Prediction and causal inference of hyperuricemia using gut microbiota

Hyperuricemia (HUA) is a symptom of high blood uric acid (UA) levels, which causes disorders such as gout and renal urinary calculus. Prolonged HUA is often associated with hypertension, atherosclerosis, diabetes mellitus, and chronic kidney disease. Studies have shown that gut microbiota (GM) affect these chronic diseases. This study aimed to determine the relationship between HUA and GM. The microbiome of 224 men and 254 women aged 40 years was analyzed through next-generation sequencing and machine learning. We obtained GM data through 16S rRNA-based sequencing of the fecal samples, finding that alpha-diversity by Shannon index was significantly low in the HUA group. Linear discriminant effect size analysis detected a high abundance of the genera Collinsella and Faecalibacterium in the HUA and non-HUA groups. Based on light gradient boosting machine learning, we propose that HUA can be predicted with high AUC using four clinical characteristics and the relative abundance of nine bacterial genera, including Collinsella and Dorea. In addition, analysis of causal relationships using a direct linear non-Gaussian acyclic model indicated a positive effect of the relative abundance of the genus Collinsella on blood UA levels. Our results suggest abundant Collinsella in the gut can increase blood UA levels.

Role of Organic Anion Transporter NPT4 in Renal Handling of Uremic Toxin 3-indoxyl Sulfate

Sodium-phosphate transporter NPT4 (SLC17A3) is a membrane transporter for organic anionic compounds localized on the apical membranes of kidney proximal tubular epithelial cells and plays a role in the urinary excretion of organic anionic compounds. However, its physiological role has not been sufficiently elucidated because its substrate specificity is yet to be determined. The present study aimed to comprehensively explore the physiological substrates of NPT4 in newly developed Slc17a3-/- mice using a metabolomic approach. Metabolomic analysis showed that the plasma concentrations of 11 biological substances, including 3-indoxyl sulfate, were more than two-fold higher in Slc17a3-/- mice than in wild-type mice. Moreover, urinary excretion of 3-indoxyl sulfate was reduced in Slc17a3-/- mice compared to that in wild-type mice. The uptake of 3-indoxyl sulfate by NPT4-expressing Xenopus oocytes was significantly higher than that by water-injected oocytes. The calculated Km and Vmax values for NPT4-mediated 3-indoxyl sulfate uptake were 4.52 ± 1.18 mM and 1.45 ± 0.14 nmol/oocyte/90 min, respectively. In conclusion, the present study revealed that 3-indoxyl sulfate is a novel substrate of NPT4 based on the metabolomic analysis of Slc17a3-/- mice, suggesting that NPT4 regulates systemic exposure to 3-indoxyl sulfate by regulating its urinary excretion.

Uric acid in health and disease: From physiological functions to pathogenic mechanisms

Owing to renal reabsorption and the loss of uricase activity, uric acid (UA) is strictly maintained at a higher physiological level in humans than in other mammals, which provides a survival advantage during evolution but increases susceptibility to certain diseases such as gout. Although monosodium urate (MSU) crystal precipitation has been detected in different tissues of patients as a trigger for disease, the pathological role of soluble UA remains controversial due to the lack of causality in the clinical setting. Abnormal elevation or reduction of UA levels has been linked to some of pathological status, also known as U-shaped association, implying that the physiological levels of UA regulated by multiple enzymes and transporters are crucial for the maintenance of health. In addition, the protective potential of UA has also been proposed in aging and some diseases. Therefore, the role of UA as a double-edged sword in humans is determined by its physiological or non-physiological levels. In this review, we summarize biosynthesis, membrane transport, and physiological functions of UA. Then, we discuss the pathological involvement of hyperuricemia and hypouricemia as well as the underlying mechanisms by which UA at abnormal levels regulates the onset and progression of diseases. Finally, pharmacological strategies for urate-lowering therapy (ULT) are introduced, and current challenges in UA study and future perspectives are also described.

Drug-drug conjugates of MEK and Akt inhibitors for RAS-mutant cancers

Controlling RAS mutant cancer progression remains a significant challenge in developing anticancer drugs. Whereas Ras G12C-covalent binders have received clinical approval, the emergence of further mutations, along with the activation of Ras-related proteins and signals, has led to resistance to Ras binders. To discover novel compounds to overcome this bottleneck, we focused on the concurrent and sustained blocking of two major signaling pathways downstream of Ras. To this end, we synthesized 25 drug-drug conjugates (DDCs) by combining the MEK inhibitor trametinib with Akt inhibitors using seven types of linkers with structural diversity. The DDCs were evaluated for their cell permeability/accumulation and ability to inhibit proliferation in RAS-mutant cell lines. A representative DDC was further evaluated for its effects on signaling proteins, induction of apoptosis-related proteins, and the stability of hepatic metabolic enzymes. These in vitro studies identified a series of DDCs, especially those containing a furan-based linker, with promising properties as agents for treating RAS-mutant cancers. Additionally, in vivo experiments in mice using the two selected DDCs revealed prolonged half-lives and anticancer efficacies comparable to those of trametinib. The PK profiles of trametinib and the Akt inhibitor were unified through the DDC formation. The DDCs developed in this study have potential as drug candidates for the broad inhibition of RAS-mutant cancers.

Quantitative analysis of the impact of membrane permeability on intestinal first-pass metabolism of CYP3A substrates

The aim of this study was firstly to investigate the effect of membrane permeability on the intestinal availability (Fg ) of 10 cytochrome P450 3A4 substrates with differing permeability (Papp ) and metabolic activity (CLint ) using Madin-Darby canine kidney II (MDCKII) cells expressing human CYP3A4 (MDCKII/CYP3A4 cells), and secondly to confirm the essential factors by simulations. A membrane permeation assay using MDCKII/CYP3A4 cells showed a significant correlation between human intestinal extraction ratio (ER) (Eg (=1 - Fg )) and in vitro cellular ER (r = 0.834). This relationship afforded better predictability of Eg values than the relationship between Eg and CLint,HIM values obtained from human intestinal microsomes (r = 0.598). An even stronger correlation was observed between 1 - Fa ·Fg and ER (r = 0.874). Simulation with a cellular kinetic model indicated that ER is sensitive to changes of PSpassive and CLint values, but not to the intracellular unbound fraction (fu,cell ) or P-gp-mediated efflux (PSP - gp ). It may be concluded that, based on the concentration-time profile of drugs in epithelial cells, transmembrane permeability influences Fg (or ER) and drug exposure time to metabolizing enzymes for P450 substrate.

Magnitude of Fruit Juice-Drug Interactions Due to Osmolality-Dependent Fluid Secretion: Differences among Apple, Orange, and Grapefruit Juices

We recently reported that the gastrointestinal (GI) fluid volume is influenced by the solution osmolality, and proposed that this effect may play a role in beverage-drug interactions. Here, we investigated whether osmolality-dependent fluid secretion can explain the difference in the magnitudes of fruit juice-drug interactions depending on the type of fruit juice (grapefruit juice (GFJ), orange juice (OJ), and apple juice (AJ)). The osmolality of GFJ, OJ, and AJ used in this study was found to be 552, 686, and 749 mOsm/kg, respectively. Measurements of intestinal fluid movement following beverage administration by the in situ closed-loop technique revealed the following rank order for fluid volume in rat ileum: AJ > OJ > GFJ > purified water, suggesting that water movement is dependent on the osmolality of these beverages. Such changes in GI fluid volume are expected to alter the luminal drug concentration, potentially contributing to the magnitude of beverage-drug interactions. Indeed, in vivo pharmacokinetic study in rats revealed that the plasma concentration of atenolol, a low-permeability drug, was the highest after oral administration in purified water, followed by GFJ and OJ, and was the lowest after administration in AJ. In contrast, antipyrine, a high-permeability drug, showed no significant difference in plasma concentration after administration in purified water and fruit juices, suggesting that the absorption of high-permeability drugs is less affected by solution osmolality. Our findings indicate that differences in the magnitude of beverage-drug interactions can be at least partly explained by differences in the osmolality of the beverages ingested.

Association between switching prescribed drugs for lower urinary tract symptoms and independence of urination in post-stroke patients: A retrospective cohort study

OBJECTIVES

Stroke patients frequently exhibit loss of independence of urination, and their lower urinary tract symptoms change with the phase of stroke. However, it is unclear whether switching prescribed drugs for lower urinary tract symptoms during hospitalization from acute care wards to convalescence rehabilitation wards affects patients' independence of urination at discharge. It is also unclear whether the impact of switching varies by stroke type. This retrospective cohort study aimed to examine these issues.

MATERIALS AND METHODS

We analyzed 990 patients registered in the Kaga Regional Cooperation Clinical Pathway for Stroke database during 2015-2019. Prescriptions for lower urinary tract symptoms from pre-onset to convalescence rehabilitation were surveyed. Logistic regression analysis was performed to examine the association between switching drugs and independence of urination based on bladder management and voiding location at discharge. Stroke types were also examined in subgroup analyses.

RESULTS

About 21 % of patients had their lower urinary tract symptoms prescriptions switched during hospitalization. Switching was positively associated with independence of bladder management (odds ratio 1.65, 95 % confidence interval 1.07 to 2.49) and voiding location (odds ratio 2.72, 95 % confidence interval 1.72 to 4.37). Similar associations were observed in different stroke types.

CONCLUSIONS

Approximately 20 % of patients had their lower urinary tract symptoms medications switched upon transfer from acute to convalescence rehabilitation wards. Switching was significantly associated with improved urinary independence at discharge. Consistent results were observed across different stroke types, suggesting that switching medications contributes to urinary independence after stroke, regardless of the etiology or severity of stroke.

Potentiation of the Uricosuric Effect of Dotinurad by Trans-Inhibition of the Uric Acid Reabsorptive Transporter 1

Urate transporter 1 (URAT1) is a transporter responsible for uric acid (UA) reabsorption by renal proximal tubules and a pharmacological target of uricosuric agents. Probenecid and benzbromarone have been used as uricosuric agents, while dotinurad was recently approved in Japan. Notably, the in vitro IC 50 of dotinurad on URAT1 is not strong enough to explain its in vivo uricosuric effect estimated based on clinical unbound plasma concentrations, suggesting the presence of mechanisms other than competition with UA uptake at the extracellular domain of URAT1 (cis-inhibition). In this study, trans-inhibition was hypothesized as the mechanism underlying URAT1 inhibition by dotinurad, wherein intracellularly accumulated dotinurad inactivates URAT1. In URAT1-expressing Madin-Darby Canine Kidney-II cells and Xenopus oocytes, pre-incubation with dotinurad potentiated the inhibitory effect more than co-incubation alone, but this effect was not observed with benzbromarone or probenecid. Under co-incubation, dotinurad inhibited UA uptake in a competitive manner (cis-inhibition). When we pre-injected dotinurad directly into oocytes and immediately measured [14C]UA uptake without coincubation (only trans-inhibition), dotinurad noncompetitively inhibited UA uptake. URAT1 is an exchange transporter for UA and monocarboxylates such as nicotinic acid (NA). Pre-injected dotinurad and extracellular UA attenuated and facilitated efflux of [3H]NA, respectively, whereas pre-injection of benzbromarone or probenecid did not affect it, suggesting that dotinurad exhibits trans-inhibition by attenuating URAT1-mediated efflux of monocarboxylates, which is a driving force for UA uptake by URAT1. Accordingly, dotinurad ameliorates URAT1-mediated UA reabsorption by both cis- and trans-inhibition, explaining its clinically stronger uricosuric effect than that estimated by the in vitro IC50 value. SIGNIFICANCE STATEMENT: The uricosuric agent dotinurad inhibits uric acid reabsorptive transporter (URAT) 1 with a clinical potency stronger than that estimated from IC 50 obtained by in vitro URAT1 inhibition. This in vivo-in vitro discrepancy was explained by the trans-inhibition effect of dotinurad on URAT1. Trans-inhibition was due to the attenuation of monocarboxylates efflux via URAT1, which is a driving force for URAT1-mediated exchange transport of uric acid. Overall, this is the first study to experimentally demonstrate trans-inhibition mechanism of URAT1.

Quantitative analysis of gastrointestinal fluid absorption and secretion to estimate luminal fluid dynamics in rats

The drug absorption profile is dependent on the luminal drug concentration, which in turn is influenced by the gastrointestinal (GI) fluid dynamics. In the present study, therefore, we aimed to examine the luminal fluid dynamics by kinetically analyzing fluid absorption and secretion along the GI tract in rats using the in situ closed-loop technique with non-absorbable fluorescein isothiocyanate-dextran 4000 (FD-4) and tritium water labeling ([3H]water) under different osmotic conditions. We found that the luminal fluid volume in the jejunum and ileum, but not the colon, gradually decreased and reached a steady state. In contrast, [3H]water almost completely disappeared in all intestinal regions. Kinetic analysis revealed the following rank order for the rate constant of fluid secretion: jejunum > ileum > colon, whereas a negligible regional difference was observed in the rate constant of fluid absorption. Fluid secretion under an isosmotic condition (300 mOsm/kg) was higher than that at 0 mOsm/kg in all intestinal regions, though no significant changes in fluid absorption were observed. Thus, the fluid secretion process appears to be the major determinant of the regional differences in GI fluid dynamics. Our findings indicate that the luminal fluid volume is altered as a result of water ingestion, absorption, and secretion, and finally reaches an apparent steady state, which is regulated mainly by the process of fluid secretion.

Apple-derived extracellular vesicles modulate the expression of human intestinal bile acid transporter ASBT/SLC10A2 via downregulation of transcription factor RARα

PURPOSE

Plant-derived extracellular vesicles (EVs) have been reported to exert biological activity on intestinal tissues by delivering their contents into intestinal cells. We previously reported that ASBT/SLC10A2 mRNA was downregulated by apple-derived extracellular vesicles (APEVs). ASBT downregulation is effective in the treatment of cholestasis and chronic constipation, similar to the beneficial effects of apples. Therefore, this study aimed to establish the mechanism of ASBT downregulation by APEVs, focusing on microRNAs present in APEVs.

RESULTS

APEVs downregulated the expression of ASBT, but no significant effect on SLC10A2-3'UTR was observed. Proteomics revealed that APEVs decreased the expression of RARα/NR1B1. The binding of RARα to SLC10A2 promoter was also decreased by APEVs. The stability of NR1B1 mRNA was attenuated by APEVs and its 3'UTR was found to be a target for APEVs. Apple microRNAs that were predicted to interact with NR1B1-3'UTR were present in APEVs, and their mimics suppressed NR1B1 mRNA expression.

CONCLUSIONS

Suppression of ASBT by APEVs was indirectly mediated by the downregulation of RARα, and its stability was lowered by microRNAs present in APEVs. This study suggested that macromolecules in food directly affect intestinal function by means of EVs that stabilize them and facilitate their cellular uptake.

Improvement of Protein Expression Profile in Three-Dimensional Renal Proximal Tubular Epithelial Cell Spheroids Selected Based on OAT1 Gene Expression: A Potential In Vitro Tool for Evaluating Human Renal Proximal Tubular Toxicity and Drug Disposition

The proximal tubule plays an important role in the kidney and is a major site of drug interaction and toxicity. Analysis of kidney toxicity via in vitro assays is challenging, because only a few assays that reflect functions of drug transporters in renal proximal tubular epithelial cells (RPTECs) are available. In this study, we aimed to develop a simple and reproducible method for culturing RPTECs by monitoring organic anion transporter 1 (OAT1) as a selection marker. Culturing RPTECs in spherical cellular aggregates increased OAT1 protein expression, which was low in the conventional two-dimensional (2D) culture, to a level similar to that in human renal cortices. By proteome analysis, it was revealed that the expression of representative two proximal tubule markers was maintained and 3D spheroid culture improved the protein expression of approximately 7% of the 139 transporter proteins detected, and the expression of 2.3% of the 4,800 proteins detected increased by approximately fivefold that in human renal cortices. Furthermore, the expression levels of approximately 4,800 proteins in three-dimensional (3D) RPTEC spheroids (for 12 days) were maintained for over 20 days. Cisplatin and adefovir exhibited transporter-dependent ATP decreases in 3D RPTEC spheroids. These results indicate that the 3D RPTEC spheroids developed by monitoring OAT1 gene expression are a simple and reproducible in vitro experimental system with improved gene and protein expressions compared with 2D RPTECs and were more similar to that in human kidney cortices. Therefore, it can potentially be used for evaluating human renal proximal tubular toxicity and drug disposition. SIGNIFICANCE STATEMENT: This study developed a simple and reproducible spheroidal culture method with acceptable throughput using commercially available RPTECs by monitoring OAT1 gene expression. RPTECs cultured using this new method showed improved mRNA/protein expression profiles to those in 2D RPTECs and were more similar to those of human kidney cortices. This study provides a potential in vitro proximal tubule system for pharmacokinetic and toxicological evaluations during drug development.

Induction of open-form bile canaliculus formation by hepatocytes for evaluation of biliary drug excretion

Biliary excretion is a major drug elimination pathway that affects their efficacy and safety. The currently available in vitro sandwich-cultured hepatocyte method is cumbersome because drugs accumulate in the closed bile canalicular lumen formed between hepatocytes and their amounts cannot be mealsured directly. This study proposes a hepatocyte culture model for the rapid evaluation of drug biliary excretion using permeation assays. When hepatocytes are cultured on a permeable support coated with the cell adhesion protein claudins, an open-form bile canalicular lumen is formed at the surface of the permeable support. Upon application to the basolateral (blood) side, drugs appear on the bile canalicular side. The biliary excretion clearance of several drugs, as estimated from the obtained permeabilities, correlates well with the reported in vivo biliary excretion clearance in humans. Thus, the established model is useful for applications in the efficient evaluation of biliary excretion during drug discovery and development.

Apple juice relieves loperamide-induced constipation in rats by downregulating the intestinal apical sodium-dependent bile acid transporter ASBT

Apples are known to exhibit various beneficial effects on human health. In the present study, we investigated the effect of continuous intake of apple juice (AJ) on constipation status. A single dose of loperamide in rats as the constipation model markedly decreased the weight and number of fecal pellets compared to saline-administered rats as a control. After the administration of AJ twice a day for seven days, recovery of defecation close to that of the control was observed in loperamide-treated rats. In addition, the total bile acid content in the feces increased from day 4 after the administration of AJ. Among hepatic and intestinal transporters and enzymes that regulate bile acids, the mRNA expression of the apical sodium-dependent bile acid transporter (Asbt, slc10a2) was decreased by AJ in rats. Furthermore, the Asbt-mediated bile acid transport activity in the rat ileum decreased after AJ administration. Moreover, in human colonic cancer-derived Caco-2 cells, AJ exposure for 24 and 48 h decreased the expressions of ASBT mRNA and protein, and the uptake activity of taurocholic acid in both 7- and 21-d cultures. Several components of AJ, such as procyanidins, decreased the expression of ASBT in Caco-2 cells. In conclusion, ASBT downregulation is a possible mechanism responsible for the constipation-relieving effect of apples, and procyanidins may play a role in downregulating ASBT, which leads to the beneficial effects of apples against constipation. Although it is generally agreed that the common dietary compositions play a role in constipation relief, the novel specific mechanism of apples found in this study would facilitate understanding food functions.

Quantitative Analysis of Gastrointestinal Water Dynamics by Means of a Physiologically Based Fluid Kinetic Model

Since the processes of dissolution and membrane permeation are affected by the water content in the gastrointestinal (GI) tract, the water dynamics in the GI tract is expected to have a significant impact on the absorption of orally administered drugs. Here, we aimed to develop a physiologically based fluid kinetic (PBFK) model using GI water kinetic parameters obtained from in situ closed-loop studies in rats in order to quantitatively predict GI water dynamics. By incorporating the experimentally measured site-specific parameters of GI water absorption and secretion into a GI compartment model, we developed a bottom-up PBFK model that successfully simulates the reported GI fluid dynamics in rats and humans observed using positron emission tomography and magnetic resonance imaging, respectively. The simulations indicate that the water volume in both the stomach and duodenum is transiently increased by water ingestion, while that in the intestine below the jejunum is unchanged and remains in a steady state in both rats and humans. Furthermore, sensitivity analysis of the effect of ingested water volume on the volume-time profiles of water in the GI tract indicated that the impact of ingested water is limited to the proximal part of the GI tract. Simulations indicated that changes in water kinetic parameters may alter the impact of the ingested water on GI fluid dynamics, especially in the proximal part. Incorporating this PBFK model into a physiologically based pharmacokinetic (PBPK) absorption model has the potential to predict oral drug absorption in a variety of GI water environments.

Biological Distribution after Oral Administration of Radioiodine-Labeled Acetaminophen to Estimate Gastrointestinal Absorption Function via OATPs, OATs, and/or MRPs

We evaluated the whole-body distribution of orally-administered radioiodine-125 labeled acetaminophen (¹²⁵I-AP) to estimate gastrointestinal absorption of anionic drugs. ¹²⁵I-AP was added to human embryonic kidney (HEK)293 and Flp293 cells expressing human organic anion transporting polypeptide (OATP)1B1/3, OATP2B1, organic anion transporter (OAT)1/2/3, or carnitine/organic cation transporter (OCTN)2, with and without bromosulfalein (OATP and multidrug resistance-associated protein (MRP) inhibitor) and probenecid (OAT and MRP inhibitor). The biological distribution in mice was determined by oral administration of ¹²⁵I-AP with and without bromosulfalein and by intravenous administration of ¹²⁵I-AP. The uptake of ¹²⁵I-AP was significantly higher in HEK293/OATP1B1, OATP1B3, OATP2B1, OAT1, and OAT2 cells than that in mock cells. Bromosulfalein and probenecid inhibited OATP- and OAT-mediated uptake, respectively. Moreover, ¹²⁵I-AP was easily excreted in the urine when administered intravenously. The accumulation of ¹²⁵I-AP was significantly lower in the blood and urinary bladder of mice receiving oral administration of both ¹²⁵I-AP and bromosulfalein than those receiving only ¹²⁵I-AP, but significantly higher in the small intestine due to inhibition of OATPs and/or MRPs. This study indicates that whole-body distribution after oral ¹²⁵I-AP administration can be used to estimate gastrointestinal absorption in the small intestine via OATPs, OATs, and/or MRPs by measuring radioactivity in the urinary bladder.

A single high-dose irradiation changes accumulation of methotrexate and gene expression levels of SLC and ABC transporters in cancer cells

Chemoradiotherapy is frequently used to treat cancer. Stereotactic body radiotherapy (SBRT) is a single high-dose radiotherapy used to treat a variety of cancers. The anticancer drug methotrexate (MTX) shows affinity for solute carrier (SLC) and ATP-binding cassette (ABC) transporters. This study investigated relationships between accumulation of methotrexate and gene expression levels of solute carrier and ATP-binding cassette transporters in cancer cells after a single and high-dose X-ray irradiation. Cancer cell lines were selected from lung and cervical cancer cell line that are commonly used for stereotactic body radiotherapy and effective with methotrexate. We examined expression levels of organic anion-transporting polypeptide (OATP)1B1, OATP1B3, OATP1B7, and organic anion transporter (OAT)1 as solute carrier transporters and multidrug resistance-associated protein (MRP)1 and MRP2 as ATP-binding cassette transporters, using real-time polymerase chain reaction and accumulation of ³H-MTX in cancer cells after 10-Gy irradiation, assuming stereotactic body radiotherapy. Cells were divided into three groups: Control without irradiation; 4 h after irradiation; and 24 h after irradiation. In control, gene expression levels of OAT1 in all cells was below the limit of measurement. After irradiation, gene expression levels of OATP1B1/1B3/1B7 showed changes in each cell line. Gene expression levels of MRP1/2 tended to increase after irradiation. Gene expression levels of OATP1B1/1B3/1B7 were much lower than those of MRP1/2. Accumulation of ³H-MTX tended to decrease over time after irradiation. Irradiation of cancer cells thus alters gene expression levels of both solute carrier transporters (OATP1B1/1B3/1B7) and ABC transporters (MRP1/2) and decreases accumulation of ³H-MTX in cancer cells over time due to elevated expression of MRP1/2.

Characterization of Aripiprazole Uptake Transporter in the Blood-Brain Barrier Model hCMEC/D3 Cells by Targeted siRNA Screening

AIM

Identification of blood-brain barrier (BBB) uptake transporters is a major challenge in the research and development of central nervous system (CNS) drugs. However, conventional methods that consider known drug uptake characteristics have failed at identifying the responsible transporter molecule. The present study aimed at identifying aripiprazole uptake transporters in BBB model hCMEC/D3 cells using a knockdown screening study targeting various transporters, including uncharacterized ones.

METHODS

We evaluated the effect of 214 types of siRNA targeting transporters on the uptake of aripiprazole, an atypical antipsychotic drug, in hCMEC/D3 cells. Aripiprazole uptake was determined using Xenopus oocytes expressing the candidate genes extracted from the siRNA screening assay.

RESULTS

The estimated unbound brain to plasma concentration ratio (K_p,uu,brain) of aripiprazole was estimated as 0.67 in wild-type mice and 1.94 in abcb1a/1b/abcg2 knockout mice, suggesting the involvement of both uptake and efflux transporters in BBB permeation. According to siRNA knockdown screening studies, organic cation/carnitine transporter 2 (OCTN2) and long-chain fatty acid transporter 1 (FATP1) were identified as candidate genes. The uptake of aripiprazole by hCMEC/D3 cells was decreased by OCTN2 inhibitors, but not by FATP1 inhibitors. A partially increased uptake of aripiprazole was observed in OCTN2-expressing Xenopus oocytes. Finally, to evaluate transporter-mediated BBB permeation of drugs, the reported and estimated K_p,uu,brain values were summarized.

CONCLUSIONS

A knockdown screening study in combination with K_p,uu,brain values showed that aripiprazole was a potential substrate of OCTN2. The technique described in this study can be applied to identifying novel BBB transporters for CNS drugs.

Evaluation of Platinum Anticancer Drug-Induced Kidney Injury in Primary Culture of Rat Kidney Tissue Slices by Using Gas-Permeable Plates

The type of method adopted for the evaluation of drug-induced kidney injury (DIKI) plays an important role during the drug discovery process. In the present study, the usefulness of cultured rat kidney tissue slices maintained on gas-permeable poly(dimethylsiloxane) (PDMS) plates for DIKI was assessed by monitoring the ATP content as a marker of cell viability. The amount of ATP in the kidney slices cultured on the PDMS plates was higher than that in the slices cultured on gas-impermeable polystyrene plates. The protein expression of organic cation transporter-2 (Oct2) was maintained for 3 d. Cisplatin showed a time- and concentration-dependent reduction in ATP in the slices with a half-effective concentration value of 24 µM, which was alleviated by cimetidine, an Oct2 inhibitor, suggesting that cisplatin-induced kidney injury in the cultured slices was regulated by the basolateral uptake transporter Oct2. Furthermore, the intensity of platinum anticancer drug-induced nephrotoxicity in the cultured slices was consistent with that of the in vivo study. In conclusion, the primary culture of rat kidney tissue slices on gas-permeable plates is expected to aid in the prediction of the extent of nephrotoxicity of drugs, even when transporters are responsible for the accumulation of drugs in kidney tissues.

3CL Protease Inhibitors with an Electrophilic Arylketone Moiety as Anti-SARS-CoV-2 Agents

The novel coronavirus, SARS-CoV-2, has been identified as the causative agent for the current coronavirus disease (COVID-19) pandemic. 3CL protease (3CLpro) plays a pivotal role in the processing of viral polyproteins. We report peptidomimetic compounds with a unique benzothiazolyl ketone as a warhead group, which display potent activity against SARS-CoV-2 3CLpro. The most potent inhibitor YH-53 can strongly block the SARS-CoV-2 replication. X-ray structural analysis revealed that YH-53 establishes multiple hydrogen bond interactions with backbone amino acids and a covalent bond with the active site of 3CLpro. Further results from computational and experimental studies, including an in vitro absorption, distribution, metabolism, and excretion profile, in vivo pharmacokinetics, and metabolic analysis of YH-53 suggest that it has a high potential as a lead candidate to compete with COVID-19.

CD38 activation by monosodium urate crystals contributes to inflammatory responses in human and murine macrophages

Cluster of differentiation (CD) 38, a major enzyme for nicotinamide adenine dinucleotide (NAD⁺) degradation, plays a key role in inflammation. Meanwhile, intracellular NAD⁺ decline is also associated with inflammatory responses. However, whether CD38 activation is involved in gouty inflammation has not been elucidated. The present study aimed to clarify the role of CD38 in monosodium urate crystals (MSU)-triggered inflammatory responses. The results showed that MSU crystals increased the protein expression of CD38 in time- and concentration-dependent manner in THP-1 macrophages and mouse bone marrow-derived macrophages (BMDMs). Moreover, intracellular NAD⁺ levels were reduced by MSU crystals along with the increased IL-1β release. However, CD38 inhibition by 78c elevated intracellular NAD⁺ levels and suppressed IL-1β release in MSU crystals-treated THP-1 macrophages and BMDMs. Interestingly, CD38 inhibition without significant elevation of intracellular NAD⁺ also decreased IL-1β release driven by MSU crystals in THP-1 macrophages. In conclusion, the present study revealed that MSU crystals could activate CD38 with the ensuing intracellular NAD⁺ decline to promote inflammatory responses in THP-1 macrophages and BMDMs, while CD38 inhibition could suppress MSU crystals-triggered inflammatory responses, indicating that CD38 is a potential therapeutic target for gout.

Influence of osmolality on gastrointestinal fluid volume and drug absorption: potential impact on oral salt supplementation

Background

The syndrome of inappropriate secretion of antidiuretic hormone (SIADH) is the most frequent cause of hyponatremia in patients with cerebrovascular disease, and is often treated with oral salt tablets. However, we have shown that osmolality-dependent variations in gastrointestinal (GI) fluid volume can alter the concentration of a poorly permeable drug in the GI tract, potentially affecting its absorption. Here, we examined the effect of ingestion of hyperosmotic solution (10% NaCl) on drug concentration and absorption in the GI tract.

Methods

The effects of osmolality on luminal fluid volume and drug absorption in rat intestine (jejunum, ileum and colon) were examined by means of an in situ closed loop method using fluorescein isothiocyanate-dextran 4000 (FD-4) and atenolol. In vivo absorption in rats was determined by measuring the plasma concentration after oral administration of the test compounds dissolved in purified water or hyperosmotic solution (10% NaCl).

Results

Administration of hyperosmotic solution directly into the GI tract significantly increased the GI fluid volume, owing to secretion of water into the lumen. After administration in hyperosmotic solution, the luminal concentration of non-permeable FD-4 was significantly lower than the initial dosing concentration, whereas after administration in purified water, the luminal concentration exceeded the initial concentration. The fraction absorbed of atenolol was markedly lower after administration in hyperosmotic solution than after administration in purified water. An in vivo pharmacokinetic study in rats was consistent with these findings.

Conclusions

Administration of hyperosmotic NaCl solution increased GI fluid volume and reduced the plasma level of orally administered atenolol. This may imply that oral salt tablets used to treat hyponatremia in SIADH patients could decrease the intestinal absorption of concomitantly administered drugs, resulting in lower plasma exposure.

Model Analysis of the Apparent Saturation Kinetics of Purine Nucleobase Uptake in Cells co-Expressing Transporter and Metabolic Enzyme

PURPOSE

This study aims to understand the effect of salvage enzyme activity on the saturable kinetics of facilitated cellular uptake of purine nucleobase by developing a cellular kinetic model incorporating equilibrative nucleobase transporter 1 (ENBT1) and adenine phosphoribosyltransferase (APRT), with adenine as a model nucleobase.

METHODS

A cellular kinetic model incorporating the functions of ENBT1 and APRT was developed using Napp software and employed for model-based analysis of the cellular disposition of adenine.

RESULTS

Simulation analysis using the developed cellular kinetic model could account for the experimentally observed time-dependent changes in the K_m(app) value of adenine for ENBT1-mediated uptake. At a long experimental time, the model shows that uptake of adenine is rate-limited by APRT, enabling determination of the K_m value for APRT. At early time, the rate-limiting step for adenine uptake is ENBT1-mediated transport, enabling determination of the K_m value for ENBT1. Further simulations showed that the effect of experimental time on the K_m(app) value for ENBT1-mediated uptake is dependent on the APRT expression level.

CONCLUSION

Our findings indicate that both enzyme expression levels and experimental time should be considered when using cellular uptake studies to determine the K_m values of purine nucleobases for facilitated transporters.

Renal Reabsorptive Transport of Uric Acid Precursor Xanthine by URAT1 and GLUT9

Xanthine and hypoxanthine are intermediate metabolites of uric acid and a source of reactive oxidative species (ROS) by xanthine oxidoreductase (XOR), suggesting that facilitating their elimination is beneficial. Since they are reabsorbed in renal proximal tubules, we investigated their reabsorption mechanism by focusing on the renal uric acid transporters URAT1 and GLUT9, and examined the effect of clinically used URAT1 inhibitor on their renal clearance when their plasma concentration is increased by XOR inhibitor. Uptake study for [³H]xanthine and [³H]hypoxanthine was performed using URAT1- and GLUT9-expressing Xenopus oocytes. Transcellular transport study for [³H]xanthine was carried out using Madin-Darby canine kidney (MDCK)II cells co-expressing URAT1 and GLUT9. In in vivo pharmacokinetic study, renal clearance of xanthine was estimated based on plasma concentration and urinary recovery. Uptake by URAT1- and GLUT9-expressing oocytes demonstrated that xanthine is a substrate of URAT1 and GLUT9, while hypoxanthine is not. Transcellular transport of xanthine in MDCKII cells co-expressing URAT1 and GLUT9 was significantly higher than those in mock cells and cells expressing URAT1 or GLUT9 alone. Furthermore, dotinurad, a URAT1 inhibitor, increased renal clearance of xanthine in rats treated with topiroxostat to inhibit XOR. It was suggested that xanthine is reabsorbed in the same manner as uric acid through URAT1 and GLUT9, while hypoxanthine is not. Accordingly, it is expected that treatment with XOR and URAT1 inhibitors will effectively decrease purine pools in the body and prevent cell injury due to ROS generated during XOR-mediated reactions.

Inhibition of the Hepatic Uptake of 99mTc-Tetrofosmin Using an Organic Cation Transporter Blocker

The accumulation of high levels of ^99mTc-tetrofosmin (^99mTc-TF) in the hepatobiliary system can lead to imaging artifacts and interference with diagnosis. The present study investigated the transport mechanisms of ^99mTc-TF and attempted to apply competitive inhibition using a specific inhibitor to reduce ^99mTc-TF hepatic accumulation. In this in vitro study, ^99mTc-TF was incubated in HEK293 cells expressing human organic anion transporting polypeptide 1B1 (OATP1B1), OATP1B3, OATP2B1, organic anion transporter 2 (OAT2), organic cation transporter 1 (OCT1), OCT2, and Na⁺-taurocholate cotransporting polypeptide with or without each specific inhibitor to evaluate the contribution of each transporter to ^99mTc-TF transportation. In vivo studies, dynamic planar imaging, and single photon emission computed tomography (SPECT) experiments with rats were performed to observe alterations to ^99mTc-TF pharmacokinetics using cimetidine (CMT) as an OCT1 inhibitor. Time-activity curves in the liver and heart were acquired from dynamic data, and the ^99mTc-TF uptake ratio was calculated from SPECT. From the in vitro study, ^99mTc-TF was found to be transported by OCT1 and OCT2. When CMT-preloaded rats and control rats were compared, the hepatic accumulation of the ^99mTc-TF was reduced, and the time to peak heart count shifted to an earlier stage. The hepatic accumulation of ^99mTc-TF was markedly suppressed, and the heart-to-liver ratio increased 1.6-fold. The pharmacokinetics of ^99mTc-TF were greatly changed by OCT1 inhibitor. Even in humans, the administration of OCT1 inhibitor before cardiac SPECT examination may reduce ^99mTc-TF hepatic accumulation and contribute to the suppression of artifacts and the improvement of SPECT image quality.

MicroRNAs in Apple-Derived Nanoparticles Modulate Intestinal Expression of Organic Anion-Transporting Peptide 2B1/SLCO2B1 in Caco-2 Cells

Plant-derived nanoparticles exert cytoprotective effects on intestinal cells by delivering their cargo to intestinal tissues. We previously reported that apple-derived nanoparticles (APNPs) downregulate the mRNA of the human intestinal transporter organic anion-transporting peptide 2B1 (OATP2B1)/SLCO2B1 and that the 3'-untranslated region (3'UTR) is required for the response to APNPs. Here, we investigated the involvement of microRNAs (miRNAs) in APNPs in suppressing OATP2B1 expression to demonstrate that APNP macromolecules directly interact with intestinal tissues. Using in silico analysis, seven apple miRNAs were predicted as candidate miRNAs that interact with the SLCO2B1-3'UTR. The APNP-mediated decrease in luciferase activity of pGL3/SLCO2B1-3'UTR was abrogated by inhibitors of mdm-miR-160a-e, -7121a-c, or -7121d-h. Each miRNA mimic reduced the endogenous expression of SLCO2B1 mRNA in Caco-2 cells. The luciferase activity of the truncated pGL3/SLCO2B1-3'UTR, which contains approximately 200 bp around each miRNA recognition element (MRE), was decreased by the miR-7121d-h mimic but decreased little by the other mimics. APNP also reduced the luciferase activity of truncated pGL3/SLCO2B1-3'UTR containing an MRE for miR-7121d-h. Thus, we demonstrated that mdm-miR-7121d-h contributes to the APNP-mediated downregulation of intestinal OATP2B1. Accordingly, plant macromolecules, such as miRNAs, may directly interact with intestinal tissues via nanoparticles. SIGNIFICANCE STATEMENT: This study demonstrates that mdm-miR7121d-h contained in apple-derived nanoparticles downregulated the mRNA expression of SLCO2B1 by interacting with SLCO2B1-3'-untranslated region directly and that SLCO2B1 mRNA might also be decreased by mdm-miR160a-e and -7121a-c indirectly. This finding that the specific apple-derived microRNAs influence human intestinal transporters provides a novel concept that macromolecules in foods directly interact with and affect the intestinal function of the host.

Drug Transcellular Transport Assay Using a High Porosity Honeycomb Film

In vitro transport studies across cells grown on culture inserts are widely used for evaluating pharmacokinetic characteristics such as intestinal membrane permeability. However, measurements of the apparent permeability coefficient of highly lipophilic compounds are often limited by transport across the membrane filters, not by transport across the cultured cells. To overcome this concern, we have investigated the utility of a high-porosity membrane honeycomb film (HCF) for transcellular transport studies. Using the HCF inserts, the apparent permeability coefficient (P_app) of the drugs tested in LLC-PK1 and Caco-2 cells tended to increase with an increase in lipophilicity, reaching a maximum P_app value at Log D higher than 2. In contrast, using the commercially available Track-Etched membrane (TEM) inserts, a maximum value was observed at Log D higher than 1. The basolateral to apical transport permeability P_app(BL→AP) of rhodamine 123 across LLC-PK1 cells that express P-glycoprotein (P-gp) cultured on HCF inserts and TEM inserts was 2.33 and 2.39 times higher than the reverse directional P_app(AP→BL) permeability, respectively. The efflux ratio (P_app(B-A)/P_app(A-B)) of rhodamine 123 in LLC-PK1 expressing P-gp cells using HCF inserts was comparable to that obtained using TEM inserts, whereas the transported amount in both directions was significantly higher when using the HCF inserts. Accordingly, due to the higher permeability and high porosity of HCF membranes, it is expected that transcellular transport of high lipophilic as well as hydrophilic compounds and substrate recognition of transporters can be evaluated more accurately by using HCF inserts.

Uptake Pathway of Apple-derived Nanoparticle by Intestinal Cells to Deliver its Cargo

PURPOSE

Food-derived nanoparticles exert cytoprotective effects on intestinal cells by delivering their cargo, which includes macromolecules such as microRNAs and proteins, as well as low-molecular weight compounds. We previously reported that apple-derived nanoparticles (APNPs) downregulate the expression of human intestinal transporter OATP2B1/SLCO2B1 mRNA. To verify the involvement of the cargo of APNPs in affecting the expression of transporters, we characterized the uptake mechanism of APNPs in intestinal cells.

METHODS

The uptake of fluorescent PKH26-labeled APNPs (PKH-APNPs) into Caco-2, LS180, and HT-29MTX cells was evaluated by confocal microscopy and flow cytometry.

RESULTS

The uptake of PKH-APNPs was prevented in the presence of clathrin-dependent endocytosis inhibitors, chlorpromazine and Pitstop2. Furthermore, PKH-APNPs were incorporated by the HT29-MTX cells, despite the disturbance of the mucus layer. Additionally, the decrease in SLCO2B1 mRNA by APNPs was reversed by Pitstop 2 in Caco-2 cells, indicating that APNPs decrease SLCO2B1 by being incorporated via clathrin-dependent endocytosis.

CONCLUSIONS

We demonstrated that clathrin-dependent endocytosis was mainly involved in the uptake of APNPs by intestinal cells, and that the cargo in the APNPs downregulate the mRNA expression of SLCO2B1. Therefore, APNPs could be a useful tool to deliver large molecules such as microRNAs to intestinal cells.

Identification of Triterpene Acids in Poria cocos Extract as Bile Acid Uptake Transporter Inhibitors

Literature reports that Poria cocos reduces blood lipid levels; however, the underlying mechanism remains unclear. Blood lipid levels are closely related to the enterohepatic circulation of bile acids, where uptake transporters playing a significant role. P. cocos extract is commonly used in traditional prescriptions and food supplements in China. We investigated the effects of P. cocos and its five triterpene acids on bile acid uptake transporters, including intestinal apical sodium-dependent bile acid transporter (ASBT) and hepatic sodium/taurocholate cotransporting polypeptide (NTCP). Triterpene acids were fingerprinted by high-performance liquid chromatography-TripleTOF and quantified by ultraperformance liquid chromatography/tandem mass spectrometry. The inhibitory effect of P. cocos and its five major representative triterpene acids on ASBT and NTCP was investigated by in vitro assays using Xenopus oocytes expressing ASBT and NTCP. P. cocos extract exhibited significant inhibitory effects with half-maximum inhibition constants of 5.89 µg/ml and 14.6 µg/ml for NTCP and ASBT, respectively. Among five triterpene acids, poricoic acid A, poricoic acid B, and polyporenic acid C significantly inhibited NTCP function. Poricoic acid A, poricoic acid B, and dehydrotumulosic acid significantly inhibited ASBT function. The representative triterpene acid, poricoic acid A, was identified as a competitive inhibitor of NTCP with an inhibitory constant of 63.4 ± 18.7 µM. In conclusion, our results indicate that both P. cocos extract and its major triterpenes are competitive inhibitors of ASBT and NTCP. Accordingly, it was suggested that competitive inhibition of these bile acid transporters is one of the underlying mechanisms for the hypolipidemic effect of P. cocos. SIGNIFICANCE STATEMENT: Poria cocos, a commonly used Chinese herbal medicine and food supplement, demonstrates significantly inhibitory effects on the function of apical sodium-dependent bile acid transporter and sodium/taurocholate cotransporting polypeptide. P. cocos has potential to reduce the blood lipid through inhibition of these uptake transporters in enterohepatic circulation of bile acid.

Assessment of drug transporters involved in the urinary secretion of [99mTc]dimercaptosuccinic acid

INTRODUCTION

We clarified the renal uptake and urinary secretion mechanism of [^99mTc]dimercaptosuccinic acid ([^99mTc]DMSA) via drug transporters in renal proximal tubules.

METHODS

[^99mTc]DMSA was added to human embryonic kidney 293 cells expressing human multidrug and toxin extrusion (MATE)1 and MATE2-K, carnitine/organic cation transporter (OCTN)1 and OCTN2, and organic cation transporter (OCT)2; to Flp293 cells expressing human organic anion transporter (OAT)1 and OAT3; and to vesicles expressing P-glycoprotein (P-gp), multidrug resistance associated protein (MRP)2, MRP4, or breast cancer resistance protein with and without probenecid (OAT inhibitor for both OATs and MRPs). Time activity curves of [^99mTc]DMSA with and without probenecid were established using LLC-PK₁ cells. Biodistribution and single photon emission computed tomography (SPECT) imaging in mice were conducted using [^99mTc]DMSA with and without probenecid.

RESULTS

[^99mTc]DMSA uptake was significantly higher in Flp293/OAT3 than in mock cells. Uptake via OAT3 was inhibited by probenecid. [^99mTc]DMSA uptake into vesicles that highly expressed MRP2 was significantly higher in adenosine triphosphate (ATP) than in adenosine monophosphate (AMP), and probenecid decreased uptake to similar levels as that in AMP. In the time activity curves for [^99mTc]DMSA in LLC-PK₁ cells, probenecid loading inhibited accumulation from the basolateral side into LLC-PK₁ cells, whereas accumulation from the apical side into cells gradually increased. Transport of [^99mTc]DMSA from both sides was low. Biodistribution and SPECT imaging studies showed that [^99mTc]DMSA with probenecid loading resulted in significantly higher accumulation in blood, heart, liver, and bladder after [^99mTc]DMSA injection compared with control mice. Probenecid induced significantly lower accumulation in the kidney after [^99mTc]DMSA injection.

CONCLUSIONS

[^99mTc]DMSA accumulates in renal proximal tubular epithelial cells from blood via OAT3 on the basolateral side, and then a small volume of [^99mTc]DMSA will be excreted in urine via MRP2. ADVANCES IN KNOWLEDGE: [^99mTc]DMSA accumulates via OAT3 in renal proximal tubular epithelial cells and is slightly excreted from the cells via MRP2. IMPLICATIONS FOR PATIENT CARE: [^99mTc]DMSA may be useful for measuring renal transport function with OAT3 in patients.

Pillar[6]arene acts as a biosensor for quantitative detection of a vitamin metabolite in crude biological samples

Metabolic syndrome is associated with obesity, hypertension, and dyslipidemia, and increased cardiovascular risk. Therefore, quick and accurate measurements of specific metabolites are critical for diagnosis; however, detection methods are limited. Here we describe the synthesis of pillar[n]arenes to target 1-methylnicotinamide (1-MNA), which is one metabolite of vitamin B3 (nicotinamide) produced by the cancer-associated nicotinamide N-methyltransferase (NNMT). We found that water-soluble pillar[5]arene (P5A) forms host-guest complexes with both 1-MNA and nicotinamide, and water-soluble pillar[6]arene (P6A) selectively binds to 1-MNA at the micromolar level. P6A can be used as a "turn-off sensor" by photoinduced electron transfer (detection limit is 4.38 × 10^-6 M). In our cell-free reaction, P6A is used to quantitatively monitor the activity of NNMT. Moreover, studies using NNMT-deficient mice reveal that P6A exclusively binds to 1-MNA in crude urinary samples. Our findings demonstrate that P6A can be used as a biosensor to quantify 1-MNA in crude biological samples.

A Novel Fluorescence-Based Method to Evaluate Ileal Apical Sodium-Dependent Bile Acid Transporter ASBT

This study aimed to demonstrate usefulness of the fluorophore-labeled bile acid derivative, N-(24-[7-(4-N,N-dimethylaminosulfonyl-2,1,3-benzoxadiazole)]amino-3α,7α,12α-trihydroxy-27-nor-5β-cholestan-26-oyl)-2'-aminoethane sulfonate (tauro-nor-THCA-24-DBD) as a substrate of apical sodium-dependent bile acid transporter (ASBT, SLC10A2), which is expressed at distal ileum for reabsorption of bile acids and to find a novel fluorescence-based method to evaluate ASBT activity. In HPLC analysis, chromatogram of tauro-nor-THCA-24-DBD showed double peaks: R- and S-isomers of the compound. When ASBT was expressed in Xenopus laevis oocytes, their uptakes were higher than those by control oocytes, demonstrating both are transported by ASBT. Therefore, results were analyzed separately as peak 1, peak 2 and sum of them. Concentration dependent uptake of tauro-nor-THCA-24-DBD in ASBT-expressing oocytes was saturable with Km 122 μM and Vmax 1.49 pmol/oocyte/30 min for peak 1, 30.7 μM and 1.34 pmol/oocyte/30 min for peak 2, and 40.6 μM and 2.36 pmol/oocyte/30 min for sum, respectively. These uptakes were decreased in the presence of taurocholic acid and in the Na⁺ free condition. Furthermore, in Caco-2 cells, tauro-nor-THCA-24-DBD uptake was also Na⁺-dependent and saturable. Additionally, these uptakes were decreased by elobixibat, a selective ASBT inhibitor. Accordingly, it was concluded that tauro-nor-THCA-24-DBD is a substrate of ASBT and useful to evaluate the intestinal ASBT transport activity.

[The inhibitors of the apical sodium-dependent bile acid transporter (ASBT) as promising drugs]

Inhibition of the apical sodium-dependent bile acid transporter (ASBT, also known as IBAT - ileal bile acid transporter, SLC10A2) leads to disruption of the enterohepatic circulation of bile acids and their excretion with fecal masses. This is accompanied by cholesterol utilization for synthesis of new bile acids. ASBT inhibitors are promising drugs for the treatment of such diseases as non-alcoholic fatty liver disease, non-alcoholic steatohepatitis, type 2 diabetes mellitus, necrotic enterocolitis, chronic constipation, atherosclerosis. To date the most known chemically synthesized inhibitors are: A3309, SHP626, A4250, 264W94, GSK2330672, SC-435. All of them are at different stages of clinical trials, which confirm the high efficacy and good tolerance of these inhibitors. Current trends in this field also include directed chemical synthesis of ASBT inhibitors, as well as their search among substances of plant origin.

[131I]MIBG exports via MRP transporters and inhibition of the MRP transporters improves accumulation of [131I]MIBG in neuroblastoma

INTRODUCTION

¹³¹I-labeled m-iodobenzylguanidine ([¹³¹I]MIBG) has been used to treat neuroblastoma patients, but [¹³¹I]MIBG may be immediately excreted from the cancer cells by the adenosine triphosphate binding cassette transporters, similar to anticancer drugs. The purpose of this study was to clarify the efflux mechanism of [¹³¹I]MIBG in neuroblastomas and improve accumulation by inhibition of the transporter in neuroblastomas.

METHODS

[¹³¹I]MIBG was incubated in human embryonic kidney (HEK)293 cells expressing human organic anion transporting polypeptide (OATP)1B1, OATP1B3, OATP2B1, organic anion transporter (OAT)1 and OAT2, organic cation transporter (OCT)1 and OCT2, and sodium taurocholate cotransporting polypeptide, and in vesicles expressing P-glycoprotein (MDR1), multidrug resistance associated protein (MRP)1-4, or breast cancer resistance protein with and without MK-571 and probenecid (MRP inhibitors). Time activity curves of [¹³¹I]MIBG with and without MK-571 and probenecid were established using an SK-N-SH neuroblastoma cell line, and transporter expression of multiple drug resistance was measured. Biodistribution and SPECT imaging examinations were conducted using [¹²³I]MIBG with and without probenecid in SK-N-SH-bearing mice.

RESULTS

[¹³¹I]MIBG uptake was significantly higher in OAT1, OAT2, OCT1, and OCT2 than in mock cells. Uptake via OCT1 and OCT2 was little inhibited by MK-571 and probenecid. [¹³¹I]MIBG uptake into vesicles that highly expressed MRP1 or MRP4 was significantly higher in ATP than in AMP, and these inhibitors restored uptake to levels similar to that in AMP. Examining the time activity curves for [¹³¹I]MIBG in SK-N-SH cells, higher expressions of MDR1, MRP1, MRP4, and MK-571, or probenecid loading produced significantly higher uptake than in control at most incubation times. The ratios of tumors to blood or muscle in SK-N-SH-bearing mice were significantly increased by probenecid loading in comparison with normal mice.

CONCLUSIONS

[¹³¹I]MIBG exports via MRP1 and MRP4 in neuroblastoma. The accumulation and tumor-to-blood or muscle ratios of [¹³¹I]MIBG are improved by inhibition of MRPs with probenecid in neuroblastoma. ADVANCES IN KNOWLEDGE: [¹³¹I]MIBG, widely used for treatment of neuroendocrine tumors including neuroblastoma, is excreted via MRP1 and MRP4 in neuroblastoma.

IMPLICATIONS FOR PATIENT CARE

Loading with probenecid, OAT, and MRP inhibitors improves [¹³¹I]MIBG accumulation.

Toxicological implication of prostaglandin transporter SLCO2A1 inhibition by cigarette smoke in exacerbation of lung inflammation

We reported that bleomycin (BLM)-induced pulmonary fibrosis was exacerbated in the prostaglandin transporter gene (Slco2a1)-deficient mice (Slco2a1(-/-)). Because cigarette smoke (CS) contributes to creating a profibrotic milieu in the respiratory region, the present study aimed to investigate the impact of CS on SLCO2A1-associated pathogenesis in the lungs of BLM-instilled mice. Bronchoalveolar lavage (BAL) fluid cell analysis indicated more severe inflammation in Slco2a1(-/-) on day 5 after BLM intratracheal instillation, and Slco2a1 deletion increased mRNA expression of pro-inflammatory cytokines (Tnf-α and Il-1β) and chemokine (Ccl5) in BAL cells. Male Slco2a1(-/-) exhibited significantly higher amounts of released Il-1β in BAL fluid, compared with female Slco2a1(-/-), male or female Slco2a1(+/+) group. The amount of PGE₂ collected in BAL fluid tended to increase in Slco2a1(-/-) compared with Slco2a1(+/+) group, whereas the PGE₂ concentrations in lung tissues were comparable between both groups. Besides, PGE₂ accumulated more in BAL fluid of male than that of female mice. Therefore, Slco2a1-deficient male mice were found to be more susceptible to BLM-treatment. Moreover, CS extracts (CSE) significantly reduced initial PGE₂ uptake by rat type1 alveolar epithelial cell-like (AT1-L) cells and human SLCO2A1-transfected cells. Exposure of AT1-L cells to CSE resulted in decreased mRNA expression of Slco2a1, suggesting that CS modulates SLCO2A1 function. These results indicate that exacerbated lung inflammation is attributed to an increase in Il-1β peptide and PGE₂ accumulation in the alveolar space, which exhibits a male predominance. SLCO2A1 inhibition by CSE is considered to be a new rationale for the lung toxicity of CS.

Mathematical modeling analysis of hepatic uric acid disposition using human sandwich-cultured hepatocytes

Uric acid is biosynthesized from purine by xanthine oxidase (XO) mainly in the liver and is excreted into urine and feces. Although several transporters responsible for renal and intestinal handling of uric acid have been reported, information on hepatic transporters is limited. In the present study, we studied quantitative contribution of transporters for hepatic handling of uric acid by mathematical modeling analysis in human sandwich-cultured hepatocytes (hSCH). Stable isotope-labeled hypoxanthine, hypoxanthine-¹³C2,¹⁵N (HX), was incubated with hSCH and formed ¹³C2,¹⁵N-labeled xanthine (XA) and uric acid (UA) were measured by LC-MS/MS time dependently. Rate constants for metabolism and efflux and uptake transport across sinusoidal and bile canalicular membranes of HX, XA and UA were estimated in the presence of inhibitors of XO and uric acid transporters. An XO inhibitor allopurinol significantly decreased metabolisms of HX and XA. Efflux into bile canalicular lumen was negligible and sinusoidal efflux was considered main efflux pathway of formed UA. Transporter inhibition study highlighted that GLUT9 strongly and MRP4 intermediately contribute to the sinusoidal efflux of UA with minor contribution of NPT1/4. Modeling analysis developed in the present study should be useful for quantitative prediction of uric acid disposition in liver.

Contribution of Prostaglandin Transporter OATP2A1/SLCO2A1 to Placenta-to-Maternal Hormone Signaling and Labor Induction

We evaluated the contribution of organic anion transporting polypeptide 2A1 (OATP2A1/SLCO2A1), a high-affinity carrier for prostaglandins (PGs), to the parturition process. At gestational day (GD) 15.5, OATP2A1 is co-localized with 15-hydroxy-PG dehydrogenase in the mouse placental junctional zone and facilitates PG degradation by delivering PGs to the cytoplasm. Slco2a1 (+/−) females mated with Slco2a1 (−/−) males frequently showed elevated circulating progesterone at GD18.5 and delayed parturition. Progesterone receptor inhibition by RU486 treatment at GD18.5 blocked the delay of parturition. In the junctional zone, PGE₂ stimulated placental lactogen II (PL-II) production, resulting in higher expression of PL-II in Slco2a1 (−/−) placenta at GD18.5. Indomethacin treatment at GD15.5 suppressed the PL-II overproduction at GD18.5 in Slco2a1 (−/−) embryo-bearing dams, which promoted progesterone withdrawal and corrected the delayed parturition. These results suggest that extracellular PGE₂ reduction by OATP2A1 at mid-pregnancy would be associated with progesterone withdrawal by suppressing PL-II production, triggering parturition onset.

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Placental OATP2A1 promotes PGE₂ degradation by delivering PGE₂ to the cytoplasm

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Placental PGE₂ stimulates the PL-II production

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Extracellular PGE₂ decrease by placental OATP2A1 promotes progesterone withdrawal

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Feto-placental OATP2A1 is associated with the initiation of parturition

Identification of the Uptake Transporter Responsible for Distribution of Acotiamide into Stomach Tissue

The acetylcholinesterase inhibitor, acotiamide, improves gastric motility and is clinically used to treat functional dyspepsia. The present study aimed to identify the transporters involved in the distribution of acotiamide in stomach tissue. Acotiamide uptake by the gastric cancer-derived model cell line, Hs746 T, was Na⁺- and pH-independent. The initial uptake velocity of acotiamide was saturable with increasing concentrations of acotiamide and was inhibited by selective serotonin reuptake inhibitors, which are potent inhibitors of the plasma membrane monoamine transporter (PMAT). The uptake of acotiamide by PMAT gene-transfected HEK293 cells was saturable, with similar K_m (197.9 μM) values to those of uptake by Hs 746T cells (106 μM). Moreover, immunoreactivity of PMAT was found in the gastric smooth muscle and vascular endothelial cells. These results suggest that PMAT contributes to the distribution of acotiamide in the stomach, where it exerts its pharmacological effects.

ABCG2 requires a single aromatic amino acid to "clamp" substrates and inhibitors into the binding pocket

ATP-binding cassette sub-family G member 2 (ABCG2) is a homodimeric ATP-binding cassette (ABC) transporter that not only has a key role in helping cancer cells to evade the cytotoxic effects of chemotherapy, but also in protecting organisms from multiple xeno- and endobiotics. Structural studies indicate that substrate and inhibitor (ligands) binding to ABCG2 can be differentiated quantitatively by the number of amino acid contacts, with inhibitors displaying more contacts. Although binding is the obligate initial step in the transport cycle, there is no empirical evidence for one amino acid being primarily responsible for ligand binding. By mutagenesis and biochemical studies, we demonstrated that the phylogenetically conserved amino acid residue, F439, was critical for both transport and the binding of multiple substrates and inhibitors. Structural modeling implied that the π-π interactions from each F439 monomer mediated the binding of a surprisingly diverse array of structurally unrelated substrates and inhibitors and that this symmetrical π-π interaction "clamps" the ligand into the binding pocket. Key molecular features of diverse ABCG2 ligands using the π-π clamp along with structural studies created a pharmacophore model. These novel findings have important therapeutic implications because key properties of ligands interacting with ABCG2 have been disovered. Furthermore, mechanistic insights have been revealed by demonstrating that for ABCG2 a single amino acid is essential for engaging and initiating transport of multiple drugs and xenobiotics.

Pharmacokinetic/pharmacodynamic modeling and simulation of dotinurad, a novel uricosuric agent, in healthy volunteers

This study aimed to investigate the pharmacokinetic and pharmacodynamic (PK/PD) profiles of dotinurad, a novel uricosuric agent, and to construct a PK/PD model to predict serum urate (SUA) levels after dotinurad administration in healthy men. PK/PD model was constructed using single-dose study data considering the physiological features of urate handling. Model validation was performed by comparing the predicted SUA levels with the SUA levels in a multiple-dose study. Dotinurad was absorbed rapidly, and its exposure increased proportionally in the tested dose ranges (0.5-20 mg) after a single-dose administration. The PK model after oral administration was described using a one-compartment model with first-order absorption. Effects on SUA and renal urate excretion of dotinurad increased with dose escalation but were apparently saturable at a dose >5 mg. The simple maximal effect (Emax) model was selected as the PD model of dotinurad on renal urate reabsorption, resulting in an estimated Emax of 0.51. The plasma concentration at the half-maximal effect of dotinurad was 196 ng/mL. Other PD parameters were calculated from the change in SUA level or urinary excretion of urate before and after dotinurad administration. The predicted SUA levels, using the PK/PD model, were well-fitted with the observed values. The constructed PK/PD model of dotinurad appropriately described the profiles of dotinurad plasma concentrations and SUA level in multiple administration study.

Quantification of Prostaglandin E2 Concentration in Interstitial Fluid from the Hypothalamic Region of Free-moving Mice

Prostaglandin E₂ (PGE₂) is a well-established chemical mediator for the generation of the fever at the hypothalamus of the brain. PGE₂ mediates fever generation via PGE receptor 3 (i.e., EP3) on neurons in the preoptic area. The role of PGE₂ has been analyzed by measuring PGE₂ concentration in cerebrospinal fluid (C_csf); however, local PGE₂ concentration at the hypothalamus may not necessarily be consistent with C_csf. In this protocol, we introduce our method to measure directly the alteration in PGE₂ concentration in interstitial fluid in the hypothalamus (C_isf) of awake (free-moving) mice using a microdialysis technique. Male mice (c57BL/6J) were anesthetized and fixed in the stereotaxic instrument, and a microdialysis probe was inserted into the hypothalamus through a guide cannula. On the fifth postoperative day, C_isf was monitored in free-moving mice that were intraperitoneally (i.p.) injected with lipopolysaccharide (LPS). PGE₂ and other eicosanoids recovered in Krebs-Ringer phosphate buffer and defused through a microdialysis probe were extracted into ethyl acetate/formic acid and then quantified with LC-MS/MS. Our method is useful to understand the role of key regulators of prostaglandin concentration such as those of transporters, which have been unappreciated in inflammation-based brain diseases.

Changes of drug pharmacokinetics mediated by downregulation of kidney organic cation transporters Mate1 and Oct2 in a rat model of hyperuricemia

The effects of hyperuricemia on the expression of kidney drug transporters and on the pharmacokinetics of several substrate drugs were examined. We first established a rat model of hyperuricemia without marked symptoms of chronic kidney failure by 10-day co-administration of oxonic acid (uricase inhibitor) and adenine (biosynthetic precursor of uric acid). These hyperuricemic rats showed plasma uric acid concentrations of up to 6 mg/dL, which is similar to the serum uric acid level in hyperuricemic humans, with little change of inulin clearance. The mRNA levels of multidrug and toxin extrusion 1 (Mate1, Slc47a1), organic anion transporter 1 (Oat1, Slc22a6), organic cation transporter 2 (Oct2, Slc22a2), urate transporter 1 (Urat1, Slc22a12) and peptide transporter 1 (Pept1, Slc15a1) were significantly decreased in kidney of hyperuricemic rats. Since Oct2, Mate1 and Oat1 are important for renal drug elimination, we next investigated whether the pharmacokinetics of their substrates, metformin, cephalexin and creatinine, were altered. The plasma concentration of metformin was not affected, while its kidney tissue accumulation was significantly increased. The plasma concentration and kidney tissue accumulation of cephalexin and the plasma concentration of creatinine were also increased. Furthermore, the protein expression of kidney Mate1 was decreased in hyperuricemic rats. Accordingly, although multiple factors may influence renal handling of these drugs, these observations can be accounted for, at least in part, by downregulation of Mate1-mediated apical efflux from tubular cells and Oct2-mediated basolateral uptake. Our results suggest that hyperuricemia could alter the disposition of drugs that are substrates of Mate1 and/or Oct2.

Uric acid analogue as a possible xenobiotic marker of uric acid transporter Urat1 in rats

The inhibitor of uric acid reabsorptive transporter URAT1 in kidney is drawing attention as a drug target for hyperuricemia. However, it is difficult to evaluate efficacy of URAT1 inhibitors in vivo using laboratory animals due to species difference in uric acid metabolism. In the present study, the usefulness of exogenously administering uric acid analogues resistant to uricase was investigated for in vivo evaluation of transport activity of rUrat1 in rats. Uptake of examined four uric acid analogues by rUrat1-expressing Xenopus oocytes was significantly higher than that by water-injected oocytes. In metabolism studies, disappearance of these compounds was negligible, while uric acid was significantly decreased. When oxypurinol was administered to rats, fractional excretion (FE) was 0.4, suggesting reabsorption of oxypurinol. Moreover, FE of oxypurinol was tended to be increased, but not statistically different, by co-administration of a uricosuric agent FYU-981, while plasma concentration of oxypurinol was not affected. These results suggested that oxypurinol is a potential uric acid analogue, although it was not suitable as a probe of uric acid in in vivo study. Our findings may contribute to discovery and development of novel uricosuric agent targeting URAT1.

Identification of MRP2 as a targetable factor limiting oxaliplatin accumulation and response in gastrointestinal cancer

Oxaliplatin is important for the clinical treatment of colorectal cancer and other gastrointestinal malignancies, but tumour resistance is limiting. Several oxaliplatin transporters were previously identified but their relative contributions to determining oxaliplatin tumour responses and gastrointestinal tumour cell sensitivity to oxaliplatin remains unclear. We studied clinical associations between tumour expression of oxaliplatin transporter candidate genes and patient response to oxaliplatin, then experimentally verified associations found with MRP2 in models of human gastrointestinal cancer. Among 18 oxaliplatin transporter candidate genes, MRP2 was the only one to be differentially expressed in the tumours of colorectal cancer patients who did or did not respond to FOLFOX chemotherapy. Over-expression of MRP2 (endogenously in HepG2 and PANC-1 cells, or induced by stable transfection of HEK293 cells) decreased oxaliplatin accumulation and cytotoxicity but those deficits were reversed by inhibition of MRP2 with myricetin or siRNA knockdown. Mice bearing subcutaneous HepG2 tumour xenografts were sensitised to oxaliplatin antitumour activity by concurrent myricetin treatment with little or no increase in toxicity. In conclusion, MRP2 limits oxaliplatin accumulation and response in human gastrointestinal cancer. Screening tumour MRP2 expression levels, to select patients for treatment with oxaliplatin-based chemotherapy alone or in combination with a MRP2 inhibitor, could improve treatment outcomes.

Effect of endogenous multidrug resistance 1 and P-glycoprotein expression on anticancer drug resistance in colon cancer cell lines

P-glycoprotein (P-gp, multidrug resistance 1 (MDR1)) overexpression confers multidrug resistance to cancer cells, and P-gp in cell lines transfected with MDR1 or selected with chemotherapeutics significantly affect the anticancer drug efficacy. Although human cancer cell line panels consisting of defined tumor cell lines expressing endogenous P-gp have been used to screen drugs in pharmaceutical industries, endogenous P-gp affecting in vitro anticancer drug efficacy is unclear. The impact of P-gp expression on anticancer drug efficacy was assessed by using five colon cancer cell lines expressing varying endogenous P-gp levels and by selecting from the Cancer Cell Line Encyclopedia (CCLE). mRNA expression of MDR1 was considered as a surrogate of the protein expression of its gene product, P-gp, in CL-11, C2BBe1 and RKO cells, whereas P-gp protein expression in plasma membranes or crude membrane fractions was lower than expected from mRNA expression in CW-2 and CL-40 cells. The EC₅₀ of paclitaxel and vinorelbine decreased in the presence of a P-gp inhibitor in CW-2 and CL-11 cells that highly express P-gp. No significant alterations in EC₅₀ were observed in the CL-40, C2BBe1 and RKO cells, which show lower P-gp expression. Accordingly, the apparent in vitro efficacy of anticancer drugs could be underestimated if the endogenous P-gp expression is higher than in CL-11 cells. The effect of P-gp needs to be carefully evaluated in cell lines that highly express P-gp, which account for 1.5% of cancer cell lines, including all cancer types, and 14.5% of colon cancer cell lines in CCLE, considering the protein expression levels in plasma membranes.