Mass spectrometry in ocular drug research.

Mass spectrometry (MS) has been proven as an excellent tool in ocular drug research allowing analyzes from small samples and low concentrations. This review begins with a short introduction to eye physiology and ocular pharmacokinetics and the relevance of advancing ophthalmic treatments. The second part of the review consists of an introduction to ocular proteomics, with special emphasis on targeted absolute quantitation of membrane transporters and metabolizing enzymes. The third part of the review deals with liquid chromatography-MS (LC-MS) and MS imaging (MSI) methods used in the analysis of drugs and metabolites in ocular samples. The sensitivity and speed of LC-MS make simultaneous quantitation of various drugs and metabolites possible in minute tissue samples, even though ocular sample preparation requires careful handling. The MSI methodology is on the verge of becoming as important as LC-MS in ocular pharmacokinetic studies, since the spatial resolution has reached the level, where cell layers can be separated, and quantitation with isotope-labeled standards has come more reliable. MS will remain in the foreseeable future as the main analytical method that will progress our understanding of ocular pharmacokinetics.

Transporter Protein Expression of Corneal Epithelium in Rabbit and Porcine: Evaluation of Models for Ocular Drug Transport Study.

The transcorneal route is the main entry route for drugs to the intraocular parts, after topical administration. The outer surface, the corneal epithelium (CE), forms the rate-limiting barrier for drug permeability. Information about the role and protein expression of drug and amino acid transporter proteins in the CE is sparse and lacking. The aim of our study was to characterize transporter protein expression in rabbit and porcine CE to better understand potential drug and nutrient absorption after topical administration. Proteins, mainly Abc and Slc transporters, were characterized with quantitative targeted absolute proteomics and global untargeted proteomics methods. In the rabbit CE, 24 of 48 proteins were detected in the targeted approach, and 21 of these were quantified. In the porcine CE, 26 of 58 proteins were detected in the targeted approach, and 20 of these were quantified. Among these, 15 proteins were quantified in both animals: 4f2hc (Slc3a2), Aqp0, Asct1 (Slc1a4), Asct2 (Slc1a5), Glut1 (Slc2a1), Hmit (Slc2a13), Insr, Lat1 (Slc7a5), Mct1 (Slc16a1), Mct2 (Slc16a7), Mct4 (Slc16a3), Mrp 4 (Abcc4), Na+/K+-ATPase, Oatp3a1 (Slco3a1), and Snat2 (Slc38a2). Overall, the global proteomics results supported the targeted proteomics results. Organic anion transporting polypeptide Oatp3a1 was detected and quantified for the first time in both rabbit (1.4 ± 0.4 fmol/cm2) and porcine (11.1 ± 5.3 fmol/cm2) CE. High expression levels were observed for L-type amino acid transporter, Lat1, which was quantified with newly selected extracellular domain peptides in rabbit (48.9 ± 11.8 fmol/cm2) and porcine (37.6 ± 11.5 fmol/cm2) CE. The knowledge of transporter protein expression in ocular barriers is a key factor in the successful design of new ocular drugs, pharmacokinetic modeling, understanding ocular diseases, and the translation to human.

Sodium-Dependent Neutral Amino Acid Transporter 2 Can Serve as a Tertiary Carrier for l-Type Amino Acid Transporter 1-Utilizing Prodrugs.

Membrane transporters are the key determinants of the homeostasis of endogenous compounds in the cells and their exposure to drugs. However, the substrate specificities of distinct transporters can overlap. In the present study, the interactions of l-type amino acid transporter 1 (LAT1)-utilizing prodrugs with sodium-coupled neutral amino acid transporter 2 (SNAT2) were explored. The results showed that the cellular uptake of LAT1-utilizing prodrugs into a human breast cancer cell line, MCF-7 cells, was mediated via SNATs as the uptake was increased at higher pH (8.5), decreased in the absence of sodium, and inhibited in the presence of unselective SNAT-inhibitor, (α-(methylamino)isobutyric acid, MeAIB). Moreover, docking the compounds to a SNAT2 homology model (inward-open conformation) and further molecular dynamics simulations and the subsequent trajectory and principal component analyses confirmed the chemical features supporting the interactions of the studied compounds with SNAT2, which was found to be the main SNAT expressed in MCF-7 cells.

Activation of Annexin A2 signaling at the blood-brain barrier in a mouse model of multiple sclerosis.

Blood-brain barrier (BBB) dysfunction is a fundamental cause of multiple sclerosis and identifying the molecules that are responsible is an urgent matter. Protein expression was comprehensively quantified at the BBB of experimental autoimmune encephalomyelitis (EAE) mice, a model of multiple sclerosis, using the SWATH method. Concerning tight junction molecules, the level of expression of Claudin-5, which, in a previous immunohistochemical analysis, was confirmed to be down-regulated by EAE, remained unchanged, but the expression of Claudin-11 and Occludin was decreased by 0.69- and 0.62-fold, respectively, in brain capillaries isolated from EAE mice. A number of other cell-cell junctional molecules including ESAM, CADM1, CADM2, CADM3, CADM4, and HEPACAM were also down-regulated. The levels of expression of intercellular adhesion molecule 1 (ICAM1) and vascular cell adhesion molecule 1 (VCAM1), which directly mediate the infiltration of lymphocytes across the BBB, were increased in EAE mice by 3.3- and 2.6-fold, respectively. The expression of CXADR, which possibly facilitates the adhesion of migrating cells, was also increased by 3.5-fold. Interestingly, various members of the Annexin A (ANXA) family were also up-regulated in brain capillaries that were isolated from EAE mice. In a pathway associated with cell infiltration and tight junction disruption, a series of molecules that are involved in ANXA2 signaling (ANXA2, PTP1B, Ahnak, S100A11, CD44, Kindlin2, Integrin α5, Fibronectin, Fibrinogen) were up-regulated. ANXA2 is selectively and abundantly expressed in endothelial cells in the brain. The daily administration of an ANXA2 inhibitor (LCKLSL peptide) significantly suppressed the development of EAE in mice. In summary, the activation of ANXA2 signaling at the BBB appear to play an important role in the pathogenesis of EAE.

A human blood-arachnoid barrier atlas of transporters, receptors, enzymes, and tight junction and marker proteins: Comparison with dog and pig in absolute abundance.

The purpose of this study was to elucidate the absolute abundance of transporters, enzymes, receptors, and tight junction and marker proteins at human blood-arachnoid barrier (BAB) and compare with those of dogs and pigs. Protein expression levels in plasma membrane fractions of brain leptomeninges were determined by quantitative targeted absolute proteomics. To realistically compare the absolute abundance of target molecules at the BAB among humans, dogs, and pigs, the unit was converted from fmol/µg-protein to pmol/cm2 -leptomeninges. Of a total of 70 proteins, 52 were detected. OAT1, OAT3, GLUT1, 4F2hc, EAAT1, EAAT2, MCT8, SMVT, CTL2, GFAP, Claudin-5, Na+ /K+ -ATPase, COMT, GSTP1, and CES1 were abundantly expressed at the human BAB (>1 pmol/cm2 ). The protein expression levels were within a 3-fold difference for 16 out of 33 proteins between humans and dogs and for 13 out of 28 proteins between humans and pigs. Both human-dog and human-pig differences in protein expression levels were within 3-fold for OAT1, OAT3, 4F2hc, xCT, OCT2, MDR1, BCRP, PEPT2, SYP, and MCT1. In contrast, OCT3, MCT4, and OATP1A2 were detected in humans but not in dogs or pigs. MRP3 was detected in dogs and pigs but not in humans. The absolute level of GLUT1 in humans was nearly the same as that in dogs but was 6.14-fold greater in pigs. No significant differences in the levels were observed between male and female dogs for nearly all molecules. These results should be helpful in understanding the physiological roles of BAB and cerebrospinal fluid pharmacokinetics in humans and their differences from dogs and pigs.

Pharmacoproteomics of Brain Barrier Transporters and Substrate Design for the Brain Targeted Drug Delivery.

One of the major reasons why central nervous system (CNS)-drug development has been challenging in the past, is the barriers that prevent substances entering from the blood circulation into the brain. These barriers include the blood-brain barrier (BBB), blood-spinal cord barrier (BSCB), blood-cerebrospinal fluid barrier (BCSFB), and blood-arachnoid barrier (BAB), and they differ from each other in their transporter protein expression and function as well as among the species. The quantitative expression profiles of the transporters in the CNS-barriers have been recently revealed, and in this review, it is described how they affect the pharmacokinetics of compounds and how these expression differences can be taken into account in the prediction of brain drug disposition in humans, an approach called pharmacoproteomics. In recent years, also structural biology and computational resources have progressed remarkably, enabling a detailed understanding of the dynamic processes of transporters. Molecular dynamics simulations (MDS) are currently used commonly to reveal the conformational changes of the transporters and to find the interactions between the substrates and the protein during the binding, translocation in the transporter cavity, and release of the substrate on the other side of the membrane. The computational advancements have also aided in the rational design of transporter-utilizing compounds, including prodrugs that can be actively transported without losing potency towards the pharmacological target. In this review, the state-of-art of these approaches will be also discussed to give insights into the transporter-mediated drug delivery to the CNS.

Regional Differences in the Absolute Abundance of Transporters, Receptors and Tight Junction Molecules at the Blood-Arachnoid Barrier and Blood-Spinal Cord Barrier among Cervical, Thoracic and Lumbar Spines in Dogs.

PURPOSE: The purpose of the present study was to quantitatively determine the expression of transporters, receptors and tight junction molecules at the blood-arachnoid barrier (BAB) and blood-spinal cord barrier (BSCB) in cervical, thoracic and lumbar spines from dogs. METHODS: The expression levels of 31 transporters, 3 receptors, 1 tight junction protein, and 3 marker proteins in leptomeninges and capillaries isolated from spines (3 male and 2 female dogs) were determined by quantitative Targeted Absolute Proteomics (qTAP). The units were converted from fmol/µg protein to pmol/cm (absolute abundance at the BAB and the BSCB in a 1 cm section of spine). RESULTS: The expression of MDR1 and BCRP were greater at the BSCB compared to the BAB (especially in the cervical cord), and the expressions at the lumbar BSCB were lower than that for the cervical BSCB. Among the organic anionic and cationic drug transporters, OAT1, OAT3, MRP1, OCT2 and MATE1/2 were detected only in the BAB, and not at the BSCB). The expression of these transporters was higher in the order: lumbar > thoracic > cervical BAB. The expressions of GLUT1, 4F2hc, EAAT1, 2, PEPT2, CTL1, and MCT1 at the BSCB of the cervical cord were higher than the corresponding values for the cervical BAB, and these values decreased in going down the spinal cord. CONCLUSION: These results provide a better understanding of the molecular mechanisms underlying the concentration gradients of drugs and endogenous substances in the cerebrospinal fluid and parenchyma of the spinal cord.

Identification and Validation of Combination Plasma Biomarker of Afamin, Fibronectin and Sex Hormone-Binding Globulin to Predict Pre-eclampsia.

The purpose of the present study was to identify a plasma protein biomarker able to predict pre-eclampsia (PE). Comprehensive quantitative proteomics using mass spectrometry with sequential window acquisition of all theoretical fragment ion spectra (SWATH-MS) was applied to plasma samples of 7 PE and 14 healthy pregnant women (for PE subjects, plasma samples were taken before onset of PE), and 11 proteins were selected as candidates potentially able to differentiate the two groups. Plasmas collected at gestational weeks 14-24 from 36 PE and 120 healthy pregnant women (for PE subjects, plasma samples were taken before onset of PE) were used to conduct selected reaction monitoring quantification analysis, optimize protein combinations and conduct internal validation, which consisted of 30 iterations of 10-fold cross-validation using multivariate logistic regression and receiver operating characteristic (ROC) analysis. The combination of afamin, fibronectin, and sex-hormone-binding globulin was selected as the best candidate. The 3-protein combination predictive model (predictive equation and cut-off value) generated using the internal validation subjects was successfully validated in another group of validation subjects (36 PE and 54 healthy (for PE subjects, plasma samples were taken before onset of PE)) and showed good predictive performance, with the area under the curve (AUC) 0.835 and odds ratio 13.43. In conclusion, we newly identified a 3-protein combination biomarker and established a predictive equation and cut-off value that can predict the onset of PE based on analysis of plasma samples collected during gestational weeks 14-24.

Gelsolin inhibits malignant phenotype of glioblastoma and is regulated by miR-654-5p and miR-450b-5p.

We have previously shown that gelsolin (GSN) levels are significantly lower in the blood of patients with glioblastoma (GBM) than in healthy controls. Here, we analyzed the function of GSN in GBM and examined its clinical significance. Furthermore, microRNAs involved in GSN expression were also identified. The expression of GSN was determined using western blot analysis and found to be significantly lower in GBM samples than normal ones. Gelsolin was mainly localized in normal astrocytes, shown using immunohistochemistry and immunofluorescence. Higher expression of GSN was correlated with more prolonged progression-free survival and overall survival. Gelsolin knockdown using siRNA and shRNA markedly accelerated cell proliferation and invasion in GBM in vitro and in vivo. The inactive form of glycogen synthase kinase-3ß was dephosphorylated by GSN knockdown. In GBM tissues, the expression of GSN and microRNA (miR)-654-5p and miR-450b-5p showed an inverse correlation. The miR-654-5p and miR-450b-5p inhibitors enhanced GSN expression, resulting in reduced proliferation and invasion. In conclusion, GSN, which inhibits cell proliferation and invasion, is suppressed by miR-654-5p and miR-450b-5p in GBM, suggesting that these miRNAs can be targets for treating GBM.

Abundant Expression of OCT2, MATE1, OAT1, OAT3, PEPT2, BCRP, MDR1, and xCT Transporters in Blood-Arachnoid Barrier of Pig and Polarized Localizations at CSF- and Blood-Facing Plasma Membranes.

The physiologic and pharmacologic roles of the blood-arachnoid barrier (BAB) remain unclear. Therefore, the purpose of the present study was to comprehensively evaluate and compare the absolute protein expression levels of transporters in the leptomeninges and plexus per cerebrum, and to determine the localizations of transporters at the cerebrospinal fluid (CSF)-facing and blood (dura)-facing plasma membranes of the BAB in pig. Using multidrug resistance protein 1 (MDR1) and organic anion transporter (OAT) 1 as blood (dura)-facing and CSF-facing plasma membrane marker proteins, respectively, we established that breast cancer resistance protein (BCRP), multidrug resistance-associated protein (MRP) 4, organic anion-transporting polypeptide (OATP) 2B1, multidrug and toxin extrusion protein 1 (MATE1), and glucose transporter 1 (GLUT1) are localized at the blood-facing plasma membrane, and OAT3, peptide transporter (PEPT) 2, MRP3, organic cation transporter (OCT) 2, xCT, monocarboxylate transporter (MCT) 1, MCT4, and MCT8 are localized at the CSF-facing plasma membrane of the BAB. The absolute protein expression levels of OAT1, OAT3, MDR1, BCRP, PEPT2, xCT, MATE1, OCT2, and 4f2hc in the whole BAB surrounding the entire cerebrum were much larger than those in the total of the choroid plexuses forming the blood-cerebrospinal fluid barrier (BCSFB). Although MRP4, OATP2B1, MCT8, GLUT1, and MCT1 were also statistically significantly more abundant in the BAB than in the choroid plexuses per porcine cerebrum, these transporters were nevertheless almost equally distributed between the two barriers. In contrast, OATP1A2, MRP1, OATP3A1, and OCTN2 were specifically expressed in the choroid plexus. These results should be helpful in understanding the relative overall importance of transport at the BAB compared with that at the BCSFB, as well as the rank order of transport capacities among different transporters at the BAB, and the directions of transport mediated by individual transporters. SIGNIFICANCE STATEMENT: We found that BCRP, MRP4, OATP2B1, MATE1, and GLUT1 localize at the blood-facing plasma membrane of the blood-arachnoid barrier (BAB), while OAT3, PEPT2, MRP3, OCT2, xCT, MCT1, MCT4, and MCT8 localize at the CSF-facing plasma membrane. 4F2hc is expressed in both membranes. For OAT1, OAT3, MDR1, BCRP, PEPT2, xCT, MATE1, OCT2, and 4f2hc, the absolute protein expression levels in the whole BAB surrounding the entire cerebrum are much greater than the total amounts in the choroid plexuses.

Comparison of Absolute Protein Abundances of Transporters and Receptors among Blood-Brain Barriers at Different Cerebral Regions and the Blood-Spinal Cord Barrier in Humans and Rats.

This work was designed to clarify the absolute abundances of transporters and receptors at different cerebral regions of the blood-brain barriers (BBB) and blood-spinal cord barrier (BSCB) in humans and rats, using physiologically relevant units (pmol/g tissue and fmol/cm2); 39 and 29 proteins including tight-junction proteins and markers were quantified in human and rat capillary samples, respectively. Protein expression levels of almost all proteins were identical within a 2-fold range between BBB and BSCB in rats, while many proteins showed >2-fold smaller expression levels in BSCB than BBB in humans. Protein expression levels of transporters and receptors in humans were remarkably smaller than those in rats in both BBB and BSCB in units of pmol/g tissue and fmol/cm2. Protein expression levels (fmol/cm2) of MDR1 and BCRP at the BBB in humans were 9.88-fold and 5.23-fold smaller than those in rats, respectively. GLUT1 expression (pmol/g tissue) at cortical BBB in a human was 2.49- and 3.76-fold greater than that at white matter BBB and BSCB, respectively. INSR and LRP1 proteins were detected at cortical BBB, but not at white matter BBB or BSCB in humans. These findings throw light on regional differences and species differences in pharmacokinetics and physiological functions in the central nervous system.

Determination of Intrinsic Creatine Transporter (Slc6a8) Activity and Creatine Transport Function of Leukocytes in Rats.

Creatine transporter (CRT) deficiency (CRT-D) results in a significant reduction of brain creatine levels, which causes various neurological symptoms in early childhood, and diagnosis of the severity of CRT-D based on the residual CRT transport activity in liquid biopsy samples would be beneficial for early intervention. The apparent reduction in creatine transport activity in CRT-D is thought to be due to reduced intrinsic CRT-mediated creatine transport per CRT protein and/or reduced absolute CRT protein expression on the plasma membranes. The purpose of this study was thus to determine the normal level of intrinsic CRT-mediated creatine transport activity based on absolute CRT protein quantification using rat CRT-overexpressing HEK293 cells (CRT/HEK293 cells), and to clarify creatine transport in erythrocyte- and leukocyte-enriched fractions isolated from the circulating blood of rats. The intrinsic creatine transport rate was calculated to be 0.237 µL/(min·fmol CRT) based on the initial uptake rate and the absolute CRT protein level in CRT/HEK293 cells. Taking into account Avogadro's constant, the creatine transport activity per CRT protein is estimated to be 1190 creatine/(min·CRT molecule) in the presence of [14C]creatine at an extracellular concentration of 5 µM. Isolated leukocyte-enriched fraction exhibited mRNA expression of CRT and partially Na+-dependent [14C]creatine transport, whereas erythrocytes showed neither. These characteristics suggest that the leukocytes contain the CRT-mediated creatine uptake system, and are available for evaluation of residual CRT transport activity in CRT-D patients.

Amyloid beta25-35 impairs docosahexaenoic acid efflux by down-regulating fatty acid transport protein 1 (FATP1/SLC27A1) protein expression in human brain capillary endothelial cells.

Decreased levels of docosahexaenoic acid (DHA), an endogenous neuroprotective compound, in the brain are associated with the development of Alzheimer's disease (AD). We previously showed that DHA is a substrate of fatty acid transport protein 1 (FATP1/SLC27A1), and FATP1 is localized at the abluminal membrane of brain capillary endothelial cells. We hypothesized that amyloid ß (Aß) decreases FATP1-mediated cellular efflux (i.e. supply to the brain) of DHA at the blood-brain barrier (BBB). Here, we tested this hypothesis using a human cerebral microvascular endothelial cell line, human cerebral microvessel endothelial cells (hCMEC/D3), as a BBB model. The efflux of DHA-d5 by hCMEC/D3 cells increased time-dependently up to 3 min. Knock-down of FATP1 with specific siRNA indicated that FATP1-mediated efflux accounts for 47.0% of this DHA-d5 efflux. In hCMEC/D3 cells treated with Aß25-35 (10 µM/24 h), which we employed as an in vitro model of the BBB in AD, FATP1 protein expression in the plasma membrane was decreased by 96.0%, which was greater than the decrease in the whole-cell lysate, and the DHA-d5 efflux was decreased by 68.3%. Of this 68.3% decrease, 45.1% (47.0 × 0.96) is accounted for by the decrease in FATP1-mediated efflux and the remaining 23.2% is presumably mediated by other mechanism(s). Thus, we have established for the first time that FATP1 is a major contributor to DHA efflux from human brain capillary endothelial cells, and its efflux activity at the abluminal membrane of the cells is blocked by Aß. This may explain the decreased DHA level in the brain of AD patients. OPEN SCIENCE BADGES: This article has received a badge for *Open Materials* because it provided all relevant information to reproduce the study in the manuscript. The complete Open Science Disclosure form for this article can be found at the end of the article. More information about the Open Practices badges can be found at https://cos.io/our-services/open-science-badges/.

Organic Anion-Transporting Polypeptide 1a4 (Oatp1a4/Slco1a4) at the Blood-Arachnoid Barrier is the Major Pathway of Sulforhodamine-101 Clearance from Cerebrospinal Fluid of Rats.

The blood-arachnoid barrier (BAB), which is formed by arachnoid epithelial cells linked by tight junctions, has generally been considered impermeable to water-soluble substances. However, we recently demonstrated that organic anion transporters 1 and 3 (Oat1 and Oat3) play roles in drug clearance at the BAB. Here, we examined whether an organic anion-transporting polypeptide (Oatp) also plays a role, using the fluorescent organic anion sulforhodamine-101 (SR-101) as a model substrate. SR-101 was injected into the cisterna magna of rats in order to minimize the contribution of choroid plexus transport. The in vivo cerebrospinal fluid (CSF) elimination clearance of SR-101 after intracisternal administration was ninefold greater than that of fluorescein-labeled inulin, a bulk flow marker. In the case of pre-administration of taurocholate, a broad-spectrum inhibitor of Oatps, or digoxin, a strong substrate/inhibitor for Oatp1a4 but not for Oatp1a1, Oat1, and Oat3, the CSF elimination of SR-101 was significantly reduced, becoming similar to that of inulin, and thus indicating complete inhibition of SR-101 clearance from the CSF. The distribution of SR-101 fluorescence was restricted to the arachnoid mater in the absence of inhibitor, whereas the fluorescence was increased in the parenchyma of the spinal cord after co-injection of taurocholate or digoxin. Immunostaining confirmed the localization of Oatp1a4 in the arachnoid mater. These results indicate that Oatp1a4 at the BAB acts as an avid clearance pathway of SR-101 in the CSF to the blood. Thus, Oatp1a4 appears to play a major role in CSF detoxification by limiting the distribution of organic anions to the brain and spinal cord.

Identification of Blood-Brain Barrier-Permeable Proteins Derived from a Peripheral Organ: In Vivo and in Vitro Evidence of Blood-to-Brain Transport of Creatine Kinase.

Certain proteins, such as inflammatory cytokines, that are released from injured or diseased organs are transported from the circulating blood through the blood-brain barrier (BBB) into the brain and contribute to the pathogenesis of related central nervous system dysfunctions. However, little is known about the protein transport mechanisms involved in the central nervous system dysfunctions. The aims of the present study were to identify BBB-permeable protein(s) derived from liver and to clarify their transport characteristics at the BBB. After administration of biotin-labeled liver cytosolic protein fraction to mice in vivo, we identified 9 biotin-labeled proteins in the brain. Among them, we focused here on creatine kinase (CK). In vitro uptake studies with human brain microvessel endothelial cells (hCMEC/D3 cells) showed preferential uptake of muscle-type CK (CK-MM) compared with brain-type CK (CK-BB) at the BBB. Integration plot analysis revealed that CK-MM readily penetrated into brain parenchyma from the circulating blood across the BBB. The uptake of CK-MM by hCMEC/D3 cells was decreased at 4 °C and in the presence of clathrin- and caveolin-dependent endocytosis inhibitors. These results indicate that entry of CK into the brain is mediated by a transport system(s) at the BBB.

Cluster of Differentiation 46 Is the Major Receptor in Human Blood-Brain Barrier Endothelial Cells for Uptake of Exosomes Derived from Brain-Metastatic Melanoma Cells (SK-Mel-28).

Brain metastasis is a frequent complication of cancer and may be mediated, at least in part, by the internalization of cancer-cell-derived exosomes into brain capillary endothelial cells. Clarifying the mechanism(s) of this internalization is of interest because it could help us to develop ways to block brain metastasis, as well as affording a potential new route for drug delivery into the brain. Therefore, the purpose of the present study was to address this issue by identifying the receptors involved in the internalization of exosomes derived from a brain-metastatic cancer cell line (SK-Mel-28) into human blood-brain barrier endothelial cells (hCMEC/D3 cells). The combination of sulfo-SBED-based cross-linking and comprehensive proteomics yielded 20 proteins as exosome receptor candidates in hCMEC/D3 cells. The uptake of PKH67-labeled exosomes by hCMEC/D3 cells measured at 37 °C was significantly reduced by 95.6% at 4 °C and by 15.3% in the presence of 1 mM RGD peptide, an integrin ligand. Therefore, we focused on the identified RGD receptors, integrin α5 and integrin αV, and CD46, which is reported to act as an adenovirus receptor, together with integrin αV. A mixture of neutralizing antibodies against integrin α5 and integrin αV significantly decreased the exosome uptake by 11.8%, while application of CD46 siRNA reduced it by 39.0%. Immunohistochemical analysis confirmed the presence of CD46 in human brain capillary endothelial cells. These results suggest that CD46 is a major receptor for the uptake of SK-Mel-28-derived exosomes by human blood-brain barrier endothelial cells (hCMEC/D3 cells).

Selective Protein Expression Changes of Leukocyte-Migration-Associated Cluster of Differentiation Antigens at the Blood-Brain Barrier in a Lipopolysaccharide-Induced Systemic Inflammation Mouse Model without Alteration of Transporters, Receptors or Tight Junction-Related Protein.

Leukocyte migration across the blood-brain barrier (BBB) is an important step in the progression of brain dysfunction in systemic inflammation. The purpose of this study was to identify the key regulatory molecule(s) at the BBB among the cluster of differentiation (CD) antigens involved in leucocyte migration in lipopolysaccharide (LPS)-induced systemic inflammation based on their absolute protein expressions. Here, we identified the absolute expression levels of 17 CD antigens in isolated brain capillaries (Bcap) of LPS-administered mice. Among them, the expression levels of CD54 and CD106 were dramatically increased in LPS-administered mice compared to the control by 6.21- and 3.67-fold, respectively. In peripheral blood mononuclear cells, the expression levels of CD11a/CD18, the counter-receptor for CD54, were similar to those of CD54 in Bcap of LPS-administered mice. On the other hand, the expression level of CD49d, part of CD29/CD49d complex, which is the counter-receptor for CD106, was under the limit of quantification. It is thus likely that CD54 at the BBB is predominantly involved in promoting leukocyte migration across the BBB in systemic inflammation. The expression levels of CD9, CD49c and CD97, which are thought to be involved in cell-to-cell interaction, were decreased by 40-60% in Bcap of LPS-administered mice. In contrast, the expression levels of 9 transporters, 2 receptors, and 1 tight junction-related protein in Bcap of LPS-administered mice were essentially unchanged compared to the control. These results suggest that enhancement of leucocyte migration in systemic inflammation involves dynamic changes of CD antigens without alterations of other major functional molecules.

Gene therapy for Glut1-deficient mouse using an adeno-associated virus vector with the human intrinsic GLUT1 promoter.

BACKGROUND: We generated an adeno-associated virus (AAV) vector in which the human SLC2A1 gene, encoding glucose transporter type 1 (GLUT1), was expressed under the human endogenous GLUT1 promoter (AAV-GLUT1). We examined whether AAV-GLUT1 administration could lead to functional improvement in GLUT1-deficient mice. METHODS: We extrapolated human endogenous GLUT1 promoter sequences from rat minimal Glut1 promoter sequences. We generated a tyrosine-mutant AAV9/3 vector in which human SLC2A1-myc-DDK was expressed under the human GLUT1 promoter (AAV-GLUT1). AAV-GLUT1 was administered to GLUT1-deficient mice (GLUT1+/- mice) via intracerebroventricular injection (1.85 × 1010 vg/mouse or 6.5 × 1010 vg/mouse). We analyzed exogenous GLUT1 mRNA and protein expression in the brain and other major organs. We also examined improvements of cerebral microvasculature, motor function using rota-rod and footprint tests, as well as blood and cerebrospinal fluid (CSF) glucose levels. Additionally, we confirmed exogenous GLUT1 protein distribution in the brain and other organs after intracardiac injection (7.8 × 1011 vg/mouse). RESULTS: Exogenous GLUT1 protein was strongly expressed in the cerebral cortex, hippocampus and thalamus. It was mainly expressed in endothelial cells, and partially expressed in neural cells and oligodendrocytes. Motor function and CSF glucose levels were significantly improved following intracerebroventricular injection. Exogenous GLUT1 expression was not detected in other organs after intracerebroventricular injection of AAV-GLUT1, whereas it was detected in the liver and muscle tissue after intracardiac injection. CONCLUSIONS: Exogenous GLUT1 expression after AAV-GLUT1 injection approximated that of physiological human GLUT1 expression. Local central nervous system administration of AAV-GLUT1 improved CSF glucose levels and motor function of GLUT1-deficient mice and minimized off-target effects.

Liver Zonation Index of Drug Transporter and Metabolizing Enzyme Protein Expressions in Mouse Liver Acinus.

The purpose of the present study was to clarify the molecular basis of zonated drug distributions in mouse liver based on the protein expression levels of transporters and metabolizing enzymes in periportal (PP) and pericentral (PC) vein regions of mouse hepatic lobules. The distributions of sulforhodamine 101 (SR-101), a substrate of organic anion transporting polypeptides (Oatps), and ribavirin, a substrate of equilibrative nucleoside transporter 1 (Ent1), were elucidated in frozen liver sections of mice, to which each compound had been intravenously administered. Regions strongly positive for SR-101 (SR-101+) and regions weakly positive or negative for SR-101 (SR-101-) were separated by laser microdissection. The zonated distribution of protein expression was quantified in terms of the liver zonation index. Quantitative targeted absolute proteomics revealed the selective expression of glutamine synthetase in the SR-101+ region, indicating predominant distribution of SR-101 in hepatocytes of the PC vein region. The protein levels of Oatp1a1, Oatp1b2, organic cation transporter 1 (Oct1), and cytochrome P450 (P450) 2e1 were greater in the PC vein regions, whereas the level of organic anion transporter 2 (Oat2) was greater in the PP vein regions. Mouse Oatp1a1 mediated SR-101 transport. On the other hand, there were no statistically significant differences in expression of Ent1, Na+-taurocholate cotransporting polypeptide, several canalicular transporters, P450 enzymes, and UDP-glucuronosyltransferases between the PP and PC vein regions. This is consistent with the almost uniform distribution of ribavirin in the liver. In conclusion, sinusoidal membrane transporters such as Oatp1a1, Oatp1b2, Oct1, and Oat2 appear to be determinants of the zonated distribution of drugs in the liver.

Evaluation of Organic Anion Transporter 1A2-knock-in Mice as a Model of Human Blood-brain Barrier.

The present study aimed to establish a humanized mouse model with which to explore OATP1A2-mediated transcellular transport of drug substrates across the blood-brain barrier (BBB) and to evaluate the usefulness of the humanized mice in preclinical studies. Sulpiride, amisulpride, sultopride, and triptans were used as probes to discriminate OATP1A2 and Oatp1a4. We generated a mouse line humanized for OATP1A2 by introducing the coding region downstream of the Oatp1a4 promoter using the CRISPR/Cas9 technique. In the mice generated, OATP1A2 mRNA in the brain was increased corresponding to disappearance of Oatp1a4. OATP1A2 was localized on both the luminal and abluminal sides of the BBB. Unfortunately, study in vivo employing sulpiride, sumatriptan, and zolmitriptan as probes did not indicate any difference in their brain-to-plasma ratio between the control and humanized mice. Quantitative targeted absolute proteomic analysis of the BBB fraction from the humanized mice revealed that almost all analyzed transporters and membrane proteins were expressed at similar levels to those in control mice. The quantitative levels of OATP1A2 differed depending on the peptide quantified, which suggests that incomplete translation or posttranslational modification may occur. The blood-to-brain transport of zolmitriptan, determined by brain perfusion in situ, was 1.6-fold higher in the humanized mice than in the controls, whereas that of sulpiride was not significantly changed. To our knowledge, we established a mouse line humanized for a BBB uptake transporter for the first time. Unfortunately, because of limited impact, there is still room for improvement of the model system.