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Boocock J, Leask M, Okada Y, Matsuo H, Kawamura Y, Shi Y, Li C, Mount DB, Mandal AK, Wang W, Cadzow M, Gosling AL, Major TJ, Horsfield JA, Choi HK, Fadason T, O'Sullivan J, Stahl EA, Merriman TR. Genomic dissection of 43 serum urate-associated loci provides multiple insights into molecular mechanisms of urate control. Hum Mol Genet 2021; 29:923-943. [PMID: 31985003 DOI: 10.1093/hmg/ddaa013] [Citation(s) in RCA: 39] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2019] [Revised: 12/23/2019] [Accepted: 01/20/2020] [Indexed: 12/17/2022] Open
Abstract
High serum urate is a prerequisite for gout and associated with metabolic disease. Genome-wide association studies (GWAS) have reported dozens of loci associated with serum urate control; however, there has been little progress in understanding the molecular basis of the associated loci. Here, we employed trans-ancestral meta-analysis using data from European and East Asian populations to identify 10 new loci for serum urate levels. Genome-wide colocalization with cis-expression quantitative trait loci (eQTL) identified a further five new candidate loci. By cis- and trans-eQTL colocalization analysis, we identified 34 and 20 genes, respectively, where the causal eQTL variant has a high likelihood that it is shared with the serum urate-associated locus. One new locus identified was SLC22A9 that encodes organic anion transporter 7 (OAT7). We demonstrate that OAT7 is a very weak urate-butyrate exchanger. Newly implicated genes identified in the eQTL analysis include those encoding proteins that make up the dystrophin complex, a scaffold for signaling proteins and transporters at the cell membrane; MLXIP that, with the previously identified MLXIPL, is a transcription factor that may regulate serum urate via the pentose-phosphate pathway and MRPS7 and IDH2 that encode proteins necessary for mitochondrial function. Functional fine mapping identified six loci (RREB1, INHBC, HLF, UBE2Q2, SFMBT1 and HNF4G) with colocalized eQTL containing putative causal SNPs. This systematic analysis of serum urate GWAS loci identified candidate causal genes at 24 loci and a network of previously unidentified genes likely involved in control of serum urate levels, further illuminating the molecular mechanisms of urate control.
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Affiliation(s)
- James Boocock
- Department of Biochemistry, School of Biomedical Sciences, University of Otago, Dunedin, New Zealand.,Department of Human Genetics, David Geffen School of Medicine at UCLA, Los Angeles, CA, USA
| | - Megan Leask
- Department of Biochemistry, School of Biomedical Sciences, University of Otago, Dunedin, New Zealand
| | - Yukinori Okada
- Department of Statistical Genetics, Osaka University Graduate School of Medicine, Osaka, Japan.,Laboratory of Statistical Immunology, Immunology Frontier Research Center (WPI-IFReC), Osaka University, Suita, Japan
| | | | - Hirotaka Matsuo
- Department of Integrative Physiology and Bio-Nano Medicine, National Defense Medical College, Tokorozawa, Saitama, Japan
| | - Yusuke Kawamura
- Department of Integrative Physiology and Bio-Nano Medicine, National Defense Medical College, Tokorozawa, Saitama, Japan
| | - Yongyong Shi
- Bio-X Institutes, Key Laboratory for the Genetics of Developmental and Neuropsychiaric Disorders (Ministry of Education), Shanghai Jiao Tong University, Shanghai, People's Republic of China
| | - Changgui Li
- Department of Endocrinology and Metabolism, The Affiliated Hospital of Qingdao University, Qingdao, People's Republic of China
| | - David B Mount
- Renal Division, Brigham and Women's Hospital, Harvard Medical School, Boston MA, USA.,Renal Division, VA Boston Healthcare System, Harvard Medical School, Boston MA, USA
| | - Asim K Mandal
- Renal Division, Brigham and Women's Hospital, Harvard Medical School, Boston MA, USA
| | - Weiqing Wang
- Department of Genetics and Genomic Sciences, Icahn Institute of Genomics and Multiscale Biology, New York, NY, USA
| | - Murray Cadzow
- Department of Biochemistry, School of Biomedical Sciences, University of Otago, Dunedin, New Zealand
| | - Anna L Gosling
- Department of Biochemistry, School of Biomedical Sciences, University of Otago, Dunedin, New Zealand
| | - Tanya J Major
- Department of Biochemistry, School of Biomedical Sciences, University of Otago, Dunedin, New Zealand
| | - Julia A Horsfield
- Department of Pathology, Otago Medical School, University of Otago, Dunedin, New Zealand
| | - Hyon K Choi
- Division of Rheumatology, Allergy and Immunology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA
| | - Tayaza Fadason
- Liggins Institute, University of Auckland, Auckland, New Zealand
| | | | - Eli A Stahl
- Department of Genetics and Genomic Sciences, Icahn Institute of Genomics and Multiscale Biology, New York, NY, USA
| | - Tony R Merriman
- Department of Biochemistry, School of Biomedical Sciences, University of Otago, Dunedin, New Zealand
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Wang X, Wang M, Ruan J, Zhao S, Xiao J, Tian Y. Identification of urine biomarkers for calcium-oxalate urolithiasis in adults based on UPLC-Q-TOF/MS. J Chromatogr B Analyt Technol Biomed Life Sci 2019; 1124:290-297. [DOI: 10.1016/j.jchromb.2019.06.022] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2019] [Revised: 06/11/2019] [Accepted: 06/20/2019] [Indexed: 01/01/2023]
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3
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Gao S, Yang R, Peng Z, Lu H, Li N, Ding J, Cui X, Chen W, Dong X. Metabolomics analysis for hydroxy-L-proline-induced calcium oxalate nephrolithiasis in rats based on ultra-high performance liquid chromatography quadrupole time-of-flight mass spectrometry. Sci Rep 2016; 6:30142. [PMID: 27443631 PMCID: PMC4957101 DOI: 10.1038/srep30142] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2016] [Accepted: 06/28/2016] [Indexed: 12/25/2022] Open
Abstract
About 80% of kidney stones are composed of calcium oxalate (CaOx) with variable amounts of calcium phosphate, and hyperoxaluria is considered as an important factor of CaOx nephrolithiasis. However, the underlying metabolic mechanisms of CaOx nephrolithiasis remain undefined. In this study, we successfully developed a rat model with hydroxy-L-proline (HLP) -induced CaOx nephrolithiasis. Rats were continuously orally administrated with HLP for 28 days. Urine and blood samples were collected from the rats treated with or without HLP at four different time points. UPLC-Q-TOF/MS was applied to profile the abundances of metabolites. To obtain more comprehensive analysis of metabolic profiling spectrum, combination of RP-LC and HILIC were applied. We identify 42 significant differential metabolites in the urine, and 13 significant differential metabolites in the blood. Pathway analysis revealed that the pathways involved in amino acid metabolism, taurine metabolism, bile acid synthesis, energy metabolism, TCA cycle, purine metabolism, vitamin metabolism, nicotinic acid and nicotinamide metabolism have been modulated by HLP treatment. This study suggested that a number of metabolic pathways are dysfunctional in the HLP induced crystal kidney injury, and further studies on those pathways are warranted to better understand the metabolic mechanism of CaOx nephrolithiasis.
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Affiliation(s)
- Songyan Gao
- School of Pharmacy, Second Military Medical University, Shanghai 200433, China
| | - Rui Yang
- Brigade of undergraduate student, Second Military Medical University, Shanghai 200433, China
| | - Zhongjiang Peng
- Department of Nephrology, Changhai Hospital, Shanghai 200433, China
| | - Hongtao Lu
- Brigade of undergraduate student, Second Military Medical University, Shanghai 200433, China
| | - Na Li
- School of Pharmacy, Second Military Medical University, Shanghai 200433, China
| | - Jiarong Ding
- Department of Nephrology, Changhai Hospital, Shanghai 200433, China
| | - Xingang Cui
- Department of Urology, The Third Affiliated hospital, Second Military Medical University, Shanghai 200433, China
| | - Wei Chen
- Department of Nephrology, Changhai Hospital, Shanghai 200433, China
| | - Xin Dong
- School of Pharmacy, Second Military Medical University, Shanghai 200433, China
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Bain MA, Milne RW, Evans AM. Disposition and Metabolite Kinetics of Oral L-carnitine in Humans. J Clin Pharmacol 2013; 46:1163-70. [PMID: 16988205 DOI: 10.1177/0091270006292851] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The pharmacokinetics of L-carnitine and its metabolites were investigated in 7 healthy subjects following the oral administration of 0, 0.5, 1, and 2 g 3 times a day for 7 days. Mean plasma concentrations of L-carnitine across an 8-hour dose interval increased significantly (P < .05) from a baseline of 54.2 +/- 9.3 microM to 80.5 +/- 12.5 microM following the 0.5-g dose; there was no further increase at higher doses. There was a significant increase (P < .001) in the renal clearance of L-carnitine indicating saturation of tubular reabsorption. Trimethylamine plasma levels increased proportionately with L-carnitine dose, but there was no change in renal clearance. A significant increase in the plasma concentrations of trimethylamine-N-oxide from baseline was evident only for the 2-g dose of L-carnitine (from 34.5 +/- 2.0 to 149 +/- 145 microM), and its renal clearance decreased with increasing dose (P < .05). There was no evidence for nonlinearity in the metabolism of trimethylamine to trimethylamine-N-oxide. In conclusion, the pharmacokinetics of oral L-carnitine display nonlinearity above a dose of 0.5 g 3 times a day.
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Affiliation(s)
- Marcus A Bain
- Sansom Institute, School of Pharmacy and Medical Sciences, University of South Australia, Adelaide, SA 5000, Australia
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Noland RC, Koves TR, Seiler SE, Lum H, Lust RM, Ilkayeva O, Stevens RD, Hegardt FG, Muoio DM. Carnitine insufficiency caused by aging and overnutrition compromises mitochondrial performance and metabolic control. J Biol Chem 2009; 284:22840-52. [PMID: 19553674 DOI: 10.1074/jbc.m109.032888] [Citation(s) in RCA: 246] [Impact Index Per Article: 16.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
In addition to its essential role in permitting mitochondrial import and oxidation of long chain fatty acids, carnitine also functions as an acyl group acceptor that facilitates mitochondrial export of excess carbons in the form of acylcarnitines. Recent evidence suggests carnitine requirements increase under conditions of sustained metabolic stress. Accordingly, we hypothesized that carnitine insufficiency might contribute to mitochondrial dysfunction and obesity-related impairments in glucose tolerance. Consistent with this prediction whole body carnitine diminution was identified as a common feature of insulin-resistant states such as advanced age, genetic diabetes, and diet-induced obesity. In rodents fed a lifelong (12 month) high fat diet, compromised carnitine status corresponded with increased skeletal muscle accumulation of acylcarnitine esters and diminished hepatic expression of carnitine biosynthetic genes. Diminished carnitine reserves in muscle of obese rats was accompanied by marked perturbations in mitochondrial fuel metabolism, including low rates of complete fatty acid oxidation, elevated incomplete beta-oxidation, and impaired substrate switching from fatty acid to pyruvate. These mitochondrial abnormalities were reversed by 8 weeks of oral carnitine supplementation, in concert with increased tissue efflux and urinary excretion of acetylcarnitine and improvement of whole body glucose tolerance. Acetylcarnitine is produced by the mitochondrial matrix enzyme, carnitine acetyltransferase (CrAT). A role for this enzyme in combating glucose intolerance was further supported by the finding that CrAT overexpression in primary human skeletal myocytes increased glucose uptake and attenuated lipid-induced suppression of glucose oxidation. These results implicate carnitine insufficiency and reduced CrAT activity as reversible components of the metabolic syndrome.
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Affiliation(s)
- Robert C Noland
- Sarah W. Stedman Nutrition and Metabolism Center, Duke University, Durham, North Carolina 27710, USA
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Meta-analysis of 28,141 individuals identifies common variants within five new loci that influence uric acid concentrations. PLoS Genet 2009; 5:e1000504. [PMID: 19503597 PMCID: PMC2683940 DOI: 10.1371/journal.pgen.1000504] [Citation(s) in RCA: 526] [Impact Index Per Article: 35.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2009] [Accepted: 05/04/2009] [Indexed: 11/19/2022] Open
Abstract
Elevated serum uric acid levels cause gout and are a risk factor for cardiovascular disease and diabetes. To investigate the polygenetic basis of serum uric acid levels, we conducted a meta-analysis of genome-wide association scans from 14 studies totalling 28,141 participants of European descent, resulting in identification of 954 SNPs distributed across nine loci that exceeded the threshold of genome-wide significance, five of which are novel. Overall, the common variants associated with serum uric acid levels fall in the following nine regions: SLC2A9 (p = 5.2×10−201), ABCG2 (p = 3.1×10−26), SLC17A1 (p = 3.0×10−14), SLC22A11 (p = 6.7×10−14), SLC22A12 (p = 2.0×10−9), SLC16A9 (p = 1.1×10−8), GCKR (p = 1.4×10−9), LRRC16A (p = 8.5×10−9), and near PDZK1 (p = 2.7×10−9). Identified variants were analyzed for gender differences. We found that the minor allele for rs734553 in SLC2A9 has greater influence in lowering uric acid levels in women and the minor allele of rs2231142 in ABCG2 elevates uric acid levels more strongly in men compared to women. To further characterize the identified variants, we analyzed their association with a panel of metabolites. rs12356193 within SLC16A9 was associated with DL-carnitine (p = 4.0×10−26) and propionyl-L-carnitine (p = 5.0×10−8) concentrations, which in turn were associated with serum UA levels (p = 1.4×10−57 and p = 8.1×10−54, respectively), forming a triangle between SNP, metabolites, and UA levels. Taken together, these associations highlight additional pathways that are important in the regulation of serum uric acid levels and point toward novel potential targets for pharmacological intervention to prevent or treat hyperuricemia. In addition, these findings strongly support the hypothesis that transport proteins are key in regulating serum uric acid levels. Elevated serum uric acid levels cause gout and are a risk factor for cardiovascular disease and diabetes. The regulation of serum uric acid levels is under a strong genetic control. This study describes the first meta-analysis of genome-wide association scans from 14 studies totalling 28,141 participants of European descent. We show that common DNA variants at nine different loci are associated with uric acid concentrations, five of which are novel. These variants are located within the genes coding for organic anion transporter 4 (SLC22A11), monocarboxylic acid transporter 9 (SLC16A9), glucokinase regulatory protein (GCKR), Carmil (LRRC16A), and near PDZ domain-containing 1 (PDZK1). Gender-specific effects are shown for variants within the recently identified genes coding for glucose transporter 9 (SLC2A9) and the ATP-binding cassette transporter (ABCG2). Based on screening of 163 metabolites, we show an association of one of the identified variants within SLC16A9 with DL-carnitine and propionyl-L-carnitine. Moreover, DL-carnitine and propionyl-L-carnitine were strongly correlated with serum UA levels, forming a triangle between SNP, metabolites and UA levels. Taken together, these associations highlight pathways that are important in the regulation of serum uric acid levels and point toward novel potential targets for pharmacological intervention to prevent or treat hyperuricemia.
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Orosz DE, Woost PG, Kolb RJ, Finesilver MB, Jin W, Frisa PS, Choo CK, Yau CF, Chan KW, Resnick MI, Douglas JG, Edwards JC, Jacobberger JW, Hopfer U. GROWTH, IMMORTALIZATION, AND DIFFERENTIATION POTENTIAL OF NORMAL ADULT HUMAN PROXIMAL TUBULE CELLS. ACTA ACUST UNITED AC 2004; 40:22-34. [PMID: 14748622 DOI: 10.1290/1543-706x(2004)40<22:giadpo>2.0.co;2] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Human proximal tubule epithelial cell lines are potentially useful models to elucidate the complex cellular and molecular details of water and electrolyte homeostasis in the kidney. Samples of normal adult human kidney tissue were obtained from surgical specimens, and S1 segments of proximal convoluted tubules were microdissected, placed on collagen-coated culture plate inserts, and cocultured with lethally irradiated 3T3 fibroblasts. Primary cultures of proximal tubule epithelial cells were infected with a replication-defective retroviral construct encoding either wild-type or temperature-sensitive simian virus 40 large T-antigen. Cells forming electrically resistive monolayers were selected and expanded in culture. Three cell lines (HPCT-03-ts, HPCT-05-wt, and HPCT-06-wt) were characterized for proximal tubule phenotype by electron microscopy, electrophysiology, immunofluorescence, Southern hybridization, and reverse transcriptase-polymerase chain reaction. Each of the three formed polarized, resistive epithelial monolayers with apical microvilli, tight junctional complexes, numerous mitochondria, well-developed Golgi complexes, extensive endoplasmic reticulum, convolutions of the basolateral plasma membrane, and a primary cilium. Each exhibited succinate, phosphate, and Na,K- adenosine triphosphatase (ATPase) transport activity, as well as acidic dipeptide- and adenosine triphosphate-regulated mechanisms of ion transport. Transcripts for Na(+)-bicarbonate cotransporter, Na(+)-H(+) exchanger isoform 3, Na,K-ATPase, parathyroid hormone receptor, epidermal growth factor receptor, and vasopressin V2 receptor were identified. Furthermore, immunoreactive sodium phosphate cotransporter type II, vasopressin receptor V1a, and CLIC-1 (NCC27) were also identified. These well-differentiated, transport-competent cell lines demonstrated the growth, immortalization, and differentiation potential of normal, adult, human proximal tubule cells and consequently have wide applicability in cell biology and renal physiology.
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Affiliation(s)
- David E Orosz
- Department of Physiology, Case Western Reserve University, Cleveland, Ohio 44106-4970, USA
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Gómez-Amores L, Mate A, Vázquez CM. L-carnitine transport in kidney of normotensive, Wistar-Kyoto rats: effect of chronic L-carnitine administration. Pharm Res 2003; 20:1133-40. [PMID: 12948009 DOI: 10.1023/a:1025080426970] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
PURPOSE To examine the effect of long-term administration of L-carnitine on L-carnitine transport in renal brush-border membrane vesicles (BBMVs) from normotensive, Wistar-Kyoto rats. METHODS Rats (n = 20) were orally administered 0.2 g carnitine/kg body weight per day for a total period of 8 weeks. Kinetic parameters of L-carnitine uptake were calculated by non-linear regression, and the relative abundance of the carnitine transporter, OCTN2, was determined by Western blot analysis. RESULTS Initial rates and maximal overshoot levels of Na+-dependent L-carnitine transport were significantly reduced in BBMVs from L-carnitine-treated rats compared with untreated animals. Similarly, the maximal transport rate (Vmax) of OCTN2 was lower in treated rats. However, no differences were observed in the Michaelis constant (Km) or the diffusion constant (Kd) between the two groups of animals. The amount of OCTN2 protein was also decreased in L-carnitine-fed rats, this reduction being similar to that of the Vmax. These results were accompanied by an increase in the serum levels and also in the renal excretion of both free and esterified carnitine in treated rats, indicating that the long-term administration of L-carnitine leads to increased renal carnitine clearance. CONCLUSION These findings suggest a downregulation of OCTN2 at the renal level, in the presence of high levels of carnitine.
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Affiliation(s)
- Lucía Gómez-Amores
- Department of Physiology and Zoology, Faculty of Pharmacy, University of Seville, E-41012 Seville, Spain
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Matera M, Bellinghieri G, Costantino G, Santoro D, Calvani M, Savica V. History of L-carnitine: implications for renal disease. J Ren Nutr 2003; 13:2-14. [PMID: 12563618 DOI: 10.1053/jren.2003.50010] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
L-carnitine (LC) plays an essential metabolic role that consists in transferring the long chain fatty acids (LCFAs) through the mitochondrial barrier, thus allowing their energy-yielding oxidation. Other functions of LC are protection of membrane structures, stabilizing a physiologic coenzyme-A (CoA)-sulfate hydrate/acetyl-CoA ratio, and reduction of lactate production. On the other hand, numerous observations have stressed the carnitine ability of influencing, in several ways, the control mechanisms of the vital cell cycle. Much evidence suggests that apoptosis activated by palmitate or stearate addition to cultured cells is correlated with de novo ceramide synthesis. Investigations in vitro strongly support that LC is able to inhibit the death planned, most likely by preventing sphingomyelin breakdown and consequent ceramide synthesis; this effect seems to be specific for acidic sphingomyelinase. The reduction of ceramide generation and the increase in the serum levels of insulin-like growth factor (IGF)-1, could represent 2 important mechanisms underlying the observed antiapoptotic effects of acetyl-LC. Primary carnitine deficiency is an uncommon inherited disorder, related to functional anomalies in a specific organic cation/carnitine transporter (hOCTN2). These conditions have been classified as either systemic or myopathic. Secondary forms also are recognized. These are present in patients with renal tubular disorders, in which excretion of carnitine may be excessive, and in patients on hemodialysis. A lack of carnitine in hemodialysis patients is caused by insufficient carnitine synthesis and particularly by the loss through dialytic membranes, leading, in some patients, to carnitine depletion with a relative increase in esterified forms. Many studies have shown that LC supplementation leads to improvements in several complications seen in uremic patients, including cardiac complications, impaired exercise and functional capacities, muscle symptoms, increased symptomatic intradialytic hypotension, and erythropoietin-resistant anemia, normalizing the reduced carnitine palmitoyl transferase activity in red cells.
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Affiliation(s)
- Mario Matera
- Department of Pharmacology 2, Medical Faculty, University of Catania, Italy
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10
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Nakanishi T, Hatanaka T, Huang W, Prasad PD, Leibach FH, Ganapathy ME, Ganapathy V. Na+- and Cl--coupled active transport of carnitine by the amino acid transporter ATB(0,+) from mouse colon expressed in HRPE cells and Xenopus oocytes. J Physiol 2001; 532:297-304. [PMID: 11306651 PMCID: PMC2278546 DOI: 10.1111/j.1469-7793.2001.0297f.x] [Citation(s) in RCA: 133] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
1. ATB(0,+) is an amino acid transporter energized by transmembrane gradients of Na+ and Cl(-) and membrane potential. We cloned this transporter from mouse colon and expressed the clone functionally in mammalian (human retinal pigment epithelial, HRPE) cells and Xenopus laevis oocytes to investigate the interaction of carnitine and its acyl esters with the transporter. 2. When expressed in mammalian cells, the cloned ATB(0,+) was able to transport carnitine, propionylcarnitine and acetylcarnitine. The transport process was Na(+) and Cl(-) dependent and inhibitable by the amino acid substrates of the transporter. The Michaelis constant for carnitine was 0.83 +/- 0.08 mM and the Hill coefficient for Na(+) activation was 1.6 +/- 0.1. 3. When expressed in Xenopus laevis oocytes, the cloned ATB(0,+) was able to induce inward currents in the presence of carnitine and propionylcarnitine under voltage-clamped conditions. There was no detectable current in the presence of acetylcarnitine. Carnitine-induced currents were obligatorily dependent on the presence of Na(+) and Cl(-). The currents were saturable with carnitine and the Michaelis constant was 1.8 +/- 0.4 mM. The analysis of Na(+)- and Cl(-)-activation kinetics revealed that 2 Na(+) and 1 Cl(-) were involved in the transport of carnitine via the transporter. 4. These studies describe the identification of a novel function for the amino acid transporter ATB(0,+). Since this transporter is expressed in the intestinal tract, lung and mammary gland, it is likely to play a significant role in the handling of carnitine in these tissues. 5. A Na(+)-dependent transport system for carnitine has already been described. This transporter, known as OCTN2 (novel organic cation transporter 2), is expressed in most tissues and transports carnitine with high affinity. It is energized, however, only by a Na(+) gradient and membrane potential. In contrast, ATB(0,+) is a low-affinity transporter for carnitine, but exhibits much higher concentrative capacity than OCTN2 because of its energization by transmembrane gradients of Na(+) and Cl(-) as well as by membrane potential.
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Affiliation(s)
- T Nakanishi
- Department of Biochemistry and Molecular Biology, Medical College of Georgia, Augusta, GA 30912, USA
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Wu X, Huang W, Ganapathy ME, Wang H, Kekuda R, Conway SJ, Leibach FH, Ganapathy V. Structure, function, and regional distribution of the organic cation transporter OCT3 in the kidney. Am J Physiol Renal Physiol 2000; 279:F449-58. [PMID: 10966924 DOI: 10.1152/ajprenal.2000.279.3.f449] [Citation(s) in RCA: 101] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We examined in this study the expression of the potential-sensitive organic cation transporter OCT3 in the kidney. A functionally active OCT3 was cloned from a mouse kidney cDNA library. The cloned transporter was found to be capable of mediating potential-dependent transport of a variety of organic cations including tetraethylammonium. This function was confirmed in two different heterologous expression systems involving mammalian cells and Xenopus laevis oocytes. We have also isolated the mouse OCT3 gene and deduced its structure and organization. The OCT3 gene consists of 11 exons and 10 introns. In situ hybridization studies in the mouse kidney have shown that OCT3 mRNA is expressed primarily in the cortex. The expression is evident in the proximal and distal convoluted tubules. The expression of OCT3 in human kidney was confirmed by RT-PCR. We have also cloned OCT3 from human placenta and human kidney. Human OCT3 exhibits 86% identity with mouse OCT3 in amino acid sequence. Human OCT3 was found to transport tetraethylammonium and a variety of other organic cations. The transport process was electrogenic. We conclude that OCT3 is expressed in mammalian kidney and that it plays an important role in the renal clearance of cationic drugs.
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Affiliation(s)
- X Wu
- Department of Biochemistry and Molecular Biology, Medical College of Georgia, Augusta, Georgia 30912, USA
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Wagner CA, Lükewille U, Kaltenbach S, Moschen I, Bröer A, Risler T, Bröer S, Lang F. Functional and pharmacological characterization of human Na(+)-carnitine cotransporter hOCTN2. Am J Physiol Renal Physiol 2000; 279:F584-91. [PMID: 10966938 DOI: 10.1152/ajprenal.2000.279.3.f584] [Citation(s) in RCA: 79] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
L-Carnitine is essential for the translocation of acyl-carnitine into the mitochondria for beta-oxidation of long-chain fatty acids. It is taken up into the cells by the recently cloned Na(+)-driven carnitine organic cation transporter OCTN2. Here we expressed hOCTN2 in Xenopus laevis oocytes and investigated with two-electrode voltage- clamp and flux measurements its functional and pharmacological properties as a Na(+)-carnitine cotransporter. L-carnitine transport was electrogenic. The L-carnitine-induced currents were voltage and Na(+) dependent, with half-maximal currents at 0.3 +/- 0.1 mM Na(+) at -60 mV. Furthermore, L-carnitine-induced currents were pH dependent, decreasing with acidification. In contrast to other members of the organic cation transporter family, hOCTN2 functions as a Na(+)-coupled carnitine transporter. Carnitine transport was stereoselective, with an apparent Michaelis-Menten constant (K(m)) of 4.8 +/- 0.3 microM for L-carnitine and 98.3 +/- 38.0 microM for D-carnitine. The substrate specificity of hOCTN2 differs from rOCT-1 and hOCT-2 as hOCTN2 showed only small currents with classic OCT substrates such as choline or tetraethylammonium; by contrast hOCTN2 mediated transport of betaine. hOCTN2 was inhibited by several drugs known to induce secondary carnitine deficiency. Most potent blockers were the antibiotic emetine and the ion channel blockers quinidine and verapamil. The apparent IC(50) for emetine was 4.2 +/- 1.2 microM. The anticonvulsant valproic acid did not induce a significant inhibition of carnitine transport, pointing to a different mode of action. In summary, hOCTN2 mediates electrogenic Na(+)-dependent stereoselective high-affinity transport of L-carnitine and Na(+). hOCTN2 displays transport properties distinct from other members of the OCT family and is directly inhibited by several substances known to induce systemic carnitine deficiency.
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Affiliation(s)
- C A Wagner
- Department of Physiology I, University of Tübingen, 72076 Tübingen, Germany.
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Uwai Y, Saito H, Hashimoto Y, Inui K. Inhibitory effect of anti-diabetic agents on rat organic anion transporter rOAT1. Eur J Pharmacol 2000; 398:193-7. [PMID: 10854830 DOI: 10.1016/s0014-2999(00)00324-1] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The interactions of sulfonylureas and a novel anti-diabetic drug, nateglinide, with rat renal organic anion transporter (rOAT1) expressed in Xenopus laevis oocytes were studied. Uptake of p-aminohippurate via rOAT1 was markedly inhibited by glibenclamide and nateglinide, and moderately by chlorpropamide and tolbutamide. The inhibition constant values (K(i)) for chlorpropamide, glibenclamide, tolbutamide and nateglinide were 39.5, 1.6, 55.5 and 9.2 microM, respectively. Kinetic analysis showed that the inhibition of p-aminohippurate uptake by glibenclamide was competitive. Sulfonylureas examined and nateglinide did not show a trans-stimulation effect on [14C]p-aminohippurate efflux from rOAT1-expressing oocytes. There was no stimulation of [3H]glibenclamide uptake via rOAT1. These findings suggested that sulfonylureas and nateglinide interact with rOAT1, but these drugs are not translocated via the transporter.
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Affiliation(s)
- Y Uwai
- Department of Pharmacy, Kyoto University Hospital, Faculty of Medicine, Kyoto University, Sakyo-ku, 606-8507, Kyoto, Japan
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Ganapathy ME, Huang W, Rajan DP, Carter AL, Sugawara M, Iseki K, Leibach FH, Ganapathy V. beta-lactam antibiotics as substrates for OCTN2, an organic cation/carnitine transporter. J Biol Chem 2000; 275:1699-707. [PMID: 10636865 DOI: 10.1074/jbc.275.3.1699] [Citation(s) in RCA: 138] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Therapeutic use of cephaloridine, a beta-lactam antibiotic, in humans is associated with carnitine deficiency. A potential mechanism for the development of carnitine deficiency is competition between cephaloridine and carnitine for the renal reabsorptive process. OCTN2 is an organic cation/carnitine transporter that is responsible for Na(+)-coupled transport of carnitine in the kidney and other tissues. We investigated the interaction of several beta-lactam antibiotics with OCTN2 using human cell lines that express the transporter constitutively as well as using cloned human and rat OCTN2s expressed heterologously in human cell lines. The beta-lactam antibiotics cephaloridine, cefoselis, cefepime, and cefluprenam were found to inhibit OCTN2-mediated carnitine transport. These antibiotics possess a quaternary nitrogen as does carnitine. Several other beta-lactam antibiotics that do not possess this structural feature did not interact with OCTN2. The interaction of cephaloridine with OCTN2 is competitive with respect to carnitine. Interestingly, many of the beta-lactam antibiotics that were not recognized by OCTN2 were good substrates for the H(+)-coupled peptide transporters PEPT1 and PEPT2. In contrast, cephaloridine, cefoselis, cefepime, and cefluprenam, which were recognized by OCTN2, did not interact with PEPT1 and PEPT2. The interaction of cephaloridine with OCTN2 was Na(+)-dependent, whereas the interaction of cefoselis and cefepime with OCTN2 was largely Na(+)-independent. Furthermore, the Na(+)-dependent, OCTN2-mediated cellular uptake of cephaloridine could be demonstrated by direct uptake measurements. These studies show that OCTN2 plays a crucial role in the pharmacokinetics and therapeutic efficacy of certain beta-lactam antibiotics such as cephaloridine and that cephaloridine-induced carnitine deficiency is likely to be due to inhibition of carnitine reabsorption in the kidney.
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Affiliation(s)
- M E Ganapathy
- Department of Medicine, Medical College of Georgia, Augusta, Georgia 30912, USA.
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