Early Increase in Blood-Brain Barrier Permeability in a Murine Model Exposed to Fifteen Days of Intermittent Hypoxia.

Obstructive sleep apnea (OSA) is characterized by intermittent repeated episodes of hypoxia-reoxygenation. OSA is associated with cerebrovascular consequences. An enhanced blood-brain barrier (BBB) permeability has been proposed as a marker of those disorders. We studied in mice the effects of 1 day and 15 days intermittent hypoxia (IH) exposure on BBB function. We focused on the dorsal part of the hippocampus and attempted to identify the molecular mechanisms by combining in vivo BBB permeability (Evans blue tests) and mRNA expression of several junction proteins (zona occludens (ZO-1,2,3), VE-cadherin, claudins (1,5,12), cingulin) and of aquaporins (1,4,9) on hippocampal brain tissues. After 15 days of IH exposure we observed an increase in BBB permeability, associated with increased mRNA expressions of claudins 1 and 12, aquaporins 1 and 9. IH seemed to increase early for claudin-1 mRNA expression as it doubled with 1 day of exposure and returned near to its base level after 15 days. Claudin-1 overexpression may represent an immediate response to IH exposure. Then, after 15 days of exposure, an increase in functional BBB permeability was associated with enhanced expression of aquaporin. These BBB alterations are possibly associated with a vasogenic oedema that may affect brain functions and accelerate neurodegenerative processes.

Loss of Blood-Brain Barrier Integrity in an In Vitro Model Subjected to Intermittent Hypoxia: Is Reversion Possible with a HIF-1α Pathway Inhibitor?

Several sleep-related breathing disorders provoke repeated hypoxia stresses, which potentially lead to neurological diseases, such as cognitive impairment. Nevertheless, consequences of repeated intermittent hypoxia on the blood-brain barrier (BBB) are less recognized. This study compared two methods of intermittent hypoxia induction on the cerebral endothelium of the BBB: one using hydralazine and the other using a hypoxia chamber. These cycles were performed on an endothelial cell and astrocyte coculture model. Na-Fl permeability, tight junction protein, and ABC transporters (P-gp and MRP-1) content were evaluated with or without HIF-1 inhibitors YC-1. Our results demonstrated that hydralazine as well as intermittent physical hypoxia progressively altered BBB integrity, as shown by an increase in Na-Fl permeability. This alteration was accompanied by a decrease in concentration of tight junction proteins ZO-1 and claudin-5. In turn, microvascular endothelial cells up-regulated the expression of P-gp and MRP-1. An alteration was also found under hydralazine after the third cycle. On the other hand, the third intermittent hypoxia exposure showed a preservation of BBB characteristics. Furthermore, inhibition of HIF-1α with YC-1 prevented BBB dysfunction after hydralazine treatment. In the case of physical intermittent hypoxia, we observed an incomplete reversion suggesting that other biological mechanisms may be involved in BBB dysfunction. In conclusion, intermittent hypoxia led to an alteration of the BBB model with an adaptation observed after the third cycle.

Effects of intermittent hypoxia with thrombin in an in vitro model of human brain endothelial cells and their impact on PAR-1/PAR-3 cleavage.

Patients with obstructive sleep apnea/hypopnea (OSA) are at high risk of cerebrovascular diseases leading to cognitive impairment. The oxidative stress generated by intermittent hypoxia (IH) could lead to an increase in blood-brain barrier (BBB) permeability, an essential interface for the protection of the brain. Moreover, in patients with OSA, blood coagulation could be increased leading to cardiovascular complications. Thrombin is a factor found increased in these populations that exerts various cellular effects through activation of protease activated receptors (PARs). Thus, we have evaluated in an in vitro BBB model the association of IH with thrombin at two concentrations. We measured the apparent BBB permeability, expression of tight junctions, ROS production, HIF-1α expression, and cleavage of PAR-1/PAR-3. Pre-treatment with dabigatran was performed. IH and higher thrombin concentrations altered BBB permeability: high levels of HIF-1α expression, ROS and PAR-1 activation compared to PAR-3 in such conditions. Conversely, lower concentration of thrombin associated with IH appear to have a protective effect on BBB with a significant cleavage of PAR-3. Dabigatran reversed the deleterious effect of thrombin at high concentrations but also suppressed the beneficial effect of low dose thrombin. Therefore, thrombin and PARs represent novel attractive targets to prevent BBB opening in OSA.

Using 99mTc-(V)-DMSA to follow the vascular calcification process in vascular smooth muscle cells based on pit-1 expression.

BACKGROUND: Vascular calcification is an established feature of atherosclerosis process. The sodium/phosphate transporter PiT-1 acts as a biosensor in vascular calcification of VSMCs. [99mTc]-Pentavalent dimercaptosuccinic acid (99mTc-(V)-DMSA) was mediated by PiT-1 transporter in tumoral cells and we propose its evaluation in a vascular calcification in vitro model. The aim of this study was to determine if 99mTc-(V)-DMSA can follow the vascular calcification process in vascular smooth muscle cells (VSMCs) based on PiT-1 expression. METHODS: From a rat aortic VSMC cell line (A7r5), we set up a model of calcification within 7 days using a calcifying medium containing a high inorganic phosphate concentration. Phosphocalcic deposits were monitored with Alizarin red and Von Kossa staining and with phase contrast microscopy. PiT-1 expression was evaluated with an immunofluorescence assay and osteopontin expression, with whole cell ELISA assay. 99mTc-(V)-DMSA uptake was measured in control and calcifying conditions and compared with optical microscopy evaluation. RESULTS: Under hyperphosphatemia conditions, the VSMC cells progressively overexpressed osteopontin protein, PiT-1 transporter, and synthetized mineralized matrix with phosphocalcic deposition. 99mTc-(V)-DMSA uptake was to 2.8±2.08%DA/mg-protein in control cells and 42±24%DA/mg-protein in calcified cells (P<0.001). PiT-1 inhibition with phosphonoformic acid completely reverse the calcium deposition as well as the 99mTc-(V)-DMSA uptake. These results demonstrated that 99mTc-(V)-DMSA in-vitro uptake is mediated by PiT-1 transporter and follow the VSMC calcification process. CONCLUSIONS: These preliminary in-vitro results showed 99mTc-(V)-DMSA uptake follow the phospho-calcic deposition mediated by PiT-1 transporter. This radiotracer may have some potential to detect changes of VSMC metabolism occurring in the atherosclerosis process.

Obstructive Sleep Apnea, Hypercoagulability, and the Blood-Brain Barrier.

Obstructive sleep apnea (OSA) is characterized by repeated episodes of intermittent hypoxia (IH) and is recognized as an independent risk factor for vascular diseases that are mediated by a multitude of mechanistic pathophysiological cascades including procoagulant factors. The pro-coagulant state contributes to the development of blood clots and to the increase in the permeability of the blood-brain barrier (BBB). Such alteration of BBB may alter brain function and increase the risk of neurodegenerative diseases. We aim to provide a narrative review of the relationship between the hypercoagulable state, observed in OSA and characterized by increased coagulation factor activity, as well as platelet activation, and the underlying neural dysfunction, as related to disruption of the BBB. We aim to provide a critical overview of the existing evidence about the effect of OSA on the coagulation balance (characterized by increased coagulation factor activity and platelet activation) as on the BBB. Then, we will present the emerging data on the effect of BBB disruption on the risk of underlying neural dysfunction. Finally, we will discuss the potential of OSA therapy on the coagulation balance and the improvement of BBB.

Intermittent Hypoxia and Its Impact on Nrf2/HIF-1α Expression and ABC Transporters: An in Vitro Human Blood-Brain Barrier Model Study.

BACKGROUND/AIMS: Obstructive sleep apnea (OSA) is characterized by repeated episodes of complete or partial obstruction of the upper airways, leading to chronic intermittent hypoxia (IH). OSA patients are considered at high cerebrovascular risk and may also present cognitive impairment. One hypothesis explored is that disturbances may be linked to blood-brain barrier (BBB) dysfunction. The BBB is a protective barrier separating the brain from blood flow. The BBB limits the paracellular pathway through tight and adherens junctions, and the transcellular passage by efflux pumps (ABC transporters). The aims of this study were to evaluate the impact of IH and sustained hypoxia (SH) on a validated in vitro BBB model and to investigate the factors expressed under both conditions. METHODS: Exposure of endothelial cells (HBEC-5i) in our in vitro model of BBB to hypoxia was performed using IH cycles: 1% O2-35 min/18% O2-25 min for 6 cycles or 6 h of SH at 1% O2. After exposure, we studied the cytotoxicity and the level of ROS in our cells. We measured the apparent BBB permeability using sodium fluorescein, FITC-dextran and TEER measurement. Whole cell ELISA were performed to evaluate the expression of tight junctions, ABC transporters, HIF-1α and Nrf2. The functionality of ABC transporters was evaluated with accumulation studies. Immunofluorescence assays were also conducted to illustrate the whole cell ELISAs. RESULTS: Our study showed that 6 h of IH or SH induced a BBB disruption marked by a significant decrease in junction protein expressions (claudin-5, VE-cadherin, ZO-1) and an increase in permeability. We also observed an upregulation in P-gp protein expression and functionality and a downregulation in BCRP. Hypoxia induced production of ROS, Nrf2 and HIF-1α. They were expressed in both sustained and intermittent conditions, but the expression and the activity of P-gp and BCRP were different. CONCLUSION: Understanding these mechanisms seems essential in order to propose new therapeutic strategies for patients with OSA.

Sera of elderly obstructive sleep apnea patients alter blood-brain barrier integrity in vitro: a pilot study.

Obstructive sleep apnea syndrome (OSAS) is characterized by repeated episodes of hypoxia during the night. The severity of the disorder can be evaluated using an apnea-hypopnea index (AHI). The physiological consequences are mainly cardiovascular and neuronal dysfunctions. One hypothesis to explain such associated neurological disorders is disruption of the blood-brain barrier (BBB), which protects the brain from endovascular cytotoxic compounds. We selected two subgroups of volunteers from the PROOF cohort study (France), a group of patients suffering newly diagnosed severe OSAS (AHI > 30/h) and a group showing no sleep apnea (AHI < 5/h). We exposed a human in vitro BBB model of endothelial cells (HBEC-5i) with sera of patients with and without OSAS. After exposure, we measured the apparent BBB permeability as well as tight junction and ABC transporter expression using whole cell ELISA. We showed that after incubation with sera from OSAS patients, there was a loss of integrity in the human in vitro BBB model; this was reflected by an increase in permeability (43%; p < 0.001) and correlated with a 50% and 40% decrease in tight junction protein expression of ZO-1 and claudin-5, respectively. At the same time, we observed an upregulation in Pgp protein expression (52%) and functionality, and a downregulation in BCRP expression (52%). Our results demonstrated that severe BBB disorder after exposure to sera from OSAS patients was reflected by an opening of the BBB.

Inflammatory stress induced by a combination of cytokines (IL-6, IL-17, TNF-α) leads to a loss of integrity on bEnd.3 endothelial cells in vitro BBB model.

The brain is a complex organ protected by the blood-brain barrier (BBB), which also has a complex organization. To play its protective role, the BBB acts by limiting the paracellular passage of potentially cytotoxic compounds through tight junctions as well as limiting transcellular passage by efflux pumps (ABC transporters). In many conditions such as sleep apnea or Alzheimer's disease, there is chronic inflammation, resulting in the presence of pro-inflammatory cytokines in the bloodstream. The effect of this chronic inflammation on the integrity of the BBB has been studied mainly through a single inflammatory molecule; but in physiological and pathological conditions, it is a combination of inflammatory cytokines. We investigated the effect of three major pro-inflammatory cytokines (IL-17, IL-6, TNF-α) used alone or in combination on the integrity of an in vitro model of BBB. Our study showed 24 h of inflammatory stress led to a BBB's opening, reflected by a significant increase of permeability, which was correlated to a significant decrease of tight junction protein expressions (ZO-1, claudin-5), involving a possible entry of cytotoxic compounds into the brain. To compensate the loss of integrity, one of defense mechanism of endothelial cells was efflux transport, which showed a significant increase in expression and functionality of ABC transport proteins (MRP-1, Pgp). This opening of the BBB was more important when pro-inflammatory cytokines were combined, which could be explained by the interaction between cytokines and the potentiation of their effect.

Direct oral anticoagulants are associated with limited damage of endothelial cells of the blood-brain barrier mediated by the thrombin/PAR-1 pathway.

Anticoagulant therapy presents iatrogenic effects such as intracerebral hemorrhage (ICH). The latest anticoagulants on the market, direct oral anticoagulants (DOACs) such as apixaban, dabigatran and rivaroxaban, are reported to cause less ICH than other anticoagulants. Next to the ICH area, the thrombin is accumulated and the blood-brain barrier (BBB) is opened. The effects of thrombin on the BBB are largely mediated by the protease activated receptor (PAR) family, especially the PAR-1 isoform. Our hypothesis is that DOACs may limit the effects of thrombin on endothelial cells (of the BBB) alteration by a mechanism probably involving PAR-1 activation. To test this hypothesis in vitro, we used HBEC-5i human brain endothelial cells as a human BBB model. The effects of thrombin under warfarin, heparin, rivaroxaban, apixaban, and dabigatran treatment on endothelial cells were then investigated by measuring of permeability and junction proteins: ZO-1 and VE-cadherin expressions and PAR-1 cleavage. Depending on the anticoagulant used, we observed three profiles of response of the endothelial cells after thrombin exposure: i) dabigatran treatment allowed maintaining the tightness of the endothelial monolayer; ii) other DOACs limited thrombin-induced alteration of the endothelial monolayer; and iii) pretreatment with warfarin and heparin did not protect from thrombin-induced BBB breakdown. Pretreatment with DOACs clearly limited the impact of thrombin on PAR-1 cleavage in our model, contrary to other anticoagulants, associated with ZO-1 and VE-cadherin expressions. In conclusion, DOACs seem to limit the alteration of the monolayer of endothelial cells of the BBB mediated by the thrombin/PAR-1 pathway.

Pharmacological characterization of the 3D MucilAir™ nasal model.

The preclinical evaluation of nasally administered drug candidates requires screening studies based on in vitro models of the nasal mucosa. The aim of this study was to evaluate the morpho-functional characteristics of the 3D MucilAir™ nasal model with a pharmacological focus on [ATP]-binding cassette (ABC) efflux transporters. We initially performed a phenotypic characterization of the MucilAir™ model and assessed its barrier properties by immunofluorescence (IF), protein mass spectrometry and examination of histological sections. We then focused on the functional expression of the ABC transporters P-glycoprotein (P-gp), multidrug resistance associated protein (MRP)1, MRP2 and breast cancer resistance protein (BCRP) in bidirectional transport experiments. The MucilAir™ model comprises a tight, polarized, pseudo-stratified nasal epithelium composed of fully differentiated ciliated, goblet and basal cells. These ABC transporters were all expressed by the cell membranes. P-gp and BCRP were both functional and capable of actively effluxing substrates. The MucilAir™ model could consequently represent a potent tool for evaluating the interaction of nasally administered drugs with ABC transporters.

Assessment of HBEC-5i endothelial cell line cultivated in astrocyte conditioned medium as a human blood-brain barrier model for ABC drug transport studies.

Endothelial cells are main components of the Blood-Brain Barrier (BBB) and form a tight monolayer that regulates the passage of molecules, with the ATP-Binding Cassette (ABC) transporters efflux pumps. We have developed a human in vitro model of HBEC-5i endothelial cells cultivated alone or with human astrocytes conditioned medium on insert. HBEC-5i cells showed a tight monolayer within 14 days, expressing ZO-1 and claudin 5, a low apparent permeability to small molecules, with a TEER stability during five days. The P-gp, BCRP, MRPs transporters were well expressed and functional. Accumulation and efflux ratio measurement with different ABC transporters substrates (Rhodamine 123, BCECF AM, Hoechst 33342) and inhibitors (verapamil, Ko143, probenecid and cyclosporin A) were conducted. At barrier level, the functionality of ABC transporters was three-fold enhanced in astrocyte conditioned medium. We validated our model by the transport of pharmacological substrates: caffeine, rivaroxaban, and methotrexate. The rivaroxaban and methotrexate were released with an efflux ratio >3 and were decreased by more than half with inhibitors. HBEC-5i model could be used as relevant tool in preclinical studies for assessing the permeability of therapeutic molecules to cross human BBB.

Pharmacological Characterization of the RPMI 2650 Model as a Relevant Tool for Assessing the Permeability of Intranasal Drugs.

The RPMI 2650 cell line has been described as a potent model of the human nasal mucosa. Nevertheless, pharmacological data are still insufficient, and the role of drug efflux transporters has not been fully elucidated. We therefore pursued the pharmacological characterization of this model, initially investigating the expression of four well-known adenosine triphosphate [ATP]-binding cassette (ABC) transporters (P-glycoprotein (P-gp), multidrug resistance associated protein (MRP)1, MRP2, and breast cancer resistance protein (BCRP)) by means of ELISA and immunofluorescence staining. The functional activity of the selected transporters was assessed by accumulation studies based on specific substrates and inhibitors. We then performed standardized bidirectional transport experiments under air-liquid interface (ALI) culture conditions, using four therapeutic compounds of local intranasal relevance in upper airway diseases. Protein expression of P-gp, MRP1, MRP2, and BCRP was detected at the membrane of the RPMI 2650 cells. In addition, all four transporters exhibited functional activity at the cellular level. In the bidirectional transport experiments, the RPMI 2650 model was able to accurately discriminate the four therapeutic compounds according to their physicochemical properties. The ABC transporters tested did not play a major role in the efflux of these compounds at the barrier level. In conclusion, the RPMI 2650 model represents a promising tool for assessing the nasal absorption of drugs on the basis of preclinical pharmacological data.

Umbelliferone Decreases Intracellular pH and Sensitizes Melanoma Cell Line A375 to Dacarbazin. Comparison with Acetazolamide.

BACKGROUND AND OBJECTIVE: The high degree of malignancy of tumour cells is linked to alterations of many physiological parameters like the intracellular pH (pHi). The pHi in cancer cell line is regulated by the carbonic anhydrase IX (CA IX). The main enzymatic function of the CA IX protein is to catalyze the hydration of carbon dioxide into bicarbonate ions and protons. CA IX expression in a broad variety of human tumor tissues is associated with resistance to therapy. One promising approach is to target the mechanism regulating pH homeostasis with carbonic anhydrase inhibitors like sulfamides and coumarins families. METHODS: In this work we have evaluated effects of umbelliferone and acetazolamide in a high resistant melanoma cell line (A375) over expressing CA IX. Impact of effective doses of CA IX inhibitors on apoptosis, intracellular pH (pHi), CA IX protein expression and functionality have been investigated. Determination of effective doses of CA IX inhibitors was performed with MTT tests. We also evaluated sensitization effect of CA inhibitors to conventional therapy as dacarbazin. RESULTS: We have used 10 µM Umbelliferone and 100 µM Acetazolamide as effective doses for 24h. These doses did not induce any apoptosis. Umbelliferone induced a more important pHi decrease than Acetalozamide from 7.3 to 7.08 and to 7.12 respectively, and a more important decrease in s-CA IX fraction showing a decrease in CA IX function. We have demonstrated that pre-treatment with umbelliferone or acetazolamide allows a better dacarbazin efficacy. CONCLUSION: We have demonstrated that inhibitors modify intracellular pH and CAIX functionality and sensitize cells to Dacarbazin. These original results complete the knowledge on Sulfamide CA IX inhibitors, bring new insights about Coumarin compounds and offer new possibilities in high grade melanoma therapies.

Is RPMI 2650 a Suitable In Vitro Nasal Model for Drug Transport Studies?

The evaluation of new intranasal medications requires the development of in vitro cell model suitable for high-throughput screening studies. The aim of a pharmacological model is to closely mimic the barrier properties of human nasal mucosa that will influence drug pharmacokinetics. In this context, the human nasal cell line RPMI 2650 has been investigated over these last years. Although the initial studies tended to demonstrate strong physiological correlations between RPMI 2650 cells and nasal mucosa, the variability of experimental designs does not allow a clear comparison of actual data. Thereby, the standardization of cell culture parameters is crucial to obtain a stronger reproducibility and increase the relevance of data. Indeed, RPMI 2650 barrier properties are heavily dependent of cell culture conditions, especially of the physiological air-liquid interface that strengthen the expression of both tight junction proteins and drug transporters. Conversely, cell culture medium and insert composition showed a minor impact on the four key parameters of a nasal barrier. Despite the recent advances in the physiological characterization of RPMI 2650 model, only limited pharmacological data are available concerning the involvement of drug transporters in drug bioavailability. The deployment of standardized bi-directional permeability studies using reference compounds is required to determine the relevance of RPMI 2650 model in the field of drug transport studies.

In Vitro Comparison of the Role of P-Glycoprotein and Breast Cancer Resistance Protein on Direct Oral Anticoagulants Disposition.

BACKGROUND: Pharmacokinetics of direct oral anticoagulants (DOACs) are influenced by ATP-binding cassette (ABC) transporters such as P-glycoprotein (P-gp) and Breast Cancer Resistance Protein (BCRP). OBJECTIVES: To better understand the role of transporters in DOAC disposition, we evaluated and compared the permeabilities and transport properties of these drugs. METHODS: Bidirectional permeabilities of DOACs were investigated across Caco-2 cells monolayer. Transport assays were performed using different concentrations of DOAC and specific inhibitors of ABC transporters. Cell model functionality was evaluated by transport assay of two positive control substrates. RESULTS: The results of transport assays suggest a concentration-dependent efflux of apixaban, dabigatran etexilate and edoxaban, whereas the efflux transport of rivaroxaban did not seem to depend on concentration. Verapamil, a strong inhibitor of P-gp, decreased DOAC efflux in the Caco-2 cell model by 12-87%, depending on the drug tested. Ko143 reduced BCRP-mediated DOAC efflux in Caco-2 cells by 46-76%. CONCLUSION: This study allowed identification of three different profiles of ABC carrier-mediated transport: predominantly P-gp-dependent transport (dabigatran), preferential BCRP-dependent transport (apixaban) and approximately equivalent P-gp and BCRP-mediated transport (edoxaban and rivaroxaban).

Glomerular filtration drug injury: In vitro evaluation of functional and morphological podocyte perturbations.

The kidney is an organ that plays a major role in the excretion of numerous compounds such as drugs and chemicals. However, a great number of pharmacological molecules are nephrotoxic, affecting the efficiency of the treatment and increasing morbidity or mortality. Focusing on glomerular filtration, we propose in this study a simple and reproducible in vitro human model that is able to bring to light a functional podocyte injury, correlated with morphologic/phenotypic changes after drug exposure. This model was used for the evaluation of paracellular permeability of FITC-dextran molecules as well as FITC-BSA after different treatments. Puromycin aminonucleoside and adriamycin, compounds known to induce proteinuria in vivo and that serve here as positive nephrotoxic drug controls, were able to induce an important increase in fluorescent probe passage through the cell monolayer. Different molecules were then evaluated for their potential effect on podocyte filtration. Our results demonstrated that a drug effect could be time dependent, stable or scalable and relatively specific. Immunofluorescence studies indicated that these functional perturbations were due to cytoskeletal perturbations, monolayer disassembly or could be correlated with a decrease in nephrin expression and/or ZO-1 relocation. Taken together, our results demonstrated that this in vitro human model represents an interesting tool for the screening of the renal toxicity of drugs.

Hydralazine is a Suitable Mimetic Agent of Hypoxia to Study the Impact of Hypoxic Stress on In Vitro Blood-Brain Barrier Model.

BACKGROUND/AIMS: Understanding cellular mechanisms induced by hypoxia is fundamental to reduce blood-brain barrier (BBB) disruption. Nevertheless, the investigation of hypoxia on cellular pathways is complex with true hypoxia because HIF-1α has a short lifetime and rapidly reverts back to a normoxic state. To overcome this difficulty, mimetic agents of the hypoxia pathway have been developed, including the gold standard CoCl2. In this study, we proposed to compare CoCl2 and hydralazine in order to determine a suitable mimetic agent of hypoxia for the study on the BBB. METHODS: We studied the cytotoxicity and the impact of these molecules on the integrity of an in vitro BBB model by comparing them to hypoxia controls. RESULTS: We showed that the impact of hypoxic stress in our in vitro BBB model is rather similar between hydralazine and CoCl2. Chemical hypoxic stress led to an increase of BBB permeability either with CoCl2 or hydralazine. Tight junction protein expressions showed that this chemical hypoxic stress decreased ZO-1 but not occluding expressions, and cells had set up a defence mechanism by increasing expression and activity of their efflux transporters. CONCLUSION: Our results demonstrated that hydralazine is a better mimetic agent and more suitable than CoCl2 because it had the same effect but without the cytotoxic effect on in vitro BBB cells.

Hypoxic Stress Induced by Hydralazine Leads to a Loss of Blood-Brain Barrier Integrity and an Increase in Efflux Transporter Activity.

Understanding cellular and molecular mechanisms induced by hypoxic stress is crucial to reduce blood-brain barrier (BBB) disruption in some neurological diseases. Since the brain is a complex organ, it makes the interpretation of in vivo data difficult, so BBB studies are often investigated using in vitro models. However, the investigation of hypoxia in cellular pathways is complex with physical hypoxia because HIF-1α (factor induced by hypoxia) has a short half-life. We had set up an innovative and original method of induction of hypoxic stress by hydralazine that was more reproducible, which allowed us to study its impact on an in vitro BBB model. Our results showed that hydralazine, a mimetic agent of the hypoxia pathway, had the same effect as physical hypoxia, with few cytotoxicity effects on our cells. Hypoxic stress led to an increase of BBB permeability which corresponded to an opening of our BBB model. Study of tight junction proteins revealed that this hypoxic stress decreased ZO-1 but not occludin expression. In contrast, cells established a defence mechanism by increasing expression and activity of their efflux transporters (Pgp and MRP-1). This induction method of hypoxic stress by hydralazine is simple, reproducible, controllable and suitable to understand the cellular and molecular mechanisms involved by hypoxia on the BBB.

Gefitinib inhibits sodium phosphate co-transporter III isoform 1 in a model of human malignant glioma.

BACKGROUND: The purpose of the present was to investigate whether the in vitro effects of gefitinib, an EGFR tyrosine kinase inhibitor, may regulate the expression of type III sodium phosphate Na/Pi co-transporters in an in vitro glioma model. MATERIALS AND METHODS: Proliferation studies, global native EGFR and phosphorylated EGFR expressions, phosphate transporter type III isoform 1(PiT1) expression and phosphate transport with 99mTc-(V)-DMSA radioligand were performed in G111 (grade II astrocytoma), U-87-MG (grade III astrocytoma) and G152 (grade IV glioblastoma) cells. RESULTS: Cells treated with gefitinib showed a significant decrease in proliferation in relation to EGFR and p-EGFR expression. Gefitinib also produced a decrease in phosphate transport mediated PIT1 expression at both the RNA and protein levels. CONCLUSION: The link between gefitinib acting on the EGFR and PiT1 regulation in these cancer cell lines was herein shown.

Is [(99m)Tc]glucarate uptake mediated by fructose transporter GLUT-5?

PURPOSE: There is growing interest in the ability of [(99m)Tc]Glucarate ([(99m)Tc]GLA) to accumulate in viable tumor cells. Recent vivo studies suggest that [(99m)Tc]Glucarate could be helpful for tumor detection. Fructose transport is thought to be implicated. It is clearly established that facilitated fructose transport in tumor cells is related to the GLUT-5 transporter. This study therefore investigated whether [(99m)Tc]GLA uptake is mediated by GLUT-5 transporter. METHODS: Different tumor cell lines were used. Modulation of GLUT-5 expression was assessed with and without antisense oligonucleotides directed against GLUT-5. GLUT-5 expression was assessed by indirect cell ELISA. To correlate GLUT-5 expression with tracer accumulation, [(99m)Tc]GLA uptake was determined after antisense treatment. A competition with fructose was also monitored. RESULTS: Inhibition of GLUT-5 expression by antisense oligonucleotides directed against GLUT-5 was effective after 24 h. An optimal of 10µM antisense oligonucleotides directed against GLUT-5 produced a 30%-40% decrease in protein expression. Modulation of [(99m)Tc]GLA uptake was monitored either by use of specific antisense oligonucleotides or by competition with fructose. Both of them produced a significant decrease of [(99m)Tc]GLA accumulation in all tested cell lines. CONCLUSION: Our results clearly demonstrate that [(99m)Tc]GLA uptake is related to GLUT-5 transporter expression and transport. In tumor imaging, [(99m)Tc]GLA may be a useful tool for non-invasive detection of malignant tumors expressing high levels of GLUT-5 transporter as, for example, breast cancers.