Donepezil, tacrine and alpha-phenyl-n-tert-butyl nitrone (PBN) inhibit choline transport by conditionally immortalized rat brain capillary endothelial cell lines (TR-BBB)

Nutritional metabolism and cerebral bioenergetics in Alzheimer's disease and related dementias

Disturbances in the brain's capacity to meet its energy demand increase the risk of synaptic loss, neurodegeneration, and cognitive decline. Nutritional and metabolic interventions that target metabolic pathways combined with diagnostics to identify deficits in cerebral bioenergetics may therefore offer novel therapeutic potential for Alzheimer's disease (AD) prevention and management. Many diet-derived natural bioactive components can govern cellular energy metabolism but their effects on brain aging are not clear. This review examines how nutritional metabolism can regulate brain bioenergetics and mitigate AD risk. We focus on leading mechanisms of cerebral bioenergetic breakdown in the aging brain at the cellular level, as well as the putative causes and consequences of disturbed bioenergetics, particularly at the blood-brain barrier with implications for nutrient brain delivery and nutritional interventions. Novel therapeutic nutrition approaches including diet patterns are provided, integrating studies of the gut microbiome, neuroimaging, and other biomarkers to guide future personalized nutritional interventions.

Protective Effects of Choline against Inflammatory Cytokines and Characterization of Transport in Motor Neuron-like Cell Lines (NSC-34)

Choline, a component of the neurotransmitter acetylcholine, is essential for nervous system functions, brain development, and gene expression. In our study, we investigated the protective effect and transport characteristics of choline in amyotrophic lateral sclerosis (ALS) model cell lines. We used the wild-type (WT) motor neuron-like hybrid cell line (NSC-34/hSOD1WT) as a control and the mutant-type (MT; NSC-34/hSOD1G93A) as a disease model. The uptake of [3H]choline was time-, pH-, and concentration-dependent. [3H]Choline transport was sodium-dependent, and, upon pretreatment with valinomycin, induced membrane depolarization. Gene knockdown of Slc44a1 revealed that choline-like transporter 1 (CTL1) mediates the transport of choline. In NSC-34 cell lines, the specific choline transporter inhibitor, hemicholinium-3 demonstrated significant inhibition. Donepezil and nifedipine caused dose-dependent inhibition of [3H]choline uptake by the MT cell line with minimal half inhibitory concentration (IC50) values of 0.14 mM and 3.06 mM, respectively. Four-day pretreatment with nerve growth factor (NGF) resulted in an inhibitory effect on [3H]choline uptake. Choline exerted protective and compensatory effects against cytokines mediators. Hence, the choline transport system CLT1 may act as a potential target for the delivery of novel pharmacological drugs, and the combination of drugs with choline can help treat symptoms related to ALS.

Blood-Brain Barrier Solute Carrier Transporters and Motor Neuron Disease

Defective solute carrier (SLC) transporters are responsible for neurotransmitter dysregulation, resulting in neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS). We provided the role and kinetic parameters of transporters such as ASCTs, Taut, LAT1, CAT1, MCTs, OCTNs, CHT, and CTL1, which are mainly responsible for the transport of essential nutrients, acidic, and basic drugs in blood-brain barrier (BBB) and motor neuron disease. The affinity for LAT1 was higher in the BBB than in the ALS model cell line, whereas the capacity was higher in the NSC-34 cell lines than in the BBB. Affinity for MCTs was lower in the BBB than in the NSC-34 cell lines. CHT in BBB showed two affinity sites, whereas no expression was observed in ALS cell lines. CTL1 was the main transporter for choline in ALS cell lines. The half maximal inhibitory concentration (IC50) analysis of [3H]choline uptake indicated that choline is sensitive in TR-BBB cells, whereas amiloride is most sensitive in ALS cell lines. Knowledge of the transport systems in the BBB and motor neurons will help to deliver drugs to the brain and develop the therapeutic strategy for treating CNS and neurological diseases.

Donepezil ameliorates oxygen-glucose deprivation/reoxygenation-induced brain microvascular endothelial cell dysfunction via the SIRT1/FOXO3a/NF-κB pathways

Ischemic stroke is a disease in which brain tissue is damaged by a sudden rupture or blockage of a blood vessel in the brain that prevents blood from flowing to the brain. Extensive literature has demonstrated the neuroprotective effect of donepezil on brain injury, and this paper attempts to further reveal the effect of donepezil on brain microvascular endothelial cells dysfunction. Human brain microvascular endothelial cells (HBMECs) were treated with oxygen-glucose deprivation/reoxygenation (OGD/R) to induced brain microvascular endothelial cell dysfunction. The OGD/R-induced cell were added with different doses of donepezil with or without Sirtuin-1 (SIRT1) inhibitor EX527. Cell viability of HBMECs was examined by cell counting kit (CCK)-8 assay. OGD/R-treated cell migration was assessed by wound healing assay while angiogenesis in HBMECs was examined by tube formation assay and Western blot analysis. Endothelial cell dysfunction was assessed employing fluorescein isothiocyanate-dextran assay and Western blotting. SIRTI/FOXO3a/NF-kB signaling pathway-related protein expressions were detected using Western blotting. After pretreatment with SIRT1 inhibitor EX527, the above experiments were done again. Donepezil increased cell viability of OGD/R-induced HBMECs, promoted cell migration and angiogenesis, decreased cell permeability, and upregulated the expressions of tight junction proteins. In addition, donepezil regulated the expressions of SIRT1/FOXO3a/NF-κB signaling pathways. However, pretreatment with the SIRT1 inhibitor EX527 reversed the protective effect of donepezil on OGD/R-induced HBMECs. In summary, Donepezil ameliorates OGD/R-induced brain microvascular endothelial cell dysfunction via the SIRT1/FOXO3a/NF-κB pathways.

Change in Cationic Amino Acid Transport System and Effect of Lysine Pretreatment on Inflammatory State in Amyotrophic Lateral Sclerosis Cell Model

Amyotrophic lateral sclerosis (ALS) is a lethal neurological disorder characterized by the deterioration of motor neurons. The aim of this study was to investigate alteration of cationic amino acid transporter (CAT-1) activity in the transport of lysine and the pretreatment effect of lysine on pro-inflammatory states in an amyotrophic lateral sclerosis cell line. The mRNA expression of cationic amino acid transporter 1 was lower in NSC-34/hSOD1^G93A (MT) than the control cell line (WT), lysine transport is mediated by CAT-1 in NSC-34 cell lines. The uptake of [³H]L-lysine was Na⁺-independent, voltage-sensitive, and strongly inhibited by inhibitors and substrates of cationic amino acid transporter 1 (system y⁺). The transport process involved two saturable processes in both cell lines. In the MT cell line, at a high-affinity site, the affinity was 9.4-fold higher and capacity 24-fold lower than that in the WT; at a low-affinity site, the capacity was 2.3-fold lower than that in the WT cell line. Donepezil and verapamil competitively inhibited [³H]L-lysine uptake in the NSC-34 cell lines. Pretreatment with pro-inflammatory cytokines decreased the uptake of [³H]L-lysine and mRNA expression levels in both cell lines; however, the addition of L-lysine restored the transport activity in the MT cell lines. L-Lysine exhibited neuroprotective effects against pro-inflammatory states in the ALS disease model cell lines. In conclusion, studying the alteration in the expression of transporters and characteristics of lysine transport in ALS can lead to the development of new therapies for neurodegenerative diseases.

Pretreatment Effect of Inflammatory Stimuli and Characteristics of Tryptophan Transport on Brain Capillary Endothelial (TR-BBB) and Motor Neuron Like (NSC-34) Cell Lines

Tryptophan plays a key role in several neurological and psychiatric disorders. In this study, we investigated the transport mechanisms of tryptophan in brain capillary endothelial (TR-BBB) cell lines and motor neuron-like (NSC-34) cell lines. The uptake of [³H]l-tryptophan was stereospecific, and concentration- and sodium-dependent in TR-BBB cell lines. Transporter inhibitors and several neuroprotective drugs inhibited [³H]l-tryptophan uptake by TR-BBB cell lines. Gabapentin and baclofen exerted a competitive inhibitory effect on [³H]l-tryptophan uptake. Additionally, l-tryptophan uptake was time- and concentration-dependent in both NSC-34 wild type (WT) and mutant type (MT) cell lines, with a lower transporter affinity and higher capacity in MT than in WT cell lines. Gene knockdown of LAT1 (l-type amino acid transporter 1) and CAT1 (cationic amino acid transporter 1) demonstrated that LAT1 is primarily involved in the transport of [³H]l-tryptophan in both TR-BBB and NSC-34 cell lines. In addition, tryptophan uptake was increased by TR-BBB cell lines but decreased by NSC-34 cell lines after pro-inflammatory cytokine pre-treatment. However, treatment with neuroprotective drugs ameliorated tryptophan uptake by NSC-34 cell lines after inflammatory cytokines pretreatment. The tryptophan transport system may provide a therapeutic target for treating or preventing neurodegenerative diseases.

Pharmacogenetic considerations when prescribing cholinesterase inhibitors for the treatment of Alzheimer's disease

INTRODUCTION

Cholinergic dysfunction, demonstrated in the late 1970s and early 1980s, led to the introduction of acetylcholinesterase inhibitors (AChEIs) in 1993 (Tacrine) to enhance cholinergic neurotransmission as the first line of treatment against Alzheimer's disease (AD). The new generation of AChEIs, represented by Donepezil (1996), Galantamine (2001) and Rivastigmine (2002), is the only treatment for AD to date, together with Memantine (2003). AChEIs are not devoid of side-effects and their cost-effectiveness is limited. An option to optimize the correct use of AChEIs is the implementation of pharmacogenetics (PGx) in the clinical practice.

AREAS COVERED

(i) The cholinergic system in AD, (ii) principles of AD PGx, (iii) PGx of Donepezil, Galantamine, Rivastigmine, Huperzine and other treatments, and (iv) practical recommendations.

EXPERT OPINION

The most relevant genes influencing AChEI efficacy and safety are APOE and CYPs. APOE-4 carriers are the worst responders to AChEIs. With the exception of Rivastigmine (UGT2B7, BCHE-K), the other AChEIs are primarily metabolized via CYP2D6, CYP3A4, and UGT enzymes, with involvement of ABC transporters and cholinergic genes (CHAT, ACHE, BCHE, SLC5A7, SLC18A3, CHRNA7) in most ethnic groups. Defective variants may affect the clinical response to AChEIs. PGx geno-phenotyping is highly recommended prior to treatment.

Involvement of a Novel Organic Cation Transporter in Paeonol Transport Across the Blood-Brain Barrier

Paeonol has neuroprotective function, which could be useful for improving central nervous system disorder. The purpose of this study was to characterize the functional mechanism involved in brain transport of paeonol through blood-brain barrier (BBB). Brain transport of paeonol was characterized by internal carotid artery perfusion (ICAP), carotid artery single injection technique (brain uptake index, BUI) and intravenous (IV) injection technique in vivo. The transport mechanism of paeonol was examined using conditionally immortalized rat brain capillary endothelial cell line (TR-BBB) as an in vitro model of BBB. Brain volume of distribution (V_D) of [³H]paeonol in rat brain was about 6-fold higher than that of [¹⁴C]sucrose, the vascular space marker of BBB. The uptake of [3H]paeonol was concentration-dependent. Brain volume of distribution of paeonol and BUI as in vivo and inhibition of analog as in vitro studies presented significant reduction effect in the presence of unlabeled lipophilic compounds such as paeonol, imperatorin, diphenhydramine, pyrilamine, tramadol and ALC during the uptake of [³H]paeonol. In addition, the uptake significantly decreased and increased at the acidic and alkaline pH in both extracellular and intracellular study, respectively. In the presence of metabolic inhibitor, the uptake reduced significantly but not affected by sodium free or membrane potential disruption. Similarly, paeonol uptake was not affected on OCTN2 or rPMAT siRNA transfection BBB cells. Interestingly. Paeonol is actively transported from the blood to brain across the BBB by a carrier mediated transporter system.

Blood-to-Retina Transport of Imperatorin Involves the Carrier-Mediated Transporter System at the Inner Blood-Retinal Barrier

This study investigated the mechanism of transporting imperatorin across the inner blood-retinal barrier (iBRB). The carotid artery single injection method was used to calculate the retinal uptake index (RUI) of [³H]imperatorin in vivo, whereas the retinal capillary endothelial cell lines were used for the in vitro uptake and mRNA expression assays. RUI value of [³H]imperatorin was greater than that of the reference compound ([¹⁴C]n-butanol). [³H]Imperatorin significantly reduced the RUI in the presence of neuroprotective organic cationic drugs at 10 mM. However, tetraethylammonium and p-aminohippuric acid showed no significant effects. [³H]Imperatorin uptake by TR-iBRB2 cells was time-, pH-, energy-, and concentration-dependent with a K_m value of 679 ± 130 μM. In addition, the uptake study showed insensitivity to sodium and membrane potential. Various organic cations including pyrilamine, nicotine, and clonidine significantly reduced the uptake of [³H]imperatorin, whereas organic anions and monocarboxylic acids did not. Furthermore, the mRNA expression level dropped markedly with rOCTN1, rOCTN2, rPMAT, and rMATE1 small interfering RNAs in the transfection study. Moreover, [³H]imperatorin uptake remained neutral with small interfering RNA transfections. Our results indicate that imperatorin transport across the iBRB involves carrier-mediated transporter system.

The "Frail" Brain Blood Barrier in Neurodegenerative Diseases: Role of Early Disruption of Endothelial Cell-to-Cell Connections

The main neurovascular unit of the Blood Brain Barrier (BBB) consists of a cellular component, which includes endothelial cells, astrocytes, pericytes, microglia, neurons, and oligodendrocytes as well as a non-cellular component resulting from the extracellular matrix. The endothelial cells are the major vital components of the BBB able to preserve the brain homeostasis. These cells are situated along the demarcation line between the bloodstream and the brain. Therefore, an alteration or the progressive disruption of the endothelial layer may clearly impair the brain homeostasis. The proper functioning of the brain endothelial cells is generally ensured by two elements: (1) the presence of junction proteins and (2) the preservation of a specific polarity involving an apical-luminal and a basolateral-abluminal membrane. This review intends to identify the molecular mechanisms underlying BBB function and their changes occurring in early stages of neurodegenerative processes in order to develop novel therapeutic strategies aimed to counteract neurodegenerative disorders.

Comparison of a Rat Primary Cell-Based Blood-Brain Barrier Model With Epithelial and Brain Endothelial Cell Lines: Gene Expression and Drug Transport

Cell culture-based blood-brain barrier (BBB) models are useful tools for screening of CNS drug candidates. Cell sources for BBB models include primary brain endothelial cells or immortalized brain endothelial cell lines. Despite their well-known differences, epithelial cell lines are also used as surrogate models for testing neuropharmaceuticals. The aim of the present study was to compare the expression of selected BBB related genes including tight junction proteins, solute carriers (SLC), ABC transporters, metabolic enzymes and to describe the paracellular properties of nine different culture models. To establish a primary BBB model rat brain capillary endothelial cells were co-cultured with rat pericytes and astrocytes (EPA). As other BBB and surrogate models four brain endothelial cells lines, rat GP8 and RBE4 cells, and human hCMEC/D3 cells with or without lithium treatment (D3 and D3L), and four epithelial cell lines, native human intestinal Caco-2 and high P-glycoprotein expressing vinblastine-selected VB-Caco-2 cells, native MDCK and MDR1 transfected MDCK canine kidney cells were used. To test transporter functionality, the permeability of 12 molecules, glucopyranose, valproate, baclofen, gabapentin, probenecid, salicylate, rosuvastatin, pravastatin, atorvastatin, tacrine, donepezil, was also measured in the EPA and epithelial models. Among the junctional protein genes, the expression level of occludin was high in all models except the GP8 and RBE4 cells, and each model expressed a unique claudin pattern. Major BBB efflux (P-glycoprotein or ABCB1) and influx transporters (GLUT-1, LAT-1) were present in all models at mRNA levels. The transcript of BCRP (ABCG2) was not expressed in MDCK, GP8 and RBE4 cells. The absence of gene expression of important BBB efflux and influx transporters BCRP, MRP6, -9, MCT6, -8, PHT2, OATPs in one or both types of epithelial models suggests that Caco-2 or MDCK models are not suitable to test drug candidates which are substrates of these transporters. Brain endothelial cell lines GP8, RBE4, D3 and D3L did not form a restrictive paracellular barrier necessary for screening small molecular weight pharmacons. Therefore, among the tested culture models, the primary cell-based EPA model is suitable for the functional analysis of the BBB.

Imperatorin is Transported through Blood-Brain Barrier by Carrier-Mediated Transporters

Imperatorin, a major bioactive furanocoumarin with multifunctions, can be used for treating neurodegenerative diseases. In this study, we investigated the characteristics of imperatorin transport in the brain. Experiments of the present study were designed to study imperatorin transport across the blood-brain barrier both in vivo and in vitro. In vivo study was performed in rats using single intravenous injection and in situ carotid artery perfusion technique. Conditionally immortalized rat brain capillary endothelial cells were as an in vitro model of blood-brain barrier to examine the transport mechanism of imperatorin. Brain distribution volume of imperatorin was about 6 fold greater than that of sucrose, suggesting that the transport of imperatorin was through the blood-brain barrier in physiological state. Both in vivo and in vitro imperatorin transport studies demonstrated that imperatorin could be transported in a concentration-dependent manner with high affinity. Imperatorin uptake was dependent on proton gradient in an opposite direction. It was significantly reduced by pretreatment with sodium azide. However, its uptake was not inhibited by replacing extracellular sodium with potassium or N-methylglucamine. The uptake of imperatorin was inhibited by various cationic compounds, but not inhibited by TEA, choline and organic anion substances. Transfection of plasma membrane monoamine transporter, organic cation transporter 2 and organic cation/carnitine transporter 2/1 siRNA failed to alter imperatorin transport in brain capillary endothelial cells. Especially, tramadol, clonidine and pyrilamine inhibited the uptake of [³H]imperatorin competitively. Therefore, imperatorin is actively transported from blood to brain across the blood-brain barrier by passive and carrier-mediated transporter.

Characteristics of L-citrulline transport through blood-brain barrier in the brain capillary endothelial cell line (TR-BBB cells)

Background

_L-Citrulline is a neutral amino acid and a major precursor of _L-arginine in the nitric oxide (NO) cycle. Recently it has been reported that _L-citrulline prevents neuronal cell death and protects cerebrovascular injury, therefore, _L-citrulline may have a neuroprotective effect to improve cerebrovascular dysfunction. Therefore, we aimed to clarify the brain transport mechanism of _L-citrulline through blood-brain barrier (BBB) using the conditionally immortalized rat brain capillary endothelial cell line (TR-BBB cells), as an in vitro model of the BBB.

Methods

The uptake study of [¹⁴C] L-citrulline, quantitative real-time polymerase chain reaction (PCR) analysis, and rLAT1, system b^0,+, and CAT1 small interfering RNA study were performed in TR-BBB cells.

Results

The uptake of [¹⁴C] _L-citrulline was a time-dependent, but ion-independent manner in TR-BBB cells. The transport process involved two saturable components with a Michaelis–Menten constant of 30.9 ± 1.0 μM (Km₁) and 1.69 ± 0.43 mM (Km₂). The uptake of [¹⁴C] _L-citrulline in TR-BBB cells was significantly inhibited by neutral and cationic amino acids, but not by anionic amino acids. In addition, [¹⁴C]_L-citrulline uptake in the cells was markedly inhibited by 2-aminobicyclo-(2,2,1)-heptane-2-carboxylic acid (BCH), which is the inhibitor of the large neutral amino acid transporter 1 (LAT1), B⁰, B^0,+ and harmaline, the inhibitor of system b^0,+. Gabapentin and _L-dopa as the substrates of LAT1 competitively inhibited the uptake of [¹⁴C] _L-citrulline. IC₅₀ values for _L-dopa, gabapentin, _L-phenylalanine and _L-arginine were 501 μM, 223 μM, 68.9 μM and 33.4 mM, respectively. The expression of mRNA for LAT1 was predominantly increased 187-fold in comparison with that of system b^0,+ in TR-BBB cells. In the studies of LAT1, system b^0,+ and CAT1 knockdown via siRNA transfection into TR-BBB cells, the transcript level of LAT1 and [¹⁴C] _L-citrulline uptake by LAT1 siRNA were significantly reduced compared with those by control siRNA in TR-BBB cells.

Conclusions

Our results suggest that transport of _L-citrulline is mainly mediated by LAT1 in TR-BBB cells. Delivery strategy for LAT1-mediated transport and supply of L-citrulline to the brain may serve as therapeutic approaches to improve its neuroprotective effect in patients with cerebrovascular disease.

In silico predictive model to determine vector-mediated transport properties for the blood-brain barrier choline transporter

The blood–brain barrier choline transporter (BBB-ChT) may have utility as a drug delivery vector to the central nervous system (CNS). We therefore initiated molecular docking studies with the AutoDock and AutoDock Vina (ADVina) algorithms to develop predictive models for compound screening and to identify structural features important for binding to this transporter. The binding energy predictions were highly correlated with r²=0.88, F=692.4, standard error of estimate =0.775, and P-value<0.0001 for selected BBB-ChT-active/inactive compounds (n=93). Both programs were able to cluster active (Gibbs free energy of binding <−6.0 kcal*mol⁻¹) and inactive (Gibbs free energy of binding >−6.0 kcal*mol⁻¹) molecules and dock them significantly better than at random with an area under the curve value of 0.86 and 0.84, respectively. In ranking smaller molecules with few torsional bonds, a size-related bias in scoring producing false-negative outcomes was detected. Finally, important blood–brain barrier parameters, such as the logBB_passive and logBB_active values, were assessed to predict compound transport to the CNS accurately. Knowledge gained from this study is useful to better understand the binding requirements in BBB-ChT, and until such time as its crystal structure becomes available, it may have significant utility in developing a highly predictive model for the rational design of drug-like compounds targeted to the brain.

Drug delivery to the brain in Alzheimer's disease: consideration of the blood-brain barrier

The successful treatment of Alzheimer's disease (AD) will require drugs that can negotiate the blood-brain barrier (BBB). However, the BBB is not simply a physical barrier, but a complex interface that is in intimate communication with the rest of the central nervous system (CNS) and influenced by peripheral tissues. This review examines three aspects of the BBB in AD. First, it considers how the BBB may be contributing to the onset and progression of AD. In this regard, the BBB itself is a therapeutic target in the treatment of AD. Second, it examines how the BBB restricts drugs that might otherwise be useful in the treatment of AD and examines strategies being developed to deliver drugs to the CNS for the treatment of AD. Third, it considers how drug penetration across the AD BBB may differ from the BBB of normal aging. In this case, those differences can complicate the treatment of CNS diseases such as depression, delirium, psychoses, and pain control in the AD population.

The acetylcholinesterase inhibitors competitively inhibited an acetyl L-carnitine transport through the blood-brain barrier

We investigated the interaction of acetylcholinesterase (AChE) inhibitors with acetyl-L-carnitine (ALCAR) transporter at the blood-brain barrier (BBB). ALCAR uptake by conditionally immortalized rat brain capillary endothelial cell lines (TR-BBB cells), as an in vitro model of BBB, were characterized by cellular uptake study using [(3)H]ALCAR. In vivo brain uptake of [(3)H]ALCAR was determined by brain uptake index after carotid artery injection in rats. In results, the transport properties for [(3)H]ALCAR by TR-BBB cell were consistent with those of ALCAR transport by the organic cation/carnitine transporter 2 (OCTN2). Also, OCTN2 was confirmed to be expressed in the cells. The uptake of [(3)H]ALCAR by TR-BBB cells was inhibited by AChE inhibitors such as donepezil, tacrine, galantamine and rivastigmine, which IC(50) values are 45.3, 74.0, 459 and 800 μM, respectively. Especially, donepezil and galantamine inhibited the uptake of [(3)H]ALCAR competitively, but tacrine and rivastigmine inhibited noncompetitively. Furthermore, [(3)H]ALCAR uptake by the rat brain was found to be significantly decreased by quinidine, donepezil and galantamine. Our results suggest that transport of AChE inhibitors such as donepezil and galantamine through the BBB is at least partly mediated by OCTN2 which is involved in transport of ALCAR.

Evidence of carrier-mediated transport in the penetration of donepezil into the rat brain

The objective of this study was to characterize the mechanism that controls the transport of donepezil into the brain. The apparent brain uptake clearance (CL(app,br)) was decreased as a function of the dose of donepezil, suggesting an involvement of a saturable transport process via transporter(s) in the penetration across the blood-brain barrier (BBB). Consistent with in vivo results, the uptake of substrates for organic cation transporters was significantly reduced by donepezil in both MBEC4 cells (i.e., a model for BBB) and HEK 293 cells expressing the transporters found in the brain, indicative of the involvement of organic cation transporters in the transport of the drug. Furthermore, donepezil transport was enhanced (p < 0.01) in HEK 293 cells expressing rOCNT1, rOCTN2, or rCHT1. The CL(app,br) was reduced up to 52.8% of the control in rats that had been pretreated with choline, while the CL(app,br) was unaffected with pretreatments with organic cations other than choline, suggesting that choline and donepezil share a common transport mechanism in the penetration across the BBB in vivo. Taken together, these observations suggest that the transport of donepezil across the BBB is mediated by organic cation transporters such as choline transport system(s).

Choline transport via choline transporter-like protein 1 in conditionally immortalized rat syncytiotrophoblast cell lines TR-TBT

Choline is an essential nutrient for phospholipids and acetylcholine biosynthesis in normal development of fetus. In the present study, we investigated the functional characteristics of choline transport system and inhibitory effect of cationic drugs on choline transport in rat conditionally immortalized syncytiotrophoblast cell line (TR-TBT). Choline transport was weakly Na(+) dependent and significantly influenced by extracellular pH and by membrane depolarization. The transport process of choline is saturable with Michaelis-Menten constants (K(m)) of 68microM and 130microM in TR-TBT 18d-1 and TR-TBT 18d-2 respectively. Choline uptake in the cells was inhibited by unlabeled choline and hemicholinium-3 as well as various organic cations including guanidine, amiloride and acetylcholine. However, the prototypical organic cation tetraethylammonium and cimetidine showed very little inhibitory effect of choline uptake in TR-TBT cells. RT-PCR revealed that choline transporter-like protein 1 (CTL1) and organic cation transporter 2 (OCT2) are expressed in TR-TBT cells. The transport properties of choline in TR-TBT cells were similar or identical to that of CTL1 but not OCT2. CTL1 was also detected in human placenta. In addition, several cationic drugs such as diphenhydramine and verapamil competitively inhibited choline uptake in TR-TBT 18d-1 with K(i) of 115microM and 55microM, respectively. Our results suggest that choline transport system, which has intermediate affinity and weakly Na(+) dependent, in TR-TBT seems to occur through a CTL1 and this system may have relevance with the uptake of pharmacologically important organic cation drugs.

Regulation of bovine brain microvascular endothelial tight junction assembly and barrier function by laminar shear stress

Blood-brain barrier (BBB) controls paracellular solute diffusion into the brain microenvironment and is maintained primarily by tight junctions between adjacent microvascular endothelial cells. Studies implicate blood flow-associated shear stress as a pathophysiological mediator of BBB function, although detailed biochemical data are scarce. We hypothesize that shear stress upregulates BBB function via direct modulation of expression and properties of pivotal tight-junction proteins occludin and zonula occludens-1 (ZO-1). Bovine brain microvascular endothelial cells (BBMvECs) were exposed to either steady or pulsatile shear stress (10 and 14 dyn/cm2, respectively) for 24 h. Sheared BBMvECs were monitored for occludin-ZO-1 expression, association, and subcellular localization, and transendothelial permeability of BBMvECs to FITC-dextran and14[C]sucrose was assessed. Actin reorganization and BBMvEC realignment were observed following steady shear stress for 24 h. Substantial increases in occludin mRNA and protein expression (2.73 ± 0.26- and 1.83 ± 0.03-fold) and in occludin-ZO-1 association (2.12 ± 0.15-fold) were also observed. Steady shear stress also induced clear relocalization of both proteins to the cell-cell border in parallel with reduced transendothelial permeability to FITC-dextran (but not sucrose). Following pulsatile shear stress, increased protein levels for both occludin and ZO-1 (2.15 ± 0.02- and 1.67 ± 0.21-fold) and increased occludin-ZO-1 association (2.91 ± 0.14-fold) were observed in parallel with a reduction in transendothelial permeability to14[C]sucrose. Shear stress upregulates BBMvEC barrier function at the molecular level via modulation of expression, association, and localization of occludin and ZO-1. The pulsatile shear model appeared to give the most profound biochemical responses.

Molecular mechanism involved in the transport of a prodrug dopamine glycosyl conjugate

We have previously demonstrated that dopamine conjugation to glucose allows it to induce therapeutic effects against Parkinson's disease after intravenous administration. In this paper we demonstrate that, unlike dopamine, the prodrug glu-dopamine is a transportable substrate of glucose transporters. Towards this, the effect of glucose-conjugation on the affinity and uptake of dopamine have been assessed in vitro, using human retinal pigment epithelium (HRPE) cells. Glucose transporter-mediated uptake was measured using [(3)H]3-O-methylglucose ([(3)H]3-O-MG) as the tracer. The uptake was found to be rapid and hyperbolically related to its concentrations (K(t)=7.8+/-1.2mM and V(max)=54+/-2 nmol/min mg protein). Inhibition experiments showed that dopamine was able to interact with glucose carriers only when conjugated to glucose (IC(50)=2.6+/-0.6mM). HPLC analysis of HRPE cell extracts showed that both dopamine and the prodrug permeate the cell, but only the uptake of the prodrug is inhibitable by glucose. This confirms that glucose transporters mediate the transport of the prodrug glu-dopamine, but not of dopamine. HRPE cells is therefore proposed as a promising model for in vitro studies involving the glucose transporter-mediated transport of drugs and their conjugates.