Category: genotype Project: Pharmacogenetics of Membrane Transporters [Table 1][1] provides HUGO Gene Nomenclature Committee (HGNC) symbols, PharmGKB submission URLs, submission dates, and release dates. [Table 2][2] provides HGNC symbols, HGNC names, synonyms, GenBank accession numbers, and locus

The human organic anion transporter, OAT3 ( SLC22A8), plays a critical role in renal drug elimination, by mediating the entry of a wide variety of organic anions, including a number of commonly used pharmaceuticals, into the renal proximal tubular cells. To understand the nature and extent of genetic variation in OAT3, and to determine whether such variation affects its function, we identified OAT3 variants in a large, ethnically diverse sample population and studied their transport activities in cellular assays. We identified a total of 10 distinct coding-region variants, which altered the encoded amino acid sequence, in DNA samples from 270 individuals ( 80 African-Americans, 80 European-Americans, 60 Asian-Americans, and 50 Mexican-Americans). The overall prevalence of these OAT3 variants was relatively low among the screened population, with only three variants having allele frequencies of > 1% in a particular ethnic group. Clones of each variant were created by site-directed mutagenesis, expressed in HEK-293 cells, and tested for function using the model substrates, estrone sulfate ( ES) and cimetidine ( CIM). The results revealed a high degree of functional heterogeneity among OAT3 variants, with three variants ( p. Arg149Ser, p. Gln239Stop, and p. Ile260Arg) that resulted in complete loss of function, and several others with significantly reduced function. One of the more common variants ( p. Ile305Phe), found in 3.5% of Asian-Americans, appeared to have altered substrate specificity. This variant exhibited a reduced ability to transport ES, but a preserved ability to transport CIM. These data suggest that genetic variation in OAT3 may contribute to variation in the disposition of drugs.

Background The human organic anion transporter, OAT3 (SLC22A8), mediates renal excretion of various drugs including cephalosporins. To test whether genetic variants of OAT3 exhibit altered function in vitro and in vivo, we conducted a series of studies. Methods Coding region variants of OAT3 were identified in an ethnically diverse population of 276 humans. Variants were constructed by site-directed mutagenesis and expressed in human embryonic kidney cells. Cellular uptake of radiolabeled estrone sulfate (ES) was determined in the presence and absence of 5 mM cefotaxime. To evaluate in vivo variant function, subjects with selected alleles were given an IV dose of 2 gm cefotaxime and serial blood and urine cefotaxime concentrations were measured. Results We discovered 10 non-synonymous OAT3 variants. In in vitro assays, three variants (F>L, A>S, V>I) showed minimally reduced ( W, I>F) showed moderately reduced (33–66%) uptake; and four (R>S, Q>X, I>R, A>V) were non-functional. Cefotaxime significantly inhibited ES uptake by all variants that retained function. Preliminary results of the in vivo trial show that two subjects (one heterozygous for I>F, and one with both Q>X and R>S alleles) had reduced cefotaxime renal clearance compared to two controls. Conclusions We identified a number of OAT3 variants with reduced function. Preliminary results suggest that individuals with these variants have reduced renal cefotaxime clearance. Clinical Pharmacology & Therapeutics (2005) 77, P96–P96; doi: 10.1016/j.clpt.2004.12.260

The human organic anion transporter, OAT3 (SLC22A8), mediates renal excretion of various endogenous substances and xenobiotics. Genetic variants in OAT3 may alter its activity, and thus affect the elimination of certain pharmaceuticals. We identified ten non-synonymous OAT3 variants by screening the exonic regions of DNA samples from an ethnically diverse population of 256 subjects. One variant, OAT3–V>A, had an allele frequency of 6% in African Americans; all others were less common. We then screened all ten variants for function. Samples of the variants were produced by site-directed mutagenesis of reference OAT3 cDNA. Reference and variant sequences were transiently expressed in a vaccinia-infected HeLa cell system, and function of their encoded transporters assessed by measuring cellular uptake of 3H-estrone sulfate. Compared with reference, five of the OAT3 variants, OAT3-F>L, -R>S, -Q>X, -I>R, and -R>W, had significantly reduced substrate transport (range = 18-36% of control). Four variants, OAT3-V>A, -A>V, -A>S, and -V>I, displayed substrate transport similar to, or exceeding, reference (range = 127-178% of control). The common variant, OAT3-I>F, showed an intermediate uptake (53% of control) of 3H-estrone sulfate, but an uptake of cimetidine similar to reference, suggesting that this variant may exhibit altered specificity. The data suggest that genetic variation in OAT3 may contribute to interindividual variation in the renal elimination of various drugs and toxins. Clinical Pharmacology & Therapeutics (2004) 75, P93–P93; doi: 10.1016/j.clpt.2003.11.356