Progress of pendrin in airway epithelia / 国际儿科学杂志

Pendrin is an electroneutral anion exchanger transporter, residing in the apical region of airway epithelium cells.It is responsible for the reabsorption of chloride(Cl -) and the exchange of bicarbonate(HCO 3－)or thiocyanate(SCN -) to the lumen.It is mainly involved in regulating the pH and thickness of airway surface liquid(ASL), mucin secretion, and airway defense, which is of great significance for maintaining the stability of the airway surface microenvironment.The expression of pendrin is significantly up-regulated in bronchial asthma, which is closely related to the pathological processes of the lung in bronchial asthma, such as airway hyperresponsiveness, neutrophil infiltration, and increased mucin secretion.Inhibiting the function of pendrin may be a new target for the treatment of bronchial asthma.

Pharmacokinetics of methotrexate mediated by organic anion transporter 3 in adjuvant induced arthritis rats / 中国临床药理学与治疗学

AIM: To explore the effects of inflammatory conditions on the pharmacokinetics of methotrexate (MTX) and its related mechanisms. METHODS: The model of adjuvant induced arthritis (AIA) was established. The expression of organic anion transporter 3 (OAT3) in kidney was detected by immunohistochemistry, Western blotting and QPCR. The plasma concentration of MTX was detected by LC-MS/MS, and the pharmacokinetics of MTX after different administration time were compared by isolated rat kidney perfusion, kidney slices, in vitro cell uptake and transport experiments. RESULTS: The expression of OAT3 was significantly increased in the kidneys of AIA rats by immunohistochemistry, Western blotting and QPCR. At the same time, the concentration of MTX was detected by the optimized LC-MS/MS. The results showed that the uptake of MTX in the kidney slices of AIA rats was significantly increased, and Pro could reduce the excretion of MTX by inhibiting OAT3. Furthermore, it was demonstrated in vitro that inflammatory pathology can promote renal excretion of MTX by increasing the expression and functional activity of OAT3.CONCLUSION: Under inflammatory pathological conditions, it can increase the expression of OAT3 in the kidney, enhance its functional activity, accelerate the uptake of MTX by the kidney, and promote the excretion of MTX.

Analysis of solute carrier organic anion transporter family member 1b1 and apolipoprotein E genes in a population from southern Yunnan / 中国基层医药

Objective:To analyze the distribution of solute carrier organic anion transporter family member 1b1 ( SLCO1B1) and apolipoprotein E ( ApoE) genes in a population from southern Yunnan. Methods:The data of 104 patients who received treatment in Southern Central Hospital of Yunnan Province (The First People's Hospital of Honghe State) between May 2019 and June 2020 were collected. The distribution of SLCO1B1 and ApoE genes and their relationship with nationality, sex, and age were analyzed and compared between different regions. Results:The percentage of patients carrying *1a/*1a, *1a/*1b, *1b/*1b, *1a/*15, *1b/*15, five phenotypes of SLCO1B1 gene, in the population from southern Yunnan was 4.81%, 32.69%, 42.31%, 12.50% and 7.69% respectively. Phenotypes *1a/*5, *5/*5, *5/*15 and *15/*15 were not detected. Normal metabolic phenotype of SLCO1B1 accounted for 79.81%, and intermediate metabolic phenotype of SLCO1B1 accounted for 20.19%. Weak metabolic phenotype was not detected. The percentage of patients carrying E2/E2, E2/E3, E3/E3, E3/E4, E4/E4, five phenotypes of ApoE gene in the population from southern Yunnan was 0.96%, 16.35%, 70.19%, 11.54% and 0.96% respectively. E2/E4 phenotype was not detected. The percentage of patients with ApoE protective phenotype, ApoE normal phenotype, and ApoE risk phenotype was 17.31%, 70.19% and 12.50% respectively. The observed polymorphism mutation frequency of SLCO1B1 and ApoE genes was consistent with the Hardy-Weinberg equilibrium ( P > 0.05), suggesting constancy and a population representation. The Fisher test showed that SLCO1B1 gene distribution differed significantly between ethnic minorities and Han nationality in southern Yunnan ( P = 0.013). There was no significant difference in SLCO1B1 gene distribution between different sexes and between different ages (all P > 0.05). There was no significant difference in ApoE gene distribution between ethnic minorities and Han nationality, between different sexes, and between different ages in the population from southern Yunnan (all P > 0.05). Conclusion:SLCO1B1 gene distribution is related to nationality in the population from southern Yunnan, but it is unrelated to sex and age. ApoE gene distribution is unrelated to nationality, sex and age.

Screening of Components with Potential Regulation Effect in Lagotis brevituba Based on Target Cell and Molecular Docking / 中国实验方剂学杂志

Objective:To study the components with urate anion transporter 1（URAT1） regulation effect and their combination mechanisms of Lagotis brevituba by integrating techniques of HK-2 cell capture，UPLC-Q-TOF-MS and molecular docking，so as to provide material and theory bases for the development of new hypouricemic medicines based on L. brevituba. Method:The HK-2 cells were applied to capture the components of L. brevituba. UPLC-Q-TOF-MS was used to identify those components. The molecular docking technique was adopted to study the interaction mechanism between the compounds and URAT1. Result:Eight components were successfully screened and identified as hyperoside，plantamajoside，kaempferol-3-O-glucoside，lugrandoside，nepitrin，isolugrandoside，homoplantaginin，luteolin，respectively. Those components could combine with URAT1 mainly through hydrogen bond，van der Waals force and hydrophobic action，which were closely related to structure and compound types. Furthermore，the LibDock score of phenylethanoids was higher than that of flavonoids. Conclusion:The integration of target cell capture，UPLC-Q-TOF-MS and molecular docking techniques could be successfully used to identify captured compounds of L. brevituba with URAT1 regulation effects and illustrate their potential combination mechanisms as well as the structure-activity relationships. The findings may provide material and theory bases for the development of new hypouricemic medicines based on L. brevituba.

Insulin-like growth factor 1 modulates the phosphorylation, expression, and activity of organic anion transporter 3 through protein kinase A signaling pathway

Organic anion transporter 3 (OAT3) plays a vital role in removing a broad variety of anionic drugs from kidney, thus avoiding their possible toxicity in the body. In the current study, we investigated the role of insulin-like growth factor 1 (IGF-1) in the regulation of OAT3. We showed that IGF-1 induced a dose- and time-dependent increase in OAT3 transport activity, which correlated well with an increase in OAT3 expression. The IGF-1-induced increase in OAT3 expression was blocked by protein kinase A (PKA) inhibitor H89. Moreover, IGF-1 induced an increase in OAT3 phosphorylation, which was also blocked by H89. These data suggest that the IGF-1 modulation of OAT3 occurred through PKA signaling pathway. To further confirm the involvement of PKA, we treated OAT3-expressing cells with PKA activator Bt2-cAMP, followed by examining OAT activity and phosphorylation. We showed that OAT3 activity and phosphorylation were much enhanced in Bt2-cAMP-treated cells as compared to that in control cells. Finally, linsitinib, an anticancer drug that blocks the IGF-1 receptor, abrogated IGF-1-stimulated OAT3 transport activity. In conclusion, our study demonstrated that IGF-1 regulates OAT3 expression and transport activity through PKA signaling pathway, possibly by phosphorylating the transporter.

A case-control study of the association between the polymorphisms of APOE and SLCO1B1 and the severity of coronary artery disease / 中华检验医学杂志

Objective The single nucleotide polymorphisms (SNPs) of APOE and SLCO1B1 were examined to explore their association with the risk and severity of coronary heart disease(CAD). Methods A total of 1267 cases of consecutive coronary heart disease (CAD)-suspected inpatients visiting department of Cardiology in Peking University Peoples' Hospital from March 2017 to november were recruited into this case-control study, and then 391 CAD cases and 223 non-CAD controls were enrolled for final analysis after screening by coronary angiography and exclusion criteria. The severity of the CAD cases were evaluated according to Gensini scores. The SNPs of APOE(388T>C, 526C>T) and SLCO1B1(388A>G, 521T>C) were detected using Real-time PCR and further verified using Sanger sequencing. Environmental risk factors were collected, and the correlations between SNPs of APOE and SLCO1B1 and the risk and severity of CAD were performed by SPSS version 16.0. Results The SNPs of all the subjects included in CAD group and non-CAD group were successfully detected, with an accordance of 100％ to Sanger sequencing. The distribution of APOE and SLCO1B1 gene were subjected to Hardy-Weinberg. The distributions of APOE gene ε3/ε3 genotypes and ε3 allele were most commonly found in both CAD group and non-CAD group (ε3/ε3: 70.8％,73.1％;ε3: 83.5％,85.2％;respectively). APOE genotypes and alleles were comparable between the CAD cases and non-CAD controls (P>0.05). The frequencies of APOE gene ε4+genotype were more likely to be found in the subgroup of CAD with Gensini score≥72 (P<0.05). The distributions of SLCO1B1 gene *1b/*1b genotypes and *1b allele were most commonly found in both CAD group and non-CAD group (*1b/*1b: 37.3％, 36.8％; *1b: 60.1％, 61.7％; respectively). There was no significant difference in genotype and allele frequencies of SLCO1B1 between the two groups and among subgroups with different severity of CAD (P>0.05). Conclusion This study observed no association between SNPs of APOE, SLCO1B1 and the risk of CAD in this population. However, APOE gene ε4 +genotype may increase the severity of CAD.

Effect of acupuncture stimulation of "Shenshu"(BL23)-"Taixi"(KI3)on levels of serum uric acid and renal URAT1 and OAT1 protein expression in hyperuricemia rats / 针刺研究

OBJECTIVE: To observe the effect of acupuncture at "Shenshu"(BL23)-"Taixi"(KI3)on the levels of serum uric acid (SUA) and expression of renal urate-anion transporter 1 (URAT1) and organic anion transporter 1 (OAT1) proteins in hyperuricemia (HUA) rats, so as to explore its underlying mechanisms in improving HUA. METHODS: A total of 25 male Wistar rats were divided into 4 groups: control (n＝6), HUA model (n＝7), BL23-KI3 (n＝6) and Ganshu (BL18)-Taichong (LR3, BL18-LR3 in short, n＝6). The HUA model was established by gavage of Oteracil Potassium (2 g/kg), once daily for 10 days, then once every other day. For rats of the BL23-KI3 group, BL23 and KI3 were stimulated with filiform needles which were rotated for 10 s at a frequency about 100 r/min, and for rats of the BL18-LR3 group, BL18 and LR3 were stimulated with the same methods to those of the BL23-KI3 group. The treatment of both acupuncture groups was conducted once daily, 6 times a week (except Sundays) for 3 weeks. The contents of SUA and serum creatinine (SCr) were assayed by using an automatic biochemical analyzer. The pathological changes of the right kidney tissue were observed under light microscope after hematoxylin eosin (H.E.) staining, the immunoactivity of URAT1 and OAT1 of the right kidney tissue was determined by immunohistochemistry, and the expression of URAT1 and OAT1 proteins of the left kidney tissue detected by Western blot (WB). RESULTS: After modeling, the content of SUA and the expression of renal URAT1 protein (shown by both immunoactivity and WB) were significantly increased (P0.05). Following acupuncture intervention, the SUA content and URAT1 expression in both BL18-LR3 and BL23-KI3 groups were considerably down-regulated (P<0.05, P<0.01), and the expression of OAT1 protein in the BL23-KI3 group (not the BL18-LR3 group) were obviously up-regulated relevant to the model group (P<0.01). The effects of BL23-KI3 were significant superior to those of BL18-LR3 in down-regulating the expression of URAT1 and up-regulating OAT1 protein (P<0.01, P<0.05). CONCLUSION: Acupuncture of "BL23" and "KI3" can effectively down-regulate SUA level in HUA rats, which may be related to its effects in down-regulating the expression of URAT1 and up-regulating the expression of OAT1 in the kidney tissue.

Effects of Chinese herb ingredients with different properties on OAT4, URAT1 and serum uric acid level in acute hyperuricemia mice / 中草药

Objective To study the effects of Chinese herb ingredients with different properties on transporters (URAT1 and OAT4) involved in renal urate reabsorption and serum uric acid level in acute hyperuricemia mice. Methods The OAT4, URAT1- overexpressed monoclonal cell line (MDCK-hOAT4, HEK293-hURAT1) was constructed. The inhibition effect and the half maximal inhibitory concentration (IC50) of different ingredients to transport activity of OAT4 and URAT1 mediating 14C-uric acid were determined. The effects of protocatechuic, liquiritigenin and isoliquiritigenin on serum uric acid levels in acute hyperuricemia mice were studied by the acute hyperuricemia mice induced by potassium oxonate and xanthine. Results The results indicated that nobiletin,liquiritigenin, isoliquiritigenin, licochalcone A with bitter flavor showed strong inhibition to OAT4. The IC50 of nobiletin, liquiritigenin, isoliquiritigenin, and licochalcone A on OAT4 were 0.556 μmol/L, 18.40 μmol/L, 6.831 μmol/L, and 6.825 μmol/L, respectively. Protocatechuic acid and liquiritigenin showed strong inhibition to URAT1 with IC50 of 7.709 μmol/L and 14.54 μmol/L, respectively. Liquiritigenin can significantly reduce the level of serum uric acid of acute hyperuricemia mice, increase the excretion of uric acid, and reduce the level of serum creatinine and blood urea nitrogen. Conclusion Nobiletin, liquiritigenin, isoliquiritigenin and licochalcone A can inhibit the transport activity of OAT4, while protocatechuic acid and liquiritigenin can inhibit the transport activity of URAT1. Liquiritigenin can significantly reduce the level of serum uric acid in acute hyperuricemia mice and protect kidney, the mechanism of which may be associated with the decreasing reabsorption of uric acid by inhibiting the activity of URAT1 and OAT4.

Gadoxetic disodium-enhanced MRI to characterize T1 relaxation values and expression level of organic anion transporters and multidrug resistance protein on hepatocyte surface membrane of normal C57BL/6 mice / 中华肝脏病杂志

Objective@#The characteristics of T1 relaxation values and the expression levels of organic anion transport system (OATP) and multidrug resistance protein carrier (MRP) on hepatocyte surface membrane were quantitatively studied to evaluate liver function in normal C57BL/6 mice with gadoxetic disodium-enhanced MRI.@*Methods@#Ten 6-weeks-old, normal C57BL/6 mice were included in this study. Gadoxetic disodium- enhanced MRI examination was performed. Longitudinal relaxation time images before and 20 min after contrast injection (hepatobiliary-specific phase) were acquired. T1-relaxation time, T1 relaxation time decline rate (△T) and rapid initial enhancement slope percentage in the first-pass study of the liver parenchyma before and after administration of gadoxetate disodium were measured. Liver parenchyma specimens were detected by Western blotting and the values ​​of OATP1, MRP2, and MRP3 were recorded. Statistical results were expressed in mean.@*Results@#The mean T1 relaxation time of 10 normal C57BL/6 mice before and after enhancement was 659.13 ± 24.07, and 408.87 ± 27.21 ms. The mean T1 relaxation time decline rate and rapid initial enhancement slope percentage in the first-pass study was 37.12% ± 4.95% and 4.14% ± 0.96% ms. Furthermore, the mean value of OATP1, MRP2 and MRP3 were 29 952.1 ± 11 475.2, 34 376.4 ± 33 228.4 and 357 308.9 ± 64 646.5.@*Conclusion@#T1-relaxation values, T1 relaxation time decline rate and rapid initial enhancement slope percentage in the first-pass study before and after gadoxetic disodium-enhanced MRI were determined in normal C57BL/6 mice as well as quantitative values of OATP1, MRP2 and MRP3 at the molecular level on the hepatocyte surface membrane were helpful for liver injury model with control study.

Uric acid transporter and the balance of serum uric acid / 国际药学研究杂志

During the uric acid production, excretion and reabsorption in the liver, kidney and intestine, several uric acid transporter proteins are involved in these processes. A large number of studies have shown that glucose transporter 9 plays an important role in the uric acid transport in the liver, kidney and intestine, and participates in the uric acid reabsorption. The ATP-binding cassette superfamily G member 2 is mainly expressed in the apical membrane of the proximal tubular epithelial cells of the kidney, which is involved in the uric acid secretion. The multidrug resistant protein 4 is expressed in the apical membrane of the renal tubular epithelial cells, which transfers uric acid from the renal tubular epithelial cells into the renal tubular lumen. The urate-anion transporter 1 as well as the organic anion transporters 1 and 3 are all the organic anion transporters belonging to the SLC22 A family of transmembrane transporters, and all participate in the uric acid transport in the kidney, especially the uric acid secretion and excretion. In this review, we summarize the research progress of these uric acid transporters, focusing on their effects on the regulation of the serum uric acid balance.

Mechanism of nephrotoxicity of rhubarb in rats / 中国中药杂志

The aim of this study was to investigate the renal toxicity of rhubarb and its mechanism. The SD rats were randomly divided into three groups: normal group and two rhubarb extract groups (16, 2 g·kg⁻¹). According to the dose conversion method between human and animal, rhubarb 16 g·kg⁻¹ and 2 g·kg⁻¹ were equivalent to 10 times and 1.25 times of human clinical dose respectively. Rhubarb extract was administered by a gastric gavage to rats once daily for 30 days. Serum urea nitrogen （BUN）, creatinine （CRE） and urine KIM-1, NGAL and renal morphology were analyzed. The expressions of OAT1, OAT3 and clusterin mRNA in kidney were measured. The results showed that the low dose of rhubarb had no obvious renal toxicity. The high dose group showed mild and moderate renal injury and a down-regulation of clusterin mRNA expression in the kidney tissue. The renal toxicity in male animals was heavier than that in female animals. There was no significant change in blood BUN and CRE in the high dose group. But urine NGAL level of the high dose group increased by 51.53% compared with normal group, of which male animals increased more significantly (<0.05, compared with the normal group). The expressions of renal OAT1 and OAT3 mRNA in the low dose group were obviously higher than that in the normal group. The results indicated that the high dose of rhubarb could cause the renal toxicity. The dosage should be controlled reasonably in the clinical use. OAT1 and OAT3 mRNA related to anionic transport in kidney tissue played a compensatory protective role in rhubarb-induced renal injury. But the compensatory effect is relatively weak at the high dose level. In addition, routine renal function indicators BUN and CRE had limitation for monitoring the kidney toxicity of rhubarb. It is suggested that urine NGAL detection might be helpful for monitoring the renal toxicity of rhubarb.

Inhibition of berberine on organ anion transporters and its bidirectional trans-membrane transport / 药物评价研究

Objective To study the inhibition of berberine on organ anion transporters (OATs) and its bidirectional trans-membrane transport.Method The transgene cell lines of the organ anion transporters including OAT1,OAT2,OAT3,OAT4,OAT7,and URAT1 were constructed and selected by animal cell transgenic method mediated by transporter Lipo 3000.Wild type (WT) cells were used as control group,and activity of OATs was verified by adding their radiolabeled substrates and inhibitors.The inhibition of 100 μmol/L berberine on the transporters was investigated in vitro.The IC50 of berberine on URAT1 was also determined.The bidirectional transport of berberine was studied through the Caco-2 model.Result The results showed that 100 μmol/L berberine inhibited the activity of OAT1,OAT2,OAT3,OAT4,OAT7 and URAT1 to (70.48±4.23)％,(69.13±1.28)％,(72.12±3.28)％,(79.77±6.49)％,(69.51 ±5.99)％ and (38.4 ± 2.67)％ respectively,the IC50 of berberine to URAT 1 was 13.19 μmol/L,the Papp (A-B) of 50 μmol/L and 100 μmol/L berberine were separately 0.28 × 10-6 and 0.40 × 10-6 cm/s,and the effiux rates were separately 3.18 and 3.15.Conclusion Berberine shows a stronger inhibition to URAT1 compared to OAT1,OAT2,OAT3,OAT4 and OAT7.Berberine may be the substrate of some effiux transporters.This study provides theoretical basis for explaining the low bioavailability ofberberine and forecasting the possible drug-drug interaction.

Effect of green tea polyphenols on uric acid level in potassium oxonate-induced hyperuricemic mice and mechanism / 中国药理学通报

Aim To investigate the effect of green tea polyphenols(GTP)on serum level of uric acid in potas-sium oxonate (PO)-induced hyperuricemic mice,and explore the potential mechanism.Methods PO and GTP were intragastricly administered to mice for seven consecutive days.Uric acid level in serum was exam-ined.Meanwhile,activity and expressions of xanthine oxidase(XOD)in liver were tested.In additon,ex-pressions of urate transporters including urate-anion transporter (URAT ) 1 , organic anion transporter (OAT)1 and 3 in kidney were analyzed.Results GTP significantly decreased the serum level of uric acid in PO-induced hyperuricemic mice.At the same time, GTP markedly reduced the activity and expression of XOD in liver of hyperuricemic mice.Finally,GTP markedly reduced the expression of URAT1 ,OAT1 and OAT3 in kidney of hyperuricemic mice.Conclusion GTP has the effect of lowering uric acid in PO-induced hyperuricemic mice through both decreasing the uric acid production and increasing uric acid excretion.

Establishment and application of cell model for screening inhibitors of organic anion transporter 1 / 中国药学杂志

OBJECTIVE: To establish a cell model stably expressing mouse organic anion transporter1( OAT1) in MDCK cells, for the purpose of screening potent OAT1 inhibitors in vitro. METHODS: Recombinant plasmid pcDNA3.1(+) -OAT1 was constructed and transfected into MDCK cells using Lipofectamine™ 2000 reagent. After the process of G418 screening, cells were collected for further validation. Cells were harvested, and the quantitative real-time reverse transcription-polymerase chain reaction (qRT-PCR) was carried out to test the OAT1 mRNA expression in MDCK-OAT1 cells. The function of the stably transfected cells were validated by the uptake activity of (6-Carboxyfluorescein, 6-CFL),a substrate of OAT1. The inhibitors of OAT1 were selected according to their inhibition activity towards the uptake of 6-CFL into the OAT1-over expressing cells in comparison with the typical inhibitor of OAT1,probenecid. RESULTS: The pcDNA3.1(+) -OAT1 was well conducted. The mRNA expression of OAT1 was significantly higher than that in mock cells; MDCK-OAT1 cells had a significantly high mRNA expression comparing with the mock cells, being 4 862 fold of that in mock cells. The uptake-ability of 6-CFL in MDCK-OAT1 and MDCK-mock cells was obviously different, with a 14.9 fold increase in comparison with mock cells. In the presence of probenecid and several monomers from Chinese herbs, fluorescence values in cell lysates were reduced to varying degrees, and results showed that rhein, luteolin, chrysin and quercetin could significantly inhibited the 6-CFL uptake mediated by hOAT1,with a reduction of more than 80% of the control. CONCLUSION: The aim to establish a cell model which could stably express OAT1 is achieved. Further study could be done using this cell model, for the screening of potential inhibitors of OAT1 from monomers of Chinese herbs,and then could be used as a tool in the research of herb-drug interaction.

Research advances in organic anion transporter / 药学学报

The organic anion transporter (OAT) subfamily is an important part of the SLC22(solute carrier 22) transporter family. OATs are expressed in many tissues, including liver, kidney, brain, placenta and so on. A great deal of attention has been paid to OAT because of its role in handling of common drugs (antibiotics, antivirals, diuretics, nonsteroidal anti-inflammatory drugs), toxins and nutrients. Data from recent metabolomics, microarray and system biology studies, phenotypes of Oat1 and Oat3 knockouts, indicate a central role of this pathway in the metabolism as well as putative uremic toxins of kidney disease. The expressions of certain OATs in conjunction with phase I and phase II drug metabolizing enzymes are regulated by nuclear receptors and other transcription factors. According to the "remote sensing and signaling hypothesis", some OATs have a strong relationship with certain particular signaling molecules. OATs may play a role in remote inter-organ communication via regulating levels of signaling molecules and key metabolites in tissues and body fluids. OATs play a significant role in the transportation of internal and external material under normal and pathological conditions.

Co-localization and interaction of human organic anion transporter 4 with caveolin-1 in primary cultured human placental trophoblasts

The human organic anion transporter 4 (hOAT4) has been identified as the fourth isoform of OAT family. hOAT4 contributes to move several negatively charged organic compounds between cells and their extracellular milieu. The functional characteristics and regulatory mechanisms of hOAT4 remain to be elucidated. It is well known that caveolin plays a role in modulating proteins having some biological functions. To address this issue, we investigated the co-localization and interaction between hOAT4 and caveolin-1. hOAT4 and caveolin-1 (mRNA and protein expression) were observed in cultured human placental trophoblasts isolated from placenta. The confocal microscopy of immuno-cytochemistry using primary cultured human trophoblasts showed hOAT4 and caveolin-1 were co-localized at the plasma membrane of the cell. This finding was confirmed by Western blot analysis using isolated caveolae-enriched membrane fractions and immune-precipitates from the trophoblasts. When synthesized cRNA of hOAT4 along with scrambled- or antisense-oligodeoxynucleotide (ODN) of Xenopus caveolin-1 were co-injected to Xenopus oocytes, the [3H]estrone sulfate uptake was significantly decreased by the co-injection of antisense ODN but not by scrambled ODN. These findings suggest that hOAT4 and caveolin-1 share a cellular expression in the plasma membrane and caveolin-1 up-regulates the organic anionic compound uptake by hOAT4 under the normal physiological condition.

Effects of Increased Uric Acid Intake on the Abundance of Urate-anion exchanger and Organic Anion Transporter Proteins in the Rat Kidney

Renal handling of uric acid mainly occurs in the proximal tubule, and bidirectional transport of urate may involve apical absorption via the urate-anion exchanger (URAT1) and basolateral uptake via organic anion transporters (OAT1 and OAT3). In rat kidneys, we investigated whether the protein abundance of URAT1, OAT1, and OAT3 is affected by the increase in uric acid intake. Male Sprague-Dawley rats were randomly divided into control and uric acid-supplemented groups, and uric acid-supplemented rats were given 0.75 g of uric acid per 180 g body weight per day for 8 days. After the animal experiment, kidneys were harvested and semi-quantitative immunoblotting was carried out from cortical homogenates using polyclonal peptide-derived antibodies to URAT1, OAT1, and OAT3. Serum uric acid level showed an increasing tendency (p=0.055) in the uric acid-supplemented rats (2.60+/- 0.27 mg/dL) compared with control rats (1.97+/-0.29 mg/dL), whereas urinary uric acid excretion was not significantly different between the uric acid-supplemented rats (3.27+/-0.40 mg/d) and control rats (2.61+/-0.34 mg/d). URAT1 protein abundance in cortical homogenates was not significantly different between the uric acid-supplemented rats (132+/-14%) and control rats (100+/-7%). However, OAT1 protein abundance was significantly (p<0.05) increased in the uric acid-supplemented rats (148+/-13%) compared with the control rats (100+/-8%). OAT3 protein abundance was not significantly different between the uric acid-supplemented rats (131+/-12%) and control rats (100+/-17%). In conclusion, OAT1 may have a regulatory role in response to the increase in uric acid intake in the rat kidney. The up-regulation of OAT1 would exert stimulation of urinary uric acid excretion and might contribute to protection from hyperuricemia.

Introduction of Organic Anion Transporters (SLC22A) and a Regulatory Mechanism by Caveolins

The kidney is an important organ for controlling the volume of body fluids, electrolytic balance and excretion/reabsorption of endogenous and exogenous compounds. Among these renal functions, excretion/reabsorption of endogenous and exogenous substance is very important for the maintenance of physiological homeostasis in the body. Recently discovered organic anion transporters (OAT or SLC22A) have important roles for renal functions. It is well known as drug transporter. Several isoforms belong to SLC22A family. They showed different transport substrate spectrums and different localizations within the kidney. Their gene expressions are changed by some stimulus. The functional transport properties are regulated by protein kinase C. In addition, the function of organic anion transporters are also regulated by protein-protein interaction, such as caveolin which is compositional protein of caveolae structure. In this review, we will give an introduction of organic anion transporters and its regulatory mechanisms.

Co-localization and interaction of organic anion transporter 1 with caveolin-2 in rat kidney

The organic anion transporters (OAT) have recently been identified. Although the some transport properties of OATs in the kidney have been verified, the regulatory mechanisms for OAT's functions are still not fully understood. The rat OAT1 (rOAT1) transports a number of negatively charged organic compounds between the cells and their extracellular milieu. Caveolin (Cav) also plays a role in membrane transport. Therefore, we investigated the protein-protein interactions between rOAT1 and caveolin-2. In the rat kidney, the expressions of rOAT1 mRNA and protein were observed in both the cortex and the outer medulla. With respect to Cav-2, the expressions of mRNA and protein were observed in all portions of the kidney (cortex < outer medulla = inner medulla). The results of Western blot analysis using the isolated caveolae-enriched membrane fractions or the immunoprecipitates by respective antibodies from the rat kidney showed that rOAT1 and Cav-2 co-localized in the same fractions and they formed complexes each other. These results were confirmed by performing confocal microscopy with immunocytochemistry using the primary cultured renal proximal tubular cells. When the synthesized cRNA of rOAT1 along with the antisense oligodeoxynucleotides of Xenopus Cav-2 were co-injected into Xenopus oocytes, the [14C]p-aminohippurate and [3H]methotrexate uptake was slightly, but significantly decreased. The similar results were also observed in rOAT1 over-expressed Chinese hamster ovary cells. These findings suggest that rOAT1 and caveolin-2 are co-expressed in the plasma membrane and rOAT1's function for organic compound transport is upregulated by Cav-2 in the normal physiological condition.

Molecular aspects of organic ion transporters in the kidney

A function of the kidney is elimination of a variety of xenobiotics ingested and wasted endogenous compounds from the body. Organic anion and cation transport systems play important roles to protect the body from harmful substances. The renal proximal tubule is the primary site of carrier-mediated transport from blood into urine. During the last decade, molecular cloning has identified several families of multispecific organic anion and cation transporters, such as organic anion transporter (OAT), organic cation transporter (OCT), and organic anion-transporting polypeptide (oatp). Additional findings also suggested ATP-dependent organic ion transporters such as MDR1/P-glycoprotein and the multidrug resistance-associated protein (MRP) as efflux pump. The substrate specificity of these transporters is multispecific. These transporters also play an important role as drug transporters. Studies on their functional properties and localization provide information in renal handling of drugs. This review summarizes the latest knowledge on molecular properties and pharmacological significance of renal organic ion transporters.