Associations between common variants in the MDR1 (ABCB1) gene and ulcerative colitis among North Indians. Pharmacogenet Genomics. 2009;19:77-85. [PMID: 19005421 DOI: 10.1097/fpc.0b013e32831a9abe]

Pharmacogenetic Study of the Impact of ABCB1 Single Nucleotide Polymorphisms on the Response to Cyclosporine in Psoriasis Patients

Psoriasis is a chronic, T cell-mediated skin disease affecting 2-3% of the Caucasian population. Cyclosporine A is a calcineurin inhibitor that acts selectively on T cells. The cyclosporine A treatment response has been suggested to be modulated by single-nucleotide polymorphisms (SNPs) in the ABCB1 gene. The aim of this research was to evaluate the effect of ABCB1 genetic variants that could affect the response to a cyclosporine treatment in Russian psoriasis patients with the ABCB1 genotype status. The ABCB1 T-129C, G1199A, C1236T, G2677T/A and C3435T SNPs in the 168 patients with psoriasis were genotyped by PCR-RFLP (polymerase chain reaction-restriction fragment length polymorphism) and TaqMan SNP genotyping assays. The ABCB1 C1236T, G2677T/A and C3435T SNPs were significantly associated with a negative response to cyclosporine therapy. A very strong association was evident for the C3435T SNP in the ABCB1 gene in the allele, dominant and recessive models (OR = 2.58, OR = 4.01, OR = 2.50, respectively). ABCB1 C1236T and G2677T/A polymorphisms were significantly associated with a negative response to the cyclosporine therapy in the codominant, dominant and recessive models (p ˂ 0.05). Additionally, the haplotype analysis identified that the TGC haplotype is significantly associated with a negative response to cyclosporine therapy in psoriasis patients (p ˂ 0.05). The current study to the best of our knowledge is the first of its kind to be performed in the Russian population. In conclusion, the present results suggest an association between the ABCB1 genetic variants and unresponsiveness to cyclosporine in the Russian population. Further, larger studies are necessary to confirm our findings and replicate them in various ethnic populations before its implementation in the clinical practice.

Inflammatory bowel disease: An Indian perspective

Inflammatory bowel disease (IBD) in recent times is causing a significant healthcare burden as both ulcerative colitis and Crohn's disease (CD) require lifelong therapy and constant monitoring. The current review highlights the concerns in a country like India with special reference to the changing trends of IBD, risk attribution and the financial issues. Indian immigrants behave like residential Indians, whereas their children show IBD prevalence similar to the West, highlighting the role of environmental triggers. However, the environmental and genetic factors in Indians with IBD are not well understood. Men appear to be more frequently affected than women in India. The disease severity is milder in the patients, both males and females, but the risk for colorectal cancer (CRC) is similar to the West. The incidence of paediatric IBD is on the rise. The major burden of IBD in the Indian subcontinent at present is in children, adolescents and teens. Cost towards the management of complications, non-adherence to treatment, differentiating tuberculosis from CD and finally screening for CRC in patients with IBD are the points to ponder in the Indian scenario.

Genetic variation in the farnesoid X-receptor predicts Crohn's disease severity in female patients

The farnesoid X receptor (FXR) is implicated in Crohn's disease (CD) pathogenesis. It is unclear how genetic variation in FXR impacts CD severity versus genetic variation in nuclear receptors such as pregnane X receptor (PXR) and the multi-drug resistance protein 1 (MDR1, ABCB1). To evaluate FXR-1G > T as a genomic biomarker of severity in CD and propose a plausible molecular mechanism. A retrospective study (n = 542) was conducted in a Canadian cohort of CD patients. Genotypic analysis (FXR-1G > T, MDR1 3435C > T and PXR -25385C > T) as well as determination of the FXR downstream product, fibroblast growth factor (FGF) 19 was performed. Primary outcomes included risk and time to first CD-related surgery. The effect of estrogen on wild type and variant FXR activity was assessed in HepG2 cells. The FXR-1GT genotype was associated with the risk of (odds ratio, OR = 3.34, 95% CI = 1.58–7.05, p = 0.002) and earlier progression to surgery (hazard ratio, HR = 3.00, 95% CI = 1.86–4.83, p < 0.0001) in CD. Female carriers of the FXR-1GT genotype had the greatest risk of surgery (OR = 14.87 95% CI = 4.22–52.38, p < 0.0001) and early progression to surgery (HR = 6.28, 95% CI = 3.62–10.90, p < 0.0001). Women carriers of FXR-1GT polymorphism had a three-fold lower FGF19 plasma concentration versus women with FXR-1GG genotype (p < 0.0001). In HepG2 cells cotransfected with estrogen receptor (ER) and FXR, presence of estradiol further attenuated variant FXR activity. MDR1 and PXR genotypes were not associated with surgical risk. Unlike MDR1 and PXR, FXR-1GT genetic variation is associated with earlier and more frequent surgery in women with CD. This may be through ER-mediated attenuation of FXR activation.

MDR1 gene polymorphisms are associated with ulcerative colitis in a cohort of Serbian patients with inflammatory bowel disease

Background

Inflammatory bowel disease (IBD) is a chronic disease of unknown etiology in which genetic factors contribute to development of disease. Single nucleotide polymorphisms (SNPs) in multidrug resistance 1 (MDR1) gene encoding transporter P-glycoprotein have been associated with IBD, but their role in disease susceptibility remains unclear. Therefore, the aim of this study was to investigate the association of three MDR1 polymorphisms, C1236T (rs1128503), G2677T/A (rs2032582) and C3435T (rs1045642), with Serbian IBD patients.

Methods

A total of 206 IBD patients, 107 Crohn's disease (CD) and 99 ulcerative colitis (UC), and 255 healthy controls were included in the study. All subjects were genotyped using TaqMan SNP genotyping assays. Comparisons between the groups were performed using the Pearson Chi-square test. False discovery rate according to Benjamini-Hochberg procedure was applied to adjust for multiple comparisons.

Results

Carriers of T allele of all three MDR1 SNPs were more common in UC patients compared to healthy controls, suggesting predisposing role of T allele of these SNPs in UC pathogenesis. Consistently, TT genotype of C1236T and TTT haplotype were also found more frequently in UC patients. On the other hand, C allele and CC genotype of C1236T and C3435T, as well as G allele and GG genotype of G2677T/A were more frequent in healthy subjects, implying protective role of these variants in UC. Likewise, CGC haplotype and CGC/CGC diplotype were more frequent in controls. Contrary to UC, no statistical difference was observed between CD patients and controls in any of the SNPs analyzed.

Conclusion

MDR1 gene variants and haplotypes were associated with UC in Serbian IBD patients, further supporting their potential role in susceptibility to UC.

Epidemiology of Inflammatory Bowel Disease in India: The Great Shift East

BACKGROUND

Inflammatory bowel disease (IBD), once considered to be a Western disease, is increasingly being reported from India and other Asian countries. The present review summarizes epidemiology and disease characteristics of IBD in India with reference to other Asian countries and the West.

SUMMARY

India is projected to have one of the highest disease burden of IBD across the globe. The overall genetic risk and microbial signature in Indian IBD patients are similar to those of patients in the West as demonstrated by the similar incidence of IBD in second-generation Indian immigrants and matching perturbations in the structural and functional component of gut microbiota in Indian studies. The concept of the hygiene hypothesis continues to remain controversial with Indian studies demonstrating contradictory findings. The disease characteristics, long-term outcomes including the risk of colorectal cancer, and the effect of pregnancy on IBD and vice versa in Indian patients with IBD are in general similar with few differences. Unlike patients in the West, very few Indian patients have a positive family history.

KEY MESSAGE

The Indian disease pattern is going through a phase of epidemiological transition with a surge in the incidence of IBD. The epidemiology and disease characteristics of IBD mirror the patterns observed in the West.

P-glycoprotein multidrug transporter in inflammatory bowel diseases: More questions than answers

The gastrointestinal barrier is constantly exposed to numerous environmental substrates that are foreign and potentially harmful. These xenobiotics can cause shifts in the intestinal microbiota composition, affect mucosal immune responses, disturb tissue integrity and impair regeneration. The multidrug transporter ABCB1/MDR1 p-glycoprotein (p-gp) plays a key role at the front line of host defence by efficiently protecting the gastrointestinal barrier from xenobiotic accumulation. This Editorial discusses how altered expression and function of ABCB1/MDR1 p-gp may contribute to the development and persistence of chronic intestinal inflammation in inflammatory bowel diseases (IBD). Recent evidence implies multiple interactions between intestinal microbiota, innate immunity and xenobiotic metabolism via p-gp. While decreased efflux activity may promote disease susceptibility and drug toxicity, increased efflux activity may confer resistance to therapeutic drugs in IBD. Mice deficient in MDR1A develop spontaneously chronic colitis, providing a highly valuable murine IBD model for the study of intestinal epithelial barrier function, immunoregulation, infectious co-triggers and novel therapeutic approaches. Possible associations of human ABCB1 gene polymorphisms with IBD susceptibility have been evaluated, but results are inconsistent. Future studies must focus on further elucidation of the pathophysiological relevance and immunological functions of p-gp and how its ambiguous effects could be therapeutically targeted in IBD.

Inflammatory bowel disease in India - Past, present and future

There is rising incidence and prevalence of inflammatory bowel disease (IBD) in India topping the Southeast Asian (SEA) countries. The common genes implicated in disease pathogenesis in the West are not causal in Indian patients and the role of "hygiene hypothesis" is unclear. There appears to be a North-South divide with more ulcerative colitis (UC) in north and Crohn's disease (CD) in south India. IBD in second generation Indian migrants to the West takes the early onset and more severe form of the West whereas it retains the nature of its country of origin in migrants to SEA countries. The clinical presentation is much like other SEA countries (similar age and sex profile, low positive family history and effect of smoking, roughly similar disease location, use of aminosalicylates for CD, low use of biologics and similar surgical rates) with some differences (higher incidence of inflammatory CD, lower perianal disease, higher use of aminosalicylates and azathioprine and lower current use of corticosteroids). UC presents more with extensive disease not paralleled in severity clinically or histologically, follows benign course with easy medical control and low incidence of fulminant disease, cancer, complications, and surgery. UC related colorectal cancer develop in an unpredictable manner with respect to disease duration and site questioning the validity of strict screening protocol. About a third of CD patients get antituberculosis drugs and a significant number presents with small intestinal bleed which is predominantly afflicted by aggressive inflammation. Biomarkers have inadequate diagnostic sensitivity and specificity for both. Pediatric IBD tends to be more severe than adult. Population based studies are needed to address the lacunae in epidemiology and definition of etiological factors. Newer biomarkers and advanced diagnostic techniques (in the field of gastrointestinal endoscopy, molecular pathology and genetics) needs to be developed for proper disease definition and treatment.

Identification of critical variants within SLC44A4, an ulcerative colitis susceptibility gene identified in a GWAS in north Indians

SLC44A4 is one of the seven novel susceptibility genes that were discovered in the first ever genome-wide association study (GWAS) on ulcerative colitis (UC) in the genetically distinct north Indians. This gene seems to be functionally relevant to disease biology as it may contribute to the associated phenotype of Vitamin B1 deficiency among UC patients, hence playing a role in disease pathogenesis. A large number of single-nucleotide polymorphisms (SNPs) are known to be distributed throughout this gene, but the functional status of most are not known. Thus, an extensive investigation of structural and regulatory variants within this gene was undertaken in this study to identify the critical variants amongst them using a combination of fine mapping, in silico and in vitro approaches. A few intronic SNPs were predicted to have regulatory roles on the basis of in silico analysis, suggesting that they may be the critical variants within SLC44A4. This highlights the importance of this gene in UC biology, thus confirming the finding of the GWAS and also warranting additional studies.

Genetic Polymorphisms of Multidrug Resistance Gene-1 (MDR1/ABCB1) and Glutathione S-Transferase Gene and the Risk of Inflammatory Bowel Disease among Moroccan Patients

Inflammatory bowel diseases (IBD) are multifactorial disorders resulting from environmental and genetic factors. Polymorphisms in MDR1 and GSTs genes might explain individual differences in susceptibility to IBD. We carried out a case-control study to examine the association of MDR1 (C1236T and C3435T), GSTT1, and GSTM1 polymorphisms with the risk of IBD. Subjects were genotyped using PCR-RFLP for MDR1 gene and multiplex PCR for GSTT1 and GSTM1. Meta-analysis was performed to test the association of variant allele carriage with IBD risk. We report that GSTT1 null genotype is significantly associated with the risk of CD (OR: 2.5, CI: 1.2–5, P = 0.013) and UC (OR: 3.5, CI: 1.5–8.5, P = 0.004) and can influence Crohn's disease behavior. The interaction between GSTT1 and GSTM1 genes showed that the combined null genotypes were associated with the risk of UC (OR: 3.1, CI: 1.1–9, P = 0.049). Furthermore, when compared to combined 1236CC/CT genotypes, the 1236TT genotype of MDR1 gene was associated with the risk of UC (OR: 3.7, CI: 1.3–10.7, P = 0.03). Meta-analysis demonstrated significantly higher frequencies of 3435T carriage in IBD patients. Our results show that GSTT1 null and MDR1 polymorphisms could play a role in susceptibility to IBD.

Genome-wide association scan in north Indians reveals three novel HLA-independent risk loci for ulcerative colitis

OBJECTIVE

Over 100 ulcerative colitis (UC) loci have been identified by genome-wide association studies (GWASs) primarily in Caucasians (CEUs). Many of them have weak effects on disease susceptibility, and the bulk of the heritability cannot be ascribed to these loci. Very little is known about the genetic background of UC in non-CEU groups. Here we report the first GWAS on UC in a genetically distinct north Indian (NI) population.

DESIGN

A genome-wide scan was performed on 700 cases and 761 controls. 18 single-nucleotide polymorphisms (SNPs) (p<5×10(-5)) were genotyped in an independent cohort of 733 cases and 1148 controls. A linear mixed model was used for case-control association tests.

RESULTS

Seven novel human leucocyte antigen (HLA)-independent SNPs from chromosome 6, located in 3.8-1, BAT2, MSH5, HSPA1L, SLC44A4, CFB and NOTCH4, exceeded p<5×10(-8) in the combined analysis. To assess the independent biological contribution of such genes from the extended HLA region, we determined the percentage alternative pathway activity of complement factor B (CFB), the top novel hit. The activity was significantly different (p=0.01) between the different genotypes at rs12614 in UC cases. Transethnic comparisons revealed a shared contribution of a fraction of UC risk genes between NI and CEU populations, in addition to genetic heterogeneity.

CONCLUSIONS

This study shows varying contribution of the HLA region to UC in different populations. Different environmental exposures and the characteristic genetic structure of the HLA locus across ethnic groups collectively make it amenable to the discovery of causative alleles by transethnic resequencing. This may lead to an improved understanding of the molecular mechanisms underlying UC.

Is the ABCB1 gene associated with the increased risk of gastric cancer development?--preliminary research

One of the most common malignant diseases, both worldwide and in Poland, is gastric cancer. The pathogenesis of gastric cancer development is not entirely clear. Next to the environmental risk factors, such as Helicobacter pylori infection or dietary habits, the host genetic factors as predispositions to gastric cancer development are discussed. A transmembrane protein that could be associated with predisposition to cancer development is P-glycoprotein (P-gp). Physiologically, P-gp is present in normal tissue of the gastrointestinal tract, where it plays a protective role by transporting xenobiotics from a cell into extracellular environment. P-gp is encoded by the highly polymorphic ABCB1 gene. The most frequent polymorphisms at positions 1236, 2677, and 3435 may affect both the function and amount of protein, thereby leading to a loss of its physiological function, which could increase the predisposition to development of many diseases, including cancer. In this study, the potential significance of the ABCB1 gene in the development and progression of gastric cancer was evaluated. In 19 tissue samples collected from patients with gastric cancer, the ABCB1 gene polymorphisms were identified at positions 1236 and 2677 by automated sequencing and SNP 3435 by the RFLP method. The relative level of ABCB1 expression was measured in 10 samples of gastric cancer and morphologically normal tissues by real-time PCR. For SNPs at positions 1236, 2677, and 3435, no statistically significant differences in genotype frequencies between gastric cancer patients and healthy individuals were found. However, genotype TT for all studied polymorphisms occurred more frequently in the group of gastric cancer patients (31.6, 26.3, 42.1%, respectively) than in the group of healthy individuals (14.6, 13.5, 21.9%, respectively). The lowest relative expression levels of ABCB1 mRNA were observed for genotypes CC of SNP 1236, CC of SNP 3435, and GG of SNP 2677 (median: 0.215, 0.160, 0.160, respectively). There was a tendency that mutant homozygote TT for SNPs at positions 1236, 2677, and 3435 occurred more frequently in the subgroup of patients with Tis or stage I of TNM classification (SNP 1236 p = 0.0760; SNP 2677 p = 0.0813; SNP 3435 p = 0.0760) than in the subgroup of patients with stage II or III. Also the expression levels were lowest (median 0.740) in the group of patients with the less advanced clinical stage of cancer (Tis or I). Preliminary research showed that the ABCB1 gene polymorphisms at positions 1236, 2677, and 3435 were not related to an increased susceptibility of gastric cancer development. However, they may be associated with the inhibition of gastric cancer progression.

Population and genomic lessons from genetic analysis of two Indian populations

Indian demographic history includes special features such as founder effects, interpopulation segregation, complex social structure with a caste system and elevated frequency of consanguineous marriages. It also presents a higher frequency for some rare mendelian disorders and in the last two decades increased prevalence of some complex disorders. Despite the fact that India represents about one-sixth of the human population, deep genetic studies from this terrain have been scarce. In this study, we analyzed high-density genotyping and whole-exome sequencing data of a North and a South Indian population. Indian populations show higher differentiation levels than those reported between populations of other continents. In this work, we have analyzed its consequences, by specifically assessing the transferability of genetic markers from or to Indian populations. We show that there is limited genetic marker portability from available genetic resources such as HapMap or the 1,000 Genomes Project to Indian populations, which also present an excess of private rare variants. Conversely, tagSNPs show a high level of portability between the two Indian populations, in contrast to the common belief that North and South Indian populations are genetically very different. By estimating kinship from mates and consanguinity in our data from trios, we also describe different patterns of assortative mating and inbreeding in the two populations, in agreement with distinct mating preferences and social structures. In addition, this analysis has allowed us to describe genomic regions under recent adaptive selection, indicating differential adaptive histories for North and South Indian populations. Our findings highlight the importance of considering demography for design and analysis of genetic studies, as well as the need for extending human genetic variation catalogs to new populations and particularly to those with particular demographic histories.

Regulatory pathways for ATP-binding cassette transport proteins in kidney proximal tubules

The ATP-binding cassette transport proteins (ABC transporters) represent important determinants of drug excretion. Protective or excretory tissues where these transporters mediate substrate efflux include the kidney proximal tubule. Regulation of the transport proteins in this tissue requires elaborate signaling pathways, including genetic, epigenetic, nuclear receptor mediated, posttranscriptional gene regulation involving microRNAs, and non-genomic (kinases) pathways triggered by hormones and/or growth factors. This review discusses current knowledge on regulatory pathways for ABC transporters in kidney proximal tubules, with a main focus on P-glycoprotein, multidrug resistance proteins 2 and 4, and breast cancer resistance protein. Insight in these processes is of importance because variations in transporter activity due to certain (disease) conditions could lead to significant changes in drug efficacy or toxicity.

Genetics of inflammatory bowel disease in Asia: systematic review and meta-analysis

BACKGROUND

Inflammatory bowel diseases (IBD) result from an interaction between genetic and environmental factors. Preliminary findings suggest that susceptibility genes differ between IBD patients in Asia and the West. We aimed to evaluate disease-predisposing genes in Asian IBD patients.

METHODS

A systematic review and meta-analysis were performed of published studies from 1950 to 2010 using keyword searches in MEDLINE, EMBASE, EBM Reviews, and BIOSIS Previews.

RESULTS

In all, 477 abstracts were identified and data extracted from 93 studies, comprising 17,976 IBD patients and 27,350 age- and sex-matched controls. Major nucleotide oligomerization domain (NOD)-2 variants in Western Crohn's disease (CD) patients were not associated with CD in Han Chinese, Japanese, South Korean, Indian, and Malaysian populations. New NOD2 mutations were, however, associated with CD in Malaysians (JW1), Han Chinese, and Indians (P268S). Autophagy-related protein 16-linked 1 (ATG16L1) was not associated with CD in East Asians (odds ratio [OR] 0.97; 95% confidence interval [CI] 0.84-1.13). Interleukin (IL)-23R was associated with CD in South Koreans (OR 1.8; 95% CI 1.16-2.82) and a single nucleotide polymorphism in IL-23R (Gly149Arg) was protective of CD in Han Chinese (OR 0.3; 95% CI 0.15-0.60). Tumor necrosis factor (TNF) superfamily gene-15 (SF15) polymorphisms were associated with CD (OR 2.68; 95% CI 1.86-3.86), while TNF-308 polymorphisms (OR 1.82; 95% CI 1.15-2.9), cytotoxic T lymphocyte antigen (CTLA)-4 (OR 2.75; 95% CI 1.22-6.22) and MICA allele (OR 2.41; 95% CI 1.89-3.07) were associated with ulcerative colitis in Asians.

CONCLUSIONS

Genetic mutations of IBD in Asians differ from Caucasians. New mutations and susceptibility genes identified in Asian IBD patients provide an opportunity to explore new disease-associated mechanisms in this population of rising incidence.

Is there evidence to claim or deny association between variants of the multidrug resistance gene (MDR1 or ABCB1) and inflammatory bowel disease?

BACKGROUND

Inflammatory bowel disease (IBD) is a complex disease with a genetic background. Crohn's disease (CD) and ulcerative colitis (UC) are the two main types of IBD. There is indication that variants in the MDR1 gene are associated with development of IBD. However, the 20 published genetic association studies (GAS) for the three most popular variants in the MDR1 gene (C3435T, G2677T/A, and C1236T) have produced inclusive results.

METHODS

In order to decrease the uncertainty of pooled risk effects and to explore the trend and stability of the risk effects, a meticulous meta-analysis, including cumulative and recursive cumulative meta-analysis, of the GAS related to the MDR1 gene with susceptibility to IBD was conducted. The risk effects were estimated based on the odds ratio (OR) of the allele contrast and the generalized odds ratio (OR(G) ).

RESULTS

The analysis showed marginal significant association for the C3435T variant in UC: the risk estimate for the allele contrast was OR = 1.11 (1.00-1.22) and OR(G) = 1.12 (1.01-1.27), indicating that a subject with high mutational load has a 12% higher probability of being diseased. The respective cumulative meta-analysis indicated a downward trend of association, as evidence accumulates with the association being significant during the whole published period. The cumulative meta-analysis for the other variants showed lack of any trend of association. However, the recursive cumulative meta-analysis showed that there is no sufficient evidence for denying or claiming an association for all variants.

CONCLUSIONS

More evidence is needed to draw safe conclusions regarding the association of MDR1 variants and development of IBD.

Inter and intra-ethnic differences in the distribution of the molecular variants of TPMT, UGT1A1 and MDR1 genes in the South Indian population

Molecular variants of polymorphic drug metabolizing enzymes and drug transporters are attributed to differences in individual's therapeutic response and drug toxicity in different populations. We sought to determine the genotype and allele frequencies of polymorphisms for major phase II drug-metabolizing enzymes (TPMT, UGT1A1) and drug transporter (MDR1) in South Indians. Allelic variants of TPMT (*2,*3A,*3B,*3C & *8), UGT1A1 (TA)6>7 and MDR1 (2677G>T/A & 3435C>T) were evaluated in 450-608 healthy South Indian subjects. Genomic DNA was extracted by phenol-chloroform method and genotype was determined by PCR-RFLP, qRT-PCR, allele specific PCR, direct sequencing and SNaPshot techniques. The frequency distributions of TPMT, UGT1A1 and MDR1 gene polymorphisms were compared between the individual 4 South Indian populations viz., Tamilian, Kannadiga, Andhrite and Keralite. The combined frequency distribution of the South Indian populations together, was also compared with that of other major populations. The allele frequencies of TPMT*3C, UGT1A1 (TA)7, MDR1 2677T, 2677A and 3435T were 1.2, 39.8, 60.3, 3.7, and 61.6% respectively. The other variant alleles such as TPMT*2, *3A, *3B and *8 were not identified in the South Indian population. Sub-population analysis showed that the distribution of UGT1A1 (TA)6>7 and MDR1 allelic variants differed between the four ethnic groups. However, the frequencies of TPMT*3C allele were similar in the four South Indian populations. The distribution of TPMT, UGT1A1 and MDR1 gene polymorphisms of the South Indian population was significantly different from other populations.

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).

Associations between variants in the ABCB1 (MDR1) gene and corticosteroid dependence in children with Crohn's disease

BACKGROUND

Corticosteroids (CS) effectively induce remission in patients with moderate to severe Crohn's disease (CD). However, CS dependence in children is a significant clinical problem associated with numerous side effects. Identification of molecular markers of CS dependence is of paramount importance. The ABCB1 gene codes for P-glycoprotein, a transporter involved in the metabolism of CS. We examined whether DNA variation in the ABCB1 gene was associated with CS dependency in children with CD.

METHODS

A retrospective study was carried out in two Canadian tertiary pediatric gastroenterology centers. Clinical information was abstracted from medical charts of CD patients (N = 260) diagnosed with CD prior to age 18 and administered a first course of CS during the 1 year since diagnosis. Patients were classified as CS-dependent if they relapsed during drug tapering or after the end of therapy. DNA was extracted from blood or saliva. Thirteen tagging single nucleotide polymorphisms (tag-SNPs) and a synonymous variation (C3435T) in the ABCB1 gene were genotyped. Allelic, genotype, and haplotype associations were examined using logistic regression and Haploview.

RESULTS

Tag-SNP rs2032583 was statistically significantly associated with CS dependency. The rare C allele of this SNP (odds ratio [OR] = 0.56, 95% confidence interval [CI]: 0.34-0.95, P = 0.029) and heterozygous genotype TC (OR = 0.52, 95% CI: 0.28-0.95, P = 0.035) conferred protection from CS dependency. A three-marker haplotype was significantly associated with CS dependence (multiple comparison corrected P-value = 0.004).

CONCLUSIONS

Our results suggest that the ABCB1 gene may be associated with CS dependence in pediatric CD patients.

Drug transporters and renal drug disposition in the newborn

The individual response to a drug in terms of drug efficacy and toxicity is highly variable; this represents a major problem in clinical practice. Potential causes for such variability include pathogenesis and severity of the disease being treated, drug interactions, patient age, nutritional status, renal and liver function and concomitant illness. Inherited differences in drug metabolism and genetic polymorphism of targets of drug therapy can have even greater influence on the efficacy and toxicity of medications. We will discuss the role of drug transporters (organic anion transporting polypeptides and Pgp), drug-related gene polymorphisms and pathologies, renal function and drug metabolism in a very special patient population, the newborn. Reliable predictions of drug pharmacokinetics in the newborn, derived from an understanding of the transport mechanisms, should allow therapeutic agents to be used more safely in this special population.

Advances in understanding the correlation between multi-drug resistance gene and ulcerative colitis

The etiology and pathogenesis of ulcerative colitis remain unclear. It has been reported that multiple drug resistant 1a (MDR 1a) knockout mice are susceptible to developing a spontaneous ulcerative colitis (UC). The incidence of C3435T gene mutation in the MDR1 gene in UC patients is significantly higher than that in healthy controls. The C3435T gene mutation can lead to decreased expression of P-glycoprotein (P-gp). The expression of P-gp in the peripheral blood lymphocytes and intestinal mucosal epithelial cells is higher in hormone-resistant UC patients than in hormone-sensitive UC patients and healthy controls. Thus, a hypothesis was proposed that the MDR1 gene polymorphism may correlate with the occurrence and progression of UC and the sensitivity to hormone therapy in UC patients. However, this hypothesis is still controversial.