Association of the Q141K polymorphism of the ABCG2 gene with the effectiveness of urate-lowering therapy in patients with gout (a pilot study)

Achieving the target serum uric acid (UA) level is a priority in the treatment of gout.Objective: to study the relationship of the ABCG2 gene polymorphism (rs2231142) with the efficacy of allopurinol and febuxostat in patients with gout.Patients and methods. The study included 82 patients with gout over 18 years of age with serum UA level >360 μmol/L who did not take uratelowering therapy.All patients were prescribed allopurinol 100 mg daily, followed by its titration until the target UA level was reached (<360 μmol/L or <300 μmol/L in patients with chronic tofus gout), up to a maximum of 900 mg/day, in patients with glomerular filtration rate <60 ml/min/1.73 m2 – up to 300 mg/day. Patients who did not reach the target UA level when using allopurinol were prescribed febuxostat 80 mg/day, which, if necessary, was increased to 120 mg/day. Monitoring of each patient was continued until the target serum UA level was reached.All patients underwent genotyping of the C>A polymorphism (rs2231142) of the ABCG2 gene. We compared the probability of achieving the target UA level, the mean values of a decrease in the serum UA level, and the mean doses of urate-lowering drugs in patients with different genotypes (CC, CA, AA) of the ABCG2 gene.Results and discussion. The target UA level in 45 (55%) of 82 patients was defined as <300 μmol/L, in the remaining 37 – as <360 μmol/L.In 26 patients, the dose of allopurinol did not exceed 300 mg/day. In 28 (34%) patients treated with allopurinol, the target UA level was achieved, in the remaining 54 (66%) patients, allopurinol was substituted by febuxostat, and in 22 (41%) of them the UA level decreased and was below the target.The CC genotype of the ABCG2 gene was detected in 51 (62%) patients, the CA genotype in 30 (37%) and the minor genotype AA in 1 (1%).The probability of achieving the target UA level during therapy with allopurinol in carriers of homozygous CC genotype and genotypes CA or AA did not differ: 17 (33%) and 11 (35%) cases, respectively, but patients with CA and AA genotypes required a significantly higher dose of allopurinol (365±102 mg/day) than patients with the CC genotype (290±85 mg/day), p=0.002. Of the 54 patients who took febuxostat and did not reach the target UA level, 30 (56%) had the CC genotype and 24 (44%) had the CA genotype, the probability of reaching the target UA level was also comparable (p=0.22).Conclusion. The probability of reaching the target serum UA level in patients with gout taking allopurinol is not associated with the C>A polymorphism of the ABCG2 gene, but the presence of CA and AA genotypes is identified with a higher dose of the drug. The C>A (rs2231142) polymorphism of the ABCG2 gene does not affect the ability to achieve the goal of therapy when using febuxostat in patients with allopurinol ineffectiveness.

Impact of ABCG2 Gene Polymorphism on the Predisposition to Psoriasis

Psoriasis is a chronic inflammatory disease which is caused by the interaction between genetic and environmental factors. Evidence shows an association of psoriasis with co-morbidities including cardiovascular diseases, metabolic syndrome and hyperuricemia. Genome-wide association studies have revealed that the ABCG2 gene encoding ATP-binding cassette G2 protein was associated with inflammation and higher serum urate concentrations. In this study, we aimed to evaluate the role of ABCG2 gene polymorphisms on the susceptibility to psoriasis. The genotype distribution of two ABCG2 single nucleotide polymorphisms (SNPs), rs2231142 and rs2231137, was examined in 410 psoriasis patients and 1,089 gender-matched non-psoriasis controls. We found that heterozygotes (GT) for rs2231142 was associated with a decreased risk of psoriasis (p = 0.001; adjusted OR = 0.532; 95% CI, 0.370–0.765) after adjusting for age, as compared with homozygotes for the major allele (GG). Subjects who carried at least one polymorphic allele (homozygote or heterozygote for the minor allele) were less susceptible to psoriasis (p = 0.002; adjusted OR = 0.594; 95% CI, 0.249–0.823) and bearing higher serum urate levels (p = 0.026) than those homozygous for the major allele. Our results indicated that the ABCG2 gene polymorphism was associated with the risk of psoriasis.

Effects of ABCB1 and ABCG2 polymorphisms on the pharmacokinetics of abemaciclib

Aim: The adverse events of the CKD4/6 inhibitor abemaciclib are known to be dose dependent. However, its pharmacokinetics vary among individuals. Abemaciclib is reported to be transported by P-glycoprotein (P-gp) and the breast cancer resistance protein (BCRP). Therefore, we evaluated whether ABCB1 and ABCG2 gene polymorphisms could be pharmacokinetic predictive factors of abemaciclib. Methods: A total of 45 patients with breast cancer able to take abemaciclib (150 mg twice daily) for 2 weeks were evaluated to determine the association among abemaciclib concentrations, adverse events, and ABCB1 1236T>C, 2677G>T/A, 3435C>T, and ABCG2 421C>A gene polymorphisms. Results: The trough concentrations of abemaciclib were higher in the group with grade 2 or greater neutropenia, anemia, and thrombocytopenia as compared with the group with grades 0 or 1. No significant association was observed between ABCB1 1236T>C, 3435C>T, and ABCG2 421C>A gene polymorphisms and abemaciclib concentrations. However, in ABCB1 2677G>T/A polymorphisms, the concentrations of abemaciclib tended to be higher in the homozygous group (AA + AT) as compared with that in the wild-type and heterozygous group (GG + GA + GT) [222.8 (80.5–295.8) ng/mL vs. 115.8 (23.6–355.2) ng/mL, P = 0.11]. Hence, the ABCB1 2677G>T/A homozygous group had a significantly higher incidence of abemaciclib withdrawal and dose reduction within 4 weeks as compared than the wild-type and heterozygous group (67% vs. 33%, P = 0.03). Conclusions: The gene polymorphism of ABCB1 2677G> T/A might be a predictor of the pharmacokinetics and tolerability of abemaciclib.

POS0352 ALLELIC VARIANTS IN THE ABCG2 GENE CAN LEAD TO HYPERURICEMIA AND GOUT

Background:The level of uric acid is largely determined by the functions of urate transporters, which are located in the kidney and intestine. The ABCG2 protein is the major excretor of uric acid and its dysfunction may lead to the development of hyperuricemia and gout.Objectives:The aim of our study was to detect the occurrence and frequency of allelic variants in the ABCG2 gene that can lead to impaired function of the ABCG2 protein and to the development of hyperuricemia and gout.Methods:We examined allelic variants of ABCG2 using PCR amplification and Sanger sequencing of all coding regions and exon-intron boundaries in 359 patients with primary hyperuricemia and gout.Results:We found a rare in-frame deletion p.K360del and 15 missense variants, two of which were common (p.V12M, p.Q141K) and 13 were very rare (p.M71V, p.G74D, p.M131I, p.R147W, p.T153M, p.I242T, p.R236X, p.F373C, p.T421A, p.T434M, p.S476P, p.S572R, p.D620N). The p.R236X variant leads to a premature stop codon. The p.V12M variant probably has a protective effect against gout (minor allele frequency – MAF – in our cohort = 0,025 / MAF in the European population = 0,061), while the p.Q141K variant increases the risk of gout (MAF in our cohort = 0,213 / MAF in the European population = 0,094) (1). As for the rare variants, the p.R147W, p.T153M, p.F373C, p.T434M, p.S476P and p.S572R according to functional analyzes reduce the function of the ABCG2 protein (2). Based on in silico prediction, the impact on reduced function is expected for variants p.M71V, p.G74D, p.M131I, p.R147W, p.I242T, p.F373C, p.T434M, p.S476P and p.S572R.Conclusion:Our data suggest that the common variant p.Q141K and most of the rare variants in the ABCG2 gene affect the function of the ABCG2 urate transporter and are a genetic risk factor for hyperuricemia and gout.References:[1]Stiburkova B, et al. Functional non-synonymous variants of ABCG2 and gout risk. Rheumatology (Oxford). 2017 Nov 1; 56(11):1982-1992.[2]Toyoda Y, et al. Functional characterization of clinically-relevant rare variants in ABCG2 identified in a gout and hyperuricemia cohort. Cells. 2019 Apr 18;8(4).Acknowledgements:This study was supported by the project for conceptual development of research organization 00023728 (Institute of Rheumatology) and RVO VFN64165.Disclosure of Interests:None declared

Amplification of ABCG2 Transporter Gene Exon 8 and 14 of Diabetic Patients

Diabetes is a serious illness affecting over 425 million people worldwide. Diabetes develops as a result of the failure of the pancreatic β-cells to produce the hormone insulin in the amount required to meet the body's needs. As a consequence of insulin deficiency, blood sugar levels rise and lead into macro vascular and micro vascular diseases of the kidneys, heart, eyes and nerves with passage of time. Elevated serum uric acid level is related with a variety of adverse health outcomes which includes gout, hypertension, diabetes mellitus, metabolic syndrome and cardiovascular diseases. Several genome-wide association studies on uric acid levels have implicated the ATP-binding cassette, subfamily G, member 2 (ABCG2) gene as being possibly causal. The aim of present study was to amplify exon 8 and exon 14 of ABCG2 gene of diabetic patients. Blood samples were collected from diabetic type II patients (n=25). Genomic DNA was extracted from blood using Phenol-Chloroform method, followed by amplification of Exon 8 and exon 14 was using Polymerase Chain Reaction (PCR). The size of amplified genes of DNA was analyzed by Gel Electrophoresis and then observed under gel documentation through UV rays.

ABCG2 polymorphism, age and leukocyte count may contribute to oral mucositis in oncopediatric patients

The study investigated the relationship between genetic polymorphisms and the development of oral mucositis in pediatric patients undergoing chemotherapy involving methotrexate. A longitudinal study was conducted with 64 patients, and oral mucositis was evaluated by the modified Oral Assessment Guide, which aims to diagnose and classify oral mucositis. Epithelial cells were obtained by mouthwash and DNA was extracted. The polymorphisms MTHFR (rs1801133), DNMT3B (rs2424913), ABCC2 (rs717620), ABCG2 (rs2231137) and ABCG2 (rs2231142) were analyzed by PCR-RFLP method. Demographic, hematological and biochemical data were collected from medical records. Statistical analysis was performed using the SPSS software adopting a p-value of 0.05. Male sex predominated (56.2%), and the mean age was 10.8 years (± 4.9). Oral mucositis affected 65.6% of the patients, of which 61.9% developed the severe form of the disease. For the ABCG2 gene (rs2231142), the rare A allele and CA genotype were more frequent in individuals with mucositis (p= 0.02; RR = 0.60; CI = 0.387 - 0.813). The severity of the disease was mainly observed in younger patients (median = 9 years; p=0.02). Patients with severe oral mucositis presented lower leukocytes count (median = 2.150 mm3) compared to patients with the mild/moderate form (median = 4.200 mm3; p=0.03). Female patients and each 10,000-platelet increase were protective factors against the onset of oral mucositis (p=0.02). It is concluded that rs2231142 polymorphism increases the likelihood of oral mucositis and younger patients and patients with low leukocytes counts are more likely to develop severe form.

The Effects of Three ABCG2 Polymorphisms on Outcome of Central Nervous System Relapses in Iranian Children With Acute Lymphoblastic Leukemia Receiving High Dose Methotrexate

Methotrexate (MTX) is the main drug for the treatment of childhood acute lymphoblastic leukemia (ALL). ABCG2 pump is the main transporter of MTX on BBB. Our aim was to investigate the possible relationship between three polymorphisms of the ABCG2 gene, and isolated CNS relapses in Iranian children with ALL receiving high dose MTX. Genotyping of three polymorphisms of the ABCG2 gene, including G34A, C376T, and C421A, was performed by the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method for 56 patients. A high frequency of C376T CT genotype was observed among the patients. There was no significant association between C376T and C421 and isolated CNS relapse (P>0.05). C376T and C421A polymorphisms are not associated with isolated CNS relapse in childhood ALL.

Mutagenesis Analysis of ABCG2 Gene Promoter of Zebrafish (Danio Rerio)

Breast cancer is the commonest cancer among women worldwide and the probability of a woman dying from breast cancer is high (about 1 in 38 of total human population (2.6%)).The main factor for mortality is due to the resistance of this particular disease to chemotherapeutic agents. One of the most well-known proteins to be found to correlate significantly with breast cancer resistance to chemotherapeutic agent is the ATP-binding cassette super-family G member 2 (ABCG2). Knowledge on ABCG2 gene regulation is still lacking in terms of how the increased cytotoxic levels are closely related to induce a hype in gene transcript levels and ultimately cause of the reduction in chemotherapeutic agents. The approach taken in this study is through mutational analysis of selected transcription factor governing the expression of ABCG2. In order to achieve this, a previously cloned ABCG2 promoter which has been isolated (around 1500 bp in size) from Danio rerio and inserted into pGL3.0 plasmid, was subjected to site-directed mutagenesis. Selected transcription factor which is AP-1 was successfully mutated by deletion of 5'- TGACGCG -3' sequence at position 1113 bp from TSS+1 where it would bind in order to define their role in ABCG2 physiological function. Sequencing result after site-directed mutagenesis shows high similarities about 98% with ABCG2 gene of Danio rerio. Upon validation, it was found that the intended AP-1 binding site has been mutated. In future work, the mutated clone here will be subjected to transfection analysis where dual-luciferase assay will be conducted to verify the loss of activity from the ABCG2 promoter upon mutation of the targeted AP-1 site. Hence, the mutagenesis analysis of ABCG2 promoter are able to provide information on the involvement of AP-1 transcription factor in multidrug resistance mechanism of breast cancer and thus will be a potential target for chemotherapeutic agent.