The Comprehensive Characterization of B7-H3 Expression in the Tumor Microenvironment of Lung Squamous Cell Carcinoma: A Retrospective Study.

Lung squamous cell carcinoma (LSCC) is refractory to various therapies for non-small cell cancer; therefore, new therapeutic approaches are required to improve the prognosis of LSCC. Although immunotherapies targeting B7 family molecules were explored as treatments for several cancer types, the expression and significance of B7-H3 in the tumor microenvironment (TME) and its relationship with other immune checkpoint molecules have not yet been investigated in detail. We used high-throughput quantitative multiplex immunohistochemistry to examine B7-H3 expression in the TME. We investigated the relationship between B7-H3 expression and prognosis as well as changes in the TME with B7-H3 expression using 110 surgically resected pathological specimens retrospectively. We examined the correlation between B7-H3 and programmed cell death-ligand 1 (PD-L1) expression in single cells. High B7-H3 expression in tumor cells was associated with a better prognosis and a significant increase in the number of CD163+PD-L1+ macrophages. Quantitative analysis revealed that there is a positive correlation between B7-H3 and PD-L1 expression in tumor and stromal cells, as well as in intratumoral tumor-infiltrating lymphocytes and tumor-associated macrophages in the same cells. CD68+, CD163+, and CK+ cells with PD-L1+ phenotypes had higher B7-H3 expression compared to PD-L1- cells. Our findings demonstrate a correlation between B7-H3 and PD-L1 expression in the same cells, indicating that therapies targeting B7-H3 could provide additional efficacy in patients refractory to PD-L1-targeting therapies.

Analysis of in vitro and in vivo metabolism of zidovudine and gemfibrozil in trans-chromosomic mouse line expressing human UGT2 enzymes.

UDP-glucuronosyltransferases (UGTs) catalyze the conjugation of various substrates with sugars. Since the UGT2 family forms a large cluster spanning 1.5 Mb, transgenic mouse lines carrying the entire human UGT2 family have not been constructed because of limitations in conventional cloning techniques. Therefore, we made a humanized mouse model for UGT2 by chromosome engineering technologies. The results showed that six UGT2 isoforms examined were expressed in the liver of adult humanized UGT2 (hUGT2) mice. Thus, the functions of human UGT2B7 in the liver of hUGT2 mice were evaluated. Glucuronide of azidothymidine (AZT, zidovudine), a typical UGT2B7 substrate, was formed in the liver microsomes of hUGT2 mice but not in the liver microsomes of wild-type and Ugt2-knockout mice. When AZT was intravenously administered, AZT glucuronide was detected in the bile and urine of hUGT2 mice, but it was not detected in the bile and urine of wild-type and Ugt2-knockout mice. These results indicated that the hUGT2 mice express functional human UGT2B7 in the liver. This finding was also confirmed by using gemfibrozil as an alternative UGT2B7 substrate. Gemfibrozil glucuronide was formed in the liver microsomes of hUGT2 mice and was mainly excreted in the bile of hUGT2 mice after intravenous dosing of gemfibrozil. This hUGT2 mouse model will enable improved predictions of pharmacokinetics, urinary and biliary excretion and drug-drug interactions mediated by human UGT2, at least UGT2B7, in drug development research and basic research.

Epigenetic programming underpins B cell dysfunction in human SLE.

Systemic lupus erythematosus (SLE) is characterized by the expansion of extrafollicular pathogenic B cells derived from newly activated naive cells. Although these cells express distinct markers, their epigenetic architecture and how it contributes to SLE remain poorly understood. To address this, we determined the DNA methylomes, chromatin accessibility profiles and transcriptomes from five human B cell subsets, including a newly defined effector B cell subset, from subjects with SLE and healthy controls. Our data define a differentiation hierarchy for the subsets and elucidate the epigenetic and transcriptional differences between effector and memory B cells. Importantly, an SLE molecular signature was already established in resting naive cells and was dominated by enrichment of accessible chromatin in motifs for AP-1 and EGR transcription factors. Together, these factors acted in synergy with T-BET to shape the epigenome of expanded SLE effector B cell subsets. Thus, our data define the molecular foundation of pathogenic B cell dysfunction in SLE.

Humanized UGT2 and CYP3A transchromosomic rats for improved prediction of human drug metabolism.

Although "genomically" humanized animals are invaluable tools for generating human disease models as well as for biomedical research, their development has been mainly restricted to mice via established transgenic-based and embryonic stem cell-based technologies. Since rats are widely used for studying human disease and for drug efficacy and toxicity testing, humanized rat models would be preferred over mice for several applications. However, the development of sophisticated humanized rat models has been hampered by the difficulty of complex genetic manipulations in rats. Additionally, several genes and gene clusters, which are megabase range in size, were difficult to introduce into rats with conventional technologies. As a proof of concept, we herein report the generation of genomically humanized rats expressing key human drug-metabolizing enzymes in the absence of their orthologous rat counterparts via the combination of chromosome transfer using mouse artificial chromosome (MAC) and genome editing technologies. About 1.5 Mb and 700 kb of the entire UDP glucuronosyltransferase family 2 and cytochrome P450 family 3 subfamily A genomic regions, respectively, were successfully introduced via the MACs into rats. The transchromosomic rats were combined with rats carrying deletions of the endogenous orthologous genes, achieved by genome editing. In the "transchromosomic humanized" rat strains, the gene expression, pharmacokinetics, and metabolism observed in humans were well reproduced. Thus, the combination of chromosome transfer and genome editing technologies can be used to generate fully humanized rats for improved prediction of the pharmacokinetics and drug-drug interactions in humans, and for basic research, drug discovery, and development.

In vivo multiple metabolic pathways for a novel G protein-coupled receptor 119 agonist DS-8500a in rats: involvement of the 1,2,4-oxadiazole ring-opening reductive reaction in livers under anaerobic conditions.

A 1,2,4-oxadiazole ring-containing compound DS-8500a was developed as a novel G protein-coupled receptor 119 agonist. In vivo metabolic fates of [14C]DS-8500a differently radiolabeled in the benzene ring or benzamide side carbon in rats were investigated. Differences in mass balances were observed, primarily because after the oxadiazole ring-opening and subsequent ring-cleavage small-molecule metabolites containing the benzene side were excreted in the urine, while those containing the benzamide side were excreted in the bile. DS-8500a was detected at trace levels in urine and bile, demonstrating extensive metabolism prior to urinary/biliary excretion. At least 16 metabolite structures were proposed in plasma, urine, and bile samples from rats treated with [14C]DS-8500a. Formation of a ring-opened metabolite (reduced DS-8500a) in hepatocytes of humans, monkeys, and rats was confirmed; however, it was not affected by typical inhibitors of cytochrome P450s, aldehyde oxidases, or carboxylesterases in human hepatocytes. Extensive formation of the ring-opened metabolite was observed in human liver microsomes fortified with an NADPH-generating system under anaerobic conditions. These results suggest an in vivo unique reductive metabolism of DS-8500a is mediated by human non-cytochrome P450 enzymes.

Alkylsulfanyl analogs as potent α2δ ligands.

We identified novel (3R, 5S)-3-aminomethyl-5-methanesulfanyl hexanoic acid (5a: DS75091588) and (3R, 5S)-3-aminomethyl-5-ethanesulfanyl hexanoic acid (6a: DS18430756) as sulfur-containing γ-amino acid derivatives that were useful for the treatment of neuropathic pain. These two compounds exhibited a potent analgesic effect in animal models of both type I diabetes and type II diabetes, and good pharmacokinetics.

Human pharmacokinetic prediction of UDP-glucuronosyltransferase substrates with an animal scale-up approach.

The aim of the current study was to evaluate the accuracy of allometric scaling methods for drugs metabolized by UDP-glucuronosyltransferases (UGTs), such as ketoprofen, imipramine, lorazepam, levofloxacin, zidovudine, diclofenac, furosemide, raloxifene, gemfibrozil, mycophenolic acid, indomethacin, and telmisartan. Human plasma clearance (CL) predictions were conducted from preclinical in vivo data by using multiple-species allometry with the rule of exponents and single-species allometric scaling (SSS) of mice, rats, monkeys, or dogs. Distribution volume at a steady state (V(ss)) was predicted by multiple-species allometry or SSS of V(ss). Oral plasma clearance (CL(po)) was calculated under the assumption that F(a) × F(g) was equivalent across species. Each of the results was compared with the observed parameter calculated from the clinical data after intravenous or oral administration. Multiple-species allometry and SSS of mice, rats, and dogs resulted in a similar accuracy of CL and CL(po) predictions. Monkeys tended to provide the most accurate predictions of human CL and CL(po). The ability to predict the half-life, which was determined from CL and V(ss) predictions, was more accurate in SSS of rats and monkeys. The in vivo fraction metabolized by glucuronidation (f(m,UGT)) in bile duct-cannulated monkeys was relatively similar to that of humans compared with other animal species, which likely contributed to the highest accuracy of SSS prediction of monkeys. On the basis of the current results, monkeys would be more reliable than other animal species in predicting human pharmacokinetics and f(m,UGT) for drugs metabolized by UGTs.

Synthesis and evaluation of novel stearoyl-CoA desaturase 1 inhibitors: 1'-{6-[5-(pyridin-3-ylmethyl)-1,3,4-oxadiazol-2-yl]pyridazin-3-yl}-3,4-dihydrospiro[chromene-2,4'-piperidine] analogs.

In continuation of our investigation on novel stearoyl-CoA desaturase (SCD) 1 inhibitors, we have already reported on the structural modification of the benzoylpiperidines that led to a series of novel and highly potent spiropiperidine-based SCD1 inhibitors. In this report, we would like to extend the scope of our previous investigation and disclose details of the synthesis, SAR, ADME, PK, and pharmacological evaluation of the spiropiperidines with high potency for SCD1 inhibition. Our current efforts have culminated in the identification of 5-fluoro-1'-{6-[5-(pyridin-3-ylmethyl)-1,3,4-oxadiazol-2-yl]pyridazin-3-yl}-3,4-dihydrospiro[chromene-2,4'-piperidine] (10e), which demonstrated a very strong potency for liver SCD1 inhibition (ID(50)=0.6 mg/kg). This highly efficacious inhibition is presumed to be the result of a combination of strong enzymatic inhibitory activity (IC(50) (mouse)=2 nM) and good oral bioavailability (F >95%). Pharmacological evaluation of 10e has demonstrated potent, dose-dependent reduction of the plasma desaturation index in C57BL/6J mice on a high carbohydrate diet after a 7-day oral administration (q.d.). In addition, it did not cause any noticeable skin abnormalities up to the highest dose (10 mg/kg).

Novel benzoylpiperidine-based stearoyl-CoA desaturase-1 inhibitors: Identification of 6-[4-(2-methylbenzoyl)piperidin-1-yl]pyridazine-3-carboxylic acid (2-hydroxy-2-pyridin-3-ylethyl)amide and its plasma triglyceride-lowering effects in Zucker fatty rats.

Starting from a known piperazine-based SCD-1 inhibitor, we obtained more potent benzoylpiperidine analogs. Optimization of the structure of the benzoylpiperidine-based SCD-1 inhibitors resulted in the identification of 6-[4-(2-methylbenzoyl)piperidin-1-yl]pyridazine-3-carboxylic acid (2-hydroxy-2-pyridin-3-yl-ethyl)amide (24) which showed strong inhibitory activity against both human and murine SCD-1. In addition, this compound exhibited good oral bioavailability and demonstrated plasma triglyceride lowering effects in Zucker fatty rats in a dose-dependent manner after a 7-day oral administration (qd).

Novel spiropiperidine-based stearoyl-CoA desaturase-1 inhibitors: Identification of 1'-{6-[5-(pyridin-3-ylmethyl)-1,3,4-oxadiazol-2-yl]pyridazin-3-yl}-5-(trifluoromethyl)-3,4-dihydrospiro[chromene-2,4'-piperidine].

Cyclization of the benzoylpiperidine in lead compound 2 generated a series of novel and highly potent spiropiperidine-based stearoyl-CoA desaturase (SCD)-1 inhibitors. Among them, 1'-{6-[5-(pyridin-3-ylmethyl)-1,3,4-oxadiazol-2-yl]pyridazin-3-yl}-5-(trifluoromethyl)-3,4-dihydrospiro[chromene-2,4'-piperidine] (19) demonstrated the most powerful inhibitory activity against SCD-1, not only in vitro but also in vivo (C57BL/6J mice). With regard to the pharmacological evaluation, 19 showed powerful reduction of the desaturation index in the plasma of C57BL/6J mice on a non-fat diet after a 7-day oral administration (q.d.) without causing notable abnormalities in the eyes or skin up to the highest dose (3mg/kg) in our preliminary analysis.

Novel and potent inhibitors of stearoyl-CoA desaturase-1. Part I: Discovery of 3-(2-hydroxyethoxy)-4-methoxy-N-[5-(3-trifluoromethylbenzyl)thiazol-2-yl]benzamide.

A series of structurally novel stearoyl-CoA desaturase-1 (SCD-1) inhibitors has been identified by optimizing a hit from our corporate library. Preliminary structure-activity relationship (SAR) studies led to the discovery of the highly potent and orally bioavailable thiazole-based SCD-1 inhibitor, 3-(2-hydroxyethoxy)-4-methoxy-N-[5-(3-trifluoromethylbenzyl)thiazol-2-yl]benzamide (23a).

Novel and potent inhibitors of stearoyl-CoA desaturase-1. Part II: Identification of 4-ethylamino-3-(2-hydroxyethoxy)-N-[5-(3-trifluoromethylbenzyl)thiazol-2-yl]benzamide and its biological evaluation.

The continuing investigation of SAR studies of 3-(2-hydroxyethoxy)-N-(5-benzylthiazol-2-yl)-benzamides as stearoyl-CoA desaturase-1 (SCD-1) inhibitors is reported. Our prior hit-to-lead effort resulted in the identification of 1a as a potent and orally efficacious SCD-1 inhibitor. Further optimization of the structural motif resulted in the identification of 4-ethylamino-3-(2-hydroxyethoxy)-N-[5-(3-trifluoromethylbenzyl)thiazol-2-yl]benzamide (37c) with sub nano molar IC(50) in both murine and human SCD-1 inhibitory assays. This compound demonstrated a dose-dependent decrease in the plasma desaturation index in C57BL/6J mice on a non-fat diet after 7 days of oral administration.

Involvement of organic anion transporters in the efflux of uremic toxins across the blood-brain barrier.

Renal failure causes multiple physiological changes involving CNS dysfunction. In cases of uremia, there is close correlation between plasma levels of uremic toxins [e.g. 3-carboxy-4-methyl-5-propyl-2-furanpropionate (CMPF), hippurate (HA) and indoleacetate (IA)] and the degree of uremic encephalopathy, suggesting that uremic toxins are involved in uremic encephalopathy. In order to evaluate the relevance of uremic toxins to CNS dysfunction, we investigated directional transport of uremic toxins across the blood-brain barrier (BBB) using in vivo integration plot analysis and the brain efflux index method. We observed saturable efflux transport of [(3)H]CMPF, [(14)C]HA and [(3)H]IA, which was inhibited by probenecid. For all uremic toxins evaluated, apparent efflux clearance across the BBB was greater than apparent influx clearance, suggesting that these toxins are predominantly transported from the brain to blood across the BBB. Saturable efflux transport of [(3)H]CMPF, [(14)C]HA and [(3)H]IA was completely inhibited by benzylpenicillin, which is a substrate of rat organic anion transporter 3 (rOat3). Taurocholate and digoxin, which are common substrates of rat organic anion transporting polypeptide (rOatp), partially inhibited the efflux of [(3)H]CMPF. Transport experiments using a Xenopus laevis oocyte expression system revealed that CMPF, HA and IA are substrates of rOat3, and that CMPF (but not HA or IA) is a substrate of rOap2. These results suggest that rOat3 mediates brain-to-blood transport of uremic toxins, and that rOatp2 is involved in efflux of CMPF. Thus, conditions typical of uremia can cause inhibition of brain-to-blood transport involving rOat3 and/or rOatp2, leading to accumulation of endogenous metabolites and drugs in the brain.

Renal clearance of endogenous hippurate correlates with expression levels of renal organic anion transporters in uremic rats.

Hippurate (HA) is a harmful uremic toxin that accumulates during chronic renal failure, and failure of the excretion system for uremic toxins is thought to be responsible. Recently, we reported that rat organic anion transporter 1 (rOat1) is the primary mediator of HA uptake in the kidney, and so now we have studied the pharmacokinetics and tissue distribution of HA after a single i.v. dose of HA to normal and 5/6 nephrectomized rats (5/6Nx rats). In control rats, the renal and biliary clearances of HA were 18.1 and 0.1 ml/min/kg, respectively. Plasma clearance decreased as dosage increased from 0.1 to 5 mg/kg, which suggests that renal tubular secretion is the primary route for elimination of HA. The plasma clearance of HA was significantly decreased in 5/6 Nx rats compared with normal rats. In 5/6 Nx rats, renal clearance of endogenous HA correlated more closely with clearance of p-aminohippurate than with that of creatinine. Protein expression of rOat1 and rOat3, assessed by Western blot analysis, was decreased in 5/6 Nx rats. Furthermore, in 5/6 Nx rats, the renal secretory clearance of endogenous HA correlated closely with protein expression of renal rOats. Thus, HA is primarily eliminated from the plasma via the kidney by active tubular secretion. The renal clearance of endogenous HA seems to be a useful indicator of changes in renal secretion that accompany the reduced levels of OAT protein in chronic renal failure.

Differential contributions of rOat1 (Slc22a6) and rOat3 (Slc22a8) to the in vivo renal uptake of uremic toxins in rats.

PURPOSE: Evidence suggests that uremic toxins such as hippurate (HA), indoleacetate (IA), indoxyl sulfate (IS), and 3-carboxy-4-methyl-5-propyl-2-furanpropionate (CMPF) promote the progression of renal failure by damaging tubular cells via rat organic anion transporter 1 (rOat1) and rOat3 on the basolateral membrane of the proximal tubules. The purpose of the current study is to evaluate the in vivo transport mechanism responsible for their renal uptake. METHODS: We investigated the uremic toxins transport mechanism using the abdominal aorta injection technique [i.e., kidney uptake index (KUI) method], assuming minimal mixing of the bolus with serum protein from circulating serum. RESULTS: Maximum mixing was estimated to be 5.8% of rat serum by measuring estrone sulfate extraction after addition of 0-90% rat serum to the arterial injection solution. Saturable renal uptake of p-aminohippurate (PAH, K(m) = 408 microM) and benzylpenicillin (PCG, K(m) = 346 microM) was observed, respectively. The uptake of PAH and PCG was inhibited in a dose-dependent manner by unlabeled PCG (IC(50) = 47.3 mM) and PAH (IC(50) = 512 microM), respectively, suggesting that different transporters are responsible for their uptake. A number of uremic toxins inhibited the renal uptake of PAH and PCG. Excess PAH, which could inhibit rOat1 and rOat3, completely inhibited the saturable uptake of IA, IS, and CMPF by the kidney, and by 85% for HA uptake. PCG inhibited the total saturable uptake of HA, IA, IS, and CMPF by 10%, 10%, 45%, and 65%, respectively, at the concentration selective for rOat3. CONCLUSIONS: rOat1 could be the primary mediator of the renal uptake of HA and IA, accounting for approximately 75% and 90% of their transport, respectively. rOat1 and rOat3 contributed equally to the renal uptake of IS. rOat3 could account for about 65% of the uptake of CMPF under in vivo physiologic conditions. These results suggest that rOat1 and rOat3 play an important role in the renal uptake of uremic toxins and the induction of their nephrotoxicity.

Bucolome, a potent binding inhibitor for furosemide, alters the pharmacokinetics and diuretic effect of furosemide: potential for use of bucolome to restore diuretic response in nephrotic syndrome.

To determine whether bucolome (5-n-butyl-1-cyclohexyl-2,4,6-trioxoperhydropyrimidine), a nonsteroidal anti-inflammatory agent, can reverse diuretic resistance of furosemide in patients with nephrotic syndrome, we examined the inhibitory effect of bucolome on the protein binding of furosemide in serum and urine. Bucolome significantly inhibited the protein binding of furosemide not only in serum but also in urine of preparation albumin (UPA), which mimics urinary albumin concentration in patients with nephrotic syndrome by ultrafiltration method. The binding percentage of furosemide to albumin was approximately 70% in UPA. With coadministration of bucolome to healthy volunteers, renal clearance of furosemide was increased, reflecting the increase of the free fraction of furosemide in serum. Furthermore, coadministration of bucolome caused a significant increase of urine volume and sodium concentration in urine. Even at higher urine levels of furosemide, the inhibitory effect of bucolome on the protein binding of furosemide in UPA remains constant, and changes in pH at weakly acidic pH levels (pH 5.5-6.5) did not alter the inhibitory effect of bucolome. Interestingly, coadministration of bucolome with furosemide in doxorubicin (Adriamycin)-induced nephrotic syndrome model rats alleviated the diuretic resistance. These results suggest that bucolome has a potent inhibitory effect on the protein binding of furosemide in the urine and can partially restore the diuretic response of furosemide in patients with nephrotic syndrome by increasing the free fraction of furosemide at the site of action.

Characterization of uremic toxin transport by organic anion transporters in the kidney.

BACKGROUND: Harmful uremic toxins, such as indoxyl sulfate (IS), 3-carboxy-4-methyl-5-propyl-2-furanpropionate (CMPF), indoleacetate (IA), and hippurate (HA), accumulate to a high degree in uremic plasma. IS has been shown to be a substrate of rat organic anion transporter 1 (rOat1) and rOat3. However, the contribution of rOat1 and rOat3 to the renal uptake transport process of IS and other uremic toxins in the kidney remains unknown. METHODS: The cellular uptake of uremic toxins was determined using stable transfectants of rOat1/hOAT1 and rOat3/hOAT3 cells. Also, the uptake of uremic toxins by rat kidney slices was characterized to evaluate the contribution of rOat1 and rOat3 to the total uptake by kidney slices using inhibitors of rOat1 (p-aminohippurate) and rOat3 (pravastatin and benzylpenicillin). RESULTS: Saturable uptake of IS, CMPF, IA, and HA by rOat1 was observed with Km values of 18, 154, 47, and 28 micromol/L, respectively, whereas significant uptake of IS and CMPF, but not of IA or HA, was observed in rOat3-expressing cells with Km values of 174 and 11 micromol/L, respectively. Similar parameters were obtained for human OAT1 and OAT3. Kinetic analysis of the IS uptake by kidney slices revealed involvement of two saturable components with Km1 (24 micromol/L) and Km2 (196 micromol/L) values that were comparable with those of rOat1 and rOat3. The Km value of CMPF uptake by kidney slices (22 micromol/L) was comparable with that of rOat3, while the corresponding values of IA and HA (42 and 33 micromol/L, respectively) were similar to those of rOat1. PAH preferentially inhibited the uptake of IA and HA by kidney slices, while pravastatin and benzylpenicillin preferentially inhibited the uptake of CMPF. The effect of these inhibitors on the uptake of IS by kidney slices was partial. CONCLUSIONS: rOat1/hOAT1 and rOat3/hOAT3 play major roles in the renal uptake of uremic toxins on the basolateral membrane of the proximal tubules. Both OAT1 and OAT3 contribute almost equally to the renal uptake of IS. OAT3 mainly accounts for CMPF uptake by the kidney, while OAT1 mainly accounts for IA and HA uptake.

Pharmacokinetics and tissue distribution of uraemic indoxyl sulphate in rats.

The purpose of the present study was to examine the pharmacokinetic properties of indoxyl sulphate, a harmful uraemic toxin that accumulates during chronic renal failure. The pharmacokinetics and tissue distribution of indoxyl sulphate were examined in normal and 5/6 nephrectomized (CRF) rats. The uptake process of indoxyl sulphate by rat renal cortical slices in vitro was also investigated. Endogenous indoxyl sulphate was found to be mainly distributed in the kidney. The rate of elimination of indoxyl sulphate from plasma was lower in CRF rats compared with sham-operated rats. The majority of intact indoxyl sulphate was excreted in the urine. In renal cortical slice experiments, uptake of indoxyl sulphate was a saturable process with a K(m) of 43.0 microm. Furthermore, sulphate conjugates, such as oestrone sulphate and dehydroepiandrosterone sulphate, inhibited the uptake of indoxyl sulphate to a greater extent than PAH. Thus, indoxyl sulphate is primarily eliminated from the plasma via the kidney by active tubular secretion, and renal uptake of indoxyl sulphate appears to be mediated by an organic anion transport system with a high affinity for oestrone sulphate and dehydroepiandrosterone sulphate.

Rat organic anion transporter 3 (rOAT3) is responsible for brain-to-blood efflux of homovanillic acid at the abluminal membrane of brain capillary endothelial cells.

The mechanism that removes homovanillic acid (HVA), an end metabolite of dopamine, from the brain is still poorly understood. The purpose of this study is to identify and characterize the brain-to-blood HVA efflux transporter at the rat blood-brain barrier (BBB). Using the Brain Efflux Index method, the apparent in vivo efflux rate constant of [3H]HVA from the brain, k(eff), was determined to be 1.69 x 10(-2) minute(-1). This elimination was significantly inhibited by para-aminohippuric acid (PAH), benzylpenicillin, indoxyl sulfate, and cimetidine, suggesting the involvement of rat organic anion transporter 3 (rOAT3). rOAT3-expressing oocytes exhibited [3H]HVA uptake (K(m) = 274 micromol/L), which was inhibited by several organic anions, such as PAH, indoxyl sulfate, octanoic acid, and metabolites of monoamine neurotransmitters. Neurotransmitters themselves did not affect the uptake. Furthermore, immunohistochemical analysis suggested that rOAT3 is localized at the abluminal membrane of brain capillary endothelial cells. These results provide the first evidence that rOAT3 is expressed at the abluminal membrane of the rat BBB and is involved in the brain-to-blood transport of HVA. This HVA efflux transport system is likely to play an important role in controlling the level of HVA in the CNS.

Renal disposition of a furan dicarboxylic acid and other uremic toxins in the rat.

The aim of this study was to understand the mechanisms that underlie the renal elimination of albumin-bound uremic toxins, particularly the highly bound furan acid 3-carboxy-4-methyl-5-propyl-2-furanpropanoic acid (CMPF), that accumulate in chronic renal failure. These toxins inhibit the binding of acidic drugs and have various other untoward effects. The pharmacokinetics and tissue distribution of CMPF plus three other such toxins, indoxyl sulfate, indole acetic acid, and hippuric acid, have been examined in the anesthetized rat. The effects of p-aminohippuric (PAH) acid and tetraethylammonium on the uptake of CMPF by rat renal cortical slices in vitro were also investigated to characterize its mechanism of uptake. Plasma and tissue concentrations of the uremic toxins were determined by high-performance liquid chromatography. The rate of elimination of the toxins from plasma was indoxyl sulfate > hippuric acid > indole acetic acid > CMPF. Although the renal clearance of CMPF was low, its main elimination pathway was via urinary excretion with active tubular secretion. In renal cortical slice experiments, mutual inhibition between CMPF and PAH was observed. In addition, alpha-ketoglutarate stimulated the uptake of CMPF by renal cortical slices. The base tetraethylammonium did not inhibit slice uptake of CMPF. The pharmacokinetics of CMPF was characterized by slow plasma clearance and localization in the kidney. Furthermore, the evidence from experiments with renal cortical slices indicates that the uptake of CMPF is mediated by an anion/dicarboxylate exchanger, similar to that for PAH.