The Membrane Transporter OAT7 (SLC22A9) Is Not a Susceptibility Factor for Osteoporosis in Europeans.

Bone production, maintenance, and modeling are a well-balanced process involving mineralization by osteoblasts and resorption by osteoclasts. Sex steroid hormones, including their conjugated forms, contribute majorly to maintaining this balance. Recently, variants in the SLC22A9 gene have been associated with osteoporosis in Korean females. We had recently shown that SLC22A9, encoding organic anion transporter 7 (OAT7), is an uptake transporter of estrone sulfate and identified several genetic variants in Europeans leading to functional consequences in vitro. We therefore hypothesized that SLC22A9 genetic variants may contribute to the pathophysiology of osteoporosis in Europeans. To test this hypothesis, we examined the associations of SLC22A9 variants with bone quality, fractures, and bone turnover markers. We genotyped SLC22A9 variants in 5,701 (2,930 female) subjects (age range, 20-93 years) extracted from the population-based Study of Health in Pomerania (SHIP and SHIP-TREND) covered by the Illumina Infinium HumanExome BeadChip version v1.0 (Exome Chip). Descriptive data (e.g., history of fractures), ultrasonography of the calcaneus, as well as serum concentrations of carboxy-terminal telopeptide of type I collagen, amino-terminal propeptide of type I procollagen, and vitamin D were determined. Comprehensive statistical analyses revealed no association between low-frequency and rare SLC22A9 variants and bone quality, fractures, and bone turnover markers. Our results indicate that single genetic SLC22A9 variants do not have a major impact on osteoporosis risk prediction in Europeans, yet findings need to be replicated in larger-scale studies.

Genome wide association study of uric acid in Indian population and interaction of identified variants with Type 2 diabetes.

Abnormal level of Serum Uric Acid (SUA) is an important marker and risk factor for complex diseases including Type 2 Diabetes. Since genetic determinant of uric acid in Indians is totally unexplored, we tried to identify common variants associated with SUA in Indians using Genome Wide Association Study (GWAS). Association of five known variants in SLC2A9 and SLC22A11 genes with SUA level in 4,834 normoglycemics (1,109 in discovery and 3,725 in validation phase) was revealed with different effect size in Indians compared to other major ethnic population of the world. Combined analysis of 1,077 T2DM subjects (772 in discovery and 305 in validation phase) and normoglycemics revealed additional GWAS signal in ABCG2 gene. Differences in effect sizes of ABCG2 and SLC2A9 gene variants were observed between normoglycemics and T2DM patients. We identified two novel variants near long non-coding RNA genes AL356739.1 and AC064865.1 with nearly genome wide significance level. Meta-analysis and in silico replication in 11,745 individuals from AUSTWIN consortium improved association for rs12206002 in AL356739.1 gene to sub-genome wide association level. Our results extends association of SLC2A9, SLC22A11 and ABCG2 genes with SUA level in Indians and enrich the assemblages of evidence for SUA level and T2DM interrelationship.

A clearance system for prostaglandin D2, a sleep-promoting factor, in cerebrospinal fluid: role of the blood-cerebrospinal barrier transporters.

Although the level of prostaglandin (PG) D(2) in cerebrospinal fluid (CSF) affects the action of D-type prostanoid receptors that promote physiological sleep, the regulatory system of PGD(2) clearance from the CSF is not fully understood. The purpose of this study was to investigate PGD(2) elimination from the CSF via the blood-CSF barrier (BCSFB). The in vivo PGD(2) elimination clearance from the CSF was 16-fold greater than that of inulin, which is considered to reflect CSF bulk flow. This process was inhibited by the simultaneous injection of unlabeled PGD(2). The characteristics of PGD(2) uptake by isolated choroid plexus were, at least partially, consistent with those of PG transporter (PGT) and organic anion transporter 3 (OAT3). Studies using an oocyte expression system showed that PGT and OAT3 were able to mediate PGD(2) transport with a Michaelis-Menten constant of 1.07 and 7.32 µM, respectively. Reverse transcription-polymerase chain reaction and immunohistochemical analyses revealed that PGT was localized on the brush-border membrane of the choroid plexus epithelial cells. These findings indicate that the system regulating the PGD(2) level in the CSF involves PGT- and OAT3-mediated PGD(2) uptake by the choroid plexus epithelial cells, acting as a pathway for PGD(2) clearance from the CSF via the BCSFB.

Frequencies of single-nucleotide polymorphisms of SLCO1A2, SLCO1B3 and SLCO2B1 genes in a Finnish population.

Organic anion transporting polypeptides 1A2, 1B3 and 2B1 (OATP1A2, OATP1B3 and OATP2B1) are expressed in tissues important for pharmacokinetics, and mediate the cellular influx of various endogenous and exogenous compounds, including drugs. The aim of the study was to investigate the frequencies of single-nucleotide polymorphisms (SNP) of SLCO1A2, SLCO1B3 and SLCO2B1 in a Finnish population. The distribution of nine non-synonymous SLCO1A2, SLCO1B3 and SLCO2B1 SNPs was determined in 552 healthy Finnish Caucasian participants by using allelic discrimination with TaqMan 5'nuclease assays. The SLCO1A2 c.38T>C (p.Ile13Thr) and c.516C>T (p.Glu172Asp) SNPs were found with variant allele frequencies of 12.9% (95% confidence interval: 11.0-15.0) and 7.2% (5.8-8.8). The variant allele frequencies of SLCO1B3 c.334T>G (p.Ser112Ala), c.699G>A (p.Met233Ile) and c.767G>C (p.Gly256Ala) were 77.0% (74.4-79.4), 76.9% (74.3-79.3) and 12.8% (10.9-14.9), respectively. None of the participants carried the SLCO1B3 c.1309G>A (p.Gly437Ser) SNP. The SLCO2B1 c.601G>A (p.Val201Met), c.935G>A (p.Arg312Gln) and c.1457C>T (p.Ser486Phe) variant allele frequencies were 2.1% (1.4-3.1), 13.6% (11.7-15.7) and 2.8% (2.0-4.0), respectively. The SLCO1B3 c.334T>G and c.699G>A SNPs were in a nearly complete linkage disequilibrium (r² = 0.99, D' = 1.00), all other SNP pairs showed only a weak correlation. In conclusion, non-synonymous sequence variations of SLCO1A2, SLCO1B3 and SLCO2B1 occur at high frequencies in the Finnish population.

Effect of methotrexate treatment on expression levels of multidrug resistance protein 2, breast cancer resistance protein and organic anion transporters Oat1, Oat2 and Oat3 in rats.

The ATP binding cassette (ABC) transporters, multidrug resistance protein 2 (Mrp2; Abcc2) and breast cancer resistance protein (Bcrp; Abcg2), and organic anion transporters (Oats) mediate excretion of methotrexate (MTX) and many other drugs. However, it is not known whether MTX treatment leads to any changes in the expression of these transporters. We examined the effect of MTX treatment on expression of Mrp2, Bcrp and Oats in rats. MTX was single injected intraperitoneally at doses of 10, 50 and 150 mg/kg, and then Western blot analysis was performed. The levels of Mrp2, Oat1 and Oat2 on day 1 after the treatment showed no significant change. Four days after injection of 150 mg/kg MTX, the Mrp2 levels in the liver and ileum, but not in the kidney, were markedly down-regulated to 20 +/- 3.6% and 8.9 +/- 3.8% (mean +/- SEM) of controls, respectively. Renal Oat1 and Oat3 were also down-regulated to 56.4 +/- 4.3% (Oat1) and 54.3 +/- 5.5% (Oat3) of controls. These effects of MTX were almost recovered by leucovorin which rescues normal cells from MTX toxicity. MTX treatment also decreased mRNA levels of constitutive androstane receptor (CAR) and pregnane X receptor (PXR) to 65.5 +/- 17.9% and 59.6 +/- 14.5% of controls in the liver, respectively. MTX treatment has no apparent effect on expression levels of Bcrp, cytochrome P450 2B6 and 3A1. In conclusion, these data indicate that MTX treatment down-regulates expression levels of Mrp2, Oat1 and Oat3, and its effects are recovered by leucovorin.