Impact of Promoter Polymorphisms on the Transcriptional Regulation of the Organic Cation Transporter OCT1 (SLC22A1).
ABSTRACT: The organic cation transporter 1 (OCT1, SLC22A1) is strongly expressed in the human liver and facilitates the hepatic uptake of drugs such as morphine, metformin, tropisetron, sumatriptan and fenoterol and of endogenous substances such as thiamine. OCT1 expression is inter-individually highly variable. Here, we analyzed SNPs in the OCT1 promoter concerning their potential contribution to the variability in OCT1 expression. Using electrophoretic mobility shift and luciferase reporter gene assays in HepG2, Hep3B, and Huh7 cell lines, we identified the SNPs -1795G>A (rs6935207) and -201C>G (rs58812592) as having effects on transcription factor binding and/or promoter activity. The A-allele of the -1795G>A SNP showed allele-specific binding of the transcription factor NF-Y leading to 2.5-fold increased enhancer activity of the artificial SV40 promoter. However, the -1795G>A SNP showed no significant effects on the native OCT1 promoter activity. Furthermore, the -1795G>A SNP was not associated with the pharmacokinetics of metformin, fenoterol, sumatriptan and proguanil in healthy individuals or tropisetron efficacy in patients undergoing chemotherapy. Allele-dependent differences in USF1/2 binding and nearly total loss in OCT1 promoter activity were detected for the G-allele of -201C>G, but the SNP is apparently very rare. In conclusion, common OCT1 promoter SNPs have only minor effects on OCT1 expression.
Project description:Insulin-sensitizer treatment with metformin is widely used in polycystic ovary syndrome (PCOS). However, the treatment effectiveness shows individual differences in PCOS patients. Organic cation transporter (OCT) 1 and 2 have been reported to mediate metformin transport in the liver and kidney, respectively. In this study, we investigated the association between the polymorphisms of OCT1 and OCT2 and the treatment effectiveness of metformin in PCOS patients. The single nucleotide polymorphisms (SNPs) of OCT1 (rs683369 and rs628031) and OCT2 (rs316019) were analyzed in 87 PCOS and 113 control women. Oral glucose tolerance tests (OGTTs), which represented metformin treatment response, were conducted at the start of treatment and after six-month treatment. The results demonstrated that the SNP frequencies of OCT1 and OCT2 were not associated with PCOS pathophysiology, and that the polymorphisms of OCT1 and OCT2 were not associated with the OGTT parameters at baseline. However, PCOS patients with the G allele of OCT1 rs683369 and/or with the A allele of OCT1 rs628031 had increased insulin sensitivity compared to those with wild-type genotype after receiving metformin treatment. Moreover, the interactions of metformin*SNP were significant in both OCT1 rs683369 (p < 0.001) and rs628031 (p = 0.001) during the treatment period. Taken together, genetic polymorphisms of OCT1 contributed to different metformin treatment responses, and further study is needed to establish personalized treatment programs using a pharmacogenomic algorithm approach in PCOS patients.
Project description:Genetic variation in OCT1 can influence the glycemic response to metformin. We evaluated the effects of the OCT1 single-nucleotide polymorphisms (SNPs), rs1867351, rs4709400, rs628031, and rs2297374, on metformin efficacy in type-2 diabetes mellitus (DM) patients.We performed a single-center prospective analysis of the distributions of these SNPs in a cohort of Han Chinese subjects in Shanghai, China (HCS), and evaluated the effects of each SNP on glycemic control in HCS DM patients following 3 months of incident metformin treatment.The allele frequencies of rs4709400 and rs628031 in our HCS control group differed from those previously reported for Han Chinese subjects in Beijing (HCB), as well as those previously reported for Caucasians and Africans, whereas the allele frequencies of rs1867351 and rs2297374 were more similar to those in HCB subjects. The DM patients with the rs1867351 T/T or rs4709400 G/G genotype exhibited greater reductions in postprandial plasma glucose (PPG), compared to those with different genotypes of these SNPs. The DM patients with the rs2297374 C/T, rs4709400 G/G, or rs628031 G/G genotype exhibited greater reductions in fasting plasma glucose (FPG), and those with the rs1867351 T/T, rs628031 A/A, or rs2297374 C/T genotype exhibited greater reductions in HbA1c , compared to those with different genotypes of these SNPs. Conclusions /interpretation: The rs1867351, rs4709400, rs628031, and rs2297374 SNPs of OCT1 have selective effects on FPG, PPG, and HbA1c in HCS DM patients in response to metformin treatment. Future studies of these SNPs in larger samples of HCS DM patients are warranted.
Project description:Background and Aims: Metformin is the most widely-used anti-diabetic drug in the United States. However, medication management fails to achieve therapeutic goals in ~20% of patients. This study attempted to identify genetic polymorphisms associated with metformin treatment failure. We studied the associations between polymorphisms in two liver and kidney organic cation transporter genes (OCT1 & OCT2) and two kidney multidrug and toxin extrusion transporter genes, (MATE1 & MATE2K) and response to metformin monotherapy. Methods: At Kaiser Permanente Southeast and Marshfield Clinic Research Foundation we identified 304 type 2 diabetes (T2DM) patients on metformin monotherapy who: were enrolled for >=6 months prior to initiation; remained on metformin >= 90 days following initiation; and had a HgbA1c measured prior to first metformin prescription and then after initiation. From this group we selected 171 patients who had not received metformin or other anti-diabetics previously, and had baseline HbA1c levels >7.0% prior to metformin initiation. We genotyped 10 SNPs, and assessed response by measuring absolute and relative change in HbA1c after after metformin initiation. Results: Three SNPs were identified that were significantly associated with reduced response to metformin, after adjustment for baseline HbA1c, dose, and ethnicity. In a dominant model, heterozygosity or homozygosity for minor A allele in the MATE1 intronic SNP, rs2289669, resulted in a smaller absolute change in HbA1c (mean of 0.45% less reduction in absolute change in HbA1c; 95% CI 0.17 to 0.74%) compared to individuals homozygous for major G allele. In a recessive model, homozygosity for minor A allele in MATE2K 5?-UTR SNP, rs12943590, resulted in smaller absolute change in HbA1c (mean of 0.43% less reduction in absolute change in HbA1c, 95% CI 0.053 to 0.86%). The reduced function SNPs in OCT1 & OCT2 were not associated with metformin response, except for rs34059508 (G465R). This SNP showed a positive (but not statistically significant) association with smaller absolute change in HbA1c (mean of 0.49%; 95% CI ?0.06354 to 1.045%). Conclusions: These three variants of metformin transporter genes may be important for personalizing treatment for patients with T2DM. A replication study in a larger population is currently being planned.
Project description:The organic cation transporter 1 (OCT1), also known as solute carrier family 22 member 1, is strongly and specifically expressed in the human liver. Here we show that the hepatocyte nuclear factor 1 (HNF1) regulates OCT1 transcription and contributes to the strong, liver-specific expression of OCT1. Bioinformatic analyses revealed strong conservation of HNF1 binding motifs in an evolutionary conserved region (ECR) in intron 1 of the OCT1 gene. Electrophoretic mobility shift and chromatin immunoprecipitation assays confirmed the specific binding of HNF1 to the intron 1 ECR. In reporter gene assays performed in HepG2 cells, the intron 1 ECR increased SV40 promoter activity by 22-fold and OCT1 promoter activity by 13-fold. The increase was reversed when the HNF1 binding sites in the intron 1 ECR were mutated or the endogenous HNF1? expression was downregulated with small interfering RNA. Following HNF1? overexpression in Huh7 cells, the intron 1 ECR increased SV40 promoter activity by 11-fold and OCT1 promoter activity by 6-fold. Without HNF1? overexpression, the increases were only 3- and 2-fold, respectively. Finally, in human liver samples, high HNF1 expression was significantly correlated with high OCT1 expression (r = 0.48, P = 0.002, n = 40). In conclusion, HNF1 is a strong regulator of OCT1 expression. It remains to be determined whether genetic variants, disease conditions, or drugs that affect HNF1 activity may affect the pharmacokinetics and efficacy of OCT1-transported drugs such as morphine, tropisetron, ondansetron, tramadol, and metformin. Beyond OCT1, this study demonstrates the validity and usefulness of interspecies comparisons in the discovery of functionally relevant genomic sequences.
Project description:BACKGROUND:Genetic variants of the organic cation transporter (OCT1) gene could influence interindividual variation in clinical response to metformin therapy. The genetic basis for the single-nucleotide polymorphism (SNP) of OCT1 gene has been established in other populations, but it remains to be elucidated in the Indian population. This study is focused on OCT1 gene variants rs2282143 (P341L, 1022C>T), rs628031 (M408V, 1222A>G) and rs622342 (1386C>A) frequency distributions in the South Indian Tamilian population. MATERIALS AND METHODS:A total of 112 unrelated healthy subjects of South Indian Tamilian origin, aged 18-60 years, of either sex were recruited for the study. Genotyping was determined using the quantitative real time-polymerase chain reaction and polymerase chain reaction followed by restriction fragment length polymorphism methods. RESULTS:Allele frequencies of rs2282143, rs628031and rs622342 polymorphisms were 8.9%, 80.3% and 24.5%, respectively. Interethnic differences in the genotype and allele frequencies of OCT1 gene polymorphism were observed when compared with other major populations. The SNPs rs2282143, T allele and rs628031, G allele were more common in Asians (5.5-16.8% and 76.2-81%) and African Americans (8.2% and 73.5%) than in Caucasians (0-2% and 57.4-60%). CONCLUSION:This is the first time the frequency of OCT1 gene polymorphism was determined in the Indian population, and is similar to the frequencies observed in African-Americans and other Asian populations but different from those in Caucasians. The data observed in this study would justify further pharmacogenetic studies to potentially evaluate the role of OCT1 gene polymorphism in the therapeutic efficacy of metformin.
Project description:BACKGROUND:Genetic variation in the genes that encode metformin transporters has been proven to cause pharmacokinetic variability and various glycemic response to metformin. Organic Cation Transporter (OCT) 1 protein encoded by the SLC22A1 gene is primarily responsible for the process of metformin influx to the hepatocytes as the target of antihyperglycemic action as well as metformin elimination through the renal. This study aimed to determine the allele frequency distribution of the SLC22A1 Met420del gene in OCT1 among the Javanese population, the largest ethnic group in Indonesia with T2DM. METHODS:The research involved 100 adult patients from 9 healthcare facilities in Yogyakarta Province. The PCR-RFLP method was employed as a genotype analysis to detect polymorphism using 5'-AGGTTCACGGACTCTGTGCT-3' forward primer and 5'-AAGCTGGAGTGTGCGATCT-3' reverse primer. RESULTS:No AA variant (wild type) type was found in the SLC22A1 Met420del gene, and only 4% of the subjects had Aa heterozygote type. The allele frequencies of A and a were 2.0% and 98.0% in all subjects, respectively. CONCLUSION:The allele frequencies in the Javanese-Indonesian population were almost the same as those in the studies involving Japanese, Chinese-Han, and Asian-American populations. This study recommends further research on the correlation between the influence of methionine deletion at codon 420 on the variability of pharmacokinetic profiles and the glycemic response to metformin as well as the incidence of gastrointestinal intolerance due to metformin administration.
Project description:Metformin is among the most widely prescribed drugs for the treatment of type 2 diabetes. Organic cation transporter 1 (OCT1) plays a role in the hepatic uptake of metformin, but its role in the therapeutic effects of the drug, which involve activation of AMP-activated protein kinase (AMPK), is unknown. Recent studies have shown that human OCT1 is highly polymorphic. We investigated whether OCT1 plays a role in the action of metformin and whether individuals with OCT1 polymorphisms have reduced response to the drug. In mouse hepatocytes, deletion of Oct1 resulted in a reduction in the effects of metformin on AMPK phosphorylation and gluconeogenesis. In Oct1-deficient mice the glucose-lowering effects of metformin were completely abolished. Seven nonsynonymous polymorphisms of OCT1 that exhibited reduced uptake of metformin were identified. Notably, OCT1-420del (allele frequency of about 20% in white Americans), previously shown to have normal activity for model substrates, had reduced activity for metformin. In clinical studies, the effects of metformin in glucose tolerance tests were significantly lower in individuals carrying reduced function polymorphisms of OCT1. Collectively, the data indicate that OCT1 is important for metformin therapeutic action and that genetic variation in OCT1 may contribute to variation in response to the drug.
Project description:Purpose:Organic cation transporters (Octs) use cations like endogenous compounds, toxins, and drugs, such as metformin, as substrates. Therefore, these proteins determine the pharmacokinetics and -dynamics of metformin and thus its efficacy. Of note, metformin is today the most commonly used pharmaceutical in the treatment of type 2 diabetes (T2DM) with nevertheless a great variability in clinical response, which attributes to genetic variances. The aim of this study was to determine the influence of intronic OCT1 SNPs on prevalence of all-cause and cardiovascular death. Patients and Methods:Genotypes of 27 intronic SNPs in OCT1 were investigated in the LURIC study, a prospective cohort of 3316 participants scheduled for coronary angiography. We investigated whether these variants were associated with all-cause and cardiovascular death in 73 individuals with T2DM under metformin therapy, in individuals without diabetes, individuals with T2DM and individuals with T2DM without metformin therapy. Results:In a multivariate Cox regression analysis adjusted for classical cardiovascular risk factors, 4 intronic OCT1 SNPs were significantly associated with all-cause and cardiovascular mortality in individuals with T2DM on metformin therapy. Conclusion:According to their OCT1 genotype, some individuals with T2DM on metformin therapy might be prone to an increased risk of cardiovascular death.
Project description:Metformin is the most widely prescribed medication for the treatment of type 2 diabetes (T2D). However, gastrointestinal (GI) side effects develop in ~25% of patients treated with metformin, leading to the discontinuation of therapy in ~5% of cases. We hypothesized that reduced transport of metformin via organic cation transporter 1 (OCT1) could increase metformin concentration in the intestine, leading to increased risk of severe GI side effects and drug discontinuation. We compared the phenotype, carriage of reduced-function OCT1 variants, and concomitant prescribing of drugs known to inhibit OCT1 transport in 251 intolerant and 1,915 fully metformin-tolerant T2D patients. We showed that women and older people were more likely to be intolerant to metformin. Concomitant use of medications, known to inhibit OCT1 activity, was associated with intolerance (odds ratio [OR] 1.63 [95% CI 1.22-2.17], P = 0.001) as was carriage of two reduced-function OCT1 alleles compared with carriage of one or no deficient allele (OR 2.41 [95% CI 1.48-3.93], P < 0.001). Intolerance was over four times more likely to develop (OR 4.13 [95% CI 2.09-8.16], P < 0.001) in individuals with two reduced-function OCT1 alleles who were treated with OCT1 inhibitors. Our results suggest that reduced OCT1 transport is an important determinant of metformin intolerance.
Project description:<h4>Background and purpose</h4>The organic cation transporter 1 (OCT1) transports cationic drugs into hepatocytes. The high hepatic expression of OCT1 is controlled by the HNF4? and USF transcription factors. Pregnane X receptor (PXR) mediates induction of the principal xenobiotic metabolizing enzymes and transporters in the liver. Here, we have assessed the down-regulation of OCT1 expression by PXR activation.<h4>Experimental approach</h4>We used primary human hepatocytes and related cell lines to measure OCT1 expression and activity, by assaying MPP(+) accumulation. Western blotting, qRT-PCR, the OCT1 promoter gene reporter constructs and chromatin immunoprecipitation assays were also used.<h4>Key results</h4>OCT1 mRNA in human hepatocytes was down-regulated along with reduced [(3) H]MPP(+) accumulation in differentiated HepaRG cells after treatment with rifampicin. Rifampicin and hyperforin as well as the constitutively active PXR mutant T248D suppressed activity of the 1.8 kb OCT1 promoter construct in gene reporter assays. Silencing of both PXR and HNF4? in HepaRG cells blocked the PXR ligand-mediated down-regulation of OCT1 expression. The mutation of HNF4? and USF1 (E-box) responsive elements reversed the PXR-mediated inhibition in gene reporter assays. Chromatin immunoprecipitation assays indicated that PXR activation sequestrates the SRC-1 coactivator from the HNF4? response element and E-box of the OCT1 promoter. Consistent with these findings, exogenous overexpression of the SRC-1, but not the PGC1? coactivator, relieved the PXR-mediated repression of OCT1 transactivation.<h4>Conclusions and implications</h4>PXR ligands reduced the HNF4?-mediated and USF-mediated transactivation of OCT1 gene expression by competing for SRC-1 and decreased delivery of a model OCT1 substrate into hepatocytes.