Characterization of Preclinical Pharmacokinetic Properties and Prediction of Human PK Using a Physiologically Based Pharmacokinetic Model for a Novel Anti-Arrhythmic Agent Sulcardine Sulfate.

PURPOSE: Sulcardine sulfate (Sul) is a novel antiarrhythmic agent with promising pharmacological properties, which is currently being evaluated in several clinical trials as an oral formulation. To meet the medication needs of patients with acute conditions, the injection formulation of Sul has been developed. The objective of this study was to systemically investigate the pharmacokinetic profiles of Sul after intravenous infusion. METHODS: This research included the plasma protein binding and metabolic stability studies in vitro, plasma pharmacokinetics, biodistribution, excretion studies in animals, and the prediction of the clinical PK of Sul injection using a physiologically based pharmacokinetics (PBPK) model. RESULTS: The metabolic stability was similarly in dogs and humans but lower in rats. The plasma protein binding rates showed a concentration-dependent manner and species differences. The pharmacokinetic behavior after intravenous administration was linear in rats within the dose range of 30-90 mg/kg, but nonlinear in dogs within 30-60 mg/kg. Sul could be rapidly and widely distributed in multiple tissues after intravenous administration. About 12% of the parent compound were excreted via the urine and only a small fraction via bile and feces,and eight metabolites were found and identified in the rat excretion. The PBPK models were developed and simulated the observed PK date well in both rats and dogs. The PBPK model refined with human data predicted the PK characteristics of the first intravenous infusion of Sul in human. CONCLUSIONS: Our study systematically explored the pharmacokinetic characteristics of Sul and successfully developed the PBPK model to predict of its clinical PK.

Human plasma concentration-time profiles of troglitazone and troglitazone sulfate simulated by in vivo experiments with chimeric mice with humanized livers and semi-physiological pharmacokinetic modeling.

Troglitazone and its major metabolite troglitazone sulfate were intravenously administered to chimeric mice with different ratios of liver replacement by human hepatocytes. Total clearances were converted to hepatic intrinsic clearances normalized to their liver weight, with the assumption that extra-hepatic elimination of these compounds was negligible. These values were plotted against the replacement indices, and postulated values for virtual 100% chimeric mice were assumed to be equivalent to those in humans. Metabolic formation ratio was estimated by comparing AUCs of troglitazone sulfate after separate administration of troglitazone and troglitazone sulfate. Liver to plasma concentration ratios were obtained from direct measurement. These parameters were extrapolated to 100% chimeric mice and subjected to semi-physiological pharmacokinetic modeling using pharmacokinetic parameters for oral administration taken from literature. Our simulated plasma concentration-time profile of troglitazone agreed well with observed values obtained in clinical study. However, the profile of troglitazone sulfate was far below the reported values. Although the possible reasons for this discrepancy remains unsolved, the combination of chimeric mice with semi-physiological PK modeling proved to be a useful tool in understanding the function of each PK parameter in human pharmacokinetics of troglitazone and its conjugated metabolite.

Oral Bioavailability and Mass Balance Studies of a Novel Anti-arrhythmic Agent Sulcardine Sulfate in Sprague-Dawley Rats and Beagle Dogs.

BACKGROUND AND OBJECTIVES: Sulcardine sulfate is a newly developed candidate drug used to control arrhythmias. The aim of this research was to investigate the pharmacokinetics, bioavailability and excretion characteristics of sulcardine in animals. METHODS: Sprague-Dawley rats were orally and intravenously given sulcardine at 20 and 40 mg/kg. Beagle dogs were also orally and intravenously dosed at 10 mg/kg. Both [3H]-labeled sulcardine and unlabeled sulcardine were given to rats. Feces, urine and bile were collected at 0-72 h for mass balance study. The contents of unlabeled sulcardine and radioactivity in samples were determined by a validated LC-MS/MS method and by liquid scintillation counting, separately. RESULTS: Sulcardine was rapidly eliminated in rats after dosing. The oral bioavailability was 34-35 % in rats, while a higher exposure was observed in dogs (bioavailability = 62.7 %). More than 90 % of dosed sulcardine was recovered, and approximately 20-40 % of the dose excreted into urine as the original form, and the remaining was found in feces and bile, most of which (about 40 %) was transformed into metabolites. No difference was observed between sexes. Metabolism may occur to a large extent after oral administration in rats but to a smaller extent in dogs. CONCLUSIONS: Sulcardine was extensively absorbed in both rats and dogs after oral administration. The mass balance data indicated that sulcardine was widely metabolized in rats after oral administration.

Determination of the novel antiarrhythmic drug sulcardine sulfate in human plasma by liquid chromatography tandem mass spectrometry and its application in a clinical pharmacokinetic study.

Sulcardine sulfate (Sul), a novel antiarrhythmic agent, is currently in phase I and phase II clinical trials. To elucidate its clinical pharmacokinetic characteristics, a rapid and accurate liquid chromatography-tandem mass spectrometry (LC-MS/MS) method has been developed and validated for the quantification of Sul in human plasma. Plasma samples were precipitated by acetonitrile and isotope-labeled sulcardine was added as internal standard. The analysis was carried out on a Capcell Pak C18 MG III column (100 × 2.0 mm, 5 µm) with 0.1% formic acid in acetonitrile solution and water (17:83, v/v) as mobile phase. The linear range was 5.0-1000 ng/mL for Sul, with a lower limit of quantification of 5.0 ng/mL. The intra- and inter-batch CVs were within ±11.0% and the accuracies were 4.9-107.3%. Our method, for the first time, allows the rapid (only 3.0 min) and accurate quantification of Sul in human plasma. The method has been successfully applied in the pharmacokinetic study of Sul in a clinical trial following oral administration of Sul to healthy volunteers. Copyright © 2016 John Wiley & Sons, Ltd.

Green tea inhibited the elimination of nephro-cardiovascular toxins and deteriorated the renal function in rats with renal failure.

Chronic kidney disease (CKD) is a major health problem worldwide. Indoxyl sulfate (IS) and p-cresyl sulfate (PCS) are highly protein-bound nephro-cardiovascular toxins, which are not efficiently removed through hemodialysis. The renal excretions of IS and PCS were mediated by organic anion transporters (OATs) such as OAT1 and OAT3. Green tea (GT) is a popular beverage containing plenty of catechins. Previous pharmacokinetic studies of teas have shown that the major molecules present in the bloodstream are the glucuronides/sulfates of tea catechins, which are putative substrates of OATs. Here we demonstrated that GT ingestion significantly elevated the systemic exposures of endogenous IS and PCS in rats with chronic renal failure (CRF). More importantly, GT also significantly increased the levels of serum creatinine (Cr) and blood urea nitrogen (BUN) in CRF rats. Mechanism studies indicated that the serum metabolites of GT (GTM) inhibited the uptake transporting functions of OAT1 and OAT3. In conclusion, GT inhibited the elimination of nephro-cardiovascular toxins such as IS and PCS, and deteriorated the renal function in CRF rats.

In vivo kinetics of the uremic toxin p-cresyl sulfate in mice with variable renal function.

Uremic toxins such as p-cresyl sulfate (PCS) are associated with increased mortality for chronic kidney disease (CKD) patients, but in vivo PCS toxicity studies are limited due to the lack of a standard animal model. To establish such a model, we measured the pharmacokinetics of PCS in mice with variable renal function. Male Balb/c mice subjected to 5/6 nephrectomy (CRF), unilateral nephrectomy (UNX), or no surgery (controls) were given PCS (po, 50 mg/kg). Blood samples were collected over time and plasma PCS concentrations were measured. Over 4 h, PCS was significantly higher in the plasma of CRF mice (63.28 ± 2.76 mg/L), compared to UNX mice (3.11 ± 0.64 mg/L) and controls (0.39 ± 0.12 mg/L). The PCS half-life was greatest in CRF mice (12.07 ± 0.12 h), compared to 0.79 ± 0.04 h in UNX mice and 0.48 ± 0.02 h in control mice. However, the potential presence of additional uremic toxins along with PCS in CRF mice and rapid PCS clearance in control mice suggest that the UNX mouse would be a better PCS model to study toxicity.

The effect of knockout of sulfotransferases 1a1 and 1d1 and of transgenic human sulfotransferases 1A1/1A2 on the formation of DNA adducts from furfuryl alcohol in mouse models.

Furfuryl alcohol is a rodent carcinogen present in numerous foodstuffs. Sulfotransferases (SULTs) convert furfuryl alcohol into the DNA reactive and mutagenic 2-sulfoxymethylfuran. Sensitive techniques for the isotope-dilution ultra performance liquid chromatography-tandem mass spectrometry quantification of resulting DNA adducts, e.g. N (2)-((furan-2-yl)methyl)-2'-deoxyguanosine (N (2)-MF-dG), were developed. To better understand the contribution of specific SULT forms to the genotoxicity of furfuryl alcohol in vivo, we studied the tissue distribution of N (2)-MF-dG in different mouse models. Earlier mutagenicity studies with Salmonella typhimurium strains expressing different human and murine SULT forms indicated that human SULT1A1 and murine Sult1a1 and 1d1 catalyze furfuryl alcohol sulfo conjugation most effectively. Here, we used three mouse lines to study the bioactivation of furfuryl alcohol by murine SULTs, FVB/N wild-type (wt) mice and two genetically modified models lacking either murine Sult1a1 or Sult1d1. The animals received a single dose of furfuryl alcohol, and the levels of the DNA adducts were determined in liver, kidney, lung, colon and small intestine. The effect of Sult1d1 gene disruption on the genotoxicity of furfuryl alcohol was moderate and limited to kidney and small intestine. In contrast, the absence of functional Sult1a1 had a massive influence on the adduct levels, which were lowered by 33-73% in all tissues of the female Sult1a1 null mice compared with the wt animals. The detection of high N (2)-MF-dG levels in a humanized mouse line expressing hSULT1A1/1A2 instead of endogeneous Sult1a1 and Sult1d1 supports the hypothesis that furfuryl alcohol is converted to the mutagenic 2-sulfoxymethylfuran also in humans.

Simultaneous determination of 9-dehydro-17-hydro-andrographolide and sodium 9-dehydro-17-hydro-andrographolide-19-yl sulfate in rat plasma by UHPLC-ESI-MS/MS after administration of xiyanping injection: application to a pharmacokinetic study.

9-Dehydro-17-hydro-andrographolide (DHA) and sodium 9-dehydro-17-hydro-andrographolide-19-yl sulfate (DHAS) are active ingredients of xiyanping injection in clinical use. A simple, rapid and sensitive UHPLC-ESI-MS/MS method was developed for the determination of DHA and DHAS in rat plasma, and the pharmacokinetics of DHA and DHAS after intravenous administration of xiyanping injection was investigated. The plasma samples were treated with methanol to precipitate out protein, and the separation of DHA and DHAS was achieved on a Waters BEH C18 column with a mobile phase consisting of acetonitrile and 10 mmol/L ammonium acetate solution at a flow rate of 0.4 mL/min. DHA, DHAS and the internal standard (internal standard, IS) diethylstilbestrol were detected at negative ion mode. The precursor-product ion pairs used in multiple reaction monitoring mode were: m/z 349.1 → 286.9 (DHA), m/z 428.9 → 96.0 (DHAS) and m/z 267.1 → 236.9 (IS). Calibration curves offered satisfactory linearity within the test range, and all correlation coefficients were >0.995. The lower limit of detection of DHA and DHAS in plasma samples were determined to be 0.1 ng/mL. The lower limit of quantitation was 0.5 ng/mL for DHA and DHAS. All the recoveries of the quality control samples were in the range of 86.0-102.4%. The ratios of matrix effect were between 89.2 and 105.1%. The method was fully validated and successfully applied to the pharmacokinetic study of DHA and DHAS in rats. The study showed that both DHA and DHAS were distributed and eliminated rapidly in rats.

Final report on the safety assessment of sodium cetearyl sulfate and related alkyl sulfates as used in cosmetics.

Sodium cetearyl sulfate is the sodium salt of a mixture of cetyl and stearyl sulfate. The other ingredients in this safety assessment are also alkyl salts, including ammonium coco-sulfate, ammonium myristyl sulfate, magnesium coco-sulfate, sodium cetyl sulfate, sodium coco/hydrogenated tallow sulfate, sodium coco-sulfate, sodium decyl sulfate, sodium ethylhexyl sulfate, sodium myristyl sulfate, sodium oleyl sulfate, sodium stearyl sulfate, sodium tallow sulfate, sodium tridecyl sulfate, and zinc coco-sulfate. These ingredients are surfactants used at concentrations from 0.1% to 29%, primarily in soaps and shampoos. Many of these ingredients are not in current use. The Cosmetic Ingredient Review (CIR) Expert Panel previously completed a safety assessment of sodium and ammonium lauryl sulfate. The data available for sodium lauryl sulfate and ammonium lauryl sulfate provide sufficient basis for concluding that sodium cetearyl sulfate and related alkyl sulfates are safe in the practices of use and concentration described in the safety assessment.

Interplay of phase II enzymes and transporters in futile cycling: influence of multidrug resistance-associated protein 2-mediated excretion of estradiol 17beta-D-glucuronide and its 3-sulfate metabolite on net sulfation in perfused TR(-) and Wistar rat liver preparations.

The hepatic disposition of estradiol 17beta-D-glucuronide (E(2)17G), a substrate of the organic anion-transporting polypeptides Oatp1a1, Oatp1a4, and Oatp1b2, was investigated in Wistar and TR(-) [multidrug resistance-associated protein (Mrp) 2-mutant] rats to elucidate how absence of Mrp2, the major excretory transporter for both E(2)17G and its 3-sulfate metabolite (E(2)3S17G), affected the net sulfation. With absence of Mrp2, lower microsomal desulfation activity and higher Mrp3 but unchanged immunoreactive protein expression of other transporters (Oatps and Mrp4) and estrogen sulfotransferase were found in TR(-) rats. In recirculating, perfused liver preparations, the rapid decay of E(2)17G and sluggish appearance of low levels of E(2)3S17G in perfusate for Wistar livers were replaced by a protracted, biexponential decay of E(2)17G and greater accumulation of E(2)3S17G, whose levels reached plateaus upon the almost complete obliteration of biliary excretion of E(2)17G and E(2)3S17G in the TR(-) liver. Much higher amounts of E(2)17G (28x) and E(2)3S17G (11x) in liver and reduced net sulfation (40 +/- 6 from 77 +/- 6% dose, P < 0.05) were observed at 2 h for the TR(-) versus the Wistar rats. With use of a physiologically based pharmacokinetic model, analytical solutions for the areas under the curve for the precursor and metabolite were obtained to reveal how enzyme- and transporter-mediated processes affected the hepatic disposition of the precursor and metabolite in futile cycling. The analytical solutions were useful to explain transporter-enzyme interplay in futile cycling and predicted that a shutdown of Mrp2 function led to decreased net sulfation of E(2)17G by raising the intracellular concentration of the metabolite, E(2)3S17G, which readily refurnished E(2)17G via desulfation.

Synthesis and biological evaluation of polysulfated oligosaccharide glycosides as inhibitors of angiogenesis and tumor growth.

A series of polysulfated penta- and tetrasaccharide glycosides containing alpha(1-->3)/alpha(1-->2)-linked mannose residues were synthesized as heparan sulfate (HS) mimetics and evaluated for their ability to inhibit angiogenesis. The compounds bound tightly to angiogenic growth factors (FGF-1, FGF-2, and VEGF) and strongly inhibited heparanase activity. In addition, the compounds exhibited potent activity in cell-based and ex vivo assays indicative of angiogenesis, with tetrasaccharides exhibiting activity comparable to that of pentasaccharides. Selected compounds also showed good antitumor activity in vivo in a mouse melanoma (solid tumor) model resistant to the phase III HS mimetic 1 (muparfostat, formerly known as PI-88). The lipophilic modifications also resulted in reduced anticoagulant activity, a common side effect of HS mimetics, and conferred a reasonable pharmacokinetic profile in the rat, as exemplified by the sulfated octyl tetrasaccharide 5. The data support the further investigation of this class of compounds as potential antiangiogenic, anticancer therapeutics.

Computer assisted modeling of ethyl sulfate pharmacokinetics.

For 12 volunteers of a drinking experiment the concentration-time-courses of ethyl sulfate (EtS) and ethanol were simulated and fitted to the experimental data. The concentration-time-courses were described with the same mathematical model as previously used for ethyl glucuronide (EtG). The kinetic model based on the following assumptions and simplifications: a velocity constant k(form) for the first order formation of ethyl sulfate from ethanol and an exponential elimination constant k(el). The mean values (and standard deviations) obtained for k(form) and k(el) were 0.00052 h(-1) (0.00014) and 0.561 h(-1) (0.131), respectively. Using the ranges of these parameters it is possible to calculate minimum and maximum serum concentrations of EtS based on stated ethanol doses and drinking times. The comparison of calculated and measured concentrations can prove the plausibility of alleged ethanol consumption and add evidence to the retrospective calculation of ethanol concentrations based on EtG concentrations.

Reversal of fluconazole resistance by sulfated sterols from the marine sponge Topsentia sp.

Bioassay-guided fractionation of the extract of Topsentia sp. led to the identification of two new sulfated sterols, geodisterol-3-O-sulfite (1) and 29-demethylgeodisterol-3-O-sulfite (2), the active constituents reversing efflux pump-mediated fluconazole resistance. Both compounds enhanced the activity of fluconazole in a Saccharomyces cerevisiae strain overexpressing the Candida albicans efflux pump MDR1, as well as in a fluconazole-resistant Candida albicans clinical isolate known to overexpress MDR1. These results provide insight into the clinical utility of combining efflux pump inhibitors with current antifungals to combat the resistance associated with opportunistic fungal infections caused by C. albicans.

Blood kinetics of ethyl glucuronide and ethyl sulphate in heavy drinkers during alcohol detoxification.

Studies of ethyl glucuronide (EtG) blood kinetics have so far been performed on healthy volunteers with ingestion of low to moderate doses of ethanol. These data are not necessarily transferable to heavy drinkers where the consumed doses of ethanol are much higher. The aim of this study was to investigate the pharmacokinetics of EtG and ethyl sulphate (EtS) in blood in heavy drinkers after termination of alcohol ingestion. Sixteen patients from an alcohol withdrawal clinic were included directly after admission. Time of end of drinking, estimated daily intake of ethanol (EDI) and medical history were recorded. Three to five blood samples over 20-43 h were collected from each patient subsequent to admission. The median EDI was 172 g (range 60-564). The first sample was collected median 2.5 h after end of drinking (range 0.5-23.5). Two patients had levels of EtG and EtS below LOQ in all samples, the first collected 19.25 and 23.5 h after cessation of drinking, respectively. Of the remaining 14 patients, one subject, suffering from both renal and hepatic disease, showed concentrations of EtG and EtS substantially higher than the rest of the material. This patient's initial value of EtG was 17.9 mg/L and of EtS 5.9 mg/L, with terminal elimination half lives of 11.9 h for EtG and 12.5 h for EtS. Among the remaining 13 patients, the initial median values were 0.7 g/L (range 0-3.7) for ethanol, 1.7 mg/L (range 0.1-5.9) for EtG and 0.9 mg/L (range 0.1-1.9) for EtS. Elimination occurred with a median half-life of 3.3 h for EtG (range 2.6-4.3) and 3.6 h for EtS (range 2.7-5.4). In conclusion, elimination of EtG in heavy drinkers did not significantly differ from healthy volunteers, and EtS appeared to have similar elimination rate. In the present work, there was one exception to this, and we propose that this could be explained by the patient's renal disease, which would delay excretion of these conjugated metabolites.

Removal of the protein-bound solutes indican and p-cresol sulfate by peritoneal dialysis.

BACKGROUND AND OBJECTIVES: Protein-bound solutes are poorly cleared by peritoneal dialysis. We examined the hypothesis that plasma concentrations of bound solutes would therefore rise as residual renal function is lost. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: Clearances of urea indican and p-cresol sulfate were measured in peritoneal dialysis patients with and without residual function. RESULTS: In patients with residual function, protein binding restricted the peritoneal indican and p-cresol sulfate clearances to 0.3 +/- 0.1 ml/min, as compared to the peritoneal urea clearance of 5.5 +/- 1.1 ml/min. The urinary indican and p-cresol sulfate clearances of 2.7 +/- 2.5 and 1.3 +/- 1.0 ml/min were closer to the urinary urea clearance of 3.9 +/- 2.2 ml/min, reflecting the superior ability of native kidney function to clear bound solutes. Urinary clearance thus provided the majority of the total indican and p-cresol sulfate clearances of 3.0 +/- 2.5 and 1.6 +/- 1.0 ml/min in patients with residual function but the minority of total urea clearance of 9.4 +/- 2.2 ml/min. Loss of residual function lowered the total clearances for indican and p-cresol sulfate to 0.5 +/- 0.2 and 0.4 +/- 0.2 ml/min, whereas the urea clearance fell only slightly. However there was only a modest increase in the plasma indican level and no increase in the plasma p-cresol sulfate level in patients with no residual function because reduction in the daily removal of these solutes accompanied the reduction in their total clearance rates. CONCLUSIONS: Reduction in the removal of indican and p-cresol sulfate kept plasma levels from rising markedly when residual function was lost.

[Methyl sulphides and their metabolites in biologic materials of workers engaged into sulfate pulping].

The authors studied serum and urine levels of methyl sulphides in workers engaged into sulfate pulping and exposed to methyl sulphides. Blood serum was studied only for dimethyldisulfide. Urine appeared to contain no methyl sulphides, but finding was increased urinary excretion of sulfates which are metabolites of methyl sulphides. Sulfates content of urine correlated with intensity and duration of exposure to methyl sulphides, so this exposure test could be used as a biologic marker in monitoring work conditions and health state of workers exposed to methyl sulphides.

A role for sulfation-desulfation in the uptake of bisphenol a into breast tumor cells.

Bisphenol A (BPA) is a widely used plasticizer whose estrogenic properties may impact hormone-responsive disorders and fetal development. In vivo, BPA appears to have greater activity than is suggested by its estrogen receptor (ER) binding affinity. This may be a result of BPA sulfation/desulfation providing a pathway for selective uptake into hormone-responsive cells. BPA is a substrate for estrogen sulfotransferase, and bisphenol A sulfate (BPAS) and disulfate are substrates for estrone sulfatase. Although the sulfated xenobiotics bind poorly to the ER, both stimulated the growth of receptor-positive breast tumor cells. Treatment of MCF-7 cells with BPAS leads to desulfation and uptake of BPA. No BPAS is found inside the cells. These findings suggest a mechanism for the selective uptake of BPA into cells expressing estrone sulfatase. Therefore, sulfation may increase the estrogenic potential of xenobiotics.

Adsorption of dyes and phenol from water on resin adsorbents: effect of adsorbate size and pore size distribution.

Batch adsorption runs of two commercial reactive dyes (methylene blue and reactive orange X-GN) and phenol from water onto two resin adsorbents (Amberlite XAD-4, a macroreticular adsorbent and ZCH-101, a hyper-cross-linked adsorbent) were carried out in the present study. Effect of adsorbate size and pore structure of the resin adsorbents on adsorption was discussed and Langmuir and Freundlich models were tested for the relevant adsorption isotherms. In the kinetic section concentration-time profiles were obtained to further elucidate the effect of adsorbate size and porous structure on adsorption mechanism. A pseudo-second-order model was proved to give a satisfactory description of the related kinetic results. Two-stage kinetic curve of methylene blue onto ZCH-101 was observed at a specific experimental condition and modeled schematically according to its specific pore size distribution. Furthermore, other kinetic experiments were performed at different ambient temperature to validate the proposed schematic model.

Uptake of chemically reactive, DNA-damaging sulfuric acid esters into renal cells by human organic anion transporters.

The procarcinogen 1-methylpyrene is activated by hepatic enzymes via 1-hydroxymethylpyrene to 1-sulfooxymethylpyrene (1-SMP), a highly reactive and mutagenic metabolite. Previously, high levels of 1-SMP DNA adducts were observed in rat kidneys after intraperitoneal administration of 1-hydroxymethylpyrene or 1-SMP. This study examined whether organic anion transporters (OAT) that are expressed at the basolateral membrane of proximal tubule cells are involved in uptake of SMP. Human epithelial kidney (HEK293) cells that stably express human OAT1 (hOAT1) and hOAT3 were used. Stable isomers of 1-SMP, (2-SMP and 4-SMP) competitively inhibited the uptake of characteristic substrates p-aminohippurate for hOAT1 and estrone sulfate for hOAT3. Both inhibitors exhibited high affinity for hOAT1 (K(i) = 4.4 microM for 2-SMP; K(i) = 5.1 microM for 4-SMP) as well as hOAT3 (K(i) = 1.9 microM for 2-SMP; K(i) = 2.1 microM for 4-SMP). The uptake rate of 4-SMP (at a concentration of 10 microM) by hOAT1- and hOAT3-expressing cells was 3.0 and 1.6 times higher, respectively, than in control cells. Uptake of the reactive isomer 1-SMP was investigated using as the end point the level of DNA adducts that were formed in the cells. After exposure to 1-SMP (10 microM), the DNA adduct level was 4.6 and 3.0 times higher in hOAT1- and hOAT3-expressing cells, respectively, than in control cells. The enhanced DNA adduct formation in hOAT-expressing cells was abolished in the presence of the OAT inhibitor probenecid. This study indicates that OAT can mediate the basolateral uptake of reactive sulfuric acid esters into proximal tubule cells and thereby participate in kidney cell damage by these compounds.