Common variants in SLC17A3 gene affect intra-personal variation in serum uric acid levels in longitudinal time series

Linkage analysis using whole exome sequencing data implicates SLC17A1, SLC17A3, TATDN2 and TMEM131L in type 1 diabetes in Kuwaiti families

Type 1 diabetes (T1D) is characterized by the progressive destruction of pancreatic β-cells, leading to insulin deficiency and lifelong dependency on exogenous insulin. Higher estimates of heritability rates in monozygotic twins, followed by dizygotic twins and sib-pairs, indicate the role of genetics in the pathogenesis of T1D. The incidence and prevalence of T1D are alarmingly high in Kuwait. Consanguineous marriages account for 50-70% of all marriages in Kuwait, leading to an excessive burden of recessive allele enrichment and clustering of familial disorders. Thus, genetic studies from this Arab region are expected to lead to the identification of novel gene loci for T1D. In this study, we performed linkage analyses to identify the recurrent genetic variants segregating in high-risk Kuwaiti families with T1D. We studied 18 unrelated Kuwaiti native T1D families using whole exome sequencing data from 86 individuals, of whom 37 were diagnosed with T1D. The study identified three potential loci with a LOD score of ≥ 3, spanning across four candidate genes, namely SLC17A1 (rs1165196:pT269I), SLC17A3 (rs942379: p.S370S), TATDN2 (rs394558:p.V256I), and TMEM131L (rs6848033:p.R190R). Upon examination of missense variants from these genes in the familial T1D dataset, we observed a significantly increased enrichment of the genotype homozygous for the minor allele at SLC17A3 rs56027330_p.G279R accounting for 16.2% in affected children from 6 unrelated Kuwaiti T1D families compared to 1000 genomes Phase 3 data (0.9%). Data from the NephQTL database revealed that the rs1165196, rs942379, rs394558, and rs56027330 SNPs exhibited genotype-based differential expression in either glomerular or tubular tissues. Data from the GTEx database revealed rs942379 and rs394558 as QTL variants altering the expression of TRIM38 and IRAK2 respectively. Global genome-wide association studies indicated that SLC17A1 rs1165196 and other variants from SLC17A3 are associated with uric acid concentrations and gout. Further evidence from the T1D Knowledge portal supported the role of shortlisted variants in T1D pathogenesis and urate metabolism. Our study suggests the involvement of SLC17A1, SLC17A3, TATDN2, and TMEM131L genes in familial T1D in Kuwait. An enrichment selection of genotype homozygous for the minor allele is observed at SLC17A3 rs56027330_p.G279R variant in affected members of Kuwaiti T1D families. Future studies may focus on replicating the findings in a larger T1D cohort and delineate the mechanistic details of the impact of these novel candidate genes on the pathophysiology of T1D.

Effects of genetic and nongenetic factors on hyperuricemia in Chinese patients with coronary artery disease

Aim: The relationship between hyperuricemia and polymorphisms of transporter genes in coronary artery disease (CAD) patients in China remains unclear. Materials & methods: A total of 258 hyperuricemia patients with CAD and 242 control patients with CAD were recruited in this case-control study. Twenty-four SNPs in genes of ABCG2, PDZK1, URAT1, OAT4, GLUT9, ABCC4, NPT1 and NPT4 were genotyped using direct sequencing in all subjects. Results: The mutation of ABCG2 rs2231142 locus increases the risk of hyperuricemia, and there is a gene dose effect in the influence of mutant heterozygotes and homozygotes. rs3825017 in URAT1 and rs62293298 in GLUT9 were also confirmed to be associated with hyperuricemia. Conclusion: Age, weight, creatinine clearance rate, diuretics and SNPs on ABCG2, URAT1 and GLUT9 were all risk factors of hyperuricemia.

Function of Uric Acid Transporters and Their Inhibitors in Hyperuricaemia

Disorders of uric acid metabolism may be associated with pathological processes in many diseases, including diabetes mellitus, cardiovascular disease, and kidney disease. These diseases can further promote uric acid accumulation in the body, leading to a vicious cycle. Preliminary studies have proven many mechanisms such as oxidative stress, lipid metabolism disorders, and rennin angiotensin axis involving in the progression of hyperuricaemia-related diseases. However, there is still lack of effective clinical treatment for hyperuricaemia. According to previous research results, NPT1, NPT4, OAT1, OAT2, OAT3, OAT4, URAT1, GLUT9, ABCG2, PDZK1, these urate transports are closely related to serum uric acid level. Targeting at urate transporters and urate-lowering drugs can enhance our understanding of hyperuricaemia and hyperuricaemia-related diseases. This review may put forward essential references or cross references to be contributed to further elucidate traditional and novel urate-lowering drugs benefits as well as provides theoretical support for the scientific research on hyperuricemia and related diseases.

An update of genetics, co-morbidities and management of hyperuricaemia

Hyperuricaemia (HU) caused by disorders of purine metabolism is a metabolic disease. A number of epidemiological reports have confirmed that HU is correlated with multiple disorders, such as chronic kidney diseases, cardiovascular disease and gout. Recent studies showed that the expression and functional changes of uric acid transporters, including URAT1, GLUT9 and ABCG2, were associated with HU. Moreover, a large number of genome-wide association studies have shown that these transporters' dysfunction leads to HU. In this review, we describe the recent progress of aetiology and related transporters of HU, and we also summarise the common co-morbidities possible mechanisms, as well as the potential pharmacological and non-pharmacological treatment methods for HU, aiming to provide new ideas for the treatment of HU.

Assessment of diagnostic biomarkers of liver injury in the setting of microcystin-LR (MC-LR) hepatotoxicity

Microcystin-leucine arginine (MC-LR) is a potent liver toxin produced by freshwater cyanobacteria, also known as blue-green algae. While harmful algal blooms are increasing in frequency and severity worldwide, there is still no established method for the diagnosis and assessment of MC-LR induced liver damage. The guidelines for MC-LR safe exposure limits have been previously established based on healthy animal studies, however we have previously demonstrated that pre-existing non-alcoholic fatty liver disease (NAFLD) increases susceptiblity to the hepatotoxic effects of MC-LR. In this study, we sought to investigate the suitability of clinically used biomarkers of liver injury, specifically alanine aminotransferase (ALT) and alkaline phosphatase (ALP), as potential diagnostic tools for liver damage induced by chronic low dose administration of MC-LR in the setting of pre-existing NAFLD. In our Leprdb/J mouse model of NAFLD, we found that while MC-LR induced significant histopathologic damage in the setting of NAFLD, gene expression of ALT and ALP failed to increase with MC-LR exposure. Serum ALT and ALP also failed to increase with MC-LR exposure, except for a moderate increase in ALP with the highest dose of MC-LR used (100 μg/kg). In HepG2 human liver epithelial cells, we observed that increasing MC-LR exposure levels do not lead to an increase in ALT or ALP gene expression, intracellular enzyme activity, or extracellular activity, despite a significant increase in MC-LR induced cytotoxicity. These findings demonstrate that ALT and ALP may be unsuitable as diagnostic biomarkers for MC-LR induced liver damage.

Gender, body mass index, and PPARγ polymorphism are good indicators in hyperuricemia prediction for Han Chinese

Hyperuricemia is closely associated with obesity and metabolic abnormalities, which is also an independent risk factor for cardiovascular diseases. The PPARγ gene, which is linked to obesity and metabolic abnormalities in Han Chinese, might be considered a top candidate gene that is involved in hyperuricemia. This study recruited 457 participants, aged 20-40 years old, to investigate the associations of the PPARγ gene and metabolic parameters with hyperuricemia. Three tag-single nucleotide polymorphisms, rs2292101, rs4684846, and rs1822825, of the PPARγ gene were selected to explore their association with hyperuricemia. Risk genotypes on rs1822825 of the PPARγ gene exhibited statistical significance with hyperuricemia (odds ratio: 1.9; 95% confidence interval: 1.05-3.57). Although gender, body mass index (BMI), serum total cholesterol concentration, or protein intake per day were statistically associated with hyperuricemia, the combination of BMI, gender, and rs1822825, rather than that of age, serum lipid profile, blood pressure, and protein intake per day, satisfied the predictability for hyperuricemia (sensitivity: 69.3%; specificity: 83.7%) in Taiwan-born obese Han Chinese. BMI, gender, and the rs1822825 polymorphism in the PPARγ gene appeared good biomarkers in hyperuricemia; therefore, these powerful indicators may be included in the prediction of hyperuricemia to increase the accuracy of the analysis.

Common missense variant of monocarboxylate transporter 9 (MCT9/SLC16A9) gene is associated with renal overload gout, but not with all gout susceptibility

Gout is a common disease caused by hyperuricemia, which shows elevated serum uric acid (SUA) levels. From a viewpoint of urate handling in humans, gout patients can be divided into those with renal overload (ROL) gout with intestinal urate underexcretion, and those with renal underexcretion (RUE) gout. Recent genome-wide association studies (GWAS) revealed an association between SUA and a variant in human monocarboxylate transporter 9 (MCT9/SLC16A9) gene. Although the function of MCT9 remains unclear, urate is mostly excreted via intestine and kidney where MCT9 expression is observed. In this study, we investigated the relationship between a variant of MCT9 and gout in 545 patients and 1,115 healthy volunteers. A missense variant of MCT9 (K258T), rs2242206, significantly increased the risk of ROL gout (p = 0.012), with odds ratio (OR) of 1.28, although it revealed no significant association with all gout cases (p = 0.10), non-ROL gout cases (p = 0.83), and RUE gout cases (p = 0.34). In any case groups and the control group, minor allele frequencies of rs2242206 were >0.40. Therefore, rs2242206 is a common missense variant and is revealed to have an association with ROL gout, indicating that rs2242206 relates to decreased intestinal urate excretion rather than decreased renal urate excretion. Our study provides clues to better understand the pathophysiology of gout as well as the physiological roles of MCT9.

Clinical consequences of mutations in sodium phosphate cotransporters

Three families of sodium phosphate cotransporters have been described. Their specific roles in human health and disease have not been defined. Review of the literature reveals that the type II sodium phosphate cotransporters play a significant role in transepithelial transport in a number of tissues including kidney, intestine, salivary gland, mammary gland, and lung. The type I transporters seem to play a major role in renal urate handling and mutations in these proteins have been implicated in susceptibility to gout. The ubiquitously expressed type III transporters play a lesser role in phosphate homeostasis but contribute to cellular phosphate uptake, mineralization, and inflammation. The recognition of species differences in the expression, regulation, and function of these transport proteins suggests an urgent need to find ways to study them in humans.

PDZ adaptors: their regulation of epithelial transporters and involvement in human diseases

Homeostasis in the body is at least partially maintained by mechanisms that control membrane permeability, and thereby serve to control the uptake of essential substances (e.g., nutrients) and the efflux of unwanted substances (e.g., xenobiotics and metabolites) in epithelial cells. Various transporters play fundamental roles in such bidirectional transport, but little is known about how they are organized on plasma membranes. Protein-protein interactions may play a key role: several transporters in epithelial cells interact with the so-called adaptor proteins, which are membrane anchored and interact with both transporters and other membranous proteins. Although most of the evidences for transporter-adaptor interaction has been obtained in vitro, recent studies suggest that adaptor-mediated transporter regulation does occur in vivo and could be relevant to human diseases. Thus, protein-protein interaction is not only associated with the formation of macromolecular complexes but is also involved in various cellular events, and may provide transporters with additional functionality by forming transporter networks on plasma membranes. Interactions between xenobiotic transporters and PSD95/Dlg/ZO1 (PDZ) adaptors were previously reviewed by Kato and Tsuji (2006. Eur J Pharm Sci 27:487-500); the present review focuses on the latest findings about PDZ adaptors as regulators of transporter networks and their potential role in human diseases.