Construction, identification and application of HeLa cells stably transfected with human PEPT1 and PEPT2

OAT1/3 regulate the absorption of CP-25 in the rat synovium

Paeoniflorin-6'-O-benzene sulfonate (CP-25) is a new ester derivative formed by esterification of paeoniflorin. We found that CP-25 inhibits the abnormal proliferation and migration of inflammatory fibroblast-like synoviocytes (FLS). However, the mechanism by which CP-25 is absorbed by FLS remains unclear. Therefore, we established a UPLC-MS/MS methodology to study the mechanism of CP-25 uptake by FLS. Our research revealed that the uptake of CP-25 by rat FLS was time- and concentration-dependent and that the concentration of CP-25 reached a dynamic equilibrium after approximately 60 min. A glucose-free environment, a low-temperature environment or the inhibition of ATP synthesis significantly reduced the absorption of CP-25 by FLS. Furthermore, we confirmed through siRNA interference and overexpression through transient transfection that organic anion transporter (OAT)1/3 play a major role in the process of active uptake of CP-25 by FLS. Additionally, we validated the absorption of CP-25 mediated by OAT1/3 in the synovia with OAT1/3 substrates and inhibitors. Moreover, the absorption of CP-25 by FLS from adjuvant arthritis rats and rheumatoid arthritis patients was significantly lower than that by FLS from normal rats and normal individuals. Taken together, our data suggested that CP-25 is absorbed by FLS through an active transport process, which is mediated primarily by OAT1/3. This study provides an experimental and theoretical basis for further exploration of the molecular mechanism involved.

Research Methods and New Advances in Drug-Drug Interactions Mediated by Renal Transporters

The kidney is critical in the human body's excretion of drugs and their metabolites. Renal transporters participate in actively secreting substances from the proximal tubular cells and reabsorbing them in the distal renal tubules. They can affect the clearance rates (CLr) of drugs and their metabolites, eventually influence the clinical efficiency and side effects of drugs, and may produce drug-drug interactions (DDIs) of clinical significance. Renal transporters and renal transporter-mediated DDIs have also been studied by many researchers. In this article, the main types of in vitro research models used for the study of renal transporter-mediated DDIs are membrane-based assays, cell-based assays, and the renal slice uptake model. In vivo research models include animal experiments, gene knockout animal models, positron emission tomography (PET) technology, and studies on human beings. In addition, in vitro-in vivo extrapolation (IVIVE), ex vivo kidney perfusion (EVKP) models, and, more recently, biomarker methods and in silico models are included. This article reviews the traditional research methods of renal transporter-mediated DDIs, updates the recent progress in the development of the methods, and then classifies and summarizes the advantages and disadvantages of each method. Through the sorting work conducted in this paper, it will be convenient for researchers at different learning stages to choose the best method for their own research based on their own subject's situation when they are going to study DDIs mediated by renal transporters.

Rapid and Sensitive Quantification of Intracellular Glycyl-Sarcosine for Semi-High-Throughput Screening for Inhibitors of PEPT-1

The peptide transporter PEPT-1 (SLC15A1) plays a major role in nutritional supply with amino acids by mediating the intestinal influx of dipeptides and tripeptides generated during food digestion. Its role in the uptake of small bioactive peptides and various therapeutics makes it an important target for the investigation of the systemic absorption of small peptide-like active compounds and prodrug strategies of poorly absorbed therapeutics. The dipeptide glycyl-sarcosine (Gly-Sar), which comprises an N-methylated peptide bond that increases stability against enzymatic degradation, is widely utilized for studying PEPT-1-mediated transport. To support experiments on PEPT-1 inhibitor screening to identify potential substrates, we developed a highly sensitive Gly-Sar quantification assay for Caco-2 cell lysates with a dynamic range of 0.1 to 1000 ng/mL (lower limit of quantification 0.68 nM) in 50 µL of cell lysate. The assay was validated following the applicable recommendations for bioanalytic method validation of the FDA and EMA. Sample preparation and quantification were established in 96-well cell culture plates that were also used for the cellular uptake studies, resulting in a rapid and robust screening assay for PEPT-1 inhibitors. This sample preparation principle, combined with the high sensitivity of the UPLC-MS/MS quantification, is suitable for screening assays for PEPT-1 inhibitors and substrates in high-throughput formats and holds the potential for automation. Applicability was demonstrated by IC₅₀ determinations of the known PEPT-1 inhibitor losartan, the known substrates glycyl-proline (Gly-Pro), and valaciclovir, the prodrug of aciclovir, which itself is no substrate of PEPT-1 and consequently showed no inhibition in our assay.

Dipeptide-modified nanoparticles to facilitate oral docetaxel delivery: new insights into PepT1-mediated targeting strategy

Oligopeptide transporter 1 (PepT1) has been a striking prodrug-designing target. However, the underlying mechanism of PepT1 as a target to facilitate the oral absorption of nanoparticles (NPs) remains unclear. Herein, we modify Poly (lactic-co-glycolic acid) (PLGA) NPs with the conjugates of dipeptides (L-valine-valine, L-valine-phenylalanine) and polyoxyethylene (PEG Mw: 1000, 2000) stearate to facilitate oral delivery of docetaxel (DTX) to investigate the oral absorption mechanism and regulatory effects on PepT1 of the dipeptide-modified NPs. The cellular uptake of the dipeptide-modified NPs is more efficient than that of the unmodified NPs in the stably transfected hPepT1- Hela cells and Caco-2 cells, suggesting the involvement of PepT1 in the endocytosis of NPs. The internalization of the dipeptide-modified NPs is proved to be a proton-dependent process. Moreover, the L-valine-valine modified NPs with shorter PEG chain exhibit distinct advantages in terms of intestinal permeability and oral absorption, resulting in significantly improved oral bioavailability of DTX. In summary, PepT1 could serve as a desirable target for oral nanoparticulate drug delivery and the dipeptide-modified NPs represent a promising nanoplatform to facilitate oral delivery of hydrophobic drugs with low bioavailability.

Active Fragment of Veronica ciliata Fisch. Attenuates t-BHP-Induced Oxidative Stress Injury in HepG2 Cells through Antioxidant and Antiapoptosis Activities

Excessive amounts of reactive oxygen species (ROS) in the body are a key factor in the development of hepatopathies such as hepatitis. The aim of this study was to assess the antioxidation effect in vitro and hepatoprotective activity of the active fragment of Veronica ciliata Fisch. (VCAF). Antioxidant assays (DPPH, superoxide, and hydroxyl radicals scavenging) were conducted, and hepatoprotective effects through the application of tert-butyl hydroperoxide- (t-BHP-) induced oxidative stress injury in HepG2 cells were evaluated. VCAF had high phenolic and flavonoid contents and strong antioxidant activity. From the perspective of hepatoprotection, VCAF exhibited a significant protective effect on t-BHP-induced HepG2 cell injury, as indicated by reductions in cytotoxicity and the levels of ROS, 8-hydroxydeoxyguanosine (8-OHdG), and protein carbonyls. Further study demonstrated that VCAF attenuated the apoptosis of t-BHP-treated HepG2 cells by suppressing the activation of caspase-3 and caspase-8. Moreover, it significantly decreased the levels of ALT and AST, increased the activities of acetyl cholinesterase (AChE), glutathione (GSH), superoxide dismutase (SOD), and catalase (CAT), and increased total antioxidative capability (T-AOC). Collectively, we concluded that VCAF may be a considerable candidate for protecting against liver injury owing to its excellent antioxidant and antiapoptosis properties.

Expression, regulation and function of intestinal drug transporters: an update

Although oral drug administration is currently the favorable route of administration, intestinal drug absorption is challenged by several highly variable and poorly predictable processes such as gastrointestinal motility, intestinal drug solubility and intestinal metabolism. One further determinant identified and characterized during the last two decades is the intestinal drug transport that is mediated by several transmembrane proteins such as P-gp, BCRP, PEPT1 and OATP2B1. It is well-established that intestinal transporters can affect oral absorption of many drugs in a significant manner either by facilitating their cellular uptake or by pumping them back to gut lumen, which limits their oral bioavailability. Their functional relevance becomes even more apparent in cases of unwanted drug-drug interactions when concomitantly given drugs that cause transporter induction or inhibition, which in turn leads to increased or decreased drug exposure. The longitudinal expression of several intestinal transporters is not homogeneous along the human intestine, which may have functional implications on the preferable site of intestinal drug absorption. Besides the knowledge about the expression of pharmacologically relevant transporters in human intestinal tissue, their exact localization on the apical or basolateral membrane of enterocytes is also of interest but in several cases debatable. Finally, there is obviously a coordinative interplay of intestinal transporters (apical-basolateral), intestinal enzymes and transporters as well as intestinal and hepatic transporters. This review aims to give an updated overview about the expression, localization, regulation and function of clinically relevant transporter proteins in the human intestine.

Transfection of primary brain capillary endothelial cells for protein synthesis and secretion of recombinant erythropoietin: a strategy to enable protein delivery to the brain

Treatment of chronic disorders affecting the central nervous system (CNS) is complicated by the inability of drugs to cross the blood-brain barrier (BBB). Non-viral gene therapy applied to brain capillary endothelial cells (BCECs) denotes a novel approach to overcome the restraints in this passage, as turning BCECs into recombinant protein factories by transfection could result in protein secretion further into the brain. The present study aims to investigate the possibility of transfecting primary rat brain endothelial cells (RBECs) for recombinant protein synthesis and secretion of the neuroprotective protein erythropoietin (EPO). We previously showed that 4% of RBECs with BBB properties can be transfected without disrupting the BBB integrity in vitro, but it can be questioned whether this is sufficient to enable protein secretion at therapeutic levels. The present study examined various transfection vectors, with regard to increasing the transfection efficiency without disrupting the BBB integrity. Lipofectamine 3000™ was the most potent vector compared to polyethylenimine (PEI) and Turbofect. When co-cultured with astrocytes, the genetically modified RBECs secreted recombinant EPO into the cell culture medium both luminally and abluminally, and despite lower levels of EPO reaching the abluminal chamber, the amount of recombinant EPO was sufficient to evolve a biological effect on astrocytes cultured at the abluminal side in terms of upregulated gene expression of brain-derived neurotropic factor (BDNF). In conclusion, non-viral gene therapy to RBECs leads to protein secretion and signifies a method for therapeutic proteins to target cells inside the CNS otherwise omitted due to the BBB.

Species Differences in Human and Rodent PEPT2-Mediated Transport of Glycylsarcosine and Cefadroxil in Pichia Pastoris Transformants

The proton-coupled oligopeptide transporter PEPT2 (SLC15A2) plays an important role in the disposition of di/tripeptides and peptide-like drugs in kidney and brain. However, unlike PEPT1 (SLC15A1), there is little information about species differences in the transport of PEPT2-mediated substrates. The purpose of this study was to determine whether PEPT2 exhibited a species-dependent uptake of glycylsarcosine (GlySar) and cefadroxil using yeast Pichia pastoris cells expressing cDNA from human, mouse, and rat. In such a system, the functional activity of PEPT2 was evaluated with [3H]GlySar as a function of time, pH, substrate concentration, and specificity, and with [3H]cefadroxil as a function of concentration. We observed that the uptake of GlySar was pH-dependent with an optimal uptake at pH 6.5 for all three species. Moreover, GlySar showed saturable uptake kinetics, with Km values in human (150.6 µM) > mouse (42.8 µM) ≈ rat (36.0 µM). The PEPT2-mediated uptake of GlySar in yeast transformants was specific, being inhibited by di/tripeptides and peptide-like drugs, but not by amino acids and nonsubstrate compounds. Cefadroxil also showed a saturable uptake profile in all three species, with Km values in human (150.8 μM) > mouse (15.6 μM) ≈ rat (11.9 μM). These findings demonstrated that the PEPT2-mediated uptake of GlySar and cefadroxil was specific, species dependent, and saturable. Furthermore, based on the Km values, mice appeared similar to rats but both were less than optimal as animal models in evaluating the renal reabsorption and pharmacokinetics of peptides and peptide-like drugs in humans.

Ghrelin upregulates PepT1 activity in the small intestine epithelium of rats with sepsis

BACKGROUND

Sepsis causes nutritional substrate malabsorption; hence, preventing gut barrier problems and improving the nutritional status in sepsis is a compelling issue.

AIMS

We tested whether ghrelin administration affects peptide transporter 1 (PepT1) activity in the intestinal epithelium of rats with sepsis.

METHODS

Sixty male Sprague-Dawley rats were randomly divided into sham-operated, sepsis, and ghrelin-treated groups. The cecum of sham-operated rats was separated after laparotomy without ligation and perforation. Sepsis group rats underwent cecal ligation and puncture (CLP). Mucosal specimens were used for immunohistochemstry, real-time PCR, and western blotting to detect PepT1 distribution, and mRNA and protein expression levels, respectively. TNF-α, IL-1β, and ghrelin levels were estimated in serum and intestinal mucosal tissue by ELISA. High-performance liquid chromatography was used to measure PepT1 uptake by the epithelial cells. Moreover, survival, body weight, and food intake of the rats were recorded during the 7-day treatment period.

RESULTS

All rats in the sham-operated group survived, and 80% of rats in the sepsis group died within 7d of CLP. Treatment with ghrelin attenuated the CLP-induced body weight loss, intestine mucosa damage, and the survival rate was better. In addition, ghrelin attenuated increases in TNF-α and IL-1β production. The expressions of PepT1 mRNA and protein were higher in ghrelin-treated group rats than in sepsis rats. Moreover, the uptake function of PepT1 was better in ghrelin-treated group rats.

CONCLUSION

Ghrelin treatment can reduce the inflammatory response and greatly upregulate the physiological function of PepT1 in intestinal epithelial cells of rats with sepsis.

Human oligopeptide transporter 2 (PEPT2) mediates cellular uptake of polymyxins

OBJECTIVES

Polymyxins are a last-line therapy to treat MDR Gram-negative bacterial infections. Nephrotoxicity is the dose-limiting factor for polymyxins and recent studies demonstrated significant accumulation of polymyxins in renal tubular cells. However, little is known about the mechanism of polymyxin uptake into these cells. Oligopeptide transporter 2 (PEPT2) is a solute carrier transporter (SLC) expressed at the apical membrane of renal proximal tubular cells and facilitates drug reabsorption in the kidney. In this study, we examined the role of PEPT2 in polymyxin uptake into renal tubular cells.

METHODS

We investigated the inhibitory effects of colistin and polymyxin B on the substrate uptake mediated through 15 essential SLCs in overexpressing HEK293 cells. The inhibitory potency of both polymyxins on PEPT2-mediated substrate uptake was measured. Fluorescence imaging was employed to investigate PEPT2-mediated uptake of the polymyxin fluorescent probe MIPS-9541 and a transport assay was conducted with MIPS-9541 and [(3)H]polymyxin B1.

RESULTS

Colistin and polymyxin B potently inhibited PEPT2-mediated [(3)H]glycyl-sarcosine uptake (IC50 11.4 ± 3.1 and 18.3 ± 4.2 μM, respectively). In contrast, they had no or only mild inhibitory effects on the transport activity of the other 14 SLCs evaluated. MIPS-9541 potently inhibited PEPT2-mediated [(3)H]glycyl-sarcosine uptake (IC50 15.9 μM) and is also a substrate of PEPT2 (Km 74.9 μM). [(3)H]polymyxin B1 was also significantly taken up by PEPT2-expressing cells (Km 87.3 μM).

CONCLUSIONS

Our study provides the first evidence of PEPT2-mediated uptake of polymyxins and contributes to a better understanding of the accumulation of polymyxins in renal tubular cells.

Simultaneous determination of three dipeptides (JBP485, Gly-Sar and JBP923) in the cell lysates by liquid chromatography-tandem mass spectrometry: application to identify the function of the PEPT1 transfected cell

A simple and rapid liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the simultaneous determination of JBP485, Gly-Sar and JBP923 in the cell lysates using methanol as a deproteinization solvent was developed and validated. Detection was performed by turbo ionspray ionization in multiple reaction monitoring mode using the transitions of m/z 147.1 → m/z 90.1 for Gly-Sar, m/z 201.1 → m/z 86.1 for JBP485, m/z 219.1 → m/z 86.1 for JBP923 and m/z 152.0 → m/z 110.0 for paracetamol (internal standard). The analytes were separated on a Hypersil ODS C18 HPLC column using isocratic elution mode with a mobile phase containing 0.1% formic acid in water-methanol (97:3, v/v) at a flow rate of 0.2 mL/min. The calibration curves were demonstrated to be linear over the concentration range of 5.00-5000 nm with coefficient of 0.9968 for Gly-Sar, 0.9975 for JBP485 and 0.9952 for JBP923. The intra- and inter-day precisions were <10.2% for each quality contro; level, and the accuracy was within ±5.6% for each analyte. The matrix effect, the extraction recovery and stabilities of LC-MS/MS analysis were also investigated. This validated method was successfully applied to the simultaneous determination of JBP485, Gly-Sar and JBP923 in the cell lysates for identification of stably transfected HeLa cells with human PEPT1.

[Expression of PEPT2 mRNA in lung tissue of rats with pulmonary fibrosis]

背景与目的

肺纤维化是肺癌放化疗后的常见病理改变，是阻碍药物转运到肺部的关键因素之一，肽转运载体已经成为合理设计肽和肽类药物的靶标，本研究旨在探讨肽转运载体2（peptide transporter 2, PEPT2）mRNA在肺纤维化大鼠肺组织中的表达。

方法

健康SD大鼠50只，随机分为5组。博莱霉素（bleomycin, BLM）7 d、14 d、28 d组：气管内一次性滴入博莱霉素溶液复制肺纤维化大鼠模型，分别于给药后7 d、14 d和28 d放血处死；生理盐水组滴入等量生理盐水，于14 d放血处死；正常组不做任何处理。各组取肺组织，光镜观察组织病理变化；检测样本羟脯氨酸含量；半定量RT-PCR检测肺组织PEPT2 mRNA表达。

结果

BLM 7 d组大鼠肺组织呈急性炎症性改变，无纤维增生；BLM 14 d组和28 d组大鼠肺组织均有纤维化改变，以28 d组最为明显。BLM 7 d组肺组织羟脯氨酸含量与正常对照组和生理盐水组相比无统计学差异（P > 0.05）；14 d组和28 d组大鼠肺组织羟脯氨酸含量均高于正常对照组和生理盐水组（P < 0.05）。各组肺组织PEPT2 mRNA的相对表达量无统计学差异（P > 0.05）。

结论

PEPT2 mRNA在博莱霉素致肺纤维化大鼠肺组织表达水平无明显变化，PEPT2可能是设计肺纤维化的新型肽类药物靶标之一。

JBP485 improves gentamicin-induced acute renal failure by regulating the expression and function of Oat1 and Oat3 in rats

We investigated the effects of JBP485 (an anti-inflammatory dipeptide and a substrate of OAT) on regulation of the expression and function of renal Oat1 and Oat3, which can accelerate the excretion of accumulated uremic toxins (e.g. indoxyl sulfate) in the kidney to improve gentamicin-induced ARF in rats. JBP485 caused a significant decrease in the accumulation of endogenous substances (creatinine, blood urea nitrogen and indoxyl sulfate) in vivo, an increase in the excretion of exogenous compounds (lisinopril and inulin) into urine, and up-regulation of the expressions of renal Oat1 and Oat3 in the kidney tissues and slices via substrate induction. To determine the effect of JBP485 on the accelerated excretion of uremic toxins mediated by Oat1 and Oat3, the mRNA and protein expression levels of renal basolateral Oats were assessed by quantitative real-time PCR, western blot, immunohistochemical analysis and an immunofluorescence method. Gentamicin down-regulated the expression of Oats mRNA and protein in rat kidney, and these effects were reversed after administration of JBP485. In addition, JBP485 caused a significant decrease in MPO and MDA levels in the kidney, and improved the pathological condition of rat kidney. These results indicated that JBP485 improved acute renal failure by increasing the expression and function of Oat1 and Oat3, and by decreasing overoxidation of the kidney in gentamicin-induced ARF rats.

OAT1 and OAT3: targets of drug-drug interaction between entecavir and JBP485

Entecavir and JBP485 (a dipeptide) exhibit the antihepatitis activities and it is possible for the two drugs to be coadministered in the treatment of hepatitis. We aimed to elucidate whether entecavir was a substrate of OAT1, OAT3, OCT, and PEPT1 and to investigate the targets of drug-drug interactions between entecavir and JBP485. Plasma and urine concentrations of entecavir following intravenous and oral administration in vivo, uptake of entecavir in kidney slices and transfected cells in vitro, were determined by LC-MS/MS. Following intravenous co-administration of entecavir and JBP485 in rats, entecavir AUC increased 1.93-fold, t1/2β was prolonged 2.08-fold, CLP decreased 49%, CLR decreased 73%, and accumulated urinary excretion decreased 54%. However, following oral co-administration, the entecavir Tmax and Cmax were not affected; the degree of change in other pharmacokinetic parameters (AUC, t1/2β, CLP, and accumulated urinary excretion) was similar to that of intravenous administration. The uptake of entecavir was nearly identical in hPEPT1- as in vector-HELA cells. In rat kidney slices, uptake of entecavir was markedly inhibited by p-aminohippurate, benzylpenicillin, JBP485, and tetraethyl ammonium. In hOAT1- and hOAT3-HEK293 cells, uptake of entecavir was significantly higher compared to vector-HEK293 cells and was markedly inhibited by p-aminohippurate, benzylpenicillin, and JBP485. Km and Vmax values of entecavir were 250 μM and 0.83 nmol/mg protein/30s (OAT1) and 23 μM and 1.1 nmol/mg protein/30 s (OAT3), respectively. Entecavir is the substrate of OAT1, OAT3, and OCT. Moreover, OAT1 and OAT3 are the targets of DDI between entecavir and JBP485.