux transporter with broad substrate specificity. P-glycoprotein has raised great interest in pharmacogenetics because it transports a variety of structurally divergent drugs, including lipid-lowering drugs. The synonymous single-nucleotide polymorphism C3435T and the nonsynonymous single-nucleotide polymorphism G2677T/A in MDR1 have been indicated as potential determinants of variability in drug disposition and efficacy. In order to evaluate the effect of G2677T/A and C3435T MDR1 polymorphisms on serum levels of lipids before and after atorvastatin administration, 69 unrelated hypercholesterolemic individuals from São Paulo city, Brazil, were selected and treated with 10 mg atorvastatin orally once daily for four weeks. MDR1 polymorphisms were analyzed by PCR-RFLP. C3435T and G2677T polymorphisms were found to be linked. The allelic frequencies for C3435T polymorphism were 0.536 and 0.464 for the 3435C and 3435T alleles, respectively, while for G2677T/A polymorphism allele frequencies were 0.580 for the 2677G allele, 0.384 for the 2677T allele and 0.036 for the 2677A allele. There was no significant relation between atorvastatin response and MDR1 polymorphisms (repeated measures ANOVA; P > 0.05). However, haplotype analysis revealed an association between T/T carriers and higher basal serum total (TC) and LDL cholesterol levels (TC: 303 +/- 56, LDL-C: 216 +/- 57 mg/dl, respectively) compared with non-T/T carriers (TC: 278 +/- 28, LDL-C: 189 +/- 24 mg/dl; repeated measures ANOVA/Tukey test; P < 0.05). These data indicate that MDR1 polymorphism may have an important contribution to the control of basal serum cholesterol levels in Brazilian hypercholesterolemic individuals of European descent.

Genotype and Allele Frequencies of C3435T Polymorphism of the MDR1 Gene in Various Jewish Populations of Israel

The human multidrug-resistant gene (MDR1) encodes for P-glycoprotein (P-gp), which is a membrane-bound efflux-transporter conferring resistance to a number of natural cytotoxic drugs and potentially toxic xenobiotics. The wobble C3435T polymorphism at exon 26 was associated with different expression levels of the MDR1 gene and substrate uptake. Differences in allele frequencies of the C3435T polymorphism have previously been demonstrated between racial groups. In this study, 500 individuals from 5 Jewish populations of Israel (Ashkenazi, Yemenite, North African, Mediterranean, Near-Eastern) were examined for C3435T polymorphism using a PCR-RFLP-based technique to calculate genotype and allele frequencies. Frequencies of the C allele were quite similar among the Ashkenazi (0.65), Yemenite (0.645), and North-African (0.615) Jewish populations. However, the frequency of this allele was slightly lower among Mediterranean Jews (0.58) and significantly lower among Near-Eastern Jews (0.445). The frequency of the C allele among Near-Eastern Jews is, therefore, significantly different from those of all other tested Jewish populations. In comparison to previously studied non-Jewish populations, the frequency of this allele among Near-Eastern Jews is different from that in West Africans (0.91) but is similar to that in whites (0.497). However, the C allele frequencies among the other 4 Jewish populations are significantly lower than that found among West Africans and significantly higher than among non-Jewish whites. These data may have important therapeutic and prognostic implication for P-gp-related drug dosage recommendation in Jewish populations.

Pharmacogenomics of MDR1/ABCB1 gene: the influence on risk and clinical outcome of haematological malignancies

Pharmacogenomics is a rapidly developing field of biomedical research, which investigates phenotypic and pharmacodynamic consequences of the genetic variations among individuals. The multi-drug resistance-1, MDR1 (ABCB1) gene belongs to ATP-binding cassette (ABC) family and encodes for membrane transporter P-glycoprotein (P-gp). A wide array of P-gp substrates comprises toxic xenobiotics and numerous commonly used medications including anti-cancer drugs. Under physiological conditions P-gp protects cells against toxins, whereas in malignant cells P-gp confers multi-drug resistance phenotype. Moreover, characteristic tissue localisation enables P-gp to influence the uptake, tissue distribution and elimination of P-gp transported drugs. A number of recent studies identified variety of single nucleotide polymorphisms (SNPs) in the MDR1 gene and demonstrated significant ethnic differences in their allelic frequency distribution. Furthermore, it was shown that some of these SNPs, especially silent C3435T polymorphism in exon 26, may alter P-gp expression and transport activity. Consequently, it is likely that specific functional MDR1 haplotypes may result with altered exposure to toxins and drugs, thus influencing predisposition to certain diseases as well as efficacy or toxicity of pharmacotherapy. In this paper, we focus on the available data concerning the impact of MDR1 polymorphism on the risk and clinical outcome of haematological malignancies. The structure and function of P-gp as well as results of studies addressing the relevance of MDR1 polymorphism in non-haematological disorders are also briefly discussed.

MDR-1 C3435T polymorphism influences cyclosporine a dose requirement in liver-transplant recipients

BACKGROUND

Cyclosporine A (CsA) is characterized by high interindividual variations in oral bioavailability and a narrow therapeutic index. CsA is a substrate for P-glycoprotein, a member of the ABC transporter family encoded by the multiple drug-resistant gene MDR1.

METHODS

Because MDR1 gene exon 26 C3435T polymorphism influences intestinal P-glycoprotein expression, we investigated whether this polymorphism was correlated with variation in CsA dose requirement and concentration/dose ratio in 44 liver-transplant recipients during 1 month after transplantation. CsA concentration was measured 2 hours after administration (C2), according to international recommendations.

RESULTS

The MDR-1 wild-type genotype (3435CC) was observed in 15 patients (34%), whereas 21 (48%) patients were heterozygous (3435CT), and 8 (18%) patients were homozygous for the mutation (3435TT). There was no significant difference between the three groups regarding corticosteroids treatment or renal function during this period. One to 3 days after liver transplantation, when every patient received a similar CsA weight-adjusted dose, the concentration/dose ratio was correlated with exon 26 single nucleotide polymorphism and was significantly higher in subjects homozygous for the mutation (P=0.012). This was confirmed 1 month after transplantation (P=0.049), when the dose was adjusted to maintain the C2 target level of 1,000 microg/L and we observed that TT patients required approximately 50% lower weight-adjusted CsA dose than wild-type patients (P=0,033).

CONCLUSIONS

These findings demonstrate that the MDR1 exon 26 C3435T polymorphism is a major determinant of CsA concentration/dose ratio in liver-transplant recipients and is predictive of the dose of CsA to be administered to achieve the target C(2) concentration.

[MDR1 genotypes related to pharmacokinetics and MDR1 expression]

The multidrug-resistant transporter encoded by the MDR1 gene belongs to the ATP-binding cassette superfamily of membrane transporters. It is involved not only in the acquisition of multidrug-resistance phenotypes in cancer cells but also in normal tissues such as the brain, kidneys, liver, and intestines. This transporter has the potential to export unnecessary or toxic exogenous substances or metabolites, and in the intestine it is thought to play a role in limiting the oral absorption of a number of structurally unrelated drugs. In 2000, Hoffmeyer et al. performed a systemic screening for MDR1 polymorphisms and suggested that a single-nucleotide polymorphism (SNP) in exon 26 of the MDR1 gene (C3435T) was associated with a lower level of intestinal MDR1 expression, and thereby with lower plasma concentrations of digoxin after oral administration. At present, over 20 SNPs have been found in the MDR1 gene. Clinical studies on the effects of C3435T on MDR1 expression and function in the tissues, and consequently on the pharmacokinetics, have been performed worldwide. In this review, the latest reports concerning the relationship of MDR1 genotypes with pharmacokinetics and MDR1 expression are summarized. Our experimental results demonstrate the importance of genetic polymorphisms at positions 3435 and 2677 in the MDR1 gene on pharmacokinetics and intestinal MDR1 expression. In the future, haplotype analysis of the MDR1 gene and subsequent classification of subjects are needed for individualized pharmacotherapy based on MDR1 genotyping.

MDR1 Ala893 polymorphism is associated with inflammatory bowel disease

Crohn disease (CD) and ulcerative colitis (UC) are overlapping chronic inflammatory bowel diseases (IBDs). Suggestive evidence for linkage at chromosome 7q has been reported for both CD and UC. Contained within this region is the gene for MDR1 (multidrug resistance), a membrane transport protein for which human polymorphisms have been reported in Ala893Ser/Thr and C3435T that alter pharmacokinetic profiles for a variety of drugs. Because mdr1 knockout mice spontaneously develop colitis, exonic regions were resequenced and tested for IBD association in a large, multicenter North American cohort. Two missense mutations, Asn21Asp and Ala893Ser/Thr, as well as the expression-associated polymorphism C3435T, described elsewhere, were genotyped in the entire cohort. Significant association of Ala893 with IBD was observed by both case-control analysis (P=.002) and the pedigree disequilibrium test (PDT [P=.00020-.00030]) but not for the Asn21Asp or C3435T polymorphisms. Significant association by PDT was observed within the subset with CD (P=.0014-.00090), with similar, nonsignificant trends in a smaller subset with UC. The Ala893Ser/Thr variant is triallelic, and the associated, common allele is Ala893, with undertransmission of the 893Ser (common) and the 893Thr (rare) variants. The Ala893 variant has decreased activity compared with the 893Ser variant; therefore, the association with human IBD is consistent with the murine model of mdr1 deficiency. Taken together, these data support the association of the common Ala893 polymorphism with IBD specifically and, more broadly, provides additional support for its contribution to interindividual pharmacogenetic variation.

Pharmacogenetics of MDR1 and its impact on the pharmacokinetics and pharmacodynamics of drugs

The multi-drug resistant transporter MDR1/P-glycoprotein, the gene product of MDR1, is a glycosylated membrane protein of 170 kDa, belonging to the ATP-binding cassette (ABC) superfamily of membrane transporters. MDR1 was originally isolated from resistant tumor cells as part of the mechanism of multi-drug resistance, but over the last decade, it has been elucidated that human MDR1 is also expressed throughout the body to confer intrinsic resistance to the tissues by exporting unnecessary or toxic exogeneous substances or metabolites. A number of various types of structurally unrelated drugs are substrates for MDR1, and MDR1 and other transporters are recognized as an important class of proteins for regulating pharmacokinetics and pharmacodynamics. In 2000, Hoffmeyer et al. performed a systemic screening for MDR1 polymorphisms and indicated that a single nucleotide polymorphism (SNP), C3435T in exon 26, which caused no amino acid change, was associated with the duodenal expression of MDR1 and thereby the plasma concentrations of digoxin after oral administration. Interethnic differences in genotype frequencies of C3435T have been clarified, and, at present, a total of 28 SNPs have been found at 27 positions on the MDR1 gene. Clinical studies on the effects of C3435T on MDR1 expression and function in the tissues, and also on the pharmacokinetics and pharmacodynamics have been performed around the world; however, there are still discrepancies in the results, suggesting that the haplotype analysis of the gene should be included instead of SNP detection, and the design of clinical trials must be carefully planned to avoid misinterpretations. A polymorphism of C3435T is also reported to be a risk factor for a certain class of diseases such as the inflammatory bowel diseases, Parkinson's disease and renal epithelial tumor, and this might also be explained by the effects on MDR1 expression and function. In this review, the latest reports are summarized for the future individualization of pharmacotherapy based on MDR1 genotyping.