[Show abstract][Hide abstract] ABSTRACT: We evaluated the integrity and function of the blood-brain barrier in 3xTg-AD mice aged 3-18 months and in APP/PS1 mice aged 8-months to determine the impacts of changes in amyloid and tau proteins on the brain vascular changes. The vascular volume (Vvasc) was sub-normal in 3xTg-AD mice aged from 6 to 18 months, but not in the APP/PS1 mice. The uptakes of [(3)H]-diazepam by the brains of 3xTg-AD, APP/PS1 and their age-matched control mice were similar at all the times studied, suggesting that the simple diffusion of small solutes is unchanged in transgenic animals. The uptake of D-glucose by the brains of 18-month old 3xTg-AD mice, but not by those of 8-month old APP/PS1 mice, was reduced compared to their age-matched controls. Accordingly, the amount of Glut-1 protein was 1.4 times lower in the brain capillaries of 18 month-old 3xTg-AD mice than in those of age-matched control mice. We conclude that the brain vascular volume is reduced early in 3xTg-AD mice, 6 months before the appearance of pathological lesions, and that this reduction persists until they are at least 18 months old. The absence of alterations in the BBB of APP/PS1 mice suggests that hyperphosphorylated tau proteins contribute to the vascular changes that occur in AD.
[Show abstract][Hide abstract] ABSTRACT: Monoclonal antibodies (mAbs) targeting blood-brain barrier (BBB) transporters are being developed for brain drug targeting. However, brain uptake quantification remains a challenge, particularly for large compounds, and often requires the use of radioactivity. Here, we have adapted an in situ brain perfusion technique for a fluorescent mAb raised against the mouse transferrin receptor (TfR) (clone Ri7). We first confirmed in vitro that the internalization of fluorolabeled Ri7 mAbs is saturable and dependent on the TfR in N2A and bEnd5 cells. We next showed that the brain uptake coefficient (Clup) of 100 μg (~220 nM) Ri7 mAbs fluorolabeled with Alexa Fluor 750 (AF750) was 0.27 ± 0.05 µl.g-1.s-1, after subtracting values obtained with a control IgG. A linear relationship was observed between the distribution volume VD (µl.g-1) and the perfusion time (s) over 30-120 s (r2 = 0.997), confirming the metabolic stability of AF750-Ri7 mAbs during perfusion. Coperfusion of increasing quantities of unlabeled Ri7 decreased AF750-Ri7 Clup down to control IgG levels over 500 nM, consistent with a saturable mechanism. Fluorescence microscopy analysis showed a vascular distribution of perfused AF750-Ri7 in the brain and colocalization with a marker of basal lamina. To our knowledge, this is the first reported use of the in situ brain perfusion technique combined with quantification of compounds labeled with near-infrared fluorophores. Furthermore, this study confirms the accumulation of the anti-transferrin receptor mAb Ri7 in the brain of mice, through a saturable uptake mechanism.
[Show abstract][Hide abstract] ABSTRACT: The influx of amyloid-β peptide (Aβ) across the blood-brain barrier is partly mediated by the receptor for advanced glycation end products. But other transporters, like Oatp (organic anion transporter polypeptide, SLC21) transporters, could also be involved. We used in situ brain perfusion to show that rosuvastatin and taurocholate, two established Oatp1a4 substrates, decreased (5-fold) the Clup of [3H]-Aβ while L-thyroxine increased it (5.5-fold). We demonstrated an interaction between Aβ and Oatp1a4 by co-immunoprecipitation and western blotting experiments, supporting the hypothesis that the rosuvastatin- and taurocholate-sensitive transporter was Oatp1a4. In conclusion, our results suggest that, in mice, the brain uptake of Aβ is partly mediated by Oatp1a4 and that L-thyroxine may play a crucial role in the inhibition of brain Aβ clearance.
Journal of Alzheimer's disease: JAD 05/2013; · 3.61 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Amyloid precursor protein (APP), a key molecule in Alzheimer's disease (AD), is metabolized in two alternative cleavages, generating either the amyloidogenic peptides involved in AD pathology or the soluble form of APP (sAPPα). The level of amyloidogenic peptides in human cerebrospinal fluid (CSF) is considered to be a biomarker of AD, whereas the level of sAPPα in CSF as a biomarker has not been clearly established. sAPPα has neurotrophic and neuroprotective properties. Stimulating its formation and secretion is a promising therapeutic target in AD research. To this end, very sensitive tests for preclinical and clinical research are required.
The tests are based on homogenous time-resolved fluorescence and require no washing steps.
We describe two new rapid and sensitive tests for quantifying mouse and human sAPPα. These 20 μl-volume tests quantify the levels of: i) endogenous mouse sAPPα in the conditioned medium of mouse neuron primary cultures, as well as in the CSF of wild-type mice, ii) human sAPPα in the CSF of AD mouse models, and iii) human sAPPα in the CSF of AD and non-AD patients. These tests require only 5 μl of conditioned medium from 5 × 10(4) mouse primary neurons, 1 μl of CSF from wild-type and transgenic mice, and 0.5 μl of human CSF.
The high sensitivity of the mouse sAPPα test will allow high-throughput investigations of molecules capable of increasing the secretion of endogenous sAPPα in primary neurons, as well as the in vivo validation of molecules of interest through the quantification of sAPPα in the CSF of treated wild-type mice. Active molecules could then be tested in the AD mouse models by quantifying human sAPPα in the CSF through the progression of the disease. Finally, the human sAPPα test could strengthen the biological diagnosis of AD in large clinical investigations. Taken together, these new tests have a wide field of applications in preclinical and clinical studies.
[Show abstract][Hide abstract] ABSTRACT: The purpose of this work was to investigate the potential of α-cyclodextrin combined to soybean oil-based formulations to modulate the release of a model drug, indomethacin. Dry emulsion, naked and coated beads were prepared from the same initial formulation using the same manufacturing process. Dry emulsion was selected to accelerate drug release while beads coated with α-cyclodextrin were designed to sustain it. Indomethacin-loaded systems were prepared, characterised and evaluated in vitro. Pharmacokinetic studies were performed in fasted and fed rats. The presence of the α-cyclodextrin coat was confirmed by confocal microscopy, and an increase of the mass and diameter of the beads. The layer of α-cyclodextrin improved their resistance in simulated gastro-intestinal fluids. In vitro, the dissolution of indomethacin was slower with coated beads than with emulsion and naked beads. Lipid-based formulations showed an increase of relative bioavailability of IND versus Indocid®. Whatever the formulation, greater and faster release of indomethacin was noticed in sodium taurocholate-rich medium and in fed rats. Compared to naked beads, an increased Cp(max) with a shorter T(max) was observed with the emulsion while T(max) and MRT were increased and Cp(max) reduced with the coated beads. Interestingly, formulations based on alpha cyclodextrin and soybean oil can modify the release of a lipophilic drug depending on the system formed.
Journal of Controlled Release 05/2012; 161(3):861-7. · 7.63 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: PLGA-PEG nanocapsules containing a liquid core of perfluorooctyl bromide were synthesized by an emulsion-evaporation process and designed as contrast agents for (19)F MRI. Physico-chemical properties of plain and PEGylated nanocapsules were compared. The encapsulation efficiency of PFOB, estimated by (19)F NMR spectroscopy, is enhanced when using PLGA-PEG instead of PLGA. PLGA-PEG nanocapsule diameter, measured by Dynamic Light Scattering is around 120 nm, in agreement with Transmission Electron microscopy (TEM) observations. TEM and Scanning Electron Microscopy (SEM) reveal that spherical core-shell morphology is preserved. PEGylation is further confirmed by Zeta potential measurements and X-ray Photoelectron Spectroscopy. In vitro, stealthiness of the PEGylated nanocapsules is evidenced by weak complement activation. Accumulation kinetics in the liver and the spleen was performed by (19)F MRI in mice, during the first 90 min after intravenous injection. In the liver, plain nanocapsules accumulate faster than their PEGylated counterparts. We observe PEGylated nanocapsule accumulation in CT26 xenograft tumor 7 h after administration to mice, whereas plain nanocapsules remain undetectable, using (19)F MRI. Our results validate the use of diblock copolymers for PEGylation to increase the residence time of nanocapsules in the blood stream and to reach tumors by the Enhanced Permeation and Retention (EPR) effect.
[Show abstract][Hide abstract] ABSTRACT: Countless studies showed that fullerene (C(60)) and derivatives could have many potential biomedical applications. However, while several independent research groups showed that C(60) has no acute or sub-acute toxicity in various experimental models, more than 25 years after its discovery the in vivo fate and the chronic effects of this fullerene remain unknown. If the potential of C(60) and derivatives in the biomedical field have to be fulfilled these issues must be addressed. Here we show that oral administration of C(60) dissolved in olive oil (0.8 mg/ml) at reiterated doses (1.7 mg/kg of body weight) to rats not only does not entail chronic toxicity but it almost doubles their lifespan. The effects of C(60)-olive oil solutions in an experimental model of CCl(4) intoxication in rat strongly suggest that the effect on lifespan is mainly due to the attenuation of age-associated increases in oxidative stress. Pharmacokinetic studies show that dissolved C(60) is absorbed by the gastro-intestinal tract and eliminated in a few tens of hours. These results of importance in the fields of medicine and toxicology should open the way for the many possible -and waited for- biomedical applications of C(60) including cancer therapy, neurodegenerative disorders, and ageing.
[Show abstract][Hide abstract] ABSTRACT: Recent reports showed that subtle modifications of nanoparticle surface properties induced dramatic changes of interactions with serum proteins. The present work was aimed to investigate the effect of the conformation of dextran chains decorating the surface of poly(alkylcyanoacrylate) (PACA) nanoparticles on the pharmacokinetic and biodistribution of a model drug associated with the nanoparticles. Doxorubicin was associated with PACA nanoparticles prepared by anionic emulsion polymerization (AEP) (Dox-AEP) and redox radical emulsion polymerization (RREP) (Dox-RREP). Nanoparticles and the free drug (f-Dox) were injected intravenously to rats to determine the pharmacokinetic and biodistribution of doxorubicin. Curves of the pharmacokinetics showed a rapid phase of distribution followed by a slower elimination phase. Pharmacokinetic parameters of the distribution phase determined for the Dox-RREP were significantly different from those of f-Dox and Dox-AEP, while no difference was observed in the elimination phase of the three formulations. Rats treated with Dox-RREP showed lower Dox concentrations in liver but higher concentrations in heart, lungs, and kidneys compared to those treated with the other formulations. Dox-RREP exhibited a new type of stealth behavior characterized by a short circulation time and a rapid distribution in highly vascularized organs bypassing the MPS. The difference in pharmacokinetic and biodistribution observed between the drugs formulated with the two types of nanoparticles was attributed to the difference in the conformation of the dextran chains stranded on the nanoparticle surface.
European journal of pharmaceutics and biopharmaceutics: official journal of Arbeitsgemeinschaft fur Pharmazeutische Verfahrenstechnik e.V 03/2012; 81(2):453-7. · 3.15 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The accumulation of amyloid-β peptide (Aβ) in the brain is a critical hallmark of Alzheimer's disease. This high cerebral Aβ concentration may be partly caused by impaired clearance of Aβ across the blood-brain barrier (BBB). The low-density lipoprotein receptor-related protein-1 (LRP-1) and the ATP-binding cassette (ABC) protein ABCB1 (P-glycoprotein) are involved in the efflux of Aβ across the BBB. We hypothesized that other ABC proteins, such as members of the G subfamily, are also involved in the BBB clearance of Aβ. We therefore investigated the roles of ABCG2 (BCRP) and ABCG4 in the efflux of [3H] Aβ1-40 from HEK293 cells stably transfected with human ABCG2 or mouse abcg4. We showed that ABCG2 and Abcg4 mediate the cellular efflux of [3H] Aβ1-40. In addition, probucol fully inhibited the efflux of [3H] Aβ1-40 from HEK293-abcg4 cells. Using the in situ brain perfusion technique, we showed that GF120918 (dual inhibitor of Abcb1 and Abcg2) strongly enhanced the uptake (Clup, μl/g/s) of [3H] Aβ1-40 by the brains of Abcb1-deficient mice, but not by the brains of Abcb1/Abcg2-deficient mice, suggesting that Abcg2 is involved in the transport of Aβ at the mouse BBB. Perfusing the brains of Abcb1/Abcg2- and Abca1-deficient mice with [3H] Aβ1-40 plus probucol significantly increased the Clup of Aβ. This suggests that a probucol-sensitive transporter that is different from Abca1, Abcb1, and Abcg2 is involved in the brain efflux of Aβ. We suggest that this probucol-sensitive transporter is Abcg4. We conclude that Abcg4 acts in concert with Abcg2 to efflux Aβ from the brain across the BBB.
[Show abstract][Hide abstract] ABSTRACT: We investigated the expression and function of Abca1 in wild-type C57BL/6, abca1(+/+), and abca1(-/-) mice brain capillaries forming the blood-brain barrier (BBB). We first demonstrated by quantitative RT-PCR and Western immunoblot that Abca1 was expressed and enriched in the wild-type mouse brain capillaries. In abca1(-/-) mice, we reported that the lack of Abca1 resulted in an 1.6-fold increase of the Abcg4 expression level compared to abca1(+/+) mice. Next, using the in situ brain perfusion technique, we showed that the [(3)H]cholesterol brain uptake clearance (Cl(up), μl/s/g brain), was significantly increased (107%) in abca1(-/-) mice compared to abca1(+/+) mice, meaning that the deficiency of Abca1 conducted to a significant decrease of the cholesterol efflux at the BBB level. In addition, the co-perfusion of probucol (Abca1 inhibitor) with [(3)H]cholesterol resulted in an increase of [(3)H]cholesterol Cl(up) (115%) in abca1(+/+) but not in abca1(-/-) mice, meaning that probucol inhibited selectively the efflux function of Abca1. In conclusion, our results demonstrated that Abca1 was expressed in the mouse brain capillaries and that Abca1 functions as an efflux transporter through the mouse BBB.
Molecular and Cellular Biochemistry 06/2011; 357(1-2):397-404. · 2.39 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Docosahexaenoic (DHA) and eicosapentaenoic (EPA) acids are n-3 polyunsaturated fatty acids with a therapeutic potential for CNS diseases. Here, using an in situ brain perfusion technique in mice, we show that [(14)C]-DHA and [(14)C]-EPA readily cross the mouse blood-brain barrier (BBB) with brain transport coefficients (Clup) of 48+/-3microlg(-1)s(-1) and 52+/-4microlg(-1)s(-1), respectively. Mechanical capillary depletion of brain homogenates showed that less than 10% of [(14)C]-DHA or [(14)C]-EPA remained in endothelial cells of the brain vasculature, demonstrating that both molecules fully crossed the BBB. Addition of bovine serum albumin decreased the Clup of [(14)C]-DHA to 0.6+/-0.3microlg(-1)s(-1), indicating that binding to albumin reduced importantly, but not totally, the passage of DHA through the BBB. The Clup of [(14)C]-DHA or [(14)C]-EPA was not saturable at concentration up to 100microM, suggesting that these compounds crossed the BBB by simple diffusion. However, long-term high-DHA dietary consumption reduced the Clup of [(14)C]-DHA to 33+/-6microlg(-1)s(-1) (-20%, p<0.01). These results confirm that the brain uptake of DHA or EPA perfused with a physiological buffer is comparable to highly diffusible drugs like diazepam, and can be modulated by albumin binding and chronic dietary DHA intake.
Neurochemistry International 06/2009; 55(7):476-82. · 2.65 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Combined evidence from neuroimaging and neuropathological studies shows that signs of vascular pathology and brain hypoperfusion develop early in Alzheimer's disease (AD). To investigate the functional implication of these abnormalities, we have studied the cerebrovascular volume and selected markers of blood-brain barrier (BBB) integrity in 11-month-old 3 x Tg-AD mice, using the in situ brain perfusion technique. The cerebrovascular volume of distribution of two vascular space markers, [3H]-inulin and [14C]-sucrose, was significantly lower (-26% and -27%, respectively; p < 0.01) in the brain of 3 x Tg-AD mice compared to non-transgenic littermates. The vascular volume reduction was significant in the hippocampus (p < 0.01), but not in the frontal cortex and cerebellum. However, the brain transport coefficient (Clup) of [14C]-D-glucose (1 microM) and [3H]-diazepam was similar between 3xTg-AD mice and controls, suggesting no difference in the functional integrity of the BBB. We also report a 32% increase (p < 0.001) in the thickness of basement membranes surrounding cortical microvessels along with a 20% increase (p < 0.05) of brain collagen content in 3xTg-AD mice compared to controls. The present data indicate that the cerebrovascular space is reduced in a mouse model of Abeta and tau accumulation, an observation consistent with the presence of cerebrovascular pathology in AD.
[Show abstract][Hide abstract] ABSTRACT: Leptin is a major determinant of energy homeostasis, acting both centrally and in the gastrointestinal tract. We previously reported that acute leptin treatment enhances the absorption of di- and tripeptides via the proton-dependent PepT1 transporter. In this study, we investigated the long term effect of leptin on PepT1 levels and activity in Caco2 cell monolayers in vitro. We then assessed the significance of the regulation of PepT1 in vivo in a model of diet-induced obesity. We demonstrated that 1) leptin regulated PepT1 at the transcriptional level, via the MAPK pathway, and at the translational level, via ribosomal protein S6 activation, in Caco2 cells and 2) this activation was systematically followed by a time- and concentration-dependent loss of leptin action reflecting desensitization. Deciphering this desensitization, we demonstrated that leptin induced a down-regulation of its own receptor protein and mRNA expression. More importantly, we showed, in mice with diet-induced obesity, that a 4-week hypercaloric diet resulted in a 46% decrease in PepT1-specific transport, because of a 30% decrease in PepT1 protein and a 50% decrease in PepT1 mRNA levels. As shown in Caco2 cells, these changes in PepT1 were supported by a parallel 2-fold decrease in leptin receptor expression in mice. Taken together, these results indicate that during induction of obesity, leptin resistance may also occur peripherally in the gastrointestinal tract, disrupting the absorption of oligopeptides and peptidomimetic drugs.
Journal of Biological Chemistry 02/2009; 284(11):6801-8. · 4.60 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The aim of the present study was to investigate the effects of recombinant interleukin (rIL)-2 treatment on paclitaxel (PLX) pharmacokinetics in the plasma and tissue of Lewis lung carcinoma-bearing mice (lung tissues and s.c. tumors). PLX pharmacokinetics studies were conducted after oral and i.v. administration of 15 and 4 mg/kg, respectively, either alone or after 3 days of rIL-2 pretreatment. The noncompartmental approach was used to determine the mean pharmacokinetic parameters using WinNonlin software (Pharsight, Mountain View, CA). The influence of rIL-2 pretreatment on physiological P-glycoprotein (P-gp) expression in lung and intestine was investigated by Western blot analysis. After oral administration of PLX, areas under the curve (AUC) in plasma, lung, and s.c. tumors were significantly higher (2.98, 2.66, and 3.41-fold, respectively) in the rIL-2 + PLX group as compared with the PLX group. However, no significant effect of rIL-2 pretreatment was observed in plasma or lung following i.v. administration of PLX. PLX AUC in s.c. tumors was significantly higher (1.37-fold) with rIL-2 pretreatment as compared with the PLX-alone group after i.v. injection. Pretreatment with rIL-2 appeared to have no effect on PLX plasma terminal half-life when PLX was administered orally or i.v. However, prolongation of PLX terminal half-life estimated from lung and s.c. tumors data had been observed. Increased PLX tissue absorption in the rIL-2-pretreated group may be explained by a decrease of P-gp expression in the intestines and lung or decreased functionality due to rIL-2. Oral administration allowed the targeted tissues a much higher PLX exposure as compared with i.v. administration.
Drug metabolism and disposition: the biological fate of chemicals 09/2008; 36(8):1729-35. · 3.74 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The in situ mouse brain perfusion method for measuring blood-brain barrier permeability was adapted to assess transport of solutes at the blood-brain and blood-eye barriers. The procedure was checked with radiolabeled markers in oxygenated bicarbonate-buffered fluid infused for 30 to 120 sec via a carotid artery. Vascular flow estimated with diazepam was 2.2-fold lower in the eye than in the brain. The vascular volume and the integrity markers sucrose and inulin indicated that a perfusion flow rate of 2.5 mL/min preserved the physical integrity of these organs. However, the brain vasculature integrity was more sensitive to acute perfusion pressure than the eye vasculature. The functional capacities of blood barriers were assessed with D-glucose; its transport followed Michaelis-Menten kinetics with an apparent K(m) of 7.6 mmol/L and a V(max) of 23 micromol/sec per g in the brain, and a K(m) of 22.9 mmol/L and a V(max) of 40 micromol/sec per g in the eye. The transport of cholesterol to the brain and eye was significantly enhanced by adding the Abca1 inhibitor probucol, suggesting an Abca1-mediated efflux at the mouse brain and eye blood barriers. Thus in situ carotid perfusion is suitable for elucidating transport processes at the blood-brain and blood-eye barriers.
Journal of cerebral blood flow and metabolism: official journal of the International Society of Cerebral Blood Flow and Metabolism 05/2008; 28(8):1449-59. · 5.46 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Physiological studies of the blood-brain barrier (BBB) are often performed in rats. We describe the functional characterization of a reproducible in vitro model of the rat BBB and its validation for investigating mechanisms involved in BBB regulation. Puromycin-purified primary cultures of brain endothelial cells, co-cultured with astrocytes in the presence of hydrocortisone (HC) and cAMP, presented low sucrose permeability (< or =0.1 x 10(-3) cm/min) and high transendothelial electrical resistance (> or =270 Omega cm(2)). Expression of specific BBB markers and their transcripts was detected by immunostaining and RT-PCR, respectively: tight junction proteins (claudin-3 and -5, ZO-1 and occludin) and transporters (P-gp, Bcrp and Oatp-2). RT-PCR experiments demonstrated a role of treatment by astrocytes, HC and cAMP in regulation of the transcript level of tight junction proteins (claudin-5 and ZO-1) as well as transporters (Mdr1a, Mrp3, Mrp4, Bcrp, Glut-1), while transcript level of Mdr1b was significantly decreased. The functionality of efflux pumps (P-gp, Mrps and Bcrp) was demonstrated in the presence of specific inhibitors (PSC833, MK571 or Ko143, respectively) by (i) assessing the uptake of the common substrates rhodamine 123 and daunorubicin and (ii) evaluating apical to basolateral and basolateral to apical polarized transport of daunorubicin. In addition, a good correlation (R=0.94) was obtained between the permeability coefficients of a series of compounds of various lipophilicity and their corresponding in vivo rodent blood-brain transfer coefficients. Taken together, our results provide compelling evidence that puromycin-purified rat brain endothelial cells constitute a reliable model of the rat BBB for physiological and pharmacological characterization of BBB transporters.
Brain Research 05/2007; 1150:1-13. · 2.83 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We investigated whether capacity-limited transport processes were involved in morphine and morphine-6-beta-D-glucuronide (M6G) neuropharmacokinetics, at the level of the blood-brain barrier (BBB), the brain extra- and intra-cellular fluids (bECF/bICF), and the bECF/cerebrospinal fluid (CSF) interfaces. We performed transcortical retrodialysis in the rat, by perfusing morphine or M6G through the microdialysis probe in the presence or absence of probenecid. We measured for each compound the in vitro and in vivo (R(D)) probe recoveries. The in vivo R(D), which takes into account the permeability of the tissue surrounding the probe, informs about the morphine and M6G distribution capabilities from bECF to adjacent fluids (bICF, CSF, plasma). We also measured plasma and CSF concentrations at three time points after having added probenecid or not. Finally, we tested several pharmacokinetic models, assuming first-order or capacity-limited processes at each brain interface, to describe experimental morphine and M6G concentrations previously obtained in rat plasma and brain fluids. We found that morphine distributes more easily outside bECF than M6G. Adding probenecid caused a 2-fold decrease and a 1.3-fold increase in morphine and M6G R(D), respectively, and 30 min after adding probenecid, plasma and CSF concentrations increased for M6G but not for morphine. The pharmacokinetic model that gave the best fit included capacity-limited processes at the BBB and bECF/bICF interface for morphine and at the BBB and bECF/CSF interface for M6G. In conclusion, morphine accumulates into brain cells thanks to a probenecid-sensitive transporter located at the bECF/bICF interface, whereas M6G is trapped in bECF thanks to transporters located at the BBB and the bECF/CSF interface.
Life Sciences 05/2006; 78(20):2302-14. · 2.30 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The aim of our study was to determine the neuropharmacokinetics of S18986 [(S)-2,3-dihydro-[3,4]cyclopentano-1,2,4-benzothiadiazine-1,1-dioxide], a new positive allosteric modulator of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid-type receptors, in the rat. We focused on its blood-brain barrier (BBB) uptake and on its brain intra- and extracellular fluid (bICF-bECF) partitioning. BBB transport of S18986 was measured using the in situ brain perfusion technique. bECF concentrations were determined by microdialysis in the two effector areas, i.e., frontal cortex (FC) and dorsal hippocampus (DH), and blood samples were collected simultaneously through a femoral catheter. Cerebrospinal fluid and brain tissue concentrations were determined using a conventional pharmacokinetic approach. Using all the experimental data, pharmacokinetic modeling was applied to describe the S18986 blood-brain disposition. The brain uptake clearance of S18986 was found to be high, about 20 mul s(-1) g(-1). Terminal half-lives were similar in plasma and brain, at around 1 h. Experimental and predicted blood and brain concentrations were a good fit with the pharmacokinetic model, which assumed first-order rate constants at each interface. Ratios of bECF to the unbound plasma area under the curve (AUC) were 0.24 in FC and 0.25 in DH, whereas ratios of bICF/plasma AUC were 1 in FC and 1.5 in DH. We conclude that despite the ratio of bECF/plasma AUC below 1, there is nevertheless an elevated BBB uptake of S18986. This can be explained by the S18986 nonhomogenous bECF/bICF partitioning, since S18986 mainly distributes into hippocampal bICF. This illustrates the importance of taking bECF/bICF partitioning into account when interpreting the neuropharmacokinetics of a drug.
Drug Metabolism and Disposition 09/2005; 33(8):1137-43. · 3.33 Impact Factor